Sunday, April 29, 2007

Comparison of biorefineries based on the biochemical and thermochemical platforms

Mark M. Wright and Robert C. Brown. Center for Sustainable Environmental Techlnologies, Iowa State University, 286 Metals Development Bldg., Ames, IA 50011

There are two major pathways to the conversion of biomass to liquid fuel: the biochemical and thermochemical pathways. The biochemical path, also known as the sugars platform, relies on enzymatic hydrolysis and fermentation. Thermochemical conversion employs gasification techniques along with catalytic upgrading.

Ethanol from corn grain fermentation is a commonly known process. Fermentation plants are generally small scale, low capital and operating cost facilities. With increasing demand, plant capacities are expected to increase with implications on the production costs. Biochemical plants are not economically suited for large-scale operation when compared to the thermochemical platform.

Biomass can be converted to synthetic fuels such as methanol, hydrogen, and Fischer Tropsch liquids through various thermochemical processes. At small scales (less than 100 million gallons per year), thermochemical processes are expensive to build and operate. Due to economies of scale, large-scale thermochemical plant’s unit costs are actually lower than biochemical plants of the same energy capacity.

The purpose of this paper is to prove that thermochemical plants are less expensive than similar biochemical facilities. An ethanol plant with 150 million gallons of gasoline equivalent capacity and $3/bu corn grain has a production cost of $1.74/gallon of gasoline equivalent. A similar methanol plant, at $50 per Mg biomass, has a production cost of  $1.19 per gallon of gasoline equivalent. This paper compares the costs of thermochemical and biochemical on an equal fuel output basis.