Air Pollution Control Part A Cyclone Basic Principles

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Air Pollution Control Part ACyclone Basic
Principles

• Yaacov Mamane
• Visiting Scientist, CNR
• Rome, Italy

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What is a Cyclone?
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Cyclone Performance for various Application
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Standard Cyclone
Dimensions
General guidelines H lt S W lt (D-De)/2 LbLc gt
3D Cone angle 7o 8o De/D 0.40.5,
(LbLc)/De 8, S/De 1
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Conventional Cyclone
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• Stokes Law
• Gravitational forces are balanced by drag and
  buoyancy forces.
• This will lead to stokes law - settling velocity
  of particles.

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When Fd Fg the settling velocity is given as
follows.
Where g gravity acceleration d particle
diameter rp particle density m - air viscosity
For example Vt (1 mm) 0.006 cm/s
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For a particle moving at high speed Vc in a
circle, the centrifugal acceleration is given by
VcVc/r. The centrifugal force is similar to the
gravity forces
Vc
But Fc gtgt Fg The equivalent settling
velocity of the centrifugal forces is taken from
Stokes Law and is given by the following Equation
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Example For a particle of 1 mm moving in a 0.3
diameter circle at 18.3 m/s
vt 0.68 cm/s
While Vt stokes is only 0.006 cm/s!!!
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Settling Chamber
W
v
h
Vt
H
Particle is entering a chamber at height h an
horizontal speed V and settling velocity Vt, may
fall inside the chamber. Time (Tl) to cross the
chamber is L / V . Time (Th) to fall inside the
chamber is h / Vt, thus we could define a
collection efficiency h Tl / Th L Vt / H V
L
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The Collection Efficiency of a settling chamber
used to collect large particles is given by the
simple expression

• L Vt / H V or
• L g d2 rp / H V 18 m
• But V Q / WH where Q is the flow through
  the settling chamber, and thus
• h L g d2 rp / H V 18 m L W g d2 rp / Q 18 m
  
• L W g d2 rp / Q 18 m
• This collection efficiency may be applied to a
  Cyclone where
• H and L of the chamber are equivalent to
• W and NpD0 of a cyclone

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h L Vt / H V for a cyclone may be written as
Since a cyclone is an elongated settling chamber
4W Do 2r
For centrifugal forces
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After rearranging the parameters the equation is
now given by
And for a turbulent flow it is then expressed by
the general term
Example Calculate efficiency for a cyclone to
collect 1 mm particles of density 1. Cyclone
width 15 cm, Vc 18.3 m/s and N 5. The
efficiency is h 0.023 And for a particle of 10
mm diameter h is larger than 1.
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Let define a parameter of importance in
particulate control, d cut , used to describe the
properties of the cyclone,
Where Dcut - cut diameter in mm m - is
viscosity N - number of rotations Vc -
tangential velocity rp - particle density W -
entrance width of the cyclone
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Pressure Drop
Number of gas inlet velocity head
Static pressure drop
Power requirement
K 16 for normal tangential inlet 7.5 for
one with an inlet vane
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Lapple Theory (laminar flow)
Number of effective turns
Gas residence time
Terminal velocity
Smallest collected diameter
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50 cut size
The collection efficiency of any size dpj
? ()
Overall efficiency
Penetration
Particle size ratio dp/dpc
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Licht Theory (turbulent flow)
(D in m)
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Arrangement
Parallel/ Battery
Series
Air Pollution Control Equipment, Theodore
Buonicore, CRC Press, 1988
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(No Transcript)
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Discharge
Handbook of Air Pollution Control Engineering
Technology, Mycock, McKenna and Theodore, Lewis
Publishers, 1995.
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Advantages Disadvantages

• Advantages
• Low capital cost
• Ability to operate at high temperatures
• Low maintenance requirements because there are no
  moving parts
• Disadvantages
• Low efficiencies for fine particles
• High operating costs (due to pressure drop)

Cyclones used for removing wood dust