Manure as Fuel

FAYETTEVILLE, Ark. — Modernizing an ancient method of producing energy, a Division of Agriculture engineering researcher at the University of Arkansas has developed a system that addresses two major problems associated with poultry farming. By using poultry litter as fuel, the system will help protect the environment and could reduce individual farmers’ energy costs by as much as 80 percent.

Tom Costello, associate professor of biological and agricultural engineering, worked with Lynndale Systems Inc., a furnace manufacturer in Harrison, Ark., to test a furnace prototype that uses litter -- a combination of poultry waste and bedding such as rice hulls and wood shavings -- as fuel to heat chicken houses. Because it is produced on site, poultry litter is easy and inexpensive to obtain. More importantly, as Costello’s team has demonstrated, its use can provide heat to offset the consumption of propane or natural gas, and thus will significantly reduce the greatest operating cost for broiler chicken growers. Perhaps most importantly, the system may help to solve the problem of what to do with excess litter.

“Initially, I came to this project as way to protect watersheds,” Costello said. “We know that applying too much litter to the land over a long period can sometimes cause nutrient loading into rivers and lakes, so I wanted to figure out a practical way to help farmers utilize their excess litter. Fortunately, the method will also save them money by reducing operating costs.”

The system is a simple closed-end loop that involves farmers’ gathering litter from a chicken house and storing it outside, somewhere close to the house’s furnace. To keep the litter dry and granular, the stock pile must be covered by a tarp. From there, farmers can use a tractor with a front-end loader to dump litter into a hopper. The hopper delivers fuel to the furnace according to the rate at which the fuel is burned. Costello said that a typical chicken house would need two to four bucket loads per day, depending on the temperature outside. A farmer could use about one ton of litter per day for space heating under typical winter conditions.

“Obviously, farms in Minnesota would consume more litter than farms in Arkansas or Georgia,” he said.

After initial ignition by a propane burner, the prototype maintains combustion with 100-percent raw litter, so it does not need additional materials for fuel. The furnace is connected to a thermostat in the chicken house that senses when heat is needed and automatically switches the furnace to deliver heated air via a duct.

Costello said tests have demonstrated the energy content of litter in the range of 4,000 to 5,000 British thermal units per pound of litter. Assuming the manufacturer makes recommended design improvements, his projections indicate that 100 tons of litter per year -- an amount easily produced at most farms -- could generate 80 percent of the total annual space-heating needs for one house. The other 20 percent could come from traditional sources such as propane or natural gas.

Another advantage is that the system produces a drier source of heat compared to typical unvented gas heaters. Houses with drier litter and lower humidity are generally a healthier environment for chickens.

Costello said the fuel is renewable and its use provides a net decrease in greenhouse gas production by reducing fossil fuel consumption. However, it does produce an ash that contains concentrated phosphorous and potassium, which cannot be applied to land in sensitive watersheds. Still, litter converted to ash results in a 10-to-one reduction in volume, Costello said, and there is a potential market for the ash to be used elsewhere as a fertilizer, and possibly as an additive to concrete mix.

Costello said the furnace prototype needs design improvements to create a commercial product that is economically feasible.

“Increased efficiency and heat output are needed, but these improvements can be reasonably expected from the manufacturer,” he said. 

Bob Dodson, Lynndale’s chief executive officer and president, said that his company expects to produce retail units of the furnace before the end of 2007.

Further work is needed to quantify air emissions and to develop markets for the ash, Costello said. The system has the potential to help many farmers use excess litter and may be an important part of a multifaceted approach to improving water quality.