Experimental simulations of methane-oriented underground coal gasification using hydrogen - The effect of coal rank and gasification pressure on the hydrogasification process

Abstract

This paper presents a series of surface experimental simulations of methane-oriented underground coal gasification using hydrogen as gasification medium. The main aim of the experiments conducted was to evaluate the feasibility of methane-rich gas production through the in situ coal hydrogasification process. Two multi-day trials were carried out using large scale gasification facilities designed for ex situ experimental simulations of the underground coal gasification (UCG) process. Two different coals were investigated: the “Six Feet” semi-anthracite (Wales) and the “Wesoła" hard coal (Poland). The coal samples were extracted directly from the respective coal seams in the form of large blocks. The gasification tests were conducted in the artificial coal seams (0.41 × 0.41 × 3.05 m) under two distinct pressure regimes - 20 and 40 bar. The series of experiments conducted demonstrated that the physicochemical properties of coal (coal rank) considerably affect the hydrogasification process. For both gasification pressures applied, gas from “Six Feet” semi-anthracite was characterized by a higher content of methane. The average CH4 concentration for “Six Feet” experiment during the H2 stage was 24.12% at 20 bar and 27.03% at 40 bar. During the hydrogasification of “Wesoła" coal, CH4 concentration was 19.28% and 21.71% at 20 and 40 bar, respectively. The process was characterized by high stability and reproducibility of conditions favorable for methane formation in the whole sequence of gasification cycles. Although the feasibility of methane-rich gas production by underground hydrogasification was initially demonstrated, further techno-economic studies are necessary to assess the economic feasibility of methane production using this process.