Method for operating an electric arc furnace and melting plant having an electric arc furnace operated according to said method
View Patent ↗In a method for operating an electric arc furnace operated with an alternating voltage, a structure-borne sound signal occurring on a wall of the electric arc furnace is detected, from which structure-borne sound signal a parameter characterizing the flicker properties of the electric arc furnace is calculated. At least one process variable of the electric arc furnace is controlled on the basis of the calculated parameter. An electric arc furnace operated according to the method is used in and for a melting plant.
1. A method for operating an alternating voltage electric arc furnace, comprising:
detecting, by a structure-borne sound sensor arranged on a wall of the electric arc furnace, a structure-borne sound signal arising at the wall;
calculating a parameter which predicts a flicker value of the electric arc furnace, the parameter being calculated based on the structure-borne sound signal, wherein the flicker value corresponds to a variation in light intensity from a light source over time caused by fluctuations of voltage in the electric arc furnace; and
controlling a process variable for the electric arc furnace by reference to the parameter to avoid flicker.
2. The method as claimed in claim 1 , wherein the parameter is a numeric measure related to a Kst value, the Kst value specifying characteristics, including at least one of weight and density, of scrap metal disposed in the electric arc furnace.
3. The method as claimed in claim 2 , wherein calculating the parameter comprises:
subjecting the structure-borne sound signal to a Fourier transformation;
determining amplitudes of the Fourier transform at a plurality of frequencies; and
calculating the parameter from the amplitudes.
4. The method as claimed in claim 3 , wherein
a measure for a low-frequency scrap movement is calculated from amplitudes of the Fourier transform at frequencies f which lie below a fundamental frequency f 0 ,
a measure for a high frequency vibration is calculated from amplitudes of the Fourier transform at frequencies f which lie above the fundamental frequency f 0 and do not include harmonic frequencies mf 0 ,
a measure which characterizes stability of the electric arc is calculated from amplitudes of the Fourier transform at frequencies f which lie at and between the harmonic frequencies mf 0 , and
the parameter is calculated from the measures.
5. The method as claimed in claim 4 , wherein the parameter is determined using:
SV
=
B
*
E
where
(
1
)
B
=
∑
n
=
n
0
n
1
F
-
α
(
f
n
)
(
2
)
where B is the measure for a low-frequency scrap movement, where E is the measure for a high frequency vibration, where F is the Fourier transform, where f n1 <f 0 and f n+1 −f n =Δf«f 0
and where
E
=
∑
n
=
n
2
n
3
F
β
(
f
n
)
(
3
)
where f n ≠m*f 0 and f n2 >f 0 , 2≤β≤10 and m is a natural number,
and
SSG
=
(
∑
k
=
2
k
max
F
(
k
f
0
)
)
*
(
∑
n
F
(
f
n
)
)
/
F
2
(
f
0
)
(
4
)
where SSG is the measure which characterizes stability of the electric arc, where f n ≠m*f 0 and f n >f 0 , where k and m are natural numbers and the frequencies f n are those used in equation (3) and k max ≤10 applies, and
K=α*SV+b*SSG (5)
where K is the parameter and where a and b are experimentally determined weighting factors.
6. The method as claimed in claim 1 , wherein calculating the parameter comprises:
subjecting the structure-borne sound signal to a Fourier transformation;
determining amplitudes of the Fourier transform at a plurality of frequencies; and
calculating the parameter from the amplitudes.
7. The method as claimed in claim 6 , wherein
a measure for a low-frequency scrap movement is calculated from amplitudes of the Fourier transform at frequencies f which lie below a fundamental frequency f 0 ,
a measure for a high frequency vibration is calculated from amplitudes of the Fourier transform at frequencies f which lie above the fundamental frequency f 0 and do not include harmonic frequencies mf 0 ,
a measure which characterizes stability of the electric arc is calculated from amplitudes of the Fourier transform at frequencies f which lie at and between the harmonic frequencies mf 0 , and
the parameter is calculated from the measures.
8. The method as claimed in claim 7 , wherein the parameter is determined using:
SV
=
B
*
E
where
(
1
)
B
=
∑
n
=
n
0
n
1
F
-
α
(
f
n
)
(
2
)
where B is the measure for a low-frequency scrap movement, where E is the measure for a high frequency vibration, where F is the Fourier transform, where f n1 <f 0 and f n+1 −f n =Δf«f 0
and where
E
=
∑
n
=
n
2
n
3
F
β
(
f
n
)
(
3
)
where f n ≠m*f 0 and f n2 >f 0 , 2≤β≤10 and m is a natural number,
and
SSG
=
(
∑
k
=
2
k
max
F
(
k
f
0
)
)
*
(
∑
n
F
(
f
n
)
)
/
F
2
(
f
0
)
(
4
)
where SSG is the measure which characterizes stability of the electric arc, where f n ≠m*f 0 and f n >f 0 , where k and m are natural numbers and the frequencies f n are those used in equation (3) and k max ≤10 applies, and
K=α*SV+b*SSG (5)
where K is the parameter and where a and b are experimentally determined weighting factors.
9. A smelting plant with an electric arc furnace, the electric arc furnace comprising:
an electrode operated using an alternating current;
a wall;
a structure-borne sound sensor arranged on the wall, to sense structure-borne sound signals of the electric arc furnace; and
a control and analysis device to analyze the structure-borne sound signals, to calculate a parameter which characterizes flicker properties of the electric arc furnace and to control a process variable for the electric arc furnace by reference to the parameter to avoid flicker,
wherein the flicker properties include a flicker value which corresponds to a variation in light intensity from a light source over time caused by fluctuations of voltage in the electric arc furnace.
10. The smelting plant of claim 9 , wherein a plurality of structure-borne sound sensors are arranged at different locations on the wall, to sense structure-borne sound signals of the electric arc furnace.
11. The smelting plant of claim 9 , wherein the control and analysis device is configured to calculate a parameter that predicts the flicker value based on a first value corresponding to a degree of scrap movement, a second value corresponding to a degree of scrap vibration, and a third value corresponding to a content of the scrap.
12. The smelting plant of claim 11 , wherein the parameter is calculated based on a product of the first value and the second value.