Monday, May 5, 2008 - 4:30 PM
5-06
The impact of biomass availability and processing cost on optimum size for biomass processing
Biomass such as agricultural or woody residues can be processed to a variety of useful energy forms. For example, straw and corn stover can be used to produce electricity via direct combustion or gasification, and transportation fuel via lignocellulosic ethanol fermentation or Fischer Tropsch synthesis of diesel from biomass derived syngas. As the scale of processing increases, the delivered cost of field sourced biomass increases due to increasing transportation distances, but the unit cost of processing the biomass decreases due to economies of scale in both capital and operating cost. Because of the competition between these cost factors, biomass processing plants have an optimum size at which output cost is minimized. In this work we consolidate available data on the above four processing alternatives, adjusting for currency and inflation. We then model biomass processing for a range of biomass availability (tonnes or GJ per gross hectare, where gross hectares includes the entire geographical area in which the biomass plant is situated) to explore optimum size as a function of delivered cost of feedstock as well as processing cost. The sensitivity of optimum plant size to a relaxation in the constraint of minimum cost is also explored as a function of these factors. Both optimum plant size and the sensitivity to a relaxation in minimum cost vary widely over the range of processing cost and feedstock availability of currently proposed biomass projects.
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