Biomass gasification is much more complex and efficient than a household wood stove. Wood chips are superheated in a low oxygen chamber where they smolder and emit wood-gas. Oxygen is then introduced on the backside of the boiler causing the gas to ignite, producing heat (at temperatures of over 1100° F) to make steam that is distributed throughout campus for heating, cooling, hot water and cooking.
Exhaust from this process circulates through a cyclone separator, forcing larger particles to drop out. The exhaust then enters the bag house where it passes through a series of filters to remove fine particulate matter. The filtration system in Middlebury’s biomass plant is rated to remove 99.7 percent of particulates, so most of what one sees coming from the smoke stack is water vapor.
Further energy efficiency measures of this project include using the exhaust from gasification to preheat the water entering the boiler and using the steam to turn turbines to cogenerate electricity before being distributed throughout campus. Additionally, ash produced in gasification is used by local farms as a soil amendment.