Investigation of Ultrafine Particulate Matter Formation during Combustion of Biomass and Lignite

Abstract

Coal and biomass-fired power plants significantly contribute to particulate matter (PM) emissions. So far, there has been extensive research on PM formation under simplified solid fuel combustion conditions (flat flame burner, laminar flows, early combustion stage), and only a few studies have concentrated on the entire combustion process under conditions. Thus, measurements of ultrafine PM size distributions are carried out in this study using a scanning mobility particle sizer (SMPS). The combustion conditions were produced by means of a swirl burner system designed for the investigation of methane-assisted pulverized solid fuel flames. A systematic variation of combustion conditions (temperature, residence time, turbulence, fuel mass flow) revealed that less swirled flows lead to more pronounced shear zones in the flame, higher axial velocities, and higher flame temperature that can promote coagulation. As future energy supply is expected to rely to a larger extent on bioenergy instead of solid fossil fuels, PM formation during the combustion of an abundant lignite from China (Zhundong coal) and biomass (walnut shells) is compared. The use of biomass causes smaller precursor particles and an overall higher particle concentration. CFD simulations are used to evaluate the conversion behavior of solid fuel particles of different size classes up to the position until those are captured by the sampling device of the SMPS measurements. The significantly different degree of conversion within the solid fuel size classes can be successfully used to interpret the measured ultrafine PM size distributions. The data presented in this paper provide an important basis for further studies to validate CFD simulations using the measurements and to further develop existing PM formation models for the different cases (swirl degree, stoichiometry, etc.) of biomass and lignite combustion.