Engines + Emissions

Harnessing Cow Power: Using Manure for Electricity

Managing a dairy farm is no easy task, especially at a time when feed costs are soaring due to expensive soy, corn and hay prices. Fortunately for farmers, recent developments in anaerobic digestion technology can help them reduce expenditures by offsetting electricity costs.

Biogas power generation has emerged as a viable alternative for dairy farms using methane-rich cattle manure, and to a lesser extent food wastes, to generate electricity.

As an example, since packaging its first Guascor® engine in 1999, Martin Machinery has sold more than 100 combined heat and power (CHP) units powered by Dresser-Rand Guascor engines to dairy farmers, who use them to convert manure into biogas through anaerobic digesters. The engine-based CHP units provide waste heat to the anaerobic digester, which converts manure into biogas at a faster rate. The power generated is sold to the grid, but oftentimes also offsets the farm’s high electricity costs. In addition, the waste heat can be used for digester and space heating or cooling (through absorption chiller cooling technologies). Some farmers convert the waste heat into steam and use it to help process the dairy milk into cheese.

Founded in 1976 in Ephrata, PA, by Harlan Martin, Martin Machinery manufactures and distributes Guascor engine-based gensets and CHP units that use fuels from decomposed animal waste (or biogas) as well as landfill gas, mine gas, and natural gas to help customers economically produce heat and power. Martin Machinery has supplied more than half of the biogas generators installed on dairy farms throughout the United States, making it a leader in this industry.

How does Biogas Power Generation Work?

Biogas power generation is a win-win solution for dairy farms. In addition to producing high efficiency on-site power generation that offsets electricity costs from the grid, a biogas power generation system: decreases greenhouse gas emissions; offers a renewable power source; controls odor; enhances a farm’s nutrient management program by using the byproducts of digestion for farm fertilizer; can add superior crop nutrient value; and creates animal bedding that can be made from excess solids.

The biogas recovery system features a variety of components that make the process possible. A collection system gathers manure and transports it to the digester. Existing liquid/slurry manure management systems can be readily adapted for this.

The digesters, commonly covered lagoons or tanks, are designed to stabilize manure and optimize biogas production. The biogas (a byproduct of decomposed manure, typically comprising about 60 percent methane and 40 percent of other gases) is then collected, treated and piped to the CHP unit.

The biogas is used to fuel an engine which drives a generator. This, in turn, produces electricity for use on-site or is supplied to the local grid. Waste heat collected from the engine exhaust and its jacket cooling system can be used for space or water heating to offset other fuel costs. Flare systems are installed to burn off excess gas, as well as serve as a back-up mechanism for the primary gas-use device (the CHP unit), should it go down for service.

Dairy farmers are also conducting studies to determine if the waste heat from the CHP unit can be used to heat cow stalls. This would give cows a more comfortable environment and, theoretically, help increase milk production.

According to EPA AgSTAR, 202 operational digesters are used across the United States, producing approximately 650 million kWh annually.

Martin Machinery has employees or service partners in seven states comprising nearly 50 associates, and offers a wide variety of custom manufactured Dresser-Rand Guascor® powered CHP units that meet both OEM and ASME standards.

Tags: Biogas, Guascor Gas Engines

other articles from insights issue Autumn / Winter 2013