JP2011179582A - Stratification elimination device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stratification elimination device which eliminates stratification of two or more liquids stored in a storage tank and different in liquid density for efficiently eliminating stratification while maximally lowering cost required for manufacturing, installation and the like of the device. <P>SOLUTION: The stratification elimination device 10 eliminating stratification of two or more liquids (LNG and the like) stored in the storage tank 1 and different in liquid density includes: a foam generation means 4 arranged in a position matching at least a liquid (LNG 3) in the lowermost layer in the storage tank 1 to generate foam. The foam generation means 4 is constituted of one of (1) an ultrasonic transducer, (2) an electric heater, and (3) a heating medium heater. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an apparatus for eliminating stratification 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.

  As a conventional published technique relating to a method for eliminating the layering that causes the rollover, a stirring method in a low-temperature liquefied gas tank disclosed in Patent Document 1 can be exemplified. In this agitation method, a gas that flushes the liquid discharged from the condenser through the expansion valve is introduced to the upper position of the conduit in the vertical direction with the inner hollow conduit submerged below the liquid level in the tank. To do. Moreover, what introduce | transduced some exit gas from an evaporative gas compressor to the upper position of a conduit | pipe as another form is also disclosed.

  According to the stirring method disclosed in Patent Document 1, it is possible to eliminate the rollover described above without using a cargo pump, that is, a jet mixing pump or a nozzle, thereby eliminating the high cost.

  However, as is clear from FIG. 2 and the like, a conduit for returning boil-off gas is provided in the tank, and an expensive piping system including a compressor, a condenser, and an expansion valve is provided as an essential configuration in the middle of the conduit. Therefore, the cost for manufacturing the facility is extremely expensive, and it is difficult to say that the high cost can be eliminated.

  Further, since it is necessary to return the desired amount of boil-off gas into the tank while compressing or condensing the boil-off gas as desired, the control and management thereof is not easy.

  On the other hand, as described above, on the premise of eliminating the increase in construction cost, there is an increasing demand for accommodating two or more liquids having different liquid densities such as mixed storage of different types of LNG in a common storage tank. In view of this, there is a demand for the development of a stratification elimination apparatus that can effectively eliminate the stratification that causes rollover while keeping the cost increase required for facility construction low.

JP-A-53-71365

  The present invention has been made in view of the above-described problems, and relates to a stratification elimination apparatus for eliminating stratification of two or more liquids having different liquid densities stored in a storage tank. It is an object of the present invention to provide a stratification elimination apparatus that can effectively eliminate stratification while keeping costs required for installation and the like as low as possible.

  In order to achieve the above object, a destratification apparatus according to the present invention is a destratification apparatus for destrating two or more liquids having different liquid densities stored in a storage tank, and at least in the storage tank. A foam generating means disposed at a position corresponding to the liquid in the lowermost layer to generate foam, wherein the foam generating means is any one of the following: (1) an ultrasonic vibrator, (2) an electric heater, (3) A heating medium heater.

  The liquid to which the stratification elimination apparatus of the present invention is applied, that is, the liquid contained in the storage tank refers to all liquids such as water and oil, and this liquid includes LNG, liquefied gas, LPG, liquefied nitrogen, liquefied hydrogen and the like are included.

  And the stratification elimination apparatus of this invention is applied to the storage tank in which 2 or more types of liquids from which liquid density differs is accommodated, and it is large that it eliminates the stratification which may arise by the difference in liquid density. The purpose is to eliminate the layering by applying heat (temperature) or pressure to the liquid to evaporate a part of the liquid to generate bubbles, and using the bubbles. That is, as typified by Patent Document 1 described above, the gas in the storage tank is returned to the contained liquid for bubbling, the liquid is lifted up using this gas, and the shower radiates from above the liquid, etc. The solution is different from the content described above. Here, in the conventional system for returning the gas into the tank, the equipment construction cost depends on the BOG piping for the air lift, the various piping constituting the return system of the BOG, the compressor, the condenser, the expansion valve, etc. installed in the system. Therefore, it is an important object of the present invention to solve this problem.

  As a measure for generating bubbles for eliminating this stratification, the apparatus of the present invention applies (1) an ultrasonic vibrator, (2) an electric heater, or (3) a heating medium heater. Yes.

  Here, the ultrasonic vibrator is a part in which a part of the liquid is locally reduced in pressure during the vibration process of the vibrator, and the liquid is vaporized to generate bubbles.

  On the other hand, both an electric heater and a heating medium heater generate heat (temperature) to a liquid and vaporize a part of the liquid to generate bubbles.

  These foam generating means can be installed with extremely simple equipment construction in which electrical wiring and heating medium piping are simply arranged in the storage tank, and each of the equipment is equipped with the above-described compressor or condenser. Compared with an expensive piping system equipped with an expansion valve, the cost is much lower.

  In addition, although any form of foam generating means has a simple equipment structure, it is possible to effectively generate bubbles in the liquid, and these foam generating means are layered into at least two layers. Since the generated bubbles move from the lower side to the upper side of the liquid, the generated layer can be effectively destroyed at the boundary between the layers of the liquid and the entire layering can be eliminated. Is. Note that “at least the lowest layer” means that the bubble generating means is arranged in a position corresponding to the liquid in the lowermost layer, and the bubble generating means is formed in the lower two layers of the layered liquid layers, for example, three layers. It means to include the distributed form.

  Furthermore, it is preferable to apply the following configurations as more specific configurations of the various forms of foam generating means described above.

  That is, when the bubble generating means is composed of ultrasonic vibrators, the ultrasonic vibrators are electrically connected to one or a plurality of lines of electric wires and are arranged in a plurality of planes in a distributed manner. A form consisting of can be applied. In addition, when the bubble generating means is composed of an electric heater, a mode is adopted in which the electric heater is electrically connected to one or a plurality of lines of electric wires and is distributed in a plane. Can do. Further, in the case where the bubble generating means is composed of a heating medium heater, it is possible to apply a form in which the heating medium heater includes a heating medium pipe extending planarly in one system or a plurality of systems and a heating medium flowing therethrough. it can.

  According to these various forms, bubbles can be generated from a plurality of foam generating means dispersed in a plane or a foam generating means spreading in a plane with respect to the liquid contained in the storage tank, and the entire liquid The effect of eliminating the layering can be further expected.

  In addition, by measuring and managing the liquid density of the liquid in each layer at the same time, for example, when the liquid is the above-mentioned LNG, the above-described stratification elimination device is operated before the occurrence of rollover after a predetermined time has elapsed. Thus, it is possible to reliably avoid the occurrence of rollover. Here, this “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, 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 layered LNG layers disappear. If the liquid density distribution in the tank can be grasped, the predetermined time can be predicted based on empirical rules based on past results in a gas-related company, experiments, simulations, and the like.

  As can be understood from the above description, according to the stratification elimination apparatus according to the present invention, it is possible to install the apparatus in the storage tank at low cost, and two or more different liquid densities generated in the storage tank. The layered state of the liquid can be effectively eliminated, and the rollover caused by this can be surely avoided.

It is the schematic diagram explaining one Embodiment of the storage tank which comprises the stratification elimination apparatus of this invention. (A), (b), (c) is the top view which showed the arrangement | positioning form of an electric wire line and an ultrasonic transducer | vibrator, respectively. It is the schematic diagram which demonstrated other embodiment of the storage tank which comprises the stratification elimination apparatus of this invention. (A), (b), (c) is the top view which showed the arrangement | positioning form of a heating-medium piping, respectively. (A) is a schematic diagram of equipment used in the bubble condensation experiment, and (b) is a photograph thereof. It is the photograph which image | photographed the state of the bubble in bubble condensation experiment.

  Hereinafter, an embodiment of a stratification elimination 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 to LNG, the liquid stored in the storage tank includes other types of liquids stored in one storage tank, such as LPG that can be stratified, water and oil, and the like. That is.

  FIG. 1 is a schematic diagram illustrating an embodiment of a storage tank equipped with a stratification elimination apparatus of the present invention. FIGS. 2a, 2b, and 2c show the arrangement of electric wire lines and ultrasonic transducers, respectively. It is the shown top view.

  The illustrated stratification elimination apparatus 10 accommodates a plurality of LNG (the liquid density is different in the LNG 1 layer, the LNG 2 layer, and the LNG 3 layer in order from the upper layer), and the roof of the storage tank 1 used for so-called heterogeneous LNG mixed storage 11, a bubble generating means 4 comprising a wire line 2 housed in a tank and extending, a plurality of ultrasonic vibrators 3 (or electric heaters) electrically connected to the wire line 2, a power source 5, A control unit 6 (accommodated in the management building K) for ON control and OFF control of the power supply 5 is generally configured.

  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.

  Each ultrasonic transducer 3 that is electrically connected to the electric wire line 2 is fixed on the bottom plate 11 ′, and is arranged in the LNG 3 layer that is the lowest layer. In addition, although illustration is abbreviate | omitted, the arrangement | positioning stand which stands up from a bottom plate may be provided and the form which installs the ultrasonic transducer | vibrator 3 on this arrangement | positioning stand may be sufficient.

  As shown in FIGS. 2a to 2c, the arrangement form of the electric wire line and the ultrasonic transducer is preferably an arrangement form in which bubbles are generated in the entire area of the bottom plate 11 ′ in plan view. .

  The bubble generating means 4 shown in FIG. 2a is a form in which a plurality of ultrasonic transducers 3 are intermittently provided on a circular electric wire line 2 along the outer periphery of the bottom plate 11 '.

  On the other hand, the bubble generating means 4A shown in FIG. 2b has a form in which a plurality of ultrasonic transducers 3 are intermittently provided on a spiral electric wire line 2A from the outer periphery of the bottom plate 11 'to the center side.

  Furthermore, the bubble generating means 4B shown in FIG. 2c has a form in which a plurality of ultrasonic transducers 3 are intermittently provided on the electric wire line 2B extending radially from the center of the bottom plate 11 '. Of course, any form other than the illustrated example may be used as long as it is a foam generating means capable of generating foam from the entire area of the bottom plate 11 ′ in plan view. Moreover, although all the illustrated examples have one electric wire line, the electric wire line may include a plurality of electric wire lines and an ultrasonic transducer 3 or the like intermittently disposed in each electric wire line.

  Here, the principle of generation of bubbles by the ultrasonic vibrator 3 is that a part of the liquid (LNG) is made into a reduced pressure atmosphere in the vibration process of the vibrator, and LNG is vaporized in this reduced pressure atmosphere to generate bubbles made of BOG. Is. On the other hand, when an electric heater is used, heat is applied to the cryogenic LNG to vaporize it to generate bubbles made of BOG.

  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. Before the rollover phenomenon occurs, the main purpose of installation of the present apparatus is to eliminate the layering formed using the illustrated layering elimination apparatus 10.

  The control unit 6 accommodated in the management building K is generally built in a computer known as hardware, and is supplied from a plurality of thermometers and liquid density meters provided at predetermined levels in the storage tank 1. Data is transmitted by wire or wireless.

  The controller 6 stores the liquid density difference between the LNG layers, the time required for rollover according to the liquid density difference, and the like, and is displayed on the computer screen. Based on the results, for example, the power supply 5 is ON-controlled within the time until the displayed rollover to activate each ultrasonic transducer 3, and a part of the lowest LNG3 layer is vaporized to form a bubble made of BOG. Is generated.

  The generated bubbles rise from the LNG3 layer to the LNG1 layer. In this rising process, for example, the lower LNG3 layer is lifted to the upper LNG2 layer, and further the LNG3 layer and the LNG2 layer are lifted to the upper LNG1 layer. By breaking the boundary, the layered state shown in the figure is eliminated, and the occurrence of the rollover described above is avoided.

  FIG. 3 is a schematic diagram illustrating another embodiment of a storage tank provided with the stratification elimination apparatus of the present invention, and FIGS. 4a, 4b, and 4c are planes showing the arrangement of the heating medium pipes, respectively. FIG.

  The illustrated destratification device 10A includes a heating medium pipe 7 accommodated and extended from the roof 11 of the storage tank 1 into the tank, and a heating medium accommodation tank 8 for providing a heating medium such as hot water and hot oil to the heating medium pipe 7. , And a control unit 6 for performing ON control and OFF control of a pump (not shown) in the heating medium storage tank 8.

  The heating medium pipe 7 is also arranged in a desired arrangement form on the bottom plate 11 '. Examples of specific forms are shown in FIGS. 4a, 4b, and 4c.

  The heating medium pipe 7 shown in FIG. 4a has a circular shape along the outer periphery of the bottom slab 11 ', and the heating medium flowing in from the inflow hole warms the LNG layer 3 through the circular flow path, and from the outflow hole. It is designed to be discharged (X4 direction).

  On the other hand, the heating medium pipe 7A shown in FIG. 4B has a spiral shape from the outer periphery of the bottom plate 11 'to the center side. The heating medium pipe 7B shown in FIG. 4c has a meandering linear shape on the bottom plate 11 '. In any of these piping forms, since the heating medium piping extends in the entire area of the bottom plate 11 'in a plane, bubbles made of BOG are effectively formed in the entire area of the layer boundary formed thereabove. Can be provided.

  As described above, the stratification elimination apparatuses 10 and 10A shown in the figure return the BOG in the storage tank to the LNG accommodated in the tank and perform bubbling, or lift up the LNG using the BOG. The stratification elimination means of the conventional structure, such as radiating LNG shower from above the LNG layer, is different in content, and the equipment construction cost and maintenance that are problematic when applying this conventional structure The increase in cost can be eliminated, and further, advanced control management when operating the stratification elimination means can be eliminated.

[Bubble condensation confirmation experiment and results]
The present inventors conducted a confirmation experiment on whether or not the bubbles made of BOG generated in the lower LNG layer can rise to the upper side without condensing and can exert an action of eliminating layering. Here, using the equipment shown in FIGS. 5a and 5b as a test apparatus, LNG from Alaska and LNG from Brunei are accommodated in a bottle to form a layered state, and methane which is the main component of BOG is placed below It was forced into the LNG layer of Brunei and the presence or absence of condensation during the bubble rising process was confirmed.

As shown in the figure, the experimental apparatus is equipped with a high-speed camera (1000 fps) that accommodates LNG in a Dewar bottle (67.5 L) and photographs changes in the shape of methane bubbles rising from the bottom of the bottle. Here, the upper layer of LNG from Alaska has a density of 422 kg / m ³ and a temperature of −160.2 ° C., and the lower layer of LNG from Brunei has a density of 452 kg / m ³ and a temperature of −159.7 to -157.2 [deg.] C. Further, the diameter of bubbles generated in the LNG layer was 11 mm, the rising speed was 0.4 m / sec, and Re = 1.1 × 10 ⁴ . The photographing result is shown in FIG.

  From the figure, it is confirmed that the bubbles from the lower layer are not reduced even when entering the cold upper layer (ΔT is about 3 ° C.). In addition, it has been confirmed that the upper and lower liquid layer boundaries are gradually lowered due to the mixing effect of the bubble accompanying liquid. Furthermore, it is the liquid head that dominates the size of the bubbles, but the change in the size of the bubbles obtained from the photographed image is about ± 3%, and the expected change with a 150 mm liquid head is 1%. It turns out that it is not very different.

  From this confirmation experiment, when different types of LNG are stored in a medium-scale to large-scale storage tank and are stratified, BOG bubbles generated from the lower LNG layer are not condensed and are not condensed. It has been demonstrated that stratification can be eliminated by rising to the layer.

  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, 11 '... Bottom plate, 12 ... Receiving piping, 13 ... LNG delivery piping, 14 ... BOG delivery piping, 15 ... Delivery pump, 2, 2A, 2B ... Electric wire line, 3 ... Ultrasonic vibration Child, electric heater, 4, 4A, 4B ... foam generating means, 5 ... power source, 6 ... control unit, 7, 7A, 7B ... heating medium piping (heating medium heater), 8 ... heating medium tank, 9 ... foam generating means 10, 10A ... Destratification device, K ... Management building

Claims (4)

A stratification elimination device that eliminates stratification of two or more liquids having different liquid densities stored in a storage tank,
The stratification elimination apparatus includes a foam generating means that generates foam by being arranged at a position corresponding to at least the lowest liquid in the storage tank,
The bubble generating means consists of any one of the following:
(1) ultrasonic transducer,
(2) Electric heater,
(3) Heat medium heater,
Stratification elimination device.   In the case where the bubble generating means is composed of an ultrasonic transducer, the ultrasonic transducer is composed of a plurality of ultrasonic transducers that are electrically connected to one or a plurality of lines of electric wires and distributed in a plane. The layering elimination apparatus according to claim 1.   When the bubble generating means is composed of an electric heater, the electric heater is composed of a plurality of heaters that are electrically connected to one line or a plurality of lines of electric wires and arranged in a plane. Stratification elimination device.   2. The layered structure according to claim 1, wherein when the bubble generating means is a heating medium heater, the heating medium heater includes a heating medium pipe extending in a planar manner in one or a plurality of systems and a heating medium flowing through the heating medium pipe. Deterrence device.

Images