PROCESS ANALYSIS AND SIMULATION OF UNDERGROUND COAL GASIFICATION (FLOW MODEL, SELF-GASIFICATION, WATER INFLUX)

This investigation pertains to the prediction of cavity growth and the prediction of product gas composition in underground coal gasification (UCG) via mathematical model. The large-scale simulation model of the UCG process is comprised of a number of sub-models, each describing definable phenomena in the process. Considerable effort has been required in developing these sub-models, which are described in this work.;The model proposed as a result of this study clearly defines the system assumptions, equations, and variables so that it can be readily applicable to other cases. The model should be effective in predicting results from other field tests as well as analyzing the CRIP (controlled retreating injection point) process, which is the most promising technique for commercialization of the UCG process.;In the first phase of the investigation, the flow field in field experiments was analyzed using five selected flow models and a combined model was developed based on the Hoe Creek II field experimental observations. The combined model was a modified tanks-in-series model, and each tank consisted of a void space and a rubble zone. In the second phase of this work, a sub-model for self-gasification of coal was developed and simulated to determine the effect of water influx on the consumption of coal and whether self-gasification of coal alone could explain the cavity growth rates estimated from field experiments. Self-gasification of coal alone was shown to be insufficient to explain the observed cavity growth. In the third phase of this work, a new sweep efficiency model was developed and coded to predict the cavity growth and product gas composition. Self-gasification of coal, water influx, and roof collapse and spalling were taken into account in the model. Predictions made by the model showed reasonable agreement with the experimental observations and calculations.