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Section 1: Procedures for Testing 1. Degree of completion of installation； 2. Preparation work for various systems (the most critical step is purging) ； 3. Individual testing: a. Circulation water pump ； b. Air compressor ； c. Instrument air supply ； d. Frozen cooling water pump ； e. Switching program ； 4. Overall test run: bare cooling. Section 2: Bare Cooling (Overall Testing) 1. Steps for bare cooling: (1) The air compressor unit is operating properly: oil system, water system, operation without load, pressure increase, cooling control. (2) The pre-cooling system is functioning properly ； (3) The purification system is operating properly: the program control valve acts accurately and correctly ； (4) Purging the fractionation tower system: it is crucial to do it thoroughly, especially the first time ； (5) Additional cooling capacity of the expander: temperature reduction ； 2. Criteria for ending the natural cooling process: Try to lower the temperature behind the expander as much as possible so that no liquid appears there. Once the temperature of the main equipment drops to between 80°C and 120°C below the ambient temperature, and equilibrium is reached, maintain this condition for 2–3 hours before concluding the process. Section 3: Startup and Operation of the Pre-cooling System 1. Process and Configuration of the Pre-cooling System (as shown in the figure below) (1) Several common process configurations: a. Process with a chiller unit ； b. Process without a chiller: Generally suitable for situations with a large amount of nitrogen ； c. Process using a cold steam turbine unit ； (2) Process characteristics 2. Operational approach ① First process: a. Inspect the equipment: When the air-cooled tower is used for the first time, the manhole should be opened to check whether the water distribution system is even ； Check whether the packing height of the air-cooled tower is appropriate ； Check whether the filler will escape (gases can carry the filler away; this is a problem that has occurred in our company), and the same applies to water cooling towers ； Water quality also needs to be checked ； Is the water pump operating properly? ； Chillers: Once shut down, it usually takes about 5 minutes before they can be restarted ； b. Check each process, mainly focusing on liquid level and flow rate; the most critical factor is the gas temperature in the air-cooled tower. c. Control results: (1) It is crucial to determine whether the stability of the liquid level in the air-cooled tower meets the required standards ； (2) The control of the water inflow rate in a water-cooled tower is related to the liquid level; it should be taken into account that there is a lag between changes in the water inflow rate and those in the liquid level. This is different from air-cooled towers, where real-time control is generally possible. d. Relationship between chiller units and water pumps: The chilled water volume is generally 1/3 of that of the cooling water ； The inlet and outlet water temperatures of chillers are generally 5°C, with a maximum of not more than 10°C℃ ； A return pipe is generally provided from the outlet of the chiller to the water-cooled tower. ②Second process: Process without a chiller unit. a. The air temperature values at the air-cooled tower are different ； b. Insulation performance ； c. Water temperature changes ； d. Molecular sieve adsorbers have different capacities ； ③Procedure operation with a chiller unit a. Prevent excessively low temperatures ； b. Effect of the separator: It needs to be checked. ④Process using liquid ammonia as a cooling source (can replace chillers) 3. Operation sequence a. Flush the water circuit – no air supplied; for the first use, flush the water circuit system first ； First, flush the water-cooled tower; once its drainage is clean, start the water pump to supply water to the air-cooled tower in order to flush it. At the same time, check the status of the equipment in operation, and also verify the water distribution situation when the access hatch of the water tank is not open (this procedure cannot be followed after aeration) ； b. Check the scouring effect ； c. Check the liquid level in terms of instrument control ； d. Introduce air — Restart the water pump and water system, including the chiller unit ； e. Switch to automatic mode ； 4. Regarding the issue of water carried in the air (referring to the problem of free water in the air exiting the air-cooled tower as a whole): ① Pressure fluctuations cause changes in flow velocity: Water is often carried along when pressure decreases; since the cross-sectional area of the air-cooled tower remains unchanged, the airflow velocity increases, which makes it easier for water to be carried along. a. Impact of the air compressor air circuit (or changes in it) ； b. Operation of subsequent valves: valves in the purification system, the main valve for supplying gas to the distillation tower system ； c. Changes in the water volume of the air-cooled tower: This mainly refers to an increase in the amount of water; in some cases, the height of the tower is increased at the water inlet located at the top of the tower, and level gauges as well as overflow pipes are added to allow water to flow back to the lower part of the tower ； Section 4: Startup Operations of the Purification System 1. Flow diagram of the purification system (as shown below) 2. Characteristics of the flow process (compared to the switching process) a. Improvement in the safety performance of the equipment ； b. Extend lifespan, reduce corrosivity ； c. Easy to maintain; the original switch-type design is located inside the tower, resulting in frequent failures and making maintenance difficult ； d. Easy to automate control ； 3. Tasks of the purification system – Safety requirements ； 4. Adsorption capacity – Requirements for adsorbents: High pressure and low temperature – ease of adsorption ； Low pressure, high temperature – easy to desorb ； It is necessary to prevent sulfides and oils from entering the purifier, as they have a severe impact on the performance of the molecular sieve; otherwise, it will lead to a decline in the adsorption capacity of the molecular sieve, a condition known as poisoning. 5. Operational approach: ① Preparation work: Verify the correctness and integrity of the equipment and valves, as well as the accuracy of the input and output signals ； ②Given and determine the opening degree of the special valve ； First bypass pressurization ； When air enters the purifier, its temperature rises by 4~6°C due to the adsorption heat. 6. Sequence of operations: a. Purge all pipes in the adsorber ； b. It can be used directly after filling the molecular sieve ； c. Purge and vent flow path ； d. Determine the flow rate (flow rate of the regenerating gas) ； e. Charging time (varies among different manufacturers) ； f. Pressure relief time ； g. Install an electric heater: Determine the temperature rise of the regenerated gas; the volume of regenerated gas differs when cooling occurs without any heating and during normal operation ； h. Relationship between the amount of regenerated gas and pressure: (For regeneration air, since it contains a certain amount of moisture, this has an impact on the temperature rise; the pressure of the regeneration air should be between 0.02 and 0.03 Mpa. It is necessary to take into account the effect of the air used as the gas generation source and WN on the temperature rise of the gas passing through the electric heater.) ； i. Determination of the temperature in the later stage of heating: the temperature of the gas fed to the molecular sieve for regeneration is 160°C, while the outlet temperature of the molecular sieve at the end of this heating stage is generally between 120 and 140°C℃ ； j. Keep the actual adjustment cycle unchanged; the heating and cooling times can be adjusted as necessary, but no adjustments should be made unless there are special circumstances ； k. Issues with the use of manual valves ； l. Different regenerating gas paths ； m. Determination of the time to supply gas to the fractionation tower: When cooled naturally, it is generally possible to proceed after 4 hours ； While driving: after 3.5 cycles ； In other words, an adsorber is used after being heated twice, so that the other one can also maintain two heating cycles. Section 5: Startup Procedures for Expanders 1. Common air-driven brake turbine expanders ； ①Schematic: ② Features: Simple operation, large expansion ratio, outlet temperature can be very low; suitable for small and medium-sized air separation units (best when without argon). ③Principle: Pressure change at the fan side: 0 MPa~0.13 MPa ； ④Operation instructions and startup process: a. Preparation work: (Sealing gas) Supply the sealing gas first, followed by the lubricating oil circulation ； (Before using the oil circuit for the first time, connect the lubricating oil inlet and outlet to the expansion machine outlet, and use an oil circulation process to clean it.) The pressure of the sealing gas must be higher than that of the oil ； b. Determine the valve on/off position ； c. Conduct a shut-off test on the opening degree of the inlet control valve (controlled by a solenoid valve); the test can be carried out without load or with an appropriately increased load. If there is an adjustable nozzle, set the control valve at 40%–70% before activating the nozzle ； d. Slowly open the nozzle by 10%~50%, doing so in stages, while observing the equipment. Try to keep the rotation speed as high as possible; the initial increase in speed should be above 10,000 revolutions per minute. Do not stop when the speed is below 10,000 revolutions per minute, and it is generally advisable to maintain a speed of at least 10,000 revolutions per minute ； e. Understand the rotation status of the unit ； f. The two expansion units are started separately: the speed of the first expansion unit must be above 70% of its maximum speed before the second expansion unit is started ； g. Precautions for startup: pressure changes, gas flow rate changes, valve opening degrees, temperature changes (temperatures before and after the expander, to assess the expander’s efficiency), etc ； 2. Pressurized turbine expander ① Schematic diagram of the process: ② Features: a. The pressure increase ratio of the pressurizer is 1.3 to 1.5 times ； b. Utilize the theory of high temperature and high enthalpy drop to increase cooling capacity ； The temperature at the inlet of the expander is around -100°C, while the temperature at the outlet is between -145°C and -165°C℃ ； c. Configure the thermosyphon vaporization evaporator ； d. Change in energy ； e. Suitable for large and medium-sized air separation units ； f. Suitable for argon production equipment ； g. Suitable for automated operations ； ③Operation instructions and startup process a. Follow the requirements in the manual ； b. Determine the valve opening degree ； c. Sequence of startup: Determine whether heating is required, slowly open the inlet control valve and nozzle, and adjust the speed based on the temperature drop (it is necessary to ensure that speed measurement is accurate) ； d. Start the other one separately ； e. Adjust the opening of the nozzle and the pressure boost valve 2 ； Section 6: Commissioning of Air Separation Units Generally, commissioning refers to the air compressor, while startup usually denotes the expansion machine. 1. Several steps in the commissioning process: ① The air compressor is operating normally ； Oil circuits, water circuits, pressure control, venting control issues ； ②The pre-cooling system is operating normally ； Liquid level, flow rate, unit (chilled water) ； ③The purification system is operating normally ； Switch valve, program ； ④Distillation tower system purging ； Blow out the equipment; inspect the control valves ； ⑤Start the expander to increase the cooling capacity ； Reduce equipment temperature ； ⑥Rapid fluid accumulation ； Liquefied air, liquid oxygen – increase the level of the main cooling liquid ； ⑦Adjust purity and yield ； 2. Purging the fractionation tower system: Purging removes impurities from the equipment ； Heating up: ① Timing for a thorough purge: a. After installation is complete, before cooling down ； b. After natural cooling, before the official test run ； c. After major repairs, before official operation ； ②Purging of individual units: After the expander is shut down or before it is started: Purging must be carried out promptly ； After the liquid pump is shut down or before it is started: purge it in a timely manner ； Liquid storage tanks and their pipelines: They must be purged before use, using dry nitrogen for purging ； ③Purging gas source: Use dry air or nitrogen; the instrument gas supply can be borrowed, and generally it is better to use nitrogen or slightly contaminated nitrogen rather than dry air ； ④Official driving purge: a. Meet the conditions for driving ； b. Purging route ； c. Purging effect ； 3. Precautions before starting the operation: a. The cold end of the main heat exchanger reaches the liquefaction temperature (-173°C) ； b. Fully utilize the refrigeration capacity of the expander: increase the speed, operate it for a longer period at high temperatures, adjust the gas volume (expansion amount); within the limits permitted by the speed, enlarge the nozzle and reduce the pressure-boost bypass ； c. As the temperature decreases and the amount of air entering the tower increases, the exhaust volume of the air compressor should be reduced ； d. Ensure the outlet temperature of the air-cooled tower by adjusting the amount of chilled water ； e. Adjust the amount of regenerated gas, adjust the heating and cooling times, and check the accuracy of the CO2 analyzer ； f. Adjust the ratio and flow rate of the rectified air to the backflow gas ； There are various methods for regulation in this regard, which need to be considered comprehensively and in an integrated manner. For example: ① Regulate the three valves that direct the flow into the three main heat exchangers ； ②The three valves that regulate the reflux gas entering the main heat exchanger ； ③Temperature regulation of the expander during adjustment ； ④Adjust the rear bypass valve of the expander ； 4. Adjustments during startup: ① Current status of material balance; ② Adjustment for cold energy imbalance ； a. Cooling capacity: b. Cooling load consumed ； Chapter 12 Normal Operation of Air Separation Units Section 1 Tasks of Normal Operation 1. Understand and improve the operations in the later stages after startup: optimize operating conditions for optimal performance, identify problems, reduce emissions, and increase product output ； 2. Different units have different specifications: double-high pressure equipment, air separation units equipped with argon, single-high pressure equipment, external liquefaction units, fully liquid-based equipment, and internal compression processes ； Section 2: Control of Cooling Capacity 1. Adjusting the cooling capacity a. The relationship between the adjustment effect of adjustable nozzles and their efficiency ； b. Influence of the bypass valve on the pressurization effect ； c. Relationship between the speed of a single expander and the load ； d. Effects of high temperature and high enthalpy drop ； e. Avoid liquid accumulation behind the machine ； f. Distribution of expanded air ； g. Operating condition of the expander itself ； How to avoid liquid carryover at the back of the machine: Liquid carryover leads to a significant drop in pressure, causing gas to flow back inside the tower, resulting in severe expansion vibrations and damage to the impeller ； 2. Reduce heat loss due to insufficient reheat: Based on the temperature difference at the hot end, it should generally be less than 3 degrees ； Heat loss due to cooling: Loss of liquid cooling capacity: Section 3 Adjustment of the optimal operating conditions 1. Pressure control: Operations are based on pressure; if there is a deviation in pressure, there will also be a deviation in temperature ； Design pressure sequence: Atmospheric pressure — Regeneration gas pressure at the molecular sieve outlet — Pipeline resistance — Resistance of the main heat exchanger — Subcooler resistance — Resistance of aluminum pipes — Pressure at the upper column outlet — Pressure at the lower part of the upper column — Pressure of the liquid oxygen column in the main cooler — Average liquid oxygen temperature — Temperature of nitrogen in the main cooler — Pressure of the lower column — Resistance of the lower column — Pressure entering the lower column — Air resistance of the main heat exchanger — Air resistance of the molecular sieve adsorber — Resistance of pipeline valves — Resistance of the air-cooled tower — Pressure at the air compressor outlet ； 2. Adjustment of operating conditions in the lower tower: a. Resistance level – determination and adjustment, reflux rate, gas-liquid ratio ； b. Material balance ； c. Results of purity adjustment ； Resistance, component variations, and the operating conditions of the tray ； 3. Several factors affecting oxygen purity a. The amount of oxygen extracted ； b. Purity of contaminated nitrogen: Adjust the purity of liquid oxygen as much as possible during operation, thereby increasing the oxygen extraction rate ； c. Relationship between Liquid Air purity and oxygen purity ； d. Effect of the volume of expanded air on the operating conditions in the upper tower: Gas flow rate into the tower with unchanged purity; Flow rate ； Temperature: (Superheat) The superheat should be less than 7°C; it cannot be too high. e. Influence of the level of the main cooling liquid: A stable level of the main cooling liquid is an important indicator of stable distillation conditions, indicating that there has been a change in the gas-liquid ratio in the upper column ； Explain the changes in cooling capacity ； Whether rising or falling, the amount of steam rising is decreasing. f. Effect of changes in air volume: The pressure in the lower column changes; as pressure increases, the condensation temperature rises, the heat exchange amount increases, and the amount of liquid oxygen that vaporizes also increases ； g. Influence of tray efficiency: Structure type: packed tower, verticality ； h. Effects of flooding: liquid leakage, liquid suspension, simultaneous occurrence of various phenomena, unstable operating conditions; it is necessary to reduce the volume first and then gradually increase it again. 4. Adjustment of pure nitrogen purity a. Return flow rate of liquid nitrogen from the lower column – adjust the opening degree of the return valve ； b. Amount of material removed ； c. Increased nitrogen production (the amount taken out at the top of the tower): Increasing the amount of liquid nitrogen fed into the tower has the greatest impact ； Impact of nitrogen contamination level 5. Adjustment of the main cooling liquid level: a. Fully submerged operation: b. Semi-submerged operation: c. Relationship with the amount of cooling capacity: Section 4: Startup and adjustment of the argon production unit 1. Conditions for starting argon production: ① Oxygen production must be operating normally first before starting the argon tower ； ②Oxygen and argon are adjusted simultaneously ； ③The argon system flow path must be purged in advance ； 2. Procedure for producing argon by complete distillation ① Purging process and purpose: a. Removing moist air ； b. Gradual cooling ； c. Use other purging gases (liquid air, liquid nitrogen, liquid oxygen) ； ②Feed liquid air to the crude argon condenser: The amount fed should be small, and care must be taken during the operation ； Because it affects the liquid and air flows entering the tower (resulting in a reduction), thereby decreasing the resistance in the tower ； After liquid air separation, the pressure in the crude argon column decreases, and the argon fraction is automatically drawn off, initiating argon production ； ③As the temperature gradually decreases, and liquid appears in the upper part of the crude argon column (liquid-air level), the relevant purge lines must be gradually reduced. (Mainly considering that the temperature of the crude argon column is also gradually decreasing, air will be drawn in from the outside.) ④ After liquid appears, carry out multiple discharges before allowing the liquid to accumulate again ； During manufacturing, assembly, and installation, emissions such as aluminum shavings and welding slag must be cleaned up properly; one should not rush the process or skimp on using the necessary liquids. ⑤The liquid that appears at the lower part of crude argon column I, once the liquid level reaches 50%, the pre-cooling liquid pump is started, and then the flow rate of the pump is adjusted. (Actually, it’s about adjusting the operating conditions.) ⑥ Once the distillation tower is functioning properly (this takes some time; the duration can be determined by one’s own judgment), and the purity level meets the requirements, the flow of gas into the argon purification tower should be increased gradually. Nitrogen or liquid nitrogen can also be fed into this tower at the same time. 3. Adjustments and precautions for argon operation conditions ① Relationship between the resistance in the crude argon column and the liquid-air level a. Design resistance: The actual resistance should be greater than the design value; it shouldn’t be assumed that a higher value indicates a problem ； b. Liquid-air level: It needs to be properly controlled ； c. Operating conditions in the tower ； d. Liquid-air level in the lower tower ； ②Stability of the argon fraction: The stability of the argon fraction is the basis for the proper operation of the crude argon column; it should be between 8% and 12%. If the argon fraction contains too much oxygen, the oxygen content in the crude argon increases, which in turn raises the resistance ； The argon extraction rate decreases, and the argon production falls. If the oxygen content is too low, the nitrogen content increases, which leads to deterioration in the operation of the crude argon column and the occurrence of nitrogen plugging. Additionally, an excessive amount of nitrogen entering the crude argon column increases its load and affects purity. ③Control of oxygen content in the argon fraction: achieved by adjusting the normal operating conditions of the main column ； ④Maintain continuous discharge of non-condensable gas to prevent nitrogen plugging ； ⑤When each operating condition is close to normal, adjust to the optimal operating condition ； ⑥During normal operation, it is necessary to prevent a negative pressure from developing in the crude argon column and to avoid pipe blockages ； ⑦Check that the readings on all instruments are correct