Control of ash deposition in pulverized coal fired boiler

Abstract

Some of the ash generated through the combustion process of solid fuels, such as pulverized coal, adheres to the tube surface during heat exchange. This causes problems of heat transfer inhibition such as slagging and fouling as well as boiler drive troubles. In this research the surface characteristics of a heat exchanger tube were changed using thermal spraying and an ash adhesion experiments were performed. The experiment was performed on a horizontal pulverized coal combustion furnace and vertical coal ash adhesion experimental furnace. The quantity of ash deposition was measured by using specimens whose surfaces were coated with various types of thermal spraying. In addition, through static contact angle evaluation, the relationship between ash deposition and high temperature wettability of thermal sprayed specimens was confirmed. This made it clear that the quantity of ash deposition changes dependent on the kind of thermal sprayed material and that there is a correlation between the adhesion work, which is able to be calculated from the static contact angle on specimens, and the ash deposition. Accordingly the liquid-bridge force, which is constructed by the condensation liquid phase effects on the ash adhesion phenomenon. In the condensation liquid phase, ash particles near the adhesion interface were analyzed by a Computer Controlled Scanning Electron Microscope (CCSEM). The results showed that the alkali element and Fe element were concentrated. Accordingly it is thought that this concentration strongly affects in the adhesion behavior by altering the melting point of ash particles and the Slagging Factor.