Carbon dioxide liquefaction device

Abstract

To provide a fuel battery power generation system capable of improving consumption efficiency of hydrogen contained in a fuel, and suppressing discharge of carbon dioxide.SOLUTION: A carbon dioxide liquefaction device 20 comprises: a liquefaction heat exchanger 5 that exchanges heat to cool and liquefy the carbon dioxide contained in a mixed gas discharged from a fuel cell 2 using cold of liquefied gas; a pressure sensor 13 that detects the internal pressure of the liquefaction heat exchanger 5; a liquid level sensor 14 that detects a liquid amount, which is the amount of liquefied carbon dioxide liquefied in the liquefaction heat exchanger 5; and a control device 1 that controls the amount of the liquefied gas sent to the liquefaction heat exchanger 5 on the basis of the internal pressure detected by the pressure sensor 13 and the liquid amount detected by the liquid level sensor 14.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a carbon dioxide liquefaction device for liquefying carbon dioxide.

Background Art

[0002] Generally, it is known to use LNG (liquefied natural gas) as fuel for a fuel cell. When LNG is used as fuel, the fuel cell emits carbon dioxide. The carbon dioxide emitted from the fuel cell is often released into the atmosphere.

Summary of the Invention

Problems to be Solved by the Invention

[0003] However, the release of carbon dioxide into the atmosphere raises concerns about its impact on the environment. In order to suppress the release of carbon dioxide into the atmosphere, there is a desire to liquefy and store carbon dioxide. An object of an embodiment of the present invention is to provide a carbon dioxide liquefaction device that efficiently liquefies carbon dioxide discharged from a fuel cell.

Means for Solving the Problems

[0004] A carbon dioxide liquefaction device according to an aspect of the present invention includes a liquefaction heat exchanger that performs heat exchange to cool and liquefy carbon dioxide contained in a mixed gas discharged from a fuel cell with the cold heat of a liquefied gas, a pressure sensor that detects an internal pressure of the liquefaction heat exchanger, a liquid amount sensor for detecting a liquid amount that is an amount of liquefied carbon dioxide liquefied by the liquefaction heat exchanger, and a control device that controls an amount of the liquefied gas to be fed into the liquefaction heat exchanger based on the internal pressure detected by the pressure sensor and the liquid amount detected by the liquid amount sensor.

Effects of the Invention

[0005] According to an embodiment of the present invention, it is possible to provide a carbon dioxide liquefaction device that efficiently liquefies carbon dioxide discharged from a fuel cell.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0007] (First Embodiment) FIG. 1 is a configuration diagram showing the configuration of a carbon dioxide liquefaction apparatus 20 according to the first embodiment of the present invention. In the drawings, the same parts are denoted by the same reference numerals, and redundant explanations are omitted as appropriate.

[0008] The carbon dioxide liquefaction apparatus 20 is not limited to being fixedly installed on land or at sea, etc., and may be provided on a moving body such as a ship, a vehicle, or an aircraft.

[0009] The carbon dioxide liquefaction apparatus 20 includes a control device 1, a fuel cell 2, a condenser 3, a compressor 4, a liquefaction heat exchanger 5, a liquefied carbon dioxide tank 6, an LNG tank 7, a pump 8, a bypass valve 9, a heater 10, a gas sensor 11, a discharge valve 12, a pressure sensor 13, and a liquid level sensor 14. Note that the carbon dioxide liquefaction apparatus 20 may include at least a control device 1 and a liquefaction heat exchanger 5 as constituent devices, and the other devices may be provided as external devices of the carbon dioxide liquefaction apparatus 20.

[0010] The mixed gas containing carbon dioxide discharged from the fuel cell 2 is passed through the condenser 3, the compressor 4, and the liquefaction heat exchanger 5 in sequence, and carbon dioxide is extracted and liquefied. The liquefied carbon dioxide is sent into the liquefied carbon dioxide tank 6. A path (pipe) is provided to connect the fuel cell 2, the condenser 3, the compressor 4, the liquefaction heat exchanger 5, and the liquefied carbon dioxide tank 6 in sequence.

[0011] The LNG taken out from the LNG tank 7 is sent as fuel to the supply destination of the LNG through the pump 8, the liquefaction heat exchanger 5, and the heater 10 in sequence. A path (pipe) is provided to connect the LNG tank 7, the pump 8, the liquefaction heat exchanger 5, the heater 10, and the supply destination in sequence.

[0012] The control device 1 performs main control for liquefying carbon dioxide in the carbon dioxide liquefaction device 20. The control device 1 may control or monitor any component device constituting the carbon dioxide liquefaction device 20. The control device 1 may be used in combination with a control device for controlling the power generation of the fuel cell 2. The control device 1 includes a computer for performing various arithmetic processes and may be composed of a plurality of computers.

[0013] The fuel cell 2 generates electricity by using oxygen in the air and hydrogen contained in the natural gas vaporized from the LNG supplied as fuel. For example, the fuel cell 2 is a solid oxide fuel cell (SOFC, solid oxide fuel cell), but other types of fuel cells may also be used. Also, although the explanation uses LNG as the fuel of the fuel cell 2, LPG (liquefied petroleum gas) may be used. The mixed gas discharged from the fuel cell 2 mainly contains water vapor and carbon dioxide, and may further contain nitrogen.

[0014] Note that the carbon dioxide liquefaction device 20 may include a device for removing or separating any substance discharged from the fuel cell 2, and such a process may be performed at any location in the process of liquefying carbon dioxide.

[0015] The condenser 3 returns the water vapor contained in the mixed gas discharged from the fuel cell 2 to water. Thereby, the condenser 3 removes water vapor from the mixed gas and extracts carbon dioxide. The condenser 3 sends the extracted carbon dioxide into the compressor 4. By completely removing moisture from the mixed gas in this way, ice formation is prevented during cooling for liquefying carbon dioxide.

[0016] Note that it may be configured in any way as long as it is configured to remove moisture from the mixed gas. For example, in order to completely remove the moisture that cannot be removed by the condenser 3, a device for removing moisture such as a dryer or a dehumidifier may be additionally provided, or these devices may be provided instead of the condenser 3. Further, the configuration for removing moisture may be provided anywhere in the path until the gas discharged from the fuel cell 2 is sent into the liquefaction heat exchanger 5.

[0017] The compressor 4 compresses the carbon dioxide sent from the condenser 3. The compressor 4 sends the compressed carbon dioxide into the liquefaction heat exchanger 5.

[0018] The liquefaction heat exchanger 5 cools and liquefies the carbon dioxide sent from the compressor 4 using the LNG supplied as fuel from the LNG tank 7 to the supply destination. Thereby, heat exchange is performed between the LNG and the carbon dioxide. The liquefaction heat exchanger 5 is provided with a pipe through which the LNG for cooling the carbon dioxide passes. The liquefaction heat exchanger 5 sends the liquefied carbon dioxide into the liquefied carbon dioxide tank 6. The LNG used for cooling in the liquefaction heat exchanger 5 is supplied as fuel to the supply destination. The supply destination may be the fuel cell 2 or any other arbitrary device. Note that the LNG to be liquefied may be pre-cooled by a cooler or the like before being sent into the liquefaction heat exchanger 5.

[0019] The liquefied carbon dioxide tank 6 stores the carbon dioxide liquefied by the liquefaction heat exchanger 5. The liquefied carbon dioxide tank 6 may be removably installed. Thereby, the liquefied carbon dioxide tank 6 storing the liquefied carbon dioxide can be transported, making it easier to process the liquefied carbon dioxide.

[0020] The LNG tank 7 is a tank for storing LNG and is a supply source for supplying LNG. The LNG stored in the LNG tank 7 is used as fuel at a supply destination such as the fuel cell 2 and is also used as a refrigerant for cooling carbon dioxide in the liquefaction heat exchanger 5. The number of LNG tanks is not limited to one, and any number may be provided.

[0021] The pump 8 is a device for sending LNG from the LNG tank 7 to the supply destination. The pump 8 may be provided in any number and at any location in the path for supplying LNG from the LNG tank 7 to the supply destination.

[0022] The bypass valve 9 is provided in the path for supplying LNG from the LNG tank 7 to the supply destination and is a device for forming a bypass path for supplying LNG to the supply destination while avoiding the liquefaction heat exchanger 5. By closing the bypass valve 9, the LNG supplied from the LNG tank 7 is supplied to the supply destination via the liquefaction heat exchanger 5. By opening the bypass valve 9, part or all of the LNG supplied from the LNG tank 7 is supplied to the supply destination without passing through the liquefaction heat exchanger 5. The bypass valve 9 may have a function of adjusting the opening degree. Thereby, the amount of LNG supplied from the LNG tank 7 to the liquefaction heat exchanger 5 can be adjusted. For example, the opening / closing or opening degree operation of the bypass valve 9 is controlled by the control device 1. In addition to the bypass valve 9, a valve for adjusting the amount of LNG supplied to the liquefaction heat exchanger 5 may be provided.

[0023] The heater 10 is a device for heating LNG into natural gas at a temperature suitable for the supply destination. When LNG is fed into the heater 10 via the liquefaction heat exchanger 5, the heater 10 further heats the LNG heated by the liquefaction heat exchanger 5. When LNG is fed into the heater 10 without passing through the liquefaction heat exchanger 5, the heater 10 heats the LNG directly supplied from the LNG tank 7. Therefore, when LNG is supplied to the heater 10 via the liquefaction heat exchanger 5, the heater 10 can reduce the heating amount of the LNG by the amount heated by the liquefaction heat exchanger 5.

[0024] The gas sensor 11 is a sensor for grasping the amount of nitrogen inside the liquefaction heat exchanger 5. The gas sensor 11 is not limited to those that can detect nitrogen as long as it can grasp the amount of nitrogen inside the liquefaction heat exchanger 5. For example, the gas sensor 11 may be a sensor for detecting the concentration of carbon dioxide. In this case, the amount of nitrogen inside the liquefaction heat exchanger 5 is determined based on the remaining concentration obtained by subtracting the amount of carbon dioxide (the concentration detected by the gas sensor 11) from the total amount of gas inside the liquefaction heat exchanger 5 (concentration 100%). The detection value detected by the gas sensor 11 is transmitted to the control device 1.

[0025] The discharge valve 12 is a valve for discharging the nitrogen accumulated inside the liquefaction heat exchanger 5. Since nitrogen is not liquefied by the cooling of the liquefaction heat exchanger 5, it accumulates inside the liquefaction heat exchanger 5. For example, when the amount of nitrogen determined based on the detection value by the gas sensor 11 exceeds a preset threshold amount, the discharge valve 12 is opened. The discharge valve 12 may have a function of adjusting the opening degree. For example, the opening / closing or opening degree operation of the discharge valve 12 is controlled by the control device 1. As a result, the nitrogen accumulated inside the liquefaction heat exchanger 5 is released into the atmosphere. The gas discharged from the discharge valve 12 may contain carbon dioxide. Also, a device (such as a filter) for suppressing the release of carbon dioxide may be provided.

[0026] The pressure sensor 13 is a sensor for detecting the internal pressure of the heat exchanger 5 for liquefaction. The pressure sensor 13 transmits the detected pressure value to the control device 1. The pressure value detected by the pressure sensor 13 is used to control the liquefaction process of carbon dioxide.

[0027] The liquid level sensor 14 is a sensor for detecting the liquid level (height of the liquid surface) of the liquefied carbon dioxide accumulated in the heat exchanger 5 for liquefaction. The liquid level of the liquefied carbon dioxide indicates the amount of liquefied carbon dioxide. The liquid level sensor 14 transmits the detected liquid level to the control device 1. The liquid level detected by the liquid level sensor 14 is used to control the liquefaction process of carbon dioxide. Note that any sensor may be used as long as it can detect a physical quantity indicating the amount of liquefied carbon dioxide, not limited to the liquid level sensor 14.

[0028] Next, the control of the liquefaction process of carbon dioxide by the control device 1 will be described. The control device 1 controls the liquefaction process of carbon dioxide so as to balance the cold heat of LNG (LNG cold heat) and the energy for liquefying carbon dioxide (liquefaction energy). When the balance between the LNG cold heat and the liquefaction energy for liquefying the fed carbon dioxide is achieved, the pressure value inside the heat exchanger 5 for liquefaction and the amount (liquid level) of the liquefied carbon dioxide are always within a certain range. The control device 1 controls the carbon dioxide liquefaction device 20 to maintain this state. Specifically, the control device 1 adjusts the inflow rate of LNG so that the pressure value detected by the pressure sensor 13 falls within a predetermined range and the liquid level detected by the liquid level sensor 14 falls within a predetermined range.

[0029] The control device 1 determines the status of the liquefaction process of carbon dioxide based on the internal pressure of the heat exchanger 5 for liquefaction detected by the pressure sensor 13 and the liquid level of the liquefied carbon dioxide detected by the liquid level sensor 14.

[0030] When the LNG cold heat is more than the liquefaction energy assumed from the amount of carbon dioxide fed in, the liquefaction process of carbon dioxide proceeds more than expected, and carbon dioxide may be solidified into dry ice. In this case, the liquid level of the liquefied carbon dioxide rises, and the internal pressure of the liquefaction heat exchanger 5 decreases.

[0031] When the LNG cold heat is less than the liquefaction energy assumed from the amount of carbon dioxide fed in, the liquefaction process of carbon dioxide lags behind the expectation. In this case, the liquid level of the liquefied carbon dioxide drops, and the internal pressure of the liquefaction heat exchanger 5 increases.

[0032] Based on the pressure value detected by the pressure sensor 13 and the liquid level detected by the liquid level sensor 14, when the control device 1 determines that the LNG cold heat is more than the assumed liquefaction energy, it controls to reduce the inflow rate of LNG. Specifically, the control device 1 controls to open the bypass valve 9 or increase the opening degree of the bypass valve 9. Note that the control device 1 may control the pump 8 to reduce the amount of LNG taken out from the LNG tank 7, or may control the operation of the fuel cell 2 to increase the amount of carbon dioxide output from the fuel cell 2.

[0033] Based on the pressure value detected by the pressure sensor 13 and the liquid level detected by the liquid level sensor 14, when the control device 1 determines that the LNG cold heat is less than the assumed liquefaction energy, it controls to increase the inflow rate of LNG. Specifically, the control device 1 controls to close the bypass valve 9 or decrease the opening degree of the bypass valve 9. Note that the control device 1 may control the pump 8 to increase the amount of LNG taken out from the LNG tank 7, or may control the operation of the fuel cell 2 to reduce the amount of carbon dioxide output from the fuel cell 2.

[0034] In addition to the control performed to balance the LNG cold heat and the liquefaction energy described above, the control device 1 constantly performs control to discharge nitrogen so that nitrogen does not accumulate inside the heat exchanger 5 for liquefaction. Nitrogen tends to stay in the upper part inside the heat exchanger 5 for liquefaction. When the control device 1 determines that nitrogen has accumulated inside the heat exchanger 5 for liquefaction based on the detection value by the gas sensor 11, the control device 1 opens the discharge valve 12.

[0035] When nitrogen accumulates inside the heat exchanger 5 for liquefaction, the internal pressure of the heat exchanger 5 for liquefaction increases regardless of the liquid level of the liquefied carbon dioxide. Therefore, in addition to the detection value by the gas sensor 11, the control device 1 may use the detection value by the pressure sensor 13 or the liquid level sensor 14 to determine whether nitrogen has accumulated.

[0036] When the gas sensor 11 is a sensor that detects nitrogen, when the detection value by the gas sensor 11 exceeds a predetermined reference value, the control device 1 outputs an open command to the discharge valve 12. When the gas sensor 11 is a sensor that detects carbon dioxide, when the detection value by the gas sensor 11 is below a predetermined reference value, the control device 1 outputs an open command to the discharge valve 12.

[0037] Note that at least one of the front stage or the rear stage of the heat exchanger 5 for liquefaction may be provided with an arbitrary cooler for cooling to liquefy carbon dioxide. The cooling method of the cooler provided in this way is not limited to that by LNG cold heat, and any cooling method may be adopted. For example, such a cooler is used when the heat exchanger 5 for liquefaction alone cannot sufficiently cool carbon dioxide.

[0038] According to this embodiment, liquefied gas (such as LNG or LPG) that is the fuel of the fuel cell 2 is used as cold heat to cool and liquefy the carbon dioxide discharged from the fuel cell 2, so that carbon dioxide can be liquefied. Further, by adjusting the amount of LNG used as cold heat according to the amount of carbon dioxide discharged from the fuel cell 2, carbon dioxide can be efficiently liquefied.

[0039] (Second Embodiment) FIG. 2 is a configuration diagram showing the configuration of a ship 30 according to the second embodiment of the present invention. A carbon dioxide liquefaction device 20 according to the first embodiment is mounted on the ship 30.

[0040] In the present embodiment, some of the component devices of the carbon dioxide liquefaction device 20 will be omitted from the description, but the ship 30 may include all of the component devices of the carbon dioxide liquefaction device 20, or some of the component devices that are not necessarily required for carbon dioxide liquefaction may be removed. Also, for the component devices described in the first embodiment, duplicate descriptions will be omitted as appropriate. Also, the arrangement of each component device in the ship 30 shown in FIG. 2 is an illustrative example, and each component device may be arranged in any manner, and the ship 30 may have any configuration or shape.

[0041] The ship 30 is a ship that obtains propulsion power from the electric power generated by the fuel cell 2. The ship 30 may be any ship as long as it is equipped with a facility for storing LNG. For example, the ship 30 may be an LNG carrier for transporting LNG, or a ship that uses LNG as fuel. Also, LNG may be used as fuel in addition to the fuel cell 2.

[0042] The ship 30 includes a control device 1, a fuel cell 2, a condenser 3, a compressor 4, a liquefaction heat exchanger 5, a liquefied carbon dioxide tank 6, an LNG tank 7, a pump 8, a bypass valve 9, a vaporizer 15, a switchboard 21, a propulsion motor 22, a diesel generator 23, a compressor 24, and a heater 25.

[0043] The control device 1 is not shown in FIG. 2, but is provided, for example, in a control room inside a living area including a bridge or the like. The control device 1 may be implemented as a part of the functions of any device or system in the ship 30.

[0044] The fuel cell 2 generates electricity using LNG supplied from the LNG tank 7 and BOG (boil off gas) generated in the LNG tank 7 as fuel. BOG is gaseous natural gas generated by vaporizing a part of the LNG stored in the LNG tank 7 due to external heat. The fuel cell 2 supplies the generated electric power to the propulsion motor 22 via the switchboard 21.

[0045] The LNG tank 7 is a tank for storing LNG inside the ship. The LNG tank 7 may be a fuel tank for storing fuel or a tank for transporting LNG.

[0046] The pump 8 supplies the LNG stored in the LNG tank 7 to the fuel cell 2 via the liquefaction heat exchanger 5 and the vaporizer 15 in sequence. The bypass valve 9 is provided in the path between the pump 8 and the vaporizer 15. The LNG passing through the bypass valve 9 bypasses the liquefaction heat exchanger 5 and is sent into the vaporizer 15.

[0047] The vaporizer 15 is a device that forcibly vaporizes LNG to generate natural gas. The natural gas generated by the vaporizer 15 is supplied to the fuel cell 2. The vaporizer 15 may be a device corresponding to the heater 10 according to the first embodiment.

[0048] The switchboard 21 supplies the electric power generated by the fuel cell 2 and the diesel generator 23 to the propulsion motor 22. The switchboard 21 is provided with a plurality of switches for respectively selecting the power supply source and the supply destination. Thereby, the switchboard 21 can form a path (wiring) by selecting an arbitrary combination of the supply source and the supply destination.

[0049] The propulsion motor 22 is an electric motor that serves as a power source for supplying power to drive the propeller by the electric power supplied from the fuel cell 2 and the diesel generator 23. The propeller is a device for obtaining the propulsion force of the ship 30. The propeller may be any device as long as the propulsion force of the ship 30 can be obtained. For example, the propulsion motor 22 rotates the rotation shaft of the propeller.

[0050] The diesel generator 23 is a generator that generates electricity by burning fuel. The diesel generator 23 may be either an oil cooker or a gas cooker. Also, the diesel generator 23 may be supplied with LNG as fuel from the LNG tank 7, or may be supplied with fuel from a fuel tank provided separately from the LNG tank 7. Note that the generator 23 is not limited to a diesel type, and may be any combustion type generator. The electric power generated by the diesel generator 23 is supplied to the propulsion motor 22 via the switchboard 21. For example, the diesel generator 23 is used to supply electric power to the propulsion motor 22 when the ship 30 is sailing in the harbor or at standby.

[0051] The compressor 24 compresses the BOG generated in the LNG tank 7. The compressor 24 sends the compressed BOG to the heater 25.

[0052] The heater 25 supplies the compressed BOG fed from the compressor 24 as fuel to the fuel cell 2.

[0053] According to the present embodiment, a ship 30 to which the carbon dioxide liquefaction apparatus 20 according to the first embodiment is applied can be configured, and the same operational effects as those of the first embodiment can be obtained.

[0054] (Third Embodiment) FIG. 3 is a configuration diagram showing the configuration of a ship 30A according to the third embodiment of the present invention.

[0055] The ship 30A has a configuration in which, in the ship 30 according to the second embodiment, the propulsion motor 22 is replaced with a propulsion motor 22A, a main engine 26 and the heater 10 according to the first embodiment are added, and the vaporizer 15 is removed. Other points are the same as those of the ship 30 according to the second embodiment.

[0056] The main engine 26 is an engine that serves as a power source for driving a propeller by burning LNG supplied from the LNG tank 7. For example, the main engine 26 rotates the rotating shaft of the propeller. The main engine 26 is, for example, a diesel engine, but is not limited to a diesel type, and any combustion type engine may be used.

[0057] The heater 10 heats the LNG fed into the main engine 26. The heater 10 heats the LNG to a suitable temperature as fuel for the main engine 26.

[0058] The propulsion motor 22A is an electric motor (power source) for boosting the power supplied from the main engine 26 to the propeller. The propulsion motor 22A supplies power for driving the propeller by the electric power supplied from the switchboard 21. For example, the propulsion motor 22A supplies power so as to boost the rotation of the rotating shaft of the propeller that rotates by the power supplied from the main engine 26.

[0059] Note that the ship 30A may be configured to supply the electric power from the switchboard 21 to any equipment in the ship without providing the propulsion motor 22A.

[0060] According to the present embodiment, in the ship 30A having a diesel engine as the main engine 26, the same operational effects as those of the second embodiment can be obtained.

[0061] (Fourth Embodiment) FIG. 4 is a configuration diagram showing the configuration of a ship 30B according to the fourth embodiment of the present invention.

[0062] The ship 30B has a configuration in which a heat exchanger 27 is added to the ship 30A according to the third embodiment. Also, a path is additionally formed so that the BOG compressed by the compressor 24 is supplied as fuel to the main engine 26 via the heater 10. Other points are the same as those of the ship 30A according to the third embodiment. Also, the ship 30B may be configured to supply the electric power from the switchboard 21 to any equipment in the ship without providing the propulsion motor 22A, in the same manner as the ship 30A according to the third embodiment.

[0063] The BOG compressed by the compressor 24 is heated by the heater 10 and supplied to the main engine 26. The main engine 26 is driven using the BOG as fuel in addition to the LNG supplied from the LNG tank 7.

[0064] The heat exchanger 27 serves as a cooler that pre-cools carbon dioxide before it is cooled (liquefied) by the liquefaction heat exchanger 5. The heat exchanger 27 is provided in the middle of the path through which carbon dioxide is sent from the compressor 4 to the liquefaction heat exchanger 5. The heat exchanger 27 is provided with a pipe through which the BOG for cooling carbon dioxide passes. The pipe for sending the BOG from the LNG tank 7 to the compressor 24 is formed to pass through the heat exchanger 27.

[0065] The heat exchanger 27 cools the carbon dioxide sent from the compressor 4 by utilizing the cold heat of the BOG. Thereby, heat exchange is performed between the BOG and the carbon dioxide. The heat exchanger 27 sends the cooled carbon dioxide to the liquefaction heat exchanger 5. The BOG used for cooling in the heat exchanger 27 is supplied as fuel to the fuel cell 2 via the compressor 24 and the heater 25.

[0066] According to the present embodiment, by providing the heat exchanger 27 that cools carbon dioxide using BOG, the efficiency of cooling carbon dioxide can be improved compared to the third embodiment.

[0067] Also, by using the BOG generated in the LNG tank 7 as fuel in the main engine 26, the fuel cost of the main engine 26 can be reduced.

[0068] (Fifth Embodiment) FIG. 5 is a configuration diagram showing the configuration of a ship 30C according to the fifth embodiment of the present invention.

[0069] The ship 30C has a configuration in which, in the ship 30B according to the fourth embodiment, the path for supplying BOG from the compressor 24 to the main engine 26 is removed and the vaporizer 15C is added. Other aspects are the same as those of the ship 30A according to the third embodiment. Also, similar to the ship 30A according to the third embodiment, the ship 30C may be configured to supply power from the switchboard 21 to any device in the ship without providing the propulsion motor 22A.

[0070] Since the vaporizer 15C has the same configuration as the vaporizer 15 according to the second embodiment, the main differences will be mainly described here. The vaporizer 15C is a heat exchanger that heats the LNG supplied to the fuel cell 2 using liquefied carbon dioxide as a heat medium. Thereby, heat exchange is performed between the carbon dioxide and the LNG.

[0071] The vaporizer 15C is provided in the middle of the path through which the LNG used as a refrigerant by the liquefaction heat exchanger 5 or the LNG that bypasses the liquefaction heat exchanger 5 and passes through the bypass valve 9 is supplied to the fuel cell 2. The vaporizer 15C is provided with a pipe through which carbon dioxide for heating the LNG passes. The pipe for sending the carbon dioxide cooled by the heat exchanger 27 to the liquefaction heat exchanger 5 is formed to pass through the vaporizer 15C.

[0072] The vaporizer 15C vaporizes the LNG by heating the LNG using carbon dioxide as a heat medium. The vaporizer 15C supplies the natural gas obtained by vaporizing the LNG to the fuel cell 2. The carbon dioxide used as a heat medium in the vaporizer 15C is sent to the liquefaction heat exchanger 5.

[0073] According to the present embodiment, the same operational effects as those of the fourth embodiment can be obtained. Furthermore, by using the carbon dioxide before liquefaction to vaporize the LNG that becomes the fuel of the fuel cell 2, the energy efficiency of liquefying the carbon dioxide and vaporizing the LNG can be improved.

[0074] Additional advantages and modifications will readily occur to those skilled in the art. Accordingly, the invention in its broader aspects is not limited to the specific details, representative embodiments, shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Explanation of Signs

[0075] 1... control device, 2... fuel cell, 3... condenser, 4... compressor, 5... heat exchanger for liquefaction, 6... liquefied carbon dioxide tank, 7... LNG tank, 8... pump, 9... bypass valve, 10... heater, 11... gas sensor, 12... discharge valve, 13... pressure sensor, 14... liquid level sensor, 20... carbon dioxide liquefaction device.

Claims

1. A heat exchanger for liquefaction that performs heat exchange to cool and liquefy carbon dioxide contained in the mixed gas discharged from a fuel cell using the cold heat of liquefied gas, A pressure sensor that detects the internal pressure of the heat exchanger for liquefaction, A liquid amount sensor for detecting the amount of liquid, which is the amount of liquefied carbon dioxide liquefied by the heat exchanger for liquefaction, A control device that controls the amount of the liquefied gas fed into the heat exchanger for liquefaction based on the internal pressure detected by the pressure sensor and the liquid amount detected by the liquid amount sensor A carbon dioxide liquefaction device, characterized by comprising the above.

2. It is provided with a valve for supplying the liquefied gas from the supply source of the liquefied gas to the supply destination without passing through the heat exchanger for liquefaction, The control device controls the amount of the liquefied gas fed into the heat exchanger for liquefaction by operating the valve The carbon dioxide liquefaction device according to Claim 1, characterized by the above.

3. A gas sensor for grasping the amount of nitrogen inside the heat exchanger for liquefaction, An exhaust valve for discharging nitrogen inside the heat exchanger for liquefaction, and The control device performs control to operate the exhaust valve to discharge nitrogen inside the heat exchanger for liquefaction based on the detection value by the gas sensor The carbon dioxide liquefaction device according to Claim 1, characterized by the above.

4. The liquefied gas that has undergone the heat exchange by the heat exchanger for liquefaction is supplied as fuel to the supply destination The carbon dioxide liquefaction device according to Claim 1, characterized by the above.

5. The supply destination includes the fuel cell The carbon dioxide liquefaction device according to Claim 4, characterized by the above.

6. A moisture removal device for removing moisture contained in the mixed gas discharged from the fuel cell in order to extract carbon dioxide The carbon dioxide liquefaction device according to Claim 1, characterized by comprising the above.

7. The moisture removal device includes a condenser for removing water vapor The carbon dioxide liquefaction device according to Claim 6, characterized by the above.

8. A ship equipped with the carbon dioxide liquefaction device according to Claim 1, A liquefied gas tank for storing the liquefied gas, The fuel cell that generates electricity using the liquefied gas supplied from the liquefied gas tank as fuel, A propeller for obtaining propulsion force using the liquefied gas supplied from the liquefied gas tank as fuel A ship, characterized by comprising the above.

9. The propeller obtains propulsion force by the electric power generated by the fuel cell The ship according to claim 8, characterized in that

10. A main engine that drives the propeller using the liquefied gas supplied from the liquefied gas tank as fuel The ship according to claim 8, characterized in that it is provided with

11. A generator that supplies electric power for the propeller to obtain propulsion The ship according to claim 8, characterized in that it is provided with

12. The propeller obtains propulsion by the electric power generated by the fuel cell and the electric power generated by the generator The ship according to claim 11, characterized in that

13. Heat exchange is performed in a liquefaction heat exchanger so as to cool and liquefy carbon dioxide contained in the mixed gas discharged from the fuel cell with the cold heat of the liquefied gas, The internal pressure of the liquefaction heat exchanger is detected, The amount of liquid, which is the amount of liquefied carbon dioxide liquefied in the liquefaction heat exchanger, is detected, Controlling the amount of the liquefied gas fed into the liquefaction heat exchanger based on the detected internal pressure and the detected amount of liquid A carbon dioxide liquefaction method characterized by including

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