Study On The Effect Of Alkali Metals On The Formation Of Fine Particulate Matters During Biomass Combustion

Biomass is the only carbon-containing renewable energy,which has the characteristics of large reserves,wide area,storage,transportable,low sulfur,low nitrogen and zero emission of carbon dioxide.However,biomass is rich in alkali metals,which are easily released and formed the fine particulate matters by homogeneous nucleation,heterogeneous condensation and collision coalescence,especially ultrafine particulate matters during biomass combustion.At present,most biomass combustion power plants are equipped with dust removal devices,but the capture rate of fine particulate matters is low?89-95%?and the cost is high,it is impossible to remove the ultrafine particulate matters.So,it is necessary to study the effect of alkali metals on the formation characteristics of fine particles during biomass combustion.In this paper,the formation characteristics of fine particles collected from Heishan Biomass Combustion Power Plant in Liaoning Province were analyzed,the study found that the particle size of fine particles is different,and the occurrence and content of constituent elements are different.Alkali metals are mainly enriched in PM_1.0 in the form of KCl and K₂SO₄.Alkali metals mainly affect the formation of PM_1.0.Biomass combustion experiments were carried out in a drop tube furnace to study the effects of combustion temperature,different straw and alkali metals on the formation characteristics of fine particulate matters combined with the chemical thermodynamic simulation.The study found that the increase of combustion temperature promotes the formation of PM_0.1 and PM_0.1¹.0.Compared with the combustion temperature of 650?,the mass concentration of PM_1.0 increased by 2.3 times and the mass concentration of PM_1.0¹0decreased by 1.3 times at the combustion temperature of 950?.The increase of temperature accelerates the sulfate reaction and promotes the condensation and nucleation of K₂SO₄.Compared with rice straw,the mass concentration of PM_1.0 and PM_1.0¹0 in corn straw decreased by 13.64%and 11.54%at the same combustion temperature.In corn straw,S/K mole ratio is larger,more K₂SO₄ is generated in PM_0.1¹.0.By water scrubbing,the content of alkali metals in PM_0.1¹.0 was obviously decreased,and the contents of the non-volatile mineral Mg,Ca and Si were increased.The addition of K promotes the generation of PM_0.1and PM_0.1¹.0.The mass concentration of PM_1.0 with 2%K and 4%K increased by 33.33%and43.94%respectively,and the number concentration of PM_0.1 increased by 20.39%and 37.90%respectively.In the process of biomass combustion,the gasification-condensation reaction of alkali metals is the key to the formation of PM_0.1 and PM_0.1¹.0.