EP0572848B1 - Method of determination of the end-point during oxygen steelmaking in a converter - Google Patents

Abstract

In a method of determination of the end point during oxygen steelmaking in a converter, it is proposed according to the invention that, during the conversion, waste gas constituents continuously escaping from the converter are analysed, preferably by mass spectrometry, and parameters are generated, from the measured values, whose significant change in time gives a signal for ending the oxygen feed.

Description

The invention relates to a method for determining the End point for the fresh process in oxygen converters at the Steelmaking.

During freshening, i.e. when blowing oxygen in or blowing it in on or in the molten steel, essentially carbon oxidized. At the end of oxygen blowing is the Carbon content relatively small. Hence the reaction now of iron with oxygen in the foreground. In addition to the fact that this reaction creates what is known as brown smoke, a strong pollution of the environment, the liquid reacts Iron oxide with the expensive refractory lining of the converter and this increases the refractory costs. At the same time the iron spreading decreased. Therefore the timely shutdown of the Oxygenation particularly important. In addition, there is an increased FeO content the slag is disadvantageous for the production of steel with a high degree of purity.

The mass spectrometric analysis of the exhaust gas components is on known from steel and iron, 1972, pages 1278 to 1283 and DE-A-2 839 316. The known processes are concerned it is an attempt to make statements in a dynamic process to get about the respective state of the molten steel.

In addition, there are various methods, the cheapest Find the switch-off time. So are general math Known models where the timing was based on before fixed values, including the melt itself, is determined.

However, since these values change from batch to batch, they are static models are unable to match the applicable for each batch Determine switch-off time. This assessment Such static models can also be found in the publication Steel and iron from 1982, No. 10, pages 515 to 519.

In contrast, dynamic models that use a signal are more likely suitable to control the fresh process satisfactorily. One of these The so-called sublance technique is dynamic methods. Here one or two samples are taken shortly before the end of the blowing the insertion of a lance in the blowing position. The carbon content is determined by a quick determination using a dependency determined from the solidification temperature. The disadvantages of sublance technology are the very high investment and maintenance costs as well as an unsatisfactory hit rate in Terms of carbon content.

Other dynamic models use gas analysis. Such models would in themselves be particularly suitable for determining the switch-off time if there were a satisfactory method for using the signals to control the fresh process. In the conventional exhaust gas analysis, the decarburization rate is determined from the measured CO and CO ₂ volume fractions, taking into account the exhaust gas rate G _A. A lower decarburization rate signals the end point. This method is not recommended due to the inadequate reproducibility of the final carbon content in the metal and the FeO content of the slag.

This is the result of the last-mentioned publication, in which even expressly states that dynamic process management was not possible at the time.

In the mass spectrometric analysis according to DE-A-2 839 316 the determined values of the exhaust gas components become one Computer fed using a certain system of equations from these values the respective percentage C content calculated. Only when the predetermined value is displayed decided whether to shut off the oxygen supply.

A method is described there in which the monitoring or measurement using a mass spectrometer and Flow meter the amount of decarburization of the melted Steel is determined. The concentration measurement of e.g. CO and CO2 via the exhaust gas analysis and the determination of the exhaust gas rate gives the decarburization rate. From the product of decarburization rate and the measuring time interval gives the amount of carbon removed, and a further summation of the amounts of carbon The total amount of gasified carbon supplies over the freshness period. A balance between the introduced and the distributed Carbon gives the final amount of carbon.

The invention is therefore based on the object of a method of the type mentioned in such a way that individually for each melt as early as possible and at a certain one Bad carbon content by switching off the oxygen supply can be decided when fresh.

• zu Beginn der Messung das Massenspektrometer mit 100 Vol-% Stickstoff beaufschlagt wird und mit der Endpunktbestimmung begonnen wird, wenn der CO-Anteil über 40 Vol-% und der Stickstoffanteil unter 40 Vol-% liegt;
• die Bedingungen (pro Zeit)
• a) Stickstoffgehalt steigt und
• b) Kohlendioxid steigt und
• c) das Verhältnis CO/N₂ fällt oder der Wert (CO/N₂) CO[100 - N₂]/100 fällt

erfüllt sein müssen und mit Hilfe eines Rechnerprogramms fortlaufend mit einer Sollkurve verglichen werden, und daß erst, wenn diese Bedingungen nach zwei bis zehn aufeinanderfolgenden Vergleichsdurchläufen vom Rechner als erfüllt erkannt worden sind, die Sauerstoffzufuhr beendet wirdThe invention achieves this object in that the exhaust gas components CO and CO ₂ and N ₂ escaping from the converter are continuously determined by mass spectrometry during the freshening, wherein:

• at the start of the measurement, the mass spectrometer is charged with 100% by volume of nitrogen and the end point determination is started when the CO content is above 40% by volume and the nitrogen content is below 40% by volume;
• the conditions (per time)
• a) nitrogen content increases and
• b) carbon dioxide rises and
• c) the ratio CO / N ₂ falls or the value (CO / N ₂ ) CO [100 - N ₂ ] / 100 falls

must be fulfilled and continuously compared with a target curve with the aid of a computer program, and that the oxygen supply is only ended when these conditions have been recognized by the computer after two to ten successive comparison runs

Further advantageous embodiments of the invention are the subject of subclaims.

In the method according to the invention, the course over time a number of exhaust gas components by mass spectrometry determined. At the end of the freshening process, the sinks Share of individual exhaust gas components, while share of others Exhaust components increase.

If the exhaust gas constituents CO, CO ₂ and N _{2 are} analyzed with the aid of the mass spectrometer, it turns out that towards the end of the freshening process the proportion of CO falls, while the proportions of CO ₂ and N ₂ increase. The increase in CO ₂ is relatively small, while the increase in N _{2 is} very significant. This is because a lot of fresh air gets into the exhaust gas stream just at the end of the fresh process. For environmental reasons, the exhaust gases have to be extracted. There is a gap between the converter opening and the exhaust hood through which more and more false air is sucked in if the suction pumps can no longer be offered enough converter gas.

Since the decrease in the CO portion or the rise in the N ₂ portion initially proceeds very moderately, it cannot be decided immediately whether the point in time for switching off the oxygen supply has already been reached. One can only be certain when the decrease in the CO content or the increase in the N ₂ content becomes significant. Before this point in time, however, the reaction of oxygen with iron may have gained the upper hand over the reaction of oxygen with carbon. For this reason, parameters are derived from the measured exhaust gas components. G _K = G _A / 100 · (100 - N ₂ - O ₂ ) ≈ G _A / 100 · (100 - N ₂ ), where N ₂ or O _{2 are} volume fractions in% in the exhaust gas.

The parameters are chosen so that they are significant Show change when the exhaust gas components are slow rise or fall.

In this way it is possible to decide on the shutdown the oxygen supply increases about 2 minutes earlier than with the known methods.

It is important for the procedure that at the beginning of the End point determination measurement of the carbon monoxide content above 40 vol% and the nitrogen content in the exhaust gas flow is below 40% by volume. Because only when these initial conditions are given there is an evaluable waste in the course of freshening of the carbon monoxide content or increase in the nitrogen content.

Since it is important in the method according to the invention that the decisive significant change in the course of the exhaust gas constituents or the parameters derived therefrom is recognized as early as possible (pattern recognition), the measured exhaust gas values are digitized as analog values with an analog-digital converter and by means of the computer program the derived parameters are formed from the digital values obtained. Measuring point for measuring point, which are approximately 3 seconds apart, is scanned and the respective time change is compared with a target state. This target state means, for example, "fall" with CO, while it means "rise" with nitrogen. If the scanning, ie the comparison of the temporal change of the measuring points with the respective target state in several runs in succession, the same tendency (CO falls constantly, N ₂ rises continuously), a signal is generated which is used to switch off the oxygen supply.

The number of comparison runs (loops) is previously fixed and is 2 to 10, preferably 7.

However, since situations in which the target states are met several times in succession can occur in the course of the measured exhaust gas values, the pattern recognition is only started when a point has been reached in the course of time from which the final drop occurs of the CO content or the final increase in the N ₂ content can be expected. This is roughly determined, for example, using one of the static models given above. However, there are other criteria, such as B. the so-called coal stop. In some steelmaking processes, for example, carbon is blown into the batch through the bottom of the converter. If there is enough carbon in the melt, the supply of carbon is stopped while freshening continues. The pattern recognition process is then 5 minutes, for example. started after the coal stop, that is, when it is approximately certain that only a little carbon can react with oxygen, the carbon monoxide content in the exhaust gas stream thus begins to decrease steadily.

Then the above conditions are beyond a predetermined one Time or previously determined number of comparison runs fulfilled, the computer generates a signal that either in DDC mode (Dynamic Digital Control) the oxygen supply ended independently or sent to the converter control center is where the oxygen supply is then terminated by the operating personnel can be. This second alternative has the advantage that the operating personnel the oxygen supply based on experience still a little bit maintained despite the signal can.

Fig. 1

den prinzipiellen Aufbau der Meß- und Auswerteapparatur am Konverter,

Fig. 2

den zeitlichen Verlauf der Volumenanteile von CO, CO₂ und N₂,

Fig. 3

den zeitlichen Verlauf des Verhältnisses von CO und N₂ multipliziert mit dem Konvertergasanteil,

Fig. 4

den zeitlichen Verlauf des Verhältnisses von CO und N₂ und

Fig. 5

ein Flußdiagramm des erfindungsgemäßen Auswerteververfahrens.

The invention is illustrated below with reference to drawings and explained in more detail. Show it:

Fig. 1

the basic structure of the measuring and evaluation apparatus on the converter,

Fig. 2

the time course of the volume fractions of CO, CO ₂ and N ₂ ,

Fig. 3

the time course of the ratio of CO and N ₂ multiplied by the proportion of converter gas,

Fig. 4

the time course of the ratio of CO and N ₂ and

Fig. 5

a flowchart of the evaluation method according to the invention.

A converter 1 is shown schematically in FIG. 1. The Oxygen blowing device is for reasons of clarity omitted. Above the converter opening 2 is in one close distance 4 to an exhaust hood 3, through which the exhaust gases get into the chimney 5 from the converter 1. The suction pumps are also not shown for reasons of clarity. A schematically illustrated branch 6 is supplied from the chimney 5 a mass spectrometer 7 with those to be analyzed Exhaust components. The measurement signals are, for example, with With the help of a pen 8 plotted over time. The analog values are scanned and fed to an analog-digital converter 9. The digitized values arrive in the computer 10 and are processed further there. After being found is the right time to turn off the oxygen supply is reached, a signal is generated by the computer 10, that in the present example via the digital output 11 to converter control station, not shown, is transmitted.

2 shows the time course of the measured volume fractions in% of carbon monoxide, carbon dioxide and nitrogen. The measurements have been started during the freshening after a predetermined time. It can be seen that at the end of freshness, ie in this case in the range of 10 to 12 minutes, the CO curve drops and the CO ₂ and N ₂ curves increase. The courses of the measurement signals are after approx. 10.5 min. clearly.

Are certain derived variables, such as. B. CO / N ₂ or CO ² (1 / N ₂ - 1/100), depending on the freshness time, so a clear course is even earlier than after 10, 5 min. to recognize.

In Fig. 3, for the same batch as in Fig. 2, there is an application of (CO / N ₂ ) * (CO [100 - N ₂ ] / 100), which corresponds to CO ² (1 / N ₂ - 1/100) , as a function of the fresh time. Here is a clear trend after about 8.5 minutes. recognizable. The course of CO / N ₂ as a function of the fresh time is shown in FIG. 4. In this case too there is a clear drop after approx. 8.5 min. to see.

The procedure is based on feeling the above time-varying sizes. This requires a computer program to create, as shown schematically in Fig. 5 and convert the analog values into digital data. The The computer program first generates the derived quantities and constantly compares the change over time with the target state.

So that this comparison is not at the beginning of the fresh process or at the beginning of the measuring time, i.e. in one area, in which no meaningful decisions have yet been made the program will only be started at a later time. In the present example, only 5 minutes after the coal stop.

At the start of the measurement, the mass spectrometer is completely exposed to nitrogen. If the measurement now begins, ie if the exhaust gases to be examined are fed to the mass spectrometer, the proportion of calibration gas nitrogen in the mass spectrometer drops. If it drops below 95%, the program is deactivated by a reset. Are the 5 min. Once the carbon supply has been reached, a query is made again as to whether the calibration gas portion of the mass spectrometer has dropped to below 95%. If this question is answered in the affirmative, the counter in the program is set to 0 and the first condition is queried. In this case the condition is "the nitrogen content increases". If the answer is no, the run is restarted. If the condition is met, the second condition is queried, in this case "the carbon dioxide content increases". If the answer is no, the run is restarted, if the answer is yes, the third condition is queried, in this case "the carbon monoxide content drops". If the answer is no, the system restarts. Otherwise, other conditions are taken into account, e.g. B. falls over time the ratio of CO to N ₂ . Another condition could be whether the gradient of the falling edge of this ratio (CO / N ₂ ) exceeds a certain value. If all conditions are met, the counter is increased by one and the conditions are queried for the next measuring point. If the number of loops reaches a previously set value, the process is ended and the signal to switch off the oxygen supply is generated.

The flow chart just explained from FIG. 5 is purely for example to understand. So it is of course possible that only two conditions are queried and that the number of passes between n = 2 and n = 10, but advantageously to 7 can be determined beforehand.

Claims (4)

1. Process for determining the end point for the refining process in oxygen converters in the manufacture of steel, in which during the refining the exhaust gas constituents CO and CO₂ and N₂ which leave the converter are determined in continuous manner by mass spectrometry, with:

   at the start of measuring, 100 vol-% nitrogen impinging on the mass spectrometer and the end point determination being started when the proportion of CO is more than 40 vol-% and that of nitrogen less than 40 vol-%;

   the following conditions (per time) having to be met:

   a) nitrogen content increases and

   b) carbon dioxide increases and

   c) the CO/N₂ ratio decreases or the value (CO/N₂) CO[100 - N₂]/100 decreases

   and being compared with a desired curve in continuous manner with the aid of a computer program, and the supply of oxygen being terminated only when, after two to ten consecutive comparison runs, the computer has recognised the latter conditions as met.
2. Process according to Claim 1,
   characterised in that
   the measured values are analog values which are digitalised and then supplied to the computer.
3. Process according to Claim 2,
   characterised in that
   the computer terminates the supply of oxygen in autonomous manner in the dynamic digital control mode (DDC mode).
4. Process according to Claim 2,
   characterised in that
   the computer sends the signal to terminate the supply of oxygen by way of a digital output to the converter control station, where the supply of oxygen is then switched off.

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