Co-Combustion of Animal Waste in Fluidised Bed Boilers: Operating Experiences and Emission Data

Crushed animal waste, given the trade name Biomal, has successfully been combusted in Fluidized Bed Boilers with low emission data. About 500 tons of Biomal were co-combusted in full scale tests in commercial boilers with wood chips, peat and sorted municipal waste. The mixing ratios varied between 30% and 65% depending on the fuel mix. In order to minimize the spread of BSE-infection among cattle a new EU legislation became effective in October 2000. This regulation stipulates that animal waste such as carcasses and SRM (Specific Risk Material) from slaughterhouses has to be destroyed by combustion. The company Konvex AB, which in Sweden is responsible for taking care of this type of animal waste, has together with S.E.P. (Scandinavian Energy Project AB) developed a cost effective concept for using animal waste as a fuel without first processing it into fat and meat meal. The Biomal fuel has been continuously co-combusted for 7 days in a 12 MW_th bubbling fluidized bed boiler and for 3 days in a 40 MW_th circulating fluidized bed boiler with very good operating performance. During the test periods ordinary emission data such as CO, SO₂, NOx, TOC etc. as well as specific compounds such as Dioxins and heavy metals were measured recorded. All data including operating parameters in the EU regulation for co-combustion of waste, EU 2000/76/EG, were met. The CO-levels were below 50 mg/m³n and the TOC-levels were most of the time undetectable and well below 10 mg/m³n. • Despite a much higher nitrogen content in the Biomal fuel compared to wood chips the NOx-emissions were unaffected or in some chases reduced by up to 50% while firing Biomal. • No increased Dioxin emission where measured.