Separating and Classifiers

Separating

Grinding with ball mill systems

SEPT-07HGRS Tikaria_Mill Workshop

Separating

Separating process

Separation in 3rd Generation SeparatorBasic 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.

Source: Chr. Pfeiffer QDK Separator

Turning cage rotor

Centrifugal Forces

Returns Air with fines

AirGuide vanes

Turning cage rotor

Centrifugal Forces

AirGuide vanes

What is the separating efficiency dependent on?

Tromp curve

Material: fineness

- Feed (A)

- Fines (F)

- Return (R) Amount of feed Feed distribution

Air: Volume (V [m3/h]) Distribution

The fineness relationship mill filter / separator fines

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

Tromp curve key parameterTromp value [%]

Separator fines

Separator return

Bypass

t ic l

r et u

The BYPASS is one of the best indicator of the

separator efficiency

Tromp curve key parameterTromp value [%]

Separator fines

Separator return

Bypass

Coarse in fines

Circulating load:

A, F & R en [t/h]A = F + R

Circulating load factor:

Amount of material

F[ - ]

Separator performance (1/2)

2'500 3'000 3'500 4'000 4'500 5'000 5'500 6'000

Cement fineness [cm2/g]

Normal

Separator performance (2/2)

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Circulating load factor u [-]

Low potential

Medium potential

High potential

Air volume

Separator specific feed load

Asl =V

AX 1’000 [kg/m3]

Asl < 2.5 [kg/m3]

Separator specific fines load

Fsl =V

FX 1’000 [kg/m3]

Fsl < 0.7 [kg/m3]

Lower air speed Finer product

Higher airspeed Coarser product

Air distribution

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

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

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

The fineness relationship mill filter / separator fines

If F finer than C check:

Send MF to the separator feed

Cut finer at the static separator (if any)

Reduce mill ventilation

Consider a static separator (or cyclone)

Separator operating point (1/2)

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Air [%] of nominal

3’500 [cm2/g]

Iso - fineness line

Separator operating point (2/2)

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Air [%] of nominal

By pass 1

Bypass 2

Bypass 3

Bypass 1 > Bypass 2 > Bypass 3

CONCLUSION is to operate the fan at 100%

Grinding with Ball Mill Systems

Separators

What is separating?Splitting a given material by particle diameter

Balls 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

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.

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.

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

Static separators and cyclones

Cyclone 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

immersion tube

cylindrical part

conical part

Static separators and cyclones

Cyclones of a cement mill separator

Static separator and cyclones

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

adjustable blades

Grit separator

Static separator and cyclones

Adjusting device blades

Grit separator

Static separator and cyclonesBasic 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.

Returns

Air + Fines

Plates

KHD V-separator

Dynamic separators 1st Generation

Basic function:

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 (13).

Fine material exits at the bottom of the casing (14).

Product fineness is adjusted by counter blade position and rods (5) (No counter blade speed adjustment is possible!)

fines chamber1

tailings cone

air vane

inside drum

fineness control valve rod

gear reducer

fan cone

counterblades

main fan blades

feed spout and intake cone

tailings outlet

fines outlet

16main shaft and distributing hub

distributing plate

air inlet

air outlet

Sturtevant

Dynamic separators 1st Generation (Sturtevant)

Internal Fan

Counter blades

External adjustment of fineness control valve rods

Internal Fan

Distributor plateAir vanes Grit cone

Counter blades

Polysius Turbopol

Dynamic separators 1st Generation (Example: Pfeiffer Heyd)

Basic function:

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

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

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

Fan Motor

Counter blades

Feed spout

Distributor plate

Dynamic Separators of 2nd Generation

separation chamber

tailings cone

air vanes

distributor plate

counterblades

feed spout

gearbox

return air duct

dust collecting

air duct to fan

cyclones

tailings outlet

fines outlet

pipe to filter

Polysius Cyclopol

Dynamic Separators of 2nd Generation (Wedag)

to filter

fresh air

Air flow direction

Basic function:

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.

Counter blades

Distributor plate

Separators of 3rd Generation

Turning cage rotor

Centrifugal Forces

AirGuide vanes

Basic function:

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

Guide vanes (in bad shape)

Example: Polysius Sepol

guide vanes

rotor blades

distributor plate

rotor shaft

feed spouts

air + fines outlet

tailings outlet

air inlet

gear box

sealing

Example: FLS O-Sepa

Air outlet+ fines

Sealing

Distributor

Guidevanes

Coarses

Centrifugal force

Air force

Gravity forcePrim.air

Coarses

Basic function:

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.

Basic function:

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 .

air inlet

rotorblades

air guidevanes

tailings outletair + finesoutlet

distributor plate

separatingzone

coarsesfines

feed spout gearbox

Example: O&K cross-flow separator

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 .

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

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.

Product fineness is adjustable by the rotational speed of the rotor.Airflow with material from mill

Returns

Fines with air

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

Sepmaster SKS

guide vanes

rotor blades

distributor plate

rotor shaft

feed spout

air + fines outlet

tailings outlet

air inlet

gear box

sealing

Basic function:

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 .

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 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 .

Rotor drive

Air inlet

Air +Fines

Returns

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

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.

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.

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 VRMBasic function:

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

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.

Pfeiffer RTKM Separator for coal mills

Separator arrangements in grinding circuits

Product

Single Pass design

Mainly used where high cooling is required

Fresh-Air

1 Feed bins

2 Mill with water injection

3 Separator with filter

4 Mill dedusting filter

Product

1 Feed bins

3 Separator with filter

4a Grit separator

5 Optional cement cooler

Standard Arrangement 1st Generation Separator

Product

1 Feed bins

3 Separator with cyclone and dedusting filter

Cyclone Air Separator

Potential Problems

Blades too short

Wear /

Clogging

Sealing not tight

Potential Problems

Wear,clogging

uneven feed distribution

Potential Problems

Breakouts

Sealing not tight

Guide vanes not correctly adjusted

Potential Problems / clogging

Cage rotor separator casing

partly clogged guide vane system

Material deposits due to insufficient airflow or airflow distribution

Reduced separation efficiency 1st and 2nd generation dynamic separators

Gap between internal fan and separating chamber bigger than 5 [mm]

Gap between counter blades and wall of separating chamber bigger than 10 [mm]

Reduced number of counter blades

Possible consequence: Desired fineness can not be achieved anymore

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