Pressure drop, in spouted beds

Minimum Spouting Velocity and Pressure Drop in Spouted Beds. Can. J. Chem. Eng.,... 

LI. Lama, R. F., Pressure drop in spouted beds. M.Sc. thesis. University of Ottawa, Canada, 1957. 

Epstein N, Lim CJ, Mathur KB. Data and models for flow distribution and pressure drop in spouted beds. Can J Chem Eng 56 436 7, 1978. 

The mechanism by which a bed of particulate solids transforms to the spouted state is best explained by following the changes that occur in the pressure drop across the bed, with varying rate of gas flow (Fig. 4). 

With further increases in gas flow, the cavity elongates to an internal spout (Fig. ob). The arch of compacted material stUl exists above the internal spout, so that the pressure drop across the bed rises further until it reaches a maximum value (Fig. 4, point B). 

In the spouted state, the pressure drop across the bed arises out of two parallel resistances, namely that of the spout, in which dilute phase transport of particles is occurring, and that of the annulus, which is a downward-... 

The hydrodynamic characteristics of a PFB are essentially the same as those of fluidized or spouted beds. However, there is no peak in the pressure-velocity curve the pressure drop increases gradually with gas velocity, even with fully developed fluidization (Figure 6.4). Although the pressure drop in the PFB is of the same order as that in the classical fluid bed for the same gas velocity and the same free cross-sectional area of the supporting grid, the PFB technology offers a lower pressure drop because of the combined effects from the following ... 

A batch of rapeseed is fluidized in a spouted bed at a pressure drop through the bed of 315 Pa. The column diameter of the bed is 15 cm while the air inlet diameter is 1.25 cm. The granules of rapeseed are 1.8 mm in diameter and their density is 1100 kg/mT Calculate the minimum spoutable velocity for rapeseed. 

Olazar M, San Jose MJ, Aguayo AT, Arandes JM, BUbao J. Pressure drop in conical spouted beds. Chem Eng J 51 53-60, 1993a. 

Tab. 4.3 Correlations for the determination of the maximal bed pressure drop in conical, conical-cylindrical and prismatic spouted beds.

Figure 11.10(b) can be modeled as a piston flow reactor with recycle. The fluid mechanics of spouting have been examined in detail so that model variables such as pressure drop, gas recycle rate, and solids circulation rate can be estimated. Spouted-bed reactors use relatively large particles. Particles of 1 mm (1000 pm) are typical, compared with 40-100 pm for most fluidizable catalysts. 

If control gas at point 1 in Fig. 37 is admitted to unlock the solids above this point, the A Pc peak, shown in Fig. 37, will first be lowered to APcl, which is, however, still above the value (AP, — APcy — APD). If the unlocking gas streams at point 2 and point 3 are successively turned on, the new peak Pc0 is eventually reached, which is below (AP, — APcy — APD). The unlocked spout now drops to its normal operating pressure drop APc0 for moving-bed uptransport, and the solids of Reactor 1 will now flow rather rapidly to Reactor 2 under the driving force (AP, — APcy — APD) — APc0. 

When unlocked, the spout operates in moving bed uptransport with a pressure drop given by Eq. (20) ... 

This explanation for the existence of a peak pressure drop is supported by experimental results obtained by Manurung (M7), who measured pressure drops separately across the upper cylindrical part and the lower conical part of the bed contained in a conical-cylindrical column as a function of both increasing and decreasing air flow. It is seen in Fig. 9 that the pressure drop across the upper part of the bed, up to the point at which the spout breaks through, corresponds to that in a packed bed and remains the same irrespective of whether the flow is increasing or decreasing. A peak well before the onset of spouting occurs only in the curve for the lower... 

An expression for the cumulative pressure drop profile in a spouted bed was derived by Mamuro and Hattori (M6) from a consideration of the balance of forces acting on a differential height dz of the annular solids (Fig. 10) ... 

Mamuro and Hattori (M6) dismissed their annulus data and used only the local air-velocity results obtained in the spout to calculate the air distribution between the spout and the annulus. The calculation, however, requires separate knowledge of spout diameter and of the vertical voidage profile in the spout. While the former could be directly measured, for the latter they had to rely on the values estimated by Mathur and Gishler for a wheat bed 25 in, deep and 6 in. in diameter with the further assumption that the same profile (voidage versus reduced bed level) is valid, not only for wheat beds of different depths, but also for soma sand. This assumption is speculative and weakens the reliability of their calculated air-distribution results as a means for verifying Eq, (37). The earlier experimental results based on pressure-drop measurements (iMlO, Tl), on the other hand, are free from the above objection, and these provide some support for the theoretical derivation of Mamuro and Hattori (Fig. 12), especially for Eq. (36), although less so for its arbitrary extension to Eq. (37). 

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