Modelling of initial deposition of biomass ash particles on walls of superheater tubes

Abstract

Condensation of gaseous alkali chloride and sulphate and adhesion of molten ash particles are still an important issue of investigation and gaining more and more attention in biomass utilization. In this work the behaviours for formation of initial deposition layer and condensation of KCl(g) and K2SO4(g) were simulated nu-merically in a 2-D computational domain of an in-line 4?4 tube bundle. The sticking and rebound efficiency of incident particles, condensation rate of gaseous salts and ash deposition rate on both of the windward and the leeward sides of tubes were obtained through transient calculation cases. The ash deposition mass on the windward side of tubes is mainly from impaction and stickiness of large ash particles. The condensation rate of KCl(g) is two orders of magnitude higher than that of K2SO4(g) on both of the windward and the leeward side of tubes. The ash deposition rate and the condensation rate on the windward side of tubes are of equal importance. While on the leeward side of tubes the condensation of salt vapours is more dominant than the inertial impaction in the forming stage of initial layer.