Research developments

Appalachian State University helps develop North Carolina LFG projects

The Appalachian Energy Center at Appalachian State University, Boone, North Carolina, recently completed a project that began in 2005 to help eight North Carolina counties produce renewable energy while reducing greenhouse gas emissions and improve their economy.

The project was funded by a grant from the Z. Smith Reynolds Foundation of Winston-Salem, North Carolina. The ZSR Foundation and the Appalachian Energy Center share the goals of protecting the environment while spurring community development throughout North Carolina.

Because of this recent grant, and previous funding from Z. Smith Reynolds Foundation, Golden LEAF Foundation, the American Recovery and Reinvestment Act (ARRA), and the work of the Appalachian Energy Center, eight new landfill gas projects in North Carolina are producing an average of over 1,700 kilowatt hours of electricity per month.

The first landfill gas to energy conversion project began in 2005 in Watauga County and was completed in 2012. The most recent projects began in 2013 in Rockingham and Edgecombe counties and were completed in 2014.

According to Dr. Jeff Ramsdell, director of the Appalachian Energy Center, “We are so pleased to have been able to contribute to the development of a number of small- to medium-sized landfill gas projects in North Carolina. These projects eliminate massive amounts of greenhouse gases while creating new income streams for the counties who operated these landfills. Since these projects began, over 90 million kilowatt hours of renewable energy have been produced for the North Carolina grid.”

Methane emissions have often been a subject of conversation. Methane is a serious greenhouse gas, 23 times more potent than carbon dioxide at storing heat in the atmosphere. Landfills are a major source of methane emissions. These landfill gas projects capture methane before it is emitted into the atmosphere and pipe it to engines which burn the methane as fuel to generate electricity. To date more than 600,000 tons of carbon dioxide equivalent have been reduced.

The Appalachian Energy Center has worked primarily with limited-resource counties with smaller landfills to develop community-based landfill gas projects through a program called Community TIES. Jason Hoyle, business analyst at the energy center explains, “Commercial landfill gas developers have made money at larger landfills for decades, but smaller landfills were ignored. We feel we have proven that landfill gas projects, even at smaller landfills, can make sense to the counties that own them as self-developed community-based projects.”

This work has directly resulted in landfill gas utilization projects in Columbus, Watauga, Wilkes, Haywood, Rockingham, and Edgecombe counties. The Energy Center has also provided assistance to projects in Gaston, Robeson and several other North Carolina counties. These eight projects have an estimated production capacity of over seven megawatts of electricity or enough to power about 5,000 average North Carolina homes.

According to Stan Steury, research scientist at the energy center, sustainable landfill-gas-to-energy projects in several North Carolina counties thanks to the Z Smith Reynolds Foundation, the Appalachian Energy Center and other partners. “Our staff has worked with county employees, equipment and service companies, utility companies, regulatory agencies and others to solve these problems,”he says. “Most of these projects would not have happened had it not been for the federal stimulus funds, but the Z. Smith Reynolds Foundation has also been instrumental in providing the Energy Center with grant funding.”

According to Steury, electricity generation is not the first choice of the Appalachian Energy Center in landfill gas development, because generators are so inefficient at converting energy in landfill gas to electricity—usually about 30 percent efficient—while boilers or furnaces burning landfill gas may have energy conversion efficiency that is more than 90 percent.The energy center has used an old technology in a new way on several projects: automotive engines fueled by landfill gas running generators.

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Centrifugal screener helps convert cooking waste into biofuel

B Green Group, Mount Kisco, New York, sees a future in converting restaurant waste oil, fat and grease into biofuels. According to the National Renewable Energy Laboratory (NREL) 4 billion pounds of trap grease available in the U.S. each year could yield about 500 million gallons of biodiesel instead of ending up in municipal waste streams. The figures for oils and fats are similar.

B Green Group is capturing part of that potential by converting more than 100 million gallons of restaurant waste fats, cooking oil and trap grease annually into high-purity feedstock which is refined by other firms into biodiesel, home heating oil, paint, animal feed and a variety of other products.

With customized equipment and a proprietary process developed by founder and CEO Andre Bernard, the company converts the cooking waste at 17 regional plants it either owns or operates as joint ventures.

B Green’s process extracts oils from the cooking waste while separating water and solids in steps that remove progressively smaller solids as the waste is converted to a liquid.

The company originally removed material in the 600 to 1550 micron range using a specially built centrifugal sifter, which proved inefficient at dewatering thick slurries. In addition, screen baskets were difficult to change and replacement parts were costly. The company replaced it with a Kason model MO Centri-Sifter centrifugal dewatering screener, which can be inclined up to 40 degrees to increase the dwell time of material within the chamber, and accordingly, the drainage rate of free liquid.

Bernard specified a 100 horsepower motor—double that of his original unit—to avoid overloading when dewatering slurries comprised of fats, oils and greases. A woven wire material was selected for the screen baskets to handle heavy loads.

Cylindrical replacement screens that cost less than previously, together with the unit’s quick-clean capability, further improved the economics of the process.

Cooking waste is gravity fed through a feed inlet and then metered into the cylindrical sifting chamber by a feed screw. With centrifugal force, rotating helical paddles, which never contact the screen, propel the waste against the screen. Liquids, and particles less than 600 micron, pass through screen apertures, discharging through the central housing outlet. Solids equal to or greater than 600 micron are ejected through the discharge spout at the downstream end of the cylinder.

To minimize downtime, the MO Quick-Clean model has a hinged door and cantilevered shaft at the discharge end, from which an operator can quickly remove the screen cylinder and paddle assembly for cleaning and inspection.

Following the centrifugal sifter, a 40-inch-diameter, four-deck Vibroscreen circular vibratory classifying screener, also from Kason, removes progressively smaller suspended solids that remain in the liquid. Effluent from the process is treated and cleaned prior to disposal. Waste solids, also treated, are discarded or burned for energy.

B Green installed seven MO centrifugal screeners at five of its newest plants. Bernard’s plans call for opening 20 plants in coming years—three in 2015 alone—each of which will have two Centri-Sifter centrifugal screeners. Bernard says he can easily sell 10 times the amount of his current output of 2 million gallons (7.5 million liters) weekly.

He concludes that biofuels decrease dependence on foreign oil, contribute to the U.S. economy and reduce carbon footprint. The feedstock is nontoxic, and if an accidental spill occurs, it biodegrades.

A Centri-Sifter centrifugal dewatering screener removes particles from restaurant waste slurry as it is converted into high-purity liquid feedstock for biodiesel.