A new method of sintering process for achieving
higher productivity.
FIELD OF INVENTION:
The present invention relates to a new method of sintering process by addition of
calcined lime in the form of lime-water solution, i.e., milk of lime (MOL) in sinter mix
for low specific consumption of calcined lime in achieving higher productivity of a
sintering plant.
BACKGROUND OF INVENTION:
Sinter is a major raw material of an iron-making process of blast furnace. Sintering
process is a pre-treatment step in the production of iron, where fine particles of iron
ores, coke, fluxes viz., lime stone & dolomite, calcined lime fines and in some plants,
also secondary iron oxide wastes (return sinter fines, mill scale), are agglomerated
by combustion. AggJomeration of the fines is necessary to enable the passage of hot
gases during the subsequent blast furnace operation.
Sintering involves the heating of fine iron ore with flux and coke fines or coal to (1300
to 1480°C) produce a semi-molten mass that solidifies into porous pieces of sinter
with the size and strength characteristics necessary for feeding into the blast
furnace. Moistened feed is delivered as a layer onto a continuously moving grate or
'strand.' The surface is ignited with gas burners at the start of the strand, and air is
drawn through the moving bed causing the fuel to burn. Strand velocity and gas flow
are controlled to ensure that 'burn through' (i.e. the point at which the burning fuel
layer reaches the base of the strand) occurs just prior to the sinter being discharged.
Sinter is produced as a combined result of locally limited melting, grain boundary
diffusion and recrystallisation of iron oxides. The solidified sinter is then broken into
pieces in a crusher and is air-cooled. Product outside the required size range is
screened out, oversize material is crushed, and undersize material is recycled back
to the sintering process. The right sized sinter product is transported to Blast

Furnace. The sinter is then charged into a blast furnace, where the sinter is reduced
by gas mainly of CO to become molten iron.
Addition of calcined lime fines in dry fines form with other raw materials of sinter is a
known practice to improve the sinter plant's productivity, as the calcined lime is a
very good process intensifier in sinter making. Lime is a binder that acts slowly, its
solidification taking place at low rate as a result of the hydration of calcium oxide and
the intergrowth of crystals of calcium hydroxide. Addition of lime fines with other raw
materials of sinter mix, improves granulation, permeability and vertical sintering
speed, which results in increase in productivity of sinter machine. It is established
that addition of (-) 3 mm calcined lime in dry fines form at a rate of 30-40 kg/ton of
sinter are optimum for achieving maximum productivity of a sinter machine.
Considering the huge requirement of dry calcined lime in the conventional method of
calcined lime addition process in sinter mix and its high cost of production of calcined
lime, a necessity to innovate a different method for addition of calcined lime of low
specific consumption in sinter mix has been felt, which can reduce the consumption
of calcined lime significantly in the process without affecting any technological
benefits of calcined lime in sinter mix achieved in improving the productivity of sinter
plant.
Research & Development Centre for Iron and Steel of Steel Authority of India Limited
(SAIL) has successfully developed a new method for addition of calcined lime in
sinter-mix in wet form as "lime-water solution" to improve quality of sinter and
productivity of sinter plant through laboratory based pot sintering tests. The new
method will reduce the consumption of calcined lime in the sintering process.
As for as the relation between fine particles and water solution, it is well known that
iso- electric point differs among particles and surface charge can be affected by pH
in solution concerned. These phenomena can effectively be applied to sintering
process by spraying milky state calcined lime solution into the iron ore mixture to
achieve technological benefits of calcined lime in sinter mix. The following are the
main features of the earlier method in sintering process have been replaced /
modified with new method / means for higher productivity of sinter on low specific
consumption of lime:

1. In the earlier system, only process 'water' at atmospheric conditions is added as
moistening / wetting medium in sinter mix at Mixing and Nodulising Drum (MND)
at an appropriate feed rate as per the requirement of moisture in the sinter mix to
facilitate wet mixing and granulation of sinter mix for better bed permeability.
2. 'Calcined lime' of (-) 3 mm size in dry fines form is added as process intensifier in
sinter-mix at an open belt conveyor, which carries other raw materials i.e., sinter-
mix from the proportioning section to Mixing and Nodulising drums (MND) in
Sinter Plant.
SUMMARY OF THE INVENTION:
The basic objective of the invention is to improve the quality of wet mixing and
granulation of sinter mix for higher productivity on low specific consumption of lime
through effective hydration of lime in the process.
Sintering is a technology for agglomeration of iron ore fines into useful Blast
Furnace burden material for hot metal production. The raw materials of sintering
mainly consists of Iron ore fines (-10 mm), coke breeze (-3 mm), lime stone &
dolomite fines (-3mm) and other metallurgical wastes. Calcined lime fines (- 3mm) in
dry form are added in sinter mix as a binder for various technological benefits. The
proportioned raw materials are then mixed and moistened using normal process
water in a mixing drum. The mix is then loaded on sinter machine through a feeder
onto a moving grate (pallet) for further sintering process to produce sinter. More
particularly, the present invention relates to a new method for sintering wherein the
addition of calcined lime fines in dry form is replaced by addition of calcined lime in
wet form of low consumption as "lime-water solution" in sinter-mix to improve the
productivity of sinter plant and quality of sinter produced.
In the new method, calcined lime is diluted in water at an appropriate concentration
ratio as "lime-water solution" and added in sinter mix for wet mixing and granulation
at Mixing and Nodulising Drum (MND) in place the earlier method of adding 'water'
alone in sinter mix at MND.

Therefore such as herein described is a new method of sintering process for
achieving higher productivity comprising the steps of: providing various raw materials
such as Iron ore fines, dolomite fines, limestone fines, calcined lime, mill scales,
return sinter fines, BOF sludge, carbonaceous material, and others used as raw
material i.e., sinter mix for sintering; charging the raw materials i.e., sinter mix into a
Mixing and Nodulising Drum of sintering machine for thorough mixing and
granulation of sinter mix before charging on to sinter machine for sintering. There in
at Mixing and Nodulising Drum, 'lime water solution' (milk of lime (MOL)) of
appropriate concentration of calcined lime in water is added in sinter mix as
wetting/moistening medium for improving the wet mixing and granulation of sinter
mix for efficient permeability of sinter bed. The increased sinter bed permeability
leads to higher productivity through faster sintering process.
In the new method, when the calcined lime is added in sinter mix as a well diluted
'lime-water solution', facilitates the lime to completes its hydration in sinter mix, well
before it is charged on to moving sinter bed. The fully hydrated lime yields maximum
technological effects to sinter mix, leads to productivity improvements. This also
leads to significant reduction in consumption of calcined lime in sinter mix, as
wastages due to un-hydrated lime in sinter mix is significantly reduced compared to
the conventional method of lime addition as dry fines in sinter mix. Therefore such as
herein described is an improved sintering process of low consumption of calcined
lime in sinter mix for achieving higher productivity and improved quality of sinter,
comprising the following steps of:
Providing various raw materials such as Iron ore fines, coke breeze, lime stones,
dolomite, mill scales, return sinter fines, carbonaceous material etc., used as raw
material for sintering; charging the raw materials into a Mixing and Balling Drum
(MBD) for homogeneous mixing and granulation of sinter mix, where in calcined lime
(CaO) in wet form as "Lime water solution" at an appropriate concentration ratio and
quantity is sprinkled in sinter mix at Mixing and Nodulising Drum instead of only
water. The MND is rotated at an appropriate speed for granule / nuclei formation of
sinter mix. Lime in sintering charges solidifies immediately after mixing of charge
when milk of lime i.e., lime water solution is added to the later. The use of mixers that
provide for the formation of a homogeneous charge appreciably accelerates the

crystallization process, since well mixed charge has large area of contact between
the calcium hydroxide particles, water and filler. Further solidification of the lime and
its carbonization take place on the sintering machine. Thus the addition of lime water
solution (milk of lime) to the sinter mix (charge) increases the agglomeration and gas
permeability of the sinter bed of charge materials and strengthens the granules in the
regions where the charge undergoes excessive moistening, drying and rapid
heating. These factors ultimately improve the productivity of the sintering machine
and the quality of the sinter.
This granulated material from the MND is then charged on to a continuously
travelling sintering machine to form sinter bed of appropriated depth for further
sintering process. The top of the sinter bed is ignited. Air is continuously drawn
downwards throughout the length by suction fan so that the flame front gradually
travels down through the bed of the sinter mix. When the combustion zone reaches
the bottom of the sinter bed, indicates that the sintering has been completed.
The disclosed method of "calcined lime addition in sinter mix in wet form as lime-
water solution" in increasing the productivity of sinter machine and quality of sinter
while reducing the consumption of calcined lime in sinter mix has been successfully
designed, developed and established through laboratory based pot sintering trials.
Different concentration ratios and quantity of lime - water solution in sinter-mix have
been tried through pot sintering tests to find out the optimum concentration ratio and
quantity of lime water solution which will provide the maximum technological benefits
in terms of higher productivity at optimum consumption of calcined lime.
BRIEF DESCRIPTION OF THE PROCEEDURE ON INVENTION (POT SINTERING
TESTS):
Figure 1 illustrates schematic representation of pot sintering unit utilized in the
present invention.
DETAILED DESCRIPTION:
Pot sintering tests were carried out on actual base materials i.e., sinter-mix collected

from Rourkela Steel Plant (RSP). Normal process water at atmospheric conditions is
used for wet mixing of sinter mix. Sample containers containing Lime-water solutions
in different concentration ratios are kept ready for use. Continuous manual stirring
was carried out in the containers having the solution to prevent settling of lime.
Sufficient numbers of pot sintering tests were carried out with different lime-water
concentration ratios and with only water. Various performance/process parameters
during pot sintering tests were collected for analysis to understand the technological
changes / benefits due to addition of calcined lime in wet form as lime solution in
sinter mix. Through these tests, optimum concentration ratios of calcined lime in
water which will yield the maximum technological benefits in sintering process on low
consumption of calcined lime are established.
The following procedure was followed in the experimental trials of pot sintering tests:
a) Collection of sinter-mix material samples from plant:
Various raw materials such as Iron ore fines, dolomite fines, limestone fines, mill
scales, BOF sludge etc., are collected from different sources at a centralized place
i.e., at pot sintering laboratory.
b) Preparation of samples for physico-chemical analysis:
The collected raw materials are subjected in to both physical and chemical analysis
tests. In physical analysis, the raw materials are screened for proper size
segregations. The size wise segregation is normally carried for all the raw materials
in the range of +10mm, +5 to -10mm, +3 to -5mm, +1mm to -3mm. In chemical
analysis, the chemical compositions of its constituents such as Fe, FeO, CaO, Si02,
AI203, MgO are calculated.
The following table# 1 shows the chemical analysis of all raw materials collected
from the plant:



c) Charge calculations for pot sintering experiment:
Charge calculations are carried out on the basis of the following three equations:
> LOI balance
> Lime availability
> MgO balance
The amount of iron ore, dolomite and lime stone in Kg are calculated through
established equations. Other raw materials such as coke breeze, burnt lime and mill
scales are taken on fixed basis as per the norms.
Once the required constituents' values are found out through the equations, the raw
materials are accordingly collected by actual weighing through a digital weighing
scale.
Raw material composition for pot sintering tests was obtained by charge calculation
with the help of charge calculation model. Experimental design was prepared.
Numbers of experiments were carried out with repeat tests.
The various parameters used for experiments in pot sintering tests are indicated in
table # 2:


d) Initial dry mixing of raw materials:
All the collected raw materials are put on a tray and mixed thoroughly manually. After
the manual mixing, the mixed raw materials are put into the 'Mixing and Balling Drum
(MBD)' for mechanized mixing for thorough mixing. The MBD is rotated at 20 - 30
rpm for about 3-5 minutes with the mixture. By five minutes rotation of MBD, the raw
materials are thoroughly and properly mixed and are ready for further experiments.
e) Preparation of charge mix:
Water (or) lime water solution requirement for the raw materials' wet mixing is
estimated based on the moisture level requirement of the mixture, which is again
depend upon the quality of input raw materials and bed-height to be maintained.
Calcined lime (Ca O) of -10 mm size fractions and of 85 % to 90% purity is mixed
with normal process water of atmospheric conditions for generation of 'lime water
solution' samples. The lime water solution samples of different concentration ratios
are prepared for using in MBD for wet mixing of sinter mix. The dry mixed raw
materials from the MBD are collected in a tray and then the measured quantity of
water for the first pot sintering test (or) lime water solution of different concentration
ratios in remaining tests is added with the raw materials. The raw materials with

water / lime water solution are mixed thoroughly by manual tools in the tray itself. In
every pot sintering test, the concentration ratio of lime water solution is varied to
study and analyze the parameters of sintering process to find the optimum
concentration ratio of lime to water, which yields maximum improvement in
productivity. In the first test, only water (without any calcined lime addition) is used
for wet mixing of sinter mix.
The wet mixture of raw materials from the tray (approximately 100 Kg) is then fed
into the MBD. The MBD is rotated at 35 to 40 rpm for about 2-3 minutes for wet
mixing of raw materials. The thoroughly wet mixed raw material from the MBD is then
collected, is commonly known as "Charge-Mix" for charging into Sinter Pot for further
sintering process.
f) Sintering process on sinter mix
The sinter pot is a cylindrical enclosure of around 600 mm height and 310 mm ID.
The bed-height is normally decided as per the actual bed-height maintained at the
respective sinter plant. It is done so as to simulate the real situation at plants, so that
the test results can be co-related to the actual situations of the particular plant.
The pot with 'charge-mix' is placed on top of the 'wind-box' of the pot sintering
system. The gap between pot and wind box is sealed by clay to any air leakages. Air
blower of capacity 2000 mm WC is switched on to create necessary suction
underneath the grate bar. The level of under grate suction is adjusted accordingly to
match with the actual suction level of particular plant. Accordingly the suction is
maintained at 1000 mm WC for sinter mix of RSP case, 950 mm WC for DSP case,
450 mm WC in case of BSL etc.
Air filtration velocity across the sinter-bed is measured using anima meter. If the
velocity across the sinter bed is between 0.35 to 0.70 m/s is considered to be in
acceptable range. If the velocity is out-off this range then the raw-materials are taken
out for moisture level optimization.
Once the measured air filtration velocity is within the acceptable range, ignition

burner is put on with additional air supply through a air blower. The ignition is put off
after 2 to 2.5 minutes of ignition. The sintering process continues as the under grate
suction remain in on position. During the sintering process, the pressure (suction)
and temperature is continuously monitored. The temperature is measured
continuously through inserted thermocouple, provided under the grate bars. Similarly
the suction level is measured through an online pressure indicator provided below
the grate bars. When the temperature reaches at its peak, i.e., after continuously
rising to a level, it starts to decline, considers being the 'sintered temperature'. It
means the sintering process is completed. Normally the total pot sintering process
takes 30 minutes of duration. However the sintering duration varies according to bed
height maintained in the pot.
The sinter pot is allowed for an hour for natural air cooling. After an hour of natural
cooling, the sinter is discharged into crusher. The crushed sinter is subjected to
strength test in a 'shatter box' (Capacity 100 Kg). The box is kept at about 2m height
above the ground level. The sinter then dropped suddenly from the shatter box on to
a steel base plate. This test is carried out for five times to confirm their strength. After
the stabilization of sinter tests, the sinter is subjected physical screening process. In
this process the sinter is classified as -5 mm, 5 to 10 mm, 10 to 25 mm, 15 to 40 mm
fractions to estimate their percentage in the total material. However, + 5 mm size
fractions of sinter is considered as final product of the sintering process.
Finally, sample of +5mm size sinter is taken to Drum Tumbler for another testing of
their strength. The Pot Sintering Unit consists of the following major sub-system/
equipment:
a. Air Blower for Ignition
b. Exhauster system for suction
c. Wind Box or Wind Main
d. Suction Hood
e. Ignition Hood
f. Sinter Pot
g. Scrubber

The following process parameters were used for the experimental set up is shown in
table # 3:

The following parameters were recorded during the experiments:
(i) Sintering time
(ii) Temperature
(iii) Suction
The following parameters were calculated through the experiments:
(i) Productivity,
(ii) VSS
(iii) Yield
(iv) Sinter Strength
The above pot sintering tests procedure is repeated with another charge mix with
different lime water solution sample of different concentration ratio and the process

performance data are collected and analysed.
The following results through different pot sintering tests were obtained:

It is found that the productivity of sintering is low at 0.80 t/m2/h, when water alone
without any calcined lime is used as wet mixing medium in sinter mix. Maximum
productivity of 0.94 t/m2/h is achieved, when calcined lime in water as lime water
solution with concentration ratio at 20 grams / litre of water. The productivity level has
started decreasing to 0.90 t/m2/h when the concentration ratio of calcined lime in
water increased to 30 grams/litre of water. However the strength of sinter (DTI) and
yield are highest at 30 grams of lime per litre of water ratio. It is to be optimized
between 20 grams to 30 grams of lime per litre of water in the lime water solution for
optimum technological benefits in sintering.
Highlights of innovation:
> Addition of 'lime-water solution' in sinter mix in place of 'water" as wetting /
moistening and granulation medium of sinter mix at Mixing and Nodulising
Drum.
> A new method for addition of calcined lime in sinter-mix. In this method
calcined lime is thoroughly diluted in water in a separate container and added

as 'lime water solution' in sinter mix for wet mixing at Mixing and Nodulising
Drum. In the solution form, calcined lime has sufficient time to complete its
reaction process, well before it added in sinter mix. Due to the thorough
reaction of lime in the solution, the effects of lime in sinter mix is fully
achieved.
> This new method of calcined lime addition in sinter mix can replace the earlier
conventional method for addition of calcined lime in dry form.
> The new method of calcined lime addition in sinter mix has significantly
reduced the consumption of lime in sinter process. Due to full assimilation of
calcined lime in water solution well before it is added in sinter mix, the effects
of lime in sintering is fully achieved. The un-reacted calcined lime in sinter mix
is totally eliminated.
> The new method of calcined lime addition in sinter mix has improved various
technological benefits such as granulation of sinter mix, bed permeability,
strength of sinter, productivity in sinter making process.
> The optimum concentration ratio of Lime water solution i.e., calcined lime in
water is 20 grams / litre, which yields the maximum productivity of sinter
machine.
> The optimum concentration ratio of Lime water solution i.e., calcined lime in
water is 30 grams / litre, which provides maximum yield and strength of sinter.
> The calcined lime is fully assimilated in water through continuous mixing and
agitation, improves mixing and balling efficiencies of sinter-mix.
> As the calcined lime is diluted in water under an enclosed condition, the dust
generation during further handling in the system is eliminated.

> As the calcined lime is thoroughly diluted in water through continuous
agitation, size fraction of input calcined lime is immaterial. It also avoids the
crushing and screening process of calcined lime as in the case of earlier
system of handling dry calcined lime.
Although the present invention has been described in the context of a preferred
embodiment, it is not intended to limit the invention to the embodiment described.
Accordingly, modifications may be made to the disclosed embodiment without
departing from the spirit and scope of the invention. It is also contemplated that
various combinations or sub-combinations of the specific features and aspects of the
embodiments discussed herein may be made. Accordingly, various features and
aspects of the disclosed embodiments can be combined with or substituted for one
another in order to form varying modes of the invention. The invention is intended to
be defined only by the claims that follow.

WE CLAIM:
1. A new method of sintering process for achieving higher productivity
comprising the steps of:
providing various raw materials such as Iron ore fines, dolomite fines, limestone
fines, calcined lime, mill scales, return sinter fines, BOF sludge, carbonaceous
material, and others used as raw material, i.e., sinter mix for sintering;
charging the raw materials i.e., sinter mix into a Mixing and Nodulising Drum of
sintering machine for thorough mixing and granulation of sinter mix before charging
on to sinter machine for sintering, wherein at Mixing and Nodulising Drum, 'lime
water solution' (milk of lime (MOL)) of optimum concentration of calcined lime in
water is added in sinter mix as wetting/moistening medium for improving the wet
mixing and granulation of sinter mix for efficient permeability of sinter bed.
2. A new method for sintering process as claimed in claim 1, wherein the optimum
concentration ratio of Lime water solution (milk of lime) i.e., calcined lime in water is
20 grams / litre, which gives productivity improvement of sinter machine by around
15% in comparison to non-addition of any calcined lime in sinter mix.
3. A new method for sintering process as claimed in claim 1, wherein optimum
concentration ratio of MOL i.e., calcined lime in water is 30 grams / litre, which
provides maximum improvement in terms of yield and strength of sinter in
comparison to non-addition of any calcined lime in sinter mix.
4. A new method for sintering process as claimed in claim 1, wherein the
calcined lime fully hydrates / assimilates in moisture at Mixing and Nodulising Drum
well before charging the sinter mix on to sinter machine for sintering process,
thereby extracting the maximum effects of calcined lime in sinter mix in improving the
mixing and granulation of sinter mix for achieving maximum permeability in sinter
bed and strength of sinter produced.
5. A new method for sintering process as claimed in claim 1, wherein calcined

lime is added in diluted form i.e., as 'lime water solution' (milk of lime) into sinter mix
for wet mixing and granulation by which, the dust generation, during handling of
calcined lime in crushing, screening, transportations, etc., in dry fines form of the
earlier conventional method is significantly reduced.
6. A new method for sintering process as claimed in claim 1, wherein the
calcined lime of regular sizes are diluted in water directly to generate 'lime water
solution' i.e., milk of lime and then transported by pumping through pipelines to user
end. This new method eliminates the earlier conventional handling processes of
calcined lime such as in storing, crushing, screening, pneumatic transportations etc.,
leads to reduction in total cost of the system.
7. A new method for sintering process as claimed in claim 1, wherein the
calcined lime is fully hydrates in sinter mix well in before charging into sintering
process, thereby wastage of calcined lime in sinter mix due to partially or un-reacted
calcined lime in the process as in the case of the earlier conventional method has
been eliminated.

ABSTRACT

The present invention relates to a new method of sintering process by addition of
calcined lime in the form of lime-water solution, i.e., milk of lime (MOL) in sinter mix
for low specific consumption of calcined lime in achieving higher productivity of a
sintering plant.