Modelling of boiler tube erosion

Erosion of boiler tubes is a significant contributor to the maintenance costs of sugar mills. In many severe cases, boiler convection banks have required a complete re-tube. a major capital cost. The problem can be particularly severe in boilers with baffled convection banks. Previous work by SRI has shown that the tube erosion rate is strongly dependent on the gas and particle flow distributions through the tube btmk. The CFD (Computational Fluid Dynamics) package FURNACE has been used to identify features of convection bank gas and particle flow patterns that contribute to tube erosion and to predict the effect of baffle modifications on these flow patterns. Tube erosion in the convection banks of many sugar mill boilers has been successfully reduced using baffle modifications determined from the CFD modelling work. This paper describes more recent work undertaken in collaboration with the University of Sydney investigating the detailed mechanisms of tube erosion from both a materials engineering and a CFD modelling perspective. Experimental work at the University of Sydney has established the important mechanisms of tube erosion and acoustic emission equipment set up at the Farleigh Mill NO.3 boiler has been used to correlate tube erosion rates with particle impact energies. The predictive capability of the FURNACE model has been improved by incorporating sub-grid models to resolve the gas and particle flow patterns around individual tubes. An empirical formula relating tube wear rates to particle-wall impacts has been derived and is used to predict erosion in the convection bank of the Farleigh Mill No.3 boiler.