Impact of Boiler Type, Heat Output, and Combusted Fuel on Emission Factors for Gaseous and Particulate Pollutants

Five different boiler types (automatic boiler, overfire boiler, boiler with down-draft combustion, and two types of gasification boilers) representing residential-scale combustion technology were tested. Boilers were fueled with various fuels (lignite, wet and dry wood, wood pellets, and mixed fuel), and the combustion emissions were measured both at nominal and reduced output. The investigated emissions comprised CO, organic gaseous compounds (OGC), and particulate matter (PM). A cyclone and a low-pressure impactor were used to determine PM emissions. It was found that the emission factors for CO, OGC, and PM depend more on boiler type and mode of operation (reduced or nominal output) than on fuel type. Data from the Dekati low-pressure impactor (DLPI) show that, in most cases, PM1 represents approximately 80% of the total PM mass. PM0.1 represents 15-30% (modern boilers) or 5-10% (old-type boilers) of the total PM mass. Comparison of the results shows that the emission factors for PM obtained by the cyclone were higher than the emission factors obtained using the DLPI.