AGING, INEFFICIENT AND EXPENSIVE to upgrade, the
Boardman Plant could have joined dozens of similar
coal-fired generating stations consigned to the
scrap heap of history as its owner prepared to
permanently mothball its 600 megawatts in 2020.
Instead, Portland General Electric is in the middle
of a grand experiment to see if the plant in eastern
Oregon can be successfully converted into the
world's largest biomass power plant.
The plant dates from the 1970s and the utility
already filed plans with state regulators to
permanently shut it down because of the cost
associated with bringing it into compliance with
early 21st-century environmental mandates currently
on the books and with any future carbon regulations.
"The mandate allows a small opening for repowering,
so we looked at biomass and natural gas, but its
large Rankine cycle boiler is very inefficient for
gas," Jaisen Mody, PGE's general manager of
generation projects, said.
"We started looking at biomass and looked at a
technology called torrefaction, and the more we
looked at it, the more it intrigued us."
But biomass power plants may fail because they don't
receive a consistent supply of fuel, which makes
securing a long-term power purchase agreement
difficult.
There are other obstacles, mainly due to the plant's
size.
"On paper, it looks like it will work, but no one
has demonstrated that on a boiler like ours with 100
percent fuel switching," Mody added.
The plan is to complete engineering studies and
reconstruction of the boiler, so that a test burn
could be performed over a few days in 2014.
Emissions data would be collected and operational
issues would be assessed. The Electric Power
Research Institute is the research partner with PGE
in the project.
If the tests prove successful and the emissions data
falls within certain parameters, the permitting
would be pursued and the project would be completed
over several years.
But as PGE emphasizes, that's a very big "if."
The other challenge is fuel sourcing. A baseload
plant of this size will require 4 million tons of
green biomass, so the plan is to run the plant at
100 percent power for six months of the year when
it's needed the most.
This is where local sourcing of green biomass and
the torrefaction process come in.
Torrefaction is a charring process of agricultural
material that essentially removes moisture -
roasting it in the absence of oxygen - that creates
a brick-like material that could be described as
green coal. It could be thought of as a half-step
below turning wood into charcoal.
PGE believes it has found a grass that will be
better than coal, which burns at 8,400 BTUs per
pound. PGE is investigating many potential plant
sources, but it believes it has found one that burns
at 10,000 BTUs per pound.
Wayne Lei, director of research and development,
said the utility found a nearby university that had
been experimenting with a plant that can replace
hardwood fiber in pulp production.
"It came to our attention that University of
Washington was testing a plant called arundo donax,
a perennial grass that grows faster, like a
switchgrass, but it's the most productive in its
class," Lei said.
The plant is prolific: An acre can yield 25 to 30
tons of the grass with a low moisture content. And
with arundo donax having similar requirements for
water and a growing season like alfalfa and corn,
crops already grown in the Columbia River Basin, the
local sourcing issue may be solved.
Coal-to-biomass conversions under way or that have
been successfully completed are well below the scope
of the Boardman Plant.
"Successful biomass plants tend to be under 100
megawatts," said Bob Cleaves, executive director of
the Biomass power Association. "Developers are
challenged by making sure that the coal plant can be
appropriately sized as a biomass opportunity as the
two tend to be different. Biomass tends to be local
in its supply and frankly few places exist that
could accommodate a few hundred megawatts in biomass
capacity."
DTE Energy has been one of the more active companies
in the conversions of old coal plants during the
past eight years, with the Detroit-based holding
company owning, operating or currently converting
plants in three states.
"We looked at the growing trend of coal plant
shutdowns and decided that if biomass made sense, we
were zeroing in on plants that could generate 40
megawatts to 50 megawatts," said Steve Sorrentino,
vice president, power and renewables. "If you're
looking at the 15-to-25-megawatt plant, that's a
tough economy-of-scale play in capital costs as well
as in fuel acquisition."
DTE Energy has completed biomass conversions in
Cassville, Wis., and Bakersfield, Calif. It has
operating biomass power plants in Woodland., Calif.,
and Mobile, Ala.
One of the first was the Wisconsin project of a
1950s plant that the Dairyland Cooperative formerly
owned and that operated sporadically in recent
years.
After feasibility studies and a power contract with
Dairyland, which was seeking renewable electricity,
permitting came in a relatively quick 15 months.
Operation started in late 2010.
"If you can do this in the range of $1,000 per
kilowatt, that's one of the other drivers,"
Sorrentino said. "When you build a new biomass
plant, the number is $4,000 to $5,000 per kilowatt."
Not all conversions come that cheaply, and perhaps
many are closer to $2,000 per kilowatt, but they're
worthwhile when there is a ready customer, as in the
case of the ongoing Stockton conversion.
The 45-megawatt plant's output will be sold to
Pacific Gas and Electric under a 25-year power
purchase agreement. "PG&E is very aggressive with
renewables," Sorrentino said. And the plant
qualifies under California's renewable portfolio
standard of 33 percent by 2020.
The plant is on track for a late 2013 opening and
will be supplied by tree trimmings and the like, as
well as wood pallets and other so-called "urban
waste."
So what is the future of coal-to-biomass
conversions?
"It's going to continue, but I don't think at the
same pace as before natural gas became so
prevalent," Cleaves said. "We think there will be a
greater trend toward co-firing as opposed to
complete conversion. In smaller projects it makes
lots of sense as small coal plants struggle to meet
EPA mandates."
Bill Opalka is editor of RenewablesBiz. This story
first appeared in EnergyBiz magazine.
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