Ignition behavior of a mixture of brown coal and biomass during the movement of fine particles in a hot air flow

Abstract

The combustion of brown coal, biomass and their mixtures was studied experimentally and analytically. The experimental research was conducted using a laboratory setup that reproduced the conditions of combustion of pulverized solid fuel in a boiler furnace. Thermogravimetric analysis was employed as part of the analytical study to determine the key characteristics of combustion of solid fuels, such as temperatures at which the ignition and burnout occur, as well as the combustion index. Scanning electron microscopy was utilized to analyze the surfaces of coal and wood particles to detect pores, cracks and channels. To determine the tendency of the solid fuel mixture to slag heat exchangers in boiler furnaces, the ash residue characteristics (iron oxide deposits, active alkali, calcium sulfate compounds) were obtained. Biomass is more reactive than brown coal. Its ignition delay times at 500 °C and 750 °C are 57 % and 25 % lower, respectively, than those for coal. The higher the biomass content in the solid fuel mixture, the lower the ignition delay time. The heating source temperature at which the coal/biomass fuel mixture ignites corresponds to the temperature at which biomass ignites. With a larger proportion of biomass, the temperature during the fuel mixture combustion goes down, while the combustion index increases. On the basis of the findings of the conducted research, optimal proportions of solid fuel components were found (80 % brown coal, 20 % biomass). Also, fuel preparation and feeding systems for pulverized fuel combustion and fluidized bed combustion of optimal fuel mixtures in a coal-fired boiler furnace were proposed.