Densified Biomass Fuel (ie. Wood Pellets): Usage Distribution and
Environmental/Climate Impacts
The EIA recently came out with some statistics on U.S. wood
pellet manufacture, usage, and other issues. The data includes only the first
half of 2016. This may be the first time that this data has been compiled or at
least presented by the EIA apparently.
The EIA data notes that 3.3 million tons were produced in 1H
2016 and 82% of that was exported. They also note that 85% of the material to
make wood pellets is wood waste, mainly from logging and saw mills. The
remaining 15% comes from trees logged. That means that a 495,000 tons of wood
pellets were derived from trees that were cut down in that 6-month period to
make wood pellets and 405,900 tons of pellets from cut trees to ship to Europe
to burn in wood-burning power plants in those six months. Actually, the weight
of trees logged is probably much higher since wood pellets are processed by
drying and reducing their moisture reduces their weight. Recently much of the
wood pellets have gone to the U.K. and specifically the Drax Power Station that
made up about 7% of U.K. electricity in 2015 by burning coal and wood biomass.
Since half is biomass, it accounted for 3.5% of 2015 U.K. electricity. That
year they imported 7.5 million tons of biomass mostly from Canada and the U.S. The
biomass, as densified wood pellets, qualifies for a subsidy as a “green” energy
source. However, it cannot really be said to be green at all. While wood
biomass and solid waste biomass may be renewable they are far from clean. In
fact, it may be dirtier than coal in terms of particulates and pollutants. It
also produces very significant greenhouse gases, although advocates suggest
that it is carbon neutral or at least carbon-lean since much of that carbon
will leak into the atmosphere eventually as the trees die and rot. However,
this takes a much longer time period. As trees take a long time to grow to
maturity the renewable-ness of grown wood is quite questionable. Wood waste can
be seen as a better source but much of the carbon from that waste is deprived
from fertilizing future trees and so theoretically reduces soil fertility.
Environmentalists are even coming to understand the
detriments of wood biomass as a clean energy source. It was the successful
harvesting of oil and gas that saved forests from being used for fuel. Electric
and gas furnaces replaced wood and coal furnaces. Gas stoves replaced wood for
cooking. This resulted in reduced coal smoke and wood smoke pollution as gas
replacing coal in power plants does today. However, the European Union’s 2020 climate
and energy program classifies wood pellets as a carbon-neutral form of
renewable energy and thus European power plants have been investing heavily
converting from burning coal to burning wood pellets. The NRDC has complained
that hardwood trees in North Carolina are being harvested from rich bottom
lands for wood pellet manufacture, resulting in significant environmental
impact. There is debate about the carbon-cycle calculations in harvesting and
burning wood biomass and much is dependent on how much waste compared to how
many trees are felled and the types of trees. One question is whether Asia or
even the U.S. will also opt to adopt burning wood pellets over burning coal.
Critics have argued that there is simply not enough waste wood to feed wood
pellet demand in the long-term so building wood-burning power plants would be
unsustainable. That is why fast-growing soft-wood trees like loblolloy pine are
already also being used. Using hardwood trees would be far less renewable.
According to one consulting company that tracks forestry trends a significant amount
of bottomland hardwood trees are being felled to produce wood pellets for
export. Data from the EIA and the IEA “show that burning wood pellets results
in major impacts on forests for very modest quantities of bioenergy. “ Carbon-cycle
accounting has revealed that “burning wood pellets releases as much or even
more carbon dioxide per unit of energy as burning coal.”
According to the graphic shown in Blakemore’s post
(referenced below)
“Burning wood, because of its lower heat efficiency, emits
12% more CO2 than coal per unit of electricity produced.”
Add to that the energy intensive processing requirements for
densifying the wood and shipping the wood overseas and its life-cycle
greenhouse gas emissions are high.
While wood pellets burn more efficiently with higher
combustion rates and less pollutants and emissions than burning logs the smoke
still pollutes and emits greenhouse gases. EPA notes that pellet stoves burn at
78% efficiency compared to 54% efficiency for regular wood stoves. There is
also less ash produced. Pellet stoves do produce more particulate matter than fuel
oil and far more than natural gas. This is problematic for any green
designation. Although some clean energy advocates like wood pellets it is
mostly a trade-off that can only have relative value compared to dirtier and
less efficient energy sources. The more than half-million tons of logged trees
cut to be pelletized with most shipped to Europe in the first 6 months of the
year also serve as important carbon sinks now deforested and not sequestering
carbon until such time as those trees can be replaced.
One can make a ‘no brainer’ argument that natural gas is
cleaner than densified wood biomass. It burns way more efficiently, produces
far less pollutants, and emits less greenhouse gases. It is not renewable in
its fossil form but is renewable as biogas from anaerobic digesters and
landfills. It can also be produced efficiently compared to wood. It is more
energy dense and so more portable as well. Thus the Europeans would be better
off burning U.S. or other LNG or even their own fracked gas or North Sea gas in
power plants than U.S. wood pellets – and air pollution would be considerably
reduced. Of course there is no subsidization of natural gas in the U.K. as
there is of wood pellets. At Drax 2015 subsidization of wood pellets amounted
to 450 million English pounds and was passed on to consumers in the form of
higher electricity prices. So basically, they are paying a higher cost for
dirtier electricity compared to natural gas. Of course that may change in the
future as inexpensive gas supplies become more readily available.
Wood pellet manufacture has ramped up over the last few
years in the southeastern U.S. mainly for export to Europe. Between 2012 and
2016 U.S. production of wood pellets basically quadrupled. It is uncertain how
long this biomass harvesting, exporting, and burning will continue but Drax has
invested in U.S. pellet mills, built a $100 million pound import terminal and
invested hundreds of millions in outfitting their plant to burn biomass.
The bottom line is that while densified biomass is
technically renewable there are serious environmental, climate, and efficiency
issues associated with it as a desired fuel source. It is often counted in
tabulations of renewable energy and sometimes erroneously in tabulations of
clean energy. While using primarily wood waste is better than felling trees
that only lessens the deforestation impact. The pollution and other climate
impacts remain. Air pollution from wood fires is a serious problem,
particularly in the developing world and shortens the lives of many, often women
and children who often tend the fires. While pellet stoves are better for
emissions and burn more efficiently than logs they are still wood.
References:
New EIA Survey Collects Data on Production and Sales of Wood Pellets –
by Energy Information Administration: Today in Energy, Dec. 14, 2016
Portland, Oregon’s Electric Utility Wants to Burn Wood Instead of Coal,
Which is a Terrible Idea – by Ben Adler, in Grist.org, Dec. 12, 2016
Taking Biomass Too Far? – by David Blakemore, posted on LinkedIn, Feb.
25, 2017
Wood Pellets: Green Energy or New Source of CO2 Emissions – by roger
Drouin, in Yale Environment 360, Jn. 22, 2015
Finding A Balance – Pellets Are the Answer,
in The Environmental Impact
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