Several pollutants can be emitted due to the incomplete combustion of biomass fuels. Mirjam Matthes and colleagues from DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH in collaboration with Ulrich Riebel from Brandenburg University of Technology Cottbus in Germany proposed a method for the emission reduction measures at a pellet boiler. They stated that the pollutants released from biomass small-scale firing systems cause major problems. They demonstrated a two-stage emission reduction method at a multifuel pellet boiler with catalytic flue gas cleaning and an electrostatic precipitation process. The tests were carried out with wood, miscanthus and corn strip waste.
In the pellet boiler the combustion takes place in a water cooled combustion chamber out of fireclay with an automatic deashing system. The combustion is regulated by three main factors, namely fuel supply, air supply in the form of primary air and secondary air and two chimney fans, which ensure negative pressure in the combustion chamber. The emission reduction measures aim at two results, on one hand removal of particulate matter and on the other hand removal of gaseous pollutants. The measures have been integrated in a temperature zone between 420 and 670 K. The precipitation has been processed using four discharge electrodes having a wire or a band form. The electrostatic precipitator has been operated in the voltage range of 16-20 kV to ensure a steady operation and avoid flashovers. The integration of both the electrostatic precipitator and the catalyst were taking place in the heat exchange zone with a bypass construction to guarantee continuous operation even during failure of the measures. The electrostatic precipitator is connected with the heat exchanger by a flue gas pipeline. The catalyst has been a commercially available metal honeycomb with a noble metal active phase. The catalyst position has been either upstream or downstream of the precipitator.
The authors successfully demonstrated a reduction of carbon monoxide and a reduction of particulate pollutants. The catalytic reduction of carbon monoxide has been about 50 % at a process temperature of 250 °C. This temperature has been achieved during full-load operation or with a catalyst heating system. Providing a periodic maintenance, the catalyst activity has been observed for several weeks. The particle precipitation efficiency depended on the used fuel type. For wood and miscanthus an average reduction of 70-80 % has been achieved, for corn strip waste only about 60 %. The differences in the collection efficiency can be induced by different particle concentration or also different type of particles. Supplemental investigations to the effects on particle number distribution showed, that particles larger than 20-30 nm are precipitated with the used system.
Mirjam Matthes1, Ingo Hartmann1 , Andreas Groll2, Ulrich Riebel2, Investigation on application and performance of emission reduction measures at a pellet boiler, Biomass conversion and Biorefinery, 2016, Volume 6, pages 301-313.Show Affiliations
- DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH, Thermo-chemical Conversion Department, Leipzig, Germany
- 2.BTU Cottbus-Senftenberg, Chair of Mechanical Process Engineering, Cottbus, Germany
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