3000 Nm3/h Methanol Conversion-PSA Hydrogen Production Plant

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Operating Procedures for 3000 Nm3/h Methanol Conversion-PSA Hydrogen Production Plant – Methanol Cracking and Conversion Section
Table of Contents
1.0 Introduction ----------------------------------------------------- 2
2.0 Properties and Specifications of Raw Materials and Products ----------------------- 3
3.0 Description of the Process Flow ------------------------------------------- 5
3.1 Process Flow --------------------------------------------- 5
3.2 Principles of Chemical Reactions ----------------------------------------- 5
4.0 Description of the Process Sequence --------------------------------------------- 6
5.0 Key Control Parameters in the Process Flow ------------------------------------- 7
6.0 Pre-startup Preparation Work --------------------------------------------- 9
7.0 Operating Procedures ------------------------------------------------- 12
7.1 Preparations before Startup -------------------------------------- 12
7.2 Startup Procedure ------------------------------------------ 12
7.3 Normal Operation ---------------------------------------------- 14
7.4 Use and Protection of Catalysts ------------------------------------ 16
8.0 Environmental and Safety Considerations -------------------------------------------- 21
9.0 Analysis Procedures -------------------------------------------------- 22
10.0 Safety Regulations -------------------------------------------------- 30
1.0 Introduction
Hydrogen is widely used in various industrial sectors of the national economy. In recent years, the number of hydrogen users has increased rapidly, and traditional hydrogen production methods can no longer meet these demands. The catalytic conversion of methanol and water to produce hydrogen and carbon dioxide allows for the easy separation of pure hydrogen and carbon dioxide using adsorption or chemical methods. Compared to electrolysis, this approach can save over 90% on electricity costs, with costs reduced by 20–40%. This new process features easy access to raw materials, a simple setup, no pollution, energy efficiency, and low cost, making it very popular among users. Those who operate and manage this device must be well familiar with these operating procedures, and only after passing the relevant assessment can they take up their duties. 2.0 Properties and specifications of raw materials and products 2.1 Properties of raw materials and products 2.1.1 Properties of raw materials (1) Properties of methanol as a raw material Its chemical name is methanol; it is also known as methyl alcohol, wood alcohol, or wood spirit. Molecular formula: CH3OH, molecular weight: 32.04. It is a colorless, transparent, flammable, and volatile liquid with an odor similar to ethanol. The specific gravity is 0.7915. Melting point: -97.80°C, boiling point: 64.7°C, vapor pressure at 20°C: 96.3 mmHg, viscosity: 0.5945 centipoise, flash point: 11.11°C, auto-ignition temperature: 385°C; the explosive limit in air is 6.0–36.5%. Methanol is one of the most commonly used organic solvents, and it is miscible with water and various organic solvents. Methanol is toxic and harmful; it has a significant impact on the optic nerve, and in severe cases it can cause blindness. (2) Properties of the raw material deionized water (omitted) 2.1.2 Properties of the product The product manufactured by this unit is methanol catalytic conversion gas, whose main components are hydrogen and carbon dioxide; their properties are described as follows: (1) Properties of hydrogen Molecular formula: H2; molecular weight: 2.0158; it is a colorless and odorless gas. Non-toxic and non-corrosive. The gas has a density of 0.0899 Kg/m³, a melting point of -259.14°C, and an autoignition temperature of 400°C. It is barely soluble in water, alcohol, ether, and various other liquids. It remains stable at room temperature; however, in the presence of a catalyst at high temperatures, it becomes highly reactive. It is extremely flammable and explosive, and can combine with many non-metals and metals. (2) Properties of carbon dioxide: Its chemical name is carbon dioxide; synonyms include carbonic anhydride, carbon oxide, and carbonic gas. Molecular formula: CO2; molecular weight: 44.01; a colorless and odorless gas. It has an acidic taste; its gas density is 1.977 Kg/m3. The melting point is -56.6°C, while the boiling point is -78.5°C (via sublimation). It dissolves easily in water to form carbonic acid, and it is soluble in ethanol, methanol, propane, chloroform, carbon tetrachloride, and benzene. It is a non-flammable gas that can be used as a fire extinguishing agent. 2.2 Raw Materials and Product Specifications 2.2.1 Raw Material Specifications Methanol: Meets the requirements of Grade 1 as specified in the national standard GB338-2004. It is recommended to use methanol production facilities with a capacity of 30Kt/y or more, to ensure no pollution during transportation ； The use of recycled methanol is strictly prohibited. Demineralized water: Meets the requirements of the national standard GB12145-89P (for direct-fired boilers), with a chloride ion content of 3 ppm or less. 2.2.2 Product specifications: (1) Composition of the converted gas: H2 – 73–74.5%, CO2 – 23–24.5%, CO – <0.9%, CH3OH – 300 ppm, saturated with H2O. (2) Pressure: 1.30 MPa. (3) Temperature: <40°C. 3.0 Process description: The process of producing gas through catalytic conversion of methanol can be divided into four steps: preheating of the feed liquid, vaporization, superheating, the conversion reaction, and cooling and condensation of the product gas, as well as purification of the product gas. 3.1 Process Flow 3.1.1 Preheating, vaporization, and superheating of the feed liquid The methanol and deionized water are mixed in a specified ratio, and then pumped into the system under pressure to undergo preheating, vaporization, and superheating until they reach the reaction temperature. Its scope of operation includes equipment such as the methanol metering tank V101, the circulating liquid storage tank V103, the raw material feed pumps P101A/B, the heat exchanger E102, the vaporization tower T101, and the superheater E101, along with the associated instruments and valves. 3.1.2 Catalytic conversion reaction process: Under the specified reaction temperature and pressure, the feed steam undergoes gas-solid catalytic conversion in the converter R101. The scope of work includes: one converter unit R101 along with its associated instruments and valves. The purpose of this process is to carry out a chemical reaction to produce a converted gas whose main components are hydrogen and carbon dioxide. 3.1.3 Conversion gas cooling and condensation process: A process in which the high-temperature conversion gas exiting from the lower part of the converter is cooled and condensed to below 40°C. Its scope of work includes the two units, heat exchanger E102 and cooler E103, along with their associated instruments and valves. 3.1.4 Conversion gas purification process: The low-temperature conversion gas, which contains hydrogen, carbon dioxide, and small amounts of carbon monoxide, methanol, and water, enters the wash tower T102 where demineralized water is used to absorb any unreacted methanol. Its scope of work includes: the water washing tower T102, the demineralized water intermediate tank V105, the gas buffer tank V104, the demineralized water feed pumps P102A/B, as well as these five pieces of equipment along with their associated instruments and valves. 3.2 Principles of chemical reactions: The mixture of methanol and water vapor undergoes a catalytic conversion reaction under pressure in a converter; hydrogen and carbon dioxide are produced as products. The reaction equations are as follows: Main reaction: CH3OH + H2O = CO2 + 3H2 + 49.5 KJ/mol. Side reactions: CH3OH = CO + 2H2 + 90.7 KJ/mol; 2CH3OH = CH3OCH3 + H2O – 24.9 KJ/mol; CO + 3H2 = CH4 + H2O – 206.3 KJ/mol. The main reaction is endothermic, so external heating using heat transfer oil is employed. After cooling and condensation, the converted gas enters the wash tower; the unconverted methanol and water are collected at the bottom of the tower for reuse. The gas at the top of the tower is sent to a pressure swing adsorption hydrogen separation unit via a buffer tank. 4.0 Description of the process flow: Refer to the P&ID for the methanol cracking hydrogen production process in the methanol conversion unit (Figure No.: 0769-32-101). Deionized water from outside the plant enters the deionized water intermediate tank V105 via valve V1093; after being metered by the deionized water feed pumps P102A/B, it is sent to the washing tower T102 where uncondensed methanol is absorbed. The absorbent solution flows from the bottom of the tower to the circulating liquid storage tank V103. Trace amounts of carbon dioxide and dimethyl ether dissolved in the mixture are discharged from the circulating liquid storage tank. Methanol from the methanol storage tank is pumped into the methanol intermediate tank V101. The raw methanol that flows out of V101 due to gravity is regulated by FV-101 and metered by FIC101, after which it is mixed with the circulating liquid from the circulating liquid storage tank V103. The mixture is then pressurized using the raw material feed pumps P101A/B and sent to the heat exchanger E102, where it is preheated by exchanging heat with the high-temperature conversion gas. Subsequently, it enters the vaporization tower T101 to be vaporized, and after being superheated to a temperature close to the reaction temperature in the heater E101, it enters the conversion furnace R101, where catalytic conversion reactions take place. The high-temperature conversion gas exiting the furnace is cooled by exchanging heat with the raw material liquid in the heat exchanger E102; after further cooling and condensation in the cooler E103, it enters the washing tower T102. The condensed liquid, together with the absorbent liquid, is depressurized via the level control valve LV-102 before being discharged back to the circulating liquid storage tank V103 for reuse. The conversion gas is metered by the flow meter FIQ103, pressure-regulated by PV-101, and then sent to the buffer tank V104 before being fed to the pressure swing adsorption system for purification. The catalyst must be reduced before use. In the reduction process, hydrogen is used as the reducing gas, while nitrogen serves as the diluting carrier gas. Process nitrogen circulates within the system. The reducing gas enters heat exchanger E102 via a Roots blower, where it exchanges heat with the hot reducing gas coming from converter R101. After being superheated to the reduction temperature in heat exchanger E101, it enters converter R101 for the catalyst reduction reaction. The reducing gas then exchanges heat in heat exchanger E102, and after being cooled and condensed in cooler E103, it returns to the Roots blower to circulate within the system. The condensed water enters tower T102 under the effect of gravity and is discharged through a drain valve. 5.0 Main Control Parameters of the Process 5.1 Vaporization Heat of Raw Materials 5.1.1 Methanol flow rate of raw materials: ~1427 Kg/h 5.1.2 Flow rate of raw material liquid: ~3186 Kg/h 5.1.3 Feed temperature in the vaporization superheating tower: ~165°C 5.1.4 Pressure at the bottom of the vaporization superheating tower (gauge pressure): 1.30 MPa 5.2 Conversion Reaction 5.2.1 Feed temperature: 200–260°C 5.2.2 Reaction temperature: 220–280°C 5.2.3 Temperature of the heat transfer oil: 235–290°C 5.2.4 Temperature of the converted gas at the outlet of the heat exchanger: 110–140°C 5.2.5 Temperature of the converted gas at the outlet of the cooling gas: <40°C 5.2.6 Reaction pressure (gauge pressure): ~1.30 MPa 5.3 Washing and Separation 5.3.1 Amount of water used for desalination before entering the tower: 820 Kg/h 5.3.2 Amount of circulating liquid (after leaving the tower): ~1764 Kg/h; Composition of the circulating liquid (wt%): Methanol 0–25% 5.3.3 Volume of converted gas exiting the tower: ~3968 Nm3/h; Composition of the converted gas (V%): Hydrogen 73–74.5%, Carbon dioxide 23–4.5%, Carbon monoxide ~0.9%, Methanol 0.03%, Methane 0.20% 5.4 Catalyst Reduction 5.4.1 Volume of gas used for reduction: ~3000 Nm3/h 5.4.2 Hydrogen content in the reduction gas: 0.5–10% 5.4.3 Reduction temperature: 110–230°C 5.4.4 Reduction pressure: ~0.05 MPa 5.5 Others 5.5.1 Pressure of cooling water at the inlet of the process unit: 0.3 MPa 5.5.2 Pressure of instrument air at the inlet of the process unit: 0.4–0.60 MPa 5.5.3 Flow rate of heat transfer oil: ~240 m3/h 6.0 Pre-Commissioning Activities All tasks that must be completed from the completion of the plant installation until commissioning are referred to as pre-commissioning activities. To ensure smooth driving, all of the following tasks must be completed one by one. 6.1 Site cleanup and inspection: After the installation is completed, the site must first be cleaned up, removing everything that is not related to the installation. Especially for import and export roads, safety and fire evacuation routes must remain unobstructed. As required by the design, a thorough inspection of the entire system is carried out in accordance with the drawings, to verify whether the equipment, pipelines, valves, instruments, electrical systems, and civil works meet the design specifications ； Check the external connection ports for any errors; if there are any, they should be corrected immediately. Special attention should be paid to checking whether the safety-related facilities meet the safety standards and are in good condition, such as fire hydrants, fire extinguishers, safety valves, flame arrestors, vent pipes, and electrical explosion-proof facilities. While cleaning up the site, it is also necessary to organize and archive various technical documents, drawings, files from the design and construction phases, on-site design modifications, various user manuals, and product samples. 6.2 System purging: The purpose of purging is to remove debris originating from the equipment and pipelines themselves or remaining from the installation process, thereby ensuring the quality of the product after it goes into operation and preventing blockages in valves, pipelines, and instruments that could disrupt normal production or even lead to safety accidents. Before purging, the relevant valves, instruments, rotameters, level gauges, and sight glasses that do not need to be purged or cannot be purged should be removed or blocked with blind flanges; they should then be reinstalled after the purging is complete. Blind plates should be installed on pipeline equipment that does not require purging, to prevent debris from being blown in. During the blowing process, use a small hammer to tap various welds in order to blow away all the slag. This equipment should be purged section by section with instrument air. The purge pressure must not exceed the pressure used in the leak test; however, the flow velocity inside the pipes during purging should preferably be greater than 20 m/s. To test for blowing out, a wooden board covered with white cloth or paper can be placed in front of the air outlet for 3 to 5 minutes; it is considered satisfactory if no stains appear on the board. 6.3 Airtightness test The purpose of the airtightness test is to check whether the equipment, valves, pipelines, instruments, connection flanges, and welds are sealed and free from leaks. The airtightness test uses compressed air, with the test pressure typically being 1.15 times the maximum operating pressure. Under the measured pressure, hold for 1 hour; if the pressure does not drop, it is considered qualified. Given that the main materials of this device, methanol and hydrogen, are flammable, explosive, and toxic substances, it is also necessary to determine the leakage rate during the airtightness test. The test pressure for the leakage rate is the design pressure, with a test duration of 24 hours; a leakage rate of ≤0.5% is considered acceptable. The leakage rate is calculated using the following formula: where P1, P2 and T1, T2 are the absolute pressures and absolute temperatures (K) at the start and end of the test, respectively, and t is the test duration (hours). The test pressures for the airtightness of various systems, as well as the systems for which leakage rates need to be determined, are shown below: Table 1: Requirements for Airtightness Tests. Sequence Number, System Name, Test Pressure (MPa), Remarks: 1. T101, E101, E102 – Main systems; R101, E103, T102; V104, P101, P102 – 1.50; Leakage rates need to be determined. 2. Low-pressure components: V101, V103, V105 – 0.06. 3. Heat transfer oil system – 0.69. 4. Cooling water system – 0.50. 6.4 Single-unit testing: The purpose of single-unit testing is to assess the performance of the main equipment and the quality of its assembly. It can be carried out in accordance with design requirements, instructions, and other relevant regulations, and includes the following main aspects: 6.4.1 Operating performance, flow rate, and outlet pressure of each type of pump ； 6.4.2 Regarding the installation of instruments and their indication and control performance, scale calibration should be carried out when necessary ； 6.4.3 Installation quality, control, regulation, testing capabilities, and regulation characteristics of each control system ； 6.4.4 Measure the volumes of raw material storage tanks, intermediate metering tanks, and various gas and liquid storage tanks. For liquid storage tanks, indicate the volume corresponding to the scale markings on the level gauge ； 6.4.5 Calibrate and mark the flow values corresponding to the scale values on the flow meter ； 6.4.6 Whether the use of each fire hydrant and fire extinguisher is flexible and convenient. 6.5 Cleaning of pipes and equipment: Pipes, equipment, valves, etc., have a considerable amount of oil and debris on their surface areas during the manufacturing process. Relying solely on blowing to clean them is not sufficient; such oil and debris, if carried onto the catalysts during production, can poison them, while if they end up in the products, they can affect the quality of those products. When there is too much debris, it can also cause blockages in pipes, valves, and instruments, so it must be removed. Generally, it can be rinsed with clean water. The water rinsing should be carried out continuously, with a flow rate of no less than 1.5 m/s. It is considered acceptable when the color and transparency of the outgoing water are visually identical to those of the incoming water. If the oil contamination is severe, it should first be cleaned with a dilute alkaline solution (below 2%), and then rinsed thoroughly with clean water. 6.6 Insulation and Painting 6.6.1 Equipment, pipes, etc. that require insulation must be insulated. For details, see the \"List of Equipment and Pipeline Insulation\". 6.6.2 Corrosion protection: The surfaces of the equipment and pipelines in this unit are protected against corrosion using paint. Apply two coats of anti-rust paint to the insulation equipment and pipes as an anti-rust layer. For uninsulated equipment and pipes, apply two coats of rust-proof paint followed by two coats of topcoat. Stainless steel equipment is not painted. 6.6.3 Coloring and Labeling: The color of the anti-corrosion topcoat for equipment and pipelines can be determined as appropriate. According to standard regulations, this device is painted with silver-white topcoat for stationary equipment, and light green topcoat for pumps. Green topcoat is used for cooling water and fire protection water pipes, red topcoat for process material pipes, and dark blue topcoat for instrument air. After the equipment is insulated and painted, its name and tag number should be indicated in a prominent location; for important material pipelines, the flow direction of the materials should also be marked. 6.7 Cold-state joint test The purpose of the cold-state joint test is to evaluate the automatic control capabilities of the operating equipment and instruments. During cold-state testing, gaseous material is replaced by air, and liquid material is replaced by water. First, conduct sequential linkage tests, and finally carry out cold-state linkage tests for the entire section. It can be done following these steps. 6.7.1 Turn on all instruments, control devices, and transmission equipment and supply power to them ； 6.7.2 Start each infusion pump and adjust the flow rate to supply water to the relevant equipment ； 6.7.3 In accordance with normal operating procedures, adjust all control points and make records on time, so that operators become familiar with the operations and can handle anticipated accidents. 6.8 Drying: Once all the tasks mentioned above are completed, the preparations prior to starting up the machine are essentially finished. Open the drain valve of the device’s pipeline to drain all the water. Since the reaction system, reduction system, and heat transfer oil system do not allow water to remain, they must be dried out. 6.9 Commissioning of the heat transfer oil boiler: After the above tasks are completed, the heat transfer oil boiler unit must be started up for a trial run prior to the installation of the catalyst. The detailed procedures should follow the instructions provided for operating the heat transfer oil boiler, including measuring the flow rate of the heat transfer oil, in order to ensure an adequate heat supply during normal operation. 7.0 Operating Procedures 7.1 Preparations before Startup 7.1.1 General preparations and inspections 1. Check the supply of water, electricity, steam, soft water, instrument air, nitrogen, hydrogen, fuel gas, etc., and contact the relevant departments to confirm the required quantities and quality standards for these supplies. 2. Close all drain valves, sewage valves, vent valves, feed valves, and sampling valves. Open the main valves for cooling water, instrument air, etc., at the process section. 3. Notify the heat transfer oil boiler room to get ready for operation, and contact them to determine the specific time of startup as well as the requirements regarding quality and quantity (pressure, temperature, flow rate, etc.). 4. Inform the analysis laboratory to prepare for production control analysis work. 5. Check the condition of the power equipment, and verify that the power supply, air supply, and signals for all instruments are functioning properly. 6. Identify product users. Since frequent shutdowns of the conversion catalyst are undesirable, do not rush to start the vehicle if the necessary preparations have not been made. 7. Check that the fire protection and safety facilities are complete and in good condition. 8. Operators, analysts, and maintenance personnel must undergo technical training and pass assessments before they can take up their duties. 7.2 Operating Procedure for Starting Up: The procedure for starting up the system with feedstock should be carried out immediately after catalyst reduction is completed, without any time interval. Catalyst reduction will be discussed in detail in 7.4. The sequence of starting up the system is generally as follows: start up the water wash tower, start up the vaporization tower, start up the converter, and increase the system pressure. After the reduction is complete, close the reduction system valves V1058, V1069, and V1046; open the converter and then close all valves in the vent line downstream of V104. Close valve V1051, which is the upstream valve of R101, to prepare for starting up the system. 7.2.1 Preparation 1. Check that the tools and protective equipment are complete and in good condition. 2. Check whether the power equipment is operating properly, fill the lubrication points with oil as specified, and turn the machine several times. 3. Check whether all measuring and control instruments are malfunctioning or in good condition, and turn on the power and gas supply switches for these instruments. 4. Notify the methanol tank and demineralized water station to supply raw materials to this unit. Bring the liquid levels in methanol intermediate tank V101 and deionized water intermediate tank V105 to ~90%, then stop feeding. 5. All valves and instruments in the catalyst reduction system shall remain in their original operating conditions (for specific conditions, refer to 7.4 Use and Protection of the Catalyst). 6. Notify the heat transfer oil furnace team to make preparations for startup. 7. Determine the feeding amount for driving the process, and clarify the relationship between the feeding amount and various parameters. 7.2.2 Commissioning of the water washing tower: 1. Open the discharge valve of the brine intermediate tank V105, as well as the inlet valves of P102A/B and the bypass valve; start the P102A/B pumps to ensure they operate properly. 2. Open the outlet valves of pump P102A/B, and close the bypass valves of P102A/B. 3. Once a liquid level appears in the bottom of wash tower T102, open the bypass valve V1080 associated with the discharge control valve of T102’s bottom section, to send brine to the circulating liquid storage tank V103. Then open the valves V1081 and V1082 located before and after the control valve, and close V1080; use valve LV-102 to maintain the liquid level LIC102 in T102 at 30–40%. 7.2.3 Commissioning of the vaporization tower: 1. Open the outlet valve of the methanol intermediate tank V101, as well as the valves before and after FIC102 and FV-101; open the outlet valve of the circulating liquid tank V103 to mix water with methanol. Open the inlet valves and bypass valves of pumps P102A/B, start the P102A/B pumps, and adjust the flow rate to ensure proper operation of FIC102. 2. Open the outlet valves of P102A/B, close the bypass valves of P102A/B, and adjust the setting of the feed pump to supply methanol to the system. Sampling and analysis were conducted at sampling point A102; the flow rate of the raw methanol was adjusted using FV-101 to achieve the desired ratio of water to methanol. 3. When the liquid level in the bottom of vaporization tower T101 reaches 10%, open the vent valve at the top of the vaporization tower. Slowly open the heat transfer oil inlet valve V1039 for tower T101, and close some of the short-circuit valves V1038, in order to adjust the amount of heat transfer oil supplied to the vaporization tower. When the gas discharge volume from the top of the tower is stable, close some of the vent valves at the top of the vaporization tower, and open the drain valves V1048 and V1049 located at the bottom of the superheater E101. Once no liquid droplets are discharged, close these drain valves V1048 and V1049, and then proceed with starting up the converter. 7.2.4 Starting up the converter: 1. Open the inlet valve V1051 of converter R101, and close all the vent valves at the top of the vaporization tower, thereby feeding water-methanol feed gas into converter R101. 2. Stabilize the temperature of the heat transfer oil furnace at 230°C, check whether the equipment, pipelines, valves, instruments, etc. are operating properly, and observe the relationships between various process parameters; if there are no abnormalities, the system pressure can be increased. 7.2.5 System Pressurization 1. Open the system pressure control valve PV-101 and the valves before and after it, and close the bypass valve. Slowly close the PV-102 valve to increase the system pressure until it reaches 1.30 MPa. Note: It is necessary to ensure that an appropriate amount of raw gas passes through the catalyst bed, so the system pressure control valve cannot be in a fully closed position. 2. Adjust the opening of the system pressure control valve PV-101 to stabilize the system pressure and the volume of the converted gas. 3. Check the feed volume of the raw material solution and its water-methanol ratio to ensure they meet the required values ； Check the amount of converted gas, and adjust the flow rate of the heat transfer oil entering the lower part of T101 via valve LV-101, to maintain the liquid level in the bottom of tower T101 between 15% and 30%. 4. Adjust FV-101 to stabilize the methanol level and bring it to the required value; adjust the setting of P102 to keep the liquid level in V103 stable as indicated by Lia103. At this point, the system has been fed with materials and brought online. Observe the overall system operation; if there are no abnormalities, the following steps can be taken to restore the system to normal operation. 7.2.6 System Stability 1. Check the cooling water volume of cooler E103 to ensure that the temperature of the converted gas entering wash tower T102 is ≤40°C. 2. Check the composition of the converted gas at the outlet of the buffer tank, adjust the ratio of water to methanol, and ensure that the concentrations of components such as carbon monoxide, methanol, and water in the converted gas at the outlet meet the specified values. 3. Once the operation of the entire system is stable, the converted gas can be delivered to the PSA-H2 unit in the subsequent section. 7.3 Normal Operation Once the entire system has been brought online, it can gradually be shifted to normal operation. 7.3.1 Establishment and maintenance of normal operating conditions 1. Adjust the parameters at various control points appropriately, based on factors such as the feed rate of the raw material liquid, the flow rate of the converted gas, the ratio of water to methanol, the liquid level in the vaporization tower, the temperature of the heat transfer oil, the composition of the converted gas, the composition of the circulating liquid, and other relevant parameters, so that the system operates within normal ranges. 2. Determine the methanol flow rate based on the required amount of conversion gas and the water-methanol ratio, and put FV-101 into automatic control. 3. Adjust the scale of P-101 according to the flow rate of the required raw materials. 4. Adjust the flow rate of P-102 according to the required liquid level in the wash tower, so as to stabilize the liquid level in V103. 5. Enable automatic adjustment of LV-102 based on the circulating fluid flow rate. 6. Adjust the inlet valve of cooler E103 to keep the temperature of the converted gas exiting E103 below 40°C. 7. Once the flow rate of the converted gas in the system stabilizes, put the system pressure PV-101 under automatic control. 8. Adjust the temperature of the heat transfer oil fed into the system appropriately, depending on the required volume and composition of the converted gas. 9. A small amount of wastewater is continuously discharged through the drain valve at the bottom of the vaporization tower, with the discharge rate controlled between 15.0 and 20.0 Kg/h. The entire system is now operating normally and stably. When the system is operating normally, record various operational parameters on schedule, and conduct regular inspections to ensure that all control points, equipment, instruments, valves, etc. are in proper condition. In the event of any abnormalities, the cause should be identified immediately, and appropriate actions taken to resolve the issue and maintain the system’s normal operation. 7.3.2 Normal shutdown procedure: 1. Stop heating the heat transfer oil furnace and maintain the circulation of the heat transfer oil. Once the reaction temperature drops below 200°C, stop supplying heat transfer oil to the gas generation unit by turning on the internal short-circuit valve of the heat transfer oil system. The shutdown of the heat transfer oil furnace is carried out in accordance with the relevant requirements for such shutdowns. 2. While the heat transfer oil furnace is cooling down, manually adjust the system pressure control valve PV-101 to gradually reduce the pressure to 0.4 MPa (or open the gas buffer tank V104; the converted gas can be used to replace the gas in the converter, and the vent valve at the top of the water scrubber T102 can be opened to reduce the pressure). 3. Close the valve V1051 leading to the conversion furnace, and slowly open the vent valve V1044 at the top of the vaporization tower; this causes the pressure in the system ahead of the vaporization tower to drop to atmospheric level. 4. While reducing the pressure in the vaporization tower system, shut down P101A/B and stop feeding material into the system. 5. Continue to reduce the pressure in the system downstream of the converter; once the pressure drops to 0.2 MPa, close the valves before and after PV-101 as well as the bypass valve. 6. Stop P102A/B and cease feeding deionized water to T102. Close the T102 tower bottom discharge valve. 7. The sections before and after converter R101 were purged sequentially using nitrogen or the gas buffer tank V104 to contain the conversion gas. Considering the impact of temperature drop on system pressure, the system sections were finally pressurized to 0.2 MPa using nitrogen or hydrogen. Once the heat transfer oil reaches the required temperature, stop the heat transfer oil circulation pump. If parking for an extended period, pressurized nitrogen is used to force the heat transfer oil back from the system into the heat transfer oil storage tank. 8. Implement protective operations or passivation on the catalyst (for specific procedures, see 7.4 Use and Protection of Catalysts). 7.3.3 Emergency Shutdown Procedures 1. Emergency shutdown procedures should be initiated in any of the following situations: (1) Power outage; (2) Disruption of cooling water supply; (3) Explosion, rupture, or fire in equipment or pipelines; (4) Severe air or liquid leaks in equipment, pipelines, or flanges that cannot be resolved; (5) Failure of critical control instruments. 2. Procedure steps: (1) Immediately notify the heat transfer oil system to stop heating, open the internal short-circuit valve of that system, and cease supplying heat transfer oil to the gas generation unit. (2) Close the converter front valve V1051 to isolate the vaporization tower system from the reaction system. Properly depressurize the system downstream of the converter. The vaporization system can maintain stable pressure. (3) Stop the feed pump P101A/B. (4) Stop the desalinated water feed pumps P102A/B. (5) Implement special protection measures for the catalyst (for specific procedures, see 7.4 Use and Protection of the Catalyst). (6) Further actions will be taken after identifying the cause of the accident. 7.4 Use and Protection of Catalysts 7.4.1 Cleaning and Preparation of the Conversion Furnace 1. Remove the upper and lower manholes from the conversion furnace. First, check whether the quality of the furnace meets the requirements; then remove all rust and debris from the upper and lower end caps inside the furnace, as well as from the tube bundles, plate tubes, and girders. If necessary, carry out acid washing or water washing, followed by wiping clean and drying it for use – ensuring that there is no rust or debris present. 2. On the lower head plate, place 2 layers of 12-mesh wire mesh according to the specified requirements. Fill the plate with washed and dried alumina ceramic balls of Φ10～12mm, then level the upper surface of these ceramic balls; it is required that there be a space of 10～15mm between the upper surface of the ceramic balls and the lower surface of the conversion furnace’s head plate. 3. Reinstall the lower and upper head manholes, purge the air, and conduct another leak test on the converter. Only after confirming that there are no leaks in the flanges of the lower head manholes can the pressure be released and the air discharged, preparing for catalyst loading. 7.4.2 Loading and Unloading of Catalysts 1. Preparation (1) Check that the maintenance tools and protective equipment are complete and in good condition. (2) Prepare specialized tools such as measuring cups, funnels, and rulers designed for loading catalysts. (3) Conduct a quality inspection on the catalyst after activation, and use a steel mesh sieve with a mesh size of 6–10 to remove any fine particles from the catalyst for later use. Catalysts that have been improperly contaminated or deteriorated due to water exposure during transportation or storage generally cannot be used. The catalyst can only be loaded into the converter once it is confirmed that its quality meets the requirements. 2. Installing the catalyst: (1) Remove the manhole on the top cover of the converter, and check again whether the interior of the converter is clean; if it is not up to standard, it must be cleaned thoroughly once more. Inspect each reaction tube individually to check for any abnormalities such as blockages. (2) Fill the catalyst into each tube at a fixed volume and mark them to avoid missing or double-filling. (3) Do not rush during loading to avoid bridge formation; when bridge formation occurs, make proper markings and address it promptly. (4) After quantitative loading is complete, check each one individually for any missing items; once it is confirmed that nothing is missing and any bridging issues have been resolved. If necessary, install it once more to ensure that the amount of catalyst in each tube is roughly equal. (5) Once all loading is complete, install the manhole and pipelines on the converter’s top head. Note: After the catalyst is loaded, a gas-tightness test must be conducted on the conversion furnace as required, to ensure that there are no leaks at the manway flanges on the furnace’s head ； Remove the lower filter from the converter, clean the debris on the screen, and reinstall the filter ； Leak checks are conducted on the equipment and pipelines that have been removed from the converter, and if necessary, further tests are carried out to ensure that the leakage rate is within acceptable limits. 3. Removing the catalyst: When it is necessary to remove the catalyst for various reasons, if a reduced or used catalyst is to be removed, it must first be passivated before disassembly (for specific procedures, see the catalyst usage instructions). (1) Open the inlet at the upper head of the conversion furnace. (2) Open the manhole at the lower head of the conversion furnace to remove the alumina ceramic balls. (3) The catalyst will be gradually exposed as the ceramic balls are removed; the catalyst is taken out, and then the catalyst in each reaction tube is removed one by one. (4) Collect the catalyst and alumina ceramic balls separately, and clean the conversion furnace thoroughly. 7.4.3 Purging of the reduction system: Since both the methanol used as raw material and the hydrogen produced in this device are flammable and explosive substances, it is necessary to purge the system with nitrogen before starting up the operation, ensuring that the oxygen level is below 0.5%. The catalyst reduction process uses hydrogen as the reducing gas; to prevent repeated reduction-oxidation cycles caused by the presence of oxygen in the system, the reduction environment must be maintained at O2 ≤ 0.5%, and the oxygen content in the nitrogen used for reduction must be below 0.1%. System replacement can be carried out in two steps. Before the displacement, open the relevant valves one by one in the direction of the displacement airflow. 1. Reduction and washing by displacement: Nitrogen is introduced through the nitrogen inlet valve V1032, and the system is displaced in the following flow direction: →C101→E102→T101→E101→R101→E102→E103→T102→V104; the gas is then vented through the vent pipe located after tank V104. 2. Vaporization system and partial pipe sections replacement: (1) Replacement of the vaporization tower T101 system: By opening the drain valves V1040 and V1041 at the bottom of tower T101 to allow exhaust, gas samples are taken from the bottom of the tower; when the O2 level is ≤0.5%, these drain valves V1040 and V1041 are closed. Open the exhaust valves at the outlets of pumps P101A/B to purge the PL103 pipeline. (2) Replacement of the NH103 pipeline: After the system has been successfully replaced, close outlet valve V1057 of R101 and open valve V1051; samples are taken at the sampling point A103. The system replacement is considered complete when the O2 level is ≤0.5%. (3) Replacement of the air bag: Drain the gas from the V102 air bag, then replace it with an appropriate amount of nitrogen 2–3 times, after which the air bag can be integrated into the system. 7.4.4 Catalyst reduction and passivation procedures 1. Preparation (1) Check that all equipment, valves, and instruments in the reduction system are in proper condition; close all valves and turn on the instruments to put them in standby mode. (2) Prepare the nitrogen and hydrogen for reduction, ensuring they meet the quality requirements. (3) Notify the heat transfer oil unit and the analysis laboratory to prepare for operation, and inform them to supply cooling water. 2. Catalyst reduction procedure: The catalyst must be reduced before use. Since the main components of this catalyst are CuO-ZnO-Al2O3, it is the active elemental copper that plays a key role in the conversion reaction; hydrogen is used as the reducing gas, while nitrogen is used as the carrier gas during the reduction process. The reduction reaction is a highly exothermic reaction; therefore, the hydrogen-to-nitrogen ratio as well as the space velocity of the reducing gas must meet the specified requirements. The reduction reaction equation is: CuO + H2 → Cu + H2O. The catalyst contains about 5% physical water, and a small amount of water is generated during the reduction process; this water must be condensed and then removed. The Roots blower in this process provides power for the circulation of reducing gas. The reduction process is as follows: (1) Open the system valves for reduction; the flow direction of the catalyst reduction gas stream is as follows: NH102→E102→E101→R101→E102→E103→NH101. Open valves V1034 and V1035 to fill bladder V102 with nitrogen to 80% of its volume. (2) Start the Roots blower to restore gas circulation in the system. (3) Open the E103 cooling water inlet and outlet valves. (4) Open the heat transfer oil inlet valve of converter R101 ； Open the heat transfer oil inlet valve V1039 of Tower T101, and close the short-circuit valve V1038. Start the heat transfer oil circulation pump to circulate the heat transfer oil system. (5) Check whether the reduction system and the heat transfer oil system are operating properly. If there are no abnormalities, notify the heat transfer oil system to raise the temperature according to the catalyst reduction procedure. (6) When the temperature of the heat transfer oil rises to 160°C, open V1038 and close the heat transfer oil inlet valve V1039 at the bottom of tower T101. (7) The specific reduction procedure shall be followed as indicated in the catalyst instruction manual. (8) During the reduction process, condensate water should be discharged regularly at the drain valve at the bottom of tank T102. Regularly supply nitrogen and hydrogen to the system. (9) Once the catalyst reduction is complete, shut down the system following these steps: a. Close the external hydrogen and nitrogen inlet valves. b. Stop the Roots blower. c. Close the reduction gas system valves V1058, V1069, V1046. At this point, it is possible to proceed with feeding the material into the conversion furnace and starting up the operation. (10) When the catalyst is being reduced, an emergency shutdown is required in case of any accidents. The operation is as follows: a. Stop supplying hydrogen gas. b. Stop heating with heat transfer oil, and maintain the circulation of the heat transfer oil. c. Identify the cause before taking further action. In the case of a temporary fault, normal operation can be resumed after it is resolved ； For long-term parking, nitrogen protection or passivation treatment is applied as appropriate. 3. Catalyst deactivation procedure: Any catalyst that has been reduced (including those that have not been fully reduced) must be deactivated before it is removed. If production is to stop for an extended period, deactivation is also necessary in order to protect the catalyst. The reactor must be kept at positive pressure before passivation, and air entry is prohibited. The passivation system is the same as the reduction system, and the valves are opened or closed in the same way. Both the passivation process and the reduction process are highly exothermic reactions; therefore, attention must be paid to the ratio of nitrogen to oxygen as well as the volume of gas circulating in the system. The passivation process occurs at a temperature below 60°C, so no external heating is required. The specific procedures for passivation shall be followed as per the catalyst instruction manual. 7.4.5 Protection of the catalyst 1. Under no circumstances shall the temperature of the catalyst layer exceed 300°C. 2. The reduced catalyst must absolutely not come into contact with oxygen or air. 3. During the use of the catalyst, attempts should be made to avoid stopping the process midway. Every time the vehicle is stopped, even with passivation or nitrogen protection measures in place, it still affects the service life of the catalyst. 4. The heating and cooling of the catalyst must be carried out slowly; rapid heating and cooling are prohibited. 5. Under the conditions of meeting production capacity and yield requirements, the catalyst should be operated at low temperatures, which helps to extend its service life. 6. It is strictly prohibited to allow toxic substances such as sulfur, phosphorus, and halogen elements to enter the system, to prevent catalyst poisoning. 7. The raw materials used in the device, such as methanol, deionized water, nitrogen, and hydrogen, must meet specified requirements, and strict testing procedures must be followed. 8. If any abnormalities are detected, especially in the reaction system, the operation should be stopped immediately for analysis and inspection; operation can resume only after the issues have been resolved. 7.4.6 Special protection measures are generally used during emergency shutdowns; special protection measures can also be employed for normal shutdowns that occur over a short period of time. For long-term shutdowns, passivation procedures can be used to protect the catalyst. 1. 2–3 cylinders of pure nitrogen should always be available on-site at the converter plant. It is also equipped with a nitrogen pressure regulator, which is connected via pipelines to the dedicated protective nitrogen inlet valve at the converter inlet. 2. When special protection is required, first reduce the system pressure to 0.2 MPa (with the heat transfer oil temperature below 200°C). Close the inlet and outlet valves of R101, open the nitrogen inlet valves V1032 and V1053A/B, and activate the nitrogen pressure regulator to maintain an outlet pressure of 0.2–0.3 MPa. Open the vent valve V1056 on the outlet pipeline of R101 and use approximately 20 m3 of nitrogen to purge the reactor; thereafter, close valve V1056 to seal the reactor. 3. Then the system cools down naturally, and the nitrogen pressure control valve is adjusted gradually to maintain the outlet pressure of the nitrogen control valve at 0.05–0.3 MPa (to ensure a positive pressure inside the conversion furnace), until the special protection mode for the conversion furnace is completed. Special note: Throughout the entire special protection process, it is essential to ensure that there is no negative pressure inside the conversion furnace. 8.0 Environmental Protection and Safety Considerations 8.1 This process utilizes an internal self-circulation system; aside from periods of shutdown and maintenance, no waste gases are emitted during normal operation. Only a small amount of gas containing CO2, methanol, etc. is released from the circulation liquid tank V103, at a rate of 2–5 Nm3/h. The composition of this gas is as follows: Component: CO2, CH3OH, H2O; Volume percentages: 91.11%, 1.98%, 6.91%. Due to the low volume of this gas, it is essentially non-toxic and can be discharged directly into the atmosphere. 8.2 A small amount of methanol-containing wastewater is discharged periodically from the bottom of vaporization tower T101; its concentration is below 0.5%, along with trace amounts of acids, bases, and other impurities. 99.5% of this wastewater is water. Due to the small volume – approximately 15.0–20.0 Kg/h on average – it can be discharged directly into the sewer system after dilution. 8.3 Safety Protection: The main materials used in this section are methanol and hydrogen, which are flammable, explosive, and toxic substances. Therefore, it is strictly prohibited for any leaks or spills to occur in the equipment and pipelines; good ventilation must be maintained inside the workshop. Methanol causes severe damage to the human optic nerve, and blindness can occur in severe cases; therefore, it is essential to wear the required protective equipment during operation and maintenance to prevent methanol from getting into the eyes. Open flames are strictly prohibited in this facility; any work involving fire must be carried out with an appropriate permit. 9.0 Analysis Procedure: This device uses methanol and deionized water as raw materials; under the action of a catalyst, methanol is converted to conversion gas, which is then separated by pressure swing adsorption to produce pure hydrogen. These procedures include catalyst reduction analysis, feedstock analysis, control analysis of the methanol conversion process, and impurity analysis in the product hydrogen. Analysis requirements: During normal operation of the plant, the concentration of the feed liquid, the concentration of the circulating liquid, and the composition of the conversion gas must be analyzed at least once every eight hours. The analysis results should be provided to the process engineers to ensure the proper functioning of the plant. During catalyst reduction, the components of the reducing gas are analyzed every half hour, and the analysis results are provided to the process operators. 9.1 Preparations before driving 9.1.1 Instrument calibration Adjust all parameters of the instrument in accordance with the instructions provided, and check to ensure that it is functioning properly. 9.1.2 Treatment of chromatography columns: Two chromatography columns with an inner diameter of 3 millimeters and a length of 2 meters were cleaned using 10% NaOH and 10% HCl solutions respectively, then washed with water, followed by cleaning with anhydrous ethanol. After that, they were dried using a vacuum pump and set aside for use. 9.2 Analysis of the catalyst reduction process: As required by the process specifications, a hydrogen-nitrogen mixture is used in the catalyst reduction process; the hydrogen content in this mixture increases gradually from 0.5% to 10%, until the hydrogen content at the inlet and outlet of the conversion furnace becomes equal, indicating that the reduction process is complete. This process takes approximately 56 hours. Requirements for the hydrogen-nitrogen mixture: The oxygen content in both the hydrogen and nitrogen to be used must be less than 0.2%. Therefore, it is necessary to first determine the oxygen content in each of the hydrogen and nitrogen gases, as well as during the purging process of the process system. 9.3 Raw Material Analysis: The process requires that the methanol in the aqueous solution fed into the vaporizer have a concentration of 48–52%. 10.0 Safety Procedures 10.1 Introduction: This production facility utilizes a methanol steam reforming process for hydrogen production, as designed by Shanghai Huaxi Design Institute. PSA Pressure Swing Adsorption Section 3.5 PSA Unit Operation 3.5.1 Tasks and Objectives The gas coming out of the third separation tank in the medium-pressure gas processing unit contains approximately 6% methane, 3% carbon monoxide, and 18% carbon dioxide. Both methane and carbon monoxide possess high calorific values, and carbon monoxide as well as carbon dioxide are toxic substances for subsequent hydrogen production equipment. The purpose of the PSA unit is to remove these toxic substances in order to obtain hydrogen with a purity of over 99%. Methane and carbon monoxide are then released as PSA off-gases and mixed into the fuel gas where they are burned, thereby allowing their thermal energy to be recovered. 3.5.2 Process Principle and Method (1) Process Principle Pressure swing adsorption technology is based on the physical adsorption of gas molecules by the surface of adsorbents (porous solid materials). It takes advantage of the fact that adsorbents readily adsorb high-boiling-point components at constant pressure, while having difficulty adsorbing low-boiling-point components; moreover, the amount of adsorption increases under high pressure (for the components to be adsorbed) and decreases under reduced pressure (for the components to be desorbed). The feed gas is passed through an adsorbent bed at high pressure; impurity components with higher boiling points than hydrogen are selectively adsorbed, while hydrogen and those impurity components with lower boiling points are not easily adsorbed and thus pass through the adsorbent bed, achieving the separation of hydrogen from the impurity components. Then, the adsorbed impurity components are desorbed under reduced pressure to regenerate the adsorbent, enabling it to be used again for adsorbing and separating impurities in the next cycle. This cycle of adsorbing impurities under pressure to purify hydrogen and desorbing the impurities under reduced pressure to regenerate the adsorbent is known as the pressure swing adsorption process. In the pressure swing adsorption process, the desorption of adsorbent impurities within the adsorption bed is achieved by reducing the partial pressure of the impurities. (2) The methods employed by this device are: ① Reducing the pressure in the adsorption bed (depressurization); ② Flushing it with the product components. Figure 3-5-1 schematically illustrates the adsorption and desorption processes in the adsorption bed. Atmospheric pressure desorption (see Figure 3-1): Pressurization process (A–B): The adsorption bed, after being regenerated through desorption, is at the lowest pressure P1 during this process, with an impurity adsorption amount of Q1 at point A. Under these conditions, the pressure is increased to the adsorption pressure P3 using the product components, while the amount of impurities adsorbed in the bed, Q1, remains unchanged (point B). Adsorption process (B–C): Under a constant adsorption pressure, the feed gas continuously enters the adsorption bed, while the product components are discharged. The amount of impurities retained in the adsorption bed gradually increases; when it reaches the specified retention amount Q3 (point C), the inflow of feed gas is stopped, and the adsorption process terminates. At this point, there is still a portion of adsorbent in the adsorption bed that has not yet absorbed impurities (if all the adsorbent has been saturated with impurities, the adsorption capacity could be Q4, at point C’). Forward process (C–D): The pressure is reduced in the direction from the incoming raw gas to the output product; the gas that flows out still consists of the product components, and it is used to increase the pressure in other adsorption beds or for flushing purposes. Figure 3-5-1: Schematic diagram of the adsorption-desorption process in the pressure swing adsorption cycle. During this process, as the pressure inside the adsorption bed continues to decrease, the impurities on the adsorbent are continuously desorbed. The desorbed impurities are then absorbed by the adsorbent that has not yet absorbed sufficient amounts of impurities; as a result, the impurities do not leave the adsorption bed, and the amount of impurities retained in the bed, Q3, remains constant. When the pressure of the adsorption bed is reduced to point D, all of the adsorbent in the bed is occupied by impurities, and the pressure is P2. Reverse operation process (D–E): Pressure is gradually reduced in the opposite direction to that used to produce products from the feed gas, until it reaches the lowest pressure P1 of the pressure swing adsorption process (usually close to atmospheric pressure). Most of the impurities adsorbed in the bed are carried out of the tower with the gas flow, while the amount of impurities remaining in the bed is Q2. Rinsing process (E–A): Based on the experimentally determined adsorption isotherms, there is still a certain amount of impurities retained in the adsorption bed at pressure P1; to desorb as much of these impurities as possible, it is necessary to further reduce the pressure inside the bed. Here, the product components discharged during the forward pressure reduction process in another adsorption bed are subjected to reverse flushing at the minimum process pressure P1. This continuously reduces the partial pressure of impurities, causing them to desorb and be carried out of the adsorption bed along with the flushing gas. After a certain degree of flushing, when the amount of impurities retained in the bed is reduced to the minimum value Q1 for the process, regeneration is terminated. At this point, the adsorption bed completes one cycle of adsorption-desorption regeneration, and the pressure is increased again for the next cycle. 3.5.3 Logistics 3.5.3.1 Raw Materials The raw material for this unit is medium-pressure gas; the composition of this raw gas is shown in Table 3-5-1: Table 3-5-1 Composition of Raw Gas Component H2 N2 CO2 CH4 CO H2O Σ V% 72.33 1.63 17.8 5.62 2.3 0.32 100 The pressure of the raw gas entering the PSA unit is 2.1 MPa; the temperature is ≤40°C, and the flow rate is 15,360.2 Nm3/h. The range for adjusting the production load is 30% to 110%. 3.5.3.2 Products The product is hydrogen, with the required quality standard being H2 ≥ 99.9% ； Among these: CO + CO2 < 10 ppm; Pressure: ≥ 2.05 MPa; Temperature: ≤ 40°C; Flow rate: 10,000 Nm3/h. By-products: The by-product is the desorbed gas, and its composition is shown in Table 3-5-2: Table 3-5-2 Composition of Desorbed Gas Component H2 N2 CO2 CH4 CO H2O Σ V% 20.73 4.46 51.01 16.10 6.59 0.92 100. Pressure of desorbed gas: 0.05 MPa; Temperature: 40°C; Gas flow rate: 5,360.2 Nm3/h. 3.5.4 Process Equipment This unit is equipped with the following process equipment: Equipment Name Tag Number Quantity Purpose Adsorbers T-401/A–H 8 units To absorb impurity components from the feed gas. Pressure Relief Tank V-401 1 unit For pressure relief during gas release. Desorbed Gas Buffer Tank V-402 1 unit To reduce fluctuations in the output pressure of the desorbed gas. Desorbed Gas Mixing Tank V-403 1 unit To reduce fluctuations in both the output pressure and composition of the desorbed gas. Among these, the adsorbers are the core equipment of this system; there are three types of adsorbents inside them – activated alumina, activated carbon, and C-type molecular sieves. The layering arrangement of these adsorbents is shown in Figure 3-5-2. 3.5.5 Process Flow The schematic diagram of the PSA-H2 system is shown in Figure 3-5-3. Figure 3-5-3 Schematic Diagram of Process Flow The feed gas (point 1) enters the pressure swing adsorption system, which consists of 8 adsorbers (T-401/A–H) along with a series of programmable valves, at a pressure of 2.1 MPa and a temperature of 40°C. The PSA system operates with 8 towers, featuring a constant-pressure desorption process in which feed is supplied to two towers simultaneously four times. The feed gas passes from the inlet side, from bottom to top, through two adsorbers that are in the adsorption phase; the adsorbent filled within these adsorbers absorbs the components in the feed gas that are readily adsorbed, while the hydrogen component, which is less easily adsorbed, flows out as product gas from the outlet side. The remaining six towers carry out the other steps respectively; the eight towers operate in an alternating cycle, with their operations overlapping in time, thereby ensuring a continuous supply of feed gas and a steady output of product gas to the outside (point ②). The desorbed gas from the PSA system comes from the reverse flushing and washing steps. At the beginning of the reverse flushing step, when the pressure is high (reverse flushing pressure P ≥ 0.1 MPa), part of the desorbed gas first enters the desorbed gas buffer tank (V-402); after its pressure is reduced by the control valve PV-406, it is discharged into the desorbed gas mixing tank (V-403) ； The desorbed gas from the section with lower reverse pressure, along with the flushing gas used in the flushing step, are also discharged through control valve XV-407 into the desorbed gas mixing tank (V-403), where they are mixed before being steadily sent outside (point ③). 3.5.6 Operation mode of the device: This device can be operated in one of the following four modes; under normal conditions, it operates in the 8-2-4/P process mode. Operation mode, Number of online adsorbers, Number of adsorbers operating simultaneously, Number of pressure equalization cycles, Adsorption bed regeneration steps, Raw material load %, Guaranteed H2 extraction rate %: 8‑2‑4/P: 8, 2, 4; Reverse flow, flushing: 100, 89; 7‑2‑3/P: 7, 2, 3; Reverse flow, flushing: 100, 85; 6‑2‑2/P: 6, 2, 2; Reverse flow, flushing: 100, 82; 4‑1‑2/P: 4, 1, 2; Reverse flow, flushing: 50, 80. 3.5.7 Pressure swing adsorption process steps: The pressure swing adsorption system in this unit is composed of 8 adsorbers, 58 programmably controlled valves, and 10 sets of control valves connected through pipelines. Each adsorber is connected to 7 programmable valves, with 2 at the inlet side and 5 at the outlet side. The coding rules for program-controlled valve identifiers are as follows: KV X × Adsorber serial number: 1, 3, 5, 7, 9, and A–H. Function codes: 1 – Raw material inlet valve; 2 – Product outlet valve; 3 – Reverse pressure release and flushing outlet valve; 4 – Forward pressure release valve; 5 – First and final pressure increase valve; 6 – Flushing inlet valve; 7 – Second, third, and fourth equalization valves; 8 – Overall reverse pressure release valve. Character codes for program-controlled valves and instrument grouping numbers are shown in Figure 3-5-4. Coding rules for program-controlled valve identifiers: 3.5.7.1 8-2-4/P operation mode. (1) Process steps: When operating in the 8-2-4/P mode, two adsorbers are in the stage of absorbing raw gas and producing hydrogen, while the remaining six adsorbers are in various stages of catalyst regeneration. Each adsorber goes through the same sequence of steps, arranged as shown in Table 3-5-3, thereby enabling continuous input of feed gas and a steady output of product hydrogen. Table 3-5-3: Timing Table for the 8-2-4/P Process
Cycle: 1 2 3 4 5 6 7 8
Pressure (MPa): 2.2 1.76 1.33 0.9 0.46 0.2 0.05 0.05 0.46 0.46 0.9 0.9 1.33 1.33 1.76 2.2
Time (s): 240 40 40 40 40 80 40 80 40 40 40 40 40 40 40 40 80

T-401/A: A E1D E2D E3D E4D PP D P E4R IS E3R IS E2R IS E1R FR
V-7115/2: E1R FR A E1D E2D E3D E4D PP D P E4R IS E3R IS E2R IS
V-7115/3: IS E2R IS E1R FR A E1D E2D E3D E4D PP D P E4R IS E3R
V-7115/4: E4R IS E3R IS E2R IS E1R FR A E1D E2D E3D E4D PP D P
V-7115/5: D P E4R IS E3R IS E2R IS E1R FR A E1D E2D E3D E4D PP
V-7115/6: E4D PP D P E4R IS E3R IS E2R IS E1R FR A E1D E2D E3D
V-7115/7: E1D E2D E3D E4D PP D P E4R IS E3R IS E2R IS E1R FR A
V-7115/8: A E1D E2D E3D E4D PP D P E4R IS E3R IS E2R IS E1R FR A

(2) Process Description
The pressure swing adsorption process of this unit will be explained by taking the various steps undergone by the first adsorber (T-401/A) during one cycle as an example. Adsorption (A): Open the programmed control valves KV1-1 and KV2-1 (close the other valves connected to adsorber T-401/A; the same applies hereafter). The feed gas enters through valve KV1-1 and passes upward through adsorber T-401/A; the impurity components in the feed gas are adsorbed and separated, and the resulting hydrogen gas exits through valve KV2-1. When the adsorption front of the adsorbed impurities moves to a certain position in the adsorber, KV1-1 and KV2-1 are turned off, stopping the inflow of feed gas and the output of product. At this point, there is still a section of adsorbent between the adsorption front in the adsorber and the outlet end that has not absorbed impurities. Process pressure: 2.2 MPa. Step execution time: ~240 s. First-stage pressure equalization drop (abbreviated as E1D): Open the programmable valves KV5-1 and KV5-4. After the adsorption step in adsorber T-401/A is completed, it is connected to the outlet end of adsorber T-401/D, which has just finished its E2R step, in order to achieve pressure equalization at the first stage. During this pressure equalization process, the adsorption front in adsorber T-401/A moves toward the outlet end, but it still does not reach that outlet end. When the pressures of the two adsorbers are roughly equal, closing valve KV5-1 completes the pressure reduction step (valve KV5-4 remains open for the subsequent final pressure increase step in T‑401/D). Process pressure: Decreases from 2.2 MPa to 1.76 MPa. Step execution time: ~40 seconds. Second-stage pressure equalization drop (abbreviated as E2D): Open the programmed control valves KV7-1 and KV7-5. After the equalization step in adsorber T-401/A is completed, it is connected to the outlet end of adsorber T-401/E, which has just finished the three-equalization-rise (E3R) step, in order to carry out a second stage of pressure equalization. During this pressure equalization process, the adsorption front in adsorber T-401/A continues to move toward the outlet end, but it has not yet reached it. When the pressures of the two adsorbers are roughly equal, the two-step pressure reduction is completed by closing valve KV7-5 (valve KV7-1 remains open for the next three-step pressure reduction in T-401/A). Process pressure: Decreases from 1.76 MPa to 1.33 MPa. Step execution time: ~40 s. Third-stage pressure equalization reduction (abbreviated as E3D): The programmable valve KV7-6 is opened, and valve KV7-1 is also kept open. After the step-two equalization process in adsorber T-401/A comes to an end, it is connected to adsorber T-401/F, which has just completed the four-equalization-rise (E4R) process, at its outlet end in order to carry out the third stage of pressure equalization. During this pressure equalization process, the adsorption front in adsorber T-401/A continues to move toward the outlet end, but it has not yet reached it. When the pressures of the two adsorbers are essentially equal, the three-step pressure reduction process is completed by closing valve KV7-6 (valve KV7-1 remains open for the next four-step pressure reduction in T‑401/A). Process pressure: Drops from 1.33 MPa to 0.9 MPa. Step execution time: ~40 s. Fourth-stage pressure equalization drop (abbreviated as E4D): The programmable valve KV7-7 is opened, and valve KV7-1 is also opened. After the three equalization steps for adsorber T-401/A are completed, it is connected to adsorber T-401/G, which has just finished its flushing (P) step, at the outlet end in order to carry out the fourth stage of pressure equalization. During this equalization process, the adsorption front in adsorber T-401/A continues to move toward the outlet end, but it has not yet reached it. When the pressures of the two adsorbers are roughly equal, close valve KV7-1; thus, the step of reducing pressure across KV7-6 is completed. Process pressure: Drops from 0.9 MPa to 0.46 MPa. Step execution time: ~40 s. Forward pressure reduction (abbreviated as FP, PP): Open the program-controlled valves KV4-1, KV6-8 and the control valve HV-502, and continue to open valve KV3-8. After the four equalization steps in adsorber T-401/A are completed, the purge gas in adsorber T-401/A flows through valve KV4-1, purge control valve HV-502, and valve KV6-8 to flush adsorber V-401/H, which has just completed the reverse purge (D) step, from top to bottom; the flushing gas is then discharged into the desorption gas mixing tank V-403 via valve KV3-8 and KHV-501. During the isobaric depressurization process, the pressure in adsorber T-401/A continues to decrease; its adsorption front keeps advancing toward the outlet end. When the pressure drops to approximately 0.2 MPa, valves KV4-1, KV6-8, KV3-8, KHV-501, and HV-502 are closed, marking the end of the isobaric depressurization step. At this point, the adsorption front has just reached the outlet end. Process pressure: Decreases from 0.46 MPa to 0.2 MPa. Step execution time: ~80 seconds. Reverse pressure relief (abbreviated as reverse relief, D): Open valves KV3-1 and KV8A. The gas with higher pressure in adsorber T‑401/A is discharged in the reverse direction through valves KV3-1 and KV8A into the desorbed gas buffer tank V‑402. When equilibrium is achieved between T‑401/A and V‑402, valve KV8A is closed; valve KV3-1 remains open, along with control valve KHV-501. The gas with lower pressure inside adsorber T‑401/A, after being discharged in the reverse direction, passes through valves KV3-1 and control valve KHV-501, and together with the gas in the desorbed gas buffer tank that has been depressurized by control valve PV-503A, it is sent out of the system through the desorbed gas mixing tank V‑403. The reverse discharge process ends when the pressure in adsorber T‑401/A approaches the output pressure of the desorbed gas (at which point valves KV3-1 and KHV-501-1 remain open for the next flushing step of T‑401/A). Process pressure: Decreases from 0.20 MPa to 0.05 MPa. Time for this step: ~40 s. Flushing (P): Open valves KV6-1 and KV4-2, as well as control valve HV-502; also keep valve KV3-1 and control valve KHV-501-1 open. Adsorber T-401/A was flushed using the counter-flow gas from adsorber T-401/B, which had just completed the E4D step, in order to further reduce the partial pressure of impurities in adsorber T-401/A and ensure thorough regeneration of the adsorbent. The purge gas is discharged into the desorption gas mixing tank V-403 via valves KV3-1 and KHV-501-1. When the pressure in adsorber T-401/B drops to the specified value, close valves KV6-1, KV3-1, KV4-2 and control valves HV-502, KHV-501, thereby ending the flushing process. Process pressure: Maintain at 0.05 MPa. Step execution time: ~80 s. Fourth-stage pressure equalization rise (abbreviated as E4R): Open valve KV7-1, and also continue to open valve KV7-3. Adsorber V-7115/1 is connected to the outlet end of adsorber T-401/C, which has just completed the three-way pressure equalization (E3D) step, in order to achieve fourth-level pressure equalization. During this pressure equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valves KV7-1 and KV7-3 are closed, thereby concluding the four-way pressure equalization step. Process pressure: Increases from 0.05 MPa to 0.46 MPa. Step execution time: ~40 s. Isolation (IS): At this time, all programmable valves connected to adsorber T-401/A are in the closed state, and the pressure of adsorber T-401/A remains unchanged. Process pressure: Maintain at 0.46 MPa. Step execution time: ~40 s. Third-stage pressure equalization rise (abbreviated as E3R): Open valve KV7-1, and also keep valve KV7-4 open. Adsorber T-401/A is connected to adsorber T-401/D, which has just completed the E2D step, at their outlet ends in order to achieve third-level pressure equalization. During this pressure equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valve KV7-1 is closed, thereby ending the three-equilibration step (valve KV7-4 remains open for the next step, namely the four-equilibration step, for T-401/D). Process pressure: Increases from 0.46 MPa to 0.9 MPa. Time for this step: ~40 s. Isolation (IS): At this point, all programmable valves connected to adsorber T-401/A are in the closed state, and the pressure of adsorber T-401/A remains unchanged. Process pressure: Maintain at 0.9 MPa. Step execution time: ~40 s. Second-stage pressure equalization rise (abbreviated as E2R): Open valves KV7-1 and KV7-5. The outlet ends of adsorber T-401/A and adsorber T-401/E, which has just completed an equalization down (E1D) step, are connected to perform a second-stage pressure equalization. During this process, the pressure in adsorber T-401/A increases. When the pressures in both adsorbers become essentially equal, valve KV7-1 is closed, marking the end of the second-stage equalization up process (valve KV7-5 remains open to facilitate the subsequent equalization down step for T-401/E). Process pressure: Increases from 0.9 MPa to 1.33 MPa. Time for this step: ~40 s. Isolation (IS): At this point, all programmable valves connected to adsorber T-401/A are in the closed state, and the pressure of adsorber T-401/A remains unchanged. Process pressure: Maintain at 1.33 MPa. Step execution time: ~40 s. First-stage pressure equalization rise (abbreviated as E1R): Open valves KV5-1 and KV5-6. Adsorber T-401/A is connected to adsorber T-401/F, which has just completed the adsorption (A) step, at their outlet ends in order to achieve pressure equalization at the first stage. During this pressure equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valve KV5-6 is closed, thereby ending this equalization step (valve KV5-1 remains open for the subsequent final pressure increase step in adsorber T-401/F). Process pressure: Increases from 1.33 MPa to 1.76 MPa. Step execution time: ~40 s. Final pressure increase (abbreviated as final charging, FR): Open the final charging flow control valve HV-501, and also keep valve KV5-1 open. After four equalization pressure increase steps, adsorber T-401/A was finally brought to the adsorption pressure gradually by using product gas to regulate the flow rate through control valve HV-501. When the pressure approaches the adsorption pressure, close valves KV5-1 and HV-502, and the final charging step is completed. Process pressure: increases from 1.76 MPa to 2.2 MPa. Step execution time: ~80 s. At this point, the adsorption and regeneration processes for adsorber T-401/A are complete, after which the next cycle begins. The step execution times and process pressures mentioned in the process description are illustrative; in actual operation, the device can adjust these times and pressures at any time according to changes in the flow rate, composition, and pressure of the feed gas. 3.5.7.2 7‑2‑3/P Operation Mode (1) Process Steps When operating in the 7‑2‑3/P mode, two of the adsorbers are in the adsorption stage where raw gas is fed in and hydrogen is produced, while the remaining five adsorbers are in various stages of catalyst regeneration. Each adsorber goes through the same sequence of steps, arranged as shown in Table 3-5-4, thereby enabling continuous input of feed gas and a steady output of product hydrogen. Table 3‑5‑4: Timing of the 7‑2‑3/P process – Periods 1, 2, 3, 4, 5, 6, 7
Time, s: 240, 40, 40, 40, 80, 40, 80, 40, 40, 40, 40, 40, 80
Pressure, MPa: 2.2, 1.66, 1.12, 0.59, 0.2, 0.05, 0.05, 0.59, 0.59, 1.12, 1.12, 1.66, 2.2

Adsorber: 1 – A, E1D, E2D, E3D, PP, D, P, E3R, IS, E2R, IS, E1R, FR; 2 – E1R, FR, A, E1D, E2D, E3D, PP, D, P, E3R, IS, E2R, IS; 3 – IS, E2R, IS, E1R, FR, A, E1D, E2D, E3D, PP, D, P, E3R; 4 – P, E3R, IS, E2R, IS, E1R, FR, A, E1D, E2D, E3D, PP, D; 5 – PP, D, P, E3R, IS, E2R, IS, E1R, FR, A, E1D, E2D, E3D; 6 – E1D, E2D, E3D, PP, D, P, E3R, IS, E2R, IS, E1R, FR, A; 7 – A, E1D, E2D, E3D, PP, D, P, E3R, IS, E2R, IS, E1R, FR, A

(2) Process description: The main steps of the 7‑2‑3/P process are illustrated by describing the operation mode with the eighth adsorber (T‑401/H) removed. The process steps within one cycle are explained using the first adsorber (T‑401/A) as an example. Adsorption (A): Open the programmed control valves KV1-1 and KV2-1 (close the other valves connected to adsorber T-401/A; the same applies hereafter). The feed gas enters through valve KV1-1 and passes upward through adsorber T-401/A; the impurity components in the feed gas are adsorbed and separated, and the resulting hydrogen gas exits through valve KV2-1. When the adsorption front of the adsorbed impurities moves to a certain position in the adsorber, KV1-1 and KV2-1 are turned off, stopping the inflow of feed gas and the output of product. At this point, there is still a section of adsorbent between the adsorption front in the adsorber and the outlet end that has not absorbed impurities. Process pressure: 2.2 MPa. Step execution time: ~240 s. First-stage pressure equalization drop (abbreviated as E1D): Open the programmable valves KV5-1 and KV5-4. After the adsorption step in adsorber T-401/A is completed, it is connected to the outlet end of adsorber T-401/D, which has just finished its E2R step, in order to achieve pressure equalization at the first stage. During this pressure equalization process, the adsorption front in adsorber T-401/A moves toward the outlet end, but it still does not reach that outlet end. When the pressures of the two adsorbers are roughly equal, closing valve KV5-1 completes the pressure reduction step (valve KV5-4 remains open for the subsequent final pressure increase step in T‑401/D). Process pressure: Decreases from 2.2 MPa to 1.66 MPa. Step execution time: ~40 s. Second-stage pressure equalization reduction (abbreviated as E2D): The programmable valves KV7-1 and KV7-5 are activated. After the equalization step in adsorber T-401/A is completed, it is connected to the outlet end of adsorber T-401/E, which has just finished the three-equalization-rise (E3R) step, in order to carry out a second stage of pressure equalization. During this pressure equalization process, the adsorption front in adsorber T-401/A continues to move toward the outlet end, but it has not yet reached it. When the pressures of the two adsorbers are roughly equal, the two-step pressure reduction is completed by closing valve KV7-5 (valve KV7-1 remains open for the next three-step pressure reduction in T-401/A). Process pressure: Decreases from 1.66 MPa to 1.12 MPa. Step execution time: ~40 s. Third-stage pressure equalization reduction (abbreviated as E3D): The programmable valve KV7-6 is opened, and valve KV7-1 is also kept open. After the equalization process in step two of adsorber T-401/A comes to an end, it is connected to adsorber T-401/F, which has just finished its flushing (P) step, at the outlet end in order to achieve third-level pressure equalization. During this equalization process, the adsorption front in adsorber T-401/A continues to move toward the outlet end, but it has not yet reached it. When the pressures of the two adsorbers are roughly equal, valve KV7-1 is closed, and the step of reducing pressure for KV7-6 is completed. Process pressure: Decreases from 1.12 MPa to 0.59 MPa. Step execution time: ~40 seconds. Forward depressurization (abbreviated as PP): Open the programmed control valves KV4-1, KV6-7, and the control valve HV-502; subsequently open valve KV3-7. After the three equalization steps in adsorber T-401/A are completed, the purge gas in adsorber T-401/A flows through valve KV4-1, purge control valve HV-502, and valve KV6-7 to flush adsorber T-401/G, which has just completed the reverse purge (D) step, from top to bottom; the flushing gas is then discharged into the desorption gas mixing tank V-403 via valve KV3-7 and KHV-501. During the forward discharge process, the pressure in adsorber T-401/A drops further, and its adsorption front continues to move toward the outlet end. When the pressure falls to around 0.2 MPa, valves KV4-1, KV6-7, KV3-7, KHV-501, and HV-502 are closed, marking the end of the forward discharge step; at this point, the adsorption front has just reached the outlet end. Process pressure: Decreases from 0.59 MPa to 0.2 MPa. Step execution time: ~80 s. Reverse pressure release (abbreviated as RD, D): Open valves KV3-1 and KV8A. The gas with higher pressure inside adsorber T-401/A is released in the reverse direction through valves KV3-1 and KV8A into the desorbed gas buffer tank V-402. When equilibrium is achieved between T-401/A and V-402, valve KV8A is closed; valve KV3-1 remains open, along with control valve KHV-501. The gas with lower pressure inside adsorber T-401/A, after being released in the reverse direction, passes through valves KV3-1 and control valve KHV-501, and together with the gas in the desorbed gas buffer tank that has been depressurized by control valve PV-503A, it is sent out of the system via the desorbed gas mixing tank V-403. The reverse release process ends when the pressure inside adsorber T-401/A approaches the output pressure of the desorbed gas (valves KV3-1 and KHV-501 remain open for the next flushing step of T-401/A). Process pressure: Decreases from 0.20 MPa to 0.05 MPa. Step execution time: ~40 seconds. Flushing (P): Open valves KV6-1, KV4-2, and control valve HV-502; subsequently open valve KV3-1 and control valve KHV-501. The counter-current purge gas from adsorber T-401/B, which has just completed the three-stage equalization drying (E3D) process, is used to flush adsorber T-401/A, thereby further reducing the partial pressure of impurities in T-401/A and ensuring thorough regeneration of the adsorbent. The purge gas is discharged into the desorption gas mixing tank V-403 via valves KV3-1 and KHV-501. When the pressure in adsorber T-401/B drops to the specified value, close valves KV6-1, KV3-1, KV4-2 and control valves HV-502, KHV-501, thereby ending the flushing process. Process pressure: Maintain at 0.05 MPa. Step execution time: ~80 s. Third-stage pressure equalization rise (abbreviated as E3R): Open valve KV7-1, and also keep valve KV7-3 open. Adsorber T-401/A is connected to adsorber T-401/C, which has just completed the E2D step, at their outlet ends in order to achieve third-level pressure equalization. During this pressure equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valve KV7-1 and KV7-3 are closed, thereby concluding the three-step pressure equalization process. Process pressure: Increases from 0.05 MPa to 0.59 MPa. Step execution time: ~40 s. Isolation (IS): At this time, all programmable valves connected to adsorber T-401/A are in the closed state, and the pressure of adsorber T-401/A remains unchanged. Process pressure: Maintain at 0.59 MPa. Step execution time: ~40 s. Second-stage pressure equalization rise (abbreviated as E2R): Open valves KV7-1 and KV7-4. Adsorber T-401/A is connected to adsorber T-401/D, which has just completed an equalization (E1D) step, at their outlet ends in order to achieve a second stage of pressure equalization. During this equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valve KV7-1 is closed, marking the end of the second equalization step (valve KV7-4 remains open for the next step, namely the third equalization step, for T-401/D). Process pressure: rises from 0.59 MPa to 1.12 MPa. Step execution time: ~40 s. Isolation (IS): At this time, all programmable valves connected to adsorber T-401/A are in the closed state, and the pressure of adsorber T-401/A remains unchanged. Process pressure: Maintain at 1.12 MPa. Step execution time: ~40 s. First-stage pressure equalization rise (abbreviated as E1R): Open valves KV5-1 and KV5-5. Adsorber T-401/A is connected to adsorber T-401/E, which has just completed the adsorption (A) step, at their outlet ends in order to achieve pressure equalization at the first stage. During this pressure equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valve KV5-5 is closed, thereby ending this equalization step (valve KV5-1 remains open for the subsequent final pressure increase step in adsorber T-401/A). Process pressure: Increases from 1.12 MPa to 1.66 MPa. Step execution time: ~40 s. Final pressure increase (abbreviated as final charging, FR): Open the final charging flow control valve HV-501, and also keep valve KV5-1 open. After three equalization and pressurization steps, adsorber T-401/A is finally brought to the adsorption pressure gradually by flowing product gas through control valve HV-501, which restricts the flow rate. When the pressure approaches the adsorption pressure, close valves KV5-1 and HV-502, and the final charging step is completed. Process pressure: increases from 1.66 MPa to 2.1 MPa. Step execution time: ~80 s. At this point, the adsorption and regeneration processes for adsorber T-401/A are complete, after which the next cycle begins. The step execution times and process pressures mentioned in the process description are illustrative; in actual operation, the device can adjust these times and pressures at any time according to changes in the flow rate, composition, and pressure of the feed gas. 3.5.7.3 6–2–2/P Operation Mode (1) Process Steps: When operating in the 6–2–2/P mode, two of the adsorbers are in the adsorption stage where raw gas is fed in and hydrogen is produced, while the remaining four adsorbers are in various stages of catalyst regeneration. Each adsorber goes through the same sequence of steps, arranged as shown in Table 3-5-5, thereby enabling a continuous feed of feed gas and a steady, continuous output of product hydrogen. Table 3–5–5: Process timing for the 6–2–2/P process
Cycle: 1 2 3 4 5 6
Time, s: 240 40 40 40 80 40 80 40 40 80
Pressure, MPa: 2.2 1.48 1.48 0.76 0.2 0.05 0.05 0.76 1.48 2.2

Adsorbers:
1: A E1D IS E2D PP D P E2R E1R FR
2: E1R FR A E1D IS E2D PP D P E2R
3: P E2R E1R FR A E1D IS E2D PP D
4: PP D P E2R E1R FR A E1D IS E2D
5: E1D IS E2D PP D P E2R E1R FR A
6: A E1D IS E2D PP D P E2R E1R FR A

(2) Process description
The main steps of the 6–2–2/P process are described below, taking into account the operation mode involving the removal of the seventh adsorber (T-401/G) and the eighth adsorber (T-401/F). The process steps within one cycle are illustrated using the first adsorber (T-401/A) as an example. Adsorption (A): Open the programmed control valves KV1-1 and KV2-1 (close the other valves connected to adsorber V-T-401/A; the same applies hereafter). The feed gas enters through valve KV1-1 and passes upward through adsorber T-401/A; the impurity components in the feed gas are adsorbed and separated, and the resulting hydrogen gas exits through valve KV2-1. When the adsorption front of the adsorbed impurities moves to a certain position in the adsorber, KV1-1 and KV2-1 are turned off, stopping the inflow of feed gas and the output of product. At this point, there is still a section of adsorbent between the adsorption front in the adsorber and the outlet end that has not absorbed impurities. Process pressure: 2.1 MPa. Step execution time: ~240 s. First-stage pressure equalization drop (abbreviated as E1D): Open the programmable valves KV5-1 and KV5-4. After the adsorption step in adsorber T-401/A is completed, it is connected to the outlet end of adsorber T-401/D, which has just finished its E2R step, in order to achieve pressure equalization at the first stage. During this pressure equalization process, the adsorption front in adsorber T-401/A moves toward the outlet end, but it still does not reach that outlet end. When the pressures of the two adsorbers are roughly equal, closing valve KV5-1 completes the pressure reduction step (valve KV5-4 remains open for the subsequent final pressure increase step in T‑401/D). Process pressure: Drops from 2.1 MPa to 1.48 MPa. Step execution time: ~40 s. Isolation (IS): At this point, all programmable valves connected to adsorber T-401/A are in the closed state, and the pressure of adsorber T-401/A remains unchanged. Process pressure: Maintain at 1.48 MPa. Step execution time: ~40 s. Second-stage pressure equalization drop (abbreviated as E2D): Open the programmable valves KV7-1 and KV7-5. After the equalization step for adsorber T-401/A is completed, it is connected to the outlet end of adsorber T-401/E, which has just finished its flushing (P) step, in order to carry out a second stage of pressure equalization. During this equalization process, the adsorption front in adsorber T-401/A continues to move toward the outlet end, but it has not yet reached it. When the pressures of the two adsorbers are essentially equal, the step of closing valves KV7-1 and KV7-5 is completed. Process pressure: Drops from 1.48 MPa to 0.76 MPa. Step execution time: ~40 s. Forward pressure reduction (abbreviated as FF, PP): Open the programmable valves KV4-1 and KV6-6, as well as the control valve HV-502; continue to open valve KV3-6. After the two-stage depressurization step in adsorber T-401/A is completed, the purge gas in adsorber T-401/A flows through valve KV4-1, purge control valve HV-502, and valve KV6-6 to flush adsorber T-401/E, which has just completed its reverse purge (V) step, from top to bottom; the flushing gas is then discharged into the desorption gas mixing tank V-402 via valve KV3-6 and KHV-501. During the isobaric depressurization process, the pressure in adsorber T-401/A1 continues to decrease; its adsorption front keeps advancing toward the outlet end. When the pressure drops to approximately 0.2 MPa, valves KV4-1, KV6-6, KV3-6, KHV-501-2, and HV-502 are closed, marking the end of the isobaric depressurization step. At this point, the adsorption front has just reached the outlet end. Process pressure: Drops from 0.76 MPa to 0.2 MPa. Step execution time: ~80 s. Reverse pressure release (abbreviated as RD): Open valves KV3-1 and KV8A. The gas at higher pressure within adsorber T-401/A is vented in reverse direction through valves KV3-1 and KV8A into degassing buffer tank V-402. When pressures in T-401/A1 and V-402 become balanced, valve KV8A is closed while valve KV3-1 remains open; simultaneously, control valve KHV-501-1 is opened. The gas at lower reverse-venting pressure from adsorber T-401/A then mixes with the gas from degassing buffer tank V-402, which has been depressurized via control valve PV-503A. This combined stream is subsequently discharged outside the plant through degassing mixing tank V-403. The reverse-venting process concludes when the pressure in adsorber T-401/A approaches the degassing outlet pressure (valves KV3-1 and KHV-501-1 remain open to facilitate the subsequent flushing process of T-401/A). Process pressure: Decreases from 0.20 MPa to 0.05 MPa. Time for this step: ~40 s. Flushing (P): Open valves KV6-1 and KV4-2, as well as control valve HV-502; also keep valve KV3-1 and control valve KHV-501-1 open. The purge gas from adsorber T-401/B, which has just completed the second equalization down (E2D) step, is used to flush adsorber T-401/A, thereby further reducing the partial pressure of impurities in T-401/A and ensuring thorough regeneration of the adsorbent. The purge gas is discharged into the desorption gas mixing tank V-403 via valves KV3-1 and KHV-501-1. When the pressure in adsorber T-401/B drops to the specified value, close valves KV6-1, KV3-1, KV4-2 and control valves HV-502, KHV-501-1, and the flushing step is completed. Process pressure: Maintain at 0.05 MPa. Step execution time: ~80 s. Second-stage pressure equalization rise (abbreviated as E2R): Open valves KV7-1 and KV7-3. Adsorber T-401/A is connected to adsorber T-401/C, which has just completed an equalization (E1D) step, at their outlet ends in order to achieve a second stage of pressure equalization. During this equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valves KV7-1 and KV7-3 are closed, marking the end of the second equalization step. Process pressure: Rises from 0.05 MPa to 0.76 MPa. Step execution time: ~40 s. First-stage pressure equalization rise (abbreviated as E1R): Valves KV5-1 and KV5-4 are opened. Adsorber T-401/A is connected to adsorber T-401/D, which has just completed the adsorption (A) step, at their outlet ends in order to achieve pressure equalization at the first stage. During this pressure equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valve KV5-4 is closed, thereby ending this equalization step (valve KV5-1 remains open for the subsequent final pressure increase step in adsorber T-401/A). Process pressure: Increases from 0.76 MPa to 1.48 MPa. Step execution time: ~40 s. Final pressure increase (abbreviated as final charging, FR): Open the final charging flow control valve HV-501, and also keep valve KV5-1 open. After the second pressure equalization step, adsorber T-401/A is finally brought to the adsorption pressure gradually by using product gas to regulate the flow rate through control valve HV-501. When the pressure approaches the adsorption pressure, close valves KV5-1 and HV-502, and the final charging step is completed. Process pressure: increases from 1.48 MPa to 2.1 MPa. Step execution time: ~80 s. At this point, the adsorption and regeneration processes for adsorber T-401/A are complete, after which the next cycle begins. The step execution times and process pressures mentioned in the process description are illustrative; in actual operation, the device can adjust these times and pressures at any time according to changes in the flow rate, composition, and pressure of the feed gas. 3.5.7.4 5–1–2/P Operation Mode (1) Process Steps: When operating in the 5–1–2/P mode, one adsorber is in the adsorption stage where raw gas is fed in and hydrogen is produced, while the other three adsorbers are in various stages of catalyst regeneration. Each adsorber goes through the same sequence of steps, arranged as in Table 3-4, thereby enabling continuous input of feed gas and a steady output of product hydrogen. Table 3-5-5: Timing of the 5-1-2/P process – Periods 1, 2, 3, 4
Time (s): 240, 40, 160, 40, 40, 160, 40, 40, 200
Pressure (MPa): 2.2, 1.38, 1.08, 0.57, 0.05, 0.05, 0.57, 1.08, 2.2

Adsorber: 1, A, E1D, PP, E2D, D, P, E2R, E1R, FR; 3, E1R, FR, A, E1D, PP, E2D, D, P, E2R; 5, D, P, E2R, E1R, FR, A, E1D, PP, E2D; 7, E1D, PP, E2D, D, P, E2R, E1R, FR, A

(2) Process description: The operating procedure of the 5-1-2/P process will be briefly explained here using an example of a single-series operation. Taking the first adsorber (T-401/A) as an example, the process flow of each step in a single cycle is illustrated. Adsorption (A): Open the programmed control valves KV1-1 and KV2-1 (close the other valves connected to adsorber T-401/A; the same applies hereafter). The feed gas enters through valve KV1-1 and passes upward through adsorber T-401/A; the impurity components in the feed gas are adsorbed and separated, and the resulting hydrogen gas exits through valve KV2-1. When the adsorption front of the adsorbed impurities moves to a certain position in the adsorber, KV1-1 and KV2-1 are turned off, stopping the inflow of feed gas and the output of product. At this point, there is still a section of adsorbent between the adsorption front in the adsorber and the outlet end that has not absorbed impurities. Process pressure: 2.1 MPa. Step execution time: ~240 s. First-stage pressure equalization drop (abbreviated as E1D): Open the programmed control valves KV5-1 and KV5-5. After the adsorption step in adsorber T-401/A is completed, it is connected to the outlet end of adsorber T-401/E, which has just finished its E2R step, in order to achieve pressure equalization at the first stage. During this pressure equalization process, the adsorption front in adsorber T-401/A moves toward the outlet end, but it still does not reach that outlet end. When the pressures of the two adsorbers are essentially equal, closing valve KV5-1 concludes the pressure reduction step (valve KV5-5 remains open for the subsequent final pressure increase step in T‑401/E). Process pressure: Decreases from 2.1 MPa to 1.38 MPa. Step execution time: ~40 s. Forward pressure reduction (abbreviated as FF, PP): Open the program-controlled valves KV4-1 and KV6-7, as well as the control valve HV-502; continue to open valve KV3-7. After the two reduction steps in adsorber T-401/A are completed, the purge gas in adsorber T-401/A flows through valve KV4-1, purge control valve HV-502, and valve KV6-7 to flush adsorber T-401/F, which has just completed its reverse purge (V) step, from top to bottom; the flushing gas is then discharged into the desorption gas mixing tank V-403 via valve KV3-6 and KHV-501-1. During the forward discharge process, the pressure in adsorber T-401/A continued to drop; when the pressure reached approximately 1.08 MPa, valves KV4-1, KV6-7, KV3-7, KHV-501-1, and HV-502 were closed, marking the end of the forward discharge step. . During the forward operation, the adsorption front of adsorber T-401/A moves toward the outlet side, but it has not yet reached the outlet. Process pressure: Decreases from 1.38 MPa to 1.08 MPa. Step execution time: ~160 seconds. Second-stage pressure equalization drop (abbreviated as E2D): Open the programmed control valves KV7-1 and KV7-7. After the equalization step for adsorber T-401/A is completed, it is connected to the outlet end of adsorber T-401/F, which has just finished its flushing (P) step, in order to carry out a second stage of pressure equalization. During this equalization process, the adsorption front in adsorber T-401/A continues to move toward the outlet end, and by the end of the equalization process it reaches that outlet end exactly. When the pressures of the two adsorbers are essentially equal, the step of closing valves KV7-1 and KV7-7 is completed. Process pressure: Decreases from 1.08 MPa to 0.57 MPa. Step execution time: ~40 seconds. Reverse pressure relief (abbreviated as reverse relief, D): Open valves KV3-1 and KV8A. The gas with higher pressure in adsorber T-401/A is released in the reverse direction through valves KV3-1 and KV8A into the desorbed gas buffer tank V-402. When equilibrium is reached between T-401/A and V-402, valve KV8A is closed; valve KV3-1 remains open, along with control valve KHV-501-1. The gas with lower pressure within adsorber T-401/A, after being released in the reverse direction, passes through valves KV3-1 and control valve KHV-501-1, and together with the gas in the desorbed gas buffer tank that has been depressurized by control valve PV-503A, it is sent out of the system via the desorbed gas mixing tank V-403. The reverse release process ends when the pressure in adsorber T-401/A approaches the output pressure of the desorbed gas (valves KV3-1 and KHV-501-1 remain open for the next flushing step of T-401/A). Process pressure: Decreases from 0.57 MPa to 0.05 MPa. Step execution time: ~40 seconds. Flushing (P): Open valves KV6-1, KV4-3, and control valve HV-502; subsequently open valve KV3-1 and control valve KHV-501-1. Adsorber T-401/A was flushed using the forward bleed from adsorber T-401/A, which had just completed an E1D step, in order to further reduce the partial pressure of impurities in adsorber T-401/A and ensure thorough regeneration of the adsorbent. The purge gas is discharged into the desorption gas mixing tank V-403 via valves KV3-1 and KHV-501-1. When the pressure in the adsorber VT-401/B drops to the specified value, close valves KV6-1, KV3-1, KV4-3 and control valves HV-502, KHV-501-1, and the flushing step is completed. Process pressure: Maintain at 0.05 MPa. Step execution time: ~160 s. Second-stage pressure equalization rise (abbreviated as E2R): Open valves KV7-1 and KV7-3. Adsorber T-401/A is connected to adsorber T-401/C, which has just completed the flushing (P) step, at their outlet ends in order to achieve a second stage of pressure equalization. During this pressure equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valves KV7-1 and KV7-3 are closed, thereby ending the pressure equalization step. Process pressure: Increases from 0.05 MPa to 0.57 MPa. Step execution time: ~40 s. First-stage pressure equalization increase (abbreviated as E1R): Open valves KV5-1 and KV5-5. Adsorber T-401/A is connected to adsorber T-401/E, which has just completed the adsorption (A) step, at their outlet ends in order to achieve pressure equalization at the first stage. During this pressure equalization process, the pressure in adsorber T-401/A increases; once the pressures of these two adsorbers are roughly equal, valve KV5-5 is closed, thereby ending this equalization step (valve KV5-1 remains open for the subsequent final pressure increase step in adsorber T-401/A). Process pressure: Increases from 0.57 MPa to 1.38 MPa. Step execution time: ~40 s. Final pressure increase (abbreviated as final charging, FR): Open the final charging flow control valve HV-501, and also keep valve KV5-1 open. After the second pressure equalization step, adsorber T-401/A is finally brought to the adsorption pressure gradually by using product gas to regulate the flow rate through control valve HV-501. When the pressure approaches the adsorption pressure, close valves KV5-1 and HV-502, and the final charging step is completed. Process pressure: rises from 1.38 MPa to 2.2 MPa. Step execution time: ~200 s. At this point, the adsorption and regeneration processes for adsorber T-401/A are complete, after which the next cycle begins. The step execution times and process pressures mentioned in the process description are illustrative; in actual operation, the device can adjust these times and pressures at any time according to changes in the flow rate, composition, and pressure of the feed gas. The PSA process is achieved by periodically switching valves, and to ensure the continuous and stable operation of the entire process, a high level of performance is required from the automatic control system. To enable operators to monitor and control the entire production process in a timely manner, this device records, displays, adjusts, controls, and provides historical reviews of all important parameters on a computer screen (CRT), along with real-time trend tracking, and is equipped with a printer for generating reports. A total of 4 automatic pressure regulation systems are installed in this pressure swing adsorption unit ； 2 sets of automatic flow accumulation and adjustment systems ； 1 set of automatic liquid level discharge system ； 2 sets of manual control systems ； 2 sets of manual programming control systems ； 1 set of program control system. In addition, 20 parameters of the recorded data are displayed together (including 3 for temperature, 11 for pressure, 2 for flow rate, 1 for composition analysis, and 3 for combustible gas leakage detection). Figure 3-5-4: Circuit diagram of the program control system. 3.5.8.1 Program control system: The DCS system outputs a DC current signal of 20–4 mA according to the pre-set step-by-step sequence of operation modes; this electrical signal is then converted into a pneumatic signal by flameproof solenoid valves, which in turn drive the program control valves to enable the switching between various stages of the adsorber process. The system circuit diagram is shown in Figure 3-5-4. All the programmable valves in the pressure swing adsorption process are controlled by the computer of the DCS system. By switching the programmable valve, it is possible to switch through all the operating modes of pressure swing adsorption. The interlock control of some control systems during the manufacturing process is also carried out by the DCS system. The DCS system also includes an expert fault diagnosis control system and an adaptive optimization control system. Expert fault diagnosis control system: This refers to a microcomputer-based expert diagnosis system that, in the event of a failure in any one or more adsorption towers of the installation, reorganizes the remaining adsorption towers so as to ensure the steady operation of the installation and meet the product requirements, thereby continuously supplying qualified product gas to subsequent processing stages. During the automatic and arbitrary switching of the device, the entire process is carried out by the computer through internal calculations and database queries, without any need for human intervention. At the same time, the computer will issue alerts to remind the operator to address any faults. Once the fault has been resolved, the main process can be resumed, preventing unplanned shutdown of the entire system. Adaptive optimization control system: This refers to a system in which, when there are changes in the flow rate of the raw material gas fed into the device, the microcomputer-based adaptive optimization control system adjusts the control programs and the operating parameters of the device accordingly, thereby ensuring that the device operates in its optimal condition. During the operation of the device, the DCS system automatically diagnoses and monitors its performance. An alarm is issued by the DCS system when any of the following situations occur: ① A fault occurs in the external components of the adsorber’s programmable valve; ② The actuator of the adsorber’s programmable valve fails; ③ A fault occurs in the control output module of the adsorber; ④ There is a fault inside the pressure transmitter of the adsorber. When the operation mode is set to automatic, in the event of any of the above situations, an alarm is issued, and the expert fault diagnosis and control system selects the preferred operation mode and the optimal switching point, thereby carrying out the switch automatically. If set to manual mode, an alarm is issued simultaneously, and selectable commands are displayed on the CRT. Since various conditions and the programs to be executed are pre-set within the program control system, once an incorrect command is entered via the keyboard, the program control system issues a warning and displays the selectable commands again; only by entering the correct command can a switch be made. For specific switching methods, please refer to the \"Procedure Switching Instructions\" for this device. 3.5.8.2 Flow Detection and Regulation System: (1) The raw gas flow rate indicator, accumulator, and regulation system (FQC-401) are used to measure and regulate the raw gas flow rate; these elements serve to reflect the processing capacity of this device and provide a basis for economic calculations. Both the cumulative and instantaneous values are displayed on the computer of the DCS system. (2) Product gas flow rate indication and accumulation system (FRQ-402): This system measures the flow rate of the product gas, primarily to reflect the production capacity of this facility and to provide a basis for economic calculations. Both the cumulative and instantaneous values are displayed on the computer of the DCS system. 3.5.8.3 Pressure control system (1) The automatic adsorption pressure control and alarm (PICAL-403) system is used to maintain the PSA adsorption pressure at a specified value of 2.1 MPa. When the control of the PSA system fails, causing the adsorption pressure to drop below the set value (2.1 MPa), the DCS system issues a audible and visual alarm at the low-limit level, and automatically reduces the opening degree of the control valve PV-501 to keep the adsorption pressure at the set value. (2) The Product Hydrogen Overpressure Relief and Control and Alarm (PICAH-502) system is used to prevent the output pressure of product hydrogen from exceeding safe levels. When fluctuations in the hydrogen demand by subsequent processes cause the adsorption pressure to rise above the set value of 2.3 MPa, the DCS system issues audible and visual alarms, and automatically increases the opening degree of the control valve PV-502 to maintain stability in both the adsorption pressure and the output pressure of product hydrogen. (3) Automatic pressure regulation system for the desorbed gas mixing tank (PIC-503A): It automatically replenishes desorbed gas into the mixing tank from the desorbed gas buffer tank based on the pressure level in the mixing tank. When the pressure in the mixing tank exceeds the set value, the control valve PV-503A closes automatically ； When the pressure in the mixing tank falls below the set value, the control valve PV-503A opens automatically to supply fluid to the mixing tank, thereby maintaining a stable outlet pressure there. (4) The superpressure relief and control as well as alarm system for the desorbed gas mixing tank (PICAH-503B) is used to maintain stable pressure in the desorbed gas mixing tank and prevent overpressure. When the pressure in the desorption gas mixing tank exceeds the set value, the control valve PV-503B opens automatically ； When the pressure in the desorption gas mixing tank falls below the set value, the control valve PV-503B automatically closes, thereby maintaining a stable pressure at the outlet of the mixing tank. (5) Instrument air pressure indication and alarm (PIAL-504) system: This system displays the instrument air pressure; when the pressure drops below the set value of 0.4 MPa, the DCS system issues audible and visual alarms to prompt adjustment of the instrument air pressure to keep it at the set value or to initiate an emergency shutdown. 3.5.8.4 Manual Remote Control System (1) Manual control of final charging flow rate (HC-501) to ensure that the final charging flow rate and pressure reach the specified values. In the final charging step, the computer controls the regulating valve (HV-501) based on the set opening and rate, gradually opening it to the manually set value. To ensure the stability of the final charging flow rate. (2) Manual rate control for the forward flow (HC-502) to ensure that the forward flow process and the final pressure during this process are maintained at specific values. The magnitude of the normal venting volume directly affects product quality, product extraction rate, and the stability of the desorbed gas output. In this system, the normal venting volume is controlled based on the set opening degree and rate of the manual control valve (HV-502). Based on the characteristics of the process, in order to prevent large fluctuations in the subsequent desorption gas system at the beginning of the flushing process, a set rate is used to gradually increase the opening degree of the sequential control valve HV-502 at the start of flushing, from a low value until it reaches the manually set opening degree. 3.5.8.5 Others (1) Raw gas gas-liquid separator liquid level automatic discharge and high-level alarm system (LISAH-501): This system enables automatic discharge of liquid at the appropriate level, ensuring that the raw gas fed into the PSA unit does not contain mechanical water. When the liquid level is between 500 and 800 mm, the switch signal generated by this system (LISAH-501) is sent to a two-position four-way solenoid valve, which controls the double-acting switch to achieve automatic discharge of the liquid ； When the rise exceeds the set upper limit of 800 mm, the computer issues an audible and visual alarm. (2) Automatic analysis and alarm of product gas (ARAL-501): An explosion-proof hydrogen analyzer is used for online analysis and monitoring of product quality; when the analyzer detects that the hydrogen purity of the product is below the lower alarm threshold of 99.5%, an audible and visual alarm is issued. At this time, the operator should promptly identify the problem and resolve it to ensure a stable supply of hydrogen that meets quality standards. (3) Reverse operation, flushing program control system (KHS-501-1, 2): It programmatically controls the opening and closing of the control valves KHV-501-1, 2, thereby maintaining stable pressure in the desorption gas mixing tank and ensuring a uniform and steady flushing process. 3.5.9 Driving: Driving is divided into initial driving and regular driving. A series of preparatory actions must be taken before initial driving, while for regular driving, it is sufficient to set certain valves and control points as specified before starting the vehicle. 3.5.9.1 Preparations before initial operation: Once the installation of the equipment is complete, and all program control systems, monitoring instruments, and automatic control systems have passed the calibration tests, the equipment can proceed to the operation phase. The following preparatory steps should be taken before starting operation: ① Equipment inspection – mainly checking the upper and lower filters of the adsorber, removing all debris from the containers, and removing any unnecessary blind flanges. ② Air purging – removing slag and other impurities from the equipment and pipelines. ③ Filling with adsorbent. ④ Airtightness test. ⑤ System purging (with nitrogen). 3.5.9.2 Airtightness test: After completing the equipment inspection, air purging, and filling with adsorbent, clean and dry nitrogen is used to check and ensure that all equipment, valves, and pipelines maintain their airtightness at their maximum operating pressure. Gas tightness testing method: Use soapy water or foaming detergent to carry out the following inspections: ① Inspect all pipe flange connections and threaded joints. ② Inspect all pipe welds. ③ Operate the manual globe valve 2–3 times with equal pressure before and after to check the valve’s packing. ④ Operate all control valves 3–4 times to check their packing. ⑤ Operate the programmable valve 5–6 times with equal pressure before and after to check its packing. ⑥ Record all locations of gas leaks. ⑦ On equipment and pipes under lower pressure, it is permissible to carefully apply pressure to address the leak points. ⑧ Equipment and pipes under higher pressure must have their pressure released first. ⑨ Handle leaks at the packing of programmable valves carefully; over-tightening will not only damage the packing but also affect the proper operation of the valve. ⑩ Keep all equipment and pipelines under their maximum operating pressure for a period of 24 hours, requiring that the average pressure drop per hour be ≤0.5%. ⑪ The gas tightness test is complete once all sealing points in the system show no leaks during this pressure retention period. 3.5.9.3 System Purging (Nitrogen) (1) Depressurizing the adsorber: ① Slowly open the product gas vent valve V459, controlling the depressurization rate at 0.1 MPa/min. ② When the pressure in the adsorber drops to 0.05 MPa, close the vent valve V459. (2) Purge process and purge blowdown: At the start, all programmable valves are set to the closed position. The principles of the purge method are as follows: gas-liquid separator → adsorber → hydrogen output pipeline → flare line or vent line → desorbed gas buffer tank → desorbed gas mixing tank → desorbed gas output pipeline (as well as fuel gas pipeline and flare line). ① Open the product gas vent valve V459 and the desorbed gas vent valve V460. ② Start the pressure swing adsorption 8-2-4 operation program. ③ By opening valve V489, nitrogen enters the device to initiate the complete replacement process. (3) Control of operational parameters during the displacement process: ① Control the opening degree of the control valve PV-501 to maintain the pressure in the adsorber at 0.20 MPa. ②In the order in which the nitrogen flow proceeds, some local vent valves along the pipeline are opened and closed intermittently or continuously for purging and flushing; samples are taken at the product gas and desorbed gas discharge points to analyze the oxygen content in the gas. After analysis of the gases from all exhaust outlets, an oxygen content of less than 0.5% (v) indicates that the purge by displacement is satisfactory. ③After the replacement is completed, if operations will not be initiated immediately, it is necessary to maintain pressure using clean and dry nitrogen. The pressure in the adsorber should be 0.2 MPa, while the pressure in the desorption gas mixing tank should be 0.01 MPa. Then, all process valves must be closed. 3.5.10 Simulation operation: After the unit has completed its airtightness tests, adsorbent filling, and nitrogen purging, it can proceed to the commissioning phase. 3.5.10.1 Simulated startup and commissioning: Before conveying the raw gas, a simulated startup and commissioning should be carried out using clean and dry nitrogen. During operation, the adsorption pressure is controlled at 0.8–1.0 MPa. During operation, check whether the control valves are operating and switching normally. Inspect the online monitoring instruments and automatic control systems. If necessary, adjust certain set parameters. Any problems that can be resolved online should be addressed promptly; those that cannot be resolved online must be documented for handling after shutdown. 3.5.10.2 Startup (1) Preparations before startup ① Check whether the stop valves before and after all safety valves in the unit are open. ② Check whether the stop valves before and after all control valves in the unit are open. ③ Check whether the stop valves before all pressure gauges and pressure transmitters in the unit are open. ④ Check whether the main instrument air valve and all instrument air valves in the unit are open. ⑤ Connect all instrument power supplies. ⑥ Check whether the on-line monitoring instruments and automatic control systems are functioning properly. 3.5.10.3 Operation via keyboard settings ① Set the operation mode to 8–2–4/P using the operation keyboard. ② Check and set the time values for each step and the cycle time period. ③ Set the control valves to manual mode with an opening degree of 60% of their full range. 3.5.10.4 Feed simulation operation (operating in 8–2–4/P mode) ① Start the 8–2–4/P process on the operation keyboard. ② Slowly open the nitrogen inlet valve V489 to allow nitrogen to enter the unit. ③ Open the product gas vent valve V459 and the desorbed gas vent valve V460. ④ Increase the pressure in the adsorber in steps of 0.1 Mpa; if there is insufficient nitrogen, pause until the adsorption pressure reaches 0.1 Mpa, while adjusting the adsorption time accordingly. ⑤ Manually adjust the opening degree of the final filling control valve HV-501 to ensure that the final filling flow meets the process requirements. ⑥ Manually adjust the opening degree of the downstream release control valve HV-502 to ensure that the downstream release flow meets the process requirements. ⑦ The adsorption pressure should be ≥0.8 Mpa; under normal conditions, the 8–2–4/P operation should last no less than 2 hours. 3.5.10.5 Stopping the nitrogen simulation operation ① Close the nitrogen inlet valve V489 to stop nitrogen supply. ② Allow the pressure in the adsorber to decrease gradually; use step-by-step operations to reduce the pressure inside the adsorber to 0.2 Mpa and the pressure in the desorbed gas buffer tank to 0.01 Mpa. Then send a shutdown signal via the operation keyboard to close the programmable valves. ③ Close valves V459 and V460. 3.5.11 Feed operation: After the unit undergoes a nitrogen simulation run, it can proceed to the feed operation phase. The following description operates primarily in an 8-2-4 manner. Other operating modes can be followed as a reference. 3.5.11.1 Pressure relief: After the device undergoes a nitrogen simulation run, the pressure in the equipment and pipelines is relieved prior to the actual operation of the device, by using the drain valves or relief valves associated with each piece of equipment. All such drain valves or relief valves are opened slowly, and they are closed immediately once the desired pressure is reached in the equipment or pipelines, in order to prevent ambient air from entering. After pressure relief: ① The pressure in the adsorbers (D-7114/1–8) and the output gas pipes is maintained at 0.05 MPa. ② ·The pressures in the desorption gas pipelines (DG-401～DG-408), the desorption gas buffer tank (D-7116), and the desorption gas mixing tanks (D-7129/1,2) are 0.01 MPa. 3.5.11.2 Startup (1) Preparations before startup: ① Check whether the shut-off valves before and after all safety valves in the unit are open. ② Check whether the shut-off valves before and after all control valves in the unit are open. ③ Check whether the shut-off valves before all pressure gauges and pressure transmitters in the unit are open. ④ Check whether the main instrument air valve and all instrument air valves in the unit are open. ⑤ Connect all instrument power supplies. ⑥ Check whether the on-line monitoring instruments and automatic control systems are functioning properly. 3.5.11.3 Valve settings: During startup, once the feed gas enters the unit, the product hydrogen is temporarily sent to the plant’s fuel gas network via the control valve PV-502, while the desorption gas passes through the desorption gas buffer tank and then through the desorption gas mixing tanks before being released outside. 3.5.11.4 Keyboard Operation Settings: (1) Set the operation on the keyboard to operate in the 8-2-4 mode. (2) Check the time values for each step. (3) Set all control systems to automatic mode and adjust the set values: ① The pressure setpoint for PICA-501 is 2.2 MPa, while the alarm setpoint is 2.0 MPa. ② The set pressure value for PICA-502 is 2.3 MPa, while the alarm set value is 2.35 MPa. ③ The set value for FQC-501 is: 15440 Nm3/h. ④ Lower limit value for ARA-501 product purity alarm: 99.5% H2. ⑤ The set value for the high-limit alarm of PIC-503 is: 0.1 MPa. ⑥ The high alarm setting value for LISA-501 is 700 mm. ⑦ The opening setting of the control valve HV-501 is set to ~35%. ⑧ The opening setting of the control valve HV-502 is set to ~35%. ⑨ Set the program-controlled valve to automatic operation mode. 3.5.11.5 Startup by feeding material ① Start the 8-2-4 process program on the operation keyboard. ② Slowly open the raw material inlet valves V401 and V402 to allow raw material gas to enter the system. ③ Increase the adsorption pressure of the adsorber in manual steps of 0.1 Mpa each time. If the amount of feed gas is insufficient, operation can be paused; at the same time, the adsorption time should be recorded and adjusted. ④ Adjust the opening degrees of control valves HV-501 and HV-502 using the operation keyboard, so that the final charging and release pressures meet the process requirements. ⑤ Once the adsorption pressure reaches 2.2 MPa, the program control system should operate entirely in automatic mode. ⑥ As the feed gas flow increases, the adsorption time should be adjusted as needed, while ensuring the purity of the product. ⑦ When the feed gas flow rate is within the specified range, the unit enters normal operating mode. 3.5.12 Operations under normal operation: To ensure the device operates at its best, it is necessary to regularly check the accuracy of all process conditions. During stable operation, the product purity and recovery rate are good. It can be observed from the CRT that the pressures and flow rates of the feed gas, product gas, and off-gas experience slight fluctuations, but their trends remain consistent within each sub-cycle. If a sub-period deviates from the normal trend, there may be a fault. 3.5.12.1 Adjustment of product hydrogen purity: When the raw materials are stable, the PSA unit can maintain a constant hydrogen purity; by adjusting the adsorption time according to different load conditions, the product can be brought to the specified purity level. It is also affected by the following factors, which require corresponding adjustments:
**Factors affecting performance** | **Adjustment methods**
① Fluctuations in process operation parameters (such as increased feed rate, reduced adsorption pressure, or lower hydrogen content in the feed gas) that are not adjusted in a timely manner | ① Operate with care and make adjustments promptly
② Changes in operating mode | ② Reduce the adsorption time before making the mode change
③ Poisoning of the adsorbent | ③ Reduce the adsorption time
④ Incomplete final charging | ④ Adjust the flow rate and opening speed of HC-501 to ensure complete charging
⑤ Desorption pressure higher than the specified value | ⑤ Adjust the desorption pressure to the specified level
⑥ Internal leakage in the programmable control valve | ⑥ Carry out immediate repairs

3.5.12.2 Setting and adjustment of adsorption time
① When the composition of the feed material changes, and if the control mode is set to capacity control, the control system will automatically reduce the adsorption time. If this does not suffice to restore purity, the adsorption time can be reduced manually. ② At low feed rates, the purity of hydrogen increases while the hydrogen recovery rate decreases; if the load is below the minimum level, adjusting the adsorption time does not help to increase the hydrogen recovery rate. At high feed rates, the adsorption time should be reduced, and if the load is above the maximum level, adjusting the time still does not improve the purity of hydrogen. ③ When switching the operation mode, especially from a multi-bed to a single-bed mode, the adsorption time should first be reduced before making the switch; once the operation is stable, the adsorption time can be gradually adjusted back to its normal value. 3.5.12.3 Adjustment of product recovery rate The following situations can lead to a decrease in the amount of raw gas processed and in the product recovery rate. Factors Affecting Performance and Adjustment Methods: ① Fluctuations in process operation parameters (such as reduced feed rate, increased adsorption pressure, higher hydrogen content in the feed gas) that are not adjusted in a timely manner. ① Operate carefully and make adjustments promptly. ② Internal leakage in control valves. ② Repair them as soon as possible. ③ Poisoning of the adsorbent. ③ Regenerate or replace the adsorbent. ④ Increased impurity content in the feed gas. ④ Adjust the opening degree and rate of HC-501 to ensure proper filling. ⑤ Desorption pressure is higher than the specified value. ⑤ Adjust the desorption pressure to the specified value. ⑥ The pressure does not reach the required level at the end of the pressure equalization process. ⑥ Adjust the pressure equalization time so that the pressure meets the requirements by the end of this process. ⑦ Pressure is too high at the end of the sequential release process. ⑦ Adjust the pressure for sequential release to the specified value. 3.5.12.4 Operations when Operating Conditions Change: (1) Changes in feed flow rate. Increasing or decreasing the amount of feed processed can affect the purity and yield of the product. An increase in the feed volume leads to a decrease in the purity of the hydrogen produced; in severe cases, it makes it difficult to regenerate the adsorbent. If the feed volume is too low, the adsorption time becomes too short, resulting in fluctuations in adsorption pressure and a decrease in hydrogen recovery rate. (2) Change in raw gas composition: During the adsorption phase, the amount of impurities present in the feed determines the adsorption time required for a given adsorption bed; therefore, when the hydrogen content in the raw gas decreases, the adsorption time should be appropriately reduced. It is necessary to adjust the adsorption time when the raw material composition changes. The rules are as follows: ① As the hydrogen content increases, the operation adsorption time should be increased accordingly to maintain the optimal operating condition of the device. ② As the hydrogen content decreases, the operation adsorption time is correspondingly reduced to maintain the optimal operating condition of the device. (3) Change in adsorption pressure: An increase in adsorption pressure facilitates the adsorption of the feedstock by the adsorbent. The adsorption pressure is influenced not only by the opening degree of PV501, which is regulated by (PICA-501), but also by the flow rate of the feedstock gas. When the adsorption pressure increases, the adsorption time can be appropriately extended, but the feed flow rate should not be increased too much. (4) Change in feed temperature: An increase in feed temperature reduces the maximum load of the adsorption tower; therefore, the feed temperature should be maintained within the designed range. When the feed temperature changes, the following adjustments should be made: ① When the feed temperature rises, reduce the adsorption time appropriately depending on the product purity and recovery rate, until the product quality meets the required standards. ② When the feed temperature decreases, the adsorption time is increased or decreased depending on the product purity and recovery rate. Generally, the adsorption time is increased as the temperature decreases, but it is necessary to ensure that the product quality remains satisfactory. If the feed temperature deviates significantly from the design value, preparations for shutting down the system should be made to avoid damaging the adsorbent or affecting the product quality. (5) Back-pressure: The adsorption bed is regenerated by applying back-pressure, so certain requirements exist regarding this back-pressure. If the back-pressure is too high, the amount of impurities remaining on the adsorbent increases, which raises the pumping load and results in poor regeneration of the adsorbent. If the reverse flow pressure is too high, the pressure in the desorbed gas mixing tank and the desorbed gas buffer tank should be reduced to bring the reverse flow pressure to the proper level. 3.5.12.5 During normal operation, the switching mode of the adsorption tower is controlled by a PSA unit control program that includes a set of functional judgment blocks; in the event of a equipment failure, a switching alarm is generated, and if automatic control is selected, the switching is carried out automatically by the program. Reason for the switch alarm: ① A fault has occurred in the external components of the program-controlled valve of the adsorption tower. ②The actuator of the program-controlled valve in the adsorption tower has failed. ③The control output module of the adsorption tower has failed. ④Internal failure of the pressure transmitter in the adsorption tower. (1) Handling of switch-over alarms: ① During the operation of the PSA unit, the DCS is capable of automatically diagnosing and monitoring its operating conditions; when the aforementioned issues occur, an alarm is issued along with a request for a switch-over. ②If the switching mode is set to automatic, the control system will select the preferred operating mode and the optimal switching point, and then carry out the switch automatically ； If the switching method is set to manual, an alarm is issued simultaneously, and the CRT displays available commands; the switching process is carried out by entering commands via the keyboard. (2) Switching of operation mode: The switching of the device’s operation mode can be carried out automatically by the program control system or manually. When automatic switching is set, the expert fault diagnosis system can automatically diagnose the operation status of the device; when a programmable valve or an input/output module fails, it selects the preferred mode of operation and the optimal switching point, and then carries out the switch automatically. When manual switching is set, a switching command can be issued by operating the keyboard. ①Set the manual switching mode. ② Select the operating mode code to be replaced. ③ After confirmation, the program control system will check whether the current step position permits switching. If the switching conditions are met, you can switch to the specified replacement allowance method after confirmation ； If the switching conditions are not met, an appropriate display will be shown on the CRT, and the system will wait until the conditions are satisfied before proceeding with the switch. ④ Before the actual switch is completed, it is necessary to cancel the switching request; the original mode that was in use at the current step should be selected again. During the device switching process, the adsorption time differs from the normal operating value. When switching from one operating mode to another, the adsorption time is temporarily controlled by the control unit; the adsorption time that applies after the switch should be adjusted accordingly based on the process conditions. After one cycle, the device continues to operate for the adsorption time set at the time of switching, until it is replaced by a newly set adsorption time; the adsorption time is adjusted promptly after the switch to ensure product purity and a high recovery rate. 3.5.13 Shutdown and restart of the unit The shutdown of the unit is divided into planned shutdowns, as well as temporary or emergency shutdowns caused by faults in the unit or power supply issues. 3.5.13.1 (1) Planned parking: For planned parking, preparations before and after parking are necessary, and the methods of these preparations depend on the duration of the parking. (2) Temporary parking: Parking for a duration of up to 24 hours. ① Close the feed gas inlet valve V401 (V402) and the product hydrogen outlet valve V427. ② Press the pause and self-check buttons to keep the PSA operation steps in their current state (and note the step number at which the program was stopped), with the programmable valves in a fully closed position. (3) Short-term parking: Parking that lasts within two weeks. The setting for the adsorption time can be appropriately reduced before parking. ① Close the feed gas inlet valve V401 (V402) and the product hydrogen outlet valve V427. ② The process continues, using the emission of each desorbed gas to gradually reduce the pressure inside the adsorber to ~0.3 MPa. ③ Stop automatic operation, and use manual control to equalize the pressure across the various adsorbers, maintaining a pressure within each adsorber of around 0.2 MPa; the pressure in the desorption gas mixing tank should be higher than atmospheric pressure. 2 Long-term parking: Parking that lasts for more than two weeks. ①The setting for the adsorption time can be appropriately reduced before parking. ②Close the feed gas inlet valve V401 (V402) and the product hydrogen outlet valve V427. ③The process continues, using the emission of gas from each desorption step to gradually reduce the pressure in each adsorber to around 0.02 MPa. ④Perform purge with nitrogen and stop automatic operation. ⑤Manually pressurize each adsorber with nitrogen to 0.2 MPa and maintain the pressure. (4) Emergency shutdown: An emergency shutdown should be initiated in the event of a failure in the pressure swing adsorption system or a power failure. ①Press the pause and self-check buttons to keep the PSA operation steps in their current state, with the programmable valves fully closed ； A sudden power outage caused all programmable valves to close completely. ②Close the feed gas inlet valves V401, V402, and the product hydrogen outlet valve V427. ③Appropriate measures shall be taken based on the specific conditions at the site. 3.5.13.2 Starting up after stopping (1) Restarting after temporary stopping ① After a temporary or emergency stop, although the DCS retains memory of the step and time at which the stop occurred, it is still necessary to check whether the pressure inside each adsorber matches the pressure at the time of stopping. If not, the corresponding program control valves should be manually activated to adjust the operating pressure, or a step-by-step approach should be used to adjust the operating conditions, in order to prevent mismatches between pressure and operating conditions that could lead to significant disruptions and serious consequences for the system. ② Set the adsorption time to 80% of the original operating time. ③ Exit the self-check mode and use the pause button to verify that all control systems are in their normal automatic operation state. ④ Open the raw material gas inlet valves V401 and V402, as well as the product hydrogen output valve V427. ⑤ While ensuring the product meets quality standards, the flow rate of the feed gas and the adsorption time are gradually adjusted to reach the design values. (2) The procedure for restarting after short-term or long-term parking is the same as that for the first start. 3.5.14 Faults and Handling Methods A fault occurs when there are abnormalities in the supply of external conditions, operational errors during operation, or failures in certain components, resulting in a decrease in product purity and thus triggering an ARAL-501 alarm. However, before the cause of the fault is identified, it is not necessary to shut down the device; continued monitoring is sufficient. At this time, the defective product gas will be vented to the flare through valves V477, V475, or control valve PV502. Once the cause of the fault is determined, a decision can be made as to whether to shut down the device or continue its operation. If a major problem occurs in the system, an emergency shutdown should be initiated. The more likely faults include the following: ① Abnormal supply of external conditions ② Operational errors ③ Equipment failures. 3.5.14.1 Abnormal supply of external conditions (1) Power outage: A power outage prevents the program control system from functioning properly. Since the program control system has no signal output, all programmable valves close automatically, causing the equipment to stop operating, which is equivalent to an emergency shutdown. Please treat it as an emergency stop. 3.5.14.2 Drop in instrument air pressure: This device requires an instrument air pressure of not less than 0.4 MPa. Once the instrument air pressure drops below 0.4 MPa, PIAL-504 triggers an automatic alarm; at this point, the instrument air supply must be adjusted promptly or the system shut down for handling. Otherwise, it will prevent the pneumatic programmable valve from opening or closing, cause the instruments in the control system to become inaccurate, lead to disruptions in the program and the overall automatic control of the system, and result in defective product gas. 3.5.14.3 Operational errors: The proper functioning of the PSA process depends crucially on whether the regeneration of the adsorbers is carried out properly; any malfunction in system operation will immediately or gradually degrade the regeneration efficiency of the towers. Since the PSA process is a cyclic process, once the regeneration of one column deteriorates, it will quickly affect and contaminate the other columns, ultimately leading to a decline in the quality of the product gas. 3.5.14.4 Fault of rapid pressure change in the adsorption bed (1) Hazards: A rapid change in the pressure of the adsorption bed will cause the bed material to become loose, with various adsorbents within it mixing together. In severe cases, the adsorbents may break apart, leading to an increase in pressure drop across the adsorption bed. Dust can escape from the sieve mesh of the adsorption bed along with the airflow, damaging the valve seats of process valves, blocking instrument pipelines, and clogging the filter at the compressor inlet. This can degrade the operational performance of the facility and even lead to its shutdown. (2) Causes of the accident: ① Valve malfunction; ② Improper use of manual valve operation. ③Driving in a non-stop area or failing to adjust the pressure of the adsorption bed first. ④ Improper use of manual stepping. (3) Accident handling ① Check which programmable valve is faulty; generally, the differential pressure across the valve should be ≤ 0.08 MPa. ② Make the correct switch. 3.5.14.5 Impurity overload accident (1) Accident symptoms: ① Decrease in product purity. ② The device’s ability to control pressure changes is reduced. (2) Cause of the accident: ① Excessive adsorption time. ② The impurity content increases suddenly (or the feed flow rate increases suddenly) over a certain period of time. ③ Improper use of manual stepping. ④ The valve is leaking. ⑤ The feed composition is out of range. ⑥ The feed contains liquid. ⑦ The feed temperature is too high or too low. ⑧ The analysis instrument has failed. (3) Accident handling ① Choose a shorter adsorption time during abnormal operations. ② When the flow rate fluctuates, the feed rate should be appropriately reduced to stabilize it. ③ In the event of a valve leak, it should be switched over promptly. ④If the feed composition is outside the specified parameters or contains liquid, or if the temperature is not appropriate, the operation must be stopped immediately; the plant can be restarted only once the raw materials meet the required standards. ⑤If the instrument malfunctions, contact the instrument repair service. 3.5.14.6 If the exhaust volume is too high, the adsorption time will either increase or decrease; the manual control valve HV-502 should be adjusted promptly. When the amount of backflow gas is excessive, the adsorption front in the adsorber advances prematurely, which not only contaminates the adsorber being flushed but also causes the adsorbent in the outlet section of the backflow adsorber itself to become contaminated ahead of time ； If the amount of gas released in the forward direction is too low, the hydrogen utilization efficiency of the adsorber decreases; meanwhile, a high initial pressure during reverse gas release also prevents the adsorber being fully regenerated. Both of the above situations lead to deteriorated adsorbent regeneration. All isobaric discharge volumes should be as close as possible to the design pressure. As the adsorption time increases, the opening degree of HV-502 should be reduced ； Conversely, if the adsorption time is reduced, the opening degree of HV-502 should be increased. 3.5.14.7 Fault of the two-position four-way valve: Gas continues to be discharged from the exhaust port of the two-position four-way valve. This is either due to a damaged sealing ring inside the valve or because the slider inside the valve is not in the correct position. Solution: The vehicle should be stopped, or the corresponding adsorber should be deactivated via a program, after which the two-position four-way valve should be replaced. 3.5.14.8 Program control system failures: These failures may manifest as no signal output, failure to switch programs, remaining in a certain state, or disrupted program execution. For details on faults and their handling, please refer to the relevant sections of the DCS system technical manual. 3.5.14.9 Program-controlled valve failure – Valve fault alarm (1) Causes of the incident: ① Failure of the valve actuator. ② Solenoid valve failure. ③ Fault in the electrical circuit (including the solenoid valve output module). ④ Leak in the instrument air pipeline. ⑤ The electrical and pneumatic signals to the valve positioner are interrupted. (2) Accident phenomenon: A valve fault alarm is triggered when the actual position of the process valve does not match its programmed position. (3) Accident handling: If a genuine valve failure alarm occurs, it is necessary to immediately switch to the alternative process. For example, if there is a failure in the programmable valve of Tower A, then Tower A or both Towers A and B should be shut down. If the switching is set to automatic, the program will carry out the switch automatically. 3.5.14.10 Methods for adjusting product purity from an unqualified state to a qualified state: A decrease in product purity indicates that impurity components have reached the outlet of the adsorber during the adsorption process, and this is caused by improper operational adjustments or failures in the automatic control system. Once the cause is identified, normal operation should be restored as soon as possible after taking corrective action. One effective method for recovery is to operate at reduced load (by decreasing the volume of gas being processed) for a period of time, and the other is to shorten the cycle time. If combining the two yields better results and faster restoration of product purity, care should be taken to shorten the cycle time while ensuring the minimum time required for the forward operation and the final voltage increase steps; in this case, the opening degrees of control valves HV501 and HV-502 should be increased appropriately. 3.5.15 Purity and recovery rate of the product hydrogen: Based on the process principles and methods, it can be seen that there is an inverse relationship between the purity of the product hydrogen and its recovery rate. The higher the purity of the product hydrogen, the lower the recovery rate of hydrogen ； Conversely, the lower the purity of the produced hydrogen, the higher the hydrogen recovery rate. In practical operations, there should be no one-sided focus on the purity of the product hydrogen; instead, the hydrogen purity should be adjusted according to the actual requirements of production in order to achieve a better hydrogen recovery rate.