Surface pressure and wear characteristics of tubes submerged in bubbling fluid beds

Abstract

An experimental investigation has examined the relationship between tube erosion and local pressure fields in bubbling fluidized beds. Tube erosion data and local distributions of tube surface pressure were measured for several tube shapes, particle sizes and superficial gas velocities. Techniques for using cast plaster to model tube shapes were developed to allow erosion measurements to be conducted in a limited time frame. The interaction of bubbles with a horizontal row of tubes resulted in an increase in static pressure at the lower surface of the tubes, consistent with observations in the literature. For bubbling beds, the local pressure distribution at the tube surface was only weakly dependent on particle size and superficial gas velocity. The erosion rate was shown to depend linearly on both the excess velocity and the local pressure at the tube surface. The local surface pressure at the tube is a useful parameter because it captures many of the effects of bubble motion. Oblong and teardrop-shaped tubes were substituted into the bottom row of the tube matrix to examine their influence on the erosion problem, but those tube shapes proved to be of limited practical interest due to high rates of erosion. Establishing erosion relationships for the oblong and teardrop-shaped tubes was complicated by an additional erosion mechanism that resulted from the tube matrix geometry.