The subject of the CFD analysis presented in this paper is the process of biomass indirect co-firing carried out in a system composed of a stoker-fired furnace coupled with a gasification reactor. The installation is characterised by its compact structure, which makes it possible to minimise heat losses to the environment and enhance the physical enthalpy of the oxidising agent – flue gases – having a favourable chemical composition with oxygen and water vapour. The test results provided tools for modelling of biomass thermal processing using a non-standard oxidiser in the form of flue gases. The obtained models were used to optimise the indirect co-combustion process to reduce emissions. An overall effect of co-combustion of gas from biomass gasification in the stoker furnace is the substantial reduction in NO emissions by about 22%.

Results of fly ashes from combustion of hard coal and co-combustion of alternative fuel (SRF) with coal in the stoker boiler WR-25 type studies have been shown. Samples of fly ashes were acquired during industrial combustion tests of hard coal and blend of coal with 10% SRF. The scope of comparative research included: chemical composition, contents of combustible parts and trace elements and also of microscopic analysis. The specific surface area SBET was established and tests of water extract were conducted. Chemical composition of mineral substance of both studied ashes is similar. Main ingredients are: SiO2, Al2O3, Fe2O3 and CaO. Fly ash from co-combustion of SRF with coal in a stoker boiler is characterized by high contents of combustible parts (on 30% level), higher than ash from hard coal combustion. Both tested ashes are characterized by specifi c surface area SBET on the level of 8–9 m2/g. In porous structure mesopores are dominant (>60%), and their volume is higher for fly ash from co-combustion of SRF with coal. Fly ash from co-combustion of waste is characterized by high contents of heavy metals. Nevertheless these metals and also other pollutants do not show leachability exceeding acceptable values for wastes different than hazardous. The microscopic structure of fly ashes from combustion of hard coal and co-combustion of alternative fuel studies showed crucial differences, especially in reference to organic material. Presented research results have shown that fly ash from co-combustion of SRF with coal in a stoker boiler can obtain the status of non-hazardous waste.