Evaluation of Newly Designed Polygeneration System with CO2 Recycle

A new coal-based polygeneration system with CO2 recycle is proposed in this paper. With the gasified coal gas containing 23 vol % CO2 and the coke oven gas containing 25 vol 96 CH4 as the dual gas sources, the system mainly produces methanol, dimethyl ether, and electric power. The system adopts CO2/CH4 reforming to modify the C/H ratio of the syngas. Particularly, the CO2, coming from the distillation tower, is recycled separately back to be a reactant during gasification and the resource gas in the reforming unit. As the CO2 concentration in the exhausted gas from the distillation tower is more than 95 wt %, this system does not require a CO2 separation unit. The system avoids the conventional water-gas shift reaction that is used to adjust the ratio of C/H in the syngas, but fully uses the CO2 produced from coal gasification, which solves the problems of CO2 capture and storage. The performance of the whole system's energy, CO2 emission, and economics are analyzed by Aspen Plus 11.1 and Aspen Icarus 11.1 software. Results indicate that the new system realizes 11.5% increase of chemical energy, 1.3% increase of internal rate of return and 33.8% reduction of CO2 emission at the expense of 8.4% of power output. Especially, the new system can save about 13-18% on energy versus single product systems. The scheme in which CO2 is recycled back to the gasifier and the reforming unit plays the most significant role in the comprehensive evaluation of energy utilization, CO2 emission control, and economy benefits of the system.