Stirling Engine for Biogas Cogen – A Case Study of Helena MT

This presentation will highlight Helena MT WWTP, which is the only WWTP in North America with a stirling engine generator. Helena is running the engine on unscrubbed biogas. The presentation will provide an overview of what a stirling engine is and further discuss how it was implemented in Helena. Small facilities would normally be deterred by the cost of gas scrubbers and the significant O&M costs of traditional CHP solutions. As a stirling engine does not require scrubbing it allows facilities a more productive option than simply flaring the gas. The electricity can be used to power part of the plant, or be connected back to the grid. The hot water output can be used to supplement the digester boiler or as radiant building heating. This technology is ideal for plants with a renewable energy focus and can take advantage of existing incentives and grants.There are many small wastewater treatment plants that would like to convert their biogas into heat and power, but due to economies of scale have been unable to do so. Gas scrubbing was cost prohibitive for the small plant of Helena MT but the Cleanergy Stirling engine is less sensitive to H2S and siloxanes than traditional CHP systems which allowed Helena MT to move forward with the technology. The Cleanergy Stirling engine also has the potential to burn low content methane gas. Waste streams from biogas scrubbing or aerobic lagoons have methane concentrations at 20-25%, which requires natural gas supplementation to flare. The Cleanergy Stirling engine can burn the waste stream without the need of a natural gas supplement.