Axial flow cyclone

The flue gas passes through a number of small diameter high-efhciency cyclonic elements arranged in parallel and contained with the separator vessel. The UOP design uses an axial flow cyclone. After the catalyst particles are removed, the clean flue gas leaves the separator. A small stream of gas, called the underflow, exits the separator through the bottom of the TSS. In an environmental application, the underflow is diverted to a fourth stage separator (FSS) that is typically a barrier filter. The underflow rate is typically 2-5% of the total flue gas rate and is set by use of a critical flow nozzle. 

Figure 7.3. Schematic diagram of the axial flow cyclone (from Ogawa, 1984).

Finally, reversible-flow cyclones can be used for gas cleansing. These have the highest turndown ratio and good efficiency versus drop size (commercial claim 3 + pm, depending on design). They do, however, have a pressure drop higher than that of vane packs and axial flow cyclones. 

Figure 53.1 shows a typical reverse-flow cyclone in which the necessary elements consist of a gas inlet that produces the vortex an axial outlet for cleaned gas, and a dust-discharge opening. There are a number of different arrangements and modiflcations that offer variations in performance and overcome some of the limitations of the conventional reverse-flow cyclone. These modiflcations can be summarized according to the following classifications [18] ... 

Gas-liquid (gas dominated) separation done by axial-and reverse-flow cyclonic devices operating at 20-200 g. These are also used for polishing at gravity separator gas outlets. 

Cyclone collectors utilize the principle of centrifugal force to separate particulates from a gas stream vortex flow is induced by the design of the gas inlet duct (Figure 23.4). The main vortex is characterized by axial flow away from the gas inlet and radial flow outward from the edge of the cyclone body. The central core has the same rotary direction, but the axial and radial velocity components are in the opposite direction to that of the main vortex. 

Over the decades that cyclones have been used, many different reverse-flow cyclone geometries have been tried to improve efficiency, prevent particle attrition, prevent erosion of the cyclone wall, or prevent particle buildup on the cyclone surfaces. However, there are a few basic types that have emerged as the most popular over the years. Some of these cyclone types are shown in Fig. 3. The cyclones shown in this figure are the tangential inlet cyclone, the volute Met cyclone, and the axial inlet cyclone. This last type of cyclone uses axial swirl vanes to impel the gas solids mixture into rotary centrifugal motion. 

In a tangential-inlet reverse-flow cyclone, the cyclone inlet translates the linear inlet gas flow into a rotating vortex flow. As shown in Fig. 1, the gas solids mixture enters an annulus region between the outer wall of the cyclone and the outer wall of the gas outlet tube. As the gas solids mixture spirals downwards, it sets up a vortex with an axial direction downward toward the solids outlet. 

A positive value iadicates vertical movement. Thea, moving from the outer wall to the air core, the axial velocity iacreases to positive values. Thus, the fluid motioa is dowa the wall of the cycloae to the apex and up the air core through the vortex finder. In the cylindrical section, the axial velocity goes negative again, approaching the vortex-finder wall. The fluid flow is then down the inner cyclone wall and the outer vortex-finder wall. There is a locus of zero axial velocity. 

To simplify the discussion, let us reconsider the velocity profiles shown in Fig. 17.3 for the basic cyclone configuration where little or no rear drive flow is present. As reactants are entrained out of the front jet, conservation of mass and momentum requires that the axial velocity of the outer jet decrease with increasing distance from the front drive. But, as the reactants are converted to products when they cross the flame sheet, mass is added at fixed area to the product flow. This causes the axial velocity of the products to accelerate toward the exhaust nozzle as in classic constant-area heat addition. Thus, one expects... 

The Reynolds stress model requires the solution of transport equations for each of the Reynolds stress components as well as for dissipation transport without the necessity to calculate an isotropic turbulent viscosity field. The Reynolds stress turbulence model yield an accurate prediction on swirl flow pattern, axial velocity, tangential velocity and pressure drop on cyclone simulation [7,6,13,10],... 

Apparatus Use a suitable Inductively Coupled Plasma Emission Spectrophotometer set to 226.502 nm for cadmium and to 371.029 for yttrium (internal standard) with an axial view mode. (This method was developed using a Perkin-Elmer Model 3300 DV equipped with a sapphire injector, low-flow GemCone nebulizer, cyclonic spray chamber, and yttrium internal standard.) Use acid-rinsed plastic volumetric flasks and other labware. 

Since the gas flow to a multiclone is axial (usually from the top), the cross-sectional area available for flow inlet conditions is given by the annular area between the outlet tubes and cyclone body. The outlet tube diameter is usually one-half the body diameter. 

Fig. 4 An iso-surface of axial vorticity in a cyclone, colored by velocity magnitude, is used to show the central vortex pathlines are used to show the swirling flow. (View this art in color at www.dekker.com.)...

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