Pneumatic transport dilute-phase

Figure 1. Recirculating fluidized bed concept—draft tube operated as a dilute phase pneumatic transport tube.

Most of the applications for the recirculating fluidized bed with a draft tube operate the draft tube as a dilute phase pneumatic transport tube. Hence we will discussed this system in more details. 

Yang, W. C., A Unified Theory on Dilute Phase Pneumatic Transport, J. Powder Bulk Solids Tech., 1 89 (1977)... 

Approximated as that for dilute-phase pneumatic transport [Wen and Miller, 1961 Basu and Nag, 1987]... 

Viscosity. Dense phase solid-gas mixtures may be required to flow in transfer line catalytic crackers, between reactors and regenerators and to circulate in dryers such as Figures 9.13(e), (f). In dilute phase pneumatic transport the effective viscosity is nearly that of the fluid, but that of dense phase mixtures is very much... 

The spouted beds (SBs) can also be used to dry polymer beads. It is an efficient solid-gas contactor. In the conventional SB there is dilute-phase pneumatic transport of particles entrained by the spouting jet in the central core region and dense-phase downward motion of the particles along the... 

Figure 3. Fluidization transition diagram from fixed bed to dilute phase pneumatic transport.

There is a greater tendency for particles to salt out in a horizontal pipe which is preceded by a downflowing vertical to horizontal bend than in any other configuration. If this type of bend is present in a system, it is possible for solids to remain on the bottom of the pipe for very long distances following the bend before they redisperse. Therefore, it is recommended that downflowing vertical to horizontal bends be avoided if at all possible in dilute phase pneumatic transport systems. 

Design a positive pressure dilute-phase pneumatic transport system to transport 900 kg/h of sand of particle density 2500 kg/m and mean particle size 100 gm between two points in a plant separated by 10 m vertical distance and 30 m horizontal distance using ambient air. Assume that six 90° bends are required and that the allowable pressure loss is 0.55 bar. 

In a dilute phase pneumatic transport system, what are the two main reasons for using a rotary airlock ... 

As the gas velocity is increased beyond 17 a point is reached at which the particles are transported out of the bed altogether either in dense-phase or in dilute-phase pneumatic transport the velocity at which this occurs is called the transport velocity, C/tr- In order to maintain a constant inventory of particles in the bed at velocities in excess of 7tr it is necessary to recycle them via external cyclones and a standpipe, a geometry known as a circulating fluidized bed. A comprehensive review of the literature on circulating systems has been given by Grace et al. (1997), and the subject is also dealt with in Chapter 19 of this handbook. 

The schematic for this system, where the draft tube is operated as a fluidized bed rather than a dilute phase pneumatic transport tube, is shown in Fig. 5. A mathematical model for the system was developed by LaNauze (1976). The driving force for solids circulation in this case was found to be the density difference between draft tube and downcomer. The solids circulation rate was also found to be affected only by the distance between the distributor and the draft tube and not by the draft tube length or height of bed above it. Because of the lower velocity in the draft tube, the... 

Most of the applications for the recirculating fluidized bed with a draft tube operate the draft tube as a dilute phase pneumatic transport tube. Typical experimental pressure drops across the downcomer, AP1.4, and the draft tube, AP2-3, show that they are essentially similar. Thus successful design of a recirculating fluidized bed with a draft tube requires development of mathematical models for both downcomer and draft tube. 

Yang WC. A unified theory on dilute phase pneumatic transport. J Powder Bulk Solids Tech 1 89-95, 1977. 

The first application of the dispersion enhancer as a de-dusting system was undertaken for a local company manufacturing polyethene pellets. The pellets were transported after manufacture in a dilute phase pneumatic transport system, which caused them to produce... 

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