CN108106047B - CO2 dual-temperature refrigeration system with ejector, method and application thereof - Google Patents

Abstract

The invention discloses a _CO2 dual-temperature refrigeration system with an ejector, a method and its application, including an ejector and a control circuit, and when the ambient temperature is lower than the set value, by adjusting the control circuit, from the medium temperature evaporator and the low pressure compressor The gas at the outlet does not enter the ejector after being mixed, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. At this time, the system works at subcritical; when the ambient temperature is higher than the set value, by adjusting the control loop, Automatically switch to operation with ejector, the gas from the outlet of the subcooler enters the ejector as the primary flow, the gas from the outlet of the medium temperature evaporator enters the ejector as the secondary flow, and the mixed gas enters the high-pressure compressor to continue the cycle. The invention introduces the injector to increase the energy efficiency ratio of the system, recovers throttling loss to a certain extent, and makes the use of CO2 in my country more efficient.

Description

CO2 dual-temperature refrigeration system with ejector, method and application thereof

technical field

The invention relates to the technical field of refrigeration, in particular to a _CO2 dual-temperature refrigeration system with an ejector, a method and an application thereof.

Background technique

Most supermarkets in our country are still using R22 as the refrigerant in the refrigeration system, but with the acceleration of the implementation process of the Montreal Protocol and the conclusion of the Kigali Amendment, they are facing a stage of accelerated phase-out of HCFCs. With the restriction, reduction and elimination of HFCs in Europe and the United States, the application of lower GWP refrigerants must be the future development trend.

In Europe, _CO2 , as an environmentally friendly natural working fluid, has been gradually promoted in supermarket refrigeration systems. Among them, the refrigeration system shown in Figure 1 below has higher energy efficiency and is widely used. In this system, the high-temperature and high-pressure refrigerant at the outlet of the compressor enters the condenser to be condensed (subcritical cycle), and then is lowered in temperature and pressure by the throttle valve, and enters the gas-liquid separator to be separated into saturated liquid and saturated gas, and the saturated gas is throttled After the valve cools down, it enters the subcooler and exchanges heat with the saturated liquid, so that the liquid is subcooled. The supercooled liquid is divided into the medium-temperature evaporator and the low-temperature evaporator after passing through different throttle valves. The refrigerant at the outlet of the low-temperature evaporator is heated and pressurized by the low-pressure compressor, and then mixed with the refrigerant at the outlet of the medium-temperature evaporator; heat exchange The final gas is mixed with the gas at the outlet of the evaporator and returned to the compressor. After entering the main compressor, the temperature and pressure are raised to complete the cycle.

The ambient temperature in China is higher than that in European countries. If CO ₂ is used directly in the supermarket refrigeration system, CO ₂ will inevitably operate under supercritical conditions, which will inevitably cause a large loss in the throttling process of the throttle valve.

To sum up, in the prior art, there is still no effective solution for how to apply CO ₂ working fluid to the refrigeration system.

Contents of the invention

In order to solve the deficiencies in the prior art, the present invention provides a _CO2 dual-temperature refrigeration system with an ejector. The present invention adds an ejector and a control circuit to realize the system with an ejector and the system without an ejector according to the ambient temperature. The flexible switching of the system improves the efficient operation of the system.

_CO2 dual-temperature refrigeration system with ejector, including ejector and control circuit, when the ambient temperature is lower than the set value, by adjusting the control circuit, the gas from the medium temperature evaporator and the outlet of the low pressure compressor will not enter the ejector after mixing , but directly mixed with the gas from the outlet of the subcooler into the high-pressure compressor, at this time the system works in subcritical;

When the ambient temperature is higher than the set value, by adjusting the control loop, it will automatically switch to the operation with ejector. The gas at the outlet of the subcooler enters the ejector as the primary flow, and the gas at the outlet of the medium-temperature evaporator and the low-pressure compressor is mixed and used as the secondary flow. The flow enters the ejector, and the gas mixed by the ejector enters the high-pressure compressor to continue the cycle.

Further, the control circuit includes a first automatic control valve and a second automatic control valve, one end of the first automatic control valve is connected to the subcooler, one end is connected to the ejector, and the third end is connected to the ejector and the high pressure on the piping between the compressors;

One end of the second automatic control valve is connected to the ejector, one end is connected to the common outlet pipeline of the medium-temperature evaporator and the low-pressure compressor, and the third end is connected to the pipeline between the ejector and the high-pressure compressor.

Further, both the first automatic control valve and the second automatic control valve are connected to a controller, and the controller automatically controls the switching states of the first automatic control valve and the second automatic control valve according to the detected ambient temperature.

Further, when the system does not have an ejector, the high-pressure compressor is connected to a condenser.

Further, when the system has an ejector, the high-pressure compressor is connected to a gas cooler or an air cooler.

Further, the working method of the CO ₂ dual-temperature refrigeration system with an ejector includes:

When the ambient temperature is lower than the set value, by adjusting the control loop, the gas from the medium-temperature evaporator and the outlet of the low-pressure compressor does not enter the ejector after being mixed, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. At this time, the system works in subcritical;

When the ambient temperature is higher than the set value, by adjusting the control loop, it will automatically switch to the operation with ejector. The gas from the outlet of the subcooler enters the ejector as the primary flow, and the gas from the outlet of the medium temperature evaporator enters the ejector as the secondary flow. After mixing The gas enters the high-pressure compressor to continue the cycle.

Further, the set value is determined according to the specific ambient temperature by comparing the COP values of the system with the injector and the system without the injector.

Further, when the ambient temperature is lower than the set value, the gas from the medium-temperature evaporator and the outlet of the low-pressure compressor does not enter the ejector after being mixed, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. The high-temperature and high-pressure refrigerant at the outlet enters the condenser and is condensed into a liquid state.

Furthermore, when the ambient temperature is higher than the set value, the gas at the outlet of the subcooler enters the ejector as a primary flow, the gas at the outlet of the medium-temperature evaporator and the low-pressure compressor mixes and enters the ejector as a secondary flow, and the gas at the outlet of the ejector Enter the high-pressure compressor to continue the cycle, and the high-temperature and high-pressure refrigerant at the outlet of the compressor enters the gas cooler to be cooled.

Further, the above-mentioned CO ₂ dual-temperature refrigeration system with an ejector can be applied to a supermarket refrigeration system.

Compared with prior art, the beneficial effect of the present invention is:

1. In the present invention, when the ambient temperature is lower than the set value, the performance of the system with an injector is worse than that of a system without an injector. In order to ensure that the system is always running efficiently, a control loop is added, which is controlled by an automatic control valve. When the ambient temperature is lower than the set value, the gas from the medium-temperature evaporator and the outlet of the low-pressure compressor does not enter the ejector after mixing, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. At this time, the system works at subcritical. As the ambient temperature rises, when the ambient temperature is higher than the set value, the system will automatically switch to the operation with the injector. The gas at the outlet of the subcooler enters the ejector as a primary flow, the gas at the outlet of the medium-temperature evaporator and the low-pressure compressor mixes and enters the ejector as a secondary flow, and the gas at the outlet of the ejector enters the high-pressure compressor to continue the cycle.

2. In the system with ejector of the present invention, the gas at the outlet of the subcooler enters the ejector as a primary flow, the gas at the outlet of the medium-temperature evaporator and the low-pressure compressor is mixed and enters the ejector as a secondary flow, and the gas at the outlet of the ejector enters the high-pressure The compressor continues to circulate, and this process can effectively utilize the energy of the gas at the outlet of the subcooler, thereby reducing the power consumption of the compressor.

3. The application of the present invention to the supermarket refrigeration system is an indispensable part of the cold chain logistics, and accounts for a large proportion in commercial refrigeration. The selection of high-efficiency, energy-saving and environmentally friendly supermarket refrigeration systems can effectively alleviate the current situation of energy shortage in my country and is conducive to sustainable development.

4. The present invention uses CO2 as the refrigerant, and its safety and environmental protection characteristics make it gradually become one of the inevitable choices for replacing refrigerants. In the long run, it has a good application prospect.

5. The present invention introduces an injector to increase the energy efficiency ratio of the system, recovers throttling losses to a certain extent, and makes the use of CO2 more efficient in my country.

Description of drawings

The accompanying drawings constituting a part of the present application are used to provide further understanding of the present application, and the schematic embodiments and descriptions of the present application are used to explain the present application, and do not constitute improper limitations to the present application.

Figure 1 shows the supermarket refrigeration system widely used in existing European countries;

Fig. ₂ is the improved band CO of the present invention Dual temperature freezing system;

Fig. 3 (a)-Fig. 3 (b) is the pressure enthalpy diagram that the present invention operates under supercritical and subcritical working conditions;

Fig. 4 Schematic diagram of comparison of COP with and without injector system.

Detailed ways

It should be pointed out that the following detailed description is exemplary and intended to provide further explanation to the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used here is only for describing specific implementations, and is not intended to limit the exemplary implementations according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural, and it should also be understood that when the terms "comprising" and/or "comprising" are used in this specification, they mean There are features, steps, operations, means, components and/or combinations thereof.

As introduced in the background technology, there is a problem of how to apply CO ₂ working fluid to the refrigeration system in the prior art. In order to solve the above technical problems, this application proposes a CO ₂ dual-temperature refrigeration system with an ejector.

The design parameters of the _CO dual-temperature refrigeration system with ejector in this application are shown in Table 1:

Table 1 Design parameters of the new dual-temperature refrigeration system with ejector

In a typical implementation of the present application, as shown in Figure ₂ , a _CO dual-temperature refrigeration system with an ejector is provided, which includes an ejector and a control circuit in the CO dual-temperature refrigeration system with an ejector. When the ambient temperature is lower than the set value, by adjusting the control loop, the gas from the medium-temperature evaporator and the outlet of the low-pressure compressor does not enter the ejector after mixing, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. When the system works in subcritical;

When the ambient temperature is higher than the set value, by adjusting the control loop, it will automatically switch to the operation with ejector. The gas at the outlet of the subcooler enters the ejector as the primary flow, and the gas at the outlet of the medium-temperature evaporator and the low-pressure compressor is mixed and used as the secondary flow. The gas flow enters the ejector, and the gas at the outlet of the ejector enters the high-pressure compressor to continue the cycle.

In this implementation example, in the above-mentioned system with an ejector, the gas after heat exchange enters the working nozzle of the ejector as a primary flow. The mixed gas from the outlet of the medium-temperature evaporator and the low-pressure compressor enters the receiving chamber of the ejector as a secondary flow, is mixed and pressurized by the ejector, and then enters the compressor. This process can effectively utilize the energy of the outlet gas of the subcooler, thereby reducing the power consumption of the compressor.

The above-mentioned injector has a simple structure, no moving parts, and no energy consumption, and can effectively recover throttling work and increase the energy efficiency ratio of the system.

In another typical implementation of the present application, the simulated calculation results of the CO ₂ dual-temperature refrigeration system with ejectors are used to verify the effectiveness of the above-mentioned system of the present application.

Among them, the simplified assumptions in the system simulation calculation include:

(1) The outlet of the evaporator is superheated steam with a degree of superheat of 10°C.

(2) The minimum heat transfer temperature difference of the condenser or air cooler is 3°C.

(3) Bitzer CO ₂ compressor is selected for the compressor, and the compressor efficiency is obtained by fitting the compressor model and working conditions.

(4) The degree of superheat of the steam at the outlet of the evaporator is 10°C.

(5) Effective degree of heat exchange of subcooler ε=0.8.

The calculation process is as follows:

The pressure-enthalpy diagrams of the system operating under supercritical and subcritical conditions are shown in Figure 3(a)-Figure 3(b) below. The numbers in Figure 2 above are labels for each state point, corresponding to the following calculation process, and the calculation is performed by MATLAB programming. 3 points are determined by the ambient temperature; 4 points are determined by the intermediate pressure; then the states of 5 points and 8 points can be determined; 6 points are determined by the throttling degree of the throttle valve; the effectiveness of the subcooler can be determined by the states of 9 points and 7 points ; The evaporation temperature of the medium temperature evaporator and the low temperature evaporator can be determined at 10 points and 11 points; The state of 15 points is obtained by steam mixing at 14 points; the primary flow at 7 points and the secondary flow at 15 points, and the state of 1 point is obtained by mixing and diffusing the ejector; the state of 2 points is obtained by combining the isentropic efficiency of the high-pressure compressor. So far, each point of the system status has been obtained.

The system COP is calculated by the following formula: Where m _m is the mass flow rate of the refrigerant in the medium temperature evaporator, m _l is the mass flow rate of the refrigerant in the low temperature evaporator, and m is the mass flow rate of the refrigerant flowing through the high pressure compressor.

After calculation, the calculation result is shown in Figure 4 below.

In yet another typical implementation of the present application, the working method of the _CO dual-temperature refrigeration system with an ejector:

The percentage increase of system COP by introducing injectors is shown in Table 2 below:

Table 2 Comparison of COP improvement with and without injector system

It can be seen from Table 2 that when the ambient temperature is lower than 20 degrees Celsius, the performance of the system with injectors is worse than that without injectors. In order to ensure that the system is always running efficiently, a control loop is added, consisting of two automatic control valves. control. When the ambient temperature is lower than 20 degrees Celsius, the gas from the medium-temperature evaporator and the outlet of the low-pressure compressor does not enter the ejector after being mixed, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. At this time, the system works in sub- critical. As the ambient temperature rises, when the ambient temperature is higher than 20 degrees Celsius, the system will automatically switch to the operation with the injector. The gas at the outlet of the subcooler enters the ejector as the primary flow, and the refrigerant at the outlet of the medium-temperature evaporator and the outlet of the low-pressure compressor are mixed, and then flows into the ejector as a secondary flow, and the mixed gas enters the high-pressure compressor to continue the cycle.

It should be noted that if the system does not pass through the ejector, it should be in a subcritical state. At this time, the gas cooler or air cooler can also be called a condenser. In transcritical operation, it is called a gas cooler, and the gas cooler is referred to as an air cooler. The selection of the temperature range in the above table is enough to explain the change trend of the system COP and the advantages and disadvantages of the system, but it does not mean that the system is only suitable for the above temperature range.

In yet another typical implementation of the present application, the application of a CO ₂ dual-temperature refrigeration system with an ejector is disclosed. The supermarket refrigeration system is an indispensable part of the cold chain logistics, accounting for a large proportion of commercial refrigeration. The selection of high-efficiency, energy-saving and environmentally friendly supermarket refrigeration systems can effectively alleviate the current situation of energy shortage in my country and is conducive to sustainable development.

In this application, _CO2 is selected as the refrigerant, and its safety and environmental protection characteristics make it gradually become one of the inevitable choices for replacing refrigerants. In the long run, it has a good application prospect.

The system introduces injectors to increase the energy efficiency ratio of the system, recover throttling losses to a certain extent, and make the use of _CO2 more efficient in our country.

Although the introduction of ejectors will increase the initial investment, it can improve the energy efficiency of the _CO2 refrigeration system. From the perspective of long-term operation, the leakage of CO ₂ refrigerant will not cause major accidents, and the cost of refrigerant charging is low; the improved system can also effectively save electric energy, thereby reducing greenhouse gas emissions in the process of power generation.

To sum up, the application has low operating cost, is safe, energy-saving and environmentally friendly, and is an effective system for reducing greenhouse gas emissions from refrigeration systems in supermarkets, and has a good application prospect.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, there may be various modifications and changes in the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included within the protection scope of this application.

Claims (11)

1. The _CO2 dual-temperature refrigeration system with ejector is characterized in that it includes ejector and control circuit, and when the ambient temperature is lower than the set value, by adjusting the control circuit, the gas from the medium temperature evaporator and the outlet of the low pressure compressor After mixing, it does not enter the ejector, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. At this time, the system works at subcritical; When the ambient temperature is higher than the set value, by adjusting the control loop, it will automatically switch to the operation with ejector. The gas at the outlet of the subcooler enters the ejector as the primary flow, and the gas at the outlet of the medium-temperature evaporator and the low-pressure compressor is mixed and used as the secondary flow. The flow enters the ejector, and the mixed gas enters the high-pressure compressor to continue the cycle. 2. band ejector as claimed in claim 1 _CO Dual temperature freezing system, it is characterized in that, described control circuit comprises first automatic control valve and second automatic control valve, one end of described first automatic control valve Connected to the subcooler, one end is connected to the ejector, and the third end is connected to the pipeline between the ejector and the high-pressure compressor; One end of the second automatic control valve is connected to the ejector, one end is connected to the common outlet pipeline of the medium-temperature evaporator and the low-pressure compressor, and the third end is connected to the pipeline between the ejector and the high-pressure compressor. 3. band ejector as claimed in claim ₂ CO Dual-temperature refrigeration system, it is characterized in that, described first automatic control valve and second automatic control valve are all connected with controller, and described controller is according to the detected The ambient temperature automatically controls the switching states of the first automatic control valve and the second automatic control valve. 4. The CO ₂ dual-temperature refrigeration system with an ejector as claimed in claim 1, wherein when the system operates without an ejector, the high-pressure compressor is connected to the condenser. 5. The CO ₂ dual-temperature refrigeration system with ejector according to claim 1, characterized in that, when the system operates with ejector, the high-pressure compressor is connected to the gas cooler. 6. The working method of the _CO2 dual-temperature refrigeration system with ejector, characterized in that it includes: When the ambient temperature is lower than the set value, by adjusting the control loop, the gas from the medium-temperature evaporator and the outlet of the low-pressure compressor does not enter the ejector after being mixed, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. At this time, the system works in subcritical; When the ambient temperature is higher than the set value, by adjusting the control loop, it will automatically switch to the operation with ejector. The gas at the outlet of the subcooler enters the ejector as the primary flow, and the gas at the outlet of the medium-temperature evaporator and the low-pressure compressor is mixed and used as the secondary flow. The flow enters the ejector, and the mixed gas enters the high-pressure compressor to continue the cycle. 7. band ejector as claimed in claim 6 The working method of the _CO double-temperature freezing system is characterized in that, the set value is based on concrete ambient temperature contrast and introduces the ejector system and the system without ejector determined by the COP value. 8. The working method of the _CO dual-temperature refrigeration system with ejector as claimed in claim 6 is characterized in that, when the ambient temperature is lower than the set value, after the gas from the outlet of the medium-temperature evaporator and the low-pressure compressor is mixed It does not enter the ejector, but directly mixes with the gas from the outlet of the subcooler and enters the high-pressure compressor. The high-temperature and high-pressure refrigerant at the outlet of the compressor enters the condenser and is condensed into a liquid state. 9. The working method of _CO dual-temperature refrigeration system with ejector as claimed in claim 6, characterized in that, when the ambient temperature is higher than the set value, the outlet gas of the subcooler enters the ejector as a primary flow, and the middle temperature The gas at the outlet of the evaporator and the low-pressure compressor is mixed and enters the ejector as a secondary flow, and the mixed gas enters the high-pressure compressor to continue circulation, and the high-temperature and high-pressure refrigerant at the outlet of the compressor enters the gas cooler to be cooled. 10. The application of the _CO2 dual-temperature refrigeration system with an ejector, characterized in that the _CO2 dual-temperature refrigeration system with an ejector according to any one of claims 1-5 can be applied to a supermarket refrigeration system. 11. The application of the working method of the _CO2 dual-temperature refrigeration system with an ejector, characterized in that the method is the working method according to any one of claims 6-9, and it is applied to a supermarket refrigeration system.