Simulation Analysis And Revamp Study Of City Gas Rectisol Process

The pressurized coal gasification technology producing rough city gas leads to generate a certain amount of hydrocarbon material, carbon dioxide, sulfur oxides, ammonia, benzene and other harmful impurities, which must be cleaned up before merged into the pipeline net of coal gas. Rectisol is a typical purification method to eliminate acid components in gas by physical absorption. The advantage of its large absorption capacity and high selectivity to H₂S, CO₂ of methanol at low temperature makes Rectisol process a good purification technique in crude gas treatment.At present, there are some large coal gasification plants using Rectisol as their purifying method in China. Most plants need to be reformed for increasing capacity or to accommodate changes in the feedstock. As an important purification part of gasification plants, the Rectisol process is usually the most complicate unit to be reformed. However, it is seldom reported by using universal simulation software to simulate the whole process. Therefore, if Rectisol process is simulated and analyzed by simulation software, technology support for existed process revamp and new process development of the Rectisol process in large scale purification plants can be provided.During the operation of a gasfication plant, many problems occur including the over limited sulfide existing in purified gas and tail gas in the rectisol process, as well as great detriment to the rectisol due to the existence of ammonia and benzene newly-added in the feed stocks. Meanwhile, the factory hopes to expand its productivity by 10%. Therefore their equipments have to be revamped in the light of great change in feed stack and for other purposes. Presently, the universal simulation software is applied, and an ameliorate PSRK thermodynamic model is adopted based on the powerful functions and an accurate property database. All kinds of units are connected step by step until the simulation of the whole flowsheet is completed. Moreover, the simulation results of all output streams had better accordance with the corresponding design data by all means. At last, the reasons for occuring over limited sulfide in purified gas are analyzed and the technologic parameters are optimized, with reasonable transformation of the program etc. Several revamp measures are proposed based on the successful simulation analysis of the design case. By introducing the azeotropic water tower and water wash tower into the process, the ammonia and benzene existed in the orginial Rectisol are efficiently gotten rid of; By newly adding a nitrogen gas stripper column, the bottlenecks of gas absorption capacity and H₂S concentration in tail gas are erased, providing necessary technical support and theoretical guidance for the transformation of the plant, as well as a reference for the revamp of similar units.