FIELD OF THE INVENTION
This invention relates to method for reduction of composite agglomerates of high
alumina (greater than or equal to 3.0% by weight) iron ore mineral processing
rejects and Jhama coal for production of reduced metallic iron product and or
iron metal agglomerates in a moving hearth furnace such as rotary hearth
furnace or tunnel kiln.
BACKGROUND OF THE INVENTION
Iron ore and coking coal are basic raw materials for iron and steel production.
Iron ores are beneficiated by wet mineral processing operations to meet the
quality requirements of iron making processes. During iron ore mineral
processing operations, the run of mine iron ore is washed and sized in order to
enhance the quality of iron ore. However, slimes or fines with mostly less than
0.5 mm size with 20 to 50 weight % of less than 20 urn size particles in it are
discarded as rejects during these operations which have alumina (AI2O3) content
in the range of 3.0 to 10.0% by weight. These iron containing rejects can not be
used directly in conventional shaft or non shaft iron making processes due to
high alumina content typically greater than 3.0% by weight. High alumina in iron
ores limit the slag fluidity during reduction process and results in inefficient
conventional blast furnace iron making process or alternative direct reduced iron
(DRI) making processes based on rotary hearth furnace or tunnel furnace.
The ironmaking processes to produce liquid iron or direct reduced iron can be

classified into five groups based on the type of critical equipments used in the
process. These ironmaking processes have shaft furnace or rotary kiln or rotary
hearth furnace or fluidized bed or other reactors as critical equipment in the
process. Currently, there are five primary processes that are in commercial use
for the production of liquid iron or direct reduced iron which includes the shaft
furnace based processes such as blast furnace, Corex, Midrex, Hylsa (HYLIII,
HYLIVM, etc.) and a rotary kiln based process known as SL/RN or Stelco-Lurgi
process. Each of these iron making processes are discussed briefly below.
Blast Furnace: The blast furnace process is based upon a moving bed
reduction furnace which reduces iron ore with coke and limestone. It consists of
weighting of the burden, charging of the blast furnace, hot product dispersal
from the blast furnace and offgas cleanup system. Iron bearing materials (iron
ore, sinter, pellets, etc), coke and flux (limestone and dolomite) are charged into
the top of the shaft. Blasts of heated air and also in most cases, a gaseous, liquid
or powdered fuels are introduced through openings at the bottom of the shaft
just above the hearth crucible. The heated air burns the injected fuel and most
of the coke charged in from the top to produce heat required by the process and
to provide reducing gas that removes oxygen from the ore. The reduced iron
melts and runs down to the bottom of the hearth. The flux combines with the
impurities in the ore to produce slag which also melts and accumulates on top of
the liquid iron in the hearth. The total furnace residence time is about 6 to 8
hours. This process produces liquid pig iron which is used in steelmaking.
Corex : The iron oxide feed to a Corex reduction shaft is in the form of lump ore

or pellets. Non-coking coal is used in the Corex process as the strength of coke
needed in the cohesive zone of the blast furnace to provide sufficient
permeability to the bed is not required. Similar to the blast furnace process, the
reduction gas moves in counter flow to the descending burden in the reduction
shaft. Then, the reduced iron is discharged from the reduction shaft by screw
conveyors and transported via feed legs into the melter gasifier. The gas
containing mainly CO and H2 which is produced by the gasification of coal with
pure O2 leaves the melter gasifier at temperatures between 1000 and 150 °C.
undesirable products of coal gasification are removed and the gas is cooled to
800-850 °C and cleaned from dust particles. After reduction of the iron ore in the
reduction shaft, the top gas is cooled and cleaned to obtain a high caloric export
gas. The main product, the hot metal can be further treated in either EAF or BOF
or can be cast and sold as pig iron.
Midrex Shaft Furnace : The Midrex™ direct reduction process is based upon a
low pressure, moving bed shaft furnace where the reducing gas moves counter-
current to the lump iron oxide ore or iron oxide pellet solids in the bed. The
reducing gas (from 10.20% CO and 80-90% H2) is produced form natural gas
using Midrex's CO2 reforming process and their catalyst (instead of steam
reforming). The iron ore burden in the shaft furnace is first heated, then reduced
by the upward flowing, counter current reducing gas that is injected through
tuyeres located in a bustle distributor at the bottom of the cylindrical section of
the shaft. The ore is reduced to a metallization typically in the range of 93% to
94% by the time it reaches the bustle area. Below the bustle area, it goes
through a transition zone and then reaches the lower conical section of the

furnace. The process can produce, lower carbon reduced iron (<1.5% C) or
higher carbon reduced iron (upto 4.0%) with suitable operations in lower conical
section of the furnace. The process can produce cold or hot DRI (Direct Reduced
Iron) as well as HBI (Hot Briquetted Iron) for subsequent use as a scrap
substitute feed to a steelmaking melting furnace (SAF, EAF or oxygen
steelmaking process).
HYLSA IVM: The Hylsa 4M process is based on a moving bed shaft furnace
(similar to HYL III process but without a reformer) which reduces iron ore
pellets, lumps or a mixture of two (from 0 to 100% of either) and operates at
typical reduction temperatures and intermediate reduction pressures. This
process requires no reformer to generate the reducing gas and the reforming of
the natural gas takes place inside the reduction reactor using the metallic iron of
the DRI product as the catalyst. The process can produce cold or hot DRI as well
as HBI.
SL/RN or Stelco-Lurgi process : The SL/RN process is a kiln based process
that uses lump ore, pellets and solid carbon (low-cost non-coking coal) and
limestone or dolomite (to absorb sulfur from high sulfur reductant) to produce
hot or cold DRI. This is the most widely used coal based direct reduction process.
The kiln is inclined downward from the feed and provided with a burner at the
discharge end to be used for startup or to inject reductant. The kiln is divided
into two process regions; preheat ad reduction. In the preheat section, the
charge is heated to about 1000 °C to drive off the moisture and reduction of FeO
and then passes into the metallization or reduction zone where the temperature

is maintained at about 1000 to 1100 °C depending upon the type of charge
used. The final iron metallization is about 93% and carbon content about 0.1 to
0.2%. The product DRI can be discharged hot or cold.
Apart from the above proven commercial ironmaking processes, many alternative
rotary hearth furnace (RHF) based ironmaking processes are being developed
which are either in pilot or semi-commercial stages of development. The rotary
hearth furnace based processes consists of the Redsmelt process, Fastmet or
Fastmelt, Itmk3, Inmetco, Iron dynamics and MauMee process. These alternative
rotary hearth furnace based iron making technologies are discussed briefly
below.
Redmelt: The Redsmelt process is based upon a rotary hearth furnace which
reduces green pellets made out of iron ore, reductant fines and binders to
produce hot, metalized DRI that is charged to Submerged Arc Furnace. Green
pellets made of iron oxide feed; reductant and binders are screened to size
between 8 to 16mm and distributed onto the RHF in a layer up to 30 kg/m2.
While traveling throughout the furnace in 12 to 18 minutes, pellets are heated up
to 1370 °C. Drying of pellets, coal devolatization and iron oxide reduction takes
place during the heating process. To prevent reoxidation of metalized iron, the
final zones of the furnace are operated in sub-stichiometric atmosphere. The hot
DRI product is then fed to the submerged arc furnace (SAF) for smelting into hot
metal and slag.
Fastmet or Fastmelt: The FastMet process is based upon a rotary hearth

furnace which reduces briquettes made out of iron ore fines, waste iron bearing
materials and pulverized coal to produce hot, metalized DRI that can be directly
charged to a specially designed electric melter (FASTMELT) or HBI. The hot DRI
product can either be collected in N2 purged transfer cans, or directly fed to the
electric furnace for melting.
ITMK3: The ITmk3 process is based upon a rotary hearth furnace similar to a
FASTMET furnace which reduces dried green pellets made out of iron ore,
reductant fines and binders at 1350 °C to produce hot, metalized hot, metalized
DRI that is charged to a Melter for complete separation of Hot Metal or the cold
iron shots (iron nuggets) from slag.
Inmetco Process: The Inmetco process is based upon a rotary hearth furnace
which reduces briquettes made out of iron ore fines, waste iron bearing materials
and pulverized coal at 1250 °C to 1300 °C for 10 to 15 minutes to produce hot,
metalized DRI that can be directed charged to an electric melter or HBI. The hot
DRI product can either be collected in N2 purged transfer cans, or directly fed to
the electric furnace for melting.
Iron Dynamics : The iron dynamics process is based upon a natural gas fired
rotary hearth furnace which reduces a carbonaceous iron oxide charge to
metallic iron solids that are charged to a SAF to complete the reduction and to
melt and desulphurize the reduced iron. The DRI at the discharge of the rotary
hearth furnace has about 85% metallization. An additive facility introduces flux,
coke, silica or other materials to the DRI transport bottles to control slag

chemistry in the submerged arc furnace. Average metallization after SAF is about
95.8%.
MauMee Process : The process is based upon rotary hearth furnace which
redcues green pellets or briquettes made out of waste iron oxide materials and
pulverized non metallurgical coal to produce hot, metalized (>90%) DRI. The
theoretical ratio of fixed carbon to iron oxide is 1.5:1 in pellets or briquettes.
MauMee process has been formulated to produce metallic iron using a carbon-to-
oxide ration of 6:1, which results in the evolution of both CO and CO2 and leaves
a residual carbon level of about 4%. The key to this process is controlling the CO
to CO2 ratio to minimize reoxidation, carbon consumption and furnace residence
time. The hot DRI product can then be supplied to the steel mill by a number of
different options.
The above mentioned alternative rotary hearth furnace based processes mainly
consists of direct reduction of iron bearing materials having alumina typically less
than 3.0% by weight. Therefore, the iron bearing materials such as iron ore
mineral processing rejects having alumina content greater than or equal to 3.0%
by weight requires a different treatment by using a specially designed slag
chemistry to result into an efficient direct reduction process. The rotary hearth
furnace based processes mentioned above uses either water or N2 gas outside of
RHF for preventing the reoxidation or cooling of the reduced product which
results in disintegration of the reduced product or requires high cost due to
additional requirement of inert gases such as Nitrogen.

Many processes based on moving or rotating or traveling hearth furnaces such as
tunnel kiln or rotary hearth furnace have been developed in the past. For
example, a rotary hearth furnace based method to produce a reduced metal
from reduction of metal oxides such as iron oxide, nickel oxide etc is disclosed in
patent number US 2006 0278040 Al, wherein high volatile matter coal as high as
35% by weight is used as reductant and the reduced metal having high crushing
strength and about 1% residual carbon is obtained in the metal nuggets. In
patent US 2006 0169103 Al, a rotary heath furnace based process is disclosed
for reduction of iron-oxide containing substance using carbonaceous reductant.
The patent deals with producing granulated metallic iron with low sulphur in it
and dolomite was used as MgO containing substance to get desired slag
chemistry and also to limit the sulfur in the final product. A method for producing
metallic iron in a moving hearth type or straight gate furnace is disclosed in
patent number EP 1764420 A2 wherein lower portion of the hearth of the
reduction melting furnace is forcibly cooled to facilitate solidification and
formation of the deposit layer on the hearth refractory to protect the hearth
while producing metallic iron. Coke was used as reductant and the process
produces metallic iron and also proposes a raw material feed device. In patent
number EP1405924 Al, a moving bed furnace process is disclosed to produce
metal nuggets by reduction of metal-oxide-containing substance and a
carbonaceous reductant. A cohesion accelerator such as calcium fluoride or
boron oxide, etc is used in the range of 0.2 to 2.5% by weight to produce high
purity, large diameter metal and high productivity of the process. A method for
producing granular metal iron is disclosed in patent number JP2009091664A,
wherein iron ore and carbonaceous reducing agent such as coke was used. In

patent number JP2009035820A, a method for producing the carbon composite
agglomerate of iron oxide and reductant is disclosed to prevent the bursting of
agglomerates in a rapid-heating reduction furnace while producing reduced iron
or metal iron. A method and apparatus for making metallic iron is disclosed in
patent number US6210462 B1, wherein a method of reduction of non
agglomerated feed mixture of iron oxide and carbonaceous reducing agent (only
mixture no pellets) in movable hearth furnace (RHF) having desulphuriser in the
mixture was used and the magnetic separation was employed to separate the
molten iron slag product. In patent number WO 1999020801 Al, a method and
apparatus for making metallic iron is disclosed where no preliminary molding of
the starting material powder (iron oxide and carbonaceous reducing agent) into
lumps or pellets shape is required. The one of important feature of the method is
increasing the surface area of the feed mixture to movable hearth furnace by
forming unevenness on the surface using a special mechanism. A method for
producing reduced iron is disclosed in patent number WO2001077395 A1,
wherein the iron oxide containing material and carbonaceous agent are formed
into small agglomerates are charged onto the hearth of reduction furnace i.e
rotary hearth furnace in a typical thickness of 30 mm to produce solid reduced
iron or further heating the solid reduced iron to melt and form coagulated molten
metallic iron. In patent number WO2000029628A1, an apparatus and method for
the direct reduction of iron oxide utilizing a rotary hearth furnace to produce high
purity carbon-containing iron metal button is disclosed. The new feature of the
method is use of cooling plate placed closed to hearth layer or refractory surface
so that the cooling plate cools the iron globules to form solid high purity iron. A
rotary hearth furnace based method for producing high purity carbon-containing

iron metal button and improved furnace apparatus is disclosed in patent number
US6413 295 B2, wherein coated agglomerates of compounds of carbon, iron
oxide, silicon oxide, magnesium oxide and or aluminium oxide are reduced in
rotary hearth furnace at temperature of at least 1450 °C to about 1600 °C. The
improved apparatus includes a cooling plate that is placed in close proximity with
the refractory or vitreous hearth layer for cooling the molten globules to form
iron metal button that are removed from hearth layer. In patent number US
20020033075 A1, a method of producing metallic iron nuggets having size of 3-
40mm in reducing or melting furnace is disclosed. The raw materials include iron
oxide containing material and carbonaceous reducing agent. Carbon content
ratio in said carbonaceous agent is at least 74.5% and volatile matter is not
more than 3.9%. A method of operating a movable hearth or traveling hearth or
rotary hearth furnace is disclosed in patent number EP969105A1, wherein a fine
coal char is first stacked onto the hearth prior to stacking of mixture of fine iron
ore and fine solid reducing material. The hearth furnace has a melting zone in
which the product after reduction is melted in an area upto a discharge port for
discharging said product to separte slag contained therein through aggregation.
In patent number WO1999016913 Al, a method of operation of rotary hearth
furnace for reducing oxides is disclosed wherein iron ore and powdery solid
reducing material is piled on the hearth in non agglomerated form. Limestone is
used as additive. The feature of the process is dividing the feed charge mixture
into small blocks. A method for making metal nuggets is disclosed in patent
number US20040154436A1, wherein the pellets or briquettes made of mixture of
metal oxide, carbonaceous reductant and cohesion accelerator 0.2 to 2.5%
comprising of at least one of calcium fluoride, boron oxide, sodium carbonate

and sodium oxide are reduced to form large metallic iron nuggets. The metal
oxide containing substance comprises at least one of iron ore, steel making dust,
steel making waste materials and metal scrap.
A new smoke pollution device for tunnel kiln is disclosed in patent number
US5603615, which can prevent the discharge of pollutants such as sulphides,
steam and ashes to atmosphere. Tunnel kiln without exterior combustion
chamber for producing coal based direct reduced iron is disclosed in patent
number CN1804049, the invention claims to enlarge the width of the tunnel kiln
upto more than 10 m and single kiln production capacity up to 0.1mtpa and
more than 0.5mtpa using suitable product quality and 1050 to 1300 °C baking
temperature. In patent number CN101497933, a method for rapidly and directly
reducing iron or hematite ore or limonites into ferrous powder is disclosed. The
hematite ore is crushed washed and subjected to magnetic separation. The ore is
mixed with coal dust, lime and calcium chloride (CaCl2) and binder. The mixture
is pressed into blanks, direct and stacked on cars to send in tunnel kiln. The
blanks are subjected to water quenching to separate iron powder and slag
automatically. Patent number CN101113488 discloses a method for
comprehensive utilization of V-Ti-bearing iron ore concentrate to produce iron
powder and vanadium pentaoxide compounds by using tunnel kiln reduction-
grinding-separation. High temperature metal recovery process is disclosed in
patent number US2003047035, for particulate metal containing dust such as
electric arc furnace dust wherein metallic values are recovered from the dust
using tunnel kiln. The mixture of metal containing dust alonwith carbonaceous
fines is heated in moving bed horizontal tunnel furnace to release volatile and

alkali metals in gaseous product principally zinc and iron. The zinc and iron are
separated from gases as process product. A new process and apparatus for
producing direct reduced iron is disclosed in patent number CN1147018, wherein
oxide of iron as raw material is mixed with bituminite, lime, coal and nutshell as
additive. The mixture is fed in to a material column reactor which is passed
through externally heated tunnel kiln for 30 to 38 hours at about 950 °C. The
process was used for direct reduction of iron-containing raw material in solid
state into metal iron. In patent number CN1142541, a coal based direct
reduction process of iron containing material is disclosed to produce sponge iron
using tunnel kiln. The mixture of iron ore, coal is fed to metallic reactor and
calcined in slope-type tunnel kiln to produce sponge iron in metallic reactors.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a process for
reduction of composite agglomerates of high alumina (greater than or equal to
3.0% by weight) iron ore mineral processing rejects and natural coke or Jhama
coal in a moving hearth furnace to produce reduce metallic iron product or iron
metal agglomerates and slag.
Another object of the invention is to propose a process for reduction of
composite agglomerates of high alumina (greater than or equal to 3.0% by
weight) iron ore mineral processing rejects and natural coke or Jhama coal in a
moving hearth furnace to produce reduce metallic iron product or iron metal
agglomerates and

slag, in which the slag chemistry constitutes an optimum ratio of Jhama coal or
natural coke and slag former to form low temperature slag for enhancing the
reduction of high alumina iron ores in the moving hearth furnace.
A still another object of the present invention is to propose a process for
reduction of composite agglomerates of high alumina (greater than or equal to
3.0% by weight) iron ore mineral processing rejects and Jhama coal in a moving
hearth furnace to produce reduce metallic iron product or iron metal
agglomerates and slag, Jhama coal layer is used on the surface of the car of the
moving hearth furnace to maintain a highly reducing atmosphere in the
immediate vicinity of the composite agglomerates during the reduction process in
the moving hearth furnace.
Yet another object of the invention is to propose a process for reduction of
composite agglomerates of high alumina (greater than or equal to 3.0% by
weight) iron ore mineral processing rejects and Jhama coal in a moving hearth
furnace to produce reduce metallic iron product or iron metal agglomerates and
slag, in which a zone wise temperature profile (distribution) in the moving hearth
furnace is maintained for efficient reduction of composite agglomerates of high
alumina iron ore mineral processing rejects and natural coal.
A further object of the present invention is to propose an improved moving
hearth furnace such as rotary hearth furnace or tunnel kiln furnace for carrying
out an efficient reduction of composite agglomerates of high alumina iron ore
mineral processing rejects and natural coke or Jhama coal.

SUMMARY OF THE INVENTION
Considering an the limitations of prior art technologies, a new method for
processing of high alumina iron ore mineral processing rejects based on moving
hearth furnace is proposed in the present invention. The invention results in
efficient direct reduction of composite agglomerates of high alumina iron ore
mineral processing rejects and Jhama coal using specially designed slag
chemistry for high alumina containing iron ore reduction. The desired slag
chemistry for low temperature slag formation is obtained using calcined or
hydrated lime slag former and maintaining particular charge basicity suitable for
obtaining high metallization in reduced metallic iron product or iron metal
agglomerates. Also one of the important feature of the present invention, is the
novel method of partial recycling of the cooled exhaust gas from moving hearth
furnace into cooling zone of the same furnace for quenching or rapid cooling of
reduced product or agglomerate within moving hearth furnace, thus avoiding the
re-oxidation of the reduced product and ensures the discharge of reduced
metallic iron product or iron metal agglomerates at temperatures less than 500
°C temperature from the moving hearth furnace.
In the present invention, a new moving hearth furnace based method such as
rotary hearth furnace or tunnel kiln is proposed for efficient reduction of
composite agglomerates made from high alumina iron ore mineral processing
rejects and Jhama coal using specially designed slag chemistry for enhancing the
reduction process of high alumina iron ores. The Jhama coal or natural coke or
special low volatile (SLV) fuel, as it is commonly known in India, is the result of

carbonization of coal in situ by igneous intrusion. The Jhama coal is used as
reductant in composite agglomerate as well as outside of composite agglomerate
on the surface of moving hearth or car surface of tunnel kiln in order to enhance
the reduction process. The high alumina iron ore mineral processing rejects in
the size range of mostly less than 0.5mm with 20-50% of less than 20 urn size
particles are mixed with Jhama coals as reductant and calcined or hydrated lime
as low temperature slag former and bentonite as binder. The reductant, slag
former and binder are added in predetermined ratio as per an innovative slag
chemistry to form composite agglomerates for achieving enhanced reduction of
high alumina iron ore mineral processing rejects and formation of low
temperature slag during reduction. These composite agglomerates are dried and
then fed to reduction process in moving hearth furnace such as rotary hearth
furnace or tunnel kiln. In moving hearth furnace reduction process, a layer of
Jhama coal is placed on the surface of the moving hearth or on the kiln cars
which helps in maintaining highly reducing atmosphere in the immediate vicinity
of the composite agglomerates subjected to reduction process. The moving
hearth furnace used in the present invention uses air required for fuel
combustion as well as the excess air required for post-combustion of the reaction
gases is supplied only in the heating or firing or combustion or reaction zone
through externally fired burners or additionally air input below the burners. One
of the important features of the present invention is that the proposed moving
hearth furnace reduction method makes uses of partially cooled exhaust gas
from moving hearth furnace for rapid cooling or quenching of the reduced
product inside the furnace cooling zone, which helps to achieve the rapid cooling
of the reduced metallic iron product and or iron metal agglomerates to less than

500 °C by preventing the reoxidation of the reduced product. This feature
eliminates the need of quenching the reduced product in water or Nitrogen gas
outside the tunnel kiln or moving hearth furnace and also prevents the
disintegration of reduced product which usually occurs in water quenching
process. This feature also eliminates the need of use of costly inert gas such as
nitrogen for quenching of the reduced product inorder to prevent its reoxidation.
The reduced metallic iron product and or iron metal agglomerate obtained from
moving hearth furnace reduction process have high iron metallization. The
reduced metallic iron product and or iron metal agglomerates can be used in
steel production which can result in low energy consumption and also improves
the productivity of the melting furnaces. Therefore, a new moving hearth furnace
based process for reduction of composite agglomerates of high alumina iron ore
mineral processing rejects and Jhama coal is proposed in the present invention.
The improved moving hearth furnace employs of the invention a partially cooled
exhaust gas from the same furnace for quenching or rapid cooling of the reduced
metallic iron product or iron metal agglomerates within cooling zone of the
furnace in order to prevent the re-oxidation of the product and also to discharge
the cooled reduced metallic iron product or iron metal agglomerates at less than
or equal to 500 °C temperature from the moving hearth furnace. Use of partially
cooled exhaust gas from the moving hearth furnace for rapid cooling within the
same furnace eliminates the need for water quenching of the reduced metallic
iron product and or iron metal agglomerates outside the reduction equipment
which is usually applied in direct reduction processes.

The invention adapts a unique slag chemistry for reduction of high alumina iron
ore mineral processing rejects in a moving hearth furnace such as rotary hearth
furnace or tunnel kiln. The invention allows forming a natural coal layer on the
hearth surface of the moving hearth furnace for making the reduction process
more effective in the furnace. The invention implements a partial recycling of the
cooled exhaust gas from the moving hearth furnace into the cooling zone of the
same furnace for quenching or rapid cooling of the reduced metallic iron product
and or iron metal agglomerates and slag, thus prevents the re-oxidation of the
reduced product and ensures discharge of the reduced product at less than 500
°C temperatures from the moving hearth furnace such as rotary hearth furnace
or tunnel kiln.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 : Shows the schematic top view of a moving hearth furnace in the
form of a rotary hearth furnace by way of example, indicating the
various heating and cooling zones in the furnace and typical
temperature in various zones of the furnace.
Figure 2 : Shows a typical temperature profile zone-wise in the rotary hearth
furnace, in which the rapid cooling temperature profile of the
reduced product remaining within the cooling zone of the rotary
hearth furnace.
Figure 3 : Shows effect of variation in charge basicity on the iron metallization

in reduced metallic iron product or iron metal agglomerate in a rotary
hearth furnace reduction process at cycle time of 16 minutes is
shown.
Figure 4: exhibits CaO-Al2O3-SiO2 slag system equilibrium phase diagram at
1400 °C showing the liquid slag region and basicity of slag in
composite agglomerates of iron ore mineral processing rejects and
natural coal with and without slag former including, the required slag
basicity in composite agglomerates to obtain reduction product as
'reduced metallic iron product' or in the form of distinct 'iron metal
agglomerate' and 'slag'.
Figure 5 : Shows the variation in percentage of total iron metal agglomerates
produced or obtained by physical screening separation and magnetic
separation of reduced iron metal agglomerates from the reduced
product at different cycle times of the rotary hearth furnace at a
charge basicity of 1.0
Figure 6 : Schematic diagram of an improved moving hearth furnace in the
form of a rotary hearth furnace showing the method for rapid cooling
and prevention of re-oxidation of the reduced metallic iron product or
iron metal agglomerates within the furnace
Figure 7 : View of the reduced product according to the invention, obtained by
reduction of composite agglomerates of iron ore mineral processing

rejects and natural coal in a rotary hearth furnace, in which, figure
7(a) is the Distinct 'reduced iron metal agglomerate' and 'slag'
obtained at charge basicity of 1.0, and figure 7(b) is the Reduced
Metallic Iron Product obtained at a charge basicity of 1.4.
Figure 8 : SEM Microgrpah's of the reduced product (A) - Microstructure of iron
metal agglomerate (b) - Microstructure of slag showing entrapped
small iron metal agglomerates
Figure 9 : Schematic diagram of a tunnel kiln reduction process for reduction of
composite agglomerates of iron ore mineral processing rejects and
natural coal showing the various heating and cooling zones, zone
wise typical temperatures and indicative residence time of composite
agglomerates in different zones of the tunnel furnace.
Figure 10 : Reduction process of composite pellets of iron ore mineral processing
rejects and natural coal in tunnel kiln including, (a) Method of placing
natural coal ion the surface of trolley, (b) Composite pellets placed
on the trolley in 30-40 mm thick layer, (c) Reduced metallic iron
product after reduction in tunnel kiln, (d) Reduced iron metal
agglomerate and slag after reduction in tunnel kiln.
Figure 11: The schematic diagram of the Tunnel kiln process flow showing the
method for rapid cooling and prevention of re-oxidation of the
reduced metallic iron product or iron metal agglomerates and slag
within cooling zone of tunnel kiln furnace.

DETAILED DESCRIPTION OF THE INVENTION
Iron ore mineral processing rejects having alumina (AI2O3) content in the range
of 3.0 to 10.0% by weight has size mostly less than 0.5 mm with 20 to 50 weight
% of less than 20 urn size particles in it are mixed with powered natural coke or
Jhama coal as reductant, powdered calcined or hydrated lime as slag former and
bentonite as binder. The typical chemical composition of different raw material
such as Iron ore mineral processing rejects as iron oxide bearing material having
high alumina greater than 3.0%, Jhama coal as reductant, calcined or hydrated
lime as slag former and bentonite as binder is shown in Table 1. The high
alumina iron bearing material, reductant, slag former and binder are mixed in
predetermined ratio as per the specially designed slag chemistry to form
composite agglomerates for achieving enhanced reduction of high alumina
containing iron bearing material and formation of low temperature slag during
reduction. The typical chemical composition of composite agglomerates used in
the moving hearth furnace reduction process obtained after mixing and
agglomeration of predetermined ratio of raw materials in order to achieve special
slag chemistry is also shown in Table 1. The raw materials at predetermined ratio
as per suitable slag chemistry are mixed and agglomerated to composite
agglomerates in the form of pellets or briquettes. The composite agglomerates
are then subjected to drying process for 30 to 120 minutes in the temperature
range of 100 °C to 200 °C. The drying process is carried out in continuously
moving steel grade belt dryer which typically uses hot air from hot air generator
as drying medium. The dried composite agglomerates are then fed to reduction
process in moving hearth furnace such as rotary hearth furnace or tunnel kiln.

A schematic top view of moving hearth furnace such as rotary hearth furnace is
shown in Fig. 1. The rotary hearth furnace consists of a flat, refractory hearth
rotating inside a stationary, circular tunnel. The feed agglomerates are placed on
moving hearth and the heat required to raise the temperature of feed
agglomerates is supplied by radiation heat from the burners or heating elements.
This furnace has total six zones starting from charge entry to exit. First five
zones are heating zones whereas the sixth zone is cooling zone. Heating zone-1
and 2 has maximum temperature up to 1100 °C and 1200 °C respectively.
Heating zone-3 to 5 are high temperature zones where maximum temperature of
1400 °C is achieved. The air required for combustion of fuel as well as for post-
combustion of reduction gas is supplied in the heating zones either through
combustion air or postcombustion excess air supplied using additional excess air
injection in the heating zones of the moving hearth furnace. Zone-6 is cooling
zone and does not contain burners or heating elements in it. This zone receives
radiation heat from adjacent high temperature heating zone and also employs
the cooled exhaust gas of furnace as cooling medium in this zone, therefore
temperatures of less than or equal to 500 °C are obtained in cooling zone
whereas in conventional rotary hearth furnaces temperatures greater than 500
°C and up to 1150 °C exist in cooling zone. A typical zone wise temperature
profile in rotary hearth furnace is shown in Fig. 2. In moving hearth furnace
reduction process, a layer of natural coal is placed on the surface of moving
hearth which helps in maintaining highly reducing atmosphere in the immediate
vicinity of the composite agglomerates subjected to reduction process. The
typical chemical analysis of Jhama coal layer is given in Table 1. The natural coal
layer is sprayed or placed on the surface of moving hearth. The composite

agglomerates are then subjected to reduction process in rotary hearth furnace
for varied cycle time at given zone wise temperature profile (Fig. 2) of the
furnace. The cycle time of reduction process in rotary hearth furnace process
was maintained typically between 16 minutes to 32 minutes. The optimum slag
composition in composite agglomerates for reduction process was obtained using
lime as slag former. The addition of slag former was carried out in such a
proportion in the charge mixture so that the reduced product from the reduction
process can be reduced metallic iron product and or distinct iron metal
agglomerate and slag. The CaO/SiO2 or the basicity in the charge of rotary
hearth furnace was varied in the range of 0.7 to 2.5. The effect of various charge
basicity on the Fe-metallization in reduced product obtained from rotary hearth
furnace at cycle time of 16 minutes is shown in Fig. 3. Highest degree of iron
metallization of about 96.5% with total iron content of about 98.5% by weight in
the reduced iron metal agglomerate was obtained with clear separation of slag
and metal at charge basicity of 1.0. Fig.4 presents the equilibrium phase diagram
at 1400 °C temperature for CaO-Al2O3-SiO2 slag system showing the liquid region
for the system. It can be seen that at charge basicity of 1.0 in composite
agglomerates of high alumina iron ore mineral processing rejects and Jhama
coal, the slag is liquid and therefore distinct iron metal agglomerate and slag was
obtained. Fig. 4 also shows the various charge basicities in the equilibrium phase
diagram where charge basicity of 0.05 corresponds to composite agglomerate of
high alumina iron ore and natural coal without addition of slag former and
charge basicity in the range of 0.7 to 2.5 obtained by addition of slag former.
The charge basicity of 1.0 is suitable for producing distinct iron metal
agglomerate and slag product from reduction process in the moving hearth

furnace due to liquid slag. Reduced metallic iron product with about 93.5% Fe-
metallization with total iron content of about 73.0% by weight was obtained at
1.4 charge basicity. From Fig. 3, it can be seen that by using proper charge
basicity in the range of 0.7 to 1.4, rescued metallic iron product having Fe-
metallization greater than 90.0% can be produced with special charge basicity of
1.0 at which distinct iron metal agglomerate and slag are produced by reduction
of composite agglomerates of high alumina iron ore mineral processing rejects
and Jhama coal in rotary hearth furnace. Increase in charge basicity due to
addition of slag former results in formation of low temperature slag and
enhancement of reduction process due to lowering of slag liquidus. Thus the
optimum addition of calcined or hydrated lime for achieving specific charge
basicity (CaO/SiO2) in the range of 0.7 to 1.4 was carried out for lowering the
liquids temperature and formation of low temperature slag. The temperature
(Fig. 2) and cycle time in rotary hearth furnace are adjusted such that the
reduction of Fe2O3 in high alumina iron ores to FeO in slag is enhanced. Further
reduction of FeO in slag to metallic Fe is enhanced by using optimum charge
basicity in the range of 0.7 to 1.4 which results in enhanced reduction of iron
oxides in composite agglomerates made from high alumina iron ore mineral
processing rejects and natural coal. The variation in percentage of total iron
metal agglomerates produced or obtained by physical screening separation
operation and magnetic separation of reduced iron product at charge basicity of
1.0 and at various cycle (residence) time of rotary hearth furnace is shown in
Fig. 5. It can be observed from Fig. 5, that for cycle time varying between 16
minutes to 32 minutes, typically about 60% of the iron metal agglomerates
produced which are having diameter greater than 8.0 mm can be recovered by

screening operation of reduced product whereas about 30% of the iron metal
agglomerates formed will be have diameter less than 8.0 mm which needs to be
separated from the reduced product using other separation technique such as
magnetic separation. At cycle time of 16 minutes of rotary hearth furnace at
charge basicity of 1.0, out of the total iron metal agglomerates produced, about
63% were having diameter greater than 8.0 mm which were recovered using the
screening operation and about 37% of the total iron metal agglomerates formed
which were having diameter less than 8.0 mm were separated using magnetic
separation technique. As the cycle time of rotary hearth furnace increases, the
weight percent of greater than 8.0 mm diameter slag free iron metal
agglomerates or the fraction which can be separated from reduced product by
physical screening increases due to availability of more time for metal
agglomeration within the furnace. As expected, increase in cycle time results in
decrease of weight percent of less than 8.0mm diameter iron metal
agglomerates or the fraction which can be recovered or separated from slag
using magnetic separation method. The reduced metallic iron product and or
reduced iron metal agglomerates and slag are discharged from the rotary hearth
furnace without its re-oxidation at temperature less than 500 °C while exiting
from the moving hearth furnace. This quenching or rapid cooling of the reduced
product without re-oxidation is achieved using partially cooled rotary hearth
furnace exhaust gas for quenching or rapid cooling of the reduced product in the
cooling zone of the rotary hearth furnace. One of the important features of the
present improved design of moving hearth furnace is to make use of part of
rotary hearth furnace exhaust gas which is cooled to about 100 to 200 °C in a
separate gas cooling unit outside of the rotary hearth furnace. Fig. 6 shows the

schematic of typical rotary hearth furnace arrangement used for achieving the
cooling of the reduced metallic iron product or reduced iron metal agglomerates
and slag to less than 500 °C while exit from rotary hearth furnace. The rotary
hearth furnace exhaust gas consists of CO2 and N2 (nitrogen) as major
constituent since most of the CO generated during reduction reactions is burned
inside the firing or combustion or heating zones to convert to CO2 by use of
excess air. Therefore, the rotary hearth furnace exhaust gas containing CO2 and
N2 as major gas components is partly diverted to a gas cooling unit for cooling
the exhaust gas to about 100-200 °C. This cooled gas is injected into cooling
zone of the rotary hearth furnace for quenching or rapid cooling of the reduced
metallic iron product and or reduced iron metal agglomerates and slag. The rapid
quenching of the reduced product using the cooled exhaust gas of rotary hearth
furnace prevents the re-oxidation of the reduced product and also ensures
cooling of the reduced product to less than 500 °C. The reduced product is
cooled to less than 500 °C within the cooling zone and discharged to atmosphere
at less than 500 °C without its re-oxidation. This feature eliminates the need of
quenching the reduced product in water or costly inert gases outside of rotary
hearth furnace and also prevents the disintegration of the reduced product which
usually occurs in water quenching processes used in direct reduction processes.
The reduced metallic iron product (Fig. 7b) or reduced iron metal agglomerate
and slag (Fig. 7a) obtained after reduction of composite agglomerates of iron ore
mineral processing rejects and natural coal are shown in Fig. 7. The reduced
metallic iron product or iron metal agglomerates and slag is removed from the
moving hearth furnace using a physical scrapper for further use of the reduced
product in steel making operation. The reduced metallic iron product obtained by

reduction process has high metallization of iron. The typical chemical
composition of reduced metallic iron product obtained by reduction of composite
agglomerates of high alumina iron ore mineral processing rejects and natural
coal is shown in Table 2. The % Fe-metallizaiton (i.e ratio of metallic iron to total
iron) in reduced metallic iron product is greater than 90%. The typical chemical
composition of reduced iron metal agglomerates and slag is also given in Table
3. The % Fe-metallization in reduced iron metal agglomerates is up to 98.0%.
Fig. 8 shows the typical micrographs of reduced iron meta agglomerate (Fig. 8a)
and slag (Fig. 8b). The micrograph of slag shows entrapped iron metal
agglomerates, which needs to be separated from slag after crushing of slag
followed by magnetic separation. The reduced metallic iron product or iron metal
agglomerates can be used in steel production which can result in low energy
consumption in the process. Therefore, a new method for reduction of composite
agglomerates of high alumina iron ore mineral processing rejects and natural
coal in a moving hearth furnace is developed in the present invention. As an
additional example of the moving hearth furnace, the reduction process of
composite agglomerates of high alumina iron ore mineral processing rejects and
Jhama coal can also be carried out in a tunnel kiln. Fig. 9 shows a schematic of a
tunnel kiln reduction process for reduction of composite agglomerates of iron ore
mineral processing rejects and natural coal. The tunnel kiln has four major
temperature zones across the length of the tunnel kiln. These temperatures
zones starting from entry are drying, preheating, firing and cooling zone. The
temperatures maintained in the four zones of the tunnel kiln during reduction
process are, less than or equal to 800 °C in drying zone, less than or equal to
1000 °C in preheating zone, less than or equal to 1400 °C in firing or combustion

zone and less than or equal to 500 °C in cooling zone. The tunnel kiln is closed
type and air required for fuel combustion as well as excess air required for
postcombustion of reaction gas typically CO, is supplied only in the firing or
combustion zone through externally fired burners or additional air input below
the burners. A layer of natural coal 500-1000 g/m2 is placed on the surface of
the trolley or moving car, and the composite agglomerates of high alumina iron
ore mineral processing rejects and natural coal are placed on it with 30-40 mm
thick layer (Fig. 10b). The tunnel kiln cars having composite agglomerates placed
on it, travels through all the four temperature zones of tunnel kiln such that total
residence or cycle time ( in to out) of composite agglomerates is maintained
typically about 60 minutes within the kiln however this residence or cycle time
may not be sacrosanct and can vary depending on the properties of the
agglomerates subjected to reduction process. The reduced metallic iron product
or iron metal agglomerates and slag are discharged from tunnel kiln without its
re-oxidation at temperatures less than 500 °C while exiting from the tunnel kiln.
Fig. 11 shows the schematic of a process flow arrangement used for achieving
the rapid cooling of the reduced metallic iron product or iron metal agglomerates
to less than 500 °C while exit from the tunnel kiln. The tunnel kiln exhaust gas
containing CO2 and N2 as major gas components is partly diverted to a gas
cooling unit for cooling the exhaust gas to about 100-200 °C. This cooled gas is
injected into cooling zone of tunnel furnace for quenching or rapid cooling of the
reduced metallic iron product or iron metal agglomerates and slag. The reduced
metallic iron product or iron metal agglomerates and slag are then removed from
the tunnel kiln cars using a physical scrapper or pneumatic hammer for further
use of the reduced product in steel making operations. The reduced metallic iron

product or iron metal agglomerate and slag obtained in tunnel kiln reduction
process of composite agglomerates of high alumina iron ore mineral processing
rejects and natural coal are shown in Fig. 10. The reduced metallic iron product
obtained from tunnel kiln reduction is shown in Fig. 10c and the reduced iron
metal agglomerate and slag is shown in Fig. lOd. The reduced metallic iron
product obtained from tunnel kiln reduction process has high metallization of iron
and typical chemical composition of it is given in Table 2. The reduced metallic
iron product and or iron metal agglomerate and slag obtained from tunnel kiln
reduction process can be used further in steel production which can result in
lowering the energy consumption of the process.

WE CLAIM
1. A process for reduction of composite agglomerates of high alumina iron
ore mineral processing rejects and natural coke or Jhama coal in a moving
hearth furnace to produce reduced metallic iron production and or iron
metal agglomerates and slag, comprising preparing the composite
agglomerates by mixing and agglomeration of high alumina iron ore
mineral processing rejects as iron oxide containing material comprising of
less than 0.5mm size particles, powdered natural coke or Jhama coal as
reductant, powdered calcined or hydrated lime as slag former and
bentonite as binder, wherein the high alumina iron ore mineral processing
rejects as iron oxide containing material has alumina (AI2O3) content of
3.0 to 10.0 % by weight and powdered Jhama coal has fixed carbon of
60.0 to 75.0% by weight, wherein the mixing is achieved by adjusting the
slag composition or slag chemistry in composite agglomerates such that
the basicity or CaO:SiO2 ratio in the composite agglomerates is in the
range of 0.7 to 1.4, and wherein the reduction process of composite
agglomerates of high alumina iron ore mineral processing rejects and
natural coke or Jhama coal is carried out in a moving hearth furnace
which is characterized by subjecting the composite agglomerates to
reduction process by placing them on a natural coke or Jhama coal layer
on the surface of the moving hearth of the furnace.
2. The method as claimed in claim 1, wherein the composite agglomerates
are either pellets or briquettes or any other form of agglomerates.
3. The method as claimed in claim 1, wherein the composite agglomerates
comprise of atleast one of high alumina iron ore mineral processing

rejects or slimes and powdered Jhama coal as reductant and powdered
calcined or hydrated lime as slag former.
4. The method as claimed in claim 1, wherein the moving hearth furnace is a
rotary hearth furnace or a tunnel kiln.
5. The method as claimed in claim 4, wherein the Jhama coal layer is placed
on the surface of moving hearth as 500-1000 gm2 having fixed carbon
60.0-75.0 % by weight, apart from the Jhama coal in composite
agglomerates in order to enhance the reduction process.
6. The method as claimed in claim 4, wherein the composite agglomerates
are placed in 30-40 mm thick layer on the natural coke or Jhama coal
layer on the surface of moving hearth.
7. The method as claimed in claim 4, wherein the composite agglomerates
are subjected to temperature profile in moving hearth furnace for given
residence or cycle time.
8. The method as claimed in claim 7, wherein the temperature profile of
moving hearth furnace such as rotary hearth furnace is less than 1100 °C
in feed or zone 1, less than or equal to 1200 °C in zone 2, less than or
equal to 1400 °C in zone 3,4 and 5, and less than or equal to 500 °C in
cooling zone, and wherein the residence or cycle time of composite
agglomerates in moving hearth furnace such as rotary hearth furnace is
about 16 to 32 minutes.

9. The method as claimed in claim 7, wherein the temperature profile of
moving hearth furnace such as tunnel kiln furnace is less than or equal to
800 °C in feed or entry or drying zone, less than or equal to 1000 °C in
preheating zone, less than or equal to 1400 °C in firing or combustion or
reaction zone, less than or equal to 500 °C in cooling zone, and wherein
the residence or cycle time of composite agglomerates in tunnel kiln is
typically about 60 minutes from trolley entry to exit with composite
agglomerates.
10. The method as claimed in claim 1, wherein the moving hearth furnace is
characterized by use of part of the furnace exhaust gas which is cooled
and injected in to cooling zone of the furnace.
11.The method as claimed in claim 10, wherein the air required for
combustion of fuel including the excess air required for post-combustion
of reaction gases (typically CO) in moving hearth enters the furnace in
zone 2 to zone 5 for example, the zones which constitute the heating or
combustion zones in the moving hearth furnace.
12.The method as claimed in claim 1, wherein a part of the exhaust gas from
the furnace is diverted to a separate cooling unit, cooled to less than 500
°C to about 100-200 °C and the cooled gas is injected in a cooling zone or
zone 6 of the rotary hearth furnace.

13.The method as claimed in claim 1, wherein the moving hearth furnace is
closed type and having a variable length or diameter selected depending
upon the composite agglomerate properties subjected to reduction
process.
14.The method as claimed in claim 1 or 13, wherein the length of the moving
hearth furnace is approximately 20 meters for tunnel kiln.
15.The method as claimed in claim 1 or 11, wherein the air required for
combustion of fuel including air required for post-combustion of reaction
gases enters the furnace only in firing or combustion or reaction zone
through burners or addition of air inputs in firing or combustion or
reaction zone of the tunnel furnace.
16.The method as claimed in claim 12, wherein the exhaust gas of the
moving hearth furnace comprises CO2 (carbon dioxide) and N2 (nitrogen)
gas its major constituent being the output of fuel combustion as well as
post-combustion of reduction reactions gas such as CO using the excess
air.
17.The method as claimed in claim 16, wherein the cooled exhaust gas is
injected into cooling zone of the moving hearth furnace or rapid
quenching or cooling of the reduction process product and prevention of
re-oxidation of the reaction process product.
18.The method as claimed in claim 1, wherein the reduced metallic iron

product or iron metal agglomerate and slag are obtained at less than or
equal to 500 °C temperature from the cooling zone of the moving hearth
furnace.
19.The method as claimed in claim 1, wherein the reduced metallic iron
product has metallic iron in the range of 50.0 to 65.0 % by weight and
total iron in the range of 50.0 to 73.0 % by weight.
20.The method as claimed in claim 1, wherein the reduced metallic iron
product is obtained at basicity (CaO/SiO2) in the range of 0.7 to 1.4 in
composite agglomerates subjected to reduction process in moving hearth
furnace.
21.The method as claimed in claim 1, wherein the iron metal agglomerates
and slag is obtained at basicity (CaO/SiO2) in the range of 0.9 to 1.1 and
more particularly at basicity of 1.0 in composite agglomerates subjected to
moving hearth furnace reduction process.
22. The method as claimed in claim 1, wherein the iron metal agglomerates
are characterized by distinct phase or iron metal in reduction process
product apart from slag.
23.The method as claimed in claim 1, wherein the iron metal agglomerates
have diameter typically in the range of 1.0 to 30 mm.

24.The method as claimed in claim 1, wherein the iron metal agglomerates
has metallic iron greater than 90.0% by weight and total iron upto 98.5%
by weight in it.
25.The method as claimed in claim 1, wherein the reduced metallic iron
product or iron metal agglomerates and slag are removed from moving
hearth furnace using a physical scrapper or pneumatic hammer
arrangement.

The invention relates to a process for reduction of composite agglomerates of
high alumina iron ore mineral processing rejects and natural coke or Jhama coal
in a moving hearth furnace to produce reduced metallic iron production and or
iron metal agglomerates and slag, comprising preparing the composite
agglomerates by mixing and agglomeration of high alumina iron ore mineral
processing rejects as iron oxide containing material comprising of less than
0.5mm size particles, powdered natural coke or Jhama coal as reductant,
powdered calcined or hydrated lime as slag former and bentonite as binder,
wherein the high alumina iron ore mineral processing rejects as iron oxide
containing material has alumina (AI2O3) content of 3.0 to 10.0 % by weight and
powdered Jhama coal has fixed carbon of 60.0 to 75.0% by weight, wherein the
mixing is achieved by adjusting the slag composition or slag chemistry in
composite agglomerates such that the basicity or CaO:SiO2 ratio in the composite
agglomerates is in the range of 0.7 to 1.4, and wherein the reduction process of
composite agglomerates of high alumina iron ore mineral processing rejects and
natural coke or Jhama coal is carried out in a moving hearth furnace which is
characterized by subjecting the composite agglomerates to reduction process by
placing them on a natural coke or Jhama coal layer on the surface of the moving
hearth of the furnace.