Sludge level detection device and sludge level detection method

Abstract

A sludge level detection device (100) is provided with: an optical-fiber-incorporated cable (1) which is disposed in an oil storage tank having a floating roof, and which incorporates an optical fiber for detecting strain generated by an external force; a cable moving / disposing device (3) which movably disposes the optical-fiber-incorporated cable in accordance with the installation position of the floating roof while one end of the optical-fiber-incorporated cable is supported by the floating roof; a cable movement support tool (2) which is provided on the cable moving / disposing device and movably supports the other end of the optical-fiber-incorporated cable (1); and a signal measurement processing device (10) for measuring a signal generated by a force applied to the optical-fiber-incorporated cable (1) and calculating a predetermined physical quantity on the basis of the signal. The level of sludge stored in the oil storage tank is detected on the basis of the physical quantity obtained by measuring, by means of the signal measurement processing device (10), the signal generated due to application of the force to the optical-fiber-incorporated cable (1) that has moved in accordance with the installation position of the floating roof.

Description

Sludge level detection device and sludge level detection method

[0001] This application relates to a sludge level detection device and a sludge level detection method.

[0002] When determining the specifications of oil storage tanks in an oil refinery, it is essential to predict and evaluate the amount and distribution of oil sludge formed by storing oil. In evaluating the amount and spatial distribution of oil sludge, the measurement method used is important, but it is known that the selection of this measurement method depends on many factors, including technical factors such as the type of sludge to be measured, the size of the oil storage tank, and the installation location, as well as operational factors such as the size and weight of the measuring equipment and the type of roof.

[0003] Incidentally, the aforementioned oil sludge is a stable, multi-component substance consisting of mineral oil, mineral mixtures, and water. However, because its formation is caused by the physicochemical interaction between petroleum or petroleum products and oxygen, water, and mechanical impurities, no two sludges in nature are identical; they are all very different.

[0004] In particular, sludge in storage tanks is known to form as a result of physical and chemical interactions between petroleum products, moisture, mechanical impurities, acids, and the materials used in the outer walls of the storage tanks. Numerous studies have shown that the hydrocarbon content in sludge ranges from 5% to 90%, the moisture content from 1% to 52%, and the solids content from 0.8% to 86%, meaning that the density of sludge can range very broadly. It is also known that the pour point ranges from -3°C to 80°C, and the flash point ranges from 35°C to 120°C (see, for example, Non-Patent Document 1).

[0005] On the other hand, petroleum storage tanks in actual use can be broadly classified into fixed-roof tanks and floating-roof tanks. The latter can be further divided into external floating-roof tanks and internal floating-roof tanks used for low-flash-point liquids such as gasoline and ethanol. In particular, the latter tank has a conical roof, and an internal floating roof moves up and down with the liquid level to contain vapors from low-flash-point fuels (see, for example, Non-Patent Document 1).

[0006] M. Monteiro et al. , “ Experimental Investigations of Various Methods of Sludge Measurements in Storage Oil Tanks“, Advances in Remote Sensing, 2015, 4, pp. 119-137

[0007] International Publication No. 2022 / 079855, International Publication No. 2014 / 083989

[0008] Therefore, based on the above circumstances, we will consider the best method for predicting and evaluating the amount and distribution of oil sludge (hereinafter also simply referred to as sludge), and organize the challenges in realizing this best method. First, we will describe conventional sludge inspection methods and tools below.

[0009] When examining conventional sludge inspection methods and tools, it is known that inspection methods (such as inspection of volume and spatial distribution) can be broadly divided into contact technologies, which require immersion of the inspection equipment (probe) in the oil, and non-contact technologies, which do not require this.

[0010] The former category includes three methods: manual probe testing, measurement of density and viscosity with respect to depth, and a method called acoustic profiling. These methods require inserting a probe from the roof of the tank, and the number and location of the probes must be appropriate to obtain good results, thus limiting the types of tanks that can be used.

[0011] On the other hand, the latter non-contact technology includes a method using infrared thermography. This technology is not limited by the type of tank. However, while the data obtained corresponds to the distribution of sludge height along the tank wall, it cannot provide data on sludge inside the tank. Therefore, it has the disadvantage of having the lowest measurement accuracy compared to the former contact method.

[0012] From the examination of the four inspection methods for sludge described above, there is no single universal method for estimating the volume and spatial distribution of sludge in petroleum storage tanks. In any of these methods, explosion prevention and fire prevention are critical issues, and accidents may occur depending on the extent of equipment damage. Therefore, it is considered necessary to combine three methods, such as directly measuring density and viscosity, acoustic profiling, and infrared thermography, to be able to inspect various types of petroleum storage tanks (see, for example, Non-Patent Document 1).

[0013] As described above, there is currently no conventional sludge inspection method that can accurately predict and evaluate the amount and spatial distribution of oil sludge using a single method.

[0014] This disclosure provides a technology to solve the above-mentioned problems, and aims to provide a detection device that measures the strain caused by bending in an optical fiber cable due to buoyancy generated by sludge in an oil storage tank, and detects the level of sludge generated in the optical fiber cable based on the distribution of shear force generated in the optical fiber cable calculated from the measurement results.

[0015] The sludge level detection device of this disclosure comprises: an optical fiber embedded cable, which is placed inside an oil storage tank that stores oil and has a liquid-level tracking section, and which contains an optical fiber that detects strain generated by an external force; a cable moving and positioning device, which has one end fixed to a predetermined position in the oil storage tank and the other end fixed to the liquid-level tracking section, and one end of the optical fiber embedded cable is supported by the liquid-level tracking section, thereby moving the optical fiber embedded cable in accordance with the installation position of the liquid-level tracking section; a cable moving support provided on the cable moving and positioning device, which moves and supports the other end of the optical fiber embedded cable; and a signal measurement processing device that measures a signal generated in the optical fiber due to a force applied to the optical fiber embedded cable, and calculates predetermined physical quantities for the optical fiber embedded cable based on the measured signal. The present invention is characterized in that, when the optical fiber-embedded cable is moved to a predetermined position within the petroleum storage tank corresponding to the installation position of the liquid-level-following part, and force is applied to the optical fiber by the substance stored inside the petroleum storage tank, the signal generated in the optical fiber is measured by the signal measurement processing device, and the level of sludge stored inside the petroleum storage tank is detected based on the amount of bending deformation obtained.

[0016] The sludge level detection device of this disclosure measures the strain caused by bending in an optical fiber cable due to buoyancy generated by sludge in an oil storage tank, and based on the distribution of shear force generated in the optical fiber cable calculated from these measurement results, it is possible to provide a detection device that detects the level of sludge generated in an oil storage tank.

[0017] This figure shows a conceptual model for explaining the sludge level detection device of Embodiment 1. This figure shows a theoretical model using a bending model of a two-point supported beam for analyzing the shear force on the cable of the sludge level detection device of Embodiment 1. This is a flowchart for explaining the method of detecting the sludge level related to the sludge level detection device of Embodiment 1. This figure shows an example of the sludge density distribution related to the sludge level detection device of Embodiment 1. This figure shows a distribution model of fiber strain measured by an optical fiber embedded cable related to the sludge level detection device of Embodiment 1. This figure shows an example of the shear force distribution calculated based on the fiber strain shown in Figure 5. This figure shows an example of the fiber strain distribution measured by an optical fiber embedded cable related to the sludge level detection device of Embodiment 1. This figure shows the results after filtering the measurement data in Figure 7. This figure explains one method of determining the sludge level based on an example of shear force distribution calculated from the data in Figure 8. This figure explains another method of determining the sludge level based on an example of shear force distribution calculated from the data in Figure 8. This figure explains the expected results of the sludge density distribution in an oil storage tank based on the data in Figure 9. This figure shows an example of a lightweight cable with a built-in optical fiber covering related to the sludge level detection device of Embodiment 1.

[0018] Therefore, in the following, we propose a newly developed inspection method to solve the above problems using a single inspection method. In particular, we will explain in detail a sludge level detection device, which is an inspection method used for sludge inspection of internal floating roof type oil storage tanks (hereinafter abbreviated as floating roof type oil storage tanks, or simply oil storage tanks) equipped with a floating roof that follows the liquid surface.

[0019] Embodiment 1. The overall configuration of the sludge level detection device according to Embodiment 1 will be described below with reference to Figure 1.

[0020] Figure 1 is a conceptual diagram showing a sludge level detection device 100 according to this embodiment 1. This sludge level detection device 100 is broadly composed of a part that includes a sensor for detecting sludge and is installed inside the internal floating roof type oil storage tank 200, which will be described below, and a part that includes a sensor signal processing device installed outside the floating roof type oil storage tank 200 and processes the signal detected by the sensor to calculate and determine the sludge level (corresponding to the sludge thickness or volume in the z direction) and spatial distribution inside the tank.

[0021] Here, the petroleum storage tank 200 has a conical or planar ceiling wall 201, a cylindrical side wall 202 which is the outer surface connected to the ceiling wall 201, and a bottom 203. Oil (hereinafter also referred to as petroleum) is stored inside this tank, and inside, including this petroleum, there are usually three layers, namely, from top to bottom, layers of air, oil, and sludge.

[0022] In this context, the changes in density, or buoyancy, of these three layers in the depth direction (hereinafter also referred to as the z-direction) are conceptually shown on the right side of Figure 1, in a form corresponding to the depth direction with the position of the floating roof 6 of the oil storage tank 200 as the reference point. In the graph shown on the right side of Figure 1, the changes in density of the oil layer and the sludge layer (shown by solid lines) are assumed to be constant in the depth direction, with the sludge layer having a larger value. On the other hand, the changes in buoyancy of the oil layer and the sludge layer are assumed to have a linear slope with respect to the depth direction, with the sludge layer having a larger slope. It should be noted that the changes in buoyancy of the sludge layer may also have a curvilinear slope with respect to the depth direction.

[0023] Furthermore, a floating roof 6 is provided on the upper surface portion of the oil layer inside this tank, which moves up and down along the vertical direction (the z direction shown in Figure 1) as indicated by the dotted arrow a, according to the amount of oil being stored. The dashed line in Figure 1 indicates the centerline of the shape of the oil storage tank 200. In Figure 1, the right side of the oil storage tank 200 is mainly shown as a cross-sectional view based on the centerline of the shape.

[0024] Next, the details of the sludge level detection device 100 will be further explained below with reference to Figure 1. First, the part including the sensor for detecting sludge, which is installed inside the petroleum storage tank 200, will be described.

[0025] In Figure 1, a cable clamp 7 is provided at the height of the floating roof 6 to fix the upper end of an optical fiber embedded cable 1, which contains an optical fiber for detecting the sludge level, to the central axis portion of the floating roof 6 of the oil storage tank 200.

[0026] In this case, the height position of the cable clamp 7 (distance from the bottom 203 of the oil storage tank 200; see the graph on the right in Figure 1) changes according to the height position of the floating roof 6, which changes as the amount of stored oil increases or decreases. That is, the cable clamp 7 is provided at one end of the cable moving and positioning device 3 for moving the position of the cable clamp 7 so that it can change in response to the change in the height position of the floating roof 6 (see the dotted arrow a in the z direction in Figure 1).

[0027] Here, this cable movement and arrangement device 3 is composed of, for example, an upper link 4b connected to the fiber-optic cable内置 cable 1 at the position of the cable clamp 7, two links including a lower link 4a which is a link different from the link 4b, a hinge 5 that rotatably connects these two links, and a drive device (not shown). Then, for example, by moving the position of the hinge 5 upward with the above drive device, the position of the cable clamp 7 can be moved upward. At this time, the installation position of the fiber-optic cable内置 cable 1 as a whole changes from the position shown by the solid line to the position shown by the dashed line in FIG. 1. Note that the lower end of the link 4a is fixed to the side wall 202 of the tank near the bottom 203 of the tank.

[0028] Further, the lower end portion of the fiber-optic cable内置 cable 1 is attached to the cable movement support tool 2. And this cable movement support tool 2 is installed movably on the above link 4a as shown by the dotted arrow b. Therefore, the lower end portion of the fiber-optic cable内置 cable 1 moves along with the cable movement support tool 2 along the link 4a in response to the position movement of the upper end portion of the fiber-optic cable内置 cable 1 whose height position changes according to the change in the height position of the floating roof 6.

[0029] In this case, the fiber-optic cable内置 cable is arranged in a form that extends radially in the radial direction when viewed from the central axis of the above oil storage tank from the position of the cable clamp 7 which is one connection position to the position of the cable movement support tool 2 which is the other connection position. Here, one end of the cable movement and arrangement device 3 where the cable movement support tool 2 is installed movably is fixed to the annular side wall 202 of the above oil storage tank 200.

[0030] In FIG. 1, the plurality of arrows shown in the central portion of the fiber-optic cable内置 cable 1 indicate that the upward plurality of arrows indicate the buoyancy applied to the fiber-optic cable内置 cable 1, and the downward plurality of arrows indicate the weight (gravity) applied to the fiber-optic cable内置 cable 1. Also, the symbol α indicates the direction of the buoyancy applied to the fiber-optic cable内置 cable 1 (the angle with respect to the normal line of the fiber-optic cable内置 cable 1), and this will be described in detail later using figures.

[0031] In the above description, the case where the floating roof 6 moves up and down in the vertical direction according to the amount of oil stored in the oil storage tank has been described. However, the present invention is not limited to this, and the same description is possible even when the position of the floating roof hardly changes in the vertical direction. Therefore, hereinafter, this floating roof 6 will also be referred to as a "liquid level follower 6".

[0032] Next, a description will be given of a part of the sludge level detection device 100 mainly including a processing device that processes a signal detected by a sensor and is installed outside the oil storage tank 200.

[0033] A signal (hereinafter, referred to as a strain signal, an optical signal, or simply a signal, assuming a signal caused by the backscattered light generated when laser light is incident on the optical fiber, which is caused by the strain generated in the optical fiber by an external force applied to the optical fiber built-in cable 1) is sequentially transmitted to a communication optical cable 8 that transmits the signal, a switch 9 having a function of individually turning on and off a plurality of signals, and a signal measurement processing device 10 that processes the signal, and the signal is processed.

[0034] Here, most of the communication optical cable 8 is arranged outside the oil storage tank 200, and one end thereof is connected to one end of the optical fiber built-in cable 1 at the cable clamp 7 position of the oil storage tank 200. In addition, in order to be able to cope with the case where there are a plurality of oil storage tanks 200 (in FIG. 1, the number of the oil storage tanks 200 is indicated by n. Here, n is a natural number of 2 or more), in the middle of the path of the communication optical cable 8, a command signal from the signal measurement processing device 10 is used to distinguish signals generated in the optical fiber built-in cable 1 provided individually for each oil storage tank, and the switch 9 is set so that the signals can be taken into the signal measurement processing device 10 and measured (refer to the switch specification 1×n shown in FIG. 1).

[0035] As described above, each optical fiber embedded cable 1 installed in the oil storage tank 200 experiences bending deformation and strain due to the external forces (including buoyancy) applied to each cable. This strain generates a frequency shift signal in the backscattered light, and the distribution of strain in each cable can be determined from this frequency shift information (for details, see, for example, Patent Document 1).

[0036] In the above explanation, we described the case where the number of oil storage tanks is n. In this case, the switch specifications are 1 × n, as shown in Figure 1. This means that the switch specifications are also changed according to the number of oil storage tanks. Specifically, when the number of oil storage tanks is 3, the switch specifications are 1 × 3. However, the value of n, which indicates the switch specifications, may be greater than or equal to the number of oil storage tanks (for example, when the number of oil storage tanks is 3, the switch specifications may be 1 × 5).

[0037] Next, a method for detecting the sludge level based on the external force applied to the fiber optic cable 1 will be explained using Figure 2. Figure 2 is a computational model (theoretical model) for evaluating the bending deformation of the fiber optic cable 1 caused by buoyancy, etc.

[0038] As shown in Figure 2, this diagram presents a "bending deformation model for a two-point supported beam," which assumes that both ends of the fiber optic cable 1 are simple support points, and that the forces from the oil region and the sludge region applied to the fiber optic cable 1 are of the magnitudes indicated by the arrows in Figure 2, and then calculates the amount of bending deformation that occurs in the fiber optic cable 1 under these conditions.

[0039] As shown in this figure, the force (magnitude) in the sludge region shows a gradual increase towards the right, and is greater throughout the entire region than the force (magnitude) in the oil region, which similarly shows a gradual increase towards the right. It is assumed that the magnitude of the force at the boundary between the sludge region and the oil region, indicated by the vertical dashed line at the intersection of these two regions, represents an intermediate value between the external forces (magnitude) in the two regions. In Figure 2, the symbol α indicating the direction of buoyancy represents the direction of the buoyancy generated on the cable, expressed as an angle relative to the normal direction of the cable.

[0040] Next, a method for determining the sludge level formed in the oil storage tank 200 from the strain generated in the fiber optic cable 1 will be explained using Figure 3. Figure 3 is a flowchart illustrating a method for detecting the sludge level formed in a floating-roof type oil storage tank. Following Figure 3, the method for detecting the sludge level according to the sludge level detection device 100 of this embodiment 1 will be explained below.

[0041] First, the strain generated in the optical fiber of the optical fiber embedded cable 1 due to the stored material in the petroleum storage tank 200 is measured (see step S1). In this case, the strain ε generated in the optical fiber is measured. f This is expressed by the following equation (1). Here, κ is the local curvature of the cable (1 / m), r is the winding radius of the spirally wound optical fiber (m), and Φ is the pitch angle of the spiral optical fiber (see, for example, Patent Document 2 for the following formulas).

[0042]

[0043] Next, the strain ε generated in the optical fiber measured above f From this, the bending moment M (Nm) generated in the optical fiber is calculated and determined by the signal measurement processing device 10 (see step S2). When determining the bending moment M, the following equation (2) is used in combination with equation (1). That is, the bending moment M can be determined from the following equation (3). Here, in equation (2), E is Young's modulus (N / m). 2 ), I is the second moment of area (m 4).

[0044]

[0045]

[0046] Next, based on the bending moment M obtained above, the shear force S generated in the optical fiber is calculated and obtained (see step S3). That is, since S = dM / dx, the shear force S is expressed by the following formula (4). That is, from the strain generated in the optical fiber, the shear force S (N) is obtained using formula (4).

[0047]

[0048] On the other hand, since the shear force S is expressed as S = dM / dx as described above, it can also be expressed by the following formula (5) by obtaining the sum of the forces applied to the optical fiber built-in cable 1. Also, buoyancy and density are expressed by the following formula (6). Here, F b (N / m) represents the buoyancy per unit length generated in the optical fiber built-in cable 1, and F w (N / m) represents the weight per unit length of the optical fiber built-in cable 1, and F R (N) represents the reaction force at x = 0 (support point) of the optical fiber built-in cable 1. Also, α represents the direction of the buoyancy (the angle with respect to the normal direction of the optical fiber built-in cable 1).

[0049]

[0050] Also, the buoyancy generated in the optical fiber built-in cable 1 in the liquid (storage substance) with density ρ and the above buoyancy F b and are expressed by formula (6) with the volume of the above liquid displaced by the optical fiber built-in cable 1 as V (m 3 / m). Here, g is the gravitational constant.

[0051] Therefore, from the calculated shear force S (see equation (5) above) and equation (6), the density ρ is obtained by the following equation (7) (see step S4). Furthermore, based on the depth distribution of the calculated shear force S, the sludge level is determined by the calculation method described below (see step S4). Next, the obtained density ρ and sludge level data are stored in the memory of the signal measurement processing device 10 and transmitted externally as needed (see step S5). After calculating the density and sludge level from the signal measured by one optical fiber cable, if necessary, the signal measurement processing device 10 commands the same flow (flow from step S1 to step S4) to repeatedly calculate the density and sludge level of the material stored in another oil storage tank from the signal measured by an optical fiber cable installed in that other oil storage tank (see step S6).

[0052]

[0053] <Method for Calculating Sludge Level> Next, we will explain in detail a specific method for determining the boundary between oil and sludge, i.e., the sludge level. Here, we will explain a method for determining the sludge level by evaluating the strain generated in the optical fiber embedded cable 1, which is installed spanning both oil and sludge, due to the bending load caused by the difference in buoyancy and weight, given typical density values ​​for both oil and sludge.

[0054] As an example in this case, for three substances—oil and two types of sludge 1 and sludge 2—the density, which is a representative physical quantity of each substance, is set to a constant value of 700 kg / m³. 3 ), 800 (kg / m 3 ), 900 (kg / m 3 Figures 4, 5, and 6 show, respectively, the relationship between the distance in the z direction (corresponding to the depth in the tank) and the density, the relationship between the distance in the z direction and the shear force, and the relationship between the distance in the z direction and the measured fiber strain.

[0055] Figure 4 shows the case where, applying the density values ​​described above, the midpoint of the line with a slope relative to distance—which represents the boundary between the oil layer (region with a horizontal distance of 7 m or less) and the sludge layer (region with a horizontal distance of 7 m or more)—is the same distance of 7 m for both sludge 1 and sludge 2 (see the dashed line in the figure). That is, assuming that the density change is linear at the boundary between the oil layer and the sludge layer, the midpoint of this density change interval (the point at a horizontal distance of 7 m) is defined here as the sludge level. Therefore, by finding this midpoint of the density change interval, it becomes possible to detect the sludge level.

[0056] Figure 5 shows the relationship between fiber strain (unit: με) measured by the optical fiber embedded cable 1 laid inside the tank and distance (unit: m) when the three types of layers shown in Figure 4 (one of which is a layer of oil only, without sludge formation (see the solid line in Figure 4)) are formed inside the tank. Figure 6 shows the shear force calculated as the value at each distance using equation (4) based on the fiber strain measured corresponding to the distance in Figure 5 (distribution diagram of shear force against distance). Note that in Figure 6, for the sake of clarity, the graph is shown with noise generated during the calculation removed.

[0057] If the shear force values ​​at each distance shown in Figure 6 are known, it can be seen that the density values ​​at each distance can be calculated using equation (7) above based on these values. Furthermore, if the changes in these density values ​​are known, the sludge level can be determined from these changes (refer to Figure 4) as the midpoint between two values ​​(indicating the endpoints) of the distance interval where the density changes significantly. Moreover, the sludge level can be determined directly using Figure 6 (graphically). This method will be explained in detail below using the curve showing the shear force characteristics of "Sludge 2" shown in Figure 6.

[0058] The shear force characteristics of sludge 2 are represented by the dotted line curve in Figure 6, which is a collection of small points. This curve has two regions where the change with respect to distance is almost constant (the slope is constant): region R1 (the region where the distance is approximately 6 m or less) and region R2 (the region where the distance is approximately 7.5 m or more). It can be seen that the characteristic of the boundary region between region R1 and region R2 is that the slope is not constant, but gradually increases as a negative value. If we denote the two boundary lines that indicate the left and right ends of this region where the slope is not constant as L1 and L2 (lines that indicate the distances passing through the left and right ends, and lines that pass through the two endpoints that are the distance values ​​of each region on the left and right, respectively; the same applies below), then the line L0 midway between these two boundary lines (here, the point indicating a distance of 7 m) is the sludge level of sludge 2 that we are looking for. It can be seen that this distance of 7 m is consistent with the "sludge level" explained earlier in Figure 4.

[0059] From equations (1), (4), (7), the flowchart in Figure 3, and the above definition of sludge level, it can be seen that if the strain value of the optical fiber at each distance is detected by measurement using the optical fiber embedded cable 1 laid in the tank, the shear force value of the optical fiber at each distance can be determined (i.e., the distribution of shear force can be determined), and a method for detecting the target sludge level can be determined from this distribution of shear force.

[0060] Under normal circumstances, the data shown in Figure 4 above is not available. Therefore, in such cases, the method for specifically detecting the sludge level will be explained below using Figures 7 to 10.

[0061] Figure 7 shows a graph illustrating the relationship between distance (in meters) and fiber strain (in με) measured using an optical fiber cable 1 laid inside the tank, for three cases: when there is no sludge in the tank (see the graph indicated by symbol a in the figure; the same applies hereafter), when the sludge level is b (see the graph indicated by symbol b in the figure; the same applies hereafter), and when the sludge level is c (see the graph indicated by symbol c in the figure; the same applies hereafter). Figure 8 shows a graph illustrating the results of filtering each data point to remove the effects of noise during measurement for each of the three cases described above.

[0062] Furthermore, Figure 9 is a graph showing the results of calculating the shear force at each distance for each of the three cases described above, based on the measurement data in Figure 8, using equation (4). The vertical axis represents the shear force (unit: N). The horizontal axis is the same as above. Here, the meanings of the symbols a, b, and c are the same as above.

[0063] Next, using the graph in Figure 9 above, we will explain the methods for specifically determining the sludge level when the sludge level is b, and the specific sludge level when the sludge level is c, and then determine the sludge level in each case.

[0064] As shown in Figure 9, the graph for sludge level b is indicated by the symbol b, and the graph for sludge level c is indicated by the symbol c. Both graphs b and c have the same overall shape as the curve showing the shear characteristics explained earlier in Figure 6, except that the curves showing the characteristics contain some noise and the position of the boundary lines differs between graph b and graph c. Therefore, in Figure 9, as in Figure 6, two boundary lines are defined in the intermediate region between the small distance region and the large distance region, and the sludge level is determined from these two boundary lines.

[0065] In graph b, the two boundary lines are L b1 , L b2 This is defined as (see graph b in Figure 9). Also, in graph c, the two boundary lines are L c1 , Lc2 This is determined (see graph c in Figure 9). Therefore, in graph b, the sludge level is L b1 , L b2 The midpoint line L b At the distance point (=7m), in graph c, the sludge level is L c1 , L c2 The midpoint line L c This point is determined to be at a distance of 8 meters.

[0066] In addition to the method of determining the sludge level using the endpoints of the two inclined regions as explained with Figure 9 above, it is also possible to determine the sludge level from the distance between the intersection of two lines A and B (refer to the distance represented by the dotted line Lb in Figure 10), based on lines A and B which are extensions of two lines representing the inclinations of two different inclined regions for the shear force characteristic curve b toward the boundary region.

[0067] Based on the examination of the shear force change characteristics (shear force distribution characteristics) in the regions of two slope lines with different slope values ​​and the boundary region between these two regions, using Figures 9 and 10, it is assumed that the sludge density in the petroleum storage tank will exhibit the density change shown in Figure 11. Specifically, the sludge level of the sludge indicated by sludge level b is 7 m, and its density can be seen to have changed as shown by the dotted line indicated by symbol b in Figure 11. On the other hand, the sludge level of the sludge indicated by sludge level c is 8 m, and its density can be seen to have changed as shown by the dotted line indicated by symbol c in Figure 11. In both cases, the density at the sludge threshold at the boundary surface (sludge level surface) indicating the presence or absence of sludge is 800 kg / m³. 3 It is. Also, the symbol L b , L c The meaning is the same as above.

[0068] In light of the above, I would like to briefly mention some measures to improve the accuracy of the measurements. From equation (6), the sensitivity regarding density is buoyancy F. b It can be seen that it depends on this buoyancy F, but from equation (5), the shear force S is equal to this buoyancy F bBecause it depends on buoyancy (the greater the buoyancy, the better), the sensitivity of this shear force is also dependent on buoyancy F. b It is clear that this depends on the buoyancy F. In other words, the sludge level also depends on this buoyancy F. b It becomes clear that it depends on [something].

[0069] Therefore, in order to improve the accuracy of the measurement, this buoyancy F b It is important to increase the sensitivity of this. Here, buoyancy F b From equation (6), the volume V (= πD) of the optical fiber-embedded cable 1 is obtained. 2 / 4. Here, since D is proportional to the outer diameter, it is predicted that increasing the volume will be effective. That is, by configuring the outer circumference of the fiber optic cable 1 to be covered with a lightweight cable 11 having a density lower than that of the fiber optic cable (having a specific gravity lower than that of the fiber optic cable), it is expected that the accuracy of the measurement can be improved (see Figure 12).

[0070] While this disclosure describes exemplary embodiments, the various features, aspects, and functions described in the embodiments are not limited to the application of any particular embodiment, but can be applied individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are conceivable within the scope of the art disclosed in this specification. These include, for example, modifications, additions, or omissions of at least one component.

[0071] 1 Fiber optic cable, 2 Cable relocation support, 3 Cable relocation and placement device, 4a, 4b Link, 5 Hinge, 6 Liquid level tracking section (floating roof), 7 Cable clamp, 8 Communication optical cable, 9 Switch, 10 Signal measurement and processing device, 11 Lightweight cable, 100 Sludge level detection device, 200 Petroleum storage tank, 201 Ceiling wall, 202 Side wall, 203 Bottom

Claims

1. An optical fiber embedded cable, which is placed inside an oil storage tank that stores oil with a liquid-level tracking section and contains an optical fiber for detecting strain generated by external forces; a cable moving and positioning device, which has one end fixed to a predetermined position in the oil storage tank and the other end fixed to the liquid-level tracking section, and one end of the optical fiber embedded cable is supported by the liquid-level tracking section, thereby allowing the optical fiber embedded cable to be moved in accordance with the installation position of the liquid-level tracking section; a cable moving support provided on the cable moving and positioning device, which moves and supports the other end of the optical fiber embedded cable; and a signal measurement and processing device, which measures the signal generated in the optical fiber due to the force applied to the optical fiber embedded cable and calculates predetermined physical quantities for the optical fiber embedded cable based on the measured signal. A sludge level detection device characterized by detecting the level of sludge stored inside the oil storage tank based on the amount of bending deformation obtained by measuring the signal generated in the optical fiber by the signal measurement processing device when a force is applied to the optical fiber embedded cable, which has been moved to a predetermined position inside the oil storage tank in accordance with the installation position of the liquid level-following part, by a substance stored inside the oil storage tank, thereby measuring the signal generated in the optical fiber.

2. The sludge level detection device according to claim 1, characterized in that the predetermined placement position is a position where the density value of the stored substance, determined from the signal due to strain generated in the optical fiber embedded cable, is greater than the density value of the petroleum.

3. The sludge level detection device according to claim 1 or 2, characterized in that the physical quantity is the shear force generated in the optical fiber embedded cable, or the density of the substance stored in the petroleum storage tank.

4. A sludge level detection device according to any one of claims 1 to 3, characterized in that it comprises three or more optical fiber-embedded cables, detects the level of sludge inside the petroleum storage tank, and determines the three-dimensional distribution of the sludge level.

5. The sludge level detection device according to claim 3, characterized in that the shear force generated in the optical fiber embedded cable is calculated by the signal measurement processing device based on the strain value detected by the optical fiber in the depth direction of the petroleum storage tank.

6. The sludge level detection device according to claim 3 or 5, characterized in that the distribution of shear force is determined by a predetermined formula based on the strain value after filtering the strain signal detected by the optical fiber embedded cable.

7. The sludge level detection device according to claim 6, characterized in that the optical fiber embedded cable is surrounded on its outer circumference by a lightweight cable with a specific gravity less than that of the optical fiber embedded cable.

8. The sludge level detection device according to any one of claims 1 to 7, characterized in that it is provided on the path of a communication optical cable that connects the optical fiber embedded cable and the signal measurement processing device and transmits signals generated in the optical fiber embedded cable to the signal measurement processing device, and is equipped with a switch for individually transmitting signals from a plurality of optical fiber embedded cables in response to a command signal from the signal measurement processing device.

9. A sludge level detection method for detecting the level of sludge using the sludge level detection device described in claim 1, characterized in that the method involves measuring a signal generated in the optical fiber due to an external force applied to the optical fiber embedded cable, and based on the measured signal, determining the distribution of shear force generated in the optical fiber embedded cable or the change in the vertical density of the substance stored in the petroleum storage tank, thereby detecting the level of sludge stored inside the petroleum storage tank.

10. The sludge level detection method according to claim 9, characterized in that the level of sludge is detected from the positions of both ends of a boundary region sandwiched between two regions, based on two regions in the optical fiber embedded cable where the value of the change in shear force with respect to the change in depth per unit length is constant and the values ​​of said change are different from each other.

11. The sludge level detection method according to claim 9, characterized in that the level of sludge is detected from the intersection of two straight lines obtained from the changes in shear force distribution in two regions where the value of the change in shear force with respect to the change in depth per unit length is constant and the values ​​of said change are different from each other, in the optical fiber embedded cable.

Images