FIELD OF THE INVENTION
The present invention relates to a method of improving heat transfer rate in a sinter plant.
More particularly, the present invention relates to a method for improving heat transfer rate
in sinter plants in order to decrease exhauster power consumption and improve sinter
quality. The invention also relates to a system for improving heat transfer rate in sinter plants
in a cost effective manner.
BACKGROUND AND PRIOR ART OF THE INVENTION
After doing extensive research in the field of sinter plant and heat control the inventors have
found that the 'Dry Fog System' has not been installed anywhere in sinter plant for the
purpose of improving heat transfer rate in order to decrease exhauster power consumption
and improve sinter quality. However, the System making dry fog on similar principle is being
used in sinter plant complex for dust suppression in the dust prone area.
The 'Dry Fog System' used at dust prone areas have only access to suppress dust.
Nowhere has it been tried known to us for process improvement of sintering plants as well
as energy conservation.
It has been observed that a steel plant having one sintering machine having sintering area
of 192 m2 achieved a production rate of 245.37 t/h in 2010-11 with a suction level of 1050
mmwc. This sinter machine alongwith 2 sinter machines (each having sintering area of 125
m2)of SP-1 caters the need to feeds four blast furnaces with 72% sinter in burden.
It was also observed that the aforesaid problem was prevailing in sinter plants operating with
following facts:
1. High alumina input from iron ore
2. Use of 38kg/ts of LD Slag (highest in SAIL)
3. Lower amount of Burnt lime consumption (11kg/ts)
Effects of above mentioned points on sinter making are as follow:
• Iron ores contains AI203 in Gypsite (AI203.3H20) form, which leads to high
temperature sintering operation to maintain sinter quality. Generally, 0.1%
increase in alumina increases solid fuel consumption by 3 kg/t.
• 38kg/ts of LD Slag consumption, leads to decrease in limestone consumption
& increase in dolomite consumption to maintain sinter basicity. Dolomite is a
refractory material which requires high heat input. Also, dolomite having high
MgO, has adverse effect on sinter quality. In general, 10kg/ts increase in
dolomite consumption increases solid fuel consumption by 1.7 kg/ts.
Due to above facts, coke breeze consumption goes upto 66kg/ts. This leads to widening
high temperature zone i.e. red hot zone in the sintering process (shown in Figure below) and
fuses green charge. These affects sinter bed permeability and decreases vertical sintering
speed.
Also, more than 50% of total bed height remains red hot at discharge zone which contributes
to higher sinter temperature at discharge zone. This had very adversely affected mechanical
equipment's viz. single roll crusher, grizzly bars, hot screen etc and reduces its life.
Since, during sintering process, highest thickness of red hot zone is found at 2/3rd of total
bed length as shown in the Fig.: 1 and has highest restriction in air flow across the bed. So,
any effort which can reduce red hot zone thickness at that zone or increase heat transfer
across the bed will improve quality of sinter produced.
The "Dry Fog System" was used for dust suppression in dust prone area of sinter plants in
the prior art. But the present inventors after doing extensive research in this field have found
that spraying of dry fog over sinter bed at a particular bed length provides significant
improvement in the heat transfer rate across the sinter bed to reduce exhauster power
consumption and improve quality of sinter produced. Such research work has enabled the
inventors to come up a new method and a system for improved heat transfer in a cost
effective way.
OBJECTS OF THE INVENTION
One object of the present invention is to overcome the disadvantages / drawbacks of the
prior art.
A basic object of the present invention is to provide an economical method to improve heat
transfer rate across the sinter bed to reduce in exhauster power consumption and improve
quality of sinter.
Another object of the present invention is to provide a system for improved heat transfer rate
across the sinter bed to reduce in exhauster power consumption and improve quality of
sinter.
These and other advantages of the present invention will become readily apparent from the
following detailed description taken in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic
understanding of some aspects of the invention. This summary is not an extensive overview
of the present invention. It is not intended to identify the key/critical elements of the invention
or to delineate the scope of the invention. Its sole purpose is to present some concept of the
invention in a simplified form as a prelude to a more detailed description of the invention
presented later.
According to one aspect of the present invention there is provided a method for improving
heat transfer rate in sinter plants, said method comprising :
spraying water in the form of dry fog on sinter bed, wherein said spraying is done at about
2/3 rd of total length of the sinter bed and in a manner that said dry fog touches top layers of
the sinter bed after getting contaminated with atmospheric air;
providing negative suction pressure below the sinter bed for suction of the dry fog inside the
bed
wherein said suction of dry fog reduces thickness of top layers thereby increasing heat
permeability of the bed.
According to another aspect of the present invention there is provided a system for
improving heat transfer rate in sinter plants, said system comprising:
plurality of nozzles fitted in staggered position on sinter bed for spraying water in the form of
dry fog on the bed; wherein said spraying is done at about 2/3 rd of total length of the sinter
bed and in a manner that said dry fog touches top layers of the sinter bed after getting
contaminated with atmospheric air;
plurality of pumps and plurality of motors operatively connected with said nozzles for
continuous supply of water at desired pressure to nozzles and to create negative suction
pressure below said sinter bed; and
a filter.
Other aspects, advantages, and salient features of the invention will become apparent to
those skilled in the art from the following detailed description, which, taken in conjunction
with the annexed drawings, discloses exemplary embodiments of the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The following drawings are illustrative of particular examples for enabling methods of the
present invention, are descriptive of some of the methods, and are not intended to limit the
scope of the invention. The drawings are not to scale (unless so stated) and are intended for
use in conjunction with the explanations in the following detailed description.
Figure 1 illustrates graphical representation of sintering bed on layer by layer basis when
sintering is taking place. Top black portion is hard sinter.
Figure 2 illustrates schematic diagram of the 'Dry Fog System'. The equipments/instruments
used for the system is shown.
Figure 3 illustrates air filtration velocity across the sinter bed with respect to wind boxes,
measured before and after installation of the system.
Figure 4 illustrates monthly average of blast furnace return sinter before and after the
innovation.
Figure 5 illustrates monthly average of specific power consumption of the plant before and
after the innovation.
Persons skilled in the art will appreciate that elements in the figures are illustrated for
simplicity and clarity and may have not been drawn to scale. For example, the dimensions of
some of the elements in the figure may be exaggerated relative to other elements to help to
improve understanding of various exemplary embodiments of the present disclosure.
Throughout the drawings, it should be noted that like reference numbers are used to depict
the same or similar elements, features, and structures.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWING
The following description with reference to the accompanying drawings is provided to assist
in a comprehensive understanding of exemplary embodiments of the invention as defined by
the claims and their equivalents. It includes various specific details to assist in that
understanding but these are to be regarded as merely exemplary. Accordingly, those of
ordinary skill in the art will recognize that various changes and modifications of the
embodiments described herein can be made without departing from the scope and spirit of
the invention. In addition, descriptions of well-known functions and constructions are omitted
for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the
bibliographical meanings, but, are merely used by the inventor to enable a clear and
consistent understanding of the invention. Accordingly, it should be apparent to those skilled
in the art that the following description of exemplary embodiments of the present invention
are provided for illustration purpose only and not for the purpose of limiting the invention as
defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a," "an," and "the" include plural referents
unless the context clearly dictates otherwise.
By the term "substantially" it is meant that the recited characteristic, parameter, or value
need not be achieved exactly, but that deviations or variations, including for example,
tolerances, measurement error, measurement accuracy limitations and other factors known
to those of skill in the art, may occur in amounts that do not preclude the effect the
characteristic was intended to provide.
Fig 1 discloses graphical representation of sintering bed on layer by layer basis when
sintering is taking place. Top black portion is hard sinter. At this layer, sintering has been
already taken place and offering least resistance to air flow across the bed. Next red hot
layer shows that at this point sintering is taking place. Coke is burning and heat produced is
used for agglomerating iron ore particles by melting its surfaces. This zone offers highest
resistance to air flow across the bed. Next layer is the green charge where preheating is
taking place. Plot below the mentioned zones shows air filtration velocity across the sinter
bed with respect to wind boxes. From the plot it is evident that air filtration velocity is
minimum at 70% of total bed length. Also red hot zone has maximum thickness at this zone.
An improvement in heat transfer rate at this zone was felt to mentioned benefits. That's why
it was decided to install the dry fog system at this zone of the sinter bed.
Any effort which can reduce red hot zone thickness or increase heat transfer across the
sinter bed will improve quality of sinter produced.
In order to do so , it is decided to spray water in the form of dry fog on the sinter bed at 2/3rd
of total bed length through compressed air assisted nozzles. As we know that heat transfer
coefficient of water is 4 times higher than air. So, 20g water/m3 of air increase heat transfer
coefficient of air by ~6%. This in turn, increases heat transfer rate across the sinter bed.
Thermal calculations, mass flow rates of air and water, position to spray dry fog above the
sinter bed etc. were decided by a no. of pilot scale experiments at our laboratory.

Arrangement made at shop floor to create above said facility is as follow:
> 4 Nos. of nozzles were fitted in the staggered position (shown in figure:1).
> 2 Nos. Of pump & motors were installed for continuous supply of water at
desired pressure to nozzles.
> 1 No. of simplex type filter was installed to get clean water in order to
prevent nozzle chocking.
'Dry Fog System' envisages controlled addition of dry fog above the top of sinter bed at
specified position. Dry fogs are prepared from controlled mixing of water and compressed air
at desired flow and pressure by the system itself. Suitable nozzles are selected for the
purpose. As evident from figure 1, red hot zone has highest thickness at around 70% of total
bed length. 'Dry Fog System' is installed above that zone and sprays water in fog form.
When these fogs with atmospheric air, touches the surface of sinter bed, it comes inside the
bed due to negative suction pressure applied below the bed. Moisten air when touches top
of red hot zone, having high temperature, it cools down a top narrow layer of hot zone. In
this way hot zone thickness reduces and increases bed permeability as on whole. From the
figure 3, it is clearly evident that air filtration velocity increases slightly after wind box no. 15
when comparing before and after the innovation.
Also, heat contained by top narrow layer of hot zone is transferred to filtering air, thus
increasing its temperature. On a whole, when these air comes out of bottom of sinter bed
has higher temperature when the system was on keeping other parameters constant.
In the present case, the wind main air temperature is increased by 5C(129-134C) leading to
reduction in specific power consumption by 5.96%, shown in figure 5 .
Also due to, improved heat transfer rate, proper augmentation of base mix sinter particle
took place leading to improvement in quality of sinter. This is strengthening by reduction in
Blast Furnace Return fines after innovation shown in figure 4.
Data/Details To Justify That The Process/Composition Is Not A Result Of Mere
Admixture Of The Various Ingredients Used:
1. Improvement in Air filtration velocity by 9% (0.32m/s to 0.35m/s)
Installation of "Dry Fog System" intensifies sintering process. This
decreases hindrance in air flow across the sinter bed by improving
permeability of the bed which in turn improves air filtration velocity. In the
plot shown in Figures 1 and 3 there are clear cut indication in
improvement in air filtration velocity after wind box no. 15. Dry fog covers
sinter bed above wind box no. 15-17.
2. Blast Furnace Return sinter decreased by 2.31% (149.61 to 146.15kg/t)
is shown in Table 2 & 3.
It clearly indicates improvement in strength of sinter. In other words it can
be say that Yield of the sinter plant has been increased.
Table 1: BF Return fines generation & Electrical Power Consumption Before
installation & commissioning of 'Dry Fog System'
3. Wind main gas temperature increased by 5C (129-134C) leading to reduction
in specific power consumption by 5.96% (42.85 to 40.30 kWh/t) in Table 1 &
2.
As water has four fold heat transfer co-efficient than air, introduction of
Dry Fog, specific heat capacity of hot air increased. This leads to faster
heat transfer between solid and gas. More heat was transferred by same
amount of waste gas which in turn increases temperature of wind main
gases. Since, higher the temperature, lesser is the density of gas and
lesser is the load on motor of the exhauster fan. In this way, exhauster
power reduced by 5.96%.
4. Unburnt carbon in sinter came down from 0.5% to 0.05%
Due to presence of moisture laden air, coke burning efficiency improved
during sintering process. Carbon analysis of return sinter confirms this
and offers high temperature within the narrower zone.
5. Hot zone in sinter discharge end reduced substantially
Due to humidification of hot air, narrowing red hot zone took place. This
carries forward to the end of sinter discharge. As a result, hot zone
thickness at the discharge zone reduced from 50% to 25%
(approximately, on visual observation).
6. Dust generation at the sinter plant came down substantially
Best Mode Of Working The Invention
The 'Dry Fog System' has been installed at SP-2, RSP where sinter plant is suffering
with high alumina iron ore (average alumina percentage in sinter 3.18; shown in table
2). In such sinter plants, coke breeze consumption goes high (up to 66kg/t on dry basis
for SP-2, RSP). Higher coke breeze consumption increase heat load in the bed and
thickness of high thickness zone which offers higher resistance to air flow across the
bed resulting in reduction in bed permeability. This system narrows down the high
temperature zone and improves heat transfer rate between solid and gas across the
sinter bed which in turn intensifies the sintering process.
1. The 'Dry Fog System' was in-house developed, designed and installed at SP-
2, RSP with very small capital expenditure.
2. It is a very simple system and easy to install.
3. After installation and commissioning of the system several technological
benefits were achieved .
4. Break Even Point for the system was obtained in less than one day of system
operation.
WE CLAIM:
1. A method for improving heat transfer rate in sinter plants, said method comprising :
spraying water in the form of dry fog on sinter bed, wherein said spraying is done at
about 2/3 rd of total length of the sinter bed and in a manner that said dry fog touches
top layers of the sinter bed after getting contaminated with atmospheric air;
providing negative suction pressure below the sinter bed for suction of the dry fog
inside the bed
wherein said suction of dry fog reduces thickness of top layers thereby increasing
heat permeability of the bed.
2. Method as claimed in claim 1 wherein said spraying of water provides controlled
addition of dry fog above the top of sinter bed at specified position.
3. Method as claimed in claim 1 providing power reduction by about 5.96%.
4. Method as claimed in claim 1 providing increase in specific heat capacity of hot air.
5. Method as claimed in claim 1 further comprising humidification of hot air narrowing
red hot zone during initial stage of sintering.
6. Method as claimed in claim 1 wherein hot zone thickness at the discharge zone is
reduced from 50% to 25% approximately.
7. Method as claimed in any preceding claim wherein said dry fog is generated by a dry
fog system.
8. A system for improving heat transfer rate in sinter plants, said system comprising:
plurality of suitable nozzles fitted in staggered position on sinter bed for spraying
water in the form of dry fog on the bed; wherein said spraying is done at about 2/3 rd
of total length of the sinter bed and in a manner that said dry fog touches top layers
of the sinter bed after getting contaminated with atmospheric air;
plurality of pumps and plurality of motors operatively connected with said nozzles for
continuous supply of water at desired pressure to nozzles and to create negative
suction pressure below said sinter bed; and
a filter.
9. System as claimed in claim 8 wherein said filter is simplex type filter.
10. System as claimed in claim 8 comprising providing improved air filtration velocity of
0.35 m/s.
11. System as claimed in claim 8 comprising providing decrease in BF return sinter from
149.61 to 146.15 kg/t.
12. System as claimed in claim 8 providing power reduction by about 5.96%.
13. System as claimed in claim 8 providing increase in specific heat capacity of hot air.
14. System as claimed in claim 8 further providing humid if ication of hot air narrowing red
hot zone during initial stage of sintering.
15. System as claimed in claim 8 is a dry fog system.
16. A method for improving heat transfer rate in sinter plants as herein substantially
described and illustrated with the accompanying drawings.
17. A system for improving heat transfer rate in sinter plants as herein substantially
described and illustrated with the accompanying drawings.

ABSTRACT

The present invention relates to a method for improving heat transfer rate in sinter plants.
The method comprises steps of spraying water in the form of dry fog on sinter bed in a
manner that said dry fog touches top layers of the sinter bed after getting contaminated with
atmospheric air and providing negative suction pressure below the sinter bed for suction of
the dry fog inside the bed. The invention also relates to a system for improving heat transfer
rate in sinter plant.