Particulate and aromatic hydrocarbon emissions from a small-scale biomass gasifier-generator system

Distributed gasification of biomass has potential as a renewable energy alternative, but the emissions from gasifier-generator systems raise potential environmental and human health concerns. Producer gas from gasifiers contains high concentrations of aromatic compounds, tars, and particulate matter. In gasifier-generator systems, producer gas is used to feed an internal combustion engine connected to a generator. Little is known about the extent to which spark-ignited engine combustion eliminates these harmful components. This study measured emissions at three locations of a 10 kW electric, fixed-bed, downdraft gasifier-generator system to determine the effectiveness of the packed-bed filter and the spark-ignited engine to reduce pollutant concentrations in the producer gas. Emissions were compared to regulated levels. Particulate matter concentrations were approximately 75 mg/Nm³ in the pre-filtered producer gas and were reduced by about 99% by the packed-bed filter to about 1 mg/Nm³. Particulate matter concentrations were below regulated levels and did not change significantly because of the combustion in the engine for the conditions tested. Combustible compounds were 99% consumed in the engine, and carbon monoxide concentrations in the engine exhaust were below regulated levels. While the concentrations of benzene and toluene in the engine exhaust were each approximately 10 ppm, it is expected that they would not exceed permissible exposure limits for ambient air if the system was installed in a properly ventilated area. Leak-free and properly maintained gasifier-generator systems could be implemented in rural communities to efficiently use woody biomass without significant risk of human exposure to carbon monoxide, particulate matter, or light aromatic hydrocarbons.