FIELD OF THE INVENTION
The present invention relates to determining free swelling of iron ore pellets,
which is one of the important quality parameters of iron ore pellets to be used in
blast furnace for making molten iron along with other iron bearing burden
materials (sinter and/or lump ore). This invention can also be employed for
measuring swelling and reducibility of chromite, Mn-ore and other oxide ore
pellets and/or agglomerates.
BACKGROUND OF THE INVENTION
Free swelling at high temperature under reducing atmosphere is one of the
critical characteristics of blast furnace. Abnormal swelling of pellets leads to
dilapidated internal structure followed by higher degree of fines generation in the
shaft region inside a blast furnace which reduces process stability and
productivity. To measure swelling behavior, standard laboratory setups are being
used to simulate the reducing atmosphere followed by standard measurement
techniques of total linear increase of the diameters or mercury displacement
measurement methods for determining apparent density of particles.
Standard tests (ISO-4698-1994, is-8624-1995) are applied in prior art to
determine the relative free-swelling index of the pellets during reduction, under
isothermal heating in an unconstrained state using a gaseous reductant. A test
portion of 18 pellets are taken in a vertical reduction tube (Fig.l) and is heated
inside a vertical electrical furnace using and inert gas at a flow rate of 10 l/min.
When the temperature approaches 900°C, the flow rate is increased to 15 l/min

and a reducing gas consisting of 30% of CO and 70% of N2, replaces the inert
gas at the same flow rate for 60 minutes. After that, the test portion is cooled at
a flow rate of 5 l/min and the free-swelling index is calculated as percentage,
using the difference between the final and initial volumes.
To measure swelling behaviour through simulation under reducing atmosphere
prior art commonly employs a horizontal tubular furnace inside which 1-2 pellet
particles are taken in an alumina crucible and the temperature is set at a fixed
value (900°C). During ramping of the temperature from ambient to the set
value, an inert atmosphere (N2/Argon) is used to maintain a predetermined
temperature profile. After the set temperature is attained the reducing gas mix
(CO and N2) is passed for a fixed period followed by cooling of the particles
under inert atmosphere.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved device to
conduct a high temperature ferrous burden characterization test for determining
free swelling behavior of iron ore pellets.
Another object of the invention is to propose a method for simultaneously
determining free swelling of multiple iron ore pellets and/or agglomerates of
different chemistry used in blast furnace in an improved test. The proposed
method yield significant reduction in time, cost, resource requirement and also
achieves measurement of reducibility along with free swelling of different iron
ore pellets/agglomerates in a single test.

SUMMARY OF THE INVENTION
According to the invention, a high temperature ferrous burden characterization
test is conducted for determining free swelling behaviour of iron ore pellets.
Pellet samples from multiple source/chemistry can be tested in a single device
and in a single experiment by serially loading the particles of different
source/chemistry (in layers) in a cylindrical crucible, separated by a steel wire
net (cut in circular shapes matching with crucible inner diameter). This modified
test yield significant reduction in time, cost, and resource requirement. This
invention also allows simultaneous measurement of reducibility along with the
measurement of free swelling of different pellets in a single test.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a prior art reduction test apparatus
Figure 2 - shows a prior art apparatus for measuring high temperature burden
characteristics
Figure 3 - shows a high temperature burden characteristics equipment according
to the invention
Figure 4 - shows arrangement of different samples according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure - 2, an improved device is employed to conduct the high
temperature ferrous burden characterization test. The device comprising a
vertical cylindrical furnace, a pre-programmed temperature controller, means for

introducing a reducing gas mixture into the furnace, and analyze the outlet gas
composition (for estimating degree of reduction), a melt collection chamber, a
load shaft for applying load and measuring bed shrinkage, a vertical crucible with
a perforated bottom plate to accommodate sample-mounted on a hollow cylinder
used for passage of gas.
A plurality of pellet particles of a particular source/chemistry is taken inside the
vertical crucible as a single layer (Fig.2) and tested without load at a fixed
temperature (900°C) and reducing gas composition (30% CO and 70% N2) for a
fixed time (60 min). Outlet gas compositions are monitored continuously.
Reducibility and swelling are the key results obtained after the test. Each of such
tests consume substantial amount of resources (consumables, gases, electricity
and man-hour).
According to the invention, pellet samples from multiple source/chemistry as
opposed to pellet sample of a particular source/chemistry can be tested in a
single experiment (Fig.3) by loading the particles of different source/chemistry
(in single layers), separated by steel wire nets (cut in circular shapes matching to
crucible inner diameter). Since maximum temperature of the swelling test is
900°C, readily available steel wire nets are used. Fig. 4 shows the actual
arrangement of the pellet samples from different sources inside the crucible
separated with the steel wire nets. A gap between two adjacent nets is
maintained at 25-30 mm so as to allow free swelling of the pellet particles.
Reducing gas mixture of 30% CO and 70% N2 is used at a controlled flow rate of
6 LPM to maintain a permissible fractional difference in the gas composition (due
to reduction of solids) across the layers such that all the layers experiences

uniform gas composition. Portion of the crucible including the particle layers are
maintained within the constant heat flux zone. Heating profile can be controlled
with the programmable temperature controller and typical temperature profile of
the blast furnace shaft, as experienced, can be applied. This arrangement and
method ensure that different pellets in different layers undergo free swelling
under identical simulation condition. Outlet gas composition is continuously
analyzed for CO and C02 to estimate fractional as well as total degree of
reduction during the test cycle.
The inventive device allows measurement of reducibility and swelling of different
pellets in a single test and comparison of high temperature characteristics of
different pellet samples under identical test conditions, and provides quicker
results and significant saving of resources. Maximum six different types of pellet
samples can be loaded in one crucible separated by wire nets, such that all the
samples can be tested in a single test instead of doing individual test with
individual sample. Hence each test run according to the invention, saves cost of
additional five conventional tests. Operating Cost (consumables, water,
electricity, manpower etc. approximately Rs. 30,000) for five tests can be saved,
every time such inventive test is done. This method can also be employed for
measuring swelling and reducibility of chromite, Mn-ore and other oxide ore
pellets and/or agglomerates.

REFERENCES
1. ISO 4698: 1994, 'Iron ore pellets - Determination of relative free Swelling
index', issued by the international Organization for Standardization (ISO),
1994.
2. Indian Standard (IS 8624-1995) 'Method for determination of swelling
index of iron ore pellets', 1st Revision, Bureau of Indian Standards, June
1995.

WE CLAIM
1. An improved device to conduct a high temperature ferrous burden
characterization test, the ferrous burden being adaptable in a blast
furnace, the device comprising:
- a furnace capable of being maintained at a temperature above
1000°C;
- a pre-programmed temperature controller to achieve a pre-determined
temperature profile for heating a substance in the furnace;
- means for introducing a reducing gas mixture into the furnace;
- an outlet port for allowing the gas mixture to exit from the furnace;
- a gas analyzer connected to the outlet port for analyzing composition
of said exited gas;
- a melt collection chamber for collecting melt formed at high
temperature;
- a load shaft for applying load and allow the measurement of the bed
shrinkage;
- a refractory made crucible with perforated bottom plate to retain the
ferrous burden sample sustaining high temperature disposed at the

center of the furnace being mounted on a hollow shaft allowing
passage of the reducing gas inside the furnace;
- a plurality samples of said ferrous burden consisting of different
chemistry, and collected from multiple sources disposed on said
crucible; and
- a plurality of wire mesh corresponding to the inner shape of the
crucible is disposed in between each layers of said plurality sample.
2. A method simultaneously for, determining free swelling of multiple iron
ore pellets or agglomerates of different chemistry used in blast furnace in
an improved device enabled to conduct a high temperature ferrous
burden characterization test, the method comprising the steps of:
- placing on crucible located inside a furnace a plurality layer of samples
interposed in each case a wire mesh maintaining a distance about 25-
30 mm;
- activating the furnace and raising the temperature maintaining a pre-
defined heating profile using a temperature controller such that the
samples are heated upto 900°C;
- supplying a reducing gas composition into the furnace for about 60-
minutes at a controlled flow rate;

- measuring red liability of different samples through analysis of the
exhaust reducing gas.
3. A method as claimed in claim 2, wherein gas flow rate, temperature
profile is controlled to maintain identical process condition across different
layers, and wherein a continuous measurement of the outlet gas
composition provide data on fractional including total degree of reduction
till 900°C.
4. A method as claimed in claim 2, wherein measuring swelling and
reducibility of chromite, Mn-ore and other oxide ore pellets and/or
agglomerates can be implemented.
5. The method as claimed in claim 2, wherein the reducing gas composition
comprises 30% CO and 70% N2.
6. The method as claimed in claim 2, wherein the controlled flow rate of the
reducing gas is about 6 LPM.

ABSTRACT

This invention describes swelling test of multiple iron ore pellets of different
chemistry or origin in a non-conventional apparatus which is used for high
temperature characterization of iron bearing burden materials and thereby
reduce time, cost and resource requirement significantly for such routine quality
control test along with additional information on reducibility and comparison of
swelling and reducibility between pellet samples under identical conditions. This
invention can also be employed for measuring swelling and reducibility of
chromite, Mn-ore and other oxide ore pellets and/ore agglomerates.