Effects of the Steam-To-Oxygen Ratio and the Equivalence Ratio on Underground Coal Gasification

Underground coal gasification is a complex physico-chemical process. UCG thermodynamic equilibrium model was established and validated, and the effects of the steam-to-oxygen ratio (R-H2O/O2) and the equivalence ratio (ER) on the gasification temperature and the gaseous products were investigated. At low ER (0.08-0.14), coal is incompletely gasificated when the gasification temperature is less than the corresponding peak temperature. At high ER (0.16-0.30), coal is completely gasificated. With the increase of R-H2O/O2, the gasification temperature decreases monotonically and finally tends to approach 850 degrees C at R-H2O/O2 = 4.5. H-2 reaches high concentration at ER = 0.18-0.24 and R-H2O/O2 = 1-3, but the change of CH4 concentration is just the opposite. CO concentration is high at R-H2O/O2<1.5. In order to reach high the utilization effectiveness of oxygen, R-H2O/O2 has the corresponding optimum value where the utilization effectiveness of oxygen reaches peak value at ER = 0.08-0.2.