Numerical study on ash accumulation and heat transfer characteristics in flue gas side of tubular air preheater

Ash accumulation in the tubular air preheater is one of the key problems affecting its safe and efficient operation. To reveal its mechanism, a numerical simulation based on the Euler-Lagrange method is conducted in this paper. The deposition and removal of ash particles on the finned tubes are described by using the critical velocity model and critical wall shear velocity model, respectively, the influence of ash accumulation growth on heat transfer is also considered by establishing an equivalent thermal resistance model. The results show that a backflow is occurred at the leeward area of the tube with the formation of trapped vortex. The ash accumulation basically occurs at the windward side of the fin and reaches a peak at the tube of Column Ⅱ under the joint action of the scour of incoming gas and the entrainment of trapped vortex. The larger gas velocity may enlarge the kinetic energy of ash particle, thence alleviates the ash accumulation mass and improves the total heat transfer coefficient of preheater. The increase of particle diameter may reduce the followability of particle with gas, which has a greater effect on the ash accumulation at the leeward side of the fin relative to the windward side. The larger longitudinal spacing between tube bundles makes the velocity distribution more evenly, which reduces the ash accumulation mass and enhances the total heat transfer coefficient. The increase of transverse spacing enlarges the particle concentration near the tube bundles, and then increases the ash accumulation mass, that at the leeward side of fin reaches a peak when P_L = 80 mm.