JPS6158740B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cooling device using a mixed refrigerant, and more particularly to a cooling device using a mixed refrigerant that can efficiently cool and remove heat in response to fluctuations in heat load. As is well known, multi-component cascade cycles are widely used as industrial cooling devices. This method uses a single component as a refrigerant and combines multiple refrigeration cycles to obtain the desired low temperature. On the other hand, the mixed refrigerant cascade cycle is considered to be superior to the single refrigerant cascade cycle in that it uses a mixed refrigerant. This cycle compresses a gaseous mixed refrigerant having a certain boiling point range and indirectly cools the compressed refrigerant with water, air, or other fluid to liquefy a portion of the compressed refrigerant. After gas-liquid separation, the condensed liquid is adiabatically expanded to generate cold, and the uncondensed components are indirectly cooled by the confluence of the cold and the low-pressure return refrigerant in the latter stage. In this method, the condensate produced here is adiabatically expanded again to generate cold, thereby obtaining the desired low temperature in the evaporator. An example of a cooling device using this mixed refrigerant cascade cycle will be explained with reference to the system diagram shown in FIG. The cooling device that performs this cycle includes a compressor 1 that compresses a mixed refrigerant, a precooler 2 that cools the compressed mixed refrigerant, and a gas-liquid separator that separates the gas-liquid mixed flow obtained in the precooler 2. a first stage expansion valve 4 for adiabatically expanding the condensate separated by the separator 3;
and a heat exchanger 5 for exchanging heat between the low-temperature flow obtained by this adiabatic expansion and the confluence of the low-pressure return refrigerant in the latter stage and the uncondensed components separated by the gas-liquid separator 3.
and a second stage expansion valve 6 which adiabatically expands the condensate obtained by the heat exchanger 5, and which exchanges heat between the low temperature flow obtained by this adiabatic expansion and the fluid to be cooled which is a heat load. The evaporator 7 constitutes a cycle. Hereinafter, the operating state of the cooling device using the refrigerant cascade cycle in this case will be explained with reference to FIG.
First, the compressor 1 compresses the gaseous mixed refrigerant returned from the cycle to 0.591M·Pa to 5M·Pa.
The compressed mixed refrigerant passes through a pipe 8 to a precooler 2
It is cooled down to room temperature by gases such as water and air, and a portion of it is condensed and liquefied. This precooler 2
The gas-liquid mixed flow obtained in
and is separated into uncondensed components and condensed liquid.
The separated condensate is sent to the first stage expansion valve 4 through the pipe 10, where it is adiabatically expanded to 104 K·Pa to 395 K·Pa to generate refrigeration. The low-temperature flow obtained by this adiabatic expansion passes through the pipe 11 and joins the low-pressure return mixed refrigerant gas from the evaporator 7 in the pipe 12 at point X, becoming a low-temperature flow in the pipe 13 and flowing into the heat exchanger 5. enter.
This low-temperature stream exchanges heat with uncondensed gas, which will be described later, in the heat exchanger 5, and then returns to the compressor 1 via a pipe 14. On the other hand, the uncondensed gas separated in the gas-liquid separator 3 is sent to the heat exchanger 5 through the pipe 15, and while passing therethrough, it is brought into contact with the low-temperature flow in the pipe 13 in countercurrent. It is condensed and liquefied through heat exchange. This condensate is sent via pipe 16 to the second stage expansion valve 6 where it expands adiabatically to generate refrigeration. The low temperature flow obtained by this adiabatic expansion passes through the pipe 17 to the evaporator 7.
The fluid 18 to be cooled is cooled while passing therethrough. The cooling device using the mixed refrigerant cascade system described above has the feature that if an appropriate mixed refrigerant is selected, extremely low temperatures can be efficiently generated with a single compressor. However, on the other hand, the external heat load varies over a wide range. That is, when the inlet temperature of the cooled fluid 18 fluctuates over a wide range, the operation of cooling the cooled fluid 18 to remove heat is performed by changing the refrigerant circulation amount, operating pressure, composition ratio, and the like. Therefore, there are drawbacks such as difficulty in control and maintenance. The purpose of the present invention is to eliminate the drawbacks of the cooling device using the mixed refrigerant cascade method described above, to be able to efficiently cool and remove heat even if the temperature of the fluid to be cooled changes over a wide range, and to provide a power source for the device. An object of the present invention is to provide a cooling device that can also reduce consumption. In order to achieve this objective, the cooling device of the present invention includes a system that guides a portion of the uncondensed components from the gas-liquid separator before the first-stage expansion valve, and an adiabatic expansion system in the first-stage expansion valve. A system for guiding a portion of the refrigerant to the outlet side of the second stage expansion valve, flow rate adjustment means provided in both systems, and means for detecting the outlet temperature of the fluid to be cooled that undergoes heat exchange in the evaporator. and the flow rate regulating means is configured to flow a large amount of refrigerant in accordance with the outlet temperature of the fluid to be cooled when it is higher than the set value of the detection means, and to flow a large amount of refrigerant accordingly when the outlet temperature of the fluid to be cooled is lower than the set value. It is characterized by being controlled so that a small amount of refrigerant flows. Embodiments of the present invention will be described below with reference to the system diagram shown in FIG. In the figure, the same reference numerals as in FIG. 1 indicate the same parts, so the explanation of these parts will be omitted. The pipe 15 that leads the uncondensed gas from the gas-liquid separator 3 to the heat exchanger 5 has an E ₁
A branch pipe 19 is provided which branches from the point and connects to a point _E2 of the pipe 10 in front of the first stage expansion valve 4. In addition, in the pipe 11 on the outlet side of the first stage expansion valve 4, there is a branch pipe which branches from point _E3 on the way and connects to point _E4 on the way in the pipe 17 on the outlet side of the second stage expansion valve 6. 20 are provided. Flow control valves 21 and 22 are provided in the middle of both branch pipes 19 and 20, respectively. Both flow rate control valves 21 and 22 have an opening degree of 18 for the fluid to be cooled.
The temperature is controlled according to the temperature at the evaporator outlet. That is, a detector 23 for detecting the temperature of the fluid 18 to be cooled is provided on the outlet side of the fluid 18 to be cooled. Both flow rate control valves 21 and 22 operate in conjunction with the detector 23 so that when the outlet temperature of the cooled fluid 18 is higher than the set value of the detector 23, the opening degree increases accordingly, and the set value When the opening is lower, the opening degree is controlled to be smaller accordingly. Next, to explain the operating state of the cooling device, the mixed refrigerant compressed by the compressor 1 is transferred to the pipe 8.
The liquid is then sent to the precooler 2, where it is cooled to room temperature by fluids such as water and air, and a portion of it is condensed and liquefied. The gas-liquid mixed stream obtained in the precooler 2 is sent to the gas-liquid separator 3 through a pipe 9, and is separated into uncondensed components and condensed liquid. The separated uncondensed gas is transferred to pipe 15.
The condensate is branched into two at _one point E, one of which passes through a branch pipe 19 and has its flow rate adjusted by a flow rate control valve 21, and is then separated from the gas-liquid separator 3 and passes through a pipe 10, and the condensate flows through _two points E. We'll meet up at The combined refrigerant is adiabatically expanded in the first stage expansion valve 4 to generate cold, and is branched into two at point _E3 on the way through the pipe 11. One of the cold streams passes through a branch pipe 20, the flow rate of which is adjusted by a flow control valve 22, and then merges with the low temperature stream passing through a pipe 17 at point _E4 . After passing through the pipe 17, this cold stream is sent to the evaporator 7, where it exchanges heat with the fluid 18 to be cooled, ie, cools and removes the heat load _Q1 of the fluid 18 to be cooled. The refrigerant leaving the evaporator 7 passes through the pipe 12 and joins the low-temperature flow from the expansion valve 4 at point X.
After passing through the heat exchanger 5 through the pipe 14, it returns to the compressor 1 through the pipe 14. The other part of the uncondensed gas branched at _point E enters the heat exchanger 5 through a pipe 15, where it exchanges heat with the return refrigerant, is cooled and condensed into liquid, and then passes through a pipe 16 into the second stage. The expansion valve 6 causes adiabatic expansion to generate cold. This cold flow passes through the pipe 17 and joins with the low temperature flow that passed through the pipe 20 at point _E4 on the way to reach the evaporator 7. Further, the other of the cold flows branched into two at point _E3 passes through pipe 11 and joins the return cold flow passing through pipe 12 at point X. In the above-mentioned cooling device, a part of the uncondensed gas is sent to the condensate liquid before the first stage expansion valve 4 through the branch pipe 19, and the cold gas is adiabatically expanded in the first stage expansion valve 4. A part is passed through the branch pipe 20 to the second
The cold air is adiabatically expanded by the stage expansion valve 6, and the amount of each supply is adjusted according to the outlet temperature of the fluid to be cooled 18, so that the evaporator 7 sends a low-temperature flow according to the heat load of the fluid to be cooled. Obtainable. That is, even if there is a variation in the heat load Q ₁ of the fluid to be cooled, it can be efficiently cooled and heat removed. Therefore, it is possible to always keep the outlet temperature of the fluid to be cooled constant. Next, the effect of absorbing the heat load Q ₁ of the fluid to be cooled will be explained in detail with reference to FIGS. 3 and 4. In Figure 3, the horizontal axis shows temperature (°C), the vertical axis shows enthalpy (J/Kg), and each curve is the first stage expansion valve 4.
This figure shows the temperature drop due to cold generation when adiabatic expansion occurs at . This curve is called a cooling curve (temperature vs. enthalpy), and each curve l ₁ , l ₂ , l ₃
and l ₄ is the inlet of the expansion valve, each curve l ₁ ′, l ₂ ′, l ₃ ′ and
l ₄ ′ indicates the exit condition. Also, the inflection point on each curve
The upper portions of c ₁ , c ₂ , c ₃ , c ₄ and c ₁ ′, c ₂ ′, c ₃ ′, and c ₄ ′ represent a gas phase, and the lower portions represent a gas-liquid mixed phase. And the curves l ₁ and l ₁ ′ are for the conventional cooling system, the curves l ₂ and l ₂ ′, and the curves l ₃ and
l ₃ ′, l ₄ and l ₄ ′ represent the cooling device according to the invention. Figure 4 shows the heat load of the fluid to be cooled in the evaporator.
This figure shows the operation of cooling and removing heat in response to fluctuations when Q ₁ increases or decreases like Q ₂ and Q _3. The horizontal axis shows temperature (°C) and the vertical axis shows heat. Indicates the load amount (J/h). The dashed curve L ₀ represents the operating line for removing heat in response to variations in heat load in a conventional cooling device, and the solid curves L ₁ , L ₂ , L ₃ and L ₄ represent the operating lines according to the present invention. There is. Further, Ei ₁ , Ei ₂ and Ei ₃ indicate the inlet of the evaporator, and E ₀₁ , E ₀₂ and E ₀₃ indicate the outlet. First, to explain Fig. 3, the temperature drop accompanying isenthalpic expansion by operating the expansion valve is as follows:
In the conventional system, when the inlet temperature is 30°C, the temperature reaches -37°C from point _A1 on the _l1 line to point _B1 on the _l1 ' line. In conventional cooling devices, the amount of uncondensed gas, the amount of condensed liquid, and the composition ratio thereof are constant, so the cold generation temperature obtained by the first stage expansion valve is limited to a constant value. This means that in FIG. 1 the temperature of the low-pressure cold stream passing through tube 13 is constant and the temperature at which the uncondensed gas passing through tube 15 is cooled while passing through heat exchanger 5 is limited, so that the temperature at which tube 16 is cooled is limited. This is because the inlet temperature of the second-stage expansion valve 6 that passes through the evaporator 7 becomes constant, and the outlet temperature associated with the generation of cold by the operation of the expansion valve 6, that is, the temperature of the low-temperature flow that passes through the pipe 17 leading to the evaporator 7 is limited. be. Therefore, in Fig. 4, the heat load on the evaporator
In the operation of cooling _Q1 and removing heat, the temperature of the evaporator is -55.5℃ at the inlet indicated by point _a0 on the operating line _L0 ,
The temperature at the outlet indicated by a ₀ ′ point is 10°C. Also, the heat load Q ₁
In the operation reduced to Q ₂ , the entrance indicated by b ₀ point is −54
℃, the outlet indicated by point b ₀ ' becomes -8℃. Conversely, in an operation where the heat load Q ₁ increases to Q ₃ , the temperature at the inlet, indicated by the c ₀ point, is −57.5°C, and the temperature at the outlet, indicated by the c ₀ ′ point, is 28°C. As mentioned above, in conventional cooling devices, when the heat load varies over a wide range, the cooling temperature at the inlet of the evaporator can only be obtained at a constant point for each variation in the heat load. This means that as the heat load fluctuates, the operating range for heat removal becomes narrower. On the other hand, in the cooling device according to the present invention, the third
In the figure, when the inlet temperature of the expansion valve is set to 30°C as in the conventional case, the temperature drop during isenthalpic expansion due to operation of the expansion valve is from point A ₂ on the l ₂ line to point B on the l ₂ ' line in one operation. It reaches _{the 2nd} point and obtains -38.5℃. In other operations, from point A ₃ on the l ₃ line to point B ₃ on the l ₃ ′ line, −41
Get ℃. Furthermore, in other operations, from A ₄ point on l ₄ line
Reach point B ₄ on the l ₄ ′ line and obtain −43°C. Therefore, compared to conventional devices, the temperature associated with cold generation due to operation of the expansion valve can be lowered. This is because a part of the uncondensed gas, which is a low boiling point component, is mixed into the condensed refrigerant liquid passing through the pipe 11 in FIG. Also tube 1
Since the temperature of the low-pressure refrigerant returning via 3 can be lowered, a portion of the uncondensed gas passing through the pipe 15 can be subcooled extensively while passing through the heat exchanger 5. This shows that the refrigerant passing through the pipe 16 can be cooled over a wide range, and the cooling temperature accompanying the isenthalpic expansion operation of the second stage expansion valve 6 can be lowered. Therefore, in the operation of removing heat in response to changes in heat load in Fig. 4, for example, the operation of removing heat from heat load _Q1 , point _a on the _L1 line and point _a2 on the _L2 line in the evaporator. , the inlet temperatures shown at point a ₃ on line L ₃ and point a ₄ on line L ₄ are -51.5℃, -48℃, -45℃, -42.5 respectively.
℃. Correspondingly, the aforementioned operating line L ₁ ,
The outlet temperatures shown at points a ₁ ′, a ₂ ′, _{a 3 ′} , and a ₄ ′ on L ₂ , L ₃ , and L 4 are 0°C, −10°C, −23°C, and −32°C, respectively.
is obtained. In addition, in the heat removal operation where the heat load Q ₁ is reduced to Q ₂ , the inlet temperatures shown at ₄ points b ₁ , b ₂ , b ₃ and b are -48℃, -45.2℃, -42℃ and -39℃, respectively. Become. Also, outlet temperatures b ₁ ′, b ₂ ′, b ₃ ′, and b ₄ ′ are -18°C, -27°C, -37°C, and -34°C, respectively, corresponding to the inlet temperature. Conversely, in a heat removal operation where the heat load Q ₁ increases to Q ₃ , the inlet temperatures shown at _four points c ₁ , c ₂ , c ₃ and c become −55°C, −52°C, −48.8°C and −46°C, respectively.
And the outlet temperatures shown at points c ₁ ′, c ₂ ′, c ₃ ′, and c ₄ ′ are 17.5℃, 7.6℃, and −5℃, respectively, corresponding to the inlet temperature.
°C and -21.5 °C are obtained. This means that in the cooling device according to the present invention, even if the heat load varies over a wide range as described above,
We show that it is possible to efficiently cool and remove heat in response to this. That is, in Fig. 2, the amount of uncondensed gas mixed into the condensed liquid from point _E1 before the first stage expansion valve 4 is adjusted, and a part of the cold adiabatically expanded at the first stage expansion valve 4 is mixed into the condensed liquid from point E1. Since the amount mixed into the outlet side of the second stage expansion valve 6 can be adjusted from _three points, heat can be removed in a wide range in response to fluctuations in heat load in the evaporator 7. Next, the power consumption of the conventional cooling device and the cooling device according to the present invention will be compared and studied. Conventionally, the temperature difference between the inlet side of the cooled fluid and the outlet side of the cooling fluid during the heat exchange operation of a heat exchanger is 10
°C, which was 5 °C in the present invention. In addition, the temperature difference between the outlet side of the cooled fluid and the inlet side of the cooling fluid is 40
℃, which was 15℃ in the present invention. On the other hand, it is known that the theoretical power consumption of a refrigeration cycle depends on the increase or decrease in entropy accompanying expansion and heat exchange operations. Particularly in heat exchange operations, it is known that by reducing the temperature difference between the fluid to be cooled and the cooling fluid, entropy decreases and theoretical power consumption decreases. Therefore, based on the above-mentioned actual measurement results, it is assumed that the heat load conditions are the same for the device of this example and the device of the conventional example (that is, the outlet and inlet temperatures of the heat exchange fluid are assumed to be the same). ) The trial calculation is as follows.

[Table] According to the above calculations, when the heat load conditions are the same, the power consumption was 80.1KW in the conventional example, but it was 66.5KW in this example, a reduction of 17%. As explained above, according to the cooling device using the mixed refrigerant of the present invention, even if the temperature of the fluid to be cooled, that is, the external heat load fluctuates over a wide range, it is possible to efficiently cool and remove heat in response to this. Moreover, the power consumption of the device can also be reduced.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a cooling system using a conventional mixed refrigerant, Fig. 2 is a system diagram of a cooling system using a mixed refrigerant of the present invention, and Fig. 3 is a system diagram of a cooling system using a mixed refrigerant of the present invention. FIG. 4 is a graph showing a comparison of the temperature drop between the conventional method and the present invention, and FIG. 4 is a graph showing a comparison of the heat removal operation in the evaporator between the conventional method and the present invention. 1... Compressor, 2... Precooler, 3... Gas-liquid separator, 4... First stage expansion valve, 5... Heat exchanger, 6...
...Second stage expansion valve, 7...Evaporator, 19,20...
Branch pipe, 21, 22...flow control valve, 23...detector.

Claims (1)

[Claims] 1 After compressing the gaseous mixed refrigerant, it is cooled in a precooler, separated into condensed liquid and uncondensed components in a gas-liquid separator, and the condensed liquid is adiabatically expanded in the first stage expansion valve to cool it. The uncondensed components are cooled in a heat exchanger by combining the cold and the low-pressure return refrigerant in the latter stage, and the uncondensed components are adiabatically expanded in a second stage expansion valve to generate cold. In a cooling device configured to obtain a target low temperature with an evaporator, a system that guides a part of the uncondensed components from the gas-liquid separator to the front of the first stage expansion valve;
A system that guides a part of the refrigerant adiabatically expanded in the first-stage expansion valve to the outlet side of the second-stage expansion valve, flow rate adjustment means provided in both systems, and an evaporator where heat is exchanged. means for detecting the outlet temperature of the fluid to be cooled, and both flow rate regulating means are configured to flow a large amount of refrigerant accordingly when the outlet temperature of the fluid to be cooled is higher than a set value of the detection means; A cooling device using a mixed refrigerant, characterized in that when the refrigerant is lower than a set value, the refrigerant is controlled to flow in a small amount accordingly.