Marine liquefied gas regasification method and system

Abstract

This invention relates to a method or system for regasifying liquefied petroleum gas (LPG) on ships. To enable LPG regasification, certain operating conditions are maintained at key points in the circulation of the heat transfer medium that exchanges heat with the LPG, thereby ensuring stable operation of the circulation. The method for regasifying LPG on ships according to this invention includes: vaporizing a first liquid heat transfer medium that has condensed after heat exchange in a first heat exchanger; supplying the vaporized first heat transfer medium to an expansion generator for expansion to generate electricity; supplying the expanded first heat transfer medium to the expansion generator; and controlling the pressure at the rear end of the expansion generator by controlling the pressure at the front or rear end of the expansion generator.

Description

Technical Field

[0001] This invention relates to a method and system for regasifying liquefied petroleum gas (LPG) on ships. In order to regasify LPG, certain operating conditions are maintained at the main points of the circulation of the heat transfer medium that exchanges heat with LPG, so as to enable the circulation to operate stably. Background Technology

[0002] Typically, natural gas is liquefied at its production site into cryogenic liquefied natural gas (LNG), which is then transported long distances to its destination by LNG carriers. LNG is obtained by cooling natural gas at atmospheric pressure to a cryogenic temperature of approximately -163°C. Compared to gaseous natural gas, LNG has a volume reduced to approximately 1 / 600, making it ideal for long-distance maritime transport.

[0003] LNG regasifiers or floating structures at sea, such as LNG RVs (LNG regasifier vessels) or LNG FSRUs (floating storage and regasification units), are used to regasify LNG (liquefied natural gas) at sea and then supply the regasified natural gas to gas demanders on shore.

[0004] These LNG regasification vessels are equipped with LNG storage tanks and regasification facilities for storing LNG. The regasification unit regasifies the LNG stored in the LNG storage tanks and supplies it to onshore demanders. The natural gas regasified in the regasification unit is transferred to onshore demanders via pipelines.

[0005] The regasification unit of an LNG regasification vessel includes: a high-pressure pump that compresses LNG stored in LNG storage tanks to the pressure required by the demander; and a vaporizer that vaporizes the high-pressure LNG compressed by the high-pressure pump into natural gas.

[0006] Seawater, readily available for both supply and demand, is primarily used as the heat source for LNG regasification in vaporizers. The cryogenic seawater, after recovering the cold energy of the LNG through direct or indirect heat exchange with it, is then discharged back into the sea. In other words, during the regasification of the LNG, the cold energy recovered from the LNG by the seawater is directly discarded at sea.

[0007] Each kilogram of LNG contains 200 kcal of cold energy. Therefore, this cold energy is not fully utilized and is wasted during the regasification process of LNG in LNG regasification vessels. Summary of the Invention

[0008] Technical problems to be solved

[0009] Therefore, the present invention provides a method and system for regasifying liquefied gas on ships, which generates electricity by recovering the cold energy wasted in the regasification process of liquefied gas, thereby improving energy efficiency, and the system can be operated stably by controlling the pressure.

[0010] Problem-solving methods

[0011] To achieve the above objectives, according to one aspect of the present invention, a method for regasifying liquefied petroleum gas (LPG) on a ship is provided. The method involves exchanging heat between LPG and a first heat transfer medium in a vaporizer to vaporize the LPG. After recovering the cold energy of the first heat transfer medium discharged from the vaporizer, the medium is recycled back to the vaporizer. The recovered cold energy is achieved by vaporizing the liquid first heat transfer medium, which has condensed during heat exchange in the vaporizer, in a first heat exchanger. The vaporized first heat transfer medium is then supplied to an expansion generator for expansion to generate electricity. The expanded first heat transfer medium is supplied to the vaporizer, and the pressure at the rear end of the vaporizer is controlled by controlling the pressure at the front or rear end of the expansion generator.

[0012] To achieve the above objectives, according to another aspect of the present invention, a marine liquefied gas regasification system is provided, comprising: a vaporizer for exchanging heat between liquefied gas and a first heat transfer medium; a first heat exchanger for vaporizing the first heat transfer medium, which has been condensed in a liquid state in the vaporizer through heat exchange; an expansion generator for expanding the first heat transfer medium vaporized in the first heat exchanger to generate electricity; and a pressure control device for controlling the pressure at the front end or the rear end of the expansion generator, wherein the pressure at the rear end of the vaporizer is controlled by controlling the pressure at the front end or the rear end of the expansion generator.

[0013] To achieve the above objectives, according to another aspect of the present invention, a method for regasifying liquefied gas on a ship is provided. This method involves exchanging heat between liquefied gas and a first heat transfer medium in a vaporizer to vaporize the liquefied gas. After recovering the cold energy of the first heat transfer medium discharged from the vaporizer, the gas is recycled back to the vaporizer. The recovered cold energy of the first heat transfer medium is achieved by vaporizing the liquid first heat transfer medium, which has condensed during heat exchange in the vaporizer, in a first heat exchanger. The vaporized first heat transfer medium is then supplied to an expansion generator for expansion to generate electricity. A heat transfer medium is supplied to the vaporizer. To control the pressure at the rear end of the expander generator, the first heat transfer medium discharged from the vaporizer is contained in the receiver and discharged from the receiver and vaporized. When the pressure measurement value of the receiver is less than the set value, the bypass mode is operated, so that the high-temperature first heat transfer medium expanded by the expander generator bypasses the vaporizer and is supplied to the receiver. When the pressure measurement value of the receiver is greater than the set value, the quenching mode is operated, so that the low-temperature first heat transfer medium discharged from the vaporizer is injected and supplied to the upper part of the receiver.

[0014] Preferably, the first heat transfer medium can undergo a phase change through heat exchange in the vaporizer and the first heat exchanger.

[0015] Preferably, the flow rate of the liquefied gas supplied to the vaporizer can be adjusted so that the temperature of the low-temperature first heat transfer medium discharged from the vaporizer after heat exchange and the temperature of the regasified gas discharged from the vaporizer after heat exchange are maintained at a set value.

[0016] Preferably, the flow rate of liquefied gas supplied to the vaporizer can be controlled based on the smaller of the output values ​​used to maintain the temperature of the first heat transfer medium discharged after heat exchange from the vaporizer at a set value and the output values ​​used to maintain the temperature of the regasified gas discharged after heat exchange from the vaporizer at a set value.

[0017] Preferably, the temperature setpoint of the first heat transfer medium is the saturation temperature of the first heat transfer medium. The temperature setpoint of the first heat transfer medium can be changed according to the saturation pressure of the first heat transfer medium to control the pressure at the rear end of the expansion generator.

[0018] Preferably, the regasified gas vaporized in the vaporizer can exchange heat with a second heat transfer medium in a micro heater to be heated to the temperature required by the gas demander.

[0019] Preferably, when the pressure at the rear end of the expansion generator is lower than a set value or the power generation load is low, the gaseous first heat transfer medium can be controlled to bypass the expansion generator and reach the rear end.

[0020] To achieve the above objectives, according to another aspect of the present invention, a marine liquefied gas regasification system is provided, comprising: a vaporizer that allows liquefied gas to exchange heat with a first heat transfer medium to be vaporized; a receiver that contains the low-temperature first heat transfer medium discharged from the vaporizer after heat exchange; a first heat exchanger for vaporizing the liquid first heat transfer medium received from the receiver; an expander generator that expands the first heat transfer medium vaporized in the first heat exchanger to generate electricity; a first heat medium pipeline that delivers the first heat transfer medium expanded in the expander generator to the vaporizer and delivers the first heat transfer medium that recovers the cold energy of the liquefied gas in the vaporizer to the receiver; a second valve that allows the first heat transfer medium to be delivered downstream of the expander generator, bypassing the vaporizer, to the receiver; a third valve that allows the first heat transfer medium discharged from the vaporizer to be supplied by injection through a nozzle at the top of the receiver; and a second control unit that opens the second valve when the pressure measurement value of the receiver is lower than a set value, and opens the third valve when the pressure measurement value of the receiver is higher than the set value.

[0021] Preferably, it may further include: a first valve for regulating the flow rate of liquefied gas supplied to the vaporizer; and a first control unit that controls the first valve to maintain the temperature of the low-temperature first heat transfer medium discharged from the vaporizer after heat exchange, and the temperature of the regasified gas discharged from the vaporizer after heat exchange at a set value.

[0022] Preferably, the temperature setpoint of the first heat transfer medium is the saturation temperature of the first heat transfer medium, and may further include a third control unit, which adjusts the temperature setpoint of the first heat transfer medium according to the pressure measurement value of the receiver.

[0023] Preferably, it may further include a microheater that further heats the regasified gas vaporized in the vaporizer to the temperature required by the gas demander.

[0024] Preferably, it may further include a second cycle that circulates a second heat transfer medium that exchanges heat with the regasified gas in the microheater to recover the cold energy of the regasified gas.

[0025] Preferably, it may further include: a third flow control valve that allows the first heat transfer medium vaporized in the first heat exchanger to bypass the expander and be delivered downstream of the expander; and a speed regulator that controls the third flow control valve according to the downstream pressure of the expander and the power generation load of the expander.

[0026] Preferably, the vaporizer can be a single-pass shell-and-tube heat exchanger.

[0027] Preferably, the micro heater can be a two-stage shell-and-tube heat exchanger.

[0028] To achieve the above objectives, according to another aspect of the present invention, a method for regasifying liquefied petroleum gas (LPG) on a ship is provided. This method involves exchanging heat between LPG and a first heat transfer medium in a vaporizer to vaporize the LPG. After recovering the cold energy of the first heat transfer medium discharged from the vaporizer, the LPG is recycled back to the vaporizer. The recovery of the cold energy of the first heat transfer medium involves vaporizing the liquid first heat transfer medium, which has condensed during heat exchange in the vaporizer, in a first heat exchanger. The vaporized first heat transfer medium is then supplied to an expansion generator for expansion to generate electricity. The expanded first heat transfer medium is supplied to the vaporizer. Before being supplied to the expansion generator, the vaporized first heat transfer medium is contained in a separation tank. When the pressure measurement value of the separation tank exceeds a set value, the front-end pressure of the expansion generator is controlled by increasing the power of the expansion generator.

[0029] Preferably, increasing the power of the expansion generator involves increasing the opening rate of the second flow control valve so that the first heat transfer medium flows from the separator into the expansion generator. The power of the expansion generator can be increased in accordance with the opening rate of the second flow control valve.

[0030] Preferably, the rotational speed of the expander generator is controlled by a sixth control unit, and the opening degree of the second flow control valve is controlled by the sixth control unit, wherein the sixth control unit receives a control signal from the fifth control unit based on the pressure measurement value.

[0031] Preferably, when the opening rate of the second flow control valve is at its maximum or the power of the expansion generator is at its maximum, the third flow control valve can be opened by the fifth control unit so that the first heat transfer medium can be transported from the separator tank to the downstream of the expansion generator.

[0032] Preferably, increasing the power of the expander generator involves first opening the third flow control valve to allow the first heat transfer medium to bypass the expander generator from the separator and be delivered downstream of the expander generator. Then, the opening rate of the third flow control valve is reduced to increase the power within the allowable range of the expander generator, and the opening rate of the second flow control valve is increased to allow the first heat transfer medium to flow from the separator tank into the expander generator.

[0033] Preferably, the rotational speed of the expander generator is controlled by a sixth control unit, and a seventh control unit that controls the position of the third flow control valve can send a signal to the sixth control unit to increase the rotational speed of the expander generator until the opening rate of the third flow control valve becomes 0%.

[0034] Preferably, the circulation flow rate of the first heat transfer medium can be determined based on the heating load of the gasifier.

[0035] To achieve the above objectives, according to another aspect of the present invention, a marine liquefied gas regasification system is provided, which controls the front-end pressure of an expander generator, comprising: a vaporizer that allows liquefied gas to exchange heat with a first heat transfer medium to be vaporized; a first heat exchanger for vaporizing the liquid first heat transfer medium condensed in the vaporizer by heat exchange; an expander generator that expands the first heat transfer medium vaporized in the first heat exchanger to generate electricity; a separator tank that contains the first heat transfer medium vaporized in the vaporizer; a second flow control valve whose opening is adjustable to supply the gaseous first heat transfer medium discharged from the separator tank to the expander generator; a third flow control valve whose opening is adjustable to allow the gaseous first heat transfer medium discharged from the separator tank to bypass the expander generator; and a sixth control unit that controls the power of the expander generator based on a pressure measurement of the separator tank and adjusts the opening of the second flow control valve based on the power of the expander generator.

[0036] Preferably, it may further include a fifth control unit, which sends an expansion generator power increase signal to the sixth control unit based on the pressure measurement value of the separation tank, and opens the third flow control valve when the expansion generator power reaches its maximum value.

[0037] Preferably, it may further include: a pressure controller for opening the third flow control valve when the pressure measurement value of the separator is higher than a set value; and a seventh control unit that sends a speed increase signal to the sixth control unit until the opening rate of the third flow control valve becomes minimum.

[0038] Invention Effects

[0039] The ship liquefied gas regasification system and method according to the present invention can generate electricity by recovering the cold energy of waste liquefied gas, thereby improving the energy efficiency of the entire system and reducing the amount of fuel consumed for power generation, thereby reducing greenhouse gas emissions.

[0040] In addition, controlling the pressure at the back end of the vaporizer by controlling the pressure of the receiver can improve reactivity in terms of controlling the temperature of the first heat transfer medium used to control the pressure at the back end of the vaporizer, as well as the flow rate of the liquefied gas to be vaporized.

[0041] In addition, by controlling the pressure on the inlet side (high-pressure side) of the expander generator, reactivity can be improved in terms of controlling the temperature of the first heat transfer medium used to control the pressure at the back end of the vaporizer, as well as the flow rate of the liquefied gas to be vaporized.

[0042] In addition, since the first heat transfer medium is used for power generation, even if the heat capacity of the first heat transfer medium in the gasifier is insufficient, the regasified gas can be heated to above the minimum delivery temperature by using a micro heater, so as to stably deliver the regasified gas to the demand side.

[0043] Furthermore, by using a micro-heater, the problem of incomplete vaporization of liquefied gas due to the thermal imbalance between the supply of liquefied gas and the supply of the first heat transfer medium during the initial startup of the regasification system can be prevented. Therefore, the system can operate stably. Attached Figure Description

[0044] Figure 1 This is a schematic diagram illustrating the configuration of a ship's liquefied gas system according to an embodiment of the present invention.

[0045] Figure 2 This is a diagram illustrating the pressure control configuration at the rear end of the vaporizer according to a first embodiment of the present invention.

[0046] Figure 3 This is a diagram illustrating the pressure control configuration at the rear end of the vaporizer according to a second embodiment of the present invention.

[0047] Figure 4 This is a diagram illustrating the inlet pressure control configuration of the expander generator according to a third embodiment of the present invention.

[0048] Figure 5 This is a diagram illustrating the inlet pressure control configuration of the expander generator according to the fourth embodiment of the present invention. Detailed Implementation

[0049] To fully understand the operational advantages of the present invention and the objectives achieved by implementing the present invention, reference must be made to the accompanying drawings illustrating preferred embodiments of the invention and the contents described in the drawings.

[0050] Hereinafter, the structure and function of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. When attaching reference numerals to the constituent elements of the various drawings, it should be noted that, as far as possible, the same constituent elements, even if labeled in different drawings, will be marked with the same numerals. Furthermore, the following embodiments can be modified into various different forms, and the scope of the present invention is not limited to the following embodiments.

[0051] In the embodiments of the invention described later, the liquefied gas can be a liquefied gas that is liquefied at low temperatures and is transportable, such as LNG (liquefied natural gas), LEG (liquefied ethane), LPG (liquefied petroleum gas), liquefied ethylene, liquefied propylene, etc. Alternatively, it can be a liquid gas, such as liquefied carbon dioxide, liquefied hydrogen, or liquefied ammonia. However, in the embodiments described later, LNG, a representative liquefied gas, will be used as an example.

[0052] Furthermore, the LNG regasification system according to embodiments of the present invention described later will be illustrated by example in use on ships, but it can also be applied on land.

[0053] Furthermore, in embodiments of the present invention, the LNG regasification vessel is any type of vessel equipped with an LNG regasification unit capable of regasifying LNG and supplying it to liquefied gas demanders. That is, it can be a self-propelled vessel such as an LNG RV (LNG regasification vessel) or a floating offshore structure such as an LNG FSRU (floating storage and regasification unit). However, in the embodiments described later, an LNG FSRU will be used as an example.

[0054] In addition, according to embodiments of the present invention, LNG regasification vessels can regasify LNG at sea and supply regasified gas (Regas) to gas demanders on shore via pipelines.

[0055] The following will refer to Figures 1 to 5 A ship liquefied gas regasification system and method according to embodiments of the present invention are described.

[0056] The ship liquefied gas regasification system according to this embodiment includes: a high-pressure pump (not shown) that compresses LNG discharged from an LNG storage tank (not shown) to a pressure required by the gas demander (not shown) or higher; a vaporizer (120) that vaporizes the high-pressure LNG compressed by the high-pressure pump through heat exchange with a first heat transfer medium; and a micro heater (130) that adjusts the temperature of the regasified gas, i.e., natural gas, vaporized by the vaporizer (120), to the temperature required by the gas demander, or heats the LNG that has not been vaporized in the vaporizer (120) to the temperature required by the gas demander after complete vaporization.

[0057] LNG storage tanks may be equipped with a supply pump (not shown) that discharges the stored LNG and supplies it to a high-pressure pump. The supply pump may be installed inside the LNG storage tank and may be a semi-submersible pump that can operate while immersed in the LNG stored in the LNG storage tank.

[0058] The high-pressure pump in this embodiment compresses the LNG to be regasified to the pressure required by the demander for regasified gas and supplies it to the vaporizer (120). The pressure required by the gas demander varies depending on the surge, but is typically about 50 to 100 bar. That is, the high-pressure pump in this embodiment can compress the LNG to about 50 to 100 bar, or, taking into account pressure loss, to a pressure slightly higher than 50 to 100 bar.

[0059] In the vaporizer (120) of this embodiment, high-pressure LNG, compressed by a high-pressure gas pump to the regasification gas pressure required by the gas demander, is vaporized into a gaseous state, or only a portion of it is vaporized, becoming a gas-liquid mixture, through heat exchange with the first heat transfer medium circulating in the first cycle. The temperature of the compressed LNG vaporized in the vaporizer (120) can vary depending on the state of the heat source (e.g., the temperature or flow rate of the first heat transfer medium and / or seawater).

[0060] The vaporizer (120) in this embodiment can be a shell-and-tube heat exchanger, and in particular, it can be a single-pass shell-and-tube heat exchanger in which the tube passes through the shell only once.

[0061] In the micro heater (130) of this embodiment, the regasified gas vaporized in the vaporizer (120) is heated to the temperature required by the gas demander and supplied to the gas demander. In addition, if there is LNG that has not been vaporized in the vaporizer (120) due to insufficient heat capacity of the first heat transfer medium, it can be fully vaporized in the micro heater (130) and heated to the temperature required by the gas demander.

[0062] The micro heater (130) in this embodiment can be a shell-and-tube heat exchanger, and in particular, it can be a two-pass shell-and-tube heat exchanger in which the tube passes through the shell twice.

[0063] Since onshore gas demanders typically require regasified gas at approximately 0°C to 10°C or 8°C to 10°C and 50 bar to 100 bar, the regasified gas supplied from the vaporizer (120) to the onshore gas demanders can be heated to approximately 0°C to 10°C and supplied to the gas demanders in the micro heater (130).

[0064] According to this embodiment, the LNG stored in the LNG storage tank flows along the liquefied gas pipeline LL, is compressed by a high-pressure pump, vaporized by a vaporizer (120), heated by a micro heater (130), and then delivered to the gas demander.

[0065] Meanwhile, a first valve (LV) can be installed in the liquefied gas pipeline LL. This first valve (LV) is located upstream of the vaporizer (120) and is used to control the flow rate of LNG supplied to the vaporizer (120).

[0066] The first valve (LV) is controlled by using the output value based on the temperature measurement value of the second temperature control unit (TIC02) and the output value based on the temperature measurement value of the first temperature control unit (TIC01), wherein the second temperature control unit (TIC02) measures the temperature of the first heat transfer medium discharged after heat exchange with LNG in the vaporizer (120), and the first temperature control unit (TIC01) measures the temperature of the natural gas discharged after vaporization in the vaporizer (120).

[0067] In this embodiment, the first temperature control unit (TIC01) can be a concept that includes a temperature measuring device TT01 that measures the temperature and a temperature controller. The temperature controller can receive the temperature measurement value transmitted by the temperature measuring device TT01, calculate the output value required to control various devices for adjusting the temperature, and send control signals to various devices.

[0068] Additionally, the second temperature control unit (TIC02) can also be a concept that includes a temperature measuring device (TT02) that measures the temperature and a temperature controller. The temperature controller can receive the temperature measurement value transmitted by the temperature measuring device (TT02), calculate the output value required to control various devices for adjusting the temperature, and send control signals to various devices.

[0069] The first control unit (LS1) that controls the first valve (LV) can be a low selector. That is, the first control unit (LS1) can control the first valve (LV) with the smaller value between the output value based on the temperature measurement value of the second temperature control unit (TIC02) and the output value based on the temperature measurement value of the first temperature control unit (TIC01).

[0070] Additionally, the ship liquefied gas regasification system according to this embodiment may include a first cycle that circulates a first heat transfer medium, which serves as a heat source and vaporizes LNG by exchanging heat with LNG in a vaporizer (120).

[0071] In this embodiment, the first heat transfer medium may be a refrigerant that undergoes a phase change during circulation in the first cycle.

[0072] Typically, ethylene glycol-water is used as the heat transfer medium for vaporizing LNG in the vaporizer (120). When ethylene glycol-water is used as the heat transfer medium, no phase change occurs during the heat exchange with LNG in the vaporizer (120) and during the heat exchange with seawater in the heat exchanger. That is, heat transfer is achieved solely through the use of sensible heat.

[0073] Conversely, as in this embodiment, when a refrigerant with phase change is used as the heat transfer medium during the heat exchange with LNG in the vaporizer (120) and during the heat exchange with seawater in the heat exchanger, heat transfer can also be achieved through latent heat. Therefore, based on the same conditions, the flow rate of the heat transfer medium to be circulated is significantly reduced compared to the case of using ethylene glycol water, thereby reducing the power of the pump used to circulate the heat transfer medium and improving the overall efficiency of the system.

[0074] The first cycle of this embodiment includes: a first pump (210) for circulating a first heat transfer medium; a first heat exchanger (220) for vaporizing the first heat transfer medium pressurized by the first pump (210); an expansion generator (230) for expanding the first heat transfer medium vaporized by the first heat exchanger (220) and converting the expansion work of the first heat transfer medium into electricity to generate electricity; and a receiver (240) for storing the first heat transfer medium condensed in the vaporizer (120) through heat exchange with LNG.

[0075] The first heat transfer medium circulates along a cycle, namely the first cycle, which is formed by flowing along the first heat medium pipeline (RL), being pressurized by the first pump (210), vaporized in the first heat exchanger (220), expanded in the expander generator (230), condensed in the vaporizer (120), and circulated back to the first pump (210) via the receiver (240).

[0076] In the first heat exchanger (220) of this embodiment, the first heat transfer medium is vaporized by heat exchange with seawater, which is drawn in by a seawater pump (not shown) and supplied to the first heat exchanger (220) along the first seawater pipeline (SL1).

[0077] In the first heat exchanger (220), seawater is cooled while the first heat transfer medium is vaporized, and the cooled seawater is discharged from the first heat exchanger (220) along the first seawater pipeline (SL1).

[0078] In this embodiment, the first heat transfer medium is vaporized in the first heat exchanger (220) using seawater as a heat source. However, steam produced by a steam generator (not shown) on the ship can be used as the heat source, or seawater and steam can be used in a complementary manner.

[0079] Complementary use of seawater and steam may include, for example, a three-flow heat exchanger in the first heat exchanger (220) for heat exchange between seawater, steam, and the first heat transfer medium; or, a primary heat exchanger for heat exchange between seawater and the first heat transfer medium and a secondary heat exchanger for heat exchange between steam and the first heat transfer medium may be installed in series to heat the first heat transfer medium in stages; or, a primary heat exchanger for heat exchange between seawater and the first heat transfer medium and a secondary heat exchanger for heat exchange between steam and the first heat transfer medium may be installed in series to regulate the heating temperature of the first heat transfer medium in the first heat exchanger (220); or, a seawater heater may be provided for heating seawater by heat exchange with steam, and the seawater heated in the seawater heater may be supplied to the first heat exchanger (220).

[0080] In addition, the first heat exchanger (220) in this embodiment can be a shell-and-tube heat exchanger or a plate heat exchanger.

[0081] A first heat transfer medium, vaporized or heated by seawater in a first heat exchanger (220), is supplied to an expansion generator (230) and expands, with the expansion work of the first heat transfer medium being converted into electricity. The electricity produced by the expansion generator (230) can be used at the ship's power demand.

[0082] Downstream of the first pump (210) in the first heat medium pipeline (RL), a first flow control valve (FV1) may be provided for controlling the flow rate of the first heat transfer medium supplied from the first pump (210) to the first heat exchanger (220).

[0083] The first flow control valve (FV1) can be controlled by the fourth control unit (LS2), which calculates the output value based on the rotational speed or load of the first pump (210), the temperature of the first heat transfer medium discharged after heat exchange from the first heat exchanger (210), and the flow rate of the natural gas discharged after heat exchange from the gasifier (120).

[0084] The fourth control unit (LS2) can be a low selector. That is, the fourth control unit (LS2) can control the first flow control valve (FV1) at the minimum value among the output values ​​based on the measured value of the rotational speed or load of the first pump (210), the output value based on the measured value of the temperature of the first heat transfer medium discharged after heat exchange from the first heat exchanger (210), and the output value based on the flow rate of the natural gas discharged after heat exchange from the gasifier (120).

[0085] In addition, according to this embodiment, the first heat medium pipeline (RL) includes a first branch pipeline (RL1), which branches upstream of the expansion generator (230) and allows the first heat transfer medium vaporized in the first heat exchanger (220) to bypass the expansion generator (230), that is, to be supplied directly from the first heat exchanger (220) to the vaporizer (120) without passing through the expansion generator (230).

[0086] When the expander (230) is unusable, such as due to a malfunction, the first branch line (RL1) is used to supply gas from the first heat exchanger (220) to the gasifier (120), thereby ensuring that the supply of natural gas to the demand side on shore is not affected.

[0087] In this embodiment, the purpose of the first branch line (RL1) is to allow the first heat transfer medium to bypass the expander generator (230) during maintenance of the expander generator (230); and to control the front-end pressure caused by the delayed response of the inlet-side valve of the expander generator (230), i.e., the second flow control valve (FV2), when the circulation flow rate of the first heat transfer medium increases due to the sharp increase in the regasification capacity of the vaporizer (120).

[0088] In addition, the first cycle of this embodiment may further include a separation tank (250) disposed between the first heat exchanger (220) and the expansion generator (230), and temporarily storing the first heat transfer medium vaporized in the first heat exchanger (220) and to be supplied to the expansion generator (230), and separating the liquid first heat transfer medium contained in the first heat transfer medium to be supplied to the expansion generator (230).

[0089] A second flow control valve (FV2) is provided in the first heat medium pipeline (RL) between the separator (250) and the expander generator (230) to regulate the flow rate of the gaseous first heat transfer medium delivered from the separator (250) to the expander generator (230).

[0090] The second flow control valve (FV2) can be controlled according to the generator load or speed of the expander generator (230), the pressure of the first heat transfer medium discharged after expansion by the expander generator (230), and the pressure of the separator (250).

[0091] In addition, the generator load or speed measurement value of the expander generator (230), the pressure measurement value of the first heat transfer medium discharged after expansion by the expander generator (230), and the pressure measurement value of the separator (250) can be used to control the second flow control valve (FV2) and the third flow control valve (FV3) installed in the first branch line (RL1) to control the gaseous first heat transfer medium to be transported from the separator (250) along the first heat medium line (RL) or the first branch line (RL1).

[0092] The second flow control valve (FV2) and the third flow control valve (FV3) are controlled by a speed governor, which controls the output value of any one or more of the following: the downstream pressure of the expander generator (230), the measured power generation load of the expander generator (230), the speed of the expander generator (230), and the pressure of the separator (250).

[0093] In the expansion generator (230), the pressure and temperature of the first heat transfer medium, which is vaporized or heated by exchanging heat with seawater in the first heat exchanger (220), can decrease as it expands.

[0094] The first heat transfer medium, which expands in the expander generator (230), is supplied to the vaporizer (120) along the first heat medium line (RL) and is cooled or condensed while exchanging heat with LNG. The first heat transfer medium, which is cooled or condensed in the vaporizer (120), is transported to the receiver (240) along the first heat medium line (RL).

[0095] The receiver (240) in this embodiment serves as a pressure vessel for collecting the first heat transfer medium condensed in the vaporizer (120), and also acts as a buffer tank, such as controlling the flow rate and pressure of the first heat transfer medium circulating in the first cycle.

[0096] According to this embodiment, it may further include means for regulating the pressure of the receiver (240), the pressure regulating means of the receiver (240) including the second valve (RV) and the third valve (QV) described later.

[0097] Additionally, according to this embodiment, it may further include: a fourth branch line (RL4) that branches off from the first heat medium line (RL) downstream of the first pump (210) and connects to the receiver (240); and a fifth branch line (RL5) that connects from the separator 250 to the fourth branch line (RL4).

[0098] In the fourth branch line (RL4), a first water level valve (LV1) is installed. This valve is used to maintain the minimum flow rate of the first pump (210). Similar to when the flow rate of the first heat transfer medium required by the first heat exchanger (220) is less than the minimum flow rate, the first water level valve (LV1) is also installed to return the excess flow rate to the receiver (240) when the discharge flow rate of the first pump (210) exceeds the required flow rate of the first heat transfer medium. The first water level valve (LV1) can be controlled according to the output value of the rotational speed of the first pump (210).

[0099] Additionally, a second water level valve (LV2) is installed in the fifth branch line (RL5). This second water level valve (LV2) is opened and closed to allow the liquid first heat transfer medium separated from the separator (250) to be recovered to the receiver (240). The second water level valve (LV2) can be controlled based on the output value of the water level measurement in the separator (250).

[0100] In this embodiment, the first heat transfer medium can be selected as a material or mixture that undergoes a phase change during the first cycle. That is, the first heat transfer medium can be vaporized when exchanging heat with seawater in the first heat exchanger (220), expanded in the expansion generator (230), and then condensed in the vaporizer (120).

[0101] In this embodiment, the first heat transfer medium can be a natural refrigerant, HFC (hydrofluorocarbon), or HFO (hydrofluoroolefin) refrigerant that poses virtually no fire or explosion hazard, either alone or in combination. For example, R-23, R-32, R-134a, R-407c, R-410A, etc., can be used alone or in combination.

[0102] Meanwhile, in the expansion generator (230), the first heat transfer medium expands isentropically, and during this process, the temperature of the first heat transfer medium decreases.

[0103] For example, if the first heat transfer medium discharged after vaporization or heating from the first heat exchanger (220) is 11°C and 5 barG, and expands to 2 barG in the expander generator (230), the temperature of the first heat transfer medium drops to approximately -10.5°C. If the -10.5°C first heat transfer medium discharged from the expander generator (230) is used as the heat source for vaporizing LNG in the vaporizer (120), the minimum temperature requirement (e.g., 8°C) for the natural gas discharged from the vaporizer (120) cannot be met.

[0104] Therefore, according to this embodiment, a micro heater (130) is further included to heat the natural gas supplied from the gasifier (120) to the gas demander to a temperature above the minimum temperature condition required by the gas demander.

[0105] As described above, according to an embodiment of the present invention, the temperature of the first heat transfer medium vaporized in the first heat exchanger (220) decreases while generating electricity in the expansion generator (230). Therefore, the temperature of the first heat transfer medium supplied to the vaporizer (120) is lower than the temperature required to heat the regasified gas to the temperature required by the gas demander. Therefore, this problem can be solved by providing a micro heater (130) downstream of the vaporizer (120).

[0106] The regasification system according to an embodiment of the present invention may further include a second cycle that circulates a second heat transfer medium for use as a heat source for heating natural gas in a micro heater (130).

[0107] In the micro heater (130), the second heat transfer medium circulates in the second cycle and exchanges heat with the natural gas, thereby heating the natural gas to the minimum temperature condition, that is, to the temperature required by the gas demander or higher. The second heat transfer medium is cooled or condensed after recovering the cold energy of the natural gas.

[0108] The second cycle of this embodiment includes: a second pump (not shown) for circulating the second heat transfer medium; a second heat exchanger (not shown) for heating or vaporizing the second heat transfer medium; and an expansion tank (not shown) for stabilizing the second heat transfer medium discharged after heat exchange by the micro heater (130).

[0109] The second heat transfer medium circulates along the circulation cycle, i.e., the second cycle, which is formed by flowing along the second heat medium pipeline (not shown) while being pressurized by the second pump, vaporized or heated in the second heat exchanger, cooled or condensed in the micro heater (130), and circulated to the second pump through the expansion tank.

[0110] In the second heat exchanger of this embodiment, the heat source for heating the second heat transfer medium can be seawater, which is drawn in by a seawater pump and supplied to the second heat exchanger along a second seawater pipeline.

[0111] In the second heat exchanger, seawater is cooled while being vaporized or heated by the second heat transfer medium, and the cooled seawater is discharged to the outside along the second seawater pipeline.

[0112] In addition, in this embodiment, seawater is described as a heat source for vaporizing or heating the second heat transfer medium in the second heat exchanger. However, steam produced by the steam generator on the ship can be used as the heat source, or seawater and steam can be used in a complementary manner, just like the first heat exchanger (220) described above.

[0113] Alternatively, the second heat exchanger in this embodiment can be a plate heat exchanger.

[0114] In this embodiment, the expansion tank is used as a buffer to cope with the volume expansion of the second heat transfer medium as the temperature changes after heat exchange in the second heat exchanger.

[0115] In addition, in the expansion tank, foreign matter such as air that has entered the second heat transfer medium can be separated from the second heat transfer medium. In the event that natural gas leaks from the micro heater and causes gas to flow into the second heat transfer medium, the gas that has entered the second heat transfer medium can also be separated from the second heat transfer medium.

[0116] In this embodiment, the second heat transfer medium can be ethylene glycol water.

[0117] In the expander generator (230), as the first heat transfer medium, which is vaporized or heated by heat exchange with seawater in the first heat exchanger (220), expands, the pressure and temperature decrease. Except where the temperature of the seawater used as a heat source in the first heat exchanger (220) is sufficiently higher than the minimum temperature condition of the gas demander, it is difficult to heat the natural gas above the minimum temperature condition because the temperature drop of the first heat transfer medium during the pressure change in the expander generator (230) is very large and the heat capacity of the first heat transfer medium is small.

[0118] Therefore, according to this embodiment, a second heat transfer medium, namely ethylene glycol water, can be used as an intermediate heat medium to heat natural gas to above the minimum temperature condition.

[0119] Typically, a high-pressure pump must be used to compress the LNG to a pressure above the minimum required level, and then it must be vaporized and heated to a temperature above the minimum required level in a vaporizer (120). For example, if the minimum temperature of the natural gas discharged from the vaporizer (120) is 8°C, the temperature of the first heat transfer medium supplied to the vaporizer (120) must be 8°C higher than the minimum temperature to meet this requirement. Considering that the minimum temperature difference between the heating fluid and the heated fluid in a typical heat exchanger is 2–3°C, the temperature of the first heat transfer medium supplied to the vaporizer (120) should be approximately 11°C or higher.

[0120] In addition, in this embodiment, since the first heat transfer medium is heated in the first heat exchanger (220) by heat exchange with seawater, the temperature of the seawater supplied to the first heat exchanger (220) should be about 14°C or higher, taking into account the minimum temperature difference between the heating fluid and the heated fluid in a typical heat exchanger.

[0121] However, even if the first heat transfer medium is heated to 11°C in the first heat exchanger (220), as described above, the temperature of the first heat transfer medium can be reduced to -10.5°C while generating electricity in the expansion generator (230).

[0122] Therefore, according to this embodiment, a micro heater (130) must be used to heat the natural gas vaporized in the gasifier (120) to the minimum temperature condition required by the gas demander, i.e., the final delivery temperature of the natural gas.

[0123] If a portion of the first heat transfer medium supplied from the first heat exchanger (220) to the expansion generator (230) is branched off and used as a heat transfer medium for heating the natural gas in the micro heater (130), the natural gas may not be able to be heated to the delivery temperature due to insufficient heat exchange performance in the micro heater (130), unless the temperature of the seawater is high enough to make the temperature difference between the first heat transfer medium exchanging heat in the first heat exchanger (220) and the seawater exceed a minimum level.

[0124] The design of the microheater (130) is difficult due to the low heat capacity and phase change of the first heat transfer medium, which creates a pinch point within the microheater (130). Therefore, this design difficulty can be overcome by using a second heat transfer medium, which can stably heat the regasified gas.

[0125] According to this embodiment, the first heat transfer medium, i.e., the refrigerant, which exchanges heat with the seawater in the first heat exchanger (220), is used only as the heat source of the vaporizer (120). The second heat transfer medium, i.e., ethylene glycol water, which exchanges heat with the seawater in the second heat exchanger and is heated, is used as the heat source of the micro heater (130) to supply so that no pinch point occurs inside the micro heater (130), thereby ensuring sufficient heat exchange performance to stably heat the natural gas to the final delivery temperature.

[0126] Furthermore, during the initial startup of the regasification system, if LNG is not supplied to the vaporizer (120), the first heat transfer medium will not condense in the vaporizer (120), and therefore the first heat transfer medium cannot circulate. Thus, it is necessary to increase the load on the vaporizer (120) while maintaining a good supply balance between LNG and the first heat transfer medium. This causes many operational difficulties.

[0127] According to this embodiment, by using ethylene glycol water as the second heat transfer medium for heating natural gas in the micro heater (130), it is possible to prevent LNG from flowing into the gasifier (120) during the initial startup of the regasification system due to the thermal imbalance between the LNG supply and the first heat transfer medium, thereby enabling stable operation.

[0128] On the other hand, in this embodiment, since the expansion generator (230) generates electricity using the first heat transfer medium, the load on the generator engine installed on the above-mentioned regasification vessel can be reduced, and the fuel consumption can be reduced.

[0129] As described above, according to this embodiment, the cold energy of the first heat transfer medium in high pressure gaseous state is used to drive the expansion generator (230) to generate electricity, and the first heat transfer medium in low pressure gaseous state after driving the expansion generator (230) is used to vaporize LNG. At this time, the pressure control of the inlet side of the expansion generator (230) as the high pressure section and the outlet side of the expansion generator (230) as the low pressure section is very important.

[0130] The receiver (240) is configured to control the outlet pressure of the expansion generator (230) and to act as a buffer to stably supply the liquid first heat transfer medium to the first pump (210).

[0131] When the regasification system is operating normally, the temperature of the first heat transfer medium from the vaporizer (120) is reduced by heat exchange with the LNG in the vaporizer (120). At this time, the temperature of the first heat transfer medium discharged from the vaporizer (120) can be adjusted by regulating the flow rate of the LNG that exchanges heat with the first heat transfer medium, that is, the flow rate of the LNG supplied to the vaporizer (120).

[0132] Since the saturation pressure of the first heat transfer medium is determined based on the temperature of the first heat transfer medium discharged after heat exchange from the vaporizer (120), the temperature of the first heat transfer medium discharged from the vaporizer (120) must be properly controlled so that the pressure of the first heat transfer medium discharged from the expansion generator (230) can also be properly executed.

[0133] That is, the pressure of the receiver (240) should be maintained at saturation pressure according to the temperature of the first heat transfer medium discharged from the vaporizer (120).

[0134] Under normal circumstances, the pressure of the receiver (240) is stably controlled and maintained according to the temperature of the first heat transfer medium. However, when problems such as a sudden increase in the gas flow rate of the first heat transfer medium entering the receiver (240) occur, the pressure of the receiver (240) may not keep up with it due to the slow reaction speed, even if the temperature of the first heat transfer medium discharged from the vaporizer (120) is normally controlled.

[0135] Therefore, in the regasification system and method according to embodiments of the present invention, the characteristic is that, as described above, even in the case of a delayed reaction rate, the back-end pressure of the expansion generator (230) is controlled, i.e., the low-pressure side pressure is controlled, in order to improve the controllability of the regasification system.

[0136] More specifically, the pressure at the rear end of the gasifier (120), i.e., by controlling the pressure of the receiver (240), can be quickly controlled.

[0137] Reference Figure 2 According to a first embodiment of the present invention, a regasification system includes: a second branch line (RL2) that branches off from the first heat medium line (RL) downstream of the expander generator (230) and connects to the receiver (240); a second valve (RV) disposed on the second branch line (RL2); a third branch line (RL3) that branches off from the first heat medium line (RL) upstream of the receiver (240) and connects to the upper end of the receiver (240); and a third valve (QV) disposed on the third branch line (RL3).

[0138] Additionally, it further includes: a first pressure control unit (PIC01) for measuring the pressure of the receiver (240); and a second control unit (BQ) for controlling the second valve (RV) and the third valve (QV) based on the output value of the pressure measurement value measured by the first pressure control unit (PIC01).

[0139] In this embodiment, the first pressure control unit (PIC01) can be a concept that collectively includes a pressure measuring device (PT01) for measuring pressure and a pressure controller. The pressure controller can receive the pressure measurement value transmitted by the pressure measuring device (PT01), calculate the output value required to control various devices for adjusting the pressure, and send control signals to various devices.

[0140] The control logic of the second control unit (BQ) is a split-range control, including a bypass mode. When the pressure measurement value of the receiver (240) measured by the first pressure control unit (PIC01) is less than the set value, in this bypass mode, the second valve (RV) is opened, so that the high-temperature first heat transfer medium supplied from the expander generator (230) to the vaporizer (120) bypasses the vaporizer (120) through the second branch line (RL2) and is supplied to the receiver (240).

[0141] In addition, the control logic of the second control unit (BQ) further includes a quenching mode. When the pressure measurement value of the receiver (240) measured by the first pressure control unit (PIC01) is higher than the set value, in this quenching mode, the third valve (QV) is opened, so that the low temperature first heat transfer medium discharged from the vaporizer (120) is injected from the upper end of the receiver (240) into the interior of the receiver (240) through the third branch line (RL3).

[0142] In bypass mode, when the pressure measurement value of the receiver (240) is lower than the set value, the second valve (RV) is opened to allow the high-temperature first heat transfer medium to enter the receiver (240), thereby increasing the pressure of the receiver (240). The outlet pressure of the expansion generator (230) can be prevented from decreasing by prior rapid control.

[0143] The bypass mode can continue until the pressure measurement value of the receiver (240) reaches the set value.

[0144] In addition, normally, the first heat transfer medium is supplied to the receiver (240) through a fluid inlet located at the middle height of the receiver (240) along the first heat medium pipeline (RL). When the quenching mode is activated, the third valve (QV) is opened, and the low-temperature first heat transfer medium is injected through a nozzle located at the top of the receiver (240), thereby reducing the internal pressure of the receiver (240) by lowering the temperature of the high-temperature gaseous first heat transfer medium present above the receiver (240). The internal pressure of the receiver (240) can be reduced by pre-emptive and rapid control, so that the outlet pressure of the expansion generator (230) does not increase.

[0145] The quenching mode can continue until the pressure measurement value of the receiver (240) reaches the set value.

[0146] Furthermore, the relationship between saturation pressure and temperature can vary from the initial set value depending on various factors, such as the actual composition of the first heat transfer medium. For example, when the first heat transfer medium is a composite refrigerant containing multiple components, the composition of the first heat transfer medium may change during operation due to factors such as the partial vaporization and disappearance of low-boiling-point components. Consequently, the relationship between pressure and temperature will also change accordingly.

[0147] In this way, the composition of the first heat transfer medium becomes different from that at the beginning of operation. If the various temperature and pressure measurements of the second control unit (BQ) are maintained at the initial set values, deviations will occur, resulting in unnecessary valve operations based on bypass mode and quenching mode.

[0148] Therefore, in order to solve this problem, the regasification system according to the second embodiment of the present invention includes a setpoint adjustment device that adjusts the saturation curve relationship between pressure and temperature.

[0149] Reference Figure 3 As a setpoint adjustment device according to an embodiment of the present invention, it may further include a third control unit (PID), which uses the pressure measurement value of the first pressure control unit (PIC01) to change the setpoint of the second temperature control unit (TIC02).

[0150] That is, the set value of the temperature of the first heat transfer medium discharged from the vaporizer (120) is adjusted according to the saturation pressure of the receiver (240). In other words, by adjusting the saturation temperature of the first heat transfer medium, even when the composition of the first heat transfer medium changes, the system can be normally controlled by adjusting the set pressure of the receiver (240), the opening time of the second valve (BV), and the third valve (QV).

[0151] The first heat transfer medium of the LNG regasification system according to this embodiment condenses by exchanging heat with the LNG in the vaporizer (120) during normal operation of the LNG regasification system and circulates the first cycle while maintaining a relatively low pressure.

[0152] In addition, in order to control the front-end pressure of the expander generator (230), that is, the pressure on the high-pressure side of the first cycle, the opening rate of the second flow control valve (FV2) and the third flow control valve (FV3) located upstream of the expander generator (230) should be adjusted in response to the flow rate of the first heat transfer medium circulating in the first cycle.

[0153] At this point, in order to maximize the power generation of the expansion generator (230), the flow should be directed to supply the first heat transfer medium to the expansion generator (230), rather than allowing the first heat transfer medium to flow into the first branch line (RL1) to bypass the expansion generator (230).

[0154] That is, in order to make the limited flow of the first heat transfer medium flow to the vaporizer (120), the smaller the opening rate of the third flow control valve (FV3) and the larger the opening rate of the second flow control valve (FV2), the more electricity is generated by the expansion generator (230), so that the whole system can operate advantageously in terms of energy efficiency.

[0155] Therefore, the regasification system and method according to the third and fourth embodiments of the present invention, described later, are characterized in that, in order to improve system efficiency, the front-end pressure of the expansion generator (230), i.e., the pressure on the high-pressure side, is controlled.

[0156] Reference Figure 4 According to the regasification method of the third embodiment of the present invention, the front-end pressure of the expander generator (230) is controlled based on the output value of the pressure measurement value based on the separator (250).

[0157] According to this embodiment, it further includes: a second pressure control unit (PIC02) for measuring the pressure of the separator (250); a fifth control unit (FB) for transmitting the pressure measurement value of the second pressure control unit (PIC02) to a sixth control unit (SIC) and adjusting the opening degree of the third flow control valve (FV3) based on the output value of the pressure measurement value of the second pressure control unit (PIC02); and a sixth control unit (SIC) for controlling the power and speed of the expander generator (230) based on the output value of the pressure measurement value of the second pressure control unit (PIC02) and adjusting the opening degree of the second flow control valve (FV2).

[0158] In this embodiment, the second pressure control unit (PIC02) may be a concept that includes a pressure measuring device (PTO2) for measuring the pressure of the separation tank (250) and a pressure controller. The pressure controller can receive the pressure measurement value transmitted by the pressure measuring device PT02, calculate the output value required to control various devices for adjusting the pressure, and send control signals to various devices.

[0159] When the pressure measurement value of the second pressure control unit (PIC02) is higher than the set value, the fifth control unit (FB) sends a signal to the sixth control unit (SIC) in a split-range control mode to prioritize opening the second flow control valve (FV2). After receiving the signal from the fifth control unit (FB), the sixth control unit (SIC) increases the power of the expander generator (230) and maintains the speed of the expander generator (230) by opening the second flow control valve (FV2) or increasing its opening degree.

[0160] At this time, even if the opening rate of the second flow control valve (FV2) is 100%, i.e. the maximum, when the pressure of the separator (250) continues to be above the set value, or when the power of the expansion generator (230) reaches the maximum value, the third flow control valve (FV3) is commanded to open through the split-range control of the fifth control unit (FB), so that the first heat transfer medium also flows into the first branch pipeline (RL1), thereby controlling the pressure of the separator (250), i.e. the front-end pressure of the expansion generator (230).

[0161] According to this embodiment, the sixth control unit (SIC) can be a governor (see reference). Figure 1 That is, according to this embodiment, in order to stably supply power, the speed governor plays the role of adjusting the opening of the second flow control valve (FV2). The speed governor is responsible for controlling the power of the expansion generator (230), such as monitoring whether the speed of the turbine of the expansion generator (230) is operating properly within the set range and controlling the speed.

[0162] On the other hand, the permissible range of power conversion speed of the expander (230) can vary depending on the manufacturer of the expander (230), averaging 10% per minute. That is, when increasing the power of the expander (230), it should be increased within the range of 10% per minute.

[0163] As described above, when converting the power (turbine speed) of the expander generator (230) based on the output value of the pressure measurement based on the separator (250), if the change in the circulation rate of the first heat transfer medium is faster than the power regulation rate of the expander generator (230), or if a problem occurs such as a sudden increase in the flow rate of the first heat transfer medium into the separator (250), the inlet pressure of the expander generator (230) will greatly exceed the required pressure range, causing the system to overload. Therefore, the expander generator (230) cannot operate stably.

[0164] To address this problem, according to the regasification method of the fourth embodiment of the present invention, a third flow control valve (FV3) is preferentially opened based on the output value of the pressure measurement value of the second pressure control unit (PIC02) to quickly control the front-end pressure of the expander generator (230).

[0165] According to this embodiment, when the pressure measurement value of the second pressure control unit (PIC02) is higher than the set value, the third flow control valve (FV3) is opened first by rapid control, and the first heat transfer medium corresponding to the pressure exceeding the set value is discharged from the separator (250) to the first branch line (RL1), so that the inlet pressure of the expansion generator (230) is reduced to the required pressure range (set value).

[0166] Furthermore, unlike the third embodiment where the fifth control unit (FB) receives pressure measurements from the pressure controller of the second pressure control unit (PIC02) to control the third flow control valve (FV3), in this embodiment, the pressure controller of the second pressure control unit (PIC02) directly sends an opening control signal to the third flow control valve (FV3) based on the output value based on the pressure measurements.

[0167] Furthermore, according to this embodiment, as Figure 5 As shown, it further includes a seventh control unit (ZIC) that controls the valve position of the third flow control valve (FV3).

[0168] In this embodiment, the seventh control unit (ZIC) adjusts the opening rate of the second flow control valve (FV2) to distribute the necessary load to the expansion generator (230) and sets the opening rate of the third flow control valve (FV3) to the closed state (SP: 0%).

[0169] As described above, according to this embodiment, when the pressure measurement value of the separator (250) is higher than the set value, the third flow control valve (FV3) is opened first to reduce the inlet pressure of the expander generator (230) to the set value.

[0170] Then, the seventh control unit (ZIC) sends a signal to the sixth control unit (SIC) to reduce the opening rate of the third flow control valve (FV3) to the maximum extent possible and to increase the power of the expansion generator (230) to the maximum.

[0171] Therefore, the sixth control unit (SIC) increases the opening rate of the second flow control valve (FV2) to the maximum extent possible, so as to maximize the power generation by changing the power of the expander generator (230) within the allowable range while maintaining the front-end pressure of the expander generator (230).

[0172] As described above, embodiments of the invention have been presented. It will be apparent to those skilled in the art that the invention may be implemented in other specific forms without departing from its spirit or scope, in addition to the embodiments described above. Therefore, the above embodiments should be considered exemplary rather than restrictive, and thus the invention is not limited to the above description, but may be modified within the scope of the appended claims and their equivalents.

[0173] <Explanation of Figure Markers>

[0174] 120: Vaporizer; 130: Micro heater

[0175] 210: First pump; 220: First heat exchanger

[0176] 230: Expander generator; 240: Receiver

[0177] 250: Separator LL: Liquefied Gas Pipeline

[0178] RL: First heat medium pipeline; RL1: First branch pipeline

[0179] RL2: Second branch pipeline; RL3: Third branch pipeline

[0180] RL4: Fourth branch pipeline; RL5: Fifth branch pipeline

[0181] SL1: First seawater pipeline; LV: First valve

[0182] FV1: First flow control valve; FV2: Second flow control valve

[0183] FV3: Third flow control valve; LV1: First water level valve

[0184] LV2: Second water level valve; RV: Second valve

[0185] QV: Third valve; TIC01: First temperature control unit

[0186] TIC02: Second temperature control unit; PIC01: First pressure control unit

[0187] PIC02: Second pressure control unit; LS1: First control unit

[0188] BQ: Second Control Unit; PID: Third Control Unit

[0189] LS2: Fourth Control Unit; FB: Fifth Control Unit

[0190] SIC: Sixth Control Unit; ZIC: Seventh Control Unit

Claims

1. A method for regasifying liquefied petroleum gas (LPG) on ships, characterized in that, The liquefied gas and the first heat transfer medium exchange heat in the vaporizer to vaporize the liquefied gas. After recovering the cold energy of the first heat transfer medium discharged from the vaporizer, it is recycled back to the vaporizer. The cold energy recovered from the first heat transfer medium is, A first heat transfer medium, which has condensed in a liquid state during heat exchange in the vaporizer, is vaporized in the first heat exchanger, and the vaporized first heat transfer medium is supplied to an expansion generator for expansion to generate electricity. The expanded first heat transfer medium is then supplied to the vaporizer. The pressure of the first heat transfer medium at the rear end of the gasifier is controlled by controlling the pressure at the front or rear end of the expander generator, wherein the front or rear end of the expander generator is determined based on the flow direction of the first heat transfer medium. In order to control the pressure at the rear end of the expansion generator, The first heat transfer medium discharged from the vaporizer is contained in the receiver, and then discharged from the receiver and vaporized in the first heat exchanger. When the pressure measurement value of the receiver is less than the set value, the bypass mode is activated, allowing the high-temperature first heat transfer medium expanded by the expander generator to bypass the vaporizer and be supplied to the receiver. When the pressure measurement value of the receiver is greater than the set value, the quenching mode is activated, so that the low-temperature first heat transfer medium discharged from the vaporizer is injected and supplied to the upper part of the receiver.

2. The method for regasifying liquefied gas on ships according to claim 1, characterized in that, The first heat transfer medium undergoes a phase change through heat exchange in the vaporizer and the first heat exchanger.

3. The method for regasifying liquefied gas on ships according to claim 1, characterized in that, The flow rate of liquefied gas supplied to the vaporizer is adjusted so that the temperature of the low-temperature first heat transfer medium discharged from the vaporizer after heat exchange and the temperature of the regasified gas discharged from the vaporizer after heat exchange are maintained at a set value.

4. The method for regasifying liquefied gas on ships according to claim 1, characterized in that, The output value used to maintain the temperature of the low-temperature first heat transfer medium discharged from the vaporizer after heat exchange at a set value. And an output value used to maintain the temperature of the regasified gas discharged after heat exchange from the vaporizer at a set value. The flow rate of liquefied gas supplied to the vaporizer is controlled based on the smaller value.

5. The method for regasifying liquefied gas on ships according to claim 1, characterized in that, The regasified gas, vaporized in the vaporizer, exchanges heat with a second heat transfer medium to be heated to the temperature required by the gas demander.

6. The method for regasifying liquefied gas on ships according to claim 1, characterized in that, When the pressure at the rear end of the expansion generator is lower than the set value or the power generation load is low, the first heat transfer medium in gaseous state is controlled to bypass the expansion generator and reach the rear end.

7. The method for regasifying liquefied gas on ships according to claim 1, characterized in that, The first heat transfer medium, vaporized in the first heat exchanger, is contained in a separation tank before being supplied to the expansion generator. When the pressure measurement value of the separator is greater than the set value, the power of the expander generator is increased to control the front-end pressure of the expander generator.

8. The method for regasifying liquefied gas on ships according to claim 7, characterized in that, The power of the expansion generator is increased by, Increase the opening rate of the second flow control valve to allow the first heat transfer medium to flow from the separator into the expansion generator, thereby increasing the power of the expansion generator in accordance with the opening rate of the second flow control valve.

9. The method for regasifying liquefied gas on ships according to claim 8, characterized in that, The rotational speed of the expander generator is controlled by the sixth control unit. The opening degree of the second flow control valve, It is controlled by a sixth control unit, which receives a control signal from the fifth control unit based on the pressure measurement value.

10. The method for regasifying liquefied gas on ships according to claim 8, characterized in that, When the opening rate of the second flow control valve is at its maximum, or when the power of the expansion generator is at its maximum, the third flow control valve is opened by the fifth control unit so that the first heat transfer medium is transported from the separator tank to the downstream of the expansion generator.

11. The method for regasifying liquefied gas on ships according to claim 7, characterized in that, The power of the expansion generator is increased by, First, the third flow control valve is opened to allow the first heat transfer medium to be transported from the separator tank, bypassing the expander generator, to the downstream of the expander generator. The opening rate of the third flow control valve is reduced to increase the power within the allowable range of the expansion generator, and the opening rate of the second flow control valve is increased to allow the first heat transfer medium to flow from the separator into the expansion generator.

12. The method for regasifying liquefied gas on ships according to claim 11, characterized in that, The rotational speed of the expander generator is controlled by the sixth control unit. The seventh control unit, which controls the displacement of the third flow control valve, sends a signal to the sixth control unit to increase the speed of the expansion generator until the opening rate of the third flow control valve becomes 0%.

13. The method for regasifying liquefied gas on ships according to claim 1, characterized in that, The circulation flow rate of the first heat transfer medium is determined based on the heating load of the gasifier.

14. A ship liquefied gas regasification system, characterized in that, include: A vaporizer that allows liquefied gas to exchange heat with a first heat transfer medium in order to be vaporized; A first heat exchanger is used to vaporize a first heat transfer medium that is condensed in the vaporizer by heat exchange; An expansion generator that expands a first heat transfer medium vaporized in the first heat exchanger to generate electricity; A pressure control device that controls the pressure at the front or rear end of the expander generator; as well as The receiver contains a low-temperature first heat transfer medium discharged from the vaporizer after heat exchange. This includes: A first heat medium pipeline, which delivers the first heat transfer medium expanded by the expansion generator to the vaporizer, and delivers the first heat transfer medium that recovers the cold energy of the liquefied gas in the vaporizer to the receiver. The second valve allows the first heat transfer medium to bypass the vaporizer and be delivered to the receiver downstream of the expansion generator; A third valve allows the first heat transfer medium discharged from the vaporizer to be supplied by injection through a nozzle at the top of the receiver; and The second control unit opens the second valve when the pressure measurement value of the receiver is lower than a set value, and opens the third valve when the pressure measurement value of the receiver is higher than the set value. Specifically, controlling the pressure at the front or rear end of the expander generator controls the pressure of the first heat transfer medium at the rear end of the gasifier. The front or rear end of the expander generator is determined based on the flow direction of the first heat transfer medium. When the pressure measurement value of the receiver is less than the set value, the high-temperature first heat transfer medium expanded by the expander generator is supplied to the receiver by bypassing the vaporizer. When the pressure measurement value of the receiver is greater than the set value, the low-temperature first heat transfer medium discharged from the vaporizer is injected and supplied to the upper part of the receiver.

15. The ship liquefied gas regasification system according to claim 14, characterized in that, Further including: A first valve is used to regulate the flow rate of liquefied gas supplied to the vaporizer; and A first control unit controls the first valve to maintain the temperature of the low-temperature first heat transfer medium discharged from the vaporizer after heat exchange, and the temperature of the regasified gas discharged from the vaporizer after heat exchange at a set value.

16. The ship liquefied gas regasification system according to claim 15, characterized in that, The temperature setpoint of the first heat transfer medium is the saturation temperature of the first heat transfer medium. It further includes a third control unit that adjusts the temperature setpoint of the first heat transfer medium based on the pressure measurement value of the receiver.

17. The ship liquefied gas regasification system according to claim 14, characterized in that, Further including: A third flow control valve allows the first heat transfer medium, vaporized in the first heat exchanger, to bypass the expansion generator and be delivered downstream of it; and The speed controller controls the third flow control valve based on the downstream pressure of the expander generator and the generator load of the expander generator.

18. The ship liquefied gas regasification system according to claim 14, wherein the front-end pressure of the expander generator is controlled, characterized in that, include: A separation tank containing a first heat transfer medium vaporized in the first heat exchanger; A second flow control valve is adjusted to supply the gaseous first heat transfer medium discharged from the separator to the expansion generator. A third flow control valve, the opening of which is adjusted to allow the gaseous first heat transfer medium discharged from the separator to bypass the expansion generator; and The sixth control unit controls the power of the expander generator based on the pressure measurement value of the separator tank, and adjusts the opening degree of the second flow control valve based on the power of the expander generator.

19. The ship liquefied gas regasification system according to claim 18, characterized in that, The system further includes a fifth control unit, which sends an expansion generator power increase signal to the sixth control unit based on the pressure measurement value of the separation tank, and opens the third flow control valve when the expansion generator power reaches its maximum value.

20. The ship liquefied gas regasification system according to claim 18, characterized in that, Further including: A pressure controller is used to open the third flow control valve when the pressure measurement value of the separator tank is higher than a set value; and The seventh control unit sends an increase signal to the sixth control unit until the opening rate of the third flow control valve becomes minimum.

21. The ship liquefied gas regasification system according to claim 14, characterized in that, The vaporizer is a single-pass shell-and-tube heat exchanger.

22. The ship liquefied gas regasification system according to claim 14, characterized in that, It further includes a micro heater that further heats the regasified gas vaporized in the vaporizer to the temperature required by the gas demander.

23. The ship liquefied gas regasification system according to claim 22, characterized in that, Further comprising a second cycle, wherein the second cycle circulates a second heat transfer medium, the second heat transfer medium exchanging heat with the regasified gas in the microheater to recover the cold energy of the regasified gas.

24. The ship liquefied gas regasification system according to claim 22, characterized in that, The micro heater is a two-stage shell-and-tube heat exchanger.

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