JP2011179949A - Instrument for measuring liquid density in storage tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an instrument for measuring liquid density in a storage tank capable of directly and simultaneously measuring the liquid densities at a plurality of desired positions (or desired levels) of the liquid stored in the storage tank with high precision, capable of extemporaneously and flexibly corresponding even to the alteration or increase of a measuring point and easy in the installation to the storage tank or the maintenance of the same. <P>SOLUTION: This liquid density measuring instrument 10 for measuring the density of the liquid stored in the storage tank 1 is equipped with a plurality of optical fibers 2 different in length having Raman probes 3 provided to the leading ends thereof, a spectroscope 6 to which the respective Raman scattered lights, which are simultaneously measured by the Raman probes 3 inherent to at least two measuring points of two or more measuring points different in height level, are transmitted and a liquid density calculation means 7 for calculating the liquid densities of the same time at the respective measuring points from the liquid components inherent to the Raman scattered lights detected by the spectroscope 6. A plurality of the Raman probes 3 are positioned at the respective measuring points. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an apparatus for measuring the liquid density of various liquids including liquefied gas such as LNG (liquefied natural gas) and LPG (liquefied petroleum gas) stored in a storage tank.

  In recent years, the issue of how to achieve various industrial activities and the reduction of carbon dioxide emissions from citizens' lives has become a national and international issue. A lively debate has been developed.

  Among them, LNG (liquefied natural gas) does not generate sulfur oxides or dust during combustion, and emits less carbon dioxide and nitrogen oxides than other fossil fuels. It is attracting attention as a so-called clean energy.

  On the other hand, in the gas-related industries in Japan, most of LNG, which is a raw material for city gas used in Japan, is imported from countries such as Australia, Alaska, Southeast Asia and the Middle East via LNG tankers. is the current situation.

Here, when referring to the density of LNG, the density of LNG varies widely for each country (production area) that is the import destination (it is said to be about 420 to 470 kg / m ³ ), and the same production area. However, the density changes due to temperature rise and evaporation due to external heat input during the transportation and storage process. In addition, spot contracts have increased along with the expansion of the LNG market, and the import destinations have also diversified. Based on these factors, if it is intended to use different storage tanks for LNG for each import destination, that is, for each density, it will be necessary to add new storage tanks and so on, resulting in a great construction cost. Therefore, existing storage tanks (generally, there are multiple above-ground, underground, and semi-underground storage tanks in the gas-related facility yard), and the density differs in one storage tank. There is an increasing need for a method for storing a plurality of LNG in a mixed manner, which is called a so-called heterogeneous LNG mixed storage.

  In the heterogeneous LNG mixed storage, when a plurality of types of LNG having different densities are stored in a storage tank, the density distribution is such that the density of LNG is higher in the lower layer, and the LNG layer unique to each density. Which is commonly referred to as “stratification”. It should be noted that this stratification occurs when LNG of different densities are stored in the storage tank, and of course does not occur when the same type of LNG is stored.

  By the way, LNG stored in the LNG storage tank is in a gas-liquid equilibrium state at normal pressure and −162 ° C., and BOG (boil-off gas) is generated by natural heat input acting on this. The tank is full. Therefore, a heat insulating structure is required for the storage tank for storing such a cryogenic LNG. However, even if it has a heat insulating structure, it is inevitable that natural heat input acts in the tank, and due to this natural heat input, the LNG inside the storage tank partially vaporizes, so that each layer For each LNG, convection occurs in the layer. The LNG layer with the greatest external heat action is the lowest LNG layer where the heat from the side and bottom of the storage tank acts. In addition, the upper layer serves as a lid, and the BOG from the lower layer It is specified that the lowest LNG layer becomes relatively hot compared to the LNG layer above it, and the liquid density of LNG decreases as this temperature rises. ing.

For example, in a two-layered LNG layer with a liquid density of the lowermost layer of 460 kg / m ³ and an upper liquid density of 450 kg / m ³ , the density of the lowermost LNG layer increases with increasing temperature. There 455 kg ^/ m 3, gradually decreased to 450 kg / ^{m 3,} in the end, it becomes a liquid density and comparable layer of LNG layer, the upper layer, the lower layer of the layer boundary disappears.

  Then, until the liquid density of the different types of LNG becomes the same level, the relatively small convection inherent in each layer is generated in each layer, but the liquid density of the upper and lower layers becomes the same level. Large convection occurs, and the heat accumulated in the lower layer by this large convection promotes the generation of a large amount of BOG, which causes the internal pressure inside the storage tank to rise rapidly, and in some cases Storage tanks can be damaged and damaged, which is one of the major risks for storage tank operations. Note that the phenomenon in which the heat accumulated in the lower LNG layer as a result of layering is released as a large amount of BOG is generated is called rollover.

  In order to prevent the above rollover, for example, the liquid density change of the lowermost LNG and the liquid density above it (which can naturally change the liquid density above) can be simultaneously performed with high accuracy. It is important to measure. And by using the measurement data measured at the same time with such high accuracy, the time until the liquid density becomes the same level between different types of LNG is specified, and various measures that cannot cause rollover are taken in advance. A storage tank operation system can be constructed.

  Here, as a conventional published technique related to the liquid density measurement in the LNG tank, the liquid density measurement apparatus in the LNG tank disclosed in Patent Document 1 can be cited. In this device, a plurality of pressure guiding pipes opened at different heights are arranged in the LNG stored in the LNG tank, and their differential pressures are measured by differential pressure sensors provided at two pressure introduction ports. Further, this apparatus further selects switching pressure communication means for sequentially selecting two pressure guiding pipes and communicating their upper ends with the pressure inlets of the differential pressure sensor, and supplies gas into the LNG through the two selected pressure guiding pipes. A gas supply device is provided, and the liquid density between the lower ends is calculated from the measured differential pressure.

  According to the liquid density measuring device disclosed in Patent Document 1, the liquid density at different heights in the LNG tank can be directly and accurately measured without being affected by composition change, temperature change, and the like. . However, the liquid density calculated by this apparatus is only an average density between two measurement points, for example, and therefore the liquid density at a desired position (desired level) of the liquid is not directly measured. In addition, since the pressure guiding tube is used, its weight is heavy. Therefore, when the liquid density measurement point in the storage tank changes or increases, the liquid density measurement of the measurement point that changes flexibly and flexibly In the first place, since the liquid density measurement point depends on the position where the pressure guiding pipe is installed, if a liquid density is to be measured in the entire area of the storage tank, a large number of liquid density measurement points are required. The arrangement of the pressure tube is forced. Furthermore, it is easy to understand that it is difficult to install the pressure guiding tube in the storage tank, and that it is not easy even if the maintenance is considered.

  On the other hand, when specifying the liquid density, the liquid refractometer and the liquid density meter, in which the refractive index of the liquid to be measured is measured using a refractometer (refractometer) and the liquid density is calculated from the measurement result in the processing unit. The technique is disclosed in Patent Document 2. More specifically, the light transmitting unit and the light receiving unit in the probe are respectively fixed to the rack, arranged so that the rack and the pinion mesh with each other, the rack is rotated by rotating the pinion, and the rack is rotated. Accordingly, the fluid refractometer is configured so that the light transmitting unit and the light receiving unit rotate on the circumference along the plane including the incident light path and the reflected light path of the measurement light with the center point of the prism as the rotation center. The fluid density meter is configured by combining a processing unit that calculates the fluid density from the refractive index measured by the fluid refractometer.

  In Patent Document 2, it is said that a wide range of refractive index and density can be measured by using this liquid refractometer and liquid density meter. However, in this wide range of measurement, the light transmitting unit and the light receiving unit are rotated. Therefore, a wide range of measurements cannot be performed at the same time, and therefore, it is not sufficient for the rollover countermeasures of the above-mentioned heterogeneous LNG mixed storage.

JP-A-10-48115 JP-A-5-203567

The present invention has been made in view of the above-described problems, and directly and accurately measures the liquid density at a plurality of desired positions (or desired levels) of the liquid stored in the storage tank. An object of the present invention is to provide a liquid density measuring device in a storage tank that can respond flexibly and flexibly to changes and increases in measurement points, and is easy to install and maintain in the storage tank.

  In order to achieve the above object, the liquid density measuring device in the storage tank according to the present invention measures the liquid density of the liquid stored in the storage tank, and the liquid density measuring device comprises: A plurality of optical fibers having different lengths with a Raman probe at the tip and two or more different height level measurement points, each of which is simultaneously measured with a Raman probe specific to at least two of the measurement points. A spectroscope to which Raman scattered light is transmitted and a liquid component specific to the transmitted Raman scattered light are detected by the spectroscope, and from the detected liquid component, at the same time at the at least two measurement points. Liquid density calculating means for calculating the liquid density, and the plurality of Raman probes are positioned at respective measurement points. .

  The “liquid” to be measured by the liquid density measuring device of the present invention refers to all liquids such as water and oil, and the “liquefied gas” contained in the liquid is LNG, LPG, liquefied nitrogen. And liquefied hydrogen.

  And the liquid density measuring device of the present invention is a case where the liquid contained in the storage tank which is a constituent element thereof has two or more different densities and is stored in layers in the storage tank for each density. , At least two kinds of Raman scattered light of two or more liquids are simultaneously measured to identify the liquid density, and the change of Raman scattered light (and liquid density) at the same position over time is simultaneously measured and calculated. Its main purpose is to (or identify). In addition, when each liquid of the above “at least two kinds of liquids” is composed of a plurality of component species, the Raman spectrum peak specific to each component species is identified from the measured Raman scattered light, and the liquid is constituted. The concentration of each component type is specified.

  For this purpose, optical fibers of different lengths extend for each level in the storage tank for storing liquid, and a Raman probe is provided at the tip of each optical fiber, and each Raman probe is positioned at a unique level position. It has been configured. A spectroscope (Raman spectroscope) is provided outside the storage tank, and the Raman scattered light measured by the Raman probe is transmitted to the spectroscope, and a liquid component (liquid component species) specific to the transmitted Raman scattered light. ) Is detected by the spectrometer, and the liquid density is calculated or specified from the detected liquid components (species) and their concentrations.

  The algorithm for calculating or specifying the liquid density using Raman scattered light can apply an appropriate physical estimation method using Raman scattered light. For example, if RSK method, Raman spectroscopy or the like is applied, Good. In this spectrometer, for example, each concentration of a plurality of liquid components is specified by a Raman spectrum (when the stored liquid is LNG, methane is 90%, ethane is 5%, pentane is 5%, etc.) and stored. Correction of the concentration of each liquid component type by taking into account temperature data, pressure data, etc. at the level position where Raman scattered light was measured, measured by temperature sensors, pressure sensors, etc. provided at multiple levels in the tank Are appropriately executed, and the density of the liquid (such as LNG) at the measurement level position is instantaneously calculated.

  By attaching a Raman probe to the end of an optical fiber that is lightweight and adjustable in length, multiple Raman probes can be easily installed at any measurement point in the storage tank, and maintenance of Raman probes, etc. In this case, it is only necessary to wind and collect the optical fiber, and the maintenance is excellent. Furthermore, even if it is desired to install the Raman probe at a separate measurement point in the storage tank in a short time, the installation is easy, and the measurement point of the already installed Raman probe can be easily changed.

  Therefore, for example, assuming that the liquid is LNG and two or more kinds of LNG having different densities are stored in the storage tank, and the mixed liquid storage of the different types of LNG is three kinds of liquid densities of the initial receiving LNG, It is only necessary to position the Raman probe at three desired level positions (measurement points) that can measure the liquid density of the three types of LNG, and the acceptance plan is changed to LNG with four types of liquid density during acceptance. When this is done, a separate Raman probe can be added to the occasion, and the level position (measurement point) of each Raman probe can be adjusted in a short time.

  When Raman probes are installed at two measurement points, two types of Raman scattered light are simultaneously measured by the two Raman probes, and Raman probes are installed at three or more measurement points. In such a case, at least two of the Raman scattered lights are simultaneously measured. For example, in the case where the Raman probes are installed at five places, five types of Raman scattered lights are obtained with all five Raman probes. Are simultaneously measured, three types of Raman scattered light are simultaneously measured at three locations, and two types of Raman scattered light are simultaneously measured at two locations.

  By performing simultaneous measurement of at least two types of Raman scattered light at at least two measurement points and calculating their liquid densities, for example, when this liquid is the above-mentioned LNG, two types at the same time Each liquid density of LNG is calculated, and it is possible to take measures against the rollover that may occur after a predetermined time. The “predetermined time” varies depending on the liquid density difference between the two types of LNG, the type of LNG to be stored (origin, density, etc.), the internal shape of the storage tank, the heat input conditions, etc. This is the time until a large amount of BOG is generated in a short time after the layer boundaries of the plurality of converted LNG layers disappear. If the liquid density distribution in the tank can be grasped, this predetermined time can be predicted based on empirical rules based on past results in gas-related companies, experiments, simulations, etc., but the present invention is applied. By doing so, it is possible to grasp the liquid density distribution in the tank with higher accuracy, leading to the realization of prediction with higher accuracy.

  The rollover countermeasure method is not particularly limited. For example, a method in which LNG is injected from a nozzle installed in the storage tank to destroy the layer boundary of the LNG, or a relatively high method. A method of paying out the lower layer LNG having a high temperature and a high density at an early stage can be exemplified.

  Further, if the liquid density calculating means of the liquid density measuring device of the present invention stores the time from the difference between the two types of liquid density until the rollover occurs, it can be calculated from the two types of Raman scattering light measured simultaneously. The liquid density of each type of liquid is calculated, and the time until rollover can be determined in a short time from the difference in liquid density.

  In addition, there are various modes shown below, for example, in the arrangement mode of a plurality of optical fibers having different lengths and the positioning mode of the Raman probe unique to each optical fiber.

  One form thereof is that a part or all of the plurality of optical fibers are bundled in the middle thereof and suspended in the storage tank, and a rigid weight is attached to the bundled optical fibers, whereby a plurality of optical fibers are attached. The above-mentioned positioning of each of the Raman probes is guaranteed.

  A plurality of optical fibers are bundled and integrated with a heavy weight, for example, a rod-shaped weight body, and the weight fibers are suspended from the roof of the storage tank, for example. By maintaining its upright posture with its own rigidity and weight, it is possible to guarantee the positioning of the Raman probe specific to each of the plurality of optical fibers, that is, the positioning of each Raman probe at the measurement point. Note that “a part or all of the optical fibers” means that when five optical fibers having different lengths are applied, all of the five optical fibers may be bundled together. This means that the two or two optical fibers are bundled into one, and the unbundled optical fibers are individually extended to other measurement points.

  In another embodiment, some or all of the plurality of optical fibers are bundled in the middle thereof and suspended in the storage tank, and the bundled optical fibers are fixed to the inner wall of the storage tank, whereby a plurality of Raman This is a form in which the positioning of each probe is guaranteed.

  According to this embodiment, by using the inner wall of the storage tank and fixing a plurality of optical fibers bundled with each other, without using a separate member for locking the bundled optical fibers, The optical fiber Raman probe can be positioned at a desired position.

  In another embodiment, a part or all of the plurality of optical fibers are bundled in the middle and suspended in the storage tank, and a support member is provided inside the storage tank. An optical fiber is fixed to the support member, whereby the positioning of each of the plurality of Raman probes is ensured.

  For example, a surface that has a window for locking a Raman probe at multiple levels on a face material, or a ladder-like support in which a plurality of horizontal beams arranged at predetermined level intervals connect two vertical beams The members, etc. are erected on the bottom plate inside the storage tank, and the Raman probes of each of a plurality of optical fibers suspended and bundled from the roof of the storage tank are fixed with corresponding levels of windows and cross beams, etc. And the like.

  The storage tank is generally equipped with a liquid receiving pipe and a liquid discharging pipe, but the optical fiber described above extends to at least one of these pipes, and the Raman probe at the tip thereof. May be arranged. For example, when the liquid is LNG, the liquid density of LNG passing through the receiving pipe and the liquid density of LNG when stored in the storage tank after a lapse of a predetermined time are input to act on LNG over that time. Since the liquid density can be changed by heat, by calculating these liquid densities, it is possible to realize highly accurate liquid density management from the beginning of LNG acceptance.

  Further, some or all of the plurality of optical fibers are bundled in the middle to form a plurality of optical fiber groups, and the plurality of bundles are suspended at different positions in the storage tank. Also good.

  This form shows an embodiment in which bundles forming an optical fiber group are suspended at a plurality of locations in an underground tank (Raman probes can exist in a three-dimensional arrangement in the underground tank). It is possible to measure Raman scattered light at multiple locations for one LNG layer, and in addition to measuring Raman scattered light of LNG layers with different densities, it is also possible to measure Raman scattered light at different plane positions in the same LNG layer Is.

  As can be understood from the above description, according to the liquid density measuring device according to the present invention, a Raman probe is arranged at the tip of an optical fiber that is light and different in length, and is positioned at a plurality of measurement points in the storage tank. By calculating the liquid density from Raman scattered light measured at the same time at at least two measurement points almost simultaneously, it is easy to add or change measurement points, and maintenance of Raman probes, etc. It is easy, and the liquid densities of liquids of different densities can be calculated or specified almost simultaneously and with high accuracy. Therefore, when this liquid is LNG, it contributes to the realization of a storage tank operation capable of reliably suppressing the rollover phenomenon caused by layering, which is a problem in mixed storage of different types of LNG. .

It is the schematic diagram explaining one Embodiment of the liquid density measuring device of this invention. It is a block diagram explaining the spectrometer and the liquid density calculation means. (A) is a figure which shows the display result in which the liquid component kind intrinsic | native to a Raman shift is specified with the spectrum peak in a spectrometer, (b) is a component from the value of both pressure data and temperature data. In the case of applying a physical estimation method that corrects the density of seeds, etc., it is a diagram illustrating that a correction coefficient assigned to each point specified from both values of pressure data and temperature data is uniquely determined. is there. It is the schematic diagram explaining other embodiment of the liquid density measuring apparatus of this invention. It is the schematic diagram explaining further another embodiment of the liquid density measuring apparatus of this invention.

  Hereinafter, embodiments of the liquid density measuring apparatus of the present invention will be described with reference to the drawings. In the illustrated example, three types of LNG layers having different liquid densities are layered in the storage tank, but two types of LNG with different densities stored in the storage tank may be used. Of course, it may be four or more. In addition, a unique Raman probe is installed for each LNG layer, and the Raman scattered light of the LNG in each layer is measured. For example, the measurement control method includes all three types in the illustrated example. Even in the control method where LNG Raman scattered light is simultaneously measured and each liquid density is calculated simultaneously, any two types of LNG Raman scattered light are simultaneously measured and each liquid density is calculated simultaneously. It may be a controlled method. Furthermore, the liquid to be measured includes, in addition to LNG, LPG that can be layered, and other different liquids contained in one storage tank, such as water and oil.

FIG. 1 is a schematic diagram illustrating an embodiment of a liquid density measuring apparatus according to the present invention, and FIG. 2 is a block diagram illustrating a spectroscope and a liquid density calculating means that are constituent elements of the liquid density measuring apparatus. is there.
The liquid density measuring device 10 shown in the figure is suspended from a roof 11 and a storage tank 1 for storing a plurality of LNG (in order from the upper layer, LNG 1 layer, LNG 2 layer, LNG 3 layer) used for so-called heterogeneous LNG mixed storage. A plurality of optical fibers 2,... And Raman probes 3,... Disposed at the tips of the optical fibers 2, .. and Raman scattered light data transmitted from each Raman probe 3,. A spectroscope 6 in which the component species and the concentration of each component species are specified; a liquid density calculating means 7 for calculating the liquid density of each LNG layer based on the data on the specified liquid component species and the concentration of each component species; It is roughly composed of

  The storage tank 1 has a receiving pipe 12 (X1 direction) for receiving LNG, an LNG discharge pipe 13 (X2 direction) for discharging the stored LNG via a discharge pump 15, and a BOG filled above the LNG1 layer. A BOG payout pipe 14 (X3 direction) is provided.

  Further, the optical fibers 2,... Having different lengths so as to correspond to the respective LNG layers are bundled with a bundle material 4 at a midway position thereof. The bundled optical fibers 2,... Are fixed to a rigid weight member 5 comprising a rigid member 51 having high bending rigidity and a weight body 52 at the tip thereof. The tip of the Raman probe 3 is positioned in the corresponding LNG layer. Even if convection or the like occurs in each LNG layer by fixing a plurality of optical fibers 2,... To a rigid weight member 5 that is rigid and heavy, each Raman probe 3, The initial positioning posture of ... is secured.

  On the other hand, the spectroscope 6 and the liquid density calculation means 7 are stored in the management building K. Generally, a computer known as hardware is applied and various control units constituting the density calculation means 7 are built therein. The results (liquid density difference, time required for rollover, etc.) are displayed on the computer screen. Then, based on the result, the manager executes the optimum storage tank operation within the time until the displayed rollover, for example.

  When LNG with different density is stored in the storage tank 1, regardless of whether it is received or not, generally, the LNG with higher density moves downward, and the LNG with different density is layered in descending order of density from below. Stored in. Therefore, in the illustrated example, the LNG 3 layer, the LNG 2 layer, and the LNG 1 layer have a higher density in this order, and each LNG layer is layered.

  Each LNG layer stratified in the storage tank 1 (at least at an extremely low temperature of about −162 ° C. at the time of reception) is heated by heat input from the outside of the storage tank 1. As density decreases, convection occurs in each layer. In the case of being composed of three LNG layers as in the illustrated example, a layer having inherent convection in each layer can also be referred to as triple convection.

  With regard to this heat input, the top and middle LNG1 and LNG2 layers are heated from the side of the storage tank 1 by heat input: Q1, whereas the lowest LNG3 layer is stored. Heat input from the side surface of the tank 1: In addition to Q1, heat input from the bottom plate: Q2 also acts, so this LNG3 layer is likely to become the highest temperature. As the temperature rises, the liquid density of the LNG 3 layer gradually decreases, the layer boundary with the LNG 2 layer above it is eliminated, and a larger convection is formed. As these are further warmed, the layer boundary between the LNG2 layer and the LNG1 layer is finally eliminated, and a so-called rollover phenomenon in which a large number of BOGs are generated in a short time can occur.

  However, in the liquid density measuring apparatus 10 shown in the figure, a unique Raman probe 3 is positioned for each LNG layer. For example, the Raman probes 3,. The measurement result is transmitted to the spectroscope 6, the liquid component species of LNG at the measurement position and the concentration of each component species are specified, and data regarding the specified liquid component species and the concentration of each component species is liquid density calculating means 7 is sent to calculate the LNG density of each LNG layer, the time required to roll over is calculated based on the difference in liquid density, etc., and appropriate measures that can be implemented within this required time can be selected It becomes.

  As shown in FIG. 1, in the storage tank 1, a Raman probe is connected to an optical fiber that is light and adjustable in length, and is suspended from the roof of the storage tank 1 and secures a positioning posture at those measurement points. Therefore, for example, it is extremely easy to change the position (measurement point) of the Raman probe, add a Raman probe as the number of measurement points increases, and maintain the Raman probe. can do.

Here, with reference to FIG. 2, the internal structure of the spectrometer 6 and the liquid density calculation means 7 will be outlined.
The Raman scattered light data simultaneously measured by the Raman probes 3,... Is transmitted to the spectroscope 6 (INPUT 1, 2,...). Here, the liquid component species of LNG and the concentration of each component species at the measurement position are determined. The specified liquid component species and the data regarding the concentration of each component species are sent to the liquid density calculation unit 71 in the hardware (computer) constituting the liquid density calculation means 7.

  In the liquid density calculation unit 71, the density of LNG is calculated based on an appropriate physical estimation formula or calculation formula (algorithm) using data on the specified liquid component type and the concentration of each component type.

Here, an outline of an algorithm for specifying a liquid component species and the like from Raman scattered light will be described.
When light collides with gas molecules, light having a longer wavelength than incident light may be scattered, which is generally called Raman scattering. Here, the relationship of the following formula 1 exists between the wavelength of incident light: λL and the wavelength of Raman scattered light: λS.

  Here, ωR is a Raman shift (frequency), and each gas has a unique value. Therefore, by spectroscopic analysis of the Raman scattered light, it is possible to specify the component type from the wavelength of the dispersed Raman light. What will be.

  For example, when LNG is mainly composed of three component species of methane, ethane, and pentane, as shown in FIG. 3a, each component species is specified from the Raman shift that gives a Raman spectrum peak, and each component species The concentration of is also specified.

  The liquid density calculation unit 71 stores the appropriate physical estimation from a plurality of component types and their concentrations and, if necessary, temperature data and pressure data of LNG at the level position where the Raman scattered light is measured. By applying a method (RSK method or the like), the liquid density of the LNG to be calculated is calculated. In FIG. 3b, points P1 and P2 specified from both values of pressure data and temperature data are applied in the case of applying a physical estimation method that corrects the density and the like of component species from both values of pressure data and temperature data. ,... Explains that the correction coefficient assigned to each is uniquely determined.

  In this way, the liquid density calculation unit 71 calculates the LNG density for each level in the storage tank 1, and transmits the calculated LNG density data for each level to the liquid density difference data storage unit 72, where Both liquid density differences are calculated and stored.

By the way, in gas-related companies, interphase data regarding the liquid density difference of multiple types of LNG and the time to roll rover has been specified by empirical rules, experiments, analysis, etc. based on past results (actually The time to rollover is related not only to the liquid density difference of LNG, but also to several factors such as the shape in the storage tank and heat input conditions). For example, when the liquid density difference of LNG is 10 kg / m ³ , the time required for rollover is specified as 5 hours and 10 hours.

  The liquid density calculation means 7 has a storage unit 73 for storing the liquid density difference and time data until rollover, which are specified by these empirical rules, experiments, analysis, and the like. From the liquid density difference transmitted from the density difference data storage unit 72, the time until rollover is specified by the calculation unit 74 and displayed on the computer screen (OUTPUT).

  Each storage unit and calculation unit are processed by a central processing unit (CPU 75), RAM and ROM (not shown) are present as internal components, each storage unit, calculation unit, CPU is a bus, etc. Of course, they are connected with each other.

In addition, the specific configuration of the liquid density calculating unit is not limited to the illustrated example, and may be an extremely simple internal configuration including only the liquid density calculating unit 71 and the CPU 75, for example.
4 and 5 are each a schematic diagram illustrating another embodiment of the liquid density measuring device of the present invention. In particular, the liquid density measuring device 10 shown in FIG. It shows an apparatus in which the positioning form of the Raman probe is changed, and there is no change in other apparatus configurations.

  The liquid density measuring apparatus 10A shown in FIG. 4 fixes the plurality of optical fibers 2... Bundled by the bundle member 4 by fixing the bundle member 4 to the inner wall of the storage tank 1 and fixing the whole. In the posture, the Raman probe 3,... At the tip of each optical fiber 2,... Is positioned in a unique LNG layer, and the positioning posture is ensured.

  On the other hand, in the liquid density measuring apparatus 10B shown in FIG. 5, a support member 5A is erected from the bottom plate of the storage tank 1, and a fixed window 5Aa is opened on the support member 5A at a position corresponding to each LNG layer. Thus, the Raman probe 3 unique to each LNG layer is locked to the fixed window 5Aa, and its positioning posture is guaranteed.

  By using the liquid density measuring devices 10, 10A and 10B of the present invention shown in FIGS. 1, 4 and 5, a plurality of types of LNG densities can be calculated or specified in as short a time as possible with high accuracy. It becomes possible to specify the liquid density difference and the like. Therefore, when taking measures to effectively suppress the rollover phenomenon, which is the biggest problem in mixed storage of different types of LNG, which will be increasingly adopted in the future, the liquid density measuring device of the present invention is extremely Useful.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Storage tank, 11 ... Roof, 12 ... Acceptance piping, 13 ... LNG delivery piping, 14 ... BOG delivery piping, 15 ... Delivery pump, 2 ... Optical fiber, 3 ... Raman probe, 4 ... Bundling material, 5 ... Rigid weight material , 51 ... Rigid material, 52 ... Weight body, 5A ... Support member, 5Aa ... Fixed window, 6 ... Spectroscope, 7 ... Liquid density calculating means 10, 10A, 10B ... Liquid density measuring device, K ... Management building

Claims (6)

A liquid density measuring device for measuring the liquid density of a liquid stored in a storage tank,
The liquid density measuring device comprises a plurality of optical fibers having different lengths, each having a Raman probe at the tip,
At two or more measurement points of different height levels, a spectroscope to which each Raman scattered light simultaneously measured by a Raman probe specific to at least two of the measurement points is transmitted,
A liquid component specific to the transmitted Raman scattered light is detected by the spectrometer, and from the detected liquid component, a liquid density calculating means for calculating a liquid density at the same time at the at least two measurement points; Comprising at least
The plurality of Raman probes is a liquid density measuring device in a storage tank, which is positioned at each measurement point.   Some or all of the plurality of optical fibers are bundled in the middle thereof and suspended in the storage tank, and a rigid weight is attached to the bundled optical fibers, whereby each of the plurality of Raman probes is attached. The liquid density measuring device in the storage tank according to claim 1, wherein the positioning is ensured.   Some or all of the plurality of optical fibers are bundled in the middle thereof and suspended in the storage tank, and the bundled optical fibers are fixed to the inner wall of the storage tank, whereby the positioning of each of the plurality of Raman probes is performed. The liquid density measuring device in the storage tank according to claim 1, which is guaranteed.   Some or all of the plurality of optical fibers are bundled in the middle thereof and suspended in the storage tank. A support member is provided inside the storage tank, and the bundled optical fibers are fixed to the support member. The liquid density measuring device in the storage tank according to claim 1, wherein the positioning of each of the plurality of Raman probes is ensured.   The storage tank is equipped with a liquid receiving pipe and a liquid discharging pipe, and the optical fiber extends into at least one of the receiving pipe and the discharging pipe, and a Raman probe at the tip thereof. The liquid density measuring device in the storage tank according to any one of claims 1 to 4, wherein   A part or all of the plurality of optical fibers are bundled in the middle to form a plurality of optical fiber groups, and the plurality of bundles are suspended at different positions in the storage tank. The liquid density measuring device in the storage tank in any one of.

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