SINTER BED HUMIDIFICATION SYSTEM AND PROCESS THEREFOR
FIELD OF THE INVENTION
The present invention relates to sinter bed humidification and the sintering
process thereof. More particularly the present invention relates to
humidification of iron ore sinter bed using cold fog and the process therefor
which would enable faster sintering speed and increase in productivity of the
sintering machine. Importantly, the process of sintering and the system
provided is adapted to increase the burn through point temperature and also
thereby improve the productivity of sintering machines.
BACKGROUND ART
It is well known that sinter is produced from finely divided iron ore, which is
roasted with coke and lime by incipient fusion. Usually, such iron ore sinter is
produced in sintering machines.
The process of sintering is essentially carried out in the steel industry for
converting iron ore fines to lumps or briquettes such as to favour feeding to
BF operation as the main iron bearing charge. In the sintering plant, iron
sintering is carried out on a moving conveyor bed on which mixed ingredients
comprising iron ore fines, coke fines, limestone fines and various iron and flux
bearing materials like flue dust, slag etc. commonly known as the sinter mix
are charged at one end of the moving bed. The top layer of the sinter mix on
the moving be'd is ignited by gas burners installed at suitable locations.
Ambient air required for the combustion of sinter mix, is sucked in through the
sinter bed from top into the wind boxes, installed below the bed, by the
operation of an exhauster fan. The variable factors that influence the
productivity of the sintering machine are the rate of airflow through the sinter
bed (m3/min) and the heat capacities of the gas and sinter mix. The rate of
airflow is not uniform throughout the length of the bed. It is ideally low ranging
between 50-70% of the sinter machine length.

Conventionally, to increase the sinter machine productivity, under grate
suction is increased introducing an exhauster of higher suction capacity and
providing better sealing for gases/air leakage. This results in higher volumetric
flow rate of air through the moving bed for sintering. An alternative method of
increasing productivity of sintering machine, the heat capacity of the air is
effectively increased by injecting steam through the bed in the 50-70% range
of the machine bed length, such that the vertical sintering speed of mix across
the depth of bed is also increased as the exchange of heat between the mix
and the humidified air is more.
In our co-pending application for Patent no. 76/KOL/2008 dated 10/01/2008
titled "A PROCESS FOR FASTER SINTERING OF IRON-ORE AND
SYSTEM / APPARATUS TO CARRY OUT SUCH PROCESS" discloses a
faster process of sintering and improving quality of sinter product and a
system apparatus/ to carry out such process. More particularly, the process is
directed to faster iron ore sintering process that would improve sinter quality in
terms of sinter strength, reduction degradation index (RDI) decreased from
existing 33.1 to 23.3, increased air filtration velocity due to increased
permeability, increased heat capacity of ambient air by preferred injection of
steam at selective pressure and controlled quantity over desired region of bed
length, humidity adjusted to about 80gm/Nm3, decrease in sinter fines in
sinter product. Importantly, the process and apparatus is adapted to reduce
the coke rate and the carbon monoxide emission in sinter exhaust gases and
also reducing exhauster power consumption by about 5%. A solenoid valve
interlocking with sinter machine drive , stops steam supply when the machine
is stopped. The present process and system thereof to carry out the process,
is therefore adapted to improve quality with reduced RDI and higher
reducibility of sinter in a faster way, having wide industrial application in steel
plants.
The metallurgical process of sintering prepares the iron ore fines to form
suitable feed for the blast furnace. Iron ore fines and coke are mixed,
moistened with water and micro-pelletized to form the charge. The charge is
loaded onto a pallet/grate and leveled to form a bed which is ignited by a gas-
fueled ignition hood. A heat wave and coke combustion zone travels down

through the bed under the influence of a suction pressure. Hot gas from the
combustion zone passes through moist charge deeper in the bed where water
evaporates. The process can be divided in five subsequent zones; preheating,
heat exchange, combustion, fusion and drying. The main purpose of sintering
is to convert weakly-bonded granules into a partially fused porous sinter cake
suitable for feeding to the blast furnace. Sintering is a complex process
involving flow of gas through a packed bed, heat and mass transfer between
gas and solids, heterogeneous chemical reactions and partial melting of
solids.
Sinter Plant-1, Durgapur Steel Plant has been provided with two sintering
machines each having 142.7 m2 sintering area. This sinter plant achieved a
productivity level of 0.66t/mm2/hr, whereas internationally achieved
productivity levels are much higher. The coke crushing index has been
reported to 72 - 77 % against the internationally value of 90 %. The suction
value was 350 mmWC as against international levels of 1700 - 2000 mmWC.
There is no lime addition option whereas high performing sinter plants use 20-
25 kg/t of sinter. For the improvement of productivity of a down draft sinter
machine and quality of product sinter, several fundamental investigations
have been investigated. Introduction of sinter bed humidification system has
also been installed in some SAIL sinter plants. But in these humidification
systems either steam or atomized water produced by compressed air has
been adopted. Under SP#1, DSP condition suction value is very low and
hence compressed air is not available. So a new humidification system should
be developed and introduced in this sinter plant. With this idea in view it is
herein disclosed that if water after cleaning is highly pressurized and passed
through a very fine specially designed nozzle it gets converted into fog
artificially. This is called Cold Fog. So 'sinter bed humidification system by
cold fog' is the main part under the scope of the present work.
The productivity of sintering machine i.e. the speed of sintering depends on
three basic parameters, which include (i) volumetric airflow rate (m3/min.), (ii)
heat capacity of gas and (iii) the heat capacity sinter mix involved. It is well
known that normally the productivity of sintering machines are increased by
increasing of volumetric flow rate by increased suction below grate and

reduction of bed resistance, preferably by lowering of bed height and
improving the average grain size of the sinter mix particles.
OBJECT OF THE INVENTION
It is the basic object of the present invention to provide for a system for
humidification for sintering bed by cold fog to produce the iron ore sinter which
would favour increasing the heat capacity of the air /gas and thereby facilitate
increasing the vertical speed of sintering.
Another object of the present invention is to provide for a simple and cost
effective manner under condition where the suction value is very low and
hence compressed air is not available. So a new humidification system is
developed and introduced in the sinter plant whereby the speed of sintering
can be improved and also the productivity of sintering machine increased to
the desired extent.
Another object of the present invention is to provide control the addition of
water in such a manner that temperature loss of the upper part of sinter bed
should not be more than 145°C and water should be vaporized from the
surface of the black sinter.
Another object of the present invention is to provide a water-fog spray system
has been interlocked with the respective sinter machine individually.
Another object of the present invention is to provide a system wherein the
variation of atrhospheric humidity level due to season" is controlled
automatically/manually varied / fixed for a certain time period (season).
Yet further object of the present invention is directed to a system for sintering
iron ore which would be adapted for increasing the heat capacity of air / gas
and in turn also increase in the vertical speed of sintering with substantial
increase in average balling index value and average sinter strength i.e T.I
(Tumbler Index).

Yet another object of the present invention is directed to a simple and cost
effective system of humidification using cold fog which would enable user
friendly application and use of sintering machine by increasing the speed of
sintering and also the productivity of the system.
The details of the invention, its objects and advantages are explained in
greater details in relation to the non-limiting following accompanying figure of
the cold fog humidification system in sinter machine in accordance with the
present invention.
SUMMARY OF THE INVENTION
Therefore such as herein described there is provided a system for sinter bed
humidification for sintering of iron ore comprising: means for providing cold
fog spray over sinter bed adapted to get automatically controlled with the flow;
selectively angled preferably 90° wide angle spray nozzles in staggered
manner covering the region where the air filtration velocity is minimum; a
plurality of sensors disposed at various locations of sinter bed to record and
send the readings to the controller; control means to control the pressure
pump and the associated valves; and valve means in the stream line adapted
to regulate the pressure and flow of cold fog as required.
To regulate the flow of the high pressure water from pump solenoid valves
and other linked valves are provided to properly regulate the flow rate of cold
fog spray and selective set of nozzles adapted to regulate/stop the spray. The
control the cold fog spraying is interlocked with the sinter machine drive such
that the spray is automatically stopped with the stoppage of the machine. The
supply of water to the number of feeders is carried out with the help of a long
header connecting the source of cold fog supply to the main header and
wherein the main header is insulated and laid parallel to the sinter machine.
Also herein described is a process for sintering iron ore adapted for faster
vertical sintering speed and higher productivity comprising: providing the
desired sinter mix in the bed of the sinter machine; providing volumetric air
flow through the sinter bed ; and increasing the heat capacity of the air during
sintering by humidification of air by cold fog spraying.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates schematic representation of the sinter bed humidification
system in accordance with the present invention;
Figure 2 illustrates schematic representation of the sinter bed humidification
system by cold fog in accordance with the present invention;
Figure 3 illustrates pictorial view of the of the sinter bed humidification system
by cold fog at SP#1, DSP in accordance with the present invention.
DETAILED DESCRIPTON
A sinter bed can be divided into three distinct zones i.e. Green sinter zone,
hot zone (molten zone) and black sinter zone (finished sinter zone) as shown
in the Figure 1. Molten zone offers resistance of air flow into the bed. It is
clear from the Figure 1 that after some time the hot zone touches the bottom
part of the bed i.e. about two-third part of a sinter machine. At this point i.e.
burn-through point (BTP) rate of heat transfer is less. Under this condition,
lower zone can never be sintered of desirable quality and it is being
discharged as usual practice. As a result productivity and sinter quality get
deteriorated. If controlled amount of steam or atomized water is sprayed
above this point it will be sucked and water gets vaporized (if water is used
instead of steam). Subsequently it passes through the lower zone, which in
turns enhances the heat transfer rate in this zone as water has the highest
specific heat capacity. So sintering process gets completed before reaching to
the discharge end as shown by dotted line of Figure 1. Water addition should
be controlled in such a manner that temperature loss of the upper part should
not be more than 145°C and water should be vaporized from the surface of
the black sinter. If water droplet instead of atomized water is used it gets
penetrated into the hot product sinter and there is a high chance of
disintegration.
In the beginning, there was no sinter bed humidification system at Sinter
Plant-1, DSP. Based on the disclosed findings, total system was designed

with specified equipment's and implemented at SP-1, DSP. Through
aerodynamic study position of cold fog spraying system has been identified in
both machines. The schematic representation of the cold fog humidification
system is shown in Figure 2, and the pictorial view of the system is shown in
Figure 3.
As apparent from Figure 1, the humidification of air is achieved by spraying
cold fog into sinter bed through nozzles provided in the pipe. The pipe can be
of diameter of about 50mm which is laid across the width of the pallet with the
arrangement of the flanged joint in one side and resting on strand on the other
so that in case of shut down or maintenance the pipe can be easily re-located.
Preferably, five numbers of parallel pipes as illustrated in the embodiment of
the Figure 2 are provided across the width at location of 50- 65% length of
machine from the charge side.
It is thus possible by way of the above arrangement of cold fog spray on the
sintering bed to increase the humidity of air from its natural range of about 10-
30 gm / Nm3 to 60 gm/Nm3 in the localized zone. The heat capacity of the air
could be increased by such injection of steel in the bed. The location of the
injection of the steel is preferably selected at the zone where the sinter
process speed is minimum i.e. volumetric flow in the air is minimum and in the
process the hot zone width extension is restricted.
The sinter bed humidification system includes an array of water fog spray
nozzles connected by means of parallel piping system from which highly
pressurized clean water is passed, through the said very fine specially
designed nozzle and the pressurized water gets converted into fog artificially.
This is called Cold Fog. The sinter bed humidification system by cold fog is
the main objective under the scope of the present work. The cold fog spraying
onto sinter bed is carried out by transverse rows of sprays preferably through
nozzles into the sinter bed in the location 50% to 65% length of the machine
from the charge side as shown in Fig 2 and 3. The location of cold fog
spraying is done selectively at the zone where the sinter process speed is
minimum (volumetric flow of air through the zone is minimum) such that the
hot zone width extension is restricted.

There is also provided a control panel which controls the high pressure pump
and electrically operated ON/OFF Valve for controlling the requisite quantity of
cold fog which is to be sprayed over the sinter bed. The control panel
comprises of electronic circuitry, which helps in controlling the pump and the
valve system. The high pressure pump is supplied with inlet water from a
purified water storage tank as shown in Figure 2.
There is also provided solenoid valve based control means for cold fog spray
over sinter bed adapted to get automatically stopped with the stoppage of
machine and thereby preventing excess moistening of sinter mix when the
machine is stopped. The nozzles provided over the sinter bed are 90° wide
angle spray nozzle, located in a staggered manner to cover the entire region
of sinter bed where the air filtration velocity is minimum and the burn raise
point temperature is achieved. The cold fog is sprayed at controlled pressure
and flow rate providing optimum improvement in the heat capacity of the
humidified air that carries up to 60gm/Nm3 moisture, said control being
effected in the system operatively by the set of valves on the header lines, the
amount depending on the moisture content of ambient air, ensuring desired
strength and RDI based improved quality of sinter product. The process
achieves reduced coke rate in sintering and thereby improving the reducibility
of the sintered ore.
The working principle of the humidification system has been designed
according to the following points:
The water-fog spray system has been interlocked with the respective
sinter machine individually.
As the variation of atmospheric humidity level is seasonal, the rpm of
the pump can be automatically/manually varied / fixed for a certain time period
(season). When the required moisture level is low i.e. in rainy season, the rpm
can be automatically/manually decreased to generate less amount of fog. On
the other hand, when the required moisture level is more i.e. in winter and
summer seasons the rpm can be automatically/manually increased to
generate comparatively higher quantity of fog with the help of control means.
The system is equipped with "ON / OFF / AUTO / manual / emergency off"
switch. The disclosed system also includes sensors which can record the

atmospheric humidity, humidity and temperature above and below at different
requisite locations of the sinter bed and thereafter the implementation /
spraying of the cold fog is controlled with respect to the recorded readings
automatically vide a controller. In an embodiment, the controller is a
programmed processor, which controls the pressure pump and the valve
simultaneously with the help of sensor readings. In another embodiment the
controller is programmed for automatic and manual operations by means of a
physical switch.
Automatic system operation has been opted when one of the machines
or both machines are off/tripped. When one of the machines is off/tripped the
water-fog spray in that machine will be stopped in auto mode and the other
machine spray will be continued with required reduction of rpm of the high
pressure pump in auto mode. The water-fog spray starts in auto mode when
machine starts again. When both machines are off / tripped the water-fog
spray in that machine will also be stopped in auto mode. The system starts
again in auto mode when cooler starts.
When both machines are off / tripped there is an option to test the fog
generation system in manual mode.
Entire operation and control of the water-fog humidification system can
be done from the control room of SP-I in the machine floor, from a new control
panel which incorporates all necessary controls and indications.
Experimental Observations
Balling index study that is ratio of +3 mm after and before balling drums was
conducted. Samples from the conveyor belts before each Balling Drum has
been collected and granulometry analysis has been carried out with the help 3
mm screen. Similarly samples have been collected from discharge end of the
Balling Drum and granulometry analysis carried out. Absolute weight and
percentage of +3 mm calculated and recorded. Physical analysis i.e. Tumbler
Index (T.I. %) of finished sinter samples was carried out before and after
installation of system. Air Filtration Velocity measurements over the sinter
beds of both machines was conducted. The major observations obtained are
as follows:

The average balling index value was 1.47 in machine#1 and 1.34 in
machine#2.
Average sinter strength i.e. T.I. (Tumbler Index) of the finished sinter
was recorded as 71.6 %.
In machine#1, average air filtration velocity was 0.26 m/s and in
machine#2, this value was 0.15 m/s.
RESULTS
Trials were conducted before and after installation Water Fog Based Sinter
Bed Humidification System. The following are the analysis of the trials:
There is an enhancement of Vertical Sintering Speed (VSS) above the
wind boxes 16, 17 & 18 where the spraying points are installed.
By the implementation of innovative idea productivity of the sinter plant
1, DSP has been increased by 7.6% from the base level of 0.66 t/m2/hr.
Average sinter strength i.e. T.I has been improved from 71.6 to 72.7%.
BENEFITS EVALUATION
Basic Plant Data
Production of Sinter Plant -1 (before innovation) : 1009092 T
(Source Sinter Plant Statistical, DSP, up to Dec'10,
Nine months)
Production of Sinter Plant-1 (after innovation) : 1085783 T
(Taking 7.6% increase in productivity)
Fixed cost of sinter production in SP-1, DSP : Rs 476 / T
Procedure of Calculation
Saving in fixed cost of sinter production (SP 1)

Total saving (annual) = Rs.33.62082 x 1085783 x 12/9 = Rs.486.73 lakhs
Anticipated Annual Benefit (AAB) = Rs. 487 lakhs

By the implementation of innovative ideas productivity has been increased by
7.6%. Accordingly, the Anticipated Annual Benefit value has jumped to Rs.
487 lakhs.
Numerous modifications may be made to the present invention, which still fall
within the intended scope hereof. Thus, it should be apparent that there has
been provided in accordance with the present invention for sinter bed
humidification system and process therefor that fully satisfies the objectives
and advantages set forth above. Although the invention has been described in
conjunction with specific embodiments thereof, it is evident that many
alternatives, modifications and variations will be apparent to those skilled in
the art. Accordingly, it is intended to embrace all such alternatives,
modifications and variations that fall within the spirit and broad scope of the
appended claims.

Claims:
1. A system for sinter bed humidification for sintering of iron ore comprising:
means for providing cold fog spray over sinter bed adapted to get
automatically controlled with the flow;
selectively angled preferably 90° wide angle spray nozzles in staggered
manner covering the region where the air filtration velocity is minimum;
a plurality of sensors disposed at various locations of sinter bed to record and
send the readings to the controller;
control means to control the pressure pump and the associated valves; and
valve means in the stream line adapted to regulate the pressure and flow of
cold fog as required.
2. A system for sinter bed humidification of iron ore as claimed in claim 1,
comprising a valve to regulate the flow rate of cold fog spray and selective set
of nozzles adapted to regulate/stop the spray.
3. A system for sinter bed humidification of iron ore as claimed in claim 1,
comprising solenoid valve means is provided to control the cold fog spraying
which is interlocked with the sinter machine drive such that the spray is
automatically stopped with the stoppage of the machine.
4. A system for sinter bed humidification of iron ore as claimed in claim 1,
comprising a long header connecting the source of cold fog supply to the main
header and wherein the main header is insulated and laid parallel to the sinter
machine which is adapted to provide supply of water to plurality of feeders.
5. A process for sintering iron ore adapted for faster vertical sintering speed
and higher productivity comprising:
providing the desired sinter mix in the bed of the sinter machine;
providing volumetric air flow through the sinter bed ; and
increasing the heat capacity of the air during sintering by humidification of air
by cold fog spraying.

6. A process for sintering iron ore as claimed in claim 5, wherein the
humidification of air by cold fog spraying is carried out in the selected
locations of the sintering machine.
7. A process for sintering iron ore as claimed in claim 5, wherein the
humidification of air by cold fog spraying is carried out in the selected location
of the sintering machine such that the water addition should be controlled in
such a manner that temperature loss of the upper part should not be more
than 145°C and water should be vaporized from the surface of the black
sinter.

8. A process for sintering iron ore as claimed in claims 5, wherein the cold fog
spraying onto sinter bed by transverse rows of sprays preferably through
nozzles into the sinter bed in the location 50% to 65% length of the machine
from the charge side.
9. A process for sintering of iron ore as claimed in claim 5, wherein the
humidity of the air is increased to about 60 gm/Nm3 in the localized zone.
10. A process for sintering of iron ore as claimed in anyone of claims 5 to 9,
wherein the location of cold fog spraying is selectively at the zone where the
sinter process speed is minimum (volumetric flow of air through the zone is
minimum) such that the hot zone width extension is restricted.

ABSTRACT

The present invention relates to humidification of iron ore sinter bed using
cold fog and the process therefor which would enable faster sintering speed
and increase in productivity of the sintering machine, importantly, the process
of sintering and the system provided is adapted to increase the burn through
point temperature and also thereby improve the productivity of sintering
machines.