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 raising pressure of a coolant; a steam generator 4 heating the coolant with a heat source and generating a drive flow; an expansion valve 5 compressing the coolant; an evaporator 6 which cools a cooled medium with the coolant compressed 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 between the evaporator 6 and the condenser 2 via the pump 3 is provided. Before the device is started, the communication mechanism is communicated, the coolant suspended in the evaporator 6 is transferred to the condenser 2, and then the device is started through the communication mechanism.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 heat 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 depressurized to 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 a communication mechanism is provided to connect the evaporator and the condenser via the pump, and before starting the system, the communication mechanism is opened to transfer the refrigerant accumulated in the evaporator to the condenser, and then the communication mechanism is closed to start the system.

[0008] Furthermore, the present invention is characterized in that, in the above invention, the communication mechanism communicates the evaporator and the steam generator with the condenser via the pump.

[0009] Furthermore, the present invention is characterized in that, in the above invention, the communication mechanism forms a first connecting passage on the upstream side of the pump that connects the lower side of the evaporator, the lower side of the steam generator, and the first inlet of the pump from before the start of the device until the start of the device, and a second connecting passage on the downstream side of the pump that connects the outlet of the pump to the second inlet of the pump, or the outlet of the condenser, or the inlet of the condenser, which is upstream of the first inlet of the pump. [Effects of the Invention]

[0010] According to the present invention, cavitation of the pump during device startup can be prevented with a simple configuration. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a circuit diagram showing the configuration of an ejector refrigeration device according to an embodiment of the present invention. [Figure 2] Figure 2 shows the state of the device before startup in an embodiment 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 flowchart showing the startup processing procedure performed by the control unit before the device is started up. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments for carrying out this invention will be described with reference to the attached drawings.

[0013] <Overall Structure> Figure 1 is a circuit diagram showing the configuration of an ejector refrigeration system according to an embodiment of the present invention. The ejector refrigeration system illustrated here recovers waste heat from waste hot water such as factory wastewater or used cooling water as a heat source to cool the cooling medium, and has an ejector 1, a condenser 2, a pump 3, and a steam generator 4 connected sequentially on a circulation path L1. The ejector refrigeration system is also provided with a branch path L2. The branch path L2 branches off from the portion upstream of the pump 3 at the branching point LS between the condenser 2 and the steam generator 4 of the circulation path L1, and supplies a portion of the refrigerant flowing through the circulation path L1 as a suction fluid to the ejector 1. The cooling medium can be water, oil, or other refrigerants. In this embodiment 1, in particular, an ejector refrigeration system that generates chilled water from the cooling water using waste heat recovered from waste hot water is illustrated.

[0014] Pump 3 circulates and supplies the refrigerant in the circulation path L1. More specifically, pump 3 is, for example, a liquid-phase variable displacement pump that pressurizes the refrigerant and supplies it to the ejector 1. Pump 3 in this embodiment 1 is driven at a rotational speed according to a drive signal provided by the control unit C, which will be described later. The steam generator 4 evaporates the refrigerant supplied from pump 3 by performing heat exchange with a heat source such as waste hot water supplied to the steam generator 4.

[0015] The branching path L2 is equipped with an expansion valve 5 and an evaporator 6. The expansion valve 5 expands and reduces the pressure of the refrigerant that has passed through the condenser 2 and been supplied via the branching point LS. The evaporator 6 evaporates the refrigerant by exchanging heat between the liquid phase refrigerant after it has passed through the expansion valve 5 and the water to be cooled supplied to the evaporator 6. An electronic expansion valve is preferred as the expansion valve 5, but a manual expansion valve, a constant pressure expansion valve, a temperature expansion valve, or other types of throttling mechanisms may be appropriately selected depending on the application and configuration.

[0016] Here, in the first embodiment, a communication mechanism is provided to communicate at least between the evaporator 6 and the condenser 2 via the pump 3. Before starting the device, this communication mechanism is made to communicate, and the refrigerant remaining in the evaporator 6 is transferred to the condenser 2. Then, this communication mechanism is closed to start the device. Note that the communication mechanism of this embodiment communicates between the evaporator 6 and the steam generator 4 and the condenser 2 via the pump 3. Since the temperature at the time of device stop is the lowest in the evaporator 6 and the refrigerant is most likely to remain, it is preferable that the communication mechanism communicates at least the evaporator 6.

[0017] This communication mechanism forms a first connection flow path on the upstream side of the pump 3 that connects the lower side of the evaporator 6, the lower side of the steam generator 4, and the first inlet of the pump from before starting the device to when starting the device, and a second connection flow path on the downstream side of the pump 3 that connects the outlet of the pump 3 and the second inlet of the pump 3 upstream of the first inlet of the pump 3 or the outlet or inlet of the condenser 2.

[0018] The first connection flow path is formed by a connection pipe L11 that connects the connection point LS1 on the lower side of the steam generator 4 and the connection point LS3 on the lower side of the evaporator 6, and a connection pipe L12 that connects the connection point LS2 formed in the middle of the connection pipe L11 and the connection point LS4 on the inlet side of the pump 3. An on-off valve V3 is provided between the connection point LS2 and the connection point LS3, and an on-off valve V2 is provided between the connection point LS2 and the connection point LS4.

[0019] Also, the second connection flow path is formed by a connection pipe L13 that connects the connection point LS5 at the outlet of the pump 3 and the connection point LS6 between the inlet of the condenser 2 and the downstream side of the condenser 2. An on-off valve V4 is provided in the connection pipe L13.

[0020] Note that in order to form the first connection flow path and the second connection flow path, an on-off valve V1 is provided between the connection point LS1 and the connection point LS5, and an on-off valve V5 is provided between the connection point LS6 and the branch point LS.

[0021] As shown in FIGS. 1 and 2, during the operation of the device after startup, the on-off valves V1 and V5 are open, the on-off valves V2, V3, and V4 are closed, and the expansion valve 5 is in a variable throttle state. On the other hand, from before the device startup to the device startup, the on-off valves V1 and V5 are closed, the on-off valves V2, V3, and V4 are open, the expansion valve 5 is fully closed, and the first connection flow path and the second connection flow path are formed. In this state, by starting the pump 3, the refrigerant retained in the evaporator 6 and the steam generator 4 is transferred to the condenser 2.

[0022] The control unit C detects the pressure, temperature, heat source temperature, etc. of the driving flow and controls the pump 3, the expansion valve 5, etc. In particular, before the device startup, the control unit C fully closes the expansion valve 5, closes the on-off valves V1 and V5, opens the on-off valves V2, V3, and V4, starts the pump 3, transfers the refrigerant retained in the evaporator 6 and the steam generator 4 to the condenser 2, and then starts the device by opening the on-off valves V1 and V5 and closing the on-off valves V2, V3, and V4.

[0023] As a result, as shown in FIG. 2, before the device startup, the refrigerant retained in the evaporator 6 and the steam generator 4 is transferred to the condenser 2 by starting the pump 3. As a result, the liquid head h of the condenser 2 rises, and the occurrence of cavitation in the pump 3 can be prevented at the time of device startup.

[0024] As shown in Figure 3, conventionally, refrigerant mainly 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. Refrigerant also accumulates in the steam generator 4. 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, causing cavitation that 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.

[0025] <Startup Procedure> Figure 4 is a flowchart showing the startup processing procedure performed by the control unit C before the device is started. As shown in Figure 4, first, before the device is started, the control unit C completely closes the expansion valve 5 (step S101). Furthermore, it switches the on-off valves V1 and V5 to close and the on-off valves V2, V3, and V4 to open (step S102). This creates a flow path from the evaporator 6 and steam generator 4 via the pump 3 to the condenser 2.

[0026] Subsequently, the control unit C starts the pump 3 (step S103) and transfers the refrigerant from the evaporator 6 and steam generator 4 to the condenser 2. Then, the control unit C determines whether a certain period of time has elapsed (step S104). If the period of time has not elapsed (step S104: No), this determination process is repeated. On the other hand, if the period of time has elapsed (step S104: Yes), the pump 3 is stopped (step S105) and the transfer of refrigerant is terminated.

[0027] Subsequently, in preparation for starting the device, valves V1 and V5 are opened, and valves V2, V3, and V4 are closed (step S106), the device is started (step S107), and this process is completed.

[0028] 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.

[0029] According to the above embodiment, before the device is started, the refrigerant accumulated in the evaporator 6 and the steam generator 4 can be transferred to the condenser 2 using the pump 3, thereby preventing cavitation of the pump 3 when the device is started.

[0030] Furthermore, in the above embodiment, there is no need to position the heavy condenser 2 at a high position, resulting in a simpler configuration, a more compact device, and a more stable center of gravity. In addition, the buffer liquid tank located downstream of the condenser 2, which is provided to ensure a sufficient liquid head h when the device is started, can be made smaller, thus further contributing to a simpler and more compact device configuration.

[0031] Furthermore, the above-mentioned on-off valves V1 to V5 can be replaced with three-way valves or multi-port directional control valves as appropriate, thereby reducing the number of valves.

[0032] 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]

[0033] 1 Ejector 2. Condenser 3 pumps 4. Steam generator 5. Expansion valve 6. Evaporator C control section h,h' liquid head L1 Circulation Route L2 Branch Route L11, L12, L13 connecting pipes LS branching point LS1~LS6 connection point V1~V5 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, A communication mechanism is provided that connects the evaporator and the condenser via the pump. An ejector refrigeration system characterized by opening a communication mechanism before starting the system to transfer the refrigerant accumulated in the evaporator to the condenser, and then closing the communication mechanism to start the system.

2. The ejector refrigeration apparatus according to claim 1, characterized in that the communication mechanism connects the evaporator and the steam generator with the condenser via the pump.

3. The aforementioned communication mechanism is, From before the device is started until the device is started, A first connecting channel on the upstream side of the pump connects the lower side of the evaporator, the lower side of the steam generator, and the first inlet of the pump, A second connecting channel downstream of the pump connects the outlet of the pump to the second inlet of the pump or the outlet or inlet of the condenser, which is upstream of the first inlet of the pump, The ejector refrigeration apparatus according to claim 2, characterized by forming

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