Method and apparatus for continuously monitoring interstitial regions in gasoline storage facilities and pipelines

IS 2 334 573 T3

DESCRIPTION

Method and apparatus for continuously monitoring interstitial regions in gasoline storage pipelines and facilities.

The present invention relates to an underground storage system and to a method for monitoring an interstitial space of an underground storage system.

Background

Current state of the art and federal proposals and regulations require that underground storage tanks used for the storage of hazardous substances meet certain environmental safety requirements. In particular, these environmental regulations require that underground storage systems include a primary containment unit and a secondary containment unit. Additionally, primary and secondary containment units must meet environmental standards that require underground storage tanks to be watertight. The term "hermetic", for the purposes of these environmental regulations, is usually defined as impervious to the contained substance to avoid the infiltration of the substance from the primary containment unit. Furthermore, for a tank to be airtight, the tank cannot be subject to physical or chemical deterioration by the substance contained during the life of the tank. Additionally, these regulations require owners or operators of underground storage tank systems with a single wall component located within 1,000 feet of a public drinking water well to implement an enhanced detection or monitoring program. leakage.

A known method for leak monitoring is disclosed in US Patent No. 6,489,824, entitled "Leak Detection Device for Double Wall Pipeline Systems and Container Systems". ”), which employs a leak detector with a vacuum pump that includes a pressure sensitive switch and an alarm device to detect leaks in a system of pipes or double-walled containers. The revealed leak detector is adapted to simultaneously monitor different containers connected to a main collecting pipe and a vacuum pump by means of vacuum pipes. Each monitored container incorporates a connector or vacuum valve to fluidly connect a control space with the leak detector. Each vacuum line has a first liquid lock on the vacuum connector to block liquid that has leaked or leaked into the vacuum lines from a leaking container and thus prevent it from entering the control spaces of the vacuum lines. leak-free containers. A second liquid lock is placed in the main collecting pipe to prevent liquid from entering the vacuum pump. Although this method can detect leaks within the control space of a container, it is a mechanically complex system that requires a considerable amount of materials and a long installation time.

Other interstitial or secondary space monitoring methods are well known in the art and include continuous leak detection using pressure monitoring techniques or brine solutions to determine the presence or absence of leaks between the storage system and the surrounding environment. However, to effectively calibrate all of these known systems and methods for operation requires long installation time and extensive knowledge of these systems. Specifically, to configure these monitoring systems for operation, the user must enter the volume of the secondary or interstitial space to be monitored, which requires specific knowledge about the layout and configuration of the containers and double-wall piping systems used in the underground storage system.

Summary of the invention

According to the present invention, there is provided an underground storage system and a method for generating a vacuum characteristic curve of an interstitial space of an underground storage system, as set forth in the appended claims.

Brief description of the drawings

For a full understanding of the disclosed device, it is necessary to refer to the following detailed description and the attached drawings where:

Fig. 1 illustrates the basic components of an example pore vacuum monitoring system;

Fig. 2 illustrates a flow chart detailing the operation of an exemplary self-learning routine;

Fig. 3 illustrates an exemplary interstitial void curve; and Fig. 4 illustrates a flow chart detailing the operation of an exemplary monitoring routine.

IS 2 334 573 T3

Detailed description

FIG. 1 illustrates an exemplary underground storage system 10 that includes an underground storage tank (UST) 12 constructed to safely contain a liquid 20 such as gasoline, diesel fuel, or other hydrocarbon. The UST 12 is a double-walled storage tank constructed with an outer wall 14, and an inner wall 16 separated to define an interstitial space 18. In this way, the UST 12 is divided into a primary containment unit and a secondary containment unit to provide the underground storage system 10 with double protection against leaks.

A submersible turbine pump (STP) 22 such as STP model number STP-75-VL2-7 manufactured by FE PETRO, INC^®, provides a means of pumping liquid 20 to a dispenser 24. The STP 22 may be fixedly or removably mounted to the UST 12 to position an inlet nozzle 22a below the surface of the liquid 20. The inlet nozzle 22a, to in turn, it provides a fluid pathway for pumping liquid 20 within the primary containment unit to dispenser 24.

A pump manifold 26, which may be an integral component of the STP 22 or a separate component fixedly attached thereto, controls the distribution of the pumped liquid 20 to the dispenser 24. The pump manifold 26 includes a siphon port 28 adapted to fluidly connect the interstitial space 18 (eg, the secondary containment unit) with the vacuum generated by the STP 22. In this way, when the STP 22 is active (eg, creating a vacuum) the siphon port 28 provides a vacuum path to the interstitial space 18 to evacuate the liquid contained therein. A control valve 30 can isolate the interstitial space 18 from the siphon port 28 to prevent a loss of vacuum when the STP 22 is idle and exposed to atmospheric pressure through the primary containment unit.

A vacuum sensor 32 communicates fluidly with interstitial space 18 and siphon port 28 to test and measure vacuum levels therein. The vacuum sensor 32 can be a continuous analog sensor, a discontinuous digital sensor, an exchange sensor, or any other device configured to test the level of vacuum within interstitial space 18. Vacuum sensor 32 can be isolated by control valve 30 to prevent atmospheric pressure measurements (ie, zero vacuum measurements) when STP 22 is idle. However, when STP 22 is active and generating a vacuum, control valve 30 opens to provide a fluid-communicating connection between vacuum sensor 32, interstitial space 18, and siphon port 28. In this manner, the vacuum sensor 32 tests and measures the change in the vacuum level within the interstitial space 18 generated by the STP 22.

In addition, the vacuum sensor 32 can be communicatively connected to a control unit 34 with a processor 36 and a memory 38. The control unit 34 and memory 38 receive and store vacuum data, system information, alarm data, etc. ., the vacuum sensor 32 or any other controlled component. Communications between control unit 34 and, for example, vacuum sensor 32 and control valve 30, can be implemented using any desired communication link, such as a wired local area network, a wireless communication link, a direct communication link, or a point-to-point wired communication link.

The processor 36 can execute a control routine to direct the installation and operation of the underground storage system 10. In particular, the control routine can be written in any process control programming language or computer language such as C ++, Visual C ++, Visual Basic, and can be compiled (if necessary) and stored in memory 38. Typically, the monitoring routine ensures the integrity of the underground storage system 10 by detecting unwanted leaks. In particular, the control routine can be executed in processor 36 to automatically learn the vacuum characteristics of interstitial space 18. In addition, the control routine may include additional subroutines adapted to run on processor 36 to continuously monitor the level of vacuum within interstitial space 18 as a function of time.

A leak port valve 40 is fluidly-communicatingly connected to control valve 30, vacuum sensor 32, and leak port 42, to provide a vacuum path between interstitial space 18. The port valve leak 40 and leak port 42 may define a removable assembly to be disconnected from interstitial space 18 when it is no longer required for installation and operation of underground storage system 10. The leak port valve 40 allows the automatic or manual creation of a calibrated or controlled leak between the interstitial space 18 and the atmospheric pressure beyond the leak port 42. Such a controlled leak causes a drop in the vacuum level within the interstitial space.

The vacuum sensor 32 may, in turn, measure the decreasing vacuum level and communicate the vacuum level data to the running control routine within the control unit 32 via the communication link. The control routine may, in turn, manipulate the vacuum level data to establish one or more vacuum characteristics of the interstitial space 18. In particular, the control routine may determine a negative vacuum level change rate based on the decreasing vacuum level data caused by the introduction of the controlled leak into the secondary containment unit. It will be understood that it is possible to establish other vacuum characteristics such as, for example, a positive vacuum level change rate, or the time for total evacuation of the official space, based on the vacuum level data.

IS 2 334 573 T3

The UST 12 can be connected to other components of the underground storage system 10. In particular, the interstitial space 18 can be fluidly-communicatingly connected to a secondary interstitial space 48 of a dispensing pipe 46 via a plurality of vacuum ports 44-44b . In operation, the double-walled dispensing tubing 46 can provide the fluid-communicating connection between the liquid 20 stored within the UST 22 and the dispenser 24. Thus, the entire underground storage system 10, including UST 12 and dispensing pipe 46, is double-walled and watertight to prevent penetration and corrosion that might be experienced during normal operating conditions.

FIG. 2 illustrates a generalized operations flow diagram of a self-calibration or self-learning subroutine 50 adapted to learn the vacuum characteristics of the interstitial space 18. The self-learning subroutine 50 determines and stores the vacuum characteristics based, in part, on the measured changes in vacuum level as a function of time. The self-learning subroutine 50 learns the vacuum characteristics without the need to determine or calculate the total volume of the interstitial space 18, the vacuum capacity of the STP 22, the sensitivity of the vacuum sensor 32, and so on. In this manner, self-learning routine 50 provides a fast and efficient means of calibrating and monitoring interstitial space 18 of any known or unknown volume or complexity. It will be understood that the self-learning routine 50 may act as a single routine independent of the control routine or other subroutines. However, the self-learning routine 50 can be integrated with the control routine to satisfy the calibration requirements of the underground storage system 10.

The self-learning routine 50 can be executed as long as a predetermined criterion has been met. In particular, the self-learning routine 50 can be executed manually as part of a regularly scheduled maintenance procedure, or automatically in response to a change in the configuration of the underground storage system 10, as part of the initial setup and configuration. of the underground storage system 10, or to compensate for a change in vacuum level over time.

A block 52 loads the stored initial settings and predetermined conditions required to execute the self-learning routine 50 from memory 38 (see FIG. 1). These initial settings and predetermined conditions may include, among other things, a desired maximum vacuum level P_max, a minimum allowable vacuum level P_min, close control valve 30, and calibrate vacuum sensor 32.

Although the desired maximum vacuum level can be set to virtually any value, empirical testing indicates a preference for a vacuum level of around 10 in Hg (254 mm Hg), which represents a feasible vacuum level that is easily distinguishable. atmospheric pressure. Similarly, the minimum acceptable vacuum level can be set to, for example, 2 in Hg (50.8 mm Hg). Usually the minimum vacuum level P_min provides a lower limit or threshold to identify when the current vacuum level P_measure within interstitial space 18 it is decreasing toward atmospheric pressure (ie, soon 0 in Hg or zero vacuum).

A block 54 causes the vacuum sensor 32 to test and measure the current vacuum level P_measure within the interstitial space 18. Generally, the vacuum sensor 32 tests the current vacuum level P_measure at regular time intervals throughout the operation of the self-learning routine 50. The memory 38 can store the vacuum level data representing the current vacuum level P_max in a historical database as a stored vacuum level P_stored. The stored vacuum level P_stored It can be permanently archived in the historical database (that is, saved in the database) or it can be temporarily stored for use in calculations, analysis, etc., to be deleted or overwritten later as new data is tested and stored.

A block 56 compares the current vacuum level P_measure with atmospheric pressure (ie, zero vacuum) to establish a vacuum reference prior to execution of the remaining steps within self-learning routine 50. Upon detection of a vacuum in interstitial space 18, a block 58 causes control valve 30 and leak port valve 40 to open and vent the sensed vacuum to atmosphere. A block 60 causes the vacuum sensor 32 to test the current vacuum level P_measure until the atmospheric pressure is detected. When the vacuum sensor 32 detects atmospheric pressure, a block 62 closes the control valve 30 and the leak port valve 40 to seal and isolate the interstitial space 18 in preparation for the execution of a portion of the evacuation procedure of the self-study routine 50.

A block 64 starts the evacuation procedure and the self-learning routine 50 begins to learn the vacuum level data required for the generation of a "rising curve" (an example of which is shown in Fig. 3 as line 102 ). In particular, block 64 activates STP 22, which, in turn, begins to evacuate interstitial space 18 through siphon port 28. A block 66 opens the control valve 30 to establish fluid-communicating communications between the STP 22, the interstitial space 18, and the vacuum sensor 32. Generally, the control valve 30 opens after an equal delay period to the amount of time required for the vacuum sensor 32 to detect the vacuum generated by the STP 22. It will be understood that the delay period associated with the vacuum sensor 32 may additionally depend on factors such as the sensitivity of the vacuum sensor 32, the vacuum capacity of the STP 22, and the total volume of the interstitial space 18.

A block 68 causes the vacuum sensor 32 to test and measure the current vacuum level P_measure within interstitial space 18 in the time interval At. A block 70 causes the processor 36 to set the stored vacuum level P_stored in position equal to current vacuum level P_measure, and store the stored vacuum level

ES 2 334 573 T3 resultant P_stored in the historical database established within memory 38. At this point, the rate of change of evacuation or upward curve vacuum level within interstitial space 18 can be calculated based on the difference between the vacuum level current and the vacuum level stored for a fixed or known time interval. A rate of change of evacuation P_evac can be described mathematically by the formula:

<img file="ES2334573T3_D0001.tif" />

The rate of change of AP evacuation_evac describes the positive or increasing slope of the evacuation curve representative of an increase in the vacuum level within the interstitial space 18. Alternatively, plotting the levels of the current vacuum level P_measure, and the stored vacuum level P_stored tested during the operation of the self-learning subroutine 50 as functions of time, it is possible to construct the evacuation curve.

A block 72 compares the current vacuum level P_measure with a desired maximum vacuum level P_max. If the current vacuum level is less than the desired maximum vacuum level, self-learning routine 50 enters loop 74 and proceeds to approve and store the current vacuum level P_measure until the desired maximum vacuum level is reached. However, when block 72 detects that the current vacuum level exceeds the desired maximum vacuum level, block 76 closes control valve 30.

Subsequently, a block 78 deactivates the STP 22 and the evacuation procedure concludes. At this point, the interstitial space 18 is sealed and isolated by the control valve 30, and the current vacuum level P_measure remains practically constant at the desired maximum vacuum level P_max.

A block 80 causes the vacuum sensor 32 to test and measure the current vacuum level Pmeasured within the sealed interstitial space 18 at each time interval At. It is expected that the current vacuum level P_measure remain at desired maximum vacuum level P_max for a fixed number of time intervals. In addition, memory 38 can store the current vacuum level P_measure, which is equivalent to the desired maximum vacuum P_max, in memory 38 as the stored vacuum level P_stored. At this point, the rate of change of vacuum level within interstitial space 18 is practically zero. In other words, the level of vacuum within the sealed interstitial space is constant. A positive or negative change in the vacuum level during this time interval represents an anomaly, such as a leak, that will trigger an alarm. A maximum rate of change of vacuum AP_max can be described mathematically by the formula:

<img file="ES2334573T3_D0002.tif" />

Vacuum change rate maximum vacuum rate AP_max represents the zero slope line corresponding to the desired maximum vacuum level P_max. It will be understood that the determination of the maximum vacuum change rate AP_max It is an optional calculation that can be carried out by the control unit 34.

A block 82 starts the decay procedure and the self-learning routine 50 begins to learn the vacuum level data required to generate the "low" or "down curve" (an example of which is shown in Fig. 3 as the line 106). In particular, the leak port valve 40 opens in response to a command issued by the control routine that is running within the control unit 34. In operation, the leak port valve 40, which may be a manual valve that requires operator intervention to open, provides a fluid path between the current vacuum level of P_measure within interstitial space 18 and the zero vacuum level of the atmosphere. In other words, the leak port valve 40 provides a trade-off between the high vacuum level within interstitial space 18 and the zero vacuum level of atmospheric pressure. The decrease of the current vacuum level P_measure within the interstitial space 18 caused by the controlled leak provides a method of characterizing the performance of the secondary containment unit in the presence of an actual uncontrolled leak.

A block 84 causes the vacuum sensor 32 to test and measure the current downstream vacuum level P_measure within interstitial space 18 in each of the time intervals At. A block 86 instructs the processor 36 to store the current descending vacuum level P_measure in memory 38 as the stored vacuum level P_stored. At this point, the rate of change of the low vacuum level or downward curve within the interstitial space 18 can be calculated based on the difference between the stored vacuum level P_stored and the current vacuum level P_measure for a fixed time interval At. A rate of downward change AP_falling can be described mathematically by the formula:

IS 2 334 573 T3

<img file="ES2334573T3_D0003.tif" />

The rate of downshift AP_dPscPndPntP represents the negative steepness of the downward curve, which is the line defined by the decreasing values ​​of current vacuum level P_measure measured by vacuum sensor 32 during the step-down procedure of self-learning routine 50.

A block 88 compares the current vacuum level P_measure with a minimum desired vacuum level P_min. It will be understood that the desired minimum vacuum level P_min it could be set to zero vacuum (ie atmospheric pressure) but will generally be higher to reduce overall system installation time. In other words, the closer to atmospheric pressure you set the desired minimum vacuum level P_min, the longer it will take for the interstitial space 18 to compensate. If the current vacuum level P_measure is greater than the desired minimum vacuum level P_min, the self-learning routine 50 enters a block 90 and proceeds to test and store the current vacuum level P_measure until the vacuum sensor 32 detects the desired minimum vacuum level P_min within interstitial space 18. However, if, at block 88, the current vacuum level P_measure is less than the desired minimum vacuum level P_min, a block 92 causes the control valve 30 to close. At this point, the self-learning routine 50 decline procedure concludes and the AP learned rates of change_evac and AP_descendentB they can be combined to produce the general vacuum characteristic curve shown in Fig. 3.

Fig. 3 illustrates a general vacuum characteristic curve 100 representing the learned rates of change AP_evac, AP_falling, and optionally derived rate AP_max, measured and derived by the operation of the autocalibration routine 50. As indicated before, line 102 represents the AP learned evacuation change rate_evacderived during self-learning routine 50 and, in particular, illustrates a positive increase in the void level of interstitial space 18 as a function of time. In physical terms, line 102 represents the sealed interstitial space 18 fluidly-communicatingly connected, through the control valve 30, to the active STP 22. A maximum time T_max represents the amount of time required for the STP 22 to increase the current vacuum level within interstitial space 18 to the maximum desired vacuum level P_max.

An upper range defined by line 102a and a lower range defined by line 102b establish the allowable amount of variation in the vacuum level of the learned line 102 during the evacuation procedure. An alarm subroutine can be activated when the current vacuum level P_measure it deviates beyond the acceptable limits established by the upper and lower ranges defined by lines 102a and 102b. For example, the alarm subroutine may determine that a leak exists within interstitial space 18 when the current vacuum level is determined to be outside the upper and lower ranges defined by lines 102a and 102b, or when the current vacuum level is not reached. desired maximum vacuum P_max by time T_max.

A line 104 represents the desired maximum vacuum level P_max and the learned maximum vacuum change rate AP_max equal to zero (that is, the vacuum is constant). In physical terms, line 104 represents the constant current vacuum level measured when interstitial space 18 is sealed and isolated from STP 22, and leak port valve 40. Isolated interstitial space 18 ensures that the current vacuum level P_measure remains practically constant at P_max during the fixed number of time intervals.

As described above, line 106 represents the AP learned rate of change._falling derived during self-learning routine 50. Line 106 illustrates a decrease in vacuum level measured within interstitial space 18 as a function of time. In particular, line 106 corresponds to a system configuration where a controlled leak has been introduced into the underground storage system 10, and the current vacuum level P_measure decreases as the vacuum within interstitial space 18 is offset by atmospheric pressure (ie, a vacuum level equal to zero).

As illustrated in FIG. 3, a permeation range 108 is defined by an upper line 108a and a lower line 108b that slope away from line 106. The permeation range 108 represents the exemplary vacuum profile for the sealed interstitial space 18 as a function of time. In other words, during normal operating conditions (for example, steady-state operations with no leaks and other variations), the current vacuum level P_measure is measured within the permeation range 108 defined by lines 108a and 108b. The steady vacuum drop represented by the permeation range 108 is attributable to the natural permeation properties of the underground storage system 10, rather than a leak or other anomaly.

However, if the current vacuum level P_measure or the rate of change of the current vacuum level AP_actIf it deviates from the range defined by lines 108a and 108b, (that is, it is outside the permeation range 108), then a leak or other anomaly within interstitial space 18 is assumed and the alarm subroutine could be activated .

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Fig. 4 illustrates a flow chart detailing the operation of an exemplary monitoring routine 120 employing the total vacuum characteristic curve 100. A block 122 causes the vacuum sensor 32 to test and measure the vacuum level. current P_measure within interstitial space 18. A block 124 compares the current vacuum level P_measurewith a minimum permitted vacuum level P_min (for example, 51 mm Hg (2 in Hg) or zero vacuum). If the current vacuum level P_measure is below a minimum permissible vacuum level P_min, a block 126 activates the STP 22 which, in turn, begins to evacuate the interstitial space 18 as indicated generally by the evacuation curve 102 illustrated in FIG. 3.

A block 128 causes the control valve 30 to open, thus establishing fluid-communicating communication between the STP 22, the interstitial space 18, and the vacuum sensor 32. Generally, the control valve 30 opens after a delay period equal to the amount of time required for the vacuum sensor 32 to detect the vacuum generated by the STP 22. A block 130 instructs the vacuum sensor 32 to test and measure the current increasing vacuum level P_measure within interstitial space 18 in each of the time intervals At.

A block 132 compares a current vacuum level change rate P_currentwith AP learned evacuation change rate_evac determined during self-learning routine 50. It will be understood that the rate of change of the current vacuum level AP_current can be determined based on the difference between the current vacuum level P_measure and the stored vacuum levels P_stored as a function of time. A rate of change of current vacuum level AP_current can be described by the formula:

<img file="ES2334573T3_D0004.tif" />

If it is determined that the rate of change of current vacuum level AP_current is less than AP learned evacuation change rate_evac, a block 134 could activate the alarm routine. However, if the current vacuum level change rate AP_current exceeds AP learned evacuation change rate_evac, a block 136 instructs the processor 36 to store the increasing current vacuum level P_measure in memory 38 as the stored vacuum level P_stored.

A block 138 compares the current vacuum level P_measure with a desired maximum vacuum level P_max. If the current vacuum level is lower than the desired maximum vacuum level P_max, the monitoring routine 120 enters a loop 140 and proceeds to test and store the current vacuum level P_measure until the maximum vacuum level P is detected_maxwanted. However, if the current vacuum level P_measure exceeds the desired maximum vacuum level P_max, a block 142 causes the control valve 30 to close.

A block 144 deactivates the STP 22 after completing the evacuation of the now sealed interstitial space 18. Thus, the monitoring routine 120 has recharged the vacuum level within the interstitial space 18. In operation, the evacuation or increase in the vacuum level of the interstitial space 18 proceeds along the learned evacuation vacuum curve 102, and the monitoring routine 120 continuously verifies that the current vacuum level P_measure stay within the predefined range defined by lines 102a and 102b. Simultaneously, the time required to recharge the interstitial space 18 to the desired maximum vacuum level P_max can be compared with the maximum time T_mSx. If the current recharge time exceeds the maximum time T_max, a leak or other abnormality is assumed and alarm routine 134 is activated.

A block 146 restarts the monitoring routine 120 such that the vacuum sensor 32 tests and measures the current vacuum level P_measure at block 122. At block 124, the current newly recharged vacuum level P_measure is compared to the minimum allowable vacuum level P_min (for example, 51 mm Hg (2 in Hg) or zero vacuum). Since the current recently recharged vacuum level P_measure is greater than the minimum allowable vacuum level P_min, a block 148 compares the current vacuum level change rate P_current with AP learned rate of change_descendingdetermined during self-learning routine 50.

As discussed above, the interstitial space 18 is sealed and the monitoring routine 120 measures the current vacuum level P_measure to determine whether the decrease in the current vacuum level P_measure it is attributable to the natural permeation properties of the underground storage system 10 or to a leak.

Furthermore, the comparison between the learned vacuum curve and the current vacuum level P_measure can be based on the difference between the rate of downward change AP_falling and the current exchange rate AP_current or simply in the difference between the current vacuum level P_measure and the Vacuum Curve itself learned.

A block 150 instructs the processor 36 to store the current vacuum level P_measure in memory 38 as the stored vacuum level P_stored. At this point, the monitoring routine 120 enters a loop 152 and proceeds to test and store the current vacuum level P_measure until the minimum allowable vacuum level is detected, at which point the STP 22 is activated to evacuate the interstitial space 18.

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Although the embodiments described herein have been directed to vacuum level measurements and analysis, it will be understood that it is possible to employ an overpressure within interstitial space 18 to provide an appropriate pressure gradient for measurement by a self-learning routine 50 and the monitoring by a 120 monitoring routine. Furthermore, it will be understood that the current vacuum level P_measure and the calculated exchange rates can be determined manually. For example, manual instructions may instruct control unit 34 to test and store the current vacuum level P_measure within the interstitial space 18. In addition, an operator can employ the exchange rate formulas and concepts discussed above along with the stored vacuum levels Pai_maDinner_dor to manually calculate the desired exchange rates.