Method and Apparatus for Measuring Slag Foaming Using Microwave Lever Meter

The present invention relates to a method and an apparatus for measuring a slag foaming level and, particularly, to a method and an apparatus for continuously measuring the slag foaming level within a converter during a blowing operation.

Slag foaming within the converter is caused during the blowing step of a steel making operation by CO bubbles accompanied by gas generation due to the specific blowing condition and/or slag contents. The slag foaming adversely affects the converter operation by causing sharp variations in the slag level and by causing occasionally sloppings.

Therefore, quantitative determination and control of slag foaming has been long desired. If continuous and quantitative determination of the slag foaming level during converter blowing is made possible, it will be possible to prevent the sloppings during the blowing operation by regulating the blowing condition in relation to the quantitatively measured slag foaming condition thereby improving the control of the entire converter operation.

The slag foaming condition in the converter has been determined heretofore by by visual observation of this condition at a time when the converter was tilted or by occasional measurements of the change in electric resistance using a sub-lance probe. However, it is impossible to continuously and quantitatively determine the slag foaming condition by these methods.

Accordingly, an object of the present invention is to provide a relatively simple method for continuously and quantitatively measuring the slag foaming level during converter blowing operation.

Another object of the present invention is to provide an apparatus for practising this method.

The slag foaming measuring method according to the present invention is characterized in that an antenna and a waveguide are provided above the top of the converter, a microwave generator and signal processing circuitry are provided in electrical connection to this antenna and waveguide. Frequency-modulated microwaves are emitted from the microwave generator into the converter, and the beat signal between these emitted waves and the waves reflected from the slag surface is detected and applied to the signal processing circuitry in which the foaming slag level in the converter during the blowing is determined. This characteristic is realized by mixing the frequency-modulated microwaves having a saw-tooth or a triangular waveform reflected from the slag surfacewith the waves reflected from a reference reflector provided at the antenna and by processing as described hereinunder the beat signal generated by these signals.

The apparatus for practising the method according to the present invention has provision for the antenna and the waveguide include water-cooling protective means and air purge means, for the microwave generator to generate frequency-modulated microwaves, and for the signal processor to process the reflected waves.

The invention will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a shematic illustration of an embodiment of apparatus according to the present invention;

FIG. 2 is a side view of an antenna and a waveguide according to the present invention with the cooling protective pipe partially cut out;

FIG. 3 is a block diagram of the antenna and the waveguide, the microwave generator and the signal processing circuitry in an embodiment of the apparatus according to the present invention;

FIG. 4 is a graph showing the relationship between the distance from the antenna to the slag surface and the cutput voltage obtained in an embodiment of the apparatus according to the present invention; and

FIG. 5 is a graph showing the change with time of the slag level measured by an embodiment of the apparatus according to the present invention.

In the present invention, an antenna and a waveguide including a water-cooled protective pipe are provided above the top of a converter, frequency-modulated microwaves having a saw-tooth waveform are emitted into the converter, the beat signal between the emitted waves and the waves reflected from the slag surface is detected, and a voltage value proportional to the distance between the slag surface and the antenna is thereby obtained using a frequency filter, an amplifying circuit, a waveform shaping circuit, and a counter circuit, thereby determining the real slag foaming condition. The relation of the beat frequency f.sub.b to the distance between the antenna and the slag surface is expressed by the following equation:

wherein:

f.sub.o is the rate of frequency of the transmitted wave

C is velocity of the electromagnetic wave

R is distance between the antenna and the slag surface

The equation (1) is solved for R as follows:

Assuming in the equation (2) that f.sub.o is constant, the value C/2f.sub.o also becomes constant. Therefore, the value of R can be obtained by obtaining the value of f.sub.b by measurement and multiplying it by the constant C/2f.sub.o. Accordingly, the slag foaming measuring method according to the present invention can be practised through the following steps:

(a) generating frequency modulated microwaves with a predetermined frequency change rate (f.sub.o) having a saw-tooth waveform;

(b) emitting the generated microwaves toward the converter and the reference reflector;

(c) mixing the waves reflected from within the converter and from the reference reflector respectively, thereby producing a beat signal;

(d) detecting only the beat signal;

(e) determining the frequency of the detected beat signal; and

(f) multiplying the determined frequency by the constant (C/2f.sub.o), thereby obtaining the value of R.

The apparatus for practising the slag foaming measuring method according to the present invention will now be described with reference to the accompanying drawings.

In FIG. 1 illustrating schematically an embodiment of the apparatus according to the present invention, the reference numeral 1 denotes a converter, reference numeral 2 denotes a water-cooled protective tube for preventing heat effects, reference numeral 3 denotes an antenna with a waveguide, reference numeral 4 denotes a microwave generator, and reference numeral 5 denotes signal processing circuitry for obtaining a voltage proportional to the distance from the beat signal. In addition, a lance is denoted by 21, the slag is denoted by 22 and the molten steel is denoted by 23.

The water-cooled protective pipe 2 is provided above the top of the converter 1, for directing the microwaves from the antenna 3 into the converter 1. The microwave generator 4 and the signal processing circuitry 5 are disposed at a position that is free from the influence of the converter and convenient for access and are connected through respective signal channels to the antenna 3.

As shown in FIG. 2, the water-cooled protective pipe 2 has a double wall structure and an air pipe 6 for air purging, and is connected to the antenna and waveguide 3 by its flange 31.

The antenna 3 is, as shown in FIG. 2, preferably provided directly with water-cooling means. Air, nitrogen and the like may be used as the gas for the air purge.

FIG. 3 shows the detailed formation of the antenna and waveguide 3, the microwave generator 4, and the signal processing circuitry 5 and their interrelation. The antenna and waveguide 3 consist of a circulator 9, a horn 10, a reference reflector 11 and a detector 12. The microwave generator 4 consists of a sweeper 7 for generating microwaves. The signal processing circuitry 5 consists of a modulated wave generating circuit 8 for frequency modulation, a frequency filter 13 for analyzing the beat signal, an amplifier circuit 14, a waveform shaping circuit 15, a counter circuit 16 and a recorder 17.

The output of the modulated wave generating circuit 8 is connected to the sweeper 7, for frequency modulating the microwaves, and the output of the sweeper 7 is connected to the antenna 3 so that the microwaves are emitted into the converter 1 through the horn 10. The reflected waves from the slag surface within the converter are received by the antenna 3 and mixed by the detector 12 with the reflected waves from the reference reflector 11 provided between the circulator 9 and the horn 10 thereby generating a beat signal. The frequency filter 13 connected to the output of the detector 12 detects only the beat signal which is then amplified by the amplifier circuit 14, converted into pulse waves by the waveform shaping circuit 15, and integrated for a predetermined length of time by the counter circuit 16. The result of each integrational counting operation, which is expressed as a voltage proportional to the distance between the antenna and the slag surface, is recorded by the recorder 17. The components used herein may be of those commonly used heretofore in the technical field of microwave radar.

FIG. 4 shows the relationship of the distance between the antenna and the slag surface to the output voltage of the counter circuit 16 of an example of the method according to the present invention in which the apparatus of the hereinabove construction and microwaves of X-band of 8-12.4 GHz are used.

FIG. 5 shows the change with time of the slag surface level in a blowing operation measured in an example of this method and an embodiment of the apparatus according to the present invention. In this example, slopping was observed at the point X in the graph of FIG. 5. The results of a measurement using the sub-lance probe are shown for comparison.

As will be evident from the foregoing description, by use of the method and the apparatus according to the present invention it is possible to continuously and quantitatively determine the slag foaming level, to predict the possibility of slopping and therefore to prevent slopping by regulating the blowing condition in relation to the quantitatively measured slag foaming condition, thereby improving the control of the entire converter opertion.