Design concept for coal-based polygeneration processes of chemicals and power with the lowest energy consumption for CO2 capture

Single coal based chemicals production processes emit large amount of CO2 during conversion of the syngas to the high H2/CO ratio feed gas for chemicals synthesis. However, the feed gas is with a low CO2 molar fraction, leading to high energy cost for CO2 capture. In this work, we try to reduce energy consumption for CO2 capture by improving its molar fraction. A new methanol and power polygeneration process is designed and analysed based on process modeling and simulation. The hierarchical conceptual design methodology is introduced to design the polygeneration more reasonably. In this process, the shifted syngas exiting from the water gas shift unit first goes into the CO2 capture unit to remove CO2. Then, the purified H2-rich syngas is mixed with the unshifted syngas and fed into the methanol synthesis to produce methanol. Then, unreacted syngas out from the methanol synthesis unit is moderately recycled to use, while the rest is used to generate power. Energy consumption for CO2 capture of the polygeneration process is 0.7 GJ/t-CO2, which is a 40.6% reduction compared to that of the single coal-to-methanol process and a 22.2% reduction to that of coal-to-hydrogen for power generation process. Techno-economic analysis shows that energy saving ratio and primary cost saving ratio are 16.5% and 13.2%, respectively.