Bed density

Bed Expansion and Bed Density. Bed density can readily be deterrnined for an operating unit by measuring the pressure differential between two elevations within the bed. This is a highly useful measurement for control and monitoring purposes. 

Bed density can then be predicted from 1 — ). The expression for is appHcable for turbulent fluidized beds and for the turbulent... 

The bed level is not weU defined in a circulating fluidized bed, and bed density usually declines with height. Axial density profiles for different CFB operating regimes show that the vessel does not necessarily contain clearly defined bed and freeboard regimes. The sohds may occupy only between 5 and 20% of the total bed volume. 

Bed Density—p. The average density of a fluidized bed of solid particles and gas. Bed density is mainly a function of gas velocity and, to a lesser extent, the temperature. 

The fact that gases have a simple equation of state makes possible the use of absorptiometry with polychromatic beams to give information about the state of a gas under conditions (in detonation waves,16 boundary layers,17 or supersonic flow18) transient or difficult of access. Temperature measurements19 have also been made. The technique is a unique method for studying the fluidization of a finely divided solid by a gas. Bed density profiles, which reveal the character and effectiveness of fluidization, have been readily determined20 without disturbing the system as probes would inevitably do. 

Findings with PDU. Work with the PDU largely paralleled the bench-scale reactor tests there was one important addition—extensive three-phase fluidization studies. As was mentioned, the PDU is equipped with a traversing gamma-ray density detector that is capable of measuring bed density to within dbO.Ol specific gravity units. Thus, we could measure and correlate fluidized bed expansion as a function of liquid and gas velocities and physical properties, and could also determine the... 

The catalyst was prepared by impregnating porous alumina particles with a solution of nickel and lanthanum nitrates. The metal loading was 20 w1% for nickel and 10 wt% for lanthanum oxide. The catalyst particles were A group particles [8], whereas they were not classified as the AA oup [9]. The average particle diameter was 120 pm, and the bed density was 1.09 kg m . The minimum fluidization velocity was 9.6 mm s. The settled bed height was around 400 mm. The superficial gas velocity was 40-60 mm s. The reaction rate was controlled by changing the reaction temperature. 

Subzwari et al. (1978) also reported that bed voidage and bed expansion increased with pressure for FCC catalyst (a Group A material). However, Knowlton (1977) reported little change in either bed density or bed expansion at with increasing pressure over the range of 1 to 70 atmospheres for large, -2000/+74 micron material. 

With the above functions and empirical correlations, it becomes possible to calculate the overall convective heat transfer coefficient hc by Eqs. (16, 4, and 22-24). Figure 26 shows a plot presented by Lints and Glicksman which compares predictions by this method with experimental data from several different sources. Reasonably good agreement is obtained over a range of bed densities corresponding to approximately 0.5 to 3% volumetric solid concentration. 

Figure 21. Typical average power spectrum plots of the bed density fluctuations measured along the bed height with the 40.6-cm jet assembly (Set Point 9).

Figure 24. Typical local bed density fluctuations as measured by the force probe.

A more detailed analysis using multivariable regression of the ibuprofen data demonstrated that a three-parameter model accurately fit the data (Table 7). The Bonding Index and the Heywood shape factor, a, alone explained 86% of the variation, while the best three-variable model, described in what follows, explained 97% of the variation and included the Bonding Index, the Heywood shape factor, and the powder bed density. All three parameters were statistically significant, as seen in Table 7. Furthermore, the coefficients are qualitatively as... 

Explained variation Bonding Index Heywood shape parameter Powder bed density Particle diameter Permanent deformation pressure... 

Care must be taken to specify properly the basis for the reaction rate. The most useful basis for design of an FBCR is the catalyst mass, that is, the rate is (—rA)m, in units of, say, mol (kg cat)-1 s-1. ( -rA)m is related to the rate per unit reactor (or bed) volume, (—rA)v through the bed density ... 

The size of reactor is chosen to accommodate this holdup. The diameter is determined from the gas flow rate, q, together with, for example, an allowable superficial linear gas velocity, u (in lieu of an allowable (- AP)) D = (4qhru)m for a cylindrical vessel. The volume could be determined from an appropriate bed density, together with an overhead space for disengagement of solid and gas phases (we assume no carryover of solid in the gas exit stream). 

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