Annals of Occupational Hygiene Advance Access originally published online on October 4, 2009
Annals of Occupational Hygiene 2009 53(8):807-813; doi:10.1093/annhyg/mep071
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Effects of Headspace and Oxygen Level on Off-gas Emissions from Wood Pellets in Storage
1 Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, British Columbia V6T 1Z3, Canada
2 Department of Occupational Medicine, Yangpu District Central Hospital, Shanghai 200090, China
3 Environemntal Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
4 Delta Research Corporation, 501 Centennial Parkway, Delta, British Columbia V4L 2L5, Canada
* Author to whom correspondence should be addressed. Tel: +604-822-4408; fax: +604-822-4408; e-mail: xbi{at}chbe.ubc.ca
Few papers have been published in the open literature on the emissions from biomass fuels, including wood pellets, during the storage and transportation and their potential health impacts. The purpose of this study is to provide data on the concentrations, emission factors, and emission rate factors of CO2, CO, and CH4 from wood pellets stored with different headspace to container volume ratios with different initial oxygen levels, in order to develop methods to reduce the toxic off-gas emissions and accumulation in storage spaces. Metal containers (45 l, 305 mm diameter by 610 mm long) were used to study the effect of headspace and oxygen levels on the off-gas emissions from wood pellets. Concentrations of CO2, CO, and CH4 in the headspace were measured using a gas chromatograph as a function of storage time. The results showed that the ratio of the headspace ratios and initial oxygen levels in the storage space significantly affected the off-gas emissions from wood pellets stored in a sealed container. Higher peak emission factors and higher emission rates are associated with higher headspace ratios. Lower emissions of CO2 and CO were generated at room temperature under lower oxygen levels, whereas CH4 emission is insensitive to the oxygen level. Replacing oxygen with inert gases in the storage space is thus a potentially effective method to reduce the biomass degradation and toxic off-gas emissions. The proper ventilation of the storage space can also be used to maintain a high oxygen level and low concentrations of toxic off-gassing compounds in the storage space, which is especially useful during the loading and unloading operations to control the hazards associated with the storage and transportation of wood pellets.
Keywords: biomass • emission factors • emission rate • off-gassing emission • oxygen level • storage space • wood pellets
Received April 22, 2009; in final form July 20, 2009