The document discusses factors that affect the generation of sinter return in the sintering process. It states that sinter return depends on the quality of input materials and the sintering process itself. The quality of input materials includes physical characteristics like particle size distribution and chemical characteristics of the iron ore fines. Maintaining the quality of inputs as per norms can minimize sinter return generation. The sintering process can also affect return generation if conditions like alumina content are not optimal. Proper particle sizes distribution of inputs and maintenance of good combustion in the sintering process help reduce return generation.

1. 1
SINTERING PLANT

2. 2
Reduction in generation of Sinter return
Generation of Sinter return depends on the following factors:
1. Quality of Input Materials.
2. Sintering Process.
QUALITY OF INPUT MATERIALS
Physical quality:
a). Iron ore fines:
- 3 mm 50 to 60%
+ 3 mm to – 5 mm 30%
+ 5 mm to – 10 mm 5%
+ 10 mm 5%
b). Crushing Index of Flux ( - 3 mm ): 90%
c). Crushing Index of Coke ( - 3 mm ): 85%
Chemical quality of Iron Ore Fines:
SiO2 2.4% Al2O3 1.8%
If the physical and chemical quality of the input raw materials
are maintained as per norms, the generation of sinter return can be minimized.

3. 3
• If micro fines (- 0.6 mm ) in iron ore fines increases, sinter
process becomes slow,Productivity decreases and sinter return
generation increases.
• If + 5 mm in ore fines increases, sinter return generation
increases as the bigger size of ore fines can not be sintered.
• If Al2O3 in iron ore fines is more, it will slow down the sinter
process,consumption of coke increases and generation of sinter
return increases.
• If over size fraction in flux is more, it will not assimilate with
sinter and remains in sinter as free lime.It will react with
moisture of air and sinter will break causing generation of sinter
return. [ CaO + H2O = Ca(OH)2 + Heat ]
• If over size fraction in coke is more, the bigger particle will
segregate in lower part of the bed and will cause over sintering
and formation of stickers. Where as the coke content in upper
part will be less and sintering will not be proper.It will, increase
sinter return generation.

4. 4
WHAT IS SINTER
Sintering is a process of agglomeration of fine mineral particles
into compact porous and lumpy mass by incipient fusion caused
by heat produced during the combustion of solid fuel within the
green mix itself.
THE NEED FOR SINTERING
(i) IOF , Metallurgical Waste , Coke breeze , Lime dust and
dolomite are used
(ii)Better reducibility and other high temperature properties
(iii) The need for charging prepared burden in Blast Furnaces
to increase productivity and lower fuel rate.
iv) Better quality of hot metal

5. 5
WHAT IS AGGLOMERATION
Agglomeration is defined as the process to convert fines materials into
lumpy mass
The process of agglomeration can be classified as follows:
i) Briquetting.
ii) Nodulising.
iii) Sintering
v) Pelletizing.
Ability to use all kinds of Raw Materials- like iron ore fines, iron bearing
waste products, flue dust, LD Slag.
It can be produced into any shapes and sizes.
It can be cured to adequate strength suiting Blast Furnace needs.
Process designed to suitable small batch operations and large scale
operations.
Excellent blast Furnace charge material in place of lump ore, reduces the
cost of smelting of ore, increases Furnace permeability there by increasing
BF productivity and lowering cost in terms of lower fuel rate.
Advantages of agglomeration

6. 6
ADVANTAGE OF SINTER
• i) Agglomeration of fines into hard, strong and irregular porous lumps
which gives better bed permeability.
•
ii) Elimination of 60 - 70 % of sulphur and Arsenic (if present) during
sintering.
• iii) Elimination of moisture, hydrated water and other volatiles on the
sinter strand with a cheaper fuel.
• iv) Increased the softening temperature and narrowing down of the
softening range.
• v) As the addition of flux takes place in sinter strand, super-fluxing
saves much more coke in the furnace.
• vi) It increases the Blast Furnace productivity.
•
vii) Lime rich bosh slag hinders reduction of silica, absorbs vaporized
silicon and sulphur to produce low- Si, low-S hot metal

7. 7
TYPES OF SINTER
• Depending upon weather bases have been incorporated in the Sinter mix,
sinters are divided into three broad classes: -
(i) Non Fluxed OR ACID SINTERS: - Those where no flux is present or is
added in the ore.
• (ii) BASIC SINTER OR Self Fluxing SINTER: - Those where sufficient
flux has been added in the sinter mix to provide a basicity that is desired
in the final slag, taking into consideration only the burden acids. An extra
flux is added to the BF burden, to take care of coke ash acids.
(iii) SUPER BASIC OR SUPER FLUXED SINTER: - In these type of
sinters an additional flux is added to the mix to provide for the desired
final slag basicity, taking into account the acids content of both ore as well
as the coke ash.

8. 8
GENERAL ARRANGEMENT OF
A SINTER PLANT
• Raw material receiving
• Stock bin proportioning
system
• Mixing and Nodulizing-
moisture addition
• Charging Station-laying of
Green mix on the strand
• Ignition
• Sintering Process
• Sinter Discharging and Hot
Sinter breaking
• Hot screen
• Cooling of sinter in Sinter
Cooler
• Cold screen
• Conveying to BF stock-house
• Dust treatment and Waste
Gas system with Waste Gas
Fan and De-dusting Fan

9. 9
RAW MIX
SRC
D/C
D/F C/S
SHAKER GATE
RAW MIX BUNKERS
ELECTRONIC FEEDERS
BALLING DRUMS
SHUTTLE DISTRIBUTOR
FURNACE
CHARGE HOPPER
DRUM
FEEDER
SINTER MACHINE
WIND BOXES
1 2 25 26
MAIN GAS COLLECTOR
TO EXH.
TO EXH.
DUST
POCKETS
(36Nos.)
ST. LINE COOLER
COOLER BLOWERS
WATER
DRUM
COOLER
-5mm
+5mm
+8mm TO BF
-8mm
TO STOCK BINS
-5mm TO STOCK BINS (HOT SINTER RETURN)
SINGLE ROLL CRUSHER
HOT SCREEN
COLD SCREEN
DISC FEEDER
SINTER MACHINE PROCESS FLOW
WATERWATER
H/S
RAW MIX

10. 10
SCHEMATIC DISTRIBUTION OF THE ZONES IN CHARGE DURING SINTERING
ON THE SINTER STRAND
ZONE OF SINTERING
ZONE OF COMBUSTIONZONE OF CHARGE
ZONE OF DRYING
ZONE OF
CONDENSATION
OF MOISTURE

11. 111
Flux Screen
+3mm
Stock Bin &
proportioning
section
-3mm
Coke breeze
from C O
PMD
Fuel Storage Coke crusher
-3mm
Sinter
M/c
Hot
screen SLC
Cold
screen
Sinter
to BF
-8mm
-5mm
-5mmHot Sinter return
Cold Sinter return
Cold Sinter return
-25 mm
Coke
from BF Nut Coke ( 15 -25 mm)screen
-15mm
Waste Bin Mill scale from SMS, HSM, Slabbing Mill
Flue Dust from BF
Sintering Plant
Material Flow Diagram
Hammer
Crusher
LD Slag, from SMS
Lime Dust from RMP
Iron Ore Fines from RMHP
-80 mm ( Limestone + Dolomite )
Crushed Flux

12. 12
RAW MATERIALS USED FOR SINTERING
1. Iron ore fines
2. Flux ( lime stone & dolomite )
3. Coke breeze
4. Waste Materials:
a). Flue dust ( From Blast Furnace but added in RMHP )
b). Mill scale ( From Slabbing Mill, H.S.M.&CCS)
c). L.D.Slag (From S.M.S.)
d). Lime dust ( From R.M.P.)
5. Sinter return ( Own generation )

13. 13
COKE CRUSHING BY FOUR ROLL CRUSHERS
( 08 Nos. CAPACITY – 16 T/Hr. EACH )
MIX COKE FROM C.O. COKE RETURN FROM B.F.
( - 15mm ) ( - 25mm )
+ 15 mm TO B.F.
MIXED WITH SINTER
-15 mm TO FUEL
STORAGE
- 15 mm
- 3 mm
-3 mm TO STOCK BINS
6 mm
2 mm
(NUT COKE SCREEN)

14. 14
FLUX CRUSHING BY HAMMER CRUSHER
( 05 Nos. CAPACITY- 250T/Hr. EACH )
+ 25mm
FLUX FROM RMHP ( + 25 mm )
HAMMER CRUSHER
(36 Hammers in each Crs.
in two rows. )
+3mm
- 3mm TO STOCK BINS
FLUX SCREEN (10 Nos. ) CAPACITY 150T/Hr.EACH
TOH/Crs
MOTOR

15. 15
STOCK BINS AND PROPORTIONING SECTION
A. TO STOCK RAW MATERIALS :
There are three similar series of over head bunker and
conveyors to feed three sinter machines at a time. Each series
contains 23 bunkers . Materials are stored in the bunkers in
following order :
BUNKER No. TOTAL BUNKER MATERIAL
1 – 6 06 Iron ore fines
7 – 13 07 Crushed flux ( - 3 mm )
14 – 17 04 Crushed coke ( - 3 mm )
18 01 Waste materials
19 – 20 02 Cold sinter return
21 01 Hot sinter return
22 – 23 02 Lime dust

16. 16
B. FIXING OF FEED RATE :
For sending raw mix to sinter machine for sintering, fixation of
feed rate of materials is done considering capacity of the sinter
machine and quality requirement of blast furnace.
Feed rate fixed is :
Iron ore fines 250 T/hr.
Flux 75 T/hr.
( Feeding of Flux depends on available lime in sinter required
in blast furnace.Available lime means CaO – SiO2 in sinter.)
Coke 20 T/hr.
Waste materials 20 T/hr.
Sinter return 60 T/hr.
Lime dust 02 T/hr.

17. 17
PROPORTIONING OF CHARGE
P. M. D.
ELECTRONIC
CONVEYOR SCALES
ELECTRONIC
FEEDER
VIBRO FEEDER
O/F FLUX COKE W/M S/R L/D
A –1
CONV.
TO
S/M -1
A –3
CONV.
TO
S/M -2
A –5
CONV.
TO
S/M -3
PRIMARY
MIXING
DRUM

18. 18
Sinter Machine Specification for each machine
There are three Sintering machines
Length - 78 M
No. of pallets - 130
Sintering area – 252M2
Bed height - 480mm
Exhauster - 02 Nos.
Aspirator - 02 Nos.
Cooler – Blower- 06 Nos.
Balling Drum - 02 Nos.
Drum Cooler - 01 No.
Straight line Cooler - 01 No.

19. 19
TYPES OF SINTER MAKING
PROCESS
• Huntington and
Heberlein Pot Process-
fpr non-Ferrous metal
Industry.
• Batch Sintering-
Greenwalt Single Pan
Process
• Allmanns Ingenoirs
Bryans Multi Pan
Process
• Dwight-Lloyd
Continuous Sintering
Process
• Pelletizing Process- This
consists of sub –
operations like
preparation of ore feed,
balling, hardening. Shaft
furnaces are used for
producing small
tonnages. Multiple
Shafts handle larger
production level.

20. 20
PRINCIPLE OF THE SINTER
MAKING PROCESS
• Iron one sintering is carried out by putting GREEN MIX after Mixing and Nodulizing drum (a
mixture of Base mode with iron ore fines, mixed with flux, coke breeze as a solid fuel, other
additions, sinter return fines, lime, moisture) over a traveling gate in form of permeable bed
and permeable bed.
• The top layer of this sinter bed is heated to the sintering temp. (1200C-1300C) inside a
Ignition Hood furnace. In the ignition hood the air is drawn downwards, through the grate
with the help of exhaust blowers (Waste Gas Fan) connected by means of Waste gas main.
• The narrow combustion zone developed initially at the top layer by layer to the sintering level.
The cold blast drawn through the bed cools the already sintered layer the thereby gets itself
heated. The heat contained in the blast is utilized in drying and preheating the lower layers in
the bed. In advance of combustion therefore each layer gets dried and preheated by the heat
transferred from the upper combustion zones. The lower portion of the bed absorbs much of
the heat in the gases.
• In the combustion zone, bonding takes place between the grains and a strong and porous
aggregate is formed. The process is over when the combustion zone has reached the lowest
layer of the bed. The sinter cake is thus tipped from the grate in hot condition . It is then
broken, cooled in sinter cooler cold sized and sent to the Blast furnace.

21. 21
MECHANISM OF SINTERING
2Fe2O3.CaO + Al2O3.SiO2 2Fe2O3 CaO.Al2O3.SiO2
(SFCA)
SILICO FERRITE OF CALCIUM
AND ALUMINIUM
2Fe2O3
SLAG BOND
2Fe2O3
2Fe2O3
Heating Cooling
Single
lump
Heating
2Fe2O3
2Fe2O3
+ CaO 2Fe2O3CaO at 12000
C
CALCIUM FERRITE

22. 22

23. 23
EQUIPMENTS IN SINTER
PLANTS
• RAW MATERIAL BINS
AND WEIGH FEEDERS
• MIXING AND BALLING
DRUM WITH WATER
INJECTION SYSTEM
• IGNITION HOOD
FURNACE WITH
BURNERS
• SINTER MACHINE-
PALLETS with GRATE
BARS
• WINDBOXES WITH
WASTE GAS MAIN
• SPIKE CRUSHER-SINGLE
ROLL CRUSHER
• VIBRATORY COLD
SCREEN FOR HEARTH
LAYER
• VIBRATORY SCREEN FOR
RETURN FINES
• CONVEYORS, RECEIVING
CHUTES AND TRANSFER
CHUTES FOR RAW
MATERIAL AND SINTER
• DEDUSTING FAN FOR
PLANT DEDUSTING
• ESPs
• LT and HT DRIVES

24. 24
PROGRESS OF SINTERING
COMBUSTION JONE
GREEN MIX
SINTER
SUCTION MAIN
WASTE GAS FAN
WIND BOX

25. 25
BED
HEIGHT
LEVEL SENSOR
FLAP
GATES
IGNITION
HOOD
FEED ROLL
HEARTH LAYER
GREEN-MIX
BIN
GREEN MIX
SHUTTLE CONVEYOR
THERMO-VISION
CAMERA
PROBES
FEDDING SYSTEM
HEAT TREAT
MENT HOOD
HEARTH
LAYER
BIN
CUT-OFFCUT-OFF
PLATEPLATE

26. 26
QUALITY ASPECT OF SINTER-
WITH RESPECT TO BLAST
FURNACES PERFORMANCE
• CHEMICAL
1. Fe% in Sinter
2. CaO % in Sinter
3. SiO2 % in Sinter
4. MgO% in Sinter
5. Al2O3 % in Sinter
6. FeO % in Sinter
7. K2O % in Sinter
• PHYSICAL
1. SINTER SIZE
ANALYSIS –in terms of
Cum+10mm and -5mm
2. TUMBLER INDEX
3. SHATTER INDEX
4. RDI (Reducibility
Degradation Index)
5. RI (Reducibility Index)
6. Softening and Melting
Test (S-M)

27. 27
FACTORS AFFECTING SINTER QUALITY
• (1) Size of The Charge Mix: The strength of sinter is directly related to the size
distribution of the charge mix. If size is large, the contact area will be less and the
strength of the sinter will be low and conversely if size is too small the contact area of
particles will be large and the strength will be high.
Ideal size of ore Fines -10 mm to + 100 mesh
Coke breeze -3.2 mm 85%
Flux - - 3.2 mm 85%
(2) Fuel content: - Variation in Fuel content in Charge Mix affect the peak Temperature
attained during sintering, the combustion zone will not be uniform leading to poor bed
permeability, This increases return fines generation
•
(3) Moisture: - The presence of moisture in the Charge mix has several advantages. It
maintains proper permeability in the bed during sintering. This is beneficial from the
point of view of heat transfer during sintering.
• (4) Re-circulating load or Return fines addition: - For higher output of the sinter strand
the circulating load should be low. A low circulating load however, reduces the
permeability of the bed. An optimum-circulating load is established for maximum output
of the acceptable sinter to the Blast Furnaces.

28. 28
Parameters Controlling Sintering
Process
• Fuel content for heat input
• Ignition intensity-
Temperature of Ignition
Hood Furnace
• Moisture content of mix to
control its permeability.
• Machine speed control to
obtain complete Burn
through
• Return Fines Addition
• Waste Gas Temperature
• Sintering Temperature or
Burn through Temperature
• Pressure drop across the
Sinter Bed- Main Suction
• Bed Height
• Calcined Lime addition- to
improve bed Permeability.

29. 29
INTENSIFICATION OF SINTERING
PROCESS
Sinter as a prepared burden material
continues to hold its prominent position in
world due to its very good metallurgical
properties such as tumbling strength,
reduction degradation index, reducibility
index, high softening temperature and low
range of softening range

30. 30
PRINCIPAL STEPS OF IRON ORE SINTERING TECHNOLOGY
TThe iron ore fines , lime stone fines, dolomite fines, lime dust,
metallurgical wastes and coke breeze are proportioned based on
charge calculations.
TThen this mix is mixed and balled in mixing and balling drums with
the addition of water and then loaded onto the pallet.
TThe sinter mix undergoes ignition as well as suction is applied under
the bed.
TThe top layer gets ignited and sintering proceeds down wards till the
end .
TThe hot sinter is screened and crushed.

31. 31
PRINCIPAL STEPS OF IRON ORE SINTERING TECHNOLOGY
TThe hot sinter is then cooled on a cooler
TThe cooled sinter is screened to remove -5mm fraction and then
transported to blast furnace.

32. 32
Need of Intensification of sintering
process
Why?
Intensification of sintering process is required
to enhance the production capacity of existing
sinter machines.
How?
Without sacrificing the quality aspects.

33. 33
What is meant by intensification?
• Accelerating sintering process for achieving higher
production without deterioration in quality.
• Production = k*A*B*V*Y
k = Constant
A = Sintering Area
B = Bulk Density of mix
V = Vertical sintering speed
Y = Yield

34. 34
Methodology of Intensification of
sintering process
Factors that influence sintering
1) MEN
2) MATERIALS
3) PROCESS PARAMETERS.

35. 35
.
•The granulometry of iron ore fines, used in
sintering, has a great influence on sinter plant
performance.
•Laboratory Experiments were conducted with
different granulometry of iron ore fines to assess its
influence on sinter quality and productivity.
•The upper size of the iron ore fines was reduced in
each of the experiments.
GRANULOMETRY OF IRON ORE FINES

36. 36
EFFECT OF IRON ORE FINES SIZE ON
SINTERING
Sl.No Size Lime %yield VSS Prod. T.I
(mm) (Kg/t) (+5mm) mm/min t/m2
/h %
1 0-15 0.0 70.6 18.6 1.182 69.3
2 0-8 0.0 76.5 19.6 1.272 68.3
3 0-8 20.0 75.6 20.1 1.326 67.2
4 0-6 20.0 80.3 20.3 1.418 67.3
5 0-5 20.0 81.0 21.6 1.489 66.7

37. 37
Chemical Quality
EFFECT OF TOTAL Fe
• Results show that lower Fe grade (< 62% Fe) ores and
concentrates will typically form SFCA (SiO2-Fe2O3-
CaO-Al2O3) as part of the final assemblage.
• Medium grade (62-65% Fe) ores will form a mixture of
SFCA and SFCA-1..
•High grade (65-68% Fe) ores will form largely SFCA-1.
• The SFCA-1 phase is the most desirable bonding phase in
iron ore sinter, since microstructures composed entirely of
SFCA-1 show higher physical strength and higher
reducibility than microstructures composed predominantly
of SFCA

38. 38
LOSS ON IGNITION
The higher LOI of iron ore fines has a detrimental
effect on sinter quality and productivity
EFFECT OF Al2O3
An increase in Al2O3 % by 1 % increases the RDI
value by 10%
EFFECT OF SiO2
Higher SiO2 in sinter will induce the formation of
glassy phases in sinter and reduce the strength of
sinter.

39. 39
COKE BREEZE SIZE
•The required coke breeze granulometry for
efficient sintering is:
+5 mm < 5 %
- 3 mm = 85-90 %
-0.5 mm < 15 %
•Presence of higher % of +5 mm slows down the
coke breeze burning rate and thus reducing
sintering rate.
• For reducing the micro-fines generation during
crushing, -3 mm should be screened out before
the crusher.

40. 40
CALCINED LIME
•Calcined lime is one of the best intensifier of
sintering process
•Preheats the sinter mix
•Enhances balling phenomena
•Replaces raw lime stone
•Calcined lime addition @ 20kg/t was found to be
optimum for SAIL sinter plants.

41. 41
PROCESS PARAMETERS
•Mixing and Balling
•Segregation of mix
•Moisture
•Ignition
•Under-grate Suction
•Preheating of sinter mix
•Use of hot air in ignition hood
•cooling

42. 42
MIXING AND BALLING REGIMES
•Generally most of the sinter plants are provided
with separate mixing and balling drums. But the
latest generation of sinter plants are provided with
a combined mixing and balling drums.
•The main purpose of mixing drum is to
homogenize the sinter mix . The diameter of the
drum , the RPM and the space factor play a major
role in achieving higher degree of mixing.

43. 43
•The balling drum (Nodulising drum) ensures that
fines are coated on the nuclei particles, thus
produce higher size balls. This facilitates in
improving the mean size of sinter mix and hence
the permeability of mix. Here again the diameter ,
RPM and space factor play a major role in
achieving higher degree of balling.
•Very little water is added in mixing drum and
major quantity of water is added in the balling
drum
•The amount of water added and the method of
water addition in the balling drum also control the
degree of balling and hence the permeability of
sinter mix.

44. 44
•
A
Laboratory model of high speed agitating mixer
Lab study at RDCIS showed improvement of strength
index with reference to conventional mixer

45. 45
MOISTURE
•As is known, faster the rate of air flow through
the bed faster is the rate of sintering.
•The rate of flow of the air through the bed is
controlled by the vacuum under the bed and the
permeability of the bed.

46. 46
SUCTION UNDER-GRATE
•The rate of flow of the air through the bed is
controlled by the vacuum under the bed and the
permeability of the bed.
•The optimization of the gas dynamics parameters of
the sinter machines enables one to achieve higher
under grate suction and thus substantial
improvements in the techno-economic parameters of
the sinter production.

47. 47
IMPROVING IN SM PRODUCTVITY PER 10 mmwc AS
A FUNCTION OF SUCTION UNDER GRATE
500 600 700 800 900 1000 110 1200 1300 1400 1500
1.2
1.0
0.8
0.6
0.4
SUCTION, mmwc
IN
C
R
E
A
SI
N
G
IN
P
R
O
D
U
C
TI
VI
T
Y,
%

48. 48
IGNITION
•To provide the required free oxygen potential in the
zones for faster burning of the fuel and also early
starting of sintering.
•Oxygen enrichment in ignition hood
•To produce a strong sinter in the upper part of the
layer;

49. 49
PRE-HEATING OF SINTER MIX
•Pre-heating of sinter mix helps in reducing the ill effects
of Re-condensation of moisture
•Pre-heating of sinter mix can be done by:
* Addition of hot water in balling drum
* Addition of steam in balling drum or raw mix hopper
* Installing gas burners inside the balling drum
* Adding hot return fines
* Addition of calcined lime

50. 50
HOT AIR IN IGNITION HOOD
• Hot air recovered from sinter cooler could be used in
the ignition hood.
•This will help in not only saving gaseous fuel, but also
increases the free oxygen potential.

51. 51
COOLING OF SINTER
•Efficient cooling of sinter will help in improving sinter
strength
•Installation of proper waste heat recovery system of
cooler will help in adding hot air in ignition hood

52. 52
Rate
Size
BTP
Temp
Sinter Quality
Temp
Free O2
Potential
Top layer
Starting of
sintering
Productivity
Rate
Method of
Addition
Balling
Permeability
Re-condensation
Under
Ignition hood
Rest of
machine
Coke
Water
Under grate
suction
Ignition

53. 53
RECENT TRENDS OF INTENSIFICATION OF
SINTERING
• High Fe, low Al2O3 iron ore fines
• Serpentine replacing dolomite
• Good quality and quantity of lime addition
• High Intensity mixer
• Divided coke addition
• Polymer addition in balling drum
• Pre-heating of sinter mix
• New sinter mix charging system
• New ignition furnaces
• Taller bed operation
• Higher under grate suction
• Taller bed circular coolers
• Process control models

54. 54