FIELD OF INVENTION:

This invention relates to a method for producing iron ore sinter using high
silica iron ore. In addition the iron ore sinter has strength, especially high
temperature properties, for use in blast furnace. Further, the improvement in
sinter quality consist of using high silica iron ore (with more than 23% SiO2
and less than 49% Fe) by replacing the pyroxenite addition in the base mix.
Use of the high silica ore, which is otherwise considered as waste, will help
in enhancing the mines life.
BACKGROUND OF THE INVENTION:
The search reveals that the available patents on this subject are very limited.
Most relevant patents on this subject have been described below:
US Patent 4168154 describes a process for sintering iron ore mixtures
containing solid fuels on sintering strands in which uniform sinter is
obtained throughout the depth of the charge by igniting the surface of the
charge and subsequently treating it with hot gases under a set of defined
conditions.

US Patent 4317676 describes the process for producing sintered iron ore
with a Dwight-Lloyd machine, and it provides a process for producing
sintered ore with high reducibility by sintering a raw material mix of a
moisture content between 4.5 and 8.0% on the pallets of said machine,
which comprises drying the surface layer of said mix on the pallets to
discharge 3 to 25%, preferably 5 to 20%, of the moisture content of the mix
from the sintering system, and thereafter, igniting the surface layer of the
mix to sinter the same with air or gas sucked downward.
US Patent 4543121 describes about a method for reducing the hydrocarbon
content of the gases produced during the agglomeration of fine iron-
containing particles by sintering them in the presence of carbonaceous
material.
US Patent 5127939 describes a method of producing iron ore sinter with
improved sinter strength, improved sinter reduction properties and
productivity by using synthetic olivine as source of MgO obtained by
calcination of serpentinite.
US Patent 5520719 provided a method for sintering an iron scrap in a
process for producing a sintered ore, which is used as a raw material in iron
making in a blast furnace.

US Patent 6682583 provided a process for producing sintered ore in which a
small amount of a water-soluble compound (a sintering aid) is added to iron
ore powder and, thereby, which product shows improved strength and no
adverse influence as an iron making raw material either without any
increase in content of an auxiliary material (CaO) serving as a binder.
The above-mentioned patents give a methodology (a) to improve the sinter
reducibility and strength by using olivine pellets (b) to produce uniform
sinter by treating sinter bed with hot gases under a set of defined conditions
(c) to reduce the hydrocarbon content of gases produced during sintering (d)
to produce sinter using iron scrap to be used in iron making and (e) to
produce iron ore sinter with improved strength using small amount of water-
soluble compound to iron powder. However, these processes does not
consider quality of iron ore i.e. gangue content especially silica content and
its effect on sinter characteristics like reduction degradation index (RDI),
reducibility index (RI) and tumbler index (TI). In addition, none of these
patents discussed about the performance of these sinters with respect to
softening-melting properties, which simulates the softening-melting
phenomenon inside the blast furnace.
Thus, there exists a need to make use of high silica iron ore with more than
23% SiO2 and less than 49% Fe in sinter making and to produce sinter,
which can be used in blast furnace without much of difficulty.

OBJECTS OF THE INVENTION:
An object of the present invention is to propose a method for producing iron
ore sinter so that it can be used in the blast furnace without affecting the
sinter strength like RDI and TI;
Another object of the present invention is to propose a method for producing
iron ore sinter to eliminate use of pyroxenite in sinter making;
Still another object of the present invention is to propose iron ore sinter
having improved softening-melting properties;
Further, object of the present invention is to propose iron ore sinter with low
carbon rate in the base mix;
Still further object of this invention is to propose iron ore sinter with existing
moisture level of 6% in the green mix;
Yet another object of this invention is to propose iron ore sinter at bed height
of 600mm and at suction of 1500 mm/WC.

BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a method for producing iron
ore sinter comprising:
screening and weighing of the raw materials;
subjecting the screened and weighed raw materials to the step of mixing and
granulation to form the green mix, and
sintering the green mix.
DETAILED DESCRIPTION OF THE INVENTION:
Sinter was made using pot grate. This process mainly consists of screening,
granulation and sintering experiments. The materials used for sinter making
are first discussed followed by the experimental procedure and experimental
results.

The granulometry of raw materials used for sintering experiments are shown
in Tables 1.

The procedure of sinter making in the laboratory consists of the following
steps - Screening and Weighing, Mixing and Granulation, and Sintering.
The flowchart for making sinter in the laboratory and testing of sinter is
shown in Fig. 1. Each of these steps is discussed in detail.
Screening and weighing: Raw materials consist of different sizes of the
material. They are screened using standard screens and separated into
various size fractions as shown in Table 1. After screening, raw materials are
weighed in a weighing machine ('Rite' make with an accuracy of 10 gm)
and used for preparation of the green mix. Typical percentages of raw
materials used in the preparation of green mix are shown in Table 2.


Mixing and Granulation: Granulation is the process where raw materials are
agglomerated using water as a binder to form pseudo-particles or granules.
The mixture of pseudo-particles formed after granulation is called 'green
mix'. This step is carried out in a circular granulation drum (Diameter =lm,
Height = 0.5 m) as follows. The granulation drum is shown in Fig. 2.
All the raw materials are taken in the granulation drum inclined at 45° and
set into rotation at a constant speed. The materials in the drum are allowed to
mix for about a minute without addition of water. This is followed by the
addition of half the amount of total water and intense mixing for about 2
minutes. The rest of the water is then added and the mixture is mixed using
shovels. The granules are allowed to grow without mixing in the last minute
of granulation. The total granulation time is 6 minutes.

Sintering: The green mix obtained from granulation is sintered in a grate pot,
the schematic of which is shown in Fig. 3. The dimensions of the pot are 400
mm x 400 mm x 600 mm. The grate of the pot is used to apply suction (upto
1500 mm WC) during the course of sintering. The pot also has five circular
openings on one face for inserting thermocouples (3). The pot sinter (2)
setup used for experimentation is shown in Fig.4. Before transferring the
green mix, the pot is filled with 10 kg of hearth (15-25 mm size fraction of
sinter from previous experiment) to support the green mix and prevent it
from falling into the suction line. The pot is then filled with green mix to the
brim and unused green mix is rejected.
The velocity of air through the pot at 600 mm WC is measured using a
digital anemometer and is used for determining the permeability of the bed.
The ignition hood (1) is fueled by coke oven gas and once temperature of
hood reaches 1100°C, it is used to cover the top of the pot and ignite the
green mix for two minutes. Simultaneously suction is applied across the pot
and is maintained at a certain value, typically 1300 or 1500 mm WC
throughout the experiment. This step typically lasts for 20-25 min.
During this process, waste gas temperature (recorded using the windbox (4)
thermocouple) increases and reaches its maximum, which is called burn-
through point (BTP). After BTP, the experiment is continued for four
minutes after which suction is stopped and the bed is allowed to cool to

room temperature. Once bed is cooled, sinter is stabilized by dropping the
sinter cake from a height of 3 m, three times onto a steel plate. The stabilized
sinter is screened into various size fractions and tested for chemical
constituents, Tumbler Index (TI), Reduction Degradation Index (RI) and
softening-melting properties.
Sinter samples for these tests are sampled by coning and quartering as
follows. The total weight of sinter of the required size is poured in the form
of a cone, flattened into a cake and divided into quarters. Two opposite
quarters are discarded and the remaining quarters are combined to make the
sample. This process is repeated until the required weight of sample is
obtained.
Table 3, 4, 5 and 6 shows the details of different process parameters,
chemistry of different sinters and their characteristics, respectively. From
these tables it is clear that there is improvement in RDI, TI, and softening-
melting properties when sinters were made by using at 10 and 20% Ore A in
the base mix. There is significant improvement in sinter RDI when 20% ore
A was used in sinter making. Also, for these sinters softening-melting range
(SM) was very low which indicates narrower cohesive zone which is
desirable. In addition, lower non-drip materials (NDM) indicates better bed
permeability of the burden when higher concentration of Ore A was used.

WE CLAIM:
1. A method for producing iron ore sinter comprising:
screening and weighing of the raw materials;
subjecting the screened and weighed raw materials to the step of mixing and
granulation to form the green mix, and
sintering the green mix.
2. The method as claimed in claim 1, wherein the step of screening and
weighing is performed using standard screens and separated into various size
fractions.
3. The method as claimed in claim 1, wherein the step of mixing and
granulation is done using water as a binder to form pseudo-particles.
4. The method as claimed in claim 3, wherein the said pseudo-particles after
granulation forms the green mix.
5. The method as claimed in claim 4, wherein the said green mix is sintered
in a sinter pot.
6. The method as claimed in claim 1, wherein the raw material comprises of
atleast 10% (A) of high silica iron ore and about 90% normal iron ore (B).

7. The method as claimed in claim 6, wherein the high silica iron ore (A)
comprises Fe-49% and silica 23% and the other normal iron ore(B) contains
Fe-62% and silica 2%.