Effects of tube orientation and gas velocity on the erosion of a tube inserted into a fluidized bed

Abstract

Erosion of in-bed tubes, water wall and downstream heat transfer surfaces by bed materials and elutriated particles has persistently plagued most fluidized bed combustion (FBC) systems. This paper presents a systematic experimental study of the effects of tube arrangement and flow condition on embedded tube erosion by using erosion-prone wax cylinders in a 21 cm × 21 cm bench-scale cold fluidized bed. The erosion tests were conducted with 550 μm microbeads glass shot at various combinations of superficial fluidizing velocity, tube orientation and location, tube-to-distributor clearance, and tube circumferential angle. It was found that tube erosion occurs at a threshold fluidizing velocity (26 cm s −1) close to the minimum fluidizing velocity (19 cm s −1), and increases almost linearly with increasing superficial velocity. The specific erosion rate of embedded wax cylinders is high and in the order of 1 mg cm −2 h −1. Under the same condition, the weight loss of in-bed horizontal tubes (0°) is the maximum, followed by 30° inclined tubes, 60° inclined tubes, and vertical tubes (90°). The erosion around a horizontal tube showed that the very bottom part of the tube experienced the heaviest erosion, which amounted to 5 times that of the tube top.