FIELD OF THE INVENTION
The present invention generally relates to a process of producing iron
agglomerate sinter with reduced consumption of solid fuel by adding an
auxiliary agent. More specially, the present invention relates to a method of
improvement in reducibility index and mean size of iron agglomerate sinter
with reduced generation of internal fines in sinter making process.
BACKGROUND OF THE INVENTION
In order to increase the productivity of blast furnace, continuous
improvement in the known sintering process including quality of the sinter is
one of the focussed areas in the art.
Sintering technology is known to have been originally developed for the
purpose of recycling of iron fines and solid wastes of steel plant in the blast
furnace. The raw materials comprising of iron ore fines, fluxes such as
limestone, dolomite and pyroxenite etc and coke breeze are granulated in a
rotating drum which sprinkles water to form granulation mix. Solid wastes
from steel plant comprising of iron and/or flux constituents are also added in
base mix of sinter. Fluxes are added to adjust sinter chemistry and provide
desired metallurgical properties whereas coke breeze is used as a fuel. The
base mix is charged onto the sinter strand from a mixing drum through a
feeder. Air is sucked at a negative pressure under the sinter strand and as a
result of this suction, combustion of solid fuel generates ignition and flame
front i.e. the maximum temperature zone is allowed to pass through the
entire sinter bed. Hot agglomerates that are formed due to incipient melting,
is broken into smaller size by a sinter breaker. Then, the sinter is crushed and
screened in the range of 5-40 mm, and sent to the blast furnace unit via a
conveyor belt.

In order to operate the blast furnace efficiently, the sinter needs to maintain
sufficient room temperature and high temperature metallurgical properties,
including narrow band of chemistry and uniform mean size. Room
temperature properties such as tumbler index (TI) and abrasion index (AI)
are the signifier to sinter strength during handling and transportation of the
sinter to the blast furnace unit whereas reducibility index (RI) and reduction
degradation index (RDI) indicate the possible behaviour of the sinter in the
blast furnace before melting.
Sinter plants need to be operated at peak performance as the increasing
demand of economical production of iron and steel products is growing
faster. Thus, there is a need for the sinter plants to have an efficient
operation with minimum consumption of energy. However availability of the
coke breeze which is used as the solid fuel is also a matter of concern. In
order to optimize the resources including energy consumption, a reduction in
solid fuel consumption is noted as an area of improvement.
Reducibility is an important characteristic of the sinter which measures the
reduction behaviour of sinter when the burden moves through the upper part
of the blast furnace. Porosity, structure of sinter and mineralogical phases
affect the reducibility of sinter. High reducibility index indicates that the sinter
reduces easily with less consumption of fuel.
Further, the main objective of a sinter plant is to achieve high productivity
with high quality at low operational cost. Fines generated in a sintering
process and during handling has been another area of concern in sinter
operation. Operation of the sinter plant with optimal generation of sinter fines
improves productivity and reduces fuel consumption. Higher optimal size of
sinter is better for permeability in blast furnace and hence helps in increasing
the efficiency of blast furnace process.
Several examples of the prior art claiming sinter property and process
modifier are mentioned below:-

Posco patent KR2003050220 discloses a technique of sinter manufacturing
process which reduces the cost of production by controlling the coke breeze
to be used by using the content of iron oxide contained in sinter return fines.
This technique intends to optimize the coke rate w.r.t content of iron oxide in
sinter return fines however content of iron oxide in return fines does not vary
significantly.
US patent US4317676 A describes a method for producing sintered ore with
high reducibility which comprises of drying the surface layer of base mix on
the pallets to discharge 3 to 25 weight % moisture content of the mix from
the sintering system, and thereafter igniting the surface layer of the base mix
with air or gas sucked downward. However the disclosure of this prior art did
not mention the quantitative improvement of reducibility of sinter and drying
the surface layer of said mix on pallets using a heat source which may affect
the production yield of the sintering process.
Taiyuan Iron & Steel Group Co patent CN201339056 teaches that a combined
blowing device which blows fuel and flux onto the mixed sinter ore, reduces
fuel consumption. This technique creates favourable conditions for low-
temperature sintering and improves the quality of sinter. However,
installation of a blowing device with precise control on the sintering machine
is necessary.
It is clear from the above discussions that various prior art exist directed to
reduce fuel consumption and improve the production yield and quality such
as reducibility of sinter. However, the prior art is silent towards improvement
of the existing sintering process including the property of sinter.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of
improvement in reducibility index and mean size of iron agglomerate sinter
with reduced generation of internal fines in sinter making process.

Another object of the invention is to propose a method of improvement in
reducibility index and mean size of iron agglomerate sinter with reduced
generation of internal fines in sinter making process, which ensures that the
produced sinter maintains the desired metallurgical properties.
A further object of the invention is to propose a method of improvement in
reducibility index and mean size of iron agglomerate sinter with reduced
generation of internal fines in sinter making process, which reduces the
consumption of solid fuel.
A still further object of the invention is to propose a method of improvement
in reducibility index and mean size of iron agglomerate sinter with reduced
generation of internal fines in sinter making process, which improves the
productivity of the sintering process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 Flow chart of producing sinter in a sintering unit.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a technique of producing sinter in a sintering
plant and transferring the produced sinter to a blast furnace. The advantages
of the new technology may be summarized as under:
a. reducing solid fuel consumption;
b. improving reducibility index (RI), thus providing an efficient iron-
making blast furnace process from reduction point of view;
c. reducing fines generation, thus improving the sinter productivity; and
d. increasing mean size of sinter.
With the view of attaining the above mentioned advantages, the present
invention provides a method of formation of base mix for sinter, which inter
alia includes :-

a. iron ore fines, LD slag, reverts from steel plants;
b. fluxes such as limestone, dolomite, quartzite, pyroxenite; and
c. solid fuel i.e. coke breeze.
Also, some of the ingredients of the base mix such as calcined lime, coke
breeze, sinter return fines, other fluxes are trimmed to achieve the desired
sinter chemistry.
The present invention also requires addition of a mineral which is a source of
boron tri-oxide (B2O3) either through trim feed in sinter process or during
formation of the base mixture preparation. The mineral can be Colemanite
(Ca2B6011.5H20), Sassolite (B(OH)3 or B2O3.3H20), Meyerhofferite
(Na2B4O7.5H2O), Borax (Na2B4O7.10H2O), Kernite (Na2B4O7.4H2O),
Hydroboracite (NaCaB5O9.8H2O), Probertite (NaCaB5O9.5H2O), Priceite
(Panderrnite) (Ca4B10O19.7H2O), lnyoite (Ca2B6O11.13H2O), Meyerhofferite
(Ca2B6O11.7H2O), Hydroboracite (CaMgB6O11.6H2O), Lnderborite
(CaMgB6O11.11H2O), Kurnakovite (Mg2B6O11.15H2O), lnderite
(Mg2B6O11.15H2O), Szaibelyite (Ascharite) (Mg2B2O5.H2O), Suanite (Mg2B2O5),
Kotoite (Mg3B2O6), Pinnoite (MgB2O4.3H2O), Boracite (Strassfurite)
(Mg3B7O13CI), Datolite (Ca2B2Si2O9.H2O), Cahnite (Ca2AsBO6.2H2O), Danburite
(CaB2Si2O8), Howlite (Ca4Si2B10O23.5H20), Vonsenite (Paigeite)
((Fe,Mg)2FeBO5), Ludwigite ((Fe,Mg)4Fe2B2O7), Tunellite (SrB6O11.4H2O ) and
mixture thereof.
In an embodiment of the invention, the mineral containing a source of boron
tri-oxide (B2O3), is introduced during formation of base mix as shown in
figure 1.
In another embodiment of the invention, the mineral, containing a source of
boron tri-oxide (B2O3), is introduced though trim feeding as shown in figure
1.

The present invention further teaches a method of adding preferably
Colemanite (Ca2B6O11.5H2O) which is a source of boron tri-oxide (B2O3) either
through trim feed in the sintering process or during formation of the base
mixture.
The present invention is directed to a method of adding preferably
Colemanite ( Ca2B6O11.5H2O) either through trim feeding at most 5 weight %
of the base mix of sinter or during base mix preparation at most 7 weight %
of base mix of sinter. Boron tri-oxide (B2O3) in Colemanite ( Ca2B6O11.5H2O) is
in the range of 38.0 to 42.0 weight %, when Colemanite is added through
said trim feeding and is in the range of 27.0 to 34.0 weight %, when
Colemanite is added during preparation of base mix .The range is fixed based
on techno-commercial point of view. It forms a low melting slag so that the
consumption of fuel is lower.
Further, the present invention requires that the sintering process be operated
by maintaining:-
a. burn through point in the range of 260 to 330 oC.
b. flame front speed in the range of 20 to 30 mm/min.
c. suction of sinter strand in the range of 950 to 1100 mm of H2O
In the present invention, the prepared base mix is subjected to granulation in
a mixing drum in such a way that at least 80 % of granulation index at 0.25
mm is achieved. The moisture content of the base mix after granulation is in
the range of 5 to 10 weight %. The continuous sinter process is carried out
on the strand of the sinter machine that conveys the bed of prepared base
mix. The combustion is incorporated in the bed by using burners fuelled by
combustion gas located in the ignition hood at the feed end of the machine.
Suction is maintained so that significant permeability of the bed is achieved.
As sinter moves along the strand of sinter machine, air is sucked in the range
of 950 to 1100 mm of H2O through the ignited bed to burn the fuel

completely. The flame front i.e. maximum temperature zone moves at a
speed of 20 to 30 mm/min. The burn through point which signifies the
completion of sintering process is in the range of 260 to 330 oC.
Hot sinter cake is then allowed to break and cool after the end of the strand.
Cold sinter is crushed in cold crusher and then allowed to screen into various
size fraction. Sized sinter in the range of 5 to 40 mm is transported to the
blast furnace unit. Chemical analysis, reducibility index (RI), tumbler index
(TI), abrasion index (AI) are done according to standard methods.
The chemistry of sinter includes at least 52 weight % of Iron (Fe); 0.2 to 1.5
weight % of boron tri-oxide (B2O3); less than 18 weight % of Iron oxide
(FeO); 1.5 to 3 weight % alumina (Al2O3); less than 3 weight % magnesium
oxide (MgO); and 1.8 to 2.5 basicity (weight % ratio of calcium oxide and
silica).
The metallurgical properties of sinter includes at least 65 % reducibility index
(RI); at least 67 % tumbler index (TI); and at most 10 % abrasion index (AI).
The examples mentioned below demonstrate the present invention; however
the invention is not limited to these examples.
The examples explain the reduction of solid fuel i.e. carbon rate, increase in
reducibility index (RI), decrease in fines generation in sintering process and
transportation to blast furnace, increase in mean size of sinter. Example 1
and 2 mentioned in tables 1 to 5 describes the base mix composition,
chemistry of base mix constituents, operating parameters, sinter chemistry
and metallurgical properties. Example 1 mentions the on-going process and
example 2 demonstrate the current invention.
Example 1: The amount of materials used in the base mix and trim feeding
are mentioned in table 1. The compositions of constituents are mentioned in
table 2. The materials are mixed mainly in the raw material blending and
bedding unit and trim addition of calcined lime, definite amount of sinter

return fines and coke breeze are made to achieve target sinter chemistry and
adequate metallurgical properties. The base mix is mixed in granulation drum
sprinkled with water so that granulation of material is achieved. The
granulation index at 0.25 mm and moisture content of base mix after
granulation are 82 to 85 % and 7 to 8 weight % respectively. The base mix
after granule formation is transferred to sinter machine where sinter mix
conveys through the sinter strand. Base mix is then ignited by ignition hood
fuelled by combustion gas. As sinter mix moves along the strand, air is
sucked down to burn the fuel at suction of 1010 to 1083 mm of H2O. The
flame front i.e. maximum temperature zone moves at a speed of 23 to 28
mm/min. The burn through point i.e. maximum wind box temperature is
obtained at temperature of 270 to 308 oC. Then hot sinter cake is fed to
sinter breaker and then allowed to cool. Cooled sinter is crushed and
screened to various size fractions. The chemistry of sinter is mentioned in
table 4. The stabilized sinter is tested for reducibility index (RI), tumbler
index (TI), and abrasion index (AI). The quality parameters are shown in
table 5. The mean size of sinter, fines generation in sintering process and
during transportation to blast furnace unit and solid fuel consumption i.e.
carbon rate are also mentioned in table 5.
Example 2: The amount of materials used in the base mix and trim feeding
are mentioned in table 1. The compositions of constituents are mentioned in
table 2. The materials are mixed mainly in the raw material blending and
bedding unit and trim addition of calcined lime, definite amount of sinter
return fines and coke breeze are made to achieve target sinter chemistry and
adequate metallurgical properties. Trim feeding of Colemanite
(Ca2B6O11.5H2O) is made in the range of 1 to 3 weight % to improve the
sintering process and property of sinter. The granulation of base mix and
sintering process remains same as mentioned in example 1 and table 3. The
chemistry of produced sinter is mentioned in table 4.The quality parameters,

mean size of sinter, fines generation in sintering process and during
transportation to blast furnace unit and solid fuel consumption i.e. carbon
rate are mentioned in table 5. The stability of the process is confirmed as
operating parameters such as suction of the bed, flame front speed and burn
through point are within the band of control limit.
The examples 1 and 2 clearly demonstrate that reducibility index (RI) of
sinter increases from 66-68 to 75-86 as shown in table 5.
Further, it is clear from table 5 that solid fuel i.e. carbon rate decreases from
50-56 to 44-47 kg/ton of sinter.
It is observed from table 5 that mean size of sinter increases from 18-19 to
20-23 mm.
Also, fines generation decreases from 43-46 to 39-40 weight % of sinter
produced, as mentioned in table 5.

According to the invention iron agglomerate sinter is produced with reduced
consumption of solid fuel. This is beneficial for the sintering process from
economic point of view and scope for improvement in productivity. Apart
from the advantage in solid fuel consumption, the invention also provides an
added advantage in improving reducibility index (RI), reduction in fines
generation in sinter making unit and during transportation to blast furnace
unit and also increase in mean size of sinter.
The improvements exhibited by the disclosed invention are as under:-
a. Solid fuel i.e. carbon rate drops by 11 to 17 weight % with
adequate metallurgical properties;
b. Reducibility index (RI) increases by 12 to 28 %;
c. Mean size of sinter increases by 9 to 25 %; and
d. Total return fines generated in sintering process and transportation
to blast furnace decreases by 10 to 12 weight % of total sinter
produced.

WE CLAIM :
1. A method of improvement in reducibility index and mean size of iron
agglomerate sinter with lower generation of internal fines in sinter
making process, the method comprising:-
- preparing a base mix essentially consisting of iron ore fines, solid plant
reverts, LD slag, fluxes and coke breeze; and
- adding a predetermined quantity of boron tri-oxide (B2O3) containing
flux/mineral in the base mix of the sinter, wherein the iron ore fines
consisting of at least 61 weight % iron (Fe); and trim feed of flux,
sinter return fines and coke breeze.
2. The method as claimed in claim 1, wherein the mineral source of said
boron tri-oxide (B2O3) is selected from a group constituting of
colemanite (Ca2B6011.5H20), Sassolite (B(OH)3 or B2O3.3H20),
Meyerhofferite (Na2B4O7.5H2O), Borax (Na2B4O7.10H2O), Kernite
(Na2B4O7.4H2O), Hydroboracite (NaCaB5O9.8H2O), Probertite
(NaCaB5O9.5H2O), Priceite (Panderrnite) (Ca4B10O19.7H2O), lnyoite
(Ca2B6O11.13H2O), Meyerhofferite(Ca2B6O11.7H2O), Hydroboracite
(CaMgB6O11.6H2O), Lnderborite (CaMgB6O11.11H2O),
Kurnakovite(Mg2B6O11.15H2O), lnderite (Mg2B6O11.15H2O), Szaibelyite
(Ascharite) (Mg2B2O5.H2O), Suanite (Mg2B2O5), Kotoite (Mg3B2O6),
Pinnoite (MgB2O4.3H2O), Boracite (Strassfurite) (Mg3B7O13CI), Datolite
(Ca2B2Si2O9.H2O), Cahnite (Ca2AsBO6.2H2O), Danburite (CaB2Si2O8),
Howlite(Ca4Si2B10O23.5H20), Vonsenite (Paigeite) ((Fe,Mg)2FeBO5),
Ludwigite ((Fe,Mg)4Fe2B2O7), Tunellite (SrB6O11.4H2O ) and mixtures
thereof.

3. The method as claimed in claim 1, wherein the mineral constituting a
source of boron tri-oxide (B2O3), is added in the base mix of sinter
through trim feeding.
4. The method as claimed in claim 1, wherein the mineral constituting a
source of boron tri-oxide (B2O3), is added during formation of base
mix.
5. The method as claimed in claim 1, wherein the mineral source of
boron tri-oxide (B2O3) is preferably Colemanite ( Ca2B6O11.5H2O).
6. The method as claimed in any of the proceeding claims, wherein
alumina and silica content in iron ore fines is less than 3.0 weight %
and 6.0 weight % respectively.
7. The method as claimed in any of the proceeding claims, wherein
moisture content in the base mix after granulation is in the range of 5
to 10 weight %.
8. The method as claimed in claim 1, wherein the granulation index at
0.25 mm is at least 80 %.
9. The method as claimed in claim 1, wherein the boron tri-oxide (B2O3)
in Colemanite ( Ca2B6O11.5H2O) is in the range of 38.0 to 42.0 weight
%, when Colemanite is added through said trim feeding.

10. The method as claimed in claim 1, wherein the boron tri-oxide (B2O3)
in Colemanite (Ca2B6O11.5H2O) is in the range of 27.0 to 34.0 weight
%, when Colemanite is added during preparation of base mix.
11. The method as claimed in claim 1, wherein the source of calcium oxide
(CaO) is fluxes such as limestone, calcined lime, dolomite and
Colemanite (Ca2B6O11.5H2O).
12. The method as claimed in claim 1 and 11, wherein calcined lime and
limestone are added in the raw mixture at most 4 weight % and 5 to
15 weight % of total base mix (including trim feeding) of sinter
respectively.
13. The method as claimed in claim 1, wherein the source of magnesium
oxide is dolomite and pyroxenite.
14. The method as claimed any of claim 1 to 13, wherein dolomite and
pyroxenite are added in the raw mixture at most 7 weight % and at
most 7 weight % of total base mix (including trim feeding) of sinter
respectively.
15. The method as claimed in claim 1 or claim 11, wherein Colemanite
(Ca2B6O11.5H2O) which is a source of boron tri-oxide (B2O3) and
calcium oxide (CaO) is added in the raw mixture through trim feeding
at most 5 weight % of total base mix (including trim feeding).

16. The method as claimed in claim 1 or claim 12, wherein Colemanite
(Ca2B6O11.5H2O) which is a source of boron tri-oxide (B2O3) and
calcium oxide (CaO) is added during formation of base mix of sinter at
most 7 weight % of total base mix (including trim feeding).
17. The method as claimed in claim 1, wherein the maximum wind box
temperature i.e. burn through point is attainable in the range of 260 to
330 oC.
18. The method as claimed in claim 1, wherein the flame front speed is in
the range of 20 to 30 mm/min.
19. The method as claimed in claim 1, wherein the suction of the sinter
strand is in the range of 950 to 1100 mm of H2O.
20. The method as claimed in claim 1, wherein the sinter produced
comprises :-
at least 52 weight % of Iron (Fe),
0.2 to 1.5 weight % of boron tri-oxide (B2O3),
less than 18 weight % of Iron oxide (FeO),
1.5 to 3 weight % alumina (Al2O3),
less than 3 weight % magnesium oxide (MgO), and
1.8 to 2.5 basicity (weight % ratio of calcium oxide and silica).

21. The method as claimed in claim 1, wherein tumbler index (TI) of the
sinter is at least 67 %.
22. The method as claimed in claim 1, wherein abrasion index (AI) of the
sinter is at most 10 %.