Field of invention: The invention relates to a process for improving coke strength of coke for
stamp charge battery.
Background of the invention:
CSR, or coke strength after reaction with C02, has become the more important means of
evaluating the quality of coking coal and of controlling blast furnace performance. It is now a
principal criterion by which coals are selected to make blast furnace coke. With the increase size
of up-coming blast furnaces and enhanced PCI (pulverized coal injection) rate it is necessary to
improve the coke strength after reaction of the coke. Tata Steel uses varied weight percentage of
prime coking coal in blend (prime coking coal has Crucible Swelling Number CSN greater than
6). Also prime coal reserve is limited. If by some means coke strength after reaction can be
increased then use of prime coking coal can be minimized. In Tata Steel coke strength after
reaction has been done following the NSC method. In which 200 g coke of 19-21 mm size is
heated in a reaction tube (78 mm diameter X 210 mm length) at 1100°C for two hours during
which C02 is passed a 5 1/min. The percentage loss in weight of coke during the above reaction
is reported as the coke reactivity test (CRI). This reacted coke is further tested by rotating in a I
drum (127 mm diameter X725 mm length) for 30 min at a speed of 20 rpm. The coke is then
screened on a 10 mm sieve and the % of + 10 mm fraction is reported as the coke strength after
reaction (CSR). Researchers have been trying various methods on how to increase the coke
strength of coal and there has been continuous focus on how to increase efficiency and hence
increase energy savings.

Objects of the invention
An object of this invention is to propose a process for improving coke strength of coke for stamp
charge battery.
Another object of this invention is to propose a process based on shear crushing to increase the
coke strength (coke strength after reaction) of coke.
Another object of this invention is to propose a process shear crushed coal can be added to coal
blend in order to improve the coke strength.
Summary of the invention
Present invention introduces a new concept of crushing by shear. In this method, coal is crushed
by shearing instead of conventional impact method. Shear crushing enable liberation of reactive
macerals on the surface and also change the shape and surface morphology of the coal particles.
When this "shear crushed" coal is added to the coal blend, it improves the coke strength after
reaction (CSR) of coke.
Detailed description of the invention
Selection of coal: For this study 4 types of coal has been used as specified in table 1. One prime
coking coal (A), two medium coking coals (Bl, B2) and weakly coking coal (C). Individual coal
and different combinations of these had been tried for carbonization experiments.

Characterization: The coals are characterized in terms of ash, volatile matter (VM), crucible
swelling number (CSN) and fluidity. The details of the tests are as follows:
Ash determination: Ash is determined by following ASTM standard D 3174-11. 1 gm of 250 mm
size sample is taken to a weighed capsule. Then the sample is placed in a cold muffle furnace
and heated gradually at such a rate that the temperature reached 450°C to 500 C by 1 hr. At the
end of the 2 hr it will reach 950°C. After cooling the weight of the sample then measured and ash
is calculated by weight difference.
VM determination: Ash is determined by following ASTM standard D 3175-11. In this test 1 gm
of 250 mm size sample is taken in a covered platinum crucible and heated in a furnace of 950 C
for 7 min. The VM is calculated by weight difference.
Crucible swelling number: Crucible swelling number test has been done by following ASTM
D720-91 (2010). In which 1 gm of sample (-0.212 mm size) is taken in a translucent squat
shaped silica crucible and the sample is leveled by tapping the crucible 12 times. The crucible is
covered with a lid and heated under standard conditions, either by a special type of gas burner or
muffle furnace. After the test the shape of coke button is compared with a standard chart and
accordingly, the crucible swelling number (0 to 9) is assigned to the coal sample.

77K? process of the current invention involves crushing the coal by conventional method coal
such that 90% of it should have size below 3.2 mm. For shear crushing, around 10-20 kg sample
is drawn from 100 kg as received coal by coning-quartering method. Then it is passed through 5
mm screen. After screening, it is subjected to crushed by shearing techniques. For blending, 10%
of shear crushed coal was blended with 90% of conventionally crushed coal. The scheme is
shown in figure 1. In an embodiment of the invention, 10 weight % of the shear crushed coal is
mixed in the coal blend. The quantity of shear crushed coal can be varied however, The method
as per claim 1, wherein of the shear crushed coal is mixed in the coal blend preferably in the
range of 10 to 15 weight %.
Carbonization tests: A number of carbonization tests were conducted in the 7-kg test oven, under
stamp charging conditions. The series of carbonization tests were carried to study the influence
of specific size fractions of coal under stamp charge conditions. Water was added to the coal
blend to obtain the desired value of moisture content. The coal cake was made inside a cardboard
box keeping the bulk density 1150 kg/m3. Tests were done with 100% individual coal and
combination of them. Then certain amount of the blend is replaced by shear crushed coal and
again carbonization tests were done with modified blend. Before charging the coal cake into the
oven, it was ensured that the empty oven temperature is 900±5°C. After 5 h of carbonization
time, the hot coke was pushed out and quenched with water. The coke samples were tested for
coke strength after reaction (CSR) and CRI (coke reactivity indices).

Table 1 shows the properties of coal used for the experiments.

Table 2 shows the design of blend for the experiments and corresponding coke quality in terms
of coke strength after reaction (CSR). Initially, coal A, B1 and C are carbonized individually
(Blend 1, 2 and 3). Individual coal was then crushed separately by shear and around 10% of the
blend was replaced by the shear crushed coal. It is found that the coke strength improve in later
cases (blend 4, 5 and 6). Blend 7, 8 and 9 are combinations of four coals. Blend 7 is the base

blend. 10% of shear crushed coal A was added to the base blend (blend 8). In blend 10, 10% of
shear crushed coal B was added. Coal can be shear crushed by any of the knowing crushing
techniques and is not limited to blend mixture or a kneader only.
As evident from table 2, one or more type of coals can be used to prepare the coal blend. The
different types of coal used as per the current invention are described in the table 1 in terms of
their properties and characteristics. Though invention is illustrated with the specified coal types
however, it is obvious that invention can be performed with other types of coals with varying
properties. The Coke strength after reaction of the coal blends prepared as per the process of the
current invention demonstrates a significant increase in the CSR. Different combinations of the
coals can be tried to achieve the desired results.

As evident from table 2 hat CSR improves significantly by addition of 10% of shear crushed
coal. In Coal crushing process, the crushing of solid matter occurs under exposure of mechanical
forces that trench the structure by overcoming of the interior bonding forces. During shearing,
the major breakage of coal macerals and minerals place by attrition. Due to the attrition the
liberation of reactive macerals are better (Ref: Application no : 1450/KOU/2013 of 24.12.2013), As
there is enrichment of reactive macerals in coal blend, it effects the fluidic property and hence
the binding between inerts and reactive are stronger. It leads to improvement of CSR.

WE CLAIM:
1. A method for increasing coke strength after reaction of coke, the method comprising
preparing a coal blend by mixing a shear crushed coal with a conventionally crushed coal
before carbonization.
2. The method as per claim 1, wherein at least 10 weight % of the shear crushed coal is
mixed in the coal blend.
3. The method as per claim 1, wherein of the shear crushed coal is mixed in the coal blend
preferably in the range of 10 to 15 weight %.
4. The method as per claim 1, wherein the conventionally crushed coal comprises up to 90
weight % of the coal blend with a particle size of less than 3.2 mm.
5. The method as per claim 1, wherein the shear crushed coal is crushed in a kneader.
6. The method as per claim 1, wherein the shear crushed coal is crushed in a blender.

7. The method as per claim 1, wherein the shear crushed coal is crushed to a size less than 5
mm.
8. The method as per claim 1, wherein one or more coal types can be used in preparing the
coal blend.

9. The method as per claim 1, wherein the coal blend is carbonized under stamp charge
conditions.
10. The method as per claim 1, wherein the coal blend is carbonized under top charge
conditions.
11. The process as claimed in claim 1, wherein the coal ash in the range of 6 to 16 weight %
on dry basis.