POWER February 2011 - 58

PLANT DESIGN
Designing Fuel Systems for Large
Biomass Plants
Compared with other solid fuel-fired plants, the systems and components required
for handling and processing biomass appear quite familiar, but important
fuel differences must be considered. A successful biomass plant
design must provide flexibility for handling the expected wide range of
biomass fuel properties and characteristics.
By Daniel Mahr, PE, Energy Associates PC
P
ower plant owners and developers
have multiple ways to include
biomass as a fuel in their fleets.
Cofiring-adding biomass generation to
existing coal-fired plants-is a relatively
inexpensive option. For large units, the
simplest approach is to cofire biomass
with coal. (For an example, see " OPG
Charts Move from Coal to Biomass, " April
2010 in POWER's online archives at www
.powermag.com.) Biomass can also be
added to a plant that has smaller, older, inefficient
coal-fired units: One or more old
units can be replaced by a modern, efficient
boiler that is designed to best utilize
solid fuels, including biomass. Greenfield
plants are a third option, but they take
The EU Cofiring Experience
The European Union (EU) has set firm goals for renewable energy
consumption, and all member states are expected to supply
20% of their energy requirements by 2020 from sustainable
forms of energy. Those renewable options include wind, landfill
gas, and biomass; solar, geothermal, and wave power are also
expected to contribute small amounts.
Because of the EU's renewable energy requirements, some
European coal-fired plants have implemented or are developing
programs that will add biomass to their fuel mix. In the
United Kingdom (UK), what appears to be the largest cofiring
project was recently brought online by Drax Power. Its 4,000MW
coal-fired Drax Power Station in Selby, North Yorkshire, is
the largest coal-fired station in the UK and provides enough
power to meet 7% of the UK's electricity needs. (See " Drax Offers
Model for Cofiring Biomass, " July 2010.) Drax Power began
experimenting with a system that blends biomass with coal,
using the existing emergency coal reclaim hopper. Based upon
the success of this project, Drax Power recently completed an
£80 million ($150 million) direct biomass injection system.
Together, the 100-MW blending and the 400-MW direct injection
systems provide 500 MW of biomass generating capacity
(Figure 1).
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POWER | February 2011
more time to bring online and obviously
involve additional siting complexities.
Whichever option a plant owner chooses,
designing a plant, or its retrofit, with the
special characteristics of biomass in mind
is critical for successful use of the various
forms of this renewable fuel. Those characteristics
affecting plant design are the focus
of this article.
Cofiring in a Utility Boiler
Many utilities have a fleet of existing
multi-unit coal-fired power plants. The
easiest way to add biomass to the fleet
is to adapt those existing plants to burn
biomass. Although doing so requires plant
additions and modifications, compared
with starting from scratch, modification
for cofiring is a relatively low-cost option.
This can be practical when the amount of
biomass available is relatively modest.
Approximately 4% to 5% biomass can
be blended with the reclaimed coal, especially
if the unit has spare mill capacity.
At increased percentages of biomass, direct
firing is advantageous. In fact, boiler
capacity can actually be improved by
biomass cofiring when unit generation is
limited due to wet coal.
Beginning in 1996, the Electric Power
Research Institute and the U.S. Department
of Energy (DOE) began a biomass
cofiring research program that continues
today. Demonstration projects were con1.
Biomass is big in the UK. The 4,000-MW Drax Power Station
recently completed a retrofit that allows it to blend biomass with coal using
the existing emergency coal reclaim hopper. Together, the 100-MW
blending and the new 400-MW direct injection system provide 500 MW
of biomass generating capacity. This photo shows the handling and storage
area of the biomass cofiring system during construction. The facility
uses wood pellets that are delivered by rail. Bottom dump rail cars are
unloaded, and the pellets are stored in four silos. The wood pellets are
reclaimed and conveyed to a fuel feed bin and then pneumatically conveyed
and injected into the combustor. Courtesy: Energy Associates
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POWER February 2011

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