Anticipating of ash agglomeration behavior in a fluidized bed by population balance equation

Ash agglomeration as a potential problem in fluidized bed gasifiers, leading to defluidization, was investigated in this study in a lab-scale fluidized bed. The experiments were carried out in batch mode in the temperature range of 600-950 degrees C and atmospheric pressure. The defluidization temperature was determined from the total pressure drop across the bed. The effect of superficial gas velocity on the defluidization temperature was also investigated. With increasing the gas velocity, the defluidization temperature increases up to about 960 degrees C, beyond which it remained almost constant. The particle size distribution at the end of the tests (defluidization state) was estimated from the population balance equation. Assuming a first order growth rate of agglomerates, the parameters of the rate equation were determined by fitting the population balance equation to the size of the agglomerates at the moment of defluidization. The results showed that as the gas velocity increases, the frequency factor of the growth rate equation initially decreases up to the fluidization number 3, after which it remains constant.