Modelling of reverse combustion linking in underground coal gasification

Reverse combustion linking (RCL) is a viable and effective linking method for underground coal gasification (UCG). A modelling tool was employed here to explore the theory of reverse combustion in porous media. Grid refinement was also applied to capture accurately the fire-front propagation. Simulation results indicated that RCL features a low-temperature process with strong coupling of mass and heat transfer and chemical reaction kinetics so that caution must be taken for successful implementation; for example, water removal by air flooding is imperative. In addition, at a higher injection rate and pressure, reaction kinetics and heat transfer become limiting factors for front propagation. Therefore, except for an expanding diameter linkage, an increase in the injection rate and pressure contribute essentially little to the linking speed in the parameter range of interest. The results also showed that the hot linkage and abundance of char in place after RCL are of benefit to UCG. In the end, favorable factors were also studied and identified for securing a successful RCL for UCG.