Refrigeration system for fishing ship

Abstract

This refrigeration system for fishing ship is provided with a plurality of oil-cooled single-stage screw compressors (4-6) and a first fish bank (2) and at least one second fish bank (3) that are cooled by the plurality of oil-cooled single-stage screw compressors (4-6). The first fish bank (2) and the second fish bank (3) have different cold insulation temperature zones. The first fish bank (2) is cooled by operating a plurality of oil-cooled single-stage screw compressors (4-6) in parallel in a single-stage compression system, and the second fish bank (3) is cooled by operating a plurality of oil-cooled single-stage screw compressors (4-6) in series in combination as a low-stage side and a high-stage side of a two-stage compression system.

Description

Fishing boat refrigeration system

[0001] This application claims priority from Japanese Patent Application No. 2024-155272, filed on September 9, 2024, the contents of which are incorporated herein by reference.

[0002] For example, in a fishing boat refrigeration system installed on a deep-sea fishing vessel, fish are brine-frozen at approximately -20°C to maintain their freshness. Furthermore, the fish hold where the fish are stored is cooled to approximately -50°C to keep the fish cold. To generate different temperature ranges for each of these processes, for example, a two-stage reciprocating compressor equipped with a low-stage side and a high-stage side is used. This type of reciprocating compressor can be switched between operating in a single-stage compression mode or a two-stage compression mode. Thus, the brine freezing process is performed by operating the reciprocating compressor in the single-stage compression mode. Furthermore, the cold keeping process is performed by operating the reciprocating compressor in the two-stage compression mode.

[0003] In recent years, due to environmental considerations, ammonia, a natural refrigerant, has increasingly been used as the refrigerant in refrigeration systems. When ammonia is used as a refrigerant, the discharge temperature during the compression process is higher than that of other refrigerants. Various technologies have been proposed to prevent deterioration of refrigeration oil caused by this high discharge temperature.

[0004] For example, a refrigeration system (refrigeration apparatus) has been proposed that includes a main refrigeration unit including at least a two-stage compressor, a condenser, an expansion valve, and an evaporator, and a secondary refrigeration unit including at least a single-stage compressor, a condenser, an expansion valve, and an evaporator. A reciprocating compressor is used as the compressor (see, for example, Patent Document 1). According to this system, condenser cooling water cooled by the evaporator of the secondary refrigeration unit is supplied to the condenser of the main refrigeration unit via a circulation pump, thereby lowering the condensation temperature of the refrigerant gas compared to when condensation is performed using cooling water at room temperature.

[0005] Japanese Patent Application Publication No. 2006-214611

[0006] However, the above-mentioned conventional technology has the drawback of complicating the refrigeration system configuration and increasing the installation space required for the refrigeration system due to the need for a secondary refrigeration unit to cool the cooling water. In particular, the installation space for refrigeration systems on fishing boats is limited, making the above-mentioned conventional technology difficult to install on some fishing boats. Furthermore, for example, when ammonia is used as a refrigerant, the discharge temperature of the reciprocating compressor becomes high. In such cases, the refrigeration oil may carbonize and clog, for example, a strainer, resulting in malfunctions or inefficient operation of the refrigeration system and potentially malfunctioning of the compressor.

[0007] An aspect of the present invention provides a refrigeration system for fishing boats that can simplify the configuration even when using a refrigerant such as ammonia, save installation space, and suppress an increase in discharge temperature to prevent malfunctions in the compressor.

[0008] The fishing vessel refrigeration system of the present invention comprises a plurality of oil-cooled single-stage screw compressors, a first fish hold cooled by the plurality of oil-cooled single-stage screw compressors, and at least one second fish hold, wherein the first fish hold and the second fish hold each have a different refrigeration temperature range, and the first fish hold is cooled by operating each of the plurality of oil-cooled single-stage screw compressors in parallel using a single-stage compression system, and the second fish hold is cooled by combining the plurality of oil-cooled single-stage screw compressors as the low-stage and high-stage sides of a two-stage compression system and operating them in series.

[0009] In this way, by using an oil-cooled single-stage screw compressor, the rise in discharge temperature can be suppressed compared to a reciprocating compressor, even when ammonia is used as a refrigerant. This prevents compressor malfunctions. Furthermore, to cool the first fish hold, multiple oil-cooled single-stage screw compressors are operated in parallel using a single-stage compression system, while to cool the second fish hold, multiple oil-cooled single-stage screw compressors are combined and operated in series as the low-stage and high-stage sides of a two-stage compression system. In this way, by switching the operating mode of the oil-cooled single-stage screw compressors, each fish hold can be maintained in a different refrigeration temperature range. In other words, it is possible to perform brine freezing and refrigeration processes for fish while suppressing the rise in discharge temperature of each oil-cooled single-stage screw compressor. This eliminates the need for a conventional cooling water cooling device, simplifying the configuration of the fishing boat refrigeration system and reducing installation space, even when using a refrigerant such as ammonia.

[0010] According to the aspects of the present invention, even when a refrigerant such as ammonia is used, the configuration of a fishing boat refrigeration system can be simplified, installation space can be saved, and the rise in discharge temperature can be suppressed, thereby preventing malfunctions in the compressor.

[0011] The present invention relates to a refrigeration system for a fishing vessel, ...

[0012] Next, an embodiment of the present invention will be described with reference to the drawings.

[0013] <Fishing Vessel Refrigeration System> FIG. 1 is a schematic diagram of a fishing vessel refrigeration system 1. The fishing vessel refrigeration system 1 is installed on a fishing vessel (not shown). As shown in FIG. 1, the fishing vessel refrigeration system 1 includes two fish holds 2, 3 (first fish hold 2, second fish hold 3) for storing fish (not shown), three oil-cooled single-stage screw compressors 4, 5, 6 (first oil-cooled single-stage screw compressor 4, second oil-cooled single-stage screw compressor 5, and third oil-cooled single-stage screw compressor 6; hereinafter simply referred to as the first compressor 4, second compressor 5, and third compressor 6) connected to the two fish holds 2, 3, and a condenser 7 provided between each of the fish holds 2, 3 and each of the compressors 4, 5, and 6. A refrigerant such as ammonia (hereinafter simply referred to as the refrigerant) flows through the fishing vessel refrigeration system 1. Hereinafter, the downstream side, upstream side, and other terms may be used based on the flow direction of the refrigerant.

[0014] Of the two fish holds 2 and 3, the first fish hold 2 freezes fish (not shown) in brine. The brine's temperature range is maintained at approximately -10°C to -20°C by compressors 4, 5, and 6. Of the two fish holds 2 and 3, the second fish hold 3 keeps the fish frozen in the first fish hold 2 at an even lower temperature. The temperature range inside the second fish hold 3 is maintained at approximately -40°C to -60°C by compressors 4, 5, and 6.

[0015] The suction ports 4a to 6a of the three compressors 4 to 6 are connected in parallel to the first fish hold 2 and the second fish hold 3 via a first connecting passage 8. A first fish hold outlet passage 9a extending from the first fish hold 2 and a second fish hold outlet passage 9b extending from the second fish hold 3 join together on the fish hold 2, 3 side of the first connecting passage 8. Three branched suction passages 10a, 10b, 10c (first suction passage 10a, second suction passage 10b, third suction passage 10c) are provided on the compressors 4 to 6 side of the first connecting passage 8.

[0016] Of the three suction passages 10a to 10c, the first suction passage 10a is connected to the suction port 4a of the first compressor 4. Of the three suction passages 10a to 10c, the second suction passage 10b is connected to the suction port 5a of the second compressor 5. Of the three suction passages 10a to 10c, the third suction passage 10c is connected to the suction port 6a of the third compressor 6. An suction valve 11 is provided in the first suction passage 10a. The suction valve 11 opens and closes the first suction passage 10a.

[0017] A first discharge passage 12a is connected to the discharge port 4b of the first compressor 4. A second discharge passage 12b is connected to the discharge port 5b of the second compressor 5. A third discharge passage 12c is connected to the discharge port 6b of the third compressor 6. Of the three discharge passages 12a to 12c, the second discharge passage 12b and the third discharge passage 12c are each provided with a discharge valve (an example of a second valve in the claims). Each discharge valve 16 opens and closes the corresponding discharge passage 12b, 12c.

[0018] Between the second discharge passage 12b and the first suction passage 10a and the third discharge passage 12c, a two-stage compression connection passage 20 is provided, which connects the discharge passages 12b, 12c and the suction passage 10a. The two-stage compression connection passage 20 includes a first low-stage passage 20a connected to the second discharge passage 12b between the second compressor 5 and the discharge valve 16, a second low-stage passage 20b connected to the third discharge passage 12c between the third compressor 6 and the discharge valve 16, and a junction passage 20c where the first low-stage passage 20a and the second low-stage passage 20b join together.

[0019] The downstream side of the junction passage 20c is connected to the first suction passage 10a between the first compressor 4 and the suction valve 11. Each of the low-stage passages 20a, 20b is provided with a low-stage discharge valve (an example of a first valve in the claims) 22. Each low-stage discharge valve 22 opens and closes the corresponding low-stage passage 20a, 20b. In other words, each low-stage discharge valve 22 opens and closes the two-stage compression connection passage 20.

[0020] The discharge passages 12a to 12c are combined and connected to the fish holds 2, 3 via a second connecting passage 13. A condenser 7 is provided in the second connecting passage 13. A first fish hold inlet passage 14a and a second fish hold inlet passage 14b are branched off from the second connecting passage 13 on the side of each of the fish holds 2, 3. The first fish hold inlet passage 14a is connected to the first fish hold 2. The second fish hold inlet passage 14b is connected to the second fish hold 3.

[0021] A first fish hold valve 15a is provided in the first fish hold inlet passage 14a. A second fish hold valve 15b is provided in the second fish hold inlet passage 14b. These fish hold valves 15a, 15b open and close the corresponding fish hold inlet passages 14a, 14b. The fish hold valves 15a, 15b also function as expansion valves.

[0022] <Operating Method of Fishing Vessel Refrigeration System> Next, a method of operating the fishing vessel refrigeration system 1 will be described with reference to Figures 2 and 3. The fishing vessel refrigeration system 1 operates in different ways when cooling the brine in the first fish hold 2 and when cooling the interior of the second fish hold 3. Therefore, first, the case of cooling the brine in the first fish hold 2 will be described.

[0023] Figure 2 is an explanatory diagram of cooling the brine in the first fish hold 2. Figure 2 corresponds to the above-mentioned Figure 1. As shown in Figure 2, when cooling the brine in the first fish hold 2, the suction valve 11, discharge valve 16, and first fish hold valve 15a are opened. Meanwhile, the second fish hold valve 15b and the low-stage discharge valve 22 are closed. As a result, a parallel refrigerant flow path 31 (see the bold line in Figure 2) in which the three compressors 4 to 6 are connected in parallel to the first fish hold 2 is formed by the connecting paths 8, 13, the discharge paths 12a to 12c, and the first fish hold inlet path 14a, and the two-stage compression connecting path 20 is blocked.

[0024] The compressors 4 to 6 are operated in parallel using a single-stage compression system, and refrigerant flows through the parallel refrigerant flow path 31 (see the arrows in FIG. 2). This causes the brine in the first fish hold 2 to be cooled via a heat exchanger (evaporator) not shown. The cooled brine freezes the fish brought into the first fish hold 2.

[0025] Next, the cooling of the interior of the second fish hold 3 will be described. Figure 3 is an explanatory diagram of the cooling of the interior of the second fish hold 3. Figure 3 corresponds to the above-mentioned Figure 1. As shown in Figure 3, when cooling the second fish hold 3, the suction valve 11, the discharge valve 16, and the first fish hold valve 15a are closed. Meanwhile, the second fish hold valve 15b and the low-stage discharge valve 22 are opened. As a result, a series refrigerant flow path 32 (see the bold line in Figure 3) in which the first compressor 4, the second compressor 5, and the third compressor 6 are connected in series to the second fish hold 3 is formed by the connecting paths 8, 13, the discharge paths 12a to 12c, the two-stage compression connecting path 20, and the second fish hold inlet path 14b.

[0026] That is, in the serial refrigerant flow path 32, the compressors 4 to 6 are combined in a two-stage compression system by opening the two-stage compression connection path 20. More specifically, the second compressor 5 and the third compressor 6 function as the low-stage side, and the first compressor 4 functions as the high-stage side. The compressors 4 to 6 combined in this way are operated in series in a two-stage compression system, and the refrigerant flows through the serial refrigerant flow path 32 (see the arrows in FIG. 3). As a result, the air inside the second fish hold 3 is cooled by a heat exchanger (evaporator) (not shown) provided inside the hold, and the fish are kept cold.

[0027] As described above, the fishing vessel refrigeration system 1 includes three compressors 4 to 6 and two fish holds 2 and 3 with different refrigeration temperature ranges. Oil-cooled single-stage screw compressors are used as the three compressors 4 to 6. Oil-cooled single-stage screw compressors cool the refrigerant by supplying oil to the compression space during compression. Therefore, even when ammonia is used as the refrigerant, the rise in discharge temperature can be suppressed compared to reciprocating compressors, and malfunctions in the compressors 4 to 6 can be suppressed.

[0028] Unlike reciprocating compressors, the compressors 4 to 6 are screw compressors and cannot be made into compound compressors (a single compressor cannot switch between single-stage and two-stage compression). These compressors 4 to 6 are used to cool the fish holds 2 and 3 by switching between single-stage and two-stage compression. More specifically, the first fish hold 2 is cooled by operating the compressors 4 to 6 in parallel using the single-stage compression system. The second fish hold 3 is cooled by operating the second compressor 5 and the third compressor 6 in series as the low-stage side of the two-stage compression system, with the first compressor 4 operating as the high-stage side of the two-stage compression system. In this way, by switching the operating mode of the compressors 4 to 6, the cold storage temperature range of the first fish hold 2 and the cold storage temperature range of the second fish hold 3 can be made different. In other words, it is possible to perform brine freezing and cold storage processes on fish while suppressing an increase in the discharge temperature of the compressors 4 to 6. As a result, there is no need for a device for cooling the cooling water as in the past, so even when using a refrigerant such as ammonia, the configuration of the fishing boat refrigeration system 1 can be simplified and installation space can be saved.

[0029] Of the two fish holds 2, 3, the first fish hold 2, which has a higher refrigeration temperature range, is cooled by operating the compressors 4 to 6 in parallel using a single-stage compression system. Of the two fish holds 2, 3, the second fish hold 3, which has a lower refrigeration temperature range, is cooled by operating the compressors 4 to 6 in series using a two-stage compression system. In this way, by operating the compressors 4 to 6 appropriately according to the refrigeration temperature range, the operating efficiency of the fishing vessel refrigeration system 1 can be improved.

[0030] The fishing vessel refrigeration system 1 includes a two-stage compression connecting line 20 and a low-stage discharge valve 22 that opens and closes the two-stage compression connecting line 20. By closing the low-stage discharge valve 22, the two-stage compression connecting line 20 is closed, thereby forming a parallel refrigerant flow path 31, and the compressors 4 to 6 are operated in parallel using the single-stage compression method. On the other hand, by opening the low-stage discharge valve 22, the two-stage compression connecting line 20 is opened, thereby forming a series refrigerant flow path 32, and the compressors 4 to 6 are operated using the two-stage compression method. In this way, with a simple structure, it is possible to reliably operate the compressors 4 to 6 for each fish hold 2, 3 using either the single-stage compression method or the two-stage compression method.

[0031] The fishing vessel refrigeration system 1 is equipped with a discharge valve 16 that opens and closes the discharge paths 12b, 12c of the second compressor 5 and the third compressor 6, which are the lower stages in a two-stage compression system. By opening this discharge valve 16, a parallel refrigerant flow path 31 is formed, and the compressors 4 to 6 are operated in parallel using the single-stage compression system. On the other hand, by closing the discharge valve 16, a serial refrigerant flow path 32 is formed, and the compressors 4 to 6 are operated using the two-stage compression system. In this way, with a simple structure and more reliably, it is possible to operate the compressors 4 to 6 for each fish hold 2, 3 using either the single-stage compression system or the two-stage compression system.

[0032] The present invention is not limited to the above-described embodiment, and includes various modifications to the above-described embodiment without departing from the spirit of the present invention.

[0033] For example, in the above embodiment, the fishing boat refrigeration system 1 has been described as having three compressors 4 to 6. However, this is not limited to this, and the number of compressors may be two or more. Even if four or more compressors are provided, the compressors may be used to cool the second fish hold 3, and may be combined and operated in series as the low-stage and high-stage sides of a two-stage compression system.

[0034] In the above embodiment, the first fish hold 2 is described as a case in which fish are brine-frozen by cooling the brine. The second fish hold 3 is described as a case in which fish are kept cold by cooling the interior of the hold. However, this is not limited to this, and any method for freezing fish in each fish hold 2, 3 can be selected. For example, the interior of the first fish hold 2 may be cooled, and the second fish hold 3 may freeze the fish with brine. It is sufficient that the cold storage temperature ranges of the fish holds 2, 3 are different.

[0035] In the above embodiment, the suction valve 11 is provided in the first suction passage 10a. The discharge valves 16 are provided in the second discharge passage 12b and the third discharge passage 12c. However, this is not limiting, and the suction valve 11 may be provided in each of the suction passages 10a to 10c.

[0036] When operating using the two-stage compression system with the compressors 4 to 6, it is sufficient to use one of the compressors 4 to 6 with its suction valve 11 closed as the high-stage compressor. In other words, it is also possible to allow or block the suction of refrigerant by each of the compressors 4 to 6 by opening or closing the discharge valve 16. On the other hand, it is sufficient to provide a discharge valve 16 on at least two of the discharge passages 12a to 12c connected to the compressors 4 to 6 used as the low-stage compressor. It is also possible to provide a discharge valve 16 on each of the discharge passages 12a to 12c.

[0037] In the above embodiment, a case has been described in which each of the three compressors 4 to 6 is operated to cool the brine in the first fish hold 2. However, this is not limited to this, and it is also possible to increase or decrease the number of compressors 4 to 6 that are operated depending on the cold storage temperature zone of the first fish hold 2.

[0038] In the above embodiment, the fishing vessel refrigeration system 1 has been described as having one first fish hold 2 and one second fish hold 3. However, this is not limited to this, and there may be two or more second fish holds 3. It is sufficient that the refrigeration temperature zone of the first fish hold 2 and the refrigeration temperature zone of the second fish hold 3 are different. It is also possible to increase or decrease the number of compressors 4 to 6 depending on the number of second fish holds 3.

[0039] DESCRIPTION OF SYMBOLS 1... Fishing vessel refrigeration system 2... First fish hold 3... Second fish hold 4... First oil-cooled single-stage screw compressor (oil-cooled single-stage screw compressor) 4a, 5a, 6a... Intake port (suction side) 4b, 5b, 6b... Discharge port (discharge side) 5... Second oil-cooled single-stage screw compressor (oil-cooled single-stage screw compressor) 6... Third oil-cooled single-stage screw compressor (oil-cooled single-stage screw compressor) 16... Discharge valve (second valve) 20... Two-stage compression connection path 22... Low-stage discharge valve (first valve) 31... Parallel refrigerant flow path 32... Series refrigerant flow path

Claims

1. A refrigeration system for a fishing vessel comprising: a plurality of oil-cooled single-stage screw compressors; a first fish hold cooled by the plurality of oil-cooled single-stage screw compressors; and at least one second fish hold, wherein the first fish hold and the second fish hold have different refrigeration temperature zones, and the first fish hold is cooled by operating each of the plurality of oil-cooled single-stage screw compressors in parallel using a single-stage compression system, and the second fish hold is cooled by combining the plurality of oil-cooled single-stage screw compressors as the low-stage and high-stage sides of a two-stage compression system and operating them in series.

2. A refrigeration system for a fishing vessel as described in claim 1, characterized in that the refrigeration temperature range of the second fish hold is lower than the refrigeration temperature range of the first fish hold.

3. A fishing vessel refrigeration system as described in claim 1 or claim 2, characterized in that it comprises: a two-stage compression connecting passage that connects the discharge side of at least one of the oil-cooled single-stage screw compressors with the suction side of at least one of the oil-cooled single-stage screw compressors; and a first valve that is provided in the two-stage compression connecting passage and opens and closes the two-stage compression connecting passage, wherein when operating in parallel using the single-stage compression method, the two-stage compression connecting passage is closed by the first valve, and when operating using the two-stage compression method, the two-stage compression connecting passage is opened by the first valve.

4. A fishing vessel refrigeration system as described in claim 3, characterized in that it is provided with a second valve that is provided on the discharge side of the oil-cooled single-stage screw compressor, which is the lower stage when using a two-stage compression system, and that opens and closes the discharge side of the oil-cooled single-stage screw compressor, so that when operating in parallel using the single-stage compression system, the discharge side of the oil-cooled single-stage screw compressor is opened, and when operating using the two-stage compression system, the discharge side of the oil-cooled single-stage screw compressor is closed.

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