CN211119988U - Multistage compression multistage condensation intermediate flash incomplete cooling medium-high temperature heat pump system - Google Patents

Abstract

The utility model proposes a multi-stage compression, multi-stage condensation, intermediate flash, incomplete cooling, multi-temperature stage, medium and high temperature heat pump system. The utility model is composed of evaporators, compressors of all levels, condensers of all levels, throttle valves of all levels and gas-liquid separators of all levels, which includes a multi-stage continuous compression working medium heat pump cycle and a continuous heating process of normal temperature water; The middle and high temperature heat pump system for the incomplete cooling of the intermediate flash evaporation in the compression multi-stage condensation can be set to multi-stage (n-stage for short) according to the process requirements. The higher the temperature rise, the more stages are set. Through the multi-stage compression and multi-stage condensation process of the refrigerant, the room temperature water is continuously heated for many times, which can significantly reduce the irreversible loss of heat exchange with the refrigerant during the heating process of the room temperature water, and the compression ratio of the compressors at all levels is small. Parallel heating and hot water heating pipelines between condensers can be used for room heating to achieve cascade utilization of heat.

Description

Multi-stage compression and multi-stage condensation intermediate flash incomplete cooling medium and high temperature heat pump system

technical field

The utility model relates to the technical field of heat pumps, in particular to a medium-high temperature heat pump system for multi-stage compression, multi-stage condensation, intermediate flash, incomplete cooling, and incomplete cooling.

Background technique

The demand for medium and high temperature hot water and steam in daily life and industry is very extensive, but the production of medium and high temperature hot water often consumes a lot of electricity and fuel resources. Heat pump products have been widely used as a clean, efficient and stable heating equipment. Further improving the energy efficiency of heat pump equipment has important practical significance and social value to promote energy conservation and emission reduction, and improve economic benefits.

The condensing temperature of the conventional medium and high temperature heat pump system is constant, the normal temperature water is directly heated in the condenser, and the temperature difference between the inlet and outlet of the normal temperature water is large. The temperature difference distribution is seriously uneven, resulting in a large average heat exchange temperature difference in the condenser, large irreversible losses in the heat exchange process, and low energy efficiency of the system. The conventional single-stage compression heat pump system using non-azeotropic working fluid has similar temperature glides in the evaporation and condensation processes, and is suitable for the conditions where the temperature changes of the heat exchange fluid at the heat source and the heat sink side are similar, but for the medium and high temperature heat pump system, the heat source The temperature change on the side is generally small, and the temperature rise of the water or steam on the heat sink side is large or large, which is much greater than the temperature drop of the fluid on the heat source side. And for the working conditions with large temperature span of heat source and heat sink, the compression ratio of conventional compressors is large, and the compressor efficiency is low.

Utility model content

The utility model provides a multi-stage compression multi-stage condensation intermediate flash incomplete cooling multi-temperature stage medium-high temperature heat pump system to solve the problems of large irreversible loss in the heat exchange process, large compression ratio and low system energy efficiency.

The technical scheme adopted by the utility model is:

Multi-stage compression and multi-stage condensation intermediate flash incomplete cooling multi-temperature stage medium and high temperature heat pump system, including multi-stage continuous compression working fluid heat pump cycle and continuous heating process of normal temperature water; multi-stage compression and multi-stage condensation intermediate flash incomplete cooling process The high temperature heat pump system can be set to multi-stage (n-stage for short) according to the process requirements. The higher the temperature rise, the more stages can be set.

A multi-stage compression and multi-stage condensation intermediate flash incomplete cooling medium and high temperature heat pump system, in the system, 3≤i≤n-1, n≥4;

The outlet of the first stage compressor 3 is connected to the inlet of the working medium side of the first stage condenser 4, the outlet of the working medium side of the first stage compressor 3 is connected to the inlet of the second stage compressor 6, and the outlet of the working medium side of the first stage condenser 4 is connected. It is connected with the inlet of the first-stage throttle valve 5, the outlet of the second-stage gas-liquid separator 9 is connected with the inlet of the first-stage throttle valve 5, and the outlet of the first-stage throttle valve 5 is connected with the inlet of the working medium side of the evaporator 2. The outlet of the working fluid side of the condenser 2 is connected to the inlet of the first stage compressor 3; the normal temperature water outlet is connected to the inlet of the heat exchange fluid side of the second stage condenser 7, and the outlet of the heat exchange fluid side of the second stage condenser 7 is connected to the third stage The heat exchange fluid (hot water or steam) side inlet of the condenser is connected, the heat exchange fluid side outlet of the i-th stage condenser 11 is connected to the heat exchange fluid side inlet of the nth stage condenser 15, and the heat exchange fluid side of the nth stage condenser 15 is connected The outlet is connected to the inlet of medium and high temperature hot water or high temperature steam;

The i-1 stage compressor outlet is connected to the i stage compressor inlet, the i stage gas-liquid separator is connected to the i stage compressor inlet, the i stage compressor outlet is connected to the i+1 stage compressor inlet, The outlet of the i-th stage compressor is connected to the working fluid side inlet of the i-th stage condenser, the working fluid side outlet of the i-th stage condenser is connected to the i-th stage throttle valve inlet, and the i+1 stage gas-liquid separator outlet is connected to the i-th stage. The inlet of the first stage throttle valve is connected, the outlet of the i-th stage throttle valve is connected with the inlet of the i-th stage gas-liquid separator, and the outlet of the i-th stage gas-liquid separator is connected with the i-1 stage throttle valve inlet;

The outlet of the n-1st stage compressor is connected to the inlet of the nth stage compressor 14, the outlet of the nth stage gas-liquid separator 17 is connected to the inlet of the nth stage compressor 14, and the outlet of the nth stage compressor 14 is connected to the nth stage condenser. The inlet of the working fluid side of the condenser 15 is connected, the outlet of the working fluid side of the nth stage condenser 15 is connected with the inlet of the nth stage throttle valve 16, the outlet of the nth stage throttle valve 16 is connected with the inlet of the nth stage gas-liquid separator 17, and the The outlet of the n-stage gas-liquid separator 17 is connected to the inlet of the n-1 stage throttle valve.

The normal temperature water flows into each temperature stage condenser in turn for heating, and is continuously heated to the process design temperature to obtain medium and high temperature hot water or high temperature steam required by the process to complete the continuous heating process of normal temperature water.

The working fluid can use pure refrigerants such as R1234ze(Z), R1234ze(E), R1233zd(E), R1224yd(Z), R1336mzz(Z), R365mfc, R1234yf, R245fa, etc., or CO ₂ /R1234ze(E), CO ₂ /R1234ze(Z), CO ₂ /R1234yf, R41/R1234ze(E), R41/R1234ze(Z), R41/R1234yf, R32/R1234ze(E), R32/R1234ze(Z), R32/R1234yf, etc. Azeotropic mixture. For non-azeotropic mixed working fluid, choose a refrigerant whose temperature glide is equivalent to the temperature difference between the inlet and outlet of the heat exchange fluid of the evaporator.

The principle for determining the number of stages is: in order to ensure that the heat exchange processes of the evaporator and the condenser are matched at the same time, according to the process requirements, the temperature rise of the normal temperature water heating and the temperature drop of the heat source heat exchange fluid are calculated (normal temperature water heating temperature rise / heat source heat exchange fluid) Cooling temperature drop), rounded up as the number of stages of the system.

The system can also connect the temperature-stage condensers in parallel with the heating and hot water heating pipelines, which can be used as a multi-stage compression and multi-stage condensation intermediate flash incomplete cooling heat pump dual supply system. The heating end can be equipped with fan coils, floor coils, radiators and other devices, and the condensers at all levels can directly provide heat for it, which is used for room heating and realizes the cascade utilization of heat.

Compared with the prior art, the advantages and positive effects of the present utility model are:

效率提高，有效提升系统的能效；(1) Compared with the conventional pure single-stage compression heat pump system, in the utility model, the normal temperature water is continuously heated in the multistage condenser, and the temperature rise of the water in the condensers at all levels is relatively low, and the condensation process of each temperature position of the refrigerant is It forms a good temperature match with the normal temperature water heating process, which can significantly reduce the heat exchange temperature difference between the heat exchange fluid and the working medium, and reduce the irreversible loss of heat exchange between the heat exchange fluid and the refrigerant.

Improve efficiency, effectively improve the energy efficiency of the system;

效率及能效，提高经济效益；(2) For a conventional single-stage compression heat pump system using a non-azeotropic working fluid, it is difficult for the working fluid in the evaporator and the condenser to match the temperature of the heat exchange fluid at the same time. Compared with the conventional non-azeotropic working fluid single-stage compression heat pump system, the heating process of the normal temperature water of the present utility model undergoes two or more consecutive temperature rises, and the temperature rise in each heating process is not high, which is different from the non-azeotropic refrigerant. The evaporation process and the condensation process at each temperature level form a good temperature match. Through the utility model, the fluids on both sides of the evaporator and the condenser can be matched at the same time, the irreversible loss of heat exchange is greatly reduced, and the system is further improved.

Efficiency and energy efficiency to improve economic benefits;

(3) The air volume of the compressor of the second stage is less, and the suction volume of the compressor is reduced. Compared with the single-stage heat pump system under the same normal temperature water temperature rise condition, the power consumption of the compressor of the present invention is significantly reduced, Compressor cost reduction;

(4) Compared with the traditional single-stage compression, the pressure ratio of the multi-stage compression process is reduced, and the isentropic efficiency of the compressor is improved. In addition, the device of the utility model is provided with an intermediate flash evaporation process to cool the superheated gas at the outlet of the compressor, the temperature of the exhaust gas is reduced, and the service life of the compressor is prolonged;

(5) The device can be used for heating, production of domestic hot water, and industrial high-temperature hot water and high-pressure steam at the same time. It has a wide range of uses and has a good development prospect.

Description of drawings

Figure 1 is a diagram of a mid-to-high temperature heat pump system for incomplete cooling of intermediate flashing with dual-stage compression and dual-condenser;

Fig. 2 is the temperature and enthalpy diagram of the middle and high temperature heat pump system in the incomplete cooling of the intermediate flashing of the two-stage pure compression double condenser;

Fig. 3 is the temperature and enthalpy diagram of the middle and high temperature heat pump system in the middle and high temperature heat pump system with incomplete cooling of intermediate flashing in two-stage non-azeotropic working fluid compression double condensers;

Figure 4 is a diagram of a dual-stage compression dual-condenser intermediate flash incomplete cooling heat pump dual-supply system;

Figure 5 is a diagram of a mid-to-high temperature heat pump system for incomplete cooling of intermediate flash in a multi-stage compression multi-stage condenser.

Detailed ways

Example 1: Intermediate and high temperature heat pump system for incomplete cooling of intermediate flashing with dual-stage compression and dual-condenser

The system consists of the first-stage heat pump cycle, the second-stage heat pump cycle and the continuous heating process of normal temperature water. The system is shown in Figure 1.

(1) If the system adopts pure working fluid, the temperature and enthalpy diagram of the middle and high temperature heat pump system in the middle and high temperature heat pump system is shown in Fig. The specific implementation is as follows:

Step 1: The first stage compressor 3 inhales the low-temperature and low-pressure working medium at the outlet of the working medium side of the evaporator 2 (state 1 in Figure 2), and compresses it into a superheated gas with medium temperature and pressure (state 2 in Figure 2) , and then the superheated gas is divided into two paths. All the way of gas flows into the inlet of the working medium side of the first-stage condenser 4, the working medium in the condenser is condensed to a saturated liquid (state 10 in figure 2), and the normal temperature water (state w1 in figure 2) is heated to a certain temperature (state w1 in figure 2) state w2). After that, the working medium enters the first-stage throttle valve 5 to be throttled and depressurized to a two-phase fluid state (state 11 in Figure 2), and the gas-liquid two-phase fluid enters the inlet of the working medium side of the evaporator 2. After the working medium evaporates and absorbs the heat of normal temperature water It becomes a saturated gas state (state 1 in FIG. 2 ) and is sucked by the first-stage compressor 3 .

The second step: the other superheated gas flowing out from the first stage compressor 3 flows into the second stage compressor 6, and the working fluid is compressed into a high temperature and high pressure fluid (state 4 in FIG. 2), and then flows into the second stage condenser 7 At the inlet of the working medium side, the working medium exchanges heat with the heat exchange fluid (hot water or steam) flowing out from the heat exchange fluid side of the first-stage condenser (states w2 and w3 in Figure 2, w2 and w3 are the same state), The heat exchange fluid is further heated to state w4 of FIG. 2 .

The third step: the working fluid flowing out of the second-stage condenser 7 (state 6 in Figure 2) flows through the second-stage throttle valve 8 to be throttled and depressurized, and becomes a gas-liquid two-phase state (state 7 in Figure 2), Then it flows into the gas-liquid separator 9 to separate the gas and liquid. The working fluid at the outlet of the gas-liquid separator 9 is divided into two paths (saturated gas and saturated liquid), and one saturated gas (state 8 in Figure 2) is mixed with the medium-pressure superheated gas at the outlet of the first-stage compressor 3 and enters the second-stage compressor 6 Compressed into high temperature and high pressure gas (state 4 in Figure 2), and another saturated liquid (state 10 in Figure 2) merges with the saturated liquid at the outlet of the working medium side of the first-stage condenser 4, and enters the first-stage throttle valve 5 After flowing to the state 11 in Figure 2, it enters the inlet of the working medium side of the evaporator 2, and the working medium absorbs heat and becomes a saturated gas state (state 1 in Figure 2), and is sucked by the first-stage compressor 3 to complete the heat pump cycle.

Step 4: Normal temperature water (state w1 in Figure 2) first flows into the first-stage condenser 4, the heat exchange fluid side is heated to state w2 (w3) in Figure 2, and then flows into the second-stage condenser 7 (state w3 in Figure 2) ) The inlet of the heat exchange fluid side is heated to the temperature required by the process (state w4 in Figure 2), and the required medium and high temperature hot water or high temperature steam is obtained, and the continuous heating process of normal temperature water is completed.

(2) If the non-azeotropic mixed working fluid is used, the matching characteristics of the refrigerant of the two-stage compression double-condenser intermediate flash incomplete cooling medium and high temperature heat pump system and the heating process of normal temperature water will be more excellent, which can further improve the energy efficiency of the system. Improve economic efficiency. Figure 3 shows the temperature and enthalpy diagram of the mid-high temperature heat pump system with incomplete cooling of the intermediate flash in the two-stage non-azeotropic refrigerant compression and double condensers.

The specific implementation is as follows:

The first step: the first-stage compressor 3 sucks the low-temperature and low-pressure working medium at the outlet of the working medium side of the evaporator 2 (see Fig. 3 state 1), and compresses it into medium-pressure superheated gas (see Fig. 3 state 2), The gas is then divided into two paths. All the way into the inlet of the working medium side of the first-stage condenser 4, the working medium in the condenser is condensed to a saturated liquid (state 8 in Figure 3), and the normal temperature water on the heat exchange fluid side (state w1 in Figure 3) is heated to a certain temperature (Figure 3 state w2). After that, the working medium enters the first-stage throttle valve 5 to be throttled and depressurized to a two-phase fluid state (state 11 in Figure 3), and the gas-liquid two-phase fluid enters the inlet of the working medium side of the evaporator 2. It is a saturated gas state (state 1 in FIG. 3 ) and is sucked by the first-stage compressor 3 .

The second step: the second-stage compressor 6 of another gas flowing out from the first-stage compressor 3, the working fluid is compressed into a high-temperature and high-pressure fluid (as shown in Figure 3, state 4), and flows into the working fluid side of the second-stage condenser 7 At the inlet, heat exchange is performed with the heat exchange fluid flowing out from the heat exchange fluid side of the first-stage condenser 4 (states w2 and w3 in Fig. 3, w2 and w3 are the same state), and the heat exchange fluid is further heated to state w4 in Fig. 3 .

The third step: the working medium flowing out of the second stage condenser 7 (state 6 in Figure 3) flows through the second stage throttle valve 8 to throttle and reduce pressure, and becomes a gas-liquid two-phase state (state 7 in Figure 3). The working medium then flows into the gas-liquid separator 9 for gas-liquid separation. The working medium at the outlet of the gas-liquid separator 9 is divided into two paths (saturated gas and saturated liquid), and one saturated gas (state 10 in Figure 3) is mixed with the medium-pressure superheated gas at the outlet of the first-stage compressor 3 and enters the second-stage compressor 6 Compressed into high temperature and high pressure gas (state 4 in figure 3), another saturated liquid (state 8 in figure 3) merges with the saturated liquid at the outlet of the working medium side of the first-stage condenser 4, and enters the first-stage throttle valve 5 After flowing to the state 11 in Fig. 3, it enters the inlet of the working medium side of the evaporator 2. After absorbing heat and evaporating (state 1 in Fig. 3), it is sucked by the first-stage compressor 3 to complete the heat pump cycle.

Step 4: Normal temperature water (state w1 in Figure 3) first flows into the heat exchange fluid side of the first-stage condenser 4 to be heated to the state w2 (w3) in Figure 3, and then flows into the heat exchange fluid side of the second-stage condenser 7 to continue heating (state w4 in Fig. 3), it is continuously heated to medium and high temperature to obtain medium and high temperature hot water or high temperature steam required by the process, and the continuous heating process of normal temperature water is completed.

Example 2: A heating and hot water heating pipeline is connected in parallel at both ends of the first-stage condenser to form a dual-stage compression dual-condenser intermediate flash incomplete cooling heat pump dual supply system. The system is shown in Figure 4.

The heating terminal 10 can be equipped with heating terminals such as fan coils, ground coils, radiators, etc. The normal temperature heat exchange fluid at the outlet of the heating terminal 10 enters the heat exchange fluid side of the first-stage condenser 4, and is heated to a certain level for the first time. temperature, the return water at the heating end exchanges heat with the high-temperature working medium flowing out from the first-stage compressor 3, the exhaust temperature of the first-stage compressor 3 decreases, and the return water at the heating end is further heated for room heating , to achieve cascade utilization of heat and reduce heat loss.

Embodiment 3: Intermediate and high temperature heat pump system with three-stage and above compression multi-condenser intermediate flash incomplete cooling.

The device can also be designed as a medium-high temperature heat pump system for incomplete cooling of the intermediate flash in the multi-stage compression multi-stage condenser according to the specific implementation needs, so as to realize the heating of the normal temperature water for many times, so as to obtain higher temperature hot water or steam, so as to Better adapt to the requirements of different processes. The middle and high temperature heat pump system of multi-stage compression multi-stage condenser intermediate flash incomplete cooling is shown in Figure 5.

The specific implementation is as follows:

Step 1: The first-stage compressor 3 inhales the low-temperature and low-pressure working medium at the outlet of the working medium side of the evaporator 1, compresses it into an intermediate-pressure superheated gas, and then divides it into two paths. All the way superheated gas flows into the working medium side of the first stage condenser 4, the working medium in the condenser is condensed, and the normal temperature water is heated to a certain temperature. After that, the working medium enters the first-stage throttle valve 5 to be throttled and reduced in pressure, and then enters the working medium side of the evaporator 1. After the working medium absorbs heat and evaporates, it is sucked into the first-stage compressor 3.

The second step: the other working medium flowing out from the first-stage compressor 3 is mixed with the saturated gas in the second-stage gas-liquid separator and then enters the second-stage compressor 6, compressed into superheated gas, and the second-stage compressor The fluid flowing out of 6 is divided into two paths, one of which flows into the working fluid side of the second stage condenser 7, and exchanges heat with the normal temperature water flowing out from the heat exchange fluid side of the first stage condenser 4, and the normal temperature water is further heated. The heated normal temperature water enters the heat exchange fluid side of the third-stage condenser. The fluid flowing out from the working medium side of the second-stage condenser 7 is mixed with the gas-liquid two-phase fluid from the third stage, and flows through the second-stage throttle valve 8 to be throttled and depressurized, changing into a gas-liquid two-phase state, and entering the first stage. The secondary gas-liquid separator 9 separates gas and liquid. The working medium at the outlet of the second-stage gas-liquid separator 9 is divided into two paths (saturated gas and saturated liquid). The saturated liquid is combined with the saturated liquid at the outlet of the working medium side of the first-stage condenser 4, and enters the first-stage throttle valve 5 to be throttled. Another fluid flow from the second stage compressor 6 enters the third stage compressor.

Step 3: The structure of the system from the 3rd level to the n-1th level is the same. To simplify the description, the 3rd level to the n-1th level are all represented by the i-th level. The other working medium flowing out from the i-1 stage compressor enters the i stage compressor 10 and is compressed into superheated gas. The superheated gas flowing out from the i stage compressor 10 is divided into two paths, one of which flows into the i stage The working fluid side of the condenser 11 exchanges heat with the heat exchange fluid flowing out from the heat exchange fluid side of the i-1 stage condenser, the heat exchange fluid is further heated, and the heated normal temperature water enters the i+1 stage condenser for exchange. Thermal fluid side. The fluid flowing out from the working fluid side of the i-th condenser 11 is mixed with the saturated liquid from the i+1-th stage and flows through the i-th stage throttle valve 12 to be throttled and reduced in pressure, and becomes a gas-liquid two-phase state, and then enters the i-th stage The stage gas-liquid separator 13 separates gas and liquid, and the working fluid at the outlet of the i-th stage gas-liquid separator 13 is divided into two paths (saturated gas and saturated liquid), and one path of the saturated gas and the outlet of the i-1 stage first-stage compressor are divided into two paths. The medium pressure superheated gas is mixed into the second stage compressor 10 of the i-th stage, and the other saturated liquid is combined with the saturated liquid at the outlet of the working fluid side of the first-stage condenser of the i-1 stage, and enters the first-stage section of the i-1 stage. throttle valve. Another fluid flowing out from the i-th stage compressor 10 enters the i+1-th stage compressor to be compressed.

Step 4: The other fluid flowing out of the n-1st stage compressor enters the nth stage compressor 14 and is compressed into superheated gas, and the superheated gas flowing out of the nth stage compressor 14 flows into the nth stage condenser 15 The working medium side, It exchanges heat with the heat exchange fluid flowing out from the heat exchange fluid side of the n-1 stage condenser, and the heat exchange fluid is heated for the last time.

Step 5: The fluid flowing out from the working medium side of the n-th stage condenser 15 flows through the n-th stage throttle valve 16 to be throttled and depressurized, and becomes a gas-liquid two-phase state, and then enters the n-th stage gas-liquid separator 17 to make the gas liquid separation. The working fluid at the outlet of the n-th stage gas-liquid separator 17 is divided into two paths (saturated gas and saturated liquid). In the stage compressor 14, the other saturated liquid is combined with the saturated liquid at the outlet of the working medium side of the n-1 stage first stage condenser, and enters the n-1 stage first stage throttle valve for throttling.

The sixth step: the normal temperature water flows into the condensers of all levels in turn, and after being continuously heated to medium and high temperature, it flows out from the heat exchange fluid side of the nth stage condenser 17 to obtain the medium and high temperature hot water or high temperature steam required by the process, and complete the continuous flow of normal temperature water. heating process.

Although the preferred embodiments of the present utility model have been described above in conjunction with the accompanying drawings, the present utility model is not limited to the above-mentioned specific embodiments, which are only illustrative and not restrictive. Under the inspiration of the present utility model, those of ordinary skill can also make many forms without departing from the scope of protection of the present utility model and the claims, which all belong to the protection scope of the present utility model.

Claims (2)

1. A multi-stage compression multi-stage condensation intermediate flash incomplete cooling medium-high temperature heat pump system is characterized in that i is more than or equal to 3 and less than or equal to n-1, and n is more than or equal to 4 in the system;

the outlet of the first-stage compressor (3) is connected with the working medium side inlet of the first-stage condenser (4), the working medium side outlet of the first-stage compressor (3) is connected with the inlet of the second-stage compressor (6), the working medium side outlet of the first-stage condenser (4) is connected with the inlet of the first-stage throttle valve (5), the outlet of the second-stage gas-liquid separator (9) is connected with the inlet of the first-stage throttle valve (5), the outlet of the first-stage throttle valve (5) is connected with the working medium side inlet of the evaporator (2), and the working medium side outlet of the evaporator (2) is connected with the inlet of the first-stage compressor; the normal-temperature water outlet is connected with a heat exchange fluid side inlet of a second-stage condenser (7), a heat exchange fluid side outlet of the second-stage condenser (7) is connected with a heat exchange fluid side inlet of a third-stage condenser, heat exchange fluid is hot water or steam, a heat exchange fluid side outlet of an i-th-stage condenser (11) is connected with a heat exchange fluid side inlet of an n-th-stage condenser (15), and a heat exchange fluid side outlet of the n-th-stage condenser (15) is connected with a middle-high temperature hot water or high-temperature steam inlet;

an outlet of the i-1 stage compressor is connected with an inlet of the i-1 stage compressor (10), an i-th stage gas-liquid separator (13) is connected with an inlet of the i-th stage compressor (10), an outlet of the i-th stage compressor (10) is connected with an inlet of the i +1 stage compressor, an outlet of the i-th stage compressor (10) is connected with a working medium side inlet of an i-th stage condenser (11), a working medium side outlet of the i-th stage condenser (11) is connected with an inlet of an i-th stage throttling valve (12), an outlet of the i +1 stage gas-liquid separator is connected with an inlet of the i-th stage throttling valve (12), an outlet of the i-th stage throttling valve (12) is connected with an inlet of the i-th stage gas-liquid separator (13), and an outlet of the i-th stage gas-liquid separator;

the outlet of the n-1 stage compressor is connected with the inlet of the n-1 stage compressor (14), the outlet of the side of the n-stage gas-liquid separator (17) is connected with the inlet of the n-stage compressor (14), the outlet of the n-stage compressor (14) is connected with the working medium side inlet of the n-stage condenser (15), the working medium side outlet of the n-stage condenser (15) is connected with the inlet of the n-stage throttle valve (16), the outlet of the n-stage throttle valve (16) is connected with the inlet of the n-stage gas-liquid separator (17), and the outlet of the n-stage gas-liquid separator (17) is connected with the inlet of the n-1 stage throttle valve.

2. The system as claimed in claim 1, wherein the working medium is pure refrigerant or CO₂/R1234zeE、CO₂/R1234zeZ、CO₂Non-azeotropic mixtures of/R1234 yf, R41/R1234zeE, R41/R1234zeZ, R41/R1234yf, R32/R1234zeE, R32/R1234zeZ, R32/R1234 yf.

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