lecture a8 - hydro cyclone

8/2/2019 Lecture A8 - Hydro Cyclone

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The Hydrocyclone

A classifying device which utilises centrifugal force to accelerate thesettling rate of particles

One of the most important device in the mineral industry

Extremely efficient in fine size separation Use in closed-circuit grinding operation; de-slimming, de-gritting and

thickening

A typical hydrocyclone


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A conical shaped vessel, open at the apex or underflow

A tangential feed inlet

A vortex finder which prevents short circuiting of feed.

Overflow

A particle in the hydrocyclone is subjected to two opposing forces; centrifugaland drag force.

Faster settling particles move to the wall where the velocity is lowest andmigrate to the apex opening.

The slower-settling particles move towards the zone of low pressure alongthe axis and are carried upward through the vortex-finder to the overflow.


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Fig: Forces acting on an orbiting particles in the hydrocyclone

The existence of an outer region of downward flow and an inner regionof upward flow necessitates a position at which there is no verticalvelocity.


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Particles thrown outside the envelope of zero vertical velocity by the greatercentrifugal force exit via the underflow while particles swept to the centre by

the greater drag force leave in the overflow.

The efficiency

The efficiency of separation or the imperfection I :

50

2575

2d

ddI

=


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Analysis of Hydrocyclone

o

0

S

X

,O

,O

f

f

S

X

,F

,F

u

uS

X

,U,U

Therefore for the feed

slurryofmass

solidsofmassX

sf

fs

f..

..

)1(

)1(=

=

and s is the density of solids and ml/gm1O2H=


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Underflow:

)1(

)1(

=

su

usuX

Overflow:

)1(

)1(

=

so

osoX

Dilution Ratio

In the feed ff

fy

X

X

solids

water=

==

1

Underflow uu

u yX

X=

=

1

Overflow oo

o yX

X=

=

1

Overall solids Balance

sss OUF +=

water balance

sosusf OyUyFy += Hence


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ou

of

s

s

yy

yy

F

U

=

and

uo

uf

s

s

yy

yy

F

O

=

ff

ss

slurry

sf

VV

mmX

==

wfs

wsf

VVV

VVV

=

+=

fw

wf

f

w

f

wf

f

s

m

m1

V

V1

V

VV

V

V

==

=


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ml/g0.1w = , ff

w X1m

m=

)X1(1V

Vff

f

s=

))X1(1(V

VX ff

f

s

ff

ssf ==

)1(

)1(X

)1()1(X

)1()11

(X

)1(XX

sf

fs

f

fs

s

ff

f

s

ff

ffff

s

f

=

=

=

=


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Example: Hydrocyclone classification

3

w m/kg1000= 3

s m/kg2700=

3

f m/kg1670=

3

u m/kg1890=

3

o m/kg1460=

637.0)7.21(67.1

)67.11(7.2

)s1(f

)f

1(s

fX =

=

=


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57.0637.0

637.01

fX

fX1

fy =

=

=

747.0)7.21(89.1

)89.11(7.2

)s1(u

)u1(suX =

=

=

34.0747.0

747.01

uXuX1

uy =

=

=

5.0)7.21(46.1

)46.11(7.2

)s1(o

)o1(soX =

=

=

0.1

5.0

5.01

o

XoX1

oy =

=

=

Now calculate:

ou

of

s

s

yy

yy

F

U

=

652.0134.0

157.0

F

U

s

s=

=


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Basis: solids.kg100Fs = ,

the solids in the underflow kg2.65Us =

and in the overflow kg8.34Os =

5.0X

ml/g46.1

kg5.0/8.34O

kg8.34O

o

0

S

=

=

=

=

637.0X

ml.g67.1

kg637.0/100F

,kg100F

f

f

S

=

=

=

=

747.0X

ml/g89.1

,kg747.0/2.65U,kg2.65U

u

u

S

=

=

=

=


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particle size (micron)

0 200 400 600 800 1000

PercentoffeedtounderfloworUs/F

s%

0

20

40

60

80

100

d75

d50

d25

I=(d75-d25)/(2*d50)

No enough data for imperfection calculation.


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Factor Affecting the cyclone Performance

Factors affecting cyclone parameters

Cut size:

Increases with cyclone diameter, feed % solids or viscosity, small apex, large vortex finder,

cyclone inclination to vertical

Decreases with flow rateClassification efficiency:

Increases with appropriate cyclone size, limiting water to underflow

Decreases with feed % solids or viscosity

Flow split of water to underflow (impacts short circuiting)

Increases with larger apex or smaller vortex finder, feed % solids or viscosity

Decreases with flow rate, inclined cyclones

Flow rate:

Increases with pressure, cyclone diameter

Decreases with feed % solids and viscosity

Several of the empirical relationships which are used to predict the cutpoint ina cyclone are as follows:

Plitt equation (1976)

large diameter cyclone

operating at high solids concentration

.

)(QhD

eDDDKd

Ls

45.038.071.0

u

063.021.1

o

6.0

i

46.0

c1

c50

s

=

1K = a constant (14.8)

=c50d cut-point of corrected 50d (m)

cD =inside diameters of hydrocyclone at the bottom of thevortex finder (cm)

iD = inside diameter of the hydrocyclone inlet (cm)


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oD =inside diameter of the overflow or vortex finder (cm)

uD =inside of the underflow or apex diameter(cm)

h = distance between bottom of vortex finder to the top ofthe underflow orificeQ =total flow rate (litres/ minutes)

S = density of solids (g.cm-3)

L =density of liquid (g.cm-3)

S = volumetric % of solids in the feed

And the volumetric flow rate eqn:

S0031.0

49.02

o

2

u

16.053.0

i

21.0

c

56.0

e

)DD(hDDP21.0Q

+=

where P is the pressure drop across the cyclone in kPa.


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The power:

kW

3600

PQPower=

Effect of pressure drop on capacity and cut-point


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The size of the apex or spigot opening determines the underflowdensity and must be large enough to discharge the coarse solids thatare being separated by the cyclone. The spigot must also permit theentry of air along the axis of the cyclone in order to establish the airvortex.

lecture a8 - hydro cyclone

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