Separation Technology

What is separating?Splitting a given material by particle diameterBalls with 2, 4 and 10 mm diameter

Separation by cutpoint of 3mm (e.g. by sieving)

> 3 mm

< 3 mm

Problem: Efficiency of separation is never perfect

Separators in Cement Manufacture

Raw Mill Circuit Cement Mill Circuit

Action of Separating Force

• Separating Force• Gravity• Centrifugal force• Aerodynamic Drag• Collision Force

Separation efficiency• The efficiency of a separation device (e.g. mill separator)

is a measure of the proportion of un-separated material following the separation process. It indicates how much fines is in the coarse fraction remaining and how much coarse is in the fines.

• The efficiency is very much dependent on the separator. Modern cage rotor separators show a far better efficiency than older static and dynamic separators.

Types of Classifying Equipment

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Basic working principles Separators• Particles are accelerated by a vortex or a

rotating device into the direction of the separator wall (Fz).

• The big particles hit the wall (in older separators) or the guide vanes (in 3rd gen. Separators) and slip down because they are too heavy for transport by the air stream.

• The small and light particles are carried out by the separator air (FL) stream supplied by an internal (older separators) or an external fan. The centrifugal force is smaller than the impulse of the air flow.

• Changes of airflow or distributor (rotor) speed (consequence higher centrifugal forces) lead to different product fineness.

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Main Separators used in Cement works

Type Main features

Static separators and cyclones No moving parts / fineness adjustment via mechanical modification

Dynamic separators 1st Generation

Counter blades, distributor plate and internal fan/Fineness control by mechanical adjustment or counter blade speed change

Dynamic separators 2nd Generation

Features as 1st Gen. / but external fans and cyclones

Dynamic separators 3rd Generation

Cage rotor instead of counter blades and distributor plate (variable speed drive) /external fan /fineness control by rotor speed change

Cyclone Separator• Basic function:

Material enters the cyclone in the air stream at the top.

A vortex is generated.

A fine vortex with opposite turning direction is generated at the bottom and carries the fine material back to the top.

Coarse material goes to the walls because of centrifugal forces, slips down and leaves at the bottom.

Fine material exits at top via the immersion tube.

view from top

tailings

feed

fines

immersion tube

cylindrical part

conical part

Static Separator• Basic function:

Material enters the separator in air stream at the bottom.

A vortex is generated in the top of the grit cone by the blades.

Coarse material goes to the walls because of centrifugal forces, slips down and leaves at the bottom.

Fine material exits at the top via the immersion tube.

Product fineness is adjustable by changing the blade position.

housing cone

tailings cone

adjusting device

rad.pos.

immersion tube

tailings

feed

fines

adjustable blades

Operation of static separator

• The cut size – controlled by angle of guide vanes and air velocity

• If angle of vane adjusted from radial in the range of 0 to 60 degrees, the induced tangential velocities increase and more particles fall down the cone, increasing the product fineness. Pressure drop across the separator also increases

• Adjustment done during commissioning and not changed.• Lengthening the central tube will also increase product

fineness.

Grit Separator

V Separator• Basic function:

Material enters the separator from the top

Coarse material slips down from plate to plate and leaves at the bottom.

Fine material leaves the separator at top together with the air.

Separation zone is the area between the plates and the series of baffles

Fineness control by air velocity

Dynamic separators 1st Generation (Example: Pfeiffer Heyd)

Basic function:

Material enters the separator at the top.

Air stream is generated by internal fan (9).

Coarse material goes to the walls because of centrifugal forces, generated by the distributor plate and counter blades, slips down at the grit cone wall and leaves at the bottom (11).

Fine material is sucked into the outside chamber (1) and exits at the bottom of the casing (12).

Product fineness is adjustable usually by rotational speed of the plate and counter blades (6+7).

fines chamber1

2

3

4

5

6

7

89

10

11

12

1

2

3

45

6

7

8

9

10

1112

tailings cone

air vane

separation chamber

distributor + counterblades

distributor plate

fines chamber

fan shaft

fan blades

feed spout

tailings outlet

fines outlet

counter blades

Airflow

Dynamic separators 1st Generation

Separator Type Heyd Variable speed drive for counter blades and distributor plate

Fan Motor

Fan

Counter blades

Feed spout

Distributor plate

Dynamic Separators of 2nd Generationseparation chamber

tailings cone

air vanes

distributor plate

counterblades

feed spout

gearbox

motor

return air duct

dust collecting

fan

air duct to fan

cyclones

tailings outlet

fines outlet

pipe to filter

8 7

14

11

6

11

5

1

9

2

9

10

3

4

1315

1

15

23

45

6

7

89

10

11

12

13

14

Polysius Cyclopol

Dynamic Separators of 2nd Generation (Wedag)

to filter

fresh air

Air flow direction

Dynamic Separators of 2nd GenerationBasic function:

Material enters the separator at the top.

Air stream is generated by the external fan and is recirculated.

Coarse material is separated by fan suction into the main casing and leaves at the bottom via a pendulum flap.

Fine material exits at the top of the casing by airflow and enters the cyclone via gas duct. The material separated by the cyclones leaves at the bottom and goes into air slides. A part of the recirculated air together with the fine dust from the cyclones goes to a filter.

Product fineness is adjustable usually by rotational speed of the plate and counter blades.

Dynamic Separators of 2nd Generation

Counter blades

Distributor plate

Vertical Mills with inbuilt separator

Sweeping action of roller blades

Operation philosophy• Swirling action induced in material stream• The sweeping action of rotor blades creates an outward

centrifugal force controlled by speed of rotor) and obstacle in path of material flow

• Direct impingement on blade imparts tangential velocity of blade to particle and throws them out of stream

• Coarse particles which are not able to remain airborne fall in the general direction of outer wall or drop out cone.

• Inefficiency occurs when particles rejected by the rotor are directed back to grinding table but re-entrained by gas stream

• Coarse particles can block the path of fine particles and cause overgriniding of fines and due to agglomeration of fines on coarse .

Material/ Gas flow in Vertical Mill- low efficiency separator

Material/ Gas flow in Vertical Mill- High efficiency separator

Separators of 3rd Generation

Feed

Air

Turning cage rotor

Centrifugal Forces

Returns Air with fines

AirGuide vanes

Basic function:

Material enters the separator at the top.

Air stream is generated by external fan.

Material falls down between rotor and guide vanes. Fines are sucked in. Coarse particles are accelerated by rotor and stopped by guide vanes, where they slip down and leave the casing at the bottom.

Fine material exits with airflow at the lower/upper part of the casing

Product fineness is adjustable by the rotational speed of rotor.

Main parts cage rotor separator

Cage rotor

Bars

Guide vanes (in bad shape)

High Efficiency Separator

Operation of HES• http://www.sturtevantinc.com/air-classifiers.php• The separator feed is directed into a rotating dispersion plate,

located at top of cage rotor.• The material starts a spiral movement due to spin of plate and

high velocity swirl of air leaving the guide vanes.• Material distributed between the guide vanes and the rotor and

forms a thin cylindrical curtain in the annular gap – classifying zone.• Air carries the material around at the rotational speed of the

rotor• The radial drag force is trying to pull the material inside the

rotor. • The centrifugal force is tying to push the material towards the

guide vanes.• Gravity is pulling the material down.

Adjustment of Fineness• Independent adjustment of separating forces- centrifugal force and

aerodynamic drag force which act in a plane perpendicular to gravity force

• Rotor speed• Increasing speed increases centrifugal force.• The centrifugal force is responsible for sorting out the coarser

particles and is proportional to the cube of diameter• Only ultrafine particles with high surface area (blaine value) will end

up as product.• Air flow

• Increasing air flow increases aerodynamic drag• The air stream is able to carry larger particles through the separation

zone than before and the fineness of final product will decrease.• Since drag is proportional to square of diameter, larger particles are

not affected much- hence blaine may not be disturbed, but % retained on 45 microns will increase.

Separators of 3rd Generation

Example: Polysius Sepol

1

23

45

6

9

10

11

7

8

1 2

3

4

5

6

5

11

7

8

9

10

guide vanes

rotor blades

distributor plate

rotor shaft

feed spouts

air + fines outlet

tailings outlet

air inlet

gear box

sealing

motor

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Separators of 3rd Generation

Example: FLS O-Sepa

Air outlet+ fines

Drive

Prim.

air

Tert.

air

Sec.

air

Feed

Sealing

Fines

Distributor

Guidevanes

Rotor

Coarses

Centrifugal force

Air force

Gravity forcePrim.air

Coarses

Basic function:

Material enters the separator at the top.

Airstream is generated by external fan.

Material falls down between the rotor and guide vanes. Fines are sucked in. Coarse particles are accelerated by the rotor and stopped by guide vanes, where they slip down and leave the casing with the tailings outlet.

Fine material exits with the airflow at the upper part of the casing .

Product fineness is adjustable by the rotational speed of the rotor.

Separators of 3rd GenerationBasic function:

Material enters the separator at the top.

Airstream is generated by an external fan.

Material falls down between the rotor and guide vanes. Fines are sucked in. Coarse particles are accelerated by the rotor and stopped by the guide vanes, where they slip down and leave the casing via the tailings outlet.

Fine material exits with the airflow at the lower part of the casing .

Product fineness is adjustable by the rotational speed of the rotor.

air inlet

rotorblades

air guidevanes

motor

shaft

tailings outletair + finesoutlet

distributor plate

separatingzone

coarsesfines

feed spout gearbox

Example: O&K cross-flow separator

Separators of 3rd Generation (FLS SEPAX)

Separators of 3rd Generation (FLS SEPAX)

Basic function of the compact version:

Material enters the separator at the bottom with the air stream. The air stream is generated by an external fan.

Material enters the rotor in the air stream via guide vanes. Fines are sucked in. Coarse particles are accelerated by the rotor and stopped by guide vanes, where they slip down and leave the casing on the side.

Fine material exits with the airflow at the top of the casing .

Product fineness is adjustable by the rotational speed of the rotor.

Additional functions roller press version:

Roller Press slabs enter desagglomerator under the compact separator where they are crushed

Fines go up in the air stream to the separator

Coarses fall down and pass through the grit separator, where additional fines are separated und go up in the air stream. Rejects go back to the press

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Separators of 3rd Generation (Polysius Sepol SM)Basic function:

Material enters the separator at the bottom with the air stream (e.g. air swept mill)

Air stream is generated by an external fan.

Material enters the rotor in the air stream via guide vanes. Fines are sucked in. Coarse particles are accelerated by the rotor and stopped by guide vanes, where they slip down and leave the casing at the bottom.

Fine material exits with the airflow at the top of the casing .

Product fineness is adjustable by the rotational speed of the rotor.

Airflow with material from mill

Returns

Fines with air

Rotor

Inspection doors

Rotor drive

Guide vanes

Separators of 3rd Generation (KHD Sepmaster)

Sepmaster SKS-D (for RP* circuits) Sepmaster SKS-LS (for ASM**)

air and fineproduct

feed material feed material

impact ring

rotordesagglomerator

coarse product

air+fines

feed material+air

coarse fraction 2

coarse fraction 1

air+fines

* Roller Press ** Air Swept Mill

Separators of 3rd Generation (KHD Sepmaster)

Sepmaster SKS

1

2

3

4

5

6

7

8

9

10

11

guide vanes

rotor blades

distributor plate

rotor shaft

feed spout

air + fines outlet

tailings outlet

air inlet

gear box

sealing

motor

1

2

3

4

5

67

8

9

1011

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Separators of 3rd Generation (KHD Sepmaster)

Basic function:

Material enters the separator at the top.

Air stream is generated by external fan.

Material falls down between the rotor and guide vanes. Fines are sucked into the rotor. Coarse particles are accelerated by the rotor and stopped by guide vanes, where they slip down and leave the casing at the bottom.

Fine material exits the separator with the airflow at the top of the casing .

Product fineness is adjustable by the rotational speed of the rotor.

Special features SKS-D: Additionally equipped with slab desagglomerator at the top (use in roller press circuits)

Special features SKS-LS: Used for air swept mills. Function is very similar to Polysius Sepol SM.

Separators of 3rd Generation (Pfeiffer QDK)

Basic function:

Material enters the separator at the top.

Air stream is generated by external fan.

Material falls down between the rotor and guide vanes. Fines are sucked in. Coarse particles are accelerated by the rotor and stopped by guide vanes, where they slip down and leave the casing at the bottom.

Fine material exits with the airflow at the lower part of the casing .

Product fineness is adjustable by the rotational speed of the rotor.

Rotor drive

Rotor

Air inlet

Air +Fines

Returns

Separators of 3rd Generation (vertical roller mill ; Loesche)

Feed

AirAir

Returns flow

Separator drive

Guide vanes

Cage rotor

Grit cone

Conical casing

Airflow with material from grinding table

Basic function:

Material enters the separator at the bottom with the air stream.

Air stream is generated by external fan.

Material enters the rotor in the air stream via guide vanes. Fines are sucked in. Coarse particles are accelerated by the rotor and stopped by guide vanes, where they slip down, leave the grit cone at the bottom and fall back on to the grinding table.

Fine material exits with the airflow at the top of the casing .

The product fineness is adjustable by rotational speed of the rotor.

Separators of 3rd Generation (Vertical roller mill)

Guide vane system

Reject cone

Cage rotor

Separators of 3rd Generation (coal grinding) in VRM

Basic function:

Coal from the grinding table enters the separator at the bottom with the air stream. (Used in vertical roller mills)

Air stream is generated by external fan.

Material enters the rotor in the air stream via guide vanes. Fines are sucked in. Coarse particles are accelerated by the rotor and stopped by guide vanes, where they slip down and leave the casing at the bottom.

Fine material exits with the airflow at the top of the casing .

Product fineness is adjustable by the rotational speed of the rotor.

Pfeiffer RTKM Separator for coal mills

Possible causes that limit the separating efficiency

The typical situations for 3rd generation separators are:

• Uneven airflow and/or feed distribution to the rotor• Reduced separating airflow due to:

• Separator fan damper (or speed) not at maximum• Fan nominal too low• Limited rotor speed due to mechanical problems or

insufficient nominal capacity of the motor and/or gear box

• Contamination of the fines by coarse product• Separator fines much finer than final product

Lower air speed Finer product

Higher airspeed Coarser product

Air distribution

FRAir

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Uneven airflow distribution• Uneven airflow distribution can be identified from (1/2):

• Observation of the ducting configuration:• General arrangement• Relative position inlet / outlet air ducts

• Uneven wear of paintings or steel along the guide vanes height

• Uneven wear of paintings or steel along the rotor blades height

• Low separator efficiency despite low material specific loads

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How to determine the airflow profile• Uneven airflow distribution can be identified and evaluated

from (2/2):• Airspeed mapping at the inlet of the separator volute• Static pressure profile in each duct ( )• Fineness comparison of the fines at each cyclone (mass

balance for each cyclone)

Solutions for even airflow profile Even airflow distribution

with air guide plates The positioning and length

of the air guide plates should be done considering the air flow distribution in the ducting (start from where the air is already evenly distributed)

Laminar and even flow across whole duct section

Good

Too short

Feed distribution

< 50 [mm]

Symptoms of uneven material distribution

Uneven wear of paintings or steel of the impact ring

Uneven pressure loss and fineness of the fines in a cyclone air separator

Separator efficiency is low in spite of low material specific loads

Configuration of airslides from separator discharge to the separator feed point(s)

Solutions evaluation

Even as much as possible material load to all separator feeding points: Adjust / install splitters Install mixing boxes Change airslides

configuration