Compressed carbon dioxide energy storage system based on phase change heat storage and regenerative coupling and deep peak regulation method

Abstract

The invention discloses a compressed carbon dioxide energy storage system based on phase change heat storage and regenerative coupling and a deep peak regulation method, relates to the technical field of energy storage, and constructs a three-stage cascade heating chain. The compressed carbon dioxide energy storage system comprises a compressor unit, a high-pressure tank, a low-pressure tank, a regeneration heater, a PCM packed bed and a turbine generator unit. An outlet of the low-pressure tank is connected with an inlet of a working medium channel in the regeneration heater through the compressor unit and the high-pressure tank, an outlet of the working medium channel in the regeneration heater is connected with an inlet of a working medium channel in the PCM packed bed, and an outlet of the working medium channel in the PCM packed bed is connected with an inlet of a heat source channel in the regeneration heater through the turbine generator set. An outlet of a heat source channel in the regeneration heater is connected with an inlet of the low-pressure tank through the first air cooler. According to the method, the output power, the energy storage density and the peak regulation response speed of the system are remarkably improved, and an efficient deep peak regulation solution is provided for renewable energy source grid connection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a compressed carbon dioxide energy storage system integrating a phase change material heat storage unit and a regenerative heat exchanger and a deep peak shaving method thereof, and is especially suitable for solving the peak load shifting demand of renewable energy integration into the power grid. BACKGROUND

[0002] With the continuous expansion of renewable energy installed capacity, the peak-valley regulation pressure of the power grid is becoming increasingly severe. Compressed carbon dioxide (CO2) energy storage technology has become one of the preferred solutions to support large-scale energy storage applications due to its low critical point temperature of working medium, high energy density, and strong heat exchange performance. However, existing research and technical practice shows that the traditional compressed CO2 energy storage system still has significant defects: during the expansion work process, the turbine inlet temperature is generally insufficient, which severely limits the output power of the system; at the same time, the waste heat after expansion work cannot be efficiently recovered and utilized, resulting in considerable energy loss. These key bottlenecks not only expose the lack of research in the core links such as thermodynamic cycle optimization, heat management strategy, and waste heat cascade utilization of the current system, but also directly restrict the large-scale application of the technology in deep peak shaving and other scenarios with extremely high requirements for flexibility and economy. SUMMARY

[0003] The present application proposes a compressed carbon dioxide energy storage system and a deep peak shaving method based on phase change heat storage and regenerative heat coupling to address the above problems, and constructs a three-stage cascade heating chain of "water preheating-regenerative heat exchange-phase change material heating", and realizes closed recovery of exhaust waste heat through dynamic control.

[0004] The technical solution of the present application is that the compressed carbon dioxide energy storage system comprises a compressor unit, a high-pressure tank, a low-pressure tank, a regenerative heater, a PCM packed bed, and a turbine generator unit; The PCM packed bed has a working medium channel and a heat source channel, and the regenerative heater also has a working medium channel and a heat source channel; The outlet of the low-pressure tank is connected to the inlet of the working medium channel in the regenerative heater through the compressor unit and the high-pressure tank, the outlet of the working medium channel in the regenerative heater is connected to the inlet of the working medium channel in the PCM packed bed, the outlet of the working medium channel in the PCM packed bed is connected to the inlet of the heat source channel in the regenerative heater through the turbine generator unit, and the outlet of the heat source channel in the regenerative heater is connected to the inlet of the low-pressure tank through the air cooler; Specifically, the outlet pipe C1 of the low-pressure tank is connected to the compressor set, then connected to the high-pressure tank through pipe C2, then connected to the inlet of the working medium passage in the regenerative heater through pipe C4, the outlet of the working medium passage in the regenerative heater is connected to the inlet of the working medium passage in the PCM packed bed through pipe C5, the outlet of the working medium passage in the PCM packed bed is connected to the turbine generator set through pipe C6, then connected to the inlet of the heat source passage in the regenerative heater through pipe C7, the outlet of the heat source passage in the regenerative heater is connected to the air cooler I through pipe C8, and the air cooler I is connected to the inlet of the low-pressure tank through pipe C9.

[0005] The inlet of the heat source passage in the PCM packed bed is connected to the steam outlet of the combined heat and power system, and the outlet of the heat source passage in the PCM packed bed is connected back to the combined heat and power system.

[0006] The compressed carbon dioxide energy storage system further comprises a water heat exchange system, which comprises a cold water tank, a cooler, a pump I, a hot water tank, a preheater, an air cooler II and a pump II connected in series to form a loop, the cold water tank is used to cool the pipe between the compressor set and the high-pressure tank, and the preheater is used to preheat the pipe between the high-pressure tank and the regenerative heater.

[0007] The PCM packed bed is a phase change heat storage packed bed, and molten salt is used as the heat storage medium, and the phase change temperature range is between 372K and 630K. This temperature range matches the steam temperature of the waste heat of the combined heat and power system and can also meet the inlet temperature requirement of the turbine.

[0008] The high-temperature side inlet of the regenerative heat exchanger is connected to the turbine exhaust port, and the low-temperature side outlet is connected to the phase change material packed bed inlet; the compressed carbon dioxide energy storage system further comprises a control module for monitoring the temperature of the exhaust side of the turbine generator set in real time and controlling the on-off state of the branch in the regenerative heater based on the monitoring result; the branch and the heat source passage in the regenerative heater are connected in parallel, and only one of them is kept in communication; When it is monitored that the temperature of the exhaust side of the turbine generator set is higher than the temperature of the inlet side of the preheater, the heat source passage in the regenerative heater is turned on to recover waste heat, so that the regenerative heater also has a working medium passage and a heat source passage for heat exchange; when the temperature of the exhaust side of the turbine generator set is lower than the temperature of the inlet side of the preheater, the heat source passage in the regenerative heater is turned off, and the branch in the regenerative heater is turned on, so that the working medium is switched to the air cooler, avoiding the efficiency loss caused by invalid heat exchange.

[0009] The preheater is a first-stage preheating channel; the regenerative heater and the preheater are arranged in series to form a second-stage preheating channel, which is located between the preheater outlet and the phase change material filling bed inlet, so that the working medium completes a two-stage temperature rising process of 'water preheating-regenerative heat exchange' before entering the phase change material bed, thereby slowing down the heat release of the PCM accumulation bed and prolonging the high output power in the energy release process; the PCM filling bed is a third-stage preheating channel; and three-stage heating is realized.

[0010] The compressed carbon dioxide energy storage system performs deep peak shaving according to the following logic: During the low load period of the power grid, the surplus electric energy is used to drive the multi-stage compressor set to extract carbon dioxide from the low-pressure tank and store it in the high-pressure tank, and at the same time, the steam generated by the cogeneration system is introduced into the PCM accumulation bed for heat storage; during the peak load period of the power grid, the high-pressure carbon dioxide flows through the preheater, the regenerative heat exchanger and the PCM accumulation bed in turn, and after three-stage heating, drives the turbine generator set to output electric energy; in this process, the opening and closing state of the regenerative heat exchange branch is dynamically controlled by real-time monitoring of the temperature of the exhaust side of the turbine generator set.

[0011] The working principle of the present application is as follows: during the low load period of the power grid, the surplus electric energy is used to drive the compressor to store carbon dioxide in the high-pressure tank, and at the same time, the surplus steam of the cogeneration system is introduced into the PCM filling bed, and the steam heat is used to make the molten salt change phase and store latent heat; during the peak load period of the power grid, the high-pressure carbon dioxide first flows through the preheater to absorb the stored sensible heat in the compression stage, then enters the regenerative heat exchanger (when the starting condition is met) to recover the turbine exhaust waste heat for two-stage temperature rising, and finally flows through the PCM filling bed to absorb the phase change latent heat of the molten salt to realize three-stage heating. The high-temperature and high-pressure carbon dioxide after gradient heating drives the turbine to generate electricity efficiently. The dynamic control of the regenerative heat exchange branch is the core: when it is monitored that the turbine exhaust temperature is higher than the inlet temperature of the water preheater, the regenerative heat exchanger is started to recover the waste heat; when the exhaust temperature is lower than the inlet temperature of the preheater, the regenerative heat exchange branch is closed, and the working medium is switched to the air cooler to avoid the efficiency loss caused by invalid heat exchange.

[0012] The present application significantly improves the turbine inlet temperature through the phase change heat storage unit, solves the problem of large expansion temperature drop of the traditional CCES, realizes closed-loop gradient utilization of exhaust waste heat through the introduction of the regenerative heat exchanger and the intelligent control strategy, greatly reduces the system loss, and finally significantly improves the output power, energy storage density and peak shaving response speed of the system, providing an efficient deep peak shaving solution for renewable energy grid connection. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The figure is a structural schematic diagram of the system of the present application.

[0014] Figure 2For temperature-entropy diagram, the differences of thermodynamic cycle paths among the traditional CCES system, CCES-PCM system and the CCES-PCM-RH of the application are compared, and the steam extraction heating and exhaust heat recovery are highlighted to improve the cycle efficiency.

[0015] Figure 3 For the temperature distribution in the PCM packed bed: (a) temperature at different times during the energy storage process and (b) temperature difference; (c) temperature distribution of the PCM packed bed in the CCES-TES system during energy release; (d) temperature distribution of the PCM packed bed in the CCES-TES-RH system during energy release.

[0016] Figure 4 (a) output power and (b) system efficiency of the CCES, CCES-TES and CCES-TES-RH systems.

[0017] Abbreviations in the figures: CCES: traditional supercritical carbon dioxide energy storage; CCES-TES: supercritical carbon dioxide energy storage with added PCM packed bed; CCES-TES-RH: supercritical carbon dioxide energy storage with added PCM packed bed and exhaust heat recovery; SPE: system energy conversion efficiency (ratio of total output power of power generation to total power consumption of input); PCR: power regulation capability ratio (ratio of power change of combined energy storage system to rated power of combined heat and power unit); ESD: energy storage density (effective power generation energy output per unit volume of supercritical CO2 storage tank). DETAILED DESCRIPTION

[0018] To clearly illustrate the technical features of the application, the application will be described in detail below with specific embodiments and in conjunction with the accompanying drawings.

[0019] The compressed carbon dioxide energy storage system has a compressed energy storage circuit and a phase change heat storage circuit.

[0020] The compressed energy storage circuit includes a compressor, a high-pressure tank (design pressure 26.25 MPa) and a low-pressure tank arranged in series. The key innovation of the application lies in the construction of a three-stage heating channel: a preheater (recovery of compression heat), a regenerative heater (dynamic waste heat recovery) and a PCM packed bed (latent heat utilization of molten salt) are connected in series in the pipeline from the outlet of the high-pressure storage tank to the inlet of the turbine, as shown in Figure 1 .

[0021] In the phase change heat storage circuit, the PCM packed bed, i.e. the phase change material packed bed, uses solar salt (60% NaNO3 + 40% KNO3) as the heat storage medium, with a phase change temperature of 218-230°C and a phase change latent heat of 94.3 kJ / kg. The heat source is the extraction steam of the combined heat and power unit. The high-temperature side inlet of the regenerative heat exchanger is directly connected to the turbine exhaust pipe, and the low-temperature side outlet is connected to the inlet of the PCM packed bed, forming a closed waste heat recovery path.

[0022] Figure 2 The temperature-entropy diagram reveals the optimization mechanism of the three-stage heating on the thermodynamic cycle. As shown in the figure, the conventional CCES system is limited in cycle efficiency due to the sharp drop of working medium temperature after expansion and the lack of exhaust heat recovery; while the CCES-PCM system with phase change thermal storage increases the turbine inlet temperature by 138.8K through the PCM packed bed, but the exhaust temperature is still as high as 405.9K, which results in significant irreversibility loss. The CCES-PCM-RH system of the patent innovatively adds a regenerative heat exchange link, so that the working medium experiences two-stage heating between the preheater and the PCM bed, which reduces the PCM heat load and further realizes the closed recovery of exhaust heat, greatly expanding the cycle work area.

[0023] Dynamic peak shaving operation process: when the grid load is low, the system starts dual energy storage: the surplus electric energy drives the compressor to pressurize CO2 to 26.25MPa for storage, and the extraction steam of 629.7K from the combined heat and power unit is introduced into the heat storage molten salt heat exchanger to heat the 372K molten salt to the molten state and store it in the hot tank. This process reduces the turbine work flow by diverting the boiler outlet steam, further reducing the unit load.

[0024] At the peak period of grid load, the high-pressure CO2 first flows through the preheater to absorb the compression sensible heat and is heated to 372K. At this time, the control module detects the turbine exhaust temperature in real time: when the exhaust temperature is higher than the preheater inlet temperature 372K, the regenerative heat exchange branch valve is automatically opened. After preheating, the working medium absorbs the exhaust heat and is heated in the regenerative heat exchanger, and then enters the PCM packed bed to exchange heat with the high-temperature molten salt, and the latent heat released by the phase change of the molten salt further heats the CO2. The CO2 driven by the three-stage heating of the turbine outputs an average power of 10.59MW, which is 64.4% higher than that of the conventional system (see Figure 4 ). In addition, the SPE, PCR and ESD of the CCES-TES-RH system are the highest, indicating that the system has the highest output power, energy storage density and peak shaving depth.

[0025] If the exhaust temperature is ≤372K (such as at the end of discharge), the control module automatically switches to the air cooling branch to avoid ineffective heat exchange. The whole process realizes heat release through the movement of the molten salt phase change interface (see Figure 3 ), compared with the CCES-TES system, the CCES-TES-RH system can still improve the CO2 temperature at the later stage of heat release, prolonging the time of high output power of the system.

[0026] There are many specific implementation ways of the present application, and the above description is only the preferred embodiment of the present application. It should be pointed out that for ordinary skilled persons in the technical field, some improvements can be made without departing from the principles of the present application, and these improvements should also be considered as the protection scope of the present application.

Claims

1. A compressed carbon dioxide energy storage system based on phase change heat storage and heat recovery coupling, characterized in that: The compressed carbon dioxide energy storage system includes a compressor unit, a high-pressure tank, a low-pressure tank, a regenerative heater, a PCM packed bed and a turbine generator unit; The PCM packed bed has a working fluid channel and a heat source channel, and the regenerative heater also has a working fluid channel and a heat source channel; The outlet of the low-pressure tank is connected to the inlet of the working fluid channel in the regenerative heater via the compressor unit and the high-pressure tank, the outlet of the working fluid channel in the regenerative heater is connected to the inlet of the working fluid channel in the PCM packed bed, the outlet of the working fluid channel in the PCM packed bed is connected to the inlet of the heat source channel in the regenerative heater via the turbine generator unit, and the outlet of the heat source channel in the regenerative heater is connected to the inlet of the low-pressure tank via air cooler 1; The inlet of the heat source channel in the PCM packed bed is connected to the steam outlet of the cogeneration system, and the outlet of the heat source channel in the PCM packed bed is connected back to the cogeneration system.

2. A compressed carbon dioxide energy storage system based on phase change heat storage and heat recovery coupling according to claim 1, characterized in that: The compressed carbon dioxide energy storage system also includes a water heat exchange system, which includes a cold water tank, a cooler, a first pump, a hot water tank, a preheater, a second air cooler, and a second pump connected in series to form a loop. The cold water tank is used to cool the pipeline between the compressor unit and the high-pressure tank, and the preheater is used to preheat the pipeline between the high-pressure tank and the regeneration heater.

3. A compressed carbon dioxide energy storage system based on phase change heat storage and heat recovery coupling according to claim 2, characterized in that: The preheater is a primary preheating channel; the regenerative heater and preheater are arranged in series to form a secondary preheating channel, which is located between the preheater outlet and the phase change material packed bed inlet, so that the working medium completes the secondary temperature rise process of "water preheating-regeneration heat exchange" before entering the phase change material bed; the PCM packed bed is a tertiary preheating channel; Realize three-stage heating.

4. The compressed carbon dioxide energy storage system based on phase change heat storage and heat recovery coupling according to claim 1 is characterized in that: The PCM packed bed is a phase change heat storage stacked bed, which uses molten salt as a heat storage medium, and its phase change temperature range is between 372K and 630K.

5. The compressed carbon dioxide energy storage system based on phase change heat storage and heat recovery coupling according to claim 1 is characterized in that: The compressed carbon dioxide energy storage system further includes a control module for monitoring the temperature on the exhaust side of the turbine generator set in real time and controlling the opening and closing state of the branch in the regenerative heater based on the monitoring result; the branch in the regenerative heater and the heat source channel are connected in parallel, and only one of the two remains connected; When it is monitored that the temperature on the exhaust side of the turbine generator set is higher than the temperature on the inlet side of the preheater, the heat source channel in the regenerative heater is turned on to recover the waste heat, so that the regenerative heater also has a working fluid channel and a heat source channel for heat exchange; when the temperature on the exhaust side of the turbine generator set is lower than the temperature on the inlet side of the preheater, the heat source channel in the regenerative heater is closed, the branch in the regenerative heater is turned on, and the working fluid is switched to the air cooler to avoid efficiency loss caused by ineffective heat exchange.

6. A deep peak regulation method for a compressed carbon dioxide energy storage system based on phase change heat storage and heat recovery coupling according to claim 1, characterized in that: The compressed carbon dioxide energy storage system performs deep peak regulation according to the following logic: During periods of low grid load, surplus electricity is used to drive a multi-stage compressor unit to extract carbon dioxide from the low-pressure tank and pressurize and store it in a high-pressure tank. At the same time, the steam generated by the cogeneration system is introduced into the PCM stacked bed for heat storage; during peak grid load periods, the high-pressure carbon dioxide flows through the preheater, regenerative heat exchanger and PCM stacked bed in sequence, and after three-stage heating, drives the turbine generator set to output electricity; during this process, the opening and closing status of the regenerative heat exchange branch is dynamically controlled by real-time monitoring of the temperature on the exhaust side of the turbine generator set.

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