Sulphur capture in circulating fluidized-bed boilers: can the efficiency be predicted?

The present state of understanding of sulphur capture in fluidized-bed comb ustion is discussed with focus on the possibilities to predict sulphur capt ure performance and the effect of intermittent reducing conditions. The fou r key factors that determine the sulphur capture performance are: (i) parti cle size distribution, including the effect of particle size reduction, (ii ) residence time as a function of particle size, (iii) reactivity as a func tion of particle size, and (iv) effect of reducing conditions. The first th ree of these can be determined and included in a model for prediction of th e sulphur capture, but the problem of how to include the effect of reducing conditions in a model is still unresolved. The conclusion must be made tha t sulphur capture performance in CFBBs cannot safely be predicted at presen t, and more research is needed before the effect of reducing conditions can be incorporated in modelling. Nevertheless, existing models can be useful to approximate the effects of, for instance, particle size reduction or cha nges in particle residence time. (C) 1999 Elsevier Science Ltd. All rights reserved.