INSTITUTE OF ADVANCED MATERIALS: THE TATA IRON AND STEEL CO. LIMITTED THE TATA IRON AND STEEL CO. LIMITTED

Environmental control in metallurgical industry, like blast furnace.

Submitted by:

AJAY KUMAR

SUHARTO CHATTERJEE

HARINANDAN KUMAR PASWAN

Of vocational training batch from

May 11, 2010 to June 24, 2010.

Shavak Nanavati Technical Institute

Jamshedpur

THE TATA IRON AND STEEL CO. LIMITTED

CERTIFICATE

I hereby certify that the students SPECIFIED BELOW have successfully completed their vocational training on “ENVIROMENTAL CONTROL IN METALLURGICAL INDUSTRY, LIKE A BLAST FURNACE” under my guidance, scheduled from 11^th May 2010 to 24^th June 2010.

· AJAY KUMAR (METALLURGICAL & MATERIALS ENGG., NIT DURGAPUR)

· SUHARTO CHATTERJEE (METALLURGICAL & MATERIALS ENGG., VNIT NAGPUR)

· HARINANDAN KUMAR PASWAN (METALLURGICAL & MATERIALS ENGG., VNIT NAGPUR)

Mr.Shambhu Nath

SR. MANEGER (A-F BLAST FURNACES)

ACKNOWLEDGEMENT

We, Ajay Kumar ( Metallurgical Engg., NIT Durgapur ), Suharto chatterjee ( Metallurgical Engg., VNIT Nagpur), Harinandan Kumar Paswan ( Metallurgical Engg., VNIT Nagpur) sincerely acknowledge the support that has been extended to us by our project guide Mr. Shambhu Nath. His timely advice, esteemed guidance and experience has been a tremendous help.

We are grateful to Mr. Amit Kumar Singh (Head Operations; A-F Blast Furnaces) for his valuable suggestions and necessary guidance.

We also express our sincere gratitude to Mr. Dipankar Gupta for his hearted help.

Working with TATA STEEL has been a wonderful experience. We are sure that this work experience will help us in the future.

Thanking you with warm regards.

CONTENT

Ø ACKNOWLEDGEMENT

Ø INTRODUCTION

Ø IMPORTANT AREAS OF BLAST FURNACE PLANT

Ø OVERVIEW OF BLAST FURNACE PLANT

Ø RAW MATERIALS AND ITS SOURCES

Ø RAW MATERIAL REQUIRED FOR MAKING 1 TON OF HOT METAL

Ø CROSS-SECTIONAL VIEW OF BLAST FURNACE

Ø FURNACE CONSTRUCTION

Ø BLAST FURNACE PROCESS

Ø BLAST FURNACE REACTIONS

Ø FACILITIES AT A-F BLAST FURNACE

Ø FORMS OF POLLUTION

Ø Iron & Steel Making Process and Air Pollutants

Ø POLLUTION IN BLAST FURNACE PLANT

Ø TYPES OF POLLUTION AND ITS CONTROL

Ø SUGGESTIONS FOR ENVIRONMENTAL CONTROL IN IRON MAKING INDUSTRY

Ø SOLID WASTE MANAGEMENT

Ø NOISE POLLUTION

Ø WATER POLLUTION CONTROL

Ø Measure taken to control environmental pollution at A-F blast furnace

Ø IMPORTAN RECOMMENDATION FOR POLLUTION PREVENTION AND CONTROL

Ø SUMMARY OF POLLUTIONT REATMENT TECHNOLOGIES

Ø CONCLUSION

INTRODUCTION

A Blast Furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron. In a blast furnace, fuel and ore are continuously supplied through the top of the furnace, while air (sometimes with oxygen enrichment) is blown into the bottom of the chamber, 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.

Blast furnaces are to be contrasted with air furnaces (such as reverberatory furnaces), which were naturally aspirated, usually by the convection of hot gases in a chimney flue. According to this broad definition, bloomeries 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.

IMPORTANT AREAS OF BLAST FURNACE PLANT

HIGH-LINE:- coke is transferred from the coke storage bin by the CT Car to the stock-house. Sinter on the other hand is transferred from the sinter storage bin to the stock-house by the Demag car except for F furnace, in F furnace sinter is transferred by conveyer belt to stock-house. Most of the time iron ore and fluxes,(limestone, pyroxinite, dolomite, quartzite) and nut Coke are brought from the flood loading bunkers(FLB) situated at the extreme end of the high line, whereas in case of emergency these raw materials are brought from RMH (Raw Material Handling) by the wagon and is stored in different high line bins designated for different furnaces.

STOCK-HOUSE: - The major raw materials utilised in iron making are iron ore and coke. Stock house at A-F Blast furnaces is having two types of charging facilities. At the A-D blast furnaces charging is being done through Larry car and skip but in F blast Furnace it is being done through the conveyors and skip. Larry car consists of two hoppers and a load cell. The car collects material from the different bins and finally dumps it into the skip. On the other hand at F Blast furnace raw materials are first collected into aweigh hopper and then dumped into the skip. Another major difference of A-D blast Furnace s with F Furnace is the screening of Ore and sinter. Also F blast furnace is having ESP dedusting facilities whereas in other furnaces it is not.

STOVE:- The hot blast air is produced by passing cold blast air through preheated chambers or ‘stoves’, and heating the air to above 1100°C. The stove is first heated up by burning gas and combustion air within the chamber and allowing the heat to be absorbed into the brickwork, or ‘chequerwork’. This mode is called on-gas. When sufficient heat has been absorbed, the stove is put on-blast. In this mode, no combustion takes place, but cold blast air is forced through the stove and absorbs the heat to become hot blast. This is then mixed with cold blast to bring it to the right temperature, and is then forced into the blast furnace via the tuyeres near its base.

COAL INJECTION: Coal injection is the most developed and well-established technology for auxiliary fuel injection in a blast furnace. This is due to abundant availability of coal for injection, uniform global distribution and coal, in association with oxygen enrichment of blast, can replace a large quantity of coke and increase blast furnace productivity.

CAST HOUSE:- From the furnace, molten iron and slag is drained (cast) into a refractory lined trough on the cast house floor. Using a skimmer, the slag is separated from the molten iron. Molten iron is transported to the Steel Melting Shop (LD # 1 & 2) by rail using torpedo ladles for processing, whilst slag is quenched with water to solidify the material then stored as by-product. During the tapping, dust, Kish, and SO₂ are generated. An extraction system is placed along the trough and pouring positions to remove the airborne materials out of the plant and into dedusting equipment. The efficiency of the dedusting equipment is reviewed from time to time

RAW MATERIALS AND ITS SOURCES

1. ORE:

IRON ORE
SINTER

2. FUEL:

COKE
NUT COKE

3. FLUXES:

LIME STONE
PYROXINITE
QUARTZ
DOLOMITE

4. INJECTANTS:

§ COAL/ TAR

RAW MATERIAL	SOURCE	COMPOSITION	SIZE
IRON ORE	Joda	Iron=66,SiO₂=1.40,Al₂O₃=1.90, Na₂O=0.039, K₂O= 0.008, TiO₂= 0.15	+10 mm to – 40 mm
IRON ORE	Noamundi	Iron = 67.26,SiO₂= 0.94,Al₂O₃=1.40,P= 0.07, Na₂O = 0.007,TiO₂= 0.14	+10 mm to – 40 mm
SINTER	SP1	Fe= 56.40,CaO= 10.00, MgO= 2.8,Al₂O₃=2.7	+10mm (62-65%)
SINTER	SP2	Fe= 57,CaO= 9.5-10,MgO= 2.25-2.8,Al₂O₃=2.5-2.8, SiO₂=3.0-4.5	+10mm (68-72%)
COKE	Stamp Charge	C=82-84%Ash=16-18%,Moisture=4 - 6.5%	+30 to –80 mm
COKE	Top Charge	C=79-81%Ash=19-21%,Moisture=4 - 6.5%	+30 to –80 mm
LIME STONE	Dehradun, Gotan	Ca O=50-53,MgO=1-2,SiO2= 1-2.5,Al2O3= 1.5, Fe2O3= 0.3-1.2	+35 to –75 mm
PYROXINITE	Sukinda	SiO2=40% , Al2O3=1.5%, MgO=30%	+35 to –75 mm
QUARTZ	Local	SiO2=96,Al2O3= 1.00, Fe= 2	+10 to –50 mm

RAW MATERIAL REQUIRED FOR MAKING 1 TON OF HOT METAL:

RAW MATERIAL		FOR C FURNACE (Kg/THM)	FOR D FURNACE (Kg/THM)	FOR F FURNACE (Kg/THM)
ORE	IRON ORE	515	450	530
ORE	SINTER	1050	1150	1000
FUEL	COKE	500	530	420
FUEL	NUT COKE	60	30	44
FLUXES	LIME STONE	Nil	15-16	Nil
	PYROXINITE	15-20	25	15-20
	QUARTZ	4-5	4-5	4-5
INJECTANTS	COAL/ TAR	65	50	128

Remark:

C and F Furnace: 16-18% coke ash is used

D Furnace: 20% coke ash

ORE:

The most commonly used iron bearing minerals are:

§ Hematite : Fe₂O₃ (70% iron)

§ Magnetite : Fe₃O₄ (72.4% iron)

Reason of using hematite as a source of iron:

Hematite is used as a source of iron ore not only because it has the widest distribution in the world but also because during transformation of hematite to magnetite, the structural metamorphosis from hexagonal to cubic gives rise to volume expansion, increased porosity, cracks and fissures. In fact, the reduction of hematite produces a porous product and large surface area thus generated results in a much higher reduction rate of hematite compared to magnetite.

SINTER:

Purpose of charging the sinter:

During mining and ore dressing operation, an enormous amount of fins (40-50 percent) is generated. Since fins can not be charged directly in to the furnace mainly because it can results in the choking of voids and thereby decreases the permeability of the bed. Hence it is necessary to agglomerate them in to lumps which are performed predominantly by sintering and pelletizing.

Advantages of sintering:

1. Agglomeration of fines in to large, strong and irregular porous lumps which gives good bed permeability.

2. Calcinations of limestone outside the furnace save 50-60kg coke rate.

3. Agglomeration of fines into hard, strong and irregular porous lumps which give good bed permeability?

4. Elimination of 60-70% of ore sulphur during sintering.

5. Elimination of moisture , hydrated water and other volatiles on the

6. Sinter stand with the cheap fuel.

7. Lower down the softening range.

8. Primary slag formed from fluxed sinter posses lower viscosity and

9. Liquids temperature and more uniform composition than in raw ores.

FUEL:

FUNCTION OF COKE IN THE BLAST FURNACE:

1. Act as a fuel by providing thermal requirements.

2. 2C+O₂ =2CO -2300kcal/kg.C

3. Provides CO for the reduction of iron oxides.

4. Reduces oxides of metalloids.

5. It carburizes the iron and lowers the melting point.

6. It provides the permeability and the mechanical support to the burden.

INJECTANTS:

Blast furnace cannot be run without certain amount of coke because of its various functions during the process. The efficiency of a blast furnace mainly depends on the quality of coke used as a fuel. Since coke is a scare and dear commodity and therefore attempts are made to reduce the coke consumption as far as possible. Fuel injection is one of the methods to reduce the coke consumption. Fuel is injected through tuyere. Fuel injected may be solid, liquid or gaseous. All these fuels are hydrogen bearers and carboneous. Since these fuels are burnt incompletely to CO and H₂before the tuyeres, the full calorific value is not obtained from them. However, they all supply hydrogen which is a more potent reducing agent than CO for the reduction of iron oxide at higher temperatures. They are used at ambient temperatures and need a certain heat for dissociation of the C-H bond. Thus their burning produces in the combustion zone a flame temperature which is lower than that obtained from the burning of coke because the latter arrives in the zone preheated to about 1400-1500⁰C. As the flame temperature increases with the blast temperature, a higher blast temperature can be utilized with the addition of such fuels maintaining, at the same time, a constant flame temperature. A larger heat input and better indirect reduction through hydrogen results in saving of coke in addition to the carbon which is already present in each fuel

FURNACE CONSTRUCTION

Foundation: it is a massive steel reinforced concrete mass partially embedded below the ground level.it should be sufficiently strong to stand the loaded of blast furnace weight, it may be about 15m dia and 6-7m thick.

Hearth: carbon blocks are used in hearth construction along with water cooled plates to protect the lining. In the hearth wall the tap hole is located 12-15cm in dia and 0.3-0.6 m above the hearth bottom and a slag notch 1.2-1.6m above the iron tap hole.

Bosh: this is the zone where melting of the burden, except coke, takes place, top of the bosh having the maximum diameter.

Mantle and columns: the furnace structure above the bosh level is supported on a heavily braced steel ring, it called mantle and it’s supported by heavy columns.

Stack: it is the frustum of a huge cone extending to 3/5 of the height. It’s increasing diameter facilitating a uniform flow of the thermally expanding burden materials. The fusion and consequent contraction of the slag and metal start in this region.

Tuyere: Immediately above the hearth are located tuyeres through which hot air blast is blown for fuel consumption.

Bell charging: the double bell charging ensures continuous charging with minimum exhaust gas leakage.

‘Bell-less Top’ charging: The charge distribution is superior and it removes the disadvantage of leakage and erosion which occurs in bells due to exit gas pressure.

Off-takes: there are four exhaust pipes at the furnace top and these rises vertically up above the furnace top and join to a bigger single pipe known as the down-comer which

Delivers gas to the gas cleaning system.

BLAST FURNACE PROCESS

Blast furnace is the “furnace used in Metallurgical process such as Smelting to reduce industrial metals from its respective ore, generally iron ".

Blast furnace contains 4 zones where the different steps of reduction of the iron take place and they are differentiated with respect to the corresponding temperatures

1. Zone of Reduction:-

It is the zone where the Iron ore gets reduced to iron oxide at the temperature of 850ºc

3Fe₂O₃ +CO → 2Fe₃O₄ + CO₂

Fe₂O₃ +CO → 2FeO + CO₂

2. Zone of Slag formation:-

It is the zone where the slag is formed by the reduction of the Calcium Carbonate (CaCO3) into Calcium Oxide (Cao). Then it combines with silicon (SiO₂₎ to form Calcium Silicate (CaSiO3₎ at 1000ºc

CaCo₃→Cao+co₂

CaO + SiO₂→CaoSio₂

3. Zone of Fusion:-

It is the zone where carbon (C) reacts with ferric oxide (FeO) to give Iron (Fe) at 1300ºc

FeO + 3C → Fe + 3Co

CO₂ + C → 2CO

4. Zone of Combustion:-

It is the zone where the compressed air is passed in which carbon (C) and oxygen (O₂₎ to form (CO₂) carbon Di Oxide

C + O₂ → CO₂

Thus at the end of the process Iron (Fe) is got. This iron is also known as Cast Iron or Pig Iron.

BLAST FURNACE REACTIONS

Primary Reactions

Iron Ore Reduction
Carbon Gasification, Heat Generation and Consumption

Secondary Reactions

Degradation of Ore and Coke
Slag-Metal Reactions in the Hearth
Cycling Na, K, S, Si, Zn, etc.

The Blast Furnace
At500°C 3Fe₂O₃ +CO → 2Fe₃O₄ + CO₂ Fe₂O₃ +CO → 2FeO + CO₂ (progressive reduction of oxide feed)
At850°C Fe₃O₄ +CO → 3FeO + CO₂ CaCO₃ →CaO + CO₂ MgCO₃→ MgO + CO₂ (Calcination of fluxes)
At1000°C FeO +CO → Fe + CO₂ (indirect reduction)
At1300°C CO₂ + C → 2CO At Equilibrium: Boudouard Equilibria Forward Reaction: Solution Loss Reaction Reverse reaction: Neumans Reversion
At1900°C C+O₂→CO₂ FeO +C → Fe + CO (direct reduction)

FACILITIES AT A-F BLAST FURNACE

Furnaces	Top Charging	Stock House	High Top pressure	Screening	Cast House	Remarks
A	Double bell	Larry car	No	Coke	ND & D Trough	Stopped due to less demand of hot metal
B	Double bell	Larry car	No	Coke	Drainable
E	Bell less top	Larry car	0.5 PSI	Coke	ND & D Trough
C	Gimbel top (first of its kind in the world)	Larry car	0.7 Bar	Coke	Non Drainable+ SG	Presently in running condition
D	Double bell	Larry car	No	Coke	ND Trough+ SG
F	Compact Bell less top	Conveyor Belt	0.83 Bar	Coke, Ore & Sinter	ND Trough+ SG

FURNACE	INNER VOLUME(m³)	WORKING VOLUME(m³)	TPD	PRODUCTIVITY (t/m³/day)
A	1066	956	1500	1.41
B	742	674	1100	1.48
E	650	592	1500(1200)	2.3
C	1070	929	2000	2.2
D	1133	1012	1900	1.68
F	1816	1582	3900	2.4

Output

Product	BY Product	BY Product
Hot Metal Typical Analysis C% -4.2- 4.5 Si% -0.5-1.0 S% -0.04- 0.08 P%-0.170-0.210 Ti%-0.06-0.09 Fe%-94-95 Temperature- 1470-1510 Deg C	Slag Typical Analysis CaO% -35.0- 37.0 SiO2% -33.0-35.0 Al2O3% -17.0- 20.0 MgO%-6.0-8.0 K2O%-0.4-0.9 FeO%-0.2-0.5	BF Gas Typical Analysis CO% -20.0- 22.0 CO2% -20.0-22.0 H2% -3.0- 5.0 Dust content: 10 mg/Nm3 (After cleaning)

FORMS OF POLLUTION

Acid rain: SO₂ and NOx generated in steel plants get absorbed by moisture in the atmosphere and when it gets supersaturated, it falls in the form of rain. This ‘acid rain’ increases the acidity of soil and groundwater.

Toxic elements: Heavy elements such as Hg, Th and Pb are most toxic. Several other elements, such as Cd, Bi, As, Cr, etc also have toxic effects. Many of these elements like lead (which condenses in the upper area of the blast furnaces) and chromium (from degradation of refractories) are generated in steel plants.

Particulates/Dust: Virtually all the iron processing steps (raw materials storage, sinter plants, blast furnaces, etc.) generate particulates. Unless controlled they can enter the lungs as dust to cause respiratory difficulties.

Gaseous and volatile compounds: CO and BF gas are highly toxic. They can prove fatal if their concentration in air exceeds 1000ppm. Coke oven and by-products effluent, such as ammonia, phenol, benzol, hydrocarbons, etc. can also be potential health hazard.

Noise pollution: Excessive noise can cause hearing impairment, stress etc. And noise levels above 75 dB are considered harmful. Blast furnaces, Oxygen plants, powerhouses, etc. are areas where noise levels are high in steel plant.

Solid wastes: Huge quantities of wastes are generated during iron making. Sinter fines, coal dust, coke breeze, bag house dust, gas cleaning plant sludge, blast furnace slag, etc. are the common solid wastes generated in steel plants amounting to approximately 1.5T per tonne of crude steel made. Therefore, waste management is an important activity in steel plant. This not only includes safe disposal so as not to affect soil and groundwater, but also includes converting the wastes into some useful commodity. Use of blast furnace slag for cement making, recirculation of BOF slag in sinter plants, use of sludge in making tiles etc. are good examples.

POLLUTION IN BLAST FURNACE PLANT

SOURCE	TYPES OF POLLUTION	LOCATION
Coal Injection	Dust Pollution	1) Charging of Raw material in Ground Hopper. 2) Magnetic Separator. 3) Storage silo. 4) Bag Filter. 5) Flame Front Equipment. 6) Bag Filter vent gate.
	BF/CO gas	1)Chimney 2) Leakage through BF gas Conveying pipes.
	Noise Pollution	1)Screener 2)Blower fan and motor 3)Conveyor System
	Heat Pollution	1)Supplying hot BF gas tube
Blast Furnace	BF/CO gas	1) Bleeder 2) Leakage through BF gas Conveying pipes.
	Toxic Element	1) Pb-at upper part of blast furnace. 2) Cr-generated from degradation of refractories.
	Noise Pollution	1) Hot blast from Tuyeres. 2) Severe noise in leaked tuyeres.
	Water pollution	Open loop cooling system arrangement in older furnaces.
Cast house	Heat Pollution	1) Hot metal during tapping. 2) Slag in runners.
	Dust Pollution	1) Evolution of fumes during drilling.
	Solid Waste	1) Generated during Iron making.
	Fumes generation and BF/CO gas	1) Gas leakage through the tuyere stocks 2) Leakage through the trough heating line. 3.) Fume generation in tapping. 4.)clay leakage

SOURCE	TYPES OF POLLUTION	LOCATION
High Line	Dust Pollution	1) Loading and unloading of coke by CT Car. 2) Loading and unloading of sinter by DEMAG Car. 3) Unloading of ore and fluxes by wagon.
High Line	Noise Pollution	1) CT Car movement 2) DEMAG Car 3) Wagon
Stock House	Dust pollution	1) During screening operation 2) Charging of LARRY Car 3) Loading of skip from LARRY Car.
Stock House	Noise Pollution	1) LARRY Car
Stove	Noise Pollution	1) Leakage through the Cold blast and hot blast lines or valves 2) Blower fan and motor. 3) During Blow off valve operation.
	Heat Pollution	1) Burning of (BF gas + CO) with Air. 2) Leakage in Hot Blast pipes. 3) Radiation losses through the heat carrying pipelines.
	Toxic gas Pollution	1) Degradation of CHEQUERS.
	BF/CO gas	1) Leakage through BF gas Conveying pipes.

SOURCE	TYPES OF POLLUTION	LOCATION
Dust Catcher	Dust Generation	1) During dust catcher evacuation 2) Transfer of dust from pug-mill to dumper. 3. Transfer off dust from the loading point to the disposal area.
Dust Catcher	BF/CO gas	1) Leakage in dust catcher valves. 2) Leakage of gas through corroded shell
Slag Granulation Plant	Water Pollution	1)Water slag interaction in cast house
	Noise Pollution	1)In pump house 2)Rotary Kiln
	Toxic Fumes	1)Near agitation tank pump house
	Soil Pollution	1)Deposits of slag granules
Cooling Tower	Heat pollution	1) During spraying of water, water droplets are cooled leading to heat transfer to the atmosphere.

TYPES OF POLLUTION AND ITS CONTROL

Air pollution and control

Ø Emission of particulate matter (dust)

Ø Emission of SO₂

Ø Green house gas emissions

Ø Fugitive emission of suspended particulate matter from CHP, Wagon Tippler, C.T. car, Demag car and ash pond.

Control

Ø EMISSION OF PARTICULATE MATTER (DUST):

In the Blast Furnace Operation huge amount of BF gas and dust is generated. The dust laden BF gas which exits from the blast furnace enters the dust catcher in which 60-70% dust is removed from the dust laden gas. The remaining dust in the gas is removed in GCP.

The dust accumulated in the dust catcher is transferred to the dumper via Pug mill with the help of pneumatic and hydraulic valves along with water (or agglomeration of dust particles), this mechanism has been devised for efficient disposal of dust with minimum dust pollution. Further the two valves and water pipe is sealed from outside which further minimizes dust emission.

In High line, due to loading and unloading of raw materials by CT car, Demag car and wagon generates huge amount of dust. The proportion of dust is reduced by efficient mechanism of loading and unloading. While loading dust is minimized by installing chute. While unloading of CT car and wagon dust is substantially reduced as the opening gate is underneath the CT car and wagon on the other hand in demag car unloading is done by the side gate.

In stock house dust is controlled by dust extraction system. Dust from the dust extraction system is sent to ESP in case of F furnace, ESP and Bag Filter in case of H furnace. In ESP dust is extracted by the ionizing the dust particles and collecting the negatively charged dust particles on a positive electrode from which dust is removed periodically.

In bag filter the dust is captured in the bag, from which dust is removed by N₂ purging. Dust from the ESP and Bag Filter is transferred to the dumper.

In F Furnace cast house dust is controlled by dust extraction system, same dust collection mechanism follow as in stock house.

In coal injection plant, the coal fine laden gas pressure in the bag filter should be optimum so that the bag filter vent gate does not open. If excess coal fine laden gas volume enters the bag filter then the filters is unable to separate the coal fines from the gas hence the vent gates automatically open to optimize the volume and in turn Pressure for Efficient Coal Fine Separation. Thus the Opening Of The Vent Gate Should Be Prevented As It Releases Huge Amount Of Coal Dust In The Atmosphere.

Ø BLAST FURNACE GAS EMISSION

Blast furnace gas is generated in the blast furnace, rises and exits from the top. There are four exhaust pipes at the furnace top and these rises vertically up above the furnace top and join to a bigger single pipe known as the down-comer which delivers gas to the dust catcher. The entire system is closed to prevent any leakage of the harmful BF gas. The BF gas from the dust catcher is further cleaned in the gas cleaning plant where water is injected which agglomerates the dust thus almost completely separating BF gas from the dust. Some portion of the BF gas is further used in the Stove and Coal Injection plant while the rest is burnt. The burning of the BF gas in air leads to the conversion of poisonous CO to non poisonous CO₂. but this process results in unwanted heat being released to the atmosphere.

Ø SAFE DISPOSAL OF SLAG:

Safe disposal of slag so as not to affect soil and groundwater also includes converting the wastes into some useful commodity. Use of blast furnace slag for cement making, recirculation of BOF slag in sinter plants, use of sludge in making tiles etc. are good examples.

Water pollution

(A) First, the suspended matter: sinter plant dust, flue dust, steel plant dust and mill scale. This is of variable grain size, but generally small—from 0 to 100 Jim—settling well down to 10 Jim and containing much iron (30 to 60 per cent). This dust is collected, treated and returned to the fabrication line, except that from blast furnace gas when it contains elements which are harmful to the blast furnace, particularly zinc. Granulated slag, soaked silicate, occurs in the form of grains a few millimeters in size, the bulk density of which may be less than one.

(B) Oils are found in the water flowing out of rolling mills particularly and originate from lubrication of mechanical elements. The oils should be separated, especially vegetable or animal oils used in cold rolling mills which present very difficult problems for their removal.

(C) In some particular manufactures (special cast irons, Spiegel cast iron, etc.), cyanides occur in the flue dust waste, up to 100 mg/I and above. Cyanides are always present anyway, but during normal operation the quantities are very low and oxidation is fast.

(D) In coke plant waste water phenols, cyanides, ammonia, etc. are found.

SUGGESTIONS FOR ENVIRONMENTAL CONTROL IN IRON MAKING INDUSTRY

AIR POLLUTION CONTROL

Ø Control of Dust emission

Ø Control of green house gas emissions

Ø Control of SO₂ Emission

Control of Dust emission

Ø During raw material acquisition the primary air pollutant emitted is particulate matter. Particulate matter is also emitted from the handling, loading, unloading, and transport of raw materials, such as coal, purchased from another source. In certain areas, exhaust from portable equipment may also be a consideration. The following methods are used to control particulate emissions generated from the quarry and handling of purchased raw materials:

1.) Fabric filters (pulse-jet or reverse-air/shaker)

2.) equipment enclosures

3.) water sprays (with and without surfactants)

4.) enclosures

5.) silos (with and without exhaust venting to wind screens fabric filters)

6.) foams

7.) mechanical collectors bins

8.) chemical dust suppressants

9.) paving

10.) Material storage buildings

11.) Bag filters,

12.) Wet scrubbers installed by the industries

Ø Fugitive dust is emitted from raw material feeders, stackers, blenders, reclaimers, conveyor belt transfer points, and bucket elevators used for transferring materials to the mill department from storage. Particulate emissions from the dry raw mills and subsequent equipment occur during temporary failure or from improperly designed or maintained seals.

The following devices are used to collect particulate matter in the raw mill and raw mix storage areas:

1.) mechanical cyclones (usually used in series with another control)

2.) fabric filters (pulse jet or reverse air/shaker)

3.) electrostatic precipitators (rarely used)

Ø In the Iron and Steel Industry there are many sources of fugitive dust from materials handling. Potential sources and causes of emissions include material storage, conveying systems, slag dumping, flue dust handling, ore sizing and fractionating, powder application and shakeout tables. Hatch designs dust control systems, utilizing Clean Plan Design techniques, to maintain a clean and safe environment. Techniques used include:

1.) Emission Inventories

2.) Close or remote capture

3.) Dust suppression techniques

4.) Process modifications to reduce emissions

5.) Collection system layout and design

Ø Dust that is collected by these means is restored to the process. For quarry operations, newer plants typically can be use the pulse-jet fabric filters while older plants employing the reverse-air or shaker-type fabric filters.

Ø Controlling particulate emissions from sources other than the kiln usually entails capturing the dust using a hood or other partial enclosure and transporting it through a series of ducts to the collectors. The type of dust collector used is based on factors such as particle size, dust loading, flow rate, moisture content, and gas temperature. The best disposal method for collected dust is to send it through the kiln creating the clinker.

Reciprocating grate clinker coolers most often employ fabric filters, but ESPs and gravel bed filters are also used with a mechanical cyclone or multiclone dust collector sometimes placed in front. Newer plants typically use pulse-jet or pulsed-plenum fabric filters and older plants use reverse-air type fabric filters which may simply be a smaller form of a kiln fabric filter. Gravel bed filters, we can also use by the steel industry, contain quartz granules; contaminated gas passes through this filter and the dust settles to the bottom of the bed.

Reciprocating grate clinker coolers most often employ fabric filters, but ESPs and gravel bed filters are also used with a mechanical cyclone or multiclone dust collector sometimes placed in front.

Ø Unloading of coal by trucks or wagons should be carried out with proper care avoiding dropping of the materials from height. It is advisable to moist the material by sprinkling water.

Ø Crushing and screening operation should be carried out in enclosed area. Centralized de-dusting facility (collection hood and suction arrangements followed by de-dusting unit like bag filter or ESP or equally effective method or wet scrubber and finally discharge of emission through a stack) should be provided to control Fugitive Particulate Matter Emissions. The stack should confirm to the emission standards notified for de-dusting units. Water sprinkling arrangement should be provided at raw material heaps and on land around the crushing and screening units

Ø Enclosure should be provided for belt conveyors and transfer points of belt conveyors. The above enclosures shall be rigid and permanent (and not of flexible/ cloth type enclosures) and fitted with self-closing doors and close fitting entrances and exits, where conveyors pass through the enclosures. Flexible covers shall be installed at entry and exit of the conveyor to the enclosures, minimizing the gaps around the conveyors. In the wet system, water sprays/ sprinklers shall be provided at the following strategic locations for dust suppression during raw material transfer:-Belt conveyor discharge/ transfer point-Crusher/screen discharge locations

Ø Extensive plantation/Green belt shall be developed along the roads and boundary line of the industry. A minimum 15 m width Green Belt along the boundary shall be maintained. However, the green belt may be designed

Control of green house gas emissions

CO₂ CAPTURE TECHNOLOGIES

The idea of capturing CO₂ from the flue gas of power plants did not start with concern about the greenhouse effect. Rather, it gained attention as a possible economic source of CO₂, Especially for use in enhanced oil recovery (EOR) operations where CO₂ is injected into oil reservoirs to increase the mobility of the oil and, therefore, the productivity of the reservoir.

To date, all commercial CO₂ capture plants use processes based on chemical absorption with a Monoethanolamine (MEA) solvent. MEA was developed over 60 years ago as a general, non-selective solvent to remove acid gases, such as CO₂ and H₂S, from natural gas streams. The process was modified to incorporate inhibitors to resist solvent degradation and equipment corrosion when applied to CO₂ capture from flue gas. As shown in Figure 2, the process allows flue gas to contact an MEA solution in the absorber. A significant way to reduce cost in chemical absorption systems is to reduce equipment size. By increasing the contacting efficiency between the CO₂ and the solvent, equipment sizes can be reduced significantly. The MEA selectively absorbs the CO₂ and is then sent to a stripper. In the stripper, the CO₂ -rich MEA solution is heated to release almost pure CO₂. The lean MEA solution is then recycled to the absorber.

Advanced coal power plants offer many new opportunities for CO₂ capture. One example is to integrate CO₂ capture with an integrated gasification - combined cycle (IGCC) power plant IGCC plants first gasify the fuel to produce a pressurized synthesis gas (mainly CO₂ and H₂ ). Next, for CO₂ capture, after removal of impurities that might foul the catalyst, the synthesis gas is reacted with steam in a shift reactor to produce CO₂ and H₂ . The CO₂ and H₂ are then separated, with the hydrogen being combusted to produce CO₂ -free energy. The CO₂ stream is available for use or disposal. The partial pressure of CO₂ is sufficiently large in an IGCC plant (as opposed to pulverized coal plants) to allow use of a physical absorbent like Selexol (diethyl ether of polyethylene glycol), which greatly reduces the energy requirements.

Currently, the biggest drawback to this approach is that IGCC power plants cost more than conventional pulverized coal-fired power plants. However, it is expected that costs of IGCC power plants will become competitive in the future.

The key challenge regarding CO₂ capture technology is to reduce the overall cost by lowering both the energy and the capital cost requirements. While costs and energy requirements for today’s capture processes are high, opportunities for significant reductions exist since researchers have only recently started to address these needs. The following approaches appear the most fruitful:

· Implement the easy opportunities first, such as those in the natural gas industry and

Industries like ammonia and ethylene.

· Improve today’s commercially available chemical absorption processes. Key research needs are to develop more energy efficient solvents and reduce equipment size and cost.

· Use oxygen instead of air for combustion, producing a flue gas from which CO₂ is easily captured. Research needs include reducing oxygen costs, addressing the problems associated with retrofitting existing plants, and optimizing the efficiency of new plants.

· Integrate CO₂ capture into advanced power plants, such as IGCC or fuel cells. Research needs to address improved separation techniques (e.g., membranes), improved shift catalysts, and heat and power integration.

Geological Storage Technology

Underground storage in geological formations is a major option for disposing of CO₂.

The main issues are uncertainties in the volumes available for storage, the long-term integrity of the storage, and the costs associated with CO₂ transport to the storage site and the storage operation itself. Storage integrity is important not only to prevent the unintended return of CO₂ to the atmosphere, but also for concerns about public safety and the potential liability should there be a catastrophic release. CO₂ gas is heavier than air and, if a large release were to occur, it could displace air at the surface and cause asphyxiation.

The main options for underground storage are

· storage in active oil reservoirs

· storage in coal beds

· storage in depleted oil and gas reservoirs

· storage in deep aquifers

· storage in mined salt domes or rock caverns

Direct Utilization Technology

In a greenhouse gas-constrained world, it is likely that the industrial sector could reduce its own CO₂ emissions by identifying processes that produce relatively pure CO₂ streams and then CO₂either capturing and sequestering CO₂ or strategically linking it to another processing operation requiring CO₂ as a feedstock.

There are numerous specific opportunities to reuse CO₂ in industrial processes, and certain processes such as ethylene and ammonia production produce high concentration CO₂ streams that are often currently released to the atmosphere. The standard way of producing hydrogen today is through steam reforming of methane which can be regulated to produce a CO₂ /H₂ mixture which is easily separable.

CH₄ + 2H₂O = CO₂ + 4H₂

This CO₂ could be sequestered or utilized in another process. With increasing interest in the use of hydrogen as an energy carrier and fuel in the future, this CO₂ source is likely to grow and create an opportunity for additional mitigation.

Even today, CO₂ from ammonia production is often used as a feedstock for urea production. Such streams would serve as a good feedstock for plastics production, production of inorganic carbonates, etc. Industrial combustion processes, like power plants, will have lower concentration streams of CO₂, making CO₂ capture more expensive as a way to mitigate emissions.

New applications might be found if further research is done on interesting potential reaction pathways. Since CO is a very stable molecule, considerable energy is required to transform it into products where the C-O bonds are broken, such as in recycling to fuels as discussed in the next section. Transformation into carbonates, carbamates, or other

Carbonate minerals that can be returned to the environment. This concept really could be

Considered as another form of geological storage.

Chemical conversion to fuels. Much interest has been generated in the possibility of converting CO₂to a transportation fuel, such as methanol, using hydrogen.

CO₂ + 3H₂ = CH₃OH + H₂O

In this reaction, each molecule of CO₂ is reacted with three molecules of hydrogen to produce one molecule of methanol. But energy is required to produce hydrogen. The most efficient pathway to hydrogen today is through steam-methane reforming (the previous equation) which is about 80% efficient. Production from coal gasification is about 50% efficient; production from electrolysis of water, about 30% efficient.

Although utilization does not seem to offer large scale opportunities for mitigation, it is important to recognize that a large number of small uses can play an important part of an

Overall mitigation strategy. Further, if CO₂ can be used as a feedstock for useful products, it provides a credit against capture costs and avoids incurring land or ocean storage costs.

CONTROL OF SO₂EMISSION

SO₂ is generated in the Blast Furnace by the combustion of coke and coal which contains sulphur. SO₂ gas usually subsequently forms white sulphate aerosols; also SO₂ gets absorbed by moisture in the atmosphere resulting in Acid Rain. SO₂is a component of BF gas which exits the Blast Furnace and should be treated before BF gas is released in the atmosphere.

Use of low-sulphur coals is quite common, but may result in reduced blast furnace output, since these fuels frequently have lower heat content. Also coal cannot be replaced in blast furnace technology. Since the price of SO₂ allowances is rising, Flue Gas Desulfurization (FGD) technologies appears to be the best choice is becoming the choice.

Method	Reaction	By product
Activated carbon	SO₂ + H₂O+.5O₂→H₂SO₄	H₂SO₄
Caustic soda	2NaOH+SO₂→ Na₂SO₃ + H₂O Na₂SO₃+H₂O+SO₂→2NaHSO₃	Na₂SO₄
Ammonia	2NH₄OH+SO₂→(NH₄)₂SO₃+H₂O (NH₄)₂SO₃+SO₃+SO₂+H₂O→2NH₄HSO₃+H₂	(NH₄)₂SO₄
Slaked lime (Limestone – Gypsum Process)	CaO+SO₂→CaSO₃ CaSO₃+O₂→2CaSO₄	CaSO₄

SOLID WASTE MANAGEMENT

RECYCLING

Granulated blast furnace slag has been used as a raw material for cement production and as an aggregate and insulating material. And granulated slags have also been used as sand blasting shot materials. Ground granulated blast furnace slag is used commercially as a supplementary cementitious material in Portland cement concrete (as a mineral admixture or component of blended cement).

DISPOSAL

It is estimated that a relatively small percentage (less than 10 percent) of the blast furnace slag generated is disposed of in landfills.

MARKET SOURCES

Blast furnace slag materials are generally available from slag processors located near iron production centers. Cements containing ground granulated blast furnace slag are available from many producers of Portland cement or directly from ground granulated blast furnace slag cement manufacturers. AASHTO M240 describes three types of blended cements containing slag.⁽³⁾ They include Portland blast furnace slag cement (type IS), slag modified Portland cement (type I (SM)), and slag cement (type S). The primary distinction among the three types is the percentage of slag they contain. Slag cement may contain Portland cement or hydrated lime (or both) while the other two are blends of Portland cement and slag only.

NOISE POLLUTION:

Noise health effects are both health and behavioral in nature^.The unwanted sound is called noise. This unwanted sound can damage physiological and psychological health. Noise pollution can cause annoyance and aggression, hypertension, high stress levels, tinnitus, hearing loss, sleep disturbances, and other harmful effects. Furthermore, stress and hypertension are the leading causes to health problems, whereas tinnitus can lead to forgetfulness, severe depression and at times panic attacks.

There are a variety of strategies for mitigating railway noise including: use of noise barriers, limitation of vehicle speeds, use of traffic controls that smooth vehicle flow to reduce braking and acceleration, and wheel design. Costs of building-in mitigation can be modest, provided these solutions are sought in the planning stage of a railway project.

Exposure of workers to Industrial noise has been addressed since the 1930s. Changes include redesign of industrial equipment, shock mounting assemblies and physical barriers in the workplace. Noise pollution can be reduced in blower house by installing quieter motors and smoother fans. Noise from blow-off valve in stove area can be reduced by improving its design.

WATER POLLUTION CONTROL

Importance of waste water considering the small quantity of water consumed, the waste water from each plant has the same measured volume as the water which flows into the plant. Because of partial and general recirculation, it is not possible to effect a summation for the whole plant, and the recirculation rate defined by:

R = (Sum of the circulation water flow of network —draught flow) / (Sum of the circulation water flow of network)

Effluent containing suspended matter (sinter plant, blast furnaces, steel plants,)

Conventional settling process in rectangular or circular tanks is used. Considering the outputs, flocculation is only seldom used: withdrawal of sludge is performed by means of pumps or, in the case of mill scale, by clamshells. The settled sludge is either thickened or dried in vacuum filters, according to its final use.

Effluent containing oils

To collect current oils, the conventional processes of natural tiotation and collection by mobile troughs are implemented. The reclaimed oils are generally incinerated. In the case of cold rolling mill oils, there is not yet any satisfactory process. A flotation technique by hydrogen micro-bubbles originating from electrolysis is being developed, and a plant is in operation on an industrial scale.

Slag granulation effluent

An efficient and commonly used means consists in directing the granulation waste waters into a filtering-bottom tank which removes the granulated slag grains whose bulk density is lower or higher than that of water.

Blast furnace flue dust effluent containing cyanides

It is difficult to apply the conventional cyanide treatments as the outflows are large (400 to 1300 m3/h per blast furnace, depending on its size) and the water contains much carbonate. If recycling is important with a passage across an atmospheric cooling agent, one benefits by a natural elimination which is accelerated by the polyphosphates, according to a process as yet unknown.

Coke plant effluent

Biological treatment coupled with the conventional settling tank seems to be the only efficient process for coke plant wastes, but the investment and operating costs make even those with the best intentions shrink from it. In several coke plants, these waters were used for coke quenching by the wet method. Many drawbacks have contributed to the abandonment of this way of operation. In conjunction with the Basin Agencies, the iron and steel industry has resumed the study of biological processes, trying to find an economically valid compromise.

MEASURE TAKEN TO CONTROL ENVIRONMENTAL POLLUTION AT A-F BLAST FURNACE

1.) provision of ESP,cast house and stock house in furnace

2.) Covering of iron in slag runner to prevent fume and dust generation during tapping.

3.) Covering of blow box area to prevent in steam entering into the cast house due to slag granulation.

4.) Evacuation of dust checker in closed container.

5.) Transfer of solid best or dust from loading point to unloading point in covered dumper.

6.) Provision of closed loop water system in newly belt furnace.

7.) Provision of deducting fun at C blast furnace.

8.) Facilities of non-drainable cast able draft at cast house.

9.) Installation of turbo ventilator at C blast furnace cast to improve work environment.

10.) Oxygen enrichment in C blast furnace stove to reduced BF and CO gas consumption to reduced co₂emission.

11.) Covering of all open spaces in the surrounding area.

12.) Using unutilized spaces of blast furnace department for plantation.

IMPORTANT RECOMMENDATION FOR POLLUTION PREVENTION AND CONTROL

Pig Iron Manufacturing

Provision of knife like gate valve in all the dust catcher.
Flue dust to be collected separately in a sealed bunker and then evacuated in a close dumper.
Installation of dedusting system in Hatch pits.
Use of conveyor system instead of Larry car in stock house.
Providing dust extraction system in all stock houses.
Using conveyor system for transfer of material from highline bunker to the high line bins. This will the movement of CT car, demag car and wagons which will ultimately result in less noise and dust pollution.
Provision of degusting system near slip pit in all stock houses.
Making alternate arrangement to reduce noise pollution blow off valve.
Pipe conveyor maybe used instead of flat conveyor to reduce dust generation.
Proper care should be taken during assembling of tuyeres stacks to prevent hot blast leakage.
Improve blast furnace efficiency by using coal and other fuels (such as oil or gas) for heating instead of coke, thereby minimizing air emissions.
Recover the thermal energy in the gas from the blast furnace before using it as a fuel. Increase fuel efficiency and reduce emissions by improving blast furnace charge distribution.
Improve productivity by screening the charge and using better tap hole practices.
Reduce dust emissions at furnaces by covering iron runners when tapping the blast furnace and by using nitrogen blankets during tapping.
Use pneumatic transport, enclosed conveyor belts, or self-closing conveyor belts, as well as Wind barriers and other dust suppression measures, to reduce the formation of fugitive dust.
Use low- NOx burners to reduce NOx emissions from burning fuel in ancillary operations.
Recycle iron-rich materials such as iron ore fines, pollution control dust, and scale in a sinter plant.
Recover energy from sinter coolers and exhaust gases.
Use dry SOx removal systems such as caron absorption for sinter plants or lime spraying in flue gases.

Liquid Effluents

Over 90% of the wastewater generated can be reused. Discharged wastewaters should in all cases be less than 5 m³/t of steel manufactured and preferably less than 1 m³/t.

Solid Wastes

Use blast furnace slag in construction materials. Slag containing free lime can be used in iron making. Blast furnace slag should normally be generated at a rate of less than 320 kg/t of iron, with a target of 180 kg/t. The generation rate, however, depends on the impurities in the feed materials. Slag generation rates from the BOF should be between 50 and 120 kg/t of steel manufactured, but this will depend on the impurity content of feed materials. Zinc recovery may be feasible for collected dust.

SUMMARY OF POLLUTION TREATMENT TECHNOLOGIES

Air Emissions

Air emission control technologies for the removal of particulate matter include scrubbers (or Semi-dry systems), bag houses, and electrostatic precipitators (ESPs). The latter two technologies can achieve 99.9% removal efficiencies for particulate matter and the associated toxic metals: chromium (0.8 milligrams per normal cubic meter, mg/Nm³), cadmium (0.08 mg/Nm3), lead (0.02 mg/Nm³), and nickel (0.3 mg/Nm³).Sulphur oxides are removed in desulphurization plants, with a 90% or better removal efficiency. However, the use of low-sulphur fuels and ores may be more cost-effective. The acceptable levels of nitrogen oxides can be achieved by using low-NOx burners and other combustion modifications. For iron and steel manufacturing, the emissions levels presented in Table 1 should be achieved.

Table 1. Load Targets per Unit of Production, Iron and Steel Manufacturing

Parameter	Maximum value
PM10	100 g/t of product (blast furnace, basic oxygen furnace); 300 g/t from sintering process
Sulphur oxides	For sintering: 1,200 g/t; 500 mg/m³
Nitrogen oxides	For pelletizing plants: 500 g/t; 250– 750 mg/Nm³; for sintering plants: 750 mg/Nm³
Fluoride	1.5 g/t; 5 mg/Nm³

Wastewater Treatment

Wastewater treatment systems typically include sedimentation to remove suspended solids, physical or chemical treatment such as pH adjustment to precipitate heavy metals, and filtration.

Solid Waste Treatment

Solid wastes containing heavy metals may have to be stabilized, using chemical agents, before disposal.

Top-Pressure Recovery Turbine Plant (TRT)

A top-pressure recovery turbine plant is installed in the downstream of gas-cleaning equipment for a blast furnace. There are two types of gas-cleaning equipment: a wet type that uses water and a dry type that does not use water. After dust is collected by either of them, blast furnace gas is led to the turbine and drives it while expanding from around the furnace top pressure to atmospheric pressure. The power generated by the turbine is transferred to the generator and converted to electric power. In conventional practice, the energy of blast furnace gas was wasted by pressure reduction at a septum valve. It is now recovered as electric power, realizing significant energy saving.

Features

1.) Energy-saving equipment used for a blast furnace of a steel plant.

2.) Power-generating equipment furnished with a function to control the top pressure of a blast furnace.

3.) Power is generated by driving a turbine using blast furnace gas generated in a blast furnace.

4.) No fuel is needed for power generation.

5.) No fuel is burned; hence, no CO₂ or other greenhouse gases are generated.

6.) Contributes to CO₂ reduction in accordance with the power generation volume.

7.) Generates less noise in comparison with a conventional septum valve, contributing to the improvement of the environment around a blast furnace

8.) No sophisticated technology is needed for operation and maintenance, which can easily be performed by blast furnace operators and maintenance personnel.

9.) Only small amounts of water, nitrogen, etc. are required for operation, which can easily be covered by existing equipment for a blast furnace.

This devise is already installed in G & H Blast Furnace and we recommend installing it in F Furnace.

CONCLUSION

The production and control practices that will lead to compliance with emissions guidelines have called for, installations of pollution control devices namely dust catcher, ESP, bag filter, etc. Tata steel has gone a long way to make it a Green Industry. With mercury rising day by day, Global Warming is a matter of huge concern as it challenges the very existence of biosphere. Also the industrialization of modern world has been contributing to air and water pollution which have adverse effect on life on Earth. A lot of research is going on to introduce economically viable green technology and. if the industries adopt these green technology then we can expect to see a better world in the near future. Although new technologies has been adopted at TATA STEEL to keep the environmental pollution under control still a lot is required to be done in this area. More greenery may be provided in and around the plant as well as township to make the environment pollution free.

INSTITUTE OF ADVANCED MATERIALS

Search anything from Google

Search This Blog

Saturday, February 23, 2013

THE TATA IRON AND STEEL CO. LIMITTED THE TATA IRON AND STEEL CO. LIMITTED

Like me on Facebook

follow me on FACEBOOK