Title of Invention

A PROCESS FOR PRODUCING HIGH STRENGTH PELLETS FROM HIGH GRADE CHROMITE CONCENTRATES.

Abstract The invention provides a process for producing high strength pellets from high grade chromite concentrates. The method comprises the steps of taking a known quantity of the chromite concentrates and mixing the chromite concentrates with optimized quantity of binders and reductants. The mixture is pellitized under required conditions and the green pellets are cured naturally for a predetermined period of time. The cured pellets are then hardened at a higher temperature in a furnace. The furnace is then cooled to room temperature.
Full Text FIELD OF APPLICATION
The present invention relates to a process for producing high strength pellets from high
grade chromite concentrates.
BACKGROUND OF THE INVENTION
The chromite ore is an indispensable raw material for iron-chromium alloy making. This in
turn is used for producing alloy steels. Naturally occurring Indian chromite ores are mostly
powdery in nature. On beneficiation of available low grade ores, also results finer size
(-1 mm) concentrates. As such these fines cannot be used in conventional AC furnaces.
A need therefore, existed for agglomeration (pelletization bricketing and sintering) of these
fines for use in iron-chromium alloy making in a conventional submerged arc furnace
(SAF).
A technology was developed by Outokumpu and commercially practised with all South
Africa ores for producing pellets after grinding to fine sizes and making pellets with
necessary binders and sintering (heat hardening).
However, with Indian chromite fines having more than 2.8 Cr/Fe, this technology could not
be applied 'as it is'. This is mainly because of high refractory nature of Indian chromite
ores.
SUMMARY OF THE INVENTION
The main object of the present invention therefore is to agglomerate high grade Indian
chromite concentrates for the production of high strength pellets similar to South African
sintered pellets under Outokumpu Technology (250 kg / pellet).
Another object of the present invention is to produce water-resistant and thermally
stable pellets for use in submerged electric arc furnace conditions.
These objects are achieved by using higher sintering temperature, additional reductants
and different binders.
According to the present invention the materials used for producing high strength pellets
from high grade chromite concentrates are
high grade chromite concentrate and fines with
Cr/Fe : 3.1
Cr2O3 : +52 %
Particle size : Below 0.5 mm with an average particle size of 100
microns is ground to below 0.15 mm (with 80 % below
0.075 mm fraction)
Moisture : 10 %
Binder : Naturally occurring inorganic compounds
Coke breeze : ~ 3 %
Thus the present invention provides a process for producing high strength pellets from
high grade chromite concentrates, comprising the steps of: taking a known quantity of
the chromite concentrates; mixing the chromite concentrates with two different naturally
occurring inorganic minerals as binders, wherein the quantity of binder 1 in the form of
alkali dipped clay is 1.5 % by weight and quantity of binder 2 in the form of a calcium
salt is 4.0 to 5.0 % by weight; pelletizing the mixture under required conditions; curing
the green pellets naturally for a predetermined period of time; heat hardening the cured
pellets at a higher temperature in a furnace; and cooling the furnace to room
temperature.
The process of the present invention will now be described.
A known quantity and quality of high grade chromite concentrates is taken and mixed with
optimized quantity of binders. From this mixture pellets are prepared using pelletizing disc
under required conditions to produce 15-30 mm size pellets. These pellets are naturally
cured for about 24 hours. After this, these pellets are heat hardened by introducing these
naturally cured pellets in a furnace. The hardening can be carried out at a temperature of
1250 degree C and for about an hour in a reducing atmosphere. The furnace is then
cooled to room temperature.
The process conditions are as follows:
Binder 1 (Inorganic mineral) quantity, % : 1.5
Binder 2 (Inorganic mineral) quantity, % : 4.0-5.0
Coke quantity, % : 3.0-3.5
Green pellets curing time, hrs : 24
Heat hardening temperature, °C : 1250 °C
Atmosphere : Reducing
Under the above process conditions it is possible to produce pellets with high compressive
strength (> 250 kg/pellet), water resistant, and thermally stable properties.
These pellets can be used as 80 -100 % feed in a submerged electric arc furnace.
WE CLAIM
1. A process for producing high strength pellets from high grade chromite
concentrates, comprising the steps of:
taking a known quantity of the chromite concentrates;
mixing the chromite concentrates with two different
naturally occurring inorganic minerals as binders, wherein
the quantity of binder 1 in the form of alkali dipped clay is
1.5 % by weight and quantity of binder 2 in the form of a
calcium salt is 4.0 to 5.0 % by weight;
pelletizing the mixture under required conditions;
curing the green pellets naturally for a predetermined
period of time;
heat hardening the cured pellets at a higher temperature
in a furnace; and
cooling the furnace to room temperature.
2. The process as claimed in claim 1, wherein the palletizing step is carried
out in a palletizing disc.
3. The process as claimed in claim 1, wherein the green pellets are naturally
cured for a period of 24 hours.
4. The process as claimed in claim 1, wherein the heat hardening of the
cured pellets is carried out in a furnace at a temperature of 1250° C.
5. The process as claimed in claim 6, wherein the heat hardening is carried
out for an hour.
6. The process as claimed in claim 6, wherein the heat hardening is carried
out in a reducing atmosphere.
7. The process as claimed in claim 1, wherein the size of the pellets is 15 -
30 mm.
8. A process for producing high strength pellets from high grade chromite
concentrates, substantially as herein described.
The invention provides a process for producing high strength pellets from high
grade chromite concentrates. The method comprises the steps of taking a
known quantity of the chromite concentrates and mixing the chromite
concentrates with optimized quantity of binders and reductants. The mixture is
pellitized under required conditions and the green pellets are cured naturally for
a predetermined period of time. The cured pellets are then hardened at a higher
temperature in a furnace. The furnace is then cooled to room temperature.

Documents:

583-kol-2004-granted-abstract.pdf

583-kol-2004-granted-claims.pdf

583-kol-2004-granted-correspondence.pdf

583-kol-2004-granted-description (complete).pdf

583-kol-2004-granted-examination report.pdf

583-kol-2004-granted-form 1.pdf

583-kol-2004-granted-form 18.pdf

583-kol-2004-granted-form 2.pdf

583-kol-2004-granted-form 3.pdf

583-kol-2004-granted-form 5.pdf

583-kol-2004-granted-gpa.pdf

583-kol-2004-granted-reply to examination report.pdf

583-kol-2004-granted-specification.pdf


Patent Number 224166
Indian Patent Application Number 583/KOL/2004
PG Journal Number 40/2008
Publication Date 03-Oct-2008
Grant Date 01-Oct-2008
Date of Filing 24-Sep-2004
Name of Patentee TATA STEEL LIMITED,
Applicant Address JAMSHEDPUR 831001,INDIA,AN INDIAN COMPANY
Inventors:
# Inventor's Name Inventor's Address
1 RAO, S. MOHAN TATA STEEL LIMITED, JAMSHEDPUR 831 001
2 RAJU, M.B.N. TATA STEEL LIMITED, JAMSHEDPUR 831 001
3 RAJU, K.S. TATA STEEL LIMITED, JAMSHEDPUR 831 001
4 RAO, N.D. TATA STEEL LIMITED, JAMSHEDPUR 831 001
5 ROY, P. TATA STEEL LIMITED, JAMSHEDPUR 831 001
PCT International Classification Number C22B 1/14
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA