The U.S. Department of Energy (DOE) is supporting the development of ethanol from lignocellulosic feedstocks as a means of building upon the energy-security benefits of corn-based ethanol and displacing conventional petroleum-based transportation fuels. DOE funds both fundamental and applied research in this area and their analysis provides a method for predicting cost benefits of proposed new research. To that end, the National Renewable Energy Laboratory (NREL) has modeled many potential process designs and estimated the economics of each process during the last 20 years. During June 2002, NREL completed a report that updates NREL's ongoing process design and economic analyses and describes a potential design and necessary targets for reaching an ethanol price of $1.07 per gallon.
 
 Private industry partners
 In a report published in 1999, NREL performed a complete review and update of the process design and economic model for the biomass-to-ethanol process utilizing co-current dilute acid prehydrolysis with simultaneous saccharification (enzymatic) and co-fermentation. The process design included the core technologies being researched under DOE funding: prehydrolysis, simultaneous saccharification and co-fermentation, and cellulase enzyme production. In addition, all ancillary areas-feed handling, product recovery and purification, wastewater treatment, lignin combustion and boiler-turbogeneration, and utilities-were included. NREL engaged Delta-T Corporation (Delta-T) to assist in the process design evaluation, the process equipment costing, and overall plant integration. Reaction Engineering Inc. (REI) reviewed the process design and costing for the lignin combustor and boiler turbogenerator and Merrick & Company reviewed the wastewater treatment.
 	
 Since then, NREL has worked with Harris Group (Harris) to perform vendor testing, process design, and costing of critical equipment identified during earlier work. This included solid/liquid separation and pretreatment reactor design and costing. Corn stover handling was also investigated to support the current focus on corn stover as a feedstock for lignocellulosic ethanol. The process design and costing for these areas were improved through vendor designs, costing, and, in some cases, vendor testing. In addition to this work, enzyme costs were adjusted to reflect collaborative efforts between DOE/NREL and enzyme manufacturers (Genencor International and Novozymes Biotech) to provide a delivered enzyme for lignocellulosic feedstocks. The June 2002 report is the culmination of NREL's work and presents an updated co-current dilute acid prehydrolysis with enzymatic saccharification and co-fermentation process.
 
 69 mmgy annually 
 The conceptual design and costs presented in the report are based on a 2010 plant start-up date and show key research targets required to achieve a $1.07/gal ethanol goal with full income tax requirements and without any applicable subsidies. The conceptual design is based on 2000 dry metric tons (2200 dry short tons) of corn stover per day and yields of 69 mmgy (approximately 90 gallons ethanol/dry short ton of corn stover). 
 	

 To achieve these design and cost goals, a 90% conversion of hemicellulose to fermentable sugar is necessary in the dilute acid prehydrolysis. The enzymatic hydrolysis section is designed for a 36 hour residence time and the necessary cellulose-to-glucose yield is 90% with a purchased enzyme cost of $0.11/gal ethanol product. The hydrolysis is followed by a 36 hour continuous fermentation where 95% of the glucose is converted to ethanol as well as 85% of all the other sugars with a contamination loss of 3% or less. The lignin residue will be combusted to provide steam and electricity to operate the facility with excess electricity sold to the grid. The economic assumptions are a 10% discounted cash flow rate of return over a 20 year plant life with 100% equity funding.
 
 Capital costs high, feedstock costs low
 The calculated total project investment is $198,000,000 ($2.90/gal of annual ethanol production) with a methodological error range of -15%/+30%. It is more capital intensive than the corn starch to ethanol process but over 25% of the capital is required for the lignin boiler and turbogenerator. The capital investment can be reduced considerably if another lignin utilization option is available. The capital costs are higher than the starch based process but, at the expected corn stover cost ($30/dry short ton), the feedstock only costs about $0.33/gal ethanol and all raw materials only cost about $0.52/gal ethanol - less than the corn starch to ethanol process. 
 	
 Full process details including process flow diagrams, stream ladders, an equipment list, and parameter assumptions are listed in the report as are full economic details including equipment costing information, operating costs, project investment assumptions, and cash flow estimates. The report is available at http://www.afdc.doe.gov/pdfs/6483.pdf or through NREL's publication Web site at http://www.nrel.gov/publications/. n

Conceptual design and costs based on a 2010 plant start-up date of 69 mmgy biomass-to-ethanol plant, calculated total project investment is $198 million

NREL releases design to reach a corn stover ethanol price of $1.07 per gallon

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Upcoming Events

2024 International Fuel Ethanol Workshop & Expo

Biodiesel Summit: Sustainable Aviation Fuel & Renewable Diesel

Carbon Capture & Storage Summit

North American SAF Conference & Expo

2025 International Biomass Conference & Expo

NREL releases design to reach a corn stover ethanol price of $1.07 per gallon