Ejector Refrigeration System

Abstract

To provide an ejector refrigerator capable of preventing cavitation of a pump when a device starts with a simple structure.SOLUTION: An ejector refrigerator has: a pump 3 boosting a coolant; a steam generator 4 heating the coolant with a heat source and generating a drive flow; an expansion valve 5 decompressing the coolant; an evaporator 6 which cools a cooled medium by the coolant decompressed by the expansion valve 5; an ejector 1 which sucks the coolant evaporated by the evaporator 6 by the drive flow of the coolant from the steam generator 4; and a condenser 2 cooling the coolant mixed with the drive flow after sucked into the ejector 1. A communication mechanism communicating a path of the heat source with the evaporator 6 when the device stops is provided. In the evaporator 6, heat exchange between the heat medium of the heat source and the medium of the evaporator 6 is performed, and the coolant suspended in the evaporator 6 is transferred to the condenser 2.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an ejector refrigeration device that can prevent cavitation of a pump during device startup with a simple configuration.

Background Art

[0002] An ejector refrigeration device uses heat source water such as factory waste warm water as a heating source to evaporate high-pressure refrigerant pressurized by a refrigerant pump, generating a driving flow for the ejector. The driving flow is sent to the ejector, and the suction flow from the evaporator is pressurized by the action of the ejector. The pressurized refrigerant is sent to the condenser and cooled and liquefied by cooling water. The liquefied refrigerant is decompressed into a low-temperature two-phase refrigerant by passing through an expansion valve and sent to the evaporator. In the evaporator, heat can be absorbed from the outside during evaporation to generate cold heat such as chilled water.

[0003] Note that Patent Document 1 discloses a heat pump that completes startup in a short time by performing waste heat of a compressor or the like while replenishing a liquid heat medium to an evaporator from the condenser side using a liquid feed pump. When starting up the heat pump, the heat medium is first evaporated in the evaporator, and then the liquid feed pump is driven to prevent cavitation in the liquid feed pump.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, when the ejector refrigeration system is shut down, condensation occurs at the coldest point, causing a large amount of refrigerant to accumulate in the evaporator. On the other hand, during startup, it is necessary to ensure a sufficient liquid head at the pump inlet, but because a large amount of refrigerant accumulates in the evaporator, it is not possible to ensure sufficient refrigerant to be held in the condenser. This results in insufficient suction head at the pump inlet during startup, leading to cavitation, which can cause pump failure and prevent stable startup.

[0006] The present invention has been made in view of the above, and aims to provide an ejector refrigeration device that can prevent pump cavitation during device startup with a simple configuration. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides an ejector refrigeration system comprising: a pump for pressurizing a refrigerant; a steam generator for heating the refrigerant with a heat source to generate a drive flow; an expansion valve for reducing the pressure of the refrigerant; an evaporator for cooling a medium to be cooled with the refrigerant reduced in pressure by the expansion valve; an ejector for sucking the refrigerant evaporated by the evaporator with the drive flow of the refrigerant from the steam generator; and a condenser for cooling the refrigerant mixed with the drive flow after being sucked into the ejector, wherein the system is equipped with a communication mechanism for connecting the path of the heat source to the evaporator when the system is stopped, and in the evaporator, the heat medium of the heat source and the evaporator refrigerant This method is characterized by performing heat exchange with the evaporator and transferring the refrigerant accumulated in the evaporator to the condenser.

[0008] Furthermore, in the above invention, when the device is stopped, the expansion valve is completely closed, and the heat from the heat source via the communication mechanism medium This method is characterized by evaporating the refrigerant in the evaporator and transferring the refrigerant to the condenser via the ejector.

[0009] Furthermore, the present invention is characterized in that, in the above invention, a check valve or a backflow prevention on / off valve is provided between the evaporator and the ejector.

[0010] Furthermore, in the above invention, an on-off valve is provided between the evaporator and the ejector, and when the device is stopped, the on-off valve is closed and the expansion valve is fully opened, and the heat from the heat source via the communication mechanism medium This is characterized by increasing the internal pressure of the evaporator and pressurizing the refrigerant to the condenser via the expansion valve.

[0011] Furthermore, the present invention, in the above invention, is characterized in that the communication mechanism comprises a first on-off valve provided on the outlet side of the heat source path in the steam generator, a connecting pipe connecting a first connection point provided between the steam generator and the first on-off valve and a second connection point provided on the inlet side of the cooled medium path in the evaporator, a second on-off valve provided in the connecting pipe, and a third on-off valve provided on the cooled medium path upstream of the second connection point, wherein when the device is stopped, the first on-off valve and the third on-off valve are closed and the second on-off valve is open. [Effects of the Invention]

[0012] According to the present invention, cavitation of the pump during device startup can be prevented with a simple configuration. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a circuit diagram showing the configuration of an ejector refrigeration device according to Embodiment 1 of the present invention. [Figure 2] Figure 2 shows the state when stopped in Embodiment 1 of the present invention. [Figure 3] Figure 3 shows the state when the device is stopped in the conventional manner. [Figure 4] Figure 4 is a circuit diagram showing the configuration of an ejector refrigeration device, which is a modified example of an embodiment of the present invention. [Figure 5] Figure 5 is a flowchart showing the shutdown processing procedure performed by the control unit shown in Figure 1 when the device is stopped. [Figure 6]FIG. 6 is a diagram showing the state at the time of stop in Embodiment 2 of the present invention. [Figure 7] FIG. 7 is a flowchart showing the stop processing procedure at the time of device stop by the control unit shown in FIG. 6.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments for carrying out this invention will be described with reference to the accompanying drawings.

[0015] <Embodiment 1> FIG. 1 is a circuit diagram showing the configuration of an ejector refrigeration device which is Embodiment 1 of the present invention. The ejector refrigeration device illustrated here recovers waste heat as a heat source from waste warm water such as industrial waste water and used cooling water, and cools a cooling medium, and has an ejector 1, a condenser 2, a pump 3, and a steam generator 4 sequentially connected on a circulation path L1. Further, a branch path L2 is provided in the ejector refrigeration device. The branch path L2 branches from a portion upstream of the pump 3 at a branch point LS between the condenser 2 and the steam generator 4 of the circulation path L1, and supplies a part of the refrigerant flowing through the circulation path L1 to the ejector 1 as a suction fluid. Note that as the cooling medium, water, oil, or other refrigerants can be targeted. In the present Embodiment 1, in particular, an ejector refrigeration device that generates cold water from cooling water by waste heat recovered from waste warm water is illustrated.

[0016] The pump 3 performs circulation supply of the refrigerant in the circulation path L1. More specifically, the pump 3 is, for example, a variable displacement pump in the liquid phase, and boosts the pressure of the refrigerant and supplies it to the ejector 1. The pump 3 of the present Embodiment 1 is driven at a rotational speed according to a drive signal given from a control unit C described later. The steam generator 4 evaporates the refrigerant supplied from the pump 3 by performing heat exchange with a heat source such as waste warm water supplied to the steam generator 4.

[0017] The branch path L2 is provided with an expansion valve 5 and an evaporator 6. The expansion valve 5 expands and depressurizes the refrigerant that has passed through the condenser 2 and is branched and supplied via the branch point LS. The evaporator 6 evaporates the refrigerant by performing heat exchange between the liquid-phase refrigerant after passing through the expansion valve 5 and the cooling water to be supplied to the evaporator 6. As the expansion valve 5, an electronic expansion valve is preferable, but a manual expansion valve, a constant-pressure expansion valve, a thermal expansion valve, etc., or other types of throttling mechanisms may be appropriately selected according to the application and configuration.

[0018] Here, in the first embodiment, a communication mechanism is provided to communicate the path of the heat source with the evaporator 6 when the device stops, and heat exchange is performed between the heat medium of the heat source and the refrigerant in the evaporator 6, and the refrigerant remaining in the evaporator 6 is transferred to the condenser. This communication mechanism has connecting pipes L11, L12, and on-off valves V1 to V5. The on-off valve V1 is provided on the outlet side of the path of the heat source in the steam generator 4. The connecting pipe L11 connects between a connection point LS1 provided between the steam generator 4 and the on-off valve V1 and a connection point LS2 provided on the inlet side of the path of the cooling water in the evaporator 6. The on-off valve V2 is provided on the connecting pipe L11. The on-off valve V3 is provided on the path of the cooling water and upstream of the connection point LS2.

[0019] Further, the connecting pipe L12 connects between a connection point LS3 on the cold water outlet side of the evaporator 6 and a connection point LS4 provided on the downstream side of the on-off valve V1. The on-off valve V4 is provided on the downstream side of the connection point LS3. The on-off valve V5 is provided on the connecting pipe L12.

[0020] As shown in FIGS. 1 and 2, during device operation, the on-off valves V1, V3, V4 are open, and the on-off valves V2, V5 are closed. On the other hand, when the device stops, the on-off valves V1, V3, V4 are closed, the on-off valves V2, V5 are open, and the heat medium of the heat source is supplied in place of the cooling water of the evaporator 6. Then, the heat medium heat-exchanged by the evaporator 6 is discharged via the connecting pipe L12.

[0021] The control unit C detects the pressure and temperature of the drive flow, the heat source temperature, etc., and controls the pump 3 and the expansion valve 5, etc. In particular, when the device is stopped, the control unit C completely closes the expansion valve 5, closes the on-off valves V1, V3, and V4, and opens the on-off valves V2 and V5, supplying the heat transfer medium from the heat source in place of the water being cooled in the evaporator 6.

[0022] As a result, as shown in Figure 2, the refrigerant that had been accumulating in the evaporator 6 absorbed the heat from the heat source. medium The liquid evaporates through heat exchange and is transferred to the condenser 2 via the ejector 1. As a result, the liquid head h of the condenser 2 rises, preventing cavitation in the pump 3 when the device is started up.

[0023] As shown in Figure 3, conventionally, refrigerant accumulates in the evaporator 6 when the system is shut down. Specifically, when the system is shut down, the temperatures of each heat exchanger are 60°C to 80°C for the steam generator 4, 5°C to 20°C for the evaporator 6, and 15°C to 35°C for the condenser 2. The temperature of the evaporator 6 is the lowest, making it easy for the refrigerant to condense and accumulate. As a result, the amount of refrigerant that should be kept in the condenser 2 decreases, leading to a shortage of the required suction head NPSHR when the pump 3 is started, and cavitation occurs, which can lead to pump 3 failure. More specifically, a pressure equivalent to the liquid head h (effective suction head NPSHA) is applied to the suction port of the pump 3. Generally, cavitation can be prevented by operating the pump 3 under conditions where the effective suction head NPSHA is greater than the required suction head NPSHR. However, if the liquid head h drops to liquid head h', and liquid head h' < required suction head NPSHR, cavitation will occur when the system is started up.

[0024] Here, as shown in Figure 4, when transferring the refrigerant from the evaporator 6 to the condenser 2, it is advisable to install a check valve CV between the evaporator 6 and the ejector 1 to prevent backflow of the refrigerant. Alternatively, instead of the check valve CV, a backflow prevention valve that closes after a certain period of time has elapsed since the device was stopped may be installed.

[0025] <Procedures for handling shutdowns> Figure 5 is a flowchart showing the shutdown procedure performed by the control unit C when the device is stopped. As shown in Figure 5, first, upon receiving an instruction to stop the device, the control unit C completely closes the expansion valve 5 (step S101). Furthermore, it switches the on-off valves V1, V3, and V4 to close and the on-off valves V2 and V5 to open (step S102). As a result, the heat transfer medium from the heat source is supplied to the evaporator 6, and the refrigerant in the evaporator 6 evaporates and is transferred to the condenser 2 side.

[0026] Subsequently, the control unit C determines whether a certain period of time has elapsed (step S103). If the period of time has not elapsed (step S103: No), this determination process is repeated. On the other hand, if the period of time has elapsed (step S103: Yes), this process is terminated.

[0027] The specified time is a sufficient time for the liquid head h to exceed the required suction head NPSHR, and is based on previously acquired data on the liquid head h. Alternatively, instead of a specified time, liquid level detection using a liquid level meter or torque detection of pump 3 may be used.

[0028] <Embodiment 2> The configuration of this second embodiment is the same as the configuration shown in Figure 1, but an on-off valve V11 is added between the evaporator 6 and the ejector 1, and the shutdown processing of the control unit C is different. In this second embodiment, when the device is stopped, the control unit C closes the on-off valve V11 and fully opens the expansion valve 5, while the opening and closing control of the other on-off valves V1 to V5 is the same. As a result, the heat from the heat source medium This increases the internal pressure of the evaporator 6, causing the refrigerant to be pumped to the condenser 2 via the expansion valve 5.

[0029] <Procedures for handling shutdowns> Figure 7 is a flowchart showing the shutdown procedure performed by the control unit C in this second embodiment when the device is stopped. As shown in Figure 7, first, upon receiving an instruction to stop the device, the control unit C fully opens the expansion valve 5 (step S201). Furthermore, it switches the on-off valves V1, V3, V4, and V11 to close and the on-off valves V2 and V5 to open (step S202). As a result, the heat transfer medium of the heat source is supplied to the evaporator 6, and the refrigerant from the evaporator 6 is pressurized and sent to the condenser 2 side via the expansion valve 5.

[0030] Subsequently, the control unit C determines whether a certain period of time has elapsed (step S203). If the period of time has not elapsed (step S203: No), this determination process is repeated. On the other hand, if the period of time has elapsed (step S203: Yes), this process is terminated.

[0031] According to the above embodiment, when the device is stopped, the refrigerant accumulated in the evaporator 6 can be transferred to the condenser 2 side using the heat transfer medium of the heat source, thereby preventing cavitation of the pump when the device is started up.

[0032] Furthermore, in the above embodiment, since the heat transfer medium to the evaporator 6 is waste hot water, the utilization of waste heat can be increased. In addition, since it is not necessary to position the heavy condenser 2 at a high position, the device can be made compact with a simple configuration and have a stable center of gravity. Moreover, the liquid tank for the buffer, which is provided downstream of the condenser 2 to ensure a sufficient liquid head h when the device is started up, can be made smaller, so the device can also be made simple and compact from this point of view as well.

[0033] Furthermore, the above-mentioned on-off valves V1~V5 and V11 can be replaced with three-way valves or multi-port directional control valves as appropriate, thereby reducing the number of valves.

[0034] It should be noted that the configurations illustrated in the above embodiments are functional schematics and do not necessarily have to be physically represented as shown. In other words, the forms of distribution and integration of each device and component are not limited to those shown, and all or part of them can be functionally or physically distributed and integrated in any unit according to various usage situations. [Explanation of Symbols]

[0035] 1 Ejector 2. Condenser 3 pumps 4. Steam generator 5. Expansion valve 6. Evaporator C control section CV check valve h,h' liquid head L1 Circulation Route L2 Branch Route L11, L12 connecting pipes LS branching point LS1~LS4 connection point V1~V5, V11 Shut-off valves

Claims

1. An ejector refrigeration system comprising: a pump for pressurizing a refrigerant; a steam generator for heating the refrigerant with a heat source to generate a drive flow; an expansion valve for reducing the pressure of the refrigerant; an evaporator for cooling a medium to be cooled with the refrigerant reduced in pressure by the expansion valve; an ejector for drawing in the refrigerant evaporated by the evaporator by the drive flow of the refrigerant from the steam generator; and a condenser for cooling the refrigerant mixed with the drive flow after being drawn into the ejector, An ejector refrigeration system characterized by having a communication mechanism that connects the path of the heat source to the evaporator when the system is stopped, causing heat exchange between the heat transfer medium of the heat source and the refrigerant of the evaporator to occur in the evaporator, and transferring the refrigerant accumulated in the evaporator to the condenser.

2. The ejector refrigeration apparatus according to claim 1, characterized in that when the apparatus is stopped, the expansion valve is completely closed, the refrigerant in the evaporator is evaporated by the heat transfer medium of the heat source via the communication mechanism, and the refrigerant is transferred to the condenser via the ejector.

3. The ejector refrigeration apparatus according to claim 2, characterized in that a check valve or a backflow prevention on / off valve is provided between the evaporator and the ejector.

4. A valve is provided between the evaporator and the ejector. The ejector refrigeration apparatus according to claim 1, characterized in that when the apparatus is stopped, the on / off valve is closed and the expansion valve is fully opened, the internal pressure of the evaporator is increased by the heat transfer medium of the heat source via the communication mechanism, and the refrigerant is pressurized and sent to the condenser via the expansion valve.

5. The aforementioned communication mechanism is, A first on / off valve provided on the outlet side of the heat source path in the steam generator, A connecting pipe connecting a first connection point provided between the steam generator and the first on-off valve and a second connection point provided on the inlet side of the path of the cooling medium in the evaporator, A second on-off valve is provided in the aforementioned connecting pipe, A third on / off valve is provided on the path of the cooling medium and upstream of the second connection point, It has, The ejector refrigeration apparatus according to any one of claims 1 to 4, characterized in that the first on-off valve and the third on-off valve are closed and the second on-off valve is open when the apparatus is stopped.

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