Predicting the performance of different fuels in fluidized bed combustion

One of the key advantages of the fluidized bed combustion technology is its potential of burning a great variety of fuels and even fuel mixtures in an efficient way. Besides many different coals, wood and other biomasses and also fuels derived from various wastes have been successfully demonstrated in a number of FBC installations around the world. However, some fuels or fuel mixtures may cause problems in FBC application. One potential problem may be higher flue gas emissions than accepted. In particular, the emissions of nitrogen oxides are strongly dependent on the fuel or fuel mixture being used. Another area of potential problems with unconventional fuels is associated with the behavior of the fuel ashes in the furnace and flue gases. The two main problems to be concerned about in this context are bed agglomeration or fouling of the convection surfaces. Consequently, it is of major interest to be able to somehow estimate the behavior of any new fuels or fuel mixtures in advance before trying them in a full-scale unit. This paper introduces two new methods to predict the performance fuels at FBC conditions. The first aims at predicting the tendency by a fuel or fuel mixture to form nitrogen oxides at typical FBC conditions. The other aims at predicting the fouling tendency of the fly ash formed during burning of a fuel or fuel mixture in a FBC. Both methods are based on advanced fuel analysis combined with a theoretical model, which describes the main reactions of the fuel nitrogen and the ash components, respectively, in the furnace and flue gases. Both methods are demonstrated for selected solid fuels including coal and some wood based biomasses.