Thermodynamic equilibrium simulation on the synthesis gas composition in the context of underground coal gasification

Abstract

Underground coal gasification is a promising technology involved with the in-situ conversion of coal resources into a high-quality synthesis gas with low cost. A thermodynamic equilibrium simulation was conducted to analyze the effects of the reaction temperature, pressure and ratio of oxygen/steam on the synthesis gas composition in the context of underground coal gasification. The results show that the increase of the gasification pressure promotes the formation of CH4 while inhibits the formation of H2 and CO in the synthesis gas under different temperatures. And the gasification pressure for the maximum low heating value (LHV) of synthesis gas shifts to larger pressures with the increasing gasification temperatures, and the corresponding maximum LHV is 7.87 MJ/m3 at the pressure of 5.6 MPa when the gasification temperature is set as 800 °C. The increase of the gasification temperature leads to an increase in the contents of H2 and CO and a decrease in CH4 content in the equilibrium synthesis gas. The gasification temperature shifts to higher values to reach the maximum LHV of synthesis gas at elevated pressures except for the slight increase of LHV within the temperature range of 700–1000 °C at 0.1 MPa. Further analysis on the effect of the ratio of oxygen/steam indicates that increasing the moisture content in the gasification agent significantly results in the enhancement of H2 and CH4 contents in the synthesis gas as well as its LHV.