Experimental study on heat transfer in an in-bed heat exchanger of an internally circulating fluidized bed

In a 2.5 MW (t) pilot internally circulating fluidized bed reactor, heat transfer coefficient between immersed tubes and bed materials in the in-bed heat exchanger was measured with help of heat transfer probes. The influences of fluidized velocity, particle diameter and bed temperature on convection heat transfer coefficient were investigated, and the local convection heat transfer coefficient around tube surface were studied as well. Results show that the convection heat transfer coefficient increases quickly with the fluidized velocity when the velocity is not high, and reaches its maximum value at 1.9~2.5 times of the minimum fluidized velocity and then decreases a little and keeps constant. Small particles can get more contact area at the tube surface, so heat transfer is enhanced. With the bed temperature increasing, the convection heat transfer coefficient increases. The local convection heat transfer coefficient in the leeward side of the tube is higher than that in the windward side due to the fluidized velocity and tube bundle structure, and the heat transfer coefficient distribution around tube surface changes with fluidized velocity increasing. A comprehensive correlation was proposed based on the experiment data and the results calculated from the correlation agree well with the results of experiments. © 2016 Chin. Soc. for Elec. Eng.