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This analysis developed detailed process flow diagrams and an Aspen Plus® model, evaluated energy flows including a pinch analysis, obtained process equipment and operating costs, and performed an economic evaluation of two process designs based on the syngas clean up and conditioning work being performed at NREL. One design, the current design, attempts to define today's state of the technology. The other design, the goal design, is a target design that attempts to show the effect of meeting specific research goals.

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Executive SummaryThe ZeaChem indirect method is a radically new approach to producing fuel ethanol from renewable resources. Sugar and syngas processing platforms are combined in a novel way that allows all fractions of biomass feedstocks (e.g. carbohydrates, lignins, etc.) to contribute their energy directly into the ethanol product via fermentation and hydrogen based chemical process technologies.The goals of this project were: 1) Collect engineering data necessary for scale-up of the indirect route for ethanol production, and 2) Produce process and economic models to guide the development effort. Both goals were successfully accomplished.The projected economics of the Base Case developed in this work are comparable to today's corn based ethanol technology. Sensitivity analysis shows that significant improvements in economics for the indirect route would result if a biomass feedstock rather that starch hydrolyzate were used as the carbohydrate source.The energy ratio, defined as the ratio of green energy produced divided by the amount of fossil energy consumed, is projected to be 3.11 to 12.32 for the indirect route depending upon the details of implementation. Conventional technology has an energy ratio of 1.34, thus the indirect route will have a significant environmental advantage over today's technology. Energy savings of 7.48 trillion Btu/yr will result when 100 MMgal/yr (neat) of ethanol capacity via the indirect route is placed on-line by the year 2010. DE-FG36-03GO13010ZeaChem, Inc.ii 1 Project DescriptionExisting technologies for fuel ethanol production all rely on direct fermentation of carbohydrates derived from corn, sugar cane and other sources. All direct fermentation routes suffer from low carbon efficiency. For example, when the fermentable sugar is dextrose: two of the six carbon atoms in the substrate are converted into carbon dioxide, giving a maximum carbon efficiency of only 67%. From a chemical energy perspective, direct fermentation is actually quite efficient. The ratio of higher heating values for ethanol and dextrose is (2 x 1369 kJ/mol)/(2807 kJ/mol) * 100 = 98%, which means that most of the chemical energy stored in the starting dextrose is preserved in the final product. However, throwing away carbon in the form of CO 2 restricts the ability of direct fermentation processes to derive chemical energy from sources other than fermentable carbohydrates.What are the consequences of this limitation? Consider processing a typical lignocellulosic biomass such as corn stover into ethanol. Roughly one-third of the energy content of the feed is present in the form of cellulose, which can be converted into dextrose with appropriate pretreatment and hydrolysis of the feedstock and then fermented with traditional direct fermentation yeasts or similar micro-organisms. Lignin and other non-fermentable materials account for approximately 40% of the energy content of the feedstock. None of this energy can be used directly for ethanol production; it can only be burned and the heat released used to g...