LD VESSEL BLOWING DEVELOPMENT PROCESS


Bottom blowing process :  

It is the modification of LD Process in which oxygen is blown through the perforated bottom of the Converter. The oxygen is enriched with hydrocarbons to continue the larger refining process and better slag metal interface take place for efficient refining, due to circulation of the liquid metal bath blowing. A typical bottom blown oxygen process is shown below.


Combined blown process :   It is known as hybrid Process. In this case oxygen is blown form both top and bottom of the Converter. This is the most efficient process. At the beginning, oxygen is blown from the top and refining is carried out. The bottom blowing is continued for further refining of the melt iron, loss is very less in this case. Durring the bottom blowing hydrocarbon is injected for sufficient heating of the bath.


Circular lance process :   In common LD the oxygen blowing lance is kept constant at certain height. The blowing produced a single refining pool at the bottom of the lance and due to high emulation slag metal sacrification becomes problem. This leade to inefficient refining at the end. To over come this difficult at civilizing lance is designed, which rotate 1 to 5rpm eccentric to the center of the bath during blowing. This result increase in yield of metal. This was first applied in Nippon kokan steel of Japan

Advantages :

● Vessel volume is less than the conventaional LD Converter as no foam is formed during blowing
● Blowing is guide than the top blown LD process. Hence better stratification of slag and metal.
● Refining process is enhanced as hydrocarbon during blowing.
● Cost of installation is less.


Multi nozzle blowing process :

For modern big LD vessel single large is not adequate for lancing. Hence multi nozzle lance is used for affective oxygen blowing. Axis of nozzel in multi nozzle lance are inclined to vertical axis by 10° to avoid interaction of wet. Impact area is increase due to use of multi nozzle lance. Multi nozzle helps in rate of high production. A three nozzle lance is generally used for higher furnace.

Thermal Efficiency of Steel Refining :

●  In steel making the impurities are oxidised to their respective oxides which are exothermic reaction. Also the dissolution of oxides in each other, in a slag formation are in exothermic process.

●  The actual amount of heat liberated during refining will have to found out in relation if metal and slag. As a standard of the elements dissolved in liquid iron at 1400℃ by oxygen at 25℃ is calculated and no heat lost to the surrounding i.e

Elements.                Temp rise ℃.                   Product
Fe                                   0.5                         FeO
Cr                                   1.5                       Cr2O3
Mn                                 0.7                         MnO
P                                    2.3                       P2O5
Si                                   3.1                        SiO2
C/C                             1.2/ 3.8                 CO / CO2

●  An addition of rise of 0.5 ℃ will be due to the dissolution of silica in the slag and 1.5 ℃ due to the dissolution of phosphorus pentoxide in slag.

●  The dominant exothermic reaction of P, C and Si oxidation reaction is very evident. The majorly heat from carbon monoxide comes out only when the end product is carbon dioxide.

●  The usual combination of SiO2 and P2O5 as basic silicate and phosphate slag and rise the temperature as expected to be range of 900-1000℃. In this process the heat generated by burning of CO to CO2 alone.

● In the steel making Process the exothermic heat is required for.
1. To heat molten iron from its usual temperature of charging 1250-1350℃ to the tapping temperature level of above 1610℃ or more.
2.  To melt the solid scraps or reduce the iron ore which is charged as a coolant.
3.  To heat any other cold charge material.
4.  To compensation heat losses to the surrounding.

●  Out of the above causes, they must be met from the exothermic heat to make the process autogenous expect metal scrap and coolant charge during refining.

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