JP2014159859A - Apparatus for re-liquefaction/pressure-rise of boil-off gas of low-temperature liquid gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for re-liquefaction/pressure-rise of boil-off gas, which uses a method for re-liquefying the boil-off gas by directly contacting the boil-off gas with delivered LNG and which sufficiently secures an interfacial area between both of the LNG and the boil-off gas and also can reduce pressure-rise power for rising the pressure of re-liquefied liquid to a supply pressure.SOLUTION: The apparatus for re-liquefaction/pressure-rise of boil-off gas includes: a boil-off gas compressor 7 compressing boil-off gas generated from low-temperature liquid stored in a storage tank 3; and a mixing device 15 mixing the boil-off gas compressed by the boil-off gas compressor 7 and the low-temperature liquid delivered from the storage tank 3. The mixing device 15 includes: a diameter-reduced portion 27 where the diameter of a flow passage is reduced; a diameter-enlarged portion 29 where the diameter of the flow passage is enlarged at the downstream of the diameter-reduced portion 27; a low-temperature liquid spouting part 31 located at the upstream side of the diameter-reduced portion 27 and spouting the low-temperature liquid delivered via a low-temperature liquid delivery pipe 13; and a boil-off gas spouting part 32 located at the upstream side of the diameter-reduced portion 27 and spouting the boil-off gas compressed by the boil-off gas compressor 7.

Description

  The present invention relates to evaporative gas ("boil-off gas", "boil-off gas", "liquefied natural gas (hereinafter sometimes referred to as" LNG ") generated in a storage tank in which low-temperature liquefied gas (hereinafter referred to as" low-temperature liquid ") is stored. BOG ").

When low temperature liquid such as liquefied natural gas (LNG) is stored in a tank, a part of the low temperature liquid in the tank evaporates due to heat input to the tank, and evaporative gas is generated. When the low-temperature liquid is LNG, an evaporating gas mainly composed of methane is generated.
In the case of a city gas production plant, the evaporated gas generated from LNG can be compressed as it is and supplied as city gas, but the compression power becomes very large. Therefore, in order to reduce power, it is conceivable to re-liquefy the vaporized gas, pressurize it in a liquid state, and then gasify it again to supply it as city gas. In order to reliquefy, the evaporative gas is compressed and cooled, but the evaporative gas is cooled and cooled by the cold heat of the LNG, that is, the low temperature liquid LNG and the compressed evaporated gas are heat exchanged. Patent Documents 1 to 3 propose examples of the reliquefaction apparatus.

In patent document 1, the system (indirect heat exchange system) which heat-exchanges LNG and the compressed vapor gas with a heat exchanger is disclosed.
Patent Document 2 discloses a method (direct contact heat exchange method) in which compressed evaporative gas is directly blown into the discharge LNG.
In Patent Document 3, as a method of injecting evaporative gas into LNG, a method in which an evaporative gas supply nozzle is arranged so as to be in a direction orthogonal to the flow direction of discharged LNG or in a direction opposite to the flow direction of LNG is disclosed. Has been.

JP S55-145897 JP H9-59657 JP H8-173781

As disclosed in Patent Document 1, in the method of exchanging heat between the LNG and the compressed evaporative gas with a heat exchanger (indirect heat exchange method), a large heat exchanger is required to secure a heat transfer area. There is a problem of becoming.
Moreover, since the direct contact heat exchange system disclosed in Patent Document 2 performs heat exchange without passing through the heat transfer surface, the heat transfer performance at the interface where both are in contact is improved. However, in the direct contact heat exchange method, it is easy to separate into two phases due to the difference in density between gas evaporative gas and liquid LNG, and the liquefaction efficiency tends to deteriorate because the interface area (heat transfer area) cannot be sufficiently secured. . Therefore, it is important how to secure the interface area between the gaseous evaporative gas and the liquid LNG, but Patent Document 2 does not disclose anything about this point.
However, even with the method of Patent Document 3, it is difficult to say that the interface area (heat transfer area) between the gaseous evaporative gas and the liquid LNG can be sufficiently secured.

  In any of the techniques of Patent Documents 1 to 3, pressure loss occurs in the heat exchange part that cools the BOG. Therefore, the pressure of the liquefied BOG at the outlet side of the reliquefaction apparatus and the LNG after the heat exchange are It becomes lower than each pressure. For this reason, it is necessary to increase the pressure by an amount corresponding to the pressure loss of the reliquefaction device with respect to the predetermined supply pressure, and there has been a problem that the boosting power (pump power, compressor power) increases.

As described above, in the method in which the evaporated gas is brought into direct contact with the LNG to be dispensed, it is important to ensure a sufficient interface area between the two. However, the development of such technology has been desired.
In addition, it has been desired to develop an apparatus that does not increase the pressure increase power of the liquid after re-liquefaction.

The injector is usually a mechanism that operates with water and water vapor, sucks water and water vapor at a low pressure generated when water vapor condenses into water, and pressurizes and discharges the liquid condensed and mixed with water vapor. It is a kind of driven liquid pump.
In order for the injector to function, it is essential that the working fluid has a property that the gas phase (corresponding to the water vapor) is condensed into the liquid phase (corresponding to the water).
In this regard, focusing on the fact that the relationship between the low-temperature liquid delivered from the storage tank and the evaporative gas satisfies this requirement, and using the principle of the injector, the low-temperature liquid and the evaporative gas are mixed and the mixed liquid is pressurized. It was thought that it can be discharged.
The present invention is based on such knowledge, and specifically comprises the following configuration.

(1) An evaporative gas reliquefaction / pressure-increasing apparatus according to the present invention includes an evaporative gas compressor that compresses evaporative gas generated from a low-temperature liquid stored in a storage tank, and a low-temperature liquid that delivers low-temperature liquid from the storage tank. A delivery pipe; a delivery pump provided in the cryogenic liquid delivery pipe; and a mixing device for mixing the evaporative gas compressed by the evaporative gas compressor and the cryogenic liquid delivered from the storage tank. ,
The mixing device includes a reduced diameter portion in which the flow path is reduced, a diameter enlarged portion in which the flow path is enlarged on the downstream side of the reduced diameter portion, and the cryogenic liquid delivery pipe on the upstream side of the reduced diameter portion. A low-temperature liquid jet part for jetting a low-temperature liquid sent out by an evaporating gas jet part for jetting evaporative gas which is also upstream of the reduced diameter part and compressed by the evaporative gas compressor,
In the mixing device, the evaporative gas is condensed and the internal pressure is reduced, so that the low-temperature liquid and the evaporative gas are continuously ejected and mixed through the low-temperature liquid ejection portion and the evaporative gas ejection portion, respectively. In addition, the liquid mixture is pressurized and discharged when passing through the enlarged diameter portion.

  In the evaporative gas reliquefaction / pressure-increasing apparatus according to the present invention, the evaporative gas and the low-temperature liquid are jetted and mixed at high speed using the mixing device. Further, since the liquid pressure of the mixed liquid is increased by the mixing device, the pressure increase range of the pump or the compressor for increasing the pressure to the supply pressure can be reduced, and the pressure increasing power is reduced.

It is explanatory drawing of the evaporative gas reliquefaction and pressure | voltage rise apparatus which concerns on one embodiment of this invention. It is explanatory drawing explaining in detail a part of evaporative gas reliquefaction and pressure | voltage rise apparatus which concerns on one embodiment of this invention.

An embodiment of the present invention will be described with reference to FIG.
The evaporative gas reliquefaction / pressure-increasing apparatus 1 according to the present invention compresses evaporative gas supplied by an evaporative gas extraction pipe 5 that extracts evaporative gas generated from a low-temperature liquid 4 (for example, LNG) in a storage tank 3. Compressor 7, evaporative gas delivery pipe 9 for delivering evaporative gas compressed by evaporative gas compressor 7 to mixing device 15, and primary pump 11 provided in storage tank 3 (“delivery pump” of the present invention) A cryogenic liquid delivery pipe 13 for delivering a cryogenic liquid, a cryogenic liquid delivery pipe 13 and an evaporative gas delivery pipe 9 are connected, and a mixing device 15 for mixing the evaporative gas and the cryogenic liquid is provided. .
On the downstream side of the mixing device 15, there is provided a mixed solution delivery pipe 17 that sends out a mixed solution of the evaporated gas re-liquefied by the mixing device 15 and the low-temperature liquid. In the case of a city gas production plant, in order to supply in a high-pressure gas state, a secondary pump 19 for further boosting the mixed solution is provided in the mixed solution delivery pipe 17, and further, a vaporizer that vaporizes a low-temperature liquid downstream thereof. 21 is provided.
The main equipment constituting the evaporative gas reliquefaction / pressure-increasing apparatus 1 will be described in detail.

<Evaporative gas delivery pipe>
The evaporative gas compressed by the evaporative gas compressor 7 is sent to the mixing device 15.
The evaporative gas delivery pipe 9 is provided with an evaporative gas flow rate control valve 23 that controls the flow rate of the evaporative gas supplied to the mixing device 15 according to the flow rate of the low temperature liquid discharged from the storage tank 3.
In FIG. 1, the evaporative gas flow control valve 23 is provided on the downstream side of the evaporative gas compressor, but may be provided on the upstream side of the evaporative gas compressor.

<Cryogenic liquid delivery pipe>
The cryogenic liquid delivery pipe 13 is a tubular body that delivers the cryogenic liquid toward the mixing device 15 by the primary pump 11 provided in the storage tank 3.
The cryogenic liquid delivery pipe 13 is provided with a cryogenic liquid flow rate control valve 25 for adjusting the flow rate of the delivered cryogenic liquid.

<Evaporative gas compressor>
The evaporative gas compressor 7 raises the evaporative gas to the same level as the discharge pressure of the primary pump 11.

<Mixing device>
As shown in FIG. 2, the mixing device 15 includes a reduced diameter portion 27 where the diameter of the flow path is reduced, an enlarged diameter portion 29 where the diameter of the flow path is increased on the downstream side of the reduced diameter section 27, and an upstream side of the reduced diameter portion 27. The low-temperature liquid ejection part 31 that ejects the low-temperature liquid delivered by the low-temperature liquid delivery pipe 13 and the evaporative gas compressed by the evaporative gas compressor 7 are also upstream of the reduced diameter part 27. And an evaporating gas ejection part 32. A straight pipe portion may be provided between the reduced diameter portion 27 and the enlarged diameter portion 29. Moreover, the evaporating gas ejection part 32 can be reduced in diameter to increase the evaporating gas ejection flow rate.
In FIG. 2, the evaporative gas ejection part 32 is provided around the low temperature liquid ejection part 31, but conversely, a low temperature liquid ejection part may be provided around the evaporative gas ejection part.
The mixing device 15 constitutes an injector and has the following operation.
In the mixing device 15, the evaporative gas supplied from the evaporative gas delivery tube 9 is condensed by being mixed with the low temperature liquid supplied from the low temperature liquid delivery tube 13, whereby the inside of the mixing device 15 is condensed into the low temperature liquid delivery tube 13. From the pressure of the low-temperature liquid supplied to the mixing device 15, and the low-temperature liquid is self-primed. On the other hand, the evaporative gas supplied to the mixing device 15 is boosted by the evaporative gas compressor 7 to a pressure equivalent to that of the low-temperature liquid supplied to the mixing device 15, and the evaporative gas is also inside the mixing device 15. Since it is in a low pressure state, it will self-prime.

The evaporative gas and the low-temperature liquid are sucked toward the reduced-diameter portion 27 in the low pressure state in the mixing device 15 and are ejected from the low-temperature liquid ejection portion 31 and the evaporative gas ejection portion 32 into the reduced-diameter portion, respectively. The vapor-phase evaporating gas is ejected at a particularly high speed, and is condensed by contacting with the low-temperature liquid jet while maintaining the speed, and becomes a mixed liquid together with the low-temperature liquid.
The kinetic energy of the evaporating gas that is a high-speed jet is transferred to the mixed liquid as it is, and the mixed liquid is accelerated more than the ejection speed of the low-temperature liquid from the low-temperature liquid ejection section 31. At the end of the reduced diameter portion, the mixed liquid in which the entire amount of the evaporated gas is completely condensed becomes a single-phase state, and the kinetic energy of the accelerated mixed liquid is decelerated when passing through the enlarged diameter portion 29 to become pressure energy. Converted. As a result, the mixed liquid obtains a discharge pressure higher than the pressure of the supplied low temperature liquid or the supplied evaporative gas, and is discharged to the mixed liquid delivery pipe 17.

In the present embodiment, a drain pipe 33 is provided in which one end side is connected to the reduced diameter portion 27 of the mixing device 15 and the other end is connected to a downstream side of a pressure control valve 37 described later in the mixed liquid delivery pipe 17. It has been.
The drain pipe 33 is provided with a valve 35 that is opened when the pressure on the mixing device 15 side becomes higher than the pressure on the downstream side of the pressure control valve 37 in the mixed liquid delivery pipe 17 by a certain value or more.
The drain pipe 33 draws out the drain (condensed low-temperature liquid) staying in the reduced diameter portion 27 at the time of start-up, makes it easy to supply the evaporated gas to the reduced diameter portion 27, and the continuous evaporative gas at the start-up time. It is intended to facilitate the condensation.
The valve 35 provided in the drain pipe 33 may be a check valve.

<Mixed liquid delivery pipe>
The mixed liquid delivery pipe 17 sends the mixed liquid of the evaporated gas and the low-temperature liquid reliquefied by the mixing device 15 to the downstream side.
The mixed liquid delivery pipe 17 is provided with a pressure control valve 37 for controlling the discharge pressure. Further, a pressure measuring unit and a temperature measuring unit may be installed on the upstream side of the pressure control valve 37, and the pressure and temperature on the discharge side of the mixing device 15 may be measured.

<Description of operation>
The operation of the evaporative gas reliquefaction / boosting device 1 configured as described above will be described.
The low temperature liquid (for example, LNG) in the storage tank 3 is sent out by the primary pump 11 and introduced into the mixing device 15. Further, the evaporative gas is supplied to the evaporative gas compressor 7 through the evaporative gas extraction pipe 5, and after being pressurized by the evaporative gas compressor 7, is introduced into the mixing device 15 through the evaporative gas delivery pipe 9.

The evaporative gas introduced into the mixing device 15 is cooled and condensed by the low-temperature liquid. Due to the condensation of the evaporative gas, the pressure of the mixing device 15 becomes a low pressure, the low temperature liquid is continuously sucked from the low temperature liquid delivery pipe 13, and is ejected from the low temperature liquid ejection part 31 into the reduced diameter part 27. Similarly, the evaporative gas is continuously sucked toward the low pressure in the mixing device 15 and ejected from the evaporative gas ejection portion 32 into the reduced diameter portion 27. The vapor-phase evaporating gas is ejected at a particularly high speed, and is condensed by contacting with the low-temperature liquid jet while maintaining the speed, and becomes a mixed liquid together with the low-temperature liquid.
The kinetic energy of the evaporating gas that is a high-speed jet is transferred to the mixed liquid as it is, and the mixed liquid is accelerated more than the ejection speed of the low-temperature liquid from the low-temperature liquid ejection portion. At the end of the reduced diameter portion, the entire amount of the evaporated gas is completely condensed, and the kinetic energy of the accelerated mixed liquid is decelerated and converted into pressure energy when the mixed liquid passes through the enlarged diameter portion. As a result, the mixed liquid obtains a discharge pressure higher than the pressure of the supplied low-temperature liquid or supplied evaporative gas. The mixed solution is discharged to the mixed solution delivery pipe 17. In the case of a city gas production plant, the mixed solution discharged to the mixed solution delivery pipe 17 is sent to the secondary pump 19, boosted by the secondary pump 19, vaporized by the vaporizer 21, and sent to the demand side as city gas.

  When the pressure of the reduced diameter portion 27 is higher than the pressure downstream of the pressure control valve 37 in the mixed solution delivery pipe 17, the valve 35 provided in the drain pipe 33 is opened, and the low temperature liquid is mixed with the mixed liquid through the drain pipe 33. It is discharged to the delivery pipe 17. When the pressure of the reduced diameter portion 27 is reduced, the valve 35 is closed, the pressure of the mixed liquid at the downstream end of the enlarged diameter portion 29 is increased, the pressure control valve 37 is opened, and the mixed liquid is discharged to the mixed liquid delivery pipe 17. .

Further, a pressure measuring means and a temperature measuring means are installed upstream of the pressure control valve 37 of the mixed liquid delivery pipe 17, and the flow rates of the low temperature liquid and the evaporative gas are controlled by the pressure and temperature of the mixed liquid measured by these means. Anyway.
The saturation temperature Ts is calculated from the pressure Pm of the mixed liquid measured by the pressure measuring means from the relationship between the pressure and temperature of the saturated liquid of the low temperature liquid obtained in advance, and the saturated liquid temperature measured by the temperature measuring means is calculated. The low-temperature liquid flow rate adjustment valve 25 and the evaporative gas flow rate adjustment valve 23 are adjusted so that the temperature Tm is maintained lower than the saturation temperature Ts.

  Instead of controlling the low-temperature liquid flow rate adjustment valve 25, a capacity control means such as an inverter may be added to the primary pump 11 that is a liquid pump to directly control the operating capacity of the primary pump 11. Similarly, instead of controlling the evaporative gas flow control valve 23, a capacity control means such as an inverter may be added to the evaporative gas compressor 7 to directly control the operating capacity of the evaporative gas compressor 7.

  Since the liquid mixture temperature Tm tends to increase as the evaporative gas flow rate increases with respect to the low temperature liquid flow rate, if the liquid mixture temperature Tm rises and approaches the saturation temperature Ts, is the low temperature liquid flow rate increased? The evaporative gas flow rate may be controlled to decrease. In general, the delivery flow rate of the cryogenic liquid is often determined by other factors, such as city gas demand, and in this case, the evaporation gas flow rate side is controlled. In addition, when the pressure and temperature conditions of the cryogenic liquid and the evaporative gas are almost constant and less fluctuating, the flow rate information obtained by the flow rate measuring means (not shown) that measures the respective flow rates of the cryogenic liquid and the evaporative gas, You may make it control so that the flow rate ratio (= evaporation gas flow rate / low-temperature liquid flow rate) of evaporation gas and low-temperature liquid may become below a predetermined value.

In the present embodiment, since the liquid pressure of the mixed liquid is increased by the mixing device 15, the pressure increase range of the pump or the compressor for increasing the pressure to the supply pressure can be reduced, and the pressure increase power is reduced.
Further, since the evaporative gas and the low temperature liquid are jetted and mixed at high speed using the mixing device 15, the evaporative gas can be effectively brought into contact with the low temperature liquid and reliquefied, and the process to the subsequent process can be performed. Restrictions can be reduced. For example, in the case of a city gas manufacturing plant, it is possible to prevent the evaporative gas from flowing into the secondary pump 19 installed on the downstream side of the mixing device 15 and causing a failure in the secondary pump 19.
Further, since the re-liquefaction of the evaporative gas is completed efficiently in a short time, the distance from the mixing device 15 to the secondary pump 19 can be set short, the degree of freedom of equipment layout can be improved, and the installation area can be reduced. There is also an effect.
In the embodiment shown in FIG. 1, the evaporative gas reliquefaction / boosting device of the present invention is applied to a city gas production plant. However, the evaporative gas reliquefaction / boosting device is applied to other uses. Therefore, it is not always necessary to install the secondary pump 19 or the vaporizer 21 in the mixed solution delivery pipe 17.

DESCRIPTION OF SYMBOLS 1 Evaporative gas reliquefaction and pressure booster 3 Reservoir 4 Low temperature liquid 5 Evaporative gas extraction pipe 7 Evaporative gas compressor 9 Evaporative gas delivery pipe 11 Primary pump 13 Low temperature liquid delivery pipe 15 Mixing device 17 Mixed liquid delivery pipe 19 Secondary pump 21 Evaporation 23 Evaporative gas flow control valve 25 Low temperature liquid flow control valve 27 Reduced diameter portion 29 Expanded diameter portion 31 Low temperature liquid ejection portion 32 Evaporative gas ejection portion 33 Drain pipe 35 Valve 37 Pressure control valve

Claims (1)

An evaporative gas compressor for compressing evaporative gas generated from the cryogenic liquid stored in the storage tank; a cryogenic liquid delivery pipe for delivering the cryogenic liquid from the storage tank; and a delivery pump provided in the cryogenic liquid delivery pipe; A mixing device for mixing the evaporative gas compressed by the evaporative gas compressor and the low-temperature liquid sent from the storage tank,
The mixing device includes a reduced diameter portion in which the flow path is reduced, a diameter enlarged portion in which the flow path is enlarged on the downstream side of the reduced diameter portion, and the cryogenic liquid delivery pipe on the upstream side of the reduced diameter portion. A low-temperature liquid jet part for jetting a low-temperature liquid sent out by an evaporating gas jet part for jetting evaporative gas which is also upstream of the reduced diameter part and compressed by the evaporative gas compressor,
In the mixing device, the evaporative gas is condensed and the internal pressure is reduced, so that the low-temperature liquid and the evaporative gas are continuously ejected and mixed through the low-temperature liquid ejection portion and the evaporative gas ejection portion, respectively. The evaporative gas reliquefaction / pressure-increasing apparatus is characterized in that the mixed liquid is pressurized and discharged when passing through the enlarged diameter portion.

Images