A carnot cell system coupled to an uninterrupted low temperature heat source and integrated optimization method thereof

Abstract

The application discloses a kind of coupling uninterrupted low-temperature heat source's Carnot cell system and integrated optimization method thereof, the system includes high-temperature heat pump system, heat storage system and power cycle system;During charging, high-temperature heat pump system operates, and the waste heat of uninterrupted low-temperature heat source module is lifted as high-grade heat energy using renewable energy power and is stored into heat storage system;During discharging, power cycle system operates, and the heat energy stored in heat storage system and uninterrupted low-temperature heat source in discharging stage are used in cascade, and the mechanical energy generated is converted into electric energy by generator and output to power grid;System configuration is not dependent on working medium type, and the comprehensive utilization rate of uninterrupted low-temperature heat source and the round trip efficiency of Carnot cell are improved;The integrated optimization method of the application encodes working medium, so that it becomes continuous variable that can be optimized synchronously, and only one optimization is needed to obtain optimal charge-discharge cycle working medium combination and system operating parameters suitable for different operating conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new thermomechanical energy storage technology, in particular to a Carnot cell system coupled with uninterrupted low-temperature heat source and an integrated optimization method thereof. BACKGROUND

[0002] Under the background of rapid development of renewable energy, combining energy storage system with renewable energy power generation can effectively solve the problem of volatility of renewable energy and instability of power system. Especially with the increasing proportion of renewable energy generation, the role of energy storage system becomes more and more important. Carnot cell is a very potential energy storage technology, which is composed of electric heating system, heat storage system and heat power generation system. In the charging stage, the heat pump system is driven by abandoned wind, abandoned light or low-cost electricity, and the generated heat energy is stored through the heat storage medium. When the power grid is in high peak load and the price is high, the heat engine cycle is used to convert the heat energy back to electricity and return to the power grid. Carnot cell has the advantages of flexible deployment, no geographical restrictions and high energy density. The current traditional system form has low utilization degree of uninterrupted heat source, lacks system configuration suitable for different working medium types and operating conditions, and has no effective working medium and parameter optimization method, which hinders the improvement and application of the comprehensive performance of Carnot cell.

[0003] The Chinese invention patent application with publication number CN117346581A proposes a waste heat utilization system based on Carnot cell, which recovers and utilizes high-temperature heat energy by inputting high-temperature waste heat into a high-temperature heat storage device, but the energy release mechanism of the system is complex, which leads to poor economy and adjustability.

[0004] The Chinese invention patent application with publication number CN118599500A proposes a mixed working medium applied to low-temperature waste heat type Carnot cell energy storage system and its system and method, which realizes efficiency improvement by setting regenerator and waste heat preheater in power cycle, but only considers subcritical operation on the system, and there is a functional conflict between the regenerator and the preheater. In addition, the system working medium needs to be given in advance, and the parameter optimization is carried out under the condition of each working medium, which cannot realize global performance optimization at one step. SUMMARY

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present application is to provide a Carnot cell system coupled with uninterrupted low-temperature heat source and an integrated optimization method thereof. The system can effectively improve the comprehensive utilization rate of uninterrupted low-temperature heat source and the round-trip efficiency of Carnot cell by coupling with uninterrupted low-temperature heat source in the charging and discharging periods. The integrated optimization method proposed in the present application codes the working medium as a continuous variable that can be optimized, so that the optimal charging and discharging cycle working medium combination and system operating parameters suitable for different operating conditions can be obtained only once.

[0006] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0007] A Carnot cell system coupled with an uninterrupted low-temperature heat source, comprising three subsystems: a high-temperature heat pump system, a heat storage system and a power cycle system, the heat energy outlet of the high-temperature heat pump system is connected with the heat energy inlet of the heat storage system, and the heat energy outlet of the heat storage system is connected with the heat energy inlet of the power cycle system; the heat energy inlets of the high-temperature heat pump system and the power cycle system are respectively connected with the waste heat outlet of the uninterrupted low-temperature heat source module 1, the electric energy inlet of the high-temperature heat pump system is connected with the electric energy outlet of the renewable energy power generation module 14, the power output shaft of the power cycle system is connected with the power input shaft of the generator 16, and the electric energy outlet of the generator 16 is connected with the electric energy inlet of the power grid 15.

[0008] During the charging process, the high-temperature heat pump system operates, and the waste heat of the uninterrupted low-temperature heat source module 1 is lifted to high-grade heat energy by renewable energy power to be stored in the heat storage system; during the discharging process, the power cycle system operates, and the heat energy stored in the heat storage system and the uninterrupted low-temperature heat source in the discharging stage are used in stages to generate mechanical energy, which is converted into electric energy by the generator 16 and output to the power grid 15.

[0009] The high-temperature heat pump system comprises a heat pump evaporator 2, a regenerator 3, a compressor 4, a heat pump condenser 5, and a throttling valve 6. The waste heat outlet of the uninterrupted low-temperature heat source module 1 is connected to the low-temperature side inlet of the heat pump evaporator 2, and the low-temperature side outlet of the heat pump evaporator 2 is connected to the waste heat inlet of the uninterrupted low-temperature heat source module 1, so that the heat from the uninterrupted low-temperature heat source module 1 is input into the heat pump evaporator 2 to make the circulating working medium in the heat pump evaporator 2 absorb heat and evaporate. The low-temperature side outlet of the heat pump evaporator 2 is connected to the low-temperature side inlet of the regenerator 3, and the circulating working medium is further heated by the regenerator 3. The low-temperature side outlet of the regenerator 3 is connected to the inlet of the compressor 4, the electric energy inlet of the compressor 4 is connected to the electric energy outlet of the renewable energy power generation module 14, and the circulating working medium is heated and pressurized by the compressor 4 to consume the electric energy generated by the renewable energy module 14. The outlet of the compressor 4 is connected to the high-temperature side inlet of the heat pump condenser 5, and the circulating working medium in a high-temperature and high-pressure state flows through the heat pump condenser 5 to exchange heat with the heat storage medium from the heat storage system and release heat. The high-temperature side outlet of the heat pump condenser 5 is connected to the high-temperature side inlet of the regenerator 3, and the circulating working medium exchanges heat with the circulating working medium at the low-temperature side outlet of the heat pump evaporator 2 through the regenerator 3 to be cooled. The high-temperature side outlet of the regenerator 3 is connected to the low-temperature side inlet of the heat pump evaporator 2 through the throttling valve 6, and the low-temperature side outlet of the heat pump evaporator 2 is connected to the waste heat inlet of the uninterrupted low-temperature heat source module 1. The circulating working medium after being cooled is throttled and expanded by the throttling valve 6 and then enters the heat pump evaporator 2 to absorb the heat of the uninterrupted low-temperature heat source. The low-temperature heat source in the heat pump evaporator 2 is heated and cooled by the circulating working medium and then input into the uninterrupted low-temperature heat source module 1 to be heated again.

[0010] The heat storage system adopts a double-tank sensible heat storage form and comprises a high-temperature heat storage tank 7 and a low-temperature heat storage tank 8. During the charging process, the outlet of the low-temperature heat storage tank 8 is connected to the low-temperature side inlet of the heat pump condenser 5, the low-temperature side outlet of the heat pump condenser 5 is connected to the inlet of the high-temperature heat storage tank 7, the heat storage medium flows through the heat pump condenser 5 from the low-temperature heat storage tank 8 into the high-temperature heat storage tank 7, exchanges heat with the high-temperature heat pump circulating working medium in the heat pump condenser 5 to be heated, and stores the heated heat storage medium into the high-temperature heat storage tank 7. During the discharging process, the outlet of the high-temperature heat storage tank 7 is connected to the high-temperature side inlet of the heat engine evaporator 9, the high-temperature side outlet of the heat engine evaporator 9 is connected to the inlet of the low-temperature heat storage tank 8, the heat storage medium flows through the heat engine evaporator 9 from the high-temperature heat storage tank 7 into the low-temperature heat storage tank 8, exchanges heat with the power circulating working medium in the heat engine evaporator 9 to be cooled, and stores the cooled heat storage medium into the low-temperature heat storage tank 8, and then the cycle is repeated.

[0011] The power cycle system comprises a heat engine evaporator 9, a turbine expander 10, a heat engine condenser 11, a working medium pump 12, and a preheater 13; the low-temperature side outlet of the heat engine evaporator 9 is connected with the inlet of the turbine expander 10, the power output shaft of the turbine expander 10 is connected with the power input shaft of a power generator 16, the electric energy outlet of the power generator 16 is connected with the electric energy inlet of an electric network 15, the circulating working medium entering the heat engine evaporator 9 exchanges heat with the heat storage medium in the heat engine evaporator 9 to absorb heat, the high-temperature and high-pressure working medium enters the turbine expander 10 to expand and work, drives the power generator 16 to rotate and generate electricity, and the generated electric energy is transmitted to the electric network 15; the outlet of the turbine expander 10 is connected with the high-temperature side inlet of the heat engine condenser 11 to cool the expanded working medium; the high-temperature side outlet of the heat engine condenser 11 is connected with the inlet of the working medium pump 12, the outlet of the working medium pump 12 is connected with the low-temperature side inlet of the preheater 13, the waste heat outlet of the uninterrupted low-temperature heat source module 1 is connected with the high-temperature side inlet of the preheater 13, the high-temperature side outlet of the preheater 13 is connected with the waste heat inlet of the uninterrupted low-temperature heat source module 1, and the low-temperature side outlet of the preheater 13 is connected with the low-temperature side inlet of the heat engine evaporator 9; the power cycle working medium cooled by the heat engine condenser 11 is compressed and pressurized by the working medium pump 12 and then input into the preheater 13, is preheated by the waste heat of the uninterrupted low-temperature heat source module 1 in the discharging stage, and then enters the heat engine evaporator 9 to absorb the heat energy stored in the high-temperature heat storage tank 7 to be warmed and evaporated, and the waste heat in the preheater 13 is cooled by the power cycle working medium and then returned to the uninterrupted low-temperature heat source module 1.

[0012] The circulating working medium in the high-temperature heat pump system and the power cycle system is one of six low-global-warming-potential organic working mediums or a mixed working medium formed by one of the six low-global-warming-potential organic working mediums and carbon dioxide, and the six organic working mediums are R1234yf, R1234ze(E), R1234ze(Z), R1224yd(Z), R1233zd(E), and R1336mzz(Z).

[0013] The heat storage medium in the heat storage system is pressurized water or heat-conducting oil, the heat storage temperature of the high-temperature heat storage tank 7 is 110-140 DEG C, and the heat storage temperature of the low-temperature heat storage tank 8 is lower than 100 DEG C and slightly higher than the temperature of the uninterrupted low-temperature heat source.

[0014] The compressor 4 of the high-temperature heat pump system adopts a screw compressor or a centrifugal compressor, and the turbine expander 10 of the power cycle system adopts an axial flow turbine expander; when a single organic working medium is used, the heat pump evaporator 2, the regenerator 3, the heat pump condenser 5, the heat engine evaporator 9, the heat engine condenser 11 and the preheater 13 all adopt plate heat exchangers; when a mixed working medium of an organic working medium and carbon dioxide is used and the mass mixing ratio of carbon dioxide is relatively high so that the high-pressure pressure of the cycle exceeds 3.5 MPa, the heat pump condenser 5, the heat engine evaporator 9 and the preheater 13 all adopt printed circuit board heat exchangers, and the heat pump evaporator 2, the regenerator 3 and the heat engine condenser 11 all adopt plate heat exchangers.

[0015] The uninterrupted low-temperature heat source is industrial waste heat, data center liquid cooling waste heat, regional heat network or geothermal heat.

[0016] The application further provides an integrated optimization method of a Carnot cell system coupled with an uninterrupted low-temperature heat source, comprising the following steps:

[0017] Step 1: by encoding the working medium of the high-temperature heat pump system and the power cycle system, the discrete working medium types in the high-temperature heat pump system and the power cycle system are converted into corresponding continuous variables, which are called working medium selection factors;

[0018] Step 2: the working medium selection factors in step 1 and system operation parameters are simultaneously input into a Carnot cell system integrated model for calculation, and a thermal economic evaluation index of the Carnot cell system is output;

[0019] The system operation parameters include the high-temperature heat storage temperature of the high-temperature heat storage tank 7, the low-temperature heat storage temperature of the low-temperature heat storage tank 8 and the pinch temperature difference of the six heat exchangers, namely the heat pump evaporator 2, the regenerator 3, the heat pump condenser 5, the heat engine evaporator 9, the heat engine condenser 11 and the preheater 13; and the thermal economic evaluation index includes round-trip efficiency, energy storage density and levelized energy storage cost;

[0020] Step 3: the thermal economic evaluation index obtained in step 2 is taken as an optimization objective function, a multi-objective intelligent optimization algorithm is used to solve the multi-objective optimization problem, and a Pareto front is obtained; the weights of the round-trip efficiency, the energy storage density and the levelized energy storage cost are determined according to different application scenarios, and an optimal result is determined on the Pareto front.

[0021] The working medium coding process is as follows:

[0022] By using a piecewise function method, the discrete organic working medium types are converted into continuous optimization variables, and by using uniform spacing, each organic working medium has the same search interval to realize fair selection;

[0023] The working medium coding expression is as follows:

[0024]

[0025] Wherein, WF is the working medium, and numbers 1-6 correspond to six kinds of organic working medium respectively; WFS is the working medium selection factor, and the interval is set as (1, 7), that is, the selection interval length of each organic working medium is 1; when the working medium selection factor is in different intervals, different organic working medium types are corresponded.

[0026] The expression of the multi-objective optimization problem in the step 3 is as follows:

[0027]

[0028] Wherein, RTE is the round trip efficiency, VED is the volume energy density, LCOS is the levelized cost of stored energy, x is the decision variable, T HST is the high-temperature heat storage temperature of the high-temperature heat storage tank 7, T CST is the low-temperature heat storage temperature of the low-temperature heat storage tank 8, and PPTD x 6 is the pinch temperature difference of the six heat exchangers in the Carnot battery system.

[0029] Compared with the prior art, the advantages of the present application are that:

[0030] 1. The Carnot battery system proposed in the present application realizes full utilization of uninterrupted low-temperature heat source in the charging and discharging stage, that is, the high-temperature heat pump cycle system of the Carnot battery utilizes uninterrupted low-temperature heat source to improve the evaporation temperature in the charging stage, and the power cycle system utilizes uninterrupted low-temperature heat source for preheating in the discharging stage, effectively improving the comprehensive utilization effect of uninterrupted low-temperature heat source and the round trip efficiency of electric energy of the Carnot battery.

[0031] 2. The Carnot battery system proposed in the present application further improves the performance of the high-temperature heat pump by adopting a regenerator in the high-temperature heat pump system, and in the power cycle system, the uninterrupted low-temperature heat source is coupled twice for preheating, which improves the performance of the power cycle, saves the regenerator in the power cycle system in the prior art, effectively reduces the heat exchanger area and investment cost, and improves the economy; in addition, the reasonable configuration of the above two subsystems makes the whole Carnot battery system not dependent on the working medium types of the high-temperature heat pump system and the power cycle system, and different working media can make the Carnot battery system operate efficiently.

[0032] 3. The Carnot battery system proposed in the present application adopts low-global-warming-potential organic working medium and carbon dioxide as alternative working medium, and one kind of organic working medium or a mixed working medium formed by one kind of organic working medium and carbon dioxide can be selected as the working medium of the high-temperature heat pump system and the power cycle system, which ensures the thermal performance and makes the whole Carnot battery become a sustainable energy storage system.

[0033] 4. The application proposes an integrated optimization method for working medium and operating parameters of a Carnot cell system. By encoding the working medium, the working medium becomes a continuous variable that can be optimized, and the optimal working medium and corresponding system operating parameters of the high-temperature heat pump system and the power cycle system can be determined at one time, saving computing resources and time, and achieving global optimization of the system comprehensive performance in one step.

[0034] 5. The Carnot cell system proposed by the application is not only suitable for industrial waste heat, but also can be applied to data center liquid cooling waste heat, regional heat network, and geothermal scenes.

[0035] Compared with the prior art, the Carnot cell system coupled with an uninterrupted low-temperature heat source can effectively improve the comprehensive utilization rate of the uninterrupted low-temperature heat source and the round-trip efficiency of the Carnot cell. The integrated optimization method proposed by the application encodes the working medium to make it a continuous variable that can be optimized, and the optimal charging and discharging cycle working medium combination and system operating parameters suitable for different operating conditions can be obtained by only one optimization. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 FIG. 1 is a structural schematic diagram of the Carnot cell system coupled with an uninterrupted low-temperature heat source of the application.

[0037] In the figure, uninterrupted low-temperature heat source module 1, heat pump evaporator 2, regenerator 3, compressor 4, heat pump condenser 5, throttling valve 6, high-temperature heat storage tank 7, low-temperature heat storage tank 8, heat engine evaporator 9, turbine expander 10, heat engine condenser 11, working medium pump 12, preheater 13, renewable energy power generation module 14, power grid 15, and generator 16.

[0038] Figure 2 FIG. 2 is a flowchart of the calculation method of the Carnot cell system integrated model provided by the application.

[0039] Figure 3 FIG. 3 is a Pareto frontier comparison diagram of the Carnot cell system integrated optimization method proposed by the application and the traditional enumeration method, wherein, Figure 3 (a) is the traditional enumeration method, Figure 3 (b) is the method of the application. DETAILED DESCRIPTION

[0040] The structural features and effects achieved by the application will be described clearly and completely in combination with the accompanying drawings.

[0041] As Figure 1As shown, a Carnot cell system coupled with an uninterrupted low-temperature heat source includes three subsystems: a high-temperature heat pump system, a heat storage system, and a power cycle system. The heat energy outlet of the high-temperature heat pump system is connected with the heat energy inlet of the heat storage system, and the heat energy outlet of the heat storage system is connected with the heat energy inlet of the power cycle system. The heat energy inlets of the high-temperature heat pump system and the power cycle system are respectively connected with the waste heat outlet of the uninterrupted low-temperature heat source module 1. The electric energy inlet of the high-temperature heat pump system is connected with the electric energy outlet of the renewable energy power generation module 14. The power output shaft of the power cycle system is connected with the power input shaft of the generator 16. The electric energy outlet of the generator 16 is connected with the electric energy inlet of the power grid 15.

[0042] During the charging process, the high-temperature heat pump system operates to store the waste heat of the uninterrupted low-temperature heat source module 1 into the heat storage system as high-grade heat energy by using renewable energy power. During the discharging process, the power cycle system operates to perform cascade utilization of the heat energy stored in the heat storage system and the low-temperature heat source in the discharging stage, and the generated mechanical energy is converted into electric energy by the generator 16 and output to the power grid 15.

[0043] The uninterrupted low-temperature heat source is a low-temperature heat source condition that continuously supplies heat throughout the day, specifically industrial waste heat, data center liquid cooling waste heat, regional heat network, or geothermal heat.

[0044] The high-temperature heat pump system includes a heat pump evaporator 2, a regenerator 3, a compressor 4, a heat pump condenser 5, and a throttling valve 6. The waste heat outlet of the uninterrupted low-temperature heat source module 1 is connected with the low-temperature side inlet of the heat pump evaporator 2, so as to input the heat from the uninterrupted low-temperature heat source module 1 into the heat pump evaporator 2 and make the circulating working medium in the heat pump evaporator 2 evaporate by absorbing heat. The low-temperature side outlet of the heat pump evaporator 2 is connected with the low-temperature side inlet of the regenerator 3, so as to further heat the circulating working medium by the regenerator 3. The low-temperature side outlet of the regenerator 3 is connected with the inlet of the compressor 4. The electric energy inlet of the compressor 4 is connected with the electric energy outlet of the renewable energy power generation module 14. The circulating working medium is heated and pressurized by the compressor 4 by using the electric energy generated by the renewable energy module 14. The outlet of the compressor 4 is connected with the high-temperature side inlet of the heat pump condenser 5. The circulating working medium in a high-temperature and high-pressure state flows through the heat pump condenser 5, exchanges heat with the heat storage medium from the heat storage system, and releases heat. The high-temperature side outlet of the heat pump condenser 5 is connected with the high-temperature side inlet of the regenerator 3. The circulating working medium exchanges heat with the circulating working medium at the low-temperature side outlet of the heat pump evaporator 2 by the regenerator 3 and is cooled. The high-temperature side outlet of the regenerator 3 is connected with the low-temperature side inlet of the heat pump evaporator 2 through the throttling valve 6. The low-temperature side outlet of the heat pump evaporator 2 is connected with the waste heat inlet of the uninterrupted low-temperature heat source module 1. The circulating working medium cooled by the throttling valve 6 is throttled and expanded and then enters the heat pump evaporator 2 to absorb the heat of the uninterrupted low-temperature heat source. The low-temperature heat source in the heat pump evaporator 2 is input into the uninterrupted low-temperature heat source module 1 after being cooled by the circulating working medium.

[0045] The heat storage system adopts a double-tank sensible heat storage form, including a high-temperature heat storage tank 7 and a low-temperature heat storage tank 8; in the charging process, the outlet of the low-temperature heat storage tank 8 is connected with the low-temperature side inlet of the heat pump condenser 5, the low-temperature side outlet of the heat pump condenser 5 is connected with the inlet of the high-temperature heat storage tank 7, the heat storage medium flows from the low-temperature heat storage tank 8 through the heat pump condenser 5 into the high-temperature heat storage tank 7, exchanges heat with the high-temperature heat pump circulating working medium in the heat pump condenser 5 to be warmed, and stores the warmed heat storage medium into the high-temperature heat storage tank 7; in the discharging process, the outlet of the high-temperature heat storage tank 7 is connected with the high-temperature side inlet of the heat engine evaporator 9, the high-temperature side outlet of the heat engine evaporator 9 is connected with the inlet of the low-temperature heat storage tank 8, the heat storage medium flows from the high-temperature heat storage tank 7 through the heat engine evaporator 9 into the low-temperature heat storage tank 8, exchanges heat with the power cycle working medium in the heat engine evaporator 9 to be cooled, and stores the cooled heat storage medium into the low-temperature heat storage tank 8, and then the cycle is repeated;

[0046] The power cycle system includes a heat engine evaporator 9, a turbine expander 10, a heat engine condenser 11, a working medium pump 12, and a preheater 13; the low-temperature side outlet of the heat engine evaporator 9 is connected with the inlet of the turbine expander 10, the power output shaft of the turbine expander 10 is connected with the power input shaft of a generator 16, and the electric energy outlet of the generator 16 is connected with the electric energy inlet of a power grid 15; the circulating working medium entering the heat engine evaporator 9 exchanges heat with the heat storage medium in the heat engine evaporator 9 to absorb heat, the high-temperature and high-pressure working medium enters the turbine expander 10 to expand and work, drives the generator 16 to rotate to generate electricity, and the generated electric energy is transmitted to the power grid 15; the outlet of the turbine expander 10 is connected with the high-temperature side inlet of the heat engine condenser 11 to cool the expanded working medium gas; the high-temperature side outlet of the heat engine condenser 11 is connected with the inlet of the working medium pump 12, the outlet of the working medium pump 12 is connected with the low-temperature side inlet of the preheater 13, the waste heat outlet of the uninterrupted low-temperature heat source module 1 is connected with the high-temperature side inlet of the preheater 13, the high-temperature side outlet of the preheater 13 is connected with the waste heat inlet of the uninterrupted low-temperature heat source module 1, and the low-temperature side outlet of the preheater 13 is connected with the low-temperature side inlet of the heat engine evaporator 9; the power cycle working medium cooled by the heat engine condenser 11 is compressed and boosted by the working medium pump 12 and then input into the preheater 13, is preheated by the waste heat of the uninterrupted low-temperature heat source module 1 in the discharging stage to be warmed, and then enters the heat engine evaporator 9 to absorb the heat energy stored in the high-temperature heat storage tank 7 to be warmed and evaporated, and the waste heat in the preheater 13 is absorbed by the power cycle working medium to be cooled and then returned to the uninterrupted low-temperature heat source module 1.

[0047] The high-temperature heat pump system is one of six low-global-warming-potential organic working fluids or a mixed working fluid formed by one of the six low-global-warming-potential organic working fluids and carbon dioxide; the circulating working fluid in the power cycle system is one of the six low-global-warming-potential organic working fluids or a mixed working fluid formed by one of the six low-global-warming-potential organic working fluids and carbon dioxide; the six organic working fluids are R1234yf, R1234ze(E), R1234ze(Z), R1224yd(Z), R1233zd(E), and R1336mzz(Z) respectively; the heat storage medium in the heat storage system is pressurized water or heat-conducting oil, the heat storage temperature of the high-temperature heat storage tank 7 is 110-140°C, and the heat storage temperature of the low-temperature heat storage tank 8 is lower than 100°C and slightly higher than the temperature of the uninterrupted low-temperature heat source.

[0048] According to the power and operating pressure of the system, the equipment of the system is selected: the compressor 4 of the high-temperature heat pump system adopts a screw compressor or a centrifugal compressor according to the capacity, the turbo-expander 10 of the power cycle system adopts an axial-flow turbo-expander; the six heat exchangers, i.e. the heat pump evaporator 2, the regenerator 3, the heat pump condenser 5, the heat engine evaporator 9, the heat engine condenser 11, and the preheater 13, adopt a plate heat exchanger or a printed circuit board heat exchanger according to the operating pressure; when a single organic working fluid is used, the six heat exchangers all adopt a plate heat exchanger; when a mixed working fluid of an organic working fluid and carbon dioxide is used and the mass mixing ratio of carbon dioxide is high so that the circulating high-pressure exceeds 3.5 MPa, the heat pump condenser 5, the heat engine evaporator 9, and the preheater 13 all adopt a printed circuit board heat exchanger, and the heat pump evaporator 2, the regenerator 3, and the heat engine condenser 11 all adopt a plate heat exchanger.

[0049] An integrated optimization method of a Carnot cell system coupled with an uninterrupted low-temperature heat source, comprising the following steps:

[0050] Step 1: By encoding the working fluids of the high-temperature heat pump system and the power cycle system, the discrete working fluid types in the high-temperature heat pump system and the power cycle system are converted into corresponding continuous variables, which are called working fluid selection factors;

[0051] The working fluid encoding process is as follows:

[0052] By using the method of piecewise function, the discrete organic working fluid types are converted into continuous optimization variables, and by using uniform spacing, each organic working fluid has the same search interval to achieve fair selection;

[0053] The working fluid encoding expression is as follows:

[0054]

[0055] Where WF is the working fluid, and numbers 1-6 correspond to six organic working fluids respectively; WFS is the working fluid selection factor, and its interval is set to (1,7), that is, the selection interval length of each organic working fluid is 1; when the working fluid selection factor is in different intervals, it corresponds to different types of organic working fluids;

[0056] Step 2: Input the working fluid selection factor and system operating parameters of step 1 into the Carnot battery system integrated model for calculation, and output the thermal economic evaluation index of the Carnot battery system;

[0057] The system operating parameters include the high-temperature heat storage temperature of the high-temperature heat storage tank 7, the low-temperature heat storage temperature of the low-temperature heat storage tank 8, and the pinch point temperature difference of the six heat exchangers, the six heat exchangers being the heat pump evaporator 2, the regenerator 3, the heat pump condenser 5, the heat engine evaporator 9, the heat engine condenser 11, and the preheater 13; the thermal economy evaluation indicators include round-trip efficiency, energy storage density, and levelized energy storage cost;

[0058] like Figure 2 As shown, the calculation process of the Carnot battery system integration model is as follows:

[0059] First, the working fluid selection factors, system operating parameters, and boundary conditions from step 1 are input into the Carnot battery system integrated model. The heat storage temperature and heat storage efficiency after standing are calculated based on the thermal insulation performance of the heat storage system. The boundary conditions include the ambient temperature, the efficiency of the turboexpander 10, the generator 16, and the working fluid pump 12, the charge and discharge time, the electricity price, the temperature of the uninterrupted low-temperature waste heat, the thermal insulation performance of the high-temperature heat storage tank 7 and the low-temperature heat storage tank 8, the equipment price, the operation and maintenance cost, and the life of the Carnot battery system.

[0060] The heat storage temperature is then input into the high-temperature heat pump system model. Assuming the superheat and condensing pressure, the compression, i.e., isentropic efficiency, is calculated. The pinch point between the heat storage medium and the high-temperature heat pump working fluid in the heat pump condenser 5 is found, and the pinch point temperature difference of the heat pump condenser 5 is calculated. The pinch point temperature difference of the heat pump condenser 5 is converged to the design value by iterating the condensing pressure. The pinch point temperature difference of the regenerator 3 is then calculated. The pinch point temperature difference of the regenerator 3 is converged to the design value by iterating the superheat, and the performance coefficient and equipment cost of the high-temperature heat pump system are then calculated.

[0061] Input the heat storage temperature into the power cycle system model, assume the condensation pressure, find the pinch point between the cooling water in the heat engine condenser 11 and the power cycle working fluid, calculate the pinch point temperature difference of the heat engine condenser 11, and iterate the condensation pressure to make the pinch point temperature difference of the heat engine condenser 11 converge to the design value; assume the evaporation pressure, find the pinch point between the heat storage medium in the heat engine evaporator 9 and the power cycle working fluid, calculate the pinch point temperature difference of the heat engine evaporator 9, and iterate the evaporation pressure to make the pinch point temperature difference of the heat engine evaporator 9 converge to the design value, and then calculate the power generation efficiency and equipment cost of the power cycle system;

[0062] Finally, the thermal economic evaluation index of the Carnot cell system is calculated and output according to the coefficient of performance of the high-temperature heat pump system and the equipment cost and the power generation efficiency and equipment cost of the power cycle system;

[0063] Step 3: The thermal economic evaluation index obtained in step 2 is taken as the optimization objective function, and a multi-objective intelligent optimization algorithm is used to solve the multi-objective optimization problem to obtain a Pareto frontier; the weights of the round-trip efficiency, the energy storage density and the levelized cost of storage are determined according to different application scenarios, and the optimal result is determined on the Pareto frontier;

[0064] The expression of the multi-objective optimization problem is as follows:

[0065]

[0066] Wherein, RTE is the round-trip efficiency, VED is the volume energy density, LCOS is the levelized cost of storage, x is the decision variable, T HST is the high-temperature heat storage temperature of the high-temperature heat storage tank 7, T CST is the low-temperature heat storage temperature of the low-temperature heat storage tank 8, and PPTD x 6 is the pinch temperature difference of the six heat exchangers in the Carnot cell system.

[0067] By setting a suitable variable optimization interval, a multi-objective intelligent optimization algorithm (such as NSGA-II) can obtain a Pareto frontier. Since the high-temperature heat pump system and the power cycle system of the Carnot cell system can use different working fluids, when there are n kinds of alternative working fluids, the working fluid combination is n 2 . The traditional optimization method needs to optimize each working fluid combination once, which consumes a large amount of time and calculation resources. The integrated optimization method proposed in the present application includes a working fluid coding method, so that the working fluid becomes an optimization variable and is automatically optimized by the optimization algorithm. Therefore, only one optimization is needed to simultaneously obtain the best working fluid combination and the corresponding system parameters.

[0068] As Figure 3 (a) shows, when there are 4 kinds of alternative working fluids, 4 optimizations are needed by using the traditional enumeration method; as Figure 3 (b) shows, when there are 4 kinds of alternative working fluids, only one optimization is needed by using the integrated optimization method proposed in the present application, which saves a large amount of time and calculation resources.

Claims

1. A Carnot cell system coupled to an uninterrupted low temperature heat source, characterized by, The system comprises three subsystems: a high-temperature heat pump system, a heat storage system, and a power cycle system, the heat energy outlet of the high-temperature heat pump system is connected with the heat energy inlet of the heat storage system, the heat energy outlet of the heat storage system is connected with the heat energy inlet of the power cycle system, the heat energy inlets of the high-temperature heat pump system and the power cycle system are respectively connected with the waste heat outlet of the uninterrupted low-temperature heat source module (1), the electric energy inlet of the high-temperature heat pump system is connected with the electric energy outlet of the renewable energy power generation module (14), the power output shaft of the power cycle system is connected with the power input shaft of the generator (16), and the electric energy outlet of the generator (16) is connected with the electric energy inlet of the power grid (15); During the charging process, the high-temperature heat pump system operates, and the waste heat of the uninterrupted low-temperature heat source module (1) is lifted to high-grade heat energy by renewable energy power and stored in the heat storage system; during the discharging process, the power cycle system operates, the heat energy stored in the heat storage system and the uninterrupted low-temperature heat source in the discharging stage are used in stages, and the mechanical energy generated is converted into electric energy by the generator (16) and output to the power grid (15); The integration optimization method of the Carnot cell system comprises the following steps: Step 1: by encoding the working medium of the high-temperature heat pump system and the power cycle system, the discrete working medium types in the high-temperature heat pump system and the power cycle system are converted into corresponding continuous variables, which are called working medium selection factors; Step 2: input the working medium selection factors of step 1 and system operation parameters into the Carnot cell system integration model for calculation, and output the thermal economic evaluation index of the Carnot cell system; The system operation parameters include the high-temperature heat storage temperature of the high-temperature heat storage tank (7), the low-temperature heat storage temperature of the low-temperature heat storage tank (8), and the pinch temperature difference of the six heat exchangers, namely the heat pump evaporator (2), the regenerator (3), the heat pump condenser (5), the heat engine evaporator (9), the heat engine condenser (11), and the preheater (13); the thermal economic evaluation index includes round-trip efficiency, energy storage density, and levelized energy storage cost; Step 3: taking the thermal economic evaluation index obtained in step 2 as the optimization objective function, solving the multi-objective optimization problem based on a multi-objective intelligent optimization algorithm to obtain a Pareto front; according to different application scenarios, the weights of the round-trip efficiency, the energy storage density, and the levelized energy storage cost are determined, and the optimal result is determined on the Pareto front.

2. A Carnot cell system coupled to an uninterrupted low temperature heat source according to claim 1, characterized in that: The high-temperature heat pump system comprises a heat pump evaporator (2), a regenerator (3), a compressor (4), a heat pump condenser (5), and a throttling valve (6); the waste heat outlet of the uninterrupted low-temperature heat source module (1) is connected with the low-temperature side inlet of the heat pump evaporator (2), the heat from the uninterrupted low-temperature heat source module (1) is input into the heat pump evaporator (2), and the circulating working medium in the heat pump evaporator (2) absorbs heat and evaporates; the low-temperature side outlet of the heat pump evaporator (2) is connected with the low-temperature side inlet of the regenerator (3), and the circulating working medium is further heated through the regenerator (3); the low-temperature side outlet of the regenerator (3) is connected with the inlet of the compressor (4), the electric energy inlet of the compressor (4) is connected with the electric energy outlet of the renewable energy power generation module (14), the electric energy generated by the renewable energy module (14) is consumed by the compressor (4) to heat and pressurize the circulating working medium; the outlet of the compressor (4) is connected with the high-temperature side inlet of the heat pump condenser (5), the circulating working medium in a high-temperature and high-pressure state flows through the heat pump condenser (5), exchanges heat with the heat storage medium from the heat storage system, and releases heat; the high-temperature side outlet of the heat pump condenser (5) is connected with the high-temperature side inlet of the regenerator (3), and the circulating working medium exchanges heat with the circulating working medium at the low-temperature side outlet of the heat pump evaporator (2) through the regenerator (3) to be cooled; the high-temperature side outlet of the regenerator (3) is connected with the low-temperature side inlet of the heat pump evaporator (2) through the throttling valve (6), the low-temperature side outlet of the heat pump evaporator (2) is connected with the waste heat inlet of the uninterrupted low-temperature heat source module (1), and the cooled circulating working medium is throttled and expanded through the throttling valve (6) and then enters the heat pump evaporator (2) to absorb the heat of the uninterrupted low-temperature heat source, and the low-temperature heat source in the heat pump evaporator (2) is heated and cooled by the circulating working medium and then input into the uninterrupted low-temperature heat source module (1) to be heated again.

3. A Carnot cell system coupled to an uninterrupted low temperature heat source according to claim 1, wherein: The heat storage system adopts a double-tank sensible heat storage form, comprising a high-temperature heat storage tank (7) and a low-temperature heat storage tank (8); during the charging process, the outlet of the low-temperature heat storage tank (8) is connected with the low-temperature side inlet of the heat pump condenser (5), the low-temperature side outlet of the heat pump condenser (5) is connected with the inlet of the high-temperature heat storage tank (7), the heat storage medium flows through the heat pump condenser 5 from the low-temperature heat storage tank (8) into the high-temperature heat storage tank (7), exchanges heat with the high-temperature heat pump circulating working medium in the heat pump condenser (5), is heated, and is stored in the high-temperature heat storage tank (7) after being heated; during the discharging process, the outlet of the high-temperature heat storage tank (7) is connected with the high-temperature side inlet of the heat engine evaporator (9), the high-temperature side outlet of the heat engine evaporator (9) is connected with the inlet of the low-temperature heat storage tank (8), the heat storage medium flows through the heat engine evaporator (9) from the high-temperature heat storage tank (7) into the low-temperature heat storage tank (8), exchanges heat with the power circulating working medium in the heat engine evaporator (9), is cooled, and is stored in the low-temperature heat storage tank (8) after being cooled, and then the cycle is repeated.

4. A Carnot cell system coupled to an uninterrupted low temperature heat source according to claim 1, wherein: The power cycle system comprises a heat engine evaporator (9), a turbine expander (10), a heat engine condenser (11), a working medium pump (12), and a preheater (13); the low-temperature side outlet of the heat engine evaporator (9) is connected with the inlet of the turbine expander (10), the power output shaft of the turbine expander (10) is connected with the power input shaft of a generator (16), the electric energy outlet of the generator (16) is connected with the electric energy inlet of a power grid (15), the circulating working medium entering the heat engine evaporator (9) exchanges heat with the heat storage medium in the heat engine evaporator (9) to absorb heat, the high-temperature and high-pressure working medium enters the turbine expander (10) to expand and work, drives the generator (16) to rotate and generate electricity, and the generated electric energy is transmitted to the power grid (15); the outlet of the turbine expander (10) is connected with the high-temperature side inlet of the heat engine condenser (11) to cool the expanded working medium; the high-temperature side outlet of the heat engine condenser (11) is connected with the inlet of the working medium pump (12), the outlet of the working medium pump (12) is connected with the low-temperature side inlet of the preheater (13), the waste heat outlet of the uninterrupted low-temperature heat source module (1) is connected with the high-temperature side inlet of the preheater (13), the high-temperature side outlet of the preheater (13) is connected with the waste heat inlet of the uninterrupted low-temperature heat source module (1), and the low-temperature side outlet of the preheater (13) is connected with the low-temperature side inlet of the heat engine evaporator (9); the power cycle working medium cooled by the heat engine condenser (11) is compressed and pressurized by the working medium pump (12) and then input into the preheater (13), is preheated by the waste heat of the uninterrupted low-temperature heat source module (1) in the discharge stage, and then enters the heat engine evaporator (9) to absorb the heat energy stored in the high-temperature heat storage tank (7) to be warmed and evaporated, and the waste heat in the preheater (13) is cooled by the power cycle working medium and then returned to the uninterrupted low-temperature heat source module (1).

5. A Carnot cell system coupled to an uninterrupted low temperature heat source according to any one of claims 1-4, characterized in that: The circulating working medium in the high-temperature heat pump system and the power cycle system is one of six low-global-warming-potential organic working mediums or a mixed working medium formed by one of the six low-global-warming-potential organic working mediums and carbon dioxide, and the six organic working mediums are R1234yf, R1234ze(E), R1234ze(Z), R1224yd(Z), R1233zd(E), and R1336mzz(Z). The heat storage medium in the heat storage system is pressurized water or heat-conducting oil, the heat storage temperature of the high-temperature heat storage tank (7) is 110-140 DEG C, and the heat storage temperature of the low-temperature heat storage tank (8) is lower than 100 DEG C and slightly higher than the temperature of the uninterrupted low-temperature heat source.

6. A Carnot cell system coupled to an uninterrupted low temperature heat source according to claim 5, wherein: The compressor (4) of the high-temperature heat pump system adopts a screw compressor or a centrifugal compressor, and the turbine expander (10) of the power cycle system adopts an axial turbine expander; when a single organic working medium is used, the heat pump evaporator (2), the regenerator (3), the heat pump condenser (5), the heat engine evaporator (9), the heat engine condenser (11) and the preheater (13) all adopt plate heat exchangers; when a mixed working medium of an organic working medium and carbon dioxide is used and the mass mixing ratio of carbon dioxide is high so that the high-pressure pressure of the cycle exceeds 3.5 MPa, the heat pump condenser (5), the heat engine evaporator (9) and the preheater (13) all adopt printed circuit board heat exchangers, and the heat pump evaporator (2), the regenerator (3) and the heat engine condenser (11) all adopt plate heat exchangers.

7. A Carnot cell system coupled to an uninterrupted low temperature heat source according to claim 6, wherein: The uninterrupted low-temperature heat source is industrial waste heat, data center liquid cooling waste heat, regional heat network or geothermal heat.

8. The integrated optimization method of a Carnot cell system coupled to an uninterrupted low-temperature heat source according to claim 1, characterized in that, The working medium coding process is as follows: By using the method of piecewise function, the discrete organic working medium types are converted into continuous optimization variables, and the same search interval of each organic working medium is ensured by uniform spacing to realize fair selection. The working medium coding expression is as follows: Wherein, WF is the working medium, and the numbers 1-6 correspond to six organic working mediums; WFS is the working medium selection factor, and its interval is set to (1, 7), that is, the selection interval length of each organic working medium is 1; when the working medium selection factor is in different intervals, different organic working medium types are corresponded.

9. The integrated optimization method of a Carnot cell system coupled to an uninterrupted low-temperature heat source according to claim 1, characterized in that, The expression of the multi-objective optimization problem in step 3 is as follows: wherein RTE is round trip efficiency, VED is volumetric energy density, LCOS is levelized cost of storage, x is decision variable, T HST is high temperature thermal storage temperature of the high temperature thermal storage tank (7), T CST is low temperature thermal storage temperature of the low temperature thermal storage tank (8), and PPTD x 6 is pinch temperature difference of the six heat exchangers in the Carnot cell system.

Images