Erosion by coal particles, fly ash impingement seriously affects the availability of utility boilers. Erosion is predominant in economizer and low temperature superheaters (LTSH) in boiler tube banks. Three tube specimens were collected from NTPC Korba from first row of economizer top bank from 500 MW steam generator. Maximum depth of erosion anywhere on tube surface can be estimated by the erosion model proposed by Chinese Boiler Thermal Association. Erosion rates on tube surface can be estimated from impact velocity and impingement angle of ash particles in flue gas in the erosion model proposed by Hameed (1992). The maximum depth of erosion wear and erosion profile of tube specimens were compared with the values evaluated from both the models. Erosion coefficients of fly ash in gas, thus achieved have good agreement with value proposed in the literature. The predicted erosion rates have resemblance, though not coherently with the erosion profile of tube specimens. Collision efficiencies, used in both erosion models were calculated for fly ash with CFD flow simulation in the computational domain of economizer and LTSH. Dust laden flow was solved in Fluent 2D RNG k-e turbulent flow model that accommodates rapid rate strain and streamline curvature on curved walls of tube surfaces. The Reynolds-averaging Navier-Stokes equations are solved for continuum gas phase and results are used in conjunction with the Lagrangian trajectory model to predict the particle rebound characteristics. The erosion distributions were found to be significantly different between the lighter and heavier particles. Erosion in downstream tubes is localized at higher tube angles near narrowest cross section and occurs mainly due to multiple collisions of coarser ash particles.

Keywords: Fly ash, Tube erosion, impact velocity, impingement angle, collision efficiency, erosion coefficient, CFD, Lagrangian approach.