Effect of Calcium Phosphates Additives on PM Emissions From the Combustion of Corn-stalk

Agricultural biomass combustion generates a large amount of particulate matters, greatly restricting its utilization in heat and electricity production. This paper investigated the effect of three calcium phosphates additives, namely CaHPO4, Ca(H2PO4)2 and Ca3(PO4)2, on the reduction of fine particulate matter emissions during cornstalk combustion. The combustion was conducted by using a fixed bed reactor and the particulate matters were collected by a Dekati low pressure impactor (DLPI). Meanwhile, the chemical compositions and crystalline phases of the residual ashes were analyzed by using X-ray fluorescence (XRF) and X-ray diffraction(XRD). It was found that the total amount of PM10, especially PM1, was reduced to varying degrees with the addition of three calcium phosphates. When the P/K molar ratio equals to 1, Ca(H2PO4)2 showed a better PM reduction effect than CaHPO4 and Ca3(PO4)2 and the highest PM10 reduction rate of 44.09% and PM1 reduction rate of 51.93% were achieved when Ca(H2PO4)2 was used. Analysis of the residual ash show that the reactions between the calcium phosphates additives and K slats in corn stalk resulted in the formation of high-melting K-Ca/Mg phosphates, such as KCaPO4, K2CaP2O7, Ca9MgK(PO4), which can reduce the formation of the PM1. It is suggested to add CaHPO4 or Ca(H2PO4)2 to corn stalk biomass according to the ratio of P/K mole ratio equal to 1 to reduce the emission of particulate matter, when economy and emission reduction effect was taken into account comprehensively. This study could provide scientific guidance for the reduction of PM emissions during the combustion of corn stalk. © 2020 Chin. Soc. for Elec. Eng.