JPH1096009A - Vacuum refining equipment - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To perform a vacuum suction inside a vacuum refining furnace by a steam ejector as a vacuum suction device to make the inside of the furnace a predetermined reduced pressure state, and to perform a vacuum refining in that state, to perform a vacuum refining process on an exhaust passage. To enable accurate and accurate analysis of exhaust gas composition. SOLUTION: In order to exhaust the inside of the vacuum refining furnace 10,
A gas analyzer 30 is provided for performing gas fractionation and analysis from a portion of the exhaust passage 18 extending from the vacuum refining furnace 10 and between the vacuum refining furnace 10 and the steam ejector 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum smelting apparatus for evacuating a smelting furnace and performing smelting under a predetermined reduced pressure.
More particularly, the present invention relates to an apparatus provided with a gas analyzer for analyzing gas in exhaust gas.

[0002]

2. Description of the Related Art In the production of Cr-containing steel typified by stainless steel, a gas containing O ₂ gas is blown into the molten steel contained in a smelting furnace in the atmosphere to produce molten steel. Of C is decarburized to lower the C level in molten steel. This decarburization refining is known as AOD method.

[0003] In this decarburization refining in the atmosphere, when the C content in the molten steel becomes low, the injected O ₂ does not work effectively for decarburization, oxidizes Cr and decarburization efficiency increases. There is a problem that gets worse.

[0004] For this reason, when the amount of carbon has dropped to a certain level, the pressure inside the furnace is reduced to about 20 to 200 Torr, and a non-oxidizing gas such as Ar gas is blown into the molten steel as a stirring gas. While the molten steel and slag are agitated, the present applicant proposes a method in which chromium oxide generated by oxidation during the above-mentioned atmospheric refining is reacted with C in the molten steel to perform decarburization and partially reduce chromium oxide. Have been.

FIG. 5 and FIG. 6 show a main part configuration of a facility for carrying out a method for producing a Cr-containing steel by combining the above-described atmospheric refining and decompression refining, and respective steps of the method. First, in FIG. 5, 12 is a furnace body in the refining furnace 10, and 14 is a tuyere for injecting gas into the molten steel 16. 22
Is a lid for closing an upper opening of the furnace body 12, and an exhaust passage 18 extends from the cover. By exhausting the gas through the exhaust passage 18, the inside of the smelting furnace 10 can be reduced in pressure. Incidentally, reference numeral 20 denotes a slag on the molten steel 16.

In this refining facility, first, atmospheric refining is performed with the lid 22 removed, and then the lid 22 is attached, and the inside of the furnace is evacuated through the exhaust passage 18 to reduce the pressure inside the refining furnace 10 to reduce the pressure. Perform refining.

When a Cr-containing steel is produced in accordance with the above method, first, as shown in FIG. 6, by air refining, that is, a gas containing O ₂ gas in molten steel, usually O ₂ gas and Ar gas as its diluent gas. Gas is blown to decarbonize C in the molten steel. Then, when the amount of C in the molten steel has decreased to a certain level, the lid is covered and then vacuum refining is performed.

[0008] Specifically, first, a non-oxidizing gas such as Ar gas is blown into the molten steel as a stirring gas, whereby the molten steel and the slag are vigorously stirred to form a metal oxide, mainly chromium oxide, in the slag. The carbon in the molten steel is reacted with carbon in the molten steel to decarbonize the carbon and partially reduce chromium oxide. And when the amount of C falls to the target level,
Next, chromium reduction is performed by adding a reducing agent,
Tapping.

According to this method, decarburization refining can be performed quickly in a short time, the amount of expensive Ar gas used can be reduced, and the yield of chromium can be improved. .

By the way, in the above-mentioned refining method, the decarburization speed is regarded as constant for the sake of convenience during the decompression refining, and the decarburization time in the decompression refining is defined based on the C value at the time of switching from atmospheric refining to decompression refining. And decarburization and refining were implemented. For example, in SUS304 refining, in the case of switching from atmospheric refining to decompression refining when the amount of C (C value) becomes 0.1%, the decarburization time in decompression refining is set to 5 minutes. Was.

However, in practice, the C value at the end of atmospheric refining is more than 0.1% due to the dispersion of the operation.
It may be 5%, or conversely 0.08%, which is less than 0.1%. In this case, if the decarburization time is uniformly set to 5 minutes in consideration of safety, If the C value at the end of the atmospheric refining is 0.08%, the decarburization will be performed excessively, resulting in inefficiencies and increased costs, and furthermore, the refining quality will be excessive. .

In this case, if the relationship between the amount of C in the molten steel and the amount of CO in the exhaust gas, which decreases as the decarburization time elapses, is determined in advance, the amount of CO in the exhaust gas can be measured during the refining operation. It is possible to determine the final decarburization refining time.

Further, by analyzing the gas in the exhaust gas, C
The danger of O explosion can be avoided. In other words, if a large amount of CO gas is generated during decompression refining, there is a risk that a CO gas explosion will occur due to the reaction between the CO gas and oxygen, but if the CO gas or oxygen amount can be constantly monitored by performing gas analysis in the exhaust gas. Such a CO gas explosion can be prevented beforehand. However, in order to achieve this purpose, it is required that the gas composition can be accurately analyzed.

[0014]

Means for Solving the Problems The present invention has been devised to solve such problems. Thus, the vacuum refining apparatus of the present invention is a vacuum refining apparatus that performs vacuum refining by performing a vacuum suction on the inside of a vacuum refining furnace by a steam ejector as a vacuum suction apparatus to make the inside of the refining furnace a predetermined reduced pressure state. A gas analyzer is provided for performing gas extraction from a portion between the refining furnace and the steam ejector on an exhaust passage extending from the refining furnace for exhausting the inside of the refining furnace. It is characterized by the following.

[0015]

As described above, according to the present invention, in a vacuum refining apparatus using a steam ejector as a vacuum suction device, gas is analyzed by separating exhaust gas from a portion between the steam ejector and the vacuum refining furnace. A gas analyzer is provided to perform the above.

The present inventors have provided a gas analyzer downstream of the steam ejector and separated and analyzed the exhaust gas from the exhaust passage from the downstream of the steam ejector.
The analysis result differs from the case where a gas analyzer is installed in the nearest part of the refining furnace, specifically, the part between the refining furnace and the steam ejector, the gas is collected from the same part, and the analysis is performed. I found it.

Although the reason is not clear at this stage, one reason is that the gas ejected by the steam ejector onto the exhaust passage causes a difference in gas composition between the downstream portion and the upstream portion of the steam ejector. Conceivable.

Alternatively, since the exhaust gas is a high-temperature gas in the immediate vicinity of the refining furnace, some reaction of the exhaust gas component occurs on the exhaust passage, and therefore, the gas is analyzed in the downstream portion of the steam ejector; It is considered that different results were obtained when gas analysis was performed on the upstream side of the steam ejector.

In any case, it is fully conceivable that the steam discharged from the steam ejector onto the exhaust passage may affect the composition of the exhaust gas in the exhaust passage. When the exhaust gas was collected from the portion and the exhaust gas was analyzed, the oxygen amount that could not be detected at the downstream portion of the steam ejector could be detected at a constant level.

According to the apparatus of the present invention, the gas in the exhaust gas can be accurately analyzed, and the progress of the refining of the molten steel can be accurately grasped based on the analysis result. CO during decarburization refining of steel
The danger of explosion can be avoided beforehand.

[0021]

Next, embodiments of the present invention will be described in detail. In FIG. 1, reference numeral 10 denotes a vacuum refining furnace. The decompression smelting furnace 10 performs, for example, atmospheric refining in which oxygen is diluted and agitated gas such as O ₂ gas and Ar gas is blown into molten steel in the air to produce stainless steel to perform decarburization refining. It is used for vacuum refining, etc., in which a stirring gas such as Ar gas is blown into molten steel to perform decarburization refining by reacting chromium oxide in slag with C in molten steel.

The vacuum refining furnace 10 includes a furnace body 12 and a lid 22 that closes an upper end opening of the furnace body 12 to seal the inside.
In addition, a tuyere 14 for blowing the stirring gas is provided near the bottom of the furnace body 12.

Reference numeral 18 denotes a vacuum refining furnace 10, specifically, a lid 22.
In the exhaust passage, two steam ejectors 24 as vacuum suction devices are provided in parallel on the exhaust passage 18, and a condenser 26 is provided downstream thereof.
Further, a plurality (four in this example) of water pumps 28 also serving as vacuum suction devices are connected in parallel to the downstream portion.

Here, the steam ejector 24 is connected to the exhaust passage 1
The condenser 26 is provided with an exhaust passage 18 by injecting steam into the vacuum passage 8 to vacuum-evacuate the interior of the vacuum refining furnace 10.
The steam injected above is cooled and condensed downstream to liquefy,
It is separated from exhaust gas.

In order to reduce the pressure inside the vacuum refining furnace 10 in this embodiment, first, the water pump 28 is operated to exhaust the inside of the vacuum refining furnace 10 through the exhaust passage 18, and the inside of the vacuum refining furnace 10 is reduced to about 250 Torr, for example. First, the pressure is reduced to the degree of reduced pressure. Then, when the degree of decompression inside the decompression refining furnace 10 reaches a predetermined degree of decompression, the steam ejector 24 is operated to accelerate the vacuum suction and reduce the pressure to the target degree of decompression.

For example, in this example, by operating both the water pump 28 and the steam ejector 24, the final degree of pressure reduction can be set to about 30 to 50 Torr.

Reference numeral 30 denotes a gas analyzer for the exhaust gas in the exhaust passage 18. In this embodiment, the gas analyzer 30 for the exhaust gas is provided at a portion between the vacuum refining furnace 10 and the steam ejector 24. Specifically, the exhaust gas separation passage 32 is connected to the exhaust passage 18 by the vacuum refining furnace 10 and the steam ejector 2.
4 and the exhaust gas on the exhaust passage 18 is collected and analyzed from the portion.

By providing the exhaust gas analyzer 30 in the vicinity of the vacuum refining furnace 10, that is, between the vacuum refining furnace 10 and the steam ejector 24, the exhaust gas analysis can be performed accurately.

FIG. 3 shows the vacuum refining apparatus.
The result of having performed the exhaust gas analysis during decompression smelting operation is shown. However, this result shows that for steel type SUS316L, vacuum decarburization refining was carried out under a degree of vacuum of 46 Torr and C: 0.066.
%, And finally shows the results when decarburizing to C: 0.005%. In the drawing, Cr-R indicates that a Cr reducing agent was added to perform Cr reduction.

On the other hand, FIG. 4 shows that a gas analyzer 30A is provided downstream of the steam ejector 24, specifically, between the condenser 26 and the water pump 28, as shown in the comparative example of FIG. 4 shows the results of exhaust gas analysis during the decompression refining operation. In this case, the decarburization and refining was performed on steel type SUS430 by decarburizing from C: 0.090% at the start of decompression decarburization at a reduced pressure of 48 Torr to finally C: 0.036%. Is shown.

As can be seen from these results, according to the apparatus of this embodiment shown in FIG. 1, exhaust gas analysis can be performed with good responsiveness, and when the gas analyzer 30A is provided at a downstream portion of the steam ejector 24, Although the detection amount of O _{2 in} the exhaust gas was zero, the O ₂ in the exhaust gas was 2
It can be detected at a value of ４4%, which is a reliable analysis result.

Although the embodiments of the present invention have been described in detail above, the present invention is applicable to a vacuum refining furnace or a vacuum refining apparatus using a vacuum suction device of another object or form, and does not deviate from the gist of the invention. Can be configured in variously modified forms.

[Brief description of the drawings]

FIG. 1 is a diagram of a vacuum refining apparatus according to an embodiment of the present invention.

FIG. 2 is a comparative example diagram shown to clarify the features of the vacuum refining device of FIG.

FIG. 3 is a diagram illustrating a result of an exhaust gas analysis performed by the apparatus of FIG. 1;

FIG. 4 is a diagram showing a result of an exhaust gas analysis performed using the apparatus of FIG. 2;

FIG. 5 is a diagram showing a main configuration of equipment for performing a combination of atmospheric refining and decompression refining.

FIG. 6 is a diagram showing an example of steps in performing atmospheric refining and decompression refining using the equipment of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Decompression refining furnace 18 Exhaust passage 24 Steam ejector 30 Gas analyzer

Claims (1)

[Claims] 1. A vacuum refining apparatus for performing vacuum evacuation by means of a steam ejector as a vacuum suction device to perform a refining operation in a vacuum decompression furnace to perform a refining operation in order to exhaust the inside of the refining furnace. A gas analyzer for performing gas analysis by performing gas analysis from a portion on the exhaust passage extending from the refining furnace and between the refining furnace and the steam ejector, and performing a gas analysis. .