| Erosion by impingement of bed materials (ash, coal, and sorbents) on in-bed components has caused serious problems to many fluidized bed combustion (FBC) systems in the past few decades. However, very few systematic studies have been made to explore this erosion phenomenon. Most earlier studies were devoted to the analysis of the mechanical and physical properties of target materials and impinging particles. These costly and time-consuming tests usually resulted in scattered data points of erosion, causing difficulties in identifying and correlating with the design and operating parameters. Analytical studies and systematic experimental studies of in-bed tube erosion are needed.; The author conducted an experimental study, supplemented with theoretical analysis, of tube erosion in a bench-scale, fluidized bed system. Erosion-prone tubes were placed inside a fluidized bed of uniformly sized glass beads to accelerate the mass removal process of the in-bed tubes. Effects of tube-to-distributor clearance, superficial velocity, tube orientation and location, tube circumferential angle, tube bundle height and configuration, and particle size on tube erosion were investigated, identified and discussed. It was found that tube erosion occurred only at a threshold fluidizing velocity (26 cm/s), close to the minimum fluidizing velocity (19 cm/s), and increased almost linearly with increasing superficial velocity. The peripheral erosion around an immersed horizontal tube had the heaviest erosion at the tube bottom, which was about four times higher than that of the tube top. The averaged specific erosion rate of a tube bundle was about one order of magnitude lower than that of a single tube under the same test conditions. The erosion of a staggered bundle was found larger by 45% than that of an in-line bundle having identical tube pitches.; Mathematical modeling of gas-particle flow in the fluidized bed with an in-bed tube was pursued to explore the particle motion and its effect on tube erosion. An erosion model was developed to describe and analyze the phenomenon of in-bed tube erosion. The predictions of this model were found to compare favorably with experimental measurements and the available literature data.; A series of improved electrostatic impact probes, based on the triboelectric effect of moving particles, and associated signal processing circuits, were developed and used as a primary standard for measuring the particle-surface collision frequency in the fluidized bed. Based on the experimental findings and derived understanding of erosion process, the design guidelines were proposed for fluidized bed systems for planning counter measures against in-bed tube erosion. |
