Advantages and disadvantages of high-variation and low-variation CO

CO has a high conversion temperature and fast reaction rate, but its concentration remains high at equilibrium; therefore it is used in the early stages of the shift process； The low-temperature shift of CO results in a slow reaction rate, but the CO content at equilibrium is low; therefore it is used in the later stages of the shift process to improve the utilization rate of the feed gas ；

To address their respective shortcomings, the high-string-low-string process method is generally used in production.

High variability seeks reaction speed; low variability seeks the rate of change

High variability characteristics: (1) The transformation reaction is exothermic; the high-variability process effectively meets the basic principle in process design, which states that higher temperatures increase the reaction rate while lower temperatures enhance the conversion rate. (2) Utilize high temperature to increase the reaction rate and remove toxic impurities (such as oxygen). ; (3) High-varying catalysts are relatively inexpensive and possess a strong resistance to substances such as oxygen and oil, which helps to extend the catalyst’s lifespan while reducing the initial investment cost. (4) Due to the high temperature of the reaction system, heat energy consumption is high. Features of low-variation: (1) As a new energy-saving process, the full low-variation process achieves significant results in terms of energy savings and reduction of consumption. The inlet temperatures at each section of the low-temperature shift reactor are all around 200°C, and the bed temperature is reduced by 100–300°C compared to that in conventional reactors, which is favorable for the equilibrium of the shift reaction. The steam-to-gas ratio decreases, resulting in a significant reduction in steam consumption; the lowest steam consumption is observed in several conversion processes. (2) It features a high heat recovery rate and minimal energy loss, allowing the heat exchange area of the heat exchange equipment to be reduced by about 1/2. (3) The requirement for the hydrogen sulfide content in semi-water gas is correspondingly reduced; the total sulfur content in the gas must be 150 mg/m3 (standard), so the sulfur content in the raw coal can be allowed to be somewhat higher. (4) Compared with the original high-temperature shift catalyst, the amount of catalyst used can be reduced by more than half, which lowers the resistance in the shift reactor bed and reduces compression power consumption. (5) The conversion rate of organic sulfur is high, reaching 98%–99%, which facilitates the copper washing process, reduces copper consumption, and stabilizes production. The waste heat recovery effect is good. Heat exchange between catalyst sections and other processes are utilized to recover heat step by step through water heaters, which in turn heat the circulating hot water in the saturated hot water tower. As a result, the temperature and saturation level of the semi-coke gas exiting the saturated tower are high, while the temperature of the gas exiting the hot water tower can be reduced to below 100°C. (6) Good waste heat recovery efficiency. Heat exchange between catalyst sections and other processes are utilized to recover heat step by step through water heaters, which in turn heat the circulating hot water in the saturated hot water tower. As a result, the temperature and saturation level of the semi-coke gas exiting the saturated tower are high, while the temperature of the gas exiting the hot water tower can be reduced to below 100°C. In short, each of the two processes has its advantages and disadvantages; the higher-temperature process is easier to operate, while the catalyst lasts longer ； Full low-temperature conversion results in significant energy savings, and a smaller amount of catalyst is required. However, it demands strict controls over hydrogen sulfide to prevent reverse sulfidation; high standards are also needed regarding gas and water quality. Corrosion is severe, so it is necessary to enhance the adsorption of oxygen scavengers at the upper part of the catalyst, imposing higher requirements on the catalyst itself. Each factory should select an appropriate process based on actual conditions.