Exploring the interplay between abrasive attrition and separation in cyclones

Abstract

It is widely known that higher cyclone inlet velocities produce a finer and tighter gas–particle separation at the cost of higher particle attrition. Few models exist that study the simultaneous interplay between these two effects in detail. In this work we present a series of progressively more complex models of abrasive attrition and cyclone separation in a circulating fluidized bed (CFB) riser.The simplest of these models treats the in-situ particle size distribution (PSD) as that of the feed material, computes attrition based on a constant diameter reduction rate with instantly vanishing fines, and uses a simple two parameter cyclone grade efficiency model. This simple model is studied as a function of feed PSD, relative attrition rate, and cyclone grade efficiency parameters. The consequences of adding more complexity to the model – via a population balance (PB) computation of the true in-situ PSD, size dependent attrition, non-vanishing attrited fines, more detailed cyclone modeling, etc – are examined as well.The purpose of these exercises is to understand the mechanistic interplay between attrition and cyclone separation efficiency and evaluate the necessity of increased model complexity for accurate prediction. From this work, it was determined that in many practically operated regimes (relatively low attrition and reasonably low cut sizes) all models give roughly the same results. However, the more complex models are useful for understanding upset and worst case scenarios as well as for systems designed in other operating regimes.