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Simulation of underground coal gasification based on a coupled thermal-hydraulic-chemical model

This paper presents a coupled thermal-hydraulic-chemical numerical model to study the temperature development and solid–gas conversion during underground coal gasification (UCG). Theoretical formulations are based on the porous medium approach, involving the gas flow, solid mass loss, and heat flow, and the chemical reactions driving the phase change and transformation of gaseous species are considered by the kinetics model. A modified empirical relationship is proposed for the increase of porosity due to combustion and gasification, and the corresponding variation of permeability is expressed by a semi-empirical relationship. A numerical solution is obtained via the coupling of the transport model and the kinetics model for the sink/source terms due to chemical reactions. Verification tests have been conducted and compared with alternative numerical solutions to build confidence in the accuracy of the implementation of the model. Evaluation of the model against literature benchmarks including temperature development and syngas composition variation indicates that the coupled model can predict the UCG process.