8 - Underground gasification of low rank coals

Abstract

The population growth in combination with the continuous improvement of living standards leads to higher world coal demand. The improved technologies yielded a method of Underground Coal Gasification (UCG) where the seam of solid carbon is converted in situ into a gaseous phase, which is environmentally friendlier and applicable in huge deep coal seems which otherwise will remain unmined. Due to the high interest, many countries all over the world have carried out UCG projects that deal with technical, economic, and environmental risks and challenges in a multidisciplinary framework. A basic step for comprehensive UCG research and development is the Process Modeling where geological data from the study area are collected for the construction of geological, hydrogeological, and geomechanical models. Additional laboratory and even field tests provide valuable information on cavities’ growth during the coal seam burning procedure. This cavity progression has direct influence on the economic and environmental factors of the project, thus, a lot of effort has been made to develop mathematic and/or numerical models, ranging from 1D to 2D symmetric and to full 3D to simulate this growth. These sites under certain cases can also be used for CO2 storage in post-UCG cavities. Further investigation requires technical matters on wells for UCG and adaptation to CO2 storage. Each activity of such scale has its own impact especially on the underground environment. Minimizing groundwater contamination is the key element for any successful UCG-CO2 procedure; therefore, a comprehensive evaluation of geological and hydrogeological factors at the site is necessary. At the end, an economic assessment of UCG-CO2 process is presented, based on a model of a combined cycle gas plant operating on UCG syngas.