The effect of temperature gradient on steel tube wastage in a bubbling fluidized bed simulator

Abstract

This paper describes a unique laboratory rig that simulates the interaction between dense particles and in-bed tubes in bubbling fluidized bed combustors. In this test rig, a tubular specimen is actuated periodically in a partially fluidized bed. A coolant can flow continuously through the specimen in order to achieve a surface temperature lower than that of the bed. Preliminary tests performed on 1018 steel both under isothermal and temperature difference conditions are described and compared. During the temperature difference test, the bed was held at 700 °C and the specimen surface at 200 °C. Results showed a wear rate five times higher under these conditions compared to the isothermal test, but neither the wear mechanism nor the circumferential wear distribution was altered. As in previous studies using isothermal test conditions, material loss was mainly caused by abrasion of the metal by the bed particles. The deposition of an adherent layer composed of bed material onto the specimen surface acted as a protection against much of the damaging impact. The degree of such deposition was significantly less on specimens tested under the temperature difference condition, and this is believed to be the main cause for the observed increase in wear.