A mathematical model to characterize effect of silica content in the boiler fly ash on erosion behaviour of boiler grade steel

Fly ash particles entrained in the flue gas of coal-fired boilers can cause serious erosion on the critical components along the flow path. Such erosion can significantly jeopardise operational life of the boiler. A first principle based theoretical model has been developed embodying the mechanisms of erosion involving cutting wear, plastic deformation wear and effect of temperature on erosion behaviour, to predict erosion rates of pertinent boiler grade steels. Various grades of steels commonly used in the fabrication of boiler components and published data pertaining to boiler fly ash has been used in modelling the phenomena. The model also provides a quantitative predictive framework to study the effect of percentage of silica content in the ash particles on the erosion potential. The erosion sensitivity of particle impact velocity, angle of impingement and variation of surface temperature of the substrate (steel) have also been studied as a function of silica content in the ash. The model has been implemented in a computer code to predict the erosion rates at room and elevated temperature for various grades of steels under different particle impact conditions. The model predictions have been found to be in good agreement with the published data. This investigation illustrated that any minor increase in silica level in the ash can considerably aggravate the erosion rates, signifying the fact that silica content in the ash plays a critical role in characterising erosion potential of fly ash.