LD PROCESS FURTHER DEVELOPMENT


Multi-Nozzle blowing Process :

For modern big LD vessel single lance is not adequate for lancing. Hence multi nozzle Lance is used for effective oxygen blowing. Axis of nozzle in multi nozzle lance are inclined to vertical axis by 10° to avoid interaction of wet impact area is increased due to use of multi nozzle lance. It helps in better blowing and rate of high production. A three nozzle lance is generally used for higher capacity furnaces.

Circulating Lance Process :

In common LD process, the oxygen blowing Lance is kept constant at certain height. The blowing produced a single refined pooled at the bottom of the Lance and due to high emulsion slag metal stratification become problem. This leads to inefficient refining at the end, to overcome this difficulty a circulating Lance is designed. Which rotates 1 to 5rpm in an eccentric to the centre of the bath during blowing. This results, increase in yield of metal. It is first applied in Nippon kokan steel in Japan.

Oxygen Lime Process | OLP


● It is nothing but the modification version of LD process which is known as LD-AC process (Linz Donawitz Arbed Centre national process in which Thomas iron are refined)

● The furnace LD-AC is same like LD process only the construction of lance is alternate in which lime powder and oxygen are injected in the furnace. The vessel volume is more than ld vessel to accommodate extra slag volume generated in this process.

Charge material :

The OLP process consists thomas iron, scrap, lime, iron oxide and dolomite, silica etc. The iron consists of the following chemistry :
Oxygen lime injection Lance - OLP process
Oxygen with lime injection lance

Carbon : 3.2 to 3.5%
Phosphorus : 1.5 to 2%
Manganese : 0.7 to 1.0%
Silicon : 0.4 to 0.6%
Sulphur : 0.4 to 0.6%

Furnace Operation :

First the converter is tilled to receive charge material. The charge consists of some slag with scrap, ore, hotmetal and one third of the total lime required then oxygen Lance is lowering into the vessel and jet of high pressure pure oxygen is applied for 5min and then predetermine amount of lime powder are injected through the Lance.

Ajax Process


● Ajax process is first developed in U.K in 1957. It is used a tilting open hearth furnace but the checker, slag pockets, pants etc are altered keeping general design of OH furnace. The downtake, slag pockets and checker are cylindrical shape and are converted to cylindrical steel shell with appropriate opening.

● The slag pocket has its axis horizontal and checker has vertical, so that the life mainly depends on the hearth and roof. The furnace is fired by come oven gas from each end. It is used alternately in association with direction of fuel firing, hence angle of 27 to 34°, the direction of fuel firing. Hence angle is to the blowing surface. The oxygen is blown at 5 to 6atm and at a flow of 30 to 35m3/min.

Operation :

● Scrap is charged in the furnace and is preheated by fuel fuel firing.then hot metal poured in and fuel supply is put off.oxygen blowing is immediately started from end by lower the Lance inside the furnunce.the other Lance is used in the next fuel cycle in this away Thomas grade pig iron should be refined.so the blowing is continued till  C drop to 1%or S and P to 0.01 - 0.15 .By this time furtiser grade slag is removed

● The second slag is prepared by charging fresh lime and ore.blowing is continue till the carbon level fell to 0.4% and bath temperature up to 1570℃. At this point oxygen lancing is stopped.and the heat is finished.and tap to tap time is about 4-6 hours.

Advantages

1. The process is fast and retained all the features of an open herth furnace, so wide range of steel are produced.
2. It runs on Thomas grade pig iron (P>1.5%)
3. It can take 100% hot metal charge easly.
4. The tilting design helps to remove slag and metal rapidly.
5. Cost of production may reduce to 60-70% standard open herth practice.

Disadvantage

1. The content of slag 10-20%. Where as it is only 9-10 % in standard open herth practice.




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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