Experimental Study on the Heat-Transfer Characteristics of a 600 MW Supercritical Circulating Fluidized Bed Boiler

Heat-transfer characteristics such as the distribution of the local heat-flux and the water-side and fire-side heat transfer coefficients of the water-wall at the dilute phase region of a 600 MW supercritical circulating fluidized bed (CFB) boiler operating at boiler loads of 60%, 80%, and 100%, were experimentally investigated. The temperature of the water-wall at furnace heights of 9 to 55 m was in situ measured using K-type thermocouples, and the water-side heat-transfer coefficient, the distribution of local heat-flux, and the fire-side heat-transfer coefficient between the furnace and water-wall were calculated based on the measured temperature result. The results showed the water-side heat-transfer coefficient was raised from 8600 W.m(-2).K-1 to 31000 W.m(-2).K-1 as the furnace height increased. Moreover, the water-side heat-transfer coefficient was large enough to ensure the heat-transfer deterioration would not take place in the water-wall tubes. Meanwhile, it was revealed that the heat-flux was higher at the corner of the furnace in the lower furnace, and the heat-flux was lower at places where the heating-surfaces arranged in the upper furnace, indicating that the distribution of local heat-flux was mainly influenced by the corner effect at the lower part of the furnace as well as the arrangement of heating-surfaces in the upper furnace. Moreover, the fire-side heat-transfer coefficient decreased from 239.1 W.m(-2).K-1 to 197.7 W.m(-2).K-1, 185.2 W.m(-2).K-1 to 153.5 W.m(-2).K-1, and 179.7 W.m(-2).K-1 to 138.3 W.m(-2).K-1 at 100% MCR, 80% MCR, and 60% MCR, respectively. Furthermore, the bed-to-wall heat-transfer coefficient was consistent with the furnace height above 30 m, owing to limited capacity of the entrainment effect of the fluidizing air, which led to the consistent voidage in the furnace. In addition, comparison between the fire-side radiation heat-transfer and convection heat-transfer showed the radiation heat-transfer was higher in the dilute phase of the furnace, which illustrated furnace temperature was one dominant factor that influences the heat transfer in the dilute phase region of the furnace.