Investigation on application and performance of emission reduction measures at a pellet boiler

Various emission reduction measures may be used to reduce the emission of gaseous and particulate pollutants in the flue gas of small-scale firing systems. Further operation of obsolete firing systems and the reduction of pollutant emission during maloperation and part-load phases reveal the need of them. Beside their effect on pollutant concentrations, the adaption of them is a major research matter. Two emission reduction measures have been investigated at a multifuel pellet boiler: catalytic flue gas cleaning and electrostatic precipitation. Test stand studies have been carried out with pellets out of wood, miscanthus, and corn strip residue. The particulate matter concentration was reduced on average by 70–80% for wood and miscanthus with the electrostatic precipitator and by 60 % for corn strip residue pellets. A dependency of the precipitation rate from particulate composition was observed. The investigations concerning the application and characterization of a catalyst demonstrate the conflict with respect to optimal process temperature for catalytic oxidation preventing blockage and thermal deactivation. Nevertheless, a carbon monoxide reduction of more than 50 % was observed. The investigations show that the reduction of carbon monoxide and particulate matter emissions from firing systems by retrofit emission reduction measures is possible. Still, further development is needed regarding an increase of particulate matter removal efficiency and a higher conversion rate for carbon monoxide and hydrocarbons.