Biomass Feasibility Project Final Report - Xcel Energy

CHAPTER VI : PRESENT APPLICATIONS OF
BIOMASS TECHNOLOGIES
Much of this study deals with future development of biomass power generation; trying to answer
questions about what kinds of biomass there are, where it is, what its characteristics are, how
much it costs, how to collect and process it, what conversion technologies to use, how to plan
and finance a project, and so on.
But there already are a number of biomass projects in Minnesota that are worth knowing about
because they can teach us lessons their developers had to learn the hard way. And there are
many other existing operations that don’t use biomass now but might do so in the future. This
chapter reviews examples of Minnesota projects to show how technology, biomass, engineering
and financing came together.
CO-FIRING
Co-firing is the use of biomass fuel mixed with other fuels, including fossil fuels. For that reason, it
is not only an additional source of energy, it also is a means of conserving and extending fossil
resources. As it currently is practiced, co-firing mixes biomass (usually wood) with another fuel
(usually coal), usually in a boiler designed for coal. The pulp and paper industry long has cofired
coal with wood waste, and so have utility power plants in areas where wood is cheap and
available. In addition to co-firing in combustion boilers, fuels also can be mixed in more
sophisticated gasification and combined-cycle technologies. In those cases, co-gasifying may
be a more precise term than co-firing.
There are several ways biomass can be co-fired with other fuels. In coal-fired plants, the most
common method is simply adding a small percentage of biomass fuel to coal. But for facilities
using natural gas or oil, biomass first must be transformed by gasification and/or biorefining into
gas or liquid fuels. Biofuels then can combine with fossil fuels to power combustion turbines, add
to the steam cycle of a cmbined-cycle power plant, or mix with other fuels in a gas boiler.
(Chiaramonti, et. al., 2007; Hughes, 2002; Sturzl, 1997)
Co-Firing Biomass with Coal
At present, by far the most common way to co-fire solid biomass is to blend it with coal.
Hundreds of U.S. industrial plants, like paper mills, burn their own processing wastes with coal to
generate energy and avoid disposal costs. There are several examples of this in Minnesota. The
Federal Energy Management Program ranked Minnesota’s potential for co-firing as “Good,”
based on the state’s average delivered price of coal, its supply of low-cost biomass residues,
and its average landfill tipping fees (FEMP, 2004).
Co-firing coal with biomass in combustion boilers offers advantages over burning biomass alone.
Boilers designed exclusively for biomass generally are smaller and less efficient (around 20%
efficiency) than larger coal-fired boilers (33 to 37% efficiency). After a coal boiler is tuned to use
mixed fuels, co-firing does not result in an appreciable loss in output. Co-firing combustion
efficiency still runs at about 33-37% (Bain, et. al., 2003).
Because of the depreciation of existing plants and their connections to existing infrastructure,
like water, sewer, roads, rail, and the electric grid, it is much cheaper to convert an existing fossil-
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Identifying Effective Biomass Strategies:
Quantifying Minnesota’s Resources and Evaluating Future Opportunities