Comparative exergy and economic analysis of deep in-situ gasification based coal-to-hydrogen with carbon capture and alternative routes

Abstract

The deep in-situ gasification based coal-to-hydrogen (deep IGCtH) is attracting attention for its unique advantage in utilizing unrecoverable coal seam. In this paper, its improvement scope in energy conversion and utilization is analyzed using advanced exergy analysis, and the efficiency from cumulative exergy consumption (CExC) perspective and economic competitiveness with Lurgi surface gasification based coal-to-hydrogen (Lurgi SGCtH), coke-oven gas-to-hydrogen (COGtH) and natural gas-to-hydrogen (NGtH) are compared. Results indicate 39.9 % and 25.1 % of the exergy destruction of deep IGCtH and Lurgi SGCtH are unavoidable, while steam methane reforming and coal gasification possess the largest improvable potential, with avoidable endogenous/exogenous destruction of 96.63 MW/81.58 MW and 162.52 MW/151.19 MW, suggesting thermodynamic improvement can also be achieved by improving other components or optimizing process structure in addition to increasing its own efficiency. The CExC of deep IGCtH outputting 1 kg hydrogen is only 83.6 % that of Lurgi SGCtH, indicating it is more efficient route with significantly energy consumption reduction and can better demonstrate its efficiency advantage under large production capacity condition. The deep IGCtH shows only 68.7 % that of Lurgi SGCtH in investment and also presents significant advantage in cost. However, its profitability advantage over NGtH loses with hydrogen price increasing and there exists lower limit on capacity of 0.46 billion Nm3 to maintain cost and profitability competitiveness over COGtH. Furthermore, deep IGCtH shows emission reduction cost advantage over Lurgi SGCtH when capture rate exceeds 80 %, and profitability will not be limited by carbon tax and coal seam thickness within the considered range.