JPH0933346A - Process monitoring method using ftir - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the detection of an abnormality and facilitate the factor analysis of the abnormality by providing a plurality of cells differed in length in parallel to each other, switching one cell to another cell differed in cell length, when an indication abnormality which is not observed in usual measurement is detected, so that the measurement can be continued. SOLUTION: When a sample S is supplied to a long cell 1 in the state where the infrared ray from a Fourier transform infrared spectrophotometer(FTIR) optical system 3 is emitted to the cell 1, the interferogram of the sample S is obtained from an infrared detector 5. This interferogram is Fourier- transformed at a high speed in a CPU 13, and converted into the infrared power spectrum transmitted by the sample S. Whether the density alue of a main component or disturbance component is within a normal range or not is judged in an abnormal condition judging unit 14. When the density value exceeds the normal range, the introduction switching instruction of sample from the CPL 13 is transmitted to a sampling unit 7, and the sample supplying route is switched in the unit 7 to supply the sample S to a short cell 2 with short optical path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention irradiates a sample supplied to a cell with infrared light and quantitatively analyzes the concentration of components contained in the sample based on the absorption spectrum obtained at that time. The present invention relates to a process monitoring method using an FTIR (Fourier transform infrared spectrophotometer).

[0002]

2. Description of the Related Art A process of a petroleum refining plant or the like has been monitored by using a gas chromatography device. However, since it is difficult to discriminate a process abnormality, in recent years, an FTIR consisting of a single cell has been used. It has come to be used for process management.

[0003]

By the way, when the refining plant is once stopped and then restarted, components other than the components to be measured are often mixed. For example, when purifying ethylene (C ₂ H ₄ ) from crude oil, Propylene (C ₃ H ₆ ) may be mixed into ethylene at the time of starting up. Compared with ethylene, this propylene absorbs infrared light more easily and has many absorption sites, and when ethylene is quantitatively analyzed by FTIR, propylene acts as an interfering component.

However, in the conventional process monitoring using FTIR, FTIR having a single cell is used, so that the following problems occur. That is, when performing process control using FTIR consisting of a single cell, it is necessary to know in advance the type of sample supplied to the cell and its concentration range. When mixed, the detected concentration of ethylene, which is the measurement target component, fluctuates due to infrared absorption by the mixed propylene, and the concentration of ethylene cannot be detected depending on the concentration of propylene, and the concentration of propylene itself is also detected. It may not be possible.

This is because propylene, which is an interfering component, has a stronger infrared absorption than ethylene, which is the component to be measured, and it is difficult to detect ethylene. This is because if the concentration of propylene, which is a component, is unexpectedly high, the concentration cannot be detected.

It is considered that such inconvenience occurs not only in the oil refining plant but also in various chemical plants.

The present invention has been made in consideration of the above-mentioned matters, and provides a process monitoring method using FTIR capable of surely detecting a process abnormality and easily analyzing the cause of the abnormality. It is an object.

[0008]

In order to achieve the above object, in the present invention (hereinafter referred to as the first invention), a sample supplied to a cell is irradiated with infrared light, and an absorption spectrum obtained at that time is obtained. In a process monitoring method using FTIR for quantitatively analyzing the concentrations of components contained in a sample based on the above, a plurality of cells having different cell lengths are provided in parallel with each other to detect an anomaly of an indication that is not seen during normal measurement. At this time, the measurement can be continued by switching to another cell having a different cell length.

The present invention (hereinafter referred to as the second invention)
Then, irradiate the sample supplied to the cell with infrared light,
In a process monitoring method using FTIR that quantitatively analyzes the concentrations of components contained in a sample based on the absorption spectrum obtained at that time, a sampling unit is provided in the preceding stage of the cell to detect an abnormal indication that is not seen during normal measurement. At that time, the diluted sample is supplied to the cell to continue the measurement.

[0010]

According to the first aspect of the present invention, for example, when an abnormality occurs in a process in a petroleum refining plant and an indication abnormality is detected due to the abnormality, a sample having a high concentration of components (interfering components) other than the normal measurement target component is detected in the cell. It is introduced into a short cell and measured. As a result, the measurement can be continued without interruption, and the concentration of the non-measurement target component and the normal concentration of the measurement target component can be detected. Then, based on the concentration detection result of the non-measurement target component, process control of the petroleum refining plant is performed so that the non-measurement target component (interfering component) disappears, whereby the original operation can be restored.

In the second aspect of the invention, when the indication abnormality is detected, the non-measurement is performed by diluting the sample mixed with the non-measurement target component having a high concentration other than the normal measurement target component to a concentration detectable level. It is possible to detect the concentration of the target component and the usual concentration detection of the target component. Also in the second aspect of the invention, the oil refining plant is process-controlled so that the non-measurement target component disappears based on the concentration detection result of the non-measurement target component, whereby the original operation can be restored.

The sample handled in both of the above inventions may be either a gas or a liquid. When the sample is a gas, nitrogen gas is suitable as the diluent gas.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings. First, the first invention will be described. FIG. 1 and FIG. 2 show an embodiment of the first invention.
FIG. 2 schematically shows the configuration of a system for carrying out a process monitoring method using FTIR (hereinafter, simply referred to as a process monitoring method), and FIG. 2 is a flowchart showing an operation in the process monitoring method.

In FIG. 1, reference numerals 1 and 2 denote cells to which the sample S is supplied. The both ends of a corrosion-resistant cylinder are sealed with infrared transmitting cell windows, and a sample inlet and outlet are provided. And are arranged optically parallel to each other,
The cell length of cell 2 is made much smaller than that of cell 1. Hereinafter, the cells 1 and 2 may be referred to as a long cell and a short cell, respectively. 3 is an FT provided on one end side of the cells 1 and 2
The IR optical system is composed of an infrared light source and an interferometer, which are not shown in detail. Reference numeral 4 denotes an optical path switching device provided between one end side of the cells 1 and 2 and the FTIR optical system 3, which is composed of one or a plurality of reflecting mirrors. It irradiates the crab.

Reference numeral 5 denotes an infrared detector provided on the other end side of the cells 1 and 2, which is, for example, a semiconductor detector. Reference numeral 6 denotes an optical path switching device provided between the other end of the cells 1 and 2 and the infrared detector 5, which is composed of one or a plurality of reflecting mirrors and transmits infrared light transmitted through either of the cells 1 or 2 to infrared rays. The light is incident on the detector 5.

The optical path switching devices 4 and 6 perform a switching operation in cooperation with each other. For example, when the optical path switching device 4 is switched to guide infrared light to the cell 1 side, the optical path switching device 6 operates as a cell. The infrared light transmitted through 1 is an infrared detector 5
It is switched so that it is incident on.

Although not shown in detail, 7 is a sampling unit provided in front of the cells 1 and 2, and comprises a plurality of solenoid valves and pipes, and is shown in accordance with a command from the sampling controller 8. A sample (for example, sample gas) S from a sample source which is not provided is supplied to one of the cells 1 and 2. Reference numerals 9 and 10 denote sample introduction paths to the cells 1 and 2, and reference numerals 11 and 12 denote sample introduction paths from the cells 1 and 2.

The switching operation of the sampling unit 7 for supplying the sample S to which of the cells 1 and 2 is interlocked with the optical path switching operation of the optical path switching devices 4 and 6.

Reference numeral 13 is a control / arithmetic unit for control / data processing of the process monitoring system, which outputs control signals to the FTIR optical system 3, the optical path switching devices 4 and 6, the sampling controller 8, and the infrared detector 5. The data is processed on the basis of the signal from to calculate the component concentration. An abnormal condition determination unit 14 is for determining whether or not the component concentration (concentration of the measurement target component or the interfering component) obtained by the control / calculation unit 13 is within a predetermined range.

As can be understood from the above description, in FIG. 1, the single line indicates the flow of the sample S, the double line indicates the optical path, and the thick line indicates the signal flow.

The operation of the process monitoring device configured as described above will be described with reference to FIG.

In the ordinary measurement, the long cell 1 is used for the measurement. That is, the optical path switching devices 4, 6 and the sampling unit 7 are switched to the long cell 1 (long optical path) side. Then, by supplying the sample S to the long cell 1 while the long cell 1 is being irradiated with the infrared light from the FTIR optical system 3, an interferogram of the sample S is obtained from the infrared detector 5 ( Step S1).

Then, the interferogram is subjected to fast Fourier transform in the control / calculation unit 13 to obtain a sample S
Is converted into the power spectrum of the infrared light transmitted through.
Further, based on the ratio of the power spectrum and the power spectrum of the comparative gas obtained in advance, the absorption spectrum of infrared light by the sample S is obtained, and then the absorbance at a plurality of wave number points in this absorption spectrum is calculated. Based on this, the concentrations of the components contained in the sample S are calculated (step S
2).

Here, in the abnormal condition discriminating unit 14, it is judged whether or not the concentration value of the main component (measurement target component) or the interference component (non-measurement target component) is within the normal range (step S3). , Step S4), if both the concentration values are within the normal range, the measurement is continued as it is. However, if both the concentration values exceed the normal range, An introduction switching command is sent to the sampling unit 7 via the sampling controller 8, whereby the sampling unit 7 switches the sample supply path and the sample S is supplied to the short cell 2 of the short optical path. At this time, an optical path switching command from the control / calculation unit 13 is sent to the optical path switching devices 4 and 6,
These 4 and 6 operate to switch the infrared light from the FTIR optical system 3 so that the short cell 2 is irradiated with the infrared light (step S5).

Then, this time, the measurement is performed using the short cell 2 in the same manner as in step S1 (step S1).
6) and the component concentration is calculated in the same manner as in step S2 (step S7).

Here, it is judged whether the density value of the disturbing component or the density value of the main component is within the normal range and whether the density value of the disturbing component is within the target range (steps S8 and S9). , Step S10), if the concentration value of the interfering component or the concentration value of the main component is out of the normal range or the concentration value of the interfering component is outside the target range (exceeds the target range), the state is kept as it is. That is, the oil refining plant is process-controlled so that the measurement is continuously performed using the short cell 2 and the interfering components are eliminated.

When the main component and the disturbing component fall within a predetermined range as a result of the above process control, the control / calculation unit 13
In response to a command from the sampling controller 8, the sampling controller 8 operates to supply the sample S to the long cell 1 of the long optical path through the sampling unit 7, and the optical path switching devices 4 and 6 operate to operate the FTIR optical system. The infrared light from 3 is switched to irradiate the long cell 1 (step S11), and the normal measurement, that is, the measurement by the long optical path is performed again (step S1).

As can be understood from the above description of the operation, according to the first aspect of the invention, the cells 1 and 2 having different cell lengths are selectively used. A very high component (interfering component) is mixed in, and in the measurement by the long cell 1, all infrared light is absorbed, and it is wisely avoided that the ordinary measurement target component cannot be measured, and continuous measurement is performed. Can be done.

Further, it is possible to reliably detect the abnormality of the process and easily analyze the cause of the abnormality.
It can greatly contribute to the smooth operation of the process.

FIG. 3 shows another embodiment of the first invention. In FIG. 3, the FTIR optical system 3 is separated into an infrared light source 15 and an interferometer 16, and the infrared light source 15 and the cell are separated. 1,
2 and 2 are arranged in front of the interferometer 16. Even when configured in this manner, the same operation as that shown in FIG.
Since the same effect is obtained, the description thereof will be omitted.

In the embodiment of the first invention described above, two cells having different cell lengths are provided in an optically parallel state, but the number of cells having different cell lengths is not limited to this. The above may be provided in an optically parallel state. Although the CPU 13 and the abnormal condition determination unit 14 are separately configured, they may be integrated, or the abnormal condition determination may be performed by the CPU 13 according to a program.

Next, the second invention will be described. 4 and 5 show an embodiment of the second invention.
5 schematically shows the configuration of a system for carrying out the process monitoring method, and FIG. 5 is a flowchart for explaining the operation in the process monitoring method. Further, in FIG. 4, the same symbols as those in FIG. 1 denote the same items.

In FIG. 4, reference numeral 21 denotes a cell to which the sample S is supplied. Both ends of a tube body having an appropriate length and having corrosion resistance are sealed with infrared transmitting cell windows, and a sample inlet and outlet are provided. Be prepared. The FTIR optical system 3 is provided on one end side of the cell 21, and the infrared detector 5 is provided on the other end side.
Are provided respectively.

Reference numeral 22 denotes a sampling unit provided in the preceding stage of the cell 21. Although not shown in detail, the sampling unit 22 is provided with a diluting device including a plurality of solenoid valves, capillaries, pipes, etc. On the basis of the above, the sample S from a sample source (not shown) is supplied to the cell 21 as it is (without being diluted), or the sample S is appropriately diluted with an appropriate diluent gas (for example, nitrogen gas) D to obtain the cell 21. Is to be supplied to.

The operation of the process monitor configured as described above will be described with reference to FIG.

In normal measurement, the FTIR optical system 3
While irradiating the cell 21 with infrared light from
The sample S is supplied to 1 without being diluted, and the interferogram of the sample S is obtained from the infrared detector 5 (step S21).

Then, the interferogram is fast-Fourier-transformed in the control / calculation unit 13 to obtain a sample S
Is converted into the power spectrum of the infrared light transmitted through.
Further, based on the ratio of the power spectrum and the power spectrum of the comparative gas obtained in advance, the absorption spectrum of infrared light by the sample S is obtained, and then the absorbance at a plurality of wave number points in this absorption spectrum is calculated. Based on this, the concentrations of the components contained in the sample S are calculated (step S2
2).

Here, it is determined whether or not the density value of the main component (measurement target component) or the interference component (non-measurement target component) is within the normal range (steps S23 and S2).
4) If both the concentration values are within the normal range, the measurement is continued as it is. However, if both the concentration values exceed the normal range, the command from the control / calculation unit 13 is the sampling controller. After being sent to the sampling unit 22 via 23, the diluting device in the sampling unit 22 operates to dilute the sample S with the dilution gas D (step S25). In this case, the control / calculation unit 13 outputs a command for setting the dilution ratio that is considered to be optimum from the obtained data.

Then, this time, the diluted sample S is supplied to the cell 21, the measurement is performed in the same manner as in step S21 (step S26), and the component concentration is calculated in the same manner as step S22 (step S22). S27).

Here, in the abnormal condition judging unit 14, it is judged whether or not the disturbing component can be measured (step S28). If the disturbing component cannot be measured even by the dilution, the dilution rate is changed (step S29). The measurement is performed again (step S26). If it is determined in the abnormal condition determination unit 14 that the interference component can be measured, whether the concentration value of the interference component or the concentration value of the main component is within the normal range and whether the concentration value of the interference component is within the target range are determined. It is determined whether or not there is (step S30, step S
31, step S32), if the density value of the interfering component or the density value of the main component is outside the normal range or the density value of the interfering component is outside the target range (exceeds the target range), step S26 Returning to step 1, the diluted sample S is continuously measured, and the petroleum refining plant is process-controlled so as to eliminate interfering components.

When the main component or the disturbing component falls within a predetermined range as a result of the above process control, the control / calculation unit 13
In response to a command from the sampling controller 23, the sampling controller 23 operates to stop the operation of the diluting device in the sampling unit 7 (step S33), and the normal measurement,
That is, the measurement is performed using the sample S that is not diluted (step S21).

As can be understood from the above description of the operation, according to the second aspect of the invention, when an abnormality occurs in the process, the sample S
Since it is designed to be diluted, as in the first aspect of the invention described above, it is possible to skillfully avoid the inability to measure the normal measurement target component, and it is possible to perform continuous measurement, and reliably detect process abnormalities. Therefore, the factor analysis of the abnormality can be easily performed, and it can greatly contribute to the smooth operation of the process.

The second invention may also be configured in the same manner as the modification shown in FIG. That is, although illustration is omitted, the FTIR optical system 3 may be separated into an infrared light source and an interferometer, and the infrared light source and the cell 21 may be arranged in the preceding stage of the interferometer.

[0044]

As described above, according to the present invention, when the process is monitored, an abnormality occurs in the process, and when the indicated abnormality is detected, the cell used for measurement has a long cell length. From short to short,
Alternatively, since the absorbance is lowered by appropriately diluting the sample, the measurement can be continued.

Further, according to the present invention, it is possible to reliably detect the abnormality of the process and easily analyze the cause of the abnormality. Therefore, the process can be operated more smoothly.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an example of a configuration of a system for carrying out a process monitoring method according to a first invention.

FIG. 2 is a flowchart for explaining an operation in the process monitoring method.

FIG. 3 is a diagram showing another embodiment of the first invention.

FIG. 4 is a diagram schematically showing an example of a configuration of a system for carrying out the process monitoring method according to the second invention.

FIG. 5 is a flowchart for explaining an operation in the process monitoring method.

[Explanation of symbols]

1, 2, 21 ... Cell, 22 ... Sampling unit, S
…sample.

Claims (2)

[Claims] 1. A process monitoring method using FTIR, which comprises irradiating a sample supplied to a cell with infrared light and quantitatively analyzing the concentration of components contained in the sample based on the absorption spectrum obtained at that time. , A plurality of cells having different cell lengths are provided in parallel with each other, and when an abnormal indication that is not seen during normal measurement is detected, the measurement can be continued by switching to another cell having a different cell length. A process monitoring method using FTIR. 2. A process monitoring method using FTIR, which comprises irradiating a sample supplied to a cell with infrared light and quantitatively analyzing the concentrations of components contained in the sample based on the absorption spectrum obtained at that time. A sampling unit is provided in the preceding stage of the cell, and when an abnormal indication that is not seen in normal measurement is detected, the diluted sample is supplied to the cell to continue the measurement. Process monitoring method using FTIR.