Table of Content

25 July 2021, Volume 43 Issue 7

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Energy Storage System Electrochemical Energy Storage Thermal Energy Storage Material and Technology

Energy Storage System

Thermo-economic analysis on the pumped thermal energy storage system based on the solid packed beds

ZHAO Yongliang, LIU Ming, WANG Chaoyang, SUN Ruiqiang, CHONG Daotong, YAN Junjie

2021, 43(7):  1-8.  doi:10.3969/j.issn.1674-1951.2021.07.001

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Pumped thermal energy storage technology will play a critical role in the future electric power system due to its large scale,low capital cost and no geographical constraints.A pumped thermal energy storage system based on solid packed beds and the reversible Joule-Brayton cycles and the effects of distinct design parameters on the system's thermo-economic performance were investigated.It can be revealed that the system roundtrip efficiency increase with the gowing of the maximum charging temperature,polytropic efficiency of the machines and porosity of packed beds.Using helium as the working fluid and magnetite as the storage material,the system's maximum roundtrip efficiency can be as high as 72.45% when the maximum charging temperature,polytropic efficiency of the machines and porosity of packed beds are 850 K,92% and 46%,respectively.The levelized energy storage cost of the system reduces with the rising of the maximum charging temperature and polytropic efficiency of the machines.Using helium as the working fluid and magnetite as the storage material,the minimum levelized cost energy storage will bottom at 0.211 dollar/（kW·h） when the maximum charging temperature,polytropic efficiency of the machines and porosity of packed beds are 850 K,92% and 40%,respectively.

Research progress of compressed air energy storage and its coupling power generation

WEI Shuzhou, LI Bingfa, SUN Chenyang, ZHOU Xing, WANG Yalong, ZOU Yifan, DENG Jingmin, WANG Jinxing

2021, 43(7):  9-16.  doi:10.3969/j.issn.1674-1951.2021.07.002

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Compressed air energy storage（CAES） is an energy storage technology that uses compressors and gas turbines to realize the conversion between air potential energy and heat energy.Since CAES can regulate and distribute the"source"and "load"across time and space,the technology has become increasingly important as high-proportion intermittent renewable energy is connected to the power grid.Energy storage systems are classified from three aspects：configuration of heat sources,adiabaticity and configuration of heat storage devices.Among them,CAES has three main application modes, diabatic CAES without heat source,diabatic CAES with heat source and adiabatic CAES with heat storage system.Analyzed from multi-energy coupling modes,CAES systems’coupling with gas turbines,internal combustion engines and renewable energy systems are introduced,respectively. Furthermore,various integration forms of CAES technology and its coupling with coal-fired power plants are analyzed,which are compared with traditional CAES,adiabatic CAES,isothermal CAES and heat storage CAES technology from the energy storage scale,advantages and disadvantages.The study is expected to provide reference for the application of CAES technology.

Development status and application prospect of power side energy storage technology

TONG Jialin, HONG Qing, LYU Hongkun, WU Ruikang, YING Guangyao

2021, 43(7):  17-23.  doi:10.3969/j.issn.1674-1951.2021.07.003

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Under the background of carbon neutrality, it is necessary to build a new power system with renewable energy as the main body.Power-side energy techniques receive attention because they are important means of remitting large-scale renewable energy grid-connected pressure.They could smooth generation output of intermittent renewable energy and improve frequency modulation and peak regulation capacity of thermal power generation units.In order to develop power-side energy storage techniques better,development status quo and typical application of existing energy storage techniques are discussed and sorted.The development trend of American and Chinese power-side energy storage techniques is analyzed.The development status quo,typical pilot applications,and performance comparison of major power-side energy storage techniques are introduced.The further prospects of power-side energy storage techniques in China are made.

Electrochemical Energy Storage

Synthesis and electrochemical performance of nano-Ge-Sn/C composite material

QIAO Xue, YANG Xuebiao, HUANG Tingting, WANG Xinyue, JIA Zichen, WANG Hongqiang

2021, 43(7):  24-29.  doi:10.3969/j.issn.1674-1951.2021.07.004

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Ge has become the most promising anode material for lithium-ion batteries due to its high theoretical capacity.Our team has prepared a nano-Ge-Sn/C composite material：carbon can improve the conductivity of Ge and adapt to the change in its volume,and Sn can further improve the conductivity of the material.Since the electric potentials of Ge and Sn to deintercalate/intercalate lithium ion are different,the component that does not participate in the reaction can be used as a matrix to buffer the volume change led by the other component in charge and discharge processes,which can improve the structural stability of the electrode.The morphology,structure and composition of the material were analyzed by SEM,EDS and XRD.The capacity of the lithium-ion battery taking this composite as its anode material was 1 292 （mA·h）/g in the first cycle discharge at a current density of 0.5 A/g,and remained at 510 （mA·h）/g after 100 cycles’ discharge.When the current density was increased to 10 A/g,the battery kept a capacity of 460 （mA·h）/g.It indicates a good cyclical stability and rate performance of this composite.

Transient electrochemical characteristics of solid oxide fuel cells under adiabatic conditions

WANG Chaoyang, LIU Ming, ZHAO Yongliang, CHONG Daotong, YAN Junjie

2021, 43(7):  30-36.  doi:10.3969/j.issn.1674-1951.2021.07.005

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Coupling energy storage equipment into energy systems can effectively improve the utilization efficiency and technical level of renewable energy.To obtain the internal thermoelectric coupling characteristics of a solid oxide fuel cell （SOFC） during the transient process switching from electrolysis mode to power generation mode, we established a dynamic model for the SOFC stack based on thermodynamics and electrochemical mechanisms. Based on the dynamic model, the stack temperature, the Nernst EMF, activation polarization voltage loss, ohmic voltage loss, the concentration polarization voltage loss and the output voltage of the cell during the switching from electrolysis mode to power generation mode were calculated. The electrochemical performances of the SOFC under isothermal and adiabatic conditions are compared. The results show if the stack operates in electrolysis mode and then in power-supply mode for 20 000 seconds each, the stack temperature will vary by 45.8 K and 101.1 K by modifying current density in step and ramp format, respectively. When the current density is identical, the maximum output voltage difference of a single cell is 0.015 V if the stack operates in adiabatic and isothermal environment.

Sodium storage performance of flower-like SnS₂

WEI Shuaijie, LI Shuaihui, ZHAO Zhipeng, LI Dan

2021, 43(7):  37-41.  doi:10.3969/j.issn.1674-1951.2021.07.006

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With the increasing consumption of lithium resources and the improvement of renewable energy-based modern electric system's requirements for large-scale energy storage equipment in the context of pursuing carbon neutrality, sodium ion batteries have become the hot spot of electrochemical energy engineering research at present. Using thioacetamide as sulfur source and SnCl₂·2H₂O as tin source, a series of three-dimensional flower-like SnS₂ with nano-porous lamellae and open frameworks were prepared by a mild hydrothermal method. The physical and electrochemical properties such as morphology, structure and specific surface area of the flower-like SnS₂ were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, specific surface analysis and electrochemical performance test. The results show that the SnS₂ prepared with a hydrothermal time of 4 h （4 h-SnS₂） processes the best crystallinity and uniform morphology. The nano-lamellae composing the flower-like structure are thin and of a large specific surface area （196.39 m²/g）, which is beneficial for shortening the Na⁺ transport path, and facilitating the full contact to electrolyte and the transfer of electrons between phase interfaces. Thus, the sodium storage performance of SnS₂ can be improved. The specific discharge capacity of 4 h-SnS₂ is maintained at 526.8 （mA·h）/g after 150 cycles at a current density of 1 A/g. This work provides basic fundamental data for the large-scale preparation and research of sodium ion batteries with SnS₂ as anode material.

State of health estimation for echelon-used batteries based on BP neural network

LI Yongqi, LEI Qikai, WANG Hao, HUA Sicong

2021, 43(7):  42-46.  doi:10.3969/j.issn.1674-1951.2021.07.007

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In the context of rapid developing energy storage industry and the gradually increasing decommissioned power batteries for vehicles, the echelon-used batteries and their application scenarios in energy storage are introduced, and the necessity of their state of health is expounded. Influence factors for battery state of health are discussed. A three-layer BP neural network is constructed by taking battery DC resistance, discharge rate and surface temperature as inputs. Experiment results show that trained by 30 echelon-used batteries, the network can effectively converge and keep the health state estimation errors of echelon-used batteries within 3%. Estimating battery state of health of batteries with BP neural network is feasibility and of great significance in sorting as well as energy storage for echelon-used batteries.

Thermal Energy Storage Material and Technology

Experimental study on phase-change discharging characteristics of modified barium hydroxide octahydrate

DOU Peng, YU Qiang, FAN Zhansheng, ZHI Ruiping, LU Yuanwei, WU Yuting, YANG Guichun

2021, 43(7):  47-53.  doi:10.3969/j.issn.1674-1951.2021.07.008

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Thermal storage technology can effectively solve the difficulty of renewable energy's grid connection. In order to obtain the phase-change heat transfer characteristics of modified barium hydroxide octahydrate in double pipes, our team prepared modified barium hydroxide octahydrate and studied its phase-change discharging characteristics in double pipes through experiments. The effects of cooling water temperature at inlet and flow rate on the phase transformation process and heat transfer performance of modified barium hydroxide octahydrate were studied. The results show that increasing the inlet flow rate of cold fluid can shorten the phase-change heat-discharge time of modified barium hydroxide octahydrate, but excessive inlet flow rate would reduce the heat transfer power; increasing the cooling water temperature at inlet has little effect on the phase-change discharging time, but it would reduce the heat transfer power as well. In the range of the experiment, the optimum inlet flow rate is 80 L/h and the maximum average heat transfer power is 251 W.

Research on natural convection heat transfer of molten salts on vertical cylinder surface during heat storage

YU Qiang, HE Cong, ZHI Ruiping, LU Yuanwei, WU Yuting, YANG Guichun

2021, 43(7):  54-61.  doi:10.3969/j.issn.1674-1951.2021.07.009

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In order to obtain the natural convection heat transfer law by of molten salts on the surface of vertical cylinders during heat charging,a numerical simulation was made on the natural convection heat transfer around a cylinder array with 2 to 8 vertical pillars whose cylindrical spacing （ S/D）=5~10 （S is the distance between two adjacent cylinders,D is the diameter of the cylinder）.The results show that the natural convection heat transfer on each cylinder surface is related to the position of the cylinder in the row and the its S/D.The average Nu（Nu_a）of the natural convection heat transfer made by molten salt around the whole cylinder array is determined by the S/D,the number of cylinders（N） and Ra.When S/D is small（S/D=5）,the Nu_a of natural convection heat transfer of molten salt on the cylinders' surface will decrease with the number of cylinders in the row.When S/D is large（S/D=10）,the Nu_a of natural convection heat transfer on the cylinders' surface will augment with the number of cylinders in the row.The research results can provide theoretical basis for the design of molten salt heat storage device.

Preparation and properties of low-cost phase-change heat storage materials based on semi-coke ash

XIONG Yaxuan, YAO Chenhua, SONG Chaoyu, WANG Huixiang, HU Ziliang, DING Yulong

2021, 43(7):  62-67.  doi:10.3969/j.issn.1674-1951.2021.07.010

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To promote the large-scale consumption of industrial solid wastes and avoid damage on environment brought by the accumulation of semi-coke ash,we proposed an innovative semi-coke ash/Na₂CO₃ shaped phase-change heat storage material which is prepared by cold compression-hot sintering（CCHS）method.Taking laser flash analyzer（LFA）,thermo-gravimetric and differential scanning calorimetry（TG-DSC）and X-ray diffraction（XRD）,the thermal conductivity,thermal storage and chemical compatibility of the shaped phase-change heat storage material were characterized.The results show that the best properties of the composite can be obtained when the mass ratio of semi-coke ash to Na₂CO₃ is 52.5∶47.5.Under this ratio,the composite's thermal conductivity is up to 0.41 W/（m∙K） between 100 and 800 ℃,and its energy storage density is up to 1 101.14 kJ/kg between 100 and 900 ℃.

Review on the stability of nanofluids

XIONG Yaxuan, SONG Chaoyu, YAO Chenhua, WANG Huihui, WANG Huixiang, HU Ziliang, WU Yuting, DING Yulong

2021, 43(7):  68-74.  doi:10.3969/j.issn.1674-1951.2021.07.011

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To achieve the goal of carbon neutralization and carbon peak,energy conversion efficiency needs to be improved.Nanofluids,as efficient heat transfer mediums,have attracted extensive attention in recent 20 years.However,the poor stability of nanofluids limit their applications in many fields.To improve the stability and promote the large-scale application of nanofluids,by summarizing the related literature,a method which can control the ion concentrations at their proper values by adjusting nanofluid' pH value is proposed.Surfactants can improve the repulsion between nanoparticles.Nanoparticle clusters can be decomposed by ultrasonic technique.The intermolecular forces between mixed nanoparticles can be utilized to improve nanofluids' stability.These methods help to solve the problem of low stability of nanofluids in long-term applications.

Preheating analysis on molten salt storage tank based on CFD method

WANG Ding, XIAO Hu, CHEN Yuxuan, YUE Song, ZHANG Yanping

2021, 43(7):  75-81.  doi:10.3969/j.issn.1674-1951.2021.07.012

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Construction a modern power system to pursue carbon neutrality need the support of energy storage technology. The preheating for molten salt storage tanks is an important link to ensure the safe operation of thermal storage system in CSP plants. Taking the molten salt storage tank of a CSP plant as the research object, the temperature distribution in the tank during the equal-step preheating process is numerically simulated based on the computational fluid dynamics （CFD） method. The influences of the preheating gas injection angle and tank size on the preheating process are explored. The results show that the temperature at the junction of the bottom plate and the side wall is the lowest during preheating. Decreasing the vertical injection angle of preheating gas or increasing its circumferential angle can effectively shorten the preheating time of the storage tank. Under the same preheating gas inlet and outlet conditions, the increase in the inner diameter of the storage tank can result in a substantial increase in the preheating time.