OPEN HEARTH STEEL MAKING


PRINCIPLE :   

Open hearth is derived in to two distinct type depending upon the refining and the type of slag formation. If acid slag is form containing Feo, MnO, SiO2 etc. It is called acid steel making. If basic slag containing CaO, FeO, P2O5, and is called basic steel making process.
                   
According to change material used OH process again subdivided in to hot metal practice and cold metal practice.

CONSTRUCTION AND OPERATION OF THE "O.H"  PROCESS :

An O.H furnace consist of following parts, these are
1.Reaction chamber ( i.e. hearth, f/c wall; refining etc.
2. Gas and air upade and down take.
3. slag pockets
4.  regenaratoes.
5. reversersing value
6. Launder or spouts
7. F/C instrument (i.e pyrometer, gas and flue flow indication, gas and flue flow indicator)
8. I - beam support
9. Burners and dog house etc.


CARBON DROP:  During oxidation carbon level decreases before 'P' removal. This is called
carbon drop. It is by adding carburizer & de-oxidiser during tapping.

As   Mn + FeO = MnO + Fe
       Si + 2FeO =  SiO2 + 2Fe

Open hearth furnace
Open Hearth Furnace

OPERATION OF DIFFERENT PARTS :


1. Reaction Chamber :  It is consist of hearth, furnace wall, roofs and side roofs also encounters burnt gaseous products. Furnace wall are subjected to both gaseous reaction and in metal slag reaction. In the hearth, refining reaction are carried out.

2. Gas and air - uptakes and down take :  Uptakes and down take are two channel through which hot gases and cold gas is allowed to pass when air blast is supplied through the channel to chamber it is called uptake and when hot gas is passes to regenerator it is called down take.

3. Slog Pockets :  As its name it collects slag particle are frequently removed from the pockets. The slag pockets prevents the passage of slag particles to regenerator.

4. Regenerator :  These are provided to the open hearth f/c when acts as heat reservoir. The burned gaseous product are allowed to pass through regenerator to tap out the sensible heat from the hot gas and the same to the clod during on blast time

5. Reverisble valve :   it connects to he regeneral, and to chimininey reverses the direction and of flowof the flow of hot laddel.

6. Launder or spouts :  It is nothing but a runner made of refractory material. It is used during tapping of refined metal  goes through this and flow to the laddle or torpedo.

7. I - beam :   It constitutes base structure of O.H furnace which is rests. The I beam structure are support the whole weight of furnace.

8. Burner and Doughhouse :  Burners are provided at the both ends of open hearth furnace to burn the fuel and air mixture to generate necessary amount of heat. Single nozzle or multi nozzle are used, the hole through the burners are inserted is called Doughhouse.

9. Furnace instructions :   Different instruments are provided to O.H furnace to support the process operations. Pyrometer is used to detect furnace atmosphere and temperature, pressure gauge are used to known the air or gas pressure. Flow indicates are also use to known the fuel flow during the operation.

10. Hearth :   This is a steel pan made from 15 to 30mm thick steel plate, rectangular in shape with the length about twice of width. At each end of the pan chill boxes are provided to cooling these part and the fire brick are also taken as at least three layers of acid or  basic bricks.

11. Walls :   The wall are heavily brace with vertical heavy steel section which is tied across the tie beams for the take up the expansion of the chamber on heating.

12. Roof :  This roof is made from silica bricks. The roof of a furnace is level longitudinal and sprung arched between front and back wall from a specially shaped bricks called as scewback. It operated at much higher roof temp.

13. Ports :   These are opening valve through which the air and the gasesous fuel enter the furnace chamber. The O.H furnace used gaseous fuels only and independent ports for air and fuel.

Auxiliarie of Open Hearth

The supoort O.H steel making process, some other supporting devices are requires these are.
1- charging M/C.
2- Hot metal crane.
3- Mixer -. 1-Active mixer
                   2- Natural mixer
4- Timming fla form.
5- Tar gun.
6- Mould train.
7-  Striffer.
8-  Internal draughting.
9-  Chimney.
10- Blower.

Mixer-.   Mixer is a liquid metal reservoir of an integrated steel palnt. It is made of a large cylindrical steel shell lined inside with chromilec bricks . Diff B.F tapping liquid metal are mixer in the mixer and a homogeneous solution is maintained on the mixer. It also few hundred tonnes of metal in liquid state for long time. Steel mixer Receives the liquid metal of uniform composition for steel making . The mixer are provided with burning to supply heat to the liquid metal and prevant chilled. In an active mixer metal refining & cararied out by adding time.



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