Patent Application
20190252096
The present invention relates to a closed cooling system applied to a superconductive cable by integrating a liquid nitrogen circulation circuit and a refrigerator unit.
In general, a superconductive cable is a cable that functions on the basis of the phenomenon that a superconductor has zero electrical resistance below a certain temperature. Such a cable provides lossless transmission of electric power and can transmit much more electric current than a conventional copper cable. In a cable using high temperature superconductors (HTS), there is a cooling system in which liquid nitrogen (LN2), which can maintain a liquid state at a temperature below minus 200 degrees Celsius and is excellent in electrical insulation performance, is used as a coolant, and liquid nitrogen is cooled and circulated through the cable. As shown in
A cooling system using the vacuum pump is an open system which is relatively simple and can be applied to a large capacity system, but requires periodic supply of a large amount of liquid nitrogen. Accordingly, it is suitable for pilot operation in the stage of development of the superconductive cable, but it is difficult to find application in a power system requiring long unattended operation.
A cooling system using the Stirling or Brayton cooler is a closed system which can be operated continuously without a periodic supply of liquid nitrogen. However, helium (He) or neon (Ne) is used as a refrigerant, and thus the available cooling capacity of the refrigerator unit is limited, and the price thereof is very high. The cooling capacity (70 K standard) of a recently developed refrigerator is only 2 kW for the Stirling cooler, 8 kW for the Brayton cooler, and the price per kW is hundreds of thousands of dollars. These coolers have been considered as the most important obstacle for developing a superconductive cable having a length of more than 1 km. Another obstacle for increasing the length of the superconductive cable is the LN2 pump. As the cable length becomes longer, the flow rate of liquid nitrogen to be circulated to maintain the cable below an allowable temperature (for example, 78 K) has to be increased more and thus the capacity of the LN2 pump is also increased greatly. The LN2 pump that has to operate at cryogenic temperature is available in some advanced countries, but the capacity (flow rate and pressure head) thereof is limited and the price thereof is very high.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an objective of the present invention is to provide a closed superconductive cable cooling system, in which nitrogen (N2) functions as both a refrigerant for a refrigerator unit and a coolant for a superconductive cable, thus requiring no provision of a pump for circulating liquid nitrogen, or other expensive devices.
In order to achieve the objective of the present invention, there is provided a superconductive cable cooling system, including: a refrigerator unit including a compressor and an after-cooler; a plurality of heat exchangers for performing heat exchange of a cooling fluid; an expansion valve for performing throttle expansion of the cooling fluid; an expander for adiabatically expanding the cooling fluid; a superconductive cable; and a plurality of branch points at which the cooling fluid is branched and joined, wherein the cooling fluid functions as both a refrigerant for the refrigerator unit and a coolant for the superconductive cable.
According to the present invention, because helium (He) and neon (Ne) are not used as a refrigerant, general-purpose air compressors and air expanders widely used in air liquefaction plants can be used instead of components that are difficult to operate and are expensive (He/Ne compressors, He/Ne turbo expanders, or the like). Furthermore, through integration of a liquid nitrogen (LN2) circulation circuit and a refrigerator, a pump for circulating liquid nitrogen is not required and the limit of liquid nitrogen circulation flow can be greatly increased. Furthermore, superconductive cable cooling is possible through only provision of an integrated cooling system, making it possible to enable easy operation of a cooling system while significantly reducing manufacturing cost and installation cost, and there is no possibility of freezing that exists in a superconductive cable cooling system in the related art, thus significantly increasing stability at cryogenic temperature.
Reference will now be made in greater detail to exemplary embodiments of the invention with reference to the accompanying drawings. The embodiments of the present invention are presented to make complete disclosure of the present invention and help those who are ordinarily skilled in the art best understand the invention. Various changes to the following embodiments are possible and the scope of the present invention is not limited to the following embodiments. Therefore, it should be understood that the shape and size of the elements shown in the drawings may be exaggeratedly drawn to provide an easily understood description of the structure of the present invention. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like elements or parts. In the following description, it is to be noted that, when the functions of conventional elements and the detailed description of elements related with the present invention may make the gist of the present invention unclear, a detailed description of those elements will be omitted.
The present invention relates to a superconductive cable cooling system including a refrigerator unit including a compressor and an after-cooler; a plurality of heat exchangers for performing heat exchange of a cooling fluid; an expansion valve for performing throttle expansion of the cooling fluid; an expander for adiabatically expanding the cooling fluid; a superconductive cable; and a plurality of branch points at which the cooling fluid is branched and joined, wherein the cooling fluid functions as both a refrigerant for the refrigerator unit and a coolant for the superconductive cable.
In the case of the first cycle similar to a standard Claude cycle, the heat exchangers include a first heat exchanger HX1, a second heat exchanger HX2, and a third heat exchanger HX3. The heat exchangers are connected to each other in parallel in order of the first heat exchanger, the second heat exchanger, and the third heat exchanger in a direction from the refrigerator unit toward the expansion valve. The cooling fluid passes through an inlet part 100 of the heat exchangers and cools the superconductive cable. Then, the cooling fluid passes through the expansion valve and flows back to the compressor through an outlet part 200 of the heat exchangers. The branch points include a first branch point P1 located on the inlet part between the first heat exchanger and the second heat exchanger and at which the cooling fluid is branched, and a second branch point P2 located on the outlet part between the third heat exchanger and the second heat exchanger and at which the cooling fluid is joined. The cooling fluid passing through the first branch point passes through the expander and is joined at the second branch point.
In other words, a portion of the cooling fluid that is branched after being cooled through the first heat exchanger HX1 is expanded through the expander E and flows into the second heat exchanger HX2, and a remaining portion of the cooling fluid is cooled to a liquid state through the second heat exchanger HX2 and the third heat exchanger HX3 and supplied to the superconductive cable. After cooling the superconductive cable, the remaining portion of the cooling fluid is expanded to a low temperature state through the expansion valve (JT valve), cools a high-pressure refrigerant through the heat exchangers HX3, HX2, and HX1, and returns to a room temperature state. All of the heat exchangers are simple countercurrent heat exchangers, and the flow numbers thereof are in the form of 2+2+2 in order of HX1, HX2, and HX3.
To help understand the first cycle, refer to the graphs of
In the case of the second cycle, the present invention includes a plurality of refrigerator units each including a compressor and an after-cooler; a plurality of heat exchangers for performing heat exchange of a cooling fluid; an expansion valve for performing throttle expansion of the cooling fluid; an expander for adiabatically expanding the cooling fluid; a superconductive cable; and a plurality of branch points at which the cooling fluid is branched and joined, wherein the cooling fluid functions as both a refrigerant for the refrigerator units and a coolant for the superconductive cable. The second cycle is similar to the first cycle, except that there is the plurality of refrigerator units. In the second cycle, the refrigerator units include a first refrigerator unit C1 connected to an outlet part of the heat exchangers, and a second refrigerator unit C2 connected to an inlet part of the heat exchangers, and the first and second refrigerator units are connected to each other in series. Furthermore, the heat exchangers include a first heat exchanger HX1, a second heat exchanger HX2, and a third heat exchanger HX3. The heat exchangers are connected to each other in parallel in order of the first heat exchanger, the second heat exchanger, and the third heat exchanger in a direction from the refrigerator units toward the expansion valve. The heat exchangers include a first inlet part 100 connected to the second refrigerator unit C2 and a first outlet part 200 connected to the first refrigerator unit C1, and the first heat exchanger HX1 further includes a second inlet part 110 through which the branched cooling fluid passes. Furthermore, the cooling fluid passes through the first inlet part 100 of the heat exchangers and cools the superconductive cable. Then, the cooling fluid passes through the expansion valve and flows back to the compressor of the first refrigerator unit C1 through the first outlet part 200 of the heat exchangers. The branch points of the second cycle include a first branch point P3 located between the first refrigerator unit C1 and the second refrigerator unit C2 and at which the cooling fluid is branched, and a second branch point P4 located on the first outlet part 200 between the third heat exchanger HX3 and the second heat exchanger HX2 and at which the cooling fluid is joined. The cooling fluid passing through the first branch point passes through the second inlet part of the first heat exchanger, passes through the expander, and is joined at the second branch point. The second cycle is a modified Claude cycle made by modifying the first cycle. In this case, another pressure stage is provided to constitute a dual-pressure stage, while maintaining a basic concept of the JT circulation type. In the first cycle, the pressure ratios of two flows (expander flow and JT flow) remain the same, whereas in the second cycle, the pressure ratios of two flows can be set differently, and thus there is flexibility in designing the operating pressure. The flow numbers of the heat exchangers are in the form of 3+2+2 in order of HX1, HX2, and HX3.
To help understand the second cycle, refer to the graphs of
The third cycle is a modified Claude cycle and is provided to overcome the efficiency limit of the JT circulation type by applying an expander circulation type rather than the JT circulation type of the first and second cycles. In the case of the third cycle, a pressure stage of the third heat exchanger is different. The heat exchangers include a first inlet part 100 connected to the second refrigerator unit C2 and a first outlet part 200 connected to the first refrigerator unit C1, and a second outlet part 210 through which the cooling fluid passing through the superconductive cable passes. The third heat exchanger HX3 further includes a second inlet part 110 connected to the expander. Furthermore, the cooling fluid passes through the first inlet part 100 of the heat exchangers, passes through the expansion valve, and flows back to the compressor of the first refrigerator unit through the first outlet part 200. The branch points of the third cycle include a first branch point P5 located on the first inlet part 100 between the first heat exchanger HX1 and the second heat exchanger HX2 and at which the cooling fluid is branched, and a second branch point P6 located between the first refrigerator unit C1 and the second refrigerator unit C2 and at which the cooling fluid is joined. The cooling fluid passing through the first branch point passes through the expander, passes through the second inlet part 110 of the third heat exchanger, passes through the superconductive cable and the second outlet part, and is joined at the second branch point. In the third cycle, the flow passing through the expander is further cooled through the third heat exchanger HX3 and supplied to the superconductive cable, and the flow passing through the JT valve constitutes a low temperature portion of each heat exchanger. The pressure stage is a dual-pressure stage, and a four-flow heat exchanger with four flows in one heat exchanger is used for the first time. The flow numbers of the heat exchangers are in the form of 3+3+4 in order of HX1, HX2, and HX3.
To help understand the third cycle, refer to the graphs of
The fourth cycle is also a modified Claude cycle as in the third cycle and is provided to overcome the efficiency limit of the JT circulation type by applying the expander circulation type rather than the JT circulation type. The fourth cycle further includes a fourth heat exchanger HX4. The heat exchangers are connected to each other in parallel in order of the first heat exchanger HX1, the second heat exchanger HX2, the third heat exchanger HX3, and the fourth heat exchanger HX4 in a direction from the refrigerator units toward the expansion valve. The first, second, and third heat exchangers include a first inlet part 100 connected to the second refrigerator unit C2, a first outlet part 200 connected to the first refrigerator unit C1, and a second outlet part 210 through which the cooling fluid passing through the superconductive cable passes. The third heat exchanger further includes a second inlet part 110 connected to the expander, and the fourth heat exchanger includes the second inlet part 110 and the first outlet part 200. In the fourth cycle, the cooling fluid passes through the first inlet part 100 of the heat exchangers, passes through the expansion valve, and flows back to the compressor of the first refrigerator unit through the first outlet part 200. Furthermore, the branch points of the fourth cycle include a first branch point P7 located on the first inlet part 100 between the first heat exchanger HX1 and the second heat exchanger HX2 and at which the cooling fluid is branched, and a second branch point P8 located between the first refrigerator unit C1 and the second refrigerator unit C2 and at which the cooling fluid is joined. The cooling fluid passing through the first branch point passes through the expander, passes through the second inlet part 110 of the third and fourth heat exchangers, passes through the superconductive cable and the second outlet part, and is joined at the second branch point. The number of heat exchangers in the fourth cycle is four, and the flow numbers of the heat exchanger are in the form of 3+3+4+2 in order of HX1, HX2, HX3, and HX4. The fourth heat exchanger HX4 serves to cool liquid nitrogen to low-temperature nitrogen leaving an outlet of the JT valve and supply the same to the cable.
To help understand the fourth cycle, refer to the graphs of
The cooling fluid applied in all of the cycles described so far is nitrogen, and the expansion valve may be a JT valve. Also, the term “cycle” used to help understand is expressed as a cooling system in the claims below.
Although the exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. It is thus well known to those skilled in that art that the present invention is not limited to the embodiment disclosed in the detailed description, and the patent right of the present invention should be defined by the scope and spirit of the invention as disclosed in the accompanying claims. Accordingly, it should be understood that the present invention includes various modifications, additions and substitutions without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0120784 | Sep 2016 | KR | national |
This application claims the benefit under 35 U.S.C. Section 371, of PCT International Application No. PCT/KR2016/012822, filed on Nov. 08, 2016, which claimed priority to Korean Patent Application No. KR 10-2016-0120784, filed on Sep. 21, 2016, the disclosures of which are hereby incorporated by the references.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2016/012822 | 11/8/2016 | WO | 00 |
