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SUMMER TRAINING
Mecon ltd, ranchi
Projecton iron making
blast furnace, sintering, palletisation and Dri
-:SUBMITTEDED BY:
NAME: -PANKAJ KUMAR
BRANCH: -MECHANICAL ENGG(b.tech)
REGD.NO:- 1201288354 (sem-7)

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College:- nm instituteof engineering &technology, Bhubaneswar,odisha (751019)
Acknowledgement
It is my pleasure to be indebted to various people, who directly or
indirectly contributed in the development of this work and who influenced my
thinking, behaviour, and acts during the course of study.
I express my sincere gratitude to hrddepartment worthy Principal
for providing me an opportunity to undergo summer training at meconlimited.
I am thankful to Mr.RAHUL, SD Eforstudy of DRI and
Agglomeration and his support, cooperation, and motivation provided to me
during the training for constant inspiration, presence and blessing.
I also extend my sincere appreciation to Mr. ABHISHEKKUMAR
CHOUDHARYwho provided me knowledge about blast furnace and valuable
suggestions and precious time in accomplishing my project report.
Lastly, I would like to thank the almighty and my parents for their
moral support and my friends with whom I shared my day-to-day experience and
received lots of suggestions that improved my quality of work.
(Pankaj kumar)

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CONTENT
1) BLAST Furnace
(i) INTRODUCTION
(ii) MODERN PROCESS
(iii) PROCESS OF ENGINEERING AND CHEMISTRY
(iv) PROCESS LAYOUT/DIAGRAM
2) Agglomeration
(A) SINTERING
(I) INTRODUCTION
(II) PRINCIPLE OF SINTER
(III) ADVANTAGE OF ADDING FLUX TO SINTER
(IV) PROPERTIES OF SINTER
(V) PRODUCT SINTER
(VI) PLANT FACILITIES
(VII) CHEMICAL REACTION
(B) PELLETISATION
(I) INTRODUCTION
(II) THERMAL PROCESS
(III) ADVANTAGES OF PELLET
(IV) PREPARATION OF RAW MATERIAL FOR PELLET
3) Direct reduced iron
(i) INTRODUCTION
(ii) REACTION MECHANISM
(iii) TYPES OFDRI
(iv) PROCESS TECHNOLOGY
(v) PROCESS STRENGHT
(vi) PRODUCT STRENGHT
(vii) WEAKNESS OF PROCESS
(viii)WEAKNESS OF PRODUCT

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BLAST FURNACE
INTRODUCTION
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial
metals, generally iron, but also others such as lead or copper.
In a blast furnace, fuel, ore, and flux (limestone) are continuously supplied through the top of
the furnace, while a hot blast of air(sometimes with oxygen enrichment) is blown into the
lower section of the furnace through a series of pipes called tuyeres, so that the chemical
reactions take place throughout the furnace as the material moves downward. The end
products are usually molten metal and slag phases tapped from the bottom, and flue
gases exiting from the top of the furnace. The downward flow of the ore and flux in contact
with an up flow of hot, carbon monoxide-rich combustion gases is a counter current
exchange process.
In contrast, air furnaces (such as reverberates furnaces) are naturally aspirated, usually by
the convection of hot gases in a chimney flue. According to this broad
definition, bloomers’ for iron, blowing houses for tin, and smelt mills for lead would be
classified as blast furnaces. However, the term has usually been limited to those used for
smelting iron ore to produce pig iron, an intermediate material used in the production of
commercial iron and steel, and the shaft furnaces used in combination with sinter
plants in base metals smelting.

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MODERN PROCESS
Modern furnaces are equipped with an array of supporting facilities to increase efficiency,
such as ore storage yards where barges are unloaded. The raw materials are transferred to
the stock house complex by ore bridges, or rail hoppers and ore transfer cars. Rail-mounted
scale cars or computer controlled weight hoppers weigh out the various raw materials to
yield the desired hot metal and slag chemistry. The raw materials are brought to the top of
the blast furnace via a skip car powered by winches or conveyor belts.[52]
There are different ways in which the raw materials are charged into the blast furnace. Some
blast furnaces use a "double bell" system where two "bells" are used to control the entry of
raw material into the blast furnace. The purpose of the two bells is to minimize the loss of hot
gases in the blast furnace. First, the raw materials are emptied into the upper or small bell
which then opens to empty the charge into the large bell. The small bell then closes, to seal
the blast furnace, while the large bell rotates to provide specific distribution of materials
before dispensing the charge into the blast furnace.[53][54] A more recent design is to use a
"bell-less" system. These systems use multiple hoppers to contain each raw material, which
is then discharged into the blast furnace through valves.[53]These valves are more accurate
at controlling how much of each constituent is added, as compared to the skip or conveyor
system, thereby increasing the efficiency of the furnace. Some of these bell-less systems
also implement a discharge chute in the throat of the furnace (as with the Paul Wurth top) in
order to precisely control where the charge is placed.
The iron making blast furnace itself is built in the form of a tall structure, lined
with refractory brick, and profiled to allow for expansion of the charged materials as they
heat during their descent, and subsequent reduction in size as melting starts to occur.
Coke,limestone flux, and iron ore (iron oxide) are charged into the top of the furnace in a
precise filling order which helps control gas flow and the chemical reactions inside the
furnace. Four "uptakes" allow the hot, dirty gas high in carbon monoxide content to exit the
furnace throat, while "bleeder valves" protect the top of the furnace from sudden gas
pressure surges. The coarse particles in the exhaust gas settle in the "dust catcher" and are
dumped into a railroad car or truck for disposal, while the gas itself flows through aventuri
scrubber and/or electrostatic precipitators and a gas cooler to reduce the temperature of the
cleaned gas.
The "cast house" at the bottom half of the furnace contains the bustle pipe, water cooled
copper tuyeres and the equipment for casting the liquid iron and slag. Once a "tap hole" is
drilled through the refractory clay plug, liquid iron and slag flow down a trough through a

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"skimmer" opening, separating the iron and slag. Modern, larger blast furnaces may have as
many as four tap holes and two cast houses.Once the pig iron and slag has been tapped,
the tap hole is again plugged with refractory clay.
Tuyeres of Blast Furnace at Gerdau, India
The tuyeres are used to implement a hot blast, which is used to increase the efficiency of the
blast furnace. The hot blast is directed into the furnace through water-cooled copper nozzles
called tuyeres near the base. The hot blast temperature can be from 900 °C to 1300 °C
(1600 °F to 2300 °F) depending on the stove design and condition. The temperatures they
deal with may be 2000 °C to 2300 °C (3600 °F to 4200 °F). Oil, tar, natural gas,
powdered coal and oxygen can also be injected into the furnace at tuyere level to combine
with the coke to release additional energy and increase the percentage of reducing gases
present which is necessary to increase productivity
Process engineering and chemistry
Blast furnace placed in an installation
1. Iron ore + limestone sinter
2. Coke
3.Elevator
4.Feedstock inlet
5.Layer of coke
6.Layer of sinter pellets of ore and limestone

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7. Hot blast (around 1200 °C)
8. Removal of slag
9.Tapping of molten pig iron
10. Slag pot
11. Torpedo car for pig iron
12. Dust cyclone for separation of solid particles
13. Cowper stoves for hot blast
14. Smoke outlet (can be redirected to carbon capture & storage (CCS) tank)
15: Feed air for Cowper stoves (air pre-heaters)
16. Powdered coal
17.Coke oven
18.Coke
19. Blast furnace gas downcomer
Blast furnaces operate on the principle of chemical reduction whereby carbon monoxide,
having a stronger affinity for the oxygen in iron ore than iron does, reduces the iron to its
elemental form. Blast furnaces differ from bloomeries and reverberatory furnaces in that in a
blast furnace, flue gas is in direct contact with the ore and iron, allowing carbon monoxide to
diffuse into the ore and reduce the iron oxide to elemental iron mixed with carbon. The blast
furnaces operates as a countercurrent exchange process whereas a bloomery does not.
Another difference is that bloomeries operate as a batch process while blast furnaces
operate continuously for long periods because they are difficult to start up and shut down.
(See: Continuous production) Also, the carbon in pig iron lowers the melting point below that
of steel or pure iron; in contrast, iron does not melt in a bloomery.
Carbon monoxide also reduces silica which has to be removed from the pig iron. The silica is
reacted with calcium oxide (burned limestone) and forms a slag which floats to the surface of
the molten pig iron. The direct contact of flue gas with the iron causes contamination with
sulfur if it ispresent in the fuel. Historically, to prevent contamination from sulfur, the best
quality iron was produced with charcoal.

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The downward moving column of ore, flux, coke or charcoal and reaction products must be
porous enough for the flue gas to pass through. This requires the coke or charcoal to be in
large enough particles to be permeable, meaning there cannot be an excess of fineparticles.
Therefore, the coke must be strong enough so it will not be crushed by the weight of the
material above it. Besides physical strength of the coke, it must also be low in sulfur,
phosphorus, and ash. This necessitates the use of metallurgical coal, which is a premium
grade due to its relative scarcity.
The main chemical reaction producing the molten iron is:
Fe2O3 + 3CO → 2Fe + 3CO2[56]
This reaction might be divided into multiple steps, with the first being that preheated blast air
blown into the furnace reacts with the carbon in the form of coke to produce carbon
monoxide and heat:
2 C(s) + O2(g) → 2 CO(g)[57]
The hot carbon monoxide is the reducing agent for the iron ore and reacts with the iron
oxide to produce molten iron and carbon dioxide. Depending on the temperature in the
different parts of the furnace (warmest at the bottom) the iron is reduced in several steps. At
the top, where the temperature usually is in the range between 200 °C and 700 °C, the iron
oxide is partially reduced to iron(II,III) oxide, Fe3O4.
3 Fe2O3(s) + CO(g) → 2 Fe3O4(s) + CO2(g)
At temperatures around 850 °C, further down in the furnace, the iron(II,III) is reduced further
to iron(II) oxide:
Fe3O4(s) + CO(g) → 3 FeO(s) + CO2(g)
Hot carbon dioxide, unreacted carbon monoxide, and nitrogen from the air pass up through
the furnace as fresh feed material travels down into the reaction zone. As the material
travels downward, the counter-current gases both preheat the feed charge and decompose
the limestone to calcium oxide and carbon dioxide:
CaCO3(s) → CaO(s) + CO2(g)
As the iron(II) oxide moves down to the area with higher temperatures, ranging up to
1200 °C degrees, it is reduced further to iron metal:
FeO(s) + CO(g) → Fe(s) + CO2(g)
The carbon dioxide formed in this process is re-reduced to carbon monoxide by the coke:
C(s) + CO2(g) → 2 CO(g)
The temperature-dependent equilibrium controlling the gas atmosphere in the furnace is
called the Boudouard reaction:
2CO CO2 + C
The decomposition of limestone in the middle zones of the furnace proceeds according to
the following reaction:

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CaCO3 → CaO + CO2
The calcium oxide formed by decomposition reacts with various acidic impurities in the iron
(notably silica), to form a fayalitic slag which is essentially calcium silicate, CaSiO3:]
SiO2 + CaO → CaSiO3
The "pig iron" produced by the blast furnace has a relatively high carbon content of around
4–5%, making it very brittle, and of limited immediate commercial use. Some pig iron is used
to make cast iron. The majority of pig ironproduced by blast furnaces undergoes further
processing to reduce the carbon content and produce various grades of steel used for
construction materials, automobiles, ships and machinery.
Although the efficiency of blast furnaces is constantly evolving, the chemical process inside
the blast furnace remains the same. According to the American Iron and Steel Institute:
"Blast furnaces will survive into the next millennium because the larger, efficient furnaces
can produce hot metal at costs competitive with other iron making technologies."] One of the
biggest drawbacks of the blast furnaces is the inevitable carbon dioxide production as iron is
reduced from iron oxides by carbon and there is no economical substitute – steelmaking is
one of the unavoidable industrial contributors of the CO2 emissions in the world
(see greenhouse gases).
Blast furnace diagram
1. Hot blast from Cowper stoves
2. Melting zone (bosh)
3. Reduction zone of ferrous oxide (barrel)
4. Reduction zone of ferric oxide (stack)
5. Pre-heating zone (throat)

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6. Feed of ore, limestone, and coke
7. Exhaust gases
8. Column of ore, coke and limestone
9.Removal of slag
10.Tapping of molten pig iron
11. Collection of waste gases

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AGGLOMERATION
Agglomeration, the sticking of particles to one another or to solid surfaces, is a natural
phenomenon. For powders and bulk solids, agglomeration can be unwanted, resulting in
uncontrolled build up, caking, bridging, or lumping. It can also be a beneficial process,
utilizing the controlled enlargement of particles to improve powder properties and obtain
high-quality products.
Production of sized lump ore in mechanized mines results in generation of large quantity of
ore fines which as such cannot be charged into furnace. Agglomeration processes such as
sintering and palletizing have been developed to utilize these iron ore fines economically.
Choice of Agglomerating
Process Four types of agglomerating processes have been developed: sintering, pelletizing,
briquetting, and nodulizing. Sintering and pelletizing are the processes of major importance.
Careful evaluation should be made of the processes, the material to be agglomerated, and
the product desired before arriving at a final decision on a commercial installation.

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SINTERING:
In technology, a process of obtaining solid and porous material and items from fine powdery
or pulverized materials at a high temperatures. The physicochemical properties and
structure of materials are also frequently altered by sintering. Sintering is used in for
example, agglomeration, coking, the preparation of poorly caking coals for coking, and the
production of ceramics and refractory items.

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Principle of Sintering:
The principle of sintering involves the heating of iron ore fines along with flux and coke fines
or coal to produce a semi-molten mass that solidifies into porous pieces of sinter with the
size and strength characteristics necessary for feeding into the blast furnace.
It is basically an agglomeration process achieved through combustion.
Advantages of Adding Flux to Sinter
Sinters are classified into acid sinter, self-fluxing sinter and super fluxed sinter.Self-fluxing
sinter brings the lime required to flux its acid components (SiO2, Al2O3). Super-fluxed sinter
brings extra CaO to the blast furnace. For self-fluxing and super-fluxed sinter, the lime
reduces the melting temperature of the blend and at relatively low temperature. In case
ofself-fluxing and super-fluxed sinter, the lime reduces the melting temperature of the blend
and at relatively low temperatures (1100 Deg. C to 1300 Deg. C) strong bonds are formed in
the presence of FeO. The following are the advantages of adding flux to the sinter
 It generates slag with the impurities present in the iron ores and solid fuels producing a
suitable matrix for cohesion of the particles
 It improves the physical and metallurgical properties of sinter
 It reduces the melting temperature of the iron ore blend
 It promotes the calcination reaction of the limestone (CaCO3 =CaO + CO2) outside of the
blast furnace hence saving heat consumption in the blast furnace.
Typical Properties Of Sinter
Item Unit Value
Fe % 56.5 to 57.5
FeO % 6.0-8.0
SiO2 % 4.0 to 5.0
Al2O3 % 1.8 to 2.5
CaO % 7.5 to 8.5
MgO % 1.6 to 2.0
Basicity (CaO/SiO2) 1.7 to 2.9
ISO Strength (+6.3mm) % >75
RDI (-3 mm) % 27-31
Iron Ore—Sintering Ore Fines:
Historically, iron ore was sourced primarily from local or regional mines. Sometimes this ore
was low grade when options were limited. In the last four decades, seaborne trade of iron
ore has grown dramatically, aided by the construction of large vessels and thus reduced

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shipping costs. The ready availability of these high-grade ores, which are ideal sinter feed,
allowed steel companies to gain the advantages that uniform sinter feed can provide to the
blast furnace by reducing operating costs and improving their competitive position. For most
of the world, the sintering process, based on coarse high-grade ore fines, is the primary
means of producing ferrous raw material feed. High-grade ore fines are characterized by
high iron content (64% to 69%), moderate levels of acidic gangue (i.e., SiO2 and Al2O3 are
less than 6%), low levels of key impurities (e.g., Mn, S, P, and alkalis), and trace amounts of
other elements.
Iron Ore—Sintering:
For blast furnace operations where sinter is the principal burden material (65% to 90%),
imported or local sintering ores are the prime feed material, followed by waste oxides and
then fluxes. With an average iron ore SiO2 level of 5.0%, the CaO–SiO2 ratio is set at about
1.5 to 2.5 to ensure good sinter physical and metallurgical properties and sufficient flux to
minimize or eliminate the need to charge raw flux directly to the blast furnace. The flux must
contain some MgO to ensure good sinter metallurgical properties and also a certain MgO
level in the blast furnace slag. The blast furnace slag MgO target varies worldwide, however,
according to different strategies for slag chemistry optimization. In any event, sinter typically
has the following chemistry: 55% Fe (in the form of Fe2O3 at 71% and FeO at 7%); 5% SiO2;
10% CaO; 2% MgO; 1% Al2O3; and 4% other. This composition implies considerable
addition of raw flux, mainly in the form of limestone and dolomite, given calcination losses of
about 50%.
The Product Sinter:
The product of the sintering process is called sinter and is having good following quality
characteristics
1. Chemical analysis
2. Grain size distribution
3. Reducibility
4. Sinter strength
Main Plant Facilities:
A sinter plant consists of following main technological units:
1. Proportioning unit.
2. Combined mixing and bailing unit
3. Sintering and cooling unit.
4. Cold sinter screening unit.
5. 5.Main exhaust fan unit.

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Chemical Reaction:
The reaction mechanism followed and subsequently the sinter minerals formed are,
however, depending on the mix composition. While magnetite, fayalite and glass containing
iron oxides are the major mineral phases for siliceous sinter, the ferrites, magnetite and
mixed calcium iron silicates are the major mineral phases for fluxed sinter. Sintering is a fast
process and it is unlikely that equilibrium will be reached during sintering.
The reaction mechanism proposed for self-fluxing sinter is summarized below:
At 800-1000°C
Crystallization of iron oxide — hematite
Dissociation of CaCO3
Sintering of hematite with quartz and lime.
At 1050-1200°C
Part of hematite + Ca0 = CaO. Fe203 + 2Ca0 = 2Ca0. Fe203
Si02 + Ca0 = Ca0 Si02 (Minor quantity)
At 1250-1350°C
Mono calcium ferrite decomposes
Magnetite + Lime + Silica = Calcium olivine’s.
Various Zones of Sintering
The sintering process consists of the passage of a heat and reaction front through a packed
bed of solids. En general, the objective is to attain a temperature wave passing through the
bed in such a way that a zone of incipient or partial fusion passes through the bed in order to
agglomerate (sinter) the fines in the bed to a porous lumpy material suitable for feed to a
blast furnace.The sintering process consists of the following five different zones:

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A) Zone of Sinter:
The gross physical character of this zone is established upon the solidification of the fluid
slag matrix, but the physical and chemical changes occur just after solidification such as
oxidation of magnetite to hematite, grain growth of iron oxide crystal.
B) Zone of Combustion and Fusion:
The oxidation of carbon to carbon monoxide and carbon dioxide provides large quantity of
heat for slag formation, and the fusion of ore particles. The burning of coke breeze by the
preheated air proceeds successively vertically downwards. The calcium limestone reacts
with the gangue constituents to form the semi-liquid slag phase. Reduction of hematite to
magnetite by Co, initiated in the calcination zone continues and a substantial portion of the-
original hematite may be reduced to FeO in the fuel content is too high.
C) Zone of Calcination:
At this level in the bed, the gas stream is sufficiently hot as to calcium carbonates and
sufficient Co is present to initiate reduction, of hematite to magnetite.
D) Dry and Preheat Zone:
The hot gaseous combustion products preheat-this zone. The preheating results in the
evaporation of moisture and hydrated water.
(e) Wet Zone:
This lowest portion of the bed has essentially the same characteristics as the original mix.
The gas stream has transferred essentially all its sensible heat to upper part of the zone and
the lower part of the zone is at the temperature of original mix.
The process continues in successive layers up to last one when due to the absence of any
cold mix the waste gas temperature shoots unto 300-350°C. The rate of sintering is very fast
and depending upon the permeability and thickness of the bed it takes 15-20 minutes for
completion.
Important Issues Related To Sinterplant
1. Use of sinter reduces the coke rate and enhances the productivity in blast furnace.
2. Sintering process helps utilization of iron ore fines (0-10 mm) generated during iron ore
mining operations.
3. Sintering process helps in recycling all the iron, fuel and flux bearing waste materials in the
steel plant.
4. Sintering process utilizes by product gases of the steel plant.
5. Sinter cannot be stored for a long time as it generate excessive fines during long storages
6. Sinter generates excessive fines during multiple handling.

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7. PELLETISING:
Pelletizing essentially consist of formation of green balls by rolling ultra-iron ore fines with
critical amount of water to which an external binder or any other additive may be added if
required. This formation of green balls is followed by drying, preheating, induration and
hardening. The process is readily adoptable when the ore is very fine which otherwise is not
suitable for sintering or cannot be sintered economically.
Major Advantages of Iron Ore Pelletizing:
 Because of spherical shape of pellets and almost no return fines generation, use of
certain percentage of pellets offer more uniform and better permeability to the
movement of gases. This in turn results in smoother furnace operation, increased
production and decreased coke rate.
 Pellets are having very high cold crushing strength; as such transportation losses are
almost negligible as compared to sinter and lump ore.
 It requires almost 1.4 to 1.5 times the sinter quality as compared to pellets for
production of same quantity of hot metal. This will increase Fe content (percentage)
in the burden and shall give better productivity at blast furnace end with respect to
only sinter and lump ore in the burden.

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Preparation of Raw Materials:
Additional materials are added to the iron ore (pellet feed) to meet the requirements
of the final pellets. This is done by placing the mixture in the pelletizer, which can hold
different types of ores and additives, and mixing to adjust the chemical composition and the
metallurgic properties of the pellets. In general, the following stages are included in this
period of processing: concentration / separation, hominization of the substance ratios,
milling, classification, increasing thickness, homogenization of the pulp and filtering.it is a
best process.
Formation of the Raw Pellets:

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Disc Pelletizer
The formation of raw iron ore pellets, also known as pelletizing, has the objective of
producing pellets in an appropriate band of sizes and with mechanical properties high
usefulness during the stresses of transference, transport, and use. Both mechanical force
and thermal processes are used to produce the correct pellet properties. From an equipment
point of view there are two alternatives for industrial production of iron ore pellets: the drum
and the pelletizing disk.
Thermal Processing:
In order to confer to the pellets high resistance metallurgic mechanics and appropriate
characteristics, the pellets are subjected to thermal processing, which involves stages of
drying, daily pay burn, burn, after-burn and cooling. The duration of each stage and the
temperature that the pellets are subjected to have a strong influence on the final product
quality.
Pelletizing Process:
The iron ore fines/ concentrate are ground in dry or wet state to 325 meshes. In case of wet
grinding, the slurry is thickened and filtered to obtain the filter cake. The ground fines/
concentrate are mixed with additives like hydrate lime or bentonite which act as binder. The
above materials are proportioned and mixed. The mix is pelletized in disc pelletizers to
obtain green balls of 9-16 mm size. These green balls are heat hardened on indurating
machine.
Plant Facilities:
The major plant facilities are as follows:

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 Raw materials receipt, storage.
 Drying and grinding.
 Ground materials storage, dosing & mixing.
 Balling.
 Induration.
 Pellet screening.
 Conveyor galleries & junction house.
 Services.
 Pellet ground storage.
 Control room & substances.
 Conveyor galleries & junction houses.
 Services.
SKETCH DIAGRAM OF STRAIGHT GRATE

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DIRECT REDUCED IRON
INTRODUCTION
Sponge Iron is iron ore reduced directly in solid state using coal gas, natrual gas or coal as
reductants and is also known as Directly Reduced Iron (DRI). The need for development and
commercialisation of sponge iron manufacturing process arose in late 50's when Electric Arc
Furnaces (EAFs) engaged in manufacturing steel started facing problems of availability of
scrap of desired quality, the traditional source of their iron metallics. The DRI processes
soon became popular and since the inception of first DRI plant in 1957 in Mexico, there has
been a continuous growth of this industry in last three decades. This is evident from the
steep rise in world DRI production during the past three decades. India, entered the sponge
iron industry only in 1980, when the coal based DRI plant of Sponge Iron India Limited (SIIL)
was commissioned at Kothagudem, in Andhra Pradesh.
2. The reasons for the tremendous growth of the sponge iron industry world over could be
attributed to the advantages of using sponge iron in electric arc furnaces, partly substituting
scrap, the conventional charge to the furnaces. Further, the use of sponge iron in other steel
manufacturing processes has also been well proven.
The advantages of sponge iron use in EAFs are summarised below:-
Uniform known composition
Low levels of residuals/tramp elements
Capability to maintain phosphorous level in steel within 0.002%
Maintenance of sulphur in steel by its removal in sponge manufacture.
Low content of dissolved gases
Uniform size and higher bulk density as compared to scrap
Capability of forming protective cover of foamy slag in the bath
Lower refining requirements of steel produced
Potential of sensible heat recovery from waste gases
Possibility of producing variety of steels.

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REACTION MECHANISM
In pre-heat zone, the reduction of iron oxide proceeds only to ferrous oxide.
Fe2O3 + CO = 2FeO + CO2……………………………………(1)
Final reduction to metallic iron occurs in the metallization zone by reaction of CO with FeO to
from CO2 and metallic iron.
FeO + CO = Fe + CO2………………………………..(2)
Most of the CO2 reacts with the excess solid fuels in the kiln and is converted to CO
according to the Boudouard reaction,
CO2 + C = 2CO ……………………………………………(3)
DRI generally based on two types:-
1.Solidreductant or coal based type
2.Gasreductant based type.
We are study only about coal based reductant type of DRI.
Coal Based Direct Reduction process:-

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Coal based direct reduction technologies involve reduction of iron oxides in a rotary kiln by
using non-coking coal as reductant. Limestone or dolomite is used as desulphurising agent.
The normal operating practice is to feed the kiln with desired proportion of iron oxide, non-
coking coal and limestone or dolomite. Some processes use optimum quantity of recycle
char in the feed for minimising coal consumption. The charge is preheated in the preheat
zone and the reduction of iron ore is effected by reducing gases derived from coal
gasification. The heat for the process is provided by burning coal volatiles and excess
carbon monoxide emerging from the charge. This is done by introducing controlled quantity
of air in the kiln free board along the preheat and reduction zones of the kiln. Part of coal is
introduced from the kiln discharge end to supply energy at discharge end, maintaining
reducing atmosphere at discharge end to prevent reoxidation of DRI and for controlling
degree of metallisation and carbon content of DRI. The separation of the product is more or
less similar in all the coal based processes and involves screening and magnetic separation
for removal of non magentic ash, char and used desulphuriser.
Different types of coal based DRI technology:-
SL/RN, CODIR, DRC, ACCAR, TDR and Jindal's are the available coal based DR
processes and the two main operations where different technologies use different
techniques are feeding/blowing coal and introduction of air for the process.
Raw Material:-
Direct reduction processes are very sensitive to chemical and physical characteristics of raw
materials used in the process. Iron ore or pellets, reductant natural gas or non-coking coal
and limestone/dolomite are the main raw materials. For the successful operations the
process licensors of DR technology have specified the characteristics of the raw materials to
be used in the process. The quality requirements of the raw materials in general are:
Iron Ore : Lumps or pellets with high iron content, low gangue content, good mechanical
strength, readily reducible and of non decrepitating variety.
Non-coking Coal : These are the reductants in the process. The characteristic desired for
non-coking coal are that the non-coking coals should have high fixed carbon content and
high volatiles content. Ash, sulphur and moisture in coal should be low. The ash fusion point
of coal is required to be high. The coal should be highly reactive and should have low coking
and swelling indices.
Limestone and Dolomite : These should have lime or lime and magnesia content of 45% or
above. The grain size of raw materials is also important factor in direct reduction process.

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Advantages of ROTARY KILN process
Process Strengths
Rotary kiln process has to compete mainly with the shaft process of making sponge iron and
in some cases with iron making blast furnace. As compared to them, the rotary kiln has
some advantages, as also some limitations, both with respect to the process and the product
it makes. The major process strengths of rotary kiln are:
(i) A rotary kiln can mix the solid charge as it heats and reduces it. Simultaneous
mixing helps in the dilution of CO2 concentration formed around the iron ore/sponge
iron particles – which is necessary for the reduction reaction to proceed.
(ii) As a large freeboard volume is available above the solid charge (about 85%), the
rotary kiln can tolerate heavily dust-laden gas. When the kiln is suitably designed, it
would be best suited for utilising the Indian high ash non-cooking coals. In shaft
reactors, generation of such dust leads to choking and channelling which leads
finally to disruption of the process.
(iii) Rotary kiln can serve the dual purpose of a coal gasifier as well as an ore reducer.
Preparation of reducing gas from coal is an expensive step, which is coming in the
way of commer- cialisation of coal gasification based DR process. Therefore, rotary
kiln DR process has proved commercially viable, even with low productivity perunit
volume, because of this capability to perform two different functions simultaneously.
(iv) In comparison to blast furnace, the temperature of reduction of iron oxide is
much lower in rotary kiln (about 1000oC as against 1500 to 2000oC in blast
furnace). This means that much less energy is required for bringing the reactants to
the temperature of reaction.
Product Strengths
Additionally the strengths of the product made by rotary kiln are:
(i) It is easy to desulphurise iron ore while making sponge iron. Consequently the sponge
iron of much lower sulphur content can be produced as compared to blast furnace hot
metal. For shaft process of sponge iron making, prior and meticulous de-sulphurisation
of natural gas is necessary to prevent poisoning of catalyst used for reforming.
(ii) Sponge iron produced from rotary kiln is obtained in close granular size range. This
permits charging in electric or other steel making furnaces in a continuous manner,
obviating the need for opening and closing of roof. Continuous charging permits partial
refining during melting stage as the particle passes through the slag layer into the mixed

26. 26
layer. If adequate melting energy is available, refining time, and consequently, operation
time can be considerably reduced.
Weaknesses of the Process
Notwithstanding the above, rotary kiln has a number of weaknesses. These are coming in
the way of its wide acceptability. The main process related weaknesses of rotary kiln are:
(i) It has very low productivity. Shaft furnaces, which make sponge iron, give upto five
times more output than rotary kilns of same inner volume. Productivity in rotary kiln is
consequently much lower.
(ii) The rotating reactor makes it difficult to incorporate process control and quality control
systems. Energy saving measures, such as use of pre-heated air, are difficult to
incorporate. To prevent ingress of atmospheric air an elaborate sealing system is
required, which has made the reactor very “engineering intensive”.
(iii) The ROTARY Kiln DR process has low energy efficiency. The stored energy
in sponge iron is about 1.7 GCal per tonne, while energy usually spent in
making it in rotary kiln is about 6 GCal per tonne. Among other things, a lot of
energy goes out in waste gases (over 2 GCal per tonne).
(iv) The RKDR process produces some sponge iron in fine form (-3 mm) which is
a little difficult to utilise in electric furnaces. While much of the fines are
generated due to the nature of ore used, the situation is aggravated by the
tumcbling action within the rotary kiln, which forces softer particles to break
down further.
Weakness of the product
In addition the sponge iron made by rotary kiln has the following
weaknesses:
(i) For charging in electric furnaces in substantial quantities, a system of
continuous charging needs to be installed. This would mean an additional
investment for the existing units, which are not having this facility.
(ii) The sponge iron from rotary kiln has much lower carbon content (usually
0.2%) than either the sponge iron from shaft furnace (0.7 to 2%) or the hot

27. 27
metal from blast furnace. Carbon in sponge iron not only helps in adding to
the opening carbon in molten bath, it also carries in chemical energy, which
helps in reducing the consumption of electric power. Too low a carbon
content comes in the way of a healthy carbon boil and, therefore, bath
carburisers need to be added. Clean carburisers are costly while coke, char
or pig iron carries with it undesirable elements like sulphur and
phosphorous.
(iii) Sponge iron from rotary kiln carries with it more gangue and phosphorous
than those from shaft furnace, mainly because shaft furnace uses cleaner
inputs. Gangue and phosphorous contents are much higher than they are in
iron and steel scrap, which means extra inputs of phosphorous and slag in
electric furnaces.
(iv) When we compare with scrap and pig iron, all sponge irons are prone to re-
oxidation and the product from rotary kiln is no exception. However,
rotary kiln sponge iron is much less susceptible to re-oxidation as
compared to sponge iron from shaft units using reformed gases. Those
who have ventured into sponge iron have to endeavour to exploit the
strengths of RKDR to the fullest extent and would have to try to mitigate
the effects of its weaknesses suitably.
Those who contemplate venturing into sponge iron have to make a
thorough analysis as to whether the strengths outweigh the disadvantages
or not in the scenario they are finding themselves in. It becomes the duty of
the process developers to put in innovations, which make greater use of
the strengths and minimise to the extent possible the weaknesses of
RKDR.
There are many basic aspects, which need to be considered for making
sponge iron in rotary kiln, the important ones being:
(i) Thermodynamics of reduction and gasification reactions (ii)
Characteristics of raw materials and their role in the process (iii) Reaction
kinetics, roles of reducibility of iron ore and reactivity of coal char and
thereby the basis of selection of iron ore and coal (iv) Movement of solids
in the rotary kiln and its residence time (v) Gas evolution and flow rate (vi)
Heat transfer, temperature profile and process model