An energy system based on green carbon cycle and its operation method and control method

Abstract

The present invention discloses an energy system based on a green carbon cycle and an operation method and a control method thereof, wherein the energy system based on the green carbon cycle includes a methanol energy supply module, a methanol regeneration module and a carbon dioxide heat pump energy storage module; the methanol energy supply module includes a methanol internal combustion engine and a first generator, and the methanol regeneration module includes a carbon dioxide capture and processing unit, a methanol synthesis unit and a water electrolysis unit; the system of the present invention adopts a park energy system with a methanol internal combustion engine as the core, and reduces the transportation cost and storage risk of fuel while taking into account environmental protection and low carbon as well as flexible and reliable energy supply. The present invention introduces supercritical carbon dioxide as a circulating working fluid, fully exploits its advantages of high energy density and low viscosity, significantly improves heat exchange efficiency, and at the same time reduces the volume of the heat exchanger and reduces flow noise, making it more suitable for user-side energy supply, and providing a new option for the planning and configuration of the park energy system.

Description

Technical Field

[0001] The present invention relates to an energy system based on green carbon cycle and an operation method and a control method thereof. Background Art

[0002] Methanol, with its characteristic of remaining liquid at room temperature and pressure, is significantly different from hydrogen, showing the advantages of being easy to store, transport, and carry. Its physical properties and safety standards are similar to those of gasoline and diesel, and its energy density is only one-sixth of that of natural gas by volume, making it an ideal choice for reducing energy transportation costs. It is particularly worth mentioning that "green hydrogen" produced by electrolysis of water from renewable energy, and further combined with carbon dioxide obtained from biomass or carbon capture technology to produce "green methanol", is not only an effective way to sequester carbon, but also a realistic path to achieving carbon neutrality. Building a cogeneration system with a methanol internal combustion engine as the core, supplemented by CCUS (carbon capture, utilization and storage) technology, can not only meet the diversified energy needs of users, but also achieve zero carbon emissions at the park level, highlighting the huge potential of distributed energy supply systems.

[0003] Carbon dioxide has excellent physical properties, especially its low critical point (7.39MPa, 31.4℃), which is far superior to air (3.77MPa, -140.5℃), giving it a series of excellent thermodynamic properties, such as low viscosity, high density and good thermal conductivity. When supercritical carbon dioxide replaces traditional water or water vapor as a circulating working fluid, it can not only significantly reduce the size of system components, such as pipe diameter and heat exchanger, but also reduce the power demand of the driving pump and reduce flow noise, making it particularly suitable for compact cooling and heating systems on the user side. More importantly, as a non-toxic and non-flammable working fluid, carbon dioxide has an extremely low global warming potential (GWP), which makes it a broad application prospect in the field of heat pumps as a substitute for traditional refrigerants such as Freon.

[0004] In light of the diverse demands and zero-carbon emissions challenges facing the park's energy system, the park has integrated a methanol internal combustion engine trigeneration system with a carbon recycling system, combined with supercritical carbon dioxide energy storage and heat pump technology, to create a high-value, forward-looking integrated energy solution. This system not only efficiently responds to user energy needs but also promotes the green transformation of the energy industry while reducing its carbon footprint, demonstrating a blueprint for future sustainable development.

[0005] In existing technologies, green methanol is primarily used as a replacement for traditional marine fuel. Furthermore, it can be used as a short-term carbon sequestration medium in CCUS technology or as a buffer for green hydrogen. However, its use in industrial park energy systems is rare. Furthermore, the thermal cycle of industrial park energy systems primarily uses water and water vapor, extracting or releasing heat through the water cycle to provide cooling or heating to users. Patent CN 117654394A discloses a system and method for producing methanol from hydrogen with near-zero emissions from renewable energy. This method produces methanol from green hydrogen produced by renewable energy generation and carbon dioxide obtained from natural gas power generation. The designed system has high requirements for the level of renewable energy power generation; Patent CN 114899884 A discloses a peak-shaving power generation system and method coupled with carbon dioxide capture and utilization. This invention uses the surplus power generation power of thermal coal-fired power units to produce hydrogen and carbon emissions during the coal combustion process to produce methanol, thereby reducing the carbon emissions of coal-fired power units; Patent CN 118105726 A discloses a method for capturing and utilizing carbon dioxide. This invention produces methanol from a hydrogen-rich gas stream obtained by decomposing ammonia to improve the capture and utilization rate of carbon dioxide.

[0006] Currently, the production and use of green methanol is primarily located near centralized wind and solar power plants or traditional fossil fuel-fired power plants, far from end users. This is primarily due to the underdeveloped consumer market for green methanol. Its current limited application as a marine fuel is a relatively limited, buyer's market, resulting in unclear economic benefits and a need for improved market mechanisms. Consequently, green methanol production currently plays a more important role in short-term carbon sequestration, aiming to reduce carbon emissions from thermal power plants. Alternatively, it can be used as a storage and transportation medium for green hydrogen, leveraging its stable chemical properties, high energy density, and convenient storage capabilities. Through methanol reforming and hydrogen production technology, methanol can be converted to hydrogen on the demand side to meet diverse energy needs. Furthermore, traditional heat pump systems and campus heating and cooling systems generally use water or steam as the circulating fluid. This not only requires extensive circulating water piping and equipment, occupying valuable building space, but also places stringent requirements on pipeline layout, especially in user-side buildings. Furthermore, the use of large circulating water flows results in higher pump power and energy consumption, resulting in increased noise and disruption, which impacts the user experience. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to solve the problem of high energy consumption and high noise caused by the common use of water or water vapor as a circulating working fluid in the park energy system. An energy system based on a green carbon cycle and its operation method and control method are provided. The system not only retains the status of methanol as the core carbon fixation medium, but also utilizes the characteristics of fast start and stop and flexible load of the methanol internal combustion engine to provide clean power for the park energy system and is committed to building a zero-carbon park. More importantly, supercritical carbon dioxide is introduced as a circulating working fluid in the system design, fully exploiting its advantages of high energy density and low viscosity, significantly improving the heat exchange efficiency, and at the same time reducing the volume of the heat exchanger and reducing flow noise, making it more suitable for the energy supply on the user side, and providing a new option for the planning and configuration of the park energy system.

[0008] The present invention solves the above technical problems through the following technical solutions:

[0009] The present invention provides an energy system based on green carbon cycle, which includes: a methanol energy supply module, a methanol regeneration module and a carbon dioxide heat pump energy storage module;

[0010] The methanol energy supply module includes a methanol internal combustion engine and a first generator, the methanol internal combustion engine drives the first generator, and the methanol energy supply module provides heat load and / or electricity load for the terminal;

[0011] The methanol regeneration module includes a carbon dioxide capture and processing unit, a methanol synthesis unit, and a hydrogen supply unit. The carbon dioxide capture and processing unit is connected to the methanol internal combustion engine and is used to collect carbon dioxide generated by the methanol internal combustion engine; the carbon dioxide capture and processing unit is connected to the methanol synthesis unit and provides carbon dioxide to the methanol synthesis unit; the methanol synthesis unit is used to generate methanol; and the hydrogen supply unit is connected to the methanol synthesis unit and is used to provide hydrogen to the methanol synthesis unit.

[0012] The carbon dioxide heat pump energy storage module includes a refrigerant circulation unit and a heat exchange circulation unit. The refrigerant circulation unit uses carbon dioxide as the refrigerant, utilizes the energy provided by the first generator to drive the compression device to compress the carbon dioxide to a supercritical state, and utilizes the expansion work of the supercritical carbon dioxide to drive the second generator to generate electricity to provide an electrical load for the terminal; the heat exchange circulation unit uses carbon dioxide as the heat exchange circulation medium, provides a cold source and a heat source for the refrigerant of the refrigerant circulation unit, and the heat exchange circulation unit provides a heat load and a cold load for the terminal.

[0013] In the present invention, the refrigerant circulation unit preferably includes a low-pressure storage tank, a cold storage heat exchanger, a compressor, a recooler, a high-pressure storage tank, a reheater, an expander and a second generator; the low-pressure storage tank, the cold storage heat exchanger, the compressor, the recooler, the high-pressure storage tank, the reheater, the expander, the cold storage heat exchanger and the low-pressure storage tank are connected in sequence to form a refrigerant circulation loop for the flow of refrigerant; the expander is also connected to the second generator to supply energy to the second generator, and the second generator provides electrical load for the terminal.

[0014] The heat exchange circulation unit preferably includes a cold storage tank and a heat storage tank, and the cold storage tank, the recooler, the heat storage tank, the reheater and the cold storage tank are connected in sequence to form a heat exchange circulation loop for the flow of heat exchange circulation medium, and the refrigerant and the heat exchange circulation medium exchange heat in the recooler or the reheater; the cold storage tank provides a cold load for the terminal, and the heat storage tank provides a heat load for the terminal.

[0015] Wherein, a fifth regulating valve is preferably provided on the feed pipeline between the low-pressure storage tank and the cold storage heat exchanger for regulating the amount of carbon dioxide entering the cold storage heat exchanger from the low-pressure storage tank.

[0016] Wherein, a sixth regulating valve is preferably provided on the feed pipeline between the high-pressure storage tank and the reheater for regulating the amount of carbon dioxide entering the reheater from the high-pressure storage tank.

[0017] Wherein, a seventh regulating valve is preferably provided on the feed pipeline between the heat storage tank and the reheater for regulating the amount of carbon dioxide entering the reheater from the heat storage tank.

[0018] Wherein, an eighth regulating valve is preferably provided on the feed pipeline between the cold storage tank and the subcooler for regulating the amount of carbon dioxide entering the subcooler from the cold storage tank.

[0019] The low-pressure storage tank is used to store liquid carbon dioxide, and the ultimate bearing pressure of the low-pressure storage tank is determined according to actual working conditions, for example, at least 8-10 MPa.

[0020] The high-pressure storage tank is used to store supercritical carbon dioxide, and the ultimate bearing pressure of the high-pressure storage tank is determined according to actual working conditions, for example, at least 20~25MPa.

[0021] Setting the ultimate bearing pressure of the low-pressure storage tank and the high-pressure storage tank can prevent supercritical carbon dioxide from rushing into the low-pressure storage tank and the high-pressure storage tank due to valve failure, causing the tanks to explode.

[0022] In the present invention, the hydrogen supply unit is preferably a water electrolysis unit, which is used to electrolyze water to produce hydrogen and oxygen. The water electrolysis unit is a conventional water electrolysis device in the art, generally including an electrolyzer and other equipment, and uses water electrolysis to produce hydrogen, which is green and environmentally friendly.

[0023] The water electrolysis unit is preferably powered by the first generator or the second generator. Furthermore, the water electrolysis unit is powered by the second generator.

[0024] Wherein, the water electrolysis unit is preferably also connected to the methanol internal combustion engine to provide oxygen for the methanol internal combustion engine.

[0025] Furthermore, the methanol regeneration module also includes an oxygen storage tank, a hydrogen storage tank and an oxygen storage tank for storing hydrogen and oxygen electrolyzed by the water electrolysis unit. The hydrogen storage tank supplies hydrogen to the methanol synthesis unit, and the oxygen storage tank supplies oxygen to the methanol internal combustion engine.

[0026] Furthermore, a fourth regulating valve is preferably provided on the connecting pipeline between the outlet of the oxygen storage tank and the methanol internal combustion engine for regulating the amount of oxygen entering the methanol internal combustion engine. A third regulating valve is preferably provided on the connecting pipeline between the hydrogen storage tank and the methanol synthesis unit for regulating the amount of hydrogen entering the methanol synthesis unit.

[0027] In the present invention, the carbon dioxide capture and treatment unit is a conventional device in the art that can capture, cool, separate and liquefy the flue gas from a methanol internal combustion engine.

[0028] Among them, the devices used for carbon dioxide capture and cooling separation in the carbon dioxide capture and treatment unit are conventional in the field, for example, including a condensing device, a gas-liquid separation device and a permeation device connected in sequence, the methanol internal combustion engine is connected to the condensing device, and the permeation device is connected to the carbon dioxide storage tank, and the carbon dioxide is purified by the permeation device.

[0029] In the present invention, the methanol synthesis unit is preferably also connected to the methanol internal combustion engine to provide methanol for the methanol internal combustion engine, so that the entire energy system consumes green carbon resources and has no additional carbon emissions to the environment. This is a feasible carbon neutrality path.

[0030] In the present invention, the methanol synthesis unit preferably includes a methanol production reactor, and the methanol production reactor is conventional in the art.

[0031] In the present invention, the carbon dioxide capture and processing unit is preferably further connected to the carbon dioxide heat pump energy storage module to supply refrigerant and / or heat exchange circulation medium to the carbon dioxide heat pump energy storage module.

[0032] In the present invention, the methanol energy supply module may further include a methanol storage tank, the outlet of the methanol storage tank is connected to the methanol internal combustion engine, and the inlet of the methanol storage tank is connected to the methanol synthesis unit.

[0033] Wherein, a first regulating valve is preferably provided on the connecting pipeline between the outlet of the methanol storage tank and the methanol internal combustion engine for regulating the amount of methanol entering the methanol internal combustion engine.

[0034] In the present invention, the methanol regeneration module may further include a carbon dioxide storage tank, the inlet of which is connected to the carbon dioxide capture and processing unit, and the outlet of which is connected to the methanol synthesis unit. Furthermore, the carbon dioxide storage tank may also be connected to the aforementioned low-pressure storage tank to replenish the circulating working fluid to the carbon dioxide heat pump energy storage module.

[0035] Wherein, a second regulating valve is provided on the connecting pipeline between the carbon dioxide storage tank and the methanol synthesis unit, for regulating the amount of carbon dioxide entering the methanol synthesis unit.

[0036] In the present invention, the green carbon cycle-based energy system preferably further includes a first heat exchanger connected to the cold storage tank and / or a second heat exchanger connected to the heat storage tank, wherein the first heat exchanger is connected to a cooling load, and the second heat exchanger is connected to a heating load. Energy exchanged through the first and second heat exchangers is supplied to the cooling and heating loads.

[0037] The present invention provides a control method for the aforementioned energy system based on green carbon cycle, which comprises the following steps:

[0038] Step 1: Determine whether the electric load, heating load and cooling load provided by the carbon dioxide heat pump energy storage module meet all current user load requirements. If yes, proceed to step 3; if not, proceed to step 2;

[0039] Step 2: starting the methanol internal combustion engine to perform methanol cogeneration, and executing step 6;

[0040] Step 3: Determine whether there is a cooling load or heating load demand. If yes, go to step 4; if no, go to step 5.

[0041] Step 4: operating the carbon dioxide heat pump energy storage module to extract cooling load and heating load from the heat exchange cycle unit of the carbon dioxide heat pump energy storage module;

[0042] Step 5: operating the carbon dioxide heat pump energy storage module to control the refrigerant circulation unit to supply electrical load;

[0043] Step 6: Determine whether the current amount of carbon dioxide collected by the carbon dioxide capture processing unit is greater than a threshold value. If yes, proceed to step 7; if not, proceed to step 8.

[0044] Step 7: Control the hydrogen supply unit to supply hydrogen, and input the hydrogen and carbon dioxide into the methanol synthesis unit to synthesize methanol;

[0045] Step 8: Improve the carbon dioxide capture rate of the carbon dioxide capture processing unit, and return to step 6.

[0046] In the present invention, when the aforementioned heat exchange circulation unit including the cold storage tank and the heat storage tank is used, in step 4, the heat load or cold load is extracted by heat exchange with the hot carbon dioxide fluid or cold carbon dioxide fluid in the heat storage tank or the cold storage tank.

[0047] In the present invention, when the aforementioned water electrolysis unit is used, in step 5, the second generator also supplies power to the water electrolysis unit; in step 7, the hydrogen supply unit is a water electrolysis unit, which generates hydrogen by electrolyzing water.

[0048] In the present invention, when the aforementioned refrigerant circulation unit including the expander and the second generator is used, the step 5 is: the refrigerant circulation unit drives the second generator through the expander to generate electricity to supply the electric load.

[0049] In the present invention, in step 6, the threshold is preferably 30-50%, for example, 40%. If the threshold is too low, the normal operation of the methanol synthesis unit will be affected. If the threshold is too high, the stored carbon dioxide is in a liquid state and requires temperature control, so excessive storage will result in unnecessary energy waste. In addition, this percentage will also be adaptively adjusted according to the size of the tank during actual application.

[0050] The present invention provides a method for operating the aforementioned energy system based on the green carbon cycle, which comprises the following steps:

[0051] Methanol energy regeneration: the methanol energy supply module is operated to supply the generated electric energy to the terminal and the carbon dioxide heat pump energy storage module; the flue gas generated by the methanol energy supply module is treated by the carbon dioxide capture and treatment unit to provide carbon dioxide for the methanol regeneration module; the methanol synthesis unit uses the hydrogen provided by the hydrogen supply unit and the carbon dioxide provided by the carbon dioxide capture and treatment unit to produce methanol; the produced methanol and / or exogenous methanol are introduced into the methanol energy supply module and burned to obtain electric energy and / or heat energy;

[0052] Carbon dioxide heat pump energy supply and energy storage: operate the refrigerant circulation unit, use the energy provided by the first generator to drive the compression device to compress the carbon dioxide to a supercritical state, and drive the second generator to generate electricity through the expansion work of the supercritical carbon dioxide to provide electrical load for the terminal; operate the heat exchange circulation unit, use carbon dioxide as the heat exchange circulation medium to provide a cold source and a heat source for the refrigerant of the refrigerant circulation unit, and the heat exchange circulation unit provides heat load and cold load for the terminal.

[0053] In the present invention, when the carbon dioxide heat pump energy storage module is the carbon dioxide heat pump energy storage module described in the aforementioned preferred solution, the carbon dioxide heat pump energy supply and storage steps are:

[0054] In the refrigerant circulation unit loop, liquid carbon dioxide absorbs heat and vaporizes in the cold storage heat exchanger, then enters the compressor to be compressed to a supercritical state, then enters the recooler to exchange heat with the carbon dioxide in the cold storage tank to cool down, then enters the reheater to exchange heat with the carbon dioxide in the heat storage tank to increase its temperature, then enters the expander to perform work, and generates electricity through the second generator. The electricity generated by the second generator is supplied to the power load and the hydrogen supply unit. The supercritical carbon dioxide flowing out of the expander enters the cold storage heat exchanger again to be cooled and liquefied to form liquid carbon dioxide.

[0055] In the heat exchange cycle, the carbon dioxide in the cold storage tank enters the recooler to absorb heat and is then stored in the thermal storage tank. The supercritical carbon dioxide in the thermal storage tank enters the reheater to release heat and is then stored in the cold storage tank. The heat load or cold load is then extracted through heat exchange with the hot carbon dioxide fluid or cold carbon dioxide fluid in the thermal storage tank or the cold storage tank.

[0056] In the present invention, when the hydrogen supply unit is a water electrolysis unit, the functional steps of the methanol energy supply module further include: generating hydrogen by electrolyzing water to supply hydrogen.

[0057] In the present invention, in the heat exchange circulation unit, the heat exchange circulation medium is preferably carbon dioxide in a supercritical state.

[0058] In the present invention, the molar ratio of carbon dioxide to hydrogen entering the methanol synthesis unit is 1:3, which is the molar ratio required for conventional methanol synthesis in the art.

[0059] In the present invention, the outlet temperature of the methanol internal combustion engine is generally 330-350°C.

[0060] In the present invention, when the flow rate of supercritical carbon dioxide is 6.89 kg / s, the cycle efficiency of the energy system based on the green carbon cycle can reach 71%, the exergy efficiency can reach 72%, and the energy storage density can reach 23 kWh / m 3 .

[0061] The positive progress effect of the present invention is:

[0062] The present invention is based on an energy system of green carbon cycle, and adopts a park energy system with a methanol internal combustion engine as its core. While taking into account environmental protection, low carbon and flexible and reliable energy supply, it reduces the transportation cost and storage risk of fuel. In addition, this energy system based on green carbon cycle introduces supercritical carbon dioxide as the refrigerant and heat exchange medium in the carbon dioxide heat pump energy storage module, fully exploiting its advantages of high energy density and low viscosity. On the one hand, it significantly improves the heat exchange efficiency, while reducing the volume of the heat exchanger and reducing flow noise, making it more suitable for the energy supply on the user side, and providing a new option for the planning and configuration of the park energy system. On the other hand, compared with other types of media, the use of carbon dioxide as a working fluid has the advantages of being non-toxic, non-flammable, and environmentally friendly, and has excellent green and environmentally friendly properties.

[0063] At the same time, the carbon dioxide heat pump energy storage module in the energy system based on the green carbon cycle of the present invention can simultaneously have heat pump and energy storage functions using a set of equipment, which can reduce equipment investment and occupied space.

[0064] Furthermore, this energy system based on the green carbon cycle can reuse the carbon dioxide produced by the combustion of green methanol to make methanol for input into the methanol internal combustion engine. This can not only form a green carbon cycle within the system, but also fix part of the carbon in the form of a circulating working fluid, thereby reducing the system's external carbon emissions and causing no additional carbon emissions to the environment. It is a practical and feasible carbon neutrality path.

[0065] The control method of the energy system based on the green carbon cycle of the present invention can enhance the coupling degree of methanol cogeneration, carbon dioxide heat pump energy storage and methanol synthesis units in the energy system by reasonably starting and stopping the equipment in the system, thereby improving the working efficiency and flexibility of the system.

[0066] The present invention's operating method for an energy system based on a green carbon cycle combines methanol energy regeneration with a carbon dioxide heat pump for energy storage. This method, while balancing environmental protection and low carbon emissions with flexible and reliable energy supply, reduces fuel transportation costs and storage risks. Furthermore, since all circulating working fluids are carbon dioxide, the system leverages its advantages, requiring smaller circulation piping diameters, reducing noise levels, and lowering pump power requirements. Furthermore, the carbon dioxide circulating working fluid can be supplemented by carbon capture from the system, achieving internal circulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a schematic diagram of the structure of an energy system based on a green carbon cycle according to Example 1 of the present invention. In the figure, a thick solid line represents electricity, a thin solid line represents liquid or supercritical fluid, and a dotted line represents gas.

[0068] Figure 2This is an operation flow chart of the methanol synthesis unit and the water electrolysis unit described in Example 2 of the present invention.

[0069] Figure 3 This is an operation flow chart of the carbon dioxide heat pump energy storage module described in Example 2 of the present invention.

[0070] Figure 4 This is a flow chart of a control method for an energy system based on a green carbon cycle according to Example 3 of the present invention.

[0071] Description of reference numerals:

[0072] Methanol internal combustion engine 1

[0073] First generator 2

[0074] Methanol storage tank 3

[0075] First regulating valve 41

[0076] Second regulating valve 42

[0077] The third regulating valve 43

[0078] Fourth regulating valve 44

[0079] Fifth regulating valve 45

[0080] Sixth regulating valve 46

[0081] Seventh regulating valve 47

[0082] Eighth regulating valve 48

[0083] Methanol production reactor 5

[0084] Electrolytic cell 6

[0085] Carbon dioxide storage tank 7

[0086] Hydrogen storage tank 8

[0087] Oxygen tank 9

[0088] Low pressure storage tank 10

[0089] High pressure storage tank 11

[0090] Cold storage heat exchanger 12

[0091] Compressor 13

[0092] Subcooler 14

[0093] Reheater 15

[0094] Expander 16

[0095] Cold storage tank 17

[0096] Heat storage tank 18

[0097] Second generator 19

[0098] First heat exchanger 20

[0099] Second heat exchanger 21

[0100] Cooling load 22

[0101] Heat load 23

[0102] Electric load 24 DETAILED DESCRIPTION

[0103] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0104] Example 1

[0105] like Figure 1 As shown, the energy system based on green carbon cycle of this embodiment includes: a methanol energy supply module, a methanol regeneration module and a carbon dioxide heat pump energy storage module;

[0106] The methanol energy supply module includes a methanol internal combustion engine 1, a first generator 2 and a methanol storage tank 3. The output end of the methanol internal combustion engine 1 is connected to the first generator 2 to drive the first generator 2 to generate electricity. The first generator 2 provides an electrical load 24 for the terminal. At the same time, the methanol internal combustion engine 1 also provides a thermal load for the terminal. The methanol storage tank 3 is connected to the methanol internal combustion engine 1. A first regulating valve 41 is provided on the connecting pipeline between the outlet end of the methanol storage tank 3 and the methanol internal combustion engine 1, which is used to regulate the amount of methanol input from the methanol storage tank 3 into the methanol internal combustion engine 1.

[0107] The methanol regeneration module includes a carbon dioxide capture and processing unit, a methanol synthesis unit, a hydrogen supply unit, a carbon dioxide storage tank 7, a hydrogen storage tank 8, and an oxygen storage tank 9. The carbon dioxide capture and processing unit includes a condensing device, a gas-liquid separation device, and a permeation device, which are connected in sequence. The methanol synthesis unit includes a methanol production reactor 5. In this embodiment, the hydrogen supply unit is a water electrolysis unit, which includes an electrolyzer 6 and other structures. The condensing device in the carbon dioxide capture and processing unit is connected to the methanol internal combustion engine 1 and is used to collect carbon dioxide produced by the methanol internal combustion engine 1. The condensed carbon dioxide enters the permeation device, which is connected to the carbon dioxide storage tank 7, where the collected carbon dioxide is stored. The carbon dioxide storage tank 7 is connected to the methanol production reactor 5 to provide carbon dioxide to the methanol production reactor 5. The methanol production reactor 5 is connected to the methanol internal combustion engine 1 to supply methanol to the methanol internal combustion engine 1. The methanol storage tank 3 is connected to the methanol production reactor 5. The electrolyzer 6 is connected to the methanol production reactor 5 to provide hydrogen to the methanol production reactor 5.

[0108] Specifically, a second regulating valve 42 is installed on the pipeline connecting the carbon dioxide storage tank 7 and the methanol production reactor 5 to adjust the input amount of carbon dioxide. A third regulating valve 43 is installed on the pipeline connecting the hydrogen storage tank 8 and the methanol production reactor 5 to adjust the amount of hydrogen entering the methanol production reactor 5. An oxygen storage tank 9 is installed on the pipeline connecting the oxygen storage tank 9 and the methanol internal combustion engine 1 to adjust the amount of oxygen entering the methanol internal combustion engine 1.

[0109] The carbon dioxide heat pump energy storage module includes a refrigerant circulation unit and a heat exchange circulation unit. The refrigerant circulation unit uses carbon dioxide as the refrigerant, uses the energy provided by the first generator 2 to drive the compression device to compress the carbon dioxide to a supercritical state, and uses the expansion work of the supercritical carbon dioxide to drive the second generator 19 to generate electricity to provide an electrical load for the terminal; the heat exchange circulation unit uses carbon dioxide as the heat exchange circulation medium, provides a cold source and a heat source for the refrigerant of the refrigerant circulation unit, and the heat exchange circulation unit provides a heat load and a cold load for the terminal.

[0110] Specifically, in this embodiment, the refrigerant circulation unit includes a low-pressure storage tank 10, a cold storage heat exchanger 12, a compressor 13, a recooler 14, a high-pressure storage tank 11, a reheater 15, an expander 16, and a second generator 19, and the heat exchange circulation unit includes a cold storage tank 17 and a heat storage tank 18. The low-pressure storage tank 10, the cold storage heat exchanger 12, the compressor 13, the hot end of the recooler 14, the high-pressure storage tank 11, the cold end of the reheater 15, the expander 16, the cold storage heat exchanger 12, and the low-pressure storage tank 10 are connected in sequence to form a refrigerant circulation loop for the flow of carbon dioxide. The expander 16 is also connected to the second generator 19 to provide energy for the second generator 19. The second generator 19 provides an electrical load 24 to the terminal and, based on the terminal load, provides electrical energy to the water electrolysis unit.

[0111] The compressor 13 is also connected to the first generator 2 and is driven by the first generator 2; the cold storage tank 17, the cold end of the recooler 14, the heat storage tank 18, the hot end of the reheater 15, and the cold storage tank 17 are connected in sequence to form a heat exchange circulation loop for the flow of carbon dioxide. The cold storage tank 17 can provide a cooling load for the terminal, and the heat storage tank 18 can provide a heating load for the terminal. A fifth regulating valve 45 is provided on the feed pipeline between the low-pressure storage tank 10 and the cold storage heat exchanger 12, a sixth regulating valve 46 is provided on the feed pipeline between the high-pressure storage tank 11 and the reheater 15, a seventh regulating valve 47 is provided on the feed pipeline between the heat storage tank 18 and the reheater 15, and an eighth regulating valve 48 is provided on the feed pipeline between the cold storage tank 17 and the recooler 14, all of which are used to control the flow of carbon dioxide in the pipeline.

[0112] In this embodiment, the energy system based on the green carbon cycle also includes a first heat exchanger 20 connected to the cold storage tank 17 and a second heat exchanger 21 connected to the heat storage tank 18. The first heat exchanger 20 is connected to the cold load, and the second heat exchanger 21 is connected to the hot load. The energy after heat exchange between the first heat exchanger 20 and the second heat exchanger 21 is supplied to the cold load 22 and the hot load 23.

[0113] Example 2

[0114] This embodiment discloses a control method for the system of embodiment 1, and its process is as follows: Figure 4 As shown, it includes the following steps:

[0115] Step 1: Determine whether the electric load, heating load, and cooling load currently provided by the carbon dioxide heat pump energy storage module meet all user load requirements. If yes, proceed to step 3; if not, proceed to step 2.

[0116] Step 2: Start the methanol internal combustion engine 1 to perform methanol cogeneration, and then proceed to step 6;

[0117] Step 3: Determine whether there is a cooling load or heating load demand. If yes, go to step 4; if no, go to step 5.

[0118] Step 4: Run the CO2 heat pump energy storage module to extract corresponding cold CO2 fluid or hot CO2 fluid from the cold storage tank 17 or the heat storage tank 18, and supply the cold load and hot load through the first heat exchanger 20 and the second heat exchanger 21;

[0119] Step 5: Run the carbon dioxide heat pump energy storage module to drive the second generator 19 to generate electricity through the expander 16 to supply electricity to the electrical load or the electrolyzer 6;

[0120] Step 6: Determine whether the current carbon dioxide storage capacity of the carbon dioxide storage tank 7 is greater than 30%. If yes, proceed to step 7; if not, proceed to step 8.

[0121] Step 7: Start the electrolyzer 6 to produce hydrogen, and store the produced hydrogen in the hydrogen storage tank 8, input the hydrogen and carbon dioxide into the methanol production reactor 5 at a molar ratio of 3:1, and store the obtained methanol in the methanol storage tank 3 after distillation and purification.

[0122] It can be understood that methanol distillation purification refers to the distillation purification of the mixed gas of methanol, hydrogen, carbon dioxide and water vapor produced in the methanol production reactor.

[0123] Step 8: Improve the operating levels of the condensing device, gas-liquid separation device, and permeation device in the carbon dioxide capture processing unit to increase the carbon dioxide capture rate, and return to step 6.

[0124] The above control method can flexibly and comprehensively control the energy system based on the green carbon cycle, including determining whether the methanol internal combustion engine performs cogeneration of heat and power, how the carbon dioxide heat pump energy storage system fully utilizes the energy of cogeneration for cooling, heating and energy storage, and fully utilizes the energy and generated carbon dioxide to prepare fuel methanol again without affecting the terminal, thereby achieving the purpose of reducing the system's external carbon emissions and having no additional carbon emissions to the environment, and being able to flexibly adjust load supply or energy storage according to terminal demand.

[0125] Example 3

[0126] This embodiment discloses the operating method of the system of embodiment 1, and its process is as follows: Figure 2 and Figure 3 As shown, it includes the following steps:

[0127] Methanol energy regeneration stage: The methanol energy supply module is operated, with part of the energy generated by the methanol internal combustion engine 1 providing the terminal with electrical load 24 and heat source, and the other part being supplied to the compressor 13 of the carbon dioxide heat pump energy storage module. The flue gas generated by the methanol internal combustion engine 1 is stored as carbon dioxide in the carbon dioxide capture and processing unit and stored in the carbon dioxide storage tank 7. The water in the electrolyzer 6 is electrolyzed to produce oxygen and hydrogen, which are stored in the oxygen storage tank 9 and hydrogen storage tank 8, respectively. The carbon dioxide in the carbon dioxide storage tank 7 and the hydrogen in the hydrogen storage tank 8 enter the methanol production reactor 5 to react and produce methanol. The produced methanol can be temporarily stored in the methanol storage tank 3 with methanol obtained from the outside, and then, as needed, enter the methanol internal combustion engine 1 with oxygen in the oxygen storage tank 9 to undergo methanol-enriched combustion to generate electricity. This cycle can achieve cogeneration of heat and power on the one hand, and provide energy for the carbon dioxide heat pump energy storage module on the other.

[0128] Energy supply and storage stage of the carbon dioxide heat pump: In the carbon dioxide heat pump energy storage module, the refrigerant circulation unit is operated, and the energy provided by the first generator drives the compression device to compress the carbon dioxide to a supercritical state. That is, in the refrigerant circulation loop, the liquid carbon dioxide absorbs heat and vaporizes after passing through the cold storage heat exchanger 12, and then enters the compressor 13 to be compressed to a supercritical state. Then, it enters the recooler 14 to exchange heat with the supercritical carbon dioxide in the cold storage tank 17 for cooling, and then enters the reheater 15 to exchange heat with the supercritical carbon dioxide in the heat storage tank 18 for heating, and then enters the expander 16 to perform work and drive the second generator 19 to generate electricity. The electricity generated by the second generator 19 is supplied to the electric load 24 and / or the electrolyzer 6 to electrolyze water. The supercritical carbon dioxide flowing out of the expander 16 enters the cold storage heat exchanger 12 again to be cooled and liquefied to form liquid carbon dioxide. In this cycle, energy production, storage and reuse are achieved.

[0129] The heat exchange circulation unit is operated, that is, in the heat exchange circulation loop, the supercritical carbon dioxide in the cold storage tank 17 enters the recooler 14 to absorb heat and is then stored in the heat storage tank 18, and the supercritical carbon dioxide in the heat storage tank 18 enters the reheater 15 to release heat and is then stored in the cold storage tank 17; in this cycle, the function of providing a cold source or a heat source for the refrigerant circulation loop and providing a cooling load or a heating load for the terminal is realized.

[0130] In the above embodiment, when the flow rate of supercritical carbon dioxide is 6.89 kg / s, the cycle efficiency of the energy system based on the green carbon cycle can reach 71%, the exergy efficiency can reach 72%, and the energy storage density can reach 23 kWh / m 3 , with very excellent energy utilization effect.

Claims

1. An energy system based on green carbon cycle, characterized in that: include: Methanol energy supply module, methanol regeneration module and carbon dioxide heat pump energy storage module; The methanol energy supply module includes a methanol internal combustion engine and a first generator, the methanol internal combustion engine drives the first generator, and the methanol energy supply module provides heat load and / or electricity load for the terminal; The methanol regeneration module includes a carbon dioxide capture and processing unit, a methanol synthesis unit, and a hydrogen supply unit. The carbon dioxide capture and processing unit is connected to the methanol internal combustion engine and is used to collect carbon dioxide generated by the methanol internal combustion engine; the carbon dioxide capture and processing unit is connected to the methanol synthesis unit and provides carbon dioxide to the methanol synthesis unit; the methanol synthesis unit is used to generate methanol; and the hydrogen supply unit is connected to the methanol synthesis unit and is used to provide hydrogen to the methanol synthesis unit. The carbon dioxide heat pump energy storage module includes a refrigerant circulation unit and a heat exchange circulation unit. The refrigerant circulation unit uses carbon dioxide as the refrigerant, utilizes the energy provided by the first generator to drive the compression device to compress the carbon dioxide to a supercritical state, and utilizes the expansion work of the supercritical carbon dioxide to drive the second generator to generate electricity to provide an electrical load for the terminal; the heat exchange circulation unit uses carbon dioxide as the heat exchange circulation medium, provides a cold source and a heat source for the refrigerant of the refrigerant circulation unit, and the heat exchange circulation unit provides a heat load and a cold load for the terminal.

2. The energy system based on green carbon cycle according to claim 1, characterized in that: The refrigerant circulation unit includes a low-pressure storage tank, a cold storage heat exchanger, a compressor, a recooler, a high-pressure storage tank, a reheater, an expander, and a second generator; the low-pressure storage tank, the cold storage heat exchanger, the compressor, the recooler, the high-pressure storage tank, the reheater, the expander, the cold storage heat exchanger, and the low-pressure storage tank are sequentially connected to form a refrigerant circulation loop for the flow of refrigerant; the expander is also connected to the second generator to supply energy to the second generator, and the second generator provides electrical load for the terminal; The heat exchange circulation unit includes a cold storage tank and a heat storage tank. The cold storage tank, the recooler, the heat storage tank, the reheater, and the cold storage tank are sequentially connected to form a heat exchange circulation loop for the flow of a heat exchange circulation medium. The refrigerant and the heat exchange circulation medium exchange heat in the recooler or the reheater. The cold storage tank provides a cooling load for the terminal, and the heat storage tank provides a heating load for the terminal. Furthermore, a fifth regulating valve is provided on the feed pipeline between the low-pressure storage tank and the cold storage heat exchanger, a sixth regulating valve is provided on the feed pipeline between the high-pressure storage tank and the reheater, a seventh regulating valve is provided on the feed pipeline between the heat storage tank and the reheater, and an eighth regulating valve is provided on the feed pipeline between the cold storage tank and the recooler.

3. The energy system based on green carbon cycle according to claim 1, characterized in that: The hydrogen supply unit is a water electrolysis unit, which is powered by the second generator. Furthermore, the oxygen generated by the water electrolysis unit is introduced into the methanol internal combustion engine to provide oxygen for its sufficient combustion; further, the methanol regeneration module also includes a hydrogen storage tank and an oxygen storage tank for storing hydrogen and oxygen electrolyzed by the water electrolysis unit. The hydrogen storage tank supplies hydrogen to the methanol synthesis unit, and the oxygen storage tank supplies oxygen to the methanol internal combustion engine.

4. The energy system based on green carbon cycle according to claim 3, characterized in that: It meets one or both of the following conditions: ① A third regulating valve is provided on the connecting pipeline between the hydrogen storage tank and the methanol synthesis unit; ② A fourth regulating valve is provided on the connecting pipeline between the oxygen storage tank and the methanol internal combustion engine.

5. The energy system based on green carbon cycle according to claim 1, characterized in that: The energy system based on the green carbon cycle meets one or more of the following conditions: ① The methanol synthesis unit is also connected to the methanol internal combustion engine to provide methanol for the methanol internal combustion engine; ② The carbon dioxide capture and processing unit is also connected to the carbon dioxide heat pump energy storage module to supply refrigerant and / or heat exchange circulation medium to the carbon dioxide heat pump energy storage module.

6. The energy system based on green carbon cycle according to claim 1, characterized in that: The energy system based on the green carbon cycle meets one or more of the following conditions: ① The methanol regeneration module further includes a carbon dioxide storage tank, which is disposed between the carbon dioxide capture and processing unit and the methanol synthesis unit; further, a second regulating valve is provided on the connecting pipeline between the carbon dioxide storage tank and the methanol synthesis unit; further, the carbon dioxide storage tank is also connected to a low-pressure storage tank for supplying refrigerant to the carbon dioxide heat pump energy storage module; ② The methanol energy supply module also includes a methanol storage tank, which is arranged between the methanol internal combustion engine and the methanol synthesis unit. Furthermore, a first regulating valve is provided on the connecting pipeline between the methanol storage tank and the methanol internal combustion engine.

7. A control method for an energy system based on a green carbon cycle according to any one of claims 1 to 6, characterized in that: It includes the following steps: Step 1: Determine whether the electric load, heating load, and cooling load provided by the carbon dioxide heat pump energy storage module meet all current user load requirements. If yes, proceed to step 3. If no, proceed to step 2. Step 2: starting the methanol internal combustion engine to perform methanol cogeneration, and executing step 6; Step 3: Determine whether there is a cooling load or heating load demand. If yes, proceed to step 4. If no, proceed to step 5. Step 4: operating the carbon dioxide heat pump energy storage module to extract cooling load and heating load from the heat exchange cycle unit of the carbon dioxide heat pump energy storage module; Step 5: operating the carbon dioxide heat pump energy storage module to control the refrigerant circulation unit to supply electrical load; Step 6: Determine whether the current amount of carbon dioxide collected by the carbon dioxide capture processing unit is greater than a threshold value. If yes, proceed to step 7. If no, proceed to step 8. Step 7: Control the hydrogen supply unit to supply hydrogen, and input the hydrogen and carbon dioxide into the methanol synthesis unit to synthesize methanol; Step 8: Improve the carbon dioxide capture rate of the carbon dioxide capture processing unit, and return to step 6.

8. The control method of the energy system based on green carbon cycle according to claim 7, characterized in that: It meets one or more of the following conditions: ① Using the energy system based on the green carbon cycle according to claim 2, in step 4, the heat load or the cooling load is extracted by heat exchange with the hot carbon dioxide fluid or the cold carbon dioxide fluid in the heat storage tank or the cold storage tank; ② Using the energy system based on the green carbon cycle according to claim 3, in step 5, the second generator also supplies power to the water electrolysis unit; in step 7, the hydrogen supply unit is a water electrolysis unit that generates hydrogen by electrolyzing water; ③ Using the energy system based on green carbon cycle according to claim 2, step 5 is: the refrigerant circulation unit drives the second generator to generate electricity to supply the electric load through the expansion machine; ④ In step 6, the threshold is 30-50%.

9. The control method of the energy system based on green carbon cycle according to claim 8, characterized in that: In step 6, the threshold is 40%.

10. An operating method of an energy system based on a green carbon cycle according to any one of claims 1 to 6, characterized in that: It includes the following steps: Methanol energy regeneration: the methanol energy supply module is operated to supply the generated electric energy to the terminal and the carbon dioxide heat pump energy storage module; the flue gas generated by the methanol energy supply module is treated by the carbon dioxide capture and treatment unit to provide carbon dioxide for the methanol regeneration module; the methanol synthesis unit uses the hydrogen provided by the hydrogen supply unit and the carbon dioxide provided by the carbon dioxide capture and treatment unit to produce methanol; the produced methanol and / or exogenous methanol are introduced into the methanol energy supply module and burned to obtain electric energy and / or heat energy; Carbon dioxide heat pump energy supply and energy storage: operate the refrigerant circulation unit, use the energy provided by the first generator to drive the compression device to compress the carbon dioxide to a supercritical state, and drive the second generator to generate electricity through the expansion work of the supercritical carbon dioxide to provide electrical load for the terminal; operate the heat exchange circulation unit, use carbon dioxide as the heat exchange circulation medium to provide a cold source and a heat source for the refrigerant of the refrigerant circulation unit, and the heat exchange circulation unit provides heat load and cold load for the terminal.

11. The method for operating an energy system based on a green carbon cycle according to claim 10, wherein: The operation method of the energy system based on the green carbon cycle meets one or more of the following conditions: ① When the energy system based on the green carbon cycle described in claim 2 is adopted, the carbon dioxide heat pump energy supply and energy storage steps are as follows: in the refrigerant circulation unit loop, the liquid carbon dioxide absorbs heat and vaporizes in the cold storage heat exchanger, enters the compressor and is compressed to a supercritical state, then enters the recooler to exchange heat with the carbon dioxide in the cold storage tank for cooling, then enters the reheater to exchange heat with the carbon dioxide in the heat storage tank for heating, enters the expander to perform work, and generates electricity through the second generator. The electricity generated by the second generator is supplied to the power load and the hydrogen supply unit, and the supercritical carbon dioxide flowing out of the expander enters the cold storage heat exchanger again for cooling and liquefaction to form liquid carbon dioxide; In the heat exchange cycle, the carbon dioxide in the cold storage tank enters the recooler to absorb heat and is then stored in the thermal storage tank. The supercritical carbon dioxide in the thermal storage tank enters the reheater to release heat and is then stored in the cold storage tank. The heat load or cooling load is then extracted through heat exchange with the hot carbon dioxide fluid or cold carbon dioxide fluid in the thermal storage tank or the cold storage tank. ② When the energy system based on the green carbon cycle as described in claim 3 is adopted, the functional steps of the methanol energy supply module also include: generating hydrogen by electrolyzing water to supply hydrogen.

12. The method for operating an energy system based on a green carbon cycle according to claim 10, wherein: The operation method of the energy system based on the green carbon cycle meets one or more of the following conditions: ① In the heat exchange circulation unit, the heat exchange circulation medium is carbon dioxide in a supercritical state; ② The molar ratio of carbon dioxide to hydrogen entering the methanol synthesis unit is 1:3; ③ The outlet temperature of the methanol internal combustion engine is 330-350°C.

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