| In an effort to develop a new fluidization process for firing cement clinker. Institute of Powder Engineering, Xi'an Univ. of Arch. & Tech. had launched a project of coarse granule fluidized bed development in early 1990's. This paper treats the heat and mass transfer mechanisms occurred in cement raw pellets. These pellets were made of ground limestone, carbon, and clay powders and the humidified mixture was rolled into small balls with diameter of 5 to 6 mm, nominated as black raw pellets.To simulate the heat transfer and limestone decomposition in the pellets, use was made of numerical method. A mathematical model of transient heat transfer was developed to describe carbon combustion, heat conduction in a raw pellet. Another model of mass transfer was also established for description of lime decomposition and diffusion of relevant gas species. Both of the models included source terms coupling with the heat and mass transfer phenomena. In both models a raw pellet was considered as a uniform distributed mass of spherical fine particles of limestone, carbon and clay of 30-45 microns in size.A computation program using Fortran 95 had been completed and used to solve the equations, and simulation was carried out under different conditions. Limestone decomposed fraction and carbon burnt fraction were used to describe the influence of various factors on the decomposition of raw pellets. Results indicated that for a pellet of 5 mm in diameter with carbon content of 5%, lime stone will be completely decomposed in about 3.4 min, and carbon burnt with 11.5 min elapsed of time, under ambient temperature of 1273K. Temperature, carbon content, gas velocity and O2 concentration were the main factorsaffecting decomposition, among which, temperature played the most important role. The influence of CO2 concentration could be ignored when temperature was higher than 1173K. The finess of limestone and carbon particles had faint effects on the decomposition at the size range from 30 to 60 microns.
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