Experimental investigation of heat transfer with ash deposition in ultra-low temperature WHRS of coal-fired power plant

Abstract

Waste Heat Recovery Systems (WHRS) have been widely adopted in coal-fired power station boilers, though their heat transfer performance is poor under ultra-low tube temperature circumstances. In this study, we have carried out experiments to reveal heat transfer deterioration and its relation with ash deposition when probe tube temperature varies from 90°C to ultra-low 40°C. Results reveal that gas-side Nusselt number has two rapid drops as the probe outer wall temperature decreases. The first drop occurs when the wall temperature is about 32°C lower than the acid dew temperature, where the deposited ash thickens due to the condensed concentrated sulfuric acid and slight corrosion is observable. The second drop occurs when the wall temperature is about 10°C greater than the water dew temperature, where the corrosion becomes severe because the concentration of sulfuric acid decreases. For engineering applications, we suggest that the tube outer wall temperature be greater than the first drop temperature to deflate poor heat transfer and surface corrosion.