6.1a. ERMUSR 11-17-2015 - Laserfiche WebLink

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Energy Inc. We've all heard the phrase"one man's trash is another man's treasure."Hometown BioEnergy(HTBE)offers a case in point. The plant uses vegetable- processing waste and livestock manure in an anaerobic digestion process to produce biogas for use in engine generator sets.The agricultural trash is a real treasure for the company. Avant Energy Inc.—the energy management company that developed,oversaw construction,and continues to manage operation of the plant for Minnesota Municipal Power Agency(MMPA)—sees tremendous opportunities to redefine the term"waste."It believes bioenergy can help utilities, large waste producers,food processors, and communities create value from waste streams and reduce overall energy costs. Its development team supports clients in the planning,design, and construction of both conventional and renewable power generation facilities. While some people may think that the plant is utilizing vital resources that could otherwise be used to fertilize area farmland, it actually increases options for the agricultural industry. Not only does it help manage disposal of the waste, but its biological process also produces a liquid fertilizer—rich in nutrients such as nitrogen, phosphorus, and potassium—that is then sold back to local farmers to spread on their land. In addition,undigested biomass is dried to create a solid fuel,which can be sold to other biomass and coal-fired facilities to fuel their boilers. A Flexible Design Variety may be the"spice of life,"but it doesn't always make for the best"seasoning"at biomass plants. When dealing with agricultural waste products, though,variety is also a fact of life. Materials are frequently exposed to weather,which means rain, sun,and wind will all significantly affect moisture content. If waste is stockpiled for any length of time prior to delivery, quality can degrade. Farm management practices—such as cleaning schedules,herd size,square footage per animal, and base bedding material—can also affect waste quality. One of Avant's key objectives when designing the HTBE facility was maintaining flexibility in the allowable feedstocks.Tolerating variety enables the plant to manage large seasonal changes in waste volumes from suppliers in the region. In addition,it allows the company to accept wastes that become available on a sporadic basis with fewer operational challenges. The process begins with feedstock delivery. The mixture of local agricultural and food processing waste includes sweet corn silage,food waste, livestock waste, and waste oils (all sourced from within a 60-mile radius).The material is transported to HTBE via truck and delivered to the plant's receiving hall. The biomass is weighed, mixed, and heated in feeding modules to prepare it for the anaerobic digestion process. "The percentages of each type of material varies; however,on average,the plant sees approximately 50% higher solid wastes and 50% liquid wastes," said Kelsey Dillon,vice president BioPower for Avant Energy. Inside the digesters,bacteria work together in the absence of oxygen to decompose organic material and produce biogas. Biogas typically contains about 55%to 70% methane, 30%to 45% carbon dioxide, and trace amounts of other gases, including sulfur in the form of hydrogen sulfide(H2S).As H2S is corrosive,it must be removed before combustion.At HTBE,the H2S is removed from the biogas through microbial processes in gas cleaners as the product leaves the anaerobic digesters. Three large, white,dome-shaped gasholders—each with a 9,000-cubic-meter capacity—store the biogas for future use in one of four 2-MW Cummins Power Generation C2000 N6C engine gensets(Figure 1).The onsite gas storage allows dispatch flexibility to provide on-peak electricity, maximizing revenue potential.The electricity produced is supplied directly to the local distribution system serving the City of Le Sueur. 160