Prediction of erosion in the convection tube banks of boilers

Since the installation of many boilers in Australian sugar mills in the 1970s, certain designs have shown consistent erosion problems with convection bank tubes. Many mills have replaced complete convection bank tube arrays to restore boiler availability to an acceptable level. The selection of modified baffle and tube geometries to reduce tube wear has relied exclusively on engineering judgement and related previous operating experience. This paper reports on the application of the boiler Computational Fluid Dynamics (CFD) code FURNACE to the prediction of tube erosion patterns in convection banks. The conventional FURNACE model has been adjusted to simulate the gas flow, heat transfer and ash particle trajectories of baffled convection banks. The relevant data predicted by FURNACE have been applied in the conventional Raask empirical correlation for tube erosion rate to predict the erosion distribution at the first tube row of a baffled convection bank. The erosion predictions are compared with direct wear measurements taken on a large suspension fired boiler. Comparison between predictions and measurements shows that the FURNACE modelling technique can successfully predict the rate and distribution of tube wear. The use of the model for alternative baffle and tube geometries is discussed.