Geldart A particles

The simulations show that for low gas velocities (t/0 = 0.009 m/s), the commonly used exponent n — 4.65 does not yield a realistic bed expansion dynamics for Geldart A particles. By using a large exponent (n — 9.6), which was determined by gas fluidization of Geldart A particles, we can get a bed expansion... 

Hot disputes exist as to whether the fine-grid TFM simulation is feasible to capture CFB flow behavior (Benyahia, 2012 Hong et al, 2015 Lu et al, 2009 Syamlal and Pannala, 2011 Wang et al, 2010). For the so-called fast fluidization with Geldart A particles, say, fluid catalytic cracking (FCC) catalyst, Lu et al (2009) pointed out that the fine-grid simulation may improve... 

Hong K, Chen S, Wang W, Li J Pine-grid two-fluid modeling of fluidization of Geldart A particles, Powder Technol, 2015. http //dx.doi.0rg/lO.lOl6/i.powtec. 2015.07.003. 

WangJ, van der Hoef MA, Kuipers JAM Why the two-fluid model foils to predict the bed expansion characteristics of Geldart A particles in gas-fluidized beds a tentative answer, Chem Eng Sci 64 622—625, 2009. 

Wang J A review of Eulerian simulation of Geldart A particles in gas-fluidized beds, Ind Eng Chem Res 48 5567-5577, 2009. http //dx.doi.org/10.1021/ie900247t. 

Geldart a group Powder Average particle size, (, )J.m Particle density, p, kg/m Angles Internal friction, deg of Repose, deg Sphericity, f... 

Fig. 4. Geldart group particle classification diagram for air at ambient conditions (6). Group A consists of fine particles B, coarse particles C, cohesive,...

The phenomenon is represented by Figs. 17-40 and 17-41 for Geldart-type A and B solids, respectively (see beginning of Sec. 17). The initial efficiency of a particle size cut is found on the chart, and the parametric hue is followed to the proper overall solids loading. The efficiency for that cut size is then read from the graph. 

The classes into which powders are grouped are given in Table 6.1, which is taken from the work of Geldart(46), and in Figure 6.13. In they are located approximately on a particle density-particle size chart. 

Large particles with a mean diameter greater than 600 Um and a density above 4000 kg m are classed as group D and whereas in Geldart B beds the bubbles tend to rise faster than the gas in the dense phase, the reverse is true of bubbles in Geldart D particle beds. Bubbles tend to coalesce horizontally rather than vertically and reach a large... 

The minimum bubbling velocity for Group A particles (or more generally, for Type A fluidization) and gas-solid systems is (Abrahamsen and Geldart, 1980 Ye et al., 2005)... 

Figure 5 Effect of grid resolution (A.) on the time-averaged dimensionless slip velocity (us/uT). Geldart group A particles are used. The ordinate is scaled with the terminal velocity of single particles (uT 21.84 cm/s) and the abscissa is scaled with the particle diameter dp. The domain size is 1.5 x 6 cm2, comparable to the coarse-grid used in normal simulations.

Figure 9.6. Bed expansion curve for typical Group A particles (from Geldart, 1986).

For a bed with Group A particles, bubbles do not form when the gas velocity reaches Umf. The bed enters the particulate fluidization regime under this condition. The operation under the particulate fluidization regime is characterized by a smooth bed expansion with an apparent uniform bed structure for Umf < U < Umb, where Umb is the superficial gas velocity at the minimum bubbling condition. The height of the bed expansion in terms of a can be estimated by [Abrahamsen and Geldart, 1980a]... 

For the emulsion phase expansion of Group A particles, //em can be correlated by [Abrahamsen and Geldart, 1980b]... 

FIGURE 12.18 Comparison of simulated bubbling fluidization of Geldart group A particles with experimental data (from Ferschneider and Mege, 1996). 

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