THE ROLE OF INORGANIC MATTER IN COAL IN THE FORMATION OF AGGLOMERATES IN CIRCULATING FLUID-BED COMBUSTORS

Circulating fluid bed combustion is increasingly being adopted for large scale power generation from low-rank coals. However, these coals often contain alkalis which are known to cause agglomeration and defluidization in CFBC systems through mechanisms that are not yet fully understood. A laboratory-scale fluid bed combustion system has been used to carry out experiments with coals containing various amounts of sodium chloride, organically bound alkali and alkali earth metals. The bed material and fine ash removed from the furnace have been characterized by various analytical techniques. It was found that, in the stirred environment of circulating fluid bed combustors, a portion of the ash is deposited on the surface of the bed particles. This ash coating contains a molten phase which causes the bed particles to stick together and/or defluidize. The ash formation studies reported in a previous paper and the interaction of ash with bed material reported in this paper describe a sequence of events that can explain the role of the inorganic matter in agglomeration and defluidization.