Wall roughness modification of a standard Lagrangian model for the prediction of saltation velocities in gas-solid flows

Abstract

The reduction of harmful emissions is an important issue in coal fired power stations and a technique used to reduce the emissions of oxides of Sulphur and Nitrogen is low NOx burners. A requirement for effective operation is to supply the burners with a uniform stream of pulverised fuel (PF) without incurring particle settling.A valuable tool in analysing multiphase flows in PF systems are numerical models in the form of Computational Fluid Dynamics (CFD) simulations. Various models can be used to simulate the transportation of particles, the closer the model is to the physics of reality, the more computationally expensive it is. Commercial CFD codes have proven to be valuable in the analysis of multiphase flows. This study evaluates a numerical technique that can offer results that reasonably predict the onset of settling at the most economic computational cost.Numerical models were compared to literature to evaluate ability of the Lagrangian model to predict the onset of settling. The standard Lagrangian model predicted excessive settling of the particle phase because the effects of wall roughness and inter-particle collisions were not accounted for. A wall roughness modification enhanced the particle distribution in the pipe and predicted better pressure drops.