Heat transfer to a horizontal tube bundle located in the freeboard of a bubbling fluidized bed combustor

The characteristics of heat transfer from bubbling gas-fired fluidized bed to a horizontal staggered water-tube bundle located in the freeboard region is experimentally investigated. The purpose is to demonstrate the effect of bed temperature on the coefficients of heat transfer by the different modes to each of the four rows of the bundle, which experiences heat transfer by convection from flue gases, luminous radiation from bed material and non-luminous radiation from gases. The bed temperature itself is varied and controlled through the fuel-air mass ratio. Sixteen runs have been conducted with bed temperature ranging from 1114 to 1429 K, resulting in an overall heat transfer coefficient in the range 74.0-105.0 W m(-2) K-1 for the first row and 58.0-65.0 W m(-2) K-1 for the last. An overall convective heat transfer coefficient from gases, and possible carried over sand particles, to the bundle is formulated. (C) 1997 by John Wiley & Sons, Ltd.