April 26, 2007 | General

Biomass Energy Fuels Corn Ethanol Production

BioCycle April 2007, Vol. 48, No. 4, p. 51
Replacing natural gas increases net energy balance, lowers costs and improves process sustainability – creating fuel from locally available feedstocks.
Diane Greer

CRITICS of ethanol produced from grains, such as corn, often question the large quantities of fossil fuels required by the process relative to the amount of transportation fuel produced. They cite this low “net energy balance” as evidence of the inefficiency of the process.
Government studies calculate the net energy balance of corn ethanol from 1.3 to 1.7. This means that for every unit of energy used to grow the corn and generate the thermal power driving the process, 1.3 to 1.7 units of energy are created in the form of ethanol.
Now biomass energy is changing the equation. Replacing natural gas with biomass energy to produce ethanol dramatically increases the net energy balance, lowers costs, facilitates compliance with emission requirements and improves the sustainability of the process. Companies employing biomass energy may also be better positioned to survive any industry shakeouts and transition to cellulosic ethanol production as the technology matures.
Biomass energy is fueling an innovative corn ethanol production process at E3 Biofuel’s plant in Mead, Nebraska in a “closed-loop” system, recycling the waste and by-products from one operation for reuse in other parts of the process. Two Biothane anaerobic digesters, each with a four million gallon capacity, generate methane gas from 300,000 tons of manure produced by 28,000 cattle in an adjacent feedlot. The methane gas fuels 100 percent of the ethanol facility.
Digester by-products include a solution of aqueous ammonia and compost. The aqueous ammonia solution is sold as fertilizer to farmers while the compost is sold as bedding for livestock or as potting soil.
Normally, methane gas produced in a digester is ‘cleaned up’ to reduce water content. “We do not waste energy cleaning up or dehydrating the methane gas,” Dennis Langley, President and CEO of E3 Biofuels said. “Anything in the facility associated with the wet gas is stainless steel, so that it does not rust.”
A by-product of the ethanol process is wet distillers grain, or wet cake, composed of the nonstarch portion of the corn (protein, oils and fibers). Many ethanol facilities employ thermal oxidizers to dry the wet cake to prevent spoilage and allow it to be transported and sold as feed.
“We do not need to dry it because we deliver it immediately to the feedlot,” Langley said. The money saved by eliminating the drying equipment almost covers the capital costs of the anaerobic digesters, Langley adds.
Another by-product of the ethanol process is warm wastewater containing thin silage. This soupy mixture is added to the digesters, helping to maintain digester temperatures and providing additional organic materials for methane production.
At full capacity, the Mead plant will process 8.5 million bushels of corn to create 25 million gallons of ethanol using biogas. Langley estimates the net energy balance is increased to about 5. Every unit of energy going into the process yields five units of energy in the form of ethanol.
Environmental benefits of the integrated process include eliminating odor, waste disposal and water pollution problems inherent in large-scale cattle operations, significantly reducing greenhouse gas emissions from the ethanol plant and cattle operation and lowering particulate emissions, primarily from the cattle operation, by 90 percent. Langley estimates reduction of 194,000 metric tons of CO2 equivalent for every 50 million gallon ethanol facility built.
Building an integrated facility is more expensive. “It costs about $20 million more per 25 million gallons of ethanol produced each year,” Langley said. But he does not think the comparison is fair, since the E3 Biofuels plants essentially capitalize the cost of energy.
Company plans call for building 15 more facilities over 5 years. Six sites are already identified. Each plant requires manure from at least 20,000 cattle. The process also works with dairy operations, although farms must be located within a 15-mile radius of a plant and have a minimum of 16,000 cows, Langley explained. Research indicates that there are roughly 550 feedlots and an equivalent number of dairies with sufficient livestock to meet the scale requirements.
Diversified Ethanol, in Eagle Grove, Iowa, is developing a grain ethanol production process similar to E3 Biofuel’s process, but at a smaller scale. The system is designed for dairy farms with 1,500-2,500 cows, smaller feedlots and hog operations. The company is currently piloting an 80,000-gallon/year unit at its headquarters in Iowa.
“The best way to integrate ethanol into rural communities is to have small-scale, on-farm integrated units, creating the fuel from locally available on-farm feedstock,” said Luke Staengl, President of Pragmatic Environmental Solutions Company and consultant to Diversified Ethanol. Like the E3 Biofuel’s system, manure from the livestock operation is treated in a digester, which produces biogas to fuel a 500,000-gallon/year ethanol plant (called the A500). Three times the amount of methane is produced as required by the plant. “The other two-thirds is converted to electricity for use on the farm or sale back to the grid,” Staengl said.
“About 30-35 percent of the cost of ethanol production is the energy input,” Staengl notes. “So you are basically taking in a free source of energy from the methane digester.”
Corn grown on the farm and normally fed directly to the animals is instead run through the ethanol process. The residue or wet cake from the process is fed to the animals. Field trials indicate animals fed the residues from a bushel of corn actually do better in terms of weight gain or milk production than animals directly fed a bushel of corn, Staengl explained.
Other by-products from the process, such as the digestate, are used on the farm as fertilizer to grow the corn while the thin silage from the ethanol process is run back through the digester to produce more biogas. “You have a very neat closed looped system,” Staengl said.
Due to its smaller scale, capital costs for Diversified plants range between $2-2.50 per annual gallon of production. For a large 100 million gallon per year facility, capital costs approach $2 per annual gallon produced.
Initial market surveys identified 10,000 farming operations where an A500 will work. Staengl is also exploring down sizing the process to an A250 (250,000 gallons/ year) as well as scaling up the process for larger operations.
Manure will also fuel the Panda Ethanol plant in Hereford, Texas. Instead of anaerobic digesters producing methane, the plant generates a synthetic gas by combusting manure in a gasification system. Gasifiers operate at high temperatures with little oxygen, converting carbon-containing materials, in this case manure, into a synthetic gas (syngas) composed primarily of carbon monoxide and hydrogen. Ash, a by-product of the process, is used in building and construction materials.
When completed in the fourth quarter of 2007, the Hereford plant will gasify 500,000 tons of cow manure annually. The resulting syngas will generate sufficient steam to produce 105 million gallons of ethanol from 40 million bushels of corn. The manure is obtained, free of charge, from nearby feedlots. Panda pays to transport the material, according to Todd Carter, President and CEO of Panda Ethanol.
Before the manure is combusted in the gasifier, it is dried to the right moisture content by placing it in windrows, for 25-45 days on average. Wet cake, a by-product of the ethanol process, is sold to the feedlots as a high protein, high fat feed.
Panda considered utilizing anaerobic digesters in their facility, but opted for gasification because of scale. “We did not see anaerobic digesters being able to manage a 100 million gallon facility,” Carter said. “Gasification is a more efficient way for our application to make steam.” The company has announced plans for three additional projects in Haskell County, Kansas and in Muleshoe and Sherman, Texas.
While manure is in abundance in Hereford, in Minnesota ethanol plants are turning towards agricultural or forestry residuals as a source of biomass energy for grain ethanol operations. Economics played a large role in Chippewa Valley Ethanol Company’s (CVEC) decision to install a biomass gasification system combusting agricultural and forestry residues. The company’s ultimate goal is to replace all the natural gas used to produce 45-million gallons of ethanol annually with biomass energy.
“The number two cost of operation for a corn ethanol plant is energy input,” Bill Lee, CVEC’s General Manager said. “We spend $15-18 million a year on natural gas. The price has almost tripled since we started 11 years ago.”
As a first step, CVEC, located in Benson, Minnesota, is installing a gasifier and new burner on one of its boilers that can combust syngas from the gasifier or co-fire it with natural gas. “We hope to replace 20-25% of our natural gas with this first gasifier,” Lee adds. This system will allow the company to gain experience operating a gasifier and to learn about system design. “That will inform the design of the second gasification system, which will displace all our natural gas,” Lee said.
Feedstock flexibility is an important feature of the new system. Differences in harvesting windows, feedstock moisture content and competition from other sources will play a role in feedstock selection for the gasifier. “We wanted to configure a system that was multifeedstock compatible,” Lee said. The plant is near an abundance of different feedstocks including agricultural residues, like corn stalks and wheat straw, wood from forestry operations and perennial grasses.
CVEC is currently conducting baling trials on four different feedstocks; corn stover, soybean stubble, wheat straw and switch grass. “Baling is probably not the most effective way to go,” Lee said. “We are eager to work with others to develop more efficient collection and transportation schemes for these materials.”
While CVEC expects to save money, they will be happy to break even. The company, which is one of the state’s first farmer-owned ethanol facilities with 975 cooperative members, has a different view of what makes for a good investment, preferring to return value back to the community, Lee said. He would rather pay its cooperative shareholders $15-18 million for biomass feedstocks to power the plant, as opposed to a gas company in Alberta.
CVEC’s upside in successfully demonstrating the gasification system extends beyond saving money on its gas bills. The company has formed a partnership with and received a significant minority stake in Frontline Bioenergy, a company that specializes in biomass gasification technologies. “It puts us in the technology development business, not just the processing business,” Lee said.
Gasifying biomass also provides a means for CVEC to satisfy another goal, reducing its carbon footprint. The new system is expected to increase the net energy balance to over 3. “We needed to look for ways to reduce our fossil fuel energy input,” Lee said. “What better way to do that than to use the materials in our own backyard?”
Meanwhile in Little Falls, Minnesota, the Central Minnesota Ethanol Cooperative (CMEC) had to bring its plant, which produces 20 million gallons of corn ethanol per year, into compliance with its air permits for volatile organic chemical (VOC). Thermal oxidizers, typically used to reduce VOC emissions at ethanol plants, would increase the company’s natural gas usage and raise its operating costs, according to Cecil Massie, Senior Project Manager at Sebesta Bloomberg & Associates and consultant to CMEC.
At the same time, CMEC was seeking ways to reduce its operating costs and find a strategic alternative to expansion as a means to increase their profitability. Expanding operations was not an option at its location. Installation of a biomass gasification system provided a novel solution, satisfying all the company’s criteria. The system reduced operating costs by replacing all the natural gas used at the facility with biomass energy and permitted the company to purchase a thermal oxidizer to achieve compliance with emission permits.
The gasification system also improved profitability. “By converting to a biomass fuel supply, the return on investment (ROI) on the biomass gasification plant is greater than the ROI CMEC would have gotten by expanding the plant,” Massie points out. CMEC’s total investment for the new system is $15 million. Payback is estimated at four years.
Seventeen sawmills in the immediate region supply low-cost biomass feedstocks to the plant under 10-year contracts. The deal was a win for both CMEC and the sawmills. “Adding the sale of the waste product to the profitability of the saw mill operations helps to stabilize their operations,” Massie said.
Instead of a gasification system, Corn Plus in Winnebago, Minnesota, installed fluidized bed technology to burn a by-product of the ethanol process, the syrup. Fluidized bed technology has been around for many years and is used by the paper industry to burn lignin and fibers.
Silage, a by-product from the ethanol process, is normally separated by a centrifuge into coarse grains and solubles. Concentrating the solubles by evaporation produces condensed distillers solubles, also called syrup. In most operations, the syrup and coarse grains are mixed together and dried to produce dried distillers grains (DDG) with solubles.
Like CMEC, Corn Plus was facing a consent decree issued by the Environmental Protection Agency (EPA) to reduce VOC emissions from its driers. Installation of thermal oxidizers to reduce emissions would have increased natural gas consumption by five to ten percent, Keith Kor, General Manager at Corn Plus says.
“I was wondering if one of our by-products, the syrup which we make quite a bit of, could ever be used as a combustion fuel,” adds Kor. As a test, he sent twenty 55-gallon drums of the syrup to an independent lab in Golden, Colorado that had a miniature-fluidized bed. They burned the syrup for three days, confirming it was a viable fuel.
“Based on the BTU value of the product, we were able to reduce our natural gas usage by 52 percent,” Kor said. “The fluidized bed produces enough steam to run the plant as well as acts as my thermal oxidizer, cleaning up the emissions from our dryer.” As a by-product, about 25 tons of ash is produced each day, which has value as fertilizer. Kor is currently exploring palletizing the ash to sell to farmers.
Kor is still selling the DDG. Although the DDG does not have as much fat content without the syrup, it contains more protein by unit of volume. Payback for the system was originally estimated at 5 years. Rising natural gas prices have shortened it to 2.5 years.
As the ethanol industry matures, utilizing biomass energy may help companies gain a competitive advantage. Carter said, “In the current natural gas pricing environment, it gives me certainty of my cost to make steam for my facility.” Langley agreed. “We are the low cost provider. As the markets shake out, which it will inevitably, we want to make sure we are the last lights on in town.”
Utilizing biomass energy, particularly agricultural and forestry residues, is also seen as a means to transition the industry to cellulosic ethanol. Currently there are limited uses for agricultural residues and inadequate incentives for farmers to develop the systems for harvesting and delivering the feedstocks to market. “There is no real market value assigned to cornstalks or wheat straw, per se,” Lee said. “By adopting gasification systems, we are building a biomass market.”
Plants are also gaining valuable experience managing the biomass supply chain. “We have the receiving and material handling equipment and the expertise and knowledge on how to move this stuff around,” said Massie. CMEC’s experience with biomass feedstock positions the plant to be “first in line to go cellulosic,” Massie adds.
Finally, converting to biomass energy also provides the industry with an interim step to reduce greenhouse gas emissions. “While we are waiting for the cellulosic ethanol industry to grow, why don’t we convert corn ethanol to biomass power?” Lee said. “In the near term we will make some huge inroads in reducing greenhouse gases in the liquid transportation section.”
Diane Greer is a freelance writer and researcher based in New York, specializing in sustainable business, green building and alternative energy. She can be reached at

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