Ash deposition and corrosion mechanisms of tubes in Waste-to-Energy plants

In order to decrease ash deposition and hot corrosion in Waste-to-Energy plants, it is necessary to understand mechanisms of the ash deposition and the corrosion, and to develop new solutions. In this study, an adhesion force between an ash pellet and an alloy specimen were firstly measured to investigate the increase mechanisms of the ash deposition and the corrosion, using a tensile testing machine with an electrical furnace. Second, mass loss of the alloy specimens was measured as hot corrosion tests based on Japanese Industrial Standards. Third, phenomenon on the interface was evaluated with production amount of molten salts which were calculated by thermodynamic equilibrium. As a result, the adhesion force and the mass loss of all specimens increased with the interface temperature, and there was exact materials dependency, which indicated that a high chromium content design to improve corrosion resistance was valid also for decrease of the ash adhesion. Moreover, it was observed that mass loss of the alloy specimens with the ash sample collected from an actual boiler had a temperature dependence, and molten salts and accelerated oxidation induced by chlorides attacked the alloy specimens. In addition, generation of HCl gas and molten salts with temperature increase was confirmed with the thermodynamic equilibrium calculations. Judging from these results, starting temperature of the adhesion could be correspond to one which the alloy started to be severely corroded.