Wednesday, July 31, 2013

Sea Water Circulation System Pakistan Steel




SEA WATER CIRCULATION SYSTEM (Pakistan Steel).

Massive water supply is one of the most vital requirements for an integrated iron and steel plant to keep cooling and running its machinery.


Pakistan Steel has a  2.5 km-long sea water channel which connects the sea water circulation system to the plant site with a consumption of 216 million gallons of sea water per day.


The Sea water Intake & Outlet  System ( including Sea water Pump House) became operational in July 1981, had started supplying sea water to main plant.

Pakistan Steel has an industrial water reservoir with a capacity of 110 million imperial gallons per day.

Tuesday, July 30, 2013

The Iron Ore & Coal Berth of Pakistan Steel at Port Qasim.



THE IRON ORE & COAL BERTH AT PORT QASIM
 ( Pakistan Steel). 

The iron ore and coal (essential raw materials) used in Pakistan Steel are imported primarily from the Canada, Brazil, Australia, Iran and India because resources of iron ore and coal in Pakistan are quality wise poor and not economically viable for manufacturing of iron & Steel in B.F.-LD-Converter route of Pakistan Steel.

  
The coal and iron ore arrive by sea in very large ships and are off-loaded at port Qasim with grab unloaders.

The Iron Ore and Coal berth commissioned in 1980 is a specialized berth for handling Iron Ore, Coal & Manganese ore for Pakistan Steel Mills.


The berth 279 meters in length is equipped with two grab unloaders (universal machines unloading capacity 1000 tonne/hour each) which handle the Vessels of upto 55,000  tonne payload.



The design capacity of the berth stands is 3.36 million tonne per annum, where two 4.5 kilometer long conveyor belts transport the raw materials to Pakistan Steel’s Stockyard.


The estimated amount of Iron ore deposits of the world over are approximately 800 billion tons.Iron exists as natural ores mostly in the form of magnetite (Fe3O4), hematite (Fe2O3).
The others forms of iron ore  like goethite (FeO(OH)), limonite (FeO(OH).n(H2O)) or siderite (FeCO3) are small and need higher benefication cost.

Ores carrying very high quantities of hematite or magnetite (greater than ~60% iron) are known as "natural ores" or "direct shipping ores", meaning they can be fed directly into iron-making Blast furnaces or Direct reduction furnaces.

Representative sources of Iron ores are found in Brazil, Australia, Russia, Ukrain, mainland China, India, America, Canada, South Africa, Iran and elsewhere. The phosphorus and sulfur contents of ores differ greatly according to their origin.



 Australia and Brazil will lead the drive towards increased worldwide steel production capacity over the next several years.



Pakistan Steel has to import approximately 1.7 million tonne of iron ore annually (minimum 60% Fe content of Iron Ore grade) and about 0.55 million tonne of  metallurgical coal to achieve 1.1 million tonne/year capacity.






It takes about half hour to reach the raw material from jetty to Pakistan steel’s stockyard.

RAW  MATERIAL HANDLING DEPARTMENT (R.M.H.D).
The coals and Iron ore are imported through tenders raised by B.M.D. Pakistan Steel and are transported via converyors  from port Qasim to stockyard where they are stored and carefully blended. Pakistan Steel’s raw material stock yard is equipped with  Boom type bucket wheel stacker- reclaimer (shown above) for loading and unloading the coal and iron ore  which are onward supplied to Coke oven, Sintering plant and Iron Making Departments through conveyor system.

As per project design, the existing production capacity of Pakistan steel is 1.1 million tonne /year which has a provision of future expansion to 2.2 million tonne/year. For that reason there is a stocking capacity available for the raw materials accordingly. Pakistan Steel is subjected to run on long term import contracts of Iron Ore and Coking Coals. Keeping in view world wide coal and iron ore price fluctuation, supply and demand dynamics, these basic inputs may be stocked up to maximum available capacity rather than facing a recent situation of raw material shortage and complete shutdown, caused a loss of billions of Rupees.

Apart from above, there is a need to closely monitor the whole process of tendering, shipping, month wise available stocks position and timely actions at any delaying stage through all time close coordination between management of Pakistan steel and ministry of production who may be held responsible / accountable for any negligence in this regard. 

Monday, July 29, 2013

Pakistan Steel's Railway Department.



PAKISTAN STEEL’S RAILWAY DEPARTMENT.

Pakistan Steel has its own railway department provided with Soviet make Locomotives, gandolas and bogies as an integral part of the project. Pakistan steel’s railway department has its own repair and maintenance locomotive workshop within its premises.


The Blast furnace molten slag is dispatched through specially designed slag cars to slag dump yard for onward processing to make it salable to market..


 Specially designed bogies are used for transportation of molten pig iron ladles from iron making department to  steel making department and to pig casting machine.


  In high production and energy efficient integrated iron and steel plants, the transport of molten pig iron between the blast furnace and steel plants is performed in a so-called torpedo vessel ( torpedo ladle) worldwide shown below rather than using hot metal ladles shown above.






Self tilting Torpedo vessel provides the following major advantages over usage of hot metal ladles:

-          Reduces the huge loss of Physical temperature of hot metal ( enormous energy ) due to transportation and handling of hot metal ladles between Iron making and Steel making departments which could be preserved & utilized for melting additional amount of scrap in LD-Converter.

-           Eliminates the number of pig iron ladles and their maintenance cost. Torpedo vessel of capacity 300 tonne may take the hot metal of two consecutive tappings of Blast furnaces of the existing volume of B.F. of  Pakistan Steel.

-          Eliminates the excessive use of overhead charging cranes in steel making department for pouring pig iron ladles into / out of 1300Ton Mixer. Self tilting torpedo vessel directly dispenses molten pig iron into converter charging ladle thereby reduces the time of Overhead charging cranes to half. This would help to enhance the efficiency and hence the production capacity of steel making department.

-          The usage of torpedo vessel is expected to save the temperature of hot metal 80-1000C which reduces the amount of hot metal required per (batch) heat and allows more scrap convert to steel. A vessel of capacity 300 tonne may be sufficient for three consecutive batches ( heats) of 130 tonne charge (Scrap + Hot metal) of LD-Converter and may eliminate the use of hot metal storage vessel ( 1300 ton Mixer) and its yearly Capital repair cost in steel making department.

Few steel plants have used Torpedo vessels for pre-treatment of hot metal to remove harmful elements Sulphur, Phosphorus  and Silicon  but these operations tend to decrease the physical temperature of hot metal and cause the excessive wear/ consumption of refractory lining of the Torpedo vessel and substantial increase in cost of operation. The said chemical elements in hot metal at Pakistan Steel are kept controlled within required limits through control of Blast furnace charge materials as such pretreatment of hot metal would not be needed currently.


Provision of this energy efficient hot metal transport vessel  may be deemed as a part of future revamp package (Phase- II expansion program). Briefly the addition of Torpedo vessel facility will be needing  modification of existing Blast furnace Cast house platform, utilization of space available for installation of second 1300 tonne Mixer at steel making department, up gradation of rail track and hauling capacity between Blast furnace and steelmaking department to endure the heavy load of this huge transport vessel.

Repair Shop Complex (Pakistan Steel)



Repair Shop Complex (C.M.D.) Pakistan Steel.

This is a repair and maintenance-providing facility in Pakistan Steel functions under Central Maintenance Department , plays vital role to fulfill the needs of different production units of Pakistan Steel.

Repair shop complex (C. M.D) provides services in capital repairs and major running repairs.  It is also incharge of breakdown services and immediate emergency repairs of various units of Pakistan Steel.

  A view of Repair shop complex.

Mechanical Repair facilities.
Heavy machine tools shop of Repair Shop Complex has capability of  handling  mechanical  spare  parts  up to  20 metric tons.

In order to describe the capabilities of heavy machine tools and fabricating facilities in the repair shop complex of Pakistan steel, few of the following illustration are taken from similar machine tool and fabrication facilities.

Appearance of heavy machine tools.

C.M.D. carries out repair/ maintenance of overhead bridge cranes up to 180 tons capacity, gantry cranes, weighbridges & cargo/passenger lifts and also undertakes repair & rectification of various equipments of different production units of Pakistan steel.



Various types of rollers of continuous casting machines and rolling mills are repaired and rebuilt at repair shop complex.

Heavy equipments like Steel ladles and slag pots are also rebuilt and repaired at Fabrication shop.



Fabrication and overhauling of ducts, GI corrugated sheet for roofing, fans, blowers and impellers etc. carried out in repair shop complex.



Electrical Repair Facilities.
Electrical repair shop undertakes rewinding of Low Tension AC induction motors upto 320 KW and DC motors upto 180 KW. Rewinding of Brake coils of over head bridge cranes of steel making department up to 180 tons  capacity which are distinctive of their kind in Pakistan.


 Overhauling of power transformers up to 1600 KVA, High Torque motors upto 800 KW and field maintenance of motor upto 7000 KW is carried out at  Electrical repair shop.

Metallurgical Facilities.
Repair shop complex have metallurgical production facilities that include molding machines, electric are furnace, cupola furnace, induction furnace, crucible furnace, shake-out grid, shot blasting machine and tumbling barrels. 


  Foundry facilities include steel castings, cast iron  and non ferrous metal castings, forge & heat treatment shops which regularly  produce various spares parts for different complexes of Pakistan Steel.



Important spare parts like LD-Converter’s Oxygen Lance copper nozzles head  and  Blast furnace copper tuyere are cast and fabricated at non-ferrous casting facilities. The dimensional accuracy of these sensitive parts are of prime importance and any deviation from standards directly effects the iron and steel production processes.

The provision of a heavy machine tools shop, foundry and fabrication facilities at repair shop complex, few discussed above in the soviet design, makes good economic sense to enhance spare & equipments availability. The above repair & fabrication facilities may be upgraded and extended to make them more efficient and economical for inside/ outside orders in future expansion program. 

Sunday, July 28, 2013

Sintering Plant ( Pakistan Steel )




SINTERING PLANT (Pakistan Steel).

Sintering is the agglomeration of fines of iron ore, manganese ore, coke breeze, limestone and dolomite along with recycled metallurgical wastes mineral particles into a lumpy porous mass by heat of combustion of fine coke added within the mass itself.

This agglomerated or lumpy mass combines efficiently in the Blast furnace charge and allow more consistent and controllable iron manufacture.

  
Pakistan Steel’s sintering plant is comprised of two sintering machines. Sintering Machine is a ( 4 meter wide and 100 meter long ) continuous circulating heat resistant steel belt (made up of 92 pellet cars or wagons linked together).



To obtain a desired product chemistry, the proportioned raw materials are obtained from 12 bunkers, sided in 2 rows which are mixed and moistened in a mixing drum. Then the raw material is passed through the shuttle conveyor into the hopper where it drops into the baling drum for mixing. The material bed depth over the grate is kept constant by adjusting the cut-off plate which is fitted with probes to sense the depth of material and automatically vary with the roll feeder speed.



The raw mix is ignited by the ignition hood, fuelled by a mixture of coke oven gas, blast furnace gas and sometimes natural gas. The carbon in the charge burns to raise the temperature (1150-1200 °C ) with the aid of the air sucked through wind box situated under the grate by means of blower fans at the bottom of sintering machine.

Burn-through area where the sintering material  is completely fused and combined by the heat of combustion of coke fines to form an agglomerate. On completion of sintering process, the sintered agglomerate is crushed by passing it through a spiked roll crusher and cooled in the rotating circular cooler. The cooled sinter is screened where sizes up to -20mm size are returnd back to the sintering plant for reprocessing and sizes +20mm diameter are sent to the discharge bunker and finally transported  to the Blast Furnace stock house through conveyor belts for preparing  the Blast furnace burden (B.F. Charge material).

Therefore Sintering Plant plays an important role in converting ore fines ( which may be the part of shipments of iron ore & coal or result of in plant handling of raw materials or metallurgical waste generated within steel plant ) into lumpy fused material chargeable in blast furnace and hence thereby helps in reduction of coke consumption and enhance the productivity of Blast furnace operation by reducing waste.

Industrially developed countries have invested in process control automation system to optimize the emission problems and energy conservation all around Sintering Machines  which may be deemed as part of revamping package of Pakistan Steel.

Coke Oven & By Product Plant ( Pakistan Steel )




COKE OVEN AND BY-PRODUCT PLANT (Pakistan Steel).   

The coke used in the Blast Furnace must have a high carbon content ( Fixed carbon ) and an appropriate  porosity as well as good strength to ensure that it gives good reactivity and does not pulverize to clog the gas flow in the Blast Furnace even at high temperatures environment that exists throughout the lower two-thirds of the Blast furnace.

The other components such as moisture, ash, sulfur, phosphorus, and alkalies are undesirable as they have adverse effects on energy requirements, blast furnace operation, hot metal quality, and refractory lining.

 Cokes that meet the above requirements are derived from bituminous coals. Coal available in Pakistan are not suitable to convert into metallurgical coke due to low carbon, high sulphur & moisture content. Therefore prime coking coals with fairly low ash and sulphur content are imported.

Pakistan Steel’s coke oven plant is comprised of two Coke Oven Batteries, each having  49 ovens. First battery was commissioned on 18 August 1981 & second battery went into production on 6 May 1985.

 A view of Coke oven battery during Capital Repair at  Pakistan Steel.

As per reports, Pakistan steel’s coke oven battery # 1 has undergone capital repair in 2008 and the battery # 2 is under capital repair currently.

 Refractory bricks Laying work for a new Coke Oven Battery.  

Coke ovens are normally operated for long periods like 25 - 30 years continuously.
Therefore refractory bricks for lining a Coke Oven Battery should have accurate shapes and precise dimensions, an excellent mechanical strength at high temperatures, hot modulus of rupture and excellent volumetric stability to work at temperatures 1350 0C.

Silica bricks have sufficiently high refractoriness under load and reliable volumetric stability at high temperatures so an enormous volume of silica bricks of standard shapes are used to construct the coking and combustion chambers of  Coke oven battery.

The roof, regenerator Checkers and Chimney flue of Coke Oven battery are constructed with high quality fireclay bricks.

In developed countries like Japan a campaign life of >40 years is achieved by employing high quality refractories and through control of standard operating parameters for Coke oven batteries.



 Coke Oven Plant is mainly comprised of following production units.

1)     Coal Handling & Processing Plant .
2)     Coke Oven Batteries.
3)     Coke Dry Quenching Plant.
4)     Coke Wet Quenching Plant.
5)     Coke Screening.
6)     By-Product Plant.
Process of Carbonization.
A blend of  bituminous coals is charged into ports (holes) on the top of the ovens and is converted into metallurgical coke by heating it in the absence of air (oxygen deficient atmosphere) to prevent combustion at high temperatures for a period of 16-18 hours (reaction time).

Refractory bricked regenerative chambers recover the heat from flue gases and retain high temperatures 11001350This heat is utilized in coking chambers.
   
In carbonization process, the lumpy coal decomposes to form plastic layers between temperatures 370°C to 470°C. As the temperature rises  further 470°C to 620°C, a marked evolution of tar and aromatic hydro carbons takes place. Upon further progress of temperature from  620°C to 1100°C, a structural development of coals take place with evolution of  hydrogen where they start softening and form plastic mass that swells and resolidifies into a porous solid coke. At temperatures 1050 - 1100°C, the entire mass is carbonized.


The red-hot coke is pushed out of the oven by pusher car through a guide into coke bucket which is transported with an Electric Locomotive  to the Coke Wet or Dry Quenching Plant.

In wet quenching heat energy of hot coke cannot be utilized because water is directly showered on hot coke & the steam is evaporated in the air. So Wet quenching process serves only as a reserve quenching facility.

Mostly dry quenching process of coke is executed. The process uses the counter flow of nitrogen gas in which energy of red hot coke is utilized to produce steam for onward supply to Turbo Blower Station. In addition dry quenching emerges as a highly reliable system to reduce air pollution. The dry quenched coke is harder, stronger and much low moisture content as compared to wet quenched. The coke is cooled and screened into pieces ranging from one inch to four inches.

The metallurgical coke contains 91- 93 % carbon, some ash and sulfur but compared to raw coal is very strong. The strong pieces of coke (with a high energy value) are required to reduce and melt the iron ore and sinter in Blast Furnace.


The cooled coke from CDCP (Coke Dry Cooling Plant) is separated into 3 fractions, BF Coke i.e. +25-70 mm which is sent to Blast Furnaces, Coke Breeze i.e. +0-15 mm which is sent to Sintering plant. The nut coke i.e., +15-25 mm is also used in the Blast Furnace.

Related video:

Coke Oven’s By-Products Recovery Plant.
Throughout the coke making process, organic compounds are recovered as gas, tar, oil, and other liquid products for reuse or conversion into by-products for sale or internal use.

The volatile matter of coal liberated during carbonization is collected in gas collecting mains at the top of the batteries in the form of raw coke oven gas passing through stand pipes and direct contact cooling with ammonia liquor spray.

SCHEMATIC FLOW DIAGRAM OF BY- PRODUCT PLANT.

Crude Coke Oven Gas.
The main by product in the process of coke making is crude coke oven gas which also has lot of valuable chemicals. The first step in the treatment of raw coke oven gas is to cool it for removal of water vapors which greatly reduces its volume. This is done in primary gas cooler. 

Tar and ammonia liquor are produced as by products in the process of coal carbonization from materials contained in the coal feedstock and water added to the process.   

 Ammonium sulfate.
The removal of ammonia from coke oven gas is carried out by bubbling and contacting the coke oven gas with a solution of 4% sulfuric acid solution to form ammonium sulfate in a saturator.

NH3 + H2SO4            ---------รจ       NH4HSO4
NH4HSO4 + NH3      ---------รจ      (NH4)2SO4

The ammonium sulphate produced by the reaction of ammonia with sulphuric acid is recovered by crystallization. The crystals are then centrifuged, washed, dried and sent to packing unit for sale.

 Dehydrated  tar.
The compounds present in the coal tar are formed ultimately from complex organic materials in the coal charge. The tars are an extremely complex mixture of organic compounds which are condensed as medium to dark liquids or solids at room temperature, mostly aromatic compounds.

The initial separation of tar and ammonia liquor is performed in a flushing liquor decanter, a unit based on gravity separation where three layers are formed, the upper layer is of ammonia water, second layer of coal tar & last layer of tar sludge. The ammonia water is pumped back into the ammonia tank where it is condensed and again send to batteries for cooling of coke oven gas.

Coke oven gas after cooling in the primary gas coolers, is sent for final purification from the remaining tar traces into electrostatic precipitators. The exracted coal tar traces are send for water separation and finally to the storage tank for sale.

Naphthalene.
To obtain clean and high purity coke oven gas, the gas cleaning processes such as removal of naphthalene & benzyl to be operated effectively which needs that the gas must be cooled in “final Gas Coolers”.

Final coke oven gas cooler plant.

Coke oven gas is send to the scrubber for removal of naphthalene where solar oil is showered from the top & gas is entered from the bottom. Content of naphthalene in the spent solar oil is 7-8%. Solar oil is stored & marketed.

After final  treatment, purified  Coke Oven Gas whose major constituents are H2 (55-60%), CH4 (23-27%), CO (5-8%), with calorific value around 16720-18810 KJ / m³ (4.6 - 5 kWh/Nm³), becomes suitable for use at coke oven batteries, thermal power plant, sintering plant, refractory & lime production unit etc.

The annual production capacity of Coke Oven & By-Product Plant is as under.

Coke:                             960000 metric tons/year.
Coke oven gas:          300- 350 M3/ ton of coal.
Ammonium sulfate:  172000 metric tons.
Dehydrated tar:         46500 metric tons.


Energy productivity.
In an integrated iron & steel plants like Pakistan Steel, Coal used in coke ovens provides not only energy in the form of metallurgical coke  for iron production in Blast furnace but also internally generates high value fuel as coke oven gas (with a calorific value of 4.6 - 5 kWh/m³N) and steam. Both are used for power generation, making such integrated iron & steel plant self sufficient of electrical power. Only when the coke oven battery of the mills goes off for capital repair, the thermal power plant of steel mill is operated on natural gas.

Further the molten pig iron produced in Blast furnace (at the expense of metallurgical Coke) have physical temperature 1400 -1450 0C which is dropped down to an average 1320 0C  due to transportation, handling and pouring of B.F hot metal ladles into/ out of storage vessel (Mixer) at Steel Making Department. This physical temperature of molten pig iron together with the chemical heat generated in LD-Converter Steel making, formulate the converter steelmaking process self-sufficient in energy.

Operational prudence needed at Coke Oven.
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. Timely maintenance of exhauster is of prime importance to the operation of the coke oven battery. It allows the close control of the gas pressure in the collecting main, which in turn affects the degree of emissions from doors, lids and off-takes. Exposure to emissions is dangerous to workers, may cause lungs and intestine cancer and malignant tumors.   

The degree of escape or release of benzole, tar compounds and acidic gases (H2S, HCN, CO2) to the surroundings are regularly  monitored to prevent exposure of plant operators to the toxic materials and prompt preventive measures be taken timely.

Need to avoid using coals of deviated chemical compositions from required standards for production of metallurgical coke or operating a coke oven at too high end temperatures than targeted range, cause the quality of metallurgical coke production below standard, excessive emission and also the refractories of Batteries are depleted faster from thermal shocks thereby shortening the Campaign life of Coke ovens batteries.

When the plant gets older after years of service, the number of cracks and openings increase in refractory bricks of chamber walls and doors owing to thermal shocks and temperature fluctuation during operation. So periodic preemptive wall repairs and sealing of door openings become indispensible with high quality silica bricks. The flame gunning methods are also used in advanced countries to patch up worn out portions of coking chambers to achieve optimum service life of campaign.

In addition to above checks, industrially developed countries have invested in process control automation system to optimize the emission problems and energy conservation all around coke oven battery operation ( e.g coke discharging system ) which may be deemed as part of revamping package of Pakistan Steel.