Article pubs.acs.org/EF
Characterization of Emissions from Grass Pellet Combustion Sriraam R. Chandrasekaran,† Philip K. Hopke,*,† Arthur Hurlbut,‡ and Mike Newtown‡ †
Center for Air Resources Engineering and Science, Clarkson University, P.O. Box 5708, Potsdam, New York 13699, United States State University of New York (SUNY)Canton, 34 Cornell Drive, Canton, New York 13617, United States
‡
S Supporting Information *
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.
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INTRODUCTION Wood combustion is a potential source for space heating in the residential sector and currently provides about 28% of the heating needs in the United States.1 Most of the research on biomass fuels has concentrated on wood and biomass residues from harvesting and garden wastes, as described by Kaufman et al. in 1999. However, agricultural areas not suitable for food production can be used for the cultivation of fast growing energy crops. Herbaceous plants and grasses are ideal energy crops requiring minimum care and harvesting support. Pellets made from these grasses could then be an alternative fuel. Grass pellets have energy content that is similar to wood, but grass has the advantage that it is rapidly renewable with multiple harvests per year: “In New York State, there are about 1.5 million acres of underutilized agricultural land that could be used to grow grass.”2 Compared to wood, grasses tend to contain significantly high amounts of sulfur, nitrogen, and chlorine along with higher concentrations of alkali and alkali earth metals.3,4 Grass fuel quality can be improved either by using soil management techniques or by using better, advanced staged combustion units and/or both if grass need to be utilized as fuels.2,4 Grass combustion has been reported to emit up to 8 times more mineral matter than wood burning, and KCl is an important component in the fly ash.3 The presence of high amounts of alkali metals in grass ash cause it to melt in the combustion pot/grate causing slagging of the ash. The grass pellets may then not burn completely leaving ash with high carbon content (up to 25%).4,5 The chlorine content in grass pellets is high, typically 0.05−1%, while for wood, chlorine concentrations are about 0.005%.6 Gaseous chlorine emissions can produce chlorinated © 2013 American Chemical Society
hydrocarbons including PCDD/PCDF, known human carcinogens.7 The amounts of chlorinated organic compounds emissions from wood are of the same order of magnitude as the nonchlorinated organic emissions.3,7 Furthermore, the deposition of fly ash on internal surfaces of the boiler/furnace causes corrosion. The objective of the current study was to characterize the emissions from combustion of different grass pellet types and one commercially available premium wood pellet.
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EXPERIMENTAL METHODS
Fuel Characteristics. Five grass pellet types with ash content ranging from 3% to 13% and a commercially available premium wood pellet with ash content 0.6% were used in this study. Grass pellets A, B, and C are from stands of mixed herbaceous species dominated by cool season grasses. All of the 3 types of grasses were grown on fields with varying mineral content. The soil analysis of the 2 fields (grass pellet types A and B were cultivated) was performed by a commercial laboratory, and the results are summarized in Supporting Information Table S1. Grass pellets A were from the first cutting of a field that was never fertilized. Grass pellets B were from the second cutting after the field was fertilized during the spring. Grass pellets C were also from the first cutting, pelletized using a mobile pelletizer. All of the 3 grass pellets A, B, and C were mowed (October) and allowed to leach (until December) in the field for 3 months, yet the chloride content was 3 times higher than grass pellet E and about a magnitude higher than the wood pellets. Grass pellets D were the switch grass pellets used in the study of appliance performance by Chandrasekaran et al. in 2013. Received: May 30, 2013 Revised: August 26, 2013 Published: August 26, 2013 5298
dx.doi.org/10.1021/ef4010169 | Energy Fuels 2013, 27, 5298−5306
Energy & Fuels
Article
Table 1. Properties of Fuela property calorific value carbon hydrogen nitrogen moisture ash sulfur chloride Li Na Mg Al K Ca V Cr Mn Fe Co Ni Cu Zn As Se Cd Sb Ba Pb
unit MJ/kg % % % % %dw % % mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg
ash ash ash ash ash ash ash ash ash ash ash ash ash ash ash ash ash ash ash ash
grass pellet A
grass pellet B
grass pellet C
grass pellet D
grass pellet E
wood pellets
18.7 ± 0.14 45.3 ± 0.1 5.93 ± 0.03 1.07 ± 0.03 7.9 ± 1.7 7.7 ± 0.8 0.09 ± 0.05 0.07 ± 0.03 158 13 533 61 535 15 670 302 710 37 524 28.9 169.9 4260 14 781 6.0 90.5 234.1 1752 5.1 5.0
