JPH04272121A - Method for analyzing component of waste gas in vacuum refining furnace - Google Patents

Abstract

PURPOSE:To continuously and accurately analyze the component of waste gas from a vacuum refining furnace even when the pressure of the waste gas is suddenly changed by keeping the pressure of the waste gas to be introduced into a mass spectrometer constant at all times and compensating the time lag in conductance control. CONSTITUTION:The waste gas from a vacuum refining furnace 1 is introduced into a mass spectrometer 4 through an exhaust duct 2 and a gas supply pipe 3 and analyzed. The opening degree of a conductance control valve 14 provided in the mid-way of an exhaust pipe 12 is adjusted, or the pipelines 5a, 5b, 5c, 5d and 5e branched from the supply pipe 3 and/or the pipelines 10a, 10b, 10c, 10d and 10e branched from the exhaust pipeline 8 are switched to fix the measured value of a vacuum gage 17 provided to the supply pipe 3 on the inlet side of the spectrometer 3. The pipeline to be switched is predicted from among the pipelines 5a, 5b, 5c, 5d and 5e and/or the pipelines 10a, 10b, 10c, 10d and 10e, and the waste gas to be analyzed is introduced into the predicted pipeline to the extent that the present analysis is not affected before the pipelines are switched.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a vacuum refining furnace that analyzes the components of exhaust gas discharged from vacuum refining furnaces such as RH, DH, and VOD during the vacuum refining process using an analyzer such as a mass spectrometer. This invention relates to an exhaust gas component analysis method.

0002

BACKGROUND OF THE INVENTION Since the amount of carbon in steel has a great effect on the quality and mechanical strength of the steel, it is important to match the carbon content to a target value in the vacuum refining process. As a method for controlling carbon content, a dynamic control method based on component analysis values of exhaust gas discharged from a vacuum smelting furnace is widely used.

[0003] As a method for analyzing the components of the exhaust gas from a vacuum refining furnace, a method of analyzing the components of the exhaust gas at normal pressure (760 Torr) is known. This method is a method in which exhaust gas at normal pressure is sampled at the outlet side of a vacuum pump (booster or ejector pump) installed at a location away from a vacuum refining furnace, and its components are analyzed using a mass spectrometer.

However, this type of analysis method has the disadvantage that it takes a long time for the exhaust gas to move, making it impossible to obtain timely analysis results over time.

[0005] Furthermore, the system for introducing exhaust gas into the mass spectrometer is equipped with a valve mechanism that makes the conductance variable.
A method for continuously analyzing the components of exhaust gas was developed in the 1980s by the Special Publication Corporation.
It is disclosed in Japanese Patent No. 11085. Hereinafter, the analytical method disclosed herein will be briefly explained.

FIG. 3 is a schematic diagram showing the configuration of an apparatus for carrying out this analysis method. In the figure, 31 is connected to a vacuum refining furnace (not shown), and is connected to a vacuum refining furnace (not shown) for exhausting exhaust gas from the vacuum refining furnace. This is an exhaust duct that serves as a flue. A gas sampling pipe 32 for sampling a part of the exhaust gas is connected to the exhaust duct 31, and the terminal end of the gas sampling pipe 32 is connected to a mass spectrometer 33 for analyzing the components of the exhaust gas. Gas sampling pipe 3
2 has three valves 3 with different conductances.
4a, 34b, 34c are interposed in parallel,
Any one of these valves can be selected and opened based on a measurement signal from a vacuum gauge 35 installed in the exhaust duct 31. In addition, valves 34a, 3
Gas sampling pipe 3 upstream from the intervening position of 4b and 34c
2 is provided with a dust trap 36 for filtering out dust. Furthermore, two vacuum pumps 37 are installed in the gas sampling pipe 32 from the upstream side to the downstream side for introducing the exhaust gas discharged from the exhaust duct 31 into the mass spectrometer 33.
, 37, and an exhaust pump 38 for exhausting the mass spectrometer 33 are provided in this order.

[0007] In a device having such a configuration, the exhaust duct 3
Exhaust gas is introduced from 1 to a mass spectrometer 33 via a gas sampling pipe 32, and the components of the exhaust gas are continuously analyzed. At this time, the pressure inside the exhaust duct 31 is measured with the vacuum gauge 35, and based on the measured value, the three valves 34a, 34b,
Since any valve is selected from 34c, the amount of exhaust gas introduced into the mass spectrometer 33 can be kept constant.
Analyze exhaust gas components with high accuracy.

[0008]

[Problems to be Solved by the Invention] However, the above analysis method has the following problems. First, since the conductance is changed based on the pressure measurement value in the exhaust duct 31, which is a flue, the mass spectrometer 33
The gas pressure on the inlet side of the system is not necessarily constant, making it impossible to perform accurate component analysis.

[0009] Furthermore, when changing the conductance, gas remaining in the pipe where the next valve is installed causes a switching delay, and the component analysis values become abnormal, making it difficult to perform accurate continuous analysis. do not have. FIG. 4 is a graph showing this state, in which the horizontal axis represents time and the vertical axis represents the component analysis value of the exhaust gas and the open/closed state of the valve. T3 in the figure is the timing for switching from valve 34a to valve 34b. It takes time until the gas remaining in the pipe where the valve 34b is installed is completely replaced with the exhaust gas to be analyzed (T4 in the figure), so this period (period from T3 to T4 in the figure) In this case, the component analysis value becomes abnormal as shown by E in the figure.

As described above, the conventional analysis method has the problem that it is not possible to continuously analyze the components of exhaust gas, especially when the pressure of exhaust gas changes suddenly and the valve has to be changed frequently. , accurate component analysis values cannot be obtained at all.

The present invention has been made in view of the above circumstances, and provides an exhaust gas component analysis in a vacuum refining furnace that allows continuous component analysis of exhaust gas to be carried out with high precision even when the pressure of the exhaust gas changes rapidly. The purpose is to provide a method.

0012

[Means for Solving the Problems] A method for analyzing exhaust gas components in a vacuum refining furnace according to the first invention according to the present application includes communicating exhaust gas discharged from the vacuum refining furnace through a flue to the flue during vacuum refining. In this method, the exhaust gas is introduced into an analysis device through a sampling tube, and the components of the exhaust gas are analyzed by the analysis device, wherein the sampling tube includes a control device that continuously changes and controls the conductance, and a pressure gauge that measures the pressure of the exhaust gas. are arranged in this order from the flue side, and the control device continuously changes and controls the piping conductance so that the measured value of the pressure gauge becomes constant.

[0013] Furthermore, in the method for analyzing exhaust gas components in a vacuum refining furnace according to the second invention according to the present application, in the first invention, the control device has a plurality of pipes having different pipe characteristics, and sequentially controls the plurality of pipes. The conductance is continuously controlled by switching, the pipe to be switched next is predicted, and the exhaust gas to be analyzed is passed through the predicted pipe before actually switching to the predicted pipe.

[0014]

[Operation] In the first invention, the gas pressure on the inlet side of the analyzer is measured, and the conductance is continuously changed and controlled based on the measured value. Therefore, the gas pressure on the inlet side of the analyzer, ie, the pressure of the exhaust gas introduced into the analyzer, is always constant.

[0015] In the second invention, the next pipe to be switched is predicted, and before actually switching to this pipe, the switching valve of this pipe is opened to the extent that the current component analysis is not affected, and the exhaust gas is removed. Connect this pipe. If you do that,
Component analysis is performed accurately even while the gas in the pipe is replaced with exhaust gas, making continuous component analysis possible.

[0016]

[Examples] Examples of the present invention will be described below. FIG. 1 is a schematic diagram showing the configuration of an apparatus for implementing the exhaust gas component analysis method of the present invention.

In the figure, reference numeral 1 denotes a vacuum refining furnace that houses a ladle (not shown) containing molten steel and vacuum refines the molten steel. The vacuum refining furnace 1 is connected to an exhaust duct 2, which is a flue for exhausting exhaust gas from the vacuum refining furnace in the direction of the white arrow in the figure. A gas sampling pipe 3 for sampling part of the exhaust gas is connected to the exhaust duct 2, and the terminal end of the gas sampling pipe 3 is connected to a mass spectrometer 4 for analyzing the components of the exhaust gas. In the middle of the gas sampling pipe 3, there are five pipes 5a, 5b, 5c, 5d, and 5e arranged in parallel with each other.
Each pipe 5a, 5b, 5c, 5
Conductance switching valves 6a, 6b, 6c, 6d, and 6e are attached to conductance switching valves 6a, 6b, 6c, 6d, and 6e, respectively. Each of the pipes 5a, 5b, 5c, 5d, and 5e has a different length or diameter, and the conductance is controlled by which one of the conductance switching valves 6a, 6b, 6c, 6d, and 6e is opened.

These conductance switching valves 6a,
A filter 7 for filtering dust is interposed in the gas sampling pipe 3 upstream from the installation positions of 6b, 6c, 6d, and 6e. Filter 7 and conductance switching valve 6a,
6b, 6c, 6d, and 6e, an exhaust pipe 8 is connected to the gas sampling pipe 3, and this exhaust pipe 8
The terminal end is connected to a vacuum pump 9 for evacuation. In the middle of the exhaust pipe 8 are five pipes 10 with different conductances.
a, 10b, 10c, 10d, 10e, each pipe 10a, 10b, 10c, 10d, 10e
conductance switching valves 11a and 1, respectively.
1b, 11c, 11d, and 11e are attached. Further, conductance switching valves 6a, 6b, 6c,
6d, 6e and the mass spectrometer 4, an exhaust pipe 12 is connected to the gas sampling pipe 3.
The terminal end of 2 is connected to a vacuum pump 13 for evacuation. A conductance adjustment valve 14 whose opening degree is variable is installed in the middle of the exhaust pipe 12.

A vacuum gauge 15 for measuring the gas pressure inside the gas sampling tube 3 is provided near the outlet side of the filter 7 of the gas sampling tube 3, and the measured value is output to the control section 16. Further, a vacuum gauge 17 for measuring the gas pressure in the gas sampling tube 3 is provided near the mass spectrometer 4 inlet side of the gas sampling tube 3, and the measured value is output to the control section 16. Further, the exhaust duct 2 is provided with a vacuum gauge 18 that measures the gas pressure within the exhaust duct 2, and the measured value is also output to the control unit 16. The control unit 16 inputs the measurement values obtained by the vacuum gauges 15, 17, and 18, and outputs an adjustment signal for adjusting the opening degree of the conductance adjustment valve 14 based on these measurement values. conductance switching valves 6a, 6b,
Switching signal for opening one switching valve from 6c, 6d, 6e and conductance switching valve 11a, 11
A switching signal for opening one switching valve is output from the switching valves b, 11c, 11d, and 11e.

Next, the operation will be explained.

First, the conductance switching valves 6a, 6
Select one switching valve from b, 6c, 6d, and 6e to open the corresponding pipe, and select one switching valve from conductance switching valves 11a, 11b, 11c, 11d, and 11e. Leave the pipe open. Further, the conductance adjustment valve 14 is set to an appropriate opening degree. By driving the vacuum pumps 9 and 13, the exhaust gas generated in the vacuum refining furnace 1 is introduced from the exhaust duct 2 through the gas sampling pipe 3 to the mass spectrometer 4, and the components of the exhaust gas are analyzed in the mass spectrometer 4. is analyzed.

In the process of conducting such component analysis,
The opening degree of the conductance adjustment valve 14 is controlled by the control unit 16 so that the measured value at the vacuum gauge 17 is constant. When a pressure change that exceeds the control range of the conductance adjustment valve 14 occurs, the conductance switching valve 6a,
6b, 6c, 6d, 6e and/or conductance switching valve 11a, 11b, 11c, 11d, 11e
is switched by the control section 16. At this time, the control unit 16
In order to avoid delays in conductance switching, the system predicts which piping should be switched next based on the measurement value of the vacuum gauge 18, and opens the conductance switching valve for that piping to the extent that it does not affect the current component analysis. , the exhaust gas is passed through the pipe to replace the gas remaining inside.

As described above, in the component analysis method of the present invention,
The gas pressure on the inlet side of the mass spectrometer 4 is measured and the conductance is controlled so that the measured value remains constant, so even if the pressure of the exhaust gas changes rapidly, the exhaust gas introduced into the mass spectrometer 4 The pressure is always constant, allowing accurate component analysis of exhaust gas. In addition, since the conductance switching valve in the piping where switching is predicted is opened slightly before the actual switching, it is possible to compensate for the delay time when switching the conductance, and it is possible to accurately replace the gas in the piping with exhaust gas. Component analysis is performed and continuous component analysis is possible.

Next, an example of pipe switching performed by implementing the component analysis method of the present invention will be described. FIG. 2 is a graph showing an example of switching from piping 5a to piping 5b, where the horizontal axis represents time and the vertical axis represents the opening degree of piping 5a (conductance switching valve 6a), ), the gas pressure on the inlet side of the mass spectrometer 4 (measured value by the vacuum gauge 17), and the component analysis value. Further, T1 indicates the timing at which piping 5b starts to open, predicting that the piping to be switched next is piping 5b, and T1
2 indicates the timing at which the switching command is actually issued, and the gas remaining in the pipe 5b is replaced with the exhaust gas from the vacuum refining furnace 1 between T1 and T2. Then, between T1 and T2, the pipe 5a and the pipe 5b
By controlling the opening degree as shown in A and B in the figure, the gas pressure on the inlet side of the mass spectrometer 4 is kept constant (see C in the figure).
be able to. As a result, exhaust gas components can be analyzed continuously without fluctuation (see D in the figure).

[0025]

[Effects of the Invention] As detailed above, in the first invention, since the conductance is controlled based on the measured value of the inlet side pressure of the analyzer, the pressure of the exhaust gas introduced into the analyzer can always be kept constant. It is possible to analyze exhaust gas components with high precision. In addition, in the second invention, the pipe to be switched next is predicted, and the predicted pipe is opened and exhaust gas is introduced in advance of the actual switching timing to the extent that it does not affect the component analysis. It is possible to compensate for time and perform accurate component analysis continuously.

As a result, according to the invention of the present application, continuous sampling and component analysis of the exhaust gas from the vacuum smelting furnace are possible, and the amount of decarburization, dehydrogenation, etc. in the vacuum smelting furnace can be stably measured. The present invention has excellent effects such as being able to control the end point carbon value, end point hydrogen value, etc. with high precision.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of an apparatus for carrying out a method for analyzing exhaust gas components in a vacuum refining furnace according to the present invention.

FIG. 2 is a graph showing an example of piping switching in the exhaust gas component analysis method of the present invention, and the relationship between the inlet pressure of the mass spectrometer and the component analysis value.

FIG. 3 is a schematic diagram showing the configuration of an apparatus for implementing a conventional exhaust gas component analysis method.

FIG. 4 is a graph showing a relationship between valve switching examples and component analysis values to explain problems in the conventional exhaust gas component analysis method.

[Explanation of symbols]

1 Vacuum refining furnace 2 Exhaust duct 3 Gas sampling pipe 4 Mass spectrometer 5a, 5b, 5c, 5d, 5e Piping 6a,
6b, 6c, 6d, 6e Conductance switching valve 8 Exhaust pipe 9 Vacuum pump 10a, 10b, 10c, 10d, 10e Piping 1
1a, 11b, 11c, 11d, 11e Conductance switching valve 12 Exhaust pipe 13 Vacuum pump 14 Conductance adjustment valve 16 Control unit 17 Vacuum gauge

Claims (2)

[Claims] 1. The exhaust gas discharged from the vacuum refining furnace through a flue during vacuum refining is introduced into an analyzer via a sampling pipe communicating with the flue, and the analyzer analyzes the components of the exhaust gas. In the analysis method, a control device that continuously changes and controls the conductance and a pressure gauge that measures the pressure of the exhaust gas are arranged in this order from the flue side in the sampling pipe, and the measured value of the pressure gauge is kept constant. A method for analyzing exhaust gas components in a vacuum refining furnace, characterized in that the control device continuously changes and controls the piping conductance so that the control device achieves the following. 2. The control device has a plurality of pipes having different pipe characteristics, continuously controls the conductance by sequentially switching the plurality of pipes, and predicts the pipe to be switched next. 2. The method for analyzing exhaust gas components in a vacuum refining furnace according to claim 1, wherein the exhaust gas to be analyzed is passed through the predicted piping before actually switching to the predicted piping.