Dynamic simulation on high-temperature corrosion behaviour of tube surface with fouling in utility boiler fired by high-chlorine coal

Abstract

A dynamic model on high-temperature corrosion with fouling-type ash deposition was established to predict the thickness distribution of corrosion layer and the outer/inner layer of ash deposit. It provides an observation on variation of heat transfer characteristics of the alloy test probe over time. This model involves the combustion characteristics of high-chlorine coal, the process of formation, migration, and deposition of fly ash particles, and the corrosion of alloy test probe. In this study, the dynamic model has been integrated into the numerical simulation of high-chlorine coal combustion in a 50 kW long-period corrosion test furnace. The prediction results show that the amount of fly ash deposition on the windward surface is the most while the least amount appears on the side surface. There is a great correlation between the corrosion layer and the inner layer of ash deposit. Because the inner layer of ash deposit and the alloy substrate are spatially adjacent, the high temperature corrosion process is greatly affected by the growth and property of fly ash deposit layer. The simulation results show that the heat flux of probe surface beneath ash deposit is 2.5 kW/m2 which is 50% of the clean surface (5 kW/m2). The changing pattern of thermal resistance versus time at different positions of the alloy surface is consistent with the variation of thickness of the corrosion layer and ash deposit layer. The windward face has the highest thermal resistance and the least heat flux due to the highest thickness of the corrosion layer and ash deposit layer. With the increase of probe wall temperature, the ratio of thermal resistance of corrosion layer to total heat transfer resistance increases, and the ratio at the side face is larger than that at other locations. And the proportion of the corrosion layer in thermal resistance for alloy TP347H reaches 8% at the probe wall temperature of 973 K.