LD PROCESS DESIGN


History of LD Process :


This process was first tried by prof. R. Durer in Switzerland. After that at Linz and Donawitzed of Austria trails plant of 2 to 5t vessel were successfully carried out to cast refined steel on 25th Jun, 1949.

In the year of 27th Nov, 1952 the first commercial LD shop of 10 to 15t capacity was made at Linz. After that the second plant was installed at Donawitzed and then first plant outside Austria was installed at Hamilton in 1954.

The LD process as a integrated steel plant was first adopted in India by German technology at Rourkela Steel Plant in 1956. The name of LD stands for Linz and Donawitzed where the process was burn, co-incidenly it also stantssfor nozzle process of professor R. Durer in Germany.

From initial 250000t annual production at Linz, the production of LD process reached to nearly 16 million tonnes in 1962, nearly 200 Millon ton in 1970 and nearly 400 million tonnes in 1980 is very rapidly increasing its percentage share in the global market.

LD Shop :


●  It is quite different from the other conventional processes. The rapid rate of production requires automatic and very efficient system of material transport and weighing.

●  A multi floor and tall shop is also required to raise and lowering the lance in the vessel.  An elaborated gas cleaning facilities are required to overcome the pollution and legilation.

●  The number of the vessels in shop in a shop may be generally two or three, two out of three vessels operate at a time. The relining facilities required to maintain a uniform high production rate should always be more then adequate. This requires an efficient process control strategy using computers and automatic spectro chemical analytical methods.

LD Shop Vertical view Relative Location
LD Shop Vertically Views

Fig : Vertical section through a LD steelmaking shop showing relative location of main equipments.

●  The plant design very much depends on whether eccentric or concentric vessel. If an eccentric vessel is used the charging and tapping is carried out on the same side or in concentric vessel this operation are carried out in an opposite direction. But now a days only concentric vessel are used for its better refractory lining life and easy to process.

●  In general hot metal is brought to the furnace by rail car in a pit and ladle is lifted by an overhead crane for pouring the metal in the vessel. Therefore a mixer is located on the ground floor like open hearth of Bessemer shops. This is used for storing of liquid hot metal that comes form blast furnace, also it maintained the balance chemistry of different terpedos by homogenization of metal.

●  The scrap is stored in the scrap yard and supplied in required lots in special charging boxes. The scrap, ferro alloys etc are charge from the working floor. The flux, iron ore and dolomite and some major manganese alloys are fed from upper floors through the charging chutes and intermediate bin path.

LD Shop Perpendicular View
LD Shop Perpendicular View
Fig :  Vertical section through a LD steelmaking shop showing the relevant location of the main equipments. This section is perpendicular to that upper image.

●  The shop is provided separate crane for handling hot metal, scrap and refined steel. Being a very rapid process the LD shop is always provided with more than adequate facilities for material handling to avoid any possible delays. So always maintained the upcoming heats schedule and planning that have casted or processed in vessel, according that the sufficient ferro alloys and micro alloys are stocked in shop.

LD Shop Simplified Cross Sectional View
LD Shop Cross Sectional View

●  A LD plant consist of the following major constituents :
1. The vessel including foundation, rotating gears and pneumatic lift etc.
2. The lance including its auxiliaries gears and pneumatic lift.
3. The hood and the waste gas treatment plant.
4. The material handling and storage facility.
5. Instrumentation and control rooms.
6. The vessel lining and wrecking accessories.
7. Secondary ladle treatment area.
8. In operation refractory shooting machine for maintenance of vessel lining.
9. Fully computerised internet servers and PLC pannel  for smoothing the automation operation.

LD Vessel :

● The vessel is divided in to three segment that is- the spherical bottom, the cylindrical body and the conical top. Each of these is a welded construction of non ageing steel plates. In the earlier design the bottom was detachable to help cooling and relining after campaign was over.

●  The morden vessel are however without joint that is the segment are welded to from one single piece. A vessel without joints is much safer, warps very little and cheaper to construction, than the one with joints. The segments are welded to achieve smooth continuity at the joints to help maintain the form of vessel. The top may be concentric or eccentric to the rest of the body.

● In the morden designs vessel a tap hole is provided at the junction of the cylindrical body and the top conical, opposite the shortest wall height of the conical top. A detachable wear plate is attached to the flange of the tap hole to support it's lining.

● The heavy weight vessel including those of the shell, the refractory lining and the charge is uniformly taken over by a steel ring, which is either welded or attached in a detachable fashion, to the shell in the plane of its center of gravity. Two trunions are attached to the ring to support the vessel freely in split bearing. The pedestal of the bearing are firmly anchored in the concert foundation. The titling gear is attached with trunions.

●  The vessel is capable of rotation through 360° but in practice it rarely exceed +-130°. It is rotated by an electric motor through a system of reduction gears. Small vessel have two pinion drives where big vessel are four pinion drives tilting arrangements. The trunions may be couple with or directly mounted on the pinions.

LD Design :

●  According to capacity of vessel the bath depth is suitable chosen in the range of 110-190cm depending upon the capacity. The depth should be maximum to prevent damage to the bottom during lancing. The trend is that the height to diameter ratio of about 1.5 is preferred. The bath area increase with increasing capacity since the depth is not increase in the same proportion.

●  The specific volume of the vessel was earlier just over one cubic metre per tonne capacity but it was reduced down to 0.75m3/ t. The modern trend is towards one m3/ t again. The total lining thickness depends upon the quality of lining, however it varies 600-1100mm. The height of the vessel design varies from 7 to 10m. The nose diameter and angle are stability of nose lining, charging ease etc and are usually around one third the shell dia and about 67° respectively.

●  The early vessels are capacity around 50 to 80t but the morden vessels are up to 400t capacity. As the vessel capacity increase the diameter of the vessel is increase since the bath depth nearer to same for vessel.







References :
1. Modern Steel Making :  Dr R.H. Tupkary and V.R. Tupkary.
2. Ironmaking and Steelmaking Theory an d Practice : A. Ghosh and A. Chatterjee
3. Steel Making : A.K.Chakravorty

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