Underground coal gasification, as an auto thermal process, includes processes of degasification, pyrolysis, and the gasification itself. These processes occur as a result of a high temperature and the management of coal combustion during addition of gasification agent. Air, water vapor mixed with air, air or water vapor enriched with oxygen, or pure oxygen, may be used as gasification agents. Resulting gas that is extracted in this process may vary in chemical composition, so it is necessary to adjust it. That is the reason why it is necessary to develop a mathematical model of the underground gasification process prior to any operations in coal deposit, in order to obtain as much accurate prediction of the process as possible. Numerical calculation provides prediction of gas mixture's chemical composition, which enables calculation of gas components' energy contents and total energy content of the gas in predicted underground coal gasification process. It is one of the main criteria in the economic assessment of underground coal gasification process. This paper, based on available data on researches in this area, provides a contribution to creation of mathematical model of underground coal gasification.

In the name of a better and safer energy future, it is our responsibility to focus our knowledge and activities to save on imported liquid and gas fossil fuels, as well as coal on which energy security of Serbia is based. The rationalization in the use of available energy resources certainly positively affects economy and the environment of a country. This paper indicates motivations for the application of the underground coal gasification process, as well as surface gasification for Serbia. The goal is to burn less coal, while simultaneously utilizing more gas from the onsite underground coal gasification, or by gasification in various types of gas generators mounted on the surface. In both cases, from the obtained gas, CO 2 , NO x , and other harmful gases are extracted in scrubbers. This means that further gas combustion byproducts do not pollute the atmosphere in comparison with traditional coal combustion. In addition, complete underground coal gasification power requirements could be offset by the onsite solar photovoltaic power plant, which furthermore enhances environmental concerns of the overall coal utilization.