FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
1 TITLE OF THE INVENTION :
A METHOD FOR PRODUCING IRON ORE PELLET WITH IMPROVED QUALITY AND INCREASED PRODUCTION AND A SYSTEM THEREOF.
2 APPLICANT (S)
Name : JSW STEEL LIMITED.
Nationality : An Indian Company.
Address : 3indal Mansion, 5-A, Dr. G. Deshmukh Marg, Mumbai - 400 026,
State of Maharastra, India.
3 PREAMBLE TO THE DESCRIPTION
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to a method for producing iron ore pellets of improved quality. More particularly, the present invention is directed to a method for producing iron ore pellets with improvement in productivity and quality by optimizing the induration machine firing temperature and damper opening of process fans at higher pellet bed height and a system thereof.
BACKGROUND OF THE INVENTION
It is well known in the art of iron and steel making that iron ore fines are converted to pellets for feeding as charge to the iron making furnaces. The applicants' steel plant is operating two pellet plants, each having 4.2 Mtpa rated capacity to feed four Blast furnaces and two Corex units. Pellets are agglomerate of iron ore, formed on heating to temperatures in the range of 1250 to 1300°C. Conventional method of production of iron oxide pellets from iron ore fines involves different steps from drying to induration. The ore fines are initially dried to a moisture content of less than 1% before being sent to a ball mill for grinding to the required fineness. The ground ore fines are now mixed with other additives like bentonite, limestone, carbon bearing sludge and iron ore slurry and then sent to balling discs to prepare green pellets/balls. These green pellets are fired in the indurating machine to get the required physical, mechanical and metallurgical properties, making them suitable feed material to iron making units. In the indurating machine, the traveling grate carries the pellets through the indurating furnace where they are subjected to the sequential zones of updraft drying, downdraft drying, preheating and firing followed by first and second stage of cooling.
To fulfill the demand of iron making units, production capacity of the pellet plant-1 induration machine was increased from 4.2 Mtpa to 5.0 Mtpa by increasing the pellet bed height from 450 mm to 550 mm, induration machine speed from 2.00 to 2.30 m/min, and process fan air flow rate by increasing motor power. To get the optimum drying, firing and cooling of the pellets in the induration machine, control flow of gas, pressure and temperature is essential. The airflows will be controlled during normal furnace operation by means of variable position dampers located at the process fan

inlets. Temperature and pressure will be the primary elements used to control these damper positions.
The optimum firing temperature is more important to get good quality pellets. If the windbox temperature is too low there will be an unfired zone at the bottom of the pellet bed. This results in poor product quality and generation of more dust. If the temperature is too high, pallets and grate bars will get overheated.
To get the good quality of pellets at higher bed height it was found necessary to optimize the pellet induration machine firing temperature and controlling damper opening of process fans.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to a method for production of iron ore pellets with improved production rate and quality by optimizing the induration machine firing temperature and damper opening of process fans at higher pellet bed height.
A further object of the present invention is directed to a method for production of iron ore pellets with improved production rate and quality wherein Pellet induration machine is equipped with 5 process fans e.g. Hood exhaust fan (HEF), Wind box exhaust fan (WBE), Wind box recuperation fan (WBR), Updraught drying fan (UDD), and Cooling air fan (CA) to control the airflow rate and temperature with in the induration machine.
A still further object of the present invention is directed to a method for production of iron ore pellets with improved production rate and quality wherein interconnected process fans in the induration machine are provided to circulate air throughout the different zones of the indurating machine in controlled manner.
A still further object of the present invention is directed to a method for production of iron ore pellets with improved production rate and quality wherein airflow within the induration machine will be controlled by variable position dampers located in the duct work or at the process fan inlets.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a method for producing iron ore pellet with improved quality and increased production comprising:
Subjecting the travelling grate carrying the green pellets through induration
furnace sequentially for
(i) updraft drying in a updraft drying zone to prevent the condensation of the water and pellet deformation ,
(ii) downdraft drying in a downdraft drying zone to remove free water of the top of the bed , said updraft drying and downward drying carried out involving drying air of sufficient temperature such as to cause rapid water evaporation not so high that the pellets are destroyed by high internal pressure ;
(iii) preheating said pellets in the preheating zone to about 500 to 1000°C;
(iv) firing the pellet charge further in the firing stage raisng the temperature followed by
(v) cooling,
wherein a plurality of interconnected process fans are operated to circulate air throughout the different zones of the indurating machine with variable position dampers located in the duct work or at the process fan inlets to control the airflow rate and temperature within the induaration machine and
controlling respective damper opening positions of process fans to maintain the firing temperature in the range of 1280-1320°C, Preferably 1300 °C for controlled duration to obtain the indurated pellets of required physical, mechanical and metallurgical properties, making them suitable feed material to iron making units.
A further aspect of the present invention is directed to a method for producing iron
ore pellet, wherein said interconnected process fans to control airflow rate at
different zones of the indurating machines involved comprise
a Hood exhaust fan (HEF);
a Wind box exhaust fan (WBE);

a Wind box recuperation fan (WBR); a Updraught drying fan (UDD); a Cooling air fan (CA).
A still further aspect of the present invention is directed to a method for producing iron ore pellet, wherein the variable positions dampers for the process fans having damper openings to control the airflow rate within the induration machine to maintain the desired optimized firing temperature comprise
Hood exhaust fan (HEF): 72 - 76%; Updraught drying fan (UDD): 66 - 68%; Wind box exhaust fan (WBE): 76 - 90%; Wind box recuperation fan (WBR): 90 - 94%; Cooling air fan (CA): 75-86%.
Yet another aspect of the present invention is directed to a method for producing iron ore pellet, wherein the induration machine speed is maintained in the range of 2.20 to 2.30m/min.
A further aspect of the present invention is directed to said method for producing iron ore pellet, which is adapted to ensure a production rate of 10085-10710 t/day and a productivity of 22.5 to 24.0%.
A still further aspect of the present invention is directed to said method for producing
iron ore pellet which is adapted to ensure properties of finished pellets comprising:
CCS: 221 -231 kg/pellet
RDI (-6.3mm): 9.8 - 10.2%
RDI (-0.5mm): 6.18 - 6.70%
T.I (+6.3mm): 94.7 - 95.0%
T.I (-0.5mm): 3.88 - 4.45%
A further aspect of the present invention is directed to a system adapted for carrying out the method of producing iron ore pellet with improved quality and increased production as described above comprise:

a travelling grate carrying the green pellets through induration furnace comprising (a) updraft drying zone to prevent the condensation of the water and pellet deformation , (b) downdraft drying zone to remove free water of the top of the bed , (c ) preheating zone (d) firing stage and (e) cooling stage.
a plurality of interconnected process control fans provided to circulate air throughout the different zones of the indurating machine with variable position dampers located in the duct work or at the process fan inlets to control the airflow rate and temperature within the induration machine and means for controlling respective damper opening positions of process fans to maintain the firing temperature in the range of 1280-1320°C, preferably 1300 °C for controlled duration to obtain the indurated pellets of required physical, mechanical and metallurgical properties, making them suitable feed material to iron making units.
Yet another aspect of the present invention is directed to said system which comprises five interconnected process control fans to control the airflow rate and temperature with in the induration machine comprising:
1) Hood exhaust fan (HEF)
2) Wind box exhaust fan (WBE)
3) Wind box recuperation fan (WBR)
4) Updraught drying fan (UDD)
5) Cooling air fan (CA)
According to a further aspect of the present invention directed to said system wherein said five interconnected process fans in the induration machine are provided to circulate air throughout the different zones of the indurating machine such that after firing, the fired pellets undergo cooling where ambient air is drawn upward through the bed, the off-gas leaving the first stage of cooling has a temperature of around 1000 °C and this gas is directed to the firing and preheating zones where it is further heated by the burners involving preferably Corex gas, the gas from the final cooling stage is of lower temperature and is used for drying of pellets, from the preheating, firing and after firing zones, the process gas is diverted

to either the wind box recuperating duct or to the wind box exhaust duct after passing through the pellet bed.
A still further aspect of the present invention is directed to said system wherein the airflow within the induration machine is controlled by means of variable position dampers located in the duct work or at the process fan inlets.
The various objects and advantages of the present invention is described in greater details with reference to the following accompanying non limiting illustrative drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows the schematic diagram of iron ore peptization process.
Figure 2: shows the schematic diagram of straight grate induration process for iron ore pellets.
Figure 3: shows the schematic diagram of flow path of process gas flow involving five interconnected process fans in the induration machine.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS.
The present invention relates to a method for production of iron ore pellets with improved production rate and quality by optimizing the induration machine firing temperature and damper opening of process fans at higher pellet bed height.
Reference is first invited to the accompanying Figure 1 that shows the schematic diagram of the iron ore pelletization process, In this process iron oxide pellets are produced from iron ore fines involving different steps from drying to induration. The ore fines are initially dried to a moisture content of less than 1% before being sent to a bail mill for grinding to the required fineness. The ground ore fines are now mixed with other additives like bentonite, limestone, carbon bearing sludge and iron ore slurry and then sent to balling discs to prepare green pellets/balls. These green

pellets are fired in the indurating machine to get the required physical, mechanical and metallurgical properties, making them suitable feed material to iron making units.
Reference is next invited to accompanying Figure 2 that shows the schematic diagram of straight grate induration process for iron ore pellets.
The green pellets, after sizing through a roller conveyor, are discharged onto the travelling grate induration machine on top of the hearth layer and between the side layers of the fired pellets. The hearth layer pellets protect the grate bars from high gas temperatures. The green pellets contain 8 to 9% free moisture and are 8 to 16 mm in size. The traveling grate carries the pellets through the indurating furnace where they are subjected to the sequential zones of updraft drying, downdraft drying, preheating and firing, after firing followed by first and second stage of cooling. The first stage of drying is updraft to prevent the condensation of the water and pellet deformation in the bottom layer of the pellet bed. For updraft drying the hot gas is recycled from the cooling zone 2. The drying is continued in a subsequent downdraft stage to remove free water of the top of the bed by relatively hot gases coming from the firing zone of the furnace. In these two zones it is necessary to use drying air of sufficient temperature to cause rapid water evaporation yet not so high that the pellets are destroyed by high internal pressures. In the preheating zone, the pellets are heated to about 500 to 1000 °C by downdraft air flowing through the bed and the hot gas is recycled from the cooling zone 1. During this stage, pellets are completely dried and reactions such as removal of combined moisture, decomposition of carbonates, coke combustion and conversion of iron oxide to hematite take place.
The reactions from the preheating zone continue in the firing stage. Here pellet charge is heated to an optimum temperature for a controlled period, and temperature is raised to 1250 to 1300°C. Strength of the pellets increases at this stage because of re-crystallization and formation of slag phase. Some of the off-gas from the firing zone is recuperated to the drying zone.
To enhance the production rate and improving the quality of the dried and indurated pellets fit for use in iron making furnace, production capacity of the pellet plant induration machine has been increased from 4.2 Mtpa to 5.0 Mtpa by increasing the

pellet bed height from 450 mm to 550 mm, induration machine speed from 2.00 to 2.30 m/min, and process fan air flow rate by increasing motor power. To get the optimum drying, firing and cooling of the pellets in the induration machine, control flow of gas, pressure and temperature is essential. The airflows Is controlled during normal furnace operation by means of variable position dampers located at the process fan inlets. Temperature and pressure will be the primary elements used to control these damper positions.
In order to optimizing the induration machine firing temperature and damper opening of process fans at higher pellet bed height according to the present invention, pellet induration machine has been equipped with 5 process fans to control the airflow rate and temperature within the induration machine as follows:
1) Hood exhaust fan (HEF)
2) Wind box exhaust fan (WBE)
3) Wind box recuperation fan (WBR)
4) Updraught drying fan (UDD)
5) Cooling air fan (CA)
Reference is now invited to the accompanying Figure 3 that shows the schematic diagram of flow path of process gas flow involving five interconnected process fans in the induration machine.
The above mentioned five interconnected process fans in the induration machine are shown in the accompanying Figure 3. These fans are provided to circulate air throughout the different zones of the indurating machine. After firing, the fired pellets undergo cooling where ambient air is drawn upward through the bed. The off-gas leaving the first stage of cooling has a temperature of around 1000 °C and this gas is directed to the firing and preheating zones where it is further heated by the burners using Corex gas. The gas from the cooling stage 2 is of lower temperature and is used for drying of pellets. From the preheating, firing and after firing zones, the process gas is diverted to either the wind box recuperating duct or to the wind box exhaust duct after passing through the pellet bed. The airflow within the induration machine is controlled by variable position dampers located in the duct work or at the process fan inlets.

Before modification of induration process and up-gradation of damper opening position, process fan damper opening vis-a-vis top firing temperature attained (with Bed height 440 -460 mm and machine speed 1.90 to 2.10m/min) are as present in following Table I:
Table I:

Process fan Damper opening,
%
HEF 77
UDD 75
WBE 70
WBR 87
CA 62

Firing temperature,°C 1260
Bed height,mm 450
Machine speed,m/min 2.00
After modification of process fans damper opening top firing temperature at higher bed height with up-gradation of damper opening position and firing temperature (Bed height 540 - 550mm and machine speed 2.20 to 2.30 m/min) according to the present invention, process fan damper opening vis-a-vis top firing temperature attained are presented in accompanying Table II:
Table II :

Process fan Damper opening, %
HEF 72- 76
UDD 66 - 68
WBE 76 - 90
WBR 90-94
CA 75-86

Firing temperature, °C 1280 - 1320 °C (preferably 1300 °C)
The pellet plant data before and after modification are presented in the following Table III showing the improvement in production rate and properties of the finished iron ore pellets produced by implementing the process.

Table III

Parameters Before modification After modification
Production, t/day 8773 10085-10710
Productivity, t/m2/day 21.7 22.5-24.0
CCS, Kq/p 217 221 -231
RDI (-6.3mm), % 10.92 9.8- 10.2
RDI (-0.5mm), % 8.08 6.18 - 6.70
T.I (+6.3mm), % 93.97 94.7 - 95.0
A.I (-0.5mm), % 4.86 3.88 -4.45
It is thus possible by way of the present invention to providing a method for production of iron ore pellets with improved production rate and quality by optimizing the induration machine firing temperature and damper opening of process fans at higher pellet bed height wherein after modification of process fan damper opening the foffowing improvements have been achieved:
(i) Average Pellet plant production increased from 8773 t/day to 10477 t/day;
(ii) Pellet productivity increased from 21.7 t/m2/day to 23.62 t/m2/day;
(iii)Pellet cold crushing strength (CCS) increased from 217 to 227 kg/pellet;
(iv)Reduction degradation index (RDI) -6.3 mm decreased from 10.92 to 10.0%;
(v) Reduction degradation index (RDI) -0.5 mm decreased from 8.08 to 6.42%;
(vi)Pellet tumbler index (T.I) +6.3 mm increased from 93.97 to 94.82%;
(vii)Pellet tumbler index (T.I) -0.5 mm decreased from 4.86 to 4.18%.

We Claim:
1. A method for producing iron ore pellet with improved quality and increased production comprising:
subjecting the travelling grate carrying the green pellets through induration furnace sequentially for
(i) updraft drying in a updraft drying zone to prevent the condensation of the water and pellet deformation,
(ii) downdraft drying in a downdraft drying zone to remove free water of the top of the bed , said updraft drying and downward drying carried out involving drying air of sufficient temperature such as to cause rapid water evaporation not so high that the pellets are destroyed by high internal pressure ;
(iii) preheating said pellets in the preheating zone to about 500 to 1000°C;
(iv) firing the pellet charge further in the firing stage raising the temperature followed by
(v) cooling,
wherein a plurality of interconnected process fans are operated to circulate air throughout the different zones of the indurating machine with variable position dampers located in the duct work or at the process fan inlets to control the airflow rate and temperature within the induration machine and
controlling respective damper opening positions of process fans to maintain the firing temperature in the range of 1280-1320°C/ Preferably 1300°C for controlled duration to obtain the indurated pellets of required physical, mechanical and metallurgical properties, making them suitable feed material to iron making units.

2. A method for producing iron ore pellet as claimed in claim 1, wherein said
interconnected process fans to control airflow rate at different zones of the
indurating machines involved comprise
a Hood exhaust fan (HEF);
a Wind box exhaust fan (WBE);
a Wind box recuperation fan (WBR);
a Updraught drying fan (UDD);
a Cooling air fan (CA).
3. A method for producing iron ore pellet as claimed in anyone of claims 1 or 2,
wherein the variable positions dampers for the process fans having damper openings
to control the airflow rate within the induration machine to maintain the desired
optimized firing temperature comprise
Hood exhaust fan (HEF): 72-76%; Updraught drying fan (UDD): 66 - 68%; Wind box exhaust fan (WBE): 76 - 90%; Wind box recuperation fan (WBR): 90 - 94%; Cooling air fan (CA): 75-86%.
4. A method for producing iron ore pellet as claimed in anyone of claims 1 to 3, wherein the induration machine speed is maintained in the range of 2.20 to 2.30m/min.
5. A method for producing iron ore pellet as claimed in anyone of claims 1 to 4, which is adapted to ensure a production rate of 10085-10710 t/day and a productivity of 22.5 to 24.0%.
6. A method for producing iron ore pellet as claimed in anyone of claims 1 to 4,
which is adapted to ensure properties of finished pellets comprising:
CCS: 221 -231 kg/pellet
RDI (-6.3mm): 9.8 - 10.2%
RDI (-0.5mm): 6.18 - 6.70%
T.I(+6.3mm): 94.7 -95.0%
T.I (-0.5mm): 3.88-4.45%

7. A system adapted for carrying out the method of producing iron ore pellet with improved quality and increased production as claimed in anyone of claims 1 to 6 comprising:
a travelling grate carrying the green pellets through induration furnace comprising (a) updraft drying zone to prevent the condensation of the water and pellet deformation , (b) downdraft drying zone to remove free water of the top of the bed, (c ) preheating zone (d) firing stage and (e) cooling stage,
a plurality of interconnected process control fans provided to circulate air throughout the different zones of the indurating machine with variable position dampers located in the duct work or at the process fan inlets to control the airflow rate and temperature within the induration machine and
means for controlling respective damper opening positions of process fans to maintain the firing temperature in the range of 1280-1320°C, preferably 1300 °C for controlled duration to obtain the indurated pellets of required physical, mechanical and metallurgical properties, making them suitable feed material to iron making units.
8. A system as claimed in claim 7 comprising five interconnected process control
fans to control the airflow rate and temperature with in the induration machine
comprising:
1) Hood exhaust fan (HEF)
2) Wind box exhaust fan (WBE)
3) Wind box recuperation fan (WBR)
4) Updraught drying fan (UDD)
5) Cooling air fan (CA)
9. A system as claimed in claim 8 wherein said five interconnected process fans in
the induration machine are provided to circulate air throughout the different zones of
the indurating machine such that after firing, the fired pellets undergo cooling where
ambient air is drawn upward through the bed, the off-gas leaving the first stage of
cooling has a temperature of around 1000 °C and this gas is directed to the firing
and preheating zones where it is further heated by the burners involving preferably
Corex gas, the gas from the final cooling stage is of lower temperature and is used

for drying of pellets, from the preheating, firing and after firing zones, the process gas is diverted to either the wind box recuperating duct or to the wind box exhaust duct after passing through the pellet bed.
10. A system as claimed in claim anyone of claims 7 to 9 wherein the airflow within the induration machine is controlled by means of variable position dampers located in the duct work or at the process fan inlets.