In fluidized bed reactors a catalyst is subjected to significant attrition. This attrition influences together with the efficiency of the solids recovery system the particle size distribution inside the fluidized bed system and thus the performance of the reactor. Furthermore the attrition is a major reason for the loss of catalyst and may thus become also decisive for the economic performance of a catalytic process.

In previous work the attrition of catalyst has been studied in detail for catalysts which have undergone attrition inside the fluidized bed for a long time already and therefore reached a constant attrition rate. It was shown already, however, that a fresh catalyst is much more fragile and shows up a much higher attrition rate at the beginning than at steady state. It took always a considerable long time until a constant attrition rate was reached. Therefore the higher attrition rate will significantly contribute to the total loss of catalyst.

The higher attrition of the fresh catalyst is due to micro cracks in the surface and the roughness of the surface. After some time the particle is more rounded and the surface has become smoother due to the attrition and thus the resistance against attrition is increased.

In a fluidized bed reactor a particle will be subjected to attrition due to different mechanisms in different parts of the system, namely attrition by gas jets near the bottom of the fluidized bed, bubble induced attrition in the fluidized bed itself and the attrition during the passage through a cyclone. All these different attrition mechanisms are described by different mathematical models with different time scales. In total they cause the aging of the particle and thus the increase of the resistance against attrition.

To be able to summarize the effect of the stresses on the particle within the different parts of the fluidized bed system the concept of the ‘stress history’ has been developed, which allows a uniform treatment of the different attrition mechanisms. This concept has been experimentally validated and been implemented into an existing population balance model. The experiments were carried out with fresh FCC catalyst.

The simulation of the time-dependent variation of the particle size distribution in the fluidized bed system illustrates the effect of the age-dependent catalyst attrition.