Study On The Influence And Elimination Of Sulfide And Ammonia Impurities In Methanol Wash Process

Chilled methanol wash is a process that uses low-temperature methanol to purify acid gases?CO₂,H₂S,COS,etc.?,which originated around 1950.The principle of this process is to take advantage of the fact that methanol has a large difference in the solubility of acid gas under low temperature conditions,and use cold methanol as the absorption solvent to remove the acid gas in the raw material gas.The process flow mainly includes absorption of acid gas,desorption of CO₂ product gas,concentration of H₂S product gas,methanol thermal regeneration,and tail gas scrubbing and emission.Chilled methanol wash is widely used in the field of desulfurization and decarbonization gas purification because of its strong absorption capacity,good selectivity,and low operating cost.Presently,the raw material gas of the chilled methanol wash process of a plant is changed.In addition to H₂S,CO₂ and other acid gases,the new raw material gas also contains CH₄S and NH₃ impurities.CH₄S and NH₃ impurities are difficult to be removed in the original chilled methanol wash process,which affects the quality of methanol.When impurities accumulate in methanol to certain extent,they will make the product of the process fail in meeting corresponding product requirements.Therefore,the original chilled methanol wash process needs to be modified to avoid the accumulation of impurities in methanol.Thus in this work,firstly Aspen Plus software and PSRK property method are used to simulate the original chilled methanol wash process.The simulation values obtained are in good agreement with the actual operating conditions of the plant,verifying the reliability of the simulated process.Later,based on the original process flow,two reconstruction schemes are proposed,and the key operation and equipment parameters of the schemes are determined through sensitivity analysis.Among them,a nitrogen stripping tower,a gas-liquid separation tank and a heat exchanger are added in Scheme I to process the laden methanol from the top of the thermal regeneration tower,thereby successfully reducing the total CH₄S and NH₃impurity content to 4 ppm.Scheme II uses the mechanism that CH₄S can react with O₂ to form dimethyl disulfide.By adding a new reactor and a distillation column?for separating methanol and dimethyl disulfide?,the CH₄S and NH₃ impurities are reduced to 6 ppm.Finally,taking case 1 of Scheme I as an example,the heat exchange network is designed.Both solutions help to solve the problem of accumulation of organic sulfur and NH₃impurities in methanol,and will help the actual plant to develop a practicable purification process for raw material gas containing CH₄S and NH₃ impurities.