Paper or QC plan on improving sulfur recovery efficiency in sulfur recovery units

Application of a New Process for Selective Catalytic Oxidation of Sulfur Recovery in the Coal Chemical Industry Abstract: Traditional processes for selective catalytic oxidation of sulfur recovery are primarily used in the coal chemical industry for the recovery of sulfur from Claus off-gases; the super/superior Claus process is a typical example of such processes. This article describes a new type of process for selective catalytic oxidation of sulfur recovery, along with the catalysts involved, which can be used to address the issue of excessive sulfur emissions in the off-gases generated during the use of conventional Claus or super Claus processes in the coal chemical industry. It can serve as an alternative sulfur recovery method for users to consider. Keywords: Selectivity; Catalytic oxidation; Sulfur recovery; Claus process; Coal chemical industry 1. Background In recent years, the coal chemical industry in China has experienced rapid development. The acidic gases generated during the purification of coal chemical plants (such as those from low-temperature methanol washing) contain approximately 20–30% sulfur. To recover sulfur from these gases, the super Claus process is generally used in China. The super/super-optimized Claus sulfur recovery technology is widely used in the natural gas and refining industries. However, when applied in the coal chemical industry, it faces issues such as a smaller scale of sulfur recovery, lower concentrations of acidic gases, complex compositions, and unstable sulfur content, which result in excessive sulfur emissions in the exhaust gases during its use in coal chemical processes. This paper introduces a new type of selective oxidation catalyst and sulfur recovery process for the catalytic oxidation of H2S in acidic gases. By utilizing the new catalyst and reactor technologies to control the reaction temperature, it is possible to reduce SO2 generation and achieve a total sulfur recovery rate of ≥99.8%. 2 Traditional sulfur recovery processes in coal chemical industry: The traditional Claus reaction is a thermodynamically equilibrium reaction, and it is limited by the sulfur dew point at the reaction temperature; even with three stages of conversion, the sulfur recovery rate is only around 98%. As requirements for environmental quality become increasingly stringent, the sulfur content in exhaust gases no longer meets the emission standards. Therefore, a wide variety of exhaust gas treatment processes have been developed. Currently, the SuperClaus process is widely used in industrial applications. 2.1 Super/Ultra-Claus Process For a long time, extensive research has been conducted to improve the sulfur recovery rate in the Claus reaction, but no significant breakthroughs have been achieved. The main constraints are as follows: (1) The Claus reaction is a reversible reaction, and its conversion rate is limited by the thermodynamic equilibrium at the reaction temperature. (2) The large amount of water generated during the Claus reaction is difficult to separate from the process gas, and at the same time the H2S concentration in the process gas continues to decrease, which further limits the shift of equilibrium toward the formation of sulfur. .(3) A certain amount of organic sulfur compounds such as COS and CS2 are generated in the thermal reaction section of the Claus unit; these do not undergo a Claus reaction with SO2. (4) The Claus reaction requires strict control of the H2S/SO2 ratio in the process gas, making the control of the entire process difficult. To address the aforementioned issues, the former Dutch company Comprimo successfully developed the SuperClaus process. The part before the secondary converter in this process is the same as that of a conventional Claus process, but a special selective catalytic oxidation catalyst is placed in the tertiary converter; the reaction is primarily governed by kinetics. Another feature is that there is no longer a requirement for a H2S/SO2 ratio of 2 – only an excess of H2S is needed. The total sulfur recovery rate can reach 99%; by adding a hydrogenation reactor before the third converter, this rate can be increased to 99.5%. The investment requirements are relatively low. However, the reactor used in this process is an adiabatic reactor, and the catalyst has a narrow range of operational temperatures; as a result, the H2S concentration at the exit of the second stage of the Claus process must be between 20% and 98%. In China, there are 3 conventional Claus converters, with a conversion efficiency of 100%, while ultra-high-performance Claus converters achieve a conversion efficiency of 2% to 15% with 99.5% efficiency. Abroad, there are 2 Claus converters and 1 hydrogenation reactor, along with 1 ultra-high-performance Claus reactor, achieving a conversion efficiency of 130%, with Clinsulf-ssp giving a conversion efficiency of 1% to 20% and 99.6% efficiency. Abroad, there are also 2 reactors with internal cooling, also achieving a conversion efficiency of 130%. The steam generated as a by-product can be utilized in the treatment of Claus process exhaust gases. A new sulfur recovery process can achieve a conversion efficiency of 0% to 25% (higher concentrations can be achieved through exhaust gas recycling), with 99.8% efficiency. In China, there are 2 reactors with internal cooling and 1 hydrogenation reactor, achieving a conversion efficiency of 120%; the steam generated as a by-product can also be used for treating Claus process exhaust gases. 5 Conclusion: Low-concentration H2S gases mainly originate from low-sulfur natural gas, refinery gas, syngas, etc. As the requirements for sulfur emission concentrations become increasingly stringent, conventional Claus + exhaust gas treatment methods incur high costs in terms of both equipment investment and operating expenses. In actual industrial plants, these methods do not perform well when the H2S concentration is in the 10%~20% range. For this reason, newly developed sulfur recovery processes address the shortcomings of other processes in this concentration range. In terms of both process performance and investment costs, this new sulfur recovery process has reached international advanced levels. It can also be used as a Claus off-gas treatment unit; with just one hydrogenation reactor and one selective oxidation reactor, a total sulfur recovery rate of 99.8% can be achieved. Therefore, this new sulfur recovery process holds broad market prospects for the recovery of low-concentration H2S in coal chemical industries.