AGGLOMERATION-2

Sinter plants:

Process description:

By sintering, the pelletisation of fine-grained, smeltable ores, iron ore in particular, to compact lumps by heating nearly to the melting or softening point is understood. Melting tendencies at the grain boundaries lead to a caking of the material.Before the sintering, the various substances are first mixed and, if desired, granulated.The iron ores are agglomerated on conveyor sinter installations, the conveyor belts

consist of a large number of wagons. These wagons that have been linked up as an endless conveyor belt which can be as big as 4 m in width and 100 m in length. The fine ore to be sintered is moistened and fed on to the circulating grid together with coke slack and additions such as limestone, quick lime, olivine or dolomite. Burners above a heat-resistant grate belt heat the material to the required temperature (1100-1200 °C). This causes the fuel in the mixture to be ignited. The carbon burns with the aid of the air

sucked through the grid into the mixture, resulting in the flame front being moved through the sintering bed. The sintering processes are completed once the flame front has passed through the entire mixed layer and all fuel has been burnt.

 

Chlorine compounds can enter into the sinter installation by means of the additive cokes slack as well by the ore from its natural chloride contents. Furthermore, returned materials such as certain filter particles, scale and sludges from waste water treatment, which are added to the materials to be sintered, which can also increase the chlorine content of the substances used. This is reflected in the waste gases from sinter

installations which contain inorganic gaseous chlorine compounds.

 

ALL ABOUT AGGLOMERATION - 1

Iron found in the nature are not in the form of lumps always and due to depletion of mines(Run of Mines) as of now, fines are costing around 90 % of total ore mining. Since fines are not suitable for Blast furnaces due to its size hence fines are agglomerated to meet the standard size for making it suitable to charge in the blast furnaces.
Sinter plants agglomerate iron ore fines (dust) with other fine materials at high temperature, to create a product that can be used in a blast furnace. The final product, a sinter, is a small, irregular nodule of iron mixed with small amounts of other minerals. The process, called sintering, causes the constituent materials to fuse to make a single porous mass with little change in the chemical properties of the ingredients. The purpose of sinter are to be used converting iron into steel.

BLAST FURNACE PROCESS-2

Now that we have completed a description of the ironmaking process, let s review the physical equipment comprising the blast furnace plant.
There is an ore storage yard that can also be an ore dock where boats and barges are unloaded. The raw materials stored in the ore yard are raw ore, several types of pellets, sinter, limestone or flux blend and possibly coke. These materials are transferred to the "stockhouse/hiline" (17) complex by ore bridges equipped with grab buckets or by conveyor belts. Materials can also be brought to the stockhouse/hiline in rail hoppers or transferred from ore bridges to self-propelled rail cars called "ore transfer cars". Each type of ore, pellet, sinter, coke and limestone is dumped into separate "storage bins" (18). The various raw materials are weighed according to a certain recipe designed to yield the desired hot metal and slag chemistry. This material weighing is done under the storage bins by a rail mounted scale car or computer controlled weigh hoppers that feed a conveyor belt. The weighed materials are then dumped into a "skip" car (19) which rides on rails up the "inclined skip bridge" to the "receiving hopper" (6) at the top of the furnace. The cables lifting the skip cars are powered from large winches located in the "hoist" house (20). Some modern blast furnace accomplish the same job with an automated conveyor stretching from the stockhouse to the furnace top.
At the top of the furnace the materials are held until a "charge" usually consisting of some type of metallic (ore, pellets or sinter), coke and flux (limestone) have accumulated. The precise filling order is developed by the blast furnace operators to carefully control gas flow and chemical reactions inside the furnace. The materials are charged into the blast furnace through two stages of conical "bells" (5) which seal in the gases and distribute the raw materials evenly around the circumference of the furnace "throat". Some modern furnaces do not have bells but instead have 2 or 3 airlock type hoppers that discharge raw materials onto a rotating chute which can change angles allowing more flexibility in precise material placement inside the furnace.
Also at the top of the blast furnace are four "uptakes" (10) where the hot, dirty gas exits the furnace dome. The gas flows up to where two uptakes merge into an "offtake" (9). The two offtakes then merge into the "downcomer" (7). At the extreme top of the uptakes there are "bleeder valves" (8) which may release gas and protect the top of the furnace from sudden gas pressure surges. The gas descends in the downcomer to the "dustcatcher", where coarse particles settle out, accumulate and are dumped into a railroad car or truck for disposal. The gas then flows through a "Venturi Scrubber" (4) which removes the finer particles and finally into a "gas cooler" (2) where water sprays reduce the temperature of the hot but clean gas. Some modern furnaces are equipped with a combined scrubber and cooling unit. The cleaned and cooled gas is now ready for burning.
The clean gas pipeline is directed to the hot blast "stove" (12). There are usually 3 or 4 cylindrical shaped stoves in a line adjacent to the blast furnace. The gas is burned in the bottom of a stove and the heat rises and transfers to refractory brick inside the stove. The products of combustion flow through passages in these bricks, out of the stove into a high "stack" (11) which is shared by all of the stoves.
Large volumes of air, from 80,000 ft³/min to 230,000 ft³/min, are generated from a turbo blower and flow through the "cold blast main" (14) up to the stoves. This cold blast then enters the stove that has been previously heated and the heat stored in the refractory brick inside the stove is transferred to the "cold blast" to form "hot blast". The hot blast temperature can be from 1600°F to 2300°F depending on the stove design and condition. This heated air then exits the stove into the "hot blast main" (13) which runs up to the furnace. There is a "mixer line" (15) connecting the cold blast main to the hot blast main that is equipped with a valve used to control the blast temperature and keep it constant. The hot blast main enters into a doughnut shaped pipe that encircles the furnace, called the "bustle pipe" (31). From the bustle pipe, the hot blast is directed into the furnace through nozzles called "tuyeres" (30) (pronounced "tweers"). These tuyeres are equally spaced around the circumference of the furnace. There may be fourteen tuyeres on a small blast furnace and forty tuyeres on a large blast furnace. These tuyeres are made of copper and are water cooled since the temperature directly in front of the them may be 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 which is necessary to increase productivity. The molten iron and slag drip past the tuyeres on the way to the furnace hearth which starts immediately below tuyere level.
Around the bottom half of the blast furnace the "casthouse" (1) encloses the bustle pipe, tuyeres and the equipment for "casting" the liquid iron and slag. The opening in the furnace hearth for casting or draining the furnace is called the "iron notch" (22). A large drill mounted on a pivoting base called the "taphole drill" (23) swings up to the iron notch and drills a hole through the refractory clay plug into the liquid iron. Another opening on the furnace called the "cinder notch" (21) is used to draw off slag or iron in emergency situations. Once the taphole is drilled open, liquid iron and slag flow down a deep trench called a "trough" (28). Set across and into the trough is a block of refractory, called a "skimmer", which has a small opening underneath it. The hot metal flows through this skimmer opening, over the "iron dam" and down the "iron runners" (27). Since the slag is less dense than iron, it floats on top of the iron, down the trough, hits the skimmer and is diverted into the "slag runners" (24). The liquid slag flows into "slag pots" (25) or into slag pits (not shown) and the liquid iron flows into refractory lined "ladles" (26) known as torpedo cars or sub cars due to their shape. When the liquids in the furnace are drained down to taphole level, some of the blast from the tuyeres causes the taphole to spit. This signals the end of the cast, so the "mudgun" (29) is swung into the iron notch. The mudgun cylinder, which was previously filled with a refractory clay, is actuated and the cylinder ram pushes clay into the iron notch stopping the flow of liquids. When the cast is complete, the iron ladles are taken to the steel shops for processing into steel and the slag is taken to the slag dump where it is processed into roadfill or railroad ballast. The casthouse is then cleaned and readied for the next cast which may occur in 45 minutes to 2 hours. Modern, larger blast furnaces may have as many as four tapholes and two casthouses. It is important to cast the furnace at the same rate that raw materials are charged and iron/slag produced so liquid levels can be maintained in the hearth and below the tuyeres. Liquid levels above the tuyeres can burn the copper casting and damage the furnace lining.

BLAST FURNACE PROCESS

The purpose of a blast furnace is to chemically reduce and physically convert iron oxides into liquid iron called "hot metal". The blast furnace is a huge, steel stack lined with refractory brick, where iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom. The raw materials require 6 to 8 hours to descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron. These liquid products are drained from the furnace at regular intervals. The hot air that was blown into the bottom of the furnace ascends to the top in 6 to 8 seconds after going through numerous chemical reactions. Once a blast furnace is started it will continuously run for four to ten years with only short stops to perform planned maintenance.

Iron oxides can come to the blast furnace plant in the form of raw ore, pellets or sinter. The raw ore is removed from the earth and sized into pieces that range from 0.5 to 1.5 inches. This ore is either Hematite (Fe₂O₃) or Magnetite (Fe₃O₄) and the iron content ranges from 50% to 70%. This iron rich ore can be charged directly into a blast furnace without any further processing. Iron ore that contains a lower iron content must be processed or beneficiated to increase its iron content. Pellets are produced from this lower iron content ore. This ore is crushed and ground into a powder so the waste material called gangue can be removed. The remaining iron-rich powder is rolled into balls and fired in a furnace to produce strong, marble-sized pellets that contain 60% to 65% iron. Sinter is produced from fine raw ore, small coke, sand-sized limestone and numerous other steel plant waste materials that contain some iron. These fine materials are proportioned to obtain a desired product chemistry then mixed together. This raw material mix is then placed on a sintering strand, which is similar to a steel conveyor belt, where it is ignited by gas fired furnace and fused by the heat from the coke fines into larger size pieces that are from 0.5 to 2.0 inches. The iron ore, pellets and sinter then become the liquid iron produced in the blast furnace with any of their remaining impurities going to the liquid slag.
The coke is produced from a mixture of coals. The coal is crushed and ground into a powder and then charged into an oven. As the oven is heated the coal is cooked so most of the volatile matter such as oil and tar are removed. The cooked coal, called coke, is removed from the oven after 18 to 24 hours of reaction time. The coke is cooled and screened into pieces ranging from one inch to four inches. The coke contains 90 to 93% carbon, some ash and sulfur but compared to raw coal is very strong. The strong pieces of coke with a high energy value provide permeability, heat and gases which are required to reduce and melt the iron ore, pellets and sinter.
The final raw material in the ironmaking process in limestone. The limestone is removed from the earth by blasting with explosives. It is then crushed and screened to a size that ranges from 0.5 inch to 1.5 inch to become blast furnace flux . This flux can be pure high calcium limestone, dolomitic limestone containing magnesia or a blend of the two types of limestone.
Since the limestone is melted to become the slag which removes sulfur and other impurities, the blast furnace operator may blend the different stones to produce the desired slag chemistry and create optimum slag properties such as a low melting point and a high fluidity.
All of the raw materials are stored in an ore field and transferred to the stockhouse before charging. Once these materials are charged into the furnace top, they go through numerous chemical and physical reactions while descending to the bottom of the furnace.
The iron ore, pellets and sinter are reduced which simply means the oxygen in the iron oxides is removed by a series of chemical reactions. These reactions occur as follows:

1) 3 Fe2O3 + CO = CO2 + 2 Fe3O4	Begins at 850° F
2) Fe3O4 + CO = CO2 + 3 FeO	Begins at 1100° F
3) FeO + CO = CO2 + Fe     or     FeO + C = CO + Fe	Begins at 1300° F

At the same time the iron oxides are going through these purifying reactions, they are also beginning to soften then melt and finally trickle as liquid iron through the coke to the bottom of the furnace.
The coke descends to the bottom of the furnace to the level where the preheated air or hot blast enters the blast furnace. The coke is ignited by this hot blast and immediately reacts to generate heat as follows:
C + O₂ = CO₂ + Heat
Since the reaction takes place in the presence of excess carbon at a high temperature the carbon dioxide is reduced to carbon monoxide as follows:
CO₂+ C = 2CO
The product of this reaction, carbon monoxide, is necessary to reduce the iron ore as seen in the previous iron oxide reactions.
The limestone descends in the blast furnace and remains a solid while going through its first reaction as follows:
CaCO₃ = CaO + CO₂
This reaction requires energy and starts at about 1600°F. The CaO formed from this reaction is used to remove sulfur from the iron which is necessary before the hot metal becomes steel. This sulfur removing reaction is:
FeS + CaO + C = CaS + FeO + CO
The CaS becomes part of the slag. The slag is also formed from any remaining Silica (SiO₂), Alumina (Al₂O₃), Magnesia (MgO) or Calcia (CaO) that entered with the iron ore, pellets, sinter or coke. The liquid slag then trickles through the coke bed to the bottom of the furnace where it floats on top of the liquid iron since it is less dense.
Another product of the ironmaking process, in addition to molten iron and slag, is hot dirty gases. These gases exit the top of the blast furnace and proceed through gas cleaning equipment where particulate matter is removed from the gas and the gas is cooled. This gas has a considerable energy value so it is burned as a fuel in the "hot blast stoves" which are used to preheat the air entering the blast furnace to become "hot blast". Any of the gas not burned in the stoves is sent to the boiler house and is used to generate steam which turns a turbo blower that generates the compressed air known as "cold blast" that comes to the stoves.
In summary, the blast furnace is a counter-current realtor where solids descend and gases ascend. In this reactor there are numerous chemical and physical reactions that produce the desired final product which is hot metal. A typical hot metal chemistry follows:

Iron (Fe)	= 93.5 - 95.0%
Silicon (Si)	= 0.30 - 0.90%
Sulfur (S)	= 0.025 - 0.050%
Manganese (Mn)	= 0.55 - 0.75%
Phosphorus (P)	= 0.03 - 0.09%
Titanium (Ti)	= 0.02 - 0.06%
Carbon (C)	= 4.1 - 4.4%

HISMELT NEW APPROACH OF IRON MAKING

HIsmelt

HIsmelt, short for high-intensity smelting, is the world's first commercial direct smelting process for making iron straight from the ore.
Fine iron ores and non-coking coals are injected directly into a molten iron bath, contained within a Smelt Reduction Vessel (SRV), to produce high quality molten pig iron. It can be considered both as a potential replacement for the blast furnace and as a new source of low cost iron units for BOF or EAF steelmaking.

HIsmelt technology brings many advantages to the steelmaking industry - such as lower operating costs; lower capital intensity, lower environmental impact, greater raw material and operational flexibility.

HIsmelt process

The core of the HIsmelt technology is the Smelt Reduction Vessel (SRV), which replaces the function of a blast furnace.
Iron ore fines are injected deep into the bath where they are reduced instantly on contact with carbon dissolved in the bath. This reaction produces iron (Fe) and carbon monoxide (CO).
Coal is also injected into the bath, where it is absorbed in the metal to replenish the carbon used in the reduction reaction.
Reaction gas (CO) and coal gasification products are generated from deep within the bath and form a fountain of mostly slag and some metal.
Hot air at 1200°C, which is enriched with oxygen, efficiently combusts the gases generated within the bath - releasing large amounts of energy.
Combustion energy is carried back to the bath via the fountain of slag and metal.
The role of the SRV and a basic flowsheet for a HIsmelt plant are explained in more detail below:


The primary product from the HIsmelt process is hot metal. Liquid iron is tapped continuously through an open forehearth and is free of slag.
Secondary products from the SRV are slag and offgas. Slag is formed from the impurities in the iron ore (gangue) and coal (ash), which are fluxed using lime and dolomite. Slag from the HIsmelt process can be utilised as a raw material in a variety of applications in the construction and agricultural industries. Offgas from the process has energy value and is cleaned, cooled and used as a fuel and for power generation.

Process benefits

The HIsmelt process has the potential to revolutionise the global steel industry - offering benefits to both new and existing steel plants. Not only can the HIsmelt technology offer a more competitive option for greenfield expansions, it can also bring new life to existing steel works by offering a technology that can reduce operating and capital costs and meets the ever-tightening environmental standards.
Compared to conventional iron making technologies, the HIsmelt® process has the potential to deliver:
• Lower operating costs;
• Greater raw material flexibility;
• Lower capital costs;
• Greater operational flexibility;
• Lower environmental impact;

Lower operating costs

Low cost ironmaking is achieved through the elimination of front-end processes such as coke ovens and sinter plants and through the use of cheaper iron ore fines, non-coking coals and the ability to directly use steel plant wastes.

The HIsmelt process delivers value to both the integrated and EAF mill sectors.

Value to integrated mills:
• No need for costly coking coke, lump ore, or pellet feeds.
• Direct use of raw materials without using sinter plants or coke batteries
• Flexible production and raw material options enable the steelmaker to optimise operating costs more easily.
• High quality hot metal - characterised by its very low phosphorus content (which allows the use of high phosphorus ore feeds) and low silicon which leads to a low slag steelmaking practice
• HIsmelt can also easily recycle many streams of carbon or iron units generated by the integrated mill (e.g. Breeze, sludge, BOF slag or mill scale)

Value to EAFs / mini-mills:
Stable supply of high-quality iron results in:
• Reduced exposure to the volatile scrap market.
• Allows the mill access to the flat product market.
• Delivers high value-in-use over other DRI or HBI, especially with hot metal charging.
• Can increase steel production rates by reducing the time to melt scrap.
Greater raw material flexibility
The HIsmelt process directly injects iron ore fines (-6mm) (no sinter, no pellets) and does not require agglomeration. The process also requires non-coking coal (no cokemaking), which is crushed and dried prior to injection into the Smelt Reduction Vessel (SRV). A wide range of coals that are not suitable for the blast furnace can be used.
A variety of feed materials can be used in the HIsmelt process, such as:
Hematite Fine iron ores:
Nominally -6mm sinter fines, however finer material is easily handled.
No blending necessary.
Typically preheated to increase process efficiency, but may be used directly.
Ores containing high levels of phosphorus can be used - process conditions allow for very effective partitioning of phosphorus to the slag.
Magnetite concentrate
By giving value to the reduced nature of this ore, HIsmelt can use this very fine concentrate without the need for pelletising and can produce iron at a lower coal rate than a blast furnace. If the concentrate has a high level of phosphorus, HIsmelt offers a further advantage.
Titano-magnetite ore and Iron Sands:
This type of ore body is very difficult to be used by the blast furnace and other iron making technologies. Its titania content makes it unsuitable for sintering and causes major problems in the slag treatment in the highly reducing zones found in blast furnaces and melter gasifiers. Since HIsmelt evolved from a very different path, it offers a very unique capacity for these abundant, easy to mine and easy to concentrate ores.
Non-coking coals:
Dried and ground to -3mm.
A wide range of coals can be utilised - from semi-anthracites to high volatile steaming coals.
Steel plant wastes:
Fine steel plant wastes and metallic fines - DRI fines, mill-scale, blended reverts and other iron sources.
BOF slag - as a flux and source of iron units.
Coke breeze.
Lower capital costsThe HIsmelt process delivers significantly reduced capital costs when compared to traditional ironmaking technology. This is due to the elimination of coke ovens and sinter and/or pellet plants, a necessary component of blast furnace ironmaking. Plant construction and operation is relatively simple because the HIsmelt technology uses many traditional ironmaking core-plant facilities, such as hot blast stoves, injection systems and power plants.
In addition, due to the raw material flexibility of the HIsmelt technology, large raw material blending yards are unnecessary and therefore significantly reduce the land requirements of a HIsmelt plant.

Greater operational flexibility
The highly responsive nature of the HIsmelt process means that it converts iron ore, coal and flux to metal, slag and energy almost instantaneously. These process capabilities allow for raw material feed rates to be changed very efficiently without affecting product quality. This operating flexibility maximises productivity, as it is easy to maintain a steady-state operating window. Unlike blast furnaces, the HIsmelt process can be started, stopped or idled with ease.

Lower environmental impact
Through the combination of high process efficiency and the elimination of coke and sinter making, the HIsmelt process meets the highest environmental standards in ironmaking. In general, a HIsmelt plant will have lower than industry best practice emissions of CO2, SO2 and NOx. Furthermore, dioxin, furan, tar and phenol creation is avoided and steel plant wastes can be recycled in an efficient manner. More recently in collaboration with ULCOS/Tata Steel, the HIsarna flow sheet has been developed which offers an opportunity to reduce the emission of greenhouse gas significantly.

End products

The main product of the HIsmelt process is hot metal, which can be used as direct charge to steelmaking processes or cast into pig iron. Slag is produced as a by-product.
The hot metal product is continuously tapped from the Smelt Reduction Vessel (SRV) via a foreheath. As slag is batch tapped through a slag notch (similar to mini blast furnaces) the hot metal is slag free.

If required, the hot metal can be treated in a hot metal desulphurisation plant to remove sulphur. The slag can be used as a valuable raw material in a variety of applications.

Comparison of hot metal quality produced by HIsmelt and blast furnace

Typical analysis	Blast furnace	HIsmelt
Carbon	4.5%	4.4 +/- 0.15%
Silicon	0.5 +/- 0.3%	<0 .01="" nbsp="" td="">
Manganese	0.4 +/- 0.2%	<0 .02="" td="">
Phosphorus	0.09 +/- 0.02% *	0.02 +/- 0.01% **
Sulphur	0.04 +/- 0.02%	0.1 +- 0.05% #
Temperature	1430 - 1500°C	1420°C

*Whilst using high phosphorus ore; # After hot metal desulphurisation Slag by-product
Slag is produced in the smelting process due to the reaction between the flux, the gangue in the ore and the ash in the coal.
Slag can be granulated or directed into pits for further processing. It can then be used as a raw material for a variety of purposes such as cement manufacture, road base and soil conditioning.

If titano-magnetite ore is used, the slag becomes a valuable co-product if its content in titania is rich enough (typically above 50 per cent) to be considered as pigment feed stock.

Operating plants

The first commercial HIsmelt plant was located in Kwinana, Western Australia with a design rate of 100 tonnes per hour of pig iron (800,000 tonnes per annum), and was owned by a Joint Venture comprising Rio Tinto (60 per cent), Nucor Corporation (25 per cent), Mitsubishi Corporation (10 per cent) and Shougang Corporation (5 per cent).  The construction of the HIsmelt Kwinana plant commenced in January 2003, and was hot commissioned in April 2005. The plant operated until December 2008 at production rates of more than 80 tonnes per hour when the global financial crisis forced the closure of the Kwinana operation.
To further develop the HIsmelt technology, Rio Tinto has signed a Development Agreement with a Chinese steelmaker.  This agreement involves the relocation of some Kwinana HIsmelt plant equipment from Australia to a new HIsmelt facility to be built in China. The new plant is expected to be commissioned in 2014. 
The partnership seeks to finalise the development of the HIsmelt technology and to work together to further improve the technology to higher levels of environmental and economic performance.

HISARANA

HIsarna

HIsarna™ represents a new phase in the global direct smelting development cycle. It is, in essence, a merger between Tata Steel developed smelt cyclone technology and HIsmelt (Rio Tinto)-developed bath smelting technology. 
The key driver from this perspective is efficient, cost-effective carbon dioxide collection for potential geological storage. HIsarna's inherently simple, once through gas flow path provides an easy carbon dioxide collection option without the need for a carbon dioxide scrubber. Other potential benefits include an ability to use thermal (steam) coals rather than metallurgical coals still in maintaining all other HIsmelt benefits

IRON MAKING ROUTES

1. BLAST FURNACE-HOT METAL
2. COREX - HOT METAL
3. FINEX - HOT METAL
4. HBI/DRI