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1. What is solubility? It is the amount of grams of a solute that can dissolve in 100 grams of solvent at a certain temperature when equilibrium is reached. 2. What is partial pressure? In a mixture of gases or liquids, the pressure exerted by a particular component is equal to the ratio of its concentration to the total pressure of the system; this pressure is known as the partial pressure of that component. 3. What is Raoult’s law? The vapor pressure of the solvent in a solution is equal to the vapor pressure of the pure solvent multiplied by its mole fraction; this is Raoult’s law. It can be expressed using mathematical formulas as follows: P1 = P1o × X1, where P1o is the vapor pressure of the pure solvent at the same temperature; P1 is the vapor pressure of the solvent in the solution; and X1 is the mole fraction of the solvent in the solution. 4. What is Henry’s law? At a constant temperature and under equilibrium conditions, the solubility of a gas in a liquid is directly proportional to its equilibrium partial pressure – this is Henry’s law. It can be expressed using a mathematical formula: P2 = KX2. Here, X2 represents the molar fraction of the gas in the liquid at equilibrium; P2 is the partial pressure of that gas above the liquid surface at equilibrium; and K is the Henry’s constant. 5. What are physical absorption and chemical absorption? If the gas dissolved in the solvent does not undergo any significant chemical reaction with the solvent, this process is called physical absorption. On the other hand, if the gas reacts chemically with the solvent or with other substances already present in the solvent after dissolving, this process is referred to as chemical absorption. 6. What is equilibrium solubility? At a certain temperature and pressure, when equilibrium is reached, the concentration of the solute in both the vapor and liquid phases no longer changes. This represents the limit at which the absorption process can proceed. The concentration of the solute in the liquid phase at the point of equilibrium is known as equilibrium solubility. 7. What is saturated vapor pressure? At a certain temperature, when the gas and liquid phases are in dynamic equilibrium, it is called a saturated state. The gas phase in this state is known as saturated vapor, and the pressure exerted by the saturated vapor is referred to as saturated vapor pressure. 8. What is evaporation? What are the operating conditions for evaporation? Evaporation is the process of concentrating a solution by heating it to cause one of its components to vaporize. Operation conditions for evaporation: The solvent in the solution must be volatile, while the solute should not be volatile; heat energy must be continuously supplied to vaporize the solvent, and the vaporized steam must be removed promptly. 9. What is distillation? What is the basis for separation by distillation? Distillation is a process that utilizes the difference in volatility of various components within a liquid mixture under certain pressures to achieve separation. Distillation separation is based on the differences in boiling points among various components. 10. What are the factors that affect absorption processes? (1) Gas flow velocity (2) Vapor/liquid ratio (3) Temperature (4) Pressure (5) Purity of the absorbent. 11. What is flooding? How can it be avoided? The phenomenon of liquid flowing back inside the tower is called flooding; when this occurs, the pressure difference across the tower increases significantly. To avoid flooding, it is first necessary to control an appropriate liquid/vapor ratio and space velocity (load). At the same time, it is necessary to prevent the liquid from foaming, improve the purity of the absorbent, and ensure that the tower plates are clean and free of contaminants. 12. What is the absorption rate? The quality of absorption can be expressed by the absorption rate; in the process of gas absorption, the absorption rate is defined as the ratio of the amount of absorbent absorbed to its original concentration in the inert gas. 13. How to improve the efficiency of tray plates? (1) Control an appropriate liquid-vapor ratio. (2) Ensure that the trays are level. (3) Prevent leakage of liquid from the trays. (4) Use an absorbent with high purity that does not form bubbles. (5) Keep the trays free from dirt and scale, and maintain an appropriate thickness of the liquid layer. 14. What is distillation? Using simple distillation to separate a mixture only allows for partial separation of the components; to obtain a product of high purity, it is necessary to employ a distillation method that involves multiple stages of partial vaporization and partial condensation – this is what is known as distillation. 15. What is the distillation section? What is the stripping section? The tray where the feed material enters is called the feed tray; the section of the tower above the feed tray is known as the distillation section, while the section of the tower below the feed tray (including the feed tray itself) is referred to as the stripping section. 16. What are the factors that affect distillation operations? How can the purity of the overhead product be improved? Factors affecting distillation: (1) There must be a reboiler at the bottom of the tower to generate steam, thereby ensuring an appropriate temperature at the bottom of the tower; (2) There must be an adequate amount of reflux at the top of the tower to ensure the purity of the overhead product; (3) The feed rate, feed composition, and feed point must be appropriate in order to maintain control over the above two aspects. (4) The pressure must be maintained at a certain level. 17. How can the purity of the distillate at the top of the tower be improved? Methods to ensure high purity at the tower top: (1) Increase the reflux flow at the top of the tower; (2) Pass fluids containing more difficult-to-vaporize components to the lower part of the tower, while it is preferable to use fluids with fewer difficult-to-vaporize components as the reflux flow at the top of the tower. 18. What are the methods for removing gases from a solution? (1) Reduced pressure (2) Heating (3) Stripping (4) Distillation 19. What is cavitation in pumps? How can it be prevented? When the absolute pressure at the pump inlet is lower than the saturated vapor pressure of the liquid, the liquid boils at that inlet, producing numerous bubbles that strike the impeller and pump casing. This causes vibration and abnormal noises in the pump, and may even lead to the detachment, cracking, and damage of the impeller. This phenomenon, in which the pump’s flow rate, head, and efficiency all decline sharply, is known as pump cavitation. To prevent cavitation in the pump, it is necessary to take into account the pump’s installation height and the liquid temperature, so that during operation the pressure at the pump inlet is greater than the saturated vapor pressure of the liquid. 20. Why is it necessary to vent a centrifugal pump before starting it? If venting is not done before starting, gas remains inside the pump casing. Since the density of gas is lower than that of liquid, the centrifugal force generated is reduced, resulting in insufficient pressure at the inlet and making it difficult to draw liquid into the pump; therefore, the pump cannot transport liquid. At the same time, if the gas is not completely expelled, gas will remain in the liquid after startup, making cavitation more likely to occur. 21. Why are most centrifugal pumps equipped with a minimum flow line? A minimum flow line ensures that a certain amount of fluid flows through the pump at all times after it is started, thereby preventing cavitation. Furthermore, when centrifugal pumps with high power are operated with the outlet valve closed, the fluid becomes increasingly hot; in severe cases, this can even damage the bearings. Installing a minimum flow line can prevent this phenomenon from occurring. 22. What are the ways heat is transferred? Heat conduction, heat radiation, and heat convection. 23. What are the ways to increase the heat transfer rate? (1) Increase the heat transfer area ； (2) Increase the average temperature difference between the cold and hot fluids ； (3) Improving the heat transfer coefficient: a. Increasing the fluid flow velocity b. Changing the flow conditions c. Taking certain proactive measures in heat exchangers where there is a phase change of the fluid, in order to minimize the thickness of the condensate film. d. Use a liquid with a high thermal conductivity as a heating agent or coolant. 24. How is heat (or cold) transferred in a heat exchanger? Heat transfer occurs in three stages: (1) The hot fluid transfers heat to the metal wall surface, through convection. (2) Heat passing through the metal wall, heat conduction. (3) Heat is transferred from the metal wall to the cold fluid through convection. 25. What are the factors that affect the heat transfer rate of a heat exchanger? (1) Heat transfer area: If certain channels in the heat exchanger become blocked during operation, the heat transfer rate decreases. (2) Heat transfer temperature difference: The heat transfer temperature is the driving force for heat exchange; a larger temperature difference results in higher heat transfer amount. (3) Heat transfer coefficient: The heat transfer coefficient is related to the flow velocity of the fluid and the cleanliness of the heat transfer surface; it is proportional to the heat load. 26. Why is counterflow commonly used for the hot and cold fluids in heat exchangers? In a heat exchanger, the average temperature difference is an indicator of the amount of heat transferred. Among counterflow, co-current, and cross-flow heat exchangers, those with counterflow configuration have the largest average temperature difference; therefore, unless there are special reasons, counterflow is the preferred arrangement in heat exchangers. 27. What is the pressure range of the operating air source for the pneumatic control valves in our factory? What is the relationship between this pressure and the output signal of the regulator? The operating air source pressure ranges from 0.02 to 0.1 MpaG, while the output range of the regulator is 0–100%. Therefore, 0% corresponds to an air source pressure of 0.02 MpaG, 50% corresponds to 0.06 MpaG, and 100% corresponds to 0.1 MpaG. 28. What are air-open and air-close valves? What symbols are used to represent them? Air-open valve: The control valve closes when no pressure signal is applied, and it opens when a pressure signal is present; it is represented by “FC”. Air shut-off valve: The control valve opens when no pressure signal is input, and it closes when a pressure signal is present. Denoted by “FO”. 29. What are the positive and negative actions of a regulator? Positive action: When the measurement signal increases, the regulating output of the regulator also increases accordingly. Reaction: As the measurement signal increases, the regulating output of the regulator decreases. 30. What are the factors that affect the accuracy of orifice plate flow meters? (1) The orifice plate is worn or clogged ； (2) The orifice plate is not installed correctly ； (3) Pressure guide tube blocked or leaking ； (4) Changes in fluid temperature cause changes in density, and the density of the fluid itself then does not match the design specifications. 31. What should be noted when switching between automatic and manual operation of a regulator? When switching from automatic to manual operation, it is important to ensure that the output signal of the regulator is suitable for manual control. Before switching the regulator back to automatic mode, it is necessary to confirm that the process being regulated maintains a certain level of stability, and that the set value matches the actual reading, before enabling automatic operation. 32. What are the properties of methanol? Methanol is the simplest of the saturated alcohols. Under normal conditions, pure methanol is a colorless, volatile flammable liquid with an odor similar to that of ethanol; it can mix with water in any proportion. Under standard conditions, methanol has a boiling point of 64.7°C, a melting point of -97.68°C, a ignition point of 464°C, a critical temperature of 240°C, and a critical pressure of 78.7 atm. At 20°C, the density of methanol is 0.791 t/m³. 33. Why is Tower T3001 divided into an upper tower and a lower tower? What is the theoretical basis for this? It is divided into an upper tower and a lower tower in order to separate methanol that has absorbed H2S from methanol that has absorbed CO2; this design is intended to meet the requirements for the regeneration of methanol. The main basis is the selectivity of solvent absorption, as the H2S concentration is low in methanol and it has a higher solubility for H2S than for CO2; furthermore, methanol that has absorbed CO2 can still absorb H2S, allowing them to be absorbed separately in the upper and lower columns. 34. Why is it necessary to draw the methanol liquid out for cooling in the upper section of Tower T3001? When methanol absorbs CO2, heat of solution is released; as the temperature rises, the solubility of CO2 in methanol decreases. When the temperature reaches a certain level, this can result in an excessive amount of CO2 in the gas coming from the top of the tower. Therefore, it is necessary to draw the methanol liquid out for cooling. 35. Why is methanol sprayed before the shifted gas enters E3001? This is because E3001 operates at low temperatures; if the shifted gas were to enter E3001 directly and then be cooled, the saturated water vapor contained in it would condense and form water, and the ice generated could block the equipment and pipelines. Spraying methanol can capture moisture and lower the freezing point of water, thereby preventing water from freezing and blocking the gas passages. 36. Why is LV-3001 placed after E3016? The methanol-water mixture coming out of V3001 contains a certain amount of CO2 gas dissolved in it; when pressure is reduced via LV-3001, the CO2 gas is released from the liquid, which results in gas blockages in the piping system. To minimize this phenomenon, LV-3001 is located after E3016, so that after throttling, the liquid immediately enters V3009 for gas-liquid separation. 37. What is the function of a demister? Which towers are equipped with demisters? A demister is also a type of separator; its main purpose is to separate the liquid carried in the gas, thereby preventing contamination of the gas and avoiding excessive loss of liquid. T3001, T3002, T3003, and T3004 are equipped with demisters. There are very strict requirements regarding the amount of liquid carried in the gas exiting these units; excessive amounts of methanol in the gas can have extremely negative effects on subsequent processes. Certain standards must be met regarding the amount of liquid carried by the gas exiting these units. 38. Why must the pressure in tower T3001 be maintained above 5.0 MpaG when establishing the methanol cycle? The reasons are: (1) A high pressure ensures a stable methanol flow rate to V3002/V3003 ； (2) If the pressure is too low, since the outlet pressure of pump P3004 is around 6.40 Mpa, this will increase the pressure difference on both sides of FV3005, causing it to lose control and making it difficult to regulate the flow rate. Meanwhile, a large pressure difference between the outlet of pump P3004 and the tower pressure will increase the methanol flow rate, exerting significant stress on the equipment. 39. What are the factors that can cause an excess of CO2 in the process gas flowing to T3001? The main ones are: (1) too low methanol circulation rate; (2) too high temperature of the methanol-depleted stream entering T3001; (3) poor regeneration efficiency at T3004; (4) low methanol absorption capacity; (5) severe fluctuations in the volume of process gas. 40. What determines the methanol circulation rate for unit 630? How can this rate be minimized? The methanol circulation rate should be set such that the CO2 level at T3001 does not exceed acceptable levels; it is necessary to reduce the temperature of the materials entering T3001 as much as possible, while simultaneously maintaining a balance of cooling capacity within the system. To minimize the circulation volume, the following points should be noted: (1) After reaching 80% load, any further increase in load must be done slowly, to ensure that the cooling capacity from the low-pressure area can be delivered in a timely manner. (2) The cooling capacity provided by the ammonia compressor to the ammonia cooler in this unit must be appropriate and not too low, in order to keep the top temperature of T3001 as low as possible. 41. What could be the reasons for an increase in the pressure difference in Tower T3001? (1) Excessively high flow rate of lean methanol ； (2) The temperature of the lean methanol is too low, causing the specific gravity of the liquid to increase and thereby increasing the column pressure drop ； (3) Gas flow velocity is too low ； (4) Blockage (or poor flow) of E3005 and E3006 causes flooding in the tower ； (5) The T3001 tray is detached, damaged, or too dirty. 42. Why can the temperature keep dropping after gas introduction with work number 630? Because methanol that has absorbed CO2 can have its temperature reduced significantly after being cooled with ammonia and then desorbed. After gas introduction, as the saturation of CO2 in methanol increases, more CO2 is released per unit volume of methanol, causing the temperature to drop continuously; after heat exchange, this results in a decrease in the temperature at the top of T3001. 43. What is the source of cooling capacity for methanol washing? (1) The ammonia refrigeration system provides the cooling capacity through liquid nitrogen supply ； (2) The cooling capacity generated after flash evaporation and stripping of high-pressure methanol rich in CO2 ； (3) The cooling capacity provided by the water cooler. 44. What is the basis for setting the pressure at V3002/V3003? It is required that the gas being analyzed contain high levels of H2 and CO and low levels of CO2; therefore, the pressure is set at 1.85 Mpa(G). 45. What is the purpose of designing the T3003 nitrogen stripping line as an inverted “U” shape? To prevent methanol liquid from flowing back into the nitrogen stripping line. 46. What is the role of nitrogen stripping at the bottom of tower T3003? What are the consequences of an excessive or insufficient amount of nitrogen? Introducing nitrogen into T3003 reduces the partial pressure of CO2 in the gas phase, thereby increasing the driving force for the separation process and allowing CO2 to be removed from methanol at lower temperatures. Within a certain range, the greater the amount of nitrogen used for stripping, the better; however, an excessive amount will lead to increased consumption of N3. An insufficient amount of nitrogen stripped will increase the load on T3004 and lead to a decrease in the H2S concentration in the gas sent to the Claus unit. Additionally, it increases the heat loss. 47. Why cannot the liquid level at the bottom of tower T3003 be too high? Otherwise, it will trigger a chain reaction that leads to the shutdown of nitrogen stripping. If the liquid level at the bottom of T3003 is higher than that in the nitrogen stripping line, liquid slugging will occur; this not only can damage the equipment but also causes the nitrogen stream carrying liquid to impact the tray plates, potentially leading to their deformation or even destruction. Additionally, when parking, the liquid level at the bottom of tower T3003 is too high, allowing methanol to easily flow back along the nitrogen stripping line. Therefore, when parking, make sure to keep the bottom level of T3003 as low as possible. 48. Why does the nitrogen stripping continue even after the gas supply is stopped at unit number 630, while the methanol cycle keeps running? This is because the methanol in the cold zone still contains a large amount of CO2 after the gas supply is stopped; if nitrogen stripping were to be halted, this large amount of CO2 would end up in tower T3004, causing overpressure in that tower. As a result, the flow rate of pump P3003 would drop significantly, and the liquid level in tower T3003 would rise sharply. 49. What precautions should be taken when venting before starting the P3001, P3002, and P3003 pumps? It is essential to close the cold engine valve during venting, as the outlet pressure of the pump is higher than the inlet pressure. If the cold engine valve remains open, the fluid at the pump’s outlet will flow back through this valve, preventing the gas inside the pump from being expelled due to the low pressure. This results in an apparent venting process that affects the proper operation of the pump. 50. What is the purpose of the V3004 design in replacing the N3 pipeline? (1) To ensure that P3004 has sufficient stable static head pressure. (2) To isolate methanol from air. 51. What are the factors that lead to low heat exchange efficiency in heat exchangers? (1) The effect of scaling; if the tube walls are scaled, it will reduce the heat transfer coefficient of the fluid ； (2) Blockages by solids or precipitates, especially in coil-type heat exchangers; if there are blockages between the shell-side tube walls, it will cause flow deviation and reduce the effective heat exchange area. 52. What is the function of the stream of methanol that flows from the bottom of T3004 to the top of T3005 via P3005? (1) It acts as a reflux stream ； (2) The water present in the recycled methanol is sent to T3005 for treatment. 53. The lower the methanol content in the wastewater at the bottom of tower C2605, the better, right? Why? No, because a lower methanol content indicates a higher temperature at the bottom of the tower, which increases the thermal load on the tower and leads to an increase in the H2O content in the gas phase at the top. This water then returns to the recycled methanol, reducing the dehydration capacity of T3005. 54. What is the basis for temperature control in T3005? The bottom temperature control in T3005 is set at the boiling point of water under the operating pressure, to ensure that the components at the bottom of the tower constitute 99.5%. 55. After the unit with serial number 630 starts operating normally, where does the methanol consumption occur primarily? It mainly takes place at the top of T3004 and at the bottom of T3005. 56. Before starting up the methanol washing unit, it is found that the water content in the methanol is too high. What measures can be taken to address this issue? (1) Establish a methanol circulation system in the system ； (2) Gradually drain the methanol at the bottom of the large container (which contains a high amount of water) into V3008, and then send it to T3005 via P3007 for dehydration ； (3) A gradual replacement with methanol can also be used; if the water content does not decrease during the dehydration process, it is necessary to check for any leaks. 57. Why can E3011 and E3015 transfer heat effectively into the tower despite being located outside T3004 and T3005? It employs a natural circulation heating method: the tubes inside the heat exchanger are positioned above the liquid level, and the temperature of the heat source is higher than the boiling point of methanol. When the methanol in these tubes is heated, it continuously vaporizes and rises. Since the density of methanol vapor is much lower than that of liquid methanol, this density difference creates a driving force that causes the methanol to keep vaporizing and rising into the tower. The liquid methanol at the bottom of the tower then continuously flows into the heat exchanger to be heated by the steam, thus establishing a natural circulation that ensures continuous heating of the methanol inside the tower. 58. What are the effects of increasing or decreasing the pressure in T3003? What are the advantages and disadvantages? Increasing the pressure: (1) It shifts the load at which CO2 is separated in the T3003 tower downward; (2) The amount of CO2 separated in the T3003 tower decreases, and it moves to the T3004 tower for separation, resulting in a loss of some cooling capacity, which ultimately causes the temperature at the top of the T3001 tower to rise slightly. Reduce pressure: (1) Raise the load for CO2 separation in Tower T3003; (2) An increased amount of CO2 being separated in Tower CT3003 can lead to excessive H2S levels in the exhaust gas. At the same time, due to the decrease in pressure, the inlet pressures of pumps P3001 and P3003 also drop, making cavitation and gas entrapment more likely to occur. 59. By what phenomena can one determine whether the pump’s filter screen is clogged? (1) The inlet pressure of the pump decreases and experiences significant fluctuations ； (2) The opening degree of the pump outlet control valve increased significantly, and the liquid level in the tower tank ahead of the pump rose slowly ； (3) The motor current increases. 60. How is the inlet pressure of C3001 maintained constant? It is controlled by PICA3003, which regulates PV3003.2 and PV3003.1. When the inlet pressure of C3001 drops, PICA3003 automatically causes PV3003.1 to open, allowing some of the process gas from the outlet of C3001 to be introduced into the inlet pipeline of C3001 ； When the inlet pressure of C3001 increases, PICA3003 automatically controls PV3003.2 to open, allowing some of the flash vapor to be sent to the cold flare via PV3003.2. 61. What are the methods for drying the system after water transportation? (1) Nitrogen drying method; (2) Using methanol in a cycle to remove moisture. 62. How can a short-term shutdown help to significantly reduce the time required before gas can be introduced again in unit 630? After gas is removed from unit 630, the circulation in the cooling area should be stopped promptly; this results in a lower temperature of the methanol in the system, and since the methanol contains a large amount of CO2, it stores a significant amount of heat. Once the process gas meets the required standards, worker number 630 initiates the methanol circulation. Once the methanol at the top of the tower reaches the bottom, gas flow is started. This approach ensures that the temperature at the top of tower T3001 remains low, facilitating rapid absorption and quick replenishment of cooling capacity, thereby allowing it to reach normal operating capacity swiftly and significantly reducing the time required for gas flow to begin. 63. Why can the load that can be handled during winter be higher than in summer? This is because the temperature of the cooling water is much lower in winter compared to summer, resulting in a significant decrease in the temperature of the transformed gas. As a consequence, the efficiency of the E3018 water cooler increases, which is equivalent to providing additional cooling capacity for unit 630. Additionally, due to the lower ambient temperatures, the cooling losses of low-temperature equipment are reduced, thereby helping to mitigate the impact of insufficient cooling capacity on the ability to increase the load. 64. Why is the temperature at the top of T3001 lower when the methanol circulation rate is lower? When the system load remains constant, the amount of cooling capacity available to the system is essentially fixed; a higher methanol circulation rate results in less cooling per unit volume of methanol, so the temperature rises. Furthermore, due to the large circulation volume of methanol and the temperature difference in the heat exchangers, cooling loss increases. Therefore, a lower methanol circulation volume results in more cooling capacity per unit volume of methanol, as well as reduced cooling losses, which in turn lowers the temperature of the methanol going to the top of T3001. 65. Why is methanol sprayed before gas introduction at 630, and why is nitrogen sparging started about half an hour in advance? Methanol is sprayed first to ensure that a certain layer of methanol liquid is formed in the pipes as well as within E3001 and V3001; this also helps to thoroughly wet the walls of the equipment and pipelines, so that condensate water and methanol can mix thoroughly everywhere after gas is introduced. Gas lift nitrogen is introduced first in order to pre-cool E3001, ensuring that the temperature of V3001 does not rise significantly during gas introduction, thereby reducing the amount of saturated water carried into T3001. 66. What conditions must be met before starting gas flow in unit 630? (1) The methanol circulation rate of 230 m³/h in the system must operate stably. (2) The temperature of the methanol entering T3001 should be around -35°C. (3) The regeneration system of T3004 must be functioning properly. (4) The methanol/water separation system of T3005 must also be operating correctly. (5) The methanol spraying system and the nitrogen stripping system must have been in operation for more than half an hour. (6) The spray water used for removing NH3 from the converter must also be in use. 67. Which liquid levels change after gas flow is started in unit 630? Why? How can system stability be maintained? After gas flow is initiated, the resistance across the tray columns increases, resulting in the formation of a certain layer of liquid within the trays and downcomers. This leads to a decrease in the amount of methanol exiting the column, causing the liquid level in V3004 to drop. To prevent the P3004 pump from shutting down, it is necessary to reduce the liquid levels in all the tanks at the appropriate time, so as to avoid an excessively low liquid level in V3004 that could cause the P3004 pump to shut down due to interlock mechanisms. After gas introduction, methanol in C3001 absorbs CO2, causing its volume to increase significantly after exiting the tower; this in turn leads to a substantial rise in the liquid level in vessel V3004. Therefore, it is necessary to adjust the liquid level promptly at this stage in order to maintain system stability. 68. Can it be determined whether the pump’s filter screen is clogged from those phenomena? ① The pressure at the pump inlet decreases and fluctuates significantly. ② The opening of the control valve downstream of the pump increased significantly, causing the liquid level in the tank upstream of the pump to rise slowly. ③ The motor current decreases. 69. Describe the procedures to be followed for work order No. 630 in the event of a plant-wide power outage. Central control: ① Manually control all LVs and FVs to store methanol in each container. ②Stop the steam to E3011 and E3015. (FV3006 FV3011 off) ③ Stop supplying ammonia to E3004, E3005, E3003, and 3013. ④Stop gas supply and remove nitrogen (turn off FV3004). On-site actions: ① Close all on-site LV and FV shut-off valves, starting with those at high pressure and then those at low pressure. ②Close all nitrogen valves. ③Close valve T3005 to shut off the main valve at T3004. 70. Why is it necessary to vent air from a centrifugal pump before starting it? If ventilation is not carried out before starting, gas remains inside the pump casing. Since the density of gas is lower than that of liquid, the centrifugal force generated is reduced, resulting in insufficient pressure at the suction inlet and making it difficult to draw liquid into the pump; therefore, the liquid cannot be transported. At the same time, if the gas is not completely expelled, air will remain in the liquid after startup, which can easily lead to cavitation. Key point: The pump suction pressure is insufficient, preventing liquid delivery; cavitation has occurred. 71. What precautions should be taken for venting before starting pumps P3001, P3002, and P3003? Be sure to close the chiller valve when venting, especially the P3003 pump. Since the outlet pressure of the pump is higher than the inlet pressure, the cooler valve opens, and the liquid at the pump’s outlet flows back through this valve. This results in low gas pressure inside the pump, preventing the gas from being expelled and creating an illusion of exhaust, which affects the proper operation of the pump. 72. Why is the cold flare in the methanol washing section controlled to be above 5°C by TIC3053 before it enters the permanent flame flare? To reduce costs, the constant-flame torch pipes are made of ordinary steel, which is not resistant to low temperatures. The material used for cold torches, on the other hand, is low-temperature resistant steel; therefore, low-pressure steam is introduced before low-temperature gases enter the constant-flame torch pipes in order to prevent the pipes from being damaged due to excessively low temperatures. Q&A on the Operation of the Sulfur Recovery Unit 1. What is the purpose of setting up the sulfur recovery unit? The raw coal used in our plant contains a high sulfur content, and if not recovered, it will pollute the environment. This unit employs the Claus sulfur recovery process to recover hydrogen sulfide-rich gases and convert them into solid sulfur flakes. The solid sulfur produced has a wide range of uses and is also economically viable. 2. What is the reaction principle of the Klaus sulfur recovery process? H2S + 1/2O2 → S + H2O (1)
H2S + 3/2O2 → SO2 + H2O (2)
2H2S + SO2 → 3S + 2H2O (3)
Reactions (1) and (2) take place in a combustion chamber, at temperatures of 1150°C–1300°C and pressures of 0.06 MPa; under strict control of the gas flow rate, hydrogen sulfide is burned to form sulfur dioxide. A mixed gas with a ratio of (H2S + CS2)/SO2 of 2/1 is provided for the catalytic reaction. This gas passes through an Al2O3-based catalyst to produce elemental sulfur according to reaction (3). 3. What are the main physical properties of sulfur? The molecular weight is 32, the melting point is 120°C, the specific gravity is 1.96–2.07, the temperature in the combustion chamber is 232°C, and the solid has a yellow color. 4. Describe the steps for cold start Main steps: (1) Confirmation of equipment, pipelines, instruments, electrical appliances, and cooling water conditions. (2) Fill the liquid sulfur vessel with sulfur until it overflows. (3) Start the reaction gas blower. (4) Light the H2S boiler and heat it using FG or LPG. (5) Introduce acidic gases and make corresponding adjustments to the operating conditions. (6) When the sulfur tank is equipped for transporting liquid sulfur, start the sulfur granulator and the sulfur pump. 5. What are the conditions for hot-starting sulfur recovery? (1) The furnace temperature of E6001 should be above 1000°C. (2) The catalyst temperature inside R6001 should be above 200°C. (3) The temperature of each unit should be above 120°C. Once these three conditions are met, acidic gases can be introduced. 6. What are the specific steps for igniting the device when it is being heated? See the \"Operation Manual\" or \"Operating Procedures.\" 7. What are the precautions to take during the heating up of the device? (1) Control the ratio of LPG to FG air properly. (2) The oxygen content in the outlet gas of Channel 2 of E6001 should be analyzed regularly, and it should be kept below 0.1~0.2% VOL. (3) When the temperature of the E6001 combustion gas exceeds 1200°C, nitrogen, S4, or steam can be introduced to control the furnace temperature and keep it below 1300°C. 8. What are the respective air-to-fuel ratios required when burning LPG, FG, and hydrogen sulfide-rich gases in E6001? Where is this ratio adjustment implemented? The combustion ratio of LPG to air volume should be controlled at 27:1. The combustion ratio of FG to air volume should be controlled at 1:1. The combustion ratio of hydrogen sulfide-rich gas to air should be maintained at 2.4:1 or higher, and this ratio is achieved in accordance with FICA6004. 9. What is the purpose of setting FICA6005? The amount of air required for the Claus reaction is adjusted by FICA6004 based on a ratio. The settings of FICA6005 are adjusted to ensure that the H2S/SO2 ratio in the exhaust gas exiting V6005 is 2:1, with fine adjustments being made using analyzer AICA6001 and FICA6005. 10. What is the model of the sulfur recovery catalyst? Model: Ø4~6mm spherical LS—971, Ø4~6mm spherical LS—300, Ø3mm spherical LS—951. 11. Why are steam injectors X6002A/B required? Since there is still some dissolved gas in the molten sulfur, it is released in V6007A/B after depressurization; to ensure the quality of the sulfur, these gases need to be removed. Since the pressure inside V6007A/B is close to atmospheric pressure, it is difficult to discharge the gas directly, so evacuation facilities X6002A/B are required. 12. What are the conditions that cause a shutdown of the sulfur recovery unit? What is the cascading effect? The interlock conditions are: (1) The sulfur recovery unit stops when the BS—6001 flame detector detects that the flame in the furnace has gone out. (2) This unit shall be shut down when the acid gas flow rate FI6001 in this unit is at low-low level. (3) This section shall be shut down when the level of the waste heat boiler is at low-low. (4) This section shall be shut down when the air pressure in the hydrogen sulfide furnace is high. (5) This section stops when the blower outlet pressure is extremely low. (6) The manual stop button is used to stop the operation of this section. Sequential consequences: (1) HIC6001 and PV6002 turn on; (2) HIC6002, FV6002, FV6004, FV6005, FV6007, and AV6002 turn on; (3) The blower stops. What is the purpose of the sequential control in the sulfur slicing machine system? Try to explain them separately? Liquid sulfur solidifies very easily; therefore, in the event of a malfunction in the sulfur slicing machine, the supply of liquid sulfur should be stopped immediately to prevent it from accumulating in large chunks on the machine and damaging it. When the crusher in the slicing machine fails, the following actions occur: (1) The operating sulfur pump stops working. (2) Close the sulfur export valves HV6042A/B. 14. Discuss the importance of the heat tracing steam in this section. The freezing point of liquid sulfur is 120°C. Although in the areas of this section where sulfur is present, the actual temperature is always several dozen degrees above the freezing point, without insulation measures, the temperature of the liquid sulfur along the pipelines will gradually drop, eventually leading to solidification and blockage of the equipment. Once a blockage occurs, it becomes very difficult to clear it. Therefore, in all areas of this section where sulfur is present, insulation steam jackets or steam coils are installed to ensure that the temperature remains above the freezing point at all times. Checking whether the insulation steam is unobstructed is one of the key aspects of on-site inspections, especially in winter. 15. When should auxiliary combustion be used for E6001? When the amount of acidic gases entering this section or the H2S content decreases, the temperature in the furnace of waste heat boiler E6001 may drop below 1100°C; burning acidic gases alone is not sufficient to maintain this temperature. In such cases, it is appropriate to use auxiliary combustion by introducing liquefied petroleum gas (LPG) or fuel gas (FG) into the furnace to enhance combustion.