Conical reverse flow

Typical particle size and feed concentration range 5-200 pm and 2-40% w/w. 

70g and ISOOOg. The combination of these forces and a swirling motion causes the coarser particles to exit as a suspension in the underflow stream at the bottom of the hydrocyclone and the finer fractions to leave through the cylindrical vortex finder at the top. With short residence times the particles and liquid move at relatively high speeds and abrasion/particle breakage can sometimes be a problem, which necessitates the use of hard internal linings. 

Many standard sizes of hydrocyclone are available with cylinder diameters of 1-30 cm and cone angles of 25°-50°. The particle cut size, which is the size equally likely to find its way into the underflow or overflow, is limited to about 5 pm and dependent on several factors including the size and geometry of the hydrocyclone, the inlet flow rate and the pressure drop across the unit. Separation is often more effective (in terms of a lower cut size) with a series of smaller diameter hydrocyclones as higher tangential velocities can be achieved. 

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The most commonly used design is the reverse-flow cyclone, as shown in Figure 10.43 other configurations are used for special purposes. In a reverse-flow cyclone, the gas enters the top chamber tangentially and spirals down to the apex of the conical section it then moves upward in a second, smaller-diameter spiral, and... 

The reverse-flow hydrocyclone shown in Figure 1.9 is a relatively cheap, compact and versatile device. The basic unit has no moving parts and comprises an inverted conical bottom section attached to a cylinder containing a tangential inlet port. Feed is injected through the port at a mean velocity between 10 and 30 m s whence geometry-induced motion causes the (usually denser) suspended particles to experience centrifugal forces of between... 

The gas bypassing results obtained from tracer gas injection studies for a flat and a conical distributor plate are shown in Fig. 4. Theflow ratio, FR, is defined as the total gas flow supplied through the draft tube gas supply and the concentric solids feeder divided by the total gas flow supplied through the downcomer gas supply. The A and Y are the actual amounts of gas passing up the draft tube and the downcomer, respectively, determined from the tracer gas injection studies. If FR equals A Y. there is no gas bypassing. If FR is less than A Y. some of the flow supplied through the downcomer gas supply passes into the draft tube. If FR is larger than A/7, the reverse is true. 

Effect of Distance between the Distributor Plate and the Draft Tube Inlet Figure 4 clearly indicates that the gas bypassing phenomenon depends not only on the design parameters but also on the operating conditions. For the conical plate at a distance from the draft tube inlet of L = 21.7 cm, gas bypasses from the draft tube side to the downcomer side at a high flow ratio and reverses the direction at a low flow ratio. When the conical plate was moved closer to the draft tube inlet atL = 14.1 cm, the gas bypassing direction was exclusively from the downcomer side to the draft tube side. 

Figure 28 shows that the pressure drop of a conical bed reaches a maximum value at the initial fluidization point (GR)i, and it drops at higher fluid rates. Inherent in this drooping pressure-drop characteristic lies the instability of conical bed operation, especially with gas as the fluidizing medium, for as soon as fluid rate reaches (GR) , the decrease in pressure drop induces higher flow from a compressible medium. As the pressure expends itself, fluid flow drops to even lower values, only to permit reaccumulation of pressure because of reversion to the higher pressure-drop region of the system. 

As illustrated in Figure 10.7, a cyclone consists of a vertical cylinder with a conical bottom, a tangential inlet near the top, and outlets at the top and the bottom, respectively. The top outlet pipe protrudes into the conical part of the cyclone in order to produce a vortex when a dust-laden gas (normally air) is pumped tangentially into the cyclone body. Such a vortex develops centrifugal force and, because the particles are much denser than the gas, they are projected outward to the wall flowing downward in a thin layer along this in a helical path. They are eventually collected at the bottom of the cyclone and separated. The inlet gas stream flows downward in an annular vortex, reverses itself as it finds a reduction in the rotation space due to the conical shape, creates an upward inner vortex in the center of the cyclone, and then exits through the top of the cyclone. In an ideal operation in the upward flow... 

The more modern design ( Messo ) has been specially designed to overcome this problem [8]. By reversing the direction of flow in the inflow area of the evaporation section, in this modified design the solution that has been superheated by the heat exchanger and is therefore undersaturated is passed over the conical surface that was previously susceptible to incrustations, before the supersaturation is created by means of the boiling process. As a result, no incrustations can form on the conical surface and the possibility of malfunctions is excluded. In this manner, it is possible to achieve operation periods of several weeks. 

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