Smaller ethanol plants built with advanced technology could stimulate the growth and development of cellulosic ethanol in a wide variety of communities with a wider selection of biomass feedstocks.

Biomass or cellulosic ethanol plants operate differently from corn ethanol plants. The differences between these two types of ethanol plants have to do with the chemical structure of biomass and its distribution. Biomass is less dense than corn, and most biomass feedstocks yield less glucose per ton than corn grain. These density and compositional differences have an impact on the design and cost of cellulosic ethanol plants. The lower density of biomass means that a greater volume of biomass is needed to make the same volume of ethanol, as compared to corn. For example, a given volume of cellulosic ethanol requires 27 volumes of switchgrass, compared to 3.6 volumes of corn grain. This feedstock volume problem works against the standard engineering assumption of economies of scale, i.e., larger plants require more biomass feedstock which must be transported from longer distances, increasing delivered feedstock costs and the greenhouse gases generated by feedstock transportation. Economies of scale are valid, but must now be balanced against the operating costs of feedstock transportation, feedstock availability at the plant, and overall greenhouse gas balance of the operation.

The biomass density problem raises the possibility that smaller ethanol plants may have a role in rural, forest and urban economies. Small plants are a better fit where local biomass feedstocks are limited in quantity. The number of such sites is much greater than the number of sites which could potentially support large bioethanol plants.

Another current barrier for cellulosic ethanol plants is their higher capital cost per annual gallon compared to corn ethanol plants. These higher capital costs are the result of the the need for pretreatment of biomass to expose the cellulose for enzymatic conversion to glucose, and to extract hemicellulose which potentially can be converted to sugars like xylose for additional ethanol production. Additionally, biomass ethanol plants may contain lignin burners and boilers which can lower net fossil energy use, but add to the plant cost. A rough comparison is that with current technology, corn ethanol plants cost $1.50-2.00 per annual gallon, or about $50-60 million for a 30 million gallon corn ethanol plant. In contrast, biomass ethanol plants may cost $6.00 or more per annual gallon.

One approach to this problem is to build larger biomass ethanol plants and reduce capital costs through economies of scale. An alternative approach outlined here would be to reduce capital costs per gallon with improved technology, allowing the construction of smaller ethanol plants with lower capital hurdle rates. Such smaller plants would be a better fit for localized sources of biomass, which are more numerous in North America, Asia, Europe and other regions.

This has implications for U.S. energy policy and the implementation of the Energy Policy Act. See the recent cellulosic ethanol paper from the Institute for Local Self-Reliance (ILSR) for policy recommendations. These issues are also discussed in our paper and House testimony on cellulosic ethanol.

Biomass is an abundant and underutilized resource which remains to be effectively used on a commercial and societal scale.  Green plants produce an estimated 1 trillion metric tons of cellulose every year. Using even a fraction of this for fuel ethanol and biogas could begin to reduce our yearly addition of more fossil carbon to the atmosphere, slowing the increase in global warming, and providing additional domestic energy supplies and jobs.  Worldwide, the use of biomass could provide social and economic benefits to many countries and reduce their dependence on imported oil, while lowering their emissions of CO2 from fossil carbon.

General Biomass offers scientific and technical consulting for cellulosic ethanol, biorefineries, and production of fuels and chemicals from biomass. We have substantial experience in technology development, patent evaluation, grant writing, grant evaluation and project management. Specific experience includes a strong knowledge of biomass structure and chemistry, cellulases and other hydrolytic enzymes, pretreatments, and ethanol plant economics.

<--Back to the top of the Page

Copyright © 2011 by General Biomass Company. All Rights Reserved.