Technology▼Solutions in the development of modular gasification technologies. Gasification is the high-temperaThe U.S. poultry industry generates In anticipation of new federal regture conversion of carbon-containing about 35.5 million tons of manure per ulations controlling runoff from animaterial into a mixture of gases made year, based on 1997 Census of Agrimal feeding operations, which are up primarily of carbon monoxide and culture data. Although the waste is expected to be finalized by EPA in hydrogen. This so-called synthesis gas rich in nutrients like nitrogen, phosDecember 2002, farmers are eagerly is commonly used to generate elecphorus, and potassium, tougher new looking to find new ways to manage tricity or make chemicals such as state laws controlling nutrient runoff their excess nutrients. They are parmethanol. Anything containing carlimit how much of it can be applied ticularly concerned because EPA’s bon, from coconut shells to used tires to land, creating a huge waste dispospolicy on manure management, to agricultural waste, can be convertal problem for farmers. which has historically focused on ed into synthesis gas. Researchers One solution is to use the manure nitrogen, is now taking a closer look have demonstrated that municipal for power. Although animal waste has at phosphorus. As a result, many sewage sludge can be gasified, resultnot traditionally been considered biofarmers are now considering energy ing in a large reduction in dioxin mass, this appears to emissions compared be changing. Much of with incineration, but the discussion at the the process works best Water Environment with dry materials. Federation’s Animal Dry poultry litter, Residuals Conference which is manure mixed in May centered on with wood shavings or generating electricity other similar materials, from animal manure. appears to be well suited For the most part, the for gasification. Several technology exists, but DOE-sponsored projects finding electric power have demonstrated that buy-back rates that electricity can be proare acceptable is anduced from gasification other story. of the waste material. In “It’s becoming insome cases, the ash can creasingly harder for even be collected and small farms to sell sold as fertilizer. their power back to One company that the utilities because is developing technoloincreased competigy to convert agriculturtion among electric al waste like poultry Community Power Corporation in Littleton, Colo., is developing small-scale moduutilities has reduced litter into electricity lar systems, such as the one pictured above, for converting waste products like the buy-back rate,” is Community Power poultry litter into electricity. says Sam Tagore of Corporation (CPC) in the Department of Littleton, Colo. CPC is Energy’s (DOE’s) Biomass Program recovery as an important part of the particularly interested in small-scale Office. The solution could be to offer solution. (5–50 kW) biopower systems that can tax incentives for renewable energy Processes like anaerobic digestion, be mass produced to lower the capifrom sources like manure, or pass which produces methane gas that tal cost. Although several companies state laws that require a certain percan be used as fuel, help address have demonstrated gasification of centage of renewable energy, he says. odor, pathogens, and excess nitropoultry litter, all currently available DOE is also promoting the developgen, but not phosphorus, says systems are for large off-farm sites, ment of new technologies, such as Tagore. Phosphorus management says John Reardon, director of adsmall-scale modular systems that can may require integration with thermal vanced technologies research at be mass-produced and placed in close processes, such as gasification, pyrolCPC. Large-scale (>1 MW) systems proximity to farms, to make waste-toysis, or direct combustion, he says. are expensive and only become ecoenergy production more economical. DOE has been particularly interested nomical when tens of thousands of COMMUNITY POWER CORPORATION
On-farm manure-to-energy production
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tons of litter are processed per year. cooled. These heavy hydrocarbons, For small farms that only produce commonly referred to as tars, create 1000 tons of chicken litter per year or problems for the gas cleanup system, less, such large-scale systems aren’t says Reardon. In addition, such resireally practical. dues can make it difficult to dispose On the other hand, on-farm moduof the ash or reuse it as fertilizer or as lar systems can offer advantages for construction building blocks. Howsmaller farms, says Reardon. For exever, PAHs can be reformed to carbon ample, because excess litter does not monoxide and hydrogen in a catalytic have to be transported to an off-site converter, says Reardon. “This reforlocation for processmation process is ing, the farmer avoids acomplished by sendpaying shipping costs. ing the producer gas Although small-scale through a bed of systems can be intercommercial reforconnected with the ming catalyst, such as electric grid, so that nickel on alumina, at electricity can be sold temperatures above back to the utility 750 °C,” he says. companies, many Researchers in farmers find the curFinland have reportrent buy-back rate of ed high levels of 2–3 ¢/kWh unacceptPAHs in fly ash (up able. An alternative to 555 mg/kg ash) that many find from the gasification Excess manure generated by the appealing is to use of straw (Environ. poultry industry can be a valuable source of fuel. such systems off-grid Sci. Technol. 2002, to supply power on 36, 2193–2197). PAHs the farm. The poultry industry uses exist in the fly ashes from all other large amounts of propane or natural feedstocks as well, but the amount gas to heat the production houses, and composition depend on the fuel and electricity is important for autotype, says lead author Arja Asikainen matic feed delivery and ventilation/ of the University of Kuopio. The Finnish researchers were able to decooling purposes, says Reardon. Such stroy the PAHs by burning the fly ash power costs could be displaced at the in a circulating fluidized bed boiler. retail rate by producing the energy on The process worked surprisingly well, site from waste materials. eliminating 99% of the PAHs, and did However, there are still problems not lead to the formation of other to overcome. During the initial testing toxic organic compounds, such as of CPC’s small modular biopower syschlorophenols, polychlorinated tem for generating electricity from biphenyls, polychlorinated benzenes, poultry litter, high levels of NOx were emitted. The problem appears to be dioxins, and furans. high levels of organic nitrogen in Because gasification does not lead poultry litter, which lead to high levto the formation of dioxins and furans, els of ammonia in the produced gas. one of the big problems associated To decrease NOx emissions, CPC has with combustion, it is gaining in popproposed using a nickel catalyst to ularity. Gasification technology has convert the ammonia to nitrogen existed for more than 40 years, but under reducing conditions. This conthere appears to be renewed interest version must take place before the in the process, particularly as lowgas is delivered to an engine for cost fossil fuels become depleted. power production. The company DOE is promoting the development plans to test new technologies for reof new small-scale modular gasificamoving ammonia from the gas tion technologies for converting biostream during future field tests mass into energy, and according to scheduled through 2003. Ben Grumbles of EPA’s Office of Although all hydrocarbons are Water, EPA is investigating options, vaporized during the gasification including gasification, for converting process, traces of harmful organic manure into energy and other valued compounds, such as polycyclic aroproducts as it prepares final effluent matic hydrocarbons (PAHs), can reguidelines for centralized animal main in the gas stream and condense feeding operations. —BRITT E. onto solid particles when the gas is ERICKSON 278 A
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