Shape cyclone

Glassification. Classification (2,12,26,28) or elutriation processes separate particles by the differences in how they settle in a Hquid or moving gas stream. Classification can be used to eliminate fine or coarse particles, or to produce a narrow particle size distribution powder. Classification by sedimentation iavolves particle settling in a Hquid for a predetermined time to achieve the desired particle size and size distribution or cut. Below - 10 fim, where interparticle forces can be significant, gravitational-induced separation becomes inefficient, and cyclone and centrifugation techniques must be used. Classification also separates particles by density and shape. Raw material separation by differential sedimentation is commonly used in mineral processiag. 

Commercial Equipment Simple cyclones are available in a wide variety of shapes ranging from long, slender units to short, large-diameter units. The body may be conical or cylindrical, and entrances may be involute or tangential and round or rectangular. 

Cyclone Separators Finer feed sohds, from 0.04 to 0.0005 m (1.5 in to 28 mesh), may be treated in dynamic separators of the Dutch State Mines cyclone type (Fig. 19-36). In cyclone separators, the medium and the feed enter the separator together tangentially at the feed inlet (1) the short cyhndiical section (2) carries the central vortex finder (3), which prevents short circuiting within the cyclone. Separation is made in the cone-shaped part of the cyclone (4) by the action of centrifugal and centripetal forces. The heavier portion of the feed leaves the cyclone at the apex opening (5), and the hghter portion leaves at the overflow top orifice (6). 

A venturi scrubber is a venturi-shaped air passage with water introduced just ahead of or into the venturi throat. The liquid-gas contact is at a maximum in the venturi throat. The relative velocity between gas and liquid aerosol droplets is high, with the gas velocities in the range of 50-100 m/s. The particles are conditioned in the throat, and condensation is the important collection mechanism. After the particles in the gas have been deposited on droplets, a comparatively simple device such as a cyclone collector can be used to collect the wetted dust. 

Cyclone boilers, like wet-bottom pulverized coal units, burn low ash fusion temperature coal, but the coal is crushed so that 95 percent is smaller than 1/4 inch.9 The coal is fed tangentially to the cyclone burners, which are mounted horizontally on the outside of the boiler and are cylindrical in shape.9 A typical cyclone burner is shown in... 

The collection efficiency usually depends on the shape of the cyclone, size and density of the particles, and incoming tangential velocity. The collection efficiency of a... 

Industrial reactors generally operate at very high velocities (of order 1 m/s) much in excess of terminal falling velocity for at least the finest powder fractions. Powder is continually elutriated and returned to the bed via cyclones. Under these conditions there is disagreement as to whether or not bubbles retain their identity and such beds have been described as "turbulent" or "fast fluidised". What little evidence there is supports the continued existence of bubbles but now in a much disturbed or heterogeneous dense phase and with a less definite shape. Until more is known about this physical situation it is not easy to see how the bubbling bed reactor models should be modified correctly to describe this flow regime. 

The factor NT varies from 0.5 to about 10, depending on cyclone shape and size. 

The efficiency predicted by Eq. 8.15 is only a rough estimate the equation estimates a shape in the efficiency-versus-particle-size curve that is different from what is actually observed. There are a number of factors not considered in this elementary derivation. First, laminar flow is assumed, but turbulent flow is often observed in practice. The effect of turbulence will be to move particles away from the cyclone walls or resuspend deposited ones. Hence, turbulence will decrease cyclone efficiency. Second, the width of the cyclone inlet is not as important a parameter as overall cyclone diameter, since it is the width of an element of gas within the cyclone that determines particle deposi-... 

At 24 h after the start of the release the plume maximum had spht into two separate parts (Fig. 5.2). The head received cyclonic rotational momentum from a meso-scale disturbance and reached DK02 after 26 h giving rise to the first peak. As the latter part of the cloud progressed it received anti-cyclonic momentum and after 36 h the plume attained a U-shaped deformation which was advected towards DK02. The rotational time scale of the eddies was not large enough (compared to the advective time scale of the plume) to cause a full revolution in the plume. 

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