Detail of palletization process. Difference between Disc and drum pelletizer. Properties parameters and Norms for testings. List of difference agglomerates testings.

1. PELLETIZATION PROCESS
Chapter 3
F.S. BE III
(Metallurgy & Materials Engg.)
Prepared by
Mr. Utkarsh V Prajapati
Assistant Professor
(Metallurgy & Materials
Engg. Dept.)

2. CONTENT
 Pelletization process
 Disc and drum pelletizer
 Theory of bonding
 Mechanism of ball formation
 Induration of pellets
 Cold bonding technique
 Testing of agglomerates

3. INTRODUCITON
 The iron ore production has significantly expanded in recent
years, owing to increasing steel demands in developing
countries.
 However, the content of iron in ore deposits has deteriorated
and low-grade iron ore has been processed.
 The fines resulting from the concentration process must be
agglomerated for use in iron and steelmaking.

4. CONT…
 Iron ore and iron ore pellets are important sources of iron for
manufacturing steel. The iron ore production has significantly
expanded in recent years, owing to increasing steel demands
in developing countries, such as China and India.
 However, the content of iron ore in deposits has deteriorated
and low-grade iron ore has been processed. The fines resulting
from the enrichment by separation after liberation by size
reduction must be agglomerated in a pelletizing plant.
 Consequently, the number of pelletizing plants is expected to
increase in the future.

5. CONT..
 The quality requirements of pellet, such as physical, chemical and
metallurgical specifications, depend on each ironmaking furnace
and those requirements influence the operation of the iron ore
pelletizing plant.
 The idea of rolling moist fine ore in a drum to form balls and then
drying and firing it was first patented by A. G. Andersson in Sweden
in 1912.
 Further development was performed to bring the idea to reality. In
1943, E. W. Davies and co-workers demonstrated the process using
an experimental shaft furnace. Commercial operation started in the
1950s in Sweden using vertical-shaft-kilns for firing the pellets. Plant
capacities were between 10,000 and 60,000 tons/year .

6. Pelletizing
process & Raw
materials
 The iron ore is mined mostly from open pit deposits through
mining operations and the raw product, “run of mine,” is
subjected to mineral processing.
 Thus, the material is exposed to a series of operations of
fragmentation, separation by size, concentration, dewatering,
etc., aiming to adequate the chemical, physical, and
metallurgical characteristics to meet the demands of
ironmaking processes.
 The particle size distribution of iron ore is a very important
requirement to be characterized after its mineral processing.

7. Cont..
 Materials containing a very fine particle size distribution are not
adequate to be used directly in the reduction reactors, requiring
to be agglomerated by different processes such as sintering or
pelletizing.
 The main used reduction reactors are the blast furnace (BF) and
direct reduction reactors (DR). In the blast furnace, iron is
reduced and melted and the most common product is liquid
iron called hot metal. In direct reduction, iron remains in solid
state and the product is the so-called direct reduced iron (DRI).

8. Cont..
 Pellets are balls formed by rolling moist concentrates and fines
iron ores of different mineralogical and chemical composition,
with the addition of additives and binder, in a horizontal drum
or in an inclined disc.
 Pellets produced to be used in ironmaking processes must have
characteristics that meet the list of quality specifications
regarding physical, chemical, and metallurgical properties.

9. Process steps
 Pelletizing feed preparation and mixing: the raw material
(iron ore concentrate, additives—anthracite, dolomite—and
binders are prepared in terms of particle size and chemical
specifications, dosed, and mixed together to feed the
pelletizing process;
 Balling process: the green pellet is the rolled pellet without any
thermal process. It is obtained under strict control of moisture
and has a spherical shape and diameter of 8–16 mm;
 Induration process: the green pellets are hardened in a high
temperature (1250 – 1350⁰C) processing at controlled heating
rates, and aiming to achieve the physical and metallurgical
requirements for handling, transportation, and final
application.

10. Properties &
standards
Type of specification Norm Description
Physical
ISO 4701 Determination of size distribution by sieving
ISO 4700 Determination of the crushing strength
ISO 3271 Determination of the tumble and abrasion index
JIS M 8711 Determination of shatter strength
Internal
procedures
(pelletizing
companies)
Determination of crashed resistance by the number of drop falls
Chemical Chemical property of the pellets
Metallurgical
ISO 4698 Determination of the free-swelling index
ISO 13930
Determination of low-temperature reduction-disintegration index
by dynamic method
ISO 11257
Determination of the low-temperature reduction-disintegration
index and degree of metallization
ISO 11256 Determination of the clustering index
ISO 7992 / ISO
7215 / ISO 11257
Determination of reduction under load/Determination of the
reducibility by the final degree of reduction index/Determination of
the low-temperature reduction-disintegration index and degree of
metallization
Internal
procedures
(pelletizing
companies)
Porosity

11. Binders
 Aiming to achieve those specifications, binders and additives are
used in the pelletizing process.
 Additives such as limestone, dolomite, and hydrated lime are
used to modify the chemical composition of the pellets, most
often for correction of the basicity.
 Certain substances such as hydrated lime serve as both additive
and binder.
 Fines of anthracite or coke are also added during the pelletizing
process for reducing the consumption of fuel required for
internally heating the ball

12.  Pellets are obtained by adding an appropriate amount of water
to the iron ore concentrate; this is a fundamental factor in the
formation and growth of pellets, which creates a surface
tension that holds the mineral grains cohesive, thus allowing
their handling.
 This cohesive tension of fine particles due to water is called
neutral tension. Neutral tension, however, is not sufficient to
keep cohesive grains as dense as iron minerals.
 Furthermore, when the pellet is heated, the vaporization of
water occurs and the pellets tend to disintegrate.

13. Importance of
binders
 To avoid such effects, binders are added to the material to be
pelletized, aiming to:
1. increase the strength of pellets before heating (green
strength);
2. prevent the collapse of pellets during the initial stages of
heating, when a large volume of gas generated by water
vaporization tends to crack the pellets.
 Evenly distributed moisture and binder in the feeding process is
decisive to improve the characteristics of pellets, especially to
avoid the formation of undesirable agglomerates before the
pellet formation.

14. Effective
binders
 Bentonite is an effective, widely used binder in the iron ore
pelletizing process. Its low price is an important factor for its
extensive use.
 However, bentonite incorporates silica and alumina, which are
undesirable contaminants to pellets.
 Additionally, it is a natural material with variable composition
depending on its origin. Obtaining a suitable binding effect
requires a relatively large amount of material, around 0.5% by
weight, which makes handling more difficult and increases
logistics costs.

15. Plant setup
Typical pellet plant using disc pelletizer as balling
technology.

16. Green ball
production
• Green ball agglomeration are economically produce in balling
drums or discs equipment.
• The balling equipment would require –
a. Rotating surface
b. Facilities for addition of moisture
c. Removal of balls of desired size
d. Recirculation of undersize and oversize should be provided.

17. Balling
technologies
• The balling equipment that can be either a disc or a
drum produces green pellets in a variable size
distribution.
I. Disc pelletizer or Balling disc
II. Drum pelletizer

18. Ballingdisc or disc pelletizer
 Fig. schematically shows a laboratory disc pelletizer.
 The balling disc basically consists of a pan with a
peripheral wall, which rotates with a certain
inclination to the horizontal.
 In general, in a balling disc, the pan angle can be
adjusted between 40 and 60°.
 These discs resemble flying saucers and are normally
3.6-5.6 m in dia.

19. Working
principle
 When the disc rotates, the feed material with less moisture than
that required for the pellets formation, is charged to the bottom
of the disc, where it get in contact with the water from the
sprayers, initiating the nucleation stage.
 At this stage, the nuclei begin to take the form of small pellets,
which by rolling action, occur in the lower section to the left of
the disc, toward the top.
 As the added ore aggregates unto the surface of the pellets,
they increase in size and the coefficient of friction is reduced
causing the pellets to acquire a centrifugal force that carries
them out of the nucleation zone.

20. Size range  This movement takes the pellets to the top of the disc following a
semicircular trajectory before returning to the base of the disc.
 The height and width of the trajectory increase as the ball size
increases until the balls hit the scraper blades. After that, they
move down and pass under the water sprayers so that they can
find fresh feed.
 The balling disc works in close circuit with the screening step,
where pellets smaller than 8 mm or larger than 16 mm are
desegregated and the material is recirculated to the balling
process.

21.  The finer is the feed i.e more the specific size better is the
quality and higher is the growth rate of pellets.
 The disc pelletizing circuit may have one ore more discs and
their operation have to be synchronized to obtain a uniform
rate of production so induration unit works smoothly.

22. Variables
 Diameter of the disc
 Height of the peripheral wall
 Angle of inclination of disc with horizontal
 Speed of rotation
 Place on the disc where mix is fed.
 Place where water is sprayed on the disc.
 Rate of feed
 Rate of moisture addition
 Rate of withdrawal of the product
 Nature and size of feed
 Desired size range of pellets and % recycled load
 Others additions like binder , flux, etc.

23. Drum pelletizer
 The balling drum equipment fundamentally consists of an
inclined rotating cylindrical shell with water sprays in its inlet
end, where the feed material is introduced to make balls.
 All formed pellets are discharged, regardless of particle size,
which is different from the disc where only balls larger than a
certain size are discharged.
 Because of this, the product has to be screened by a roller
screen, which has increasingly replaced vibrating screen to
extract undersize and oversize.

24. Drum
pelletizer
 The drums usually have a length-to-diameter ratio of 2.5–3.5
and very low slope with angles of inclination of the drum axis
to the horizontal between 2 - 10°.
 The optimum rotating speed is generally between 25 and 35%
of the critical speed that is the speed in which balls will
centrifuge causing their degradation.
 Speed control is necessary to develop a correct rolling and
tumbling action to produce balls.

25. Drum
pelletizer
Typical balling drum arrangement

26. Variables
 Speed of rotation
 Angle off inclination
 Diameter of drum
 Rate of feed
 Depth of material in residence (loading)
 Moisture content
 Nature and size of feed
 Any other additions such a binder and flux.

27. Comparison
Disc pelletize
 High speed – 15-30 rpm
 Pellet growth by layering
 Closed size product
 Circulating load is less (15%
less)
 Screening is adopted if close
size range is required
 Space required will be less
 Cost is less
 Commonly use for iron ore
Drum pelletizer
 Low 10-15 rpm
 Mostly growth by
assimilation
 Wide range product
 Circulating load more
 Screening is must
 More space is required
 Cost is more for installation

28. Theory of
bonding
 Production of hardened pellets starts with the production of
green balls in the first place.
 The nature of bonds and how these are formed need to be
properly understood for proper designing of the equipment
and the process of palletization.

29. Theory of
balling
1. Dry material does not pelletize and presence of moisture is
essential to roll the powder into balls.
2. Surface tension of water in contact with the particles plays a
dominant role in binding the particles together in green
condition.
3. Rolling of moisture material leads to the formation of balls of
very high densities.
4. The ease with which material can be rolled into balls is
almost directly proportional to the surface area of particles
i.e fineness.

30. Water particle
system
1. The pendular state , when water is present just at the point of
contact of the particles and surface tension holds the
particles together as shown in figure.
2. The funicular state, when some pores are fully occupied by
water in an aggregate system.
3. The capillary state, when all the pores are filled with water
but there is no coherent film covering the entire surface of
the particles.

31.  So the bond strength under these three conditions of green ball
produced from a given material will be obtained by compacting
the material to the minimum porosity and with just sufficient
water to saturate the voids.
 The critical moisture can be assessed by determining the
porosity of an aggregate.
 The factors that alter the porosity also affect its critical
moisture level and an efficient balling process is required to
produce balls of uniform properties in spite of these non
uniformities.

32. MECHANISMOF
BALL FORMATION
 The ball formation is two stage process
1. Nucleation or seed formation
2. Growth

33. Cont…
 The formation of balls on a pelletiser depends primarily on the
moisture content.
 If moisture is less than the critical amount its distribution tends
to be non uniform , major amount being present in the
granulated material leaving the non granulated material
relatively dry.
 If the moisture level is more than the critical amount ,growth
rate is more but the balls produced are liable to deformation
because of their plasticity.

34. Cont.…
 The seeds generally have slight excess of water.
 It imparts a certain degree of plasticity which is necessary for
its growth.
 Growth takes place by either layering or assimilation.
 It has been observed that the size of the balls produced in a
pelletiser from a charge containing right amount of moisture
depends on the time and speed of the pelletiser, i.e. the
number revolution.
 The general nature of the variation is shown in figure.

35. Figure shows three regions
can be observed
1. Nucleation formation
2.Transition region
3. Ball growth region

36. Nuclei
formation
region
 When a wet particle comes in contact with another wet or dry
particle a bond is immediately formed between the two .
 Similarly several such particles initially join during rolling to
form a highly porous loosely held aggregate and crumbs which
undergo re-arrangement and partial packing in short duration
to form small spherical , stable nuclei.
 This nuclei later to grow into balls.
 Surface tension of water alone is the binding force in these
nuclei.

37. Transition
region
 After nuclei are formed they pass through a transition period in
which the plastic nuclei further re-arrange and get compacted
to eliminate the air voids present in them.
 The system moves from a pendular state through funicular
state to the capillary state of bonding.
 Rolling action causes the granules to densify further.
 The granules are still plastic with a water film on the surface
and capable of coalescing with other granules. The size range
of granules in this region is fairly wide.

38. Growth
The plastic and relatively wet granules grow if they are
favourite oriented. In this process some granules may even
break because of impacts ,abrasion , etc.
i. Growth by assimilation is possible when balling proceeds
with out the addition of fresh feed material.
ii. Growth by layering is possible when balling proceeds with
the addition of fresh feed material.

39. Growth by
Assimilation
 If no fresh feed material is added for balling the rolling action
may break some of the granules , particularly the small ones,
and the material coalesces with those which grow.
 The bigger the ball the larger it will grow under these
conditions. Since smaller granules are weaker they are the first
victim and growth of the bigger balls takes place at their
expense.
 The ball with the higher % of moisture therefore grow to larger
size but the strength of the resulting balls is low.

40. Growth by
layering
 Growth of the seeds is said to be taking place by layering when
the balls pick up material while rolling on a layer of fresh feed.
 The amount of material picked up by the balls is directly
proportional to its exposed surface.
 In practice fresh material is always supplied to the pelletiser
continuously while withdrawing equivalent amount of balls
from the circuit.
 The conditions are , therefore more suitable for growth to take
place by layering.

41. Induration of
pellets
 The final use of iron ore pellets in ironmaking reactors requires
minimum mechanical properties. Pellets must withstand
tumbling and falling during transport and mechanical loading
inside the reactors due to the charge weight. In order to
increase its mechanical strength, green pellets are thermally
treated in the induration process.
 Pellets undergo drying, firing, and cooling steps.
 First, the water in the form of moisture is removed from the
pellets in the drying steps. There is water in the pores and
capillaries of pellets, that is, between different ore particles. In
the case of porous ores, water may also be found in the pores
of individual grains.

42. Cont..
 Since this type of pores are normally smaller in size than the
pellet pores, the temperature required to eliminate this water is
expected to be higher.
 In the industrial process, the maximum temperatures reached
in the solid phase during the drying steps are approximately
300°C.
 To finalize the induration process, pellets are cooled down by
contact with flow of ambient air. The resulting heated air is
used in the upstream steps of firing and drying.

43. Vertical shaft
furnace
 It was developed in the 1950s and is shown in principle in
figure. The green or dried pellets are fed vertically
downwards in a central shaft of usually a rectangular cross
section.
 Vertical shaft furnace system is the most traditional facility.
However, vertical shaft furnaces are not as common as the
traveling grate or grate kiln systems.
 Fuel is burned in two fire chambers , one on each long side of
the shaft, and the hot gases are allowed to enter the main
shaft through multiple flues.
 It is in a way counter current gas solid heater.
 The fired pellets are cooled in the lower portion and if any
chunks are formed these are broken by the chunk breakers
and cooled pellets discharge form the bottom .

44.  Cooling air , introduced from below , gets pre heated and is
either taken out to burn the fuel in the chamber or to make
available preheated gas for completing the combustion in the
firing zone of the shaft.
 A furnace has a shaft of around 4x2 m c/s and is nearly 20m in
height from discharge rates.
 The temperature of combustion chamber is 1300 C.
 The furnace contains nearly 200t of pellets and production rate
of hardened pellets is around 1200-1200 t per day.

45.  Shaft furnaces are more energy efficient than the
traveling grate or grate-kiln systems. The shaft furnace is
well suited for pelletizing magnetite, but not hematitic or
limonitic ore materials
 Disadvantages of shaft furnaces are low unit productivity
and difficulty in maintaining uniform temperature in the
combustion zone.
 Hot spots may occur which cause pellets to fuse together
into large masses, producing discharge problems. It is
also very difficult to produce fluxed pellets in a shaft
furnace.

46. Straight grate
process
 The most widely used industrial processes for pellet induration
are the straight grate and the grate-kiln.
 The straight grate process is composed of a single furnace
where an endless line of pallet cars moves. A layer of indurated
pellets is arranged at the bottom of each car to protect it
against the heat.
 The green pellets are then charged on top of the hearth of
indurated pellets. A schematic diagram of this process is shown
in Figure.

47. Cont.…
Straight grate induration process

48. PROCESSING ZONES
Drying Section Heating Section Heat Recovery Section
Pre-heating (Ramp)
450-1200oc
Firing
First Cooling
1320- 650oc
Second
Cooling
1300-1320oc 280oc280oc
Down-
Updraft draft
Drying Drying
(UDD) (DDD)
280-
320oc
1 2 3 4 6 7
Travel
Temperature
1400
1200
1000
800
600
400
200
0

49. Cont.…
 The process is designed to enhance heat recovery. Therefore,
two flows of ambient air are heated while cooling the hot
indurated pellets. These flows are directed to other zones of the
furnace.
 The drying of green pellets is performed in two stages by
blowing warm air through the bed of pellets.
 In the first stage, the hot air from the cooling zone is blown
from the bottom. In the second drying stage, hot air from the
firing zone is blown on the top of the car.
 The use of both updraft and downdraft drying ensures a more
uniform treatment along the height of the bed of pellets.

50. Cont.…
 The high temperature phase is divided into three steps: pre-
heating, firing, and after-firing. In all these phases, pre-heated
air is fed into burners to produce flue gases that flow through
the bed of pellets from the top.
 The burners are usually fired with gaseous fuels, such as natural
gas or atomized liquid fuels, such as diesel.
 Pellets close to the top are treated at higher temperatures for
longer times, while pellets at the bottom reach lower peak
temperatures for shorter residence times. It is been reported.

51. Cont.…
 That pellets at the top may reach 1300°C for 6 minutes while
pellets at the bottom peak at 1200°C with no residence time.
 These values may vary, but the difference is large enough to
generate pellets with different mechanical strengths and
different metallurgical properties.
 This is a disadvantage for the straight grate in comparison to
the grate-kiln process.

52. Grate-kiln
process
 In the grate-kiln process, shown in Figure, there are three
different reactors. The drying, pre-heating, and cooling steps
are similar to that of the straight grate process.
 The general concept of heat recovery by using hot gases from
downstream in the process for drying and for feeding the
burners is also present. However, a rotary kiln is used for the
firing step.
 The pre-heating zone is divided into two steps: tempered pre-
heating zone and pre-heating zone, where maximum
temperatures may reach between 1000 and 1100°C.

53. Figure :Grate
kiln Process

54. Cont.…
 Pellets need to gain some mechanical strength during pre-
heating to withstand the tumbling inside the rotating kiln
where firing is performed.
 The firing in the rotating kiln generates pellets with more
uniform properties. The movement of the kiln causes pellets to
mix during the firing treatment and the temperature is more
even among different pellets.
 The furnace is heated with a flame on the discharge side.
Besides gaseous and liquid fuels, solid fuels such as coal may
also be used.

55. Cont.…
 After firing, pellets are discharged in a pallet car for the cooling
stages.
 Therefore, pellets undergo more charging and discharging
operations during the grate-kiln process than in the straight
grate.
 This causes a greater generation of fines during the process.
However, the final pellet properties are more uniform, and
fines generation during transport for final use is therefore
expected to be lower for pellets produced in the grate-kiln
process.

56. Cont.…
 The worldwide pelletizing capacity is divided into 60% for
the straight grate process and 40% for the grate-kiln.
 Both systems are used to produce quality blast furnace
and direct reduction pellets.

57. Comparison
 The induration time for continuous grate is very short, next is
that for grate kiln and shaft furnace require to long.
 Fuel consumption of shaft furnace is only slightly less than that
of others.
 Power consumption is much higher than that of a cont. grate
and which itself is higher than that of the grate kiln machine.
 Capital outlay is much higher than others.
 Maintenance cost of travelling grate is more.
 Overall production cost is highest for continuous grate, lowest
for shaft furnace and intermediate for grate kiln.

58. Introduction
 An important factor that affects the output and
efficiency of blast furnace operati0n in the quality of
burden charge in the furnace.
 Some tests have been carried out to establishment of
these tests also helps to identify those materials which
would jeopardize efficient and smooth furnace
operation.

59. Testing
 Shatter tests
 Tumbling and abrasion test
 Compression test
 Porosity
 Reducibility
 Low temperature breakdown
 Reduction degradation index test (RDI)

60. THANK YOU