Sulfur-resistant shift test questions

Write it yourself; we’re all waiting for that, let’s hold on for now. Haha

1. What are the tasks involved in changing a position, and what are the principles behind such changes? Task: Adjust the composition of the process gas through transformation reactions, reduce the carbon monoxide content, and increase the hydrogen content in order to meet the hydrogen-to-carbon ratio requirements of the methanol synthesis process. Principle: Under certain pressure and temperature conditions, and with the action of a catalyst, carbon monoxide and water vapor present in the gasified raw coal gas undergo a shift reaction to produce hydrogen and carbon dioxide, while heat is released. The reaction equation is as follows: 2. What are the model numbers of the catalysts used for this transformation and their main components? The catalyst model in question is the QDB-04 sulfur-resistant shift catalyst, which exists in the form of cobalt oxide and molybdenum oxide at the time of leaving the factory; its active components are cobalt sulfide and molybdenum sulfide. 3. What is the transformation rate? The degree of conversion of carbon monoxide is usually expressed by the conversion rate, which is defined as the ratio of the amount of CO that has been converted to the amount of CO before conversion. In actual production, the converted gas contains not only CO but also components such as hydrogen, carbon dioxide, and nitrogen; the conversion rate can be calculated based on the composition of the gases before and after the reaction ； Under certain conditions, the conversion rate at which the conversion reaction reaches equilibrium is known as the equilibrium conversion rate; it represents the maximum conversion rate under those conditions. Based on 1 mole of dry feed gas, the relationship between the equilibrium conversion rate and the equilibrium constant is given by: KP = (c + ax)(d + ax) / (a – ax)(b – ax), where a, b, c, and d represent the molar fractions of carbon monoxide, water vapor, carbon dioxide, and hydrogen in the gas before the reaction, respectively ； x—equilibrium transformation rate, % ； Under large-scale industrial production conditions, it is impossible for the reaction to reach equilibrium; therefore, the conversion rate cannot actually reach the equilibrium conversion rate. When necessary, the degree of proximity between the actual conversion rate and the equilibrium conversion rate can be used to assess the quality of the production conditions. 4. List the factors that affect the chemical equilibrium of transformation reactions? ① Temperature ； ② Pressure ； ③ vapor ratio ； ④ The impact of carbon dioxide ； ⑤ The impact of side effects. ⑥ Airspeed. (Detailed explanations can be found in the training materials.) ) 5. Principle of catalyst sulfidation? Why is sulfidation required for cobalt-molybdenum-based sulfur-resistant catalysts before use? The true active components in cobalt-molybdenum catalysts are COS and MOS2; therefore, they must be sulfided to acquire conversion activity. The purpose of sulfidation is also to prevent cobalt-molybdenum oxides from being reduced to their metallic state, as metallic cobalt-molybdenum can facilitate the methanation of carbon monoxide and hydrogen. This highly exothermic reaction can cause a significant rise in temperature, thereby damaging the catalyst. The sulfidation reaction is a reversible reaction; therefore, fluctuations in the sulfur content of the feed gas can lead to sulfur loss from the catalyst, thereby reducing its activity. Cobalt-molybdenum catalysts have hydrogenation properties; therefore, when the amount of unsaturated hydrocarbons in the feed gas is high, a severe exothermic reaction occurs. 6. List the stages of catalyst heating for sulfidation Heating stage, constant-temperature removal of adsorbed water stage, heating stage, constant-temperature leveling of bed temperature, sulfidation stage. For details, see the temperature rise reduction curve of the catalyst. 7. What issues should be considered when loading a modified catalyst? It should be noted that: ① The catalyst should not be loaded on overcast days, in humid conditions, or during rain or snow. ② The catalyst should be filled in layers; each layer must be leveled before the next one is added. The bed formed after filling must be even and uniform. ③ The free fall height during catalyst loading shall not exceed 0.5 meters. ④ During the loading process, it is necessary to keep the converter clean; pads should be used when walking on the catalyst. ⑤ Do not drop the catalyst tank to prevent the catalyst from being crushed. ⑥ The catalyst should be sieved before loading. 8. What are the causes of overheating in converter furnaces? Main factors: ① Water-gas peroxide. ② The resistance of the shift converter increases due to factors such as catalyst pulverization, resulting in localized overheating in the bed. ③ When driving to pick up gas, the amount and pressure of the gas were not properly controlled. ④ The CO content in water gas is too high. ⑤ The system pressure increased suddenly. ⑥ The inlet temperature is too high, or there is a low drift in the inlet temperature indication. 9. How to extend the service life of the catalyst? ① The inlet temperature of the converter is kept within the specified range, and during the initial stage of catalyst use, the lower limit of the catalyst temperature range should be utilized as much as possible. ② When heating the catalyst for vulcanization, it is necessary to strictly follow the heating and vulcanization procedure. ③ It is strictly prohibited to bring water or oxygen into the furnace. ④ Avoid maintaining a high water vapor ratio for extended periods, and avoid sulfur-free operations. ⑤ Try to avoid large fluctuations in load and frequent start-stop operations. ⑥ Strictly control the furnace temperature to prevent the bed layer from overheating and avoid significant fluctuations in its temperature. ⑦ Control the rate of pressurization and depressurization carefully; do not make it too fast. ⑧ Raise the temperature slowly during gas introduction to prevent the introduction of catalyst poisons. 10. What are the phenomena during the desulfurization of transformation catalysts? What are the causes of desulfurization? How to prevent it? Phenomenon: Catalyst activity decreases, the sulfur content at the outlet of the shift gas is higher than that in the inlet syngas, and sulfur release occurs from the catalyst. Factors affecting it: ① Excess water-to-vapor ratio ； ② The bed temperature is too high ； ③ The concentration of hydrogen sulfide in the process gas is too low. A lower water vapor ratio, a lower bed temperature, and a higher H2S concentration help to suppress the occurrence of desulfurization reactions. In production, the occurrence of reverse sulfidation is primarily prevented by ensuring that the hydrogen sulfide content in the process gas remains above the allowable level. Generally, based on operational experience, a level of not less than 1000 ppm is recommended. 11. Which components in water gas may affect the performance of shift catalysts? ① Water vapor: Excessively high levels of water vapor in gas over an extended period can cause the catalyst to break down. ② Oxygen: Excess oxygen content in the gas can cause a sharp rise in the temperature of the catalyst bed, leading to catalyst sintering. ③ Hydrogen sulfide: An insufficient level of hydrogen sulfide in gas can lead to the desulfurization of the catalyst, reducing its activity. ④ Toxins: Toxins in gas such as AS2O3, Cl-, NH3, CN-, P2O5, and hydrocarbons can cause catalyst poisoning and loss of activity. ⑤ Dust and other impurities present in gas can easily clog the micropores on the surface of the catalyst, reducing its specific surface area. 12. What is dew point temperature? At a certain pressure and water vapor content, as the temperature of the system decreases, when the temperature drops to a level where the vapor pressure equals the saturated vapor pressure at that temperature, the water vapor will condense. This temperature point is known as the dew point temperature. 13. What factors cause the deactivation of conversion catalysts? ① Factors such as water and oxygen present in water gas cause the loss, pulverization, caking, and sintering of the active components of the catalyst. ② The catalyst becomes desulfurized and deactivated due to reasons such as a decrease in the hydrogen sulfide concentration in the process gas. ③ Loss of active components due to sintering. ④ The catalyst is poisoned by the introduction of toxins. ⑤ The specific surface area of the catalyst decreases due to the blockage of micropores by impurities, high-temperature sintering, and other reasons. ⑥ The reduced activity at low temperatures is caused by the catalyst being used at high temperatures for an extended period of time. ⑦ Incomplete catalyst sulfidation or a sudden rise in temperature during sulfidation exceeding 500 degrees leads to the sintering of the active components, the sublimation of molybdenum, and physicochemical changes in the active components of the carrier. 14. Why is pressure relief and replacement necessary after the transformation system is shut down? The process gas in the shift converter contains a high water vapor ratio; if it is not replaced after shutdown, as the temperature of the catalyst bed drops, water vapor will condense within the shift converter, which is detrimental to the catalyst. Therefore, after the conversion system is shut down, it must be purged with nitrogen and kept under pressure to prevent air from entering. 15. How does the conversion system perform nitrogen purging? What is the nitrogen displacement index? ① Close the raw gas boundary valve and the converter gas boundary outlet valve (located in the low-temperature methanol washing area); set the pressure control valve of the converter system to manual mode to slowly release pressure. ② After the system has been depressurized, open the blind flange on the nitrogen valve in the process pipeline at the system inlet. ③ In the conversion system, adjust the control valves on the process gas pipelines to manual mode and open the stop valves. ④ Close the system pressure control valve, open the nitrogen valve on the system inlet pipeline, and fill the system with nitrogen ； When the pressure reaches 0.4 MPa, close the nitrogen inlet valve and open the system pressure relief valve to release pressure ； Do it several times. ⑤ The gas replacement is considered successful when the dew point inside the analysis device is ≤ -30°C, CO + H2 ≤ 0.5%, and O2 ≤ 0.1%. 16. What are the principles for increasing or decreasing the load in a transformation system? ① When increasing the load, follow the principle of small amounts multiple times, depending on the temperature of the catalyst bed. ② Load reduction in a unit is usually carried out in the event of failures in the units before or after it, and it can also occur when the catalyst’s activity within that unit declines; the latter situation can affect the units before and after it as well. Therefore, load reduction must be coordinated with the preceding and following processes. 17. Why is a constant-temperature stage required during the catalytic heating reduction of sulfides? How to operate it? For the temperature-raising reduction of sulfidation in conversion catalysts, a constant temperature phase is necessary. This constant temperature is required to evaporate the moisture present in the catalyst, preventing the catalyst particles from breaking apart due to rapid evaporation of moisture as temperature rises. Additionally, maintaining a constant temperature helps to reduce the temperature differences across different points in the catalyst bed, ensuring a uniform rate of temperature increase. This allows all parts of the catalyst to be fully reduced or sulfided, thereby achieving the best level of catalyst activity. The constant temperature should be maintained in accordance with the catalyst’s heating and reduction (sulfidation) curve; the heating rate should be reduced before reaching the constant temperature, and the space velocity should be increased gradually during that phase, using an electric heater to keep the temperature of the gas at a constant level. 18. What are the symptoms of sulfur-resistant catalyst deactivation? Under normal operating conditions, the composition and flow rate of the gas entering the shift converter remain unchanged; however, the CO content in the gas exiting the shift converter increases. To maintain normal parameters, it is necessary to raise the bed temperature. 19. What are the factors that increase CO levels in transformed air? How to handle it? Reason: ① The catalyst temperature is too low, affecting the conversion rate ； ② Excessive load or too rapid increase in dosage leads to an increased gas space velocity, exceeding the maximum space velocity allowed when the catalyst is operating under normal conditions ； ③ Back-sulfidation occurs, reducing the catalyst’s activity ； ④ The operation is unstable, with fluctuations in pressure and temperature. ⑤ The catalyst activity declines or there are voids in the catalyst layer, causing gas short-circuiting. Catalyst poisoning ； ⑥Internal leakage in the heat exchanger or rupture of the explosion-proof plate. Solution: ① Increase the reaction temperature ； ② Reduce load or increase load gradually ； ③ Increase the inlet hydrogen sulfide concentration and inlet temperature, or re-sulfurize ； ④ Stable operation, stable pressure, and temperature. ⑤ Reduce load or shut down to replace the catalyst. ⑥ Equipment for parking and maintenance. 20. What are the factors that affect the temperature of the catalyst layer? How to stabilize the furnace temperature? ① Load variation. During the production process, the amount of gas added or removed should be adjusted promptly by using the temperature control valves for the furnace and various intermediate and waste heat exchangers, in order to regulate the temperatures at each stage as well as at the inlet. When the load is increased, the water-vapor ratio should be raised promptly to intensify the conversion reaction, thereby maintaining stability in the temperature of the catalyst layer and preventing an increase in CO levels ； During load reduction, the water vapor ratio should be reduced promptly, and the inlet temperatures of each section should be increased to maintain stability in furnace temperature and the CO levels in the shift gas. Therefore, appropriate adjustments should be made in a timely manner based on the catalyst layer temperature when the load changes. ② Changes in gas composition. Changes in the carbon monoxide content in the gas cause fluctuations in the temperature of the catalyst layer. In such cases, it can be addressed by adjusting the gas inlet temperature, adjusting the water vapor ratio, and other similar methods. If the upward trend in catalyst layer temperature cannot still be suppressed, the production load can be reduced directly until shutdown. 21. How to protect the sulfur-resistant shift catalyst while parking and driving? When parking or driving, prevent air and water from entering the catalyst bed to avoid the condensation of water vapor in the bed. After the shift converter is shut down and depressurized, it should be purged with dry gas or nitrogen. To reduce the temperature, blind flanges are used to isolate the shift converter from the system, and nitrogen is used to maintain a slight positive pressure inside the converter. The nitrogen used for this purpose must be dry, with an oxygen content of less than 0.5%. When restarting the converter after it has been shut down, the temperatures of the pipes and equipment are low; as a result, steam will condense in these cold pipes and equipment, thereby introducing water into the catalyst bed of the shift converter. For this reason, maintain a low moisture ratio at the beginning of driving. 22. What precautions should be taken regarding transformations in production operations? ① To fully utilize the low-temperature activity of catalysts, in practical operations, it is crucial to stabilize the furnace temperature and control the water vapor ratio properly. ② In the event of a sudden reduction in production volume, measures should be taken promptly to maintain the temperature at the inlet to the converter and the temperature of the bed layer. 23. What is the effect of the space velocity on the conversion reaction? Air velocity refers to the volume of fluid that passes through a unit volume of catalyst per unit of time. The value of the space velocity determines the production capacity of the catalyst and is also related to the conversion rate. If the air velocity is too low, the heat of reaction is minimal, the temperature of the catalyst bed drops, and the conversion rate is low ； If the space velocity is too high, the gas has little time to come into contact with the catalyst; it leaves the catalyst bed before a reaction can occur, which results in a decrease in the conversion rate. The selection of air velocity is related to the performance of the catalyst. 24. What is the cause of the sudden rise in catalyst bed temperature? How to handle it? The main reason for the sharp rise in the catalyst bed temperature is: ① An increase in the oxygen content in the raw gas fed into the catalyst bed. ② The load increases suddenly, and adjustments are not made in time, such as a sudden rise in carbon monoxide levels in gas. ③ Due to improper operation, the temperature regulation bypass line was reduced in size or shut off. A sudden rise in the temperature of the catalyst bed will reduce the catalyst’s activity, cause the conversion catalyst to undergo desulfurization reactions, and even damage the catalyst. Therefore, the cause must be identified immediately and appropriate action taken: ① Adjust the temperature control bypass valve accordingly. ② Adjust the inlet temperature of the conversion furnace. ③ If oxygen is present in the gas, production should be reduced; if necessary, an emergency shutdown should be initiated, while the upstream process units should be notified to identify the cause and take corrective action. 25. What are the reasons for the decrease in catalyst bed temperature? How to handle it? The main reasons for the decrease in catalyst bed temperature are: ① Reduced load, such as a decrease in the amount of gas or a reduction in the CO content in the gas. ② Excessive water in the gas caused a sudden drop in the temperature of the catalyst bed. ③ Catalyst deactivation and aging. ④ Improper operations such as a decrease in inlet temperature. A decrease in the temperature of the catalyst bed reduces the reaction rate and the conversion efficiency; it is necessary to take appropriate measures to restore the normal temperature of the bed. The specific measures are as follows: ① Reduce the valve on the bypass line for temperature control, thereby increasing the temperature of the gas entering the furnace, while also increasing the volume of gas fed into the furnace. ② If there is too much water in the gas, reduce the pressure of the first intermediate waste heat boiler and adjust the amount of boiler feedwater added. ③ Keep the liquid level of the first water separator within the specified range. ④ Strengthen management and operate with care. 26. What are the reasons for the increased resistance in a conversion system? How should it be handled and prevented? Reason: ① Increased resistance in the catalyst bed. A. The catalyst has poor quality, low strength, and is prone to pulverization. B. The operating temperature fluctuates greatly and frequently, causing the catalyst particles to expand and contract repeatedly until they break apart. C. The bed temperature is too high for too long, causing the catalyst to sinter. D. Water enters the catalyst bed. ② Waste heat boilers and heat exchangers have high resistance. Fly ash and impurities from raw gas clog the waste heat boilers and heat exchangers. Solution: ① Sieve or replace the catalyst when parking. ② Clean the waste heat boiler and heat exchangers when parking. Preventive measures: ① Use catalysts with high strength, good performance, and low tendency to powder. ② The catalyst should be used and maintained properly; the operating temperature must not exceed the allowed limit, and temperature changes should be gradual with minimal fluctuations. 27. How to use and maintain sulfur-resistant shift catalysts properly in normal production? (For reference only) ① Control the temperature of the catalyst bed properly. ② The temperature of the low-temperature catalyst bed should be maintained within its active temperature range; it must not exceed this limit. The temperature at the inlet of the bed should be 30°C higher than the dew point temperature of the gas. ③ The temperature of the catalyst bed should decrease from top to bottom, with the inlet temperature of the last section of the bed being kept as close as possible to the lower limit of the operating temperature. ④ At the beginning of use, the bed temperature of low-temperature shift catalysts should be kept as low as possible and increased gradually, with an increase of no more than 10°C per year in general. ⑤ The fluctuation range of the bed operation temperature should not exceed 10°C/h. The main approaches include: A. Controlling the appropriate water vapor ratio and hydrogen sulfide content; to prevent reverse sulfidation reactions, based on the operating temperature of the catalyst, and while ensuring the required conversion rate, the gas production unit is coordinated to maintain as low a water vapor ratio as possible, and the hydrogen sulfide content in the gas should also be kept at the minimum level necessary to meet the operating conditions. B. Strictly control the oxygen content in the process gas entering the catalyst bed; it must not exceed 0.5%. If the bed temperature rises due to excessive oxygen content, the bypass should be activated or the furnace temperature reduced by decreasing the feed rate. C. It is strictly prohibited to introduce water into the furnace, as water can dissolve the active components in the catalyst, causing it to become permanently inactive. Additionally, water can lead to the sudden cooling and fragmentation of the catalyst, as well as an increase in the pressure difference across the catalyst bed. D. Adjust the amount added or removed slowly to prevent excessive fluctuations in furnace temperature. If the bed temperature exceeds its limit for a short period of time, it can lead to the resulfidation of the catalyst. In case of a sudden significant reduction in flow rate or temporary shutdown, the amount of steam supplied should be reduced immediately, or even cut off, to prevent reverse sulfidation reactions caused by an excessively high water vapor ratio in a short period of time. 28. List the preparatory work before heating the catalyst for sulfidation? ① After the catalyst is loaded, a gas-tightness test must be conducted using nitrogen until it passes. ② The system should be purged with nitrogen to an acceptable level; the drain water from the drainage lines must be completely drained, and sampling of these drainage lines shows that the O2 level is ≤0.1%. ③ Sufficient amount of nitrogen with a purity >99.9% is available on standby. ④ If CS2 is used as a vulcanizing agent, it should first be stored in a CS2 tank for use, and a dedicated person should keep track of the amount of CS2 added and the remaining amount. ⑤ The nitrogen heater for startup is ready for operation. ⑥ It is capable of providing a sufficient supply of hydrogen-rich gas or hydrogen. 29. What are the precautions when heating a conversion catalyst for sulfidation? ① Strengthen the N2 separator for emissions, but when sulfiding the catalyst, care should be taken not to empty it in order to prevent H2S poisoning. To prevent the catalyst from overheating, it is necessary to adhere to the principle of \"increasing sulfur content without raising temperature, and raising temperature without increasing sulfur content\" ； The hot spot in the catalyst bed should be strictly controlled to no more than 450°C. ② If the bed temperature rises too rapidly and exceeds 500°C, CS2 supply must be stopped immediately, hydrogen supply should be halted, the nitrogen inlet temperature reduced, and the nitrogen flow rate increased to lower the temperature. ③ When hydrogen is added, the temperature of the catalyst bed must be kept around 200°C, and a dedicated person should regularly monitor the H2 concentration to maintain it between 25% and 35%. Strictly prevent excessive hydrogen concentrations to avoid catalytic reduction reactions. ④ Someone must be responsible for controlling the amount of CS2 added; it should be introduced slowly and steadily to prevent excess amounts from causing the bed temperature to rise too high or leading to condensation within the system. It is advisable to keep the H2S level at the outlet at no more than 15 g/m3. The addition temperature of CS2 should be between 230–250°C, as CS2 undergoes hydrolysis only at temperatures above 200°C. If CS2 accumulates in the catalyst bed, once the temperature rises above 200°C, sudden hydrolysis of CS2 occurs, leading to a sharp increase in the bed temperature ； However, when the temperature exceeds 250°C and CS2 is added, H2 may cause a reduction reaction of CoO or MoO3, which can also lead to a sharp rise in the bed temperature; both of these phenomena can result in catalyst deactivation. ⑤ After the sulfidation process is complete, the system is thoroughly purged with nitrogen to ensure it is free of contaminants, and N2 is continuously added until H2S levels in all drain samples analyzed are zero. 30. What are the requirements for transforming the original driving conditions? ① All system equipment and pipelines have been installed in place and meet the production requirements; the system has been thoroughly purged and cleaned, is airtight, and the nitrogen displacement process was successful. ② The instrument control facilities are properly installed, and the DCS in the control room has been installed and tested. ③ The roads within the area are clear, all safety facilities are in place, and the safety valves have been calibrated. ④ The necessary technical materials are available; the operators have sufficient technical preparation for starting up the system, the roles of each person are clearly defined, and the plan is comprehensive. ⑤ The relevant utility facilities are ready for use. ⑥ The rotating equipment has passed individual testing and joint testing successfully. ⑦ The converter catalyst has been loaded as required. 31. What are the phenomena and hazards associated with water entrainment in the steam generated by various waste boilers, and how should it be addressed? Phenomenon: High-temperature alarm for the waste boiler; water may emerge from the safety valve at the top of the waste boiler, and there may be water hammer sounds in the steam outer pipe. Harm: ① It reduces the quality of the steam produced, as ions such as Ca2+, Mg2+, and Cl1- present in the waste boiler water end up in the steam system. ② Water hammer in the outer pipe may cause circulation in the outer pipe and the valve. ③ When 0.5MPa steam contains water, it affects factors such as the temperature of the shift converter. Solution: The control room instructed the site to immediately open the waste discharge valve in order to reduce the temperature to normal levels. 32. What are the hazards of adding an excess amount of the reagent Na3PO4 used in various waste boilers? Adding trisodium phosphate to the boiler water not only serves to prevent scaling, but it also has the adverse effect of increasing the conductivity of the boiler water and raising the Na+ content in the steam. If an excessive amount is added, it will cause a significant increase in the conductivity of the boiler water, as well as elevated Na+ levels in the steam. In severe cases, this can lead to a vapor-liquid azeotrope phenomenon. Over time, it can also result in problems such as deterioration of the convective tube bundles, phosphorus deposition at the tube ends, and severe caustic corrosion in the water phase. Therefore, as long as there is a certain residual amount of phosphate in the boiler water (above 10 ppm), it is better to keep its level low.

The original poster has really gone to a lot of trouble; the information provided is quite comprehensive. It’s great. I’m sharing it first, thank you