Biomass Feasibility Project Final Report - Xcel Energy

Co-firing. The cheapest and quickest way to put biomass to work generating electricity is to
meter it into an existing coal-fired power plant. Most coal plants can digest up to 5% biomass
without major modifications. Gases from gasified biomass also may be co-fired in natural gas
“peaking” plants, so called because they fire up that expensive fuel in periods of peak demand,
like hot summer days when air conditioners run full blast.
Combined Heat and Power (CHP). Both fossil fuels and biomass have been widely used in CHP
plants. This is a strategy that uses steam for power turbines and heat for industrial processes or
space heating. CHP often is called “co-generation” because of its dual purpose.
Biomass in the form of waste streams in industrial plants has fueled co-generation for well over a
century. Burning wastes is essential to the economics of pulp and paper mills and lumber mills,
most of which dispose of their wood wastes that way and, in the process, generate much of
their power and all of their process steam. The forest products industry is primarily responsible for
the ranking of biomass as the second largest category of renewable energy in the U.S., after
hydroelectricity.
Co-generation has the advantage of increasing the overall energy efficiency of its host plant by
using steam for purposes beyond power generation. It has the potential to do even more than
that. Academic and corporate researchers are developing new technologies that may turn
major industrial facilities, like paper mills, into exporters of power to the grid.
Municipal applications of CHP are rare in Minnesota, but three noteworthy examples, St. Paul
District Energy and the plants of the Laurentian Energy Authority in Hibbing and Virginia on the
Iron Range, burn woody biomass in centralized energy plants to heat urban districts and
generate power for Xcel Energy’s renewable portfolio.
Gasification in ethanol plants. Ethanol is raising concerns among environmentalists, food and
feed processors and livestock producers, but it is a well established Minnesota industry with 16
plants and more to come. Natural gas is a major cost item for ethanol plants, and so several are
using, or planning to use, gasified biomass as a substitute. The Central Minnesota Ethanol Cooperative
(CMEC) in Little Falls has made the big step of installing a gasifier. It uses its former gas
boiler for process heat and power generation and is the only Minnesota ethanol plant selling
power to a utility – one MW to Xcel Energy. Another project, Chippewa Valley Ethanol
Company in Benson, is in the process of installing two gasifiers and plan to market its technology
to other ethanol producers.
Municipal waste treatment. The St. Paul Metro Plant uses a fluidized-bed incinerator burning biosolids
to produce steam that heats the plant in winter and generates 5 MW of power for internal
use in the summer. The Empire Waste Water Treatment Plant in Dakota County burns bio-gas
from an anaerobic digester to make steam and generate power, an example of a strategy
discussed earlier – using gaseous or liquid fuels from biomass to fuel turbine generators.
Bio-power from manure. Two projects, one large and one small, are generating electricity from
animal wastes. The Fibrowatt plant in Benson makes up to 55 MW of power from turkey litter
(manure and wood shavings used for bedding) to sell to Xcel Energy. The Haubenschild farm
near Princeton uses bio-gas from manure to generate 135 kW for internal use and for sale to the
local power co-op.
Page iv
Identifying Effective Biomass Strategies:
Quantifying Minnesota’s Resources and Evaluating Future Opportunities