Catalytic Oxidation of Emissions from Residential Wood fired boilers

University dissertation from Stockholm : Kemiteknik

Abstract: The European Commission has set a target of doubling theenergy supply from renewable sources from 6% in 1997 to 12% in2010. An increased usage of biofuels will play an importantrole in meeting this target. The Swedish government is alsoactively supporting a changeover from nuclear power to anincreased use of biofuels but have at the same time set "cleanair" environmental goals that must not be obstructed by theincreased usage of biofuels. To be able to simultaneously meetthese objectives, the development of new and improvedtechnologies for low emission equipment must be continued.Biofuels are today utilised in large-scale combined heat andpower plants as well as in residential heating, especially thelatter is often connected with high levels of harmfulemissions. This thesis describes the utilisation of oxidationcatalysts for the abatement of emissions from residentialboilers, which is one promising technique for the developmentof low emission boilers. The overall aim has been to developthis technique to the stage of commercial manufacture ofcatalytic boilers.The first part of the thesis reviews the use of biofuels inresidential heating with special emphasis on the emissions fromsuch appliances. Some general aspects of applied catalysis arediscussed and previous experience from the use of oxidationcatalysts in wood fired stoves are summarised.The second part of the thesis consists of a summary anddiscussion of the experimental work on oxidation catalysts inwood fired boilers, papersI-VI. Three different boilers were used for theseinvestigations, a traditional over-fired boiler based onnatural draught, a down-draught boiler using forced airsupplyand a modern down-draught boiler equipped with a flue gas fan.In paperIpellet based catalysts were evaluated, papersII-Vfocused on monolithic catalysts and in paperVIthe use of net-based catalysts were evaluated.The conclusion is that the integration of monolithiccatalysts in modern down-draught boilers has a large potentialfor the development of low emission wood fired boilers. It isshown that the emissions of carbon monoxide and hydrocarbons,with the exception of methane, is oxidised effectively over thecatalyst. A number of important aspects for optimal integrationof the catalyst in the boiler are demonstrated, as well as theeffect of combining primary measures with oxidation catalysts.The technology is at a stage where field trials are the nextstep for answering the main remaining issue, the lifetime ofthe catalyst.Keywords:biomass, wood, combustion, residentialboilers, applied catalysis, catalytic oxidation, VOC, carbonmonoxide

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