Biofuels attract increasing interest in power plant technology as sources of carbon dioxide neutral fuels. Besides using solid pulverised biomass as an additional fuel in coal-fired boilers a further possibility to run a combined coal and biomass process is to pre-pyrolyse or pre-gasify biomass and to inject the gas as reburn fuel into the coal-fired boiler. Within the pretreatment process the solid feedstock is separated into a high energy gas and a solid residue. The gas can be used as a reburn fuel in the coal-fired boiler with excellent NOx reduction properties, the solid residue can be used in further processes or has to be disposed. At the Institute for Process Engineering and Power Plant Technology the pyrolysis and gasification of different biomass has been investigated with special emphasis on the gas and tar composition and on the NOx reduction efficiency of the produced gas. The gasification experiments have been carried out in an electrically heated lab-scale entrained flow reactor and in an electrically heated fluidised bed reactor in understoichiometric atmosphere, for the reburn experiments a pulverised fuel combustion reactor was available. The gas and tar composition as well as the NOx reduction efficiency have been analysed at temperatures of the entrained flow reactor between 400 degreesC and 1300 degreesC and of the fluidised bed reactor between 600 degreesC and 900 degreesC and air ratios of the pyrolysis/gasification process between 0 and 0,4. Detailed results of the investigations using pyrolysis gas from coal [7, 8], sewage sludge [17], or biomass [18] for NOx reduction are published elsewhere. To get information about the path of different feedstock components during pyrolysis the quality and quantity of pyrolysis char depending on temperature has been analysed and reported in [17, 18].
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