Process Design and Economics for Biochemical Conversion of Lignocellulosic Biomass to Ethanol Dilute-Acid Pretreatment and Enzymatic Hydrolysis of Corn Stover D. Humbird, R. Davis, L. Tao, C. Kinchin, D. Hsu, and A. Aden National Renewable Energy Laboratory Golden, Colorado P. Schoen, J. Lukas, B. Olthof, M. Worley, D. Sexton, and D. Dudgeon Harris Group Inc. Seattle, Washington and Atlanta, Georgia NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. Technical Report NREL/TP-5100-47764 May 2011 Contract No. DE-AC36-08GO28308 Process Design and Economics for Biochemical Conversion of Lignocellulosic Biomass to Ethanol Dilute-Acid Pretreatment and Enzymatic Hydrolysis of Corn Stover D. Humbird, R. Davis, L. Tao, C. Kinchin, D. Hsu, and A. Aden National Renewable Energy Laboratory Golden, Colorado P. Schoen, J. Lukas, B. Olthof, M. Worley, D. Sexton, and D. Dudgeon Harris Group Inc. Seattle, Washington and Atlanta, Georgia Prepared under Task No. BB07.2410 NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. National Renewable Energy Laboratory Technical Report 1617 Cole Boulevard NREL/TP-5100-47764 Golden, Colorado 80401 May 2011 303-275-3000 • www.nrel.gov Contract No. DE-AC36-08GO28308 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:[email protected] Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: [email protected] online ordering: http://www.ntis.gov/help/ordermethods.aspx Cover Photos: (left to right) PIX 16416, PIX 17423, PIX 16560, PIX 17613, PIX 17436, PIX 17721 Printed on paper containing at least 50% wastepaper, including 10% post consumer waste. Executive Summary The U.S. Department of Energy (DOE) promotes the production of ethanol and other liquid fuels from lignocellulosic biomass feedstocks by funding fundamental and applied research that advances the state of technology in biomass collection, conversion, and sustainability. As part of its involvement in the program, the National Renewable Energy Laboratory (NREL) investigates the production economics of these fuels. This report describes in detail one potential biochemical ethanol conversion process, conceptually based upon core conversion and process integration research at NREL. The overarching process design converts corn stover to ethanol by dilute-acid pretreatment, enzymatic saccharification, and co-fermentation. Ancillary areas—feed handling, product recovery, wastewater treatment, lignin combustion, and utilities—are also included in the design. Detailed material and energy balances and capital and operating costs were developed for the entire process, and they are documented in this report and accompanying process simulation files, which are available to the public. As a benchmark case study, this so-called technoeconomic model provides an absolute production cost for ethanol that can be used to assess its competitiveness and market potential. It can also be used to quantify the economic impact of individual conversion performance targets and prioritize these in terms of their potential to reduce cost. Furthermore, by using the benchmark as a comparison, DOE can make more informed decisions about research proposals claiming to lower ethanol production costs. Building on design reports published in 2002 and 1999, NREL, together with the subcontractor Harris Group Inc., performed a complete review of the process design and economic model for the biomass-to-ethanol process. This update reflects NREL’s current vision of the biochemical ethanol process and incorporates recent progress in the conversion areas (pretreatment, conditioning, saccharification, and fermentation), optimizations in product recovery, and an improved understanding of the ethanol plant’s back end (wastewater and utilities). The major process updates in this design report are the following: • Feedstock composition is updated to a carbohydrate profile closer to the expected mean. • Pretreatment reactor configuration is revised with significant new detail. • Whole-slurry pH adjustment of the pretreated biomass with ammonia replaced the previous conditioning practice of overliming, eliminating a solid-liquid separation step. • Enzymatic hydrolysis and fermentation are modeled as a batch process with a continuous high-solids hydrolysis reactor upstream of the batch reactors. • On-site enzyme production is included to increase transparency on the cost of enzymes. • Wastewater treatment section is redesigned to handle inorganics in the ethanol stillage. The conceptual design presented here reports ethanol production economics as determined by 2012 conversion targets and “nth-plant” project costs and financing. For the biorefinery described here, processing 2,205 dry ton/day at 76% theoretical ethanol yield (79 gal/dry ton), the ethanol selling price is $2.15/gal in 2007$. iii Ethanol Production Process Engineering Analysis Corn Stover Design Report Case: 2012 model DW1102A Dilute Acid Pretreatment with Enzymatic Hydrolysis and Co-Fermentation All Values in 2007$ Minimum Ethanol Selling Price (MESP): $2.15 /gal Gasoline-Equivalent MESP: $3.27 /gal gasoline equivalent Contributions: Feedstock $0.74 /gal Enzymes $0.34 /gal Non-Enzyme Conversion $1.08 /gal Ethanol Production 61.0 MMgal/yr (Ethanol at 68 °F) Ethanol Yield 79.0 gal / dry U.S. ton feedstock Feedstock + Handling Cost $58.50 /dry U.S. ton Internal Rate of Return (After-Tax) 10% Equity Percent of Total Investment 40% Capital Costs Manufacturing Costs (cents/gal ethanol) Pretreatment $29,900,000 Feedstock + Handling 74.1 Neutralization/Conditioning $3,000,000 Sulfuric Acid 2.4 Saccharification & Fermentation $31,200,000 Ammonia 6.5 On-site Enzyme Production $18,300,000 Glucose (enzyme production) 19.3 Distillation and Solids Recovery $22,300,000 Other Raw Materials 12.9 Wastewater Treatment $49,400,000 Waste Disposal 2.5 Storage $5,000,000 Net Electricity -10.8 Boiler/Turbogenerator $66,000,000 Fixed Costs 17.5 Utilities $6,900,000 Capital Depreciation 22.0 Total Installed Equipment Cost $232,000,000 Average Income Tax 12.3 Average Return on Investment 56.6 Added Direct + Indirect Costs $190,500,000 (% of TCI) 45% Manufacturing Costs ($/yr) Feedstock + Handling $45,200,000 Total Capital Investment (TCI) $422,500,000 Sulfuric Acid $1,500,000 Ammonia $4,000,000 Installed Equipment Cost/Annual Gallon $3.80 Glucose (enzyme production) $11,800,000 Total Capital Investment/Annual Gallon $6.92 Other Raw Materials $7,900,000 Waste Disposal $1,500,000 Loan Rate 8.0% Net Electricity -$6,600,000 Term (years) 10 Fixed Costs $10,700,000 Capital Charge Factor (Computed) 0.131 Capital Depreciation $13,400,000 Average Income Tax $7,500,000 Denatured Fuel Production (MMgal/yr) 61.7 Average Return on Investment $34,600,000 Denatured Fuel Min. Sales Price $2.18 Denaturant Cost ($/gal denaturant) $2.10 Specific Operating Conditions Enzyme Loading (mg/g cellulose) 20 Maximum Yields (100% of Theoretical) Saccharification Time (days) 3.5 Ethanol Production (MMgal/yr) 80.3 Fermentation Time (days) 1.5 Theoretical Yield (gal/U.S. ton) 103.9 Ethanol titer (wt%) 5.4% Current Yield (Actual/Theoretical) 76.0% Excess Electricity (kWh/gal) 1.8 Plant Electricity Use (kWh/gal) 3.9 Plant Water Usage (gal/gal) 5.4 Figure ES-1. Economic summary for ethanol production iv Table of Contents 1 Introduction ........................................................................................................................................... 1 1.1 Background and Motivation ................................................................................................1 1.2 Process Overview .................................................................................................................2 1.3 Technoeconomic Analysis Approach ..................................................................................5 1.4 About nth-Plant Assumptions ...............................................................................................6 1.5 Review of Related Technoeconomic Studies ......................................................................7