A coal-based polygeneration system of synthetic natural gas, methanol and ethylene glycol: Process modeling and techno-economic evaluation

Coal to synthetic natural gas(CtSNG) industry is an effective way to alleviate the contradiction between supply and demand of natural gas in China. However, the product structure of the traditional CtSNG process is single and the carbon utilization rate is low, so there may be potential risks of product and coal price fluctuations. In order to address these issues, a coal-based polygeneration process of SNG, methanol and ethylene glycol (CtSMEG) was proposed in this study and compared with the CtSNG process. The entire CtSMEG system was first modelled and simulated by Aspen Plus, then the detailed techno-economic analysis was performed and the carbon balance and exergy balance were established. In addition, its carbon utilization efficiency, exergy effi-ciency and CO2 emissions were compared to that of the traditional CtSNG process. The results showed that the carbon utilization efficiency and exergy efficiency of the CtSMEG system were increased by 35.3 % and 27.3 % respectively, and the CO2 emissions and wastewater discharge were reduced by 0.613 kg/kg-production and 1719.3 kg/h. Although the total capital investment of the CtSMEG system was higher than that of the CtSNG process, the net present value was better than that of the CtSNG process. According to these findings, the CtSMEG system would be an effective way to overcome the problems of the current CtSNG process.