Study On Particulate Matter Formation Characteristics In Conventional And Oxy-Biomass Combustion

Biomass is a renewable energy resource that includes forestry and agricultural residues,energy crops and various forms of biogenic waste.Bioenergy currently supplies about 10%of the global energy supply.Biomass can be directly utilized via combustion to produce heat or indirectly by converting it to forms of biofuels.Biomass combustion technology is diverse and advancing rapidly.Most practical combustor devices such as boiler,stoves and engines use gas,liquid or solid fuels as their energy source.Although gaseous and liquid fuels are simple,convenient and clean,their resources are limited.Biomass is therefore finding increasing use in both large and small-scale utilization.However,biomass combustion is one of major contributors to air pollution.The production of particulate matter（PM）in form of smoke plumes causes major respiratory diseases and haze challenges.Despite the major challenges brought about by PM from biomass burning,little information is currently available on the quantity of emissions.This paper mainly studies the conventional and oxy-combustion process of biomass fuels with interest on the factors governing the formation of PM to reduce the emission of PM.This study was conducted on a fixed bed reactor and a biomass boiler.The factors considered include temperature（600^oC-1200^oC）,combustion atmospheres（O₂/N₂ and O₂/CO₂）,types of biomass（cornstalk,wood,wheat straw,rice husk,and peanut shell）,biomass fuel particle sizes（44-149μm）.The oxy-biomass combustion was performed under the atmosphere（21%O₂/30%CO₂,30%O₂/70%CO₂,50%O₂/50%CO₂,70%O₂/30%CO₂,90%O₂/10%CO₂,and100%O₂）for the fixed bed reactor with comparison to 21%O₂/79%N₂ conventional combustion.The biomass boiler studies were done under the atmospheres（21%O₂/79%CO₂,and30%O₂/70%CO₂）for oxy-biomass combustion and 21%O₂/79%N₂ for conventional combustion.The fixed bed combustion results show that the PM indication from each complete combustion process has a bimodal distribution.Maximum particle production is achieved during volatile combustion followed by char combustion towards termination of the process.The PM formulation pattern was almost congruent among the combustion of five biomass types.Rice husk was identified as the fuel with the highest PM formation potential,giving between 25 to 35%more PM compared to the rest of the fuels.Increase in temperature leads to decrease in burnout time in both conventional and oxy-combustion atmospheres considered.Considering combustion within temperature between 600^oC to 1200^oC,at 600^oC the PM generated during combustion of each biomass starts to increase followed by a gentle decrease until a significant lowest point is attained,afterwards the PM increases again attaining a significant peak and finally decreases rapidly forming a trend,forming the characteristics of two major peaks and one valley.The PM emission from conventional combustion ranges from 0.2 mg/g to 1.7 mg/g.Decreasing biomass particle size leads to increase in PM formation in most cases.Oxy-biomass combustion leads to more PM generation in comparison to conventional combustion in many cases.Oxidizer between 21%and 50%is associated with highest PM formation under all temperatures and biomass.The PM emission from oxy-biomass combustion ranges from 0.2mg/g to 1.8 mg/g.The biomass boiler combustion results show that PM emission ranges from 0.1 mg/g to 1.0mg/g under oxy-biomass conditions and above 2.2 mg/g in conventional combustion.In the case of the emission particle size distribution,the results show that conventional combustion yields more PM_2.5.5 than oxy-biomass combustion in 21%oxidizer level.Under oxy-biomass combustion increase in oxidizer leads to decrease in PM generation and increase in PM diameter.