Scale fluidized bed

Glicksman, L. R., Mullens, G., and Yule, T. W., Tube Wear Tests in the MIT Scaled Fluidized Bed, Proc. ofEPRI Workshop (1987b)... 

Yang, W. C., Newby, R. A., and Keaims, D. L., Large-scale Fluidized Bed Physical Model Methodology and Results, Powder Technol., 82 331 (1995)... 

Werdmann, C. C., and Werther, J., Solids Flow Pattern and Heat Transfer in an Industrial Scale Fluidized Bed Heat Exchanger, Proc. 12th Intern. Conf. on Fluid. Bed Comb., 2 985-990 (1993)... 

One of the strengths of the KTGF, although still under development, is that it can offer a very clear physical picture with respect to the key parameters (e.g., particle pressure, particle viscosity, and other transport coefficients) that are used in the TFMs. The TFMs based on KTGF requires less ad hoc adjustments compared to the other two types of models. Therefore, it is the most promising framework for modeling engineering-scale fluidized beds. 

An advantage of this approach to model large-scale fluidized bed reactors is that the behavior of bubbles in fluidized beds can be readily incorporated in the force balance of the bubbles. In this respect, one can think of the rise velocity, and the tendency of rising bubbles to be drawn towards the center of the bed, from the mutual interaction of bubbles and from wall effects (Kobayashi et al., 2000). In Fig. 34, two preliminary calculations are shown for an industrial-scale gas-phase polymerization reactor, using the discrete bubble model. The geometry of the fluidized bed was 1.0 x 3.0 x 1.0 m (w x h x d). The emulsion phase has a density of 400kg/m3, and the apparent viscosity was set to 1.0 Pa s. The density of the bubble phase was 25 g/m3. The bubbles were injected via 49 nozzles positioned equally distributed in a square in the middle of the column. 

For the discrete bubble model described in Section V.C, future work will be focused on implementation of closure equations in the force balance, like empirical relations for bubble-rise velocities and the interaction between bubbles. Clearly, a more refined model for the bubble-bubble interaction, including coalescence and breakup, is required along with a more realistic description of the rheology of fluidized suspensions. Finally, the adapted model should be augmented with a thermal energy balance, and associated closures for the thermophysical properties, to study heat transport in large-scale fluidized beds, such as FCC-regenerators and PE and PP gas-phase polymerization reactors. 

Recently, Hays et al. [26] reported on of several cases where particle clustering was inferred in flnidized bed systems. In the first case, they attempted to reproduce why highly variable entrainment rates were observed in a commercial-scale fluidized bed even though steady-state was presumed. Tests were conducted in a 6 inch (15-cm) diameter fluidized column with a static bed height of 52 inches (132 cm) of the same Geldart Gronp A powder (dp5o of 55-60 microns) used in the commercial process. The test unit was operated in batch mode at a superficial gas velocity of 0.66 ft/sec (0.2 m/sec). 

Studies at Mobil Research have shown that light olefins instead of gasoline can be made from methanol by modifying both the ZSM-5-type MTG (Methanol-to-Gasoline) catalyst and the operating conditions. Work carried out in micro-scale fluidized-bed reactors show that methanol can be completely converted to a mixture of hydrocarbons containing about 76 wt% C2-C5 olefins. The remaining hydrocarbons are 9% C1-C5 paraffins, of which the major component is isobutane, and 15% C6+, half of which is aromatic. 

Most industrial-scale fluidized beds employ a type of jet or perforated-plate distributor (Gunn, 1968). 

R. L. Patel and co-workers, "Reactivity Characterization of Solid Fuels in an Atmospheric Bench-Scale Fluidized-Bed Combustor," presented at the 1988... 

The present paper presents batch autoclave data on the direct hydrocracking of a single sub-bituminous coal from the Powder River basin of southeastern Montana. Comparative data were also obtained with the Pittsburgh Seam bituminous coal that was used in the previous work (I). Data on the regeneration of simulated spent melts from such an operation are also given in a continuous bench-scale, fluidized-bed combustion unit. 

Example 5.4 Design a geometrically similar laboratory-scale cold model fluidized bed to simulate the hydrodynamics of a large-scale fluidized bed combustor. Also specify the operating conditions for the cold model. The combustor is a square cross section column with a width of 1.0 m and a height of 6 m. The fluidized bed combustor is operated at a temperature of 1,150 K, a superficial gas velocity of 1.01 m/s, and a bed height of 1.06 m. Particles with a density of2,630 kg/m3 and a diameter of677ptm are used for the combustor. The cold model is operated at a temperature of 300 K. Air is used for both the cold model and hot model fluidized beds. The physical properties of air are... 

Reaction kinetics may be determined for a fixed-bed reactor, provided measurements are performed under conditions comparable to those that prevail in the fluidized-bed reactor (for example the same solids composition and particle-size distribution, and the same activity state) [98] However, the kinetic parameters can also be determined directly by measurements in a bench-scale fluidized-bed apparatus [99]... 

Van Deemter, J. Mixing patterns in large-scale fluidized beds, in Fluidization (J. R. Grace and J. M. Matsen, eds.), p. 69. Plenum Press, New York, 1980. 

Flow maldistribution of the phases can render the evaluation of RTD data very difficult. In some cases, maldistribution may exist in small units but it may not exist in large-scale units (e g., trickle-bed reactors). While in some other cases, such as three-phase fluidized-bed reactors, nonuniform gas distribution in large-scale units may cause undesirable recirculation and dead zones. Uniform gas distribution can usually be achieved in the small-scale fluidized-bed reactor. 

Catalytic butane dehydrogenation can be successfully carried out in a laboratory scale fluidized bed reactor operating at 310 °C and at atmospheric pressure. The catalytic particles have diameter 310 pm and density 2060 kg/m. Such a reactor is 150 mm in diameter and has a fixed 500 mm long catalytic bed. When the catalyst bed is fluidized with butane blown at a velocity of 0.1 m/s, it becomes 750 mm thick. 

The chars were produced in a process development unit scale fluidized-bed flash pyrolyser (90 from pulverized Mlllmerran and Wandoan subbituminous coals from Queensland, Australia. Mlllmerran coal was pyrolyzed at various temperatures between 500 and 800 C and Wandoan coal at 550°C. The resulting chars were screened to yield a size fraction with a median mass size around 80 pm. Hie properties of the chars are presented in Table I. 

Fuel-bound Nitrogen Conversion Results from Gasification of Biomass in two Different Small Scale Fluidized Beds... 

Van der Honing, G. Volatile and Char Combustion in Large Scale Fluidized Bed Coal Combustors", Ph.D dissertation, Twente University, Netherlands, 1991. Konnov A. A., Detailed Reacrion Mechanism for Small Hydrocarbons Combustion, Release 0.4, http //homepages.vub.ac.be/ akonnov/, 1998. 

Each test was carried out in an atmospheric bench-scale fluidized bed reactor shown schematically in Figure 1. The main reactor consists of a 321 stainless steel tube with an inside diameter of 73 mm and a length of 1 m. The tube is encased in an electric furnace used to preheat the reactor. At the top, the reactor expands into a 127 mm square section with a cross-sectional area 4 times larger than the main reactor column. This section is used to disengage larger bed and partially reacted fuel particles from... 

Fig. Schematic of the bench-scale fluidized-bed reactor system.

Hovmand, S. Freedman, W. Davidson, J.F. Chemical reaction in a pilot scale fluidized bed. Trans. Inst. Chem. Eng. 1971, 49, 149-162. 

Matsui et compared experimental data on the steam gasification of coal char from a laboratory-scale fluidized-bed reactor with the Kunii and Levenspiel model. Good agreement was reported when the bubble diameter was treated as a fitted constant. 

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