Recondensation system for recondensing boil-off gases and related methods
By dynamically controlling the subcooling state of boil-off gas using a sensor assembly and control device, the system addresses rapid demand fluctuations, ensuring stable operation and reducing costs and safety risks in ship recondensation systems.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TGE MARINE GAS ENG GMBH
- Filing Date
- 2024-05-15
- Publication Date
- 2026-06-01
AI Technical Summary
Existing recondensation systems for boil-off gas (BOG) in ships are inadequate due to rapid fluctuations in demand, leading to insufficient subcooling and potential damage to high-pressure pumps, which are critical for efficient operation and safety.
A sensor assembly and subcooling control device dynamically adjust the supply of compressed boil-off gas to maintain a desired subcooling state at the intake of high-pressure compressors, using valves and pumps to minimize deviations from setpoints, ensuring stable operation.
This approach reduces capital and operating expenses, minimizes the risk of damage, and optimizes the use of BOG as a fuel, enhancing the efficiency and safety of ship operations.
Smart Images
Figure 2026517491000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a recondensation system for recondensing boil-off gas (BOG) from liquid propulsion gas supplied as a power source for the main engine of a ship, comprising one or more liquefied gas tanks; one or more compressors fluidly connected to the liquefied gas tanks and configured to extract and compress boil-off gas from the tanks; a low-pressure connection fluidly connected to the compressors and configured to supply the compressed boil-off gas to low-pressure consumption equipment; an extraction pump fluidly connected to the liquefied gas tanks and configured to extract and compress liquefied gas from the tanks; a recondensation device fluidly connected to the compressors and extraction pumps, wherein a supply valve for controlling the fluid flow of compressed liquefied gas to the recondensation device is located on the intake side of the recondensation device; and a high-pressure compressor fluidly connected to the outlet of the recondensation device and configured to compress the recondensed liquefied gas to an outlet pressure for supplying it to high-pressure consumption equipment. In the context of the present invention, unit components such as tanks, compressors, and pumps are mainly described in the singular form. However, this explicitly includes the use of multiple unit components of the same type, such as multiple tanks, compressors, and pumps. [Background technology]
[0002] The use of recondensers in LNG regasification terminals, or floating storage and regasification units (FSRUs), i.e., stationary floating LNG terminals equipped with regasification units, is prior art. In this type of unit, subcooling liquefied gas extracted from one or more liquefied gas tanks is mixed with compressed gas, particularly boil-off gas from the tanks, then absorbed and recondensed, further processed, and finally supplied to consuming equipment via a piping system. Such processes have been shown to be energy efficient in that they first absorb BOG into the flow of liquefied gas at a low pressure, for example, 10-15 bar, and then increase the pressure of the resulting mixture. Existing recondensers in LNG regasification terminals or FSRUs are characterized by exhibiting very small fluctuations in the relevant process parameters, particularly the amount of gas or liquid processed and the pressure, and the requirements for process control or adjustment are less stringent compared to applications on ships.
[0003] Traditionally, conventional fuels such as heavy fuel oil (HFO) and marine diesel fuel (MDO) have been used as power sources for ocean-going vessels. However, due to changing environmental protection requirements and the impact of legal frameworks, alternative fuels have become increasingly discussed in recent years. LNG is already used as a fuel and is therefore part of existing technology. For liquefied gas to be used as a fuel gas, the existence of technology to efficiently utilize BOG (bubble overgrowth) generated during liquefied gas storage is essential.
[0004] Simply adapting existing strategies applied in LNG regasification terminals and FSRUs is not satisfactory. This is because the demand for flammable gas can fluctuate rapidly depending on the ship's power needs, due to the selective starting of onboard generators and rapid load changes caused by ship acceleration. Consequently, the amount of liquefied gas processed in the recondenser can also change very rapidly, while the amount of boil-off gas processed typically changes relatively slowly. Under these operating conditions, systems designed for LNG regasification terminals and FSRUs are unsuitable. Here, complete absorption and recondensation of BOG is a critical prerequisite for the operation of downstream units, particularly high-pressure pumps, which also require a subcooled liquid state at the intake. Residual gas bubbles and insufficient subcooling can negatively impact the lifespan of these units and may even directly cause damage or failure. [Overview of the project]
[0005] Against this backdrop, the object of the present invention is to further improve the above-mentioned type of recondensation system and overcome the shortcomings of the prior art as much as possible. In particular, a device is provided that ensures that the respective suction conditions are met for a high-pressure pump.
[0006] According to the present invention, the objective is achieved in the above-described type of recondensation system by the following configuration: a sensor assembly configured to detect the subcooling state of the fluid on the intake side of a high-pressure compressor, and a subcooling control device configured to control subcooling to minimize the difference between the detected subcooling state and one or more subcooling setpoints by controlling the output of a supply valve and / or a compressor and / or an extraction pump, wherein the subcooling setpoints correspond to at least a set subcooling state in the high-pressure compressor.
[0007] This means that the subcooling state of the fluid on the intake side of the high-pressure compressor corresponds to at least one set subcooling state in the high-pressure compressor. Unique advantages of the present invention include the ability to save on capital expenditures (CAPEX) compared to alternative solutions for handling boil-off gases, and reduced operating costs (OPEX) due to lower power consumption and maintenance costs. Furthermore, by using the apparatus according to the present invention, the boil-off gas supplied to the main engine can be consumed by the main engine's auxiliary drive unit (e.g., a shaft generator), reducing or completely avoiding the operation of generators during navigation. This has positive effects on exhaust emissions and operating costs. For example, compared to alternative solutions that use a service tank containing a considerable amount of liquefied gas as a recondenser and / or separator, the present invention avoids the risk of potential damage to the hull structure due to liquefied gas leakage. [Modes for carrying out the invention]
[0008] According to one embodiment, the sensor assembly is configured to decrease the opening of the BOG supply valve when the detected subcooling state is less than the subcooling setpoint, and to increase the opening of the BOG supply valve when the detected subcooling state is greater than the subcooling setpoint. In this way, the supply flow of compressed boil-off gas to the recondenser is controlled according to the desired subcooling setpoint. For example, if the detected subcooling state deviates significantly from the subcooling setpoint, the amount of compressed boil-off gas supplied to the recondenser can be reduced by closing the supply valve. In this way, dynamic control is achieved, and the desired subcooling state is ensured at the intake side of the high-pressure compressor even when the amount of liquefied gas extracted from the extraction pump fluctuates due to fluctuations in the power demand for the ship's propulsion. The liquefied gas, including the recondensed boil-off gas compressed by the high-pressure compressor, is preferably supplied to the ship's propulsion system.
[0009] According to one embodiment, the sensor assembly includes a temperature sensor configured to detect the temperature of the fluid on the intake side of the high-pressure compressor and a pressure sensor configured to detect the fluid pressure on the intake side of the high-pressure compressor, and the sensor assembly is configured to determine the subcooling state from the temperature and fluid pressure.
[0010] According to one embodiment, the subcooling setpoint is a first subcooling setpoint, and the subcooling control device is further configured to reduce the compressor output when the detected subcooling state is less than a second subcooling setpoint, and to increase the compressor output when the detected subcooling state is greater than a second subcooling setpoint, where the second subcooling setpoint is greater than the first subcooling setpoint. In this way, in addition to controlling the supply of compressed boil-off gas to the recondenser, the compressor output is also operated.
[0011] In the context of this application, the expressions "small subcooling," "decreased subcooling," or "small subcooling setting" are used when subcooling or the setting increases in the mathematically negative region. The expressions "large subcooling," "increased subcooling," or "increased subcooling setting" are used when subcooling or the setting decreases in the mathematically negative region.
[0012] In one embodiment, a valve for controlling the fluid supply to the compressor is located between the tank and the compressor, and the subcooling control device is configured to control the fluid supply to the compressor via this valve. Alternatively or additional means, changes in the compressor's drive speed may be achieved by a frequency converter. In another embodiment, lifting, clearance volume, or bypass control valves may be provided for the compressor valve to control the compressor's capacity.
[0013] According to one embodiment, the subcooling control device is further configured to reduce the output of the extraction pump when the detected subcooling state is greater than a third subcooling setpoint, where the third subcooling setpoint is greater than the second subcooling setpoint. In this way, the pump output of the extraction pump can be directly controlled.
[0014] In particular, the third subcooling setting is greater than the first and second subcooling settings, and the second subcooling setting is greater than the first subcooling setting. By selecting subcooling settings in this way, the recondensation system will always operate in an economically optimal state. Starting from a scenario where a high subcooling state exists as the initial state, the supply valve is opened first, then the compressor output is increased, and finally the rotational speed of the extraction pump is decreased.
[0015] According to one embodiment, the first subcooling setting value is selected to be as close as possible to the saturation value. According to one embodiment, the second and third subcooling setting values have a temperature difference of 2 to 20 K from the first subcooling setting value. For non-LNG liquefied gases, the subcooling setting value is selected by an appropriate method and may differ from the values described above.
[0016] According to one embodiment, the control device is configured as a central control device. According to another embodiment, the control device comprises multiple control units, and in particular, a separate control unit is provided for each sub-cooling setpoint control unit. According to one embodiment, a separate control unit can be provided for each valve or each pump / compressor output control unit to be controlled.
[0017] According to one embodiment, the recompression device includes a static mixer for mixing liquefied gas and compressed and precooled boil-off gas. Such a recompression device is also called an in-line recompressor and functions by utilizing turbulent flow. For this purpose, the static mixer has a large exchange surface area for dissolving the bubbles of compressed boil-off gas into the liquefied gas stream. According to another embodiment, a blade or a coaxially arranged pipe structure may be used as the static mixer.
[0018] According to one embodiment, a buffer container is fluidly connected to the compressor and is configured to store the compressed boil-off gas from the compressor. In particular, a low-pressure connection part is fluidly connected to the buffer container. The buffer container is used for temporarily storing the compressed boil-off gas, thereby playing a role in leveling the demand fluctuations caused by low-pressure consumer devices or the demand fluctuations on the recompression device side.
[0019] According to one embodiment, the buffer container includes a bypass valve, a supply of additional vaporized liquefied gas via a supply regulating valve, and a pressure sensor configured to detect the internal pressure of the buffer container, and at least one regulator is provided to control the internal pressure so that the internal pressure of the buffer container is higher than the minimum internal pressure and lower than the maximum internal pressure.
[0020] Thereby, in particular, it is ensured that the compressed boil-off gas is supplied to the low-pressure consumer devices within a defined pressure range. Preferably, in combination with a further pressure regulator, it is ensured that the low-pressure consumer devices are supplied at a defined pressure.
[0021] According to one embodiment, the recompression system further includes a high-pressure re-liquefaction device fluidly connected to a buffer container for precooling the compressed boil-off gas, and further, the high-pressure re-liquefaction device is also fluidly connected to the recompression device. According to one embodiment, a heating device is arranged between the tank and the compressor and is configured to heat the boil-off gas extracted from the liquefied gas tank. Further, a cooling device is arranged between the compressor and the buffer container and is configured to cool the compressed boil-off gas. As an alternative, the compressed BOG may be cooled against the suction gas flow in a heat exchanger.
[0022] Preferably, the compressor and the extraction pump are controlled such that the suction pressure of the boil-off gas at the suction side of the recompression device is higher than the suction pressure at the suction side of the liquefied gas. Thereby, it is ensured that the boil-off gas flows into the liquefied gas stream.
[0023] The present invention has been described with respect to a recompression system. Further, the present invention also relates to a ship. To achieve the above object with respect to a ship, the present invention includes a recompression system according to any of the foregoing embodiments, particularly when the high-pressure consuming device is the main engine of the ship. Examples of ships include container ships, cruise ships, ferries, cargo ships, and the like. In a ship equipped with the recompression system according to the present invention as a high-pressure consuming device, it is possible to supply fuel gas to the main engine of the ship, and at the same time, for example, low-pressure consuming devices such as generators and steam generators can be supplied with boil-off gas compressed to a low pressure.
[0024] The ship can enjoy the same advantages and preferred embodiments as the recompression system according to the present invention, and vice versa. In this regard, reference should be made to the above discussion, the content of which is incorporated herein.
[0025] Furthermore, the present invention also relates to the use of a recondensation system according to any of the embodiments described above to recondense a liquid propulsion gas supplied as a power source for the main engine of a ship, particularly when the liquid propulsion gas is selected from the following list: LNG, ethane, LPG, ammonia. This use can enjoy the same advantages and preferred embodiments as the recondensation system and the ship according to the present invention, and vice versa. In this regard, the above discussion should be referred to, and its contents are incorporated herein.
[0026] Furthermore, the present invention also relates to a method for recondensing boil-off gas. The present invention achieves the object described above with respect to a method by having the following steps: extracting boil-off gas from a liquefied gas tank; compressing the extracted boil-off gas and supplying the compressed boil-off gas to a low-pressure consumption device; supplying any excess compressed boil-off gas not consumed by the low-pressure consumption device to a re-condenser; supplying the liquefied gas extracted from the liquefied gas tank to a re-condenser; dissolving the compressed boil-off gas in the liquefied gas using the re-condenser to obtain a mixture of compressed boil-off gas and liquefied gas; compressing the mixture to an outlet pressure for a high-pressure consumption device using a high-pressure compressor; and supplying the compressed mixture to a high-pressure consumption device, wherein the subcooling state of the mixture at the inlet side of the high-pressure compressor is detected, and subcooling is controlled by controlling the output of the supply valve and / or compressor and / or extraction pump so as to minimize the difference between the detected subcooling state and one or more subcooling setpoints, where the subcooling setpoints correspond to at least a set subcooling state in the high-pressure compressor.
[0027] In summary, this ensures that a desired subcooling state in the high-pressure compressor, i.e., a subcooling state defined primarily by the specifications of the high-pressure compressor, is maintained, and as a result, a method or control method for responding to highly dynamic requirements on a ship is provided. Ultimately, this method can enjoy similar advantages and preferred embodiments as the recondensation systems, ships, and uses according to the present invention, and vice versa. In this regard, the above discussion should be referred to, and its contents are incorporated herein.
[0028] According to a further embodiment of the method, if the detected subcooling state is less than the subcooling setpoint, the opening of the supply valve is reduced, and if the detected subcooling state is greater than the subcooling setpoint, the opening of the supply valve is increased.
[0029] According to a further embodiment of the method, the subcooling setpoint is a first subcooling setpoint, and the compressor output is reduced when the detected subcooling state is less than a second subcooling setpoint, and increased when the detected subcooling state is greater than a second subcooling setpoint, where the second subcooling setpoint is greater than the first subcooling setpoint. In this way, the compressor used to compress the boil-off gas, or its fluid supply, can also be operated in accordance with the detected subcooling state.
[0030] According to a further embodiment of the method, if the detected subcooling state is greater than a third subcooling setpoint, the output of the extraction pump is reduced, and if the detected subcooling state is less than a third subcooling setpoint, the output of the extraction pump is increased. Here, the third subcooling setpoint is greater than the second subcooling setpoint. In this way, the pump capacity of the extraction pump can also be operated according to the detected subcooling state.
[0031] According to a further embodiment of the method, compressed boil-off gas is supplied to a buffer container configured to store compressed boil-off gas, which is then supplied from the buffer container to a high-pressure reliquefaction unit for pre-cooling and subsequently to a recondenser.
[0032] The present invention will be described in further detail with reference to the following preferred embodiments and accompanying drawings.
[0033] Figure 1 shows a block diagram of a first embodiment of the recondensation system according to the present invention.
[0034] Figure 2 shows a block diagram of a second embodiment of the recondensation system according to the present invention.
[0035] Figure 3 shows a schematic diagram of the boil-off gas recondensation method according to the present invention.
[0036] Figure 1 shows a first embodiment of the recondensation system 2 according to the present invention. The recondensation system 2 includes a liquefied gas tank 7 that contains boil-off gas 4 and liquefied gas 6. The boil-off gas 4 is supplied to a suction gas container / separator 9 via a boil-off gas line 54. The boil-off gas 4 is optionally heated in a heating device and then sent to a compressor 8. The compressor 8 compresses the boil-off gas 4. The compressed boil-off gas 4 is sent from the compressor 8 to a cooling device 46, which optionally has a heating function 44, and from there to a buffer container 31. Alternatively, the returned boil-off gas 4a can be supplied to the tank 7 from a return line 55 via a suction-side bypass valve 32.
[0037] The compressed boil-off gas is supplied from the buffer container 31 to the low-pressure connection 10 via a control valve 60b that functions as a pressure regulating valve, and from there to the low-pressure consuming device N. In particular, supply to the low-pressure consuming device N is given top priority. However, the amount required by the low-pressure consuming device N may be insufficient to maintain the pressure in the liquefied gas tank 7 within an acceptable range during navigation. The compressed boil-off gas 13 not consumed by the low-pressure consuming device N is supplied from the buffer container 31 to the recondenser 14 via an optionally interposed high-pressure reliquefied device 42 and supply valve 16. Furthermore, the liquefied gas 6 is supplied to the recondenser 14 by an extraction pump 12 via a liquefied gas line 56, particularly to the intake side of the recondenser 21. The recondenser 14 is equipped with a static mixer 40. In the recondenser 14, the compressed and potentially pre-cooled boil-off gas 11 is dissolved into the flow of liquefied gas 6, and in particular, the compressed boil-off gas 11 is supplied metrically via a supply valve 16. The mixture 48 of the compressed boil-off gas 11 and liquefied gas 6 is discharged from the outlet 15 of the recondenser 14 and subsequently compressed by a high-pressure compressor 18.
[0038] At the suction port side 20 of the high-pressure compressor 18, the fluid pressure p F The subcooling state U of mixture 48 was detected. actual The pressure is determined. From the high-pressure compressor 18, the mixture 48 is sent to the high-pressure buffer container 52 or high-pressure consumption device H via the high-pressure reliquefaction device 42 and the high-pressure heating device 50, where the outlet pressure p a It is supplied by [unclear]. In particular, high-pressure consuming equipment H is the main engine of a ship. Outlet pressure p a The pressure is, for example, 300 bar. The pressure supplied to the low-pressure consuming device N is, for example, 6-8 bar. Depending on the operating mode, the liquefied gas mixture 48 may be returned to the liquefied gas tank 7 via the control valve 60c. The buffer container 31 is associated with a buffer container pressure sensor 36, and the internal pressure p of the buffer container 31 is monitored. internalIt is configured to detect and control the following. If the consumption of the low-pressure consumption device N exceeds the amount of vaporized gas 4 in the tank 7, the pressure in the buffer container 31 can be maintained by vaporizing the liquefied gas via the low-pressure evaporator 58 and low-pressure gas heater through the pressure regulating valve 34. In this case, the recondensation system is not normally operated. Devices 58 and 76 (see Figure 2) can also be integrated into a single device.
[0039] Figure 2 shows an alternative embodiment of the recondensation system with emphasis on control and regulation aspects. In this embodiment as well, boil-off gas 4 is extracted from the liquefied gas tank 7 via the boil-off gas line and supplied to the heating device 44. From there, the boil-off gas 4 is sent to the compressor 8 via the valve 30. The valve 30 works in conjunction with the valve control unit 74d to regulate the suction pressure of the compressor 8. The pressurized boil-off gas 5 is sent from the compressor 8 to the buffer container 31, from there to the low-pressure connection 10 or low-pressure consumption device N via the control valve 60b in a known manner. The pressurized boil-off gas 5 is sent from the buffer container 31 to the supply valve 16 and optionally to the recondenser 14 via the high-pressure reliquefaction device 42. The recondenser 14 is again supplied with liquefied gas 6. This liquefied gas 6 is extracted by the extraction pump 12. The mixture 48 of liquefied gas 6 and dissolved compressed boil-off gas 5 is sent from the recondenser 14 to the high-pressure compressor 18, and from there to the high-pressure consuming device H via the high-pressure heater 50.
[0040] When the consumption of the low-pressure consumer device N exceeds the amount of the vaporized gas 4 in the tank 7, the pressure in the buffer container 31 can be maintained by vaporizing the liquefied gas through the pressure regulating valve 34 in the low-pressure evaporator 58 and the low-pressure gas heater. The bypass valve 32 is controlled by the valve control unit 74a and enables the flow to be returned to the suction side of the compressor. The suction side valves 34 to the evaporator 58 and the superheater 76 are controlled by the valve control unit 74b. Further, the supply valve 16 is controlled by the control unit 38a. The control unit 38b controls the output P of the extraction pump 12 via the power control unit 72a. Further, the control of the suction pressure valve 30 and / or the adjustment of the output setting of the compressor are carried out by the control unit 38c, adding the valve control unit 74d (set value regulator 74d), by changing the rotational speed or adjusting the valve lift / clearance pocket. The valve control unit 74a is responsible for controlling the pressure regulating bypass valve 32. The control devices 74a, 74b, 74c further control the buffer container 31 by adjusting the bypass valve 32 (74a), the low-pressure evaporator / heater valve 34 (74b), and the valve 30 that regulates the suction pressure of the compressor 8, as well as by changing the rotational speed and / or adjusting the valve lift / clearance pocket, so that the internal pressure p internal is higher than the minimum internal pressure and lower than the maximum internal pressure.
[0041] Furthermore, the sensor device 22 is arranged at the suction side 20 of the high-pressure compression device 18 and is configured to detect the sub-cooling state U of the fluid at the suction side 20. The control unit 38a is part of the sub-cooling control device 28. The sub-cooling control device 28 controls the opening degree of the supply valve 16 according to the detected sub-cooling state U actual and controls the opening degree of the supply valve 16 according to the detected sub-cooling state U actual and according to the detected sub-cooling state U actualThe system is configured to minimize the difference between the subcooling setting value U1 and the high-pressure compressor 18. The subcooling setting value U1 can be stored, for example, in the subcooling control device 28. In particular, the subcooling setting value U1 corresponds to the set subcooling state in the high-pressure compressor 18. The sensor device 22 includes a temperature sensor 26 and is configured to detect the temperature of the fluid at the intake side 20 of the high-pressure compressor 18. Furthermore, the sensor assembly 22 includes a pressure sensor 24 and detects the fluid pressure p at the intake side 20 of the high-pressure compressor 18. F It is configured to detect the fluid temperature and fluid pressure p F Subcooling state U actual To decide.
[0042] The subcooling control device 28 is configured based on the control units 38a to 38c and controls the output of the supply valve 16 and / or the compressor 8 and / or the extraction pump 12 to control the detected subcooling state U actual The subcooling state U is set such that the difference between it and one or more subcooling setting values U1, U2, U3 is minimized. actual It is configured to control the subcooling settings U1 to U3, where each subcooling setting corresponds to at least the set subcooling state in the high-pressure compressor 18.
[0043] The subcooling set value U1 is the first subcooling set value U1. The subcooling control device 28 further controls the detected subcooling state U actual If the value is smaller than the second subcooling setting value U2, the compressor output is reduced, and the detected subcooling state U actual The system is configured to increase the compressor output when the detected subcooling state U1 is greater than the second subcooling set value U2, where the second subcooling set value U2 is greater than the first subcooling set value U1. Furthermore, the subcooling control device 28 controls the detected subcooling state U actualIf the value is greater than the third subcooling setting value U3, the output P of the extraction pump 12, especially the rotational speed, is reduced, and the detected subcooling state U actual The system is configured to increase the output P of the extraction pump P if it is smaller than the third subcooling setting value U3, where the third subcooling setting value U3 is larger than the second subcooling setting value U2.
[0044] Here, the control device 28 includes multiple control units 38a to 38c and individual valve control units 70a to d, but it can also be configured as a central control device.
[0045] Figure 3 shows a schematic diagram of method 100 for recondensing the boil-off gas 4. Method 100 comprises the following steps. Step 102: Step of extracting boil-off gas 4 from liquefied gas tank 7. Step 104: A step of compressing the extracted boil-off gas 4 and supplying the compressed boil-off gas 5 to the low-pressure consumption device N. Step 106: A step of supplying the compressed boil-off gas 5 that was not consumed by the low-pressure consumption device N to the re-condenser 14. Step 108: A step of supplying the liquefied gas 6 extracted from the liquefied gas tank to the recondenser 14. Step 110: A step in which compressed boil-off gas 5 is dissolved in liquefied gas by a re-condenser 14 to obtain a mixture 48 of compressed boil-off gas and liquefied gas. Step 112: A step of compressing the mixture 48 by a high-pressure compressor 18 to the outlet pressure for the high-pressure consumer equipment H, and supplying the compressed mixture 48 to the high-pressure consumer equipment H. Here, the subcooling state U at the intake port side 20 of the high-pressure compressor 18 of the mixture 48 actual When this is detected (particularly as shown in Figure 2), the output of the supply valve 16 and / or the compressor 8 and / or the output of the extraction pump 12 is controlled to resolve the detected subcooling state U. actual The subcooling state U is set so that the difference between it and one or more subcooling setting values U1 to U3 is minimized. actualThis is controlled, and here the subcooling set values U1 to U3 correspond to the set subcooling state in at least the high-pressure compressor 18. [Explanation of symbols]
[0046] 2. Re-condensation system 4. Boil-off gas (BOG) 4a Returned boil-off gas (BOG) 5. Compressed boil-off gas 6. Liquefied Gas (LNG) 7. Liquefied gas tank 8 Compressor 9. Suction gas separator 10 Low-voltage connection section 11. Compressed boil-off gas that may have been pre-cooled 12 Extraction pumps 13. Unconsumed boil-off gas 14 Recondenser 15 Recondenser outlet 16 Supply valve 18. High-pressure compressor 20. Inlet side of high-pressure compressor 21 Inlet side of the recondenser 22 Sensor Assembly 24 Pressure Sensors 26 Temperature Sensor 28 Subcooling control device 30. Valve between the tank and the compressor 31 Buffer Container 32 Bypass Valve 34. Supply control valve to the low-pressure evaporator 36 Buffer Container Pressure Sensor 38a~38c Control Unit 40 Static Mixer 42 High-pressure reliquefaction unit 44 Heating device 46 Cooling device 48. Mixture of compressed boil-off gas and liquefied gas 50 High-pressure heating device 52 High-voltage buffer container 54 Boil-off gas line 55 Return line 56 Liquefied Gas Line 58 Low-pressure evaporator 60a~60d Control valve 72a Output control by adjusting pump speed 74a~74c Buffer container pressure adjustment via valve control 74d Compressor suction gas control 76 Low-pressure heating device 100 ways 102 Extraction of boil-off gas from liquefied gas tanks 104 Compression of extracted boil-off gas 106 Supply of unused boil-off gas to the recondenser. 108 Supply of liquefied gas extracted from the liquefied gas tank to the recondenser. 110 Dissolution of compressed boil-off gas into liquefied gas 112 Compression of a mixture using a high-pressure compressor N Low-voltage power consumption equipment H High-voltage consumer equipment Pump capacity (especially head) of the extraction pump. p a Outlet pressure p F Fluid pressure at the intake side of the high-pressure compressor p internal Internal pressure of the buffer container U1 1st subcooling setting value U2 Second Subcooling Setting Value U3 Third Subcooling Setting Value U actual Subcooling state of the fluid at the intake side of the high-pressure compressor
Claims
1. A recondensation system (2) for recondensing boil-off gas (4) from liquid propulsion gas supplied to drive the main engine of a ship, Liquefied gas tank (7) and A compressor (8) is fluidly connected to a liquefied gas tank (7) and configured to extract and compress boil-off gas (4) from the liquefied gas tank (7), A low-pressure connection section (10) is fluidly connected to the compressor (8) and supplies the compressed boil-off gas (5) to a low-pressure consumption device (N), An extraction pump (12) is fluidly connected to the liquefied gas tank (7) and configured to extract and pump liquefied gas (6) from the liquefied gas tank (7), A recondenser (14) is fluidly connected to the compressor (8) and the extraction pump (12), The recondenser (14) has a supply valve (16) positioned on its intake side (21) for controlling the fluid flow of compressed boil-off gas (11), which may be pre-cooled, to the recondenser (14), The outlet (15) of the recondenser (14) is fluidly connected, and the mixture of the recondensed liquefied gas, particularly the compressed boil-off gas and the liquefied gas (48), is supplied to the outlet pressure (p) of the high-pressure consumption device (H). ａ The system includes a high-pressure compressor (18) configured to compress to ) Subcooling state of the fluid on the intake side (20) of the high-pressure compressor (18) (U ａｃｔｕａｌ A sensor assembly (22) configured to detect ) and By controlling the output of the supply valve (16) and / or the compressor (8) and / or the extraction pump (12), the detected subcooling state (U ａｃｔｕａｌ ) and at least one subcooling setting value (U １ ~U ３ The difference between the above and the subcooling state (U ａｃｔｕａｌ The system includes a subcooling control device (28) configured to control the following: The aforementioned subcooling setting value (U １ ~U ３ A recondensation system characterized in that it corresponds to at least a set subcooling state in the high-pressure compressor (18).
2. The sensor assembly (22) decreases the opening degree of the supply valve (16) when the detected sub-cooling state (U ａｃｔｕａｌ ) is smaller than the sub-cooling set value (U １ ), and increases the opening degree of the supply valve (16) when the detected sub-cooling state (U ａｃｔｕａｌ ) is larger than the sub-cooling set value (U １ ). The recondensation system according to claim 1, which is configured as such.
3. The sensor assembly (22) includes a temperature sensor (26) configured to detect the temperature of the fluid on the suction port side (20) of the high-pressure compressor (18). The sensor assembly (22) detects the fluid pressure (p) at the intake side (20) of the high-pressure compressor (18). Ｆ It has a pressure sensor (24) configured to detect ), The sensor assembly (22) measures temperature and fluid pressure (p Ｆ ) to the aforementioned subcooling state (U ａｃｔｕａｌ A recondensation system according to claim 1 or 2, configured to determine ).
4. The aforementioned subcooling setting value (U １ ) is the first subcooling setting value (U １ ) and the subcooling control device (28) detects the subcooling state (U ａｃｔｕａｌ ) is the second subcooling setting value (U ２ If it is smaller than ), the output of the compressor is reduced, and the detected subcooling state (U ａｃｔｕａｌ ) is the second subcooling setting value (U ２ The system is configured to increase the output of the compressor if it is greater than the second subcooling setting value (U ２ ) is the first subcooling setting value (U １ A recondensation system according to any one of claims 1 to 3, which is larger than ).
5. The recondensation system according to claim 4, wherein a valve (30) for operating the fluid supply to the compressor (8) is located between the tank (7) and the compressor (8), and the subcooling control device (28) is configured to control the fluid supply to the compressor (8) via the valve (30).
6. The subcooling control device (28) detects the subcooling state (U ａｃｔｕａｌ ) is the third subcooling setting value (U ３ If it is greater than ), the output (P) of the extraction pump (12) is reduced, and the detected subcooling state (U ａｃｔｕａｌ ) is the third subcooling setting value (U ３ The system is configured to increase the output (P) of the extraction pump (12) if it is smaller than the third subcooling setting value (U ３ ) is the second subcooling setting value (U ２ A recondensation system according to any one of claims 1 to 5, which is larger than ).
7. The control device (28) is configured as a central control device and / or has a plurality of control units (38a to 38c), and in particular each subcooling set value (U １ ~U ３ The recondensation system according to any one of claims 1 to 6, further comprising individual control units (38a to 38c) corresponding to the above.
8. The recondensation system according to any one of claims 1 to 7, wherein the recondensation apparatus (14) has a static mixer (40) for mixing the liquefied gas with a boil-off gas (11) that may be compressed and pre-cooled.
9. The recondensation system according to any one of claims 1 to 8, further comprising a buffer container (31) fluidly connected to the compressor (8) and configured to store compressed boil-off gas (5) from the compressor (8), wherein the low-pressure connection (10) is fluidly connected to the buffer container (31).
10. The buffer container (31) includes a bypass valve (32) and a supply adjustment valve (34) for supplying additional vaporized liquefied gas, and the internal pressure (p) of the buffer container (31). ｉｎｔｅｒｎａｌ The buffer container (31) is equipped with a pressure sensor (36) configured to detect the internal pressure (p ｉｎｔｅｒｎａｌ The recondensation system according to any one of claims 1 to 9, further comprising at least one regulator (74a to 74c) configured to control such that the internal pressure is higher than the minimum internal pressure and lower than the maximum internal pressure.
11. The recondensation system according to claim 10, further comprising a high-pressure reliquefaction device (42) fluidly connected to the buffer container (31) for pre-cooling the compressed boil-off gas (5), wherein the high-pressure reliquefaction device (42) is fluidly connected to the recondensation device (14).
12. A recondensation system according to any one of claims 1 to 11, wherein a heating device (44) or a cooling device (46) is positioned between the compressor (8) and the buffer container (31), or the heating device (44) is positioned between the liquefied gas tank (7) and the compressor (8) and configured to heat the boil-off gas (4) extracted from the liquefied gas tank (7), and / or the cooling device (46) is positioned between the compressor (8) and the buffer container (31) and configured to cool the compressed boil-off gas (4).
13. The recondensation system according to any one of claims 1 to 12, wherein the compressor (8) and the extraction pump (12) are controlled such that the suction pressure of the boil-off gas (5) at the suction port side (21) of the recondenser (14) is higher than the suction pressure of the liquefied gas (6) at the suction port side (21).
14. A ship equipped with a recondensation system (2) according to any one of claims 1 to 13, wherein the high-pressure consumption device is the ship's main engine.
15. Use of a recondensation system according to any one of claims 1 to 13, for the condensation of a gas supplied to drive the main engine of a ship, in particular a boil-off gas (BOG), wherein the liquid propulsion gas is selected from the group consisting of LNG, ethane, LPG, and ammonia.
16. A method (100) for recondensing boil-off gas (4), The process (102) involves extracting boil-off gas (4) from the liquefied gas tank (7), The process (104) involves compressing the boil-off gas (4) extracted by the compressor (8) and supplying the compressed boil-off gas (5) to a low-pressure consumption device (N), A step (106) of supplying the compressed boil-off gas (5) that was not consumed by the low-pressure consumption device (N) to the re-condenser (14), The process (108) involves supplying the liquefied gas (6) extracted from the liquefied gas tank (7) to the recondenser (14) by an extraction pump (12), Step (110) is to dissolve the compressed boil-off gas (5) in the liquefied gas (6) using the re-condensing device (14) to obtain a mixture (48) of the compressed boil-off gas and the liquefied gas, wherein the boil-off gas (11), which may be compressed and pre-cooled, is supplied to the re-condensing device (14) via an interposed supply valve (16), The process includes compressing the mixture (48) using a high-pressure compressor (18) to the outlet pressure for a high-pressure consumer (H), and supplying the compressed mixture (48) to the high-pressure consumer (H), Subcooling state of the mixture (48) at the intake port side (20) of the high-pressure compressor (18) (U ａｃｔｕａｌ ) is detected, and the output of the supply valve (16) and / or the compressor (8) and / or the extraction pump (12) is controlled to detect the detected subcooling state (U ａｃｔｕａｌ ) and at least one subcooling setting value (U １ ~U ３ The difference between the above and the subcooling state (U ａｃｔｕａｌ ) is controlled, and the subcooling set value (U １ ~U ３ ) is a method corresponding to at least one set subcooling state in the high-pressure compressor (18).
17. The detected subcooling state (U ａｃｔｕａｌ ) is the subcooling setting value (U １ If the value is smaller than the detected subcooling state (U ａｃｔｕａｌ ) is the subcooling setting value (U １ The method according to claim 16, wherein the opening degree of the supply valve (16) is increased if it is greater than ).
18. The aforementioned subcooling setting value (U １ ) is the first subcooling setting value (U １ ) and the detected subcooling state (U ａｃｔｕａｌ ) is the second subcooling setting value (U ２ If it is smaller than ), the output of the compressor is reduced, and the detected subcooling state (U ａｃｔｕａｌ ) is the second subcooling setting value (U ２ If it is greater than the second subcooling setting value (U ２ ) is the first subcooling setting value (U １ A method greater than ) or the method according to claim 16 or claim 17.
19. The detected subcooling state (U ａｃｔｕａｌ ) is the third subcooling setting value (U ３ If the value is greater than the detected subcooling state (U ａｃｔｕａｌ ) is the third subcooling setting value (U ３ If it is smaller than the third subcooling setting value (U ３ ) is the second subcooling setting value (U ２ The method according to any one of claims 16 to 18, wherein the value is greater than )
20. The method according to any one of claims 16 to 19, wherein the compressed boil-off gas (5) is supplied to a buffer container (31) configured to store the compressed boil-off gas (5), and the compressed boil-off gas (5) is optionally supplied from the buffer container (31) to a high-pressure reliquefaction device (42) for pre-cooling of the compressed boil-off gas, and then supplied to the recondensation device (14).