This paper deals with the numerical modelling of heavy residual fuel oil combustion. Some results of combustion-generated nitric oxide and coke are presented. The emissions of both species are greatly affected by a gas temperature and thus the modelling of soot concentration, which affects radiation heat transfer is of vital importance. The calculated results of three combustion cases, the thermal inputs of which are 1.8,3.5 and 36 MW, respectively, are compared with the measured ones