Abstract
Modelling of the underground coal gasification process is dependent upon a range of sub-models. One of the most important is the calculation of the cavity growth rate as a function of various operating conditions and coal properties. While detailed 1-dimensional models of coal block gasification are available, it is not easy to couple them directly with reactor models, which aim to simulate the complete process. In this paper, a 0-dimensional cavity growth sub-model is presented. The model is based on the concept of a surface reaction and incorporates physics to account for moisture evaporation, water influx, coal pyrolysis, coal thermo-mechanical fragmentation and the build up of an ash layer on the char. The model is validated using measurements from laboratory experiments on coal cores and coal blocks. A comparison of calculated results from several UCG field trials shows that the model can provide good estimates of cavity growth rate for reasonable input parameters. Finally, simulation results of cavity growth in the combustion and gasification zones as a function of the bulk gas temperature, gas pressure, water influx rate, ash layer thickness and coal fragmentation behaviour are presented.
Highlights
In this paper, a 0-dimensional submodel for simulating the cavity growth process in underground coal gasification is described
This paper provides a review of previous work, describes the coal block gasification process, develops the mathematical basis for the 0-dimensional cavity growth submodel and compares results of the model with measured laboratory combustion experiments and estimates of cavity growth rates from several field trials
It is observed that higher gas pressure leads to an increase in the cavity growth rate, primarily due to an increase in heat and mass transfer associated with higher Grashof numbers
Summary
A 0-dimensional submodel for simulating the cavity growth process in underground coal gasification is described. This paper provides a review of previous work, describes the coal block gasification process, develops the mathematical basis for the 0-dimensional cavity growth submodel and compares results of the model with measured laboratory combustion experiments and estimates of cavity growth rates from several field trials. Perkins and Sahajwalla (2005) have presented a 1-dimensional model of coal block gasification that was validated through comparison with both measured data from laboratory experiments and observations from field trials. G. Perkins model between coal and the gases flowing through the underground reactor, while Kuyper used a similar surface reaction model when investigating the detailed fluid flow and transport phenomena in a UCG channel (1994). It is envisaged that such a model will have the advantages of being able to directly use kinetic data measured in the laboratory and represent local heat and mass transport phenomena in detail
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