Particulate Emission Reduction in Small-Scale Biomass Combustion Plants by a Condensing Heat Exchanger

Use of biomass fuels for energy purposes has gained increasing importance as a method to reduce greenhouse gas emissions. In comparison to gaseous and liquid fossil fuels, the emissions of particulate matter are higher, leading to concerns about the availability of cost-effective techniques to reduce aerosol emissions in small-scale biomass combustion plants. In this work, the applicability of reducing aerosol emissions by stimulating condensation of aerosol-forming vapors on the heat-exchanger furnaces is investigated. A first-order estimation indicates that the heat-exchanger passage has to be in the order of millimeters to obtain a higher wall condensation rate compared to heterogeneous condensation, a result verified with purpose-built heat exchangers connected to a grate furnace. The measurements show that heat exchangers with an equivalent tube diameter of approximately 2 mm can reduce the aerosol emissions by approximately 70% compared to conventional boiler designs.