Bokaro Steel Plant, SAIL

Ashish kumar jha7 t h sem.

Vocational Training Report

1. Sail

2. Bokaro Steel Plant

3. Air Separation Unit

4. Propane Gas Unit

5. Protective Gas Plant

6. By-product Plant

7. Primary Cooler & Exhauster

8. Tar Distillation Unit

9. Ammonia Removal

10. Benzol Recovery Unit

11. Energy Management Department.

12. Gas Analysis

13. GMBS

14. Conclusion

Content

Steel Authority of India Limited Maharatna ISO Certification Domestic Construction Engineering Railway defense etc.

Foreign markets.

Introduction

There are five integrated steel plants (ISP) under SAIL as follow:• Bhilai Steel Plant (BSP) in Chhattisgarh• Bokaro Steel Plant (BSL) in Jharkhand• Durgapur Steel Plant (DSL) in West Bengal• IISCO Steel Plant (ISP) in West Bengal• Rourkela Steel Plant (RSL) in Orissa

Contd…

Contd…• Special steel plant:• Alloy Steel Plant (ASP) in West Bengal• Salem Steel Plant (SSP) in Tamil Nadu• Visvesvaraya Iron and Steel Plant (VISL) in Karnataka• Chandrapur Ferro Alloy Plant

• Subsidiary:• SAIL Refractory Company Limited

• Joint ventures:• NTPC SAIL Power Company Pvt. Limited (NSPCL)• Bokaro Power Supply Company Pvt. Limited (BPSCL)

• Fourth integrated plant in the Public Sector, started taking shape in 1965 in collaboration with the Soviet Union.

• Incorporated as a limited company on 29th January 1964, and was later merged with SAIL, first as a subsidiary and then as a unit, through the Public Sector Iron & Steel Companies Act.

• First Swadeshi steel plant, built with maximum indigenous content in terms of equipment, material and know-how.

• In its earlier stage it was famous as ‘Employer of more than one lakh people’.

• At present its production capacity is 6.5 MTPA liquid steel.

Bokaro Steel Plant

Flat products Hot Rolled Coils,

Hot Rolled Plates,

Hot Rolled Sheets,

Cold Rolled Coils,

Cold Rolled Sheets,

Tin Mill Black Plates (TMBP) and

Galvanized Plain and Corrugated (GP/GC) Sheets.

• Separates atmospheric air

• Nitrogen

• oxygen

• In some cases argon and other rare inert gases.

• Fractional distillation (cryogenic method)

• high purity gases

• energy-intensive.

• Refrigeration cycle (Joule–Thomson effect) , and then cooling may be done by using either of the following heat exchanger:• Two pairs of regenerative heat exchanger (Linde Frankl process).• A recuperative regenerative heat exchanger (Kellogg's process).

Air Separation Unit

• Process flow diagram:

GAS BOILING POINTOXYGEN -183.5oCARGON -185.6oCNITROGEN -195.6oC

• A comparison of boiling point of different air components:

There are 5 units at Bokaro Steel Plant in which ASU 1 & 2 are shut down and other three are working. ASU 3 & 4 are similar but ASU 5 is modern. A comparison between old technology and modern technology is shown as follow:

Old Modern Moisture and carbon dioxide is

removed in heat exchanger by cooling process air to -130oC to -140oC at which CO2 liquefies.

Moisture and carbon dioxide is removed by passing process air through drier consisting of alternate beds of molecular sieve and activated alumina.

Heat exchanger is used in pairs having interchangeable waste nitrogen and process air streams.

Simple arrangement of heat exchanger is used with fix waste nitrogen and process air streams

Cryogenic temperature is achieved by cooling process air through heat exchanger, waste nitrogen being cooling media.

Cryogenic temperature is achieved by passing process air through Turbo-Expanders working on principal of Joule-Thompson effect.

• Steel Melting Shop (SMS). • Used to burn fuel gases. • Gaseous nitrogen is used as substrate.

• Liquid propane is brought and stored at propane gas unit in an underground tank having capacity of 5 ton.

• Then the liquid propane is converted to gaseous form in a vaporizer at about 75 C to 80 C. Then the propane gas is send to other units as per requirement.

• .Its main consumers are Slabbing Mill, Continuous Casting Shop, and Hot Strip Mill. Propane gas is generally used for cutting of slabs, slab scarfing, reheating. Sometime propane gas is mixed with coke oven gas to increase its calorific value.

• Special care should be taken to avoid exposure to this gas. Inhalation of propane causes shortness of breath, headache, drowsiness, and unconsciousness. Direct contact with skin causes frostbite, pain, redness, and blisters. Eye contamination causes impaired vision.

• In the following table a comparison between propane and acetylene shows the use of propane instead of other industrial gases:

Propane Gas Unit

Properties Acetylene(C2H2) Propane(C3H8)State Gaseous Liquid and gasAppearance Colorless ColorlessOdor Garlic like OdorlessSpecific Gravity 0.906 1.573Flash Point -32oC -156oCAuto Ignition Temperature 305oC 470oCCalorific Value (Kcal/Kg) 11573 10985Calorific Value (Kcal/M3) 13508 22250Expansion Rate ---- 250Maximum Allowable Pressure 15 PSIG Cylinder rating

Burn Velocity (M/Sec) 6.9 3.7Back Fire Tendency High LowToxicity High LowExplosion Sensitivity To Impact High Stable

Explosion Sensitivity To Electricity High Explodes

Explosive Limit (%Air Volume) 2.4-52.3 2.4-9.5

Explosive Limit(% Oxygen) 3.0-93 2.4-57Effect On Environment Generates solid waste Environment friendlyOzone Depletion And Global Warming Yes Less as compared to acetylene

Cost Of Energy (Rs/Gcal) 18500 5500Tangible Save Annually ---- < 60 millionIntangible Benefits ---- Faster preheat, higher penetration, faster

& smoother metal works.

Protective Gas Plant• Protective gas is a mixture containing 95% nitrogen gas and 25%

hydrogen gas.

• It is used to provide an inert atmosphere by forming a layer over steel surface during the annealing of steel sheets. This inert layer protect the steel sheets from direct contact with the atmosphere preventing corrosion.

• So the only consumer of protective gas plant is Hot Rolling Mill. Protective gas is prepared by cracking of ammonia gas as follow:

2 NH3 → N2 + 3 H2

• Liquid ammonia is sent to cracking unit where it is heated to 800oC. Coke oven gas mixed with air is used as fuel for heating.

• At temperature above 800 C ammonia is decomposed into 3 parts hydrogen and 1 part nitrogen. Now the product stream is sent to a mixer where more nitrogen gas from ASU is mixed to achieve the required composition of 95% nitrogen and 25% hydrogen.

• In the process of converting coal into coke using the coke oven, the volatile matter in the coal is vaporized and driven off.

• The functions of the by-product plant are to take the gas streams from the coke ovens to process them to recover by-product coal chemicals and to condition the gas so that it can be used as a fuel gas.

• In order to make raw coke oven gas suitable for use as a fuel gas at the coke oven battery and elsewhere in the steelmaking facility the by-product plant must:• Cool the coke oven gas to condense out water vapor and contaminants.• Remove tar aerosols to prevent gas line/equipment fouling. • Remove ammonia to prevent gas line corrosion.• Remove naphthalene to prevent gas line fouling by condensation.• Remove light oil for recovery and sale of benzene, toluene and xylene.• Remove hydrogen sulfide to meet local emissions regulations governing the

combustion of coke oven gas.

By-Product Plant

• The by-product plant also condition the flushing liquor that is returned to the coke oven battery, and treat the waste water that is generated by the coke making process.

• In a by-product coke oven the evolved coke oven gas leaves the coke oven chambers at high temperatures approaching 2000 F. This hot gas is immediately quenched by direct contact with a spray of aqueous liquor (flushing liquor). The resulting cooled gas is water saturated and has a temperature of 176 F.

• Raw coke oven gas also contains various contaminants, which give coke oven gas its unique characteristics. These consist of:

• Tar vapors• Light oil vapors (aromatics), consisting mainly of benzene, toluene and xylene

(BTX)• Naphthalene vapor• Ammonia gas• Hydrogen sulfide gas• Hydrogen cyanide gas

Contd..

Process diagram:

• The first step in the treatment of raw coke oven gas is to cool it to remove water vapor and so greatly reduce its volume, which is done in the Primary Cooler. There are two basic types:

• In a Spray Type Cooler the coke oven gas is cooled by direct contact with a recirculated water spray, cooling water being itself cooled externally in heat exchangers.

• In the Tubular Type, the coke oven gas is cooled indirectly by flowing across horizontally mounted tubes through which cooling water is pumped. Thus the cooling water does not come into contact with the coke oven gas and so it can be cooled in a cooling tower.

• With cooling of coke oven gas, water, tar and naphthalene condense out, collecting in the primary cooler system and is discharged to the tar distillation plant.

• The Exhauster is a large blower that provides the motive force to induce the coke oven gas to flow from the coke oven battery and through the by-product plant. It allows the close control of the gas pressure in the collecting main, which in turn affects the degree of emissions.

Primary cooler & Exhauster

• As the coke oven gas is cooled, water, tar and naphthalene condense out. The condensate collects in the primary cooler system and is discharged to the tar distillation unit.

• The tar precipitators typically use high voltage electrodes to charge the tar particles and then collect them from the gas by means of electrostatic attraction.

• By distillation, the coal tar is separated into a number of fractions graded arbitrarily by temperatures in the tar still. These fractions are usually called light oil, carbolic oil, middle oil, creosote oil, heavy oil, anthracene oil, soft pitch and hard pitch.

• Naphthalene is removed from coke oven gas using wash oil in a gas scrubbing vessel. The vessel may be packed or it may be the "void" type in which the wash oil is sprayed into the gas in several stages.

• The wash oil is regenerated by stripping out the naphthalene from the wash oil using steam in a still. In many plants, naphthalene removal is integrated with the similar process of light oil removal.

Tar Distillation Unit

• Because of the corrosive nature of ammonia, its removal is a priority in coke oven by-product plants. Historically the removal of ammonia from coke oven gas has yielded one of the more profitable by-products that of ammonium sulfate.

• The ammonium sulfate process can take various forms but all basically involve contacting the coke oven gas with a solution of sulfuric acid. Variations include the use of an absorber, in which the sulfuric acid solution is sprayed into the gas, or the use of a saturator in which the gas is bubbled through a bath of sulfuric acid solution.

• The sulfuric acid reacts readily with the ammonia in the coke oven gas to form ammonium sulfate. This is then crystallized out, removed from the solution and dried for sale typically as a fertilizer.

• The sulfuric acid used in the ammonia removal process is produced at sulfuric acid plant by Contact Process. The sulfuric acid is also used for washing of steel sheets.

Ammonia Removal Unit

• The raw gases issuing from the coke oven contain benzol and its homo logues as vapors and the recovery of these valuable substances constitutes another important source of profit in by-product coke making.

• Besides their use in the manufacture of explosives which are by no means confined to military purposes, the vast development of the Indian chemical industry insures a market for large quantities of benzol products.

• These substances pass on as vapors in the gas and are extracted only when the gas is washed with “wash oil" having absorbent or solvent proper ties with respect to these vapors. Of the total light oil recovered from the carbonization of the coal, 95 per cent results from washing the gas, and only 5 per cent is found in the tar.

• Previous to treatment with the absorbing oil, the gas should be cooled to a suitable temperature. The water not only acts as a cooling medium, but mechanically washes a large portion of the naphthalene out of the gas.

Benzol Recovery Unit

• Benzol washers are tall steel towers of the hurdle type, affecting a very intimate and prolonged contact between gas and oil. The counter current principle is used in washing operation.

• The light oil produced by the distillation of the wash oil is a mixture of benzol, toluol, xylol and solvent naphtha with a small amount of other substances. The light oil is accumulated in a drain tank and portions are taken for distillation in still.

• The heating is accomplished by means of internal steam coils and a direct steam spray. The benzol and toluol are principally distilled off by indirect heat, using the steam coils, and the higher boiling constituents, xylol, solvent naphtha, etc., are then distilled over by introducing steam directly into the still.

• In conclusion the By Product Plant produce is summarized in the following table, with the use of products or waste so produced in different part of plant.

Stream DestinationCoke oven gas Used as a fuel gas for coke oven batteries

Flushing liquor Recirculated to the batteries

Waste water Send to treatment plant

By-products Sold in the market

High levels of power requirement and rising energy costs represent a major challenge for the steel industry. The Energy Management Department deals with all the energy need of the plant. The major source of energy in a steel plant is burning of different gases as follow :

• Blast Furnace Gas is a by-product of blast furnaces where iron ore is reduced with coke into metallic (pig) iron. The gas has a very low heating value of around 900Kcal/Nm3. The calorific value is low due to lower percentage of combustible components (hydrogen and carbon monoxide).

• Coke Oven Gas is a by-product of industrial coke production from pit coal; coke gas is created by high-temperature dry distillation of coking coals in the absence of oxygen. . Its calorific value(4000Kcal/Nm3) is high due to higher percentage of combustible components (hydrogen, carbon monoxide, methane, and unsaturated hydrocarbons).

• Most of the time the calorific value of the gas required as fuel in different units of plant falls is such that neither pure coke oven gas nor pure blast gas can be used. Then a mixture of these two gases in a varying proportion called Mix Gas is used as a fuel

Energy Management Department

• Converter Gas is created from pig iron during the steel production process. The gas consists of about 65% carbon monoxide, 15% carbon dioxide, 15% nitrogen and small amounts of hydrogen and methane. Due to high carbon monoxide content, it is very poisonous gas.There is no proper storage and handling facility for converter gas at Bokaro Steel Plant. So the converter gas is burnt in situ and then the combustion product which is not poisonous is discharged into atmosphere. This type of burning is called Bleeding of gas.

Components [calorific value ]

Blast Furnace Gas Coke Oven Gas

Carbon dioxide(CO2) [noncombustible]

17.0% 3.00%

Oxygen(O2) [noncombustible]

0.20% 1.00%

Hydrogen(H2) [2590Kcal/Nm3]

4.20% 56.6%

Carbon monoxide(CO) [3040 Kcal/Nm3]

24.5% 5.20%

Nitrogen(N2) [noncombustible]

54.1% 9.00%

Unsaturated hydrocarbons(CmHn) [17000 Kcal/Nm3]

---- 2.40%

Methane(CH4) [8560 Kcal/Nm3]

---- 22.8%

• The gas analysis provides information regarding gases percentage composition and their respective calorific value. Following are the three types of gas analysis based on purpose or point of operation:• Surrounding air analysis- The first and must analysis is of

atmospheric air in the area surrounding the working site..• Fuel gas analysis-This is the analysis of gas mixture to be used as fuel..• Flue gas analysis-This is the analysis of gases leaving after combustion. This

analysis help in regulating air supply to the combustion process and complete combustion of fuel gases.

• All types of gas analysis are done by an apparatus called Orsat Gas Analyzer. An Orsat gas analyzer is a piece of laboratory equipment used to analyze a gas sample for its oxygen, carbon monoxide and carbon dioxide content.

• It was patented before 1873 by Mr. H Orsat.

Gas Analysis

• The different solutions used for gas analysis in Orsat Apparatus are described sequentially as follow:A. Colored Saline Water: B. Potash Solution.C. Pyrogallol Potash Solution.D. Bromine Water Solution.E. Ammoniacal Cuprous Chloride.

• Sometime the Orsat apparatus also comes with a Steel U Tube having cupric oxide (CuO) wire pieces inside it and a heater arrangement. This arrangement is provided for measuring percentage of hydrogen gas and methane gas

Orsat Gas Analyzer

• This is the unit where gases are stored, mixed and send to their respective consumers as per requirement.

• The mixing of coke oven gas and blast furnace gas takes place by providing a pressure difference of about 250 mmwc between both lines.

• The mixing process is shown by a simple and general diagram as follow:

Gas Mixing and Boosting Station

• Boosting accounts for loss of pressure during distribution of gas by pipelines throughout the plant. Booster increases gas pressure.

• As the consumer specifications are based on mix gas pressure and mix gas calorific value. This can be seen in the following table showing customer requirements for gas mixing and boosting station.

• Sometime it also provides pure coke oven gas (free of naphthalene and sulfur) for scarfing at slabbing mill.

Consumer Number Of Boosters

Specified Gas Pressure (mmwc)

Specified Gas Calorific Value

(Kcal/Nm3)Reheating furnace at Hot Strip Mill.

8 1800-2000 1800-2300

Soaking pit at Slabbing Mill.

4 800-900 1200-1500

Annealing furnace at Cold Rolling Mill

3 2000 1800-2000

• The opportunity of getting vocational training at such a famous and prestige organization is an opportunity of lifetime.

• It helped me in understanding that despite of technology advancement and modern machinery, proper co-ordination between employees and their experiences is the key to a proper functioning and growing plant.

• The expansion proposal of Bokaro Steel Plant consist of two phase.• Increasing its production capacity(liquid steel) from 6.5 MMTPA to 10

MMTPA by 2015.• From 10 MMTPA to 15 MMTPA by 2017.

• The quality of corporate life is excellent in BSL but the management should take initiative to satisfy the:

“There is a little bit of SAIL in everybody’s life”…

Conclusion