Simulation and optimization of sulfur content of tail gas under typical abnormal operation conditions of rectisol

During coal gasification,the synthesis gas usually contains a proportion of acidic gas,such as H_2 S and SO_2,especially,excessive H_2 S could induce the catalyst damage and environmental pollution.The low temperature methanol has high solvent capacity for H_2 S,whereas,low capacity for CO and H_2. Thus,the rectisol process using the low temperature methanol as the adsorbing medium has been widely used in purification of synthesis gas,which is an essential purification process for major gasification plants.However,the systematic study on the tail gas control is insufficient due to the irregular variation of the gas component and operational parameters in the industrial process.The factors influencing the tail gas out of limit should be clarified,and the possible regulating scheme should be specified.Based on the data from the industry,the simulation of rectisol process was set up by using Aspen Plus software.After comparing the simulated process data of rectisol with the industrial parameters,a high reliability model was obtained.According to the reliability analysis,two process parameters,i.e.,reflux rate in the middle part of methanol absorption tower,top temperature of carbon dioxide desorption tower,were found have critical influence on the sulfur content of the tail gas.Sensitivity tools were used to explore the optimal operating conditions on controlling the tail gas sulfur content at three abnormal feeding conditions.Thus,it can provide theoretical basis and data support for the actual production of the enterprise.The optimal conditions for typical abnormal working conditions are as follows: the volume fraction of H_2 S in the feed of abnormal working conditions No.1-3 is 0.52%,0.42%,0.35% respectively,methanol reflux rate is adjusted to be 58%,58%,59%,and the temperature at the top of the CO_2 desorb tower are adjusted to be-57,-56,-55 ℃.