BioCycle December 2008, Vol. 49, No. 12, p. 43
New projects include university’s biomass research and gasification facility, a turkey-litter fueled power plant, and a farmers’ co-op gasifying agricultural residues.
Minnesota is home to several large-scale projects working to replace fossil fuels with biomass heating. In western part of the state, the University of Minnesota campus in Morris (UM-Morris) plans on meeting 80 percent of its heating and cooling needs using a new biomass research and gasification facility. The plant represents a major step towards the university’s goal of reaching energy independence by 2010.
At peak capacity, the plant will burn 3,000 pounds/hour of biomass material, generating 19 million BTUs for the campus. The $9 million facility, funded by state and federal agencies and agricultural trade groups, could save the university $270,000 annually in energy costs.
The plant will burn up to 8,000 tons/year of corn stover (stalks, husks and cobs), along with wood chips and possibly some grasses. Construction of the facility finished in the summer of 2008, and the testing phase began in September, according to project manager Joel Tallaksen with the University of Minnesota West Central Research and Outreach Center. “We’re hoping to have it fully operational in the next couple of months,” Tallaksen said in early November. In midwinter, the university will also use its natural gas and fuel oil burners as a supplemental heating source for the 1 million square feet of space on campus.
The UM-Morris biomass gasifier is made by London, Ontario-based KMW Systems. Bales of corn stover are resized in a Haybuster R-1100 tub grinder. Material is conveyed toward the bunker as needed from a walking-floor storage trailer. A hydraulic ram is used to force material into the gasifier. Biomass is gasified into syngas in the entrained flow, atmospheric pressure-inclined grate gasifier. Oxygen is added to the syngas stream, causing it to combust. Heat from combustion turns water into steam in the boiler.
Pollutants are removed from the emissions by a wet scrubbing unit. For example, when corn stover is gasified it creates chlorine gas, which reacts with hydrogen to create hydrochloric acid (HCl). To remove the HCl, emissions are processed with a sodium hydroxide mixture in a scrubber that neutralizes the HCl and reduces the associated risks of exposure. Additionally, scrubbers are installed to “clean” the emissions stream to comply with air quality rules. Ash is collected in a wagon or hopper, to be used as fertilizer.
Initially, the plant is burning about 50 percent wood waste, supplementing the natural gas used to fuel the facility. UM-Morris officials are also evaluating other crops, such as wheatstraw and prairie grass. They have identified 677,000 tons of ag residue within a 100-mile radius. “We have done a lot of work with the local DNR (Department of Natural Resources) and Fish and Wildlife Service offices, to look at harvesting prairie grass,” Tallaksen explains. “They have established native plantings in the wildlife management areas.” He notes that the ag residue and grasses produce about 7,000 BTUs per pound, compared to 9,000 to 11,000 BTUs for wood, depending on the type.
This heating season, Tallaksen began testing moisture levels of incoming material. “If it’s 18 percent moisture, we pay 18 percent less than the total weight,” he says. “We know the vendors are going to raise prices to compensate for that, but at least we’ll know what we’re getting. For our process we can use very wet material, but we can’t store it wet. So, we don’t want material that is much over 20 percent moisture. We will accept 20 to 30 percent moisture.”
Compared to wood, the physical properties of corn stover are also more of a challenge to feed into the system. “You can break up wood chips so they are easy to get into the system,” observes Tallaksen. “But corn stover is long and stringy, so it gets stuck and jams up the augers.” The university is still experimenting to determine what size material works best, using a research grinder to test material sizes, ranging from powder to seven inches long.
As with any large biomass project, developing a stable supply of feedstocks will be essential, Tallaksen notes. “We haven’t developed a market yet but it’s coming, with two other biomass plants in the area,” citing Chippewa Valley Ethanol and Fibrominn (see below). “Developing a market is also a challenge for people who are not used to contracting this type of material; it takes a lot of vehicles and people to move around, and it’s kind of a new thing for us. It will take a while before it’s fully understood.”
In rural areas like Morris, soil conservation is another concern, he continues. “One question we have is how much of the ag residue we can remove from the fields and still keep the soils intact; that’s something the researchers are working on.”
FIBROMINN POWER PLANT
Twenty miles to the south, in Benson, Minnesota, is the world’s largest turkey litter-fueled power plant, and the first in North America. The plant is equipped to generate and export about 55 megawatts/hour (MWH), more than 400,000 MWH/year, about as much energy as 40,000 homes use annually. To do that, it consumes 90 to 100 semitruck loads of biomass per day.
The $200 million project is owned by Fibrominn, a subsidiary of Fibrowatt. The founders of Fibrowatt in the U.S. were the developers and operators of three similar plants in Great Britain. Fibrominn signed a 21-year contract to sell its power to Xcel Energy. Although the biomass power costs more to produce than coal-generated energy, Xcel pays more for the electricity, based on the state of Minnesota’s commitment to alternative energy.
After two years of construction, the plant was fired up in April 2007 for testing and began full operation in October 2007. The most challenging aspect of using poultry litter is variability in content and moisture, says Terry Walmsley, Fibrowatt’s Vice President of environmental and public affairs. “Depending on how many flocks are in a barn before clean out, 10 to 20 percent of the litter is bedding material, with the rest manure.” Even within the state, there is variation in types of bedding materials used and other management practices, he adds.
All deliveries are brought to a fully enclosed fuel hall. Trucks back into the reception area and material is deposited
in a concrete pit that can hold one to one and half days worth of deliveries. The plant accepts 2,000 to 3,000 tons/day of fuel, for which it pays a small fee, based on fuel quality.
Overhead cranes move the material from the pit onto a concrete storage pad. The fully enclosed, concrete and metal fuel hall measures about one acre in size. By maintaining negative pressure, and using air from the fuel hall in the combustion process, “we pride ourselves in being able to store more than 10,000 tons of material without odors,” Walmsley explains.
The plant blends other forms of biomass with the litter as bulking agents, so called “opportunity materials,” such as wood chips and other forestry residue, sunflower husks, corn stover and soybean hulls. The material is sized to two-inches using a Rader Disc Screen. “The litter is easily below that size, although some of the other material isn’t,” notes Walmsley. “One advantage of using poultry litter as fuel is that turkey growers use fairly fine-grained material for bedding, which eliminates the need for grinding to produce suitable furnace fuel.”
After two to four days of storage, the material is “delumped” and conveyed into a buffer-hopper, which injects it into the furnace. The gasification facility uses a Foster Wheeler boiler and Detroit Stoker grate system which generates high-pressure steam at a rate of up to 490,000 BTUs/pound/hour.
Fibrominn works with turkey growers within a large region, but concentrates on collecting litter within a roughly 50-mile radius. “We provide a very valuable service in the form of manure management for the growers,” says Walmsley. “Unlike working with wood suppliers who have market ups and downs, growers can use us year-round, which also ensures that we always have access to the biomass supply.” Fibrominn’s long-term contracts with growers include incentives for providing better quality fuel, which includes minimized moisture content.
One characteristic of using litter as fuel is a relatively high ash “burden” of 10 to 15 percent, Walmsley notes. Fibrominn sells its ash to North American Fertilizer, LLC, which has an adjacent plant. “They meet the market demand based on the need for nutrients for growing corn, soybeans and sugar beets,” he says. Fibrowatt is in the process of developing three additional poultry litter biomass fuel plants in North Carolina, and sees opportunities for more in a number of areas around the U.S., mainly in the South and on the East Coast.
CHIPPEWA VALLEY ETHANOL
Benson is also the home of Chippewa Valley Ethanol Co., a farmers’ cooperative that plans to begin burning corn cobs in its boiler system on an experimental basis. By next year, the 980-member co-op expects to meet 90 percent of the plant’s energy needs by replacing natural gas with wood chips, corn cobs and other ag-related residue.
In 2003, the plant completed a major expansion that increased its annual ethanol output from 15 million to 47 million gallons. In April, the plant began burning wood chips in its new, biomass-equipped system. Because it is ramping up gradually, as of November, wood chips had replaced only about 10 percent of its natural gas consumption, according to General Manager Bill Lee. “We’re doing some ‘debugging,’ and we’re also working through some air quality constraints,” says Lee, as part of a permit with the Minnesota Pollution Control Agency. “There’s a question of how cobs compare (to wood chips) in the emissions they produce. We think it’s very comparable, but there is not a lot of data out there. We hope to do some cob work this winter.”
When the plant eventually reaches the 90 percent biomass level in late 2009, it will burn slightly over 250 tons/day. According to Lee, to reach that point, “we’ve got some more pieces to add to the system.” Limitations on local availability of wood is one reason the plant will eventually burn cobs and other types of ag residue. The co-cop buys wood from several processors and aggregators. “The quantities of economical wood biomass available are fairly small, but we’ve been able to tap into some of that,” he continues. “But we’re not the only game in town, with two other plants in the area that also burn wood chips. The impact of the housing market collapse on the wood products industry has also reduced our supply. Generally, the supply is lower than we had hoped, and the price is going up.”
The wood chips are brought in on walking-floor trailers, run through metal-removing and “scalping” equipment to take out oversized material, and lifted into a Ladig storage silo. “Biomass has problematic flow-properties, so the Ladig system has a rotating-tooth auger to convey the material into the center,” says Lee. The chips are pneumatically conveyed into the fluid-bed gasifier made by Frontline Bioenergy, an Ames, Iowa firm partially owned by the co-op. The biomass gasifier installed earlier this year is the first of its kind in commercial operation in the U.S.
How much the plant will save on energy costs partially depends on the cost of natural gas. “Natural gas is now around $6.50 per dekatherm; it was $14 a few months ago,” says Lee. “We think we can break even at about $5.50 [comparing biomass to gas].” The plant will retain its ability to run 100 percent on natural gas, so that it can take advantage of any price drops, he adds.
Earlier this year, the co-op received a $150,000 state Commerce Department grant to analyze the comparative merits of two types of corn cob collection and storage systems, along with $50,000 grants from the Minnesota Corn Promotion and Research Council, and Minnesota’s Agricultural Utilization Research Institute.
“For the study, we have contracted with farmers to handle collection and storage, in or near farmers’ fields,” says Lee. The 980-member co-op has held three public demonstrations for area corn growers to see its new biomass system. “We want local farmers to be in that business, and we’re paying people to participate in the study. So this whole effort is part R&D, to analyze the field-to-facility economics, and part marketing. We may see new co-ops formed to aggregate capital to build these [biomass collection] systems. Because we have multiple users of biomass in this area, the economics are more favorable for farmers.”
Lee expects to see the price for cobs eventually settle in the $40 to $50/ton range. “For 150 bushels an acre of corn, we ought to be getting close to three-quarters ton of cobs per acre,” he calculates. “We grind about 16.5 million bushels per year of corn in our ethanol plant; if we had that yield of cobs from the same farmers, it would provide 75 percent of our thermal energy needs. However, we may always use wood as a certain percentage. Our gasifier is capable of handling a pretty wide range of biomass feedstocks – sunflower hulls, corn stover etc., but cobs represent a large, relatively sustainable form of feedstock we can buy from our own co-op members.”
Dan Emerson is a freelance writer in Minneapolis, Minnesota.