JPH0621837B2 - Gas leak detection method for gas lines - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas leak detection method for a gas line for detecting an abnormality such as a gas leak in a gas pipe, a plant or a gas pipeline, and particularly a minute pressure fluctuation. The present invention relates to a gas leak detection method for a gas line that can reliably detect an abnormality such as a gas leak.

[Problems to be Solved by Prior Art and Invention]

Fluids that leak due to breakage or destruction of pipelines include liquids and gases. The liquid transfer system related to the former is used when a predetermined pressure is applied to the inside of a pipe to transfer a liquid such as oil to a predetermined place. In this liquid transportation system, various liquid leakage detection methods have been developed for the purpose of detecting oil leakage from the pipeline, and
It is actually used in the pipeline. By the way, in such a system, when the liquid leaks from the pipeline, pressure fluctuations normally occur at the upstream point, the intermediate point and the downstream point from the leak point as shown in FIG. Therefore, as is clear from the figure, at the upstream point 1, relatively large pressure fluctuations occur at the liquid leakage start st and at the liquid leakage end en and propagate to the intermediate point 2 and the downstream point 3 and are therefore relatively simple. In addition, the leakage of the liquid can be reliably detected.
This is because the liquid is an incompressible fluid, so that the volume is almost constant regardless of the pressure change, in other words, the pressure decreases even with a very slight mass transfer, and thus it is easy to detect. Japanese Patent Application Laid-Open No. 51-1511 discloses such a prior art.
80, U.S. Pat. No. 3,962,905, and JP-A-59-24320.

On the other hand, gas leak detection is not so easy. There are two possible reasons. One of them is
This is because the gas is a compressible fluid, and the amount of line pack of the gas dynamically changes inside the pipeline. In other words, the pressure drop is caused by mass transfer because the pressure and the gas density are in a proportional relationship.
This means that even if a gas leak occurs, the pressure does not decrease unless the gas density at the measurement position decreases. Therefore, for example, even if the gas pressure or the gas flow rate changes at one end of the pipeline, it takes a considerable time for the influence to appear at the other end of the pipeline, and
The influence of the change in the pressure and the like is attenuated and diffused while propagating in the pipeline, and arrives in the form of a considerably changed pressure. Furthermore, the effect does not always appear with a fixed time delay. Therefore, detecting gas leakage is very difficult.

The other one is that even if the gas leaks due to the breakage of the pipeline, the change in the gas pressure accompanying it is very small compared to the liquid level in terms of signal level, and the attenuation and diffusion of the gas pressure is severe, It is difficult to distinguish from various changes in gas pressure and the like that occur under normal plant operation.

Therefore, since the gas leak detection has the above-mentioned special factors, if the liquid leak detection method is directly applied to the gas leak detection method, a false alarm is frequently generated during the operation of the plant, and each time, the gas leak detection method occurs. The plant had to be shut down, and there was a risk of causing a major accident by overlooking the gas leak when it actually occurred.

Therefore, conventionally, some gas leakage detection methods have been adopted or proposed, which are rooted in gas-specific properties different from liquid leakage detection. These will be briefly described below.

One of them is a method of using a gas detector that measures a leaked gas component and judges that there is a gas leak, and this is the mainstream of current gas leak detection methods. That is, this gas detector is installed in a place where leakage gas is likely to float in the yard, in a valve house in the case of a gas pipeline, or in a patrol car for patrol. , The presence of gas leakage is detected.
However, this gas leakage detection method has a problem in feasibility, for example, in the case of a plant because it is necessary to install a large number of gas detectors except for monitoring by a patrol car, and monitoring by a patrol car is also necessary. It is not suitable for monitoring the entire plant including the above.

Another method is a method in which leakage noise is generated at the gas leakage hole when gas leaks, and the leakage noise is detected by a portable microphone. This gas leakage detection method becomes extremely difficult to detect gas leakage as it moves away from the gas leakage hole, regardless of the case where a portable microphone is installed near the gas leakage hole. It is a problem in terms of sex.

Yet another method is to install a pressure detector at the origin or destination of the gas pipeline or in the middle of the pipeline, and set the pressure detected by this pressure detector and the preset upper and lower limit set values. To detect gas leakage. In addition, US Pat. No. 3,962,905 is a system that determines that a leak has occurred when the pressure drop rate exceeds a predetermined amount from the relationship between the gas leak amount and the pressure drop. Although this gas leakage detection method indirectly determines gas leakage, it has a problem that it cannot be detected unless a large amount of gas leaks.

The present invention has been made in view of the above circumstances, and enables minute pressure changes caused by gas leakage to be reliably detected by being distinguished from pressure fluctuations that occur during plant operation, for example, while also adding various conditions. An object of the present invention is to provide a gas leak detection method for a gas line that can accurately and quickly detect gas leaks based on appropriate data.

[Means and Actions for Solving Problems]

Therefore, according to the gas leak detection method for a gas line according to the present invention, both measurements are performed by measuring the pressure fluctuation due to the leading wave obtained via the gas medium in the gas pipe across the fluid resistance portion on the gas pipe. After the pressure difference is calculated, this pressure difference data is statistically processed in time series, and the difference between the statistical amount of the past plural data and at least the present data or the statistical amount including the present data is set in advance. When it exceeds the value, it is judged that the gas medium leaks.

In the statistical processing, the arithmetic processing is carried out based on three statistical arithmetic algorithms for grasping different pressure characteristic changes related to gas leakage, or at least the optimum one predetermined among the three statistical arithmetic algorithms is selected. One or more statistical arithmetic algorithms are selected to perform arithmetic processing.

〔Example〕

An embodiment of an apparatus to which the method of the present invention is applied will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of a gas leakage detection device including a gas line 11. In this device, if the pressure detector 13 can be installed at the gas leak point 12, a relatively large pressure fluctuation can be detected at st1 at the start of gas leak, as is clear from FIG.
The pressure detector 1 is located at a position distant from the gas leak point 12 on the downstream side.
In the case where No. 4 is installed, the pressure only gradually decreases as shown in FIG.

On the other hand, when the differential pressure detector 16 is provided so as to capture the pressure fluctuations from both ends of the valve 15 functioning as the flow path low antibody which is installed on the downstream side of the gas leak point 12, the fourth pressure difference is detected.
As shown in the figure, it was confirmed that a relatively large differential pressure is generated due to the pressure reduction due to the leading wave at st2 after the start of gas leakage. Therefore, as the gas detecting means in this method, the pressure detector 14 is installed on either one or both of the upstream side and the downstream side of the gas leak point 12 to detect the gas pressure, or a gas flow meter is installed. Although the flow rate may be detected by the valve 15, it is desirable that the valve 15 is installed on one or both of the upstream side and the downstream side of the gas leak point 12.
It is effective to install the differential pressure detector 16 on the line connecting the upstream side and the downstream side of the above to detect the differential pressure.

Reference numeral 17 denotes an A / D conversion means, which amplifies a minute signal related to gas leakage such as pressure and flow rate or a minute differential pressure detection signal output from the differential pressure detector 16 by a predetermined amplification degree, In addition, the signal is converted into a digital signal proportional to the amplified output value, output, and sent to the interface 18. 1
Reference numeral 9 is a sequence program or C for controlling predetermined arithmetic processing and necessary components based on an external command.
It is PU. A bus 20 is derived from this CPU 19, and in addition to the interface 18, a ROM
A (read only memory) 21, a RAM (random access memory) 22, an input / output buffer 23, etc. are connected. The ROM 21 stores, for example, fixed constants for sequence programs and calculations, as well as three gas leakage detection algorithms A1 to A3 for grasping different pressure characteristic changes related to gas leakage. Incidentally, if an example is given about each algorithm A1-A3, Is the street. Here, P is a differential pressure detection signal, i is the i-th sampling, Δt is an arbitrary calculation cycle, and C is a set value for judging gas leakage by the judgment means described later. That is, the algorithm A1 is a comparison between the average value of the sampling data from n times before to the previous time and the current sampling data, and represents the differential pressure deviation of the current data from the average data up to the previous time. Algorithm A2 has been used m times before n times.
This is a comparison between the average value up to the previous time and the average value from (m + 1) times before to the present time, and represents the differential pressure value between the past average value and the current time average value. The algorithm A3 individually compares the sampling data from n times before to the previous time and the sampling data of this time, and performs a logical product (AND) or a logical sum (OR).
Is what you get. Here, _{conjunct, (P in -P i) /} Δt> C AND (P i- (n-1) -P i / Δt> C AND (P i- (n-2) -P i / Δt > C AND ...... AND (P _i-1 −P _i ) / Δt> C, which is the change value of the difference (pressure difference) between a plurality of past individual data and the current data within a certain fixed time. This means that when all the values exceed the set value C, it is judged that there is a gas leak.

On the other hand, the logical sum is (P _in -P _i ) / Δt> C OR (P _{i- (n-1)} -P _i / Δt> C OR (P _{i- (n-2)} -P _i / Δt> C OR …… OR (P _i-1 −P _i ) / Δt> C, which is the change value of the difference (pressure difference) between a plurality of past individual data and the current data within a certain fixed time. ,
This means that gas leakage is judged when any one of the change values exceeds the set value.

These algorithms A1 to A3 are read and selected by the CPU 19 through the input / output buffer 23 from an input key 24 such as a snap switch or a keyboard generally used. The RAM 22 temporarily stores the data of the arithmetic processing result, the transmission data coming from the partner side slave station, and the like. An output device 25 is a very simple means, for example, provided with a lamp for displaying gas leakage and other abnormalities, and further, a CRT display for displaying images such as characters and figures, and a printing device. Etc. are provided. In short, it is selected and used in consideration of various conditions such as CPU processing capacity, program, and price.

A valve control unit 26 receives control data from the CPU 19 via the input / output buffer 27 connected to the bus 20 and controls the valve 15 based on this data. Further, a telecontelemeter 30 having a slave station function can be connected to the bus 20 via an interface 28. The slave station 30 is installed in each device of the present invention, and the data from each slave station is transmitted to the master station (not shown) or necessary data sent from the master station to each slave station 30. To receive. Although not shown, the master station is connected to a host computer, where the operating status of the entire plant is grasped, necessary data processing is performed, and necessary data and the like are displayed on a display unit provided on the operation panel. In addition to enabling monitoring, the entire line is controlled based on the monitoring result.

Next, the function of the method of the present invention can be roughly divided into the following.
The processing shown in the figure is performed. That is, the gas pressure, the gas flow rate or the differential pressure of the gas line 11, the detection means A, the data sampling means B, the data update processing means C, the relative value data calculation means D, and the gas leakage based on the relative value data. It has a judging means E for judging the existence or nonexistence of a gas leakage place and the like, and additionally, the relative value data and the result data judged by the judging means E are incidentally supplied to the master station via the telecontelemeter 30. Transmission control means F for transmitting to the valve control section 26, line control means G for sending line data to the valve control section 26 by transmitting relative value data and determination result data, and failure of detection system such as gas pressure, gas flow rate or differential pressure. It has a diagnostic means H for diagnosing the presence or absence.

Specifically, the detection means A and the sampling means B
Is a function of sequentially sampling a digital differential pressure detection signal detected by the differential pressure detector 16 or the like at a predetermined cycle using a clock. This predetermined cycle is determined as follows, for example. In other words, pressure detection including differential pressure must detect transient pressure wave fluctuations that instantaneously pass through the installation location of the detector, and moreover, the effects of pressure fluctuations that occur during normal operation of a plant, etc. It is necessary to detect as much as possible. The pressure fluctuations that occur when a leak occurs vary depending on the pipeline pressure, inner diameter, leak amount, etc., but by numerically or experimentally comparing the pressure fluctuations during normal operation and gas leakage, It is possible to know the upper limit of the sampling period that is hardly affected by the pressure fluctuation under normal operation and the lower limit of the sampling period that can reliably detect the transient minute pressure fluctuation. Therefore, the sampling cycle is determined in relation to the data processing resolution of the constituent elements in the subsequent stage, but it is desirable to perform sampling with the above sampling cycle as a guide.

Next, the data update processing means C sequentially updates the data sampled by the sampling means B and updates the RAM.
The data is stored in the table 22. The update at that time is determined by the capacity of the data storage area and which leak detection algorithm is used to obtain the relative value data.

The relative value data calculating means D selects the leak detection algorithm desired by the operator from a plurality of leak detection algorithms, and based on this, the ROM 21 and the RAM 2 are selected.
It has a function to read out necessary data from 2 and perform processing according to an algorithm to obtain relative value data.

The determination means E uses the upper limit and the lower limit set values or any one of them set according to each gas leakage detection algorithm, and further compares them with relative value data based on past empirical data, Determine if there is a leak. Further, the judgment means E receives the data of the diagnosis result output from the detection system diagnosis means H and sends the necessary data to the transmission control means F and the valve control means G. Furthermore, these data can be used to determine the location of gas leaks as needed. That is, the pressure wave generated by the occurrence of gas leakage propagates to the upstream side and the downstream side of the gas leakage point at approximately (sonic velocity-gas flow velocity) and (sonic velocity + gas flow velocity), respectively. If a pressure or differential pressure detector is installed, L = a + b ΔT = {a / (sonic velocity-gas velocity)}-{b / (sonic velocity + gas velocity) from the pressure wave detection time interval ΔT of each detector. } It is possible to easily estimate the gas leakage occurrence point by the simultaneous equations of. a and b are the distances from the gas leakage point to the detector installation location.

Next, the operation of the apparatus to which the method of the present invention is applied will be described. The differential pressure detection signal detected by the differential pressure detector 16 or the like is A /
The data is sent to the D conversion means 17, where it is amplified by a predetermined amplification degree and converted into digital data, and then sent to the bus 20 via the interface 18 using a plurality of bit lines. At this time, the CPU 19 determines, for example, 1se.
The differential pressure detection data on the bus 20 is sampled using the clock of the c cycle, and the known data stored in the table of the RAM 22 is sequentially updated and stored. Therefore, normally, when a raw signal is detected by a differential pressure detector installed upstream of the gas leak point 12, a signal including noise shown in FIG. 6 is detected, but the sampling means B thins it out. Processing is also done at the same time.

Then, the CPU 19 sequentially samples the differential pressure detection data at a predetermined cycle, and performs the following processing for each sampling data. A desired gas leakage algorithm is designated in advance from the input key 24, but the designation of the algorithm may be sequentially changed in the course of data processing in the middle. In this designation, for example, the algorithm A1 has a relatively short processing time for presence / absence of leakage. Algorithm A2 is resistant to noise, but requires processing time. In this way, the algorithm is specified based on past experience and the like while considering the state of the line and the importance of the plant. Then, for example, the CPU 19 causes the ROM 2 to follow the designation.
A gas leakage algorithm such as A2 is read out from 1 and selected, and the average value from n times before to m times before and the average value from (m + 1) times before to this time are compared for each sampling, and the past average value and the current average value are compared. Calculate the pressure difference. FIG. 7 is a diagram obtained by sequentially plotting the relative value data obtained by the algorithm A2 as an example. Then, the relative value data thus obtained is judged by the judging means E. This judgment means E is the leakage judgment set value c.
The upper limit set value Vu and the lower limit set value Vd, which are compared with the relative value data obtained for each sampling, and when the set values Vu and Vd are exceeded, it is determined that the gas is leaking, and it is necessary. Such a component is displayed on the output device 25, or the control valve 15 is opened and closed by the line control means G including the valve control 26 through the input / output buffer 27.
0 is given a command, and in response to this, the telecontelemeter 30
Takes in the data from the judging means E through the interface 28, converts it into a desired signal and transmits it to the master station (not shown).

〔The invention's effect〕

As described in detail above, according to the method of the present invention, since the pressure difference is obtained by sandwiching the flow path resistor installed on the gas pipe,
The leading wave of the pressure wave propagating through the gas medium in the gas pipe due to an abnormality such as damage or breakage of the gas pipe can be detected accurately and quickly, and can be detected with high resolution. By statistically processing the differential pressure data in time series, not only large leaks but also small leaks containing noise can be accurately selected by selecting the signal caused by the leak without being affected by the noise. You can judge the existence.

Therefore, it is possible to provide a gas leak detection method for a gas line which is very effective in terms of safety measures for a plant having a gas line and environmental aspects.

[Brief description of drawings]

1 to 7 are shown for explaining one embodiment of the method of the present invention. FIG. 1 is an overall configuration diagram of an apparatus to which the method of the present invention is applied, and FIGS. FIG. 5 is a functional block diagram of the method of the present invention, FIG. 6 is a raw data diagram of differential pressure at the time of gas leakage, and FIG. 7 is different leakage detection alcoholism. FIG. 8 is a relative value data diagram obtained by the above, and FIG. 8 is a pressure fluctuation diagram at the time of liquid leakage. 11 ... Gas line, 12 ... Gas leak point, 13, 14
...... Pressure detector, 15 …… Valve, 16 …… Differential pressure detector, 1
9 ... CPU, 21 ... ROM, 22 ... RAM, 24
...... Input key, 25 …… Output device, 26 …… Valve control unit,
30 ... Telecontelemeter, A ... Detection means, B ...
Sampling means, C ... Data update processing means, D ...
Relative value data calculation means, E ... Judgment means, F ... Transmission control means, G ... Line control means, H ... Detection system diagnostic means.

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-51-151180 (JP, A) JP-A-56-162029 (JP, A) JP-B-59-24320 (JP, B2) US Patent 3962905 (US , A)

Claims (4)

[Claims] 1. A method for detecting gas leakage in a gas line for detecting gas leakage caused by damage or destruction of gas piping, wherein a differential pressure is measured across a flow path resistor installed on the gas piping. Thus, after the differential pressure is obtained from the pressure fluctuation due to the leading wave propagating through the gas medium in the gas pipe due to an abnormality such as damage or destruction of the gas pipe, the differential pressure data is time-sequentially calculated. Statistical processing is performed, and the statistic of multiple past data is compared with at least the current data or the statistic including this data to calculate the statistic of multiple past data and at least the statistic including this data or this data. A gas leak detection method for a gas line, which is characterized in that a leak of a gas medium is detected when the difference exceeds a predetermined set value. 2. The gas of a gas line according to claim 1, wherein the statistical processing is a processing based on a plurality of statistical calculation algorithms for grasping different pressure characteristic changes related to gas leakage. Leak detection method. 3. The statistical processing selects and processes at least one predetermined optimal statistical operation algorithm from a plurality of statistical operation algorithms for grasping different pressure characteristic changes related to gas leakage. A gas leak detection method for a gas line according to claim (1). 4. A plurality of statistical calculation algorithms are composed of A1 to A3 described below.
The method for detecting gas leakage in a gas line according to item (3). However, in the above equation, P means a differential pressure detection signal, i means i-th sampling, Δt means an arbitrary calculation cycle, and C means a set value.