Mainstream Awarded Contract from the U.S. Department of Agriculture
Anaerobic digesters are capable of producing methane-rich biogas from animal manure and also offer the advantages of controlling odors, reducing pathogens, and minimizing the environmental impact of the waste. The biogas produced from anaerobic digesters is a renewable, distributed source of energy that can be used to generate electricity to offset power consumption on farms. Unfortunately, biogas is a sour gas that is rich in hydrogen sulfide (H2S), a highly corrosive gas that quickly embrittles the cast iron and steel used for many engine components. As a result, conventional engine-generators fail after several months of exposure to the high levels of H2S in biogas. No small (<25 kW) engines are currently available that can use this fuel without pretreatment to remove the H2S – a process that adds complexity, cost, consumables, and maintenance. As a result, many smaller biodigester installations simply flare the biogas rather than extracting any useful work from the fuel. The objective of this project is to develop an engine that is inexpensive, low-maintenance, high-efficiency, biogas-tolerant and does not require preconditioning of the biogas to remove H2S. The overall approach involves the replacement of materials for selected components, engine modifications to control H2S in the crankcase, and careful selection of engine oil. The anticipated result of this project is a first prototype, the small, biogas-fueled engine that is purpose-built for corrosion resistance, fuel economy, and reduced emissions of H2S. The engine generator will have commercial applications for anaerobic digester installations at the cow, pig, and chicken farms. Households that have small-scale digesters for processing yard waste and food waste would also benefit from the technology.