Bed-to-tube heat transfer characteristics with an immersed horizontal tube in the pressurized fluidized bed at high temperature

Abstract

High-temperature and high-pressure conditions have great effects on the heat transfer characteristics of the immersed horizontal tube and understanding them will provide an industrial reference for the arrangement and optimization of heat exchanger in the pressurized fluidized bed furnace. In this study, the pressurized fluidized bed apparatus was developed to investigate the effects of factors such as pressure, temperature, particle size and gas velocity on the local and average heat transfer coefficients of the immersed horizontal tube. The experimental results showed the improved heat transfer at elevated pressure and high temperature. When the bed temperature increased from 400 °C to 800 °C, the proportion of the radiative heat transfer increased significantly, but it did not exceed 15%. The maximum heat transfer coefficients in the process of increasing the fluidization number were also measured in this study and fit well with the prediction results of the Shah model. The distribution of circumferential local heat transfer coefficients showed differences at low fluidization numbers and high fluidization numbers. The model proposed for the immersed horizontal tubes in the pressurized fluidized bed predicted the experimental data points from this study and other different sources well with the absolute average deviation of 11.86%.