No abstract

Combined torrefaction and pelletization can effectively improve the quality of the biomass fuel. In this work, particulate matter (PM) emissions from combustion of corn stalk pellets derived from the torrefaction and pelletization process were investigated using a fixed-bed reactor combined with a Dekati low-pressure impactor (DLPI). The obtained ash samples were subjected to various analytical techniques. Results indicated that, after torrefaction, the lower heating value (LHV) of the torrefied sample increased by 8−28% with an increase of the ash content by 9−30% and a decrease of the O content by 14− 48%. Although 10−41% Cl and 27−60% S were released in the torrefaction, the absolute content of Cl increased from 7.6 mg/g for raw corn stalk to 9.2 mg/g for torrefied biomass at 300 °C. In comparison to the raw pellet, the total PM emission from torrefied pellets increased by 25−68% with the torrefaction temperature increasing, largely resulting from the increase of PM 0.1−1 . Chemical composition analysis of the PM showed that torrefaction changed PM 1 composition from being dominated by KCl to mainly K 2 SO 4 . The variation of PM emission characteristics between the raw pellet and torrefied biomass pellet could be attributed to the changes of the contents and occurrence forms of ash-forming species in the torrefaction process. Although combined torrefaction and pelletization clearly enhanced the fuel properties of the corn stalk, it also increased PM emissions, especially PM 1 , to various degrees. Therefore, effective countermeasures are needed to mitigate the PM emission issues in industrial application.

To understand the influence of P-containing compounds on particulate matter (PM) emissions from the combustion of agricultural residues, the combustion of cornstalk was performed with the addition of a phosphorus-based additive, namely, ammonium dihydrogen phosphate (NH4H2PO4), in a fixed-bed combustion system. Simultaneously the ash samples, including PM collected by a Dekati low-pressure impactor (DLPI) and residual ash, were analyzed with variant analytical techniques. It was found that NH4H2PO4 addition significantly reduced PM0.1 and PM0.1–1 yields but increased PM1–10 yields. The maximum PM0.1 and PM1 reduction efficiency can reach up to 50% at an optimal P/K molar ratio equal to 1. Meanwhile, the addition of NH4H2PO4 to cornstalk changed the chemical composition of PM1 from being dominated by KCl and KOH/K2CO3 with a small amount of K2SO4 to a system dominated by KPO3 and KCl with a small amount of K2SO4. Simultaneously, the possible PM1 reduction mechanism was proposed. In addition, the residual ash after combustion was rich in K- and P-containing species, indicating a potential utilization as a fertilizer. It showed that the addition of NH4H2PO4 is a promising approach to reduce PM1 emissions during the combustion of agricultural biomass.