An extended version of the countercurrent backmixing model suitable for solid mixing in two-dimensional fluidised beds

In this work, a new mathematical model to describe axial and lateral mixing in fluidised beds is presented. The model is an extension of previous vers ions of the countercurrent backmixing model (CCBM) that were restricted to axial mixing only. The fluidised bed is divided into parallel 'mixing colum ns', which are convective currents induced by the bubbles. Each mixing colu mn has a central upflowing stream of solids and two adjacent moving downwar ds. The practical application of the model requires a minimum knowledge of the bubble properties and the definition of one empirical parameter: the ex change coefficient between countercurrent phases, K, The model can be rapid ly solved with the proposed algorithm and reproduces semi-quantitatively th e main features observed in mixing experiments carried out in a bidimension al fluidised bed of coal and PVC as tracer. (C) 2001 Elsevier Science BN. A ll rights reserved.