Project Description with Process Details

M/s Sundaram Steels Pvt Ltd. is presently having a kiln of capacity 1 x 90 TPD Sponge Iron Plant to produce Direct Reduced Iron (DRI). As a part of their expansion program the company would like to install additional 1 x 90 TPD with 2 x 12 t of Induction Furnaces, 15 t Ladle Refining Furnace (LRF) and Continuous Casting Machine (CCM) to produce billet as a final product. To keep the initial investment in optimum level, the production capacity of the plant has been fixed as about 72,000 TPA. The above capacity will be made by updating the existing facilities and augmentation of additional kiln and melting facilities of suitable capacity, installing billet caster to produce billet.

The flow diagram of Manufacturing Process & Mass Balance diagram and the plant layout plan is enclosed as Figure 2.2 and 2.3 respectively. The description of manufacturing process is given below:-

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Fig: 2.2 Manufacturing Process & Mass Balance Diagram

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Sponge Iron Process

This process utilizes non-coking coal as reducing agent along with lumpy rich grade iron ore. The reduction is carried out in an inclined horizontal rotary kiln, which rotates at a predetermined speed. DRI gases flow counter-current to the kiln feed. The temperature at the product discharge end in a rotary kiln is about 950-1050o_{C compared to 750-900}o_{C towards the feed end. The}

counter-current flow of hot DRI gases enables it to remove the moisture content from feed. The hot DRI gases contains huge amount of fine dust comprising oxides and unburned carbon and toxic carbon monoxide. The raw

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material feed side of rotary DRI Kiln has a natural structure below the After Burner Chamber (ABC) that acts as Dust Settling Chamber (DSC). About 15- 20% coarse dust settles in DSC by means of gravity. In ABC, the CO content of gases is converted to CO2. This conversion process is exothermic and the

temperature of gases rises to 1000-1050 o_C.

A temperature profile ranging from 800-1050 o_{C is maintained along the length}

of the kiln at different zones and as the material flows down due to gravity the ore is reduced. The hot reduced sponge iron along with semi-burnt coal, discharged from kiln is cooled in water-cooled cylindrical rotary cooler to a temperature of 100–200 degree centigrade. The discharge from cooler consisting of sponge iron, char other contaminations are passed on through magnetic separators so that sponge iron can be separated from other impurities.

Later the sponge iron is screened into two size fractions i.e_{. –3 mm & +3 mm +3}

mm fraction directly goes for usage, -3 mm fraction can be either used directly where ever it is possible or is to be briquetted by using molasses and hydrated lime as binders.

The basic reactions in this process are as follows: C + O2 = CO2

CO2 + C = 2CO

Fe2O3 + CO = Fe3O4 + CO2

Fe3O4 + CO = FeO + CO2

FeO + CO = Fe + CO2

Utilization of char for a centralized power generation unit

For coal based sponge iron plants, disposal of char is a problem and mostly receives adverse public reaction as this is dumped in an unscientific way by

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many small producers. Char should be mixed with coal or coal washery rejects and used as fuel for generation of power. It is a techno-economically viable option for plants having capacity of 200 TPD and above. Also the smaller capacity individual Sponge Iron Plants (Capacity up to 100 TPD) and operating in clusters can collectively install common unit for power generation.

Char can be sold to local entrepreneurs for making coal briquettes. It can also be mixed with coal fines, converted to briquettes and can be used in brick kilns.

Principle of melting in Induction Furnace (IF)

The principle of melting in induction furnace is that the electrical coil surrounding the cylindrical crucible acts as primary and the metallic charge as secondary. When an electrical current is passed through the primary coils, the electromagnetic field cause induced current to flow through the metallic charge, making it melt. As soon as pool of liquid metal from the scrap charged in the furnace has been formed a pronounced stirring action takes place in the molten metal, which helps to accelerate further melting of charge. The melting is rapid comparing to other processes with only a slight loss of easily oxidisable elements. In fact there is hardly any loss of alloying elements.

Induction Furnace (IF) construction

The shape of furnace is like a vertical cylindrical crucible made of refractory ramming mass. It is fitted in a steel shell suitably insulated. Between the shell and refractory crucible winding of copper tubing is placed. Fire bricks are placed at the bottom of the shell, and the space between steel former and the coil is rammed with fine grains of acidic or basic refractory material. The steel former melts during the melting of charge in the crucible.

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When the electrical current is switched on, the eddy currents developed between primary copper coil and heavier secondary current in the metallic charge melt the charge to the desired temperature. The entire process of melting is taking place silently without any noise pollution.

No serious refining for adjustment of chemistry or removing the non-metallic inclusion is carried out. Normally the steel melting scrap of good quality is used. In an empty furnace, first 10 to 15% scrap is charged on the melting of which continuous charging of sponge iron at 100 to 130 kg/min. rate is commenced. Sponge iron and scrap charging sequence is decided by the Induction Furnace. Towards end of the heat, sponge iron charging is discontinued and heat completed by addition of steel scrap.

However, to get the desired chemistry of bath, some additions are made. In case carbon in bath is high, low carbon sponge iron is added to reduce it. It will also dilute sulphur and phosphorous contents. In the sponge iron, phosphorus still exists in the oxide form even after reduction. In this way, a distribution of phosphorus between the slag and metal phase corresponding to the equilibrium is attained. This is one of the essential advantages of sponge iron as compared to scrap. A typical coreless Induction Furnace is shown below.

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of Metal in the Crucible of an Forces acting in the Crucible Induction Furnace of an Induction Furnace

M/s Sundaram Steels Pvt Ltd. is presently having a kiln of capacity 1 x 90 TPD Sponge Iron Plant to produce Direct Reduced Iron (DRI). As a part of their expansion program the company would like to install additional 1 x 90 TPD with 2 x 12 t of Induction Furnaces, 15 t Ladle Refining Furnace (LRF) and Continuous Casting Machine (CCM) to produce billet as a final product. To keep the initial investment in optimum level, the production capacity of the plant has been fixed as about 72,000 TPA.

This project is based on the concept of continuous casting machine with hot charging of molten metal at 1050-1100 degree Celsius directly to the rolling mill without reheating by the reheating furnace thus avoiding any coal/fuel operated reheating thus resulting into pollution less production of the end product. However, provision of oil fired reheating furnace has been kept as standby.

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Induction Furnace

Induction furnaces have increased in capacity to where modern high-power- density induction furnaces are competing successfully with electric arc furnace. However, fewer chemical reactions are possible in induction furnaces compared to an arc furnace; melt analysis control in induction furnace is not possible. The melt will generally be as per the composition of charge mix selected. Induction melting is more sensitive to quality of charge materials when compared an electric arc furnace, limiting the types of scrap that can be melted.

The inherent induction stirring provides excellent metal homogeneity. Induction melting produces a fraction of the fumes that result from melting in an electric arc furnace (heavy metal fumes and particulate emissions). A new generation of industrial induction melting furnaces has been developed during the last 25 years. The development of flexible, constant power- tracking, medium-frequency induction power supplies has resulted in the widespread use of the batch melting methods in modern foundries / steel plants. These power units incorporate heavy duty silicon-controlled rectifiers that are able to generate both the frequency and the amperage needed for batch melting and are able to achieve electrical efficiency levels exceeding 97%, a substantial improvement over the 85% efficiency typical of induction power supplies of the 1970s. The new designs allow maximum utilization of furnace power throughout the melting cycle with good control of stirring. Some of the largest commercial units are capable of melting at nearly 60 t per hour and small furnaces with very high power densities of 700 to 1,000 kWh/ t can now melt a cold charge in 30 to 35 minutes. Medium Frequency Induction Furnace (MFIF) technology is well established in India. Its advantages are production of general quality steel products at a lower investment, lower gestation period, technology suitable at a lower

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production level, higher metallic yield, less pollution etc and where high quality steel production is neither necessary nor proposed.

The operating cost of MFIF process, however, depends mainly on the aimed product quality, cost of charge-mix and electric power tariff. It is important to note that a MFIF is basically a melting tool and no appreciable refining is possible and envisaged in the furnace crucible. The chemical quality of liquid steel produced in MFIF (particularly with respect to phosphorous, tramp elements, etc) is therefore, controlled largely by dilution of elements by selecting a proper charge-mix composition or by using selected pedigree charge–mix to achieve a meltdown chemical composition close to that of the final steel grade. Further it has fairly less investment cost and lower gestation period as compared to other steel making processes as stated above.

Considering the merits and demerits of the above steel making processes, the Induction Furnace process has been selected for production of steel for the proposed plant.

R

efining

Presently, more and more steel works are carrying out final refining operations and final adjustments of chemistry and temperature in a separate vessel and use the primary units as melting and bulk refining vessel only. The correction and homogenization of steel composition and steel temperature, desulphurization, final de-carbonization and degassing can be efficiently carried out in the secondary refining vessel. Secondary refining technologies need to be selected depending on the specific requirements of products and cost effectiveness.

Ladle furnace is most popular among the secondary refining units. Use of ladle furnace has come to ensure the above benefits except degassing. Ladle

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furnace utilizes regular power transformer and therefore, electrical power consumption is not high as well as a strong grid support is not necessary unlike high power electric arc furnace. In the proposed project steel from MFIF is further treated in a Ladle Refining Furnace (LRF) for analysis and temperature correction, homogenization of chemical composition and temperature, inclusion morphology control, desulphurization, etc including holding of heat during any delay in casting operation or maintenance of sequence casting operation. The Ladle furnace will be equipped with inert gas bottom stirring facilities.

Billet and Bloom Production

The proposed project is aiming to produce 72,000 TPA CC billet. Balance amount billet will be produced in house. For this purpose, Continuous Casting Technology is recommended for adoption. Adoption of Continuous Casting Technology for the proposed plant has the following main advantages:

• Higher yield

• Lower investment

• Lower operating cost

•

• Less space

• Less pollution

Selection of Plant Capacity & Facilities

The capacity of the proposal is envisaged is around 72,000 TPA of Billet. To keep the initial investment in optimum level and to optimize of

available resources it has been decided to install additional 1 x 90 TPD kiln for sponge iron with two Induction furnaces of melting capacity 12 t and one 15 t Ladle Furnace and the combined capacity of these units is estimated at 76,000 TPA of liquid steel which is corresponding to production of 72,000 TPA of Billets. Considering tap to tap time 60 mins per IF with 2 crucibles,

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there will be maximum no of Tapping 24 from two furnaces as with the available power it is considered to operate only one furnace at a time.

Proposal

The technologies in steelmaking process will be followed in this steel plant. These will include heavy duty rectifiers in Induction Melting Furnace (IF) to generate both the frequencies and amperage needed for batch melting with higher electrical efficiency, refining of steel in Ladle Refining Furnace (LRF) using IF as only melting unit, mechanical addition of flux and ferro-alloys, casting of liquid steel into billets through Continuous Casting Machine (CCM), electromagnetic stirring and Nitrogen shrouding in CCM.

The main plant facilities will comprise the following facilities:-

• 2 x 90 TPD kiln for Sponge Iron production

• Two 12 t Induction Furnace, two crucibles each

• One 15 t Ladle Furnace

• One Continuous Casting Machine

In addition to above the plant will have following auxiliary facilities which will include the following:-

Raw material storage, like Iron ore, Coal/Lignite, dolomite, scrap, sponge iron, lime, ferro-alloys,

Slag Dump and processing area

Mill scale and bag filter dust storage area

Main Step down Sub-station (MSDS) with local sub-stations at Steel Melting.

Separate Water re-circulation facilities individually for Steel Melting and DRI kiln with makeup facilities from plant ground water network system

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Oxygen and Nitrogen manifolds with distribution network Air compressors for Steel Melting.

Air pollution control equipment with Bag Filter, necessary ducting, Chimney, etc.

All the above areas and facilities will be suitably located within the plant premises

Fume Extraction System (APCD i.e. Air Pollution Control Device)

The proposed fume extraction will consist of primary as well secondary emission.

Existing

(90 TPD Kiln)

ESP

with stack height- 30 m

Additional

(1 X90 TPD Kiln)

ESP

with stack height- 30 m Particulate Matter

concentration in discharged gases will remain <50 mg/Nm3

(2x 12 t Induction Furnace and LRF)

Primary & Secondary emission Bagfilters, with stack height-- 30 m

Particulate Matter concentration in discharged gases will remain <50 mg/Nm3

Material handling area Dust extraction/ dust suppression system

Water requirement in the existing plant and additional water requirement

a) Industrial use

b) Drinking, Sanitation and Horticulture purpose

The water requirement for the proposed steel plant is mostly for cooling purpose with a small part of the requirement being for drinking and dust

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suppression etc. To minimize the requirement of fresh water drawn from the source, recirculation system has been adopted. The effluent discharged from the toilet blocks will be led to soaking pit. There will be zero discharge of effluent to the outside of plant boundary.

Re-circulation System

To meet the cooling water and process water requirement for various technological units and auxiliary units separate recirculation network have been considered. Each network will have pump houses .Each pump house will have separate group of pumps. Cold water will be supplied to the consumers and hot return water will be collected and pumped to the cooling towers. In the entire recirculation system fresh make up water will be added for making up losses. The major re-circulation systems are as follows:

• Kiln for sponge iron production water re-circulation system

• Induction Furnace Water re circulation system

• LRF water circulation system

• CCP water circulation system

The main facilities of the above system will constitute pumping installations, storage reservoirs, distribution network, cooling towers where necessary etc.

Total requirement of makeup water is estimated around 107 m3_/day.

Table-2.2: Water Requirement Application Exiting (m3_/day) Additional (m3_/day) Total (m3_/day) (1)Industrial Process 20 75 95 (2)Domestic 3 9 12 Total 23 84 107

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Fig. 2.4: Water balance Diagram