Series loop power generation system and method using cold energy of liquefied gas

Abstract

The present invention relates to a multi-loop power generation system and method using cold energy of a liquefied gas, in which power is generated by recovering waste cold energy of a liquefied gas by means of a series loop. The series loop power generation system using cold energy of a liquefied gas, according to the present invention, comprises: a main refrigerant cycle in which power is generated by recovering cold energy of a liquefied gas while a main refrigerant stream circulates, and which comprises a main refrigerant turbine-generator for generating power by driving a turbine by means of the main refrigerant stream, and a first main refrigerant economizer for recovering the cold energy of the liquefied gas by enabling a portion of the main refrigerant stream to undergo heat exchange with the liquefied gas; and an auxiliary refrigerant cycle which is provided in series with the main refrigerant cycle so as to be detachable therefrom, and in which power is generated by recovering residual cold energy of the main refrigerant cycle while an auxiliary refrigerant stream circulates, and which comprises an auxiliary refrigerant turbine-generator for generating power by driving a turbine by means of the auxiliary refrigerant stream, and an auxiliary refrigerant economizer for cooling the auxiliary refrigerant stream expanded in the auxiliary refrigerant turbine-generator, by recovering residual cold energy of any one or more among the main refrigerant stream and the liquefied gas from which the cold energy has been recovered in the main refrigerant cycle.

Description

Series loop power generation system and method using cold energy from liquefied gas

[0001] The present invention relates to a series loop power generation system and method for recovering and generating power from waste cold heat of liquefied gas using a series loop.

[0002] Natural gas is liquefied at extremely low temperatures at its production site, forming liquefied natural gas (LNG). This is then transported long distances to its intended destination. Natural gas is liquefied by cooling it from atmospheric pressure to the cryogenic temperature of approximately -163°C, creating LNG. Liquid natural gas, or LNG, has a volume roughly 1 / 600th that of gaseous natural gas, making it ideal for storage and transportation.

[0003] Natural gas stored in a liquid state is regasified using a regasification facility to produce natural gas in a gaseous state, and is supplied to each demander in a gaseous state.

[0004] Basically, the regasification facility is composed of a high-pressure pump that compresses natural gas, i.e. LNG, in a liquid state stored in a storage tank 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.

[0005] Seawater, which is readily available, is primarily used as a heat source for vaporizing LNG in vaporizers. The low-temperature seawater, which recovers its cold energy through direct or indirect heat exchange with the LNG, is then discharged back into the sea.

[0006] The energy required to transform liquid LNG into gaseous natural gas reaches 200 kcal per kg. A significant amount of energy is wasted in the process of vaporizing liquid natural gas, leaving it largely unused and being dumped into the ocean by seawater.

[0007] Cold thermal power generation is one of the technologies that effectively utilizes the cold energy of LNG. A typical commercial cold thermal power generation system operates in a closed loop, where high-temperature, high-pressure gaseous refrigerant is reduced to low pressure through an expander, which then drives a turbine to generate electricity. The low-pressure refrigerant is liquefied through heat exchange with LNG, pressurized using a pump, and vaporized through heat exchange with seawater to create a high-temperature, high-pressure gas. This high-temperature, high-pressure gaseous refrigerant is then circulated back to the expander, a process that repeats.

[0008] A basic LNG cold-heat power generation system is composed of a vaporizer that vaporizes LNG by exchanging heat with a refrigerant, a pump that pressurizes the refrigerant discharged from the vaporizer after heat exchange with the LNG, a heat exchanger that heat-exchanges the refrigerant pressurized by the pump with a heat source, a turbine that expands the refrigerant discharged from the heat exchanger after heat exchange, and a generator that generates electricity from the expansion work generated by driving the turbine.

[0009] Here, the refrigerant circulates through a closed cycle consisting of a vaporizer, pump, heat exchanger, and turbine, undergoing a phase change in which it condenses while exchanging heat with LNG in the vaporizer and vaporizes while exchanging heat with seawater in the heat exchanger.

[0010] The conventional LNG cold power generation system, which consists of a single cycle, has the disadvantage of low power generation efficiency due to the relatively large loss caused by latent heat as the refrigerant undergoes phase change, and the system becomes large due to the low density of the working fluid in the low-pressure section.

[0011] In addition, the LNG cold power generation system, which is composed of a conventional single cycle, has to control the operating pressure and temperature of the cycle so that the refrigerant can be completely condensed in the vaporizer and completely vaporized in the heat exchanger, and the temperature of the refrigerant must be kept as low as possible to maximize the expansion ratio while maintaining a temperature above the freezing point, making it difficult to control and limiting improvements in efficiency.

[0012] Accordingly, the present invention aims to achieve the above-described object by providing a series loop power generation system utilizing the cold heat of liquefied gas, which improves the power generation efficiency of a conventional liquefied gas cold heat power generation system composed of a single cycle.

[0013] The challenges addressed by the present invention are not limited to those mentioned above. Other technical challenges not mentioned will be readily apparent to those skilled in the art, as described below.

[0014] According to one aspect of the present invention for achieving the above-described object, there is provided a main refrigerant cycle for generating power by recovering cold heat of liquefied gas while a main refrigerant stream circulates; and an auxiliary refrigerant cycle which is provided in series so as to be detachably connected to the main refrigerant cycle and for generating power by recovering residual cold heat of the main refrigerant cycle while an auxiliary refrigerant stream circulates; wherein the main refrigerant cycle includes a main refrigerant turbine-generator for generating power by driving a turbine with the main refrigerant stream; and a first main refrigerant economizer for recovering cold heat of the liquefied gas by heat-exchanging a portion of the main refrigerant stream with the liquefied gas; wherein the auxiliary refrigerant cycle includes an auxiliary refrigerant turbine-generator for generating power by driving a turbine with the auxiliary refrigerant stream; A series loop power generation system utilizing the cold heat of liquefied gas is provided, comprising: an auxiliary refrigerant economizer that cools the auxiliary refrigerant stream expanded in the auxiliary refrigerant turbine-generator by recovering residual cold heat from at least one of the liquefied gas and the main refrigerant stream from which cold heat has been recovered in the main refrigerant cycle;

[0015] Preferably, the auxiliary refrigerant economizer may include at least one of a first auxiliary refrigerant economizer that recovers residual heat of the liquefied gas by heat-exchanging the auxiliary refrigerant stream with the liquefied gas from which the cold heat has been recovered in the first main refrigerant economizer; and a second auxiliary refrigerant economizer that recovers residual heat of the main refrigerant stream by heat-exchanging the auxiliary refrigerant stream with the main refrigerant stream cooled while recovering the cold heat of the liquefied gas in the main refrigerant cycle.

[0016] Preferably, the system may further include a liquefied gas heater for heating liquefied gas heated by heat exchange in the first refrigerant economizer and supplied to a gas demand source; and a primary refrigerant heater for heating a primary refrigerant stream circulated to the primary refrigerant turbine-generator.

[0017] Preferably, the auxiliary refrigerant economizer comprises a first auxiliary refrigerant economizer that recovers residual heat of the liquefied gas by heat-exchanging the auxiliary refrigerant stream with the liquefied gas from which the refrigerant heat has been recovered in the first main refrigerant economizer; and the auxiliary refrigerant cycle further comprises a liquefied gas heating line branched from the liquefied gas line upstream of the liquefied gas heater and connected to the liquefied gas stream inlet side of the first auxiliary refrigerant economizer; so that the liquefied gas can be supplied to the gas demander after being heated through at least one of the first auxiliary refrigerant economizer and the liquefied gas heater.

[0018] Preferably, the auxiliary refrigerant economizer comprises a second auxiliary refrigerant economizer for recovering residual refrigerant heat of the main refrigerant stream by heat-exchanging the cooled main refrigerant stream while recovering refrigerant heat of the liquefied gas in the auxiliary refrigerant stream and the main refrigerant cycle; and the auxiliary refrigerant cycle further comprises a main refrigerant heating line branched from a line through which the main refrigerant stream flows upstream of the main refrigerant heater and connected to a main refrigerant stream inlet side of the second auxiliary refrigerant economizer; so that the main refrigerant stream can be circulated to the main refrigerant turbine-generator after being heated through at least one of the second auxiliary refrigerant economizer and the main refrigerant heater.

[0019] Preferably, two or more of the above main refrigerant heaters can be provided in series or parallel.

[0020] Preferably, the primary refrigerant cycle may operate as a Brayton cycle, and the secondary refrigerant cycle may operate as a Rankine cycle.

[0021] Preferably, the primary refrigerant cycle may include: a primary refrigerant branching section provided upstream of the first primary refrigerant economizer and branching the primary refrigerant stream into a plurality of primary refrigerant streams, including a first primary refrigerant stream to be supplied to the first primary refrigerant economizer; a plurality of primary refrigerant economizers provided in parallel to cool the plurality of primary refrigerant streams by direct or indirect heat exchange with the liquefied gas, and provided in one-to-one correspondence with the plurality of primary refrigerant streams, including the first primary refrigerant economizer; and a plurality of primary refrigerant compressors provided in one-to-one correspondence with the plurality of primary refrigerant economizers, and compressing one primary refrigerant stream cooled by one of the plurality of primary refrigerant economizers and supplying the compressed primary refrigerant stream to another primary refrigerant economizer as a refrigerant for cooling another primary refrigerant stream.

[0022] Preferably, the method may further include an additional auxiliary refrigerant cycle, which is detachably installed in series at the rear end of the auxiliary refrigerant cycle and generates power by further recovering residual cold heat of the liquefied gas from which cold heat has been recovered in the auxiliary refrigerant cycle while the additional auxiliary refrigerant circulates.

[0023] Preferably, the main refrigerant and the auxiliary refrigerant may be selected from a group including a single refrigerant selected from the group consisting of evaporated gas of the liquefied gas, hydrogen, helium, nitrogen, oxygen, neon, argon, carbon compounds having 5 or fewer carbon atoms, and freon refrigerants, or a group including a mixed refrigerant in which two or more of these are mixed.

[0024] Preferably, the first primary refrigerant economizer and the auxiliary refrigerant economizer may be a plate-type heat exchanger, a plate-fin type heat exchanger, a printed circuit board type heat exchanger, an aluminum bonded heat exchanger, or a coil wound type heat exchanger.

[0025] Preferably, the first primary refrigerant economizer and the auxiliary refrigerant economizer may be one or more multi-stream heat exchangers.

[0026] Preferably, the auxiliary refrigerant cycle may further include an auxiliary refrigerant pump that pressurizes a liquefied auxiliary refrigerant stream while recovering residual refrigerant heat from the auxiliary refrigerant economizer; and an auxiliary refrigerant heater that vaporizes the auxiliary refrigerant stream pressurized by the auxiliary refrigerant pump and recirculates it to the auxiliary refrigerant turbine-generator.

[0027] Preferably, two or more auxiliary refrigerant heaters may be provided in series or parallel.

[0028] According to another aspect of the present invention for achieving the above-described object, a series loop power generation method using the cold heat of liquefied gas is provided, comprising: a main refrigerant power generation step for recovering cold heat of liquefied gas while a main refrigerant stream circulates to generate power; and an auxiliary refrigerant power generation step for recovering residual cold heat of the main refrigerant power generation step while an auxiliary refrigerant stream circulates to generate power; wherein the main refrigerant power generation step comprises: a main refrigerant turbine driving step for generating electric power by driving a turbine with the main refrigerant stream; and a first main refrigerant cold heat recovery step for recovering cold heat of the liquefied gas by heat-exchanging a portion of the main refrigerant stream with the liquefied gas; wherein the auxiliary refrigerant power generation step comprises: an auxiliary refrigerant turbine driving step for generating electric power by driving a turbine with the auxiliary refrigerant stream; and an auxiliary refrigerant cold heat recovery step for recovering residual cold heat of at least one of the liquefied gas and the main refrigerant stream by heat-exchanging the auxiliary refrigerant stream with at least one of the liquefied gas and the main refrigerant stream transported from the main refrigerant power generation step.

[0029] Preferably, the auxiliary refrigerant cold heat recovery step may include at least one of a first auxiliary refrigerant cold heat recovery step of recovering residual cold heat of the liquefied gas by heat-exchanging the auxiliary refrigerant stream with the liquefied gas from which cold heat has been recovered in the first main refrigerant cold heat recovery step; and a second auxiliary refrigerant cold heat recovery step of recovering residual cold heat of the main refrigerant stream by heat-exchanging the auxiliary refrigerant stream with the main refrigerant stream cooled while recovering cold heat of the liquefied gas in the main refrigerant power generation step.

[0030] Preferably, the method further comprises a step of heating the liquefied gas heated by heat exchange in the first main refrigerant heat recovery step to a temperature required by the gas demander and supplying the liquefied gas to the gas demander; and the step of supplying the liquefied gas to the gas demander may include at least one of a first auxiliary refrigerant heat recovery step of heating the liquefied gas from which the heat has been recovered in the first main refrigerant heat recovery step by heat-exchanging it with the auxiliary refrigerant stream; and a liquefied gas heating step of heating the liquefied gas from which the heat has been recovered in the first main refrigerant heat recovery step.

[0031] Preferably, the method further includes a step of heating the liquefied gas heated by heat exchange in the first main refrigerant heat recovery step to a temperature required by the gas demander and supplying the liquefied gas to the gas demander; and the step of supplying the liquefied gas to the gas demander may include a first auxiliary refrigerant heat recovery step of heating the liquefied gas, from which the heat has been recovered in the first main refrigerant heat recovery step, by heat-exchanging it with the auxiliary refrigerant stream; and a liquefied gas heating step of further heating the liquefied gas heated in the first auxiliary refrigerant heat recovery step.

[0032] Preferably, the auxiliary refrigerant power generation step may further include an auxiliary refrigerant pressurizing step of pressurizing the liquefied auxiliary refrigerant stream while recovering the remaining refrigerant heat of the liquefied gas in the auxiliary refrigerant cold heat recovery step; and an auxiliary refrigerant heating step of vaporizing the pressurized auxiliary refrigerant stream in the auxiliary refrigerant pressurizing step and recirculating it to the auxiliary refrigerant turbine driving step.

[0033] Preferably, the primary refrigerant power generation step may further include a primary refrigerant compression step for compressing the primary refrigerant stream cooled while recovering the cold heat of the liquefied gas in the first primary refrigerant cold heat recovery step; and a primary refrigerant heating step for heating the primary refrigerant stream cooled while recovering the cold heat of the liquefied gas in the primary refrigerant power generation step and recirculating it to the primary refrigerant turbine driving step.

[0034] Preferably, the primary refrigerant heating step may include at least one of a second auxiliary refrigerant cold heat recovery step of recovering the cold heat of the liquefied gas in the primary refrigerant power generation step and heat-exchanging the cooled primary refrigerant stream with the auxiliary refrigerant stream to recover the remaining cold heat of the primary refrigerant stream; and a primary refrigerant additional heating step of heating the cooled primary refrigerant stream while recovering the cold heat of the liquefied gas in the primary refrigerant power generation step.

[0035] Preferably, the primary refrigerant heating step may include a second auxiliary refrigerant cold heat recovery step of recovering the cold heat of the liquefied gas in the primary refrigerant power generation step and heat-exchanging the cooled primary refrigerant stream with the auxiliary refrigerant stream to recover the remaining cold heat of the primary refrigerant stream; and a primary refrigerant additional heating step of further heating the primary refrigerant stream heated in the second auxiliary refrigerant cold heat recovery step.

[0036] Preferably, the primary refrigerant power generation stage can operate in a Brayton cycle, and the secondary refrigerant power generation stage can operate in a Rankine cycle.

[0037] The serial loop power generation system and method using the cold energy of liquefied gas according to the present invention can produce clean energy using the ultra-low temperature cold energy that is wasted without consuming fuel or undergoing oxidation.

[0038] In addition, by applying a serial loop, the cold energy of the liquefied gas is recovered over multiple cycles, thereby further improving energy production efficiency compared to a system applying a single loop.

[0039] Additionally, it can be applied modularly to existing liquefied gas terminals and other sites equipped with liquefied gas vaporization facilities, minimizing disruption or alteration to existing facilities. In particular, existing liquefied gas vaporizers can be utilized.

[0040] In addition, it is efficient because the number of loops connected in series can be easily adjusted according to the capacity or type of liquefied gas in a modular form.

[0041] In addition, the refrigerant introduced into the compressor can be cooled to reduce the energy consumed for compression, the expansion ratio can be maximized to optimize the system, and the cold energy utilization efficiency, i.e., the power generation efficiency, of the cold energy power generation system can be improved.

[0042] In addition, by branching the expanded refrigerant stream from the turbine-generator, cooling some of it by recovering the cold heat of the liquefied gas in a heat exchanger and then compressing it, and cooling the remaining part by recovering the remaining cold heat of the compressed refrigerant stream after recovering the cold heat of the liquefied gas and then compressing it, the refrigerant before compression can be cooled using only the cold heat of the liquefied gas without having a separate cooling cycle.

[0043] Additionally, the expansion energy obtainable from the turbine-generator can be maximized by further recovering cold heat in the auxiliary refrigerant cycle before supplying the refrigerant compressed in the compressor to the turbine-generator.

[0044] Additionally, applying a series loop cycle can increase the overall power generation efficiency compared to applying a single loop cycle under the same conditions.

[0045] Additionally, by using different refrigerants depending on the operating temperature, the compression means can be replaced with a pump, which has much lower installation and operating costs, making it economical.

[0046] Additionally, since it is possible to use easily available refrigerants such as nitrogen and evaporative gas, the operating costs (OPEX) required for refrigerant replenishment can be reduced.

[0047] The effects of the present invention are not limited to those described above. Other effects not mentioned will be readily apparent to those skilled in the art from this specification and the accompanying drawings.

[0048] FIG. 1 is a drawing schematically illustrating the basic configuration of a series loop power generation system using the cold energy of liquefied gas according to the first embodiment of the present invention.

[0049] FIG. 2 is a schematic diagram illustrating a series loop power generation system using the cold energy of liquefied gas according to a second embodiment of the present invention.

[0050] FIG. 3 is a PT diagram for explaining the phase while the main refrigerant circulates through the cycle according to one embodiment of the present invention.

[0051] In order to fully understand the operational advantages of the present invention and the objects achieved by the embodiments of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

[0052] Hereinafter, the configuration and operation of preferred embodiments of the present invention will be described in detail with reference to the attached drawings. When adding reference numerals to components in each drawing, it should be noted that, as much as possible, identical components are indicated with the same numerals even if they are shown in different drawings. In addition, the following embodiments may be modified in various different forms, and the scope of the present invention is not limited to the following embodiments.

[0053] In the embodiments of the present invention described below, the liquefied gas may be a liquefied gas that can be transported by liquefying gas at a low temperature, and may be, for example, a hydrocarbon-based liquefied gas such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), liquefied ethylene gas, or liquefied propylene gas. Alternatively, it may be a non-hydrocarbon-based liquefied gas such as liquefied carbon dioxide, liquefied hydrogen, or liquefied ammonia. However, in the embodiments described below, the liquefied gas will be described by taking LNG as an example.

[0054] In addition, the power generation system and method using the cold heat of liquefied gas according to the embodiments of the present invention described below can be applied on land where a heat exchanger for recovering the cold heat of liquefied gas is provided, such as a liquefied gas introduction terminal, a liquefied gas thermal power plant, a liquefied gas filling station, and a liquefied gas fuel-propelled mobility. In the embodiments of the present invention described below, the power generation system using the cold heat of liquefied gas will be described by taking as an example one provided at a liquefied gas introduction terminal.

[0055] In addition, the power generation system and method using cold energy from liquefied gas according to embodiments of the present invention described below can also be applied to ships or oceans. Here, the term "ship" may include all types of ships equipped with LNG regasification facilities capable of regasifying LNG and supplying it to gas demanders, including ships with self-propulsion capabilities such as LNG RVs (Regasification Vessels) and liquefied gas fuel-propelled ships, as well as offshore structures floating on the sea such as LNG FSRUs (Floating Storage Regasification Units).

[0056]

[0057] Hereinafter, a series loop power generation system and method using liquefied gas cooling according to embodiments of the present invention will be described with reference to the attached drawings.

[0058] The serial loop power generation system using the cold heat of liquefied gas according to the present embodiment may include a main refrigerant cycle (100) that generates power by recovering cold heat of LNG while the main refrigerant circulates, and an auxiliary refrigerant cycle (300) that is provided downstream of the main refrigerant cycle (100) and generates power by recovering residual cold heat of LNG from which cold heat has been recovered in the main refrigerant cycle (100) while the auxiliary refrigerant circulates.

[0059] In this embodiment, the serial loop power generation system is described as being equipped with a two-stage tandem loop cycle in which two loop cycles, such as a main refrigerant cycle (100) and an auxiliary refrigerant cycle (300), are connected in series. However, the serial loop power generation system according to the present invention may include a multi-stage serial loop cycle of two or more stages, such as one or more auxiliary refrigerant cycles (300) connected to the main refrigerant cycle (100).

[0060] For example, it may be equipped with a 3-stage tandem loop cycle in which three loop cycles, including a main refrigerant cycle, an auxiliary refrigerant cycle, and an additional auxiliary refrigerant cycle, are connected in series.

[0061] In the case of a two-stage serial loop cycle in which two loop cycles are connected in series as in this embodiment, the main refrigerant circulating in the main refrigerant cycle (100) first recovers the cold heat of LNG and generates power, and the auxiliary refrigerant circulating in the auxiliary refrigerant cycle (300) secondarily recovers the remaining cold heat of at least one of the LNG and the main refrigerant, from which the cold heat was first recovered in the main refrigerant cycle (100), and generates power.

[0062] In the case of a three-stage serial loop cycle in which three loop cycles are connected in series, in the first stage, the main refrigerant circulating in the main refrigerant cycle recovers the cold heat of LNG and the cold heat of the main refrigerant itself to generate power, in the second stage, the auxiliary refrigerant circulating in the auxiliary refrigerant cycle further recovers the residual cold heat of at least one of the LNG and the main refrigerant from which the cold heat was first recovered in the main refrigerant cycle to generate power, and in the third stage, the auxiliary refrigerant circulating in the additional auxiliary refrigerant cycle can further recover the residual cold heat of at least one of the main refrigerant or the auxiliary refrigerant from which the cold heat was recovered in the auxiliary refrigerant cycle to generate power.

[0063] Each loop cycle connected in series may include a turbine-generator that generates electricity by driving a turbine using the refrigerant circulating in each loop cycle connected in series, an economizer that cools the refrigerant expanded in the turbine-generator with the cold heat of LNG, a compressor that compresses the refrigerant cooled in the economizer, and a heater that heats the refrigerant compressed in the compressor. The refrigerant heated in the heater may be recycled back to the turbine-generator.

[0064] Each loop cycle may be equipped with one or more economizers that recover the cold heat of the LNG or the cooling heat of the working fluid circulating in each loop cycle to cool the refrigerant expanded in the turbine-generator. The process of recovering the cold heat of the LNG in the economizer may be performed in two or more stages.

[0065] Additionally, each loop cycle constituting the series loop power generation system can operate as a Brayton cycle or a Rankine cycle.

[0066] However, among the loop cycles composed of multiple stages, the loop cycle placed at the very first stage may be operated as a Brayton cycle for the purpose of recovering a large amount of cold energy since the temperature of the liquefied gas is at an extremely low temperature, and the loop cycle placed at the very last stage may be operated as a Rankine cycle to control the temperature of the liquefied gas to the temperature required by the liquefied gas demander.

[0067] Additionally, downstream of the loop cycle operating with the Brayton cycle, at least one loop cycle operating with the Rankine cycle may be arranged.

[0068] In this embodiment, it will be described based on a two-stage serial loop cycle including a main refrigerant cycle (100) operating in a Brayton cycle upstream and an auxiliary refrigerant cycle (300) operating in a Rankine cycle downstream of the main refrigerant cycle (100).

[0069] Meanwhile, each loop cycle is equipped with N economizers, capable of recovering cold heat or residual cold heat from LNG across N stages. Furthermore, a compressor corresponding to each economizer may be equipped at the rear of each of the N economizers.

[0070] As the temperature of a fluid decreases, its density increases, thus reducing the energy consumed for compression. According to the present embodiment, the refrigerant stream (RL, CL) discharged from a turbine-generator is divided into two or more streams at a branch point, cooled in each economizer, and then compressed, thereby reducing the energy consumed for compression.

[0071] Meanwhile, the higher the temperature of the fluid introduced into the turbine, the more energy generated by expansion. According to the present embodiment, by providing a heater to heat the compressed refrigerant stream (RL, CL) before supplying it to the turbine-generator, the energy generated by expansion, i.e., the amount of power generated, can be increased.

[0072] When the loop cycle is equipped with N stages, the loop cycle may further include a branching section that branches the refrigerant circulating in the loop cycle into N refrigerant streams upstream of the economizer, and a joining section that joins the N refrigerant streams back into one stream downstream of each economizer.

[0073] Here, the economizer may be a plate type heat exchanger, a plate-fin type heat exchanger, a printed circuit heat exchanger (PCHE), a brazed aluminum heat exchanger (BAHX), or a coil-wound heat exchanger (CWHX).

[0074] In addition, although the drawings attached to this specification illustrate an example in which multiple economizers are provided as individual heat exchangers, at least two of the multiple economizers may be provided as a multi-stream heat exchanger as a single cold box.

[0075] In addition, multiple economizers may be provided as one cold box, such as the economizers of each cycle, for example, the main refrigerant economizers of the main refrigerant cycle (100), or economizers of different cycles, for example, at least one main refrigerant economizer among the main refrigerant economizers of the main refrigerant cycle (100) and at least one auxiliary refrigerant economizer among the auxiliary refrigerant economizers of the auxiliary refrigerant cycle (300), may be provided as one cold box.

[0076] The confluence is not limited to converging N refrigerant streams into a single refrigerant stream. The confluence may confluence the N streams into a number of refrigerant streams equal to the number of heaters that heat them. For example, if two heaters are installed in parallel, the confluence may confluence the N refrigerant streams into two refrigerant streams and supply them to the two heaters.

[0077] The branch section may be provided downstream of the turbine-generator and upstream of the economizer, or may be provided upstream of the turbine-generator.

[0078] That is, the branch section may distribute and supply the expanded refrigerant stream from one or more turbine-generators to each economizer, or may distribute the refrigerant stream from the branch section into N refrigerant streams and then supply them to each of N turbine-generators. If the branch section is installed upstream of the turbine-generator, N turbine-generators may be installed in one-to-one correspondence with N economizers.

[0079] The drawing illustrates, as an example, that a branch section (120, 320) of each loop cycle is provided downstream of each turbine-generator (110, 310) to branch the expanded refrigerant stream from one turbine-generator (110, 310) into N refrigerant streams and supply them to each economizer (130, 140b, 330, 340). This embodiment is described based on this.

[0080] However, the branch (120, 320) of each loop cycle may be provided upstream of the turbine-generator (110, 310) of each loop cycle, and may be configured to branch into N refrigerant streams at the branch (120, 320), and each refrigerant stream may be divided and supplied to N turbine-generators, expanded respectively, and then divided and supplied to N economizers respectively.

[0081] In this embodiment, the branch section (120, 320) may mean a point where the line through which the expanded refrigerant stream flows in the turbine-generator (110, 310) is divided into N. The branch section (120, 320) may be equipped with a distributor or valve.

[0082] The first embodiment of the present invention illustrated in FIG. 1 is described as an example in which the main refrigerant cycle (100) is provided in two stages including two economizers (130, 140b). Meanwhile, the second embodiment of the present invention illustrated in FIG. 2 is described as an example in which the main refrigerant cycle (100) is provided in nine stages including nine economizers (130, 140b, 140c, 140d, 140e, 140f, 140g, 140h, 140i). However, the number of stages of the main refrigerant cycle (100) is not limited.

[0083] Meanwhile, in the present embodiments, the primary and secondary refrigerants may be fluids of different substances. In describing the present embodiments, the terms "primary" and "auxiliary" are merely used to distinguish the primary and secondary refrigerants, and do not imply that one refrigerant is primarily used and the other is used as an auxiliary refrigerant.

[0084] The operating pressure of the main refrigerant cycle (100) of the present embodiment may be 5 barg or higher or the critical pressure of the main refrigerant circulating in the main refrigerant cycle (100). In addition, the operating temperature of the main refrigerant cycle (100) of the present embodiment may be -60°C or lower or 0°C or lower.

[0085] The primary and secondary refrigerants may be different substances or the same substance.

[0086] The main refrigerant and auxiliary refrigerant of the present embodiment may each be a single refrigerant selected from the group consisting of hydrogen, helium, nitrogen, oxygen, neon, argon, carbon compounds having 5 or fewer carbon atoms, and freon refrigerants, or a mixed refrigerant of two or more of these.

[0087] Meanwhile, the auxiliary refrigerant of the present embodiment may be a hydrocarbon compound, i.e., an organic compound.

[0088] Additionally, in this embodiment, the primary refrigerant and the secondary refrigerant may be substances that do not reach the freezing point even at the point where the lowest temperature is reached during each cycle.

[0089] Additionally, the main refrigerant may be a vaporization gas of a liquefied gas or a mixture containing vaporization gas of a liquefied gas, and the auxiliary refrigerant may be a single or mixture having a boiling point higher than that of the main refrigerant.

[0090] By using the evaporation gas of the liquefied gas, which is the target of cold heat recovery, as the main refrigerant, not only can the cold heat of vaporization of the liquefied gas be recovered without reaching the freezing point while the main refrigerant circulates through the main refrigerant cycle (100), but also the cost of processing the evaporation gas can be reduced and there is the advantage of easy supply.

[0091] When using nitrogen as a refrigerant, the freezing point of nitrogen is an extremely low temperature of approximately -210℃ at normal pressure, so nitrogen can be used as a refrigerant that does not reach the freezing point while circulating the cycle as a single refrigerant.

[0092] In addition, nitrogen is an inert gas that is easy to obtain from the air, so it is inexpensive and safe to purchase, and since it does not contain carbon, it can be vented into the air, which has the advantage of not requiring a flare device. When the power generation system according to the present embodiment is applied on land where a liquefied gas regasification facility such as a liquefied gas terminal is installed, or when the power generation system according to the present embodiment is applied at sea where a liquefied gas regasification facility such as an FSRU is installed, in any case, equipment for generating and supplying nitrogen is installed for the purpose of purging or maintaining the regasification facility. That is, when nitrogen is used as the working fluid of the power generation system according to the present embodiment, the working fluid can be easily supplied even without a separate nitrogen generation / supply device, and installation and operating costs can be reduced by using the installed equipment.

[0093] Meanwhile, the power generation system using the Brayton Cycle, which uses supercritical carbon dioxide as a working fluid, is not suitable for recovering cold heat because the freezing point of carbon dioxide, which is the working fluid, is approximately -78.5℃ at normal pressure, and thus the problem of freezing may occur during the process of recovering cold heat from LNG supplied at approximately -155℃.

[0094] In addition, carbon dioxide is a greenhouse gas that causes environmental pollution, is an acid gas that causes equipment corrosion, and is dangerous to the human body when exposed to a certain concentration or higher for a long period of time. In addition, in order to maintain carbon dioxide at a pressure higher than the critical pressure, the system must be maintained in a high-pressure environment with an operating pressure of 200 barg or higher, making it difficult to apply in practice.

[0095] In this embodiment, boil-off gas (BOG) containing methane (CH4) as its main component and generated by natural vaporization of LNG, the liquefied gas of this embodiment, is used as a main refrigerant, and as an auxiliary refrigerant, propane (C3H8), a representative organic refrigerant, is used as a single refrigerant, as an example.

[0096] First, referring to FIG. 1, a series loop power generation system utilizing cold energy from liquefied gas according to a first embodiment of the present invention will be described.

[0097] The series loop power generation system according to the present embodiment may include a primary refrigerant cycle (100) in which a primary refrigerant stream (RL) circulates and primarily recovers cold heat from LNG to generate power, and an auxiliary refrigerant cycle (300) arranged in series downstream of the primary refrigerant cycle (100) and in which an auxiliary refrigerant stream (CL) circulates and recovers residual cold heat from at least one of LNG or the primary refrigerant from which cold heat has been recovered in the primary refrigerant cycle (100) to generate power.

[0098] The primary refrigerant cycle (100) may include a primary refrigerant turbine-generator (110) that generates power by driving a turbine using a primary refrigerant stream (RL), and a primary refrigerant branch unit (120) that branches the primary refrigerant stream (RL) expanded in the primary refrigerant turbine-generator (110) into two streams including a first primary refrigerant stream (RL1) and a second primary refrigerant stream (RL2).

[0099] The first main refrigerant stream (RL1) and the second main refrigerant stream (RL2) are names used to distinguish and describe the streams that are divided by branching the main refrigerant stream (RL). The first main refrigerant stream (RL1) and the second main refrigerant stream (RL2) are the same substance that flows along different paths after branching at the main refrigerant branching section (120), is compressed, and joins into one main refrigerant stream (RL) upstream of the main refrigerant heater (170) to circulate the main refrigerant cycle (100).

[0100] In addition, the primary refrigerant cycle (100) of the present embodiment may include a first primary refrigerant economizer (130) that heat-exchanges LNG supplied through a liquefied gas line (LL) with a first primary refrigerant stream (RL1), a first primary refrigerant compressor (150a) that compresses the first primary refrigerant stream (RL1) cooled by heat-exchanging with LNG in the first primary refrigerant economizer (130), a second primary refrigerant economizer (140b) that heat-exchanges the first primary refrigerant stream (RL1) compressed in the first primary refrigerant compressor (150a) with a second primary refrigerant stream (RL2), and a second primary refrigerant compressor (150b) that compresses the second primary refrigerant stream (RL2) cooled by heat-exchange with the first primary refrigerant stream (RL1) in the second primary refrigerant economizer (140b).

[0101] According to the present embodiment, the expanded primary refrigerant stream (RL) in the primary refrigerant turbine-generator (110) is divided into at least two streams including a first primary refrigerant stream (RL1) and a second primary refrigerant stream (RL2), and the remaining cold heat of the first primary refrigerant stream (RL1), from which cold heat is recovered from LNG in the first primary refrigerant economizer (130), is further recovered in the second primary refrigerant economizer (140b), thereby increasing the flow rate of the circulating refrigerant and thus increasing the amount of electricity produced by the turbine.

[0102] The first main refrigerant stream (RL1) heated by heat exchange in the second main refrigerant economizer (140b) and the second main refrigerant stream (RL2) cooled by heat exchange in the second main refrigerant economizer (140b) can be combined into the main refrigerant stream (RL) and recirculated to the main refrigerant turbine-generator (110).

[0103] The primary refrigerant cycle (100) of the present embodiment is provided upstream of the primary refrigerant turbine-generator (110), and may further include a primary refrigerant combining unit (160) that combines a first primary refrigerant stream (RL1) heated in a second primary refrigerant economizer (140b) and a second primary refrigerant stream (RL2) cooled in a second primary refrigerant economizer (140b) into one primary refrigerant stream (RL).

[0104] The first main refrigerant stream (RL1) and the second main refrigerant stream (RL2) that are recycled to the main refrigerant turbine-generator (110) after heat exchange in the main refrigerant economizer (130, 140b) can be combined into the main refrigerant stream (RL) at the main refrigerant junction (160) and transferred to the main refrigerant turbine-generator (110).

[0105] Additionally, the primary refrigerant cycle (100) according to the present embodiment may further include a primary refrigerant heater (170) for heating the primary refrigerant stream (RL) recycled to the primary refrigerant turbine-generator (110).

[0106] The heat source for heating the main refrigerant stream (RL) in the main refrigerant heater (170) of the present embodiment may be seawater (SW), fresh water, combustion gas, or the atmosphere, but is not limited thereto.

[0107] By heating the main refrigerant stream (RL) introduced into the main refrigerant turbine-generator (110) using the main refrigerant heater (170), the inlet temperature of the turbine-generator can be increased, thereby increasing the expansion work that can be generated through the turbine, i.e., the power generation amount of the main refrigerant turbine-generator (110).

[0108] The drawing illustrates an example in which one main refrigerant heater (170) is provided. However, this is not limited to this, and one or more main refrigerant heaters (170) may be provided in series or in parallel.

[0109] For example, two main refrigerant heaters (170) are installed in series, and the main refrigerant streams that have been branched into multiple flows are combined into one main refrigerant stream (RL) at a junction, and can be heated in two stages while sequentially passing through the two main refrigerant heaters (170) connected in series.

[0110] As another example, two primary refrigerant heaters (170) may be installed in parallel, and the primary refrigerant streams that were branched into multiple flows may be combined into two primary refrigerant streams at a junction, and the two combined primary refrigerant streams may be distributed and supplied to two primary refrigerant heaters (170) installed in parallel.

[0111] Referring to FIG. 3, the primary refrigerant remains in a critical region (CA) maintained at a pressure higher than the critical pressure while circulating the primary refrigerant cycle (100), and therefore, the phase of the primary refrigerant becomes a compressible fluid or a supercritical fluid.

[0112] Since the primary refrigerant is maintained above the critical pressure while circulating in the primary refrigerant cycle (100), the pinch point of the primary refrigerant economizer (130, 140b) does not exist inside the device, or at least the effect occurs at a low temperature near the end of the heat exchanger, thereby maximizing heat exchange performance. In addition, since slugging does not occur, there is almost no piping stress applied to the piping through which the working fluid flows.

[0113] Additionally, in this embodiment, the primary refrigerant may be maintained in a supercritical state while circulating the primary refrigerant cycle (100). If the primary refrigerant is maintained in a supercritical state, the primary refrigerant flows in a high density state, allowing the size of the power generation system to be reduced.

[0114] Meanwhile, according to the present embodiment, LNG supplied to the first primary refrigerant economizer (130) along the liquefied gas line (LL) may be heated by losing cold heat while exchanging heat with the first primary refrigerant stream (RL1) in the first primary refrigerant economizer (130), or at least partially vaporized. LNG that has lost cold heat while exchanging heat with the first primary refrigerant stream (RL1) in the first primary refrigerant economizer (130) may be supplied to a gas consumer through the liquefied gas line (LL).

[0115] The serial loop power generation system according to the present embodiment may further include a liquefied gas heater (200) provided downstream of the first primary refrigerant economizer (130) and heating LNG that is heated by heat exchange in the first primary refrigerant economizer (130) and supplied to a gas demand source.

[0116] The heat source for heating LNG in the liquefied gas heater (200) of this embodiment may be seawater (SW), fresh water, combustion gas, or the atmosphere, but is not limited thereto.

[0117] LNG introduced in a liquid state from the first primary refrigerant economizer (130) to the liquefied gas heater (200) can be heated in the liquefied gas heater (200) and completely vaporized. In addition, LNG introduced in a gaseous state from the first primary refrigerant economizer (130) to the liquefied gas heater (200), i.e., regasification gas, can be heated to a temperature required by a gas demander in the liquefied gas heater (200). The regasification gas transferred from the liquefied gas heater (200) to the gas demander can satisfy the temperature conditions required by the gas demander.

[0118] The drawing illustrates an example in which one liquefied gas heater (200) is provided. However, this is not limited to this, and one or more liquefied gas heaters (200) may be provided in series or in parallel.

[0119] For example, two liquefied gas heaters (200) may be installed in series, and LNG may be heated in two stages by sequentially passing through the two liquefied gas heaters (200) connected in series. As another example, two liquefied gas heaters (200) may be installed in parallel, and LNG may be distributed and supplied to the two liquefied gas heaters (200) installed in parallel.

[0120] The auxiliary refrigerant cycle (300) of the present embodiment can be connected in series to the above-described main refrigerant cycle (100) in one or more stages.

[0121] In addition, the auxiliary refrigerant cycle (300) may be in a modular form that can be easily attached or detached from the main refrigerant cycle (100), or may be connected to the main refrigerant cycle (100) in a structure that can be easily opened or closed. The auxiliary refrigerant cycle (300) can be easily attached or detached or connected or closed without changing the basic configuration of the main refrigerant cycle (100) or interfering with its operation.

[0122] For example, the main refrigerant cycle (100) is installed in a liquefied gas introduction terminal, and an additional cycle, i.e., an auxiliary refrigerant cycle (300) connected in series with the main refrigerant cycle (100), can be connected in a module form so as to be detachably connected to the main refrigerant cycle (100).

[0123] The auxiliary refrigerant cycle (300) may be connected through at least one of a liquefied gas line (LL) (hereinafter referred to as a “first connection point”), which is connected to the first main refrigerant economizer (130) and the liquefied gas heater (200) and through which liquefied gas flows, and a line (hereinafter referred to as a “second connection point”), which is connected to the main refrigerant junction (160) and the main refrigerant heater (170) and through which the main refrigerant stream (RL) flows.

[0124] When the auxiliary refrigerant cycle (300) is connected through the first connection point, the cold heat of the liquefied gas transferred after the cold heat is recovered from the first main refrigerant economizer (130) can be additionally recovered. In addition, when connected through the second connection point, the auxiliary refrigerant cycle (300) can additionally recover the cold heat of the main refrigerant stream (RL) transferred from the main refrigerant junction (160). In addition, when connected through both the first connection point and the second connection point, the cold heat of the liquefied gas and the cold heat of the main refrigerant stream (RL) can both be recovered and utilized.

[0125] The auxiliary refrigerant cycle (300) of the present embodiment may include an auxiliary refrigerant turbine-generator (310) that generates power by driving a turbine using an auxiliary refrigerant stream (CL), an auxiliary refrigerant economizer (330, 340) that cools the auxiliary refrigerant stream (CL) expanded in the auxiliary refrigerant turbine-generator (310), an auxiliary refrigerant pump (360) that pressurizes the liquid auxiliary refrigerant stream (CL) generated while being cooled in the auxiliary refrigerant economizer (330, 340), and an auxiliary refrigerant heater (370) that is provided downstream of the auxiliary refrigerant pump (360) and heats the auxiliary refrigerant stream (CL) pressurized in the auxiliary refrigerant pump (360) and recirculates it to the auxiliary refrigerant turbine-generator (310).

[0126] The auxiliary refrigerant stream (CL) that is expanded while generating power in the auxiliary refrigerant turbine-generator (310) and then supplied to the auxiliary refrigerant economizer (330, 340) may be in a gaseous state or a gas-liquid mixed state. The auxiliary refrigerant stream (CL) in a gaseous state or a gas-liquid mixed state may be phase-changed into a liquid state through heat exchange in the auxiliary refrigerant economizer (330, 340) or may be supercooled without a phase change in the liquid state.

[0127] The liquid auxiliary refrigerant stream (CL) discharged after heat exchange from the auxiliary refrigerant economizer (330, 340) is pressurized by the auxiliary refrigerant pump (360) and transferred to the auxiliary refrigerant heater (370). The pressurized liquid auxiliary refrigerant stream (CL) supplied to the auxiliary refrigerant heater (370) can change into a gaseous state while being heated by heat exchange.

[0128] That is, unlike the main refrigerant stream (RL) that is maintained above the critical pressure while circulating the main refrigerant cycle (100), the auxiliary refrigerant stream (CL) that is circulated through the auxiliary refrigerant cycle (300) can undergo a total of two phase changes through heat exchange in the auxiliary refrigerant economizer (330, 340) and the auxiliary refrigerant heater (370).

[0129] The heat source for heating the auxiliary refrigerant stream (CL) in the auxiliary refrigerant heater (370) of the present embodiment may be seawater (SW), fresh water, combustion gas, or the atmosphere, but is not limited thereto.

[0130] The drawing illustrates an example in which one auxiliary refrigerant heater (370) is provided. However, this is not limited to this, and one or more auxiliary refrigerant heaters (370) may be provided in series or in parallel.

[0131] For example, two auxiliary refrigerant heaters (370) are installed in series, and auxiliary refrigerant streams that have been branched into multiple flows are combined into one auxiliary refrigerant stream (CL) at a junction, and can be heated in two stages while sequentially passing through two auxiliary refrigerant heaters (370) connected in series.

[0132] As another example, two auxiliary refrigerant heaters (370) may be installed in parallel, and the auxiliary refrigerant stream may be distributed and supplied to the two auxiliary refrigerant heaters (370) installed in parallel.

[0133] Meanwhile, when the auxiliary refrigerant cycle (300) is connected to the liquefied gas line (LL) through the first connection point, the auxiliary refrigerant economizer (330, 340) may include a first auxiliary refrigerant economizer (330) for recovering residual cold heat of LNG by heat-exchanging the auxiliary refrigerant stream expanded in the auxiliary refrigerant turbine-generator (310) and LNG from which cold heat has been primarily recovered in the main refrigerant cycle (100).

[0134] LNG, which has lost its cold heat during heat exchange in the first primary refrigerant economizer (130), can be transported to the gas demand source after the remaining cold heat is further recovered in the auxiliary refrigerant cycle (300) before being supplied to the gas demand source through the liquefied gas line (LL). In addition, the auxiliary refrigerant stream can change into a liquid state while recovering the remaining cold heat of the LNG in the first secondary refrigerant economizer (330).

[0135] In addition, when the auxiliary refrigerant cycle (300) is connected to the liquefied gas line (LL) through the first connection point, a liquefied gas heating line (LL1) may be provided that connects the first main refrigerant economizer (130) and the liquefied gas heater (200) and branches off from the liquefied gas line (LL) through which the liquefied gas flows and is connected to the first auxiliary refrigerant economizer (330).

[0136] The liquefied gas heating line (LL1) branches off from the liquefied gas line (LL) downstream of the first main refrigerant economizer (130) and is connected to the liquefied gas inlet side of the first auxiliary refrigerant economizer (330), and can be connected from the liquefied gas outlet side of the first auxiliary refrigerant economizer (330) to the liquefied gas line (LL) upstream of the liquefied gas heater (200).

[0137] In addition, a liquefied gas bypass line (LL2) connected from the liquefied gas outlet side of the first auxiliary refrigerant economizer (330) to the liquefied gas line (LL) downstream of the liquefied gas heater (200) may be further included.

[0138] LNG, from which cold heat has been recovered in the first main refrigerant economizer (130), can be heated by passing through at least one of the liquefied gas heater (200) and the first auxiliary refrigerant economizer (330) and then supplied to a gas demand source.

[0139] In the case where the auxiliary refrigerant cycle (300) is not connected to the first connection point, the liquefied gas (including regasified gas) from which cold heat has been recovered in the first main refrigerant economizer (130) as described above can be transported to a gas demand source via the liquefied gas heater (200), and in the case where the auxiliary refrigerant cycle (300) is connected to the liquefied gas line (LL) through the first connection point, the flow of LNG is as follows.

[0140] The liquefied gas from which cold heat has been recovered in the first main refrigerant economizer (130) can be heated by first recovering cold heat through heat exchange with the auxiliary refrigerant stream in the first auxiliary refrigerant economizer (330).

[0141] At this time, if the temperature of the LNG discharged from the first auxiliary refrigerant economizer (330) is lower than the temperature required by the gas demander, the LNG discharged from the first auxiliary refrigerant economizer (330) is supplied to the liquefied gas line (LL) upstream of the liquefied gas heater (200) through the liquefied gas heating line (LL1), and can be transported to the gas demander after being heated to the temperature required by the gas demander in the liquefied gas heater (200).

[0142] If the temperature of the LNG discharged from the first auxiliary refrigerant economizer (330) satisfies the temperature required by the gas demander, the LNG discharged from the first auxiliary refrigerant economizer (330) is supplied to the liquefied gas line (LL) at the rear end of the liquefied gas heater (200) through the liquefied gas bypass line (LL2), and can be transported to the gas demander by bypassing the liquefied gas heater (200).

[0143] In this embodiment, the temperature required by the gas demand source may be approximately 0°C.

[0144] Meanwhile, LNG from which cold heat has been recovered in the first main refrigerant economizer (130) may be distributed into two streams, one stream recovering cold heat in the first auxiliary refrigerant economizer (330) and the other stream recovering cold heat in the liquefied gas heater (200), and then the two streams may be combined and supplied to a gas demand source.

[0145] In this case, the flow rate of LNG is distributed into two flows so that, among the flow rates of LNG discharged while cold heat is recovered from the first main refrigerant economizer (130), the maximum flow rate that the load of the first auxiliary refrigerant economizer (330) can handle is supplied to the first auxiliary refrigerant economizer (330), and the remainder is supplied to the liquefied gas heater (200).

[0146] By maximizing the flow rate of LNG supplied to the first auxiliary refrigerant economizer (330) and minimizing the flow rate of LNG heated in the liquefied gas heater (200), the amount of power generation that can be generated in the auxiliary refrigerant cycle (300) can be maximized while minimizing the heating duty of the liquefied gas heater (200), thereby improving the power generation efficiency of the entire cycle.

[0147] Meanwhile, when the auxiliary refrigerant cycle (300) is connected to the main refrigerant cycle (100) through a second connection point, the auxiliary refrigerant economizer (330, 340) may include a second auxiliary refrigerant economizer (340) for recovering residual cold heat of the main refrigerant stream (RL) by heat-exchanging the auxiliary refrigerant stream expanded in the auxiliary refrigerant turbine-generator (310) and the main refrigerant stream (RL) transferred from the main refrigerant junction (160) of the main refrigerant cycle (100).

[0148] The primary refrigerant stream (RL), which recovers its own cooling heat from the primary refrigerant economizers and is recycled to the primary refrigerant turbine-generator (110) through the primary refrigerant junction (160), can be transferred to the primary refrigerant turbine-generator (110) after further recovering the remaining cooling heat in the auxiliary refrigerant cycle (300). The auxiliary refrigerant stream can be phase-changed to a liquid state while recovering the remaining cooling heat of the LNG in the second auxiliary refrigerant economizer (340).

[0149] In addition, when the auxiliary refrigerant cycle (300) is connected to the main refrigerant cycle (100) through the second connection point, the auxiliary refrigerant cycle (300) and the main refrigerant cycle (100) can be connected by a main refrigerant heating line (RLa) that connects the main refrigerant junction (160) and the main refrigerant heater (170) and branches from a line through which the main refrigerant stream (RL) flows and is connected to a second auxiliary refrigerant economizer (340).

[0150] The main refrigerant heating line (RLa) branches off from the line through which the main refrigerant stream (RL) flows downstream of the main refrigerant junction (160) and is connected to the main refrigerant inlet side of the second auxiliary refrigerant economizer (340), and can be connected from the main refrigerant outlet side of the second auxiliary refrigerant economizer (340) to the upstream side of the main refrigerant heater (170).

[0151] In addition, a main refrigerant bypass line (RLb) connected from the main refrigerant outlet side of the second auxiliary refrigerant economizer (340) to the downstream side of the main refrigerant heater (170) may be further included.

[0152] The main refrigerant stream (RL) recycled from the main refrigerant junction (160) to the main refrigerant turbine-generator (110) may be heated by passing through at least one of the main refrigerant heater (170) and the second auxiliary refrigerant economizer (340) and then supplied to the main refrigerant turbine-generator (110).

[0153] In the case where the auxiliary refrigerant cycle (300) is not connected to the main refrigerant cycle (100) through the second connection point, the main refrigerant stream (RL) joined at the main refrigerant joining portion (160) as described above can be transferred to the main refrigerant turbine-generator (110) via the main refrigerant heater (170), and the flow of the main refrigerant stream (RL) in the case where the auxiliary refrigerant cycle (300) is connected to the main refrigerant cycle (100) through the second connection point is as follows.

[0154] The primary refrigerant stream (RL) can first be heated by recovering residual cold heat through heat exchange with the secondary refrigerant stream in the secondary refrigerant economizer (340).

[0155] At this time, if the temperature of the main refrigerant stream (RL) discharged from the second auxiliary refrigerant economizer (340) is lower than the temperature of the heat source used in the main refrigerant heater (170), the main refrigerant stream (RL) discharged from the second auxiliary refrigerant economizer (340) can be supplied upstream of the main refrigerant heater (170) through the main refrigerant heating line (RLa), and after being further heated in the main refrigerant heater (170), can be supplied to the main refrigerant turbine-generator (110).

[0156] By heating the main refrigerant stream (RL) supplied to the main refrigerant turbine-generator (110) as much as possible to increase the volume of the main refrigerant stream (RL), the power generation of the main refrigerant cycle (100) can be increased.

[0157] If the temperature of the main refrigerant stream (RL) discharged from the second auxiliary refrigerant economizer (340) is higher than or equal to the temperature of the heat source used in the main refrigerant heater (170), the main refrigerant stream (RL) discharged from the second auxiliary refrigerant economizer (340) can be supplied downstream of the main refrigerant heater (170) through the main refrigerant bypass line (RLb), bypassing the main refrigerant heater (170) and being transferred to the main refrigerant turbine-generator (110).

[0158] Meanwhile, the main refrigerant stream (RL) recycled to the main refrigerant turbine-generator (110) may be divided into two flows, one flow recovering residual cold heat in the second auxiliary refrigerant economizer (340), and the other flow recovering cold heat in the main refrigerant heater (170), and then combining the two flows to supply them to the main refrigerant turbine-generator (110).

[0159] In this case, the flow rate of the main refrigerant stream (RL) is distributed into two flows. Among the flow rates of the main refrigerant stream (RL) recycled to the main refrigerant turbine-generator (110), the maximum flow rate that the load of the second auxiliary refrigerant economizer (340) can handle is supplied to the second auxiliary refrigerant economizer (340), and the remainder is supplied to the main refrigerant heater (170).

[0160] By maximizing the flow rate of the main refrigerant stream (RL) supplied to the second auxiliary refrigerant economizer (340) and minimizing the flow rate of the main refrigerant stream (RL) heated in the main refrigerant heater (170), the flow rate of the main refrigerant stream (RL) that cannot be supplied to the auxiliary refrigerant cycle (300) among the main refrigerant streams (RL) recycled to the main refrigerant turbine-generator (110) is heated in the main refrigerant heater (170), thereby reducing the load on the main refrigerant heater (170) and increasing the amount of power generation that can be generated in the main refrigerant cycle (100) and the auxiliary refrigerant cycle (300).

[0161] Meanwhile, when the auxiliary refrigerant cycle (300) is connected to both the first connection point and the second connection point, the auxiliary refrigerant economizer (330, 340) may include both the first auxiliary refrigerant economizer (330) and the second auxiliary refrigerant economizer (340) described above.

[0162] Additionally, in this case, the auxiliary refrigerant cycle (300) may include an auxiliary refrigerant branch unit (320) that branches the expanded auxiliary refrigerant stream (CL) in the auxiliary refrigerant turbine-generator (310) into two streams including a first auxiliary refrigerant stream (CL1) and a second auxiliary refrigerant stream (CL2).

[0163] The first auxiliary refrigerant stream (CL1) branched from the auxiliary refrigerant branch (320) can be cooled while recovering the cold heat of LNG in the first auxiliary refrigerant economizer (330), and the second auxiliary refrigerant stream (CL2) branched from the auxiliary refrigerant branch (320) can be cooled while recovering the cold heat of the main refrigerant in the second auxiliary refrigerant economizer (340).

[0164] The first auxiliary refrigerant stream (CL1) and the second auxiliary refrigerant stream (CL2) are names used to distinguish and describe streams that are branched off from the auxiliary refrigerant stream (CL). The first auxiliary refrigerant stream (CL1) and the second auxiliary refrigerant stream (CL2) may be the same material that is branched off from the auxiliary refrigerant branching section (320), cooled, and then joined into one auxiliary refrigerant stream (CL) upstream of the auxiliary refrigerant heater (370) to circulate through the auxiliary refrigerant cycle (300).

[0165] In addition, when the auxiliary refrigerant cycle (300) is connected to both the first connection point and the second connection point, the auxiliary refrigerant cycle (300) may further include an auxiliary refrigerant combining unit (350) provided in front of the auxiliary refrigerant pump (360) and combining a first auxiliary refrigerant stream (CL1) in a liquid state generated while recovering residual cold heat of LNG in the first auxiliary refrigerant economizer (330) and a second auxiliary refrigerant stream (CL2) in a liquid state generated while recovering residual cold heat of the main refrigerant stream (RL) in the second auxiliary refrigerant economizer (340) into one auxiliary refrigerant stream (CL).

[0166] In this embodiment, a first auxiliary refrigerant stream (CL1) and a second auxiliary refrigerant stream (CL2) in a liquid state are combined into one auxiliary refrigerant stream (CL) at an auxiliary refrigerant junction (350) and then pressurized by an auxiliary refrigerant pump (360) is described as an example.

[0167] However, instead of having an auxiliary refrigerant junction (350), a pump for pressurizing a first auxiliary refrigerant stream (CL1) may be provided downstream of the first auxiliary refrigerant economizer (330), and a pump for pressurizing a second auxiliary refrigerant stream (CL2) may be provided downstream of the second auxiliary refrigerant economizer (340). Alternatively, an auxiliary refrigerant junction may be provided downstream of each pump to combine the pressurized first auxiliary refrigerant stream (CL1) and the second auxiliary refrigerant stream (CL2) into one auxiliary refrigerant stream.

[0168] According to one embodiment of the present invention described above, the remaining cold heat of LNG from which cold heat has been recovered in the main refrigerant cycle (100) is further recovered in the auxiliary refrigerant cycle (300), thereby recovering and utilizing the cold heat of LNG to the maximum extent possible.

[0169] In order to recover the remaining cold heat of LNG in the auxiliary refrigerant cycle (300) using the auxiliary refrigerant after recovering the cold heat of LNG in multiple stages in the primary refrigerant cycle (100) using the primary refrigerant, the number of required equipment may increase compared to the case where the cold heat of LNG is recovered using only one cycle, but the amount of power generated from the turbine-generator of each cycle is greater than the amount of power consumption required to operate the increased number of equipment such as the compressor, and as a result, the power generation efficiency is improved.

[0170] The lower the temperature of the fluid, the higher its density, which reduces the compression work, and the expansion energy generated is greater than the compression energy consumed, which maximizes the amount of power generated.

[0171]

[0172] Referring to FIG. 2, in the case of a series loop power generation system according to the second embodiment of the present invention, in which the liquefied gas is LNG, the main refrigerant is LNG boil-off gas, i.e., methane, the auxiliary refrigerant is propane, the main refrigerant cycle (100) comprises nine economizers (130, 140b, 140c, 140d, 140e, 140f, 140g, 140h, 140i) to recover the cold heat of LNG, and the auxiliary refrigerant cycle comprises two economizers (330, 340) as in the first embodiment to recover the residual cold heat of LNG, it was confirmed that the efficiency was improved compared to the case in which the cold heat of LNG was recovered using a single loop cycle.

[0173] More specifically, it was confirmed that the series loop power generation system according to the present embodiment had an efficiency improvement effect of approximately 53.9% compared to a power generation system that recovers cold heat from LNG using an organic Rankine cycle that uses propane as a refrigerant.

[0174] Hereinafter, the simulation results of the second embodiment of the present invention illustrated in FIG. 2 will be described in more detail.

[0175] The first embodiment described above was a two-stage serial loop power generation system including a two-stage primary refrigerant cycle (100) including two economizers (130, 140b) and in which LNG boil-off gas is circulated as a refrigerant for recovering cold heat of LNG, and an auxiliary refrigerant cycle (300) including two economizers (330, 340) and in which propane is circulated as a refrigerant for recovering cold heat of LNG from which cold heat was first recovered in the primary refrigerant cycle (100).

[0176] The second embodiment is a modified example of the first embodiment, and differs from the first embodiment in that the main refrigerant cycle (100) is a nine-stage cycle including nine economizers (130, 140b, 140c, 140d, 140e, 140f, 140g, 140h, 140i). Although a detailed description is omitted for components using the same drawing reference numerals, the operating principles and effects thereof can be applied in the same manner as in the first embodiment described above.

[0177] The simulation was performed with a primary refrigerant turbine-generator (110) at approximately 160 kg / cm 2 (gauge pressure), the main refrigerant stream (RL) of about 10℃, i.e. LNG boil-off gas, is supplied and drives the turbine, and about 100 kg / cm 2 It was performed based on expansion by (gauge pressure).

[0178] The evaporation gas discharged from the main refrigerant turbine-generator (110) is branched into nine streams including a first main refrigerant stream (RL1), a second main refrigerant stream (RL2), a third main refrigerant stream (RL3), a fourth main refrigerant stream (RL4), a fifth main refrigerant stream (RL5), a sixth main refrigerant stream (RL6), a seventh main refrigerant stream (RL7), an eighth main refrigerant stream (RL8), and a ninth main refrigerant stream (RL9) at the main refrigerant branch (120).

[0179] The flow rates of the first main refrigerant stream (RL1), the second main refrigerant stream (RL2), the third main refrigerant stream (RL3), the fourth main refrigerant stream (RL4), the fifth main refrigerant stream (RL5), the sixth main refrigerant stream (RL6), the seventh main refrigerant stream (RL7), the eighth main refrigerant stream (RL8), and the ninth main refrigerant stream (RL9) may be the same or may be distributed differently.

[0180] The first primary refrigerant stream (RL1) is introduced into the first primary refrigerant economizer (130) and is cooled by recovering the cold heat of the LNG through heat exchange with LNG supplied through the liquefied gas line (LL).

[0181]

[0182] *The simulation assumes that the temperature of LNG supplied through the liquefied gas line (LL) is approximately -138.5℃ and 75.10 kg / cm 2 It was conducted based on (gauge pressure).

[0183] The first primary refrigerant stream (RL1) is cooled to about -131.2°C and discharged through heat exchange in the first primary refrigerant economizer (130), and LNG is heated to about -39.70°C and discharged.

[0184] The first primary refrigerant stream (RL1) cooled while recovering cold heat of LNG in the first primary refrigerant economizer (130) is compressed in the first primary refrigerant compressor (150a) and then supplied to the second primary refrigerant economizer (140b).

[0185] In the second main refrigerant economizer (140b), the second main refrigerant stream (RL2) branched from the main refrigerant branch section (120) and the first main refrigerant stream (RL1) compressed in the first main refrigerant compressor (150a) undergo heat exchange. Through heat exchange in the second main refrigerant economizer (140b), the second main refrigerant stream (RL2) is cooled and discharged, and the first main refrigerant stream (RL1) is heated and discharged.

[0186] The second main refrigerant stream (RL2) cooled by heat exchange in the second main refrigerant economizer (140b) is compressed in the second main refrigerant compressor (150b) and then supplied to the third main refrigerant economizer (140c), and the heated first main refrigerant stream (RL1) is transferred to the main refrigerant junction (160).

[0187] In the third main refrigerant economizer (140c), the third main refrigerant stream (RL3) branched from the main refrigerant branch section (120) and the second main refrigerant stream (RL2) compressed in the second main refrigerant compressor (150b) undergo heat exchange. In the third main refrigerant economizer (140c), the third main refrigerant stream (RL3) is cooled by heat exchange, and the second main refrigerant stream (RL2) is heated and discharged.

[0188] The third main refrigerant stream (RL3) cooled by heat exchange in the third main refrigerant economizer (140c) is compressed in the third main refrigerant compressor (150c) and then supplied to the fourth main refrigerant economizer (140d), and the heated second main refrigerant stream (RL2) is transferred to the main refrigerant junction (160).

[0189] Through this process, in the 9th main refrigerant economizer (140i), which is the last stage economizer of the main refrigerant cycle (100), heat is exchanged between the 9th main refrigerant stream (RL9) branched from the main refrigerant branch section (120) and the 8th main refrigerant stream (RL8) compressed in the 8th main refrigerant compressor (150h), which is the preceding stage. Through heat exchange in the 9th main refrigerant economizer (140i), the 9th main refrigerant stream (RL9) is cooled, and the 8th main refrigerant stream (RL8) is heated and discharged.

[0190] The ninth main refrigerant stream (RL9) cooled by heat exchange in the ninth main refrigerant economizer (140i) is compressed in the ninth main refrigerant compressor (150i).

[0191] The 8th main refrigerant stream (RL8) heated by heat exchange in the 9th main refrigerant economizer (140i) and the 9th main refrigerant stream (RL9) compressed in the 9th main refrigerant compressor (150i) are transferred to the main refrigerant junction (160).

[0192] As a result of the simulation, the temperature of the primary refrigerant stream (RL) generated by the confluence of the first to ninth primary refrigerant streams (RL1 to RL9) at the primary refrigerant confluence (160) is approximately -28.46°C.

[0193] Meanwhile, this simulation is about 5.449 kg / cm with auxiliary refrigerant turbine-generator (310). 2 (gauge pressure), an auxiliary refrigerant stream (CL) of about 10℃, i.e. propane gas, is supplied to drive the turbine and about 2.5 kg / cm 2 It was performed based on expansion by (gauge pressure).

[0194] Auxiliary refrigerant stream (CL) of approximately 2.5 kg / cm 2 By expanding to (gauge pressure), the amount of power generation that can be generated through the auxiliary refrigerant cycle (300) can be maximized. If the outlet pressure is higher than this, the pressure difference between the inlet and outlet of the turbine decreases, reducing the amount of power generation. In addition, if the outlet pressure is lower than this, the temperature of the auxiliary refrigerant decreases further, reducing the temperature difference between the main refrigerant and the auxiliary refrigerant that have passed through the economizer, resulting in less cold heat that can be recovered.

[0195] Additionally, this simulation was conducted on the basis that the auxiliary refrigerant cycle (300) is connected to both the first connection point and the second connection point.

[0196] That is, the expanded auxiliary refrigerant stream (CL) in the auxiliary refrigerant turbine-generator (310) is branched into a first auxiliary refrigerant stream (CL1) and a second auxiliary refrigerant stream (CL2). At this time, the flow rates of the first auxiliary refrigerant stream (CL1) and the second auxiliary refrigerant stream (CL2) may be the same or may be distributed differently.

[0197] The first auxiliary refrigerant stream (CL1) is introduced into the first auxiliary refrigerant economizer (330) and cooled by heat exchange with LNG supplied to the first auxiliary refrigerant economizer (330) through the liquefied gas line (LL), i.e., LNG at approximately -39.70°C from which the cold heat was first recovered in the first main refrigerant economizer (130), thereby recovering the remaining cold heat of the LNG.

[0198] As a result of the simulation, LNG is heated to approximately -12.83°C by heat exchange with the first auxiliary refrigerant stream (CL1) in the first auxiliary refrigerant economizer (330). At this time, the LNG heated in the first auxiliary refrigerant economizer (330) can be heated to the required temperature of the gas demand source, i.e., approximately 0°C or higher in this embodiment, in the liquefied gas heater (200) and then transported to the gas demand source.

[0199] The second auxiliary refrigerant stream (CL2) is introduced into the second auxiliary refrigerant economizer (340) and is cooled while recovering the residual cold heat of the LNG by heat exchange with the main refrigerant stream (RL) transferred from the main refrigerant cycle (100), i.e., the main refrigerant stream (RL) of about -28.46°C generated while recovering the cold heat of the LNG in the main refrigerant cycle (100).

[0200] As a result of the simulation, the main refrigerant stream (RL) is heated to approximately -12.83°C by heat exchange with the second auxiliary refrigerant stream (CL2) in the second auxiliary refrigerant economizer (340). The main refrigerant stream (RL) heated in the second auxiliary refrigerant economizer (340) may be recirculated to the main refrigerant turbine-generator (110) or further heated in the main refrigerant heater (170) and then recirculated to the main refrigerant turbine-generator (110).

[0201] The first auxiliary refrigerant stream (CL1) cooled while recovering the residual cold heat of LNG in the first auxiliary refrigerant economizer (330) and the second auxiliary refrigerant stream (CL2) cooled while recovering the residual cold heat of the main refrigerant stream (RL) in the second auxiliary refrigerant economizer (340) are heated to about 10°C in the auxiliary refrigerant heater (370), and in this process, the auxiliary refrigerant stream (CL) changes into a gaseous state and can be recycled to the auxiliary refrigerant turbine-generator (310).

[0202] As a result of the simulation, through the above process, the amount of power produced from the main refrigerant turbine-generator (110) was approximately 21.4 kW per 1 MT of LNG, and the amount of power produced from the auxiliary refrigerant turbine-generator (310) was approximately 6.0 kW, resulting in a total of 27.4 kW of power being generated.

[0203] Meanwhile, the simulation results show that in the case of a power generation system that recovers cold heat using an organic Rankine cycle using propane as a refrigerant under the same conditions of LNG, that is, recovers cold heat of LNG by exchanging heat between LNG and propane refrigerant in a heat exchanger (not shown), compresses the propane refrigerant cooled by heat exchange with LNG, heats the compressed propane refrigerant by heat exchange with seawater or fresh water, and then expands it in a turbine-generator to recover electric power, the amount of electric power generated in the turbine-generator was confirmed to be approximately 17.8 kW per 1 MT of LNG.

[0204] That is, it was confirmed that the series loop power generation system according to the present embodiment has an efficiency improvement effect of approximately 53.9% compared to the conventional propane single loop power generation system.

[0205]

[0206] As described above, embodiments of the present invention have been described. It will be apparent to those skilled in the art that the present invention can be embodied in other specific forms, in addition to the embodiments described above, without departing from the spirit or scope thereof. Therefore, the above-described embodiments should be considered illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description, but may be modified within the scope of the appended claims and their equivalents.

[0207] <Explanation of symbols>

[0208] 100: Main refrigerant cycle

[0209] 110: Main refrigerant turbine-generator

[0210] 120: Main refrigerant branch

[0211] 130, 140b, 140c, 140d, 140e, 140f, 140g, 140h, 140i: Main refrigerant economizer

[0212] 150a, 150b, 150c, 150d, 150e, 150f, 150g, 150h, 150i: Main refrigerant compressor

[0213] 160: Main refrigerant junction

[0214] 170: Main refrigerant heater

[0215] 200: Liquefied gas heater

[0216] 300: Auxiliary refrigerant cycle

[0217] 310: Auxiliary refrigerant turbine-generator

[0218] 320: Auxiliary refrigerant branch

[0219] 330: First auxiliary refrigerant economizer

[0220] 340: Second auxiliary refrigerant economizer

[0221] 350: Auxiliary refrigerant junction

[0222] 360: Auxiliary refrigerant pump

[0223] 370: Auxiliary refrigerant heater

[0224] RL, RL1, RL2, RL3, RL4, RL5, RL6, RL7, RL8, RL9: Main refrigerant streams

[0225] RLa: Main refrigerant heating line

[0226] RLb: Main refrigerant bypass line

[0227] CL, CL1, CL2: Auxiliary refrigerant stream

[0228] LL: Liquefied gas line

[0229] LL1: Liquefied gas heating line

[0230] LL2: Liquefied gas bypass line

Claims

1. A primary refrigerant cycle in which the primary refrigerant stream circulates and generates power by recovering the cold heat of the liquefied gas; and An auxiliary refrigerant cycle is provided in series so as to be detachable from the main refrigerant cycle, and generates power by recovering residual cold heat of the main refrigerant cycle while the auxiliary refrigerant stream circulates; The above main refrigerant cycle is, A primary refrigerant turbine-generator that generates electric power by driving a turbine with the primary refrigerant stream; and A first primary refrigerant economizer that recovers cold heat from the liquefied gas by heat-exchanging a portion of the primary refrigerant stream with the liquefied gas; The above auxiliary refrigerant cycle is, An auxiliary refrigerant turbine-generator that generates electric power by driving a turbine with the auxiliary refrigerant stream; and A series loop power generation system utilizing the cold heat of liquefied gas, comprising an auxiliary refrigerant economizer that cools the auxiliary refrigerant stream expanded in the auxiliary refrigerant turbine-generator by recovering the residual cold heat of at least one of the liquefied gas and the main refrigerant stream from which the cold heat has been recovered in the main refrigerant cycle.

2. In claim 1, The above auxiliary refrigerant economizer is, A first auxiliary refrigerant economizer that recovers residual heat of the liquefied gas by heat-exchanging the auxiliary refrigerant stream and the liquefied gas from which the cold heat has been recovered in the first main refrigerant economizer; and A series loop power generation system utilizing the cold heat of liquefied gas, comprising at least one of: a second auxiliary refrigerant economizer that recovers the cold heat of the liquefied gas in the auxiliary refrigerant stream and the main refrigerant cycle by heat-exchanging the cooled main refrigerant stream to recover the remaining cold heat of the main refrigerant stream; 3. In claim 1, A liquefied gas heater that heats liquefied gas heated by heat exchange in the first main refrigerant economizer and supplied to a gas demand source; and A series loop power generation system utilizing cold energy of liquefied gas, further comprising a main refrigerant heater for heating a main refrigerant stream circulated to the main refrigerant turbine-generator.

4. In claim 3, The above auxiliary refrigerant economizer is, A first auxiliary refrigerant economizer that recovers residual heat of the liquefied gas by heat-exchanging the auxiliary refrigerant stream and the liquefied gas from which the cold heat has been recovered in the first main refrigerant economizer; The above auxiliary refrigerant cycle is, Further comprising a liquefied gas heating line branching from the liquefied gas line upstream of the liquefied gas heater and connected to the liquefied gas stream inlet side of the first auxiliary refrigerant economizer; A series loop power generation system utilizing the cold energy of liquefied gas, wherein the liquefied gas is heated through at least one of the first auxiliary refrigerant economizer and the liquefied gas heater and then supplied to the gas demand source.

5. In claim 3, The above auxiliary refrigerant economizer is, A second auxiliary refrigerant economizer that recovers the remaining cold heat of the main refrigerant stream by heat-exchanging the cooled main refrigerant stream while recovering the cold heat of the liquefied gas in the auxiliary refrigerant stream and the main refrigerant cycle; The above auxiliary refrigerant cycle is, Further comprising a main refrigerant heating line branched from the main refrigerant stream flowing line upstream of the main refrigerant heater and connected to the main refrigerant stream inlet side of the second auxiliary refrigerant economizer; A series loop power generation system utilizing the cold heat of liquefied gas, wherein the above-mentioned main refrigerant stream is heated through at least one of the second auxiliary refrigerant economizer and the main refrigerant heater and then circulated to the main refrigerant turbine-generator.

6. In claim 1, The above main refrigerant cycle is, A primary refrigerant branch unit provided upstream of the first primary refrigerant economizer and branching the primary refrigerant stream into a plurality of primary refrigerant streams, including a first primary refrigerant stream to be supplied to the first primary refrigerant economizer; A plurality of primary refrigerant economizers, which are provided in parallel to cool the plurality of primary refrigerant streams by direct or indirect heat exchange with the liquefied gas, and which are provided in one-to-one correspondence with the plurality of primary refrigerant streams, including the first primary refrigerant economizer; and A series loop power generation system utilizing the cold energy of liquefied gas, comprising: a plurality of primary refrigerant compressors, each of which is provided in one-to-one correspondence with the plurality of primary refrigerant economizers, and which compresses one primary refrigerant stream cooled by one of the plurality of primary refrigerant economizers and supplies the compressed primary refrigerant stream to another primary refrigerant economizer as a refrigerant for cooling the other primary refrigerant stream.

7. In claim 1, A series loop power generation system utilizing the cold heat of liquefied gas, further comprising an additional auxiliary refrigerant cycle which is detachably installed in series at the rear end of the auxiliary refrigerant cycle and generates power by further recovering the remaining cold heat of the liquefied gas from which the cold heat has been recovered in the auxiliary refrigerant cycle while the additional auxiliary refrigerant circulates.

8. In claim 1, The above auxiliary refrigerant cycle is, An auxiliary refrigerant pump for pressurizing a liquefied auxiliary refrigerant stream while recovering residual cold heat from the auxiliary refrigerant economizer; and A series loop power generation system utilizing the cold energy of liquefied gas, further comprising an auxiliary refrigerant heater for vaporizing the auxiliary refrigerant stream pressurized by the auxiliary refrigerant pump and recirculating it to the auxiliary refrigerant turbine-generator.

9. A main refrigerant power generation stage in which the main refrigerant stream circulates and recovers the cold heat of the liquefied gas to generate power; and An auxiliary refrigerant power generation stage that recovers residual cold heat from the main refrigerant power generation stage while the auxiliary refrigerant stream circulates and generates power; The above main refrigerant generation stage is: A main refrigerant turbine driving step for generating power by driving a turbine with the main refrigerant stream; and A first main refrigerant heat recovery step for recovering the cold heat of the liquefied gas by heat-exchanging a portion of the main refrigerant stream with the liquefied gas; The above auxiliary refrigerant generation step is: An auxiliary refrigerant turbine driving step for generating power by driving a turbine with the auxiliary refrigerant stream; and A series loop power generation method using cold heat from liquefied gas, comprising an auxiliary refrigerant cold heat recovery step for recovering residual cold heat from at least one of the liquefied gas and the main refrigerant stream by heat-exchanging the auxiliary refrigerant stream with at least one of the liquefied gas and the main refrigerant stream transferred from the main refrigerant power generation step.

10. In claim 9, The above auxiliary refrigerant heat recovery step is: A first auxiliary refrigerant heat recovery step for recovering residual heat of the liquefied gas by heat-exchanging the auxiliary refrigerant stream and the liquefied gas from which heat has been recovered in the first main refrigerant heat recovery step; and A series loop power generation method using the cold heat of liquefied gas, comprising at least one of: a second auxiliary refrigerant cold heat recovery step for recovering the cold heat of the liquefied gas in the auxiliary refrigerant stream and the main refrigerant power generation step by heat-exchanging the cooled main refrigerant stream to recover the remaining cold heat of the main refrigerant stream; 11. In claim 9, In the first main refrigerant cooling heat recovery step, the liquefied gas heated by heat exchange is heated to a temperature required by the gas demander and supplied to the gas demander; further comprising; The step of supplying the above liquefied gas to the gas demand source is: A first auxiliary refrigerant heat recovery step for heating the liquefied gas from which heat has been recovered in the first main refrigerant heat recovery step by heat-exchanging it with the auxiliary refrigerant stream; and A series loop power generation method using cold heat from liquefied gas, comprising at least one of: a liquefied gas heating step for heating liquefied gas from which cold heat has been recovered in the first main refrigerant cold heat recovery step; 12. In claim 9, In the first main refrigerant cooling heat recovery step, the liquefied gas heated by heat exchange is heated to a temperature required by the gas demander and supplied to the gas demander; further comprising; The step of supplying the above liquefied gas to the gas demand source is: A first auxiliary refrigerant heat recovery step for heating the liquefied gas from which heat has been recovered in the first main refrigerant heat recovery step by heat-exchanging it with the auxiliary refrigerant stream; and A series loop power generation method using the cold heat of liquefied gas, comprising a liquefied gas heating step for further heating the liquefied gas heated in the first auxiliary refrigerant cold heat recovery step.

13. In claim 9, The above main refrigerant generation stage is: A primary refrigerant compression step for compressing a cooled primary refrigerant stream while recovering the cold heat of the liquefied gas in the first primary refrigerant cold heat recovery step; and A series loop power generation method using the cold heat of liquefied gas, further comprising a main refrigerant heating step for recovering the cold heat of the liquefied gas in the main refrigerant power generation step and heating the cooled main refrigerant stream to recirculate it to the main refrigerant turbine driving step.

14. In claim 13, The above main refrigerant heating step is: A second auxiliary refrigerant heat recovery step for recovering the remaining heat of the main refrigerant stream by heat-exchanging the cooled main refrigerant stream with the auxiliary refrigerant stream while recovering the heat of the liquefied gas in the main refrigerant power generation step; and A series loop power generation method using the cold heat of liquefied gas, comprising at least one of: a primary refrigerant additional heating step for heating the cooled primary refrigerant stream while recovering the cold heat of the liquefied gas in the primary refrigerant power generation step; 15. In claim 13, The above main refrigerant heating step is: A second auxiliary refrigerant heat recovery step for recovering the remaining heat of the main refrigerant stream by heat-exchanging the cooled main refrigerant stream with the auxiliary refrigerant stream while recovering the heat of the liquefied gas in the main refrigerant power generation step; and A series loop power generation method using cold heat from liquefied gas, comprising a main refrigerant additional heating step for further heating the main refrigerant stream heated in the second auxiliary refrigerant cold heat recovery step.

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