JPH07181097A - Method for detecting new leak source under track leak gas atmosphere - Google Patents

Abstract

PURPOSE:To detect a new leak source accurately by a method wherein the statistic properties of a trace leak gas BGL is extracted and the BGL concentration estimated therefrom is removed from the concentration data or the variation thereof is monitored. CONSTITUTION:The time series data of BGL concentration measured by a plurality of high sensitivity sensors 20 set in a plant 40 is processed statistically along with the time series data of the speed and direction of wind measured by a wind speed/wind direction measuring apparatus 30 thus extracting the temporal/spatial properties of BGL inherent to the plant 40. The gas concentration estimated from the statistic properties is then subtracted from a gas sensor data sampled every moment and the time series of the difference is monitored or the statistic properties of BGL themselves are monitored thus detecting a new leakage. Furthermore, trade-off between the error rate and the missing rate can be managed rationally and reduced sufficiently through the simulation leak test of actual plant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a gaseous substance such as a gas or a vapor leaked from an apparatus or equipment of the plant in a plant handling a combustible or toxic substance in a gaseous, liquid or solid state. The present invention relates to a detection system for detecting abnormal leakage that newly occurs even in a very small leak gas (BGL) environment unique to a plant with a low false alarm rate and a missing rate.

[0002]

2. Description of the Related Art In the "High Pressure Gas Control Law" which regulates industries such as chemical industry and petroleum refining, gas sensors are installed at the outer edge of a facility handling combustible gas at intervals of 20 m or less, and the gas sensor explodes. It is specified that it has a detection performance capable of detecting a combustible gas showing a concentration equal to or higher than a quarter of the limit, and a catalytic combustion type combustible gas detector has been generally used as a detector corresponding to this. By the way, the legally set concentration of isobutane, which is a standard indicator substance for combustible gas detectors, is 4500 ppm, and for ethylene, it is 675
It is 0 ppm. In recent years, a hot wire semiconductor type, which has a higher detection sensitivity than the contact combustion type, has begun to be used as a type of combustible gas detector. The semiconductor flammable gas detector can confirm the change in the indicated value at a concentration of about 1 ppm for flammable gases such as ethylene and isobutane, but other background concentrations are high in the actual plant yard. Therefore, it has not been used for the detection of minute leaks of about several ppm while having a high-sensitivity measurement capability.

The cause of the background density is
(I) In plants that have been operated for many years after construction, there is always a minute leakage that does not exceed the legally set concentration, and it fluctuates on the order of several PPM, and (ii) also flammable. 5 to 1 depending on atmospheric temperature / humidity change
This is because there is a “zero point” variation equivalent to 0 ppm.

Due to the above-mentioned problems, there is no method for detecting early minute leaks using industrial gas detectors, except for expensive equipment such as infrared spectrophotometry or gas chromatography. It was Therefore, there is no published method for identifying abnormal leakage in the normal minute leakage gas atmosphere.

[0005]

In a plant that has been built for a long time, the concentration is lower than the gas detector reporting standard (1/4 of the lower explosion limit concentration) specified by law, but it is always small. There is a small amount of leak gas (hereinafter referred to as BGL: background leak). Under such a BGL environment, the increase in gas concentration due to abnormal leakage that newly occurs due to damage to the gasket of the pipe flange or valve gland is not clearly seen, so there is a high possibility that it will not be discovered until it develops into a large leak. It was

In general, the false alarm rate and the false alarm rate have mutually contradictory properties. If the alarm setting is lowered to prevent the false alarm, false alarm will occur, and if the alarm setting is increased to prevent false alarm, the false alarm rate will be lost. The information will increase. The purpose of the present invention is to reasonably balance both the false alarm rate and the false alarm rate.
Even in the environment, a new abnormal leak is identified and an alarm is issued, and the BGL concentration range that the gas detection system is trying to detect is directly affected by zero-point drift due to changes in atmospheric temperature and humidity of the high-sensitivity gas sensor. Therefore, it is to provide a method for improving the accuracy of the sensor by correcting this influence.

[0007]

The above object is to detect gas leaking from a plant in a plant handling combustible or harmful substances in which a very small amount of leaked gas (BGL) is always present, as shown in the present invention. Using a system consisting of a group of high-sensitivity gas sensors, an anemometer and a wind direction meter, and a data processing system that processes these sensor signals, time series data of BGL concentration and wind direction wind speed observed by multiple sensors during normal operation From time series data of BGL
Of the new leakage source by extracting the statistical properties of BGL concentration and removing the BGL concentration estimated based on this statistical property from the observed concentration data, or by monitoring the changes in the statistical properties themselves. It can be solved by applying the detection method.

There are the following three methods for statistically processing the time series data of the gas sensor and extracting the properties of BGL. (A) Macromass balance method (method of estimating the total amount of BGL in the target yard) One of the reasons why the BGL concentration fluctuates irregularly is that there is no wind or a slight breeze of 0.5 m / sec or less within the yard within a certain time. It is considered that the gas is retained in the room and that the gas moves in the next time interval. This method defines a total amount of BGL in the yard that changes momentarily due to a change in the wind direction and wind speed, and attempts to identify a new leak by defining the past BGL concentration data.

Assuming that there is no new outflow or intrusion from the outside, the rate of decrease of the gas existing in the target yard is determined by the amount of gas itself η at that time.
(M ³ ), the wind speed v (m / sec), and the average moving distance (pseudo yard radius) L (m) of the gas until reaching the outside of the yard can be expressed as follows.

Dη / dt = − (v / L) η (1) From the equation (1), the reference time t = 0 When gas amount eta ₀ in, η = η ₀ e ^{chromatography (v / L) t} ............................ ..... (2) On the other hand, when the amount of gas newly generated in the time section from t = 0 to t = T is φ (m ³ / sec), the gas generated at this time is t = T The remaining amount is (L / v) φ (1－e－ ^{(v / L) T} ) ....................... (3) Therefore, when considering the data in intervals of T seconds, η _N (m ³ )
The gas becomes η _{n + 1} after T seconds by using (2) and (3).

Η _{n + 1} = η _n e- ^{(v / L) T} + (L / v) φ (1-e- ^{(v / L) T} ) .... (4) The pseudo yard radius is a plane For a typical plant, L =
(S / π) 1/2, for a three-dimensional plant L =
(3V / 4π) 1/3 is determined. However, S shows a plant area and V shows a plant volume. For a time average over a sufficiently large T, equation (4) can be expressed as:

Η _AV = (L / v _AV ) φ _AV ........................ (4) ' The sensor average BGL concentration C _AV is C _AV = μ (L / v _AV V) φ _AV ..................... (5) μ: Expressed as a correction coefficient for judgment. Expected BGL concentration from the average value of all sensors actually observed

[0013]

[Outer 1] A new abnormal leak is detected by monitoring the corrected sensor data after subtracting. That is,

[0014]

[Equation 1] Then, there is no new leak.

[0015]

[Equation 2] Then, a new leak occurs.

ΔC is an appropriately set threshold parameter. Here, how to take the average time T is determined in accordance with changes in the weather conditions peculiar to the system installation place. (B) Spatial correlation method BGL of each gas sensor at a certain sampling time interval
When the correlation between the time averages was examined, it was found that there was a certain relation that did not depend on the time, and that this represented the spatial characteristics peculiar to the target plant. In the short term, the BGL gas that is constantly floating in the plant changes according to the wind direction and wind speed data at that time, but if the time average is taken over a certain period of time, the relationship between the BGL gas sensor data will vary depending on the equipment. It is thought to represent some pattern associated with gas transfer paths in a dense plant.

Now, the total amount of leakage in the target yard is φ (m3)
Then, if the average BGL concentration Cm of all sensors is proportional to φ, then Cm = Kφ. ........... (6) Therefore, the total of the BGL concentrations of the N sensors is constant.

[0018]

[Equation 3] Here, if C ₁ changes to 0.5 * C ₁ , there is a possibility that C ₂ and C ₃ adjacent to each other may change to 1.2 * C ₂ and 1.3 * C ₃ , respectively. Therefore, an appropriate weighting factor a =
Even if (a ₁ , a ₂ , ..., A _N ) is introduced, it is considered that the sum total constant of the equation (7) holds.

[A _i ] [C _j ] ^T = constant (Σa _i * C _i = K) ... (8) [a _i ] is a space that affects the pattern of the BGL distribution Considered as a vector. Representing the i-th BGL value from equation (8)

[0020]

[Equation 4] If you rewrite this,

[0021]

[Equation 5] The BGL concentration of the sensor i can be expressed by the linear sum of the BGL concentrations of other sensors plus a constant term. Here, the coefficient a _j 'is a coefficient representing the spatial correlation existing between the sensor i and the sensor j. If there is time series data of BGL concentration collected in the past, BGL estimated value of each sensor when regression analysis is performed using this.

[0022]

[Outside 2] Formula (9) 'for calculating is created. Focusing on the difference between the newly observed concentration C _{i of} the sensor i and the sensor i estimated using the spatial correlation coefficient up to this point, a new leak can be detected as follows.

[0023]

[Equation 6] Then there is no new leak.

[0024]

[Equation 7] Then there is a new leak. However, k is an integer from 1 to n. φ is 1
It is a binary variable that takes a value of 0 or 0.

[0025]

[Equation 8] When, when _{φ i = 1, φ i =} 0, Δ is the appropriate threshold. (C) Method by statistical test Matching between the fluctuation pattern of BGL time history measured by the gas sensor (reference data block) and the latest data time series (current block) collected in a certain time interval is statistically performed. As a method (non-parametric test) to be performed on, for example, run test or Man-Whitney
There is a U test.

Here, a method of judging the presence or absence of new leakage using the U test will be described. Now, calculate the BGL total amount φ defined by the previous macro mass balance method at each time,
Create φ time series data. The number of BGL total time series data of the current block is N ₁ , and the BG of the reference block is BG
Let L be the total amount of time-series data, N ₂ . Both of the N ₁ + N ₂ total BGL total amount data are arranged in descending order, and the ranks of the BGL total amount data belonging to the current block are summed, and this is designated as R ₁ . In _{this, U = N 1 N 2 +} N 1 (N 1 +1) / 2 - R 1 E = N 1 N 2/2, V = N 1 N 2 (N 1 + N 2 +1) / 12 Z = If (Z) obtained by (UE) V / 2 exceeds the threshold of U-test continuously for a set number of times or more, it is determined that there is a leak.

The determination threshold of Z is determined according to the significance level of the test. For example, in the actual verification test by the inventors, the following determination was made, and if the new leakage amount is more than twice the total BGL amount, the detection probability within 20 minutes is 95% or more, and the false alarm rate is 15% or less. Met. New leak identification cycle: 1 minute Number of consecutive tests required for leak detection: 20 times U-test threshold: 90% Significance level Z
= 1.65 95% significance level Z = 1.96 99% significance level
Z = 2.57 99.8% significance level Z = 3.09 Further, the correction of the influence of atmospheric temperature and humidity change of the high sensitivity gas detector described in claim 3 is as follows. Know the relationship between the concentration of combustible gas in the atmosphere measured under a certain temperature and humidity condition and the indicated value of the sensor (hereinafter referred to as "reference calibration curve"). Sensor indication when the flammable gas concentration is "zero" under different temperature and humidity conditions (hereinafter called "zero point"),
The difference between the "zero point" and the "zero point" of the "reference calibration curve" is subtracted from the sensor instruction when measuring the flammable gas under the conditions. (Hereinafter referred to as "correction instruction value") "correction instruction value"
Is applied to the “reference calibration curve” to obtain a correction value for the measured value of flammable gas. A sensor installed at a fixed point in a facility subject to detection of flammable gas may have some leakage at the time of measurement, and therefore does not always indicate a "zero point". For this reason, it is necessary to measure the "zero point" under the conditions of almost the same temperature and humidity as the measurement point and in the presence of almost no combustible gas. However, it is difficult for a sensor installed at a fixed point to track the "zero point" fluctuations of a day and to be frequently under those conditions. Therefore, on behalf of the sensors in the facility, an independent sensor for constantly measuring the "zero point" (hereinafter referred to as "correction sensor") is installed, and the fluctuation of the "zero point" is used to correct the fluctuations of other sensors. To use.

Select a location near the combustible gas detection target facility where the temperature and humidity conditions are nearly equal and almost no combustible gas comes, and install a high-sensitivity sensor as a "correction sensor". Although it is difficult to find an ideal place that completely satisfies these conditions, the correction effect of the present invention does not disappear even under incomplete conditions. In order to compensate for these conditions, a method of covering the sensor with a special resin film that selectively permeates only moisture in the atmosphere, and adsorption that supplements only the flammable gas in the atmosphere that passes through the gas detection part of the sensor The use of agents is also conceivable.

Since the "correction sensor" serves as a reference for other sensors, it is desirable to install a standby redundant sensor in consideration of failure and reliability of measured values within the scope of cost constraint. However, since the information on the zero point drift from the correction sensor is applied to all the other sensors, only one functionally needs to be used. The accuracy of detecting a new leak by these means is evaluated by the incidences of false alarms (reporting when there is no new leak) and missing reports (not reporting when there is a new leak). When the total amount of BGL is Qm3 / hr, the present invention provides a new leakage of about 1.5 times as much as 1 leakage.
It can be found with a false alarm rate and missing rate of 0% or less (defined by the time ratio of the new leakage continuation time and the reporting time). However, the target marginal false alarm rate and missing alarm rate can be adjusted according to the psychological reaction of the plant operator.

That is, in the former macro mass balance method, the threshold value for the corrected sensor data (from the actual measurement value to the predicted BG
In the latter spatial correlation method, it is possible to make adjustments by taking parameters such as parameter k (when more than k out of n sensors exceed the threshold value, it is considered as a new leak). is there. In the former case, the higher the threshold value and in the latter case, the higher the parameter k is, the more false alarms decrease, but the false alarm increases. Therefore, do not treat alarms in a uniform manner, first set a parameter that produces a low miss rate even if there are some false alarms, issue a caution, and then refer to additional information after that. It is also a practical countermeasure to adopt a two-step method that issues an alarm with a parameter with a lower false alarm.

[0031]

[Operation] A plant that has been in operation for a long time since construction has a high possibility of fire or explosion due to leakage of flammable gas from aged deterioration parts such as piping gaskets and pump shaft sealing parts, so early There is a need to detect small amounts of gas diffusion. Therefore, industrial gas sensors such as hot-wire semiconductor type sensors that can detect low concentration regions far below the lower limit concentration of explosion, which is an alarm set value by law, have come to be marketed. Sensitive sensors are replacing older sensors that have reached the end of their useful life.

However, in an actual existing plant, since very small BGLs are always present, even if a high-sensitivity gas sensor is installed, a signal that is a sign of a new abnormal leak is generated by this BGL. It was buried in the inside and could not achieve the above needs. In addition, when detecting a new leak under such a BGL environment, an error (not reported) that is not issued when originally required to be issued and an error that is issued when not issued (misreport) I face the problem of how to reasonably trade off two conflicting error modes.

The present invention provides time-series data of BGL concentration measured by a plurality of high-sensitivity sensors installed in the plant,
And, the time series data of the wind speed and the wind direction at that time are statistically processed, the temporal and spatial properties of BGL peculiar to the plant are extracted, and the gas concentration value estimated from the statistical properties is calculated. It is possible to detect new leaks by monitoring the time series subtracted from the gas sensor data taken from moment to moment, or by monitoring the statistical nature of BGL itself. It has been confirmed by a simulated leakage test in an actual plant that the discovery method proposed in the present invention can reasonably manage the tradeoff between the false alarm rate and the missing rate, and reduce both until it is sufficiently used. .

Further, in order to effectively utilize the discovery of a new leak under the BGL environment, the present invention proposes a method for always automatically correcting the zero point drift due to the temperature and humidity changes of the gas sensor itself. This makes it possible to more markedly identify the sign of new leakage from a slight change in gas concentration.

[0035]

[Example] Next, "leak detection system for gas, steam, etc.,
An embodiment in which the present invention is applied to the equipment shown in the embodiment of the wind direction and wind speed measuring device (Japanese Patent Laid-Open No. 05-231979) will be described with reference to the drawings. However, the present invention is not limited to the embodiment using the multi-point sampling module described below, and in the case of using a high-sensitivity sensor in a minute leak gas atmosphere even in the conventional point monitoring type gas detection system. Is applicable to. Target Plant: FIG. 1 is a plan view of a plant in which a leak point and a gas leak detection system according to an embodiment of the present invention are installed. This example is an example applied to a liquefied ethylene production plant, and as shown in FIG. 1, L1XL2 = 80 mX
Eight sets of module sets M ₁ , M ₂ , M ₃ , M ₄ , M ₅ , M ₆ , M ₇ , consisting of the sampling module 10 and the sensor module 20 in a plant yard 40 of 50 m.
M ₈ is installed. Sampling module 10,
Also, the sensor module 20 is disclosed in Japanese Patent Laid-Open No. 05-2319.
The same as 79 was used.

The sampling module 10 is 2-3 above the ground.
It is placed at a height of m, screws are attached to the side of the gas pipe at intervals of 2 m, 20 air conduits open at both ends and connected to the air conduit, and a perforated plate is attached to the tip to prevent rainwater from entering. Conical air sampler
The gas pipe is connected to the suction pump from the center through the sensor module.

The air collected by the sampling module 10 is introduced into the housing from the sample air inlet nozzle, enters one half of the housing, rises in the space separated by the baffle plate, and is opened on the cylindrical side surface of the punch plate. The gas enters the inside of the sensor through a plurality of holes provided, flows around the gas sensor, moves down one half of the housing, is drawn by the suction pump from the sample air outlet nozzle, and is discharged to the atmosphere from the pump outlet. The gas sensor is in this case a detection sensor for ethylene gas. Generally, when the present invention is applied to a plant, a sensor for a substance handled in the plant is used, but the most preferable model at the present time is a hot wire semiconductor type sensor, and various types are commercially available. The higher the detection sensitivity, the better, but about 1-10 ppm is desirable.
The detected signal is sent to the data processing device via the signal line. The atmospheric gas concentration collected by each sampling module 10 detected by each sensor module 20 and the data measured by the wind direction and wind speed measuring device 30 are transmitted to a data processing device. Temperature and humidity correction of high sensitivity sensor: FIG. 2 shows the calibration curve for ethylene of the hot wire semiconductor gas sensor. From this, it can be seen that the sensor indicated value may be reversed depending on the difference in relative humidity, but has a positive correlation with absolute humidity. Therefore, if some error is allowed, the indicated value can be corrected using the absolute humidity. FIG. 3 shows the principle of the measurement error correction method for the hot wire semiconductor gas sensor according to the present invention.

The present inventors examined the approximation of the “calibration curve” with an algebraic expression. As a result, the following three formulas were obtained. 1) When ethylene concentration is 5ppm or less I = kC + I ₀ ..................... (10) 2) When the ethylene concentration is 5 ppm or more I = a (logC) ⁿ + c .............................. .... (11) or I = a '(logC) ² + b' (logC) + c '... (12) Here, each character shows the following.

I: Sensor indicated value (% to upper limit) I ₀ : Sensor “zero point” indicated value (% to upper limit) C: Ethylene concentration (ppm) k, a, n, c, a ′, b ', C': Coefficients of algebraic formula Further, as shown in Fig. 2, since the "calibration curves" under different temperature and humidity conditions are almost parallel in the range where the ethylene concentration is low, the semiconductor gas sensor due to the difference in temperature / humidity conditions It was found that when the "calibration curves" of (1) were moved in the direction of the vertical axis, they almost overlap each other.

[0040] The relationship between the concentration of combustible gas in the atmosphere measured under a certain temperature and humidity condition and the sensor indicated value-a "standard calibration curve" has been obtained, but in reality, the influence of temperature and humidity during use This causes the calibration curve to change. Therefore, if the change amount ΔI of the “zero point” due to the influence of temperature and humidity is known by the “correction sensor” described above, if the sensor indication value I is replaced with (I−ΔI) and substituted into the calibration curve,
In the region where the concentration is 10 ppm or less, the gas concentration after temperature and humidity correction can be known as a fairly good approximation. 1) When the ethylene concentration is 5 ppm or less I-ΔI = kC + I0 ............ (10) '2) Ethylene concentration Is 5ppm or more I-ΔI = a (logC) n + c (11) 'or I-ΔI = a' (logC) 2 + b ' (LogC) + c '.. (12)' Also, it is desirable that the frequency of sensor correction by the above method is as frequent as possible, but considering the capacity and price of the device used for communication of measurement data and calculation, 1 to 1 A range of once per hour is reasonable. The range of 5 to 20 minutes is desirable under the weather conditions in Japan.

In the plant of FIG. 1, 50 from the outer edge of the plant.
One sensor of the same type was installed outdoors, opposite the plant side of the office at a distance of m, and was used as a "correction sensor".
Atmosphere around this "correction sensor" was sampled in a polyurethane resin gas sample bag, and in order to accurately evaluate the effect of temperature / humidity, the "zero point" of all sensors was measured within 20 minutes after sampling. It was measured. For confirmation, this atmosphere was analyzed by gas chromatography and it was confirmed that hydrogen and hydrocarbon were not mixed in the gas. Table 1 shows the "zero point" readings measured under different atmospheric conditions. Next, the same 50 liters of atmospheric air was sampled in a gas sample bag, and ethylene concentration adjusted by injecting and diluting 99.9% or more of ethylene was 0,
Using the sample gas of 5, 20, 50 and 200 ppm, the indicated value of each sensor is recorded and the calibration curve is determined. Table 2
Is the coefficient of the above-mentioned formulas (11) to (12) obtained as a result. As shown in Tables 3 and 4, the difference in the measured concentration between the case without the above correction and the case with the above correction is 10 pp.
It can be seen that it is considerably reduced in the low concentration region of m or less. New leakage detection under BGL environment: Monitoring sensor data with the above correction enables detection of BGL of 10 ppm or less existing in the plant. When artificial leakage is artificially generated in such a BGL environment, the data observed by the sampling module is, as shown in FIG. 4, the same as to when the new leakage started and when it ended. Does not give clear information.

Therefore, the above-described two methods (macro mass balance method or spatial correlation method) were used to determine the new leakage under the BGL environment. For safety reasons, it is not possible to increase the simulated leak amount indefinitely at the actual plant in operation. Therefore, the sensor data observed in the experiment with a leak amount of 5 m ³ / hr performed at the time of regular repair (environment without BGL) Was proportionally multiplied to prepare data of a simulated leak test of 5 m ³ / hr or more (environment without BGL). By superimposing BGL data on a day when the weather condition is similar to that at the time of regular repair, it is possible to create simulated leak test data under the BGL environment.

With respect to these simulated leak test data, how much new leak detection accuracy the above two methods have,
Alternatively, in order to evaluate at least how much new leak amount can be detected under the BGL environment, the false alarm rate and the missed report rate are defined as follows.

False alarm rate: The ratio of alarm time to the time when there is no new leakage within the data collection time.

Missing alarm rate: The ratio of the time during which no alarm is reported to the new leakage duration within the data collection time.

When the method proposed in the present invention was evaluated with such a definition, the results were as shown in FIG. 5 (spatial correlation method) and FIG. 6 (macro mass balance method). When one of the false alarm rate and the missed report rate improves, the other tends to worsen. Of course, the larger the new leakage amount, the clearer the judgment becomes. Now, assuming that the acceptance criterion for determination is “both false alarm rate and missed report rate are 10% or less”, the detection results of the two methods are as follows. The total amount of BGL at this time is about 5-10 m ³ / hr.

Spatial correlation method Macromass balance method (1) Minimum new leak amount 12m ³ / hr 6-10m ³ / hr (2) Recommended reporting standard 6 thresholds in all modules 4.0-4.5ppm parameters or 7 Is issued.

The permissible criterion for the determination assumed here is the "false alarm rate,
The adequacy of “both miss rates are 10% or less” may vary depending on the subjectivity of the plant operator. Although it is difficult to generalize all the results of the examples described here, it is possible to make a judgment with a considerably low false alarm and missing rate for a new leakage of about 15 m ³ / hr.

[0049]

[Table 1] It is a table | surface which shows the "zero point" indication value of the heat ray semiconductor type gas sensor measured on different atmospheric conditions.

[0050]

[Table 2] It is a table which shows the coefficient of the "standard calibration curve" of a heat ray semiconductor type gas sensor.

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

INDUSTRIAL APPLICABILITY The present invention has the following effects because the statistical property of BGL fluctuation is extracted and the estimated BGL obtained by using it is monitored from the gas sensor. Although it is less than the reporting standard defined by law, it is possible to easily report a new leakage even in a BGL environment due to a minute leakage that always exists in the actual plant yard. Even in a BGL environment due to a minute leak, it is possible to determine a new leak with a low false alarm rate and a low miss rate.

[Brief description of drawings]

FIG. 1 is a plan view of a plant to which a detection system according to an embodiment of the present invention is applied.

FIG. 2 is a diagram showing a calibration curve for a hot wire semiconductor gas sensor with respect to ethylene gas.

FIG. 3 is a diagram showing the principle of a measurement error correction method for a hot wire semiconductor gas sensor.

FIG. 4 is a diagram showing an example of a gas sensor indication value at the time of a new leak under a BGL environment.

FIG. 5 is a diagram showing a false alarm rate and a false alarm rate of new leakage detection under a BGL environment by a spatial correlation method.

FIG. 6 is a diagram showing false alarms and missing-report rates of new leak detection under the BGL environment by the macro mass balance method. It is a table showing the effect of temperature and humidity correction of the hot wire semiconductor gas sensor.

[Explanation of symbols]

M _{1 to} M ₇ module 10 Sampling module 20 Sensor module 30 Wind direction / speed measuring device 40 Plant yard

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Saburo Takahashi 1-6 Takasago, Takaishi, Osaka Prefecture Mitsui Toatsu Chemical Co., Ltd. (72) Inventor Masahiko Tsuchiya 2-8-1, Akanehama, Narashino, Chiba Toyo Engineering Ring Co., Ltd. (72) Inventor Ippanta Kishiguchi 2-8-1 Akanehama, Narashino-shi, Chiba Toyo Engineering Co., Ltd. (72) Inventor Yoshio Kawauchi 2-8-1 Akanehama, Narashino, Chiba Toyo Inside Engineering Co., Ltd.

Claims (4)

[Claims] 1. In a plant that handles combustible or harmful substances in which a very small amount of leaked gas (BGL) is always present, a group of high-sensitivity sensors for detecting gas leaked from the plant, an anemometer, and these sensors. A method for detecting a new leak source in a minute leak gas atmosphere, characterized by performing the following by using a system composed of a data processing system for processing sensor signals. The statistical properties of BGL were extracted from the time-series data of the BGL concentration and the time-series data of the wind direction and wind speed that were normally observed by multiple sensors, and the BGL concentration estimated based on the above statistical properties was observed. A newly generated abnormal leakage is detected by monitoring the data removed from the concentration data or the statistical property of BGL itself. 2. The method for detecting a new leak source in a minute leak gas atmosphere according to claim 1, wherein a BGL model is used by a macro mass balance method or a spatial correlation method. 3. An automatic zero-point correction method comprising the following steps (a), (b) and (c), for zero-point fluctuations of a gas sensor due to temperature and humidity changes. (A) A correlation between a known sample gas concentration under constant temperature and humidity conditions and a sensor indication value for the sample gas concentration is created. (B) The sensor indication value measured under the temperature and humidity conditions different from (a) is stored. (C) Due to the temperature and humidity changes of the zero point by the gas sensor independent of the one used in (a) and (b) above, which is placed under the same temperature and humidity conditions as (b), but with virtually no gas. The zero point fluctuation is measured, and this is used to correct the sensor reading in (b). 4. The method for detecting a novel leakage source according to claim 1, wherein the automatic zero correction method according to claim 3 is included in a data processing system.