The article deals with the current problem of optimizing flue gas cleaning systems at thermal power plants (TPPs) to increase the efficiency of power plants and reducing harmful emissions into the atmosphere. It was established that the main pollutants generated during the combustion of solid fuel at a TPP are nitrogen oxides, sulphur oxides, and particulate matter (PM). Primary and secondary methods of reducing emissions were reviewed, among which special attention was paid to technologies of selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) of nitrogen oxides. Flue gas cleaning processes were simulated in COMSOL Multiphysics environment to evaluate the kinetics of NO reduction reactions with the participation of ammonia under reciprocating flow. A numerical experiment established that the NH₃:NO ratio within 1.3–1.4 is required for the effective course of the NO reduction reaction. It was found that temperature is a key factor affecting the conversion rate and catalyst efficiency, which requires detailed control under practical conditions. The influence of fuel type on emissions was also analysed. The obtained results can be used to develop new strategies for the modernization of combined heat and power plants (CHPP), justify the choice of fuel and combustion modes, and implement effective emission control methods.