Residential-Scale Biomass Boiler Emissions and Efficiency Characterization for Several Fuels

Abstract

Detailed particulate and gaseous emission characterizations were conducted on six commercially available residential-scale wood pellet boilers. The objective of the study was to define emission factors for these six different appliances burning wood pellets, grass pellets, and a blend of grass pellets and corn as fuels under low and high loads. Continuous monitoring of criteria pollutants, including PM 2.5 , NO x , SO 2 , and CO, was conducted using an EPA CTM-039 dilution sampling system. The PM 10 emissions with wood as the fuel ranged between 14 and 17 mg/MJ and between 16 and 21 mg/MJ at low and high loads, respectively. The PM 10 emissions from grass were found to be higher for all of the appliances compared to wood pellets at both low and high loads (28−33 and 37−44 mg/MJ, respectively). CO emissions, an indication of combustion efficiency, were found to be higher for the grass pellets, indicating less complete combustion. NO x and SO 2 emissions were also higher for grass and grass/corn blends, attributable to the higher fuel N and S. PM samples collected on Teflon and quartz substrates were analyzed for ions and trace elements. Semi-volatile organic compounds collected on quartz and polyurethane foam (PUF) plugs were also analyzed. Levoglucosan, a molecular marker for wood combustion, was the predominant organic compound found in the grass combustion PM 2.5 and ranged between 6 and 100 μg/MJ for grass and between 9 and 130 μg/MJ for wood. Polycyclic aromatic hydrocarbon (PAH) emissions were relatively higher for grass combustion ranging from 10 to 700 μg/MJ than for wood combustion ranging from about 5 to 200 μg/MJ. Dioxin and dibenzofuran emissions were found to be substantially higher for grass pellet emissions compared to wood pellet emissions at both high and low loads for all of the appliances.

Joint measurements of PM<sub>2. 5</sub> and light-absorptive PM in woodsmoke-dominated ambient and plume environments

“…Our analysis also suggests that the PM 2.5 -DC relationships can be potentially utilized to distinguish different combustion and operating conditions of woodsmoke sources. It is expected that cleaner burns would have a larger slope, i.e., less organic aerosol per unit woodsmoke PM (Chandrasekaran et al, 2011(Chandrasekaran et al, , 2013. In other words, the different combustion conditions lead to different chemical compositions and absorption cross sections, which can be potentially captured by high time resolution light absorption-measurements.…”

Characterization of Emissions from Grass Pellet Combustion

“…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. Grass pellets E were blue stem grass with low ash content of about 2.8%.…”

Untapped Potential: Opportunities and Challenges for Sustainable Bioenergy Production from Marginal Lands in the Northeast USA

“…Research and development is therefore required for appropriate combustion technologies. For instance, some of these issues can potentially be resolved by blending grass with lower ash content fuels such as corn grain [116] and by ensuring consistent physical and chemical quality of grass pellets. Because grass feedstocks from heterogeneous marginal lands are likely variable in composition and thus in physical pellet quality, pellet quality standards (akin to those in place for wood pellets) are essential for small-scale combustion and advisable for large-scale combustion.…”

“…They concluded that combustion process optimization is essential, not only for each type of fuel but also at each operational load. Attempting to burn grass in a boiler optimized for wood will most likely result in very inefficient combustion and high emissions of particulates and undesirable chemical compounds [116,124].…”