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.