JP3160827B2 - Method and apparatus for sequential and continuous measurement of carbon, hydrogen and nitrogen concentrations in molten steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to carbon, hydrogen,
The present invention relates to a method and an apparatus capable of sequentially and continuously measuring a nitrogen concentration.

[0002]

2. Description of the Related Art It is extremely important to control the concentrations of carbon, hydrogen and nitrogen in molten steel at a steelmaking site. In reality, there are various cases in which the concentration of nitrogen and hydrogen needs to be managed depending on the smelting equipment, or the concentration of nitrogen and carbon needs to be managed. These, carbon, hydrogen,
Among the nitrogen concentration controls, carbon concentration measurement has recently attracted particular attention, and among them, the measurement of carbon concentration in ultra-low carbon steel sheets has been of greatest interest. Measurement of carbon concentration in ultra-low carbon steel sheets has attracted attention for the following reasons.

Conventionally, ultra-low carbon steel sheets have been widely used mainly for automotive steel sheets. While ultra-low carbon steel sheets have better spreadability and deep drawability than low carbon steel sheets,
There is a disadvantage that the mechanical strength is insufficient. Therefore, various devices have been devised to increase the mechanical strength of the ultra-low carbon steel sheet while maintaining the spreadability. For example, methods of adding Ti, Nb, Mn, P and the like have been studied, and it has been widely recognized that an important factor in controlling these is the trace control of carbon. If it is possible to control the trace amount of carbon, the type and amount of additives may be reduced, and the steel industry establishes a manufacturing technology that can control molten steel having a carbon concentration of 10 ppm to 100 ppm with an accuracy of about several ppm. Is required. From such a background, establishment of a rapid measurement method of trace carbon in molten steel is expected.

As a method for rapidly measuring the carbon concentration in molten steel,
Conventionally, a coagulation temperature measuring method and an emission spectroscopic analysis method of a sample have been known, but these methods are not suitable for rapid measurement of a low-level carbon concentration. Further, some techniques for estimating the carbon concentration in the RH degassing device have been tried. This is due to the CO that evolved from the molten steel into the suction gas during the vacuum suction process.
Gas and CO ₂ gas are sampled, and the amount of decarburization is estimated by integrating the gas while analyzing it with a mass spectrometer. However, in addition to the difficulty of gas sampling itself from the vacuum system, the calculation error tends to increase because the total amount of gas is unknown. It is difficult to estimate the concentration accurately. When the carbon concentration in the molten steel is at a low level, the estimation is more difficult, and it has not yet been established as a rapid measurement method for the concentration of trace carbon. In addition, several types of rapid carbon concentration measuring methods have been proposed, but all of them have many problems as a trace carbon concentration measuring method.

As described above, it is expected to establish a method for rapidly measuring the concentration of trace carbon. On the other hand, in addition to carbon, it is also desired to develop an apparatus capable of continuously measuring each concentration of a plurality of elements in molten steel such as hydrogen and nitrogen. ing. Further, although it is not required to perform the continuous measurement of the three elements as described above, there is a strong demand for the continuous measurement of the two elements, such as the measurement of the concentration of nitrogen and carbon, the measurement of the concentration of nitrogen and hydrogen, in actual steelmaking sites.

As a pioneering technique for measuring the concentration of a plurality of elements such as carbon, hydrogen, and nitrogen, Japanese Patent Publication No. Hei. 502,776 which deals with batch measurement of hydrogen alone as a central problem is known. ing. this is,
The main purpose of this technique is to measure hydrogen concentration.The outline of the technique is to blow a carrier gas, which is an inert gas, into molten steel and to bubble it. By measuring the concentration of hydrogen, the hydrogen concentration in the molten steel is estimated. As an application of the technique, it is suggested that the technique is applicable to batch measurement of carbon monoxide and nitrogen while focusing on hydrogen measurement.

The outline of the configuration of this apparatus is as follows. A probe as a gas blow-in / recovery section in which a predetermined range of a lower end portion is positioned in molten steel to be measured, a gas supply source for a carrier gas to the probe, and a gas analysis means. And a circulation circuit. The probe includes a gas injection pipe whose lower end is curved in a U-shape, and a gas recovery pipe whose open end is located above the U-shaped curved portion of the gas injection pipe, and the gas injection pipe is provided above the gas injection pipe. This is a configuration in which a bell-shaped member for efficiently collecting the carrier gas blown out from the opening end of the tube is provided. The bell-shaped member is made of a porous material, and gas is recovered through the porous material to prevent molten steel from entering the recovery pipe.

On the other hand, the gas circulation circuit has a configuration in which a filter, a thermal conductivity meter, a pump, a four-way stock cock, a pressure gauge, and a flow meter are sequentially incorporated along the gas flow direction.

The hydrogen concentration measuring apparatus blows a carrier gas supplied from a cylinder into molten steel through a gas blowing pipe to bubble the molten steel, and removes the carrier gas mixed with dissolved hydrogen in the molten steel into a gas recovery pipe. In the process of circulating the collected carrier gas through the gas circulation circuit, the carrier gas is equilibrated with the hydrogen concentration in the molten steel, and the hydrogen component is measured by a thermal conductivity meter.

In order to apply this technique to the measurement of the concentration of carbon, hydrogen and nitrogen, the single thermal conductivity meter is replaced with a group of thermal conductivity meters connected in series, and a preceding stage of each thermal conductivity meter is used. ,
A filter for removing unnecessary gas components is arranged in each case.
The first thermal conductivity meter located upstream of the carrier gas flow direction measures the total partial pressures of carbon monoxide, hydrogen, nitrogen and the carrier gas, and then passes through a hydrogen filter, and then the second thermal conductivity meter After measuring the total partial pressure of carbon monoxide, nitrogen and carrier gas, and further passing through a carbon monoxide filter, measuring the total partial pressure of nitrogen and carrier gas with a third thermal conductivity meter, and finally After passing through a nitrogen filter, the partial pressure of only the carrier gas is measured, and the partial pressure difference between these steps is determined to obtain the partial pressures of carbon monoxide, hydrogen, and nitrogen.

[0011]

As mentioned above, although the possibility of continuous measurement of carbon monoxide, hydrogen and nitrogen is suggested in the above-mentioned apparatus, a specific method for measuring carbon is not disclosed. There is no disclosure of a method for rapidly measuring trace carbon in molten steel, which has been attracting attention in recent years, and it has not been able to respond to the demands of steelmaking sites in recent years. Further, in the above-mentioned apparatus, the carrier gas recovered from the molten steel is commonly used for measuring the concentrations of carbon monoxide, hydrogen and nitrogen, and is filtered one by one in the process of passing through the gas circulation circuit, so that the monoxide is removed. Although it is intended to measure the concentrations of carbon, hydrogen, and nitrogen, this method includes elements that cannot be implemented in principle and is not practical.

First, in this apparatus, an object to be measured is a single component which is dissolved in molten steel such as hydrogen or nitrogen in an atomic state and has a certain equilibrium partial pressure determined by temperature and pressure. It is effective only in certain cases, and cannot be applied at all when the object to be measured is carbon. That is, the carbon itself present in the molten steel does not have a specific partial pressure at a normal refining temperature, and therefore cannot be taken out alone by mixing it with a carrier gas as a gas.

In the above technique, the measurement of hydrogen concentration and the concentration of carbon monoxide are continuously performed using a common carrier gas, but this is impossible. That is, when the recovery of hydrogen in the carrier gas is performed in an environment having a high oxygen concentration, hydrogen and oxygen react in the carrier gas to generate water, so that the original hydrogen concentration cannot be measured. The measurement of the hydrogen concentration must be performed in a low oxygen concentration environment. On the other hand, recovery of carbon monoxide in a carrier gas is not possible in an environment with a low oxygen concentration because carbon monoxide itself is not generated. Must be done in the environment. As described above, the preconditions for measuring the hydrogen concentration and the preconditions for measuring the carbon concentration are different, so it is impossible to use the carrier gas recovered from the molten steel commonly for both the hydrogen concentration measurement and the carbon concentration measurement. is there.

When the concentration of a specific element is to be measured by a thermal conductivity meter, the difference between the thermal conductivity of the element to be measured and the thermal conductivity of the carrier gas itself is made as large as possible from the viewpoint of improving the measurement accuracy. However, there is a significant difference between the thermal conductivity of hydrogen and the thermal conductivity of nitrogen, making it difficult to perform hydrogen concentration measurement and nitrogen concentration measurement using a common carrier gas. Is required. Thus, Patent Publication No.
No. 3 of carbon, hydrogen and nitrogen using the technology described in
It is not possible to perform continuous measurement of elements, and at steelmaking sites, by installing multiple independent devices of a single function type for the purpose of measuring the concentration of specific elements only, it is possible to respond to the demand for concentration measurement of multiple elements. That is the current situation. In addition, it takes time and effort to set up the measuring device due to the installation of multiple independent devices, and it takes a lot of time to complete the measurement of all necessary elements, and the measurement results cannot be effectively used for feedback control of the refining equipment. There were also problems.

The present invention has been made in view of the above situation, and it is an object of the present invention to provide a method and an apparatus capable of sequentially and continuously measuring the concentrations of carbon, hydrogen and nitrogen in molten steel with a single apparatus. It is also an object of the present invention to provide a method for quickly and accurately measuring a very small amount of carbon concentration.

[0016]

Means for Solving the Problems As a result of diligent studies, the present inventors have obtained the following idea regarding trace carbon measurement. First, for the measurement of hydrogen and nitrogen in molten steel, the configuration described in the above-mentioned publication can be used, in which a carrier gas is blown into the molten steel and collected, and this blowing and collection is repeated and a component to be measured in the carrier gas is analyzed. Then, the carrier gas is changed according to the element to be measured, or the type of the carrier gas is devised, and a plurality of specific element measuring means are provided corresponding to the element to be measured, or the type of the specific element measuring means is devised. In that case, it was considered that the gas supply / recovery probe and the gas circulation circuit could be shared. The next problem is how to measure the concentration of trace carbon in molten steel. Here, the inventor has obtained the following new idea.

When molten steel containing trace amounts of carbon and oxygen coexists in a vacuum or with a gas having a low carbon monoxide concentration,
A small amount of carbon monoxide is produced and released from molten steel, and the equilibrium concentration of carbon monoxide is correlated with the oxygen concentration as well as the carbon concentration in the molten steel. If it is possible to estimate the carbon concentration in the molten steel by analyzing the concentration of the released carbon monoxide, it is possible. When estimating the carbon concentration, the oxygen concentration in the molten steel, which is the other parameter, needs to be known or its change must be predicted. In the case of smelting equipment, the oxygen concentration in molten steel is several hundred p
pm, and therefore, in such an environment, it is determined that the carbon monoxide concentration in the gas released from the molten steel is defined by the carbon concentration in the molten steel, and There is no problem even if the carbon concentration is uniquely determined by the value of the carbon concentration in the molten steel.

A further problem that emerges is how to specifically promote the production and release of carbon monoxide from molten steel. This is also the case with the hydrogen concentration measuring apparatus. We thought that the adopted method, which is a method of blowing and collecting carrier gas, could be used. That is, if a carrier gas containing no carbon monoxide is blown into the molten steel for bubbling, a large reaction interface between the molten steel and the bubbles can be secured and constantly updated by the stirring force of the bubbling. It was possible to promote the reaction between a trace amount of carbon and oxygen, and focused on the fact that oxidized carbon, that is, carbon monoxide, could be produced. Then, when this method was applied, expected results were obtained.

The method for sequentially and continuously measuring the concentrations of carbon, hydrogen and nitrogen in molten steel according to the present invention based on the above viewpoints has the following configuration. That is, an inert gas serving as a carrier gas selected according to an element to be measured among a plurality of elements of carbon, hydrogen and nitrogen in the molten steel is blown into the molten steel by bubbling, and a gas supply immersed in the molten steel is supplied. While circulating or passing the carrier gas containing the element to be measured collected through the collection probe in the gas circulation circuit, the concentration and concentration of the element to be measured in the carrier gas are changed by repeating the blowing and collection of the carrier gas once or a plurality of times. After equilibrating with or approaching the equilibrium state of each element concentration in the gas, the carbon concentration is measured by a plurality or single specific element concentration measuring means provided in the gas circulation circuit or in the gas circuit branched from the circulation circuit. Measuring the concentration of a specific element of hydrogen or nitrogen, and then discharging the measured carrier gas out of the circulation circuit Is characterized by repeating a series of concentration measurement procedure of a specific element to complete, the other elements of the new varied unmeasured carrier gas by the.

According to the present invention, the type of carrier gas is changed in accordance with the change of the element to be measured to carbon, hydrogen and nitrogen, and the used carrier gas is discharged out of the gas circulation circuit system each time. Although the measurement procedure of the method is fundamental, by devising the type of carrier gas in relation to the element to be measured, the same type of carrier gas can be used for each of the measurements of carbon, hydrogen, and nitrogen.

More specific embodiments of the present invention are as follows. A carrier gas containing helium or argon as a main component is blown into the molten steel for bubbling, and the hydrogen component in the molten steel is diffused into the carrier gas by the stirring force of the bubbling, and is recovered through a gas supply and recovery probe immersed in the molten steel. While circulating or passing the carrier gas through the gas circulation circuit, the blowing and collection of the carrier gas is repeated once or more times to gradually increase the hydrogen concentration in the carrier gas and reduce the hydrogen concentration in the molten steel to the value. Hydrogen concentration measuring means provided in the gas circulation circuit or in a circuit branching off from the gas circulation circuit when the carrier gas whose hydrogen concentration has almost reached the equilibrium value after a predetermined number of circulations or a predetermined time has elapsed is equilibrated with the concentration. Hydrogen concentration measuring method by discharging the carrier gas out of the gas circulation circuit system. And bubbling by blowing a carrier gas containing helium or argon as a main component into the molten steel, and reacting carbon and oxygen in the molten steel at the interface between the molten steel and the bubbles by the stirring force of the bubbling, so that carbon monoxide and carbon monoxide are contained in the carrier gas. As well as producing carbon dioxide,
While circulating or passing a carrier gas containing carbon monoxide and carbon dioxide recovered through a gas supply and recovery probe immersed in molten steel through a gas circulation circuit provided with carbon oxide concentration measuring means, Is repeated once or more times to gradually increase the concentration of carbon oxide in the carrier gas and bring the value closer to a value equilibrium with the concentrations of carbon and oxygen in the molten steel. The concentration of carbon oxide in the carrier gas at the time when a predetermined time has elapsed is measured by the carbon oxide concentration measuring means,
A carbon concentration measuring step of estimating the carbon concentration in the molten steel from the correlation between the carbon oxide concentration and the oxygen concentration in the molten steel measured separately or simultaneously; and a carrier gas containing helium or argon as a main component. Blowing is performed by blowing into the molten steel, and the nitrogen component in the molten steel is diffused into the carrier gas by the stirring force of the bubbling, and the carrier gas recovered through the gas supply and recovery probe immersed in the molten steel is subjected to nitrogen concentration measuring means. While circulating or passing through the gas circulation circuit provided in, the carrier gas is repeatedly blown and collected one or more times to bring the nitrogen concentration in the carrier gas closer to a value equilibrium with the nitrogen concentration in the molten steel. By measuring the nitrogen concentration in the carrier gas after a predetermined number of circulations or a predetermined time has elapsed by the nitrogen concentration measuring means. Having at least two steps, the hydrogen concentration measuring step is selected from; a nitrogen concentration measuring step that
In each of the carbon concentration measuring step and the nitrogen concentration measuring step, a gas supply / recovery probe and a gas circulation circuit are commonly used.

Since nitrogen has a slower diffusion rate than carbon monoxide and hydrogen, it takes much time to reach equilibrium. In order to avoid this, the approximate value of the equilibrium value of the nitrogen concentration is predicted from the rise curve of the nitrogen concentration measured at the beginning of the measurement, and the equilibrium state is established by forcibly adding nitrogen gas from the nitrogen gas cylinder based on the predicted value. Early realization is also preferable from the viewpoint of quick measurement.

Further, the apparatus for sequentially and continuously measuring the concentrations of carbon, hydrogen and nitrogen in molten steel which realizes the above-mentioned point in an apparatus has the following configuration. A supply source of an inert gas serving as a carrier gas provided singly or plurally in accordance with the element to be measured; a gas blowing section having a gas blowing pipe having an open end; and an open pipe end of the gas blowing pipe. A gas supply / recovery probe including a gas recovery unit that recovers a carrier gas in a gas recovery tube via a porous member positioned above the molten steel; and a carrier gas supplied from the carrier gas supply source. A gas circulation circuit for circulating a predetermined number of times or a predetermined time via the gas supply / recovery probe by a forced circulation pump; and a carbon oxide concentration measuring means provided in the gas circulation circuit or in a gas circuit branched from the gas circulation circuit. A specific element concentration measuring means group such as a hydrogen concentration measuring means, a nitrogen concentration measuring means, etc .; and an integral or separate constitution with the gas supply / recovery probe Calculating means for calculating the carbon concentration in the molten steel by inputting both data of the carbon oxide concentration measured by the carbon oxide concentration measuring means and the oxygen concentration measured by the oxygen concentration measuring means; Means;

In the measurement in a smelting facility where the oxygen concentration is known or can be predicted, it is not necessary to provide an oxygen concentration measuring means.

It is preferable that each specific element measuring means is provided with a preliminary processing section for removing harmful components in the carrier gas which cause measurement errors.

Various types of specific element measuring means can be adopted. An infrared gas analyzer is used as carbon oxide concentration measuring means, a semiconductor gas sensor is used as hydrogen concentration measuring means, and a thermal conductivity meter is used as nitrogen concentration measuring means. This is advantageous in terms of device characteristics.

[0027]

The apparatus for sequentially and continuously measuring the concentrations of carbon, hydrogen and nitrogen in molten steel according to the present invention operates as follows. First,
A carrier gas corresponding to the element to be measured is supplied from a gas supply source, and the carrier gas is blown into the molten steel through a gas blowing pipe of a gas supply and recovery probe. The blown carrier gas bubbling the molten steel, diffuses the element to be measured in the molten steel into the carrier gas by the stirring force of the bubbling, and recovers the same through a gas recovery pipe of a gas supply and recovery probe. Bubbling not only recovers gas molecules such as hydrogen and nitrogen dissolved in the molten steel into the carrier gas, but also bubbling promotes the reaction between carbon and oxygen in the molten steel at the interface between the molten steel and bubbles, resulting in monoxide. Produces carbon,
This carbon monoxide is also recovered. At this time, a small amount of carbon dioxide generated together with carbon monoxide is also recovered by the carrier gas.

The carrier gas floats upward,
After being recovered by the gas recovery pipe via the porous member, it is circulated in the gas circulation circuit. Next, the carrier gas is circulated through the gas circulation circuit a predetermined number of times or for a predetermined time to approach equilibrium, and then the concentration of the target element to be measured in the carrier gas is measured by a specific element concentration measuring means installed in the gas circulation circuit. Measure. In some cases, the carrier gas is passed only once without circulating the gas circulation circuit a plurality of times.

The carrier gas is carbon as an element to be measured,
Different ones are used for each of hydrogen and nitrogen, and are discharged out of the gas circulation system at the end of each measurement, and a new carrier gas is always used for the next measurement.

The specific measurement of the concentration of the specific element is performed directly with respect to hydrogen and nitrogen by means of a hydrogen concentration measuring means and a nitrogen concentration measuring means arranged in the gas circulation circuit system or in the gas circuit branched from the gas circulation circuit, respectively. However, with respect to carbon, the concentration of carbon monoxide and the concentration of carbon dioxide in the carrier gas (hereinafter, both concentrations are collectively referred to as the concentration of carbon oxide) are measured by a carbon oxide concentration measuring means installed in a circulation circuit. The measurement result and the oxygen concentration value measured by the oxygen concentration measuring means are processed by the arithmetic processing means to estimate the concentration. In the case where the oxygen concentration is close to the saturation state or in a measurement at a refining facility where the oxygen concentration is known or can be predicted, the oxygen concentration can be considered to be constant. In this case, the carbon concentration is uniquely determined based only on the carbon oxide concentration. Can be estimated.

In the hydrogen concentration measurement, equilibrium is reached early, but in the carbon concentration measurement and the nitrogen concentration measurement, a considerable time is required until the equilibrium is reached. Is estimated. For example, in the carbon concentration measurement, without waiting for the carbon oxide concentration in the molten steel and the carbon oxide concentration in the released carrier gas to equilibrate, the circulation number or the circulation time of the gas circulation circuit became a predetermined value. The carbon oxide concentration is measured at each stage. This is based on the concentration of carbon monoxide and the concentration of carbon dioxide at a predetermined number of circulations or circulation time, as long as the relationship between the carbon oxide concentration at a predetermined number of circulations or circulation time and the carbon concentration in molten steel is established in advance. This is because the carbon concentration in the molten steel can be specified. By not waiting until the state is close to equilibrium, quick measurement becomes possible, and the measurement result can be reflected in feedback control of the refining equipment.

In the case of measuring the concentration of nitrogen having a particularly low diffusion rate, an approximate value of the equilibrium value of the nitrogen concentration is predicted from a rising curve of the nitrogen concentration measured at the beginning of the measurement, and based on the predicted value. It is appropriately adopted that nitrogen gas is forcibly added from a nitrogen gas cylinder to achieve an equilibrium state at an early stage.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a known graph showing the relationship between carbon monoxide partial pressure (P _CO ) and carbon concentration in molten steel.
Book curve oxygen activity (a _O) is 300ppm respectively,
The graph shows the relationship between the carbon monoxide partial pressure (carbon monoxide concentration) and the carbon concentration at 400 ppm, 500 ppm, and 600 ppm. As is clear from this table, if the value of the oxygen activity (oxygen concentration) is known, the carbon concentration in the molten steel can be uniquely estimated by measuring the carbon monoxide concentration in the gas phase. Further, as understood from the graph, it is possible to measure the concentration of trace carbon in the range of 10 ppm to 100 ppm by measuring the concentration of carbon monoxide in the range of 1% to 15%. Can be accurately estimated by measuring the concentration of carbon monoxide on the order of%. The present invention utilizes this principle for measuring carbon concentration in molten steel.

FIG. 2 is a schematic explanatory view of one embodiment of the sequential continuous measuring apparatus according to the present invention. This apparatus includes a gas circulation circuit L1 having a carbon oxide concentration measurement section A and a nitrogen concentration measurement section B arranged in the middle of a circulation circuit, a gas branch circuit L2 having a hydrogen concentration measurement section C arranged in the middle, and the gas circulation circuit L1. It is obtained by a gas supply / recovery probe P which is replaceably connected by a connector (not shown), an oxygen concentration measuring unit D, a carbon oxide concentration measuring unit A and an oxygen concentration measuring unit D provided independently of the gas circulation circuit L1. And an arithmetic unit E for calculating the carbon concentration in the molten steel based on the measured values obtained. However, when the oxygen level in the equipment is high and the level is stable as represented by the RH degassing apparatus, the oxygen concentration can be assumed to be constant. As shown in FIG. 3, the oxygen concentration measuring section D and the like can be removed. In the drawings used in the following description, the oxygen concentration measurement unit D and the like are not particularly shown, but are provided as necessary.

As shown in FIG. 4, the gas supply and recovery probe P has a configuration in which a gas blowing pipe 1 having an open end and a gas recovery pipe 2 are inserted into a holding member 3 such as a paper pipe. Is located above the opening end of the gas injection pipe 1. At the lower end of the holding member 3, a skirt-shaped member 4 for gas collection, which is open downward, is attached. Since the skirt member 4 is immersed in the molten steel,
A material that does not dissolve at least during the measurement time and that does not elute the component that causes a measurement error is selected. For example, a quartz tube or the like is used. Further, the gas injection pipe 1 also needs to be not melted in the molten steel and free from elution of unnecessary components. Therefore, at least a portion of the gas injection pipe 1 immersed in the molten steel is formed of a refractory such as zirconia. You. Further, a refractory 7 is coated on the front end surface of the holding member 3 for the purpose of protecting the holding member 3 from the heat of molten steel. Although not shown, a low melting point member that melts by molten steel is sealed in the opening end of the gas injection pipe 1 so that the opening end is automatically opened when the gas injection pipe 1 is positioned at a predetermined depth in the molten steel. It is also preferable to configure them.

The skirt member 4 is filled with a porous refractory 5 such as porous alumina on the bottom side of the expanded portion. The porous refractory 5 has a function of passing only the carrier gas released from the molten steel and preventing the intrusion of the molten steel.
A portion of the reduced diameter portion of the skirt-shaped member 4 adjacent to the porous refractory 5 is filled with granular alumina, and a filter 6 for removing dust, dust and the like in the collected carrier gas is provided. Functioning. The gas injection pipe 1 penetrates the filter 6 and the porous refractory 5 and the open end thereof is positioned in the molten steel Z, while the open end of the gas recovery pipe 2 passes through the porous refractory 5 and the filter 6. The carrier gas thus immersed in the upper layer of the filter 6 can be recovered. Although not shown, connectors for connecting the gas blow-in pipe 1 and the gas recovery pipe 2 to a gas circulation circuit L1, which will be described later, are attached to the base end side of the holding member 3 so that the gas supply and recovery probe P can be detached. It is configured to facilitate disposal of the probe after use.

The porous refractory 5 has a function of preventing the intrusion of molten steel by passing only the carrier gas, but when the oxygen level in the molten steel is high, FeO or MnO And the like, and a lower oxide such as this easily erodes the porous refractory 5 and blocks the pores. Therefore, in order to cope with such a phenomenon, as shown in FIG. 5, the gas supply Y such that a gas reservoir Y for blocking the contact between the porous refractory 5 and the molten steel Z is formed in the space inside the skirt member 4. It is necessary to delicately control the volume and gas recovery.

FIG. 3 shows an example of a gas circulation circuit L1 and a gas branch circuit L2 as a recovered gas analyzer connected to the gas supply and recovery probe having such a configuration. The gas circulation circuit L1 includes a pump 10, a flow meter 11, a valve 12,
Pressure gauge 13, pressure gauge 14, H ₂ O filter 15, switching valve 16, the bypass passage 17, the switching valve 18, the valve 1
9. An infrared gas analyzer 20 as an oxygen concentration measuring unit D is arranged in order from the upstream side to the downstream side in the carrier gas flow direction, and a flow control valve 27 and a pressure gauge 28 are provided between the valve 12 and the valve 19. An argon gas cylinder 30, a nitrogen gas cylinder 31, and a helium gas cylinder 32 are arranged with a gas mixer 29 interposed therebetween. Further, a nitrogen concentration measuring section B, which is constituted by arranging an oxidation furnace 21, a CO ₂ filter 22, and a thermal conductivity meter (TCD) 23 in series, is disposed in parallel with the bypass passage 17, and the switching valve 16 is provided. ,
By operating the switch 17, one of the bypass path 17 and the nitrogen concentration measuring section B can be selected as a carrier gas passage. Further, a gas branch circuit L2 is connected from the pump 10 to the flow meter 11, and a flow control valve 24 is connected to the gas branch circuit L2.
A hydrogen concentration measuring section C composed of an H ₂ O filter 25 and a semiconductor gas sensor 26 is disposed via the.

The reason why the H ₂ O filter 15 is arranged in the gas circulation circuit L1 at the passage point of the carrier gas immediately after recovery is that the H ₂ O has an error when measuring the concentrations of carbon monoxide and carbon dioxide with an infrared gas analyzer. It is because it causes.

The reason why the infrared gas analyzer 20 is used as a specific device of the carbon oxide concentration measuring section A is that the size that can be incorporated in the analyzer is compact, and that the analysis is quick and accurate. . In measuring the carbon oxide concentration by the infrared gas analyzer 20, an argon gas is used as a carrier gas.

The reason why the thermal conductivity meter 23 is used as the nitrogen concentration measuring section B is that nitrogen is a stable gas, and there is no other appropriate analysis method. This is because highly accurate analysis can be performed even on a stable gas. When using a thermal conductivity meter, it is preferable that the difference between the thermal conductivity of the element to be measured and the carrier gas is large in order to improve the measurement accuracy, and when nitrogen is the element to be measured, nitrogen and thermal conductivity Is selected as the carrier gas. In addition, since nitrogen diffuses into the carrier gas at a slower rate than hydrogen or carbon monoxide, equilibrium may not be reached only by circulating the gas circulation circuit L1 more than ten times. May be delayed. In the present embodiment, in order to solve such inconvenience, while roughly predicting the equilibrium value of the nitrogen concentration from the rising curve of the nitrogen concentration measured at the beginning of the measurement,
The gas mixer 29 is controlled based on the predicted value to forcibly add nitrogen gas to the carrier gas from the nitrogen gas cylinder 31 so as to achieve the equilibrium state at an early stage. Further, by interposing the oxidation furnace 21, carbon monoxide in the carrier gas is forcibly oxidized to carbon dioxide,
This carbon dioxide is removed by the CO ₂ filter 22 in order to eliminate the presence of carbon monoxide, whose thermal conductivity is very close to that of nitrogen, causing an error when measuring the nitrogen concentration. is there.

The hydrogen concentration measuring section C is connected to the gas circulation circuit L
The reason why hydrogen is incorporated in the gas branch circuit L2 instead of being incorporated in the middle of the path 1 is that it is not necessary to circulate hydrogen in the gas circulation circuit L1 a plurality of times due to its high diffusion rate. There are two reasons that the measured carrier gas cannot be returned to the gas circulation circuit L1 because a large amount of oxygen needs to be supplied to the surface. When measuring the hydrogen concentration by the semiconductor gas sensor 26, argon gas or nitrogen gas is used as a carrier gas. Helium gas can be used, but from the viewpoint of cost, argon gas or nitrogen gas is more advantageous.

FIGS. 8, 9 and 10 show how the hydrogen concentration measuring unit C, the nitrogen concentration measuring unit B and the carbon oxide concentration measuring unit A are switched in the sequential continuous measuring apparatus having such a configuration. For example, in an actual steelmaking site, continuous measurement of hydrogen and nitrogen and continuous measurement of carbon and nitrogen are required. The oxygen concentration of the molten steel for which the measurement of the hydrogen concentration is desired is low, while the oxygen concentration of the molten steel for which the measurement of the carbon concentration is desired is high, and the target steel type is generally different.

For example, when measuring the hydrogen concentration first, helium gas is supplied from the helium gas cylinder 32 to the gas circulation circuit L1, and this helium gas is led to the gas supply / recovery probe P via the gas circulation circuit L1. Then, the molten steel is bubbled by blowing into the molten steel from the gas injection pipe 1, and the carrier gas having passed through the molten steel is recovered by the gas recovery pipe 2 into the gas circulation circuit L 1. The collected carrier gas passes through the bypass path 17 and the pump 10 as shown in FIG. 8, and then is guided to the gas branch circuit L2 without returning to the gas circulation circuit L1 again.
After being exposed to the oxidizing gas on the way, the hydrogen concentration is measured by the semiconductor gas sensor 26, and then discharged out of the gas branch circuit L2. At this time, the carrier gas passes through the infrared gas analyzer 20, but the indicated value detected by the infrared gas analyzer 20 is insignificant, so that the infrared gas analyzer 20 is kept in an inactive state.

When measuring the nitrogen concentration, the switching valves 16 and 18 are operated so that the carrier gas after passing through the H ₂ O filter 15 passes through the nitrogen concentration measuring section B as shown in FIG. Switch. The flow to the gas branch circuit L2 is shut off by the flow control valve 24. In this state, fresh helium gas not contaminated from the helium gas cylinder 32 is supplied to the gas supply / recovery probe P,
After bubbling the molten steel with the carrier gas, the carrier gas is recovered. The recovered carrier gas is passed through the nitrogen concentration measuring section B, circulated through the gas circulation circuit L1, and repeatedly blown and collected into the molten steel so as to bring the nitrogen concentration in the carrier gas closer to an equilibrium state. Thermal conductivity meter 2
The indicated value of 3 is constantly monitored, and the measurement is completed by reading the balanced value. In order to compensate for the slow diffusion speed of nitrogen, addition of an appropriate amount of nitrogen gas from the nitrogen gas cylinder 31 is appropriately adopted. The measured carrier gas is discharged out of the gas circulation circuit L1 and is prepared for the next measurement.

When the concentrations of carbon monoxide and carbon dioxide are measured, as shown in FIG.
8 is operated to disconnect the nitrogen concentration measuring section B from the gas circulation circuit L1, and set so that the carrier gas passes through the bypass path 17. Then, in this state, a fresh argon gas which is not contaminated from the argon gas cylinder 30 is supplied to the gas supply / recovery probe P by a predetermined amount.
This carrier gas is blown into the molten steel through the gas injection pipe 1 of the gas supply / recovery probe A1, and the reaction between carbon and oxygen in the molten steel is promoted by bubbling to generate carbon monoxide and carbon dioxide. The carrier gas containing carbon monoxide and carbon dioxide is recovered by the gas recovery pipe 2 and analyzed by the infrared gas analyzer 20. The collected carrier gas is circulated through the gas circulation circuit L1 many times while passing through the infrared gas analyzer 20, and repeatedly blown and collected into the molten steel to bring the nitrogen concentration in the carrier gas closer to an equilibrium state, thereby achieving gas circulation. The corresponding beak values of carbon monoxide and carbon dioxide in the infrared gas analyzer 20 at the stage of circulating the circuit L1 a predetermined number of times or for a predetermined time are read, and the carbon oxide concentration in the molten steel is measured based on this value, Based on this measured value, the carbon concentration in molten steel
It is estimated with the measurement accuracy of.

The gas circulation is performed several times or for a predetermined time in order to improve the measurement accuracy by increasing the concentration of carbon oxide in the carrier gas toward the equilibrium state. It is well known that the same effect can be obtained even if the gas circulation is performed only once by extending the gas injection depth instead of repeating the gas circulation. Absent. The reason why the number of times of gas circulation is repeated or the circulation time is limited is to perform a quick measurement, and the tendency of the carbon oxide concentration to increase due to the repeated gas circulation is within a specified range as long as the measurement equipment is the same. If a relationship between the carbon oxide concentration measured when circulated a predetermined number of times or for a predetermined time in the same equipment and the carbon concentration in the molten steel is established, the carbon in the molten steel can be determined using this relationship. This is because it has been demonstrated that the concentration can be measured with high accuracy. The specific number of gas circulations depends on the measurement conditions.
When 100 cc of argon gas was circulated 10 times,
The measurement of the carbon concentration was completed with a measurement accuracy of pm. The time required for this measurement is about 30 seconds, and it is possible to track and analyze the carbon concentration in the molten steel that changes every moment in almost real time, and the value of the carbon concentration obtained by this measurement is refined. It was confirmed that it could be used for equipment feedback control.

In order to estimate the carbon concentration in the molten steel from the carbon oxide concentration obtained from the infrared gas analyzer 20, the measurement is also performed with reference to the measured value of the oxygen concentration measuring section D constituted by using an oxygen concentration cell or the like. . In the present embodiment, the oxygen concentration measuring unit D is configured separately from the carbon oxide concentration measuring unit A, but it is also possible to incorporate an oxygen sensor into the gas supply / recovery probe P. When the oxygen level in the molten steel is high and the level is stable as represented by the RH degassing apparatus, the oxygen concentration can be assumed to be constant. Alternatively, the carbon concentration in the molten steel may be directly estimated from the measurement result of the infrared gas analyzer 20 without measuring the oxygen concentration.

As described above, the hydrogen concentration measurement, the nitrogen concentration measurement, and the carbon concentration measurement are performed on the steel type to be measured while changing the carrier gas for each measurement. The immersion work of
It is not necessary to repeat as long as the steel type to be measured does not change, and it is possible to respond only by switching the carrier gas while maintaining the state of being immersed in the molten steel, for example, to continuously perform hydrogen concentration measurement and nitrogen concentration measurement or In addition, the carbon concentration measurement and the nitrogen concentration measurement can be continuously performed. At current steelmaking sites, carbon, hydrogen and nitrogen are used for the same type of steel.
Although there is no requirement for concentration measurement for all the elements, the selection of the carrier gas and the selection of each specific element concentration measuring means is appropriately selected in consideration of the characteristics of the specific device, so that carbon,
There is also a possibility that sequential measurement of all three elements, hydrogen and nitrogen, can be performed sequentially.

In the above-described embodiment, the carrier gas is replaced with another one for the hydrogen concentration measurement and the nitrogen concentration measurement or the carbon concentration measurement and the nitrogen concentration measurement even if the concentration measurement is for the same steel type. It is possible that the same type of carrier gas may be used depending on the specific device configuration of the means, and furthermore, depending on the processing sequence of each concentration measuring means and the content of the preliminary processing, the carrier gas may not be re-injected again. There is also a possibility that a carrier gas that has reached an equilibrium state for each element such as hydrogen and nitrogen in molten steel may be commonly used. In this case, the number of gas cylinders can be reduced.

What has been described above is the case where the semiconductor gas sensor 26 is used as the hydrogen concentration measuring means, the thermal conductivity meter 23 is used as the nitrogen concentration measuring means, and the infrared gas analyzer 20 is used as the carbon oxide concentration measuring means. However, the combination of each specific element concentration measurement and the specific device is selected in consideration of the measurement environment and the required measurement accuracy. For example, as shown in FIG. An accurate thermal conductivity meter 33 is arranged, and a bypass path 17, a pretreatment unit 34 for measuring the carbon oxide concentration, and a pretreatment unit 35 for measuring the nitrogen concentration are arranged side by side in the front part of the heat conductivity meter 33. It is also considered that each part can be alternatively selected by operating the switching valves 36 and 37.

Finally, an outline of an operation mode of the gas circulation circuit L1 employed in the present apparatus will be described with reference to FIGS. In the figure, the arrows described on the gas circulation circuit indicate the gas flow direction. Also, the valves 19 and those indicated by solid lines in the valves 19 indicate the connection status of the gas circuit, and furthermore, [ON], [OF
F] represents the operation / stop of the pump 10.

In a standby state before connecting the gas supply / recovery probe P, the flow control valve 27 is closed and the pump 10 is also stopped. The pump 10 is operated to release the air in the pipe from the blowing side, and the carrier gas released from the cylinder is released from the blowing side. The gas supply / recovery probe P is mounted while the pump 10 is operating or stopped. For example, when the tip of the probe P on the blowing side is sealed with a low melting point member or the like, the mounting of the probe P is recognized by the pressure rise due to the operation of the pump 10, and the blowing side is also switched to the carrier gas circuit. If the tip of the blowing side is not sealed with the low melting point member, the pump 10 is immediately stopped to switch to the carrier gas circuit, and wait for the probe P to be immersed. When the gas supply / recovery probe P is immersed in the molten steel at a predetermined depth, the blowing end sealed by the low melting point member is melted by the heat of the molten steel, and the carrier gas is released into the molten steel. And
The immersion of the probe is recognized by the pressure drop, and the carrier gas is released from both the blow side and the suction side. (FIG. 6) The pump 10 is operated to discharge the residual gas in the pipe to the outside of the system, and the preparation for gas circulation is completed. After the cylinder 10 is separated from the circulation circuit, the circulation of the carrier gas is started, and the measurement of the carbon oxide concentration by the infrared gas analyzer 20 is started. (FIG. 7) When the measurement is completed, the pump 10 is stopped, the probe P is pulled up, and the carrier gas is released from the blowing side and the suction side for an arbitrary time to prepare for the next measurement.

Thus, the circulation of the carrier gas in the gas circulation circuit L1 is performed, and the concentration of the specific element is measured. Note that the gas circulation circuit L1 is merely an example, and another configuration may be arbitrarily adopted as long as the configuration allows circulation of the carrier gas.

[0055]

According to the present invention, a carrier gas selected according to an element to be measured is blown into molten steel through a single gas supply / recovery probe which is commonly used, and is bubbled.
The carrier gas recovered from the molten steel by bubbling is passed or circulated in a single gas circulation circuit that is commonly used, and the concentration of typical elements such as carbon, hydrogen or nitrogen is measured during this passage or circulation. When the measurement of the concentration of the target element to be measured is completed, the carrier gas is replaced anew and the concentration of the next specific element is measured. Accurate measurement can be performed continuously without changing measurement equipment. In addition, even if the element to be measured changes, the main parts such as the gas supply / recovery probe and the gas circulation circuit can be used in common, so new installation work of the measuring device is unnecessary,
The total cost of the measuring equipment can be reduced and the maintenance of the measuring equipment can be facilitated.

In the present invention, a small amount of carbon and oxygen in molten steel are caused to react by the stirring force of bubbling to generate carbon monoxide and carbon dioxide, and the concentrations of the carbon monoxide and carbon dioxide are measured. Since it was decided to estimate the carbon concentration in the molten steel, it was possible to measure a trace amount of carbon concentration that could not be directly measured by the conventional method. In addition, since this measurement can be performed very quickly, it is possible to grasp the carbon concentration in the molten steel that changes every moment in almost real time, and the measurement result can be used for feedback control of the refining equipment.

When the oxygen concentration in the molten steel is known and the measurement of the oxygen concentration can be omitted, the measuring device can be simplified and the measuring time can be further shortened.

When measuring the concentration of nitrogen, which has a particularly low diffusion rate, an approximate value of the equilibrium value of the nitrogen concentration is predicted from the rise curve of the nitrogen concentration measured at the beginning of the measurement. If nitrogen gas is forcibly added from a gas cylinder to achieve an equilibrium state early, nitrogen concentration measurement can be performed very quickly.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between carbon monoxide and carbon in molten steel.

FIG. 2 is a schematic explanatory diagram of one embodiment of a sequential and continuous measurement device according to the present invention.

FIG. 3 is a schematic explanatory view showing another embodiment of the sequential continuous measuring device according to the present invention.

FIG. 4 is a sectional view showing an embodiment of a gas supply and recovery probe.

FIG. 5 is a sectional view of a main part showing a state in which a gas reservoir is formed in the skirt member in the embodiment.

FIG. 6 is a schematic explanatory view showing an operation mode of the gas circulation circuit.

FIG. 7 is a schematic explanatory view showing an operation mode of the gas circulation circuit.

FIG. 8 is a schematic explanatory view showing a flow path of a carrier gas when measuring a hydrogen concentration.

FIG. 9 is a schematic explanatory view showing a flow path of a carrier gas when measuring a nitrogen concentration.

FIG. 10 is a schematic explanatory diagram showing a flow path of a carrier gas when measuring a carbon oxide concentration.

FIG. 11 is a schematic explanatory view showing another embodiment of the sequential continuous measurement device according to the present invention.

[Explanation of symbols]

A Carbon Oxide Concentration Measuring Section B Nitrogen Concentration Measuring Section C Hydrogen Concentration Measuring Section D Oxygen Concentration Measuring Section E Arithmetic Unit L1 Gas Circulation Circuit L2 Gas Branch Circuit P Gas Supply / Recovery Probe S Slag Y Gas Reservoir Z Molten Steel 1 Gas Injection Pipe 2 Gas collecting tube 3 holding member 4 skirt member 5 porous refractories 6 filter 7 refractory 10 pump 11 flow meter 12 valve 13 pressure gauge 13 pressure gauge 14 pressure gauge 15 H ₂ O filter 16 switching valve 17 bypass passage 18 switching valve 19 Valve 20 Infrared gas analyzer 21 Oxidation furnace 22 CO ₂ filter 23 Thermal conductivity meter 24 Flow control valve 25 H ₂ O filter 26 Semiconductor gas sensor 27 Flow control valve 28 Pressure gauge 29 Gas mixer 30 Argon gas cylinder 31 Nitrogen gas cylinder 32 Helium gas cylinder 33 Thermal conductivity meter 34 Oxidation Pretreatment unit 36 switching valve 37 switching valve for pre-processing unit 35 the nitrogen concentration determination oxygen concentration measurement

Continued on the front page (72) Inventor Hiroaki Kosaka 16-16 Minami-Beppu-cho, Settsu-shi, Osaka Inside Yamasato Electronite Co., Ltd. Knight Co., Ltd. (56) References JP-A-7-72139 (JP, A) JP-A-57-125348 (JP, A) JP-A-3-261847 (JP, A) JP-A-1-502776 (JP) , A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 33/20 G01N 1/22

Claims (4)

(57) [Claims] An inert gas which is a carrier gas selected according to an element to be measured among plural elements of carbon, hydrogen and nitrogen in a molten steel is blown into the molten steel to be bubbled, and is immersed in the molten steel. While circulating or passing the carrier gas containing the element to be measured recovered through the gas supply and recovery probe through the gas circulation circuit, the blowing and collection of the carrier gas is repeated once or plural times to measure the element to be measured in the carrier gas. After equilibrating the concentration with each element concentration in the molten steel or approaching the equilibrium state,
The concentration of a specific element of carbon, hydrogen or nitrogen is measured by a plurality or a single specific element concentration measuring means provided in the middle of the gas circulation circuit or in the gas circuit branched from the circulation circuit, and then measured. The carbon in molten steel, characterized by repeating a series of concentration measurement procedures for a specific element completed by discharging the carrier gas out of the circulation circuit system, for the other elements not yet measured by changing the carrier gas anew, A method for sequentially and continuously measuring hydrogen and nitrogen concentrations. 2. A gas supply source comprising an inert gas serving as a carrier gas provided singly or plurally in accordance with an element to be measured; a gas blowing section having a gas blowing pipe having an open end; A gas supply / recovery probe including a gas recovery unit that recovers a carrier gas in a gas recovery pipe through a porous member positioned above the open pipe end in the molten steel, and supplied from the carrier gas supply source. A gas circulation circuit for circulating a carrier gas by a forced circulation pump through the gas supply / recovery probe for a predetermined number of times or for a predetermined time; and carbon oxide provided in the gas circulation circuit or in a gas circuit branched from the gas circulation circuit. A specific element concentration measuring group such as a concentration measuring unit, a hydrogen concentration measuring unit, a nitrogen concentration measuring unit, etc .; Oxygen concentration measuring means separately constructed, and both data of the carbon oxide concentration measured by the carbon oxide concentration measuring means and the oxygen concentration measured by the oxygen concentration measuring means are inputted to calculate the carbon concentration in the molten steel. A continuous processing device for sequentially measuring the concentrations of carbon, hydrogen and nitrogen in molten steel, comprising: 3. A sequential processing of carbon, hydrogen and nitrogen concentrations in molten steel according to claim 2, wherein each specific element measuring means is provided with a pretreatment section for removing harmful components in the carrier gas which causes a measurement error. measuring device. 4. An infrared gas analyzer as a carbon oxide concentration measuring means, a semiconductor gas sensor as a hydrogen concentration measuring means, and a thermal conductivity meter as a nitrogen concentration measuring means.
Or a continuous continuous measuring device for carbon, hydrogen and nitrogen concentrations in molten steel according to 3 above.