Training 4 LF Heating Functions
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Transcript of Training 4 LF Heating Functions
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4. LF heating function
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The LF heating function are summarised as follows:
1. Heating with submerged arcs.
2. Stirring and rinsing of the steel with inert gas.
3. Refining under a basic white slag.
4. Inert gas atmosphere in the ladle furnace.
5. Serving as buffer between melting and casting.
6. Reducing overall consumption values and costs!
LF heating function
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LF heating function
Generation of Hot-Spot
WearArc Deflection - Hot Particle
Jet
ELECTRIC ARC
The electric arc burns between
electrode and metal bath at atemperature of 4000 - 8000C
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Power input into a ladle furnace is
influenced by:Arc power input
Refractory type and quality
Metal and slag temperature. Thermal profile in the refractory
lining.
Metal and slag composition.
Slag thickness.
Type and power of stirring
Ladle furnace geometry. Temperature, C
Bath Height,m
Slag-Metal
Interface L
Arc Power Input Limitation
Transmission of Heat to Metal Bath
Arc Power
2.0 MW/m
LF heating function
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Selection of operating point for the ladle furnace. The ladle furnace
operator can set independent variables only, which define the so called
operating point of a ladle furnace..
1. Secondary voltage.
2. Electrode current.
The choice of operating point will then decide what values will be
obtained of the independent variables active, and reactive power, power
factor heating rate
LF heating function
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Electrical parameters:
Active and apparent power
Arc power
Refractory wearing index
Power factor
LF heating function
E x a m p l e O p e r a ti n g P o i n ts fo r L a d l e F u r n a c e
0 1 0 2 0 3 0 4 00
2
4
6
8
1 0
1 2
1 4
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
1 .4
E le c t ro d e C u r re n t , kA
P o w e r, A r c P o w e r, M W ,R e a c t . P o w e r, M V A r ,
A r c L e n g t h , c m P o w e r F a c t or
A c ti v e P o w e r
M W
A rc P o w e r
M W
R e a c t iv e P o w e r
M V A r P o w e r F a c t o r
A rc L e n g th
c m
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Phase Displacement Between Current
and V oltage at cos = 0.80
0 90 180 270 360-1
-0.5
0
0.5
1
Cycle An gle, degrees
Relative Value Of Voltage And C urrent
Voltage
Current
S uffic ient voltage for reigniting the electricwhen the current passes through zero.
.
Experience shows that a power factor of
cos = 0.78 to 0.80 is ideal for ladle
furnace operation .
With a liquid slag of the proper
composition it is possible to operate up to
0.90 without problems.
There is no purely technically motivated
lower limit for the power factor.
Since P = S*cos it follows that S = P /
cos.
The transformer must be dimensioned onthe basis of the required active power.
LF heating function
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Electrode current.
M A X I M U M E L E C T R O D E C U R R E N TF O R V A R I O U S E L E C T R O D E G R A D E S
2 5 0 3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 01 0
2 0
3 0
4 0
5 0
6 0
7 0
E l e c t r o d e D i a m e t e r , m m
M a x i m u m c u r r e n t , k A
S t a n d a r d I m p r e g n a t e d
LF heating function
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Cycle Diagram (typical)
LF heating function
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Where does the electric energy
go ?
Heating of the steel
Fusing of the slag builders.
Heating of the slag.
Melting of the alloys.
Resistive losses in power
supply systems and electrodes
Losses to refractory,
roof, off gas and ambient.
Utilisation of Electric Ener , kWh/tonne
100 ton LF, Steel rade 20CrNi4
Slag Heating
Metal Heating
Melting AlloysFusing Slagbuilders
Refract., Ambient
Resisitive Losses
0.5
18.2
9.28.4
42.4 16.8
LF heating function
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C pick up during Power on
The extent of this carbon pick-up
depends on the following factors
Oxygen activity in the metal
bath.
Metal bath stirring method. Arc length.
C pick-up during heating
0 20 40 60 80 100
0
10
20
30
Arc length [mm]
(ppm/min)
C-pick-upgas stiring
C-pick-upInd. stir
LF heating function
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Nitrogen pick up
Electric arc heating is potentially cause a substantial pick-up of atmospheric
gases, notably nitrogen
N2 2N 2 [N]
P ic k - u p o f N i t r o g e n a s F u n c t io n
o f S la g T h i c k n e s s
K S C
0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 00
1 0
2 0
3 0
4 0
S la g T h i c k n e s s , m m
N i t r o g e n P ic k - u p , p p m
LF heating function
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Temperature Distribution after LF Treatment
1%
13%
70%
16%
0%
0% 20% 40% 60% 80% 100%
10C
5C
0C
-5C
-10C
Tempdevia
tion
Frequency
N = 100
Temperature Distribution Final Temperature in LF
LF heating function
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End
LF heating function