Fachdokumente Online der Landesanstalt für Umwelt Baden-Württemberg

zur LUBW   zum Ministerium für Umwelt, Klima und Energiewirtschaft   zum Ministerium für Ländlichen Raum und Verbraucherschutz   zum Ministerium für Verkehr und Infrastruktur  

Development of a furnace construction to realise both burnout improvement and simultaneous NOx-reduction in industrial wood firings in the range of 100 to 1000 kW


The emissions during the combustion of natural wood chips in current automatic firings are NOx < 200 mg/m³ and particle < 50 mg/m³. During the combustion of chipboard residues NOx emissions can reach 1000 mg/m³ and particle 500 mg/m³, as they accrue particularly at furniture industry and carpenters. This high emissions are not acceptable with regard to a further thermal utilisation of wood residues. Therefore in this project a new construction of the firing system is done, based on the experiences made at industrial wood firings in previous investigations. A further emission reduction requires the complete burnout of particles and the separation of the remained particles before they are transported through the heat exchanger. There carbonic particles could be a key factor in forming Polychlorinated Dioxin and Furan anew. In the first project step the burnout zone of a staged furnace was optimised to improve particle burnout with simultaneous particle separation. Concerning the particle burnout there were achieved good results with the new burnout zone. The investigations treating NOx reduction showed, that the recoverable success depends mainly on the conditions in the primary zone where the fuel is fed. Here the fuel must be burned or gasified with lack of air, which was possible with air dry wood chips of a homogenous piece size of about 3 cm. Burning with lack of air was not possible with very fine dry fuels such as residuals of chip board processing. To achieve defined conditions independent of the fuel properties in this part of the furnace it was necessary to construct it anew. At the new manufactured combustion chamber hot gas from the end of combustion chamber or exhaust gas is taken to reduce primary air. This part was combined with the well working burnout zone of the existing firing. The combustion behaviour of this combined furnace was investigated and optimised on the IVD test stand. During continuously combustion of coated chipboards (fuel N-content 4,3 % dry matter) NOx concentrations of 437 mg/m³ (13 % O2) were measured, which corresponds to a 40 % reduction in comparison with an common underfed boiler. CO concentrations with 30 mg/m³ (13 % O2) were on a very low level as well as particle concentration of 47 mg/m³ (13 % O2) without additional precipitation. The results show, that a significant emission reduction could be achieved by primary measures. Now, a low emission firing for the combustion of difficult fuels from wood manufacturing industry is available.


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