Heat transfer characteristics in a large-scale bubbling fluidized bed with immersed horizontal tube bundles

This work investigates heat transfer characteristics in a bubbling fluidized bed with a submerged superheater tube bundles under conditions of an integrated fluidized bed heat exchanger (Integrated Recycle Heat Exchanger, Intrextm) of a large-scale circulating fluidized bed boiler. The effect of mean bed particle size, normalized suspension density, and fluidizing number on the average heat transfer coefficient between the immersed horizontal tubes and the bed was evaluated. The physical parameters of bed particles and fluidizing air in the external heat exchanger were measured at different CFB unit loads. Bubble fraction and contacting time of emulsion phase on the heat transfer surface were calculated on the basis of operating data of fluidized bed heat exchanger. A mechanistic heat transfer model was used to predict the heat transfer coefficient. Depending on emulsion density and the local dynamics of gas and bed particles, the average heat transfer coefficient (havg) varied in a range of 255–381 W/(m2K), showing an increasing trend with the decrease in bed particle size. Moreover, havg decreased with increasing emulsion contact time on the tube surface with the reduction of the solids mixing. Obtained results were compared with literature data.