Simulation And Improvements Of Rectisol Wash Process In Coal Chemical Industry

Fossil fuel combustions in industries and power plants worldwide have been themain sources of CO2emitted to the atmosphere. The increasing anthropogenic CO2emissions have resulted in global warming which leads to climate changes and causesmany serious environmental problems. Therefore, immediate actions for reducingCO2emission should be taken or the consequences can be dramatic.The recovery of CO2from fossil fuel-fired industrial plants or power plants canbe a good choice to alleviate the harmful influence of CO2emission on environment.However, for large-scale coal-based methanol and ammonia plants, a high amount ofCO2is produced by coal gasification whose existing CO2recovery efficiency is only65%or even lower. The technology of Rectisol wash as an efficient and economicalprocess for acid gas removal has successfully been used to produce a variety ofproduct gases, such as, methanol synthesis gas, ammonia synthesis gas, hydrogen andfuel gas. The main purpose of this study was to increase the efficiency of CO2recovery from crude synthesis gas by improving the performance of processconfiguration.In this work, a typical one-stage Rectisol wash process was simulated and theimproved process was developed to increase the CO2recovery rate and purity of theCO2gas stream separated from the crude synthesis gas using the commercialsimulation software ProMax3.2. The CO2desorption from solvent was conducted bymeans of expansion with the internal heat. Sensitivity analyses were performed tostudy the influences of operating parameters on the CO2gas and sour gas streams, andthe energy consumption of the improved process.The traditional Rectisol wash process was simulated using software ProMax3.2and property method of SRK Polar. The whole Rectisol wash process can be dividedinto the following five sections: scrubbing column, flash vessels for syngas and CO2recovery, H2S enrichment column, hot-regeneration column, methanol/CH3OHfractionating column. They all got introduced and simulated.The CO2recovery rate could rise up to83.8-92.0%and a CO2purity rangingfrom98.9%to99.8%can also be achieved by controlling the pressure of S104andS105. Sensitivity analyses indicated that the stage number and pressure of D102both influenced the H2S concentration in CO2gas. More stage number and higher pressureof D102would reduce the H2S concentration in CO2gas. The pressure reduction ofS108contributed to the increasing of CO2recovery rate and H2S concentration in sourgas. Comparisons between the improved and the original processes showed that theCO2recovery rate of the improved process largely increased from34.8%of theoriginal process to92.1%with the same CO2purity (99.0%), and the total equivalentwork per unit CO2significantly dropped from1014.0kJ/kg CO2to388.0kJ/kg CO2,though the total equivalent work slightly increased. The results also showed that thechanges of CO2and H2S concentrations in the purified synthesis gas of the improvedprocess were small and can be negligible, while the H2S concentration in the sour gasstream was improved slightly.