Abstract
The technical feasibility of underground coal gasification (UCG) has been established through many field trials and laboratory-scale experiments over the past decades. However, the UCG is site specific and the commercialization of UCG is being hindered due to the lack of complete information for a specific site of operation. Since conducting UCG trials and data extraction are costly and difficult, modeling has been an important part of UCG study to predict the effect of various physical and operating parameters on the performance of the process. Over the years, various models have been developed in order to improve the understanding of the UCG process. This article reviews the approaches, key concepts, assumptions, and limitations of various forward gasification UCG models for cavity growth and product gas recovery. However, emphasis is given to the most important models, such as packed bed models, the channel model, and the coal slab model. In addition, because of the integral part of the main models, various sub-models such as drying and pyrolysis are also included in this review. The aim of this study is to provide an overview of the various simulation methodologies and sub-models in order to enhance the understanding of the critical aspects of the UCG process.
Highlights
Coal is the most abundant and widespread type of fossil fuel, with reserves of economically recoverable coal estimated to be about 900 gigatons (GT), 64% of major fossil fuels [1]
The effect of operating conditions, such as temperature, pressure, injected gas composition and flow rate, and steam/O2 ratio on gas composition or cavity growth rate are revealed by a number of models
For most of the cases, the results are in qualitative agreement among the models
Summary
Coal is the most abundant and widespread type of fossil fuel, with reserves of economically recoverable coal estimated to be about 900 gigatons (GT), 64% of major fossil fuels [1]. The total amount of coal potential including the economically non-recoverable part is reported to be 18 terratons [2], most of which are too deep or too costly to be mined by traditional methods. With the current trends of energy consumption, and the rise of developing countries, the total fossil fuel reserve is expected to be the same while the total energy consumption is increasing around the world. In order to increase the recoverable fossil fuel reserve, it is important to find appropriate technology to extract the non-recoverable part of the reserves economically. Underground coal gasification is a method of in-situ conversion of deep un-minable coal into gaseous products with a higher heating value through controlled combustion with oxygen/air and gasification with steam. The development of the underground (in-situ) coal gasification (UCG) technique is paving the way to access deep coal seams. Studies suggest that the use of UCG could potentially increase the world’s coal reserves by as much as 600 GT [3], which represents a 70% increase [2]
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