Q&A on Gas Generation Chemical Processes II

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40 What are the factors that affect the conversion rate? Answer 1: Abnormal catalyst deactivation: a. Over-temperature. b Fluctuations in operating conditions, especially large fluctuations in operating temperature. c Toxic effects. The number of start-stop cycles is high, especially the number of redox cycles. Note that the oxygen content in the cracking gas must be within the specified limits. When parking, be careful to seal the furnace to prevent air from entering. II. Physical blockage: A film – also known as a crust – formed on the surface of the catalyst by dust, carbon black, salts, and solid volatiles renders the catalyst inactive. 40 What are the advantages of pressure swing conversion? Answer: It can speed up reaction rates and increase the catalyst production capacity ； Lower power consumption compared to atmospheric pressure shift reaction ； The equipment is compact in size, has a tight layout, and requires low investment ； The high condensation temperature of water vapor in the wet shift gas facilitates the recovery and utilization of thermal energy. 41 What are the disadvantages of pressure conversion? Answer: Pressurized conversion promotes the formation of the following side reactions: 2CO → C + CO2, 2CO + 2H2 → CH4 + CO2, CO + 3H2 → CH4 + H2O, CO2 + 4H2 → CH4 + 2H2O. ① The deposition of carbon tends to occur on the surface of the catalyst, reducing its activity. ②The formation of methane not only consumes H2 and CO but also increases the inert gases in the syngas, which is detrimental to synthesis. On the other hand, pressure causes severe corrosion of the equipment. 42 How to adjust the furnace temperature for T2, T3/161A? Answer: (1) Turning on T2(f) can lower the intermediate transformer temperature and raise the secondary intermediate transformer temperature ； (2) When the temperatures of both the first and second type of heat exchangers are high, T2(f) is already fully open; T3(f) can then be opened to lower the temperature. 43 161A: How to adjust the wash water temperature? Answer: (1) Adjust it using the wash water to preheat the aqueous phase feed line. Turning it on raises the water temperature, while turning it off lowers it. (2) Adjust using the intermediate heat exchanger feed line. Turning it on raises the water temperature, while turning it off lowers it. (3) Adjust the wash water feed line using the carbon black water heat exchanger. Turning it on can raise the water temperature, while turning it off lowers the temperature of the washing water. (4) Adjust using the wash water preheater gas-phase feed line. Turning it on raises the water temperature, while turning it off lowers it. 44 161A: What is the impact of wash water temperature on medium-frequency conversion? Answer: (1) Increasing the temperature of the washing water raises the temperature of the vaporized gas accordingly; at the same time, the amount of saturated steam in the vaporized gas increases, causing the temperature of the medium-temperature converter to drop. (2) By lowering the temperature of the washing water, the temperature of the vaporized gas decreases accordingly; at the same time, the amount of saturated steam in the vaporized gas reduces, causing the temperature of the medium-temperature converter to rise. How is the variable steam ratio controlled in 45 A? Answer: (1) The H2O/CO molecular ratio generally remains around 3. (2) Increase the temperature of the gasified gas to raise the saturation of steam. (3) Add saturated steam regulation. 46 What are the means for adjusting the furnace temperature in Model B? Answer: (1) Changes in catalyst temperature are adjusted by adding steam using T6. Increasing the temperature of the steam boiler will cause it to drop ； Conversely, the temperature rises. However, the amount of steam is insufficient to meet the requirements of the reaction, which causes the furnace temperature to drop as well, resulting in substandard gas. (2) T7 plus deionized water adjustment. (3) T2 feed line adjustment. Turning it on can reduce the first intermediate value and increase the second intermediate value. When the temperatures in stages 1 and 2 are high and T2 is fully open, T3 can be turned on. (4) Adjustment of the aqueous phase feed line in the wash water preheater. (5) Adjustment of the secondary line in the intermediate heat exchanger. (6) The gasification gas system regulates the temperature of the medium-temperature furnace by adjusting the temperature of the gasification gas. 47 What are the differences in the installation process of the heat exchanger in A and B? Answer: (1) The heat exchanger in A has an outlet valve and an inlet valve ； The heat exchanger in B has an outlet valve but no inlet valve. (2) In A, the heat exchanger has secondary air entering from below and exiting from above ； In B, the heat exchanger has secondary air entering from above and exiting from below. 48 What are the differences in the processes of A and B wash water preheaters? Answer: (1) A is horizontal ； B is vertical. (2) The A wash water preheater has a bypass line (medium-pressure gas) ； There is none for B. (3) There is a manual valve at the gas inlet in the A wash water preheater ； There is none for B. 49 What are the main differences in the process flows of the variable system in A and B? Answer: (1) In A, it becomes a large furnace (with two layers of catalyst), and in B, it becomes a small furnace (with one layer). No. 1 furnace becomes a small furnace (with one layer of catalyst), while No. 2 furnace becomes a large furnace (with two layers). (2) Variation in A: The intermediate heat exchanger is installed after the first raw material preheater. Variant B: The intermediate heat exchanger is installed before the first raw material preheater. (3) Variation in A: The preheaters for the first and second raw materials, as well as the preheater for washing water, are of horizontal type. Variant B: The preheaters for the first and second raw materials, as well as the preheater for washing water, are vertical in design. (4) A system without deoxygenated water in A. Variant B has a deoxygenated water system. What are the variable parking handling steps in 50 161B? Answer: (1) Stop the deoxygenated water supply, that is, shut off T7 and its manual valve. (2) Stop the steam supply, that is, close T6 and its manual valve. (3) Cut off the gasification gas, that is, close K1 and its manual valve. (4) Close the main valves for deoxygenated water and its steam, and open the drain for discharge. 51 What are the reasons for the aging of medium-activity catalysts? Answer: (1) H2S poisoning. (2) The gasified gas carries water. (3) Cut off the gasified gas if its carbon black content is high. (4) The operating temperature is too high. What is the purpose of the 52 170B system in placing ZnO desulfurization before primary decarburization? Answer: To ensure that the sulfur compounds in CO2 gas are no higher than 3PPM, thereby meeting the requirements for CO2 concentration in the urea production process. 53 170A What is the function of a steam ejector? Answer: It serves as a buffer. Mixing the steam evenly with the ZnO-desulfurized gas facilitates the CO conversion reaction. 54 How to reduce the formation of medium-side reactions? Answer: Increase the temperature ； Increase the steam volume. 55 What are the hazards of water carried in vaporized gas? How to prevent it? Answer: Hazards: (1) Causes the catalyst to become powdered, reducing its activity. (2) System resistance increases. Prevention: (1) Observe the changes in H6/152 during normal operation, and increase the activation of K1 drain. (2) Closely monitor the changes in T2 and bed temperature. (3) In an emergency, cut off the gas immediately and close K1 and its manual valve. 56 What is the function of the wash water preheater? Answer: The main purpose is to recover thermal energy. In addition, it has the following three functions: (1): Raise the temperature of the washing water, thereby indirectly increasing the temperature of the medium-frequency furnace. (2) Reduce the intermediate gas temperature to meet the requirements of subsequent processes. (3) Adjust the solution regeneration temperature of the decarburization system. 57 When is the best time to put the wash water preheater into use? Why? Answer: It is most appropriate to operate the wash water preheater simultaneously with the start of steam supply to the gasifier, before gas is introduced into the gasifier. Reason: If it is started after gas is introduced into the gasification furnace, it can easily lead to accidents such as a lack of water supply in the furnace or shutdown, due to the vaporization of water or improper operation. 58 How to put the wash water preheater into operation? Answer: (1) Before starting the water pump, first check the aqueous phase valve of the wash water preheater. The drain valve should be closed, while the aqueous phase bypass line and the upstream and downstream manual valves should be opened. (2) After the water pump is started, slowly open the drain valve to release air; once the tank is filled with water and water begins to flow out, the drain valve can be closed. (3) Properly shut down the aqueous phase feed line; make adjustments only after the medium pressure has returned to normal. 59 What is the harm of water vapor condensation to low-temperature shift catalysts? Answer: (1) The condensation and evaporation of water vapor on the catalyst will damage its physical strength, causing the catalyst to break apart and become powdered, which in turn leads to an increase in bed resistance and gas deviation. (2) Medium-temperature gases generally contain 100–700 PPM of NH3; when water vapor condenses, they react easily with active copper, resulting in the loss of active material and a severe decline in catalyst activity. (3) The repeated condensation and evaporation of water vapor in the bed will accelerate the migration of chlorides within the bed, causing the poisoned area to expand rapidly as well as the catalyst’s activity to decline swiftly. (4) During operation, it should be noted that in normal production, the inlet temperature of the low-temperature converter must be above 180°C, higher than the steam dew point temperature to prevent the formation of condensate. 60 What are the measures to extend the service life of copper catalysts? Answer: Sulfur prevention ； Halogen resistance ； Anti-clog device ； Overheat protection ； Prevent water vapor condensation ； Uniformly packed catalyst ； Use more catalyst or small-particle catalyst ； Stable operating conditions. 61 What is the reason for the formation of nickel carbonyl in the methanation reaction? Answer (1) The reduced and activated methanation catalyst, namely Ni, has a very large surface area; under these conditions, it is more favorable for CO to react with Ni to form nickel carbonyl ； (2) From a thermodynamic perspective, increasing the CO partial pressure and lowering the temperature are favorable for its formation ； (3) Sulfur, ammonia, and chlorine are catalysts for the formation of nickel carbonyl ； (4) O2, water vapor, and the presence of oxide coatings on metal surfaces can control the formation of nickel carbide. 62 What are the properties of methanation catalysts? Answer: (1) Nickel catalysts exhibit high activity and selectivity; the concentration of CO + CO2, which is 0.7–1.0% in the secondary alkaline scrubbing gas, can be reduced to 10 PPM or lower through methanation, thereby ensuring the proper operation of the ammonia synthesis catalysts. (2) Compounds such as S and As can strongly chemisorb onto the surface of nickel metal, poisoning the catalyst and rendering it inactive. It is a cumulative and irreversible poisoning. To ensure a long lifespan for the catalyst, it is necessary to reduce the levels of S and As. (3) At low temperatures, CO reacts with the nickel metal in the catalyst to form highly toxic nickel carbonyl, resulting in the loss of active nickel. During start-up and shutdown, care must be taken to ensure that the bed temperature is maintained at ≥250°C while introducing gas. After stopping the operation, when the bed temperature is below 250°C, it should be purged with nitrogen. (4) The reduced catalyst will catch fire spontaneously when exposed to air. When discharging waste catalysts, the factory must take passivation and **measures. 63 What are the forms in which chromium exists in medium-temperature catalysts and what is its role? Answer: In medium-temperature catalysts, chromium exists mainly in the form of Cr2O3, and it is generally considered to act as a stabilizer rather than a promoter. It prevents the catalyst from sintering at high temperatures, which would otherwise lead to grain growth and a reduction in surface area. During the catalyst manufacturing process, the vast majority of hexavalent chromium is converted to trivalent chromium. If there is an excessive amount of residual hexavalent chromium in the catalyst, it will affect the proper progress of reduction. The reaction of Cr2O3 being reduced by H2 or CO is a highly exothermic reaction. Therefore, residual hexavalent chromium in medium-temperature catalysts is a concern worth paying attention to. 64 What are the high and low limits for the pressure control of nitrogen under reduced pressure in the blower system? Why? Answer: Pressure of reduced N2 (pressure at the fan inlet): 0.05 MPa ≤ P ≤ 0.1 MPa. (1) When the pressure P is less than 0.05 MPa, a negative pressure may be created, allowing air to enter the system. If this occurs during the reduction process, it can cause a sudden rise in the temperature of the catalyst layer, leading to overheating, even the destruction of the catalyst, as well as fire and explosion accidents. If the catalyst is heated in its reduced state, this can cause the catalyst to be oxidized and the bed temperature to rise excessively, thereby damaging the catalyst. (2) The blower system equipment and pipelines are all at atmospheric pressure; when the pressure exceeds 0.1 MPa, accidents such as explosions may occur, damaging the equipment and pipelines. 65 Explain the phenomenon of intermediate-temperature catalyst poisoning by H3S? Answer: The reaction is: Fe3O4 + 3H2S + H2 ↔ 3FeS + 4H2O. Since it is a reversible reaction, H2S is not a permanent poison. It is generally believed that when the H2S concentration in the gas is below 200PPM, the activity remains unaffected. Once poisoned, the catalyst’s activity can also recover rapidly when pure feed gas is used again. However, if this reversible process is repeated, it will actually accelerate the rate of decline in activity, and it will cause the catalyst to break down due to repeated phase changes. 66 Explain the H2S poisoning phenomenon in low-volatility catalysts? Answer: Cu + H2S = CuS + H2 (1) CuO + H2S = CuS + H2O (2) ZnO + H2S = ZnS + H2O (3) Reactions (1) and (2) will cause the active centers of the catalyst to become poisoned and lose their activity rapidly. The more sulfur is absorbed by the catalyst, the more its activity is lost. If the sulfur absorption activity is 100%, it decreases by 80% after absorbing 0.1% of sulfur. After absorbing 0.2% sulfur, the activity drops to 63%. 67 Explain the H2S poisoning phenomenon in methanation catalysts? Answer: The sulfur that enters the methane processing stage exists mainly in the form of H2S. H2S can react with Ni in the catalyst on its surface, thereby poisoning the catalyst. Reaction equation: 3Ni + 2H2S ↔ Ni3S2 + 2H2. 68 Describe the passivation process of low-temperature catalysts Answer: Follow the heating procedure to reduce the furnace temperature to 150°C using N2; introduce air into the N2 atmosphere, keeping the initial oxygen level below 0.3%. Based on the temperature changes in the catalyst layer, when the temperature rise does not exceed 50°C, the oxygen concentration can be gradually increased until it is fully switched to air. Once no further temperature rise occurs, the pressure can be raised to 0.4 MPa; after remaining stable for more than 2 hours without any significant temperature increase, the pressure can be reduced, indicating that the passivation process is complete. 69. Describe the deactivation process of methanation catalysts Answer: Follow the heating procedure to reduce the furnace temperature to 150°C using N2; introduce air into the N2 atmosphere, keeping the initial oxygen level below 0.3%. Based on the temperature changes in the catalyst layer, the oxygen concentration can be gradually increased until it is completely switched to air, provided that the temperature rise does not exceed 20°C. Once no further temperature increase occurs, the pressure is raised to 0.4 MPa; after staying at this level for more than 2 hours without any significant temperature rise, the pressure is reduced, indicating that the passivation process is complete. What should be noted when operating a 70-degree washing water preheater? If it’s not done properly, which process will be affected? Answer: Keep the line connected to the wash water preheater in the open position, then turn on the aqueous phase drain, and slowly open the aqueous phase inlet valve. After the drain water has been removed, open the inlet valve and the aqueous-phase outlet valve fully to prevent pressure buildup in P2. If the hot water phase valve is opened too quickly, it will cause a water cut-off in 152#G8. 71 Medium Variation 161B: On-site parking sequence? Answer: For K1 main valve and K1 auxiliary line valve → stop the wash water preheater; then open the auxiliary line valves and close the inlet and outlet valves → drain all drains. What is the shutdown sequence for unit 72161A? Answer: Close the K1 manual valve and the transformer outlet valve; maintain positive pressure inside the furnace, and use medium-pressure nitrogen to replenish pressure if necessary. 73 How to handle long-term parking? Answer: Close the main high-pressure steam valve and the main deoxygenated water valve → After the system has been purged with nitrogen, maintain the pressure at 74. Should the low-temperature transformation and desulfurization tank systems be shut down? Answer: Turn off F21 → turn off T22 → turn off the low-temperature conversion inlet and outlet valves. A: Turn off the manual valves before and after G21 as well as the auxiliary line valves → turn off T21 → turn off the low-temperature conversion inlet and outlet valves. How to determine whether steam contains water and whether 152#H6 contains liquid? Answer: If it is found that the inlet temperature T2 in both sets A and B drops significantly, it indicates that steam contains water. The solution is to turn off T2 and T3, enable steam drain to carry away water, and reduce the steam supply from the control room. When there is a significant drop in the inlet T2 of a single set, it indicates that the previous system H6 is carrying liquid. Handling method: Emergency shutdown. First, turn off deoxygenated water T7, then turn off steam T6 (F1); close the K1 manual valve, activate the steam drain, and close the intermediate outlet valve. (When both intermediate inlet sets descend slowly at the same time, it indicates that the pressure for temperature and pressure reduction has decreased.) Relatively more deoxygenated water is added, so the amount of deoxygenated water should be reduced and the temperature for temperature and pressure reduction should be increased. ) 76 How to determine low-temperature steam moisture carryover and primary liquid carryover? Answer: If it is found that both low-pressure inlet T22 values decrease simultaneously, it indicates that the steam contains water. And when the low-variation inlet T22 drops, it indicates gas carrying liquid. (When both low-temperature inlet T22 values gradually decrease simultaneously, it indicates a drop in the low-temperature steam pressure; in such cases, the amount of deoxygenated water added should be reduced, and the temperature for temperature and pressure reduction should be increased.) ) What are the reasons for high temperature in the 77 methanation furnace and how to address it? Answer (1): The oxygen content in the vaporized gas is above the standard. (Medium variation) Treatment: Adjust the oxygen/gas ratio and adjust the F18 flow rate. (2) The CO content in the low-variation inlet air is high. Treatment: Cool down with cold N2; shut down the system in severe cases. (3) Excessive CO2 content in the secondary gas: Treatment – cool with nitrogen; in severe cases, shut down the system. (4) The nitrogen purity is insufficient, and the oxygen content is too high. Action: Stop. Stop nitrogen addition in connection with synthesis. (5) The alkali pump is evacuated, or its pumping volume is significantly reduced, or it stops working. 78* How should the operation be performed when adjusting the oil addition or removal amount? Answer: The amount of steam added is determined based on the changes in bed temperature. When the amount of oil reduction is not significant, medium-pressure steam generally does not need to be reduced ； When the oil volume reduction exceeds 300 kilograms, the medium and low-pressure steam volumes should be reduced to rapidly increase the furnace temperature. 79 What should be done when the methanation temperature rises gradually? Answer: First, consider opening T24 and T25. Next, consider the secondary reactor bed layer and inlet T7, with the aim of reducing the temperature in the secondary reactor in order to lower the temperature of the secondary gas at the methanation inlet. Once again, check whether a secondary gas analysis is appropriate. 80 What should be noted when the methanogenesis temperature is high? Answer: First, check whether the low-temperature conversion and secondary gas analysis meet the requirements, and whether the CO content in the medium-temperature conversion stage is less than 3.5%. Next, check whether the pump flow rate of pump #169 and the solution temperature are appropriate. 81 What should be done when an emergency forces the switch to two separate parking systems? Answer: First, close the deoxygenated water valve ； Close the main valves at the temperature and pressure reduction outlets for A and B again ； Finally, cut down K1 for the main felling ； Low-variation inlet and outlet valve ； Methanation inlet valve and outlet purified gas main valve ； Medium-pressure gas outlet valve. 82 What systems should be checked before driving a vehicle? Answer: The vaporization gas system, steam system, condensate system, wash water system, medium and low pressure nitrogen systems, as well as the pipelines and valves, must be properly installed and maintained. 83 A Medium-pressure pressure testing, leak detection, and replacement? Answer: 1) Close the K1 manual valve, the branch line and the main valve leading to station No. 160, the P6 cylinder valve, the P6 control valve, and the manual vent valve. 2) Close all hot N2 valves. 3) Close the P21 and F1 control valves as well as the manual valve. 4) Open the inlet and outlet valves of the wash water preheater. 5) Close the drain and sampling valves on the equipment and pipelines. 6) Use medium-pressure nitrogen for dispatching to pressurize the system. 7) Pressure testing and leak testing are based on the P6 indication, with a pressure increase rate of 0.1 Mpa/Min. 84 What are the reasons for high CO levels in the exhaust gas, and how to address them? Answer: 1) Low steam ratio——increase steam supply. 2) Low furnace temperature——raise the furnace temperature. 3) Poor catalyst activity——increase operating temperature or reduce load. 4) Cavities in the catalyst causing gas to take a short circuit——take appropriate measures such as replacement. 5) Catalyst poisoned by H2S——increase steam supply. 6) Heat exchanger leakage——shut down the system. 7) Large fluctuations in furnace temperature——stabilize operations. Under what circumstances should this position initiate an emergency shutdown? Answer 1) Vaporized gas; liquid in the primary and secondary gas streams; temperature drop in the furnace layer. 2) Power outage, water outage, steam outage. 3) The difference between primary and secondary analysis leads to overheating in low-temperature methanation. 4) Severe system leakage, fire, and explosion. 5) Secondary gas for significant fluctuations in furnace temperature. 6) Over-temperature and over-pressure. 7) The alkali pump is evacuated or stopped. What precautions should be taken during operation of the 86 medium-temperature catalyst in its later stages? Answer 1) The amount of steam added should be increased or decreased gradually, and the temperature should be kept as stable as possible to avoid large fluctuations. 2) Pay attention to fluctuations in low furnace temperatures; operate at the upper limits for T2 and T3 to prevent overheating due to low temperatures and to avoid a drop in furnace temperature. 3) Be aware of steam carrying water (H6/152# with liquid). How many layers are there in the 87C variable furnace? How many tons of catalyst is loaded in each unit? What model of catalyst should be installed? What is the variable inner diameter in C? Answer: It is divided into three layers in total. The first and second layers each contain 13T, the lower layer contains 22T, and the catalyst model is BN113. The effective inner diameter of the furnace is ∮2.6 meters, with a refractory lining thickness of 200 mm. What is the role of each control system in 88C? Answer 1) The main function of the K1 control system is to supply gas during startup, shutdown, and resumption of operation, and to cut off the amount of control inlet gas in case of an accident. 2) The T2 control system functions as a bypass valve for the second feed preheater, regulating the temperature of the medium-temperature upper bed layer. On means cooling down, off means warming up. The temperature of the lower layer can also be adjusted; turning it on raises the temperature ； Shutting it down means cooling down. 3) The T3 control system functions as a bypass valve for the primary feed preheater, regulating the temperature of the upper layer in C. Turning it on lowers the temperature, while turning it off raises it. 4) The function of the G1 control system is to regulate the steam inlet volume at the upper section of C. What is the difference between 89C and the A and B sets in terms of intermediate variation? Answer 1) The entire unit consists of one furnace, divided into two sections and three layers. 2) Gas is introduced to the second floor, with a cold gas branch line installed. What preparations should be made before starting the vehicle at 90°C? Answer 1) Perform system purging; check according to the flowchart to ensure that the equipment is properly arranged, that the instruments are sensitive and functional, that the valves operate smoothly, and that the analysis points are unobstructed. 2) Install the catalysts for each layer as required by the design. 3) System pressure testing and leak checking. 4) Before driving, it must be verified that N2 has been used for displacement, with O2 levels below 0.5%. 5) Catalyst heating. 6) Catalytic reduction. 7) After the reduction is complete, gas is introduced at atmospheric pressure; after 4 hours, the pressure is gradually increased to switch to pressurized operation. In 91C medium variants, if overheating occurs during heating and reduction, what is the cause of this overheating? How to handle it? Answer 1) Excessive amount of H2+CO was used during reduction. Treatment: Cut off the valve, and cool with cold nitrogen. 2) The pressure is too low, allowing air to be drawn in. Treatment: Increase pressure; the system has been successfully purged. 3) Too little steam is added. Treatment: Increase the steam volume and reduce the steam temperature. 4) The temperature control of hot N2 is too high. Treatment: Adjust the electric heater to lower the temperature of the hot nitrogen. What should the initial CO concentration be when using the 92 medium-activity catalyst in temperature-induced reduction? What should the H2O/CO ratio be? At what level can reduction be considered complete? Answer: The initial concentration is controlled at 0.5%; high-pressure steam is introduced in a ratio of H2O/CO of 4–5, raising the CO concentration to over 12%. When the temperature of the catalyst bed remains stable and the H2 content at the outlet increases significantly, it can be considered that the reduction process is complete. What are the reasons for the excessive CO content in the 93 medium-pressure gas, and what are the corrective measures? Answer: Causes and treatment measures 1) Low steam ratio – Increase the amount of steam. 2) Low furnace temperature – Raise the furnace temperature. 3) Poor catalyst activity – Increase the operating temperature or reduce the load. 4) Catalyst poisoning by H2S – Increase steam supply to remove sulfur. 5) Cavities in the catalyst allowing gas to take a short circuit – Carry out appropriate repairs or replacements. 6) Shut down the system for maintenance. What are the causes of excessive temperature in the catalyst bed of the 94 medium-pressure converter, and what are the treatment measures? Answer: 1) Excess oxygen content in the cracking gas (contact 152# to adjust the O2/gas ratio or calibrate the F18 flow meter). 2) Insufficient steam (increase or decrease the amount of steam supplied). 3) Low steam pressure (contact the dispatch team to increase or decrease the pressure). 4) Excessively high inlet temperature (reduce the T2 inlet temperature). What are the causes of the low temperature in the 95 medium-pressure bed layer and what are the corrective measures? Answer: 1) Excessive amount of steam added (reduce the amount of steam). 2) Low temperature of the cracking gas (increase the temperature of the cracking gas). 3) Water in the cracking gas (improve the drainage of water from the cracking gas; shut down the system in severe cases). 4) Water in the steam (increase the steam temperature and improve the drainage of steam). 5) Catalyst degradation (replace the catalyst). After the quality of the gas deteriorates, how can one determine whether it is a catalyst issue or a equipment issue? Answer: When the process conditions (temperature, pressure, gas flow rate) remain stable and the system resistance does not change significantly, but the quality of the gas deteriorates, a leak in the heat exchanger can be suspected. Under normal conditions, if the quality of the gas gradually deteriorates, the furnace temperature drops, the steam volume decreases, and the system resistance increases, this can indicate catalyst aging, which can be determined by taking samples from the furnace. What are the main differences in process setup between systems 96 170A and B? Answer 170A: Wet PS gas → primary C removal → zinc oxide S treatment → low-temperature transformation → secondary C removal. 170B: Wet PS gas → zinc oxide S removal → primary C removal → low-temperature transformation → secondary C removal. 97 Why must nitrogen be added during methanation before it enters the furnace? Answer 1) To dilute the CO2 and CO concentrations in the secondary gas and prevent overheating during methanation ； On the other hand, to increase the air velocity. 2) To remove oil contamination and protect the methanation catalyst from poisoning. How to handle liquid carried in the primary gas stream in the 98 B system? Answer: 1) Immediately open the cylinder valve and the manual vent valve, then isolate the gas from the system, and contact 169# for handling. 2) In mild cases, drain the leak by opening the alkali wash separator drain; in severe cases, carry out step 1). 99 How to deal with severe overheating in methanation? Answer: Immediately cut off the gas and turn on P6; after opening the furnace, vent it to relieve pressure. When the furnace temperature rises sharply, cooling nitrogen is introduced through the valve before starting the furnace to reduce the temperature. 100 What is the effect of increasing the main pipe pressure on this system? Answer 1) It affects the deterioration of primary and secondary temperament ； 2) Low transformation, methanation overheating ； 3) To carry liquid with the primary and secondary gases. Processing: Hold pressure at P6 and vent, then cut off the gas supply. The base pump evacuates, and the system is depressurized after intermediate transformation. P6 pressure holding venting or medium-pressure conversion and gas mixing.