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WOOD PELLETS: EMISSION CHARACTERIZATION AND
CONTROL Olga Petrov, PhD Candidate
Department of Chemical and Biological Engineering University of British Columbia
Biomass and Bioenergy Research Group [BBRG] Clean Energy Research Center
Bridge/CIHR Strategic Training Fellow
November 17, 2014 WPAC AGM 2014: Sustainable Growth, Vancouver, BC
UBC Wood Pellet Workshop
Outline
¨ Introduction ¨ Biomass Pellet Manufacturing Industry
¤ Pellet production process ¤ Process related emissions
¨ Wood pellet conversion for energy ¤ Point source emissions: Particulate matter and gaseous contaminants
¨ Pollution prevention and emission control ¨ Research directions
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Introduction
¨ Growing demand for biomass
¨ Paths towards sustainable development
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Source: Olsson & Kjällstrand, 2004
Introduction cont’d
¨ Biomass, wood
pellet market rapidly growing
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Source: NGO Briefing
Biomass Pellet Manufacturing Industry
¨ 42 pellet plants (2012)
¨ 3 million tonnes annual production capacity
¨ BC ~ 65% of Canadian capacity and production with 150,000 –
400,000 tonnes per plant annually
¨ Alberta, Quebec, New Brunswick, Nova Scotia, and Newfoundland
collectively ~ 35%
¨ Canadian exports mostly to Europe
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Source: WPAC
Biomass Pellet Manufacturing Industry cont’d
Pellet production process
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¨ Emissions associated with each step of pellet production including: ¤ Receiving and storage of the raw material (wood) ¤ Sizing the wood residue ¤ Drying ¤ Additional size reduction of the dried wood [hammer mills] ¤ Pelletizing – compressing the wood fines into pellets ¤ Cooling ¤ Storage, bagging
And ¨ Combustion of the process waste - heat for dryers
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Source: ESI, 2010
Biomass Pellet Manufacturing Industry cont’d
Process related emissions
¨ Point and volume source as well as fugitive emissions include: ¤ Particulate matter (PM), including condensable PM
¤ Total organic compounds (TOC)
¤ Carbon monoxide (CO) small amounts
¤ Oxides of nitrogen (NOx)
¤ Carbon dioxide (CO2) – close to neutral if biomass harvested sustainably
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Biomass Pellet Manufacturing Industry cont’d
Process related emissions
¨ Particulate matter: ¤ Dryers are the main source of particles emissions ¤ Pelletizers and coolers are also significant sources unless collected
with cyclones ¤ Hammer mills - larger PM upstream of dryers than downstream ¤ Conveyors ¤ Sawdust piles sources of fugitive dust
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Biomass Pellet Manufacturing Industry cont’d
Process related emissions
Average Permitted PM Emissions (kg/tonne) [Adopted from ESI, 2010]
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Biomass Pellet Manufacturing Industry cont’d
Process related emissions
Note: values are based on wood pellet mills and similar facilities: 10 in US, 1 in Germany, 2 in Quebec and 8 in BC
PM emission limits for biomass power plants vs permitted wood mills emissions
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Biomass Pellet Manufacturing Industry cont’d
Process related emissions
[Adopted from ESI, 2010]
¨ Volatile organic compounds (VOCs): ¤ Storage
¤ Handling of wood raw material
¤ Drying and pelletizing
¤ [Transport]
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Biomass Pellet Manufacturing Industry cont’d
Process related emissions
¨
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Biomass Pellet Manufacturing Industry cont’d
Process related emissions
Example of estimated VOCs (based on AP-42) from uncontrolled particleboard dryers
[Adopted from ESI, 2010]
¨ Experimental study Olsson & Kjällstrand, 2004 ¤ Higher with lower efficiency burners ¤ Benzene was the most noticeable aromatic hydrocarbon
Comparison of emissions from burning pellets in different combustors
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Wood pellet conversion for energy Point source emissions
Wood pellet conversion for energy cont’d
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¨ A LCA study Pa et al., 2011 ¤ Emission factors for pellet gasification
Wood pellet conversion for energy cont’d
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¨ Study by Ghafghazi et al., 2011
[Note: Partial table presented here]
Pollution prevention and emission control Fugitive emissions
q Raw wood material (sawdust, shavings) handling and storage ¤ Fugitive dust (usually PM >10µm) as a function on plant location and layout due
to impacts of exposure to weather elements, pile dimensions, material characteristics etc.
¤ Prevention & control: use of logs or decreased material quantity at the site, enclosure and containment, wind barriers, dust suppressants, etc
q Debarking, chipping: minor PM emissions, usually no emission controls q Conveyors should be enclosed
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¨ Pollution prevention strategies: ¤ Homogenous and lower moisture (dry) content raw material where possible
¤ Maximize energy conservation and fibre recovery
¤ Efficient, low emissions, low inlet temperature dryers with recirculating airflow;
¤ Efficient combustion systems with low emissions.
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Pollution prevention and emission control Point source emissions
¨ Engineered controls: ¨ Cyclonic PM collectors – high efficiency for large PM, used as pre-
cleaners ¨ Fabric filters – high efficiency for fine PM, not appropriate for the
material with a high moisture content ¨ ESP, wet and dry – high efficiency for fine PM, not appropriate for
condensable PM ¨ High efficiency scrubbers – venturi type, high energy use ¨ Regenerative Thermal Oxidizers – for VOC control
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Pollution prevention and emission control Point source emissions
¨ Engineered controls costs: ¨ Variable based on parameters such as boiler capacity
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Pollution prevention and emission control Point source emissions
Pollution control Estimated costs (US $) Comment
cyclone 7-10K A multicyclone up to 16K
Fabric filter/baghouses 100K Additional ~10K maintenance costs
ESP (dry & wet) 1,000-5,000K Average maintenance ~5K
High efficiency scrubber (venturi) 100-800K -
¨ Direct industrial emission measurement instead of emission factors which could overestimate emissions
¨ Emission characterization of different wood raw material ¨ Emission characterization of pellet derived products – torrefied pellets ¨ Pollution prevention strategies should have priority over controls
¨ BACT
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Research directions
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References
ESI (Beauchemin, P.,Tampier, M). (2010). Emissions and Air Pollution Controls for the Biomass Pellet Manufacturing Industry. Professional Report prepared for The BC Ministry of the Environment
Ghafghazi, S., Sowlati, T., Sokhansanj, S., Bi, X., & Melin, S. (2011). Particulate matter emissions from combustion of wood in district heating applications. Renewable and Sustainable Energy Reviews, 15(6), 3019–3028. doi:10.1016/j.rser.2011.04.001
Johansson, L. S., Leckner, B., Gustavsson, L., Cooper, D., Tullin, C., & Potter, A. (2004). Emission characteristics of modern and old-type residential boilers fired with wood logs and wood pellets. Atmospheric Environment, 38(25), 4183–4195. doi:10.1016/j.atmosenv.2004.04.020
NGO briefing Sustainability issues for solid biomass in electricity, heating and cooling. (n.d.). Available at: http://www.birdlife.org/sites/default/files/attachments/EU-Joint-NGO-briefing-biomass-sustainability-energy-March2012.pdf Olsson, M., & Kjällstrand, J. (2004). Emissions from burning of softwood pellets. Biomass and Bioenergy, 27(6), 607–611. doi:10.1016/j.biombioe.2003.08.018
Pa, A., Bi, X. T., & Sokhansanj, S. (2011). A life cycle evaluation of wood pellet gasification for district heating in British Columbia. Bioresource Technology, 102(10), 6167–6177. doi:10.1016/j.biortech.2011.02.009
Sippula, O., Hokkinen, J., Puustinen, H., Yli-Pirila�, P., & Jokiniemi, J. (2009). Particle Emissions from Small Wood-fired District Heating Units. Energy Fuels, 23(6), 2974–2982. doi:10.1021/ef900098v
WPAC. Canadian wood pellet production. Available at: http://www.pellet.org/production/production