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EERC Update

Biomass Power Options for Existing Ethanol Plants
By Bruce Folkedahl
As corn-to-ethanol production increases and natural gas prices appear steady or poised to rise, more facilities are interested in fueling their production with biomass residues. One of the first steps in assessing energy options at existing corn-to-ethanol plants is exploring potential available feedstocks.

For utilization of biomass to be economically viable for heat and power, even with high fossil fuel costs, plants need to look for the opportune biomass fuels available to them. Biomass that has already been processed and designated as a renewable fuel, such as a pelletized biomass, tends to be more costly on a heating basis than most fossil fuels.

Finding opportune fuels requires a regional search where the plant operates. The biomass may already be getting land-filled or be considered a nuisance material that can be obtained for little more than trucking cost. In many cases, trucking is the largest cost for biomass used as a fuel source since most biomass materials are far less energy-dense than fossil fuels. Biomass generally tends to contain more moisture than fossil fuels, which lowers its energy density.

Flexibility is a key element when considering biomass as a fuel. Many of the plant's biomass resources will not be available on a continuous basis, requiring plant engineers to consider several different kinds of biomass as energy fuels over the course of a year.

Corn stover may be ideal immediately after the corn harvest, but in late winter and early spring another source such as wood biomass may be required. Plants using more than one consistent fuel source must conduct a careful evaluation of the conversion process design to ensure its adaptability to the various biomass fuels under consideration.

Additional considerations include biomass storage. Coal can be brought in by the trainload and stored on the ground, and natural gas is just another pipe into the plant. However, biomass requires more storage area per unit of energy potential. In addition, drying may be necessary to prevent spoilage, odors and feeding problems within the conversion process.

Another key issue is the permitting process, which should start as early as possible to ensure enough lead time to facilitate anticipated start-up dates. Once the potential biomass feedstocks have been identified, engineering studies will need to be completed to assess how the biomass will be converted to heat and power.

There are four basic ways to utilize biomass for heat and power: 1) direct combustion with the biomass as the sole fuel source, 2) cofiring biomass with fossil fuels, 3) gasification of the biomass to produce a synthetic natural gas or syngas, and 4) fast pyrolysis to produce a combustible syngas and a combustible liquid from the biomass. These will be discussed further in next month's issue.

Bruce Folkedahl is a senior research manager at the EERC in Grand Forks, N.D. He can be reached at bfolkedahl@undeerc.org or (701) 777-5243.
 

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