The impact of system configuration on material utilization in the coal-based polygeneration of methanol and electricity

This study analyzes the material utilization flow, including element carbon (C) and hydrogen (H), together with the energy saving ratio to quantify the material utilization and energy conversion in a coal-based polygeneration system producing methanol and electricity. The C utilization ratio and H utilization ratio are defined from the perspective of material utilization, representing what percentage of element C or H is converted to final chemical product. In this study, three system configurations are considered: 1) parallel and series connections between the chemical and power sections; 2) a once-through and circulation types of methanol synthesis processes; and 3) the use of a water gas shift process. The results indicate that the series systems have better energy and material utilization performance. The detailed material utilization flow of the series systems is shown in the Sankey diagram, which illustrates how the carbon-based molecules and hydrogen-based molecules are converted and where these two elements are lost. For a series system, omitting the shift process can benefit both H utilization and energy conversion performance, with a suboptimal C utilization ratio; and the unreacted gas circulation can improve effectively the material utilization while make the energy conversation worse, which should be weighted by project designers. (C) 2014 Elsevier Ltd. All rights reserved.