Dynamic reactivity and comminution behaviour of particles in CFBC

Steady state population balance modelling has widely been used to simulate the particle size distribution (PSD) of different material (fuel, ash, sand or limestone particles) in fluidized bed combustion (FBC) and circulating fluidized bed combustion (CFBC). The steady state approach cannot be used to study the effect of rapid changes in dynamic conditions, where the fuel with different reactivity and PSD and the PSD of its ash vary, but a dynamic model is more appropriate.

Bench scale reactors can be applied to study basic comminution and reaction rate behaviour of materials with a fuel batch input, which is more easily operated than a reactor with a continuous feed. Then however, the dynamic population balance approach is required to interpret the results, extract model parameters from measurements and convert them applicable for steady state models or models that divide the PSD into a few fractions.

The stability of combustion in FBC and CFBC depends much on the char inventory in the bed, which is affected by the size and reactivity of the fuel and the operational conditions (temperature, oxygen level). Dynamic population model can be applied to study the change of the char inventory due to changes in fuel or in operational conditions. These changes are quite rapid compared to the slow changes in the PSD of ash in the bed after fuel is changed to another. The steady state and the time required to approach steady can also be simulated with the dynamic model by continuing the calculation long time.

A dynamic population balance model is applied to study reactivity and comminution behaviour of particles. Tests are carried out in a pilot scale CFB and bench scale fluidized bed reactors.