B. Leckner and L.-E. Åmand
Co-combustion, co-firing, sludge, emissions, fluidized bed combustion, phosphorous
There are several options for co-combustion of biomass or waste with coal. In all cases the fuel properties are decisive for the success of the arrangement: contents of volatile matter and of potential emission precursors, such as sulphur, nitrogen, chlorine, and heavy metals. The content of alkali in the mineral substance of the fuel is important because of the danger of fouling and corrosion. Research activities at Chalmers University of Technology include several aspects of the related problem areas. An example is given concerning emissions from co-combustion in circulating fluidized bed with coal or wood as base fuels, and with sewage sludge as additional fuel. Two aspects of the properties of sludge are studied: emissions of nitrogen and sulphur oxides as well as of chlorine, because the contents of the precursors to these emissions are high. The possibility of utilizing the phosphorous in sludge as a fertilizer is also discussed. The results show that emissions can be kept below existing emission limits if the fraction of sludge is sufficiently small (<25%), but the concentration of trace elements in the sludge ash prevents the sludge from being used as a fertilizer.
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