Training 4 LF Heating Functions

8/11/2019 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

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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

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End

LF heating function

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Training 4 LF Heating Functions