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( J ! j j { - r ( r / r r P 1 l'a p}Gj 'i: f J°C9f 14�� flff GsJ 011.Hij?;ipril P 1'1„ f At IL-4/A'liltfl Eli f 'f ktt, ■E■ ■■■ 111 In rg_ y _ ■ ■ G ■ ■ II III 11 111 ,. _. Courtesy Avant Energy Inc Using agricultural and food-processing waste products, Hometown BioEnergy is helping the Minnesota Municipal Power Agency meet state-mandated renewable energy standards while also providing a valuable fertilizer for area farmers and sol- id biomass as a fuel for other facilities. Aaron Larson e've all heard the phrase "one cess also produces a liquid fertilizer—rich in allows the company to accept wastes that man's trash is another man's trea- nutrients such as nitrogen, phosphorus, and become available on a sporadic basis with sure." Hometown BioEnergy potassium—that is then sold back to local fewer operational challenges. (HTBE)offers a case in point.The plant uses farmers to spread on their land. In addition, The process begins with feedstock deliv- vegetable-processing waste and livestock undigested biomass is dried to create a solid ery. The mixture of local agricultural and manure in an anaerobic digestion process to fuel,which can be sold to other biomass and food processing waste includes sweet corn produce biogas for use in engine generator coal-fired facilities to fuel their boilers. silage, food waste, livestock waste, and sets.The agricultural trash is a real treasure waste oils(all sourced from within a 60-mile for the company. A Flexible Design radius).The material is transported to HTBE Avant Energy Inc.—the energy manage- Variety may be the "spice of life," but it via truck and delivered to the plant's receiv- ment company that developed,oversaw con- doesn't always make for the best "season- ing hall.The biomass is weighed,mixed,and struction,and continues to manage operation ing" at biomass plants. When dealing with heated in feeding modules to prepare it for of the plant for Minnesota Municipal Power agricultural waste products, though, variety the anaerobic digestion process. Agency (MMPA)—sees tremendous op- is also a fact of life.Materials are frequently "The percentages of each type of material portunities to redefine the term "waste." It exposed to weather, which means rain, sun, varies; however, on average, the plant sees believes bioenergy can help utilities, large and wind will all significantly affect moisture approximately 50% higher solid wastes and waste producers, food processors, and com- content.If waste is stockpiled for any length 50%liquid wastes,"said Kelsey Dillon,vice munities create value from waste streams and of time prior to delivery,quality can degrade. president BioPower for Avant Energy. reduce overall energy costs.Its development Farm management practices—such as clean- Inside the digesters,bacteria work togeth- team supports clients in the planning,design, ing schedules, herd size, square footage per er in the absence of oxygen to decompose and construction of both conventional and re- animal,and base bedding material—can also organic material and produce biogas.Biogas newable power generation facilities. affect waste quality. typically contains about 55% to 70% meth- While some people may think that the One of Avant's key objectives when de- ane, 30% to 45% carbon dioxide, and trace plant is utilizing vital resources that could signing the HTBE facility was maintaining amounts of other gases, including sulfur in otherwise be used to fertilize area farmland, flexibility in the allowable feedstocks. Tol- the form of hydrogen sulfide(H2S).As H2S it actually increases options for the agricul- erating variety enables the plant to manage is corrosive,it must be removed before com- tural industry. Not only does it help manage large seasonal changes in waste volumes bustion.At HTBE,the H2S is removed from disposal of the waste,but its biological pro- from suppliers in the region. In addition, it the biogas through microbial processes in gas 28 www.powermag.com POWER I December 2014