JP4415030B2 - Liquid storage tank leak detection system and leak detection method - Google Patents

Description

  The present invention relates to a leakage detection system and a leakage detection method for detecting leakage of liquid from a liquid storage tank installed in a gas station, a factory, or the like. In addition, in this application, "leakage" shall mean both the outflow of the storage liquid from a liquid storage tank, and the inflow of rain water, groundwater, etc. to a liquid storage tank.

  Since the liquid storage tank buried underground is used for a long time, holes or cracks are generated due to corrosion of the partition wall, or the liquid stored inside flows out to the outside for other reasons, or Rainwater, groundwater, etc. may flow from the outside.

  Conventionally, in order to detect such leakage, batch inspections such as a gas pressurization method, a liquid pressurization method, a fine pressurization method, and a fine depressurization method are regularly performed.

  According to the above batch inspection performed in the form of periodic inspection, it is possible to detect leaks with high accuracy. However, since periodic inspections are usually performed only once a year, there is no leakage during that period. If it occurs, it cannot be detected early.

  Therefore, in order to detect leaks at an early stage, recently, the liquid level of the liquid storage tank is constantly monitored using the liquid level sensor for inventory management of the liquid storage tank, and the liquid level sensor is used for measurement. A method of determining the presence or absence of liquid leakage based on the liquid level data is being used in combination with the periodic inspection (see, for example, Patent Documents 1 and 2).

  Specifically, in this leakage detection method, a predetermined level is detected by the liquid level sensor during the liquid level stable period when it is determined that there is substantially no change in the liquid level over time, as in the case where no liquid enters or exits the liquid storage tank. The liquid level is measured over the leakage judgment time, the change in the liquid level is obtained based on the measured change in the liquid level, and it is determined that there is a leak if the change in the liquid level is equal to or greater than the reference leakage judgment change amount. To do.

  In this leak detection method, the reference leak determination change amount is generally set to 0.38 L / h, which means that the leak amount when a 0.3 mm hole is formed in the wall surface of the liquid storage tank is about 0.1. This is adopted because it is 38 L / h, and the same reference leak determination change amount is adopted regardless of whether the tank capacity is large (for example, 60 KL tank) or small (for example, 10 KL tank).

  However, if the tank capacity (tank dimensions) is different, the amount of change in the liquid amount changes even if the amount of change in the liquid level is the same. For example, if the liquid storage tank is cylindrical and placed horizontally, if the liquid level is at the center of the tank diameter and the tank diameter is the same as 2400 mm, the liquid level changes by 0.01 mm, and 60 KL In the case of a tank, the amount of liquid of about 0.34 L changes, and in the case of a 10 KL tank, the amount of liquid of about 0.07 L changes.

  Thus, when the tank capacities are different, the amount of change in the liquid level is different when the same reference leak determination change amount occurs. Specifically, when the tank capacity is large, the amount of change in the liquid level when the reference leakage determination change amount occurs is smaller than when the tank capacity is small. Therefore, when the tank capacity is large, it is difficult to judge leaks based on changes in the liquid level compared to when the tank capacity is small. To ensure the accuracy, the leak judgment time is made longer than when the tank capacity is small. There is a need.

Therefore, conventionally, as shown in Table 1, for example, the leakage determination time is set for each tank capacity.

However, when there is liquid in and out intermittently, day or night, such as a 24-hour gas station, a sufficiently long liquid surface stabilization period that satisfies the leakage judgment time shown in Table 1 is obtained. In some cases, it was difficult to detect leaks.
JP 2001-97500 A Japanese Patent No. 3746057

  The problem to be solved by the present invention is to enable leakage detection even in an environment where a long liquid level stabilization period cannot be obtained, such as a 24-hour gas station. More specifically, it is to provide a leakage detection means for a liquid storage tank that can shorten the leakage determination time.

  Conventionally, the leakage determination time is set for each tank capacity as described above. This is because when the tank capacity is different, the amount of change in the liquid level is different when the same reference leakage determination change amount occurs. However, for example, in the case of a cylindrical and horizontal liquid storage tank, the amount of change in the liquid level when the same reference leak determination change amount occurs differs depending on where the liquid level in the tank is. Specifically, when the liquid level is at the center of the tank diameter, the change in the liquid level is the smallest when the reference leak determination change occurs, and the liquid level is far from the center of the tank diameter. Along with this, the amount of change in the liquid level increases. Conventionally, this is not considered at all, and a uniform leak determination time is set for each tank capacity. That is, this uniformly set leak determination time is not optimized according to the liquid level, but is set assuming that the liquid level is at the center of the tank diameter for safety. Therefore, when the liquid level is shifted upward or downward from the center of the tank diameter, the leakage determination time is consumed more than necessary.

  On the other hand, the present invention pays attention to the change in the liquid level depending on the liquid level of the liquid storage tank when there is a certain change in the liquid level that is the liquid storage tank. By setting an optimal leakage determination time according to the above, the minimum leakage determination time is always set, and as a result, the leakage determination time is shortened.

  That is, the leak detection system according to the present invention includes a liquid level sensor that measures the liquid level of the liquid storage tank, and a predetermined liquid level sensor that determines that there is substantially no time change in the liquid level. In the liquid storage tank leakage detection system, the calculation unit includes a calculation unit that calculates a change in the liquid level based on a change in the liquid level measured during the leakage determination time of the liquid and determines whether or not the liquid leaks. The amount of change in the liquid level when the liquid level changes by a predetermined level at the liquid level from the liquid level data measured by the liquid level sensor and the dimension data of the liquid storage tank ΔV is calculated, and the leakage determination time is determined by a calculation formula having a proportional relationship with the liquid amount change amount ΔV.

  Further, the leakage detection method of the present invention is a liquid level measured by a liquid level sensor during a predetermined leakage determination time during a liquid level stable period in which it is determined that there is substantially no change in the liquid level in the liquid storage tank. Liquid level data measured by the liquid level sensor at the start of liquid leakage detection in the liquid storage tank leakage detection method for determining the liquid leakage based on the change in liquid level And from the dimensional data of the liquid storage tank, a liquid amount change amount ΔV when the liquid level changes by a predetermined level at the liquid level, and a calculation formula having a proportional relationship with the liquid amount change amount ΔV, The leak determination time is determined.

  As described above, the liquid amount change amount ΔV referred to in the present invention is a liquid amount change amount when the liquid level changes by a predetermined level at the liquid level at the start of the determination of the presence or absence of liquid leakage. The liquid amount change amount ΔV is a value corresponding to the liquid level. The smaller the value, the larger the change amount of the liquid level when a predetermined liquid amount change, for example, a reference leak determination change amount occurs. Become. Therefore, when the liquid amount change ΔV is small, it is possible to accurately determine whether there is a leak even if the leak determination time is short compared to when the liquid amount change ΔV is large. That is, the smaller the liquid amount change amount ΔV, the shorter the required leakage determination time, and it can be said that the liquid amount change amount ΔV and the necessary leakage determination time are in a proportional relationship. Therefore, in the present invention, the leakage determination time is determined by a calculation formula having a proportional relationship with the liquid amount change amount ΔV. As a result, the minimum necessary leakage determination time can be set according to the liquid level, and the leakage determination time can be shortened.

  As a calculation formula used in the present invention, the following formula (1) can be used.

  Leakage determination time = liquid amount change amount ΔV / reference leakage determination change amount (1)

  Here, as described above, the liquid amount change amount ΔV is a liquid amount change amount when the liquid surface level changes by a predetermined level at the liquid surface level at the time of starting the determination of the presence or absence of liquid leakage. The predetermined level is preferably a liquid level change level that can be reliably detected by the liquid level sensor according to the resolution of the liquid level sensor to be used. For example, when the resolution of the liquid level sensor is 0.01 mm, the predetermined level is 0.05 mm. In addition, as described above, the reference leakage determination change amount is a change amount of liquid amount per hour in which it is determined that there is a leak if there is a change in the liquid amount beyond this in the determination of the presence or absence of leakage. Is 0.38 L / h.

  This equation (1) makes it possible to calculate the minimum leakage determination time necessary for reliably detecting the reference leakage determination change amount as a change in the liquid level by the liquid level sensor when the reference leakage determination change amount occurs.

  In addition, in order to improve the reliability of the leak determination, a predetermined safety factor is applied to the leak determination time calculated by the above formula (1), that is, the leak determination time calculated by the following formula (2) is adopted. You may make it do. For example, the safety factor is 1.1 with a margin of 10%.

  Leakage determination time = (Liquid volume change amount ΔV / reference leak determination change amount) × safety factor (2)

  In the present invention, the minimum necessary leakage determination time can be set according to the liquid level, and the leakage determination time can be shortened. Accordingly, leakage detection can be performed even in an environment where a long liquid level stabilization period cannot be obtained, such as a 24-hour gasoline station.

  Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings.

  FIG. 1 is a system configuration diagram of a leak detection system of the present invention.

  The leak detection system shown in FIG. 1 includes a liquid level sensor 2 that constantly measures the liquid level of the liquid storage tank 1, a liquid temperature sensor 3 that constantly measures the liquid temperature of the liquid storage tank 1, the liquid level sensor 2, and the liquid level. The liquid level data and liquid temperature data measured by the temperature sensor 3, the database 4 for accumulating the measurement time data, the dimension data of the liquid storage tank, and the like, and the data accumulated in the database 4 are calculated to finally detect whether there is a leak And an arithmetic unit 5 for determining And the leak detection signal from the calculating part 5 is transmitted to the alarm output and display means 6. Further, a POS system 7 and a weighing machine 8 are connected to the database 4 as external devices via a communication line 9, and various data from these external devices are stored in the database 4.

  Various sensors can be used as the liquid level sensor 2, but it is preferable to use a sensor capable of measuring a change in liquid level or liquid level with high resolution, such as a magnetostrictive sensor. The liquid temperature sensor 3 is built in the liquid level sensor 2 in the embodiment, but may be provided separately from the liquid level sensor 2.

  The database 4 can be constituted by a computer memory. The calculation unit 5 can be constituted by a CPU of a computer. As will be described in detail later, the calculation unit 5 includes the liquid level data measured by the liquid level sensor at the time when the determination of the presence or absence of liquid leakage is started, and From the dimensional data of the liquid storage tank, the liquid amount change ΔV when the liquid level changes by a predetermined level at the liquid level is calculated, and leakage is calculated by a calculation formula proportional to the liquid amount change ΔV. Determine the judgment time. Then, the calculation unit 5 determines the amount of liquid based on the change in the liquid level measured by the liquid level sensor during the leakage determination time in the liquid level stable period in which it is determined that there is substantially no change in the liquid level. Is determined, and the presence or absence of liquid leakage is determined.

  Hereinafter, the leak detection method by the leak detection system of this invention is demonstrated.

  FIG. 2 is a flowchart showing the entire process of the leak detection method of the present invention. In the leakage detection method shown in the figure, first, leakage detection data is collected by the liquid level sensor 2 and the liquid temperature sensor 3 shown in FIG. 1 (S1).

  FIG. 3 is a flowchart showing the leakage detection data collection process. In the leakage detection data collection process, first, it is confirmed whether or not the measurement time interval of the liquid level and the liquid temperature by the liquid amount sensor and the liquid temperature sensor is a predetermined time (1 second in the embodiment) (S1). -1). Next, measurement time data is acquired (S1-2), and loading of the liquid level data and liquid temperature data of the liquid storage tank is started (S1-3, S1-4). Thereafter, it is confirmed whether or not there is a change in events such as supply (unloading) and discharge (liquid supply) of the liquid to the liquid storage tank while the liquid level data and liquid temperature data are being captured (S1-5). If the event has changed, the event data is acquired (S1-6), and the liquid level data and the liquid temperature data are stored in the database together with the measurement time data and the event data (S1-7).

  Returning to FIG. 2, the leakage detection data collection in step S1 is always performed continuously. When actually detecting leakage, it is first determined whether or not the calculation unit 5 is already in the leakage detection operation. (S2) If the leak detection operation is not being performed, it is determined whether or not the present time is the liquid level stable period. In the embodiment, the event data stored in the database is referred to, and it is determined whether or not a predetermined time (20 minutes in the embodiment) has passed since the occurrence of the immediately preceding event. That is, if a predetermined time or more has passed since the occurrence of the immediately preceding event, it is determined that the liquid level is stable and the liquid level does not substantially change with time. If it is determined that the present time is the liquid level stable period, leak detection can be performed, and then a leak determination time is set (S4).

  FIG. 4 is a flowchart showing this leakage determination time setting step. In the leakage determination time setting step, first, the liquid level data at the current time point, that is, when the determination of the presence / absence of leakage is started is obtained from the database (S4-1), and the tank dimension data is called from the database (S4-2). Then, from this liquid level data and tank dimension data, a liquid amount change amount ΔV when the liquid level changes by a predetermined level (0.05 mm in the embodiment) at the liquid level is calculated (S4-3). . Next, the leakage determination time is calculated by the following equation (2) (S4-4). Here, the reference leakage determination change amount was 0.38 L / h, and the safety factor was 1.1.

  Leakage determination time = (Liquid volume change amount ΔV / reference leak determination change amount) × safety factor (2)

  For example, in a cylindrical horizontal tank (tank capacity 10 kL) with a diameter of 1440 mm and a total length of 6518 mm, when the liquid level is 288 mm (20% of the diameter), the change in liquid volume when the liquid level drops by 0.05 mm The amount ΔV is 0.36 L. From the above equation (2), the leakage determination time = (0.36 / 0.38) × 1.1 = 1.04 hours (63 minutes). As previously shown in Table 1, since the leak judgment time in the case of a tank capacity of 10 kL has been uniformly set to 1.5 hours, the leak judgment time can be shortened by about 30 minutes in this embodiment. That's right.

  Returning to FIG. 2, when the leakage determination time is set, leakage detection is started (S5). When leak detection is started, the process returns to step S1 and further proceeds to step S2. In this case, since the leakage detection operation is being performed, the process proceeds from step S2 to step S6. In this step S6, it is determined whether or not the leakage determination time has elapsed or whether an event has occurred. If the leakage determination time has elapsed or an event has occurred, the leakage detection is terminated (S7). Then, liquid level data is obtained from the liquid level data and the tank size data collected at each measurement time collected during the leak detection, and the liquid volume data is corrected based on the liquid temperature data at the measurement time to correct the liquid volume. Data is generated (S8), and from this corrected liquid volume data, liquid temperature data, and measurement time data, the continuous liquid volume / liquid temperature change data (liquid volume) indicating the liquid volume during the leak detection and the liquid temperature change over time. Change data and liquid temperature change data) are generated (S9).

  Next, the liquid temperature change data is analyzed to determine whether or not the temperature change rate during leakage detection is equal to or less than a specified value (0.02 ° C./h in the embodiment) (S10). When the rate of temperature change exceeds a specified value, an error due to temperature change increases, so it is determined that the reliability of the liquid amount change data is low, and is not used as leakage determination data described later. In other words, in the present embodiment, only the liquid amount change data having a temperature change rate equal to or less than the specified value is used for leak determination, and the accuracy is improved.

  If the temperature change rate is within the specified value, it is next determined whether or not the liquid amount change data satisfies the leakage determination time set in step S4 (S11).

  Those satisfying the leakage determination time set in step S4 are formally used for leakage determination, and the liquid amount change data (created in step S9) and the reference leakage determination change amount (0.38 L / h) are used. Comparison is made (S12), and the possibility of leakage is determined based on whether or not the change in liquid volume based on the liquid volume change data is equal to or greater than the reference leak determination change quantity (0.38 L / h) (S13). If the change in liquid volume is equal to or greater than the reference leak determination change amount (0.38 L / h), it is determined that there is a leak (S14), and a leak detection signal is generated (S15). This leakage detection signal is transmitted to the alarm output and display means 6 shown in FIG. On the other hand, when it is determined that there is no leakage (S16), the process returns to step S1.

  The present invention is applicable as a leakage detection system that detects leakage of liquid from any liquid storage tank installed in a gas station, factory, or the like.

It is a system configuration figure of a leak detection system of the present invention. It is a flowchart which shows the whole process of the leak detection method of this invention. It is a flowchart which shows the data collection process for leak detection in the leak detection method of this invention. It is a flowchart which shows the leak determination time setting process in the leak detection method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid storage tank 2 Liquid level sensor 3 Liquid temperature sensor 4 Database 5 Calculation part 6 Alarm output and display means 7 POS system 8 Weighing machine 9 Communication line

Claims (4)

A liquid level sensor that measures the liquid level of the liquid storage tank, and a liquid level measured by the liquid level sensor during a predetermined leak judgment time during the liquid level stability period when it is determined that there is substantially no change in the liquid level. In a liquid storage tank leak detection system having a calculation unit that determines a change in the amount of liquid based on a change in level and determines whether there is a leak of liquid,
From the liquid level data measured by the liquid level sensor and the dimension data of the liquid storage tank at the time when the calculation unit starts determining whether or not there is leakage of the liquid, the liquid level has changed by a predetermined level at the liquid level. A liquid storage tank leak detection system characterized in that the liquid amount change amount ΔV is calculated and the leak determination time is determined by a calculation formula having a proportional relationship with the liquid amount change amount ΔV. The leak detection system for a liquid storage tank according to claim 1, wherein the following formula (1) is used as the calculation formula.
Leakage determination time = liquid amount change amount ΔV / reference leakage determination change amount (1)
Here, the reference leakage determination change amount is a liquid amount change amount per hour when it is determined that there is leakage if there is a further change in the liquid amount in the determination of the presence or absence of leakage. Changes in the liquid level based on changes in the liquid level measured by the liquid level sensor during a predetermined leak judgment time during the liquid level stabilization period when it is determined that the liquid level of the liquid storage tank is substantially unchanged over time. In the liquid storage tank leak detection method for determining the presence or absence of liquid leak,
Liquid level change when the liquid level changes by a predetermined level at the liquid level from the liquid level data measured by the liquid level sensor and the dimension data of the liquid storage tank at the start of determining whether there is a liquid leak A leak detection method for a liquid storage tank, comprising: calculating an amount ΔV, and determining the leak determination time by a calculation formula having a proportional relationship with the change amount ΔV of the liquid amount. The leak detection method for a liquid storage tank according to claim 3, wherein the following formula (1) is used as the calculation formula.
Leakage determination time = liquid amount change amount ΔV / reference leakage determination change amount (1)
Here, the reference leakage determination change amount is a liquid amount change amount per hour when it is determined that there is leakage if there is a further change in the liquid amount in the determination of the presence or absence of leakage.

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