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New Energy Economics: Is Biofuel the Most Valuable Component of a Cellulosic Biorefinery?

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Cole Gustafson, NDSU Biofuels Economist Cole Gustafson, NDSU Biofuels Economist
The final value depends critically on prevailing prices.

By Cole Gustafson, Biofuels Economist

NDSU Extension Service

One of my projects is to participate in a team study that seeks to determine the feasibility of collecting wheat straw for a proposed cellulose to biofuel processing plant near Spiritwood. As part of the project, I recently had a chance to learn more about the unique conversion process being considered.

The conversion process is a proprietary method developed by Inbicon, a Danish biofuel company. Inbicon actually is a subsidiary of Dong (Danish Oil and Natural Gas) Energy. Dong Energy has 5,100 employees, had $8.5 billion (U.S.) in revenue in 2009 and supplies Denmark with most of its electrical power. The firm has a goal of moving from 15 percent renewable energy to 85 percent by 2040.

Inbicon has been charged with leading the transition to renewable energy and has a large-scale wheat straw-to-biofuel plant that is operating near Kalundborg, Denmark. In addition to Spiritwood, Inbicon is developing its technology in New York and Illinois.

The technical process of converting wheat straw to biomass actually is quite straightforward and involves water, enzymes and yeast. The incoming straw is detwined and ground. After that, water is added and the mixture is taken through an enzymatic hydrolysis process to break down the wheat straw cellulose into simple sugars. Finally, yeast is added to convert those sugars into biofuel. From there, the biofuel is distilled and processed using existing technology identical to the corn ethanol industry.

The Danish plant has a capacity of processing 30,000 tons of wheat straw annually. From this straw, 4,300 tons of ethanol are produced. This is a feedstock-to-biofuel weight ratio of 98 to 6. At this point, we can see how much more material must be handled to obtain cellulosic biofuel.

In a traditional corn ethanol plant, roughly 2.8 gallons of ethanol are produced from each bushel of corn (56 pounds per bushel). If each gallon of ethanol weighs 6.59 pounds per gallon, the feedstock to biofuel weight ratio is 3 to.03. Thus, more than twice the weight of incoming feedstock is required to produce a similar volume of biofuel.

I often get asked what is left over after a cellulosic feedstock is converted to biofuel. In Inbicon’s wheat straw process, it is cattle feed and lignin. With 30,000 incoming tons of wheat straw, 11,100 tons of cattle feed are produced. However, this isn’t the type of feed that livestock producers are accustomed to obtaining from a biofuel plant. In traditional corn ethanol plants, a coproduct of the process is distillers dried grains. This product is a high protein animal feed that has a deep golden yellow color. The cattle feed coproduct from a wheat straw cellulosic biofuel process is a liquid sugar or molasses. Not all of the readily available sugars in the straw are converted to biofuel. Therefore, the residual sugars are sold to the livestock industry as feed in a liquid form.

The final coproduct of the wheat straw-to-cellulosic biofuel conversion process is 11,100 tons of lignin. This black char-looking product is usually pelleted and burned as a biofuel. The site of the Danish Inbicon plant is next door to an electrical utility that utilizes the lignin to replace coal and produce renewable electricity. It is no coincidence that the wheat straw biofuel plant near Spiritwood also is being constructed next to an electrical power generation plant. This reduces the logistic costs of transporting the biofuel and provides a ready market.

With biofuel actually being the smallest coproduct, based on weight, what is the most valuable product of the plant? Interestingly, one can start the analysis by examining the energy content of each coproduct produced.

First, an energy term used is joule, which is a scientific unit of energy. One billion joules is a gigajoule (GJ).

In this case, we have 432,000 GJ per year of wheat straw energy input. The output is 114,800 GJ of biofuel energy, 112,500 GJ of energy in cattle molasses and 181,100 GJ of lignin energy.

The amount of energy in the product produced is relatively similar to the wheat straw energy input. Therefore, the final value depends critically on prevailing prices. In Europe, prevailing energy prices place a premium on renewable electrical power. Therefore, the lignin is the most valuable component produced by the wheat straw biofuel plant. Given America’s thirst for liquid transportation fuels, the biofuel (ethanol) is the most valuable component.


NDSU Agriculture Communication

Source:Cole Gustafson, (701) 231-7096, cole.gustafson@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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