POWER RECOVERY SYSTEM

Abstract

 Provided is a power recovery system for recovering, as power, cold energy of a liquefied gas via a working fluid for heating the liquefied gas, including: a condenser; a gas-liquid separation tank; a cryogenic pump; an evaporator; a cryogenic turbine; and a first conduit configured to supply the working fluid condensed by the condenser to the gas-liquid separation tank, the first conduit being configured such that an outlet port of the first conduit is located below a liquid level of the gas-liquid separation tank.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a power recovery system for recovering, as power, cold energy of a liquefied gas via a working fluid for heating the liquefied gas.

[0002] This application claims the priority of Japanese Patent Application No. 2021-152416 filed on September 17, 2021, the content of which is incorporated herein by reference.

BACKGROUND

[0003] A Liquefied gas (for example, a liquefied natural gas) is liquefied for the purpose of transportation or storage, and is raised in temperature and vaporized by a heat medium such as seawater when supplied to a supply destination such as a city gas or a thermal power generation. There is a power recovery system (for example, a cryogenic power generation cycle) for recovering cold energy as power instead of discarding the cold energy in seawater when a liquefied gas is vaporized.

[0004] ORC (Organic Rankine Cycle) is known as a cryogenic power generation cycle for a liquefied natural gas. The ORC is a cycle process where a low-temperature working fluid, which circulates in a closed loop and has a lower boiling point than water, is cooled and condensed by the liquefied natural gas in a condenser (steam condenser), and then boosted by a pump, and heated and evaporated with seawater, etc. being as a heat source in an evaporator, and the resulting steam is introduced into a cryogenic power generation turbine to obtain power.

[0005] In the ORC, a temperature of the working fluid is lowered to a saturated vapor pressure in the condenser, but when the working fluid is then boosted by the pump, the working fluid may locally evaporate (gasify) in a pump portion, causing cavitation. If the cavitation is caused in the pump portion, the pump may be damaged. Further, if a gas is sucked into the pump, normal driving of the pump may be affected.

[0006] For this reason, Patent Document 1 discloses an ORC machine where a liquid reservoir tank is installed between a condenser and a pump and a large water level head is disposed between the liquid reservoir tank and the pump, in order to suppress gasification in a pump portion. In the ORC machine of Patent Document 1, a working fluid is introduced from a top (ceiling surface) of the liquid reservoir tank.

Citation List

Patent Literature

[0007] Patent Document 1: JP5608755B

SUMMARY

Technical Problem

[0008] If gasification in the pump portion is to further be suppressed with the technique disclosed in Patent Document 1, it is necessary to increase a capacity of the liquid reservoir tank and to provide a large water level head between the reservoir tank and the pump. However, since the ORC of the cryogenic power generation cycle uses a working fluid with a boiling point lower than the atmospheric temperature (for example, 25°C), the larger the capacity of the reservoir tank, the larger a heat transfer area with the surrounding atmosphere, which heats the working fluid stored in a liquid reservoir pump, making bubble generation (gasification) easier in the pump portion. In addition, a temperature difference between the heated pump and the working fluid is also large, which further facilitates gasification.

[0009] In view of the above, an object of at least one embodiment of the present disclosure is to provide a power recovery system capable of normally driving a pump by suppressing occurrence of cavitation in a pump portion as well as suppressing gas suction into the pump through suppression of gasification of a working fluid in the pump portion.

Solution to Problem

[0010] In order to achieve the above object, a power recovery system according to at least one embodiment of the present disclosure is a power recovery system for recovering, as power, cold energy of a liquefied gas via a working fluid for heating the liquefied gas, including: a condenser configured to condense the working fluid by heat exchange between the working fluid and the liquefied gas; a gas-liquid separation tank configured to separate the working fluid condensed in the condenser into liquid and gas, and to store the working fluid; a cryogenic pump configured to boost the working fluid in liquid form supplied from the gas-liquid separation tank; an evaporator configured to evaporate the working fluid boosted by the cryogenic pump, by heat exchange between the working fluid and a heating fluid introduced from outside the power recovery system; a cryogenic turbine configured to be driven by the working fluid in gas form generated in the evaporator; and a first conduit configured to supply the working fluid condensed by the condenser to the gas-liquid separation tank, the first conduit being configured such that an outlet port of the first conduit is located below a liquid level of the gas-liquid separation tank.

Advantageous Effects

[0011] According to a power recovery system of the present disclosure, it is possible to provide a power recovery system capable of normally driving a pump by suppressing occurrence of cavitation in a pump portion as well as suppressing gas suction into the pump through suppression of gasification of a working fluid in the pump portion.

BRIEF DESCRIPTION OF DRAWINGS

[0012] 

FIG. 1 is a schematic configuration diagram schematically showing the overall configuration of a power recovery system according to an embodiment of the present disclosure.

FIG. 2 is a schematic configuration diagram schematically showing the overall configuration of the power recovery system according to an embodiment of the present disclosure.

FIG. 3 is a schematic configuration diagram schematically showing the overall configuration of the power recovery system according to an embodiment of the present disclosure.

FIG. 4 is a schematic configuration diagram schematically showing the overall configuration of the power recovery system according to an embodiment of the present disclosure.

FIG. 5A is a schematic cross-sectional view of a gas-liquid separation tank according to an embodiment of the present disclosure.

FIG. 5B is a schematic cross-sectional view of the gas-liquid separation tank according to an embodiment of the present disclosure.

FIG. 5C is a schematic cross-sectional view of the gas-liquid separation tank according to an embodiment of the present disclosure.

FIG. 5D is a schematic cross-sectional view of the gas-liquid separation tank according to an embodiment of the present disclosure.

FIG. 6A is a schematic view showing an example of a case in which the power recovery system is installed in a floating structure according to an embodiment of the present disclosure.

FIG. 6B is a schematic view showing an example of a case in which the power recovery system is installed in a land liquefied gas terminal according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0013] Some embodiments of the present disclosure will be described below with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions and the like of components described or shown in the drawings as the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present disclosure.

[0014] For instance, an expression of relative or absolute arrangement such as "in a direction", "along a direction", "parallel", "orthogonal", "centered", "concentric" and "coaxial" shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function.

[0015] For instance, an expression of an equal state such as "same", "equal", and "uniform" shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference that can still achieve the same function.

[0016] Further, for instance, an expression of a shape such as a rectangular shape or a tubular shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved.

[0017] On the other hand, the expressions "comprising", "including" or "having" one constitutional element is not an exclusive expression that excludes the presence of other constitutional elements.

[0018] The same configurations are indicated by the same reference characters and may not be described again in detail.

(Application example of power recovery system)

[0019] FIG. 6A is a schematic view showing an example of a case in which a power recovery system 1 is installed in a floating structure 101 according to an embodiment of the present disclosure.

[0020] As shown in FIG. 6A, the power recovery system 1 according to an embodiment of the present disclosure is installed in the floating structure 101. The floating structure 101 is a structure capable of floating on water. The floating structure 101 has a propulsion device configured to drive a propulsor such as a propeller, and includes a vessel capable of self-propelling by driving the propulsion device or a floating body without the propulsion device. In the floating structure 101, a liquefied gas in liquid form is stored, and the liquefied gas in liquid form is warmed and vaporized by seawater, etc., and flowed into an engine 111 to obtain a propulsive force. When the liquefied gas is vaporized, the power recovery system 1 recovers cold energy as electric power instead of discarding the cold energy in seawater.

[0021] FIG. 6B is a schematic view showing an example of a case in which the power recovery system 1 is installed in a land liquefied gas terminal 102 according to an embodiment of the present disclosure.

[0022] As shown in FIG. 6B, the power recovery system 1 according to an embodiment of the present disclosure is installed in the land LNG (liquefied gas) terminal 102. The land LNG (liquefied gas) terminal 102 receives and stores a liquefied gas transported by an LNG carrier. Then, when the liquefied gas is supplied to a supply destination 112 for the liquefied gas, such as a city gas or a thermal power plant, the liquefied gas is warmed by seawater, etc. to be returned to a gas. When the liquefied gas is vaporized, the power recovery system 1 recovers cold energy as electric power instead of discarding the cold energy in seawater.

[0023] Herein, although the power recovery system 1 of the present disclosure is described by taking the liquefied natural gas (LNG) as a specific example of the above-described liquefied gas, the present disclosure is also applicable to a liquefied gas (liquefied petroleum gas, liquid hydrogen, etc.) other than the liquefied natural gas.

(Overall configuration of power recovery system 1)

[0024] FIGs. 1 to 4 are each a schematic configuration diagram schematically showing the overall configuration of the power recovery system 1 according to an embodiment of the present disclosure.

[0025] The power recovery system 1 according to an embodiment of the present disclosure is a system for recovering, as power, cold energy of a liquefied gas via a working fluid for heating the liquefied gas. The power recovery system 1 according to an embodiment of the present disclosure includes a condenser 2, a gas-liquid separation tank 4, a cryogenic pump 6, an evaporator 8, and a cryogenic turbine 10, as shown in FIGs. 1 to 4. The condenser 2, the gas-liquid separation tank 4, the cryogenic pump 6, the evaporator 8, and the cryogenic turbine 10 are connected to each other by a circulation passage 3. The working fluid circulates in the circulation passage 3 while changing its state to a liquid or a gas, thereby driving the power recovery system 1.

[0026] The condenser 2 is configured to condense the working fluid by heat exchange between the working fluid and the liquefied gas. The condenser 2 is internally provided with a heating-side conduit 21 into which the working fluid circulating in the circulation passage 3 flows and a heated-side conduit 22 into which the liquefied gas introduced from outside the power recovery system 1 flows, thereby configuring such that the working fluid and the liquefied gas exchange heat. In the condenser 2, by the heat exchange, the working fluid is cooled and condensed, and the liquefied gas is heated.

[0027] The circulation passage 3 includes a first conduit 31 connecting the condenser 2 to the gas-liquid separation tank 4, a second conduit 32 connecting the gas-liquid separation tank 4 to the cryogenic pump 6, a third conduit 33 connecting the cryogenic pump 6 to the evaporator 8, a fourth conduit 34 connecting the evaporator 8 to the cryogenic turbine 10, and a fifth conduit 35 connecting the cryogenic turbine 10 to the condenser 2. The working fluid circulates in the circulation passage 3 while changing its state to the liquid or the gas, thereby driving the power recovery system 1.

[0028] In the following description, an "upstream side" means an upstream side in a flow direction of the working fluid flowing through the circulation passage 3, and a "downstream side" means a downstream side in the flow direction of the working fluid flowing through the circulation passage 3.

[0029] The first conduit 31 is disposed on the downstream side of the condenser 2 and the upstream side of the gas-liquid separation tank 4, and connects the condenser 2 to the gas-liquid separation tank 4. An upstream end portion of the first conduit 31 is connected to a downstream end portion of the heating-side conduit 21 of the condenser 2. The downstream side of the first conduit 31 is connected to the gas-liquid separation tank 4. The working fluid in liquid form condensed by the condenser 2 flows in the first conduit 31 and is supplied to the gas-liquid separation tank 4.

[0030] The gas-liquid separation tank 4 is configured to separate the working fluid condensed in the condenser 2 into liquid and gas, and to store the working fluid. The gas-liquid separation tank 4 internally forms, with a liquid level 41 as a boundary, a gas-phase portion 42 made of a working fluid in gas form above the boundary and a liquid-phase portion 43 made of the working fluid in liquid form below the boundary.

[0031] Further, the gas-liquid separation tank 4 is installed such that a ceiling surface 44 of the gas-liquid separation tank 4 is located vertically below the condenser 2. That is, it is configured such that the upstream end portion of the first conduit 31 is located vertically above a downstream end portion of the first conduit 31 and the working fluid flows in the first conduit 31 by natural flow.

[0032] In the illustrated embodiment, the gas-liquid separation tank 4 has a columnar shape. However, the shape of the gas-liquid separation tank 4 is not particularly limited, as long as the gas-liquid separation tank 4 can separate the working fluid into liquid and gas and can store the working fluid. The shape of the gas-liquid separation tank 4 can be selected as appropriate in accordance with the embodiment, such as columnar, spherical, rectangular solid, etc. When the gas-liquid separation tank 4 has the spherical shape, the above-described ceiling surface 44 corresponds to a highest portion of the sphere and a later-described bottom surface 45 corresponds to a lowest portion of the sphere, respectively.

[0033] A temperature in the gas-phase portion 42 of the gas-liquid separation tank 4 is not lower than a saturated vapor temperature, and is either the saturated vapor temperature or a temperature slightly higher than the saturated vapor temperature due to an external influence. A temperature in the liquid-phase portion 43 of the gas-liquid separation tank 4 is influenced by the gas-phase portion 42 having the temperature not lower than the saturated vapor temperature at the liquid level 41, and thus has a temperature gradient such that the temperature decreases from a liquid level 41 side to a bottom surface 45 side of the liquid-phase portion 43 in the vertical direction.

[0034] The second conduit 32 is disposed on the downstream side of the gas-liquid separation tank 4 and the upstream side of the cryogenic pump 6, and connects the gas-liquid separation tank 4 to the cryogenic pump 6. An upstream end portion of the second conduit 32 is located in the liquid-phase portion 43 of the gas-liquid separation tank 4 and is open to allow the working fluid in liquid form to flow into the interior of the second conduit 32. A downstream end portion of the second conduit 32 is connected to an intake port of the cryogenic pump 6. The working fluid in liquid form stored in the liquid-phase portion 43 of the gas-liquid separation tank 4 flows through the second conduit 32 and is supplied to the cryogenic pump 6.

[0035] The cryogenic pump 6 is configured to boost the working fluid in liquid form supplied from the gas-liquid separation tank 4. The working fluid in liquid form having flowed in from the intake port is boosted by a boosting part (for example, an impeller, etc.) of the cryogenic pump 6 and flows out from a discharge port.

[0036] Further, the cryogenic pump 6 is installed vertically below the bottom surface 45 of the gas-liquid separation tank 4. That is, it is configured such that the upstream end portion of the second conduit 32 is located vertically above the downstream end portion of the second conduit 32 and the working fluid flows in the second conduit 32 by a head difference between the liquid level 41 and the intake port of the cryogenic pump 6 and a suction force of the cryogenic pump 6.

[0037] The form of the cryogenic pump 6 is not particularly limited, as long as the cryogenic pump 6 can boost the working fluid. For example, the form can be selected as appropriate in accordance with the embodiment, such as a turbo pump (a centrifugal pump, a mixed flow pump, an axial-flow pump, etc.), a positive displacement pump (a reciprocating pump, a rotary pump), etc.

[0038] The third conduit 33 is disposed on the downstream side of the cryogenic pump 6 and the upstream side of the evaporator 8, and connects the cryogenic pump 6 to the evaporator 8. An upstream end portion of the third conduit 33 is connected to the discharge port of the cryogenic pump. A downstream end portion of the third conduit 33 is connected to an upstream end portion of a heated-side conduit 81 of the evaporator 8. The working fluid in liquid form boosted by the cryogenic pump 6 flows in the third conduit 33 and is supplied to the evaporator 8.

[0039] The evaporator 8 is configured to evaporate the working fluid boosted by the cryogenic pump 6, by heat exchange between the working fluid and a heating fluid introduced from outside the power recovery system 1. The evaporator 8 is internally provided with the heated-side conduit 81 into which the working fluid boosted by the cryogenic pump 6 flows and a heating-side conduit 82 into which the heating fluid introduced from outside the power recovery system 1 flows, thereby configuring such that the working fluid and the heating fluid exchange heat. In the evaporator 8, by the heat exchange, the working fluid is heated and evaporated, and the heating fluid is cooled.

[0040] The above-described heating fluid can be any medium having a higher temperature than the working fluid boosted by the cryogenic pump 6, such as steam, hot water, seawater, or engine cooling water introduced from outside the power recovery system 1. In the present embodiment, cooling water for the engine 111 of the floating structure 101 described above is used as the heating fluid. Since the cooling water for the engine 111 has a higher temperature than seawater, etc., heat exchange efficiency in the evaporator 8 can be increased compared to a case where seawater, etc. is used as the heating fluid.

[0041] The fourth conduit 34 is disposed on the downstream side of the evaporator 8 and the upstream side of the cryogenic turbine 10, and connects the evaporator 8 to the cryogenic turbine 10. An upstream end portion of the fourth conduit 34 is connected to a downstream end portion of the heated-side conduit 81 of the evaporator 8. A downstream end portion of the fourth conduit 34 is connected to an inlet portion of the cryogenic turbine 10. The working fluid in gas form subjected to heat exchange and heated in the evaporator 8 flows in the fourth conduit 34 and is supplied to the cryogenic turbine 10.

[0042] The cryogenic turbine 10 is configured to be driven by the working fluid in gas form generated in the evaporator 8. The cryogenic turbine 10, for example, has a rotational shaft and an impeller formed from at least one rotor blade disposed in the rotational shaft, and is configured such that the working fluid having flowed in from the inlet portion acts on the rotor blade to rotate the rotational shaft.

[0043] Further, the rotational shaft of the cryogenic turbine 10 is connected to a generator 12. The generator 12 is configured to generate electricity by using a driving force of the cryogenic turbine 10 as a drive source.

[0044] That is, since the power recovery system 1 includes the cryogenic turbine 10 and the generator 12, the cold energy of the liquefied gas can be recovered as power (electric power).

[0045] The fifth conduit 35 is disposed on the downstream side of the cryogenic turbine 10 and the upstream side of the condenser 2, and connects the cryogenic turbine 10 to the condenser 2. An upstream end portion of the fifth conduit 35 is connected to an outlet portion of the cryogenic turbine 10. A downstream end portion of the fifth conduit 35 is connected to the upstream end portion of the heating-side conduit 21 of the condenser 2. The working fluid in gas form having driven the cryogenic turbine 10 flows in the fifth conduit 35 and is supplied to the condenser 2.

(Position of outlet port 311 of first conduit 31)

[0046] FIGs. 5A to 5D are each a schematic cross-sectional view of the gas-liquid separation tank 4 according to an embodiment of the present disclosure.

[0047] In the power recovery system 1 according to an embodiment of the present disclosure, an outlet port 311 of the first conduit 31 is configured to be located below the liquid level 41 of the gas-liquid separation tank 4, as shown in FIGs. 5A to 5D.

[0048] Since the outlet port 311 of the first conduit 31 is located below the liquid level 41 of the gas-liquid separation tank 4, the working fluid condensed by the condenser 2 is directly supplied to not the gas-phase portion 42 but the liquid-phase portion 43. Therefore, compared to a case where the outlet port 311 of the first conduit 31 is located above the liquid level 41 of the gas-liquid separation tank 4, that is, a case where the working fluid condensed by the condenser 2 is supplied to the liquid-phase portion 43 via the gas-phase portion 42, the working fluid is not warmed in the gas-phase portion 42, making it possible to supply the working fluid to the liquid-phase portion 43 while the working fluid is in a low-temperature state. Then, the working fluid in liquid form can flow in in the low-temperature state also when the working fluid is supplied from the gas-liquid separation tank 4 to the cryogenic pump 6, making it possible to suppress gasification of the working fluid in the pump portion of the cryogenic pump 6. Whereby, the occurrence of cavitation in the pump portion of the cryogenic pump 6 is suppressed, as well as gas suction into the cryogenic pump 6 is suppressed, making it possible to normally drive the cryogenic pump 6.

[0049] In an embodiment, the outlet port 311 of the first conduit 31 may be configured to be located below in the vertical middle of the gas-liquid separation tank 4, as shown in FIGs. 5A to 5D.

[0050] In general, the liquid level 41 of the gas-liquid separation tank 4 is located above an intermediate position (50% position). Therefore, according to such configuration, the working fluid condensed by the condenser 2 is directly supplied to not the gas-phase portion 42 of the gas-liquid separation tank 4, but the gas-liquid separation tank 4 from the outlet port 311 of the first conduit 31 disposed in the liquid-phase portion 43 of the gas-liquid separation tank 4.

[0051] In an embodiment, as described above, the power recovery system 1 further includes the second conduit 32 configured to supply the working fluid in liquid form stored in the gas-liquid separation tank 4 to the cryogenic pump 6. Then, as shown in FIGs. 5A to 5D, the outlet port 311 of the first conduit 31 and an inlet port 321 of the second conduit 32 are located in a range of 0% to 25%, where a position of the bottom surface 45 is defined as a 0% position and a position of the ceiling surface 44 is defined as a 100% position in the vertical direction of the gas-liquid separation tank 4.

[0052] According to such configuration, the outlet port 311 of the first conduit 31 and the inlet port 321 of the second conduit 32 are located in the range of 0% to 25% (that is, on the bottom surface 45 side) in the vertical direction of the gas-liquid separation tank 4. Therefore, the working fluid having flowed out from the outlet port 311 of the first conduit 31 to the liquid-phase portion 43 flows into the inlet port 321 of the second conduit 32 and is supplied to the cryogenic pump 6, without being warmed in the liquid-phase portion 43 vertically above, where the temperature of the working fluid increases, and while being maintained in the low-temperature state. Whereby, it is possible to suppress gasification of the working fluid in the pump portion of the cryogenic pump 6.

[0053] In an embodiment, the first conduit 31 and the second conduit 32 are inserted into the gas-liquid separation tank 4 from the bottom surface 45, as shown in FIG. 5A. The first conduit 31 and the second conduit 32 extend from the bottom surface 45 vertically upward in the liquid-phase portion 43 below the liquid level 41.

[0054] In an embodiment, the first conduit 31 and the second conduit 32 are inserted into the gas-liquid separation tank 4 from a lateral surface 46, as shown in FIG. 5B. The first conduit 31 and the second conduit 32 extend from the lateral surface 46 toward the horizontal direction in the liquid-phase portion 43 below the liquid level 41.

[0055] In some embodiments, the first conduit 31 includes an internal conduit 31B inserted into the gas-liquid separation tank 4 from above the liquid level 41 of the gas-liquid separation tank 4 and extending downward relative to the liquid level 41, as shown in FIGs. 5C and 5D. Then, the above-described outlet port 311 is formed in a downstream end portion of the internal conduit 31B.

[0056] According to such configuration, since the first conduit 31 is inserted into the gas-liquid separation tank 4 from above the liquid level 41 of the gas-liquid separation tank 4, a distance which the first conduit 31 is exposed to the atmosphere having the higher temperature than the working fluid condensed by the condenser 2 is reduced compared to a case where the first conduit 31 is inserted into the gas-liquid separation tank 4 from below the liquid level 41. Whereby, it is possible to suppress heating of the working fluid in the first conduit 31 by heat input from outside, outside the gas-liquid separation tank 4.

[0057] In an embodiment, the first conduit 31 includes an external conduit 31A disposed outside the gas-liquid separation tank 4 and the internal conduit 31B disposed inside the gas-liquid separation tank 4, as shown in FIG. 5C. The first conduit 31 is inserted into the gas-liquid separation tank 4 from the ceiling surface 44. The internal conduit 31B extends from the ceiling surface 44 vertically downward to the liquid-phase portion 43 below the liquid level 41.

[0058] In an embodiment, the first conduit 31 includes the external conduit 31A disposed outside the gas-liquid separation tank 4 and the internal conduit 31B disposed inside the gas-liquid separation tank 4, as shown in FIG. 5D. The first conduit 31 is inserted into the gas-liquid separation tank 4 from the lateral surface 46 of the gas-liquid separation tank 4. The internal conduit 31B includes an internal horizontal conduit 31B1 extending toward the horizontal direction from the lateral surface 46, and an internal vertical conduit 31B2 extending vertically downward from a downstream end portion of the internal horizontal conduit 31B 1 to the liquid-phase portion 43 below the liquid level 41.

[0059] In an embodiment, as shown in FIGs. 5A to 5D, the outlet port 311 of the first conduit 31 is located above the inlet port 321 of the second conduit 32 in the vertical direction of the gas-liquid separation tank 4.

[0060] According to such configuration, even if the working fluid flowing through the first conduit 31 includes bubbles, it is possible to suppress inflow of the bubbles, which have flowed out from the outlet port 311, to the inlet port 321 of the second conduit 32.

[0061] In some embodiments, the above-described working fluid includes a fluid with a boiling point lower than 0°C.

[0062] According to such configuration, the power recovery system 1 can be operated by using the fluid with the boiling point lower than 0°C as the working fluid. For example, propane can be given as this working fluid, but the present disclosure is also applicable to a case where a working fluid other than propane is used as the working fluid flowing through the circulation passage 3.

(Recirculation conduit 5)

[0063] In an embodiment, as shown in FIG. 2, the power recovery system 1 further includes a recirculation conduit 5 branching off from between the cryogenic pump 6 and the evaporator 8 and configured to reflux the working fluid boosted by the cryogenic pump 6 to the gas-liquid separation tank 4. Then, an outlet port 51 of the recirculation conduit 5 is disposed to be located below the liquid level 41 of the gas-liquid separation tank 4, as shown in FIGs. 5A and 5B.

[0064] According to such configuration, since the outlet port 51 of the recirculation conduit 5 is located below the liquid level 41 of the gas-liquid separation tank 4, the working fluid condensed by the condenser 2 is directly supplied to not the gas-phase portion 42 but the liquid-phase portion 43. Therefore, the working fluid having flowed out from the outlet port 51 of the recirculation conduit 5 to the liquid-phase portion 43 flows into the inlet port 321 of the second conduit 32 and is supplied to the cryogenic pump 6, without being warmed in the gas-phase portion 42 vertically above, where the temperature of the working fluid increases, and while being maintained in the low-temperature state. Whereby, it is possible to suppress gasification of the working fluid in the pump portion of the cryogenic pump 6.

[0065] In the embodiment shown in FIG. 2, an upstream end portion of the recirculation conduit 5 is connected to the third conduit 33 connecting the cryogenic pump 6 to the evaporator 8. Further, a valve 5V is disposed on the downstream side of the upstream end portion of the recirculation conduit 5, thereby configuring such that the recirculation conduit 5 can be opened and closed. Furthermore, the third conduit 33 is provided with a valve 33V on the downstream side of a connection position with the upstream end portion of the recirculation conduit 5, thereby configuring such that the third conduit 33 can be opened and closed.

[0066] The valve 33V is closed and the valve 5V is opened, when the cryogenic pump 6 is started. Whereby, the working fluid in liquid form stored in the gas-liquid separation tank 4 flows through the second conduit 32, is sucked into the cryogenic pump 6 to be boosted, and is discharged to the third conduit 33. Then, the working fluid in liquid form flows through recirculation conduit 5 and is refluxed to the gas-liquid separation tank 4. Thus, the working fluid in liquid form circulates between the gas-liquid separation tank 4 and the cryogenic pump 6 when the cryogenic pump 6 is started.

[0067] The valve 33V is opened and the valve 5V is closed, when the cryogenic pump 6 reaches a predetermined operating state (when the cryogenic pump 6 is operated) after the cryogenic pump 6 is started. Whereby, the working fluid boosted by the cryogenic pump 6 circulates in the circulation passage 3 without flowing through the recirculation conduit 5.

[0068] In an embodiment, as described above, the outlet port 51 of the recirculation conduit 5 is disposed to be located in the liquid-phase portion 43 below the liquid level 41 of the gas-liquid separation tank 4. Then, the outlet port 51 of the recirculation conduit 5 is preferably located in the range of 0% to 25%, where the position of the bottom surface 45 is defined as the 0% position and the position of the ceiling surface 44 is defined as the 100% position in the vertical direction of the gas-liquid separation tank 4.

[0069] According to such configuration, the working fluid having flowed out from the outlet port 51 of the recirculation conduit 5 to the liquid-phase portion 43 flows into the inlet port 321 of the second conduit 32 and is supplied to the cryogenic pump 6, without being warmed in the liquid-phase portion 43 vertically above, where the temperature of the working fluid increases, and while being maintained in the low-temperature state. Whereby, it is possible to suppress gasification of the working fluid in the pump portion of the cryogenic pump 6.

[0070] In an embodiment, as shown in FIGs. 5A and 5B, the outlet port 51 of the recirculation conduit 5 is located above the inlet port 321 of the second conduit 32 in the vertical direction of the gas-liquid separation tank 4.

[0071] According to such configuration, even if the working fluid flowing through the recirculation conduit 5 includes bubbles, it is possible to suppress inflow of the bubbles, which have flowed out from the outlet port 51, to the inlet port 321 of the second conduit 32.

[0072] In an embodiment, the recirculation conduit 5 is inserted into the gas-liquid separation tank 4 from the bottom surface 45, as shown in FIG. 5A. The recirculation conduit 5 extends from the bottom surface 45 vertically upward in the liquid-phase portion 43 below the liquid level 41.

[0073] In an embodiment, the recirculation conduit 5 is inserted into the gas-liquid separation tank 4 from the lateral surface 46, as shown in FIG. 5B. The recirculation conduit 5 extends from the lateral surface 46 toward the horizontal direction in the liquid-phase portion 43 below the liquid level 41.

[0074] In an embodiment, as shown in FIGs. 5A and 5B, the outlet port 51 of the recirculation conduit 5 is located farther from the inlet port 321 of the second conduit 32 than the outlet port 311 of the first conduit 31. That is, the outlet port 311 of the first conduit 31 is located closer to the inlet port 321 of the second conduit 32 than the outlet port 51 of the recirculation conduit 5.

[0075] According to such configuration, the working fluid can quickly be introduced from the outlet port 311 of the first conduit 31 to the inlet port 321 of the second conduit 32.

(First auxiliary conduit 7)

[0076] In an embodiment, as shown in FIGs. 3 and 4, the power recovery system 1 includes a first auxiliary conduit 7 for supplying the working fluid condensed by the condenser 2 to the gas-liquid separation tank 4. Then, an outlet port 71 of the first auxiliary conduit 7 is configured to be located above the liquid level 41 of the gas-liquid separation tank 4, as shown in FIGs. 5A and 5B.

[0077] According to such configuration, since the gas-phase portion 42 above the liquid level 41 of the gas-liquid separation tank 4 is provided with the outlet port 71 of the first auxiliary conduit 7 above the liquid level 41 of the gas-liquid separation tank 4, the working fluid flowing in from the first auxiliary conduit 7 is directly supplied to the gas-phase portion 42. Consequently, the temperature in the gas-phase portion 42 above the liquid level 41 of the gas-liquid separation tank 4 decreases, making it possible to obtain a low saturated vapor pressure. A pressure at an outlet of the cryogenic turbine 10 is also decreased when a pressure (saturated vapor pressure) in the gas-phase portion 42 above the liquid level 41 of the gas-liquid separation tank 4 is decreased, making it possible to improve turbine efficiency.

[0078] In an embodiment, an upstream end portion of the first auxiliary conduit 7 is connected to the first conduit 31 connecting the condenser 2 to the gas-liquid separation tank 4, as shown in FIGs. 3 and 4. Further, the downstream side of the first auxiliary conduit 7 is connected to the gas-liquid separation tank 4 from vertically above the gas-liquid separation tank 4 (above the liquid level 41). Then, the outlet port 71 of the first auxiliary conduit 7 is disposed to be located in the gas-phase portion 42 above the liquid level 41 of the gas-liquid separation tank 4, as shown in FIGs. 5A and 5B.

[0079] Further, in an embodiment, the first auxiliary conduit 7 is inserted into the gas-liquid separation tank 4 from the ceiling surface 44, as shown in FIG. 5A. The first auxiliary conduit 7 extends from the ceiling surface 44 vertically downward in the gas-phase portion 42 above the liquid level 41.

[0080] In an embodiment, the first auxiliary conduit 7 is inserted into the gas-liquid separation tank 4 from the lateral surface 46, as shown in FIG. 5B. The first auxiliary conduit 7 extends from the lateral surface 46 toward the horizontal direction in the gas-phase portion 42 above the liquid level 41.

(Control device 9, first valve 31V, second valve 7V)

[0081] In an embodiment, as shown in FIGs. 3 and 4, the power recovery system 1 includes a first valve 31V capable of regulating the flow rate of the working fluid flowing through the first conduit 31, a second valve 7V capable of regulating the flow rate of the working fluid flowing through the first auxiliary conduit 7, and a control device 9 capable of controlling respective valve opening degrees of the first valve 31V and the second valve 7V. The control device 9 is configured to control the respective valve opening degrees of the first valve 31V and the second valve 7V such that a difference ΔT between a temperature T1 in the gas-phase portion 42 above the liquid level 41 of the gas-liquid separation tank 4 and a liquid temperature T2 of the working fluid in liquid form, which is flowed out from the gas-liquid separation tank 4 and is to be sucked into the cryogenic pump 6, is greater than a first threshold and less than a second threshold which is greater than the first threshold.

[0082] According to such configuration, the difference ΔT is controlled between the first threshold and the second threshold. A temperature difference between the liquid temperature T2 and the temperature T1 in the gas-phase portion 42, which is the saturation temperature, is small if the difference ΔT is less than the first threshold, making it easier for the working fluid at the liquid temperature T2 to be gasified when the working fluid flows into the cryogenic pump 6 or even is heated by a little bit in the pump portion of the cryogenic pump 6. On the other hand, the temperature T1 in the gas-phase portion 42 is high and the gas-phase portion 42 has a high saturated vapor pressure if the difference ΔT is greater than the second threshold, which may decrease the turbine efficiency of the cryogenic turbine 10. Therefore, control is performed by using the difference ΔT as a control parameter and providing the difference ΔT with the first threshold and the second threshold, making it possible to increase the turbine efficiency without causing gasification of the working fluid.

[0083] The second valve 7V is disposed in the first auxiliary conduit 7, making it possible to control the flow rate of the working fluid flowing through the first auxiliary conduit 7. Further, the first valve 31V is disposed in the first conduit 31 on the downstream side of a connection position with the upstream end portion of the recirculation auxiliary conduit 7, making it possible to control the flow rate of the working fluid flowing through the first conduit 31. Furthermore, the first valve 31V and the second valve 7V are connected to an actuator (such as a motor) so that their valve opening degrees can automatically be adjusted.

[0084] The gas-phase portion 42 has the high saturated vapor pressure and the pressure at the outlet of the cryogenic turbine 10 increases as the temperature T1 rises, which may decrease the turbine efficiency. Further, the temperature of the working fluid supplied to the cryogenic pump 6 increases as the liquid temperature T2 rises, which may easily gasify the working fluid in the pump portion of the cryogenic pump 6.

[0085] In order to decrease the temperature T1, it is preferable to adjust the second valve 7V in a valve-opening direction and the first valve 31V in a valve-closing direction so that more working fluid in liquid form condensed by the condenser 2 flows to the first auxiliary conduit 7. Whereby, the amount of the working fluid supplied from the outlet port 71 of the first auxiliary conduit 7 to the gas-phase portion 42 of the gas-liquid separation tank 4 increases, making it possible to decrease the temperature T1.

[0086] However, the amount of the working fluid flowing through the first conduit 31 is decreased by adjusting the second valve 7V in the valve-opening direction and the first valve 31V in the valve-closing direction. Consequently, the working fluid is less likely to be supplied from the outlet port 311 of the first conduit 31 to the liquid-phase portion 43 of the gas-liquid separation tank 4, raising the liquid temperature T2 in the liquid-phase portion 43 of the gas-liquid separation tank 4.

[0087] On the other hand, in order to decrease the temperature of the liquid temperature T2, it is preferable to adjust the second valve 7V in the valve-closing direction and the first valve 31V in the valve-opening direction so that more working fluid in liquid form condensed by the condenser 2 flows to the first conduit 31. Whereby, the amount of the working fluid supplied from the outlet port 311 of the first conduit 31 to the liquid-phase portion 43 increases, making it possible to decrease the liquid temperature T2.

[0088] However, the amount of the working fluid flowing through the first auxiliary conduit 7 is decreased by adjusting the second valve 7V in the valve-closing direction and the first valve 31V in the valve-opening direction. Consequently, the working fluid is less likely to be supplied from the outlet port 71 of the first auxiliary conduit 7 to the gas-phase portion 42 of the gas-liquid separation tank 4, raising the temperature T1 in the gas-phase portion 42 of the gas-liquid separation tank 4.

[0089] That is, there is a trade-off between the temperature T1 and the liquid temperature T2, in which the liquid temperature T2 increases if the temperature T1 is to be decreased and the temperature T1 increases if the liquid temperature T2 is to be decreased. Therefore, the first threshold and the second threshold are provided for the difference ΔT between the temperature T1 and the liquid temperature T2.

[0090] If the temperature T1 rises, the temperature difference between the temperature T1 and the liquid temperature T2 increases, increasing the difference ΔT. Then, the second valve 7V is adjusted in the valve-closing direction and the first valve 31V is adjusted in the valve-opening direction so that the difference ΔT is not greater than the second threshold. Whereby, it is possible to maintain a state where the temperature T1 is decreased, the difference ΔT is reduced, and the difference ΔT is less than the second threshold.

[0091] Further, if the liquid temperature T2 rises, the temperature difference between the temperature T1 and the liquid temperature T2 decreases, reducing the difference ΔT. Then, the second valve 7V is adjusted in the valve-closing direction and the first valve 31V is adjusted in the valve-opening direction so that the difference ΔT is not less than the first threshold. Whereby, it is possible to maintain a state where the liquid temperature T2 is decreased, the difference ΔT is increased, and the difference ΔT is greater than the first threshold.

[0092] The control device 9 is an electronic control unit for controlling the valve opening degrees of the first valve 31V and the second valve 7V, and may be configured as a microcomputer including a CPU (processor), a memory such as a ROM or a RAM, a storage device such as an external storage device, an I/O interface, a communication interface, etc. which are not shown. Then, later-described control of the valve opening degrees of the first valve 31V and the second valve 7V may be implemented by, for example, causing the CPU to operate (for example, calculate data) in accordance with an instruction of a program loaded to a main storage device of the above-described memory.

[0093] In an embodiment, as shown in FIG. 4, a first sensor 131 is installed in the gas-phase portion 42 of the gas-liquid separation tank 4 such that the temperature T1 can be measured and transmitted to the control device 9. A second sensor 132 is installed near the cryogenic pump 6 in the second conduit 32 such that the liquid temperature T2 can be measured and transmitted to the control device 9. The first sensor 131 and the second sensor 132 are configured to continuously transmit, as signals, the measured temperature T1 and liquid temperature T2 to the control device 9 through a wired or wireless communication line.

[0094] The control device 9 performs feedback control such that the difference ΔT between the temperature T1 and the liquid temperature T2 described above becomes a value greater than the first threshold and less than the second threshold. Specifically, the control device 9 calculates respective valve opening degrees of the first valve 31V and the second valve 7V, at which the difference ΔT becomes the value greater than the first threshold and less than the second threshold, and outputs command signals of the calculation to the first valve 31V and the second valve 7V. The first valve 31V and the second valve 7V adjust the valve opening degrees based on the input command signals. This series of control is repeated every predetermined time, thereby maintaining such that the difference ΔT becomes the value greater than the first threshold and less than the second threshold.

(Second recirculation conduit 15)

[0095] In an embodiment, as shown in FIG. 2, the power recovery system 1 further includes a second recirculation conduit 15 branching off from the recirculation conduit 5 and configured to reflux the working fluid boosted by the cryogenic pump 6 to the condenser 2, a first reflux valve 16V capable of regulating the flow rate of the working fluid flowing through the second recirculation conduit 15, a second reflux valve 17V capable of regulating the flow rate of the working fluid flowing on the downstream side of a branch position from the second recirculation conduit 15 in the recirculation conduit 5, and the control device 9 capable of controlling respective valve opening degrees of the first reflux valve 16V and the second reflux valve 17V

[0096] Then, the control device 9 is configured to control the respective valve opening degrees of the first reflux valve 16V and the second reflux valve 17V such that the working fluid boosted by the cryogenic pump 6 is refluxed to the gas-liquid separation tank 4 if the liquid temperature of the working fluid boosted by the cryogenic pump 6 is below a predetermined temperature (third threshold), and the working fluid boosted by the cryogenic pump 6 is refluxed to the condenser 2 if the liquid temperature of the working fluid boosted by the cryogenic pump 6 exceeds the predetermined temperature (third threshold).

[0097] If the working fluid whose temperature rises to not lower than the predetermined temperature due to heat input from the cryogenic pump 6 is refluxed to the gas-liquid separation tank 4, the temperature of the working fluid stored in the gas-liquid separation tank 4 may be raised. Therefore, according to such configuration, if the temperature of the working fluid rises to not lower than the predetermined temperature (third threshold) due to the heat input from the cryogenic pump 6, the working fluid is refluxed to the condenser 2 and is supplied to the gas-liquid separation tank 4 after the temperature of the working fluid is decreased in the condenser, making it possible to suppress the temperature rise of the working fluid stored in the gas-liquid separation tank 4.

[0098] In the embodiment shown in FIG. 2, the first reflux valve 16V is disposed in the second recirculation conduit 15, making it possible to control the flow rate of the working fluid flowing through the second recirculation conduit 15. Further, the second reflux valve 17V is disposed on the downstream side of the branch position from the second recirculation conduit 15 in the recirculation conduit 5, making it possible to control the flow rate of the working fluid flowing through the recirculation conduit 5 on the downstream side of the branch position. Furthermore, the first reflux valve 16V and the second reflux valve 17V are connected to an actuator (such as a motor) so that their valve opening degrees can automatically be adjusted. Moreover, a third sensor 133 capable of measuring the temperature of the working fluid flowing through the recirculation conduit 5 (the liquid temperature of the working fluid boosted by the cryogenic pump 6) is installed on the upstream side of the branch position from the second recirculation conduit 15 in the recirculation conduit 5. The third sensor 133 is configured to continuously transmit, as a signal, the measured temperature of the working fluid to the control device 9 through the wired or wireless communication line.

(Gas vent pipe 11)

[0099] In an embodiment, as shown in FIG. 4, the power recovery system 1 further includes a gas vent pipe 11 branching off from the first conduit 31 and configured to discharge the working fluid in gas form that has not been condensed in the condenser 2 to outside the first conduit 31.

[0100] According to such configuration, if the working fluid is not sufficiently liquefied in the condenser 2, the gas in the first conduit 31 can be discharged to the outside by providing the gas vent pipe 11 in the first conduit 31. Whereby, it is possible to suppress inflow of the gas to the liquid-phase portion 43 located below the liquid level 41 of the gas-liquid separation tank 4 and suction of the gas into the cryogenic pump 6 portion.

[0101] In the embodiment shown in FIG. 4, the gas vent pipe 11 branches off from the first conduit 31 and extends vertically upward. Then, a downstream end portion of the gas vent pipe 11 is located vertically above the liquid level 41 of the gas-liquid separation tank 4.

[0102] Further, in the embodiment shown in FIG. 4, the downstream end portion of the gas vent pipe 11 is connected to a discharge gas conduit 14. The discharge gas conduit 14 connects the gas vent pipe 11 to the gas-liquid separation tank 4. A downstream side of the discharge gas conduit 14 is connected to the gas-liquid separation tank 4 from vertically above the liquid level 41 of the gas-liquid separation tank 4, as shown in FIGs. 5A and 5B. Then, an outlet port 141 of the discharge gas conduit 14 is disposed to be located in the gas-phase portion 42 above the liquid level 41 of the gas-liquid separation tank 4. According to such configuration, the working fluid in gas form discharged to outside the first conduit 31 can be circulated within the power recovery system 1 without being released to outside the power recovery system 1. Thus, it is possible to suppress a loss of the working fluid circulating in the power recovery system 1.

[0103] Further, in an embodiment, the discharge gas conduit 14 is inserted into the gas-liquid separation tank 4 from the ceiling surface 44, as shown in FIG. 5A. The discharge gas conduit 14 extends from the ceiling surface 44 vertically downward in the gas-phase portion 42 above the liquid level 41.

[0104] In an embodiment, the discharge gas conduit 14 is inserted into the gas-liquid separation tank 4 from the lateral surface 46, as shown in FIG. 5B. The discharge gas conduit 14 extends from the lateral surface 46 toward the horizontal direction in the gas-phase portion 42 above the liquid level 41.

[0105] The present disclosure is not limited to the above-described embodiments, and also includes an embodiment obtained by modifying the above-described embodiments or an embodiment obtained by combining these embodiments as appropriate.

[0106] The contents described in some embodiments described above would be understood as follows, for instance.

1) A power recovery system (1) according to one aspect is a power recovery system (1) for recovering, as power, cold energy of a liquefied gas via a working fluid for heating the liquefied gas, including: a condenser (2) configured to condense the working fluid by heat exchange between the working fluid and the liquefied gas; a gas-liquid separation tank (4) configured to separate the working fluid condensed in the condenser (2) into liquid and gas, and to store the working fluid; a cryogenic pump (6) configured to boost the working fluid in liquid form supplied from the gas-liquid separation tank (4); an evaporator (8) configured to evaporate the working fluid boosted by the cryogenic pump (6), by heat exchange between the working fluid and a heating fluid introduced from outside the power recovery system; a cryogenic turbine (10) configured to be driven by the working fluid in gas form generated in the evaporator (8); and a first conduit (31) configured to supply the working fluid condensed by the condenser (2) to the gas-liquid separation tank, the first conduit (31) being configured such that an outlet port (311) of the first conduit (31) is located below a liquid level (41) of the gas-liquid separation tank (4).
With the power recovery system according to the present disclosure, since the outlet port of the first conduit is located below the liquid level of the gas-liquid separation tank, the working fluid condensed by the condenser is directly supplied to not the gas-phase portion but the liquid-phase portion. Therefore, compared to a case where the outlet port of the first conduit is located above the liquid level of the gas-liquid separation tank, that is, a case where the working fluid condensed by the condenser is supplied to the liquid-phase portion via the gas-phase portion, the working fluid is not warmed in the gas-phase portion, making it possible to supply the working fluid to the liquid-phase portion while the working fluid is in a low-temperature state. Then, the working fluid in liquid form can flow in in the low-temperature state also when the working fluid is supplied from the gas-liquid separation tank to the cryogenic pump, making it possible to suppress gasification of the working fluid in the pump portion of the cryogenic pump. Whereby, the occurrence of cavitation in the pump portion of the cryogenic pump is suppressed, as well as gas suction into the cryogenic pump is suppressed, making it possible to normally drive the cryogenic pump.

2) The power recovery system according to another aspect is the power recovery system (1) as defined in 1), further including: a second conduit (32) configured to supply the working fluid in liquid form stored in the gas-liquid separation tank (4) to the cryogenic pump (6). The outlet port (311) of the first conduit (31) and an inlet port (321) of the second conduit (32) are located in a range of 0% to 25%, where a position of a bottom surface is defined as a 0% position and a position of a ceiling surface is defined as a 100% position in a vertical direction of the gas-liquid separation tank (4).
According to such configuration, the outlet port of the first conduit and the inlet port of the second conduit are located in the range of 0% to 25% (that is, on the bottom surface side) in the vertical direction of the gas-liquid separation tank 4. Therefore, the working fluid having flowed out from the outlet port of the first conduit to the liquid-phase portion flows into the inlet port of the second conduit and is supplied to the cryogenic pump, without being warmed in the liquid-phase portion vertically above, where the temperature of the working fluid increases, and while being maintained in the low-temperature state. Whereby, it is possible to suppress gasification of the working fluid in the pump portion of the cryogenic pump.

3) The power recovery system according to still another aspect is the power recovery system (1) as defined in 1) or 2), wherein the working fluid includes a fluid with a boiling point lower than 0°C.
According to such configuration, the power recovery system can be operated by using the fluid with the boiling point lower than 0°C as the working fluid. For example, propane can be given as this working fluid, but the present disclosure is also applicable to a case where a working fluid other than propane is used as the working fluid flowing through the circulation passage.

4) The power recovery system according to yet another aspect is the power recovery system (1) as defined in any one of 1) to 3), further including: a recirculation conduit (5) branching off from between the cryogenic pump (6) and the evaporator (8) and configured to reflux the working fluid boosted by the cryogenic pump (6) to the gas-liquid separation tank (4). An outlet port (51) of the recirculation conduit (5) is located below the liquid level of the gas-liquid separation tank (4).
According to such configuration, since the outlet port of the recirculation conduit is located below the liquid level of the gas-liquid separation tank, the working fluid condensed by the condenser is directly supplied to not the gas-phase portion but the liquid-phase portion. Therefore, the working fluid having flowed out from the outlet port of the recirculation conduit to the liquid-phase portion flows into the inlet port of the second conduit and is supplied to the cryogenic pump, without being warmed in the liquid-phase portion vertically above, where the temperature of the working fluid increases, and while being maintained in the low-temperature state. Whereby, it is possible to suppress gasification of the working fluid in the pump portion of the cryogenic pump.

5) The power recovery system according to yet another aspect is the power recovery system (1) as defined in 4), further including: a second recirculation conduit (15) branching off from the recirculation conduit (5) and configured to reflux the working fluid boosted by the cryogenic pump (6) to the condenser (2); a first reflux valve (16V) capable of regulating a flow rate of the working fluid flowing through the second recirculation conduit (15); a second reflux valve (17V) capable of regulating a flow rate of the working fluid flowing on a downstream side of a branch position from the second recirculation conduit (15) in the recirculation conduit (5); and a control device (9) capable of controlling respective valve opening degrees of the first reflux valve (16V) and the second reflux valve (17V). The control device (9) is configured to control the respective valve opening degrees of the first reflux valve (16V) and the second reflux valve (17V) such that: the working fluid boosted by the cryogenic pump (6) is refluxed to the gas-liquid separation tank (4) if a liquid temperature of the working fluid boosted by the cryogenic pump (6) is below a predetermined temperature; and the working fluid boosted by the cryogenic pump (6) is refluxed to the condenser (2) if the liquid temperature of the working fluid boosted by the cryogenic pump (6) exceeds the predetermined temperature.
If the working fluid whose temperature rises to not lower than the predetermined temperature due to heat input from the cryogenic pump is refluxed to the gas-liquid separation tank, the temperature of the working fluid stored in the gas-liquid separation tank may be raised. Therefore, according to such configuration, if the temperature of the working fluid rises to not lower than the predetermined temperature (third threshold) due to the heat input from the cryogenic pump, the working fluid is refluxed to the condenser (2) and is supplied to the gas-liquid separation tank after the temperature of the working fluid is decreased in the condenser, making it possible to suppress the temperature rise of the working fluid stored in the gas-liquid separation tank.

6) The power recovery system according to yet another aspect is the power recovery system (1) as defined in any one of 1) to 5), further including: a first auxiliary conduit (7) configured to supply the working fluid condensed by the condenser (2) to the gas-liquid separation tank (4), the first auxiliary conduit (7) being configured such that an outlet port (71) of the first auxiliary conduit (7) is located above the liquid level (41) of the gas-liquid separation tank (4).
According to such configuration, since the gas-phase portion above the liquid level of the gas-liquid separation tank is provided with the outlet port of the first auxiliary conduit above the liquid level of the gas-liquid separation tank, the working fluid flowing in from the first auxiliary conduit is directly supplied to the gas-phase portion. Consequently, a temperature in the gas-phase portion above the liquid level of the gas-liquid separation tank decreases, making it possible to obtain a low saturated vapor pressure. A pressure at an outlet of the cryogenic turbine is also decreased when a pressure (saturated vapor pressure) in the gas-phase portion above the liquid level of the gas-liquid separation tank is decreased, making it possible to improve turbine efficiency.

7) The power recovery system according to yet another aspect is the power recovery system as defined in 6), further including: a first valve (31V) capable of regulating a flow rate of the working fluid flowing through the first conduit (31); a second valve (7V) capable of regulating a flow rate of the working fluid flowing through the first auxiliary conduit (7); and a control device (9) capable of controlling respective valve opening degrees of the first valve (31V) and the second valve (7V). The control device (9) is configured to control the respective valve opening degrees of the first valve (31V) and the second valve (7V) such that a difference ΔT between a temperature T1 of a gas phase above the liquid level (41) of the gas-liquid separation tank (4) and a liquid temperature T2 of the working fluid in liquid form, which is flowed out from the gas-liquid separation tank (4) and is to be sucked into the cryogenic pump (6), is greater than a first threshold and less than a second threshold which is greater than the first threshold.
According to such configuration, the difference ΔT is controlled between the first threshold and the second threshold. A temperature difference between the liquid temperature T2 and the temperature T1 in the gas-phase portion, which is the saturation temperature, is small if the difference ΔT is less than the first threshold, making it easier for the working fluid at the liquid temperature T2 to be gasified when the working fluid flows into the cryogenic pump or even is heated by a little bit in the pump portion of the cryogenic pump. On the other hand, the temperature T1 in the gas-phase portion is high and the gas-phase portion has a high saturated vapor pressure if the difference ΔT is greater than the second threshold, which may decrease the turbine efficiency of the cryogenic turbine (10). Therefore, control is performed by using the difference ΔT as a control parameter and providing the difference ΔT with the first threshold and the second threshold, making it possible to increase the turbine efficiency without causing gasification of the working fluid.

8) The power recovery system according to yet another aspect is the power recovery system (1) as defined in any one of 1) to 7), further including: a gas vent pipe (11) branching off from the first conduit (31) and configured to discharge the working fluid in gas form that has not been condensed in the condenser (2) to outside the first conduit (31).
According to such configuration, if the working fluid is not sufficiently liquefied in the condenser, the gas in the first conduit can be discharged to the outside by providing the gas vent pipe in the first conduit. Whereby, it is possible to suppress inflow of the gas to the liquid-phase portion located below the liquid level of the gas-liquid separation tank and suction of the gas into the cryogenic pump portion.

9) The power recovery system according to yet another aspect is the power recovery system (1) as defined in any one of 1) to 8), wherein the first conduit (31) includes an internal conduit (31B) inserted into the gas-liquid separation tank (4) from above the liquid level (41) of the gas-liquid separation tank (4) and extending downward relative to the liquid level.

[0107] According to such configuration, since the first conduit is inserted into the gas-liquid separation tank from above the liquid level of the gas-liquid separation tank, a distance which the first conduit is exposed to the atmosphere having the higher temperature than the working fluid condensed by the condenser is reduced compared to a case where the first conduit is inserted into the gas-liquid separation tank from below the liquid level. Whereby, it is possible to suppress heating of the working fluid in the first conduit by heat input from outside, outside the gas-liquid separation tank.

Reference Signs List

[0108] 

1

Power recovery system

2

Condenser

3

Recirculation passage

4

Gas-liquid separation tank

5

Recirculation conduit

5V

Valve

6

Cryogenic pump

7

First auxiliary conduit

7V

Second valve

8

Evaporator

9

Control device

10

Cryogenic turbine

11

Gas vent pipe

12

Generator

131

First sensor

132

Second sensor

133

Third sensor

14

Discharge gas pipe

15

Second recirculation conduit

16V

First reflux valve

17V

Second reflux valve

21

Heating-side conduit

22

Heated-side conduit

31

First conduit

31V

First valve

311

Outlet port

31A

External conduit

31B

Internal conduit

31B 1

Internal horizontal conduit 31B2 Internal vertical conduit

32

Second conduit

321

Outlet port

33

Third conduit

33V

Valve

34

Fourth conduit

35

Fifth conduit

41

Liquid level

42

Gas-phase portion

43

Liquid-phase portion

44

Ceiling surface

45

Bottom surface

46

Lateral surface

81

Heated-side conduit

82

Heating-side conduit

101

Floating structure

111

Engine

102

Land LNG (liquefied gas) terminal

112

Destination

Claims

1. A power recovery system for recovering, as power, cold energy of a liquefied gas via a working fluid for heating the liquefied gas, comprising:

a condenser configured to condense the working fluid by heat exchange between the working fluid and the liquefied gas;

a gas-liquid separation tank configured to separate the working fluid condensed in the condenser into liquid and gas, and to store the working fluid;

a cryogenic pump configured to boost the working fluid in liquid form supplied from the gas-liquid separation tank;

an evaporator configured to evaporate the working fluid boosted by the cryogenic pump, by heat exchange between the working fluid and a heating fluid introduced from outside the power recovery system;

a cryogenic turbine configured to be driven by the working fluid in gas form generated in the evaporator; and

a first conduit configured to supply the working fluid condensed by the condenser to the gas-liquid separation tank, the first conduit being configured such that an outlet port of the first conduit is located below a liquid level of the gas-liquid separation tank.

2. The power recovery system according to claim 1, further comprising:

a second conduit configured to supply the working fluid in liquid form stored in the gas-liquid separation tank to the cryogenic pump,

wherein the outlet port of the first conduit and an inlet port of the second conduit are located in a range of 0% to 25%, where a position of a bottom surface is defined as a 0% position and a position of a ceiling surface is defined as a 100% position in a vertical direction of the gas-liquid separation tank.

3. The power recovery system according to claim 1 or 2,
wherein the working fluid includes a fluid with a boiling point lower than 0°C.

4. The power recovery system according to claim 1 or 2, further comprising:

a recirculation conduit branching off from between the cryogenic pump and the evaporator and configured to reflux the working fluid boosted by the cryogenic pump to the gas-liquid separation tank,

wherein an outlet port of the recirculation conduit is located below the liquid level of the gas-liquid separation tank.

5. The power recovery system according to claim 4, further comprising:

a second recirculation conduit branching off from the recirculation conduit and configured to reflux the working fluid boosted by the cryogenic pump to the condenser;

a first reflux valve capable of regulating a flow rate of the working fluid flowing through the second recirculation conduit;

a second reflux valve capable of regulating a flow rate of the working fluid flowing on a downstream side of a branch position from the second recirculation conduit in the recirculation conduit; and

a control device capable of controlling respective valve opening degrees of the first reflux valve and the second reflux valve,

wherein the control device is configured to control the respective valve opening degrees of the first reflux valve and the second reflux valve such that:

the working fluid boosted by the cryogenic pump is refluxed to the gas-liquid separation tank if a liquid temperature of the working fluid boosted by the cryogenic pump is below a predetermined temperature; and

the working fluid boosted by the cryogenic pump is refluxed to the condenser if the liquid temperature of the working fluid boosted by the cryogenic pump exceeds the predetermined temperature.

6. The power recovery system according to claim 1 or 2, further comprising:
a first auxiliary conduit configured to supply the working fluid condensed by the condenser to the gas-liquid separation tank, the first auxiliary conduit being configured such that an outlet port of the first auxiliary conduit is located above the liquid level of the gas-liquid separation tank.

7. The power recovery system according to claim 6, further comprising:

a first valve capable of regulating a flow rate of the working fluid flowing through the first conduit;

a second valve capable of regulating a flow rate of the working fluid flowing through the first auxiliary conduit; and

a control device capable of controlling respective valve opening degrees of the first valve and the second valve,

wherein the control device is configured to control the respective valve opening degrees of the first valve and the second valve such that a difference ΔT between a temperature T1 of a gas phase above the liquid level of the gas-liquid separation tank and a liquid temperature T2 of the working fluid in liquid form, which is flowed out from the gas-liquid separation tank and is to be sucked into the cryogenic pump, is greater than a first threshold and less than a second threshold which is greater than the first threshold.

8. The power recovery system according to claim 1 or 2, further comprising:
a gas vent pipe branching off from the first conduit and configured to discharge the working fluid in gas form that has not been condensed in the condenser to outside the first conduit.

9. The power recovery system according to claim 1 or 2,
wherein the first conduit includes an internal conduit inserted into the gas-liquid separation tank from above the liquid level of the gas-liquid separation tank and extending downward relative to the liquid level.

Drawing