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Feb. 3, 2010
By Janet Wong
Using wood pellets in place of
coal to fire Ontario’s power plants reduces their output of greenhouse
gas emissions by as much as 91 per cent, says new research from the
Faculty of Applied Science and Engineering.
“Our study
investigates, on a life cycle basis, 100 per cent wood pellet firing
and co-firing with coal in two coal power-generating stations in
Ontario,” said Professor Heather MacLean
of U of T’s Civil Engineering Department and lead author of a study in
the January 2010 edition of Environmental Science and Technology. “The
results were significant. We found that greenhouse gases from these
power plants were reduced by 91 per cent when employing wood pellets
instead of coal, and 78 per cent when using wood in place of a natural
gas combined cycle.”
The wood pellets used in the study were
made from roundwood harvested from the Great Lakes-St. Lawrence forest
region. The researchers compared greenhouse gases (GHG) and some air
pollutant emissions of wood pellets with those resulting from current
coal and hypothetical natural gas power plants. Their analysis included
the impact from resource extraction (coal mining, natural gas
production or forest harvesting), fuel processing, transportation to
the generating station and combustion to produce electricity.
“Our
study is the first one that analyzes 100 per cent biomass usage in coal
generation power stations,” said MacLean. “The results from the
analysis are expected to provide valuable insights for decision making
in the sustainable development of future electricity generation
systems.”
Coal electricity generation was responsible for 15 per
cent of Ontario’s total GHG emissions in 2007. The Ontario government
has committed to eliminating the use of coal for electricity generation
by Dec. 31, 2014. In contrast, the European Union has rules requiring
member countries to generate 20 per cent of their electricity from
renewable sources by 2020 and wood pellets are currently used for
electricity generation in Europe. Some utilities in the United States
are now beginning to use wood pellets. Currently, there are no
utilities in Canada that use wood pellets as a renewable energy
resource.
“Wood pellets, provided they are sustainably and
responsibly produced, are a low-GHG fuel that can effectively displace
conventional fossil fuels in electricity generation or for thermal
applications such as heating or hot water,” said MacLean. “Biomass
co-firing and 100 per cent biomass usage should be considered along
with other options such as wind or solar technology for electricity
generation to reduce GHG emissions and increase renewable electricity
generation.”
However, she acknowledges that biomass may not be
economically competitive for electricity production except in niche
markets where forestry harvesting occurs in abundance and costs are
low. To make significant gains in reducing GHG emissions, a combination
of conservation, efficiency improvement and renewable energy sources is
needed.
While using coal to generate electricity is the lowest
cost option, it is also the most environmentally detrimental. As our
society transitions to a more sustainable economy, it is important to
consider both the costs and benefits of alternatives that can lead us
along this transition path, MacLean said. “Evaluating the merits of
using wood pellets for electricity generation requires a weighing of
the issues, in particular: How great are the environmental benefits
this method can achieve? How great are the economic costs to implement
the method? How does this method compare to other sustainable
alternatives? This is the sort of thinking that must be undertaken by
policy makers whose job is to decide what the energy sector of tomorrow
should look like,” she notes.
“Climate change and reducing greenhouse gas emissions are some of the critical issues facing the world today,” said Professor Cristina Amon,
Dean of the Faculty of Applied Science and Engineering. “When it comes
to these pressing issues, our faculty and engineers are at the
forefront of environmental research. This study led by Professor
MacLean provides policy makers and governments with data that will help
them make informed decisions about the potential and feasibility of
this type of renewable energy.”
Using wood pellets in place of
coal to fire power plants, however, is only part of the solution to
lowering Canada’s output of greenhouse gases, MacLean adds. Coal-fired
electricity generation was responsible for about 13 per cent of GHG
emissions in 2006 in Canada – 95.1 million tonnes of carbon dioxide
equivalents (CO2-eq). “Converting all of these plants to wood pellets
would eliminate the vast majority of these emissions. Assuming a 91 per
cent reduction in GHG emissions, as estimated in our study, about 86.5
million tonnes of GHG emissions could be reduced through switching to
100 per cent pellets firing, provided that adequate biomass was
available to produce that quantity of pellets and that the impact on
forest carbon storage was not great,” she said.
But coal-fired
electricity generation is only one source of GHG in Canada. Canada’s
goal is to reduce its GHG emissions by 20 per cent from 2006 levels by
2020 – a reduction of 144 million tonnes of CO2-eq. Canada’s total GHG
emissions in 2006 was 721 million tonnes of CO2-eq. Therefore, notes
MacLean, meeting or exceeding aggressive GHG emission reduction targets
would require an economy-wide effort. “There is no silver bullet in
tackling climate change. Targets will only be met through the combined
contribution of many smaller-scale solutions, of which wood pellets is
just one.”
MacLean is also cross-appointed to the Department of
Chemical Engineering and Applied Chemistry and the School of Public
Policy and Governance at U of T. She conducted this research with Yimin Zhang and Jon McKechnie of U of T’s Civil Engineering Department, Denis Cormier of FPInnovations-FERIC, Robert Lyng of Ontario Power Generation, Warren Mabee of the School of Policy Studies and the Department of Geography at Queen’s University, and Akifumi Ogino of the National Agriculture and Food Research Organization in Japan.
The research was supported by Ontario Power Generation and the Natural Sciences and Engineering Research Council.
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