16 research outputs found
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Scale-up circulating fluidized bed coal combustors
Circulating fluidization is a promising technology for designing efficient coal combustors with high solid feed rates. Unfortunately, limited understanding of circulating fluidized beds (CFB) has rendered design extrapolations from pilot reactors to full-scale plants both empirical and expensive. In CFBs, hydrodynamics and heat transfer are difficult to predict, and the behavior of the flow under scale-up is unclear. Thus the objectives of this research were to quantify the effect of scale-up on the hydrodynamics of CFB combustors, to carry out a rigorous analysis of the flow and heat transfer in vertical gas-solid risers, and to interact with industry at all stages of this work. The importance of this research resides in the great number of CFB coal-burning powerplants that may benefit from its results. At the completion of this work, the results have exceeded the expectations outlined in the original proposal. The present report summarizes these accomplishments, which have led to five archival publications, two reviewed conference papers, twelve presentations, various quarterly reports, and the award of five graduate degrees
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The Scale-Up of Large Pressurized Fluidized Beds for Advanced Coal-fired Power Processes
More refinement was added to the five sample ports that were installed along the cold model riser. Each sample port is now equipped with an electrically actuated X ball-valve that can be operated from a switch in the main control panel area. These actuated ball valves control the on/off position of the sample port. They are switched on for a desired period of time for sample collection during a test run. They are particularly useful for the hard-to-reach sampling locations near the top of the riser where manually operating a ball-valve could be difficult
Diffusion as mixing mechanism in granular materials
We present several numerical results on granular mixtures. In particular, we
examine the efficiency of diffusion as a mixing mechanism in these systems. The
collisions are inelastic and to compensate the energy loss, we thermalize the
grains by adding a random force. Starting with a segregated system, we show
that uniform agitation (heating) leads to a uniform mixture of grains of
different sizes. We define a characteristic mixing time, , and
study theoretically and numerically its dependence on other parameters like the
density. We examine a model for bidisperse systems for which we can calculate
some physical quantities. We also examine the effect of a temperature gradient
and demonstrate the appearance of an expected segregation.Comment: 15 eps figures, include
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Scale-up of circulating fluidized bed coal combustors
This experimental project has been aimed at quantifying the effects of scale-up upon the hydrodynamics of CFB coal combustors. To this end, we have constructed a cold CFB facility with the ability to recirculate, -- rather than discard, -- fluidization gas mixtures of adjustable density and viscosity. Hydrodynamic analogy between the cold bed and a coal combustor is achieved by matching all relevant dimensionless parameters (Glicksman, 1984; Louge, 1987). Several choices of gas composition and particle properties make the cold flow analogous to that in combustors of diameters in the range 0.3 to 1m. Therefore, for the first time, scale-up effects are quantified directly using cold flow facility. 8 refs
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Fluid dynamics of pressurized, entrained coal gasifiers. Technical progress report, April 1, 1995--June 30, 1995
A study of the fluid dynamics of Pressurized Entrained Coal Gasifiers (PECGs) is being conducted. The idea is to simulate the flows in generic industrial PECGs using dimensional simulitude. A unique entrained gas-solid flow facility with the flexibility to recycle rather than discard gases other than air has been utilized. By matching five dimensionaless parameters, suspensions in mixtures of helium, carbon dioxide and sulfur hexafluoride simulate the effects of pressure and scale-up on the fluid dynamics of PECGs
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Fluid dynamics of pressurized, entrained coal gasifiers. Tenth quarterly technical progress report, April 1, 1996--June 30, 1996
Pressurized, entrained gasification is a promising new technology for the clean and efficient combustion of coal. Its principle is to operate a coal gasifier at a high inlet gas velocity to increase the inflow of reactants, and at an elevated pressure to raise the overall efficiency of the process. Unfortunately, because of the extraordinary difficulties involved in performing measurements in hot, pressurized, high-velocity pilot plants, its fluid dynamics are largely unknown. Thus the designer cannot predict with certainty crucial phenomena Re erosion, heat transfer and solid capture. In this context, we are conducting a study of the fluid dynamics of Pressurized Entrained Coal Gasifiers (PECGs). The idea is to simulate the flows in generic industrial PECGs using dimensional similitude. To this end, we employ a unique entrained gas-solid flow facility with the flexibility to recycle -rather than discard- gases other than air. By matching five dimensionless parameters, suspensions in mixtures of helium, carbon dioxide and sulfur hexafluoride simulate the effects of pressure and scale-up on the fluid dynamics of PECGs. Because it operates under cold, atmospheric conditions, the laboratory facility is ideal for detailed measurements
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Dense inclined flows: Theory and experiments. Quarterly technical progress report, January 1, 1995--March 31, 1995
Rapid, gravity-driven flows of granular materials down inclines pose a challenge to our understanding. Even in situations in which the flow is steady and two-dimensional, the details of how momentum and energy are balanced within the flow and at the bottom boundary are not well understood. Thus we have undertaken a research program integrating theory, computer simulation, and experiment that will focus on dense entry flows down inclines. The effort involves the development of theory informed by the results of simultaneous computer simulations and the construction, instrumentation, and use of an experimental facility in which the variables necessary to assess the success or failure of the theory can be measured. In the present reporting period, we have continued a series of measurements in the chute facility with a flat, frictional boundary. At several inclinations between 15.5{degrees} and 20{degrees}, and at several gate openings for each angle, we have measured mass flow rate and mass holdup, as well as granular temperature and collision frequency at the bottom wall of the chute. By recording simultaneously the collisional normal stress at the bottom wall and the mass holdup above it, the experiments reveal the fraction of the weight of particles that is supported by direct impact
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Dense inclined flows: Theory and experiments. Final report
Rapid, gravity-driven flows of granular materials down inclines pose a challenge to our understanding. Even in situations in which the flow is steady and two-dimensional, the details of how momentum ad energy are balanced within the flow and at the bottom boundary are not well understood. Thus we have undertaken a research program integrating theory, computer simulation, and experiment that focuses on such flows. the effort involves the development of theory informed by the results of simultaneous computer simulations and the construction, instrumentation, and use of an experimental facility in which the variables necessary to assess the success or failure of the theory can be measured. A goal of the project is to provide a sound theoretical and experimental base for a better understanding of the behavior and properties of multiphase flow and solid transport