Nitrogen oxides (NOx) is one of the harmful emissions from power plants. Efforts are made to reduce NOx emissions by researchers and engineers all the times. NOx emissions are from three resources during the combustion: prompt NO, fuel NO and thermal NO. The last one – thermal NO, which is described by ‘Zeldovich-mechanism’, is the main source for NOx emissions. The thermal NO emission mainly results from the high combustion temperature in the combustion process. In order to control the NO formation, the control of peak combustion temperature is the key factor, as well as the oxygen concentration in the combustion areas. Flameless oxidation (FLOX) and continuous staged air combustion (COSTAIR) are two relatively new technologies to control the combustion temperature and the reaction rate and consequently to control the NOx emissions.In this study both FLOX and COSTAIR technologies are assessed based on a 12 MWe, coal-fired, circulating fluidised bed combustion (CFBC) power plant by using ECLIPSE simulation software, together with a circulating fluidised bed gasification (CFBG) plus normal burner plant. Two different fuels – coal and biomass (straw) are used for the simulation. The technical results from the study show that the application of FLOX technology to the plant may reduce NOx emissions by 90% and the application of COSTAIR technology can reduce NOx emissions by 80–85% from the power plant. The emissions from the straw-fuelled plants are all lower than that of coal-fuelled ones although with less plant efficiencies.