FIELD OF THE INVENTION
The present invention relates to an improved process for the preparation of
Pellet-Sinter Composite Agglomerate (P-SCA) of iron oxide fines for use in blast
furnace.
BACKGROUND OF THE INVENTION
Fines generation rate during lump ore preparation in India is increasing day by
day. In addition to the generated fines and natural iron ore fines source like
bluedust, friable ores etc, upgradation of lowgrade ore also produce a substantial
quantify of fine concentrates. Agglomeration process like sintering and
pelletization are well established process but with certain limitations like raw
materials size restriction, energy consumption etc. There has been a continuous
endeavor to minimize the prior art limitations including increase in utilization of
iron ore fines in existing process of agglomeration. Reference may be made to
(H. K. Peters, A. G. Waters and S. K. Nicol, 5th Int. Symp. on 'Agglomeration',
Brighton, UK, The Institution of Chemical Engineers, 51-70), which teaches
balling of green sinter mix, in which micro fines particles in the mix, transform to
green balls to improve permeability of sinter bed, fines quantity, and
productivity. However, it has the limitation of accepting micro-fines to certain
extent.
Reference may be made to (J. Pal et al, Ironmaking and Steelmaking,
http://dx.doi.org/10.1179/1743281212Y.0000000069), which describes Micro
pelletization of ultrafines waste/concentrates wherein fines of iron oxides are
palletized to hard pellets (2-6 mm) and then used in sintering. The process
needs high proportion of lime for strength-development of the micropellets which
increases the basicity of sinter.
Reference may be made to (T. Jiang, G.H. Li, H.T. Wang, K.C. Zhang and
Y.B.Zhang , Ironmaking and Steel Making, 2012, Vol. 37 (1) 1-7) which discloses
pellets made up of fine iron ore concentrate and blended with basic sinter mass,
the blended mixture is finally sintered into a composite agglomerate in which
acid pellets are embedded in basic sinter. Investigators found a series of
advantages over traditional sintering or palletizing in this prior art process such
as ability to use diverse iron bearing materials, significant improvement in the
material bed permeability and productivity, low energy consumption, and ability
to prepare a low basicity charge with good metallurgical performance. Although
the investigators reported tumbler index, reduction degradation index and
softening melting point of the composite mass, however, nothing has been
reported on the crushing strength of the pellets in sinter bed after completion of
sintering.
Reference may be made to Indian Application No. 2375/DLE,2009, wherein C02
was used for strengthening of micropellets for its cold handling and subsequent
use in sintering. The drawback of this prior art is high lime percentage in
micropellets that restricts its use in sintering.
Reference may be made to Chinese Patent No.CN200510032095, 2005 wherein
the pellets are made up of fine iron ore concentrate and blended with basic
sinter mass wherein the mixture is finally sintered into composite agglomerate in
which acid and pellets are embedded in basic sinter. Apart from fine utilization,
there are other advantages like energy saving and improvement in productivity.
Coke powder/anthracite is used in forming the pellets for generating heat to
improve pellet-strength. However, the carbon particles used in the pellet may
increase porosity in indurated pellets. Thus, in-spite of increasing heat
generation in the pellet, strength improvement becomes difficult due to in crease
in porosity.
Earlier investigators have developed composite agglomerate from China iron ore
but nothing has been reported on the strength of the pellets in composite
agglomerates that is very essential for the blast furnace burden.
Thus, the prior art indicates the green balling has a limitation of accepting fines.
Use of micropellets is restricted due to its high lime and costly binder content.
Composite agglomeration may be the best process that has lot of advantages as
mentioned above. However, crushing strength improvement of the pellet is
necessary, since the pellet has to withstand the heavy load of burden during
movement and reduction in the shaft of blast furnace. Improvement of crushing
strength may be possible by generating in-situ heat in the pellet. Strength
improvement by presence of carbon in the pellet as a heat source may be
difficult due to formation of pores in the indurated pellets.
From the hereto known prior art it is seen that no attempt has so for been made
to improve strength to the composite agglomerate by incorporating iron or lower
iron oxide bearing materials like LDS, mill scale or DRI fines.
DETAIL DESCRIPTION OF THE INVENTION
According to the invention, the strength of pellets in sinter bed is improved by
adding some heat contributing materials inside the pellets for example, LD
Sludge, mill scale or DRI fines. The in-situ heat in the pellet produced due to
oxidation of metallic iron and its lower oxides (FeO and Fe304 present in LS
sludge) during sintering as per reactions (1) - (4).
Fe + 1/202 = FeO; ? H= 63800 Cal/mole (1)
3Fe0 + 1/202 = Fe304; ? H= 76400 Cal/mole (2)
2/3Fe304 + 1/602 = Fe203; ? H= -18266 Cal/mole (3)
2Fe + 3/202 = Fe203; ? H = - 196800 Cal/mole (4)
The above reaction produces heat without generation of any gaseous product
unlike oxidation of carbon. Thus, the process reduces the change of pore
formation in the pellet.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an improved
process for preparation of Pellet-Sinter Composite Agglomerate (P-SCA of iron
oxide fines for use in blast furnace which enhances the strength the composite
agglomerates.
Another object of the present invention is to propose an improved process for
preparation of Pellet-Sinter Composite (P-SCA) of iron oxide fines for use in blast
furnace in which in-situ heat is generated by oxidation of metallic iron and its
lower oxides in the added LDS/ mill scale/ DRI fines.
Still another object of the present invention is to propose an improved process
for preparation of Pellet-Sinter Composite Agglomerate (P-SCA) of iron oxide
fines for use in blast furnace that decreases the energy consumption in sintering
with respect to conventional sintering.
Yet another object of the present invention is to propose an improved process
for preparation of Pellet-Sinter Composite Agglomerate (P-SCA) of iron oxide
fines for use in blast furnace that decreases the flux consumption and pyroxenite
consumption.
A further object of the present invention is to propose a process for preparation
of pellet - sinter composite Agglomerate, in which the strength of the pellets is
enhanced.
According to the invention, the composite agglomerate is developed using steel
plant's waste materials containing metallic iron or lower iron oxide for generating
in-situ heat in the pellets on oxidation during sintering and helps improving pellet
strength. Hence this novel approach improves the pellet strength as well as inter
quality for Indian iron ore.
According to the invention Linz Donawiz converter Sluge (LDS) / mill scale/ DRI
fines are used for in-situ heat source in pellets for development of good quality
composite agglomerate containing basic sintered mass and acid pellet utilizing
Indian iron ore fines. This invention is useful in blast furnace iron making where
developed P-SCA can be used as a charge material replacing existing sinter and
pellet both.
Accordingly, the present invention provides an improved process for preparation
of Pellet-Sinter Composite Agglomerate (P-SCA) of iron oxide fines for use in
blast furnace, which comprises the steps of:
i. mixing iron ore micro fines of size range between : - 52 mesh to -
350, metallic iron or lower iron oxide containing waste iron oxides
selected from a group consisting of Linz Donawiz converter Sludge
(LDS)m mill scale, direct reduced iron (DRI) fines, and bentonite in a
ratio respectively ranging between 95 : 4.5 to 85 : 14.5 : 0.5; keeping
the basicity in the range of 0.05-2.5;
ii. pelletizing the obtained mixture to 7-17 mm diameter pellets in a
pelletizer using 7-14% water;
iii. preparing a sinter mix by mixing iron ore fines of zing : -10 mm,
slacked lime, lime stone MgO bearing materials for example,
pyroxenite, coke, and moisture in a range between 70-90%, 0.5-4%,
1-15%, 3-5%, 4-7% and 6-10% respectively, maintaining the basicity
in the range of 0.2 to 3.5;
iv. mixing the obtained green pellets and the sinter mix in a rotary mixer
in a ratio of 5:95 to 75:25;
v. sintering the prepared mix in a pot sintering machine raising the
temperature ranging between 1250-1450°C; and
vi. discharging the sinter cake and breaking to lump to obtain the Pellet
Sinter Composite Agglomerate (P-SCA) lumps.
In an embodiment of the present invention, to provide in-situ heat in the pellet,
metallic iron or lower iron oxide containing waste iron oxides for example, Linz
Donawiz converter Sludge (LDS) or mill scale were used. Direct reduced iron
(DRI) fines in the pellet mix or carbon containing fines in surface may also be
used for this purpose.
In another embodiment of the present invention, LDS has composition: Fe(metallic)
: 15-25%; Fe304: 30-60%; Fe0: 30-60%, mill scale has composition : Fe304: 30-
80%; Fe0: 50-1000%. Direct reduced iron (DRl) fines of composition:
Fe(metalliC):60-95% may also be used for the same purpose.
In yet another embodiment of the present invention, the iron ore fines have
composition : Fe(tot): 45-67%; St02 : 0.3-5%; Al203 : 0.3-3%; S: 0.06%; P:0.02-
0.06%.
In still another embodiment of the present invention, the slacked lime have
composition: CaO: 75-96%; Si02 : 0.5-6%; Al203: 0.5-5%; MgO: 0.5-5%.
In still yet another embodiment of the present invention, the lime stone has the
composition : CaO: 35-55%; Si02 :0.5-7%; Al203: 0.5-5%; MgO: 0.5-5%; L0l: 30-
45%.
In still yet another embodiment of the present invention, pyroxenite was used as
MgO bearing material and its composition is: MgO: 25-45%; Si02: 35-70%; Al203:
0.1-4%. Olivine of composition MgO: 35-70%; Si02: 20-50%; or dolomite of
compositin: MgO: 15-35%; Ca0:15-35%; Sio2 :l-6%; may also be used in place
of Pyroxenite.
In still yet another embodiment of the present invention, the coke breeze has a
composition of Fix Carbon: 65-90% and Ash: 7-33%; VM:0-3%.
In a further embodiment of the present invention, bentonite has chemical
composition: Si02: 50-65%; Al203: 20-40%; moisture : 7-12%.
The novelty of the present invention resides in that in order to generate in-situ
heat in the pellets for improving its sintering process and crushing strength, steel
plant's waste materials containing, metallic iron or lower iron oxides viz. LDS, mill
scale or DRI fines is used. During sintering at high temperature at sinter bed,
oxygen present in air passes through the pores of the pellets and oxidizes the
metallic Fe and its lower iron oxides to provide heat as per reactions (1) to (4)
without generating any gaseous product. Thus, it leads to increase the
temperature inside the pellet and promotes the step of sintering to increase its
strength. Additives like, LDS, mill scales etc.used in this process is a waste
material cheaply available in steel plants. The inventive step which enables to
realize the invention basically resides in mixing of iron ore micro fines of size
range between: -52 mesh to -350, metallic iron or lower iron oxide containing
waste iron oxides viz. Linz Donawiz converter Sludge (LDS) or mill scale or direct
reduced iron (DRI) fines and benotonite in a ratio ranging between 95 : 4.5 :
0.5 to 85 : 14.5 : 0.5; keeping the basicity in the range of 0.05-2.5.
The following examples are given by way of illustration of the working of the
invention in actual practice and therefore should not be construed to limit the
scope of the present invention.
Example -1
The strength properties of Green pellets made from the mixture of iron or micro
fines LDS or mill scale or DRI fines are presented in Table-1. The strength in
green condition looks satisfactory to withstand handling for subsequent
processing.
Table-1
Green properties of the pellets to be added in sinter mix
Example-2
After sintering of the composite mix the pellet were separated to measure CCS.
Table-2 depicts the high CCS of the pellets which can improve the sinter
property. When there is no additive for in-situ heat generation, the pellet has
lower strength with wide variation.
Table-2
Properties of the pellets after induration in sinter bed (separated from P-SCA)

Example-3
Table 3 shows a very good tumbler index and shatter index in P-SCA and it is
comparable with a good quality sinter made as per conventional process, though
P-SCA uses higher amount of fines in sintering through the use of pellets. It
consumes lower amount of coke breeze, lower lime and lower MgO containing
fluxes.
Example - 4
Table 4 shows that P-SCA has excellent Reducibility index (Rl) and Reduction
degradation Index (RDI). Rl is much better than Normal sinter in identical
condition and RDI is comparable even at lower overall basicity level.
Thus, the above examples indicate that iron containing additive improves the
strength of the pellets in sinter bed. The developed sinter is usable in blast
furnace that has comparable properties even at lower basicities with good quality
normal sinter made under identical sintering condition. Advantageously, the
developed P-SCA consumes higher amount of micro fines less amount of the flux
and MgO bearing materials.
The main advantages of the present invention are:
1. A wide range of iron ore fines with higher amount of micro-fines (30-60 %
excess with respect to the normal sintering) can be used. Thus, it is a very
suitable process to utilize iron ore concentrate.
2. Improves the permeability of sinter bed.
3. Use of waster materials containing metallic iron or Fe304, FeO (LD sludge mill
scale etc.) increases CCS of pellets in sinter bed by generating the in-situ heat
for bonding.
4. Production of good quality agglomerate (P-SCA) in combination of acid pellets
and basic sinter with lower overall basicity is possible.
5. Rl of P-SCA is superior to the normal sinter and other properties are
comparable in identical sintering conditions.
6. Lower amount of lime consumption and pyroxenite consumption in P-SCA.
7. Energy consumption (coke breeze rate in sintering process) and C02 emission
is lower than the normal sintering.
8. Equivalent sinter property is achievable with lower overall basicity also.
9. Self life of P-SCA is more than normal sinter.
10. The pellet in P-SCA has higher angle of repose than conventional pellets
which provides improved charge distribution in the blast furnace.
WE CLAIM:
1. An improved process for preparation of Pellet-Sinter Composite
Agglomerate (P-SCA) of iron oxide fines for use in blast furnace,
comprising the steps of:-
i. mixing iron ore micro fines of size range between : -52 mesh to -350,
metallic iron or lower iron oxide containing waste iron oxides for example,
Linz Donawiz converter Sludge (LDS) or mill scale or direct reduced iron
(DRI) fines and bentonite in a ratio ranging between 95: 5 : 0.5 to
85 :14.5: 0.5 respectively keeping basicity in a range of 0.05-2.5,
ii. pelletizing the obtained mixture to 7-17 mm diameter pellets in a pelletizer
using 7-14% water;
iii. preparing a sinter mix by mixing iron ore fines of size : -10 mm, slacked
lime, lime stone, Mg0 bearing materials like pyroxenite, coke and moisture
in a range between 70-90%, 0.5-4%, 1-15%, 3-5%, 4-7% and 6-10%
respectively, keeping the basicity in a range of 0.2 to 3.5;
iv. mixing the obtained green pellet and the sinter mix in a rotary mixer in a
ratio of 5:95 to 75:25;
v. sintering the prepared mix in a pot sintering machine raising the
temperature ranging between 1250-1450°C; and
vi discharging the sinter cake and breaking to lump to obtain the Pellet Sinter
Composite Agglomerate (P-SCA) lumps.
2. An improved process as claimed in claim 1, wherein to provide in-situ heat in
the pellet, metallic iron or lower iron oxide containing waste iron oxides for
example, Linz Donawiz converter Sludge (LDS) or mill scale, optionally, direct
reduced iron (DRI) fines in the pellet mix or carbon containing fines in surface
is used.
3. An improved process as claimed in any of claims 1 or 2, wherein the LDS has
composition: Fe(metallic): 15-25% Fe304: 30-60%; Fe0: 30-60%, the mill scale
composition: Fe304: 30-80%; Fe0: 50-100%, the direct reduced iron (DRI)
fines having a composition: Fe(metallic): 60-95% is used .
4. An improved process as claimed in any of claims 1-3, wherein the iron ore
fines have composition: Fe (tot): 45-67%, Si02 : 0.3-5%; AI203 : 0.3-3%;
S:0.02-0.06%; P: 0.02-0.06%.
5. An improved process as claimed in any of claims 1-4, wherein the slacked
lime have composition Ca0: 75-95%; Si0 : 0.5-6%; Al203:0.5-5%; Mg:
0.5-5%.
6. An improved process as claimed in any of claims 1-5, wherein the lime
stone has the composition : Ca0:35-55%; Si02: 0.5-7%; AI203 : 0.5-5%;
MgO: 0.5-5%; L0I: 30-45%.
7. An improved process as claimed in any of claims 1-6, wherein pyroxenite
is used as MgO bearing material and its composition is: Mg0: 25-45%; Si02:
35-70%; Al203 :0.1-4% . Olivine of composition MgO: 35-70%; Si02 :20-
50%; or dolomite of composition: MgO: 15-35%; Si02 : 1-6%; may also be
used in place of Pyroxenite.
8. An improved process as claimed in any of claims 1 -7, wherein the coke
breeze has a composition of Fix Carbon: 75-90%' Ash: 7-33% and VM:0-
3%.
9. An improved process as claimed in any of claims 1-8, wherein bentonite
has chemical composition: Si02: 50-65%; AI203: 20-40%; moisture; 7-12%.
10. An improved process for preparation of Pellet-Sinter Composition
Agglomerate (P-SCA) of iron oxide fines for use in blast furnace substantially
as herein described with reference to the examples.

ABSTRACT

In the present invention an improved process for preparation of Pellet-Sinter
Composition Agglomerate (P-SCA) of iron oxide fines for use in blast furnace is
disclosed which uses Indian iron ore to utilize the micro-fines in sintering . The
prior art although describes a process of composite agglomeration with china ore
wherein carbon powder was used in pellet mix as heat source. Since, the carbon
enhances porosity in the pellet, not much strength improvement of the pellet is
possible according to prior art. This invention utilizes waste materials containing
metallic iron or lower iron oxide viz. LD sludge, mill scale or DRI fines in the
pellet, which are not susceptible to pore formation in the pellet but provide good
strength. The process yields a very good quality sinter even at the lower basicity
that is usable in the blast furnace. It increases the fines acceptability and
decreases energy consumption and flux consumption.