1. AIR SEPERATION TECHNOLOGIES USED IN CEMENT INDUSTRY

2. AIR SEPARATION TECHNOLOGIES USED IN CEMENT INDUSTRY
GENERAL
- DEFINITION OF AIR SEPARATION – FORCES INVOLVED
SEPARATOR TYPES USED IN CEMENT INDUSTRY
* STATIC SEPARATORS
- CONE TYPE SEPARATORS
- V-TYPE SEPARATORS
* DYNAMIC SEPARATORS
- FIRST GENERATION SEPARATORS
- SECOND GENERATION SEPARATORS
- THIRD GENERATION ( HIGH EFFICIENCY ) SEPARATORS
A TOOL TO EVALUATE SEPARATOR PERFORMANCE – TROMP CURVE
RELATIONS BETWEEN OPERATING VARIABLES AND PERFORMANCE CRITERIA OF SEPARATORS
QUALITY ASPECT OF CEMENT IN RELATION TO SEPARATION
LATEST DEVELOPMENTS IN AIR SEPARATION TECHNOLOGIES
DISCUSSIONS

3. SEPARATION
“Separation is a method to differentiate particles according to their size exploiting the fact that different particles can obtain different velocities when moving in a fluid under a certain force”.
Air separation is the method of separating dry particulate materials into two distinct size fractions, one above and the other below a defined cut-point which normally range from 1 micron to 300 micron. It has a widespread use in many industries such as cement, coal, ceramic, pulp and paper, fertiliser and pharmaceutics.
The most important application of air separators is to reduce overgrinding in a mill by separating the mill output into coarse and fine fractions, so that fines can be removed as soon as they are produced and the coarse returned for further grinding. It can be used also to produce products to meet higher requirements by having for instance a more suitable particle size distribution. In many applications it is used to enhance the operation of some other process.
No single design of air separator is capable of satisfying the diverse range of requirements of the many process which air separation can be applied. In this relation a number of different types of separators have been developed to meet special industrial requirements.

4. FORCES ACTING ON PARTICLES
First Generation C
(?) R D G
High Energy
(uplift of material)
Second Generation C R D G I
BLADE
Intermediate Energy
(uplift of material)
ROD I
(Impact) D C R G
Low Energy
(displacement of material)
Third Generation

5. Forces acting; Gravitation: Drag Force: where Centrifugal Force:
m: particle mass
g: acceleration due to gravity
: particle-air density difference
c: drag coefficient
a: projected particle area
u: air velocity
v: particle velocity
: air viscosity
f: function
dp: particle diameter
dr: rod diameter
where
Centrifugal Force:
Impact Force (efficiency of capture):

6. STATIC SEPARATORS
VANE TYPE SEPARATORS
Principle: Static separators have no moving parts and separation is executed by chances in air velocity and direction. As seen in figure 1, the air stream carrying particles is converted from a directional flow through the outer cone into a rotating flow by guide vanes. The particles are subject to centrifugal force, the coarse particles move to the outer wall of the inner cone and spiral down it to enter the reject stream and the fine particles move into an upward spiral in the center of the cone and are carried away. The effect of separation depends on the air volume, the feed rate and the adjustment of the vane angles. As air volume increases i.e.increase in air velocity,centrifugal force increases and separation becomes more efficient. The product size can roughly be adjusted by changing the angle of the vanes. When closing the vanes, finer particles will be selected and the product becomes finer. The limit to the closing of the vanes is the level of pressure drop one can tolerate in the separator.
Static separators are mostly used in mill ventilation circuits. The particles that are being transported can be too coarse to be added to the finished product. These separators can remove the coarser fraction that goes back to the mill for regrinding, while the finer fraction is added to the finished product.

7. V-SEPARATOR
Principle: This separator was developed to be used in combination with high pressure grinding rolls. The cake produced by the grinding rolls required deagglomeration before separation into the coarse and fine particles. The V-Separator was designed to do both duties.
As seen in the Figure , the feed is directed down through baffles to meet the rising air flow. The weak compacts are broken as they collide with the baffles and the fine and coarse particles are liberated. The coarse particles can not be carried by the air flow and slide down to go back to the grinding rolls. The fine particles are entrained in the air and swept upwards through a further set of baffles. The V-Separator fines normally have Blaine surfaces around 1800 cm2/g, and this pre-classified material goes into a high efficiency separator closed circuited with a ball mill.
The separation size is adjusted by changing the air flow rate. Like the static cone separator it is inexpensive; has a low energy consumption and is reasonably efficient at coarse sizes even with high solid to air ratios up to 4 kg/m3.

8. DYNAMIC SEPARATORS
Air separation became important in the latter part of 19th century when tube mills were developed to produce large volumes of portland cement which had become a significant building material. The grinding process highlighted the need for efficient separation of fine particles from mill discharge and static separators proved to be inadequate. Askham air separator was patented for this duty by Mumford and Moodie in 1985 which was the basis of the first generation of dynamic separators.
Common characteristics of dynamic air separators are;
- internal rotors that are also feed distribution plates,
- airflows generated by internal or external fans,
- collision plates that assist rejection of coarse particles,
First generation dynamic separators and their evolution during 120 years into second and third generation separators that improve rejection of coarse particles and minimise by-pass will now be discussed.

9. FIRST GENERATION DYNAMIC SEPARATORS
Dynamic separators started with the Askham air separator in These type of separators became known as the first generation separators. The Sturtevant Whirlwind separator shown in the following Figure was a popular first generation separator which consists of a funnel-shaped casing, within which is a second funnel with an annular space between the two. The separation is affected by a current of air which is produced by a fan revolving in the upper part of the casing. The material is fed on to a spinning distribution plate and dispersed into an air stream created by a circulating fan. The spinning plate imparts a centrifugal force to throw particles in the separation zone. Large particles drop out in the inner cone and leave the apparatus. The current induced by the fan passes upwards and outwards between the fan blades carrying with it the finer particles which are thrown into the outer casing. The air carrying fines returns to the fan inlet via return air vanes because of change in air direction and velocity, and the fines is discharged through the fines chute.
A problem with the first generation of air separators is that no external air is added and the circulating air becomes very hot ( >120 degrees C ). This has an adverse effect on the gypsum in finished cement so that these units are more appropriate on mills grinding raw materials than clinker.

10. The main advantages of the first generation classifiers were reasonable classification of very fine products on an industrial scale which had not previously been possible and relatively low capital cost.
The main problems were
- fine particles were not removed from the recycling air effectively and they accumulated in the coarse product leading to a high recycle of finished product to the mill,
- the circulating air became very hot (>120 degrees C). This was unsuitable for cement clinker circuits in which the gypsum could be affected and first generation units have been preferred for circuits grinding raw materials for processing in the kiln,
- the sizing distribution and surface area of the fine product were difficult to change although this problem was reduced when the auxiliary fan with the separate variable speed drive was used,
- the distribution of feed on the disk and dispersion in the air were uneven and this exacerbated the problem of high recycle.
For nearly 80 years classifiers of this type were used in cement plants and many are still used today. The demand for cement increased rapidly in the 1950s and there was also a continuing need to improve cement quality, which meant closer control of size distribution. The deficiencies of the first generation air classifier had to be corrected and attemps to do this resulted in the design of the second generation of dynamic classifiers.

11. STERTEWANT FIRST GENERATION DYNAMIC SEPARATOR

12. SECOND GENERATION DYNAMIC SEPARATORS
First generation separators suffered from high by-pass and difficulty in changing the particle size distribution and surface area of the fine product and in the 1950s these problems were outweighing the advantage of relatively low cost. One solution was to remove the fines from the circulating air and this led to a second generation separator becoming available in 1960 whose main features were
- an external fan to circulate the air which replaced the internal fan,
- several external planetary cyclones which replaced the fines cone,
- independent control of separator speed and air circulation.
The air containing the fines went from classifier to the cyclone where the solids were removed through the apex, and then to the fan which recycled it back to the separator. The separation is based on the same principle as the first generation separators. The main advantages of the second generation separators were better removal of fines, sharper separation, lower by-pass and continious control of the fineness. The main disadvantage was their large size. The problems were incomplete dispersion of the feed and removal of the fines from the recycling air which was still incomplete, and a rather erratic cut size. For some years after they came on the market they were preferred to the first generation units when new circuits were being installed but they had a relatively short life because of their size and they were replaced by the third generation separators.

13. SECOND GENERATION SEPARATOR

14. SECOND GENERATION SEPARATOR

15. SECOND GENERATION DYNAMIC SEPARATORS
Operation principle: Same principle as in first generation separators
Main Features: - an external fan to circulate the air which replaced the internal fan
- several external planetary cyclones which replaced the fines cone
- independent control of the separator speed and air circulation
Advantages: more efficient separation of fines in cyclones, higher efficiency
- independent adjustment of separator speed and air circulation gives a larger
regulation range and better efficiency with fine separation because of more circulating air
- adjustment of fineness without stopping the separator
- material cooling by adjustment of fresh air inlet damper
Disadvantages: - incomplete dispersion of feed
- a rather erratic cut size

16. THIRD GENERATION DYNAMIC SEPARATORS
By the 1970s a new dynamic separator, third generation type, was being designed with the objectives of decreasing by-pass, and giving a better precision of separation and decreasing cut size. The O-SEPA separator installed in a plant in 1979 was the first of the third generation of air separators. Some improvements were
the air entered the classifier horizontally and had a uniform velocity across the flow,
the distribution plate was at the top of the air flow and the feed fell as a completely dispersed curtain of particles,
particles passed through a rotating cage before entering the fine stream, and the collision of the particles with the bars of the cage assisted in rejecting the coarser particles from the flowing air,
the product size could be adjusted on-line by changing the rotor speed,
the dust laden air from the mill was used as classifying air without impairing the classification efficiency because the air left the separator and the fines were removed before it was recycled.
In operation the air passes through the stationary guide vanes and the feed material is dispersed in the annular gap between these and the rotor. After passing through the vanes the air moves in a horizontal vortex. The air carries the fine material tangentially across the face of the rotor that is turning in the same direction as the vortex. The coarse particles are separated by a combination of gravity, centrifugal and impact forces and fall into the collecting cone at the base. The fine particles are conveyed to a dust collector. The sharp classification and low by-pass reduced the circulating load in tube mill-separator circuits and allowed an increase in feed rate by 20-40%. The specific energy consumption was reduced by 15-35%.

17. PRINCIPLE OF OPERATION
Material is first dispersed on the distribution table and falls down into the gap between the cage and the guide vanes forming a thin curtain of material. After passing through the vanes the air moves in a horizontal vortex. The air carries the fine material tangentially across the face of the rotor that is turning in the same direction as the vortex. The coarse particles are separated by a combination of gravity, centrifugal and impact forces and fall into the collecting cone at the base. The fine particles are conveyed to a dust collector. The sharp classification and low by-pass reduced the circulating load in tube mill-separator circuits and allowed an increase in feed rate by 20-40%. The specific energy consumption was reduced by 15-35%. Large air flows are very important for good efficiency. Qf/Qa ratio of such separators is around 2 kg/m3 up to 2,5 kg/m3, provided the fines are always lower than 1 kg/m3.

18. THIRD GENERATION DYNAMIC SEPARATOR

19. FINENESS CONTROL IN HES
Fineness Control: The fineness of the product can be controlled in three ways.
- by varying the volume (velocity) of the air flowing through the separator. As the volume is increased the product becomes coarser.
- by changing the speed of cage rotor. As the speed is increased fineness increases.
- by changing the annular setting of the guide vanes. A setting towards the redial position will give a coarser product, whilst finer product will be obtained by going to as near tangential setting as required.
It is readily seen that the product fineness control is much easier with the HES than the other types. By playing with the first two variables it can be made without stopping of the grinding circuit and from the control room.

20. USE OF HES
The use of HES become widespread as these units offer several combined advantages which can be given as;
mill system production increase of 20-40% for existing ball mills or a propertional reduction in the size of new mills producing ordinary cement.
specific power reduction of 15 to 35% in the grinding department.
lower cement temperature, which minimises or eliminates mill internal coating and the tendency for false or pack set in the cement.
simple separator rotor speed control of product fineness making it no longer necessary to stop the mill to make separator adjustments when changing the product fineness. The amount of fringe cement is much less.
smaller relative separator size and ability to accept dusty process air which reduces the amount of auxiliary equipment and power consumption, thereby classifying all cement through one machine for more uniform physical properties.
ability to have better control of cement strength, and to enhance characteristics such as coarse particle residue. Variations of these characteristics are minimised resulting in higher confidence in cement quality.
ability to make special cement products that were previously very difficult, such as coarse oil well and fine masonry blends.
the investment payback period is sufficiently low for cement manufacture

21. A TOOL TO EVALUATE SEPARATOR PERFORMANCE - TROMP CURVE
There are various methods of defining the separation efficiency. However it has long been realised that the best and most common method is to use the Tromp Curve which is a graph showing the proportion of feed fractions which will pass into the tailings and go back to the mill on the ordinatehaving a linear scale, and the mean size of the fractions on the abscissa having logarithmic scale.
Table x gives the data taken from an actual plant. Weight percentage of three different streams are given for each size fractions concerned. For each individual particle size of the separator feed the curve indicates the weight percentage which goes into the finished product and into the rejects. With experience and a good data base one can analyze a tromp curve and deduce valuable information about the separator and the circuit from the curve characteristics which are:
Cut point: The cut point d50 corresponds to 50% of the feed passing to the coarse stream. It is therefore the size which has equal probability of passing to either coarse or fine streams.
Sharpness: The sharpness of separation is defined as d75/d25, where d75 and d25 denote the sizes with Tromp values of 75% and 25%. For an ideal separation this would be 1.
Imperfection: The imperfection of separation is usually defined as I=[ d75-d25 ] / 2d50. The lower the imperfection the better the separation.
By-Pass: The percentage of the lowest point on the tromp curve is referred as the by-pass. It indicates a portion of each size fraction which bypasses the classifying action. Expressed in an other way, it is part of the feed which passes to the coarse stream without being classified. Experience has shown that the by-pass parameter variea with classifier feed rate , and hence it is difficult to describe a single Tromp curve which is representative of the classifier.
Fish Hook: It is the portion of fines returning back into rejects. In certain separators, mainly in those having rotating vanes, the fine particle stream from a primary classification is met by a circulating air stream containing still finer particles which recoat the separated particles causing them to behave as coarse particles. This secondary action leads to a fish-hook pattern of Tromp curve. A similar effect can be seen in separators in which there is incomplete feed dispersion at the separator entry, or even within the classification zone, whereby aggregates of fine particles may be classified as coarse particles and thus report to the coarse stream. If during the size analysis, these aggregates are dispersed, the analysis give more fines than the separator did.

22. MADDE DENKLİĞİNİN HESAPLANMASI

24. MADDE DENKLİĞİNİN İKİ TEMEL AŞAMASI
I. Ham verileri kullanarak O/F’nin en iyi tahmini değerinin hesaplanması
II. Belirlenen O/F değerini kullanarak analiz değerlerinin düzeltilmesi

27. HAM VERİLERLE DÜZELTİLMİŞ VERİLERİN KARŞILAŞTIRILMASI

28. İnce

32. İDEAL VE GERÇEK SEPARATOR PERFORMANSLARININ
KARŞILAŞTIRILMASI

39. MOVIE CLIP-TROMP CURVE

40. GRADUAL EVOLUTION AND CORRESPONDING IMPROVEMENT IN THE PERFORMANCE OF AIR SEPARATORS SINCE 1885
Type Precision d50(microns) By-pass (%) RRB slope
Static
1st generation
2nd generation
3rd generation

41. LV-TECHNOLOGY

42. LV-TECHNOLOGY

43. LV-TECHNOLOGY
GUIDE VANES
SEAL RING
ROTOR BLADES
GRIT CONE

44. LV TECHNOLOGY CLASSIFIER FOR VERTICAL ROLLER MILL

45. SEPARATOR IMPROVEMENTS AIM AT
Improving Performance
Optimizing airflow-reducing volume ( >600gm/m3)
Reducing Internal Material Circulation
Reducing Pressure Drop
Reducing Fan Power
Increasing Grinding Efficiency

46. A TYPICAL LV MODIFICATION

47. CLAIMED BENEFITS OF LV CLASSIFIER
Vertical Roller Mills:
% Increased production
1.0 – 5.0 kWh/t Saving in power consumption of both mill and fan
Vibration level decreasing
Cement strength increases

48. TROMP AND EFFICIENCY CURVES OF A BALL MILL-LV SEPARATOR SYSTEM

49. RELATIONS BETWEEN OPERATING VARIABLES AND PERFORMANCE CRITERIA OF SEPARATORS
The fact that the separator runs in a circuit means that operating variables of the circuit may change. These variables can be feed rate, feed fineness, rotor speed, air ventilation and so forth. In reviewing separator performance some over-riding relations, which affect efficiency, must be known and if possible would be expressed mathematically.One of these relations relates to the feed concentration, i.e. Kg feed to separator/ m3 of separator air sweep =Qf/Qa ). It is claimed to tie up the combined effect of circulating load, system output and fan speed as well as blade position and number and also separator sweep on high efficiency separators. Its effect on by-pass of two separators is given below.
What the above graph shows is that as separator feed is increased by-pass also increases prowided that the amount of separator internal airsweep remains the same. Increasing sweep through the separator with more fan, more speed, more blades or larger diameter fan should reduce the by-pass. Therefore reducing sweep through closing the diaphragm will reduce efficiency or increase by-pass. In general high efficiency separator operators have the luxery of being able to adjust separator draft as separator feed changes and adjust cage rotor speeds to control fineness. It is seen from the graph that for an HES the curve is flatter, which means that they can withstand bigger changes in Qf/Qa with a much smaller effect on by-pass. It can be seen that the general rule is to strive for the largest amount of internal air flow or the lowest Qf/Qa ratio that still meets product quality constrains.
Qf/Qa ratios suggested for different separators are roughly given below.
HES nd. Gen st. Gen Static Sep.
< 1.0

50. RELATION BETWEEN DUST LOAD AND BY-PASS

51. TABLE OF SPECIFIC LOADING RATIOS
O-SEPA O-SEPA** S-D SEPOL SEPAX RANGE
SEPARATOR FEED
KG/AM3 OF AIRFLOW
1.39
2.25
2.23
1.7
1.8
SEPARATOR PROD.
0.49
0.76
0.73
0.62
0.72
T/H*M2 OF ROTOR
SURFACE AREA
22.8
30.46
22.81
21.38
20.6
20-22
7.99
10.24
7.49
7.72
8.25
8.0-11

52. POSSIBLE SEPARATOR ADJUSTMENTS AND THEIR EFFECTS
Resulting Change
Type of Adjustment
By pass
Fines Output
Fineness
MAIN FAN
More blades or larger diameter
Fewer blades or small diameter
Higher speed
SELECTOR BLADES
More blades
Fewer blades
Higher speed (if double shaft)

53. POSSIBLE SEPARATOR ADJUSTMENTS AND THEIR EFFECTS
DIAPHRAGM or VALVES
% opening
SEPARATOR FEED RATE
Varies with the mill circuit type
SEPARATOR FEED
FINENESS
Varies with the mill
circuit type
ROTOR SPEED *
AIR FLOW *
Applies only to 2nd and 3rd generations.