The interest to study the combustion processes has two benefits: transformation of chemical energy to thermal energy, which basically is a source of heat, the usage of exhaust gases as heat carrier used as a working body. For the modelling of combustion process of lignite in “PP Kosova B” accurate data for the analysis of dominant constituents were used. The Methodology of this research is based on laboratory research, famous equations of different authors and the special program Matlab. After the substitution of input values in the program that calculates burned moles of lignite constituents, the obtained results from the program Matlab for excess amount of air have been systematised in tables and diagrams.