MODELING OF ASH DEPOSITION IN LARGE-SCALE COMBUSTION FACILITIES BURNING PULVERIZED COAL

Traditional approaches to the prediction of the deposition behavior of a coal usually involve the use of empirical indices and ASTM ash fusi on temperatures. These approaches, however, can give misleading result s and are often unreliable. In recent years, considerable effort has b een made in the development of models which overcome some of the defic iencies of the traditional approaches, as reviewed in the first part o f this paper. In spite of advances, these models still fail to describ e the effect of deposition on boiler operation. The second part of thi s paper documents the efforts in the Advanced Combustion Engineering R esearch Center (ACERC) to integrate an ash deposition model with a com prehensive 3D coal combustion model. An ash deposition submodel, which includes the effects of both ash chemistry and operating conditions o n slagging deposits, has been incorporated into the comprehensive comb ustion code, PCGC-3. The submodel includes a statistically-based parti cle cloud model for determination of impaction rates of fly ash on boi ler walls. The fraction of impacting particles that stick to the surfa ce is determined from the physical characteristics (viscosity) of both the particles and the deposit surface. The model includes a descripti on of deposit growth which approximates both the physical properties a nd chemistry of the deposit as a function of combustion conditions (op erating conditions). A key feature of the model is its ability to acco unt for the effect of deposition on operating conditions in the boiler . Simulations of deposition in both pilot-scale and utility-scale comb ustion facilities are reported in the paper. (C) 1997 Elsevier Science Ltd.