Emissions of Mercury and Cadmium when Co-Firing Municipal Sewage Sludge and/or Waste Pellets with Biomass in a CFB Boiler

Paper in proceeding, 2012

Mercury (Hg) and cadmium (Cd) are the two most toxic heavy metals listed among trace elements. Emission limit values for these exist when burning waste in European Union (EU)countries. These emission limits are also valid for the case of co-combustion of waste fractions with a clean biomass as wood chips originating from stem wood. This has been studied in the 12MWth boiler located at Chalmers University of Technology by means of co-combustion of municipal sewage sludge and/or sorted, crushed and pre-dried waste pellets from IcoPower in the Netherlands. As base fuel a clean biomass was used consisting of only stem wood in the form of wood chips. Emissions of Hg and Cd were measured in the stack. An evaluation was also made of the importance of a highly efficient textile bag filter for the prevention of these emissions. Due to higher concentrations of Hg and Cd in the waste fuel streams, higher loading of Hg and Cd into the boiler was attained. The distribution of Hg and Cd into the outgoing flue-gas and fly ash streams was also determined.