A comparative study of exergy efficiency, environmental impact, and economic performance of various in-situ coal gasification utilization schemes

Underground coal gasification (UCG) projects primarily utilize the produced syngas for fuel or power, leading to insufficient use of valuable H2 and CH4. This results in low energy efficiency and reduced economic benefits. To enhance in-situ coal gas utilization, this study employs HYSYS to simulate three schemes: graded purification for liquefied natural gas (LNG) and liquefied hydrogen (LH2) production, methanol synthesis, and methane production. The schemes are evaluated based on efficiency, investment, product value, CO2 equivalent in tail gas, wastewater volume, and water consumption. A comprehensive evaluation index system was established, and the AHP-EWM method was applied. Results indicate that the graded purification scheme (75.85) outperforms both the methanol synthesis (72.18) and methane production (65.13) schemes. Therefore, graded purification for LNG and LH2 production shows significant advantages. Given the high CO2 content in UCG syngas, future research should explore coupling this process with Carbon Capture, Utilization, and Storage (CCUS) to mitigate emissions and establish a cost-effective path for carbon sequestration and resource utilization.