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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
Tikaria_Mill Workshop
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.
Tikaria_Mill Workshop
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
Tikaria_Mill Workshop
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
Tikaria_Mill Workshop
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
Tikaria_Mill Workshop
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
Tikaria_Mill Workshop
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