Investigation of flue gas temperature on particle formation in biomass combustion

Amid the global carbon reduction, there's a pressing need to gradually wean off our dependence on fossil fuels. Utilizing biomass in coal-fired boilers presents a means to lower carbon dioxide emissions. However, biomass contains a high content of alkali and alkaline earth metals, leading to the formation of substantial fine particulate matter. This results in severe slagging, high-temperature metal corrosion, and heightened concentrations of fine particulate emissions. To investigate the influence of flue gas temperature in the furnace on the formation of biomass fly ash, an experimental flat-flame combustion system was set up. By adjusting the ratio of fuel to oxidizer, the temperature above the flat-flame burner was varied. Experimental studies were conducted on the formation characteristics of biomass combustion particulates at different flue gas temperatures. Equipment such as an Electrical Low Pressure Impactor (ELPI), a colorimetric temperature measurement system, and a scanning electron microscope were used to measure the morphology, size distribution, elemental content, and surface temperature of the particulates. It was found that when the flue gas temperature was 1800 K, the surface temperature rise rate of biomass particles in the initial stage of combustion was significantly higher than at 1500 K and 1200 K. The release of Cl and K elements increased during combustion, and the proportion of Cl and K in the generated PM₁ also increased by 3%−5%. At the same time, high temperatures also led to an increased degree of sintering in PM_1～10, with molten fly ash particles tending more towards a smooth spherical surface. As the flue gas temperature decreased to 1200 K, the number of porous structures in PM_1～10 increased, and a large number of pores appeared on the surface. At the same time, the decrease in flue gas temperature intensified the condensation of inorganic vapor in the gas phase, and the generation of PM₁ increased to 4.27 mg/m³. The research results show that the flue gas temperature affects the formation process of biomass fly ash. In order to achieve efficient and clean utilization of biomass resources, it is necessary to optimize combustion conditions, improve the combustion efficiency of biomass, and reduce environmental pollution.