Method for determining status of floating roof and floating roof monitoring system

Abstract

A method for determining a state of a floating roof of a storage tank using a radar level gauge system disposed above the floating roof of the tank and a floating roof monitoring system are provided. The radar level gauge system is controllable to selectively evaluate reflected energy traveling toward the radar level gauge system along each of a plurality of different propagation directions. The method comprises the following steps: radiating an electromagnetic transmit signal by the radar level gauge system toward the floating roof; receiving an electromagnetic reflection signal by the radar level gauge system resulting from reflection of the transmit signal at the floating roof; selectively evaluating, by the radar level gauge system, reflected energy traveling from the floating roof toward the radar level gauge system along each of the plurality of different propagation directions based on the reflection signal; and determining the state of the floating roof based on the selective evaluation.

Description

Technical Field

[0001] The present invention relates to a monitoring system and to a method of determining the status of a floating roof of a storage tank. Background Art

[0002] In some tanks, particularly storage tanks for petroleum products such as those used in refineries, a floating roof is often used that floats on the liquid product in the tank and is therefore vertically displaceable. Therefore, the floating roof is able to track the level of the liquid product as the product is discharged from or filled into the tank. This type of floating roof is used to prevent product vapor from leaking from the tank into the atmosphere and to prevent rain, etc., from entering the space defined by the tank wall and the floating roof. Typically, protection against leakage and ingress is enhanced by sealing devices installed along the periphery of the floating roof to provide a seal and sliding contact with the inner wall of the tank. Furthermore, the use of a roof that floats on the liquid product minimizes the volume between the liquid surface and the roof, thereby minimizing the amount of gaseous product in the tank.

[0003] The floating roofs used for these purposes are usually manufactured as large steel structures with floating devices (pontoons) and have a weight of about one hundred tons and a diameter of several tens of meters. With regard to size and environmental aspects, it is important to monitor the normal operation and undisturbed floating of the floating roof so that any disturbance of the floating roof can be identified at an early stage.

[0004] Different situations causing interference with normal operations and floating have been observed in the past.

[0005] When the tank is being filled, a portion of the floating roof may become lodged against the inner wall of the tank. As filling proceeds, the floating roof may then be partially submerged by the liquid product, potentially leading to a dangerous situation.

[0006] When draining a tank, a portion of the floating roof may become lodged against the tank's inner wall. As the drain progresses, large amounts of air can enter the space between the liquid and the floating roof. If the roof subsequently collapses, an explosive atmosphere can form above the collapsed roof.

[0007] Regulations are becoming increasingly stringent to minimize evaporation of liquid from floating roof tanks. This has resulted in floating roof designs that exhibit higher friction in the seals between the perimeter of the floating roof and the inner wall of the tank. This increased friction can increase the risk of the roof becoming stuck.

[0008] Functional and flotation anomalies may also occur if a large amount of rain or snow is present on the roof or is unevenly distributed on the roof. This may cause the roof to sink or tilt and collapse.

[0009] These problems, as described above, have been a concern in the oil industry for many years, and the need for systems that address these problems appears to be growing.

[0010] Various existing methods of monitoring floating roofs are based on measuring the relative position or inclination of several locations on the floating roof when in operation.There are also monitoring methods that combine the above methods with, for example, video monitoring or detecting the presence of gas on top of the floating roof. Summary of the Invention

[0011] In view of the above, a general object of the present invention is to provide improved monitoring of floating roofs, in particular where uncomplicated equipment installation is required.

[0012] Aspects of the present invention are based on the recognition that selective evaluation of reflected energy from a floating roof travelling in each of a plurality of different propagation directions can be used as a basis for determining the state of the floating roof and this allows floating roof monitoring using a single radar level gauge system arranged above the floating roof.

[0013] According to a first aspect of the present invention, there is provided a method for determining a state of a floating roof of a storage tank using a radar level gauge system arranged above the floating roof, the radar level gauge system comprising a transceiver, an antenna arrangement, and a processing circuit, wherein the radar level gauge system is controllable to selectively evaluate reflected energy traveling toward the antenna arrangement along each of a plurality of different propagation directions, the method comprising the steps of: radiating, by the radar level gauge system, an electromagnetic transmit signal toward the floating roof; receiving, by the radar level gauge system, an electromagnetic reflected signal generated by reflection of the transmit signal at the floating roof; selectively evaluating, by the radar level gauge system, reflected energy traveling from the floating roof toward the antenna arrangement along each of the plurality of different propagation directions based on the reflected signal; and determining the state of the floating roof based on the selective evaluation.

[0014] According to a second aspect of the present invention, there is provided a floating roof monitoring system for determining the state of a floating roof of a storage tank, the floating roof monitoring system comprising a radar level gauge system for arrangement above the floating roof, the radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals; an antenna device coupled to the transceiver for radiating the electromagnetic transmit signal toward the floating roof and receiving an electromagnetic reflection signal generated by reflection of the transmit signal by the floating roof; and a processing circuit configured to: control the transceiver to generate and transmit the electromagnetic transmit signal; selectively evaluate reflected energy traveling from the floating roof toward the antenna device along each of a plurality of different propagation directions based on the electromagnetic reflection signal generated by reflection of the transmit signal at the floating roof and received by the transceiver; and determine the state of the floating roof based on the selective evaluation.

[0015] Embodiments of the method and system according to the present invention allow for the determination of various aspects of the floating roof's condition. These aspects may include, for example, an indication of the local inclination of the floating roof, the location of a plurality of predetermined locations on the floating roof, the stress distribution in the roof, the positioning of the floating roof relative to the liquid product in the tank, and the like. Based on the information determined regarding the condition of the floating roof, an early warning can be provided to the tank operator indicating that the floating roof is not functioning as intended, and optionally also indicating the type of failure.

[0016] In the context of this application, the term "selectively evaluating" should be understood to mean evaluating at least one characteristic of reflected energy traveling from the floating roof separately for different propagation directions. Examples of the at least one characteristic to be evaluated may include, for example, the magnitude of the reflected energy, the distance from the source (reflection point / reflection area) of the reflected energy, etc.

[0017] The antenna arrangement can be implemented in the form of a radiating antenna that can be controlled to transmit in different directions and / or receive from different directions. Such an antenna can be physically movable, and / or the preferred direction of transmission / reception can be electronically controllable. In the latter case, the antenna can be a so-called patch antenna that can be controlled using phased array control methods that are well known per se. Alternatively, or in combination, the antenna arrangement can include multiple antennas that are configured to transmit / receive in different directions.

[0018] A "transceiver" may be one functional unit capable of transmitting and receiving electromagnetic signals, or may be a system comprising separate transmitter and receiver units.

[0019] It should be noted that the processing circuitry may be provided as one device or as a plurality of devices working together.

[0020] In summary, the present invention therefore relates to a method for determining a state of a floating roof of a storage tank using a radar level gauge system arranged above the floating roof, the radar level gauge system being controllable to selectively evaluate reflected energy travelling towards the radar level gauge system along each of a plurality of different propagation directions, the method comprising the steps of: radiating, by the radar level gauge system, an electromagnetic transmit signal towards the floating roof; receiving, by the radar level gauge system, an electromagnetic reflection signal resulting from reflection of the transmit signal at the floating roof; selectively evaluating, by the radar level gauge system, based on the reflection signal, reflected energy travelling from the floating roof towards the radar level gauge system along each of the plurality of different propagation directions; and determining the state of the floating roof based on the selective evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings which show a currently preferred embodiment of the invention, in which:

[0022] Figure 1 schematically illustrates an exemplary floating roof tank installation including a floating roof monitoring system according to an embodiment of the present invention;

[0023] Figure 2 is Figure 1 Schematic diagram of an exemplary radar level gauge system included in a floating roof monitoring system;

[0024] Figure 3 is a flow chart schematically illustrating an example embodiment of the method according to the present invention;

[0025] Figures 4A to 4B Schematically illustrates an example embodiment of the method and system according to the present invention;

[0026] Figures 5A to 5B schematically illustrates other example embodiments of the method and system according to the present invention; and

[0027] Figure 6 Further exemplary embodiments of the method and system according to the invention are schematically shown. DETAILED DESCRIPTION

[0028] Figure 1 A floating roof monitoring system 1 according to an exemplary embodiment of the present invention is schematically shown. The floating roof monitoring system 1 is arranged at a storage tank 3 having a tank wall 5 and a floating roof 7. The floating roof 7 floats on a liquid product 9 in the storage tank 3. As mentioned in the background section, the product 9 may be a petroleum product or a product having sufficient density to float the floating roof 7 (typically at a high pressure). Figure 1 any other liquid product on a float not shown in the drawing.

[0029] like Figure 1 As shown schematically, the floating roof monitoring system 1 comprises a radar level gauge system 11 for being arranged above the floating roof 7 and radar level gauges to be arranged in corresponding target areas 15a to 15c of the floating roof 7. Figure 1 It should be noted that an embodiment of the floating roof monitoring system 1 according to the present invention may comprise only the radar level gauge system 11, in particular when the floating roof 7 already has a structure suitable for reflecting microwaves.

[0030] In addition to the floating roof monitoring system 1, Figure 1 The tank 3 in the tank also has a filling level determination system 17 comprising a radar level gauge unit 19 , of a configuration known per se, mounted on a stationary pipe 21 for measuring the filling level of the product 9 in the tank 3 .

[0031] Figure 2is Figure 1 FIG. 1 is an enlarged view of the radar level gauge system 11 included in the floating roof monitoring system 1, which schematically shows the functional components of the radar level gauge system 11. Figure 2 The radar level gauge system 11 comprises a transceiver 23, an antenna arrangement (here in the form of a patch antenna 25), a processing circuit 27, a communication interface 29 and a communication antenna 31 for enabling wireless communication between the radar level gauge system 11 and an external unit, such as a control system (not shown). Figure 2 The radar level gauge system 11 in the embodiment can be controlled to selectively evaluate reflected energy travelling in a plurality of different propagation directions towards the antenna arrangement 25. This can be achieved in a manner known per se, for example by controlling the superposition of energy picked up by the patches of the patch antenna 25 by physically pointing the antenna in different directions at different times or by providing the radar level gauge system 11 with an antenna arrangement comprising a plurality of antennas oriented in mutually different directions.

[0032] The radar level gauge system 11 included in the floating roof monitoring system 1 can be supported by means of suitable supporting means (e.g. Figure 2 The support 33 (shown schematically in FIG) is fixedly attached to the tank wall 5.

[0033] exist Figure 2 In the exemplary embodiment of the invention, the communication to / from the radar level gauge system 11 is shown as wireless communication. Alternatively, for example, communication can be performed via an analog and / or digital wired communication channel. For example, the communication channel can be a two-wire 4mA to 20mA loop, and a signal representing the state of the floating roof can be transmitted by providing a certain current corresponding to the filling level on the two-wire 4mA to 20mA loop. Digital data can also be sent across such a 4mA to 20mA loop using the HART protocol. In addition, a purely digital communication protocol such as Modbus or Foundation Fieldbus can be used.

[0034] In the following, reference will be made to Figure 3 An example embodiment of the method according to the present invention is described with reference to the flowchart in FIG. 1 and the other figures indicated herein.

[0035] In a first step 100, an electromagnetic transmission signal S is radiated towards the floating roof 7 by the radar level gauge system 11 included in the floating roof monitoring system 1. T The transmission signal S T The transmission signal S may be formed by a set of measurement scans (ie one or more measurement scans), or the transmission signal S T Furthermore, depending on the specific implementation of the monitoring system and method according to the present invention, the emission signal S TA substantially fixed radiation pattern may be presented, or it may be directed sequentially to different target areas 15a to 15c on the floating roof 7 along different propagation directions.

[0036] In the following step 101 , the radar level gauge system 11 included in the floating roof monitoring system 1 receives the transmitted signal S via the antenna device 25 . T The electromagnetic reflection signal S generated by the reflection at the floating roof 7 R .

[0037] Upon receiving the reflected signal S R Then, in step 102, the radar level gauge system 11 generates the reflected signal S R Selectively evaluating the propagation direction r from the floating roof 7 along each of a plurality of different propagation directions R The reflected energy travels towards the antenna device 25 .

[0038] Based on the selective evaluation performed in step 102, the state of the floating roof 7 is then determined in step 103. Then, in step 104, depending on the determined state of the floating roof 7, a signal indicating the determined state may be provided continuously or conditionally.

[0039] Figures 4A to 4B Example embodiments of the method and system according to the invention are schematically shown.

[0040] Figure 4A is a schematic diagram of a floating roof monitoring system 1, wherein the radar level gauge system 11 included in the floating roof monitoring system 1 is configured to generate a transmission signal S T , and transmits and radiates the transmission signal S substantially vertically toward the first target area 15a of the floating roof 7 T The radiated energy of the transmitted signal is along Figure 4A The vertical line 35 in the can have its maximum value. Figure 3 As explained in the flowchart in (step 101), the reflected signal S is received. R , and selectively evaluating the reflected energy traveling from the floating roof 7 toward the antenna arrangement 25 for each of a plurality of different propagation directions (step 102). Figure 4A In the example embodiment shown, the estimated propagation direction is in the R The reflected radiation pattern is indicated and arrives in the direction of the antenna arrangement 25 .

[0041] exist Figures 4A to 4B In the example embodiment of , the selective evaluation step (step 102) involves determining, for each of a plurality of propagation directions, a measurement indicative of the amount of reflected energy travelling from the first target area 15a towards the antenna arrangement 25. Figure 4BIn the selective evaluation, the propagation direction is determined by the propagation direction and Figure 4A The corresponding angle α between the vertical lines 35 in is represented.

[0042] The step of determining the state of the floating roof (step 103) here comprises estimating the inclination angle α1 of the first target area 15a based on measurement results indicating the amount of reflected energy traveling from the first target area 15a towards the antenna device 25 determined for each of a plurality of propagation directions. Figure 4B In this case, if Figures 4A to 4B As shown, the direction of the maximum amount of reflected energy (indicated by angle α1) corresponds to the inclination angle of the floating roof 7 at the first target area 15a. The deviation or change in the inclination angle of the floating roof 7 at the first target area 15a may indicate that the floating roof 7 is tilting (e.g., Figure 4A In either case, the estimated tilt angle α1 may be compared to a predetermined threshold tilt angle and a signal indicating this may be provided when the estimated tilt angle α1 exceeds the predetermined threshold tilt angle.

[0043] Figures 5A to 5B Further exemplary embodiments of the method and system according to the invention are schematically illustrated.

[0044] Figure 5A is a schematic diagram of a floating roof monitoring system 1, wherein the radar level gauge system 11 included in the floating roof monitoring system 1 is configured to generate, transmit and radiate the following transmission signal S T , the transmitted signal S T The first signal portion S comprises a first target area 15a directed substantially vertically towards the floating roof 7. T1 , a second signal portion S directed to the second target area 15b T2 and a third signal portion S directed to the third target area 15c T3 . Figure 5A The floating roof monitoring system 1 in the embodiment of the present invention may optionally include microwave reflector devices arranged in the target areas 15a to 15c. It should be noted that the first signal portion S T1 , the second signal part S T2 and the third signal portion S T3 Can be used as a single narrow beam signal or as a wide beam signal S T part of it for emission / radiation.

[0045] As mentioned above Figure 3As illustrated in the flowchart in FIG. 1 (step 101), a reflected signal is received and then the reflected energy traveling from the floating roof 7 toward the antenna arrangement 25 is selectively evaluated for each of a plurality of different propagation directions (step 102). Figure 5A In the example embodiment shown, the evaluated propagation direction is the direction from the respective target area 15 a to 15 c to the antenna arrangement 25 .

[0046] exist Figures 5A to 5B In the example embodiment of the embodiment of the present invention, the selectivity evaluation step (step 102) includes: based on S T1 With S R1 The timing relationship between the first position (x1, y1, z1) of the first target area is determined based on S T2 With S R2 The timing relationship between the second position (x2, y2, z2) of the second target area is determined, and the timing relationship between the second position (x2, y2, z2) of the second target area is determined based on S T3 With S R3 The timing relationship between them determines the third position (x3, y3, z3) of the third target area.

[0047] The step of determining the state of the floating roof (step 103) here comprises determining a representation of the floating roof 7 based on the respective position of each of the target areas 15a to 15c of the floating roof 7. Figure 5B The representation of the floating roof 7 in the form of a plane with the direction and magnitude of the inclination is determined based on the representation of the three positions in the . Figures 4A to 4B As further described for a single target area, a more complex representation of the floating roof 7 can be formed. Such a representation, which carries information about the global orientation of the floating roof 7 as well as information about the local inclination, can be used to determine shape changes of the floating roof 7. If the determined representation of the floating roof 7 fails to meet at least one predetermined criterion, a signal indicating this can be provided.

[0048] In any of the example embodiments described so far, the transmission signal S T and the reflected signal S R A measurement indicating the vertical distance between the radar level gauge system 11 of the floating roof monitoring system 1 and the floating roof 7 is determined, and the state of the floating roof 7 can be additionally determined based on the measurement.

[0049] For example, if it is determined based on the vertical distance that the floating roof 7 moves less or more than expected when product 9 is added to the tank 3 at a known addition rate or removed from the tank 3 at a known removal rate, this can be regarded as an indication that the floating roof 7 is not following the movement of the liquid product 9 in a satisfactory manner, and a signal indicating this can be provided.

[0050] Furthermore, it is possible to determine the filling level from the filling level determination system 17 (see Figure 1 ) obtains a measurement indicating the filling level of the product 9 in the tank 3, and the determination of the state of the floating roof 7 can be additionally based on the measurement indicating the filling level. For example, a larger-than-expected difference between the level of the product 9 and the level of the floating roof 7 can indicate the presence of an aerated gap between the surface of the liquid product 9 and the floating roof 7.

[0051] Figure 6 Further example embodiments of the method and system according to the present invention are schematically shown. Figure 6 The floating roof monitoring system 1 schematically shown in FIG. 1 comprises a radar level gauge system 11 and a first microwave reflector device 13a, a second microwave reflector device 13b and a third microwave reflector device 13c. Figure 6 In an exemplary configuration, each of the microwave reflector devices 13a to 13c includes a retroreflector 35a to 35c for microwave radiation, an attachment structure 37a to 37c for attaching the microwave reflector device 13a to 13c to a target area 15a to 15c of the floating roof 7, and optionally also includes a sensing device 39a to 39c. In embodiments including the optional sensing device 39a to 39c, the sensing device 39a to 39c can be, for example, a battery-powered tilt sensor or any other type of useful sensor. Advantageously, each sensing device 39a to 39c is capable of wireless communication with the radar level gauge system 11 included in the floating roof monitoring system 1 and / or an external system, such as a host system. Signals from the sensing devices 39a to 39c included in the microwave reflector devices 13a to 13c can be used to enhance the determined representation of the floating roof 7, which in turn can be used to provide enhanced information about the state of the floating roof 7.

[0052] Those skilled in the art will appreciate that the present invention is by no means limited to the preferred embodiments described above. Instead, numerous modifications and variations are possible within the scope of the appended claims.

Claims

1. A method for determining a state of a floating roof of a storage tank using a radar level gauge system arranged above the floating roof of the tank, the radar level gauge system comprising a transceiver, an antenna device and a processing circuit, wherein: The radar level gauge system is controllable to selectively evaluate reflected energy travelling towards the antenna arrangement in each of a plurality of different propagation directions, the method comprising the steps of: radiating an electromagnetic transmission signal from the radar level gauge system toward the floating roof; receiving, by the radar level gauge system, an electromagnetic reflection signal generated by reflection of the transmission signal at the floating roof; selectively evaluating, by the radar level gauge system based on the reflected signal, reflected energy traveling from the floating roof toward the antenna arrangement along each of the plurality of different propagation directions; and determining a state of the floating roof based on a selective evaluation, in: The radiating step includes: radiating the transmission signal toward a first target area on the floating roof; The step of selectively evaluating comprises determining, for each of the plurality of propagation directions, a measurement indicative of an amount of reflected energy travelling from the first target area towards the antenna arrangement; and The step of determining the state of the floating roof comprises estimating the inclination of the first target area based on a measurement result indicating the amount of reflected energy travelling from the first target area toward the antenna device determined for each of the plurality of propagation directions, wherein the propagation direction of the maximum amount of reflected energy is taken to correspond to the inclination of the first target area.

2. The method according to claim 1, further comprising the steps of: comparing the estimated inclination of the first target area with a predetermined threshold inclination; and When the estimated tilt angle exceeds the predetermined threshold tilt angle, a signal indicating this is provided.

3. The method according to claim 1 or 2, wherein: The method further comprises the steps of: determining a measurement indicating a vertical distance between a reference position of the radar level gauge system and the floating roof based on a timing relationship between the transmitted signal and the reflected signal; and The determination of the status of the floating roof is additionally based on measurements indicative of the vertical distance.

4. The method according to claim 1 or 2, wherein: The method further comprises the steps of: acquiring a measurement indicative of a fill level of product in the tank; and The determination of the state of the floating roof is additionally based on measurements indicative of the filling level.

5. A floating roof monitoring system for determining a state of a floating roof of a storage tank, the floating roof monitoring system comprising a radar level gauge system for arrangement above the floating roof, the radar level gauge system comprising: transceivers for generating, transmitting and receiving electromagnetic signals; an antenna device coupled to the transceiver for radiating an electromagnetic transmission signal toward the floating roof and receiving an electromagnetic reflection signal generated by reflection of the transmission signal by the floating roof; as well as processing circuitry configured to: controlling the transceiver to generate and transmit an electromagnetic transmission signal; selectively evaluating reflected energy traveling from the floating roof toward the antenna arrangement along each of a plurality of different propagation directions based on an electromagnetic reflection signal generated by reflection of the transmit signal at the floating roof and received by the transceiver; as well as determining a state of the floating roof based on a selective evaluation, Wherein, the processing circuit is configured to: determining, for each of the plurality of propagation directions, a measurement indicative of an amount of reflected energy traveling from a first target area on the floating roof toward the antenna arrangement; estimating an inclination of the first target area based on a measurement result indicating an amount of reflected energy travelling from the first target area towards the antenna arrangement determined for each of the plurality of propagation directions, wherein the propagation direction of the maximum amount of reflected energy is taken to correspond to the inclination of the first target area; and A state of the floating roof is determined based on the estimated inclination angle.

6. The floating roof monitoring system according to claim 5, further comprising at least a first microwave reflector device, the first microwave reflector device being arranged in at least the first target area on the floating roof.

7. The floating roof monitoring system according to claim 6, wherein: The first microwave reflector device comprises a retroreflector for microwave radiation.

8. The floating roof monitoring system according to claim 6, wherein: The floating roof monitoring system includes a first microwave reflector device disposed in a first target area on the floating roof, and a second microwave reflector device disposed in a second target area on the floating roof laterally spaced from the first target area.

9. The floating roof monitoring system according to claim 8, wherein: the first microwave reflector apparatus comprising a first sensing device for sensing a characteristic of the floating roof at the first target area, and a first communication circuit for providing a signal indicative of the sensed characteristic; as well as The second microwave reflector apparatus includes a second sensing device for sensing a characteristic of the floating roof at the second target area, and a second communication circuit for providing a signal indicative of the sensed characteristic.

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