Basic Hydrogen Production Operation Test Questions

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1. What are the preparatory tasks before starting up a hydrogenation unit? Comprehensive purging of the equipment, water flushing, individual unit testing, furnace drying, calibration of instruments and ESD systems, initial airtightness testing of the reaction system ； After passing the acceptance inspection by China Communications, the project enters the stages of integrated commissioning and trial operation with feedstock. The main tasks include: water circulation testing, cold oil circulation testing, hot oil circulation testing, catalyst loading, nitrogen leak testing, hydrogen leak testing, catalyst sulfidation, and switching between different crude oils. 2. What are the procedures for dealing with abnormal shutdowns of hydrogenation units and the precautions to take? 1). In the event of severe accidents such as high-pressure leaking into low-pressure areas, uncontrolled temperature rise in the reactor bed, overpressure in the hydrogen-related systems with no way to relieve that pressure, or serious cracks and leaks in these systems, the system’s emergency pressure relief button is activated; the reactor feed heater is shut down, the feed pump stops operating, and the pressure relief valves automatically release pressure. 2). Go to the site to close the gas valve of the reaction feed heater; decide whether to turn off the pilot light based on the furnace temperature and the conditions at the site, and close the outlet valve of the hydrogenation feed pump. 3). Shut down the new hydrogen compressor and the water injection pump ； Scale inhibitor pump. 4). The hydrogen-containing system continues to depressurize; if the temperature of the catalyst bed is high, nitrogen can be introduced into the system when its pressure drops below 3.5 Mpa in order to cool it down and displace the gas. 5). The distillation system shall be switched to internal circulation, and gas stripping for venting shall be stopped; in the event of a large-scale hydrogen or oil-gas leak, the distillation furnace shall also be completely shut down. 6) The cyclohydrogen desulfurization tower diverts the feed gas to an alternate route, while the solvent continues to circulate. 7) Operators on site should maintain close communication with those in the control room, and ensure proper control of the liquid levels in high-pressure vessels such as the high-pressure separator and the cyclohydrogen desulfurization tower, in order to prevent accidents where low liquid levels in these vessels lead to high pressure leaking into the low pressure system. 8) It is important to inform the production department before activating the emergency pressure relief system, and to keep the flare system unobstructed. Pay attention to other low-pressure devices connected to the low-pressure fuel gas, such as raw material tanks, to prevent pressure overloading; close the vent valve of their proportional control pressure valves if necessary. 3. What harm does water cause to hydrogenation catalysts? In a reaction system, a small amount of water exists mostly in gaseous form. At low concentrations, it has little to no effect on the catalyst’s activity and stability. However, when liquid water or high-concentration water vapor comes into contact with the catalyst, it causes the metals on the catalyst to aggregate, the crystals to deform, and the catalyst’s shape to change, thereby compromising its mechanical strength, activity, and stability. 4. What to do in case of a long-term power outage in the hydrogenation unit? 1). In the event of a power outage of the unit, it is required that a dedicated person be assigned to turn the cyclic hydrogen compressor by hand in order to ensure the safety of the large-scale machinery ； Open the valve for venting hydrogen; maintain a hydrogen flow rate of 2000 Nm3/h to ensure gas flow through the reactor bed. If the reactor temperature is under control, reduce the system pressure to 3.5 Mpa and stop venting hydrogen as well as adding hydrogen as a fertilizer ； The operator inside should switch the temperature control to manual mode, close the fuel gas control valve, and inform the operator outside to turn off the fuel gas nozzles of the furnace as well as the valves of the pilot lights. The flue gas dampers should be opened to reduce the temperature; if the furnace temperature becomes too high, steam should be introduced to lower it ； 2). Strengthen communication between internal and external operations, maintain an appropriate level in the high-pressure liquid level as well as in the liquid level of the recycle hydrogen desulfurization tower, to prevent accidents caused by excessively low liquid levels in these systems, which could lead to pressure fluctuations ； 3). The internal operators should control the liquid levels in each tower and vessel. Based on actual conditions, they must decide whether to close the liquid control valves of these towers and vessels, so as to prevent significant fluctuations in their liquid levels. If the liquid level in any reflux drum becomes excessively high, it can be drained into an underground tank. When draining the liquid, safety must be ensured; personnel should stand on the upwind side. 4). The field operator is responsible for monitoring the liquid level in the high-pressure section, maintaining close communication with the control room staff to adjust this liquid level and ensure its stability. The field operator should go to the site to close the outlet valves of all pumps that are not in use; feed pumps, lean liquid pumps, and injection pumps should be handled first ； 5) Inform the field operators to divert the acidic gas to the flare line; divert circulating hydrogen, light fraction gas, and fuel gas to the bypass line, and flare the light fraction gas and fuel gas, while maintaining the pressure and liquid level in each desulfurization tower. 6) The field operators should stop the stripping steam, vent it on-site, close the valves for high-quality diesel output, and direct the unqualified product to the discharge route. 7) Contact the production department to find out the cause of the power outage, and decide whether to take shutdown measures or wait for power to be restored based on the duration of the outage. 8) After power is restored, the reaction system should first be pressurized with nitrogen to 3.5 Mpa before starting the circulation pump. 5. What is the effect of pressure on hydrogenation reactions? The effect of reaction pressure is reflected through the partial pressure of hydrogen. The hydrogen partial pressure in the system is determined by the operating pressure, hydrogen-to-oil ratio, purity of the recycled hydrogen, and the gasification rate of the feedstock. Increasing the hydrogen partial pressure facilitates the progress of the hydrogenation reaction and accelerates its rate. An increase in hydrogen partial pressure is beneficial for the catalyst reaction. Increasing the hydrogen partial pressure can, on the one hand, suppress coking reactions and reduce the catalyst deactivation rate ； On the other hand, it can improve the removal rate of sulfur, nitrogen, and metal impurities, while simultaneously promoting the hydrogenation saturation reaction. Therefore, the hydrogen partial pressure in the reaction system should be increased as much as possible, within the limits permitted by the equipment and operating conditions. 6. What are the principles for handling accidents in hydrogenation units? 1). In the event of an accident at the facility, the personnel on duty must immediately inform the department head, the technical supervisor in charge of the facility, the on-duty shift leader, the production management department, as well as the fire and gas prevention teams. They must then carry out emergency initial rescue actions in accordance with the standard operating procedures and accident response plans, in order to control the situation and prevent the accident from spreading ； 2). Once the leader arrives at the scene, under their unified command, all efforts should be made to carry out rescue operations ； 3) Whether it is a fire, explosion, or poisoning incident, the first step is to find a way to cut off the source of danger, move those who are injured or poisoned to a safe place, and provide first aid ； 4). During emergency response, the safety of the rescuers must be ensured first to prevent the accident from escalating. In the event of production accidents such as power outages, shutdowns, or water supply interruptions, handle them calmly in accordance with the principles of “shutting down the furnace, stopping feedstock input, relieving pressure, prioritizing equipment protection, and safeguarding the catalyst” ； 5) The personnel on duty must, in accordance with the requirements outlined in the procedures for critical operations, contact the relevant personnel for guidance and fill out the confirmation form. 7. What are the steps for an emergency shutdown of the hydrogenation unit? 1). Immediately shut down the reaction furnace; the operator on site should close the gas valve of the heating furnace, extinguish the pilot light, stop the air preheater, and open the flue dampers and quick-opening air valves. 2). Stop the hydrogen feed pump and close the outlet valve. 3). Shut down the new hydrogen compressor and recycle hydrogen compressor, and contact the production department. 4). The hydrogen-handling system continues to be depressurized; if the temperature of the reactor bed is high, high-pressure nitrogen from the pipeline network at the outlet of the recycle hydrogen compressor is used to inject nitrogen into the hydrogen-handling system in order to lower its temperature. 5). Change the distillation system to internal circulation to maintain the liquid level in each column vessel as required. 8. How to handle the stopped circulating water? ⑴Report to the production management department, department supervisors, and the duty officer; treat the unit as if it is shut down. ⑵The internal operator changed the temperature control of the reactor and fractionator to manual mode, and closed the fuel gas flow control valve. Notify the field operators to go to the site to close the fuel gas flow control valves and main burner valves of the reactor and distillation furnace, as well as the pilot light valve; shut down the air preheater, open the flue dampers and quick-opening air valves of the heater, and introduce steam into the furnace chamber to cool it down. ⑶Go to the site for outdoor operations, stop all operating pumps, and close the outlet valves. ⑷The outdoor operation system diverts the feed gas to the cyclic hydrogen desulfurization tower, ensuring that the liquid levels in each tower are not depleted. ⑸The pressure of the hydrogen-containing system under internal operation monitoring must be maintained at a positive level; if the pressure is low but the temperature of the bed remains high, the personnel in charge of external operations should be informed so that nitrogen can be introduced at the compressor inlet to lower the temperature. ⑹After the device is depressurized, the operator must pay attention to the pressures and liquid levels at high and low levels, in order to prevent the liquid level from rising too high or from the system becoming under pressure, as well as to avoid high pressure from leaking into the low-pressure area. ⑺After the circulating water is restored, follow the normal startup procedures: first start the fractionation unit, then the reactor, and finally the desulfurization system. 9. What are the factors that affect the degree of hydrogenation in a reaction? 1). As the reaction temperature increases, the depth increases ； 2). Catalyst activity increases, and the depth increases ； 3). Changes in the properties of the crude oil ； 4). The purity of recycled hydrogen increases, and its depth increases as well ； 5). The reactor pressure increases, and the depth increases ； 6). As the reactor space velocity increases, the depth decreases. 10. What are the reasons for high sulfur content in refined diesel and what are the treatment methods? Reason: 1). The raw material has a high sulfur content, and the reaction temperature is low. 2). The proportion of cracked diesel in the raw materials is not well controlled. If the proportion of catalytic cracking diesel in the feedstock is too low, it results in too low an increase in reaction temperature; the average reaction temperature in the bed is low, and the degree of reaction is insufficient, all of which lead to a higher sulfur content in the product. 3). The gas-oil ratio is too low. 4). High air velocity. 5). Fluctuations in the operation of the fractionation section resulted in incomplete removal of hydrogen sulfide. 6). Internal leakage occurs in high-pressure heat exchangers and similar devices. Since the shell side is at the pump outlet and the pressure there is higher than that on the tube side, the feed material mixes into the reaction products, and it cannot be effectively removed using a stripping tower. 7). Catalyst coking has occurred, resulting in a significant decrease in its activity. Treatment method: 1). Adjust the ratio of raw materials and appropriately raise the reaction temperature to meet the required sulfur content in the product. 2). Increase the load on the recycle hydrogen compressor to raise the gas-oil ratio. 3). Appropriately reduce the space velocity. 4). Careful adjustment is required, with all operational parameters strictly controlled within the specified process limits. 5). If the leakage volume is significant, shut down operations for handling. 6). If it is confirmed that the catalyst activity has declined significantly, catalyst regeneration or replacement with a new catalyst is required. 11. What are the precautions during hydrogenation shutdown? 1). To prevent overheating of the reactor bed, the principle of cooling first and then reducing the flow rate should be followed. 2). To prevent damage to the catalyst, after feeding to the reactor is stopped, the system should be kept circulating with the highest possible amount of recycled hydrogen until the oil in the feed lines and the reactor is completely purged. 3). After stopping the feed, flush hydrogen should be introduced immediately into the fresh feed line; the introduction of hydrogen must be done slowly to prevent high-pressure flanges from leaking due to thermal shock ； When a flange leaks due to cooling, steam should be used immediately to purge the oil and gas in order to prevent ignition. 4). During shutdown, the pressure limits must be respected; the cooling rate should not exceed 25°C/h. Before opening the reactor, it must be cooled to below 40°C, and it must also be purged thoroughly with nitrogen in order to reduce the risk of spontaneous ignition of hydrocarbon-oxygen mixtures and ferrous sulfide. 5). The distillation system should avoid vacuum formation due to overcooling in the columns; if the columns are not to be purged temporarily, nitrogen should be introduced into the top reflux drum to maintain positive pressure. 6). Before the contaminated oil is discharged into the contaminated oil system, it must first be degassed to prevent hydrogen sulfide from causing harm to operators. 12. What is the effect of conversion temperature, pressure, and water-to-carbon ratio on the contents of CO, CO2, and H2 at the outlet? 1). As the conversion reaction temperature increases, the CO content at the outlet of the converter rises; the reaction pressure increases, which also leads to an increase in the CO content at the outlet of the converter. An increase in the water-to-carbon ratio results in a decrease in the CO content at the outlet of the converter. 2). As the reaction temperature increases, the CO2 content at the outlet of the conversion furnace decreases; as the reaction pressure rises, the CO2 content at the outlet of the conversion furnace increases. An increase in the water-to-carbon ratio also leads to an increase in the CO2 content at the outlet of the conversion furnace. 3). As the conversion reaction temperature increases, the H2 content at the outlet of the converter rises; the reaction pressure increases, causing the H2 content at the outlet of the converter to decrease. An increase in the water-to-carbon ratio leads to an increase in the H2 content at the outlet of the converter. 13. Precautions for supplying 1.0 MPa steam to the equipment? 1). Drain the water from the pipeline before introducing steam. 2). Slowly open the boundary valve to warm the pipeline. 3). Once steam is detected at the various low points, close the vents and then slowly increase the opening of the boundary valve. 4). After the pressures on both sides become equal, fully open the boundary valve; be careful to prevent water hammer when introducing steam. 14. What is the procedure for dealing with prolonged power outages in hydrogen production? 1). Close the interconnecting valves between the desulfurization system and the conversion system to prevent substandard raw materials from entering the conversion system and damaging the catalysts used in subsequent processes. 2). Close the control valve and upstream/downstream valves for furnace feeding to prevent internal leakage caused by improper closure of the emergency valve. 3). Close the fuel line control valve of the heating furnace, as well as the valves upstream and downstream, to prevent fuel leakage that could cause the furnace to burn out; depending on the situation, a small amount of continuous burning can be maintained. 4). Close the outlet valve of the raw material compressor to prevent backflow in the system. 5). Improve the startup procedure for the desulfurization system, put the startup cooler into operation, and vent the desulfurized gas to the flare system, controlling the venting rate to be no more than 0.3 Mpa/min to prevent damage to the equipment and catalysts due to too rapid venting. 6). When the system pressure drops to a slight positive value, nitrogen is introduced at the inlet of the heating furnace to displace the oil and gas in the reactor bed and pipelines. When pressurizing, it is important to ensure that the pressure in the desulfurization system is lower than that in the conversion system, in order to prevent desulfurized gas from entering the conversion system and damaging the catalysts. 7). Open the bypass of the pressure-controlled valve in the converted medium-low voltage system to vent the oil and gas in the system to the flare system. Control the pressure release rate to no more than 0.3 Mpa/min. 8). Control the steam supply to the furnace to be between 30% and 50% of the normal value; any excess steam should be fed into the grid or vented. Stop supplying steam to the furnace once the inlet temperature of the converter drops below the catalyst hydrolysis temperature. 15. What are the emergency shutdown steps for the hydrogen production plant? During an emergency shutdown, the safety of personnel and equipment must be ensured first. 1). In the event of an emergency shutdown, it is necessary to report immediately to the workshop and the factory’s production management department. 2). Immediately notify the relevant upstream and downstream devices. 3). The shift leader coordinates and directs the relevant personnel to safely shut down the equipment. 4). When shutting down operations, the principle of focusing on priorities first and then on less important matters must be followed. First, address the accident points or important control points, and then deal with the other systems. 5). The conversion system should maintain gas flow as much as possible to protect the catalyst and facilitate production recovery after an accident. 6. Take necessary measures to protect the safety of personnel, the environment, equipment, and catalysts during the shutdown process. 16. What are the types of hydrogenation catalysts? Hydrogenation catalysts include cobalt-molybdenum LYT-701, LYT-702, LYT-704, LYT-704G, and LYT-UDS; the desulfurization catalyst is LYT-310G, while the dechlorination catalyst is LYT-601. 17. What are the normal shutdown procedures and precautions for the hydrogen production unit? 1). Reduce production rate; pay attention to lowering the temperature at the converter inlet at a rate of 20–25°C/h. The principle of reducing load is to first reduce the amount of raw material, then the amount of hydrogen added, followed by the process steam, and finally lower the furnace temperature. 2). Establish a cycle for the conversion and intermediate transformation systems, being careful to avoid methanation reactions induced by the hydrogenation catalyst; strive to increase the pressure at the compressor inlet to ensure the highest possible circulation volume in the system. 3). Cut out the PSA or methanation system. 4). Shut down the desulfurization system for cooling; ensure that feeding to the desulfurization unit is stopped, and close all valves connecting the desulfurization system to the conversion system. 5). Stop supplying hydrogen and steam, and be careful to prevent catalyst hydrolysis. During the pressure relief of the conversion system gases, the conversion furnace should cool at a rate of 30–40 degrees per hour to prevent overheating; depending on the actual conditions, some burners can be turned off. 6). Shut down the converter; make sure to isolate each reactor and fill it with nitrogen to maintain a pressure of 0.5 Mpa. 18. What are the reasons for the increase in pressure drop in the converter tubes? 1). The desulfurized gas is not up to standard, causing poisoning of the converter. 2). Incomplete entry of hydrocarbons into the hydrogenation reactor for conversion leads to coking. 3). Unqualified steam causes salt deposition inside the furnace tubes. 4). Water carried in the steam causes hydrolysis of the converter. 5). Excessively high or low space velocity causes coking of the converter. 6). Excessive number of start-up and shutdown cycles. 7). The quality of the converter unit is poor. 8). Service life of the converter. 19. How to protect the activity of hydrogenation catalysts? Catalyst activity has a significant impact on hydrogenation processes, product yield, and product properties; increasing its activity allows for lower reaction temperatures and pressures, as well as higher space velocities or lower hydrogen-to-oil ratios. As the operation cycle lengthens, the catalyst activity gradually decreases; at this point, it is necessary to increase the reaction temperature accordingly in order to maintain a certain level of catalyst activity. During the production process, the level of operational skill as well as various incorrect operating methods have a significant impact on the catalyst’s activity. To protect the catalyst’s activity, it is necessary to follow the principle of increasing the amount first and then the temperature, as well as reducing the temperature first before reducing the amount, during the production process. Furthermore, the reaction space velocity and hydrogen-to-oil ratio must be maintained above minimum levels to prevent catalyst damage. During various shutdown processes, it is necessary to flush the system with hot hydrogen mixed with oil, in order to prevent the catalyst from being damaged due to operating at excessively low space velocities. During startup, dehydration and low-temperature oil feeding must be strictly followed to prevent catalyst breakdown and reduction. 20. What are the normal shutdown procedures and precautions for the hydrogenation unit? Shutdown steps: 1). Reduce the production load, first by lowering the temperature and then by reducing the volume. 2). Cut through the circulating hydrogen desulfurization tower and use the crossover line. 3). Reduce the reaction to the minimum level, and stop the hydrogen feed pump. Open the hot hydrogen line to supply oil. 4). The operator should pay close attention to the high-level liquid level and the interface level. 5). Fractionation shortens the cycle, lowers the bottom temperature of the tower, resulting in substandard products. Turn off the furnace nozzles and the pilot light to cool down. 6). Stop the new hydrogen compressor and the feed water pump when the reaction no longer consumes hydrogen. 7). When the level of the high-pressure liquid no longer rises and there is no temperature increase in the reaction, the flow of hot hydrogen carrying oil stops. 8). Hydrogen evolution was carried out at a constant temperature with the reaction pressure reduced to 5.0 MPa and the furnace outlet temperature at 250°C. 9). The cooling rate of the reaction furnace shall not exceed 20–25°C/h; the heating should be turned off when the temperature drops to 200°C. Close the upstream and downstream valves of the fuel gas. 10). The reaction pressure is reduced by displacing with nitrogen to maintain pressure. 11). After the distillation temperature drops, close the valves upstream and downstream of the fuel gas to maintain pressure and liquid level. 12). Prolonged shutdown to depressurize the liquid level in the tower and purge the pipelines. Precautions: 1). To prevent overheating of the reactor bed, it is necessary to follow the principle of cooling first and then reducing the flow rate. 2). The cooling rate should not exceed 25°C/h. 3). The distillation system should avoid vacuum formation due to overcooling in the columns; if steam purging is not carried out temporarily, nitrogen should be introduced into the reflux drum first to maintain positive pressure. 4). Prevent hydrogen sulfide from causing harm to operators. 5). Preventing accidents where high voltage affects low voltage systems. 21. How should a heating furnace be operated during strong winds or rainy, overcast weather? 1). If the wind is weak, it has little impact on the heating furnace; however, when the wind is strong, it is necessary to appropriately reduce the position of the flue dampers and air valves to prevent excessive suction caused by strong winds, which could cause the heating furnace to shut down and disrupt operations. 2). On overcast and rainy days, the air pressure is low, which affects the draft in the chimney; it is therefore necessary to open the flue dampers sufficiently to increase the chimney draft and ensure normal operation. 22. What are the functions of lubricating oil? Lubricants have seven functions: (1) lubrication, (2) cooling, (3) flushing, (4) sealing, (5) vibration damping, (6) protection, and (7) load relief. 23. Key points for starting up hydrogen production? (1) First, verify the process to prevent interference between different processes as well as any leaks or losses. (2) Before ignition, check that all viewing ports are in the closed position, that the baffles and air valves are functioning properly, and that all gas valves are closed. (3) Check whether the readings of all instruments are normal, whether the control valves operate smoothly, and whether the pumps are functioning properly. (4) The furnace must be heated in accordance with the specified heating curve. (5) Conditions for introducing steam for conversion and reduction: The steam pressure is increased in accordance with a specific curve to 2.0 MPa; the temperature at the entry point of the conversion process is ≥450°C, and the temperature in the medium-pressure bed is ≥220°C. Once the steam quality meets the requirements, steam produced internally is used, with its volume gradually increased to 6 tons. (6) Reduction conditions for the conversion catalyst: inlet temperature ≥ 480°C, bed outlet temperature ≥ 800°C, hydrogen concentration in the recycle gas ≥ 65%, and reduction time of 8 hours. (7) After desulfurization feeding, overheating of the adiabatic hydrogenation reactor should be avoided. (8) Once the desulfurized gas meets the required standards, it is recycled; in this gas, sulfur removal occurs first, followed by oxygen removal, then saturation of monoolefins, nitrogen removal, and finally aromatic saturation. 30. What is the impact of the properties of the feed oil on diesel hydroprocessing? The properties of the feed oil determine the direction of the hydrogenation refining reaction and the amount of heat released; they serve as the main criteria for determining the hydrogen-to-oil ratio and the reaction temperature. An increase in the olefin content and dry point of the feed oil accelerates catalyst coking ； If the impurity content, particularly the nitrogen level, increases, it is necessary to reduce the space velocity or increase the temperature to ensure the quality of the refined product ； Olefins and sulfides indicate high heat generation, rising temperatures, and high hydrogen consumption; therefore, the hydrogen-to-oil ratio should be increased appropriately. 31. How to deal with reactor over-temperature? In the event of excessive temperature rise in the reactor bed, one possible solution is to increase the amount of cold hydrogen used; reduce the temperature at the furnace inlet appropriately and increase the capacity of the recycle hydrogen compressor. If this still does not suffice, it is necessary to immediately switch to another feedstock to stop the supply of low-quality oil to the unit ； In severe cases, the heating furnace shuts down, and large-scale air cooling is employed to prevent overheating and excessive liquid levels. At the same time, it is necessary to avoid bubbling due to high liquid levels, which could result in false liquid level readings. Efficient liquid removal must be ensured at the compressor inlet, and the recycle hydrogen desulfurization tower should be disabled to prevent solvent contamination. The fresh hydrogen compressor should be controlled manually to prevent the system’s hydrogen pipeline network from being overwhelmed. 32. What are the characteristics of hydrorefining? Hydrorefining is an important method used by refineries to improve the quality of oils and fats, primarily aimed at producing final products that meet relevant standards and specifications or satisfying the raw material requirements of downstream facilities. Hydrorefining can effectively hydrolyze non-hydrocarbon compounds such as sulfur, hydrogen, nitrogen, and oxygen present in the feed oil, hydrogenate and saturate olefins and aromatics, and remove impurities such as metals and asphaltenes. It offers advantages including a wide range of feedstocks that can be processed, high liquid yield, and good product quality. 33. What is the role of recycled hydrogen in hydrogenation reactions? Maintain a high hydrogen partial pressure in the reaction system ； Cyclic hydrogen, acting as a heat transfer medium, can limit the temperature rise in the catalyst bed ； It promotes the uniform distribution of the liquid feed throughout the entire catalyst bed, thereby suppressing the formation of hot spots and improving reaction performance. 34. In what areas is hydrogen consumed in hydrorefining? ⑴Hydrogen consumption in chemical reactions; (2) Hydrogen consumption due to the emission of waste hydrogen; (3) Hydrogen loss through dissolution; (4) Hydrogen loss due to mechanical leaks. 35. What is a catalyst? What are the basic characteristics of catalyst action? A catalyst is a substance that can participate in a reaction and accelerate or slow down the rate of that chemical reaction, without its own properties or quantity changing before or after the reaction. The basic characteristic of a catalyst is that it alters the reaction pathway, changes the activation energy of the reaction, and modifies the reaction rate constant, but it does not affect the chemical equilibrium of the reaction. 36. What are the major steps for starting up hydrogenation? (1) Preparatory work before commencement ； (2) Nitrogen displacement ； (3) Nitrogen airtightness ； (4) Catalyst drying ； (5) Catalyst presulfurization ； (6) Switch the feed oil and adjust the operation. 37. What are the components of a catalyst? Based on their role in catalytic reactions, they are divided into three categories: the main active component, additives, and carriers. 38. What is the bromine value? What does the bromine number of oils represent? A certain sample of oil is titrated using a potassium bromate-potassium bromide standard titrant, and the bromine content per 100 grams of oil at the end of the titration represents the bromine value. The higher the bromine value, the higher the content of unsaturated hydrocarbons in the oil. 39. What are the steps in the catalyst reaction process? (1) The reactants diffuse through the membrane on the outer surface of the catalyst particles to reach the outer surface of the catalyst ； (2) Diffusion of reactants from the outer surface to the inner surface of the catalyst ； (3) Adsorption of reactants on the inner surface of the catalyst ； (4) The reactants react on the inner surface of the catalyst to form products ； (5) Desorption of the product from the inner surface of the catalyst ； (6) The product diffuses from the inner surface of the catalyst to its outer surface ； (7) The product diffuses outward through the membrane from the outer surface of the catalyst. 40. Startup procedures for hydrogen production plants (I). Items to be checked during startup: (1) All containers and equipment have been carefully inspected before being filled; their interiors are clean and undamaged, and the internal components are properly installed. (2) The converters and waste heat flue linings were carefully inspected after drying; they were intact and in good condition. (3) All pipes and equipment have been inspected; valves, orifice plates, pressure measurement points, vent and drain valves, safety valves, steam traps, etc., are all correctly installed, and the equipment and pipes have been thoroughly cleaned and purged. (4) All instruments and control valves have passed inspection and commissioning. Power is supplied to the solenoid valves and transmitters. The air supply for the control valve is connected. All primary instruments, the valves on the signal tapping pipes and on the pulse pipelines leading to the transmitter shall be opened, as well as the valves in front of all safety valves. (5) All vent valves, drain valves, valves leading to the ground pipe, and valves on the sampling tube are closed. (6) Moving equipment such as pumps, compressors, and fans have been inspected in accordance with the specific instructions and subjected to operation tests, showing good performance. (7) The interlock system has been inspected, is functioning properly, and has been properly configured. (8) All safety valves have been inspected and found to be in good condition, with their pressure settings adjusted appropriately. (9) All equipment and pipelines have undergone airtightness testing as well as N2 purging. (10) All temporary blind plates removed. (11) All control valves in the control room should be in manual mode, and the valves they control should be in the closed position. (12) The stop valves on all process pipelines at the site are in the closed position. (13) All blind flanges on the main process streams shall be changed to open flanges. (14) All various raw materials and auxiliary materials are ready for receipt. (15) The materials required for startup have been delivered to the plant area. (II) Ignition and temperature rise of the raw material preheating furnace: 1. Establish a separate circulation system for the desulfurization system. Follow the compressor operation procedures to start the compressor, create a nitrogen circulation flow within the desulfurization system, and properly control the pressure at the compressor inlet as well as the system’s circulation rate. 2. Ignition and heating: Light the permanent flame in the heating furnace, then ignite the burners as required for temperature increase, and control the rate of temperature rise in accordance with the process specifications. During the heating process, maintain stable pressure in the desulfurization system to ensure normal circulation; if the system pressure is insufficient, nitrogen can be added at the compressor inlet. Raise the desulfurization system to normal temperature and wait for feeding. (III) Establish circulation in the water system: (1) Preparation work: ① The water inlet process has been adjusted and verified. ② Control instruments, control valves, etc. have been tuned and are ready for use. ③The feed water pump is now ready for operation. ④ The safety accessories of the steam drum are in use, and the local vent valve of the steam drum has been opened. (2) Feed water into the deaeration tank: Install a level control valve for the deaeration tank to maintain its liquid level at 50%; use steam for deaeration. Install a water seal in the deaeration tank and introduce external steam into it to carry out the deaeration process. The pressure in the deaeration tank is controlled between 0.02 and 0.04 MPa. (3) Feed water to the drum: Redirect the water supply flow, start the drum feedwater pump to supply water to the drum. Open the vent valve at the top of the drum while feeding water, activate the drum level control valve to maintain the drum level at 50%, and activate the drum safety valve. Regular and intermittent drainage from the drum is used for flushing to ensure that the drum water meets the required standards. When the drum liquid level reaches 50%, stop the drum feedwater pump. In the future, it will be decided whether to add more units based on the actual level of the drum liquid. (IV) Ignition and heating of the converter: Once a water circulation system is established in the drum, the converter can be ignited and heated. (1) Establish a conversion and intermediate transformation cycle process: Improve the nitrogen conversion and intermediate transformation cycle process, fill the system with pure nitrogen as required, and start the compressor to establish the cycle. (2) Verify ignition conditions ① The circulation system is operating normally. ②The induced draft fans and blowers have started up and are operating normally. ③The negative pressure in the conversion furnace chamber has been stabilized between 30 and 50 Pa. ④The drum liquid level and the water system are operating normally. ⑤The converter furnace gas has been subjected to a hot work analysis and has passed. ⑥The converter fuel has been led to the manual valves of each burner. ⑦For devices equipped with an interlock self-protection system, the converter interlock self-protection system should be activated first. ⑧The circulating gas has passed the sampling analysis (oxygen content < 0.5%). Strictly control and stabilize the compressor inlet pressure and flow rate; if the pressure is insufficient, N2 can be added at the compressor inlet. Activate all air coolers and heat exchangers in the circulation system. (3) Ignition and temperature rise: Principle of ignition – ignite at regular intervals; the purpose of this is to ensure a uniform temperature distribution within the furnace. Stabilize the fuel gas pressure and direct the fuel gas to just before the final valve of each burner manual valve in the converter. When igniting, use one hand to insert the ignition gun into the ignition hole and light it, while using the other hand to open the valve of the small burner in order to ignite the burner. Before ignition, adjust the opening degree of the air valve. After lighting the burners, adjust the settings of the burners and air valves to ensure complete combustion of the fuel. During the heating process of the converter, if the heating rate does not meet the required levels, additional burners can be activated or the settings of the existing burners can be adjusted; however, it is essential to maintain short flames with a blue color from multiple burners. After adjusting the burner, close attention should be paid to changes in the oxygen content and flue gas temperature. At the same time, adjust the negative pressure in the furnace to ensure normal flame combustion, and pay attention to changes in the inlet temperature of the medium-shift reactor, so as to allow the medium-shift reactor to heat up in sync with the conversion furnace. After the converter is ignited, the heating rate is controlled in accordance with the process specifications; generally, the heating rate is set at 50°C/h, and operation is maintained at a constant temperature once the conditions for hydrogen and steam supply are met. Note: A. When igniting, efforts should be made to ensure a uniform temperature distribution within the furnace. B. During the processes of conversion and gradual temperature increase, it is advisable to use multiple burners at low settings when igniting; at the same time, care must be taken to ensure that the ignited burners are evenly distributed across the top of the furnace. If the first ignition attempt with C fails, the burner must be turned off immediately. The furnace can be reignited only after it has been ventilated and no fuel gas remains inside; otherwise, there is a risk of explosion. (V). Grid connection of self-generated steam (1) Steam generation in the drum: As the temperature of the converter rises, the temperature of the water in the drum also increases gradually, leading to steam generation. Once steam is produced in the drum, it is necessary to start the feedwater pump to supply water; a cascade control system is used to regulate the feedwater flow and thus maintain a stable level of water in the drum. Precautions: Operators of Unit A should check whether the values on the on-site level gauges and pressure gauges match those shown on the DCS. B controls the pressure rise rate of the drum through the silencer manual valve, which is generally maintained at 0.2–0.3 MPa/h. (2) Steam grid connection 1. Confirm process parameters: A The steam temperature reaches or exceeds the dew point temperature ； The B vapor pressure remains stable ； The liquid level in vessel C is kept stably at 50%. 2. Grid connection procedure: The operator in station A adjusts the steam pressure control valve; the operator outside the station slowly closes the local vent valve, and drains water from the steam pipes as well as warms them up prior to grid connection ； The operators inside Unit C open the steam pressure control valve depending on the pressure in the drum, to ensure that the pressure does not rise too high, and direct the steam into the external system’s steam network. Note: When connecting to the steam system, the operations must be carried out slowly and smoothly to avoid severe fluctuations in the drum pressure and liquid level; efforts should be made to keep the drum pressure stable and the drum liquid level at 50%. (VI). Conversion, medium-temperature catalyst reduction – Conditions for steam supply in the conversion furnace: (1) Inlet temperature of the conversion furnace: >450℃ ； (2) Converter outlet temperature: >800℃ ； (3) Minimum temperature in the medium-reactor bed: >200°C. 1. Steam supply: According to the calculated water-to-hydrogen ratio, self-produced steam (when its pressure is 0.3~0.5 Mpa higher than that at the inlet of the converter and it meets the quality requirements with a stable drum liquid level) or system steam is supplied to the converter. Pay attention to the following points after steam is supplied: After steam is introduced into the conversion furnace, its temperature changes significantly; it is necessary to make timely adjustments by increasing the number of burners ； B should analyze the boiler water quality in a timely manner. 2. Ammonia addition in the converter: After steam is introduced, ammonia is added at the inlet of the converter, with the hydrogen content in the gas exiting the converter being gradually increased to over 65%. After adding steam and ammonia, the furnace temperature should be adjusted promptly, and additional burners should be used to ensure a uniform temperature distribution within the conversion furnace, thereby preventing low temperatures or localized overheating. Special attention must be paid to the temperature at the inlet of the conversion furnace, which must not be lower than the dew point temperature. Reduction time: 8–12 hours. 7. Feedstock introduction to the desulfurization system: The conditions for feedstock introduction have been met; the reduction of the shift and medium-shift catalysts is complete, and the system is operating stably. The bed temperatures in all reactors of the desulfurization system have reached the required levels. Start the feed to the desulfurization system of the raw material compressor, and control the temperatures at various points in the reactor. (8). Combined desulfurization system: After the conversion and medium-pressure shift catalyst reduction are completed, confirm that the desulfurization system is integrated into the conversion and medium-pressure shift cycle system; raise the pressure in the desulfurization system to match that of the conversion and medium-pressure shift systems, and then connect the desulfurization system. Precautions: When initiating operation to connect to the desulfurization system, it is essential to confirm that the process is correct. The connection process should be carried out slowly, and any abnormal pressure changes should be investigated promptly to determine the cause before proceeding further. After calculating the water-to-carbon ratio, the converter first increases the steam supply, then adjusts the furnace temperature, and finally increases the feed rate. Conduct sample analysis in a timely manner to determine the methane analysis results; generally, the methane content