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    Basic Research and Application Technology of Physical Energy Storage
  • Basic Research and Application Technology of Physical Energy Storage
    WANG Ding, LIU Shizhen, SHI Dongbo, XIE Yonghui
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    A novel compressed carbon dioxide (CO2) energy storage system based on gas-liquid phase change was proposed to promote the development of large-scale and high-efficiency energy storage technology. The overall pressure level of the proposed system is lower than the critical pressure of CO2, which effectively reduces the difficulty of component manufacturing and improves the economic performance of system. Thermodynamic and economic analyses of the system were carried out and results show that the energy storage efficiency of system is 65.35% under typical design conditions and the investment payback period is about 5.50 years. The results of exergy analysis show that the maximum exergy destruction belongs to turbine which is 1.23 MW, and the evaporator has the minimum exergy efficiency which is 9.41%. The results of parameter analysis show that increasing the CO2 condensation temperature, compressor isentropic efficiency and turbine isentropic efficiency, or decreasing the temperature difference between the cold end and hot end of heat exchanger 2, and the temperature difference between the cold end of heat exchanger 3, can improve the energy storage efficiency and shorten the investment payback period of the proposed system.
  • Basic Research and Application Technology of Physical Energy Storage
    LÜ Xiuye, JIANG Jun, HAO Ning, LIU Chuanliang
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    Since the pressure and temperature of the compressed air in the gas storage are constantly changing during gas storage process in the compressed air energy storage system, which directly affects the output power of the compressor and the actual gas storage capacity, the temperature rise effect of the compressed air under adiabatic condition of 15 m pipeline steel was analyzed by numerical solution of differential equation, taking a gas storage of pipeline steel as an example. And Fluent was used for simulation verification. Considering the temperature rise of the pipeline steel and different heat transfer conditions, the thermal calculation for the gas storage process of the long-distance pipeline steel of 3 024 m was carried out. The coupling calculation of the gas storage process and the work process of the compressor was processed to obtain the change rules of the pressure and temperature of the compressed air in the gas storage process, the output power of the compressor, the actual gas storage capacity of the gas storage and other parameters. Results show that the mass mean temperatures of the compressed air at the end of inflation were 315.39 K, 311.65 K, 301.52 K and 291.35 K, and the gas storage capacities were 244.64 t, 252.60 t, 275.77 t and 301.35 t, when the comprehensive heat transfer coefficients of 0 W/(m2·K), 1 W/(m2·K),5 W/(m2·K) and 25 W/(m2·K) were adopted respectively.
  • Basic Research and Application Technology of Physical Energy Storage
    LIU Chang, ZHU Yangli, ZHANG Hualiang, TAO Hailiang, LI Jun, ZUO Zhitao, CHEN Haisheng
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    Taking the last-stage blades in the expander of compressed air energy storage (CAES) system as research object, based on centrifugal force conditions, an efficient equivalent crown constraint model was proposed and the simulation results of the cyclic symmetry constraint model and the multi-blade model were compared. Simultaneously, a constitutive program capable of simulating elastoplasticity and failure behavior was developed. Results show that compared with other models, the simulation results of the equivalent crown constraint model are close to the full-size model results, showing both precision and efficiency advantages. The written constitutive subroutine can effectively simulate the deformation-load response curve of 17-4ph steel. Specifically, when failure begins to occur at about 1/4 of the radial position of the blade, the failure area grows rapidly.
  • Basic Research and Application Technology of Physical Energy Storage
    LIU Xikai, WANG Ding, LIU Shizhen, ZHANG Di
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    A CO2 energy storage system with absorption refrigeration cycle was proposed, which adopted a split flow method to divert a portion of CO2 to the secondary compressor, the heat generated by the secondary compression was provided to the absorption refrigeration cycle, which provided cooling capacity for the main CO2 in system, and used the high-pressure storage tank to store CO2 in the liquid state, to improve the system energy storage efficiency. Thermodynamic analysis and multi-objective optimization of the system were carried out. Results show that the absorber, first stage compressor, turbine and post stage heat exchanger have relatively high exergy destruction under design condition. The system energy storage efficiency increases with the increase of condensation pressure, the adiabatic efficiency of compressor and turbine. However, the system energy storage efficiency decreases with the increase of the storage pressure. The optimal energy storage efficiency and energy density of the system are 68.70% and 0.153 kW·h/m3, respectively.
  • Basic Research and Application Technology of Physical Energy Storage
    ZHANG Bin, WANG Guanglei, XU Zhen, ZHOU Guangjie
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    Gas turbine combined cooling, heating and power (CCHP) technology has excellent development and application prospects. However, there are many problems such as low efficiency in partial load operation, strong coupling of thermal-electrical output and inflexible regulation of thermoelectric ratio etc. To solve these problems, a novel CCHP system based on gas turbine and constant-pressure compressed air energy storage (CAES) was developed. The thermodynamic models of components such as the compressor, combustion chambers, turbine, waste heat boiler, heat exchanger, injector and water pumps/turbine, were developed and used to analyze the operational characteristics of the CCHP system under an extraction-release gas flow regulation strategy. Results show that when the extraction-release coefficient is between 0 and 0.2, the CCHP system has a thermoelectric ratio regulating range of 0.58-2.27. During the variable load operation process, the primary energy utilization rate of the CCHP system changes within the range of 58.1%-59.5%, and the exergy efficiency is no less than 32.2%. For the developed CCHP system, the high comprehensive energy efficient and flexibility can be achieved under wide operating conditions.
  • Basic Research and Application Technology of Physical Energy Storage
    CHEN Biao, WANG Wei, GAO Song, LI Yihuan, ZHANG Wenzheng, FANG Fang
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    A co-optimization method was proposed for capacity allocation and frequency control parameters of thermal power-energy storage system considering flexible, economical and environment friendly operation. Firstly, a coordinated control strategy was designed for primary frequency regulation of combined thermal power and energy storage based on automatic allocation of power-energy storage by low-pass filter and the self-recovery of energy storage state was considered. Subsequently, considering frequency control performance, operational cost and pollutant emission of the system, a co-optimization model was developed for capacity allocation and frequency control parameters of thermal power-energy storage system, and a solution method based on particle swarm algorithm was provided. Finally, simulation verification was performed using a specific thermal power-energy storage system as an example. Results show that the coordinated control strategy and the co-optimization method are effective.
  • Basic Research and Application Technology of Physical Energy Storage
    SHI Xingping, LIU Yixue, WANG Yan, ZHANG Qianxu, AN Xugang, LÜ Kai, HE Qing
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    Due to its unique advantages of large storage scale and without limitation by geographical conditions, liquefied air energy storage (LAES) can participate in peak-regulation transformation of existing coal-fired power units to promote the construction and development of new power systems. Therefore, a novel LAES system coupled with coal-fired power unit was proposed, and the thermodynamic and economic models of the coupling system were established to analyze the influence of the change of energy storage capacity on the coupling system. Results show that a 44.2 MW/176.8 MW·h LAES system can be selected for comprehensive considerations when coupling with a 670 MW coal-fired unit.Considering three low-load (30%THA, 40%THA, and 50%THA) conditions for the coal-fired power unit,the round-trip efficiency of the coupling liquefied air energy storage system is about 51%, which is about 9 percentage points higher than that of the independent LAES system. The rate of return on investment of the coupling LAES system is close to 10%, and the investment can be recovered within 14 years. The sensitivity analysis results show that it is beneficial to improve the economic performance of the system through enlarging the difference between peak and valley electricity prices.
  • Basic Research and Application Technology of Electrochemical Energy Storage
  • Basic Research and Application Technology of Electrochemical Energy Storage
    ZHOU Fanyu, ZENG Jinjue, WANG Xuebin
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    For the unstability issue arising from the high ratio of renewable energy sources in power grid under the background of carbon neutralization, the demand features of various scenarios in the power grids for energy storage were introduced. The characteristics and development status of electrochemical energy storage technologies including supercapacitors, alkali-metal-ion capacitors and batteries, flow batteries, other secondary batteries, and hydrogen-based energy were discussed. The challenges and prospects of electrochemical energy storage technologies for large-scale energy storage in power grids were analyzed. Finally, it is figured out that the electrochemical energy storage technologies should be developed in the direction of "high performance, high safety and low cost".
  • Basic Research and Application Technology of Electrochemical Energy Storage
    ZHOU Runyi, HUANG Yanzhong, QI Yiheng, ZHANG Chuanzhi, ZHOU Meiqi, YANG Huachao, BO Zheng
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    High-power energy storage devices have significant advantages such as the high power density and rapid charge-discharge speeds. High-power energy storage devices have been widely used for a variety of applications requiring high power output and quick response time, such as grid frequency regulation, emergency starting for military armored vehicles, and energy recovery of port lifting equipment. Focusing on the mainstream power storage devices including supercapacitors, high-power metal ion batteries and metal ion hybrid capacitors, the basic working principles of various high-power electrochemical energy storage technologies were introduced, and the improvement strategies and research progress of domestic and foreign scholars in the electrode materials and electrolytes of high-power electrochemical energy storage devices were systematically summarized. Finally, the future research directions and application trends of high-power electrochemical energy storage technologies were forecasted.
  • Basic Research and Application Technology of Electrochemical Energy Storage
    SUN Peifeng, LU Wanglin, BAI Peng, LU Qiliang, XU Guochang, JIANG Xin, XU Fan
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    The key technologies and research progress of lithium battery and supercapacitor hybrid energy storage system used for frequency regulation in auxiliary thermal power units were discussed, such as power/capacity optimization configuration of different types of energy storage, application of high-voltage cascade and modular multilevel (MMC) topology structure, and hybrid energy storage control strategies. The demonstration project of domestic hybrid energy storage assisted frequency regulation for thermal power units was introduced. Finally, the domestic development prospects of hybrid energy storage systems were prospected.
  • Basic Research and Application Technology of Electrochemical Energy Storage
    TONG Xi, CHEN Heng, GOU Kaijie, XU Gang, LIU Wenyi, ZHANG Guoqiang
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    In order to verify the feasibility of participating in the electricity market and carbon market under the coordinated scheduling of electrochemical energy storage and pumped storage, a multi energy complementary system including thermal power units, wind power, photovoltaic power, pumped storage, and electrochemical energy storage was constructed. Considering the levelized cost of electricity (LCOE) and carbon emission cost, with the objective function of minimizing the sum of energy purchase cost, LCOE, carbon emission cost, and wind and solar abandonment cost, the Cplex solver in MATLAB was called for scheduling optimization solution. Taking the typical summer day data of a certain regional power grid in the northwest as an example, the time-of-use electricity price and tiered carbon trading mechanism were introduced, and six scenarios were set up, including different energy storage systems participating and different carbon trading mechanisms. Results show that the electricity market revenue and carbon market revenue are the highest and the system carbon emissions are the lowest under the collaborative scheduling of pumped storage and electrochemical energy storage, which verifies the feasibility of the proposed energy storage collaborative configuration scheme and scheduling optimization scheme.
  • Basic Research and Application Technology of Electrochemical Energy Storage
    WANG Jinjun, GOU Kaijie, CHEN Heng, CHEN Honggang, XU Gang, ZHANG Guoqiang
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    To achieve effective integration of renewables and reduce the instantaneous power fluctuations of wind power, a hybrid energy storage system (HESS) combining lithium battery-based energy storage and flywheel-based power storage was used to stabilize wind power fluctuations. Firstly, the improved k-means algorithm was used to obtain the typical daily data, and empirical mode decomposition (EMD) was used to disassemble it to obtain the HESS flattening task. Based on the comprehensive consideration of power capacity and charging-discharging efficiency constraints of various energy storage systems, a coordinated HESS energy management system was constructed. Moreover, with the minimum costs of hybrid energy storage system and wind power opportunity compensation as the objective function, a baseline variable and fluctuation penalty coefficient were introduced for correction, and a HESS capacity allocation model for stabilizing wind power fluctuations was developed. Finally, with the actual grid-connected data, a configuration scheme with optimized smoothing effect and economic performance was obtained. Results show that the cumulative under-compensation of wind power in the proposed configuration scheme is reduced by 91.8%, and the economic performance is increased by 49.99%. The optimal wind-storage ratio is 1∶0.16, of which the flywheel and lithium battery is 1∶4.65.
  • Basic Research and Application Technology of Molten Salt Energy Storage Integrated Energy System
  • Basic Research and Application Technology of Molten Salt Energy Storage Integrated Energy System
    ZHANG Yuheng, SONG Xiaohui, YANG Ronggui, LI Xiaobo
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    A coupled system based on reheated steam extraction and molten salt thermal storage was presented, and the operation processes and efficiency of the system were analyzed. In order to match the main steam temperature, electric heating was used to elevate the molten salt temperature after heat exchanging with extracted steam during the charging process. On this basis, the effects of average temperature difference in charging process, temperature difference of pinch point in discharging process and lower storage temperature of molten salt on system performance parameters were studied. Results show that with a fixed temperature difference of 10 K of the charging process, increasing the temperature difference of pinch point from 5 K to 15 K, the maximum equivalent round-trip efficiency reduces from 88.2% to 85.0%, and the optimal heat storage temperature will increase from 314 ℃ to 324 ℃. With fixed pinch point of 10 K, the round-trip efficiency decreased from 89.5% to 85.8% when the average temperature difference of the charging process increased from 5 K to 15 K. With both temperature differences of 10 K, the maximum equivalent round-trip efficiency is 87.1%, and the minimum load of the unit is reduced from 30% to 24.3%.
  • Basic Research and Application Technology of Molten Salt Energy Storage Integrated Energy System
    LI Yingbao, LUO Runhong, HUANG Jie
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    A "green electricity" molten salt energy storage system was proposed, and mechanism model analysis on the key components of the molten salt heat storage system was analyzed, so as to conduct the mathematical model identification experiment and analyze dynamic characteristics. Results show that the molten salt heat storage system generally exhibits the characteristic of large inertia. Through the design of multistage heating and heat exchange devices, the temperature, flow rate and pressure of molten salt and steam in the molten salt system can be effectively controlled, improving the quality of heating steam and ensuring the stability of the entire system, meeting the thermal and power generation needs.
  • Multi-energy Coupling Optimization Operation Strategy and Heat Storage Technology
  • Multi-energy Coupling Optimization Operation Strategy and Heat Storage Technology
    YAO Lujin, WANG Wei, LIN Hongyu, LIU Jizhen
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    The large-scale development and grid-connection of offshore and onshore wind power poses challenges to the stability of the power grid, and microgrid is an effective way to address the optimal operation of the distributed generation systems. Comprehensive considering the system operation economy and carbon emission environmental benefits of the microgrid cluster, a low-carbon day-ahead scheduling model for the interactive microgrid cluster based on distributed shared energy storage was proposed. Firstly, a pricing strategy was proposed based on the traditional real-time pricing to follow the net load of the microgrid, considering the uncertainty of wind power. Subsequently, the user satisfactions to price-based and incentive-based demand responses were defined according to the load characteristics of the microgrid users. Then, the stepped carbon trading mechanism was introduced to construct the carbon emission cost model, and the carbon emission chains of the system operation were partitioned by the life cycle assessment. Finally, the distributed energy storage resources were utilized for day-ahead optimal scheduling, based on the interactive operation of the microgrid cluster. The simulation example shows that the proposed interactive scheduling model eliminates the previous wind curtailment issue, and reduces the carbon emission by 32.14 t and the total system operation cost by 15.05%, compared with the independent microgrid cluster.
  • Multi-energy Coupling Optimization Operation Strategy and Heat Storage Technology
    WU Maoqian, QIAO Lei, SONG Mingshu, LIU Shengguan, LEI Qi'an, CHONG Daotong
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    In order to improve the peak regulation capacity of combined heat and power (CHP) units and realize the thermoelectrolytic decoupling of the unit by using the heat network heat storage, the dynamic simulation models of a 350 MW cogeneration unit and its heat supply network system were established. The dynamic characteristics of the heat supply network and its heat users during the heat storage/release process and the influence of ambient temperature on the peak regulation capacity of the unit were studied. Results show that the lag time of the heat user increases with the increase of its distance from the first heat exchange station, and it is also directly affected by the heat load of itself and indirectly affected by the heat load of the other heat users. The relative heat storage/release power of the heat supply network first changes rapidly and then changes slowly after the change of the extraction steam flow rate. The temperature of the heat user changes approximately linearly, and its change rate increases with the increase of the variation range of the extraction flow rate, and the starting time of change is also advanced. The maximum peak regulation capacity of the unit increases slightly with the decrease of ambient temperature. When the ambient temperature decreases from 0 ℃ to -15 ℃, the peak regulation capacity of the unit increases from 23.8 MW to 29.7 MW. Increasing the heat storage time and the heat storage temperature and decreasing the heat release temperature can improve the peak regulation capacity of the unit.
  • Multi-energy Coupling Optimization Operation Strategy and Heat Storage Technology
    WANG Yihan, ZHANG Zicheng, LIU Shuli, SHEN Yongliang, WANG Zhihao
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    A new thermochemical energy storage material with lower cost and better performance was prepared, and the feasibility of its application in buildings was explored. The easily mined volcanic rocks in Yunnan area were used as the matrix. Two preparation schemes were proposed that MgCl2 and CaCl2 were combined with either raw volcanic rocks or pickled volcanic rocks powder and were repressed into blocks. These prepared materials were nominated as stone-MgCl2, stone-CaCl2, block-MgCl2 and block-CaCl2, respectively. Their characterization, differential scanning calorimetry (DSC) analysis, economic analysis and feasibility analysis were conducted. Results show that the main pore structure of raw volcanic rocks is macropore (the pore size>100 nm), which can be easily filled by hydrated salts. The thermochemical energy storage density of stone-CaCl2, stone-MgCl2, block-CaCl2 and block-MgCl2 is 641 kJ/kg, 983 kJ/kg, 440 kJ/kg and 733 kJ/kg, respectively. The energy storage cost of prepared stone-CaCl2 and stone-MgCl2 is as low as 0.010 7 yuan/kJ and 0.017 4 yuan/kJ, respectively. Comparing with the existing materials, they have obvious advantages in the view of economy. When they are combined with renewable energy, these prepared materials have obvious potential for pollutant reduction and are also suitable for the northern regions with high heating demand.
  • Multi-energy Coupling Optimization Operation Strategy and Heat Storage Technology
    LI Jinhang, TONG Xi, CHEN Heng, PAN Peiyuan, XU Gang, LIU Wenyi
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    In order to solve the problem of collaborative low-carbon optimal scheduling of integrated energy system (IES) with multiple types of energy storage (MTES), a two-layer model of low-carbon economy of multiple types of energy storage-integrated energy system (MTES-IES) was developed. Moreover, by building the hydrogen energy hub to make full use of the heat energy lost in the process of hydrogen conversion, and the energy utilization efficiency of the whole system was increased by cascade utilization of energy. In the two-layer optimization model, the upper layer aims at the economic optimization of MTES system, and the lower layer realizes the optimal low-carbon economic operation of IES. The Karush-Kuhn-Tucher (KKT) condition was used to transform the lower model into the constraints of the upper model, and the large M method was used to linearize the problem. Three different scenarios were simulated and analyzed. Results show that the proposed MTES-IES two-layer model can reduce the operating cost of the system and realize the overall low-carbon operation of the system by coordinating and optimizing the operation and scheduling strategies of different subsystems.