PRESENTED BY: ARVIND KUMAR(aecagra chemical engg.)
Cyclone separators provide a method of removing particulate matter from air streams at low cost and low maintenance. In general, a cyclone consists of an upper cylindrical part referred to as the barrel and a lower conical part referred to as cone. The air stream enters tangentially at the top of the barrel and travels downward into the cone forming an outer vortex. The increasing air velocity in the outer vortex results in a centrifugal force on the particles separating them from the air stream. When the air reaches the bottom of the cone, an inner vortex is created reversing direction and exiting out the top as clean air while the particulates fall into the dust collection chamber attached to the bottom of the cyclone.
In the agricultural processing industry, 2D2D (Shepherd and Lapple, 1939) and 1D3D (Parnell and Davis, 1979) cyclone designs are the most commonly used abatement devices for particulate matter control. The D’s in the 2D2D designation refer to the barrel diameter of the cyclone. The numbers preceding the D’s relate to the length of the barrel and cone sections, respectively. A 2D2D cyclone has barrel and cone lengths of two times the barrel diameter, whereas the 1D3D cyclone has a barrel length equal to the barrel diameter and a cone length of three times the barrel diameter. The configurations of these two cyclone designs are shown in figure 2. Previous research (Wang, 2000) indicated that, compared to other cyclone designs, 1D3D and 2D2D are the most efficient cyclone collectors for fine dust (particle diameters less than 100 μm).
CYCLONE SEPARATORS** Works on the principle of spinning the gas stream so that particles ofhigher mass fall out in proportion to the velocity.** The tendency of particles to move in a straight line when thedirection of the gas stream is changed is the primary mechanism ofimparting centrifugal motion.** Removes particles of diameter > 10 microns. But efficiency is > 95%only for particles greater than 25 microns.** There are however three different types: high volume cyclone (lowefficiency), medium cyclone and high efficiency cyclone (lowthroughputs).
Cyclones and centrifugal collectors are utilized in various industries. such as chemical, coal mining and handling, combustion fly ash, metal melting, metal working, metal mining, rock products, plastics and wood products. Common uses of cyclones and inertial separators are the collection of grinding, crushing, conveying, machining, mi xing, sanding, blending and materials handling dust and for particle collection
Co llection Efficienc y of a Cyc lone:** First, the number of revolutions Ne in the outer vortex is given by (1)** To be collected the particles must strike the wall within the amount oftime the gas travels in the outer vortex. The gas residence time in theouter vortex is given by (2)** Maximum radial distance travelled by a particle is the width of theinlet du ct W. Assume that centrifugal force quickly accelerates theparticle to its terminal velocity in the radial direction. The terminalvelocity that will allow a particle to be collected in time is t (3)Remember that Vt is given by the Stokes law (4)Eliminating between (2) and (3) and equating (3) to (4) we get tThe above gives the minimum particle diameter that will be collected.
The theoretical equation derived has a major flaw – it states that allparticles with diameter larger than dp will be collected with 100%efficiency, which is NOT correct.Lapple derived a semi-empirical relationship which gives the “50% cutdiameter” dpc., which is the diameter of particles collected with 50%efficiency.Lapple then derived a general curve for standard conventional cyclonesthat can be used to predict the collection efficiency of any given particlesize. This has been further enhanced by an algebraic relationshipbetween collection efficiency and cut diameter obtained by Theodoreand DePaola:Note that is the collection efficiency for the jth particle size range and jdpj is the characteristic diameter for that size range.The overall efficiency of the cyclone is the weighted average of theefficiencies for various size ranges
Diameter: 6 to 10” (15 to 25 cm) Inlet Velocities: 50 to 60 ft/s (15 to 20 cm/s) Volumetric Rates: ◦ 500 to 1000 ft3/s (15 to 20 m3/min) ◦ Capacities as high as 30,000 ft3/min have been manufactured.
•Large diameter cyclones are less efficient than small diameter ones.•However, large D will have lower P.•P in cyclones related to the number of velocity heads of loss, Hv Vg2 g H v P(inches of fluid) 2 g L•Note: Vg2/2g is one velocity head (Vg is the inlet gas velocity)•L corrects for P in terms of fluid height.* Lapple’s observation: HW Hv K 2 K = 16 for std. Cyclone D (tangential gas entry) e Vg2 g HW P K 2 2 g L De P : simple cyclones (0.5 to 2” of water); high efficiency (2 to 6” water).
(Know dp from size distribution curve, Qp, Tg, P from stack sampling) Choose a dpc Repeat with different dpc (Obtain required efficiency) Locate optimum dpc on optimization curve to get correct D) 1 P 2Q2 2 Q2 D1 3 2 D2 D1 Q and P2 P 1 2 P1 1 Q1 D2 Note: Q1 = 0.094 m3/s; P1 = 1,000 kg/m3; D1 = 0.254 m.
Hc: height of cyclone inlet duct (m) Hv: pressure drop expressed in number of inlet velocity heads K: (1) cyclone pressure drop constant (equations 7 and 10) (2) orifice meter coefficient (3) cut-point correction factor K1D3D: cut-point correction factor for 1D3D cyclone K2D2D: cut-point correction factor for 2D2D cyclone L: (1) air stream travel distance in the outer vortex (m) (2) total inlet loading rate ( equation 78 only g/m3) L1: air stream travel distance in the barrel part (m) L2: air stream travel distance in the cone part (m) Lc: length of cyclone body (m)