Construction and evaluation method of thermo-chemical heat storage cycle driven by generalized heat engine for generalized heat pump

Abstract

The application discloses a method for constructing and evaluating a thermo-chemical heat storage cycle driven by a generalized heat engine and a generalized heat pump, and relates to the technical field of thermo-chemical energy storage, and comprises the following steps: S1, taking the thermo-chemical heat storage cycle as a research object, regarding the reactants and products of the thermo-chemical reaction as cycle working medium, and regarding the forward and reverse thermo-chemical reaction conditions as cycle operation parameters; S2, decoupling the thermo-chemical heat storage cycle into an endothermic energy storage stage and an exothermic energy release stage according to time; S3, constructing a generalized heat engine process; S4, constructing a generalized heat pump process; and S5, energy conversion evaluation. The method for constructing and evaluating the thermo-chemical heat storage cycle driven by the generalized heat engine and the generalized heat pump is adopted, the energy conversion essence of heat-work-heat in the thermo-chemical heat storage cycle is revealed, the irreversible loss caused by factors such as temperature difference can be quantified, and the method provides a basis for performance optimization of a heat storage system.

Description

Technical Field

[0001] This invention relates to the field of chemical energy storage technology, and in particular to a method for constructing and evaluating thermochemical thermal storage cycles based on generalized heat engines driving generalized heat pumps. Background Technology

[0002] With the large-scale development of renewable energy, thermochemical energy storage (TCES) technology, with its high energy density, extremely low heat loss, and excellent long-term storage potential, has become a key means to mitigate the intermittency and volatility of renewable energy generation such as solar power. TCES utilizes reversible chemical reactions to achieve the cyclical conversion of thermal energy and chemical energy. In the endothermic energy storage stage, reactants absorb heat and convert it into products to accumulate chemical energy; in the exothermic energy release stage, the products convert energy back into thermal energy through a reverse reaction.

[0003] Current evaluation methods for thermochemical energy storage are mostly based on the first law of thermodynamics, using enthalpy change of reaction. While this method provides intuitive engineering data, it neglects the inherent directional requirements of chemical reactions, making it difficult to scientifically distinguish between chemical thermal energy storage and sensible or latent heat energy storage driven by temperature differences, based on the essential driving force of reaction affinity. This results in a lack of thermodynamic consistency when measuring the impact of reaction spontaneity on system benefits at different operating temperatures. Furthermore, existing evaluation logic focuses only on macroscopic energy balance results, failing to delve into the internal energy flow mechanisms of the conversion process, particularly lacking in-depth interpretation and analysis of TCES systems from a thermodynamic cycle perspective. This makes it difficult for researchers to accurately quantify irreversible system losses caused by factors such as temperature hysteresis, hindering clear theoretical guidance for performance optimization and material selection in thermal storage systems. Therefore, there is an urgent need to construct a theoretical framework and evaluation method that can uniformly describe the essence of chemical thermal energy storage cycles and accurately quantify the degree of internal energy efficiency degradation. Summary of the Invention

[0004] The purpose of this invention is to provide a method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump. By constructing a theoretical model of a generalized heat engine and a generalized heat pump, and taking the generation and utilization of work capacity as the core of evaluation, this invention solves the problem that existing evaluation methods based on reaction enthalpy change cannot accurately reflect changes in energy quality and reaction directionality.

[0005] To achieve the above objectives, this invention provides a method for constructing and evaluating a thermochemical thermal storage cycle based on a generalized heat engine driving a generalized heat pump, comprising the following steps: S1. The thermochemical thermal storage cycle is taken as the research object, the reactants and products of the thermochemical reaction are regarded as the working fluid, and the forward and reverse thermochemical reaction conditions are used as the cycle operation parameters. S2. Based on the target reversible thermochemical reaction system, the thermochemical thermal energy storage cycle is decoupled into an endothermic energy storage stage and an exothermic energy release stage according to time. S3. Construct a generalized heat engine process in the heat storage process. High-temperature heat energy drives the originally non-spontaneous endothermic chemical reaction at the storage temperature and converts it into the work capacity of the products. S4. Construct a generalized heat pump process in the exothermic energy release process. The energy-making capacity of the consumed products drives the reverse chemical reaction, so that the exothermic reaction releases heat at a temperature higher than the storage temperature, thus completing the release of high-temperature heat energy to the user end. S5. Energy conversion evaluation: Clarify the energy conversion path of heat-work-heat, and equate the thermochemical thermal storage cycle with a coupled system of a generalized heat engine driving a generalized heat pump across the time dimension, and evaluate the individual and overall performance indicators.

[0006] Preferably, in a thermochemical thermal storage cycle, the generalized work is defined by the storage temperature. and reference pressure Based on this, the work capacity generated during the heat storage phase or the work capacity utilized during the heat release phase.

[0007] Preferably, the generalized work capacity in S3 is calculated using the increment of ε, where the increment of ε is: in, Ex For the increment, Ex ph For physics Ex ch For chemical purposes; Chemical potential (CVP) characterizes the usable work potential resulting from differences in the composition of a substance. CVP is calculated as follows: in, For the generation of a mole, Gibbs free energy, n e and These represent the molar amount and chemical effective energy of an element in a compound, respectively, with the mixing-related terms included for mixtures. T 0 S mix .

[0008] Preferably, the work capacity generated in the thermal storage stage of S3 under the reference state is: in, The maximum theoretical potential of the system in its storage state to drive the reverse reaction and perform work is related to the storage temperature. T Standard reaction Gibbs free energy change at 0 equal.

[0009] Preferably, when the heat storage stage is completely reversible, ignoring the changes in enthalpy and entropy with temperature, the energy efficiency of the generalized heat engine in S3 is: in, This indicates the amount of heat absorbed by the heat source during the heat storage process. This represents the enthalpy change of the standard reaction. This represents the entropy change of the standard reaction; The reaction occurs at the transition temperature The temperature is determined by Defined, calculated as The energy efficiency of a generalized heat engine is equal to that of a Carnot cycle operating within the same temperature range.

[0010] Preferably, the efficiency of the generalized heat engine in S3 is: in, This represents the thermal efficiency corresponding to the input heat at the heat source temperature. Under reversible conditions, the thermal efficiency of this heat storage process can reach 1. When irreversible factors exist in the heat storage process, the thermal efficiency is... <1.

[0011] Preferably, the energy efficiency of the generalized heat pump in S4 is: in, This represents the maximum potential, theoretically, that it possesses in its stored state for driving the reverse reaction and performing work. This represents the heat released to the low-temperature heat source during the heat release phase. This represents the enthalpy change of the standard reaction. This represents the entropy change of the standard reaction. This indicates the amount of heat released during the heat release process at a low-temperature heat source.

[0012] Preferably, the efficiency of the generalized heat pump in S4 is: in, Indicates temperature The heat released to the user For the energy consumed in performing tasks For the output heat corresponding to the heating temperature, in ideal reversible conditions... =1, deviating from the invertible condition <1.

[0013] Preferably, the total energy efficiency is defined as: Total efficiency is defined as: .

[0014] Therefore, this invention employs the aforementioned method for constructing and evaluating thermochemical thermal storage cycles driven by generalized heat engines and generalized heat pumps. It analyzes the thermochemical thermal storage cycle as a coupled process of generalized heat engine generating work capacity—time-based storage—and generalized heat pump consuming work capacity for heating, thus clarifying the conversion path from thermal energy to work capacity and back to thermal energy. The evaluation indicators are directly related to Gibbs free energy and γ increment, accurately reflecting the directionality and driving force requirements of chemical reactions, thus overcoming the shortcomings of simple enthalpy analysis that ignores changes in energy quality and the constraints of reaction spontaneity.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method for constructing and evaluating a thermochemical thermal storage cycle based on a generalized heat engine driving a generalized heat pump, as described in this invention. Figure 2 This is a schematic diagram of the thermochemical heat storage cycle based on a generalized heat engine driving a generalized heat pump, as described in this invention. Figure 3 This is a schematic diagram of the thermochemical heat storage cycle principle based on the actual preheating and cooling processes of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0019] Example Please see Figures 1-3 This invention provides a method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump, comprising the following steps: S1. The thermochemical energy storage cycle is taken as the research object, the reactants and products of the thermochemical reaction are regarded as the working fluid of the cycle, and the forward and reverse thermochemical reaction conditions are used as the cycle operation parameters.

[0020] S2. Based on the target reversible thermochemical reaction system, the thermochemical energy storage cycle is decoupled into an endothermic energy storage stage and an exothermic energy release stage according to time.

[0021] S3. In the process of heat absorption and energy storage, a generalized heat engine process is constructed. High-temperature heat energy drives the originally non-spontaneous endothermic chemical reaction at the storage temperature and converts it into the work capacity of the products, realizing the generalized heat engine process of "heat-work" conversion.

[0022] S4. A generalized heat pump process is constructed in the exothermic energy release process. The work capacity of the generated products is consumed to drive the reverse chemical reaction (exothermic direction), so that the exothermic reaction releases heat at a temperature higher than the storage temperature, and completes the release of high-temperature heat energy to the user end, realizing the generalized heat pump process of "work-heat" conversion.

[0023] S5. Energy conversion evaluation: Clarify the energy conversion path of "heat-work-heat". The thermochemical thermal storage cycle is equivalent to a coupled system of a generalized heat engine driving a generalized heat pump across the time dimension. Based on this, evaluate its individual and overall performance indicators.

[0024] In a thermochemical thermal storage cycle, the generalized work is defined as the work done at the storage temperature. (and reference pressure) Based on this, the work capacity generated during the heat storage stage (and utilized during the heat release stage) is considered. Thermodynamically, this work capacity can be calculated using increments, comprising both physical and chemical increments. in, Ex For the increment, Ex ph For physics Ex ch For chemistry.

[0025] Physical ☐ can be expressed according to the classical definition as: in, h and s These represent specific enthalpy and specific entropy, respectively, with the subscript 0 indicating the baseline state. , ).

[0026] Chemical potential (CVP) is used to characterize the usable work potential resulting from differences in the composition of a substance. The calculation method for CVP is as follows: in, For the generation of a mole, Gibbs free energy,n e and These represent the molar amount of each element in the compound and its chemical effective energy, respectively. For mixtures, the mixing-related factors must also be considered. T 0 S mix .

[0027] The work capacity (chemical increment) generated in the reference state during the thermal storage stage is: in, The maximum theoretical potential of the system in its storage state to drive the reverse reaction and perform work is related to the storage temperature. T Standard reaction Gibbs free energy change at 0 equal.

[0028] The energy efficiency of a generalized heat engine (heat storage stage) is defined as: in, It represents the heat absorbed by the heat source during the heat storage process, including the heat of reaction and sensible heat.

[0029] When the thermal storage stage is completely reversible, neglecting the changes in enthalpy change and entropy change with temperature, the above equation can be simplified to: in, This represents the enthalpy change of the standard reaction. This represents the standard reaction entropy change. The reaction occurs at the transition temperature. The temperature is determined by Defined and calculated as: That is, at this point, the energy efficiency of the generalized heat engine is equal to that of the Carnot cycle operating in the same temperature range.

[0030] The efficiency of a generalized heat engine (heat storage stage) is defined as: In particular, under ideal conditions, the above equation can be simplified to: in, This represents the thermal efficiency corresponding to the input heat at the heat source temperature. Under reversible conditions, the thermal efficiency of this heat storage process can reach 1. When irreversible factors exist in the heat storage process (such as a non-zero chemical reaction affinity or a temperature difference in heat transfer), the thermal efficiency is... <1.

[0031] The energy efficiency of a generalized heat pump (heat release stage) is defined as: in, In physical terms, it refers to the maximum potential that a system possesses in its storage state, theoretically, that can be used to drive a reverse reaction and perform work. This indicates the heat released to the low-temperature heat source during the heat release phase.

[0032] Under reversible conditions, the above equation can be simplified to: in, This represents the enthalpy change of the standard reaction. This represents the entropy change of the standard reaction. This indicates the amount of heat released during the heat release process at a low-temperature heat source.

[0033] The heat release efficiency of a generalized heat pump is defined as... In particular, under ideal conditions, the above equation can be simplified to: in, Indicates temperature The heat released to the user For the energy consumed in performing tasks This is the heat output at the supply temperature. Ideally, when reversible... =1, deviating from the invertible condition <1.

[0034] The total energy efficiency of a thermochemical thermal storage cycle is defined as the product of the generalized heat engine energy efficiency and the generalized heat pump energy efficiency. The total energy efficiency is: The overall efficiency of a thermochemical thermal storage cycle is defined as the product of the generalized heat engine efficiency and the generalized heat pump efficiency. The overall efficiency of a thermochemical thermal storage cycle is: This embodiment takes a typical thermochemical reaction system, the CaCO3 / CaO system, as the research object for a thermochemical thermal storage cycle, which includes two stages: a thermal storage process and a heat release process. The thermal storage process absorbs heat from a high-temperature heat source to drive a non-spontaneous chemical reaction at room temperature, thus storing energy. The heat release process releases heat through a reverse reaction to meet external heat demand.

[0035] In this embodiment, the performance evaluation method proposed in this invention is used to systematically evaluate the energy efficiency, thermal efficiency, and irreversible losses of the thermochemical thermal storage cycle under given operating conditions.

[0036] The present invention will be further described below with reference to the accompanying drawings, but the present invention is not limited to this embodiment.

[0037] S1. Select a common reaction system As the research object, CaCO3 / CaO / CO2 is regarded as the working fluid in the cycle, and the forward and reverse thermochemical reaction conditions are set as shown in Table 1.

[0038] S2, based on the reaction system The thermochemical energy storage cycle is decoupled over time into an endothermic energy storage stage and an exothermic energy release stage.

[0039] S3. Constructing a generalized heat engine process, in the heat absorption and energy storage stage, at ambient temperature... and high temperature reaction temperature A generalized heat engine process is constructed by connecting two isothermal processes through the preheating of reactants and the cooling of products. The reactant CaCO3 absorbs heat from a high-temperature heat source and converts it into the work capacity of the products CaO / CO2, thus realizing a generalized heat engine process of "heat-work". Figure 3 (1-2-3-4).

[0040] S4. Constructing a generalized heat pump process, during the heat release and energy excitation phase, at the ambient temperature... and low temperature reaction temperature A generalized heat pump process is constructed by connecting two isothermal processes through preheating of reactants and cooling of products. The work capacity of the products CaO / CO2 is consumed to drive a reverse chemical reaction (exothermic direction), completing the energy release to the user end and realizing a generalized heat pump process of "work-heat". Figure 3 (4-5-6-1) S5. Energy conversion evaluation, clarifying the reaction system. The energy conversion path of "heat-work-heat" is used to calculate the generalized heat engine, generalized heat pump and overall performance indicators, as shown in Table 2.

[0041] Table 1. Conditions for forward and reverse thermochemical reactions

[0042] Table 2 Energy Conversion Evaluation

[0043] Compared to traditional evaluation metrics centered on reaction enthalpy change, an evaluation framework based on the generation and utilization of work capacity reveals more deeply the essential characteristics of thermochemical energy storage as a unique thermodynamic cycle system. This framework clarifies that the overall efficiency of such systems depends on the coupling performance of the heat storage and release steps, thus providing a more guiding perspective for analyzing and optimizing system performance.

[0044] Thus, the method of this invention not only provides overall numerical values ​​of system performance, but also reveals the essential energy conversion mechanism of thermochemical thermal storage, which involves "converting thermal energy into work capacity and then converting work capacity back into thermal energy," providing an operable evaluation tool for system design optimization.

[0045] Therefore, this invention employs the aforementioned method for constructing and evaluating thermochemical thermal storage cycles based on generalized heat engines driving generalized heat pumps. It analyzes the thermochemical thermal storage cycle as a coupled process of generalized heat engine generating work capacity—time-separated storage—generalized heat pump consuming work capacity for heating, thus clarifying the conversion path from thermal energy to work capacity and back to thermal energy. The evaluation indicators are directly related to Gibbs free energy and γ increment, accurately reflecting the directionality and driving force requirements of chemical reactions, thus overcoming the shortcomings of simple enthalpy analysis in neglecting changes in energy quality and the constraints of reaction spontaneity.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump, characterized in that, Includes the following steps: S1. The thermochemical thermal storage cycle is taken as the research object, the reactants and products of the thermochemical reaction are regarded as the working fluid, and the forward and reverse thermochemical reaction conditions are used as the cycle operation parameters. S2. Based on the target reversible thermochemical reaction system, the thermochemical heat storage cycle is decoupled into an endothermic energy storage stage and an exothermic energy release stage according to time. S3. Construct a generalized heat engine process in the heat storage process. High-temperature heat energy drives the originally non-spontaneous endothermic chemical reaction at the storage temperature and converts it into the work capacity of the products. S4. Construct a generalized heat pump process in the exothermic energy release process. The energy-making capacity of the consumed products drives the reverse chemical reaction, so that the exothermic reaction releases heat at a temperature higher than the storage temperature, thus completing the release of high-temperature heat energy to the user end. S5. Energy conversion evaluation: Clarify the energy conversion path of heat-work-heat, and equate the thermochemical thermal storage cycle with a coupled system of a generalized heat engine driving a generalized heat pump across the time dimension, and evaluate the individual and overall performance indicators.

2. The method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump according to claim 1, characterized in that: In thermochemical heat storage cycles, the generalized work is based on the storage temperature. and reference pressure Based on this, the work capacity generated during the heat storage phase or the work capacity utilized during the heat release phase.

3. The method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump according to claim 2, characterized in that: In S3, the generalized work capacity is calculated using the increment of 㶲, where the increment of 㶲 is: in, Ex For the increment, Ex ph For physics Ex ch For chemistry; Chemical potential (CVP) characterizes the usable work potential resulting from differences in the composition of a substance. CVP is calculated as follows: in, For the generation of a mole, Gibbs free energy, n e and These represent the molar amount and chemical effective energy of an element in a compound, respectively, with the mixing-related terms included for mixtures. T 0 S mix .

4. The method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump according to claim 3, characterized in that: The work capacity generated in the thermal storage stage of S3 under the reference state is: in, The maximum theoretical potential of the system in its storage state to drive the reverse reaction and perform work is related to the storage temperature. T Standard reaction Gibbs free energy change at 0 equal.

5. The method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump according to claim 4, characterized in that: When the heat storage stage is completely reversible, and ignoring the changes in enthalpy and entropy with temperature, the energy efficiency of the generalized heat engine in S3 is: in, This indicates the amount of heat absorbed by the heat source during the heat storage process. This represents the enthalpy change of the standard reaction. This represents the entropy change of the standard reaction; The reaction occurs at the transition temperature The temperature is determined by Defined, calculated as The energy efficiency of a generalized heat engine is equal to that of a Carnot cycle operating within the same temperature range.

6. The method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump according to claim 5, characterized in that: The efficiency of the generalized heat engine in S3 is: in, This represents the thermal efficiency corresponding to the input heat at the heat source temperature. Under reversible conditions, the thermal efficiency of this heat storage process can reach 1. When irreversible factors exist in the heat storage process, the thermal efficiency is... <1.

7. The method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump according to claim 6, characterized in that: The energy efficiency of the generalized heat pump in S4 is: in, This represents the maximum potential, theoretically, that it possesses in its stored state for driving the reverse reaction and performing work. This represents the heat released to the low-temperature heat source during the heat release phase. This represents the enthalpy change of the standard reaction. This represents the entropy change of the standard reaction. This indicates the amount of heat released during the heat release process at a low-temperature heat source.

8. The method for constructing and evaluating a thermochemical thermal storage cycle driven by a generalized heat engine and a generalized heat pump according to claim 7, characterized in that: The efficiency of the generalized heat pump in S4 is: in, Indicates temperature The heat released to the user For the energy consumed in performing tasks For the output heat corresponding to the heating temperature, in ideal reversible conditions... =1, deviating from the invertible condition <1.

9. The method for constructing and evaluating a thermochemical thermal storage cycle for a generalized heat engine-driven generalized heat pump according to claim 8, characterized in that: Total energy efficiency is defined as: Total efficiency is defined as: 。

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