JP7195512B2 - Liquid tank inventory measurement method, device, and monitoring system - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inventory amount measuring method, device, and monitoring system based on the detection value of a liquid level gauge provided in a tank for storing liquid.

Oils that are distributed as gasoline and kerosene are supplied by wholesalers to general gas stations commonly called gas stations and private gas stations that are large-scale consumers. Gas stations store gasoline and kerosene in underground tanks. Each tank is equipped with a liquid level gauge that measures the amount of inventory (stored amount) in the tank, and a monitor installed on the ground or in the tank control room shows the amount of inventory calculated based on the detected value of the liquid level gauge. be able to.

Tanks and pipes buried underground as hazardous materials facilities make it difficult to check for leaks from the time the installation is completed. The presence or absence of leakage from tanks is determined by inspections required by law once every three years or once a year.

Leakage of underground tanks is determined by legally prescribed inspections once every three years or once a year. It does not guarantee that there will be no leaks. Therefore, the presence or absence of leakage during that period is confirmed by the owner of the hazardous materials facility by recording daily liquid level gauge data and sales data from the liquid level gauge of the refueling machine.

The liquid level meter installed in each fueling machine is measured in advance for each fueling machine, and the error is within ±0.5%. Therefore, it can be estimated that the measured value of the liquid level meter is almost accurate. The inventory amount of the tank is obtained by theoretically obtaining the relationship between the position of the liquid level and the inventory amount according to the shape of the tank, and calculating the inventory amount from the detection value of the liquid level gauge by the obtained arithmetic expression.

However, in underground tanks, there is variation between the inventory amount calculated from the detected value of the liquid level gauge and the true inventory amount. In underground tanks, deformation and inclination of the tank occur due to subsidence of the ground after backfilling, groundwater conditions, soil pressure, etc. As a result, the relationship between the level gauge detection value and the true inventory amount deviation or error occurs.

The tank is supplied with liquid from a tank truck. Normally, petroleum products are stored from tank trucks in units of 2 kL (kiloliters), but they are not constant due to evaporation during transportation, making it difficult to measure the amount of evaporation. Therefore, it is not possible to correct the relational expression between the detection value of the liquid level gauge and the stock amount based on the amount of oil supplied from the tank truck.

As described above, the presence or absence of tank leakage is checked by the owner of the facility for hazardous materials by daily recording the data of the liquid level gauge and the data of the liquid volume gauge. For example, at a general gas station, the amount of liquid in the underground tank is measured by a liquid level gauge every day. The amount of inventory on the day is the amount obtained by adding and subtracting the amount of inventory (amount received from tank trucks) and the amount of shipment (sales) to the inventory amount of the previous day (hereinafter referred to as "calculated inventory amount"). However, due to the measurement accuracy of the liquid level gauge and the deformation of the underground tank, there is a unique error in the calculated inventory amount for each individual tank.

For this reason, it is difficult to detect tank leaks, etc., even if the inventory amount obtained from the detected value of the liquid level gauge (hereinafter referred to as "detected inventory amount") is compared with the calculated inventory amount, resulting in various errors. Detecting leaks based on measured values including , requires considerable skill, and it is extremely difficult to quickly detect minute errors.

Based on the new knowledge of the inventors, this invention makes it possible to estimate the error of the liquid level gauge installed in the tank, thereby making it possible to estimate the inventory amount of the tank from the detected value of the liquid level gauge. It provides a means to accurately estimate, enabling more accurate and rapid detection of leaks from tanks and piping connected to the tanks, as well as enabling more accurate measurement of inventory levels for individual tanks. Therefore, it is an object of the present invention to make it possible to monitor the operational state of the tank more quickly and accurately in normal times and in emergencies.

This invention is based on the new finding that the error of a liquid level gauge installed in an underground oil tank fluctuates finely at short time intervals p, and that the whole fluctuates periodically between certain upper and lower limits. It is based on In the present invention, a calibration function that approximates the true inventory amount from the inventory amount detected by the liquid level gauge based on the measurement data of the past liquid level gauge 4 and the liquid level gauge 5 that measures the amount of goods discharged from the tank. is obtained for each tank to estimate the true inventory amount.

The method for measuring the inventory amount in a liquid tank according to the present invention comprises a liquid level gauge 4 installed in the tank 2 for detecting the inventory amount of the liquid in the tank, and a liquid level gauge 4 for measuring the amount of liquid discharged from the tank 2. A method for measuring an inventory amount of a liquid tank including a quantity meter 5.

In the method of the present invention, the detection data of the liquid level gauge 4 received at each predetermined time interval p and the amount of delivery measured by the liquid level gauge 5 within the time interval are stored, and from the stored data of the predetermined period, The relationship between the true inventory amount of the liquid in the tank 2 and the detected inventory amount detected by the liquid level gauge 4 is estimated, and the detection data of the liquid level gauge 4 is corrected based on the estimated relationship to determine the inventory of the tank. Quantity.

A preferred apparatus for carrying out the method of the present invention is a memory for storing the detected inventory quantity _xt calculated by the calculating means 15 and the corrected inventory quantity _Xt corrected by the deviation correcting means 32 at predetermined time intervals p. Means 34, Small Interval Setting Means 38 for partitioning the interval of data used to obtain the calibration function from the data stored in the storage means into small intervals s, and the calibration function obtained from the data of the partitioned small intervals. and a deviation correction means 32 for correcting the newly acquired detected inventory quantity with the calibration function obtained by the learning means to obtain the corrected inventory quantity. there is

In addition, the underground tank monitoring system of the present invention includes the management computer 3, the detection value of the liquid level gauge 4 or the detected inventory amount calculated by the calculation means 15 and the time corresponding to the liquid level gauge 5 at each predetermined time interval p. Equipped with a transmitter 16 for transmitting the shipping quantity weighed within the interval p to the management computer 3 via the Internet 6, the inventory quantity measuring device of the present invention is stored in the storage means with the time axis as the horizontal axis. The management computer 3 is provided with display means 36 for graphically displaying the corrected stock amount for a plurality of days.

The width or number of the sub-intervals s set in the sub-interval setting means 38 is obtained by detecting the fluctuation cycle of the detection error of the liquid level gauge from the stored data of the predetermined interval, and combining the detected cycle with the order of the calibration function to be obtained. The width of the sub-section s to be divided can be obtained and automatically set based on .

According to this invention, not only leakage from the main body of the underground tank but also leakage from the buried piping connected to the underground tank can be accurately detected. In addition, it is possible to quickly detect errors and malfunctions of measuring devices such as liquid level gauges and liquid level gauges, and to monitor the operational state of tanks in normal times and in emergencies.

In addition, since the present invention can collect data using existing equipment such as liquid level gauges, liquid volume gauges, and wiring connected to them, it can be introduced at low cost, and operating costs are also low.

In addition, according to the monitoring system of the present invention, for a plurality of tanks, the corrected inventory amount obtained from the inventory amount detected by the liquid level gauge, the outgoing amount by the liquid level meter, and the incoming amount from the tank truck when necessary are quickly managed. Since the results are automatically sent to a computer and displayed, it is possible to build a system for constant monitoring by skilled analysts.

A graph showing an example of periodic fluctuations in the deviation of the amount of inventory detected by the liquid level gauge Block diagram of a general gas station equipped with the monitoring system of this invention Graph (b) of corrected inventory quantity corrected by the method of the present invention and graph (a) of detected inventory quantity before correction A graph showing the error in the amount of inventory detected by the liquid level gauge with the amount of inventory on the horizontal axis for four underground tanks.

Embodiments of the present invention will be described below with reference to the accompanying drawings. When the inventors of the present application measured in detail the changes in the inventory amount and the delivery amount of oil tanks buried underground, the error in the inventory amount detected by the liquid level gauge was as shown in FIG. It was found that it varies finely and fluctuates periodically between certain upper and lower limits as a whole. In Fig. 1, the horizontal axis is the passage of time, the left vertical axis is the inventory amount (broken line), and the right vertical axis is the error between the detected value of the liquid level gauge and the theoretical value (solid line), measured every 5 minutes for 3 days. showing the data.

Based on this knowledge, the inventors of the present application have learned the relationship between the inventory amount detected by the liquid level gauge (detected inventory amount) and the true inventory amount using AI techniques, and can correct errors in the detected inventory amount. I got the idea that it might be, and completed the present invention.

In the present invention, a calibration function for determining the true inventory amount from the detected inventory amount is obtained for each underground tank based on past measurement values. In the present embodiment, the calibration function was obtained by applying cubic spline regression, which is a non-parametric regression analysis of machine learning methods that approximate complex functional forms.

That is, x is the amount of detected inventory, and detection time t = 2, ..., T,
f(x _t = f(x _{t - 1} ) + received quantity at - delivered quantity bt
A function (calibration function) close to the function f(x _t ) that satisfies Manage health.

It is difficult to find calibration functions that correspond to phenomena with complex curvilinear structures. However, the periodicity of the deviation between the change in the detected inventory amount found by the inventors of the present application and the change in the inventory amount calculated from the shipping amount (calculated inventory amount) is added, and the predetermined interval used to obtain the calibration function A complex structure is modeled by dividing the data group into a plurality of small intervals s, finding a polynomial that fits the measured data for each small interval, for example, by moving the boundaries of adjacent small intervals and finding for each small interval By connecting the ends of the polynomials, we were able to obtain an appropriate calibration function from the measured data of the complex structure.

By dividing the interval in which the data used to obtain the calibration function is collected according to the amount of data, m−1 small intervals s are set, and m nodes that serve as boundaries of these small intervals are defined as t ₁ · . . . as t _m , the calibration function by cubic spline regression

の係数ｗ₀、ｗ₁、ｗ₂、ｗ₃、ｗ_j+3（ｊ＝１・・・ｍ）を求めて、検出在庫量ｘを補正して真の在庫量とするのである。

The coefficients w ₀ , w ₁ , w ₂ , w ₃ , w _j+3 (j=1 .

The above inventory amount correction calculation can be performed at any stage in the process of displaying the true inventory amount from the detection value of the liquid level gauge. An embodiment of the present invention will be described below with reference to FIG. FIG. 2 is a diagram schematically showing a general gas station, and a tank 2 is buried under the site where the building 1 is built. Petroleum (for example, gasoline) is stored in the tank 2 , and the position of the liquid level is detected by a liquid level gauge 4 . The tank 2 has an entrance 21 and an exit 22. - 特許庁The petroleum in the tank 2 is received from a tank truck 23 through an entrance 21, and supplied from an exit 22 through an embedded pipe 24 to a consumer (usually an automobile) from a fueling machine 25. The fueling machine 25 is provided with a liquid level meter 5 for measuring the amount of petroleum that has flowed out from the fueling nozzle 26 . Although only one tank 2 and one fuel dispenser 25 are shown in the drawing, a plurality of tanks 2 and fuel dispensers 25 are usually provided.

The liquid level gauge 4 converts the detected position of the liquid level of petroleum into an electric signal and sends it to the monitor 11 installed in the building 1 through the signal line 7 . The monitor 11 shown in the figure is a monitor of conventional construction, and calculates the stock amount of petroleum in the tank from the position of the liquid level and displays it on the display 12 . This calculation is based on a calculation formula that theoretically obtains the relationship between the inner dimension of the tank and the position of the liquid level.

A liquid level meter 5 provided in the fueling machine 25 converts the leaving amount measured when fueling is performed into an electrical signal and sends the electrical signal to the POS terminal 13 . The POS terminal 13 calculates a price based on the received weighing signal, exchanges money, and sends sales data to a POS system computer (not shown). The POS terminal 13 may be built in the refueling machine 25 or installed in the building 1 . The input terminal 14 of the POS terminal and the transmitter 16 provided in the monitor 11 are connected by a branch signal line 8, and the weighing signal sent from the liquid meter 5 to the POS terminal 13 is , is sent to the transmitter 16 .

The reason why the transmitter 16 obtains the detected value of the liquid level meter 5 from the input terminal 14 of the POS terminal is that the data processed by the POS terminal 13 includes data such as sales at gas stations. On the other hand, the method of obtaining data directly from the liquid level meter 5 requires a large number of new wirings.

A general monitor 11 includes a display 12, a calculation means 15 for calculating an inventory quantity theoretically obtained from the detected value of the liquid level gauge 4, and the calculation result of the calculation means 15 is displayed on the display 12. A display means and a warning means for displaying a warning when the calculation result is equal to or less than a predetermined amount are provided. The example monitor 11 further comprises a transmitter 16 .

The transmitter 16 transmits the inventory amount calculated by the calculation means 15 of the monitor to the management computer 3 installed in the management company 9 at predetermined short time intervals (for example, 3 to 30 minute intervals, preferably 3 to 10 minutes). do. The transmitter 16 also divides the weighing signal input from the branch signal line 8 into a predetermined amount of data (for example, about 1 kbyte) and transmits the division signal to the management computer 3 via the Internet at each division timing.

The management computer 3 includes a receiver 31, a deviation correction means 32, a storage amount calculation means 33, a storage means 34, a web page creation/transmission means 35, a display means 36, a learning means 37, and a small section setting means 38. there is

The receiver 31 receives data transmitted from the transmitter 16 of the monitor at predetermined time intervals p. The storage means 34 stores the detected inventory quantity x _t received at each time and the corrected inventory quantity X _t corrected by the deviation correction means 32 .

A small interval s corresponding to the order of the calibration function to be obtained is set in the small interval setting means 38 . When automatically setting a small interval s, a small interval calculation that calculates the corresponding small interval s by detecting a period in which the difference between the leveled detected inventory amount and the calculated inventory amount in the past predetermined interval has an extreme value Means 39 are provided. The learning means 37 obtains the calibration function f(x _t ) by the machine learning method described above.

The deviation correcting means 32 corrects the newly received detected inventory quantity x _t using the calibration function obtained by the learning means 37 to obtain the corrected inventory quantity X _t . The new detected inventory quantity, corrected inventory quantity, and weighing data are sequentially stored in the storage means 34 .

The display means 36 displays a graph of the stored corrected inventory quantity _Xt on the monitor of the management computer 3 with the horizontal axis as the time axis. The web page creating/transmitting means 35 creates a web page of the graph and uploads it to a web server (not shown). The person in charge of the gas station can view the Web page with the browser 17 that has been granted viewing authority.

FIG. 3(a) is a graph of detected inventory quantity-calculated inventory quantity (before correction), and FIG. 3(b) is a graph of detected inventory quantity-calculated inventory quantity (after correction). The corrections used reduce the standard deviation of the difference between actual and calculated inventory by 54%. In the graph (a) before correction, the original error is masked by the error of display deviation of the liquid level gauge, and it is difficult to judge tank abnormality such as leakage. On the other hand, in graph (b) after correction, errors other than the liquid level error, such as the presence of a tank bag due to the liquid level gauge calibration, remain, but the deviation of the detected inventory amount of the liquid level gauge is removed. error becomes clear, making it easier to judge tank abnormalities.

A person in charge of monitoring or an analyst of the management company 9 quickly detects abnormal operation of the measuring instruments 4 and 5, leakage from the underground tank 2 or the buried pipe 24, etc., based on the data displayed on the display of the management company 9. By analyzing data for several days, it will be possible to detect deformation of tanks due to earthquakes, etc.

There is a relationship between the cycle of the error change, the division width when dividing into small intervals s, and the obtained calibration function, and a quadratic calibration function is obtained by dividing into small intervals 1.5 times the period. In addition, by averaging data measured at short intervals for the data at the start and end, errors in short cycles can be corrected.

When the existing monitor 11 is not used, the transmitter 16 directly transmits the detection value of the liquid level gauge 4, and the calculation means 15 for calculating the inventory amount from the detection value of the liquid level gauge and the calculation result are specified. Warning means for generating a warning when the amount becomes equal to or less than the amount can be provided on the management computer 3 side. Further, the storage means 34, the small interval setting means 38, and the learning means 37 of the present invention can be provided in the computing means 15 of the monitor 11 to correct the detected stock amount.

By sending the measurement data to the tank manufacturer's browser, an analyst with expert knowledge of the tank can check the delivery status, liquid leakage, and other abnormalities based on the sent data. Having a skilled analyst check several days' worth of measurement data (for example, three days' worth of data) enables a quick response in the event of an abnormality. By extracting the data only at night, when there is no entry/exit, it becomes easier to monitor leaks. Also, by displaying the deviation data for each tank, it is possible to discover manufacturing problems of individual tanks.

4(a), (b), (c), and (d) show how the deviation of the detected inventory amount of the liquid level gauge detected by the method of this invention changes for four different underground tanks. is a graph showing the inventory amount in the tank on the horizontal axis.

In the tank shown in Fig. 4(a), when the inventory increases, the increase/decrease tends to be positive, and when the inventory decreases, the increase/decrease tends to be negative. It is assumed that there is.

In the tank of FIG. 4(b), there is a tendency that the amount of increase/decrease becomes negative when the amount of inventory increases, and the amount of increase/decrease tends to become positive when the amount of inventory decreases. This is presumed to be due to the size difference between the liquid level gauge and the tank (the tank size is larger).

In the tank of FIG. 4(c), the trend of increase and decrease is reversed when the inventory amount is about half of the total capacity.

In the tank shown in FIG. 4(d), a reversal tendency of the error is seen at a plurality of points, and it is presumed that the difference is caused by the difference in the tank table of the liquid level gauge.

2 Tank 3 Management Computer 4 Liquid Level Gauge 5 Liquid Level Gauge 6 Internet 13 POS Terminal 14 Input Terminal 16 Transmitter 32 Deviation Correcting Means 33 Storage Amount Calculating Means 34 Storage Means 36 Display Means 37 Learning Means 38 Small Section Setting Means 39 Small Sections computing means

Claims (5)

Equipped with a liquid level gauge (4) installed in a tank (2) for detecting the stock amount of liquid in the tank, and a liquid level gauge (5) for measuring the amount of the liquid discharged from the tank. A method for measuring an inventory amount of a liquid tank, comprising:
The detection data of the liquid level gauge received at each predetermined time interval (p) and the amount of shipment measured by the liquid level gauge within the time interval are stored, and the liquid level gauge is detected from the stored data of the predetermined period. is detected, the period is divided into small intervals (s) based on the detected interval, the calibration function for each small interval is connected to obtain a calibration function, and the amount of liquid in the tank is calculated. estimating the relationship between the true inventory amount and the detected inventory amount detected by the liquid level gauge, correcting the detection data of the liquid level gauge based on the estimated relationship, and calculating the inventory amount of the tank; A method of measuring the amount of inventory in a tank. A liquid level gauge (4) is installed in the tank (2) to detect the liquid level in the tank, and the detected inventory amount is calculated based on the detected liquid level and the shape and dimensions of the tank. A liquid tank inventory quantity measuring device comprising computing means (15) and a liquid level meter (5) for measuring the quantity of the liquid discharged from the tank,
storage means (34) for storing the detected inventory quantity x _t calculated by the calculating means at predetermined time intervals (p) and the corrected inventory quantity X _t after being corrected by the deviation correcting means (32);
small interval setting means (38) for detecting a variation period of the detection error of the liquid level gauge from the data for the predetermined period stored in the storage means and dividing the period into small intervals (s) based on the period ; ,
a learning means (37) for connecting calibration functions obtained from data of partitioned sub-intervals (s) to obtain a calibration function for correction calculation;
a deviation correction means (32) for obtaining the corrected inventory amount by correcting the newly acquired detected inventory amount with the calibration function obtained by the learning means;
Equipment for measuring the amount of inventory in liquid tanks. The extreme value of the difference between the detected inventory quantity stored in the storage means (34) and the calculated inventory quantity calculated from the outbound quantity measured by the liquid level meter is obtained, and the width or 3. The liquid tank inventory quantity measuring device according to claim 2 , further comprising a sub-section calculation means (38) for setting the number of sections. A liquid level gauge (4) is installed in the tank (2) to detect the liquid level in the tank, and the detected inventory amount is calculated based on the detected liquid level and the shape and dimensions of the tank. A liquid tank inventory monitoring system comprising computing means (15) and a liquid level meter (5) for measuring the amount of the liquid discharged from the tank,
The detection value of the liquid level meter or the inventory amount calculated by the calculating means and the shipping amount measured within the corresponding time interval (p) by the liquid level meter at each predetermined time interval (p) are transmitted via the Internet (6). and a transmitter (16) for transmitting data to a management computer (3) via a transmitter (16), wherein the management computer includes the measuring device according to claim 2 or 3 , and a plurality of days stored in the storage means with the time axis as the horizontal axis. and display means (36) for graphically displaying the corrected stock amount in minutes. 5. The underground tank monitoring system according to claim 4 , wherein said transmitter obtains measurement data of said liquid level meter from an input terminal (14) of a POS terminal connected to said liquid level meter.

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