A carbon dioxide heat pump system with ejector and expander and method of operation

Abstract

The present application relates to heat pump and geothermal energy utilization technical field, especially in a kind of carbon dioxide heat pump system and operating method with ejector and expander, it includes main compressor, gas cooler, regenerator, high-pressure split node, expander, ejector, medium-pressure gas-liquid separation liquid accumulator, low-pressure evaporator inlet throttle valve, low-pressure evaporator, low-pressure return gas split node, low-pressure supercharger, medium-pressure gas tank, collaborative controller, low-temperature heat source unit, heat source side circulating pump, reversible motor / generator, external power grid;The system can solve the problems that the working condition adaptation range of single pressure energy utilization device in existing transcritical carbon dioxide heat pump is limited, the flow rate of ejector and the flow rate of expander are lack of cooperation, the available output power of expander and the demand power of low-pressure supercharger are not matched, and the controlled pressure reduction path is insufficient when pressure energy utilization device starts, stops or overhauls.

Description

Technical Field

[0001] This invention relates to the field of heat pump and geothermal energy utilization technology, and in particular to a carbon dioxide heat pump system with ejector and expander and its operation method. Background Technology

[0002] The cycle performance of a transcritical carbon dioxide heat pump depends not only on the compression and heat exchange processes but also significantly on the pressure reduction method of the high-pressure working fluid. After releasing heat, the high-pressure carbon dioxide needs to be reduced to a pressure level compatible with the low-pressure side of the cycle before entering the evaporator side. In actual operation, the high-pressure side pressure, the high-pressure side heat exchange outlet condition, the evaporation pressure, and the cycle mass flow rate will change with the heat source conditions, heat sink conditions, and operating load, resulting in variations in the available pressure difference and the scale of pressure energy. Pressure energy utilization devices used to replace or assist throttling elements not only need to complete the specified pressure reduction process but also need to adapt to changes in inlet conditions, outlet back pressure, and mass flow rate; otherwise, the relevant devices may deviate from their effective operating range and adversely affect the stability of the working fluid cycle.

[0003] To reduce throttling losses, studies have shown that ejectors can replace or partially replace throttling elements. Ejectors utilize the high-speed jet formed during the depressurization process of a high-pressure fluid to entrain a low-pressure fluid, achieving a certain degree of pressure recovery through mixing and diffusion. However, their entrainment capacity and outlet pressure are affected by the inlet conditions of the driving and entraining flows, the outlet back pressure, the nozzle structure, and critical flow conditions, thus limiting the efficient operating range of fixed-geometry ejectors.

[0004] Another method of utilizing pressure energy involves incorporating an expander in the depressurization path, allowing the high-pressure working fluid to output mechanical work during the depressurization process. Expanders can reduce irreversible losses caused by direct throttling, but their output power, isentropic efficiency, and stable operating range are affected by inlet conditions, pressure ratio, mass flow rate, rotational speed, and external load. Furthermore, engineering problems such as two-phase expansion, sealing, leakage, and variable operating condition regulation need to be addressed. Ejectors and expanders utilize the pressure energy of high-pressure working fluids differently. Ejectors primarily reduce the subsequent compression demand of low-pressure fluids through ejection and pressure recovery, without directly outputting mechanical work; expanders, on the other hand, convert some pressure energy into mechanical work, but need to be matched with the power-consuming equipment or power generation load. Therefore, the effective operating ranges and their sensitivity to operating conditions are not entirely the same for the two types of devices.

[0005] Existing technologies have proposed solutions such as ejectors, multiple ejectors, expanders, and mechanical coupling of expanders and compression equipment to improve the pressure energy utilization efficiency of transcritical carbon dioxide cycles. However, the performance of these solutions typically depends on specific configurations, design conditions, and control conditions. When the heat source temperature, heat sink temperature, operating load, and system pressure level change, the pressure energy utilization device may deviate from its effective operating range, leading to a decrease in recovery capacity or a deterioration in cycle stability.

[0006] Therefore, existing transcritical carbon dioxide heat pumps still need to solve the following problems: when operating conditions change, how to rationally utilize the high and low pressure difference according to the actual working range of different pressure energy utilization devices, take into account pressure recovery, mechanical work utilization and working fluid circulation stability, and maintain the necessary controlled pressure reduction process when related devices are inefficient, unavailable or in a state of change of operating conditions. Summary of the Invention

[0007] The main objective of this invention is to provide a carbon dioxide heat pump system with an ejector and an expander, and its operation method. This system and operation method can solve the problems of limited operating range of single pressure energy utilization device in existing transcritical carbon dioxide heat pumps, lack of coordination between ejector flow rate and expander processing flow rate, mismatch between expander available output power and low-pressure booster required power, and insufficient controlled pressure reduction path when the pressure energy utilization device is started, stopped or under maintenance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A carbon dioxide heat pump system with ejector and expander includes a main compressor, a gas cooler, a regenerator, a high-pressure splitter node, an expander, an ejector, a medium-pressure gas-liquid separator and receiver, a low-pressure evaporator inlet throttle valve, a low-pressure evaporator, a low-pressure return gas splitter node, a low-pressure booster, a medium-pressure gas storage tank, a coordinating controller, a low-temperature heat source unit, a heat source-side circulation pump, a reversible electric generator, and an external power grid. The gas outlet of the medium-pressure gas storage tank, the main compressor, the carbon dioxide side channel of the gas cooler, the regenerator, and the high-pressure diversion node are connected in sequence. The first outlet of the high-pressure diversion node is connected to the medium-pressure gas-liquid separator and reservoir via an expander branch, an ejector branch, and a safety throttling branch; the second outlet of the high-pressure diversion node is connected to the medium-pressure gas-liquid separator and reservoir via a bypass branch, so that the expander branch, the ejector branch, the safety throttling branch, and the bypass branch constitute a parallel pressure-reducing branch from the high-pressure side to the same medium-pressure side; The gas phase outlet of the medium-pressure gas-liquid separator is connected to the medium-pressure gas storage tank via the medium-pressure side channel of the regenerator, and the liquid phase outlet of the medium-pressure gas-liquid separator is connected to the low-pressure return gas diversion node via the inlet throttle valve of the low-pressure evaporator and the low-pressure evaporator. The first outlet of the low-pressure return gas diversion node is connected to the ejector inlet, and the second outlet of the low-pressure return gas diversion node is connected to the medium-pressure gas storage tank via a low-pressure booster, so that the ejector branch and the mechanical booster branch of the low-pressure booster form a parallel boosting path from the same low-pressure return gas diversion node to the medium-pressure side. The low-temperature heat source unit is connected to the heat source side channel of the low-pressure evaporator and the built-in geothermal heat exchanger in the medium-pressure liquid storage tank through a heat source side circulation pump. The expander is mechanically connected to one side shaft of the reversible electric generator via an expander-side coupling, and the low-pressure booster is mechanically connected to the other side shaft of the reversible electric generator via a low-pressure booster-side coupling. The reversible electric generator is electrically connected to the external power grid. The collaborative controller can adjust the opening and closing states of the injector drive flow inlet isolation ball valve, injector jet flow inlet isolation ball valve, expander inlet isolation ball valve, safety throttling branch normally closed isolation valve, and bypass branch gate valve according to the equipment operating status, liquid phase inventory, and shaft power status. This allows the system to switch between composite mode, expander independent mode, injector independent mode, safety throttling mode, and bypass mode, thereby broadening the operating conditions and maintaining stable heating and circulation.

[0009] A safety throttling branch and a bypass branch are connected in parallel between the high-pressure diversion node and the medium-pressure gas-liquid separator and reservoir. The safety throttling branch is equipped with a normally closed safety throttling isolation valve and a throttling valve in sequence, and the bypass branch is equipped with a bypass gate valve and a bypass throttling valve in sequence, so that the ejector branch, expander branch, safety throttling branch and bypass branch have a common high-pressure inlet and a common medium-pressure outlet.

[0010] The expander branch is provided with an expander inlet isolation ball valve, an expander, and an expander outlet check valve in sequence along the carbon dioxide flow direction; the injector branch is provided with an injector drive flow inlet isolation ball valve on the drive flow inlet side, an injector outlet check valve on the outlet side, and an injector ejector flow inlet isolation ball valve on the ejector flow inlet side; the low-pressure booster is provided with a low-pressure booster inlet isolation ball valve on the inlet side and a low-pressure booster outlet check valve on the outlet side.

[0011] The output shaft of the expander is connected to one side shaft of the reversible electric generator via an expander-side coupling, and the input shaft of the low-pressure booster is connected to the other side shaft of the reversible electric generator via a low-pressure booster-side coupling. The output mechanical power of the expander is transmitted to the low-pressure booster via the expander-side coupling, the shaft of the reversible electric generator, and the low-pressure booster-side coupling. The reversible electric generator supplements insufficient power or absorbs excess power through electromagnetic torque.

[0012] The collaborative controller determines the operating status of each device based on the ejector's ejection capability and back pressure allowable range, the expander's allowable flow rate and speed range, the low-pressure booster's exhaust capability and power requirements, and the reversible electric generator's allowable power. It also determines the current available operating mode by combining the liquid phase storage status of the medium-pressure gas-liquid separator and the mechanical power balance between the expander, low-pressure booster, and reversible electric generator. Under the available operating mode, it determines the high-pressure side flow rate, low-pressure side flow rate, ejector adjustment amount, expander load or speed, low-pressure booster speed, and reversible electric generator power status.

[0013] The regenerator includes a high-pressure side channel and a medium-pressure side channel that are isolated from each other for heat exchange. The medium-pressure gas from the medium-pressure gas-liquid separator absorbs heat from the high-pressure carbon dioxide from the gas cooler, causing the medium-pressure gas from the medium-pressure gas-liquid separator to be heated before entering the medium-pressure gas storage tank, and causing the high-pressure carbon dioxide from the gas cooler to be cooled and its specific enthalpy to be reduced. The medium-pressure gas storage tank receives the exhaust gas from the low-pressure booster and provides medium-pressure gaseous carbon dioxide to the main compressor.

[0014] The water-side outlet of the gas cooler is connected to the hot water buffer tank. The hot water buffer tank and the heating-side circulating water pump supply heat to the heating load. The return water end of the heating load is connected to the water-side inlet of the gas cooler to form a closed hot water supply loop. The heat source-side channels of the low-temperature heat source unit, the heat source-side circulating pump, the low-pressure evaporator, and the medium-pressure liquid storage tank with built-in geothermal heat exchanger are connected in series to form a heat source-side loop. Both the hot water supply loop and the heat source-side loop are isolated from the carbon dioxide circulating heat exchange.

[0015] The low-temperature heat source unit is one or more of the following: geothermal well heat exchange unit, closed underground pipe, geothermal tailwater isolation heat exchange unit, and industrial low-temperature waste water circuit; when the low-temperature heat source unit adopts geothermal heat source, the heat source side circulation pump drives the geothermal side heat transfer medium to flow through the heat source side channel of the low-pressure evaporator and the geothermal heat exchanger built into the medium-pressure liquid storage tank.

[0016] The present invention also provides a method for operating a carbon dioxide heat pump system with an ejector and an expander, comprising the following steps: Step 1: Collect the ejector flow rate, expander's available output power, low-pressure booster's required power, reversible electric generator's power status, mechanical power balance between expander and low-pressure booster, and liquid phase storage status of medium-pressure gas-liquid separator. Step 2: Based on the above equipment operating status, determine the available operating modes among the compound mode, expander independent mode, injector independent mode, safety throttling mode, and bypass mode; Step 3: Select the target mode from the available operating modes, and after the target pressure reduction branch establishes the allowable pressure difference and permissible flow rate, accept the high-pressure carbon dioxide, while the low-pressure return gas is raised to the medium-pressure side via the injector or low-pressure booster. Step 4: Based on the difference between the available output power of the expander, the required power of the low-pressure booster, and the mechanical transmission losses, the reversible electric generator is put into electric mode, generator mode, or near-zero power exchange mode. Step 5: Correct the branch allocation based on the pressure, flow rate, liquid phase inventory and mechanical power feedback after the mode switch; when the target mode no longer meets the equipment operating status requirements, redetermine the available operating mode and perform switching, downgrading or controlled shutdown.

[0017] Furthermore, in the composite mode, the expander inlet isolation ball valve, the injector drive flow inlet isolation ball valve, the injector ejector flow inlet isolation ball valve, and the low-pressure booster inlet isolation ball valve are opened, while the normally closed isolation valve of the safety throttling branch and the bypass branch gate valve are closed. High-pressure carbon dioxide is distributed to the expander and the injector at the high-pressure split node, and low-pressure return gas is distributed to the injector and the low-pressure booster at the low-pressure return gas split node. The high-pressure side split and the low-pressure side split are coordinated by the ejector's ejection capacity and the mechanical power balance between the expander, the low-pressure booster, and the reversible electric generator.

[0018] Furthermore, when the pressure difference or pressure ratio between the high-pressure side and the medium-pressure side enters the stable operating range of the expander, and the ejector does not meet the preset ejection requirements, the expander enters an independent mode: the expander inlet isolation ball valve and the low-pressure booster inlet isolation ball valve are opened, and the ejector drive flow inlet isolation ball valve, the ejector ejector flow inlet isolation ball valve, the safety throttling branch normally closed isolation valve, and the bypass branch gate valve are closed, so that the high-pressure carbon dioxide is reduced to medium pressure through the expander, and the low-pressure return gas is raised to medium pressure through the low-pressure booster. Mechanical power is transmitted between the expander and the low-pressure booster through the expander-side coupling, the shaft of the reversible electric generator, and the low-pressure booster-side coupling, and the reversible electric generator supplements the insufficient power or absorbs the surplus power.

[0019] Furthermore, when the pressure difference between the high-pressure side and the medium-pressure side is lower than the stable operating boundary of the expander, but within the effective ejection zone of the ejector, the ejector enters the independent ejector mode: the ejector drive flow inlet isolation ball valve and the ejector ejector flow inlet isolation ball valve are opened, and the expander inlet isolation ball valve, the normally closed isolation valve of the safety throttling branch and the bypass branch gate valve are closed, so that the high-pressure carbon dioxide is reduced to the medium pressure through the ejector, and the low-pressure return gas is preferentially handled by the ejector; when the actual ejection capacity of the ejector is insufficient to handle all the low-pressure return gas, the low-pressure booster inlet isolation ball valve is opened, the reversible electric generator operates in electric mode, and the low-pressure booster is driven by the low-pressure booster coupling to handle the remaining low-pressure return gas.

[0020] Furthermore, when both the injector and expander malfunction, are both cut off by protection, or cannot maintain permissible operating conditions, a safe throttling mode is entered: the injector drive flow inlet isolation ball valve, the injector ejector flow inlet isolation ball valve, the expander inlet isolation ball valve, and the bypass branch gate valve are closed; the normally closed isolation valve of the safe throttling branch is opened, and the throttling valve of the safe throttling branch is adjusted, so that the carbon dioxide from the high-pressure diversion node is reduced to medium pressure and enters the medium-pressure gas-liquid separator and storage tank; the low-pressure return gas is raised to medium pressure by the low-pressure booster and is powered by the reversible electric generator operating in electric mode, providing the required power to the low-pressure booster via the low-pressure booster side coupling; when the external power grid or the low-pressure booster is unavailable, controlled unloading and shutdown are performed.

[0021] Furthermore, during planned startup, shutdown, commissioning, or maintenance, the bypass mode is entered: the injector drive flow inlet isolation ball valve, the injector ejector flow inlet isolation ball valve, the expander inlet isolation ball valve, and the normally closed isolation valve of the safety throttling branch are closed; the bypass branch gate valve is opened, and a controlled pressure drop from the high-pressure side to the medium-pressure side is established by the bypass branch throttling valve; the low-pressure return gas is raised to the medium pressure by the low-pressure booster compressor, and the reversible electric generator operates in electric mode and provides power to the low-pressure booster compressor through the coupling on the low-pressure booster compressor side.

[0022] Furthermore, the differential power between the expander, the low-pressure turbocharger, and the reversible electric generator is adjusted as follows: when the available output power of the expander is insufficient to meet the power demand and mechanical transmission losses of the low-pressure turbocharger, the reversible electric generator draws power from the external power grid and supplements the insufficient power to the low-pressure turbocharger through its rotating shaft; when the available output power of the expander exceeds the power demand and mechanical transmission losses of the low-pressure turbocharger, the reversible electric generator absorbs the remaining mechanical power and outputs electrical energy to the external power grid; when the available output power of the expander is basically matched with the power demand and mechanical transmission losses of the low-pressure turbocharger, the reversible electric generator maintains a near-zero power exchange state.

[0023] The beneficial effects of this invention are as follows: The carbon dioxide heat pump system and operating method with ejector and expander of this invention have the following technical features and advantages in practical use: 1. This invention enables two pressure energy utilization methods to share the high-pressure inlet and medium-pressure back pressure by setting an ejector and an expander in parallel between the same high-pressure diversion node and the same medium-pressure gas-liquid separator and storage tank, and can allocate high-pressure flow according to the operating status of each device, thereby reducing the system's dependence on the effective working area of ​​a single device; by setting an ejector path and a low-pressure booster path at the same low-pressure return gas diversion node, the low-pressure return gas that the ejector can actually handle and the remaining low-pressure return gas have clear destinations, and the high-pressure side distribution is linked to the low-pressure side distribution by the ejector mass relationship and the mechanical power balance relationship between the expander, the low-pressure booster and the reversible electric generator; 2. In this invention, the output mechanical power of the expander is transmitted to the low-pressure booster via the expander-side coupling, the shaft of the reversible electric generator, and the low-pressure booster-side coupling. This reduces the intermediate conversion link where pressure energy is first converted into electrical energy and then into mechanical energy. The reversible electric generator supplements or absorbs the power difference, thereby adapting to the needs of startup, changing operating conditions, and utilization of surplus power. The medium-pressure gas-liquid separator receives the outlet flow of each high-pressure step-down branch, and the medium-pressure gas tank simultaneously receives the separated gas and the exhaust gas of the low-pressure booster. The gas-liquid separation and gas buffering stabilize the supply of the medium-pressure liquid phase to the intake boundary of the main compressor. 3. The composite mode, expander independent mode, and ejector independent mode in this invention are used to cover different pressures, flow rates, and effective working areas of the equipment; the safety throttling mode and bypass mode respectively undertake automatic fault degradation and planned detour, which helps to avoid immediate interruption of the cycle when a single pressure energy utilization device exits; the regenerator uses medium-pressure gas to reduce the temperature and specific enthalpy of high-pressure carbon dioxide and increase the temperature of the gas entering the medium-pressure gas storage tank, thereby improving the suction safety of the main compressor. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the carbon dioxide flow direction in the composite mode of the present invention; Figure 3 This is a schematic diagram of the carbon dioxide flow direction in the independent mode of the expander of the present invention; Figure 4 This is a schematic diagram of the carbon dioxide flow direction in the independent mode of the injector of the present invention; Figure 5 This is a schematic diagram of the carbon dioxide flow direction in the safe throttling mode of the present invention; Figure 6 This is a schematic diagram of the carbon dioxide flow direction in the bypass mode of the present invention; Figures 1 to 6 In the diagram, solid lines represent carbon dioxide pipelines, and dashed lines represent mechanical connections. Figures 2 to 6 The black arrows on the carbon dioxide pipeline indicate the flow direction of carbon dioxide in the corresponding mode. Branches without flow direction arrows indicate that they do not carry carbon dioxide flow in that mode. Reference numerals: 1—Main compressor; 2—Gas cooler; 3—Regenerator; 4—High-pressure diversion node; 5—Expander; 51—Expander inlet isolation ball valve; 52—Expander outlet check valve; 53—Expander side coupling; 6—Ejector; 61—Ejector drive flow inlet isolation ball valve; 62—Ejector outlet check valve; 63—Ejector ejector flow inlet isolation ball valve; 7—Safety throttling branch normally closed isolation valve; 71—Safety throttling branch throttling valve; 8—Bypass branch gate valve; 81—Bypass branch throttling valve; 9—Medium-pressure gas-liquid separator reservoir; 10—Low-pressure... 11—Evaporator inlet throttle valve; 12—Low-pressure evaporator; 13—Low-pressure return gas diversion node; 14—Low-pressure booster compressor; 15—Low-pressure booster compressor inlet isolation ball valve; 16—Low-pressure booster compressor side coupling; 17—Low-pressure booster compressor outlet check valve; 18—Medium-pressure gas storage tank; 19—Coordination controller; 10—Heating load; 11—Hot water supply buffer tank; 102—Heating side circulating water pump; 11—Low-temperature heat source unit; 12—Heat source side circulating pump; 13—Medium-pressure liquid storage tank built-in geothermal heat exchanger; 14—Reversible electric generator; 15—External power grid. Detailed Implementation

[0025] Specific Embodiment 1: To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that: In the present invention, unless otherwise specified, all embodiments and preferred methods mentioned herein can be combined to form new technical solutions. In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions. The "scope" disclosed in the present invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively. Unless otherwise stated, the technical and scientific terms used herein have the same meaning as those skilled in the art.

[0026] As per the instruction manual Figure 1 As shown, the system of this invention uses carbon dioxide as the circulating working fluid and is set with three pressure levels: high pressure, medium pressure, and low pressure. The medium-pressure gas storage tank 14 provides medium-pressure gaseous carbon dioxide to the main compressor 1, which compresses it to high pressure and then sends it into the carbon dioxide side channel of the gas cooler 2. The high-temperature, high-pressure carbon dioxide releases heat to the heating circulating water in this channel, completing useful heating and reducing its temperature and specific enthalpy. It then enters the high-pressure side channel of the regenerator 3 for further heat exchange before entering the high-pressure diversion node 4.

[0027] The gas cooler 2 includes a carbon dioxide side channel and a water side channel that are isolated from each other in terms of heat exchange. The water side outlet of the gas cooler 2 is connected to the hot water buffer tank 161, and heat is supplied to the heating load 16 after passing through the heating side circulating water pump 162. The low-temperature return water after heating is connected to the water side inlet of the gas cooler 2 to form a closed hot water supply loop. The gas cooler 2 is not necessarily limited to a single heat exchange flow pattern. Its internal arrangement can adopt a general counterflow, near counterflow, or multi-pass crossflow-counterflow arrangement. The selected arrangement should meet the full-process heat exchange temperature difference requirements under the allowable pressure drop.

[0028] The regenerator 3 includes a high-pressure side channel and a medium-pressure side channel. The high-pressure carbon dioxide from the gas cooler 2 is further cooled and its enthalpy is reduced in the high-pressure side channel, while the medium-pressure gas from the gas phase outlet of the medium-pressure gas-liquid separator 9 absorbs heat and is heated in the medium-pressure side channel. The two streams of carbon dioxide are separated by a heat exchange wall and do not mix directly. The medium-pressure gas heated by the regenerator 3 enters the medium-pressure gas storage tank 14.

[0029] The high-pressure carbon dioxide, further cooled by the regenerator 3, enters the high-pressure diversion node 4. The high-pressure diversion node 4 provides a common high-pressure inlet for the ejector branch, expander branch, safety throttling branch, and bypass branch. The outlets of the four branches are all connected to the medium-pressure gas-liquid separator reservoir 9, so that each branch has a basically consistent medium-pressure back pressure boundary.

[0030] The injector branch, along the drive flow direction, sequentially includes an injector drive flow inlet isolation ball valve 61, an injector 6, and an injector outlet check valve 62. An injector jet inlet isolation ball valve 63 is located between the low-pressure return gas split node 12 and the jet inlet of the injector 6. The injector drive flow inlet isolation ball valve 61 and the injector jet inlet isolation ball valve 63 primarily function as opening / closing and isolation valves, and are not used for continuous throttling and flow regulation.

[0031] The expander branch, along the direction of carbon dioxide flow, includes, in sequence, the expander inlet isolation ball valve 51, the expander 5, and the expander outlet check valve 52. The expander 5 reduces the high-pressure carbon dioxide to medium pressure and outputs mechanical work.

[0032] The safety throttling branch includes a normally closed isolation valve 7 and a throttle valve 71. The normally closed isolation valve 7 is closed under normal pressure energy utilization mode and opens only when both the ejector 6 and expander 5 fail, are both protected off, or cannot maintain permissible operating conditions. The throttle valve 71 is used to establish a controlled pressure drop and necessary flow rate from the high-pressure side to the intermediate-pressure side during degradation.

[0033] The bypass branch includes a bypass branch gate valve 8 and a bypass branch throttle valve 81. The bypass branch is mainly used to bypass the injector branch, expander branch, and safety throttle branch during planned start-up, shutdown, commissioning, or maintenance isolation. The triggering conditions for the bypass branch and the safety throttle branch differ: the safety throttle branch is triggered by a fault or equipment unavailability condition and assumes automatic degradation, while the bypass branch is triggered by planned operation and is used to establish or maintain the basic circulation boundary.

[0034] The medium-pressure gas-liquid separator 9 receives carbon dioxide from any of the high-pressure step-down branches that are in operation and performs gas-liquid separation under medium pressure. The gas phase enters the medium-pressure side channel of the regenerator 3, while the liquid phase is reduced to low pressure via the low-pressure evaporator inlet throttle valve 10 and then enters the low-pressure evaporator 11. The liquid level in the medium-pressure gas-liquid separator 9 can be used as an observation of the liquid phase inventory.

[0035] The low-pressure carbon dioxide in the low-pressure evaporator 11 absorbs heat from the heat transfer medium on the low-temperature heat source side and evaporates, forming low-pressure return gas which enters the low-pressure return gas diversion node 12. The carbon dioxide channel of the low-pressure evaporator 11 is heat-isolated from the heat source side channel, and its heat exchange area, flow channel form, and heat transfer medium flow rate should meet the requirements of the full-process heat exchange temperature difference, allowable pressure drop, and outlet condition under the corresponding operating conditions.

[0036] The first outlet of the low-pressure return gas diversion node 12 is connected to the ejector 6 via the ejector jet inlet isolation ball valve 63, and the second outlet is connected to the low-pressure booster 13 via the low-pressure booster inlet isolation ball valve 131. The low-pressure return gas processed by the ejector 6 mixes with the high-pressure drive flow in the ejector 6 and rises to medium pressure, and then enters the medium-pressure gas-liquid separator reservoir 9 via the ejector outlet check valve 62.

[0037] The low-pressure return gas, which is not processed by the injector 6, is raised to medium pressure by the low-pressure booster 13 and enters the medium-pressure gas storage tank 14 through the low-pressure booster outlet check valve 133. The inlet of the low-pressure booster 13 should be maintained as gaseous carbon dioxide that meets its permissible superheat or dryness conditions. When a risk of liquid carryover is detected in the intake gas, the co-controller 15 should limit its inlet flow rate and adjust the low-pressure evaporator inlet throttle valve 10.

[0038] The output shaft of the expander 5 is mechanically connected to one side shaft of the reversible electric generator 18 via the expander-side coupling 53, and the input shaft of the low-pressure booster 13 is mechanically connected to the other side shaft of the reversible electric generator 18 via the low-pressure booster-side coupling 132.

[0039] The output mechanical power of the expander 5 can be transmitted sequentially to the low-pressure booster 13 via the expander-side coupling 53, the shaft of the reversible electric generator 18, and the low-pressure booster-side coupling 132. When the available output power of the expander 5 is insufficient, the reversible electric generator 18 operates in motor mode and supplements the insufficient power; when the available output power of the expander 5 is excessive, the reversible electric generator 18 operates in generator mode and absorbs the surplus power; when the mechanical power is basically matched, the reversible electric generator 18 maintains a near-zero power exchange state.

[0040] The reversible electric generator 18 can be equipped with bidirectional converter and grid connection protection functions, which can be integrated into the motor drive cabinet or external power grid interface.

[0041] The hot water supply circuit consists of a gas cooler 2, a heating load 16, a hot water supply buffer tank 161, and a heating-side circulating water pump 162. The heating-side circulating water pump 162 drives the heating circulating water to flow sequentially through the gas cooler 2 and the heating load 16. The hot water supply buffer tank 161 is used to buffer short-term changes in return water flow and temperature, reducing the disturbance of heating load fluctuations on the outlet state of the gas cooler 2 and the high-pressure side control.

[0042] The heating load 16 can be for building heating, domestic hot water, or process hot water. The hot water flow rate and supply and return water temperatures should be adjusted according to the heating load demand, the allowable pressure drop of the gas cooler 2, and the temperature difference of the entire heat exchange process. The heating load type does not change the parallel pressure reduction on the high-pressure side, the parallel pressure increase on the low-pressure side, or the mechanical connection relationship between the expander 5, the reversible electric generator 18, and the low-pressure booster 13.

[0043] The low-temperature heat source unit 17 can be a geothermal well heat exchange unit, a closed underground pipe, a geothermal tailwater isolation heat exchange unit, an industrial low-temperature waste water circuit, or other low-temperature heat source interface that can provide heat to the low-pressure evaporator 11.

[0044] A heat source-side circulating pump 171 drives a low-temperature heat source-side heat transfer medium to flow through the heat source-side channel of the low-pressure evaporator 11 and the geothermal heat exchanger 172 built into the medium-pressure liquid receiver. The heat source-side channel is heat-isolated from the carbon dioxide channel. The low-temperature heat source unit 17 only provides heat to the low-pressure evaporation process and the medium-pressure liquid phase heating. Its specific heat source type does not change the bidirectional adjustment relationship of parallel pressure reduction on the high-pressure side, parallel pressure increase on the low-pressure side, and differential power.

[0045] The coordinating controller 15 is connected to the main compressor 1, ejector 6, low-pressure evaporator inlet throttle valve 10, low-pressure booster 13, heating-side circulating water pump 162, heat source-side circulating pump 171, reversible electric generator 18, and the isolation valves and throttle valves of each branch. It should be noted that, to avoid cluttered lines in the attached diagrams... Figures 1 to 6 Not all control signal lines were drawn.

[0046] The collaborative controller 15 first determines the operating status of the injector 6, expander 5, low-pressure booster 13 and reversible electric generator 18 based on the equipment calibration data and manufacturer performance diagram. Then, it determines the current available operating mode by combining the liquid phase inventory and the mechanical power balance between expander 5, low-pressure booster 13 and reversible electric generator 18.

[0047] After high-pressure carbon dioxide enters high-pressure diversion node 4, it is distributed to the injector branch, expander branch, safety throttling branch, and bypass branch according to the current operating mode. Under any operating condition, the sum of the carbon dioxide mass flow rates of each actually connected branch should be equal to the inlet mass flow rate of high-pressure diversion node 4. Branches in the closed state do not participate in flow distribution.

[0048] The low-pressure return gas from the outlet of the low-pressure evaporator 11 enters the low-pressure return gas splitting node 12 and flows to the inlet of the ejector 6 and the inlet of the low-pressure booster 13, respectively. Under conditions of no leakage or abnormal accumulation, the total amount of low-pressure return gas received by the two branches should be equal to the outlet return gas volume of the low-pressure evaporator 11. After the high-pressure drive flow and the low-pressure ejector flow are mixed, they are discharged together from the ejector outlet.

[0049] The medium-pressure gas-liquid separator 9 receives carbon dioxide from the ejector 6, expander 5, safety throttling branch, or bypass branch, and discharges it to the outside through the gas phase outlet and liquid phase outlet, respectively. When the total amount of carbon dioxide entering the medium-pressure gas-liquid separator 9 is greater than the total output of its gas and liquid phases, the total carbon dioxide inventory in the separator increases; when the total input is less than the total output, the total inventory decreases; when the total input and output are approximately equal, the total inventory remains relatively stable. Phase transitions can occur between the gas and liquid phases, but these phase transitions do not change the total mass of carbon dioxide in the separator.

[0050] The intermediate-pressure gas storage tank 14 receives carbon dioxide from the gas phase outlet of the intermediate-pressure gas-liquid separator 9, as well as carbon dioxide pressurized by the low-pressure booster 13, and provides suction gas to the main compressor 1. When the total amount of gas entering the intermediate-pressure gas storage tank 14 is greater than the suction volume of the main compressor 1, the gas inventory in the intermediate-pressure gas storage tank 14 increases; when the amount entering is less than the suction volume of the main compressor 1, the gas inventory decreases; when the two are approximately equal, the gas inventory remains relatively stable. The intermediate-pressure gas storage tank 14 buffers instantaneous flow fluctuations between different branches through the above-mentioned inventory changes.

[0051] The power distribution among expander 5, low-pressure booster 13, and reversible electric generator 18 should simultaneously consider the available output power of expander 5, the required power of low-pressure booster 13, and the mechanical losses generated by couplings, bearings, and speed matching mechanisms. When the available output power of expander 5 is insufficient to drive low-pressure booster 13 and compensate for mechanical losses, reversible electric generator 18 enters motoring mode and supplements the insufficient power; when the available output power of expander 5 exceeds the required power of low-pressure booster 13 and mechanical losses, reversible electric generator 18 enters generator mode and absorbs the remaining power; when the two are basically matched, reversible electric generator 18 maintains a near-zero power exchange state.

[0052] For a system boundary that includes a carbon dioxide cycle, a hot water supply circuit, and a low-temperature heat source side circuit, the input heat from the low-temperature heat source, the input work of the main compressor 1, the input work of the reversible electric generator 18 in electric mode, and the input work of each circulation pump should correspond to the useful heat obtained by the heating load 16, the output work of the reversible electric generator 18 in power generation mode, environmental heat dissipation, mechanical and electrical losses, and changes in energy within the system.

[0053] Composite mode such as Figure 2 As shown. The injector drive flow inlet isolation ball valve 61, injector ejector flow inlet isolation ball valve 63, expander inlet isolation ball valve 51, and low-pressure booster inlet isolation ball valve 131 are opened, while the normally closed isolation valve 7 of the safety throttling branch and the bypass branch gate valve 8 are closed. High-pressure carbon dioxide is distributed to the injector 6 and expander 5 at the high-pressure splitting node 4; low-pressure return gas is distributed to the injector 6 and low-pressure booster 13 at the low-pressure return gas splitting node 12. The co-controller 15 stabilizes the medium-pressure state and mechanical power balance by adjusting the effective flow area of ​​the injector 6, the load or speed of the expander 5, the speed of the low-pressure booster 13, and the power state of the reversible electric generator 18.

[0054] Expander independent mode such as Figure 3 As shown, this is mainly used when the pressure difference or pressure ratio between the high-pressure side and the medium-pressure side enters the stable operating range of the expander 5, and the ejector 6 does not meet the preset ejection requirements. The ejector drive flow inlet isolation ball valve 61 and the ejector ejector flow inlet isolation ball valve 63 are closed, while the expander inlet isolation ball valve 51 and the low-pressure booster inlet isolation ball valve 131 are opened. All or mainly of the high-pressure carbon dioxide is reduced to medium pressure via the expander 5, and all or mainly of the low-pressure return gas is increased to medium pressure via the low-pressure booster 13. Injector independent mode, such as Figure 4As shown, this is mainly used when the pressure difference between the high-pressure side and the medium-pressure side is lower than the stable operating boundary of the expander 5, but still within the effective ejection zone of the ejector 6. The expander inlet isolation ball valve 51 is closed, and the ejector drive flow inlet isolation ball valve 61 and the ejector ejector flow inlet isolation ball valve 63 are opened. All or mainly of the high-pressure carbon dioxide is reduced to medium pressure via the ejector 6, and the low-pressure return gas is preferentially ejected by the ejector 6. When the actual ejection capacity is insufficient to handle all the low-pressure return gas, the remaining low-pressure return gas is raised to medium pressure via the low-pressure booster 13. The power required by the low-pressure booster 13 is provided by the reversible electric generator 18 operating in electric mode and via the low-pressure booster side coupling 132.

[0055] Safety throttling mode such as Figure 5 As shown. When both the injector 6 and expander 5 malfunction, are both cut off by protection, or cannot maintain permissible operating conditions, the injector drive flow inlet isolation ball valve 61, the injector ejector flow inlet isolation ball valve 63, the expander inlet isolation ball valve 51, and the bypass branch gate valve 8 are closed. The normally closed isolation valve 7 of the safety throttling branch is opened, and the high-pressure carbon dioxide is reduced to medium pressure by the throttling valve 71 of the safety throttling branch. The low-pressure return gas is connected to the low-pressure booster 13, and the reversible electric generator 18 operates in electric mode. If the external power grid 19 or the low-pressure booster 13 is also unavailable, controlled unloading and shutdown are performed.

[0056] Bypass mode such as Figure 6 As shown. During planned startup, shutdown, commissioning, or maintenance, the injector drive flow inlet isolation ball valve 61, injector ejector flow inlet isolation ball valve 63, expander inlet isolation ball valve 51, and safety throttling branch normally closed isolation valve 7 are closed. The bypass branch gate valve 8 is opened, and a controlled pressure drop from the high-pressure side to the medium-pressure side is established through the bypass branch throttling valve 81. The low-pressure return gas is raised to medium pressure by the low-pressure booster 13, and the reversible electric generator 18 operates in electric mode.

[0057] The mode determination does not use unverified fixed differential pressure values. The effective range of the expander 5 independent mode, the effective range of the ejector independent mode, and the overlapping range of the combined mode are all determined by the performance diagrams, calibration data, or test results of the corresponding equipment under actual carbon dioxide inlet conditions, back pressure, and flow conditions.

[0058] When multiple modes are all currently available operating modes, the coordinating controller 15 can select a target mode based on one or more of the following indicators: external power demand, pressure fluctuation, liquid phase inventory deviation, mechanical power margin, and switching frequency; the selected target mode must not exceed the allowable operating boundaries of the injector 6, expander 5, low-pressure booster 13, and reversible electric generator 18.

[0059] During mode switching, the coordinating controller 15 first confirms the back pressure at the target branch outlet and the pressure of the medium-pressure gas-liquid separator reservoir 9, and then gradually establishes the target branch flow rate. Once the target branch flow rate and the speeds of the expander 5, reversible electric generator 18, and low-pressure booster 13 are within the allowable range, the original branch is gradually unloaded and isolated. The injector outlet check valve 62, expander outlet check valve 52, and low-pressure booster outlet check valve 133 open or close based on the forward and reverse pressure difference to suppress backflow on the medium-pressure side and reverse impact on the branch.

[0060] During startup, the bypass mode can be used first to establish the pressure and liquid phase storage of the medium-pressure gas-liquid separator 9 and the low-pressure evaporation circuit. Then, the main compressor 1, the heating-side circulating water pump 162, the heat source-side circulating pump 171, and the low-pressure booster compressor 13 can be started. After the target pressure level, the outlet status of the low-pressure evaporator 11, and the speed of the reversible electric generator 18 and the low-pressure booster compressor 13 have stabilized, the mode can be switched to the composite mode, the expander independent mode, or the ejector independent mode.

[0061] When shutting down, first reduce the heating load and the input from the low-temperature heat source side, unload the ejector 6, expander 5, low-pressure booster 13 and reversible electric generator 18, and then switch to bypass mode or controlled shutdown state. During the shutdown process, avoid simultaneously isolating and continuously heating the closed pipe section filled with high-pressure carbon dioxide. If necessary, release the pressure rise caused by thermal expansion through a safety pressure relief or pressure equalization passage.

[0062] When the liquid phase inventory of the medium-pressure gas-liquid separator 9 is close to the lower limit, the main compressor 1 has a risk of liquid carryover during intake, the expander 5, the reversible electric generator 18 or the low-pressure booster 13 shows an overspeed trend, or the outlet pressure of any working branch cannot match the medium-pressure back pressure, the coordination controller 15 should limit the flow of the relevant branch, reduce the load, switch to an available degraded mode or execute a controlled shutdown, and should not forcibly maintain the original mode by simply increasing the control gain.

[0063] The medium-pressure gas-liquid separator 9 should be equipped with a liquid level protection, demisting and pressure relief structure that is appropriate for the carbon dioxide pressure level; the medium-pressure gas storage tank 14 should be equipped with pressure, temperature and anti-liquid hammer protection.

[0064] When the temperature or flow rate on the low-temperature heat source side changes, the coordinating controller 15 adjusts the flow rate of the circulating pump 171 on the heat source side and the opening degree of the inlet throttle valve 10 of the low-pressure evaporator 11 based on the evaporation pressure, outlet status, and minimum allowable heat exchange temperature difference of the low-pressure evaporator 11. When the capacity on the low-temperature heat source side is insufficient, the evaporation load should be limited or switched to an available operating mode. The nominal output should not be maintained by reducing the necessary superheat or exceeding the heat exchange temperature difference boundary.

[0065] In embodiments employing geothermal well heat exchange units, closed-loop buried pipes, or geothermal tailwater isolation heat exchange units as the low-temperature heat source unit 17, the geothermal heat transfer medium flows only through the heat source side channel of the low-pressure evaporator 11 via the heat source side circulation pump 171. The temperature, flow rate, corrosion prevention, and scale prevention conditions of the geothermal interface should be determined according to on-site resources. This geothermal implementation method only changes the form of the low-temperature heat source interface and does not change the parallel pressure reduction on the high-pressure side, the parallel pressure increase on the low-pressure side, or the power regulation relationship between the expander 5, the reversible electric generator 18, and the low-pressure booster 13.

[0066] The core technical relationships of this invention are: parallel distribution of the high-pressure side injector and expander, parallel distribution of the low-pressure side injection ejector and mechanical booster, and the mechanical power transmission and differential power bidirectional adjustment relationship formed by the mechanical connection of expander 5 to one side shaft of reversible electric generator 18 through expander-side coupling 53, and the mechanical connection of low-pressure booster 13 to the other side shaft of reversible electric generator 18 through low-pressure booster-side coupling 132; the cooperative controller 15 changes the available output power of expander 5 through high-pressure side shunt, changes the required power of low-pressure booster 13 through low-pressure side shunt, and forms five operating modes around the above physical relationships. The above shows and describes the basic principles, main features, and advantages of this invention. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of this invention. Various changes and modifications can be made to this invention without departing from the spirit and scope of this invention, and all such changes and modifications fall within the scope of this invention as claimed.

Claims

1. A carbon dioxide heat pump system with an ejector and an expander, characterized in that, Includes main compressor (1), gas cooler (2), regenerator (3), high pressure diversion node (4), expander (5), ejector (6), medium pressure gas-liquid separator (9), low pressure evaporator inlet throttle valve (10), low pressure evaporator (11), low pressure return gas diversion node (12), low pressure booster (13), medium pressure gas storage tank (14), coordinating controller (15), low temperature heat source unit (17), heat source side circulation pump (171), reversible electric generator (18), and external power grid (19); The gas outlet of the medium-pressure gas storage tank (14), the main compressor (1), the carbon dioxide side channel of the gas cooler (2), the regenerator (3) and the high-pressure diversion node (4) are connected in sequence; The first outlet of the high-pressure diversion node (4) is connected to the medium-pressure gas-liquid separator (9) via the expander branch, the ejector branch and the safety throttling branch; the second outlet of the high-pressure diversion node (4) is connected to the medium-pressure gas-liquid separator (9) via the bypass branch, so that the expander branch and the ejector branch, the safety throttling branch and the bypass branch constitute a parallel pressure-reducing branch from the high-pressure side to the same medium-pressure side; The gas phase outlet of the medium-pressure gas-liquid separator (9) is connected to the medium-pressure gas storage tank (14) through the medium-pressure side channel of the regenerator (3), and the liquid phase outlet of the medium-pressure gas-liquid separator (9) is connected to the low-pressure return gas diversion node (12) through the low-pressure evaporator inlet throttle valve (10) and the low-pressure evaporator (11). The first outlet of the low-pressure return gas splitting node (12) is connected to the ejector inlet of the injector (6), and the second outlet of the low-pressure return gas splitting node (12) is connected to the medium-pressure gas storage tank (14) via the low-pressure booster (13), so that the ejector branch of the injector (6) and the mechanical booster branch of the low-pressure booster (13) form a parallel boosting path from the same low-pressure return gas splitting node (12) to the medium-pressure side; The low-temperature heat source unit (17) is connected to the heat source side channel of the low-pressure evaporator (11) and the geothermal heat exchanger (172) built into the medium-pressure liquid storage tank through the heat source side circulation pump (171); The expander (5) is mechanically connected to one side shaft of the reversible electric generator (18) via an expander-side coupling (53), the low-pressure booster (13) is mechanically connected to the other side shaft of the reversible electric generator (18) via a low-pressure booster-side coupling (132), and the reversible electric generator (18) is electrically connected to the external power grid (19). The coordinating controller (15) can adjust the opening and closing states of the injector drive flow inlet isolation ball valve (61), injector jet flow inlet isolation ball valve (63), expander inlet isolation ball valve (51), safety throttling branch normally closed isolation valve (7) and bypass branch gate valve (8) according to the equipment operating status, liquid phase inventory and shaft power status, so that the system can switch between compound mode, expander independent mode, injector independent mode, safety throttling mode and bypass mode, so as to broaden the operating conditions and maintain the stability of heating and circulation.

2. A carbon dioxide heat pump system with ejector and expander according to claim 1, characterized in that, A safety throttling branch and a bypass branch are connected in parallel between the high-pressure diversion node (4) and the medium-pressure gas-liquid separator (9). The safety throttling branch is equipped with a safety throttling branch normally closed isolation valve (7) and a safety throttling branch throttle valve (71) in sequence. The bypass branch is equipped with a bypass branch gate valve (8) and a bypass branch throttle valve (81) in sequence, so that the ejector branch, expander branch, safety throttling branch and bypass branch have a common high-pressure inlet and a common medium-pressure outlet.

3. A carbon dioxide heat pump system with ejector and expander according to claim 1, characterized in that, The expander branch is provided with an expander inlet isolation ball valve (51), an expander (5), and an expander outlet check valve (52) in sequence along the carbon dioxide flow direction; the injector branch is provided with an injector drive flow inlet isolation ball valve (61) on the drive flow inlet side, an injector outlet check valve (62) on the outlet side, and an injector induced flow inlet isolation ball valve (63) on the induced flow inlet side; the low-pressure booster (13) is provided with a low-pressure booster inlet isolation ball valve (131) on the inlet side and a low-pressure booster outlet check valve (133) on the outlet side.

4. A carbon dioxide heat pump system with ejector and expander according to claim 3, characterized in that, The output shaft of the expander (5) is connected to one side shaft of the reversible electric generator (18) through the expander side coupling (53), and the input shaft of the low-pressure booster (13) is connected to the other side shaft of the reversible electric generator (18) through the low-pressure booster side coupling (132). The output mechanical power of the expander (5) is transmitted to the low-pressure booster (13) through the expander side coupling (53), the shaft of the reversible electric generator (18) and the low-pressure booster side coupling (132). The reversible electric generator (18) supplements the insufficient power or absorbs the surplus power through electromagnetic torque.

5. A carbon dioxide heat pump system with ejector and expander according to claim 4, characterized in that, The coordinating controller (15) determines the operating status of each device based on the ejection capability and back pressure allowable range of the injector (6), the allowable flow rate and speed range of the expander (5), the exhaust capability and power requirements of the low-pressure booster (13), and the allowable power of the reversible electric generator (18). It also determines the current available operating mode by combining the liquid phase storage status of the medium-pressure gas-liquid separator (9) and the mechanical power balance status between the expander (5), the low-pressure booster (13), and the reversible electric generator (18). Under the available operating mode, it determines the high-pressure side flow rate, low-pressure side flow rate, injector adjustment amount, expander load or speed, low-pressure booster speed, and reversible electric generator power status.

6. A carbon dioxide heat pump system with ejector and expander according to claim 5, characterized in that, The regenerator (3) includes a high-pressure side channel and a medium-pressure side channel that are isolated from each other for heat exchange. The medium-pressure gas from the medium-pressure gas-liquid separator (9) absorbs the heat from the high-pressure carbon dioxide from the gas cooler (2), so that the medium-pressure gas from the medium-pressure gas-liquid separator (9) is heated and enters the medium-pressure gas storage tank (14), and the high-pressure carbon dioxide from the gas cooler (2) is cooled and its specific enthalpy is reduced. The medium-pressure gas storage tank (14) also receives the exhaust gas from the low-pressure booster (13) and provides medium-pressure gaseous carbon dioxide to the main compressor (1).

7. A carbon dioxide heat pump system with an ejector and an expander according to claim 6, characterized in that, The water-side outlet of the gas cooler (2) is connected to the hot water buffer tank (161). The hot water buffer tank (161) and the heating-side circulating water pump (162) supply heat to the heating load (16). The return water end of the heating load (16) is connected to the water-side inlet of the gas cooler (2) to form a closed hot water supply loop. The heat source side channels of the low-temperature heat source unit (17), the heat source side circulating pump (171), the low-pressure evaporator (11), and the medium-pressure liquid storage tank built-in geothermal heat exchanger (172) are connected in series to form a heat source side loop. The hot water supply loop and the heat source side loop are both isolated from the carbon dioxide circulating heat exchange.

8. A carbon dioxide heat pump system with ejector and expander according to claim 1, characterized in that, The low-temperature heat source unit (17) is one or more of the following: geothermal well heat exchange unit, closed underground pipe, geothermal tailwater isolation heat exchange unit, and industrial low-temperature waste water circuit; when the low-temperature heat source unit (17) adopts geothermal heat source, the heat source side circulation pump (171) drives the geothermal side heat transfer medium to flow through the heat source side channel of the low-pressure evaporator (11) and the geothermal heat exchanger (172) built into the medium-pressure liquid storage tank.

9. A method for operating a carbon dioxide heat pump system with an ejector and an expander as claimed in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Collect the ejector flow rate of the ejector (6), the available output power of the expander (5), the required power of the low-pressure booster (13), the power status of the reversible electric generator (18), the mechanical power balance status between the expander (5) and the low-pressure booster (13), and the liquid phase storage status of the medium-pressure gas-liquid separator (9). Step 2: Based on the above equipment operating status, determine the available operating modes among the compound mode, expander independent mode, injector independent mode, safety throttling mode, and bypass mode; Step 3: Select the target mode from the available operating modes, and make the target pressure reduction branch accept high-pressure carbon dioxide after establishing the allowable pressure difference and allowable flow rate, while making the low-pressure return gas rise to the medium-pressure side via the injector (6) and / or low-pressure booster (13); Step 4: Based on the difference between the available output power of the expander (5), the required power of the low-pressure booster (13), and the mechanical transmission loss, the reversible electric generator (18) is put into electric state, power generation state, or near-zero power exchange state. Step 5: Correct the branch allocation based on the pressure, flow rate, liquid phase inventory and mechanical power feedback after the mode switch; when the target mode no longer meets the equipment operating status requirements, redetermine the available operating mode and perform switching, downgrading or controlled shutdown.

10. The method for operating a carbon dioxide heat pump system with an ejector and an expander according to claim 9, characterized in that, In the composite mode, the expander inlet isolation ball valve (51), the injector drive flow inlet isolation ball valve (61), the injector ejector flow inlet isolation ball valve (63), and the low-pressure booster inlet isolation ball valve (131) are opened, and the safety throttling branch normally closed isolation valve (7) and the bypass branch gate valve (8) are closed. High-pressure carbon dioxide is distributed to the expander (5) and the injector (6) at the high-pressure split node (4), and low-pressure return gas is distributed to the injector (6) and the low-pressure booster (13) at the low-pressure return gas split node (12). The high-pressure side split and the low-pressure side split are coordinated by the ejection capacity of the injector (6) and the mechanical power balance between the expander (5), the low-pressure booster (13), and the reversible electric generator (18). The differential power between the expander (5), the low-pressure booster (13), and the reversible electric generator (18) is adjusted as follows: when the available output power of the expander (5) is insufficient to meet the power demand and mechanical transmission loss of the low-pressure booster (13), the reversible electric generator (18) draws power from the external power grid (19) and supplements the insufficient power to the low-pressure booster (13) through its rotating shaft; when the available output power of the expander (5) exceeds the power demand and mechanical transmission loss of the low-pressure booster (13), the reversible electric generator (18) absorbs the remaining mechanical power and outputs electrical energy to the external power grid (19); when the available output power of the expander (5) is basically matched with the power demand and mechanical transmission loss of the low-pressure booster (13), the reversible electric generator (18) maintains a near-zero power exchange state.

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