Separation tangential

Twin-screw extruders have an important role in the compounding industry. There are various possible geometries for twin-screw extruders. These include directions of screw rotation and level of intermesh. Two screws can rotate in the same direction (co-rotating) or in opposite directions (counter-rotating). The screws may be separated, tangential, intermeshed and fully intermeshed and self-wiping. 

The simplest type of centrifugal device is the cyclone separator (Fig. 3.4), which consists of a vertical cylinder with a conical bottom. The centrifugal force is generated by the fluid motion. The mixture enters in a tangential inlet near the top, and the rotating motion so created develops centrifugal force which throws the particles radially toward the wall. 

The Process. If a mixture is handled that consists of several ingredients, which are more or less uniform in themselves but vary distinctly from one to another, each ingredient should be handled separately up to the final processing step, then proportioned and mixed just before this step. When pneumaticady conveying a fine fluidizable powder into a bin, a tangential entry into the side of the bin should be used rather than going in at 90° either to the side wad or the top. 

Mechanical Gleaning. A cleaner is a hydrocyclone device utilizing fluid pressure to create rotational fluid motion (20). Pulp is introduced tangentially near the top of the cleaner. Contaminants denser than water such as chemically treated toner inks and sand migrate toward the outer wall of the cleaner and exit in a separate (reject) stream. For most forward cleaners, optimal ink removal efficiency is obtained at a pulp consistency of 0.2—0.3%. Most forward cleaners deinking efficiency declines at pulp feed consistencies greater than 0.4%. However, a cleaner said to be efficient at 1.2% pulp consistency has been reported (39). 

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). 

Filtration Cross-flow filtration (microfiltration includes cross-flow filtration as one mode of operation in Membrane Separation Processes which appears earlier in this section) relies on the retention of particles by a membrane. The driving force for separation is pressure across a semipermeable membrane, while a tangential flow of the feed stream parallel to the membrane surface inhibits solids settling on and within the membrane matrix (Datar and Rosen, loc. cit.). 

In normal process service, the superficial vapor velocity at the inlet of tangential-entry vapor-liqiiid separators is limited to about 120 to 150 ft/s. Higher velocities may lead to ... 

A slide surface is a surface where the tangential velocity can be discontinuous as shown in Fig. 9.9. Separate velocities are calculated for each side. Slide lines are useful for modeling phenomena such as sliding friction or flow through pipes. 

In a stationary impeller, the flow is expeeted to follow the blade shape and exit tangentially to it. A high adverse pressure gradient along the blade passage and subsequent flow separation are not eonsidered to be general possibilities. 

The rotor or impeller of the radial-inflow turbine eonsists of a hub, blades, and in some eases, a shroud. The hub is the solid axisymmetrieal portion of the rotor. It defines the inner boundary of the flow passage and is sometimes ealled the dise. The blades are integral to the hub and exert a normal foree on the flow stream. The exit seetion of the blading is ealled an exdueer and it is eonstrueted separately like an indueer in a eentrifugal eompressor. The exdueer is eurved to remove some of the tangential veloeity foree at the outlet. 

Figure 14-7. Thrust and separating load as a percentage of transmitted tangential load. (Courtesy of Lufkin Industries, Inc.)...

Cyclone Separators Cyclone separators are described in Chapter 7. Typically used to remove particulate from a gas stream, the gas enters tangentially at the top of a cylinder and is forced downward into a spiral motion. The particles exit the bottom while the gas turns upward into the vortex and leaves through the top of the unit. Pressure drops through cyclones are usually from 13 to 17 mm water gauge. Although seldom adequate by themselves, cyclone separators are often an effective first step in pollution control. 

Tangential crossflow filtration Process where the feed stream sweeps the membrane surface and the particulate debris is expelled, thus extending filter life. The filtrate flows through the membrane. Most commonly used in the separation of high-and-low-molecular weight matter such as in ultrapure reverse osmosis, ultrafiltration, and submicron microfiltration processes. 

Figure 12-38. Tangential inlet knockout drum with separate liquid catchtank.

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