Heat transfer to tubes in freeboard space of fluidized bed combustors. Progress report, August 1, 1980-January 31, 1981

Abstract

The existing room temperature fluidized bed facility was modified to carry out tests at high flow rates. Tests were carried out to determine the effect of increase in humidity of air on heat transfer coefficients. At low air flow rates, where the static charge effect is low, data without injection of steam were compared with the results for the same flow rates with steam injection. Increasing relative humidity to 65 percent changed the heat transfer coefficient by less than 2 percent. There are several investigations on heat transfer behavior of tubes in the submerged region, some of which are given in the references quoted. The data are mostly at low gas flow rates. Fluidized bed combustion operation calls for high gas flow rates. There are not enough data on heat transfer behavior of tubes in submerged region for high gas flow rates to compare with the anticipated results of this project in freeboard region at high flow rates. For this reason, the first tests were carried out with a submerged horizontal tube at midpoint of an 18 inch high static bed at room temperature. The test particles were 300 ..mu..m and 850 ..mu..m mean diameter glass beads. The maximum superficial gas velocity, U/sub sg/, for 300 ..mu..m mean diameter particles was 3.5 m/sec. At these high gas velocities, local and circumferentially averaged heat transfer coefficients were measured. They are tabulated in Tables. To better visualize the variation heat transfer coefficient as a function of superficial gas velocity, they are plotted. The variation of local heat transfer coefficient around the tube at different gas flow velocities is also shown.