The sand as additional bed material is fed into combustion chamber during start-up of the boiler and when a coal with low ash content is fired or co-fired with other fuel
(i.e. biomass). The behavior and the particle size distribution of granular materials are very difficult to predict in the circulating fluidized bed due to a vigorous movement of particles. A number of population balances
in CFB boilers which consider some important fluid dynamic processes [9–11], such as attrition, fragmentation, segregation, particle shrinking, char combustion, and heat transfer[12–14]are presented in the literature. Another key parameter which is very important in the mass balance is the stress history of particles [15]. In order to map all parameters mentioned above in the mass balance model, the CFB furnace
chamber is considered for two flow regimes separately.