An advanced coal-based zero-emission polygeneration system using water-gas shift reaction and syngas recycle to achieve different methanol and electricity distributions

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To achieve different products distributions and improve energy conversion performance for the coal utilization with zero carbon emission, an advanced polygeneration system incorporating the methanol synthesis and Allam power cycle (an oxy-combustion, direct-fired supercritical carbon dioxide Brayton cycle) is proposed. The water-gas shift reaction is combined with the syngas recycle to obtain different products (i.e., methanol and electric power) distributions. Moreover, different from the conventional coal-to-methanol process, the carbon dioxide generated by the shift reaction is not separated from the shifted syngas but enters the Allam cycle, which can be simply split from the cooled exhaust without additional energy penalty. In other words, the carbon dioxide separation energy penalty of the methanol production is reduced to zero by connecting the coal-to-methanol process and the Allam cycle. In this study, the material flow and energy conversion characteristics of the proposed polygeneration system is revealed. The influences of the carbon monoxide shift ratio and syngas recycle ratio on the methanol productivity, net electric power throughput and the corresponding fuel saving ratio are comprehensively analyzed. The optimum strategy of the combination of the water-gas shift reaction and syngas recycle is obtained with the methanol/electricity energy ratio ranging from 0.75 to 2.71; and the highest fuel saving ratio soars to 5.79% as the methanol/electricity ratio is 1.55 at the carbon monoxide shift ratio of 0.17 and the syngas recycle ratio of 0.8.