The bubble eruption process was studied in two-and three-dimensional (2D and 3D) beds using a high-speed video system for flow visualization. The results show the existence of four different ejection mechanisms; one occurring with singlebubble eruptions in both 2D and 3D beds, two others occurring in 2D and 3D beds with two bubbles coalescing at the bed-free surface, and the fourth occurring only in 3D beds with bubbles coalescing at the bed surface. E. K. LEVY, H. S. CARAM, J. C. DILLE, and SERGIO EDELSTEIN Energy Research CenterLehigh University Bethlehem, PA 18015 SCOPEParticle elutriation is an extremely complex phenomenon which is not very well understood from a mechanistic viewpoint. Most of the available information consists of correlations of experimental data which give elutriation rate as a function of characteristics of the bed material and operating conditions; only a few investigators have studied elutriation from the fundamental perspective required for undertaking the development of quantitative mechanistic models.In developing such physical models, information is needed on the rate and velocity at which solids are thrown above the bed by bubble eruptions. There is conflicting evidence in the literature concerning the mechanisms for solids ejection, some investigators claiming that it is principally bubble wake material which is ejected and others reporting that the bulge material at the bubble nose is thrown above the bed.In the present investigation, flow visualization experiments were performed using a high-speed video system to obtain video tape records of the eruption process. Bubble eruptions of a wide variety were examined to determine if differences exist: between eruptions in two and three dimensional beds; between small, slow moving bubbles and large, fast moving bubbles; or between single bubbles and bubbles which coalesce near the bed surface. The objectives were to establish the source of the elutriated material, determine if more than one ejection mechanism occurs, and if so, establish when the various mechanisms are important. CONCLUSIONS AND SIGNIFICANCEFour different mechanisms of bubble eruption and particle ejection were observed during the course of this study. The most common eruption type was the bulge bursting mechanism which occurred in both two-and three-dimensional geometries. With this type of eruption, the bulge layer stretches and moves upward as the bubble approaches the free surface. After rising to a maximum height somewhat less than the bubble diameter and becoming leaner, the bulge particles fall back to the bed surface. The bubble wake shows a vortex structure and remains intact, gradually rising to a height of about one half that attained by the bulge before settling back onto the surface of the bed.With a pair of three-dimensional bubbles coalescing just below the free surface, a series of events occurs. The bulge material for the leading bubble is thrown above the bed. As a result of the coalescence of the two bubbles, the layer of solids between the bubbles co...

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The development of pressurized fluidized bed combustors (PFB) as an efficient, economical, and enviromentally acceptable means of utilizing the nation’s coal reserves has been underway for a short time. Although at least a dozen PFB facilities are in existence or under construction, and other PFB plants (1) are being designed, the technology is not fully developed. This paper presents the results of an investigation into achieving high efficiency with a PFB system. The base case was a novel cycle, with the PFB combustor is located at an intermediate pressure between the maximum cycle pressure and atmospheric pressure. This configuration eliminates many of the technical problems associated with conventional PFB systems, and has a higher heating value net efficiency of 38 percent. Gas reheat, topping combustion, carbonizer systems, and compressor intercooling are added to the base system to yield a cycle efficiency of 45 percent.