Catalytic wall flow filters for soot abatement from biomass boilers

In recent years rising costs of fossil fuels and, on the other hand, the availability of economic incentives and the development of advanced equipment solutions has made biomass combustion an attractive and efficient alternative for the production of heat and electricity at different scales of the plant. In fact, biomass is a renewable energy source widely used for energy production but, unfavourably, it is an important source of inhalable fine PM in ambient air as well. Among the different technologies for the abatement of these pollutants, wall flow catalytic filters may represent an efficient solution, since they combine physical filtration processes with catalytic oxidative reactions. The analysed filters, made of Silicon Carbide and loaded with 20%wt of Copper Ferrite (CuFe2O4), were properly shaped to be tested in the sampling line at the exhaust of a 30 kW pellet boiler located at ENEA research facilities. The paper presents the main experimental results related to the filter regeneration, the critical operative phase in order to provide adequate performance and service life of the filters. In the tests, regeneration, obtained by means of a high-temperature electrical heater wrapped around the filter housing, started when the pressure drop in the filter exceeded 600 Pa (the transition value from depth filtration to cake filtration) and the heater temperature was gradually increased from 180 °C to 500 °C. Tests showed high efficiency in PM reduction of wall-flow catalytic filters, moreover a relation between the beginning of the regeneration and the temperature of the flue gas at the filter outlet, in the range 220-280 °C, was found. The results provided useful information for the future researches, which will be focused on a microwave-based regeneration system, since both the matrix and the catalyst have good dielectric properties.