Characterization of Emissions from Grass Pellet Combustion

Abstract

Emission factors of pollutants from combustion of five different types of grass pellets with ash content ranging from 3% to 13% were measured and compared to a premium type wood pellet with ash content 0.6% at low and high loads, respectively. The effects of fuel properties on the grass pellet combustion emissions were also studied. Criteria pollutants including PM2.5, NOx, SO2, and CO were continuously monitored using an EPA CTM-039 dilution sampling system. PM10 emissions from grass combustion were found to be higher when compared to wood pellet emissions at both low and high loads (26–40 and 36–60 mg MJ–1, respectively). The PM2.5 emissions were strongly correlated to the ash content of the fuel (R2 = 0.939). CO emissions were found to be higher for grass combustion indicating an incomplete combustion. PM2.5 samples collected on Teflon and quartz substrates were analyzed for ions and trace elements. About 60–75% of the PM2.5 fraction was recovered that included K of about 20–30%, sulfate about 16–25%, and chloride of about 10–15%. Semivolatile organic compounds collected on quartz and polyurethane foam (PUF) were also analyzed for molecular markers, PAHs and PCDD/Fs. PAH emissions were strongly correlated to the CO (r2 = 0.80). The PCDD/F emissions were clearly a function of chlorine content of the fuel (r2 = 0.98). A strong correlation exists between emitted levoglucosan and PM2.5 indicating levoglucosan, a molecular marker for cellulose combustion (r2 = 0.87). All of the emissions were found to be higher for grass pellets compared to wood pellets and are higher at high loads than at low loads.