Economic analysis of a modified dry grind ethanol process with recycle of pretreated and enzymatically hydrolyzed distillers’ grains
Introduction
The dry grind process converts the entire corn kernel into two main products of economic value, ethanol and dried distillers’ grains (DDGS). While ethanol has typically been known as a key component in alcoholic beverages, its rapidly growing use as an automotive fuel, through subsidies and high oil prices, makes it a product of high value. The DDGS co-product is sold as animal feed for swine, cattle, and chickens due to its protein, amino acid, and energy content. However, DDGS also contains some unconverted starch and sugar precursors to ethanol, which, if processed, could increase the ethanol yield of a dry grind facility. Increasing ethanol yields would increase the revenue from ethanol of the dry grind process, and could also enhance the value of the DDGS by creating a product with higher concentrations of protein for animal feed.
A process has been proposed which takes the distillers’ grains from the conventional dry grind process and recycles them for further processing and fermentation, resulting in higher yields of ethanol and an enhanced dried distillers’ grains (eDDGS) product with increased protein levels (Kim et al., 2008a, Kim et al., 2008b). The conventional process (Fig. 1), or “base” process, grinds the corn and breaks it down into simple sugars to be fermented into ethanol. The ethanol is then separated by distillation off the top of a column, while the bottom products are further processed to separate water from the distillers’ grains. The proposed modifications (Fig. 2) would subject the material from the bottom of the distillation column to further processing, including a pretreatment heating step and subsequent hydrolysis of polymeric sugars and residual starches by enzymes, and then separate the sugar-rich “pretreated” liquid to be recycled back through the original hydrolysis and fermentation processes in order to increase ethanol yields (Kim et al., 2008a, Kim et al., 2008c). The remaining distillers’ grains not recycled with the pretreated liquid would be dried and sold as eDDGS, an animal feed with higher protein levels than conventional DDGS.
A dry milling model, called the DM model based on dry milling of corn (Dale and Tyner, 2006a), was developed using MS Excel (Microsoft Corporation, 2003) to monitor the financial feasibility of the conventional dry grind process given market trends for the costs of corn, the price of ethanol, and other product and input prices. Validation of this model included comparisons of capital costs and variable costs against industrial estimates from the Ethanol Production Handbook (BBI Int., 2003) and a 2002 Cost of Production Survey (Shapouri and Gallagher, 2005), respectively. In the 100 million gallon nameplate range, the DM model calculated capital and variable costs valued at 97% and 103% of their respective industrial estimates (Dale and Tyner, 2006a). Calculations performed at other nameplate ranges were similarly close. Thus, there is confidence that the DM model can be utilized to determine the financial feasibility of the conventional dry grind process, and can be augmented with a technology module and adjusted pricing to analyze the financial costs and benefits of the dry grind process with pretreated liquid.
Section snippets
Methodology
The DM model is based on the process in Fig. 1, which takes yellow dent corn, hydrates the ground corn particles, breaks down the starch into simple sugars using enzymes, and then ferments the simple sugars into ethanol. The ethanol is then separated from the remaining distillers’ grains, which are also processed in order to sell to the animal feed market. The DM model takes specific flow rates (ethanol output, water recycle), conversion rates (hydrolysis and fermentation yields), and product
Results
Based on a dry grind nameplate level of 100 million gallons of ethanol, a corn price of $3.82 per bushel, and a denatured ethanol price of $2.23 per gallon (Table 1), the DM model predicts an NPV of $162 million (Table 4) over the 25 year life of the project, with operations beginning in year 3. This includes a $33.5 million yearly net operating benefit (Table 5), not including initial annual loan payments of $11 million (Table 4). The loan pays off 60% of the total capital investment of $148
Summary and conclusions
Based on the conservative practice of utilizing swine feed models to determine the value of dried distillers’ grains, the eDDGS product does not show an increase in value as anticipated compared to the base DDGS due to the loss of lysine through the pretreatment and enzymatic hydrolysis processes, lysine being a particularly important amino acid in the swine diet. While using a swine diet might seem restrictive as other animals may benefit more from the high protein content in eDDGS, it is not
Acknowledgements
This work was supported by US Department of Energy (Contract: DE-FG36-04GO14220) in cooperation with Midwest Consortium for Biobased Products and Bioenergy. We would like to thank Michael Ladisch, Youngmi Kim, Nate Mosier, Paul Preckel, Brian Rickert, and Todd Hubbs for their assistance with parts of the analysis.
References (15)
- et al.
Process simulation of modified dry grind ethanol plant with recycle of pretreated and enzymatically hydrolyzed distillers’ grains
Bioresour. Technol.
(2008) - et al.
Composition of corn dry-grind ethanol by-products: DDGS, wet cake, and thin stillage
Bioresour. Technol.
(2008) - et al.
Enzyme hydrolysis and ethanol fermentation of liquid hot water and AFEX pretreated distillers’ grains at high solids loadings
Bioresour. Technol.
(2008) The Ethanol Plant Development Handbook
(2003)- Bloomberg.com, 2007. Bloomberg Energy Prices. <http://www.bloomberg.com/markets/commodities/energyprices.html>...
- Chemical Engineering, 2007. Economic Indicators: Marshall and Swift Equipment Cost Index. Chemical Engineering...
- Chicago Board of Trade, 2007. Agricultural Products. <http://www.cbot.com/cbot/pub/page/0,3181,963,00.html> (accessed...
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