Training materials and technical Q&A on transformation

Some materials prepared by me. 11. Briefly describe the principle and purpose of transformation reactions. Answer: The so-called transformation refers to the chemical reaction in which CO and steam in syngas react to produce H2 under certain temperature, pressure, and catalyst conditions. Chemical equation: CO + H2O = CO2 + H2 + Q. Purpose: First, to convert CO into hydrogen as much as possible; second, to transform the organic sulfides that are difficult to remove from water gas into inorganic sulfides such as H2S, which are easier to eliminate. 12. Function of the separator tank at the converter inlet. Answer: (1) Remove some of the condensate water. (2) Remove some dust, carbon black and other solid impurities, and adsorb As, Cl‑, etc. (3) Carry away some ammonium salts. 13. The main function of the pre-transformer reactor. Answer: (1) The reactor is filled with a protective agent, which is mainly spent catalyst or low-temperature catalyst. It serves to block and filter solid impurities such as coal dust and carbon black, as well as to adsorb components like As and Cl‑ that are toxic to the catalyst, thereby protecting the activity of the sulfur-resistant shift catalyst, preventing poisoning, and extending its lifespan. (2) It has a certain capacity for transformation, capable of converting part of the carbon dioxide to reduce the reactions in the rear section and ensure compliance. (3) Provide part of the reaction heat for medium transformation. 14. Briefly describe the principle and purpose of transformation reactions. Answer: The so-called transformation refers to the chemical reaction in which CO and steam in syngas react to produce H2 under certain temperature, pressure, and catalyst conditions. Chemical equation: CO + H2O = CO2 + H2 + Q. Purpose: First, to convert CO into hydrogen as much as possible; second, to transform the organic sulfides that are difficult to remove from water gas into inorganic sulfides such as H2S, which are easier to eliminate. 15 Why are two medium-temperature conversion stages and one low-temperature conversion stage required? Answer: It is mainly to address the issues of rate and speed – converting most of the CO into CO2 at a high temperature at a very fast pace, and converting CO into hydrogen as much as possible at a lower temperature. If only medium-temperature conversion is used, a large amount of catalyst is required, and significant amounts of water vapor are consumed. By using low-temperature conversion, the total amount of catalyst needed is reduced, as is the amount of water vapor consumed. This results in higher heat recovery efficiency and fewer energy losses; moreover, the heat exchange area required for heat exchange equipment can be reduced by about 1/2, which helps to save costs and yield better economic benefits. 16. Why should a sulfur-resistant catalyst be chosen for the conversion? Answer: Because the H2S content in the syngas produced by the vaporization furnace is 0.15%. If zinc oxide desulfurization is used before the transformation, the amount of zinc oxide required is too large, resulting in high operating costs and poor economic efficiency. Choosing a sulfur-resistant catalyst is beneficial for process design, helps to overcome hot and cold problems, facilitates heat balance, and improves thermal efficiency. 17. Why is a certain amount of hydrogen sulfide required when converting the incoming gas? Answer: The conversion catalyst exhibits relatively high activity only in its sulfided state, and the sulfidation reaction is a reversible reaction. If the hydrogen sulfide concentration in the gas is low, desulfurization of the catalyst occurs, reducing it and causing a significant drop in its activity. Therefore, the sulfur content in the process gas is required to be greater than 0.01%. 18. Types and characteristics of sulfur-resistant catalysts. Answer: Medium-temperature shift catalysts are classified into two main categories based on their composition: iron-chromium series and cobalt-molybdenum series. Iron-based catalysts have high catalytic activity and good mechanical strength; they can tolerate small amounts of sulfides, possess excellent heat resistance, a long service life, and are relatively low in cost ； The outstanding feature of cobalt-molybdenum catalysts is their good resistance to sulfur, making them suitable for gas containing high levels of sulfides, but they are expensive. Major series include QCS from Qilu, QBD from Qingdao Lianxin, C25 from Panjin, and XH from Xiamen University, among others. 19. Properties of the Qilu QCS-01 conversion catalyst. Answer: The QCS-01 catalyst is a cobalt-molybdenum-based sulfur-tolerant CO shift catalyst that contains novel components and special additives. The catalyst possesses excellent mechanical strength ； The catalyst features high activity, good selectivity, and excellent stability ； The catalyst has strong adaptability to high space velocities and high water vapor ratios, offers considerable operational flexibility, and has a long service life, typically ranging from 3 to 8 years. Suitable for shift processes that produce gas via the partial oxidation of heavy oil or residue, or gasification, to promote the shift reaction of sulfur-containing gases. Temperature: 200–500°C; Pressure: 1.0–10.0 Mpa; Space velocity: 1000–4000 h-1 (for dry gas, up to 6000 h-1); Water-gas ratio: 0.3–2.0; Sulfur content in the process gas: ≥0.01% (v/v). Physical and chemical properties: Color and shape; Unit: The oxidation state is light green, and it is in strip form. External dimensions: mm; Diameter Ф3.5–4.0. Bulk density: kg/l, 0.70–0.80. Crushing strength: N/cm, ≥100 (average value). Support: Mg–Al–Ti spinel; Active component: Co–Mo; Additives: rare earths, 20%. Properties of Qilu QCS-03 conversion catalyst. Answer: The QCS-03 catalyst is a second-generation cobalt-molybdenum-based sulfur-tolerant carbon monoxide shift catalyst that contains novel components and special additives. The catalyst possesses excellent mechanical strength ； The catalyst features high activity, good selectivity, and excellent stability ； The catalyst has strong adaptability to high space velocities and high water vapor ratios, offers considerable operational flexibility, and has a long service life, typically ranging from 3 to 8 years. Suitable for shift processes that produce gas via the partial oxidation of heavy oil or residue, or gasification, to promote the shift reaction of sulfur-containing gases. Temperature: 200–500°C; Pressure: 1.0–10.0 Mpa; Space velocity: 1000–4000 h-1 (for dry gas, up to 6000 h-1); Water-gas ratio: 0.3–2.0; Sulfur content in the process gas: ≥0.01% (v/v). Physical and chemical properties: Color and shape; Unit: The oxidation state is light green, and it is in strip form. External dimensions: mm; Diameter Ф3.5–4.0. Bulk density: kg/l, 0.80–0.90. Crushing strength: N/cm, ≥140 (average value). Matrix: Mg--Al--Ti spinel; Active components: Co--Mo; Additives: m/m, rare earths 21. Principle of presulfidation reaction. Answer: The conversion catalysts QCS-01 and QCS-03 are cobalt-molybdenum-based sulfur-resistant conversion catalysts. These new catalysts are in an oxidized state, and they must be sulfided before use; only sulfided catalysts are active. The main reaction equations for the sulfidation process are as follows: CoO + H2S = CoS + H2O + 3.2 Kcal; MoO3 + 2H2S + H2 = MoS2 + 3H2O + 11.5 Kcal. 22. Why do cobalt-molybdenum-based sulfur-resistant catalysts need to be sulfided before use? Answer: Since the actual active components in cobalt-molybdenum catalysts are COS and MOS2, sulfidation is necessary for them to possess 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. So it needs to be vulcanized before use. 23. Catalyst presulfurization method. Answer: Catalyst presulfurization is generally divided into wet presulfurization and dry presulfurization. Wet pre-vulcanization is the pre-vulcanization using a vulcanizing agent and distillate oil in a liquid or semi-liquid state in the presence of hydrogen. Dry presulfurization is a presulfurization process that is carried out in the presence of hydrogen, either by directly using H2S at a certain concentration or by injecting organic sulfides into the circulating hydrogen. Wet pre-vulcanization is further divided into two types: in one type, the sulfur required for the catalyst vulcanization process is added from the outside to carry out pre-vulcanization ； Another method is pre-vulcanization using the sulfur present in the vulcanizing oil itself. The sulfur required for the presulfurization process of this device is supplied externally by adding dimethyldisulfide (DMDS) or CS2. 24. What are the commonly used vulcanizing agents? Answer. There is hydrogen sulfide, dimethyldisulfide (DMDS), and CS2. 25. What are the main active components and support of a conversion catalyst? Answer: The active components of the catalyst are CoO3 and MoO3; the support is (MgO, Al2O3), with the remaining amount being a new substance. 26. What issues should be considered when introducing gas to a conversion catalyst for the first time? Answer: (1) When introducing air into the system, the steam pipe heating and the heat exchanger must be preheated properly, and the drain discharge must also be satisfactory. Sufficient amount of nitrogen should be provided to prevent overheating during gas connection. (2) Maintain the catalyst bed temperature at no less than 270°C. (3) The pressurization process should be slow; when the pressure reaches 1.0–1.5 Mpa, it is advisable to operate for 3–4 hours before gradually increasing the pressure, so that the catalyst can continue to undergo deep sulfidation under pressure and thus exhibit better catalytic activity. 27. What precautions should be taken when sulfiding a conversion catalyst? Answer: (1) In principle, no temperature increase is applied during vulcanization to prevent overheating during the vulcanization process. Since the method of adding hydrogen and disulfide involves cyclic sulfidation, only a small amount of gas is released from the system during the sulfidation process. Carbon disulfide needs to be hydrolyzed and dehydrogenated on the surface of the catalyst; therefore, a certain level of hydrogen must be present in the recycled gas. It is necessary to analyze the hydrogen content in the recycled gas before adding carbon disulfide, and after each addition of carbon disulfide, the hydrogen content at the inlet of the recycler right after the shift reactor should be analyzed promptly. The hydrogen content after the shift reactor is required to be between 10% and 15%. (2) During sulfidation, the bed space velocity must be strictly controlled at 400–500 h-1 to ensure thorough contact and reaction between the catalyst and the sulfiding agent. (3) If the bed temperature rises too rapidly and exceeds 450°C, CS2 supply must be stopped immediately, the inlet temperature of N2 should be reduced, and the flow rate of the circulating gas increased to cool down the bed. (4) There must be a dedicated person in charge of adding CS2, and the addition rate of CS2 should be slow and steady to prevent an excess of CS2 from causing overheating of the bed layer or condensation and adsorption within the system; it is advisable to keep the H2S level at the outlet at no more than 15 g/m3. After the sulfidation process is complete, the system is thoroughly purged with nitrogen to ensure it meets the required standards; H2S levels are zero in all samples taken for analysis, and the system is maintained at positive pressure. 28. What precautions should be taken when loading the conversion catalyst? Answer: (1) Take moisture-proof measures during transportation and loading to prevent the catalyst from getting wet. (2) During transportation, screening, lifting, and filling, handle with care; do not drop or roll the catalyst tanks. (3) During loading, the specified falling height must also not be exceeded to prevent the catalyst from being crushed. (4) When spreading the contact coal into the equipment, it should be distributed evenly across the entire surface; it is not allowed to be spread in one area and piled up in mounds before being raked apart, to prevent dust accumulation and uneven resistance. The amount of catalyst to be filled must comply with the specifications; it should neither be insufficient nor excessive. (5) When working inside the equipment, be sure to take care not to damage the internal components, and secure the area around the thermocouple tube. 29. How to extend the lifespan of conversion catalysts. Answer: 1. During normal operation, while meeting the requirements for CO content in the exhaust gas, try to keep the inlet temperature as low as possible (30°C above the dew point) ； 2. Prevent overheating, overpressure, and overload, as well as prevent the process gas from dropping to its dew point temperature ； 3. Control the liquid level in the inlet separator to prevent water carryover ； 4. Prevent toxic substances from entering the reactor. 5. Appropriate water vapor ratio. 6. The catalyst loading results in good sulfidation effects. 30. Briefly describe the measures to prevent catalyst damage during parking. Answer: (1) When starting the compressor to establish a circulation, it should be done when the load on the equipment is low, ensuring smooth operation ； (2) When stopping feeding, nitrogen should be used to displace the air promptly ； (3) Control the cooling rate of the reactor ； (4) The pressure reduction during parking should be gradual. (5) Be careful to prevent water vapor from condensing during cooling. 31. Which factors affect the load of the conversion reactor? Answer: (1) Catalyst performance ； (2) Reaction heat ； (3) Reaction space velocity ； (4) Preheating temperature of raw materials ； (5) Quality of raw materials ； (6) Pressure difference in the reactor (7) Heat distribution in the reactor. 32. Write the equation for the catalyst sulfidation reaction? Answer: (1) Sulfidation reactions: CoO + H2S → CoS + H2O; MoO3 + 2H2S + H2 → MoS2 + 3H2O. (2) Side reactions: Transformation reaction: CO + H2O(g) → CO2 + H2; Methanation reactions: CO + 3H2 → CH4 + H2O; CO2 + 4H2 → CH4 + 2H2O. 33. State the operating temperatures and water vapor ratios for R2101, R2102, R2103, and R2104 Answer: The operating temperature at the inlet of the pre-conversion reactor is around 280–310°C. The operating temperature of Reactor No. 1 is around 310–415°C, while that of Reactor No. 2 is around 248–267°C. The operating temperature of the low-temperature conversion reactor is around 240–241.9°C. The H2O/dry gas ratio in the pre-conversion reactor is 1.51; in Reactor No. 1 it is 1.28, at the inlet of Reactor No. 2 it is 0.80, and at the inlet of the low-temperature conversion reactor it is 0.73. The overall CO conversion rate is 98.60%. The CO content in the transformed gas at the low-temperature outlet is ≤0.4% (on a dry basis). 37. What measures can be taken to improve the conversion rate of transformations? Answer: (1) Increase the temperature at the reactor inlet and outlet ； Appropriately increase the water-to-vapor ratio ； (2) Reduce the temperature difference in the reactor ； (3) Select a catalyst with high activity ； (4) Use high-quality raw materials. 38. What are the main factors that affect the transformation effect? Answer: (1) Catalyst activity, (2) Temperature, (3) Space velocity, (4) Water vapor ratio, (5) Hydrogen sulfide concentration, (6) Properties of the feedstock, (7) Bed pressure drop. 39. What is sulfur capacity? Answer: Sulfur capacity refers to the weight of sulfur that can be absorbed by each unit weight of desulfurizing agent. Saturated sulfur capacity is, under certain experimental conditions, the maximum amount of sulfur that can be absorbed by a unit weight of desulfurizing agent. In other words, when the sulfur content in the feed gas entering the desulfurizer and that in the gas exiting the desulfurizer is equal, the desulfurizer can no longer absorb sulfur. The sulfur capacity of the desulfurizer after it has been removed is called the saturated sulfur capacity. Penetration sulfur capacity is the weight of sulfur that a desulfurizer can absorb under certain operating conditions, while ensuring the required purity levels of the process. In other words, when the sulfur content in the process gas exiting the system exceeds the specified purity threshold, all of the waste desulfurizing agent is immediately removed, and the sulfur capacity determined from an average sample is referred to as the penetration sulfur capacity. Generally, the product manual will specify the weight penetration sulfur capacity under certain operating conditions. Theoretical sulfur capacity is the sulfur capacity calculated based on its chemical reaction equation. 40. What is sulfur penetration? Answer: During the desulfurization process, the saturated zone in the upper layer continues to expand; the absorption zone in the middle layer remains essentially unchanged but shifts downward; the purification zone in the lower layer gradually shrinks until it eventually disappears. At this point, the sulfur content at the outlet of the desulfurization reactor increases rapidly, exceeding the specified limits – this phenomenon is known as sulfur penetration. 41. Briefly describe the properties of zinc oxide desulfurization agents. Zinc oxide desulfurizers are classified according to their operating temperature range: high-temperature (100–300 degrees) zinc oxide desulfurizers, and low-temperature (30–120 degrees) zinc oxide desulfurizers. The zinc oxide content in high-temperature zinc oxide desulfurizers is greater than 90%; examples of such products include T305\T306\JX-4C, etc ； The zinc oxide content of the zinc oxide desulfurizer used at normal temperature is 70%, with models such as KT310\T307\JX-4D, etc. 42. What are the main factors affecting zinc oxide desulfurization? Answer: (1) The properties of the desulfurization agent itself, temperature, space velocity, water vapor ratio, and the type and concentration of sulfides. 43. Why is zinc oxide desulfurization necessary before methanation? Answer: The main active component of methanation catalysts is nickel, with active alumina and magnesium oxide serving as carriers. Before use, the catalysts must be activated by reducing nickel oxide to nickel in order to become active. Hydrogen sulfide reacts with nickel to form nickel sulfide. If a methanation catalyst absorbs 0.1% sulfur and 0.05% chlorine, it loses most of its activity and becomes poisoned. 44. Principle of zinc oxide desulfurization. Answer: At certain temperatures and pressures, zinc oxide can react with H2S to form ZnS, which is difficult to dissociate. ZnO can also absorb various organic sulfides. The chemical reaction is: ZnO + H2S = ZnS + H2O. 45. Effect of temperature on zinc oxide desulfurization. Answer: The zinc oxide desulfurization process is exothermic, but higher temperatures are more conducive to improving the desulfurization efficiency, as some organic sulfur compounds can be converted into inorganic sulfur at higher temperatures. Additionally, the sulfur capacity of the desulfurizing agent increases with temperature; raising the temperature can enhance this capacity, especially towards the end of its usage life. However, temperatures above 420°C can cause hydrocarbons to crack and form carbon deposits. 46. Effect of space velocity on zinc oxide desulfurization. Answer: Provided there is sufficient linear velocity and no gas film effect, using a lower space velocity is beneficial for improving desulfurization efficiency. But the size and utilization rate of the equipment also need to be taken into consideration. The typical space velocity range is 1000–2000 h-1, while the liquid space velocity is 1–6 h-1. 47. What are the characteristics of zinc oxide desulfurization? Answer: (1) Zinc oxide can directly absorb inorganic sulfur. (2) In the presence of hydrogen, some organic sulfur can be converted into inorganic sulfur. (3) It has a high sulfur capacity and good absorption performance, enabling the sulfur content in the feed gas to be reduced to below 0.2×10-6. (4) It has a low conversion capacity for thiophene and its derivatives, and cannot be used alone; it must be used in series with a hydrodesulfurization catalyst. (5) It cannot be regenerated and is expensive. 48. Reasons for unqualified zinc oxide desulfurization gas and treatment methods. Answer: (1) Reasons for the unsatisfactory sulfur content in the desulfurized gas: (1) The sulfur content in the gas entering the zinc oxide oxidation reactor is above the specified limit. 　　 (2) The reactor bed temperature is too low. (3) Reactor bed offset flow, desulfurizer sulfur penetration. (4) Excessive load. 　　(II) Corresponding treatment methods: 　　 (1) Switch to raw materials with sulfur content within the specified limits, stabilize pressure and flow rates, and increase the hydrogen supply ； 　　 (2) Increase the outlet temperature of Furnace-1 to keep the desulfurization bed temperature at around 350°C ； 　　 (3) Replace with a new desulfurizer. (4 Reduce the load. 49. Properties of ZnO: Answer: (1) ZnO cannot completely decompose certain non-reactive sulfides, such as cyclic compounds like thiophene; these organic sulfur compounds require the use of cobalt-molybdenum catalysts along with H2 for conversion ； (2) The ZnO reaction is controlled by internal diffusion; when the concentration of sulfides in the incoming gas is high, internal diffusion increases, causing the ZnO near the inlet to become saturated with sulfur first. Over time, this saturated layer expands, and sulfur leakage occurs near the outlet. When the sulfur content at the outlet exceeds 1 ppm, it is considered that sulfur has penetrated. 50. Precautions for using ZnO. Answer: (1) ZnO is used for desulfurization, but it has low strength, with a maximum free fall distance of <600 mm ； (2) Never allow ZnO to come into contact with steam condensate, otherwise a hydration reaction will occur, causing ZnO to crumble and break down ； (3) In the presence of H2O and CO2 contained in the raw materials, ZnO can form basic zinc carbonate and zinc carbonate. Therefore, the gas-to-air ratio must not exceed 0.3. 51. Principles and purposes of the methanation reaction. Answer: Principle: Methanation refers to the chemical reaction in which CO, CO2, and H2 present in syngas undergo a reaction to produce methane under certain temperature, pressure conditions, and in the presence of a catalyst. Methanation is divided into two types: trace methanation and bulk methanation. The purpose of the methanation reaction is to completely remove carbon-containing oxides from syngas, as they are harmful substances for synthesis catalysts or downstream hydrogenation processes. Through the catalytic action of the catalyst, carbon oxides are reduced to the inert gas CH4, thereby eliminating their toxic effect on the synthesis catalyst and achieving complete purification. The methanation reactions are as follows: CO + 3H2 → CH4 + H2O + heat; CO2 + 4H2 → CH4 + 2H2O + heat. Both of these reactions are highly exothermic; for every 1% (by molecules) of CO and CO2 in the inlet gas, the theoretical temperature increase is 72°C and 60°C respectively. 52. Why is desulfurization necessary for the methaneation feed gas? Answer: To prevent excessive sulfur from entering the furnace and poisoning the catalyst. The catalyst loses much of its activity when it adsorbs 0.1–0.2% sulfur; absorption of 0.3% sulfur results in almost complete deactivation. 53. The main active components and carriers of methane catalysts. Answer: The main active component of methaneation catalysts is nickel, with carriers such as activated alumina and magnesium oxide; rare earth elements (RE2O3) are used as promoters. 54. Why is heating and reduction necessary before using a methaneation catalyst? What chemical reactions occur during the reduction process? Answer: Before use, the methanation catalyst exists in the form of nickel oxide; therefore, it must be reduced and activated before use. As the reducing agents (H2, CO) are oxidized, NiO in the multi-component catalyst is reduced to active metallic nickel, and pores are formed within the catalyst during this reduction process. Al2O3, on the other hand, does not get reduced; it serves to separate and support the catalyst, allowing nickel to be in a uniformly dispersed microcrystalline state. As a result, the catalyst gains a larger specific surface area, as well as higher activity and thermal stability. The following chemical reactions occur during the reduction process: NiO + H2 == Ni + H2O; NiO + CO == NiO + CO2. 55. How to determine the end point of reduction in a methanation catalyst? Answer: (1) The concentration of CO + CO2 in the gas exiting the methanation unit is ≤10 ppm; (2) No condensate is discharged from the outlet of the methanation water separator; (3) The H2 concentration in the gas entering and exiting the methanation unit is essentially the same; (4) The temperature at the hot spot in the catalyst bed remains constant at 400–420°C for 6–8 hours or more. 56. How do methane catalysts prevent the formation of nickel carbonyl? Answer: While driving the process, heat it to 300°C using a gas free of CO (such as N2), and then introduce the process gas; or use the process gas itself to raise the temperature above 200°C as quickly as possible. When shutting down the system, lower the temperature below 200°C, and use a gas free of CO to displace and remove the process gas. 57. Properties of methane Answer: Methane is a colorless and odorless gas. Its solubility is such that it is slightly soluble in water, but soluble in alcohol and ether. Density (at standard conditions): 0.717 grams per liter; boiling point: -161.5°C; melting point: -182.48°C. Heat of combustion (kJ/mol): 889.5, Critical temperature (°C): -82.6, Critical pressure (MPA): 4.59. Flash point (°C): -188, Ignition temperature (°C): 538. Under certain conditions, methane can undergo halogenation reactions (with Cl2, Br2) and thermal decomposition (into C, H2, C2H2). 58. How to extend the service life of methanation catalysts? Answer: (1) Prevent poisons such as sulfur, arsenic, and halogens from entering the furnace and poisoning the catalyst. (2) Stable transformation and decarburization operations to prevent overheating of the methanation reactor caused by excessive levels of CO and CO2. (3) During temporary shutdown, the temperature of the methanation reactor bed must remain above 200°C; the inlet valve should be closed, and if necessary, a blind flange should be installed or nitrogen should be introduced to prevent CO from the process gas from entering the reactor and reacting with the active nickel in the catalyst to form nickel carbonyl. (4) For long-term shutdowns, the furnace should be purged with nitrogen and kept under positive pressure at all times; it is essential to prevent a negative pressure from forming inside the furnace, which could allow air to enter and cause the catalyst to oxidize and get damaged. (5) Prevent internal leakage in the anti-thermal exchange Device. (6) Stabilize the operating conditions of the production process, with fluctuations in the peak temperature not exceeding ±5°C per hour. (7) Reduce the frequency of starting, stopping, loading, and unloading the system; strictly control the speed of loading and unloading to minimize the impact of airflow on the mechanical strength of the catalyst. (8) During startup and shutdown, strictly control the pressure release rate to prevent it from being too fast. (9) The condensate within the equipment should be drained each time it is started up or shut down, in order to reduce catalyst pulverization and thereby minimize the impact on its activity. 59. What issues should be considered when heating and reducing methanation catalysts? Answer: (1) During reduction, a large amount of water is released, so it is necessary to drain the water separator in a timely manner. The water output is 65–75 kg (chemical water)/t of catalyst. (2) Since there is also a NiCO3 phase in the methanation catalyst, CO2 is released at 300°C, and this CO2 also participates in the methanation reaction. If a cyclic heating method is used, the emission rate must be increased at this time to maintain CO2 levels

II. Overview of the Process 1. Basic reaction principle of carbon monoxide conversion Carbon monoxide in semi-water gas reacts with water vapor according to the following equation: CO + H2O(g) = CO2 + H2 ΔH0 = -41.16 kJ/mol This is a reversible exothermic reaction that results in an increase in the volume of the dry gas. The conversion process is a self-heating process; a decrease in the temperature at the exit of the conversion furnace inevitably leads to a decrease in the temperature at its inlet, which requires the catalyst to have a low activation temperature. The operating temperature for the CO conversion reaction is determined by the active temperature range of the catalyst used. It is necessary to consider both increasing the conversion rate of CO and ensuring that the reaction proceeds at a sufficient speed. Therefore, at the initial stage of the conversion reaction in actual production, when the system is far from equilibrium, it is advisable to maintain a high operating temperature as much as possible to increase the reaction rate and enable the reaction to proceed more quickly. Most of the CO in the feed gas is converted at this stage; when equilibrium is reached later in the reaction, the operating speed should be reduced appropriately to shift the reaction equilibrium to the right and increase the final conversion rate of CO. Under the condition that the CO content after conversion meets the process requirements and an appropriate equilibrium temperature difference is maintained, the lower the outlet temperature of the conversion furnace, the lower the required steam-to-gas ratio, and thus the less steam is consumed. From the perspective of chemical equilibrium, lowering the temperature, increasing the steam volume, and removing carbon dioxide can shift the equilibrium to the right, thereby achieving a higher conversion rate of carbon monoxide ； From the perspective of the reaction mechanism, increasing the temperature facilitates an increase in the reaction rate. The reaction is influenced by both kinetics and thermodynamics; in medium-voltage converters, kinetics play a dominant role, while in low-voltage converters, reaction equilibrium is the key factor. 2. Transformation process: The pressure of the semihydrated gas coming from the compression stage is reduced to 0.75 MPa. It first enters an oil remover to have any oil and water removed from it, after which it goes to the bottom of the saturation tower, where it comes into counterflow contact with hot water sprayed from the upper part of the tower. The heated gas exits the top of the saturation tower at a temperature of 123–127°C, with a vapor-to-gas ratio of approximately 0.35–0.4. It then enters the bottom of the main heat exchanger, where it exchanges heat with the gas that has undergone transformation, resulting in a temperature increase to 310–330°C. From there, it moves to the upper section of the medium-temperature converter, with steam being added at the bottom of the main heat exchanger. The hotspot temperature in the upper section of the medium-pressure converter is controlled between 440–460°C, depending on the oxygen content in the semi-water gas and the temperature of the gas entering the converter. The hotspot temperature in the lower section of the medium-transformer furnace is controlled at around 450°C, using cold gas for adjustment. After exiting and entering the upper tube bank of the main heat exchanger to exchange heat with semi-water gas, it enters the lower tube bank of the first-stage cooler; after being cooled by hot water to 180–210°C, it proceeds to the upper section of the low-temperature reformer. The exit temperature of the upper section of the low-pressure shift reactor is approximately 250–280°C. The shifted gas is cooled to 180°C by a second cooler before entering the lower section of the low-pressure shift reactor; the exit temperature from this lower section is around 210°C. After passing through the first water heater, the temperature of the gas entering the hot water tower is about 75–85°C. It then goes through the second water heater and the gas cooler, where it is cooled by circulating water, resulting in an exit temperature of approximately 35°C before entering the reforming and desulfurization section. The steam required during the conversion process mainly comes from the saturated tower, with any deficiency being made up by additional steam; the steam pressure is 0.2 MPA higher than that of semi-water gas. The steam pressure is too low, resulting in unstable shift operation; therefore, more steam is also required. Water flow: The water exiting the hot water tower is at 100°C; it is pressurized by a hot water circulation pump and then passes through the first water heater in sequence. After passing through the secondary cooler and the primary cooler, the fluid enters the top of the saturation tower; at this point, the temperature of the hot water is 140–150°C. The hot water exiting the saturation tower mixes with the make-up water supplied by the make-up water pump, and then flows into the hot water tower. The total solid content in the water after heating is strictly controlled at 500 mg/L, with the chloride ion concentration in the water being ≤50 mg/L. III. Production Operation Methods 1. Operation control during normal production 1.1. Temperature control in the upper and lower sections of the medium-frequency furnace The temperature of material entering the medium-frequency furnace should be as low as possible, but it must not be below 280°C; too low an entry temperature leads to unstable furnace temperatures. For normal furnace temperature control, an inlet (1#) bypass valve is used in conjunction with the opening degree of the main valve for feeding gas into the furnace. If the furnace temperature continues to rise even when the gas bypass valve is fully open, the main gas valve should be closed slightly. When the temperature continues to rise, the control room should be notified promptly to reduce output or even shut down the plant. The temperature in the lower section of the medium-pressure converter does not exceed 480°C, and it is regulated using the cold gas (2#) bypass valve. 1.2. Temperature control in the upper section of the low-temperature reactor: The temperature of the gas entering the upper section is determined by the activity of the catalyst; for new catalysts, it is generally 200–250°C, while for old catalysts it is usually 220–250°C. When the gas flow rate is high, the upper limit can be used. The temperature increase in the upper section is typically 30–60°C, and the means of adjustment involve controlling the main valve for gas entry and valve #3. 1.3. Control of the furnace temperature in the lower section of the low-temperature converter: The temperature of material entering the lower section is 170–190°C at the beginning of use with new catalysts, and this value increases gradually to 180–200°C over time. The furnace temperature must be 20°C higher than the dew point temperature. The temperature rise in the lower section is generally around 15°C, and it is adjusted using valve No. 4 in the lower section as well as the main valve. 1.4. Gas-to-gas ratio control: The gas-to-gas ratio is determined by factors such as the CO concentration in semi-water gas, the production load, catalyst activity, and the CO concentration in the shifted gas. When the CO content in semi-water gas is 25–26%, the gas-to-vapor ratio is approximately 38–42%. When the CO concentration in semi-water gas is 30–32%, the gas-to-vapor ratio is 43–45%. The optimal gas-to-vapor ratio is the critical CO concentration in the converted gas plus 2–3%; a slight margin provides advantages for operation. 1.5. Control of the quality of circulating hot water: The total solid content in the circulating hot water in the saturated hot water tower should be less than 500 PPm. It is possible to reuse the process condensate and steam condensate after passing through the secondary water heater, which helps to reduce the total solid content in the circulating hot water. To prevent scaling in the heat exchangers, the backflow valves in the separation sections at the bottom of the heat exchangers need to be emptied regularly. The pH value in the circulating hot water should be maintained between 8 and 9. If it falls below this range, ammonia should be added accordingly; if it exceeds this range, the amount of wastewater discharged can be increased slightly. To maintain stable water quality, it is necessary to continuously add water and discharge wastewater during operation. 1.6. Adjustment of steam consumption: The amount of steam used should be appropriate. Excessively high levels of steam do not have a significant effect on reducing the CO concentration in the shift gas; on the contrary, they can cause desulfurization reactions in the low-temperature catalysts, thereby affecting the operation of subsequent units. If too little steam is used, any fluctuations in steam pressure or changes in the O2 content in the semi-wet gas can easily lead to CO concentrations that exceed the allowed limits in the shift gas. A steam main pressure that is 0.2 Mpa higher than that of semi-water gas is key to the stability of the shift unit. Other measures include: 1.6.1. Adjusting the opening degree of the steam valve in a timely manner according to changes in gas volume and steam pressure; if the steam-to-gas ratio remains below the specified value for an extended period, additional gas should be supplied for a while once the steam pressure returns to normal. 1.6.2 To prevent large amounts of water from being added to the hot water tower, water should be supplied continuously; if it is necessary to increase the amount of water, the steam supply should be increased appropriately in advance. 1.6.3. Adjust the hot water circulation rate to its optimal value; at this point, the temperature of the converted gas at the outlet of the hot water tower is lowest, and the amount of steam required is also minimal. 1.7. Operation for receiving semi-water gas: When starting up the system, in order to prevent damage to the packing inside the saturation tower, the bypass valve of the main valve for the inlet of semi-water gas to the second stage is opened first. Once the pressure behind the valve approaches that before the valve, the main valve is slowly opened, after which the bypass valve is closed. 1.8. Operation for supplying semi-water gas: To prevent damage to the packing inside the hot water tower and the shift tower, the conversion unit should supply gas to the subsequent processes slowly. First, open the bypass valve of the main gas supply valve; once the pressure behind the valve equals the pressure in front of it, then open the main valve. When the main valve is opened to 2/3 of its full position, close the bypass valve. 1.9. Key points for using heat exchangers: Proper use of heat exchangers can extend their service life. 1.9.1. The hot water circulation shall begin when the gas temperature at the outlet of the low-temperature converter reaches 200°C; it is strictly prohibited to allow gas with a high concentration of H2S at temperatures above 200°C to flow into the first and second stage coolers under \"dry burning\" conditions. 1.9.2. When the gas temperature is below 200°C, it is prohibited to supply cooling water to the first and second stage coolers. 1.9.3. The hot water pump can be stopped only 15 minutes after the vehicle has come to a stop; water circulation must be started before the vehicle is driven away. 1.9.4. For long-term parking, the water on the water side of the first and second stage coolers must be drained completely. 1.9.5. Strictly control the total hot water content at ≤500PPm, and the chloride concentration at ≤50mg/l. 1.9.6. Once the hot water circulation volume is set, do not adjust it frequently. 1.9.7. During cold start-up, steam can be supplied to the hot water tower to raise the water temperature to 60–90°C. IV. Starting, stopping, and reversing of individual units: 1. Starting and stopping of centrifugal pumps 1.1. Preparatory work before starting the pump 1.1.1. Thoroughly inspect the pump as well as the area around it to ensure there are no debris or unnecessary objects; such items should be removed immediately. 1.1.2. An appropriate amount of lubricating oil is present in the oil tank. 1.1.3. Rotate the pump several times to check the tightness of the packing and whether there are any noises from the pump body. 1.1.4. Request an electrician to check the insulation of the motor. 1.1.5. Open the pump inlet valve to introduce liquid into the pump, and open the exhaust valve to remove all gas from inside the pump. 1.1.6. Turn on the cooling water and seal water, and check for smooth flow. 1.2. Starting the pump 1.2.1. Once all preparation work is complete, and the start button light is on, the motor may be started. 1.2.2. After starting, observe the outlet pressure and current of the pump to check whether the motor and the pump are operating properly. 1.2.3. Once normal operation is established, slowly open the pump outlet valve to adjust the desired flow rate. 1.3 Shutting down the pump 1.3.1 Close the pump outlet valve, press the button to stop the motor, and bring the pump to a stop. 1.3.2. Then close the pump inlet valve to relieve the pressure inside the pump and drain all the water. 1.3.3. Turn off the cooling water. 1.4. Pump reversal 1.4.1. Start the standby pump following the normal startup procedure. 1.4.2. Switching to the backup pump can be carried out only after confirming that there are no issues with it. 1.4.3. Gradually open the outlet valve of the standby pump, while slowly closing the outlet valve of the pump in use. 1.4.4. Adjust the outlet valve of the standby pump to the desired setting. 1.4.5. Verify that the standby pump is in good condition, then shut down the pump that is currently in use. 1.4.6. Starting, stopping, and switching of pumps in emergency situations: In the event of an accident or when a serious fault occurs in the operating equipment or motor, the pump must be… 1.5. Emergency shutdown and startup 1.5.1. Under normal circumstances, the backup pump should be started immediately, followed by the emergency shutdown of the pump that is currently in use. 1.5.2. In cases such as excessive fluid flow or a motor fire, the pump in use can be stopped urgently first, after which the backup pump can be activated. 1.5.3. When shutting down a conventional centrifugal pump, first close the pump’s outlet valve and then stop the motor. In emergency situations, it is also possible to first stop the motor and then close the outlet valve, in order to prevent large amounts of gas from entering low-pressure equipment.