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Air Separators

All practical dry powder separators use AIR to

accomplish the separation of coarse and fines.

All designs have some degree of inherent

inefficiencies.

Qf/Qa principle is important for all air

classifiers.

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O-S e

pa

Arrang

em

ent

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Principle of the

High-Efficiency Separator

Cage Rotat ion

Guide Vane Dir ect ion

Unif or m

Flow distribution

Inlet

Plenum

Feed

Feed Classi f icat ion ZoneOSEPA Details

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O-Sepa Separator

Wear plates and air

seal should be

inspected regularly

Guide vanes and rotor

cage may require

annual hard facing

Check ceramic tiling Remove build-up

inside intakes

A i r S e a l

B u f fe r P la te

D i s p e r s i o n P l a t e

G u i d e V a n e s

S w i r l B l a d e

P a r t i ti o n P l a t e

F e e d

S e c o n d a r y

A i r In takeP r im a r y

A i r In takeTer tia r y A i r

I n t a k e &

D a m p e r

H o p p e r

F l a p G a t e

S h a f t A s s e m b l y

D r i v e S u p p o r t

C o u p l i n g

R e d u c e r

M o t o r

R e d u c e r S u p p o r t

E x i t D u c t ( To D u s t

C o l le c t o r & F a n )

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Key Separator Relations

Circulating Load

% Recovery

Tromp Curve Qf/Qa

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Circulating Load C.L. = R/F (used by Lafarge)

Others define it as C.L. = A/F

No right way, but be sure to ask! Governs efficiency

A: Separator Feed

F: Fines

R: Rejects

(or Tails)

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% Recovery Standard definition for efficiency

Quantity of Fines recovered from

quantity available in the feed

Quick way to determine

performance%Recovery =

f(x)F

a(x)A

=fines X (feed - rejects)

feed X (fines - rejects)

X 100

X 100

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Tromp Curves

Graph tells a great deal about theperformance of the separator

efficiency

sharpness of cut

agglomeration (grinding aid)

mechanical state

Probability vs. log plot

Plots probability of rejects vs. size

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How to read- perfect screen A perfect screen will give

a graph with a vertical

line

The line occurs at the

sieve size

The area below the line

is reject1 1 0 4 5 1 0 0

0

5 0

1 0 0

P a r t i c l e S i z e , m ( lo g s c a l e )

A r e a a b o v e

c u r v e

i s f in i s h

p r o d u c t

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How to read - overloaded (Bypass)

The more you load the

separator, the greater

the chance some fineswill be rejected

This is called (Tromp)

Bypass Also applies if you

reduce internal air flow

1 1 0 4 5 1 0 0

0

5 0

1 0 0

P a r tic l e S iz e , m ( lo g s c a le )

Coarse Rejects

Rejected Fines

(Bypass)

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How to read - imperfection

Akin to a hole in your screen

Imperfection describes the

slope of the cut line

Related to a mechanical design

problem (or improper

maintenance)

1 1 0 4 5 1 0 0

0

5 0

1 0 0

P a r t ic l e S i z e , m ( lo g s c a le )

C o a r s e R e j e c ts

R e j e c t e d F i n e s

( B y p a s s )

C o a r s e P a r t ic l e s i n F i n e s

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What we dont want

Splitter gate

A flat tromp curve means

that the separators

beginning to look like asplitter gate

Opposite to a perfect

screen

1 1 0 4 5 1 0 0

0

5 0

1 0 0

P a r t i c l e S iz e , m ( lo g s c a l e )

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Example 1

1000100101

1

2

3

4

5

6

7

Example Tromp Curve (Sturtevant)

Particle Size, m, (x)

100

99.38

93.32

69.15

50.00

30.85

6.68

0.62

Bypass = 56%

Acuity Limit = 25 m

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Example 2

1000100101

1

2

3

4

5

6

7

Example Tromp Curve (OSEPA)

Particle Size, m, (x)

100

99.38

93.32

69.15

30.85

6.68

0.62

50.00

Bypass = 8%Acuity Limit = 11 m

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Interpretations

1 10 45 100

0

50

100

Particle Size, m (log scale)

Indicatesagglomeration(grinding aidproblem)

1 10 45 100

0

50

100

Particle Size, m (log scale)

Over fed

Under fed

1 10 45 100

0

50

100

Particle Size, m (log scale)

Good

Mechanical

Shape

Poor

Mechanical

Shape

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Qf/Qa Related to circulating load Qf is the separator feed rate (kg/hour)

Qa is the air flow (m3/hour)

So Qf/Qa is in units of kg/m3

the lower the Qf/Qa, the more efficient the separator

Qf/Qa should be less than 2 kg/m3 for good operation

1.0 1.5 2.0 2.5 3.0 3.5

0

10

20

30

40

50

60

70

80

Bath

Sturtevant

Qf/Qa vs Bypass - O-Sepa & Sturtevant

Qf/Qa (kg feed/m3 separator sweep)

O-Sepa

Sturtevant

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Typical

Mill Circuit

1 m / s

2 5 m / s

5 m / s

1 0 m / s

Dust Collector

Clean Airto Vent orRecirc toSeparator

Fresh Feed

Separator Reject

Mill Discharge

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Questions

What is the basic purpose or function of an air separator? The more heavily loaded the separator, the more efficient the

separation. True or False?

If the separator feed is 150 t/hr, and the reject rate is 100 t/hr,

what is the circulating load?

If the separator feed is 150 t/hr and the airflow is 50,000 m3/hr,what is the Qf/Qa? Would this be considered good operation?

The %recovery calculation is based on samples of the

separator feed, fines, and rejects, and is a quick way to

determine separator performance. True or False?