THE INFLUENCE OF PARTICLE RESIDENCE TIME DISTRIBUTION ON THE REACTIVITY IN FLUIDIZED-BED REACTORS

The influence of particle residence time distribution on the average c onversion rate (or reactivity) of particles undergoing a non-catalytic ps-solid reaction inside a continuously operated fluidized bed reacto r is evaluated. A so-called beta-factor is defined as the ratio of the actual reactivity in the reactor and the reactivity of a batch of par ticles that react under similar circumstances and that all have a conv ersion extent equal to the average conversion extent in the reactor. T he beta-factor concept is elaborated for shrinking core conversion beh aviour. According to Heesink et al. (1993), three extreme types of con version behaviour are distinguished: core reaction limitation, product -layer diffusion limitation and grain reaction limitation. For each ty pe of behaviour a mathematical function is derived that expresses beta as function of average particle conversion, maximum attainable conver sion (with regard to pore plugging) and a new-defined expansion factor , which is a measure for the expansion (or shrinking) of the reacting solid during conversion. These functions can be easily incorporated in fluidized bed reactor models,