Effects of P-based additives on agricultural biomass torrefaction and particulate matter emissions from fuel combustion

The large scale utilization of agricultural biomass as fuel is restricted by the feedstock properties of low energy density, high moisture content, heterogeneous composition and chemical impurities. In this work, torrefaction of biomass fuel with NH4H2PO4 additive was carried out to investigate the effects of NH4H2PO4 mixing ratio and torrefaction temperature on the properties of the torrefied fuel and particulate matter (PM) emission characteristics from combustion. The results show many benefits from NH4H2PO4 addition in biomass feedstock: 1) the removal of O and retention of C can be enhanced leading to lower mass and energy losses during torrefaction, 2) more Cl and S are released to gas phase leading to a lower absolute content of Cl and S in the torrefied fuel, and 3) the occurrence of alkali and alkaline earth metals change significantly. Moreover, the emissions of the fine particulate matters (PM1) from the torrefied fuels are clearly reduced when NH4H2PO4 is added and the reduction rate is closely related to P/K molar ratio with the maximum reduction rate achieved at P/K molar ratio equal to 1. These results suggest that the proposed method can effectively upgrade the fuel qualities and reduce PM1 emissions from the fuel combustion. [Display omitted]