Systematic discussion on hydrogen production methods
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The main processes currently in use in China are as follows: 1. Hydrogen production from methanol. To reduce energy consumption and costs in chemical manufacturing, and as a substitute for the energy-intensive process of \"hydrogen production by water electrolysis,\" advanced methanol steam reforming–pressure swing adsorption technology is employed to produce pure hydrogen as well as a mixed gas rich in CO2. Through further processing, both hydrogen and carbon dioxide can be obtained. II. Hydrogen production by water electrolysis: Serial electrolyzers (resembling filter presses) with iron as the cathode and nickel as the anode are commonly used to electrolyze aqueous solutions of potassium hydroxide or sodium hydroxide. Oxygen is produced at the anode, and hydrogen is produced at the cathode. This method is costly, but it yields high product purity, allowing for the production of hydrogen with a purity of over 99.7%. Hydrogen of this purity is commonly used for: ① as a reducing agent, protective gas, and for the heat treatment of permalloy in the electronics, instruments, and metering industries; ② as a reducing agent in the powder metallurgy industry for producing tungsten, molybdenum, cemented carbides, etc.; ③ in the production of semiconductor raw materials such as polysilicon and germanium; ④ in the hydrogenation of fats and oils; ⑤ as a cooling gas in hydrogen-cooled generators. Factories such as the Beijing Electron Tube Factory and the Academy of Sciences Gas Plant produce hydrogen using the water electrolysis method. III. Hydrogen production by the water-gas method: Bituminous coal or coke is used as a raw material, and it reacts with steam at high temperatures to produce water gas (C+H2O→CO+H2—heat). After purification, it is passed together with water vapor over a catalyst to convert the CO present into CO2 (CO + H2O → CO2 + H2), resulting in a gas with a hydrogen content of over 80%. This gas is then compressed and introduced into water to dissolve out the CO2; the remaining CO is removed using a solution containing copper formate ammonium (or copper acetate ammonium), thereby yielding relatively pure hydrogen. This method is cost-effective and allows for high production volumes; it makes use of numerous pieces of equipment and is commonly employed in ammonia synthesis plants. Some also use CO and H2 to produce methanol, while in a few places less pure gas containing 80% hydrogen is used to create liquid fuel. This method is widely used by places such as the Beijing Chemical Engineering Laboratory and many small nitrogen fertilizer plants across the country. IV. Hydrogen production from syngas generated by petroleum thermal cracking and natural gasA large amount of hydrogen is produced as a by-product of petroleum thermal cracking. This hydrogen is commonly used for gasoline hydrotreating, as well as in petrochemical and fertilizer plants. This method of hydrogen production is employed in many countries around the world. In China, it is utilized at various petrochemical bases, such as the Qingyang Fertilizer Plant and the petrochemical base in the Bohai Oilfield. It is also adopted in some other locations (e.g., at the Bayway and Baton Rouge hydroprocessing plants in the United States). V. Hydrogen production by cryogenic processing of coke oven gas: The preliminarily purified coke oven gas is cooled and pressurized, causing other gases to liquefy while leaving hydrogen behind. This method is used in a few places (such as the Ke Mepobo plant in the former Soviet Union). VI. By-product hydrogen from the electrolysis of brine
In the chlor-alkali industry, a large amount of relatively pure hydrogen is generated as a by-product. Apart from being used for the synthesis of hydrochloric acid, there is still an excess amount available; this can also be purified to produce ordinary hydrogen or pure hydrogen. The hydrogen used in the Second Chemical Plant is a by-product of electrolyzing saltwater. VII. By-products of the brewing industry: When corn is fermented to produce propanol and butanol, more than 1/3 of the gases emitted from the fermentation tanks are hydrogen. Through multiple purification steps, ordinary hydrogen (with a purity of over 97%) can be produced. By passing this ordinary hydrogen through silica gel columns cooled to below –100°C using liquid nitrogen, impurities such as small amounts of N2 can be further removed, resulting in pure hydrogen with a purity of over 99.99%. Beijing’s brewing factories produce this by-product hydrogen, which is used for heating quartz products and supplied to other companies.
Review of Methanol Pyrolysis for Hydrogen Production 【Abstract】Hydrogen has a wide range of industrial applications. In recent years, due to the rapid development of fine chemicals, the anthraquinone process for hydrogen peroxide production, powder metallurgy, oil and fat hydrogenation, hydrogenation of forestry and agricultural products, bioengineering, petroleum refining hydrogenation, and clean hydrogen-fueled vehicles, the demand for pure hydrogen has increased dramatically. Technology for hydrogen and carbon dioxide production via steam reforming of methanol 1. Introduction Hydrogen has a wide range of industrial applications. In recent years, due to the rapid development of fine chemicals, the anthraquinone process for hydrogen peroxide production, powder metallurgy, oil and fat hydrogenation, hydrogenation of forestry and agricultural products, bioengineering, petroleum refining hydrogenation, and clean hydrogen-fueled vehicles, the demand for pure hydrogen has increased dramatically. In areas where there is no readily available hydrogen source, using traditional methods of generating gas from petroleum, natural gas, or coal for hydrogen separation requires substantial investment; it’s equivalent to half that of producing ammonia, and is only suitable for large-scale users. For small and medium-sized users, electrolysis of water can be used to produce hydrogen conveniently, but it requires a high amount of energy – up to ~6 kWh per cubic meter of hydrogen produced. Moreover, the purity of the hydrogen obtained is not ideal, as it contains many impurities. Additionally, there are limitations regarding the scale of production. As a result, in recent years many manufacturers that previously used electrolysis to produce hydrogen have carried out technical upgrades to adopt new processes based on the conversion of methanol vapor into hydrogen. 2. Process principle and characteristics
This process uses readily available methanol and demineralized water as raw materials. At temperatures ranging from 220 to 280°C, these materials are catalytically converted on a special catalyst into a conversion gas whose main components are hydrogen and carbon dioxide. The principles involved are as follows:
Main reactions:
CH3OH = CO + 2H2 + 90.7 KJ/mol
CO + H2O = CO2 + H2 –41.2 KJ/mol
Overall reaction:
CH3OH + H2O = CO2 + 3H2 + 49.5 KJ/mol
Side reactions:
2CH3OH = CH3OCH3 + H2O –24.9 KJ/mol
CO + 3H2 = CH4 + H2O +206.3 KJ/mol
After cooling and condensation, the resulting conversion gas has the following composition:
H2: 73–74%
CO2: 23–24.5%
CO: ~1.0%
CH3OH: 300 ppm
Water content: saturated
This conversion gas can be easily used in technologies such as pressure swing adsorption to separate and extract pure hydrogen. At present, nearly a hundred companies in China are using this technology. Years of operation have shown that this process is mature, easy to operate, stable in performance, and pollution-free. This process technology has the following features: 1. The cracking and conversion of methanol vapor are completed in one step on a specialized catalyst. 2. By using pressurized operation, the resulting conversion gas does not require further pressurization and can be directly fed into the pressure swing adsorption separation unit, thereby reducing energy consumption. 3. Compared with the electrolytic method, power consumption is reduced by over 90%, production costs can be lowered by 40–50%, and the purity of hydrogen is high. Compared with coal gas generation, this process is simpler in design and easier and more stable to operate. Although coal gasification has lower raw material costs, it involves a long process, high investment, and causes significant pollution with many impurities; it requires desulfurization and purification processes, making it unsuitable for small and medium-scale installations. 4. Special catalysts feature high activity, good selectivity, low operating temperature, and long service life. 5. The use of heat transfer oil as a circulating heating medium meets the process requirements, requires less investment, results in lower energy consumption, and reduces operating costs. 3 Process Flow The process flow is shown in the figure. Methanol and deionized water are mixed in a certain ratio, preheated in a heat exchanger, and then fed into a vaporization tower. The resulting water-methanol vapor is superheated in a boiler heater before entering a converter where it undergoes catalytic cracking and conversion reactions on a catalyst bed; the resulting converted gas contains approximately 74% hydrogen and 24% carbon dioxide. After heat exchange and cooling condensation, this gas enters a wash absorption tower. The unconverted methanol and water are collected at the bottom of the tower for reuse, while the gas at the top of the tower is sent to a pressure swing adsorption unit for purification. Depending on the different requirements for product gas purity and trace impurity levels, a four-tower or more tower process is employed, enabling a purity level of 99.9–99.999%. A pressure swing adsorption unit designed with a processing capacity of 1500 Nm3/h of converted gas and a purity of 99.9% can achieve a hydrogen recovery rate of over 90%. Carbon dioxide in the converted gas can be purified to food grade using pressure swing adsorption units, for use in the beverage and wine industries. This can **reduce production costs**. In the process setup, carbon dioxide is first separated using a pressure swing adsorption unit, after which the hydrogen-rich conversion gas is pressurized and fed into the same unit for further purification. This process uses simple raw materials, and the associated utility requirements are low, making them easy to meet. Based on years of operational data from industrial plants, the consumption of raw materials and energy is as follows: methanol – 0.57 tons; desalinated water – 0.32 tons; electricity – 220V/380V, 150 kWh; instrument air – 80 Nm3/h. The production cost is 2.0–3.0 yuan per Nm3 of pure hydrogen; if carbon dioxide can be recovered and sold, the cost of the product can be reduced to 1.5–2.0 yuan. (The workshop costs vary slightly depending on the scale of the installation and fluctuations in the market price of methanol.) ) 5 Environmental Protection 5.1 Waste gases: This technology employs an internal material recycling process, so that basically no waste gases are emitted during normal operation. Only a small amount of gas containing CO2 and CH3OCH3 is released from the raw material storage tanks. Taking a hydrogen production facility with a capacity of 1000 Nm3/h as an example, the amount of such gas is 1.0–1.7 Nm3/h. The composition of this gas is as follows: Component CO2 CH3OCH3 H2 CH3OH H2O Percentage 84.03 2.66 1.00 3.24 11.38 Due to the low volume of this gas, it is essentially non-toxic and can be discharged directly into the atmosphere. The off-gas from the pressure swing adsorption process is discharged into the atmosphere after passing through a flame arrester; it contains large amounts of carbon dioxide, along with small amounts of hydrogen and trace amounts of carbon monoxide and water vapor, so it does not cause pollution to the environment. 5.2 Waste liquids: In this process, only a small amount of wastewater is discharged periodically from the bottom of the vaporization tower; this wastewater contains less than 0.5% methanol. After dilution, it meets the emission standards for Category II pollutants as specified in GB8978-88, and can thus be discharged directly into the sewer system. 5.3 Waste residues: The heat transfer oil boiler room contains a certain amount of coal ash from combustion, which can be processed collectively. (Only coal-fired heat transfer oil systems have waste residues. ) 6. Status of promotion and application: The list of entities that have already carried out technology transfer or provided complete sets of equipment is as follows: The Southwest Chemical Research Institute is currently able to supply methanol steam reforming hydrogen production units of various scales, ranging from 20 to 5000 Nm3/h. It can handle technical tasks such as design, installation guidance, staff training, and operation, as well as provide complete engineering packages including hardware equipment like machinery, electrical systems, and instruments. After the installation is put into operation, follow-up services such as regular technical inspections are provided to ensure its stable operation. 7 Conclusion Industrial practice has shown that this technology is advanced and mature ； It has a simple design, is easy to operate, and runs stably. This process holds good market prospects, especially for small and medium-sized hydrogen users. The catalyst specifically designed for this process has been continuously improved. It not only retains its advantages of high activity and high selectivity, but also has seen significant progress in terms of catalyst lifespan. The catalyst used by Guangzhou Jinzhujiang Chemical Co., Ltd. has been in service for over 4 years. Process description: The production process for methanol catalytic conversion to produce gas can be divided into four steps: preheating of the raw material liquid, vaporization, superheating, the conversion reaction, and cooling and condensation of the product gas, as well as purification of the product gas. This device consists of two completely independent systems; in the following description, the designations for equipment, valves, control valves, etc. are omitted for each system. 1 Process Flow 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 work includes equipment such as the methanol metering tank, circulation liquid storage tank, raw material feed pump, heat exchanger, vaporization tower, superheater, as well as the associated instruments and valves. 1.2 Catalytic conversion reaction process: Under specific reaction temperature and pressure, the feed steam undergoes gas-solid phase catalytic conversion in the conversion furnace. The scope of work is: one converter unit and its accompanying instruments and valves. The purpose of this process is to carry out a chemical reaction to produce a conversion gas whose main components are hydrogen and carbon dioxide. 1.3 Conversion gas cooling and condensation process: The process of cooling and condensing the high-temperature conversion gas coming from the lower part of the converter to below 40°C. Its scope of work includes: heat exchangers and coolers, two types of equipment, along with the associated instruments and valves. 1.4 Shift gas purification process: A process in which low-temperature shift gas containing hydrogen, carbon dioxide, and small amounts of carbon monoxide, methanol, and water enters a water scrubber, where demineralized water absorbs the unreacted methanol. Its scope of work includes five pieces of equipment: the water washing tower, the desalinated water intermediate tank, the gas buffer tank, and the desalinated water feed pumps, along with the associated instruments and valves. 2.0 Main Control Parameters of the Process 2.1 Vaporization Superheating of Raw Materials 2.1.1 Flow rate of raw material methanol: 1134 kg/h 2.1.2 Flow rate of raw material liquid: ~2590 Kg/h 2.1.3 Feed temperature in the vaporization superheating tower: ~165 °C 2.1.4 Pressure at the bottom of the vaporization superheating tower (gauge pressure): 1.1 MPa 2.2 Conversion Reaction 2.2.1 Feed temperature: 200–260 °C 2.2.2 Reaction temperature: 220–280 °C 2.2.3 Temperature of the heat transfer oil: 235–290 °C 2.2.4 Temperature of the converted gas at the outlet of the heat exchanger: 110–140 °C 2.2.5 Temperature of the converted gas at the outlet of the cooler: <40 °C 2.2.6 Reaction pressure (gauge pressure): ~1.1 MPa 2.3 Water Washing and Separation 2.3.1 Amount of water used for desalination before entering the tower: 636 Kg/h 2.3.2 Amount of circulating liquid (after leaving the tower): ~1469 Kg/h; Composition of the circulating liquid (wt%): Methanol 0–25% 2.3.3 Amount of converted gas exiting the tower: ~3135 Nm3/h; Composition of the converted gas (V%): Hydrogen 73–74.5%, Carbon dioxide 23–24.5%, Carbon monoxide ~0.8%, Methanol 0.03%, Methane 0.20% 2.4 Catalyst Reduction 2.4.1 Flow rate of the reduction gas: ~2100 Nm3/h 2.4.2 Hydrogen content in the reduction gas: 0.5–10% 2.4.3 Reduction temperature: 110–230 °C 2.4.4 Reduction pressure: ~0.05 MPa 2.5 Others 2.5.1 Pressure of cooling water in the feed section: 0.3 MPa 2.5.2 Pressure of instrument air in the feed section: 0.4–0.60 MPa 2.5.3 Flow rate of the heat transfer oil: ~160 m3/h Principle of the Chemical Reaction: A mixture of methanol and water vapor undergoes a catalytic conversion reaction under pressure in a converter; the reaction produces hydrogen and carbon dioxide. 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 – 24.90 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. Properties of Raw Materials and Products 1.1 Properties of Raw Materials ⑴ Properties of Methanol as a raw material: Its chemical name is methanol; it is also known as methyl alcohol, wood alcohol, or pyroligneous alcohol. 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; explosive limit in air: 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 has **effects; it has a significant impact on the optic nerves, and in severe cases, can cause blindness. ⑵ Properties of the demineralized raw water (omitted). 1.2 Properties of the product: The product generated by this unit is methanol catalytic conversion gas, whose main components are hydrogen and carbon dioxide. Its 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 density is 0.0899 Kg/m3, the melting point is -259.14°C, the boiling point is -252.8°C, and the auto-ignition temperature is 400°C. It is very slightly soluble in water, alcohol, ether, and various liquids. It remains stable at room temperature, but becomes highly reactive at high temperatures in the presence of catalysts; it is highly flammable and explosive, and can combine with many non-metals and metals. ⑵ Properties of carbon dioxide: Its chemical name is carbon dioxide; other names include carbonic anhydride and carbonic gas. Molecular formula: CO2, molecular weight: 44.01; a colorless and odorless gas. It has a sour taste. Its gas density is 1.977 Kg/m³. The melting point is -56.6°C, and the boiling point is -78.5°C (sublimation). It readily dissolves in water to form carbonic acid. It is soluble in ethanol, methanol, acetone, chloroform, carbon tetrachloride, and benzene. It is a non-flammable gas and can be used as a fire extinguishing agent. Raw materials and product specifications. 2.1 Specifications for raw materials. Methanol: It must meet the requirements of the first-grade product standards stipulated in the national standard GB338-92. It is recommended to use methanol production facilities with a capacity of 30Kt/y or higher, so as to ensure no pollution during transportation ； The use of recycled methanol is strictly prohibited. Deionized water: Meets the requirements of **GB12145-89P (DC boilers), with a chloride ion content of less than or equal to 3 ppm. 2.2 Product specifications: (1) Composition of the conversion gas: H2 – 73–74.5%, CO2 – 23–24.5%, CO – <0.8%, CH3OH – 300 ppm, saturated with H2O. (2) Pressure: 1.1 MPa. (3) Temperature: <40°C. Operating procedures: 1. Preparations before startup: 1.1 General preparations and inspections: Check the supply of water, electricity, steam, soft water, instrument air, nitrogen, hydrogen, fuel, etc., and coordinate with relevant departments to ensure that the quantity and quality of these supplies meet the required standards. 2. Close all drain valves, sewage valves, vent valves, feed valves, and sampling valves. Open the main valves for cooling water, instrument air, etc., leading to 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. Notify 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 management and maintenance personnel must undergo technical training and pass assessments before they can take up their duties. 2 Driving Procedure: The feeding and startup procedure should be carried out immediately after the catalyst reduction is completed, with no time interval. The sequence of starting up the system is generally as follows: start the water scrubber, then the vaporization tower, followed by the converter, and finally increase the system pressure. After the reduction is complete, close the reduction system valve, open all valves from the converter to the vent line, then close the relevant valves to prepare the system for startup. Note: The operating load while driving is generally set at 30% to 60% of the full load, and it should be gradually increased to the full load once the system becomes stable. 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 functioning properly and in good condition; then turn on the power and air supply switches of the instruments. 4. Notify the methanol storage tank and demineralized water station to supply raw materials to this unit. Bring the liquid levels in the methanol intermediate tank and the demineralized water intermediate tank to ~90%, then stop feeding. 5. All valves and instruments in the catalyst reduction system shall remain in their original operating conditions. 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. 2.2 Starting up the water washing tower: 1. Open the discharge valve of the desalinated water intermediate tank, the inlet valve of the desalinated water feed pump, and the bypass valve; start the feed pump to ensure normal operation of the desalinated water pump. 2. Open the feed outlet valve for the desalinated water from the pump, close the bypass valve for the desalinated water feed, and use the control valve to adjust the return flow rate so that it reaches the desired value. 3. Once a liquid level appears in the bottom of the wash tower, open the bypass valve of the discharge control valve for the tower bottom to send deionized water to the circulating liquid tank; then open the valves before and after the control valve to maintain the liquid level in the wash tower at 30–40%. 2.3 Commissioning of the vaporization tower: 1. Open the outlet valve of the methanol intermediate tank, as well as the valves before and after the methanol flow meter; open the outlet valve of the circulating liquid storage tank to mix water with methanol. Open the inlet valve of the methanol feed pump and the bypass valve, then start the pump to ensure its proper operation. 2. Open the outlet valve of the methanol feed pump, close the bypass valve of the methanol feed pump, and adjust the gauge on the feed pump to supply methanol to the system. Sampling and analysis are carried out at the sampling point, and by adjusting the flow rate of the methanol feedstock, the water-methanol ratio is brought to the desired value. 3. When the liquid level at the bottom of the vaporization tower reaches 10%, open the vent valve at the top of the vaporization tower. Slowly open the bypass valves as well as the inlet and outlet valves for the heat transfer oil entering the tower, and use the control valve 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, open the drain valve at the bottom of the superheater; once no liquid droplets are discharged, close the drain valve, and then proceed with starting up the converter. 2.4 Starting up the conversion furnace: 1. Open the inlet valve of the conversion furnace and close the vent valve at the top of the vaporization tower, thereby feeding water-methanol feed gas into the conversion furnace. 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. 2.5 System pressure increase: 1. Open the valves before and after the flow meter, close the bypass valve, open the system pressure control valve along with its valves before and after it, and then close the bypass valve. Slowly close the valve to increase the system pressure until it reaches 1.1 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 degree of the system pressure control valve 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, adjust the flow rate of the heat transfer oil entering the lower part via valves, and maintain the liquid level in the tower bottom at 15–40%. 4. Adjust to stabilize the amount of desalinated water supplied to the washing tower and bring it to the required level, thereby maintaining a stable liquid level. 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 bring the system back to normal operation. 2.6 System stability: 1. Check the cooling water volume of the cooler to ensure that the temperature of the converted gas entering the wash tower 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 sent to the PSA-H2 unit in the subsequent section. 3 Normal operation: Once the entire system has been brought online, normal operations can be carried out step by step. 7.3.1 Establishment and maintenance of normal operating conditions 1. Appropriate adjustments are made to various control parameters based on 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, as well as the parameters at various control points, so that the system operates within normal ranges. 2. Determine the methanol flow rate based on the required amount of converted gas and the water-methanol ratio, and set the control valve to automatic mode. 3. Set the control valve to automatic mode based on the required flow rate of deionized water. 4. Adjust the flow rate of the feed pump for the raw material solution according to the desired volume of converted gas and the ratio of water to methanol. 5. Set the control valve to automatic regulation based on the circulating fluid flow rate. 6. Adjust the cooling water inlet valve to keep the temperature of the converted gas below 40°C. 7. Once the flow rate of the converted gas in the system stabilizes, activate the system pressure control valve for automatic regulation. 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 liquid discharge 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 normal condition. If any abnormalities are detected, the cause should be identified immediately, and appropriate actions taken to resolve the issue and maintain the system’s normal operation. 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 to gradually reduce the pressure to 0.4 Mpa (or open the gas buffer tank; the converted gas can be used in the converter for replacement, and the vent valve at the top of the water scrubber should be opened to lower the pressure). 3. Close the valve leading to the conversion furnace, and slowly open the vent valve at the top of the vaporization tower; the pressure in the system ahead of the vaporization tower is reduced to atmospheric pressure. 4. While reducing the pressure in the vaporization tower system, stop the feed pump to cease feeding material into the system. 5. Continue to reduce the pressure in the system downstream of the converter; once it reaches 0.2 Mpa, close the valves before and after the converter as well as the bypass valve. 6. Stop the desalination water pump to cease supplying desalinated water to the wash tower. Close the discharge valve at the bottom of the wash tower. 7. Replace the sections before and after the conversion furnace using nitrogen or gas buffer tank gas respectively; considering the impact of temperature drop on system pressure, it is advisable to maintain the pressure in each section of the system at 0.2 Mpa using nitrogen or hydrogen. After the heat transfer oil is cooled to a specified 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. Perform protective operations or passivation on the catalyst. 3.3 Emergency Shutdown Procedure 1. An emergency shutdown procedure should be initiated in any of the following situations: (1) Power outage. ⑵ Stop the cooling water. ⑶ Equipment and pipelines explode, break, and catch fire. ⑷ Severe air or liquid leaks from equipment, pipes, or flanges that cannot be resolved. ⑸ A critical control instrument has failed. 2. Operating steps: ⑴ Immediately notify the heat transfer oil system to stop heating, open the internal short-circuit valve of the heat transfer oil system, and cease supplying heat transfer oil to the gas generation unit. ⑵ Close the front valve of the converter to isolate the vaporization tower system from the reaction system. Appropriate pressure relief in the system downstream of the converter. The vaporization system can maintain stable pressure. ⑶ Stop the raw material feed pump. ⑷ Stop the desalinated water feed pump. ⑸ Special protective measures are taken for the catalyst. ⑹ Further action will be taken after the cause of the accident is determined. Instruction Manual for CNZ-1 Methanol-to-Hydrogen Catalyst. The CNZ-1 catalyst is a type of catalyst whose active component is copper. A new type of catalyst composed of oxides of copper, zinc, aluminum, etc. It exhibits high activity and good selectivity for the conversion of methanol vapor into hydrogen and carbon dioxide.
This process uses readily available methanol and demineralized water as raw materials. At temperatures ranging from 220 to 280°C, these materials are catalytically converted on a special catalyst into a conversion gas whose main components are hydrogen and carbon dioxide. The principles involved are as follows:
Main reactions:
CH3OH = CO + 2H2 + 90.7 KJ/mol
CO + H2O = CO2 + H2 –41.2 KJ/mol
Overall reaction:
CH3OH + H2O = CO2 + 3H2 + 49.5 KJ/mol
Side reactions:
2CH3OH = CH3OCH3 + H2O –24.9 KJ/mol
CO + 3H2 = CH4 + H2O +206.3 KJ/mol
After cooling and condensation, the resulting conversion gas has the following composition:
H2: 73–74%
CO2: 23–24.5%
CO: ~1.0%
CH3OH: 300 ppm
Water content: saturated
This conversion gas can be easily used in technologies such as pressure swing adsorption to separate and extract pure hydrogen. At present, nearly a hundred companies in China are using this technology. Years of operation have shown that this process is mature, easy to operate, stable in performance, and pollution-free. This process technology has the following features: 1. The cracking and conversion of methanol vapor are completed in one step on a specialized catalyst. 2. By using pressurized operation, the resulting conversion gas does not require further pressurization and can be directly fed into the pressure swing adsorption separation unit, thereby reducing energy consumption. 3. Compared with the electrolytic method, power consumption is reduced by over 90%, production costs can be lowered by 40–50%, and the purity of hydrogen is high. Compared with coal gas generation, this process is simpler in design and easier and more stable to operate. Although coal gasification has lower raw material costs, it involves a long process, high investment, and causes significant pollution with many impurities; it requires desulfurization and purification processes, making it unsuitable for small and medium-scale installations. 4. Special catalysts feature high activity, good selectivity, low operating temperature, and long service life. 5. The use of heat transfer oil as a circulating heating medium meets the process requirements, requires less investment, results in lower energy consumption, and reduces operating costs. 3 Process Flow The process flow is shown in the figure. Methanol and deionized water are mixed in a certain ratio, preheated in a heat exchanger, and then fed into a vaporization tower. The resulting water-methanol vapor is superheated in a boiler heater before entering a converter where it undergoes catalytic cracking and conversion reactions on a catalyst bed; the resulting converted gas contains approximately 74% hydrogen and 24% carbon dioxide. After heat exchange and cooling condensation, this gas enters a wash absorption tower. The unconverted methanol and water are collected at the bottom of the tower for reuse, while the gas at the top of the tower is sent to a pressure swing adsorption unit for purification. Depending on the different requirements for product gas purity and trace impurity levels, a four-tower or more tower process is employed, enabling a purity level of 99.9–99.999%. A pressure swing adsorption unit designed with a processing capacity of 1500 Nm3/h of converted gas and a purity of 99.9% can achieve a hydrogen recovery rate of over 90%. Carbon dioxide in the converted gas can be purified to food grade using pressure swing adsorption units, for use in the beverage and wine industries. This can **reduce production costs**. In the process setup, carbon dioxide is first separated using a pressure swing adsorption unit, after which the hydrogen-rich conversion gas is pressurized and fed into the same unit for further purification. This process uses simple raw materials, and the associated utility requirements are low, making them easy to meet. Based on years of operational data from industrial plants, the consumption of raw materials and energy is as follows: methanol – 0.57 tons; desalinated water – 0.32 tons; electricity – 220V/380V, 150 kWh; instrument air – 80 Nm3/h. The production cost is 2.0–3.0 yuan per Nm3 of pure hydrogen; if carbon dioxide can be recovered and sold, the cost of the product can be reduced to 1.5–2.0 yuan. (The workshop costs vary slightly depending on the scale of the installation and fluctuations in the market price of methanol.) ) 5 Environmental Protection 5.1 Waste gases: This technology employs an internal material recycling process, so that basically no waste gases are emitted during normal operation. Only a small amount of gas containing CO2 and CH3OCH3 is released from the raw material storage tanks. Taking a hydrogen production facility with a capacity of 1000 Nm3/h as an example, the amount of such gas is 1.0–1.7 Nm3/h. The composition of this gas is as follows: Component CO2 CH3OCH3 H2 CH3OH H2O Percentage 84.03 2.66 1.00 3.24 11.38 Due to the low volume of this gas, it is essentially non-toxic and can be discharged directly into the atmosphere. The off-gas from the pressure swing adsorption process is discharged into the atmosphere after passing through a flame arrester; it contains large amounts of carbon dioxide, along with small amounts of hydrogen and trace amounts of carbon monoxide and water vapor, so it does not cause pollution to the environment. 5.2 Waste liquids: In this process, only a small amount of wastewater is discharged periodically from the bottom of the vaporization tower; this wastewater contains less than 0.5% methanol. After dilution, it meets the emission standards for Category II pollutants as specified in GB8978-88, and can thus be discharged directly into the sewer system. 5.3 Waste residues: The heat transfer oil boiler room contains a certain amount of coal ash from combustion, which can be processed collectively. (Only coal-fired heat transfer oil systems have waste residues. ) 6. Status of promotion and application: The list of entities that have already carried out technology transfer or provided complete sets of equipment is as follows: The Southwest Chemical Research Institute is currently able to supply methanol steam reforming hydrogen production units of various scales, ranging from 20 to 5000 Nm3/h. It can handle technical tasks such as design, installation guidance, staff training, and operation, as well as provide complete engineering packages including hardware equipment like machinery, electrical systems, and instruments. After the installation is put into operation, follow-up services such as regular technical inspections are provided to ensure its stable operation. 7 Conclusion Industrial practice has shown that this technology is advanced and mature ； It has a simple design, is easy to operate, and runs stably. This process holds good market prospects, especially for small and medium-sized hydrogen users. The catalyst specifically designed for this process has been continuously improved. It not only retains its advantages of high activity and high selectivity, but also has seen significant progress in terms of catalyst lifespan. The catalyst used by Guangzhou Jinzhujiang Chemical Co., Ltd. has been in service for over 4 years. Process description: The production process for methanol catalytic conversion to produce gas can be divided into four steps: preheating of the raw material liquid, vaporization, superheating, the conversion reaction, and cooling and condensation of the product gas, as well as purification of the product gas. This device consists of two completely independent systems; in the following description, the designations for equipment, valves, control valves, etc. are omitted for each system. 1 Process Flow 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 work includes equipment such as the methanol metering tank, circulation liquid storage tank, raw material feed pump, heat exchanger, vaporization tower, superheater, as well as the associated instruments and valves. 1.2 Catalytic conversion reaction process: Under specific reaction temperature and pressure, the feed steam undergoes gas-solid phase catalytic conversion in the conversion furnace. The scope of work is: one converter unit and its accompanying instruments and valves. The purpose of this process is to carry out a chemical reaction to produce a conversion gas whose main components are hydrogen and carbon dioxide. 1.3 Conversion gas cooling and condensation process: The process of cooling and condensing the high-temperature conversion gas coming from the lower part of the converter to below 40°C. Its scope of work includes: heat exchangers and coolers, two types of equipment, along with the associated instruments and valves. 1.4 Shift gas purification process: A process in which low-temperature shift gas containing hydrogen, carbon dioxide, and small amounts of carbon monoxide, methanol, and water enters a water scrubber, where demineralized water absorbs the unreacted methanol. Its scope of work includes five pieces of equipment: the water washing tower, the desalinated water intermediate tank, the gas buffer tank, and the desalinated water feed pumps, along with the associated instruments and valves. 2.0 Main Control Parameters of the Process 2.1 Vaporization Superheating of Raw Materials 2.1.1 Flow rate of raw material methanol: 1134 kg/h 2.1.2 Flow rate of raw material liquid: ~2590 Kg/h 2.1.3 Feed temperature in the vaporization superheating tower: ~165 °C 2.1.4 Pressure at the bottom of the vaporization superheating tower (gauge pressure): 1.1 MPa 2.2 Conversion Reaction 2.2.1 Feed temperature: 200–260 °C 2.2.2 Reaction temperature: 220–280 °C 2.2.3 Temperature of the heat transfer oil: 235–290 °C 2.2.4 Temperature of the converted gas at the outlet of the heat exchanger: 110–140 °C 2.2.5 Temperature of the converted gas at the outlet of the cooler: <40 °C 2.2.6 Reaction pressure (gauge pressure): ~1.1 MPa 2.3 Water Washing and Separation 2.3.1 Amount of water used for desalination before entering the tower: 636 Kg/h 2.3.2 Amount of circulating liquid (after leaving the tower): ~1469 Kg/h; Composition of the circulating liquid (wt%): Methanol 0–25% 2.3.3 Amount of converted gas exiting the tower: ~3135 Nm3/h; Composition of the converted gas (V%): Hydrogen 73–74.5%, Carbon dioxide 23–24.5%, Carbon monoxide ~0.8%, Methanol 0.03%, Methane 0.20% 2.4 Catalyst Reduction 2.4.1 Flow rate of the reduction gas: ~2100 Nm3/h 2.4.2 Hydrogen content in the reduction gas: 0.5–10% 2.4.3 Reduction temperature: 110–230 °C 2.4.4 Reduction pressure: ~0.05 MPa 2.5 Others 2.5.1 Pressure of cooling water in the feed section: 0.3 MPa 2.5.2 Pressure of instrument air in the feed section: 0.4–0.60 MPa 2.5.3 Flow rate of the heat transfer oil: ~160 m3/h Principle of the Chemical Reaction: A mixture of methanol and water vapor undergoes a catalytic conversion reaction under pressure in a converter; the reaction produces hydrogen and carbon dioxide. 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 – 24.90 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. Properties of Raw Materials and Products 1.1 Properties of Raw Materials ⑴ Properties of Methanol as a raw material: Its chemical name is methanol; it is also known as methyl alcohol, wood alcohol, or pyroligneous alcohol. 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; explosive limit in air: 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 has **effects; it has a significant impact on the optic nerves, and in severe cases, can cause blindness. ⑵ Properties of the demineralized raw water (omitted). 1.2 Properties of the product: The product generated by this unit is methanol catalytic conversion gas, whose main components are hydrogen and carbon dioxide. Its 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 density is 0.0899 Kg/m3, the melting point is -259.14°C, the boiling point is -252.8°C, and the auto-ignition temperature is 400°C. It is very slightly soluble in water, alcohol, ether, and various liquids. It remains stable at room temperature, but becomes highly reactive at high temperatures in the presence of catalysts; it is highly flammable and explosive, and can combine with many non-metals and metals. ⑵ Properties of carbon dioxide: Its chemical name is carbon dioxide; other names include carbonic anhydride and carbonic gas. Molecular formula: CO2, molecular weight: 44.01; a colorless and odorless gas. It has a sour taste. Its gas density is 1.977 Kg/m³. The melting point is -56.6°C, and the boiling point is -78.5°C (sublimation). It readily dissolves in water to form carbonic acid. It is soluble in ethanol, methanol, acetone, chloroform, carbon tetrachloride, and benzene. It is a non-flammable gas and can be used as a fire extinguishing agent. Raw materials and product specifications. 2.1 Specifications for raw materials. Methanol: It must meet the requirements of the first-grade product standards stipulated in the national standard GB338-92. It is recommended to use methanol production facilities with a capacity of 30Kt/y or higher, so as to ensure no pollution during transportation ； The use of recycled methanol is strictly prohibited. Deionized water: Meets the requirements of **GB12145-89P (DC boilers), with a chloride ion content of less than or equal to 3 ppm. 2.2 Product specifications: (1) Composition of the conversion gas: H2 – 73–74.5%, CO2 – 23–24.5%, CO – <0.8%, CH3OH – 300 ppm, saturated with H2O. (2) Pressure: 1.1 MPa. (3) Temperature: <40°C. Operating procedures: 1. Preparations before startup: 1.1 General preparations and inspections: Check the supply of water, electricity, steam, soft water, instrument air, nitrogen, hydrogen, fuel, etc., and coordinate with relevant departments to ensure that the quantity and quality of these supplies meet the required standards. 2. Close all drain valves, sewage valves, vent valves, feed valves, and sampling valves. Open the main valves for cooling water, instrument air, etc., leading to 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. Notify 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 management and maintenance personnel must undergo technical training and pass assessments before they can take up their duties. 2 Driving Procedure: The feeding and startup procedure should be carried out immediately after the catalyst reduction is completed, with no time interval. The sequence of starting up the system is generally as follows: start the water scrubber, then the vaporization tower, followed by the converter, and finally increase the system pressure. After the reduction is complete, close the reduction system valve, open all valves from the converter to the vent line, then close the relevant valves to prepare the system for startup. Note: The operating load while driving is generally set at 30% to 60% of the full load, and it should be gradually increased to the full load once the system becomes stable. 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 functioning properly and in good condition; then turn on the power and air supply switches of the instruments. 4. Notify the methanol storage tank and demineralized water station to supply raw materials to this unit. Bring the liquid levels in the methanol intermediate tank and the demineralized water intermediate tank to ~90%, then stop feeding. 5. All valves and instruments in the catalyst reduction system shall remain in their original operating conditions. 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. 2.2 Starting up the water washing tower: 1. Open the discharge valve of the desalinated water intermediate tank, the inlet valve of the desalinated water feed pump, and the bypass valve; start the feed pump to ensure normal operation of the desalinated water pump. 2. Open the feed outlet valve for the desalinated water from the pump, close the bypass valve for the desalinated water feed, and use the control valve to adjust the return flow rate so that it reaches the desired value. 3. Once a liquid level appears in the bottom of the wash tower, open the bypass valve of the discharge control valve for the tower bottom to send deionized water to the circulating liquid tank; then open the valves before and after the control valve to maintain the liquid level in the wash tower at 30–40%. 2.3 Commissioning of the vaporization tower: 1. Open the outlet valve of the methanol intermediate tank, as well as the valves before and after the methanol flow meter; open the outlet valve of the circulating liquid storage tank to mix water with methanol. Open the inlet valve of the methanol feed pump and the bypass valve, then start the pump to ensure its proper operation. 2. Open the outlet valve of the methanol feed pump, close the bypass valve of the methanol feed pump, and adjust the gauge on the feed pump to supply methanol to the system. Sampling and analysis are carried out at the sampling point, and by adjusting the flow rate of the methanol feedstock, the water-methanol ratio is brought to the desired value. 3. When the liquid level at the bottom of the vaporization tower reaches 10%, open the vent valve at the top of the vaporization tower. Slowly open the bypass valves as well as the inlet and outlet valves for the heat transfer oil entering the tower, and use the control valve 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, open the drain valve at the bottom of the superheater; once no liquid droplets are discharged, close the drain valve, and then proceed with starting up the converter. 2.4 Starting up the conversion furnace: 1. Open the inlet valve of the conversion furnace and close the vent valve at the top of the vaporization tower, thereby feeding water-methanol feed gas into the conversion furnace. 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. 2.5 System pressure increase: 1. Open the valves before and after the flow meter, close the bypass valve, open the system pressure control valve along with its valves before and after it, and then close the bypass valve. Slowly close the valve to increase the system pressure until it reaches 1.1 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 degree of the system pressure control valve 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, adjust the flow rate of the heat transfer oil entering the lower part via valves, and maintain the liquid level in the tower bottom at 15–40%. 4. Adjust to stabilize the amount of desalinated water supplied to the washing tower and bring it to the required level, thereby maintaining a stable liquid level. 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 bring the system back to normal operation. 2.6 System stability: 1. Check the cooling water volume of the cooler to ensure that the temperature of the converted gas entering the wash tower 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 sent to the PSA-H2 unit in the subsequent section. 3 Normal operation: Once the entire system has been brought online, normal operations can be carried out step by step. 7.3.1 Establishment and maintenance of normal operating conditions 1. Appropriate adjustments are made to various control parameters based on 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, as well as the parameters at various control points, so that the system operates within normal ranges. 2. Determine the methanol flow rate based on the required amount of converted gas and the water-methanol ratio, and set the control valve to automatic mode. 3. Set the control valve to automatic mode based on the required flow rate of deionized water. 4. Adjust the flow rate of the feed pump for the raw material solution according to the desired volume of converted gas and the ratio of water to methanol. 5. Set the control valve to automatic regulation based on the circulating fluid flow rate. 6. Adjust the cooling water inlet valve to keep the temperature of the converted gas below 40°C. 7. Once the flow rate of the converted gas in the system stabilizes, activate the system pressure control valve for automatic regulation. 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 liquid discharge 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 normal condition. If any abnormalities are detected, the cause should be identified immediately, and appropriate actions taken to resolve the issue and maintain the system’s normal operation. 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 to gradually reduce the pressure to 0.4 Mpa (or open the gas buffer tank; the converted gas can be used in the converter for replacement, and the vent valve at the top of the water scrubber should be opened to lower the pressure). 3. Close the valve leading to the conversion furnace, and slowly open the vent valve at the top of the vaporization tower; the pressure in the system ahead of the vaporization tower is reduced to atmospheric pressure. 4. While reducing the pressure in the vaporization tower system, stop the feed pump to cease feeding material into the system. 5. Continue to reduce the pressure in the system downstream of the converter; once it reaches 0.2 Mpa, close the valves before and after the converter as well as the bypass valve. 6. Stop the desalination water pump to cease supplying desalinated water to the wash tower. Close the discharge valve at the bottom of the wash tower. 7. Replace the sections before and after the conversion furnace using nitrogen or gas buffer tank gas respectively; considering the impact of temperature drop on system pressure, it is advisable to maintain the pressure in each section of the system at 0.2 Mpa using nitrogen or hydrogen. After the heat transfer oil is cooled to a specified 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. Perform protective operations or passivation on the catalyst. 3.3 Emergency Shutdown Procedure 1. An emergency shutdown procedure should be initiated in any of the following situations: (1) Power outage. ⑵ Stop the cooling water. ⑶ Equipment and pipelines explode, break, and catch fire. ⑷ Severe air or liquid leaks from equipment, pipes, or flanges that cannot be resolved. ⑸ A critical control instrument has failed. 2. Operating steps: ⑴ Immediately notify the heat transfer oil system to stop heating, open the internal short-circuit valve of the heat transfer oil system, and cease supplying heat transfer oil to the gas generation unit. ⑵ Close the front valve of the converter to isolate the vaporization tower system from the reaction system. Appropriate pressure relief in the system downstream of the converter. The vaporization system can maintain stable pressure. ⑶ Stop the raw material feed pump. ⑷ Stop the desalinated water feed pump. ⑸ Special protective measures are taken for the catalyst. ⑹ Further action will be taken after the cause of the accident is determined. Instruction Manual for CNZ-1 Methanol-to-Hydrogen Catalyst. The CNZ-1 catalyst is a type of catalyst whose active component is copper. A new type of catalyst composed of oxides of copper, zinc, aluminum, etc. It exhibits high activity and good selectivity for the conversion of methanol vapor into hydrogen and carbon dioxide.
The methanol-to-hydrogen process is mature and should be widely used in non-petroleum chemical industries. In the petroleum chemical industry, dry gas is commonly used to produce hydrogen, with fuel gas being obtained as a by-product
Description of the hydrogen production process by water electrolysis: Producing hydrogen and oxygen through water electrolysis is a relatively mature process. Its main components include: electrolyzer, gas-water separation tank, alkali addition tank, washing tank, dehydration tank, buffer tank, cooling water tank, etc. The electrical, instrumentation, and related equipment components mainly include: DC electrolysis power supply (abbreviated as electrolysis power supply), power supply cooling circulation pump (abbreviated as power supply cooling pump or power pump), electrolyte circulation pump (abbreviated as circulation pump), electrolysis system cooling circulation pump (abbreviated as electrolysis cooling pump or cooling pump), make-up water pump, solenoid valve, pressure transmitter, temperature transmitter, differential pressure transmitter, flow meter, pressure gauge, pressure reducing valve, flashback arrestor, pure water production device, etc. The schematic diagram of the hydrogen production process by electrolyzing water is shown in Figure 1. Figure 1 Schematic diagram of the hydrogen production process by water electrolysis. The unit for pressure is Mpa, with 3 digits after the decimal point. The unit for differential pressure is kPa, with 2 digits after the decimal point; the unit for flow rate is m3/h, also with 2 digits after the decimal point. The unit for temperature is °C, with 1 digit after the decimal point. The unit for cumulative flow rate is m3, also with 1 digit after the decimal point. The unit for cumulative operating time is h, with 1 digit after the decimal point. All solenoid valves are electrically operated valves, opening when powered and closing when power is cut off. I. Control of the electrolysis power supply DDY, the power supply cooling pump DLB, the circulation pump XHB, and the cooling pump LQB. Table 1 shows the corresponding input-output relationships between the electrolysis system and the cooling system. Signal source, Control content, Notes: Input number, Name of signal source; Output number, Name of control object. AI1 (PT101), Hydrogen pressure PH; DO1, DO2 (digital signals). Electrolysis power supply DDY, Power supply cooling pump DLB, Circulation pump XHB, Cooling pump LQB. The operation of the electrolysis power supply DDY, the power supply cooling pump DLB, and the circulation pump XHB is controlled based on the hydrogen pressure PH. The start and stop of the cooling pump LQB are controlled based on the system temperature TE. For the AI2 (TT101) system, the temperature TE (electrolyte temperature): 1. The hydrogen pressure PH is converted by the pressure transmitter PT101 into a 4–20mA DC signal. Based on this hydrogen pressure PH, the operation and shutdown of the electrolysis power supply DDY (which is controlled by a digital signal to start or stop), as well as the power cooling pump DLB and the circulation pump XHB (both of which are controlled in synchronization with the electrolysis power supply DDY based on the hydrogen pressure PH), are regulated. The hydrogen pressure can be set via the touch screen: ○ The upper limit value for hydrogen pressure (referred to as the pressure setting upper limit), PHH, can be set within the range of 0–3.00 Mpa (with a reference value of 0.40 Mpa) ； ○The setting range for the lower limit value of hydrogen pressure (abbreviated as the pressure setting lower limit), PHL, is 0~3.00 MPa (reference value: 0.35 MPa). The reference value is the figure recommended for use when the device is first turned on (or when data is lost due to a long power outage). ○3 When the hydrogen pressure PH is higher than the upper pressure setting PHH, that is, PH＞PHH, DO1 outputs OFF, and the electrolysis power supply DDY, the power pump DLB, and the circulation pump XHB stop operating ； ○4 When the hydrogen gas pressure PH is lower than the lower pressure setpoint PHL, i.e., PH < PHL, the DO1 output turns ON, and the electrolytic power supply DDY, power pump DLB, and circulation pump XHB are energized and operate. 2. When the temperature of the electrolysis system (actually the temperature of the electrolyte in the electrolysis system, referred to as the electrolysis temperature) TE is converted by the temperature transmitter TT101 into a 4–20mA DC signal, the on/off state of the electrolysis power supply DDY is controlled based on this electrolysis temperature TE. The electrolysis temperature control value can be set on the touch screen: ○ The upper limit setting for the electrolysis system temperature (referred to as the upper limit for electrolysis temperature control) TEH ranges from 55~95°C (with 90°C as a reference value) ； ○2 The lower limit setting value for the electrolysis system temperature (referred to as the lower limit for electrolysis temperature control), TEL, ranges from 50 to 90°C (reference value: 85°C). ○3 When the temperature TE of the electrolysis system exceeds the upper limit TEH for electrolysis temperature control, that is, when TE > TEH, an alarm signal is generated; DO9 turns ON while DO1 turns OFF. The electrolysis power supply DDY, the power pump DLB, and the circulation pump XHB stop operating, but the other systems continue to function normally. ○4 When the temperature TE of the electrolysis system is below the lower limit TEL for electrolysis temperature control, i.e., TE＜TEL, the alarm is cleared, DO9 turns OFF, and the electrolysis system resumes normal operation. 3. The operation of the cooling pump LQB is controlled based on the electrolysis temperature TE; the upper and lower limits for the cooling temperature can be set on the touch screen: ○1 The upper limit value for the electrolysis cooling temperature (referred to as the upper cooling temperature limit) TCH ranges from 30~90°C (with 90°C as a reference value) ； ○2. The set value for the lower limit of the electrolytic cooling temperature (referred to as the lower limit for cooling temperature control), TCL, ranges from 30 to 90°C (with a reference value of 85°C). ○3 When the electrolysis temperature TE exceeds the upper limit of the cooling control value TCH, that is, TE > TCH, the DO2 output is set to OFF and the cooling pump LQB stops operating. ○4 When the electrolysis temperature TE is below the lower limit of the cooling control value TCL, that is, TE＜TCL, the alarm is cleared, DO9 turns OFF, and the electrolysis system resumes normal operation. The block diagram of the electrolysis and cooling control process is as follows: II. Water replenishment control for the gas-water separation tank. Table 2 shows the relationship between inputs and outputs for the water replenishment control of the gas-water separation tank. Signal source, Control content, Description: Input number, Name of signal source; Output number, Name of control object. DI1 (L1L): Lower limit of liquid level in the hydrogen-alkali addition tank. DO3, DO4: Solenoid valves for water replenishment in the hydrogen-alkali addition tank, BV1, BV2. These solenoid valves are controlled based on the liquid levels in the hydrogen-alkali addition tank and the oxygen-alkali addition tank, in order to determine when they should be opened or closed. DI2 (L1H): Upper limit of liquid level in the hydrogen-alkali addition tank. DI3 (L2L): Lower limit of liquid level in the oxygen-alkali addition tank. DI4 (L2H): Upper limit of liquid level in the oxygen-alkali addition tank. A liquid level switch is installed in each of the hydrogen-alkali addition tank and the oxygen-alkali addition tank, and these switches are used to control the solenoid valves BV1 and BV2. The lower limit contact of the hydrogen plus alkali tank level switch is L1L (corresponding to the digital input number DI1), the upper limit contact of the hydrogen plus alkali tank level switch is L1H (DI2). The lower limit contact of the oxygen plus alkali tank level switch is L2L (DI3), and the upper limit contact of the oxygen plus alkali tank level switch is L2H (DI4). 1. Opening conditions for the make-up water solenoid valves BV1 and BV2 (both open simultaneously): Either the level switch L1L is activated (DI1 is ON), or the level switch L2L is activated (DI3 is ON); in either case, DO3 and DO4 output a signal of ON, causing the make-up water solenoid valves BV1 and BV2 to open at the same time. 2. Closing conditions for the make-up water solenoid valves BV1 and BV2 (each closes separately): When the liquid level switch L1H in the alkali tank goes off (DI2 is OFF), DO3 outputs OFF, thereby closing the make-up water solenoid valve BV1. When the level switch L2H of the alkali addition tank is disconnected (DI4 is OFF), DO4 outputs OFF, thereby shutting off the make-up water solenoid valve BV2. 3. The liquid level status of the hydrogen and alkali tank is displayed in three ways: low level, normal, and high level. Low level: The level switch L1L is activated (DI1 is ON) + the level switch L1H is activated (DI2 is ON). Normal: Level switch L1L is off (DI1 is OFF) + level switch L1H is on (DI2 is ON). High liquid level: Liquid level switch L1L is disconnected (DI1 is OFF) + Liquid level switch L1H is disconnected (DI2 is OFF). 4. The liquid level status of the oxygen and alkali tank is displayed in three ways: low level, normal, and high level. Low level: The level switch L2L is activated (DI3 is ON) + the level switch L2H is activated (DI4 is ON). Normal: Level switch L2L is off (DI3 is OFF) + level switch L2H is on (DI4 is ON). High liquid level: Level switch L2L is disconnected (DI3 is OFF) + Level switch L2H is disconnected (DI4 is OFF). The block diagram of the water replenishment process for the gas-water separation tank is as follows: • III. Control of the water replenishment pump BSB and the water replenishment solenoid valves BV3, BV4: A set of level switches is installed in each of the hydrogen washing tank and the oxygen washing tank. The lower limit switch for the level switch in the hydrogen washing tank is L3L (DI5), while the upper limit switch is L3H (DI6); for the oxygen washing tank, the lower limit switch is L4L (DI7) and the upper limit switch is L4H (DI8). These switches are used to control the water replenishment pump BSB and the water replenishment solenoid valves BV3, BV4. Table 3: Correspondence Table between Inputs and Outputs for the Control of Water Supply to the Washing Tanks. Signal Source, Control Content, Description: Input Number, Name of Signal Source; Output Number, Name of Control Object. DI5 (L3L): Lower limit of liquid level in the hydrogen washing tank (the lower limit indicates a low liquid level). DO5, DO6, DO7: Solenoid valves for water supply to the hydrogen washing tank (BV3) and oxygen washing tank (BV4); BSB: Water supply pump. Based on the liquid level in the hydrogen washing tank, this controls the start/stop of the water supply pump BSB as well as the opening/closing of the solenoid valves BV3 and BV4. DI6 (L3H): Upper limit of liquid level in the hydrogen washing tank (the upper limit indicates a high liquid level). DI7 (L4L): Lower limit of liquid level in the oxygen washing tank. DI8 (L4H): Upper limit of liquid level in the oxygen washing tank. 1. Conditions for starting the pump and opening the valves (the pump and both solenoid valves must be activated simultaneously): Either the lower limit switch for L3L (DI5) or the lower limit switch for L4L (DI7) can be activated, or both can be activated. In that case, the power to the water supply pump is turned on (DO7 becomes ON), and at the same time, the solenoid valves BV3 and BV4 are opened (DO5 and DO6 become ON). 2. Valve and pump shutdown conditions: When the high-level switch L3H (DI6) of the hydrogen scrubber tank is opened, the water replenishment solenoid valve BV3 is closed (DO5 is OFF). When the high liquid level contact L4H (DI8) of the oxygen scrubber tank is disconnected, the make-up water solenoid valve BV4 is closed (DO6 is OFF). After both solenoid valves BV3 and BV4 are completely closed, turn off the make-up water pump (DO7 is OFF). 3. The liquid level status of the hydrogen washing tank is displayed in three ways: low level, normal, and high level. Low level: The level switch L3L is activated (DI5 is ON) + the level switch L3H is activated (DI6 is ON). Normal: Level switch L3L is open (DI5 is OFF) + Level switch L3H is closed (DI6 is ON). High liquid level: Level switch L3L is disconnected (DI5 is OFF) + Level switch L3H is disconnected (DI6 is OFF). 4. The liquid level status of the oxygen scrubber tank is displayed in three ways: low level, normal, and high level. Low level: The level switch L4L is activated (DI7 is ON) + the level switch L4H is activated (DI8 is ON). Normal: Level switch L4L is off (DI7 is OFF) + level switch L4H is on (DI8 is ON). High liquid level: Level switch L4L is disconnected (DI7 is OFF) + Level switch L4H is disconnected (DI8 is OFF). The flow diagram for water replenishment in the washing tank is as follows: IV. Differential pressure control system (pressure balance between hydrogen and oxygen). The differential pressure Pd between the pressures of oxygen and hydrogen is converted by the pressure transmitter PdT101 into a 4–20mA DC signal, and the opening and closing of the oxygen discharge solenoid valve PV1 are controlled based on this differential pressure Pd. Table 4: Correspondence table between control inputs and outputs of the oxygen exhaust solenoid valve PV1. Signal source, Control content, Description: Input number, Name of signal source; Output number, Name of control object. AI3: Pressure difference Pd (ΔP) between oxygen and hydrogen. DO8: Pressure-reducing oxygen exhaust solenoid valve PV1. The opening and closing of this valve are controlled based on the pressure difference Pd between oxygen and hydrogen. Pd = Oxygen pressure – Hydrogen pressure. The upper limit value for this pressure difference required for oxygen exhaust (referred to as the upper pressure difference setting) and the lower limit value (referred to as the lower pressure difference setting) can be set on the touch screen. The range for setting the upper pressure difference setting PdH is from -3 kPa to +3 kPa, with a reference value of 0.50 kPa ； ○The setting range for the lower limit of the pressure difference PdL is -3 kPa to +3 kPa, with a reference value of -0.50 kPa ； ○3 When the differential pressure Pd exceeds the upper set value PdH, that is, Pd＞PdH, DO8 outputs a signal of ON, and the oxygen discharge solenoid valve PV1 opens. ○4 When the differential pressure Pd is below the lower set limit PdL (i.e., Pd＜PdL), DO8 outputs OFF, and the oxygen discharge solenoid valve PV1 closes. ⑤The set range for the alarm pressure difference value PdA is 3.00 to 5.00 kPa, with a reference value of 3.50 kPa. When the absolute value of the pressure difference between oxygen and hydrogen, │Pd│, is greater than PdA, an alarm signal is generated; DO9 becomes ON while DO1 becomes OFF. The flow diagram of the differential pressure control system is as follows: V. Instantaneous Flow and Cumulative Flow The flow rate of hydrogen, QH, is converted by the flow transmitter FT101 into a 4–20mA DC signal; it is necessary to display both the instantaneous flow rate QH and the cumulative flow rate QA on the touch screen. Table 5: Correspondence Table between Hydrogen Flow Signal and Input/Output Parameters
Signal Source | Control Content | Description
Input Number | Name of Signal Source | Output Number | Name of Control Object
AI4 | Flow transmitter FT101 | None | None; displays instantaneous flow QH and cumulative flow QA
VI. Alarm Display, Recording, and Querying
It is required to have an alarm record query page on the touch screen, where all alarms are recorded in chronological order and can be viewed there. When the memory is full, the earlier records are erased in a cyclic manner. Additionally, there should be an alarm cancellation button on this page; pressing this button stops the alarm, causing DO9 to go OFF. However, if the alarm conditions are still met, the alarm will restart after 60 seconds (DO9 turns ON). To prevent the relay from operating frequently at the alarm threshold as well as alarms caused by interference, it is required that the alarm conditions persist for more than 3 seconds before an alarm signal is generated (DO9 turns ON). There must be a 3-second interval between two alerts from the same source; in other words, once the alarm conditions are no longer present, the alarm is automatically cleared. If the alarm conditions reappear, another alert can only be triggered after at least 3 seconds have passed. If the alarm is manually cleared, then a 60-second delay is required before another alert can occur from the same source. 1. An alarm is triggered when the hydrogen pressure PH > (PHH + 0.05 MPa); DO9 is ON while DO1 is OFF ； The alarm name displayed when the alarm is triggered is “Excessive hydrogen pressure”. 2. An alarm is triggered when the system temperature (AI1) exceeds the set upper limit; the name of this alarm is “Excessively high electrolyte temperature”. 3. An alarm is issued when the liquid level in the hydrogen alkali addition tank is too low while the liquid level in the oxygen alkali addition tank is too high (DO9 is ON and DO1 is OFF). Since the alkali addition tank is connected to the gas-water separation tank, their liquid levels are identical; the name of this alarm is “Excessive difference in liquid levels between the two gas-water separation tanks (high oxygen level, low hydrogen level)”. 4. An alarm is triggered when the liquid level in the oxygen alkali addition tank is too low while the liquid level in the hydrogen alkali addition tank is too high (DO9 is ON and DO1 is OFF); the name of this alarm is “Excessive difference in liquid levels between the two gas-water separation tanks (low oxygen level, high hydrogen level)”. 5. An alarm is triggered when the liquid level in the hydrogen washing tank is too low while the liquid level in the oxygen washing tank is too high; DO9 turns ON and the electrolysis power supply is disconnected, while DO1 turns OFF. The name of the alarm is “Excessive difference in liquid levels between the two washing tanks (high oxygen level, low hydrogen level).” 6. An alarm is triggered when the liquid level in the oxygen scrubber tank is too low while the liquid level in the hydrogen scrubber tank is too high; DO9 is ON and DO1 is OFF. The name of the alarm is “Excessive difference in liquid levels between the two scrubber tanks (low oxygen, high hydrogen).” 7. When the absolute value of the pressure difference Pd between oxygen and hydrogen is greater than the set alarm pressure value PdA, i.e., │Pd│＞PdA, an alarm signal is generated; DO9 becomes ON while DO1 becomes OFF. The name of the alarm is “Excessive pressure difference between oxygen and hydrogen.” 8. When the high-power DC electrolysis power supply DDY fails, it sends a fault signal (DI13 turns ON), triggering an alarm signal; DO9 turns ON, while the electrolysis power supply is turned off and DO1 turns OFF. The alarm message displayed in this case is “DC electrolysis power supply failure”. The alarm process flowchart is as follows: VII. Content displayed on the PLC main screen VIII. I/O point list for the hydrogen-oxygen separation system 1. There are a total of 4 analog (AI) input points, as shown in Table 5. Table 5: Analog Input (AI) Points Table
Serial Number | Quantity | Signal Source and Type | Installation Location | Notes
1 | 1 | Pressure transmitter PT101 | Above the hydrogen gas-water separator | Pressure of the hydrogen system; range: 0–1.0 MPa
2 | 1 | Temperature transmitter TT101 | At the top of the oxygen gas-water separator | Temperature of the electrolysis system; range: 0–150°C
3 | 1 | Differential pressure transmitter PdT101 | Between the two gas-water separators | Pressure difference between oxygen and hydrogen; range: -5 kPa to +5 kPa
4 | 1 | Flow transmitter FT101 | On the hydrogen pipeline after the dehumidification tank | Hydrogen flow rate; instantaneous flow rate range: 0–45 m³
Total: 4 points, all transmitting standard 4–20 mA DC signals.
2. Digital Input (DI): A total of 14 points, as shown in Table 6. Table 6: Digital Input (DI) Points Table
Serial Number | Quantity | Signal Source | Installation Location | Description
1 | 1 | From level gauge L1, on the alkali addition tank in the hydrogen system | When the liquid level is too low, the low-level contact L1L closes
2 | 1 | From level gauge L1, on the alkali addition tank in the hydrogen system | When the liquid level is too high, the high-level contact L1H opens
3 | 1 | From level gauge L2, on the alkali addition tank in the oxygen system | When the liquid level is too low, the low-level contact L2L closes
4 | 1 | From level gauge L2, on the alkali addition tank in the oxygen system | When the liquid level is too high, the high-level contact L2H opens
5 | 1 | From level gauge L3, on the washing tank in the hydrogen system | When the liquid level is too low, the low-level contact L3L closes
6 | 1 | From level gauge L3, on the washing tank in the hydrogen system | When the liquid level is too high, the high-level contact L3H opens
7 | 1 | From level gauge L4, on the washing tank in the oxygen system | When the liquid level is too low, the low-level contact L4L closes
8 | 1 | From level gauge L4, on the washing tank in the oxygen system | When the liquid level is too high, the high-level contact L4H opens
9 | 1 | From the electrolysis circulation pump contactor, inside the control box | When the electrolysis circulation pump is operating, the auxiliary contact of contactor KM1 closes
10 | 1 | From the electrolysis cooling pump contactor, inside the control box | When the electrolysis cooling pump is operating, the auxiliary contact of contactor KM2 closes
11 | 1 | From the power supply cooling pump contactor, inside the control box | When the power supply cooling pump is operating, the auxiliary contact of contactor KM3 closes
12 | 1 | From the make-up water pump contactor, inside the control box | When the make-up water pump is operating, the auxiliary contact of contactor KM4 closes
13 | 1 | From the DC electrolysis power supply DDY, in the DC electrolysis power supply box | When there is a fault with the DC electrolysis power supply DDY, the power failure contact closes
14 | 1 | From the flow transmitter, on the hydrogen pipeline after the dehydration tank | The flow transmitter sends out flow pulse signals for flow accumulation
Total: 14
3. Analog Output (AO): Not used this time. 4. There are a total of 9 digital output (DO) points, as shown in Table 7. Table 7: Table of Digital Output (DO) Points. Sequence Number, Quantity, Signal Purpose, Installation Location, Notes: 1, 1: (1) Controls the high-power DC electrolysis power supply DDY; (2) controls the electrolyte circulation pump XHB; (3) controls the power supply cooling water circulation pump (referred to as the power pump) DLB. A control contact is provided on the DC electrolysis power supply itself. The circulation pump XHB is installed in the electrolyte circulation pipeline, while the power supply cooling pump DLB is installed in the piping of the water cooling system of the electrolysis power supply DDY. When the hydrogen pressure (AI1) PH is below the lower pressure set point PHL, the electrolysis power supply DDY starts operating to carry out electrolysis; at the same time, the power to the circulation pump XHB and the power cooling pump DLB is turned on (DO1 is ON). When the hydrogen pressure is above the upper pressure set point, the electrolysis power supply DY stops supplying current, and the power to the circulation pump XHB and the power cooling pump DLB is turned off (DO1 is OFF). The control of the electrolysis cooling water circulation pump (referred to as the cooling pump) LQB: The electrolysis cooling water circulation pump (referred to as the cooling pump) is installed in the electrolysis cooling water circulation pipeline. When the electrolyte temperature (AI3) TE exceeds the upper limit of the cooling setting, DO2 is ON, and the cooling pump LQB is activated; when the electrolyte temperature is below the lower limit of the cooling setting, DO2 is OFF, and the power to the cooling pump LQB is turned off. 3 1 Control solenoid valve BV3 for adding water to the hydrogen gas-water separation tank. BV3 is installed on the pipeline between the hydrogen gas-water separation tank and the hydrogen gas washing tank. When either one or both of the low liquid level switches of the hydrogen gas-water separation tank and the oxygen gas-water separation tank are activated, BV3 and BV4 are turned on simultaneously (DO3 and DO4 become ON). When the high liquid level contact of the hydrogen gas-water separation tank is disconnected, the hydrogen gas make-up solenoid valve BV3 is closed (DO3 becomes OFF); when the high liquid level contact of the oxygen gas-water separation tank is disconnected, the oxygen gas make-up solenoid valve BV4 is closed (DO4 becomes OFF). 4 1 Controls the solenoid valve BV4 for supplying water to the oxygen gas-water separation tank. BV4 is installed on the pipeline between the oxygen gas-water separation tank and the oxygen gas washing tank. 5 1 Controls the water supply pump BSB. Installed on the make-up water pipeline of the hydrogen and oxygen scrubber tanks. When either one or both of the low liquid level contacts for the hydrogen and oxygen scrubber tanks are activated simultaneously, the make-up water pumps BSB, BV1, and BV2 are turned on at the same time (DO5, DO6, and DO7 are all ON). When the high liquid level contact of the hydrogen scrubber tank is disconnected, close the hydrogen scrubber tank make-up water solenoid valve BV1 (DO6 turns OFF). When the high liquid level contact of the oxygen scrubber tank is disconnected, close the hydrogen scrubber tank make-up water solenoid valve BV2 (DO7 turns OFF). When both high liquid level contacts of the scrubber tanks are disconnected, close the make-up water pump BSB (DO5 turns OFF). 6 1 Solenoid valve BV1 for controlling water supply to the hydrogen washing tank. BV1 is installed on the pipeline between the hydrogen washing tank and the water supply pump. 7 1 Solenoid valve BV2 for controlling water supply to the oxygen washing tank. BV2 is installed on the pipeline between the oxygen washing tank and the water supply pump. 8 1 Pressure relief and exhaust solenoid valve PV1: This valve is installed on the exhaust pipeline behind the oxygen gas-water separator. Pd = oxygen pressure – hydrogen pressure; when the pressure difference Pd exceeds the set upper limit, the pressure relief and exhaust solenoid valve PV1 is activated (DO8 becomes ON). When the pressure difference Pd is below the lower set limit for the pressure difference, the pressure-reducing exhaust solenoid valve PV1 is closed (DO8 is OFF). 9 1: Alarm output, connected to a flash alarm; the reason for the alarm is displayed on the touch screen. There are 8 possible alarm reasons: 1. Excessively high hydrogen pressure. 2. Excessively high electrolyte temperature. 3. Large difference in water level between the two gas-water separation tanks (high oxygen level, low hydrogen level). 4. Large difference in water level between the two gas-water separation tanks (low oxygen level, high hydrogen level). 5. Large difference in water level between the two washing tanks (high oxygen level, low hydrogen level). 6. Large difference in water level in the washing tanks (high hydrogen level). 7. Large difference in pressure between hydrogen and oxygen. 8. Fault in the high-power DC electrolysis power supply. The flash alarm is installed on the control panel of the hydrogen-oxygen machine; when an alarm occurs, DO9 turns ON. It is connected to the flash alarm, and an alarm sound is emitted along with the flashing light, while the electrolysis power supply is also turned off (DO1 turns OFF). Note: An alarm cancellation button needs to be provided on the touch screen. 1. An alarm is triggered when the hydrogen pressure PH is greater than (PHH + 0.05 Mpa); the name of the alarm is “Excessively high hydrogen pressure”. 2. An alarm is triggered when the system temperature (AI1) exceeds the set upper limit; the name of this alarm is “Excessively high electrolyte temperature”. 3. An alarm is issued when the liquid level in the hydrogen alkali addition tank is too low, while the liquid level in the oxygen alkali addition tank is too high; the name of this alarm is “Excessive difference in liquid levels between the two gas-water separation tanks (high level in oxygen tank, low level in hydrogen tank)”. 4. An alarm is triggered when the liquid level in the oxygen alkaline addition tank is too low while the liquid level in the hydrogen alkaline addition tank is too high; the name of this alarm is “Excessive difference in liquid levels between the two gas-water separation tanks (low oxygen level, high hydrogen level).” 5. An alarm is triggered when the liquid level in the hydrogen scrubber tank is too low while the liquid level in the oxygen scrubber tank is too high; the name of this alarm is “Excessive difference in liquid levels between the two scrubber tanks (high oxygen level, low hydrogen level).” 6. An alarm is triggered when the liquid level in the oxygen scrubber tank is too low while the liquid level in the hydrogen scrubber tank is too high; the name of this alarm is “Excessive difference in liquid levels between the two scrubber tanks (low oxygen, high hydrogen).” 7. When the absolute value of the pressure difference Pd between oxygen and hydrogen is greater than the set alarm pressure difference value PdA, i.e., │Pd│＞PdA, an alarm signal is generated, with the alarm title being “Excessive pressure difference between oxygen and hydrogen.” 8. When there is a fault in the electrolytic power supply and (DI13 is ON), an alarm is issued, with the alarm name being “DC Electrolytic Power Supply Fault”. Total 9, actually 9 points are used. It is recommended to reserve 1–2 DO points, 2–4 DI points, and 1 AI point (4–20mA) when designing the hardware. 5. For the 4 analog quantities, it is necessary to plot the parameter curves and record them. Click on “Trend” to display the following screen; click on one of the curves, and a dialog box will appear, as shown in Figure 2. Figure 2 Analog trend chart
Signal Source | Control Content | Description
Input Number | Name of Signal Source | Output Number | Name of Control Object
AI4 | Flow transmitter FT101 | None | None; displays instantaneous flow QH and cumulative flow QA
VI. Alarm Display, Recording, and Querying
It is required to have an alarm record query page on the touch screen, where all alarms are recorded in chronological order and can be viewed there. When the memory is full, the earlier records are erased in a cyclic manner. Additionally, there should be an alarm cancellation button on this page; pressing this button stops the alarm, causing DO9 to go OFF. However, if the alarm conditions are still met, the alarm will restart after 60 seconds (DO9 turns ON). To prevent the relay from operating frequently at the alarm threshold as well as alarms caused by interference, it is required that the alarm conditions persist for more than 3 seconds before an alarm signal is generated (DO9 turns ON). There must be a 3-second interval between two alerts from the same source; in other words, once the alarm conditions are no longer present, the alarm is automatically cleared. If the alarm conditions reappear, another alert can only be triggered after at least 3 seconds have passed. If the alarm is manually cleared, then a 60-second delay is required before another alert can occur from the same source. 1. An alarm is triggered when the hydrogen pressure PH > (PHH + 0.05 MPa); DO9 is ON while DO1 is OFF ； The alarm name displayed when the alarm is triggered is “Excessive hydrogen pressure”. 2. An alarm is triggered when the system temperature (AI1) exceeds the set upper limit; the name of this alarm is “Excessively high electrolyte temperature”. 3. An alarm is issued when the liquid level in the hydrogen alkali addition tank is too low while the liquid level in the oxygen alkali addition tank is too high (DO9 is ON and DO1 is OFF). Since the alkali addition tank is connected to the gas-water separation tank, their liquid levels are identical; the name of this alarm is “Excessive difference in liquid levels between the two gas-water separation tanks (high oxygen level, low hydrogen level)”. 4. An alarm is triggered when the liquid level in the oxygen alkali addition tank is too low while the liquid level in the hydrogen alkali addition tank is too high (DO9 is ON and DO1 is OFF); the name of this alarm is “Excessive difference in liquid levels between the two gas-water separation tanks (low oxygen level, high hydrogen level)”. 5. An alarm is triggered when the liquid level in the hydrogen washing tank is too low while the liquid level in the oxygen washing tank is too high; DO9 turns ON and the electrolysis power supply is disconnected, while DO1 turns OFF. The name of the alarm is “Excessive difference in liquid levels between the two washing tanks (high oxygen level, low hydrogen level).” 6. An alarm is triggered when the liquid level in the oxygen scrubber tank is too low while the liquid level in the hydrogen scrubber tank is too high; DO9 is ON and DO1 is OFF. The name of the alarm is “Excessive difference in liquid levels between the two scrubber tanks (low oxygen, high hydrogen).” 7. When the absolute value of the pressure difference Pd between oxygen and hydrogen is greater than the set alarm pressure value PdA, i.e., │Pd│＞PdA, an alarm signal is generated; DO9 becomes ON while DO1 becomes OFF. The name of the alarm is “Excessive pressure difference between oxygen and hydrogen.” 8. When the high-power DC electrolysis power supply DDY fails, it sends a fault signal (DI13 turns ON), triggering an alarm signal; DO9 turns ON, while the electrolysis power supply is turned off and DO1 turns OFF. The alarm message displayed in this case is “DC electrolysis power supply failure”. The alarm process flowchart is as follows: VII. Content displayed on the PLC main screen VIII. I/O point list for the hydrogen-oxygen separation system 1. There are a total of 4 analog (AI) input points, as shown in Table 5. Table 5: Analog Input (AI) Points Table
Serial Number | Quantity | Signal Source and Type | Installation Location | Notes
1 | 1 | Pressure transmitter PT101 | Above the hydrogen gas-water separator | Pressure of the hydrogen system; range: 0–1.0 MPa
2 | 1 | Temperature transmitter TT101 | At the top of the oxygen gas-water separator | Temperature of the electrolysis system; range: 0–150°C
3 | 1 | Differential pressure transmitter PdT101 | Between the two gas-water separators | Pressure difference between oxygen and hydrogen; range: -5 kPa to +5 kPa
4 | 1 | Flow transmitter FT101 | On the hydrogen pipeline after the dehumidification tank | Hydrogen flow rate; instantaneous flow rate range: 0–45 m³
Total: 4 points, all transmitting standard 4–20 mA DC signals.
2. Digital Input (DI): A total of 14 points, as shown in Table 6. Table 6: Digital Input (DI) Points Table
Serial Number | Quantity | Signal Source | Installation Location | Description
1 | 1 | From level gauge L1, on the alkali addition tank in the hydrogen system | When the liquid level is too low, the low-level contact L1L closes
2 | 1 | From level gauge L1, on the alkali addition tank in the hydrogen system | When the liquid level is too high, the high-level contact L1H opens
3 | 1 | From level gauge L2, on the alkali addition tank in the oxygen system | When the liquid level is too low, the low-level contact L2L closes
4 | 1 | From level gauge L2, on the alkali addition tank in the oxygen system | When the liquid level is too high, the high-level contact L2H opens
5 | 1 | From level gauge L3, on the washing tank in the hydrogen system | When the liquid level is too low, the low-level contact L3L closes
6 | 1 | From level gauge L3, on the washing tank in the hydrogen system | When the liquid level is too high, the high-level contact L3H opens
7 | 1 | From level gauge L4, on the washing tank in the oxygen system | When the liquid level is too low, the low-level contact L4L closes
8 | 1 | From level gauge L4, on the washing tank in the oxygen system | When the liquid level is too high, the high-level contact L4H opens
9 | 1 | From the electrolysis circulation pump contactor, inside the control box | When the electrolysis circulation pump is operating, the auxiliary contact of contactor KM1 closes
10 | 1 | From the electrolysis cooling pump contactor, inside the control box | When the electrolysis cooling pump is operating, the auxiliary contact of contactor KM2 closes
11 | 1 | From the power supply cooling pump contactor, inside the control box | When the power supply cooling pump is operating, the auxiliary contact of contactor KM3 closes
12 | 1 | From the make-up water pump contactor, inside the control box | When the make-up water pump is operating, the auxiliary contact of contactor KM4 closes
13 | 1 | From the DC electrolysis power supply DDY, in the DC electrolysis power supply box | When there is a fault with the DC electrolysis power supply DDY, the power failure contact closes
14 | 1 | From the flow transmitter, on the hydrogen pipeline after the dehydration tank | The flow transmitter sends out flow pulse signals for flow accumulation
Total: 14
3. Analog Output (AO): Not used this time. 4. There are a total of 9 digital output (DO) points, as shown in Table 7. Table 7: Table of Digital Output (DO) Points. Sequence Number, Quantity, Signal Purpose, Installation Location, Notes: 1, 1: (1) Controls the high-power DC electrolysis power supply DDY; (2) controls the electrolyte circulation pump XHB; (3) controls the power supply cooling water circulation pump (referred to as the power pump) DLB. A control contact is provided on the DC electrolysis power supply itself. The circulation pump XHB is installed in the electrolyte circulation pipeline, while the power supply cooling pump DLB is installed in the piping of the water cooling system of the electrolysis power supply DDY. When the hydrogen pressure (AI1) PH is below the lower pressure set point PHL, the electrolysis power supply DDY starts operating to carry out electrolysis; at the same time, the power to the circulation pump XHB and the power cooling pump DLB is turned on (DO1 is ON). When the hydrogen pressure is above the upper pressure set point, the electrolysis power supply DY stops supplying current, and the power to the circulation pump XHB and the power cooling pump DLB is turned off (DO1 is OFF). The control of the electrolysis cooling water circulation pump (referred to as the cooling pump) LQB: The electrolysis cooling water circulation pump (referred to as the cooling pump) is installed in the electrolysis cooling water circulation pipeline. When the electrolyte temperature (AI3) TE exceeds the upper limit of the cooling setting, DO2 is ON, and the cooling pump LQB is activated; when the electrolyte temperature is below the lower limit of the cooling setting, DO2 is OFF, and the power to the cooling pump LQB is turned off. 3 1 Control solenoid valve BV3 for adding water to the hydrogen gas-water separation tank. BV3 is installed on the pipeline between the hydrogen gas-water separation tank and the hydrogen gas washing tank. When either one or both of the low liquid level switches of the hydrogen gas-water separation tank and the oxygen gas-water separation tank are activated, BV3 and BV4 are turned on simultaneously (DO3 and DO4 become ON). When the high liquid level contact of the hydrogen gas-water separation tank is disconnected, the hydrogen gas make-up solenoid valve BV3 is closed (DO3 becomes OFF); when the high liquid level contact of the oxygen gas-water separation tank is disconnected, the oxygen gas make-up solenoid valve BV4 is closed (DO4 becomes OFF). 4 1 Controls the solenoid valve BV4 for supplying water to the oxygen gas-water separation tank. BV4 is installed on the pipeline between the oxygen gas-water separation tank and the oxygen gas washing tank. 5 1 Controls the water supply pump BSB. Installed on the make-up water pipeline of the hydrogen and oxygen scrubber tanks. When either one or both of the low liquid level contacts for the hydrogen and oxygen scrubber tanks are activated simultaneously, the make-up water pumps BSB, BV1, and BV2 are turned on at the same time (DO5, DO6, and DO7 are all ON). When the high liquid level contact of the hydrogen scrubber tank is disconnected, close the hydrogen scrubber tank make-up water solenoid valve BV1 (DO6 turns OFF). When the high liquid level contact of the oxygen scrubber tank is disconnected, close the hydrogen scrubber tank make-up water solenoid valve BV2 (DO7 turns OFF). When both high liquid level contacts of the scrubber tanks are disconnected, close the make-up water pump BSB (DO5 turns OFF). 6 1 Solenoid valve BV1 for controlling water supply to the hydrogen washing tank. BV1 is installed on the pipeline between the hydrogen washing tank and the water supply pump. 7 1 Solenoid valve BV2 for controlling water supply to the oxygen washing tank. BV2 is installed on the pipeline between the oxygen washing tank and the water supply pump. 8 1 Pressure relief and exhaust solenoid valve PV1: This valve is installed on the exhaust pipeline behind the oxygen gas-water separator. Pd = oxygen pressure – hydrogen pressure; when the pressure difference Pd exceeds the set upper limit, the pressure relief and exhaust solenoid valve PV1 is activated (DO8 becomes ON). When the pressure difference Pd is below the lower set limit for the pressure difference, the pressure-reducing exhaust solenoid valve PV1 is closed (DO8 is OFF). 9 1: Alarm output, connected to a flash alarm; the reason for the alarm is displayed on the touch screen. There are 8 possible alarm reasons: 1. Excessively high hydrogen pressure. 2. Excessively high electrolyte temperature. 3. Large difference in water level between the two gas-water separation tanks (high oxygen level, low hydrogen level). 4. Large difference in water level between the two gas-water separation tanks (low oxygen level, high hydrogen level). 5. Large difference in water level between the two washing tanks (high oxygen level, low hydrogen level). 6. Large difference in water level in the washing tanks (high hydrogen level). 7. Large difference in pressure between hydrogen and oxygen. 8. Fault in the high-power DC electrolysis power supply. The flash alarm is installed on the control panel of the hydrogen-oxygen machine; when an alarm occurs, DO9 turns ON. It is connected to the flash alarm, and an alarm sound is emitted along with the flashing light, while the electrolysis power supply is also turned off (DO1 turns OFF). Note: An alarm cancellation button needs to be provided on the touch screen. 1. An alarm is triggered when the hydrogen pressure PH is greater than (PHH + 0.05 Mpa); the name of the alarm is “Excessively high hydrogen pressure”. 2. An alarm is triggered when the system temperature (AI1) exceeds the set upper limit; the name of this alarm is “Excessively high electrolyte temperature”. 3. An alarm is issued when the liquid level in the hydrogen alkali addition tank is too low, while the liquid level in the oxygen alkali addition tank is too high; the name of this alarm is “Excessive difference in liquid levels between the two gas-water separation tanks (high level in oxygen tank, low level in hydrogen tank)”. 4. An alarm is triggered when the liquid level in the oxygen alkaline addition tank is too low while the liquid level in the hydrogen alkaline addition tank is too high; the name of this alarm is “Excessive difference in liquid levels between the two gas-water separation tanks (low oxygen level, high hydrogen level).” 5. An alarm is triggered when the liquid level in the hydrogen scrubber tank is too low while the liquid level in the oxygen scrubber tank is too high; the name of this alarm is “Excessive difference in liquid levels between the two scrubber tanks (high oxygen level, low hydrogen level).” 6. An alarm is triggered when the liquid level in the oxygen scrubber tank is too low while the liquid level in the hydrogen scrubber tank is too high; the name of this alarm is “Excessive difference in liquid levels between the two scrubber tanks (low oxygen, high hydrogen).” 7. When the absolute value of the pressure difference Pd between oxygen and hydrogen is greater than the set alarm pressure difference value PdA, i.e., │Pd│＞PdA, an alarm signal is generated, with the alarm title being “Excessive pressure difference between oxygen and hydrogen.” 8. When there is a fault in the electrolytic power supply and (DI13 is ON), an alarm is issued, with the alarm name being “DC Electrolytic Power Supply Fault”. Total 9, actually 9 points are used. It is recommended to reserve 1–2 DO points, 2–4 DI points, and 1 AI point (4–20mA) when designing the hardware. 5. For the 4 analog quantities, it is necessary to plot the parameter curves and record them. Click on “Trend” to display the following screen; click on one of the curves, and a dialog box will appear, as shown in Figure 2. Figure 2 Analog trend chart
Hydrogen production by water electrolysis, hydrogen production by ammonia decomposition, hydrogen production from catalytic dry gas, hydrogen production by methanol cracking, hydrogen production via natural gas conversion, hydrogen production from coke oven gas. . I just finished this, but I can’t upload large files
No, it should be encrypted