Two Dimensional Modelling of Multiphase Flows in Fluidised Beds

There is increasing interest in the development of new technologies for the power generation industry using low rank coal for economic and environmental reasons. Most of the major technologies being investigated involve fluidised beds, serving roles as gasifiers, combustors or driers. Physical modelling is done on a small scale pilot plant and the results are used to validate numerical models. The computational code CFDS-FLOW3D allows various aspects of fluidised beds to be modelled, making scale-up from small pilot to large scale production plant more reliable. This paper is concerned with the development of a multiple particle size model in order to realistically represent multiphase flow in fluidised beds. An isothermal multiphase Eulerian-Eulerian finite volume model is used to simulate the two-dimensional transient behaviour of a gas-solid fluidised bed containing a central jet. The model is made up of three phases, one gas and two solid, where each phase is described in terms of continuum equations for the conservation of mass and momentum. The interchange of momentum between the gas and solid phases is accounted for by a fluid-particle friction coefficient. Work is being undertaken to validate, improve and compare relationships for particle-particle interactions in multiphase flows.