Integrated Intelligent Energy

Review of CaO/Ca（OH）2 chemical heat storage technology for CSP

XU Qili，SUN Jie*

2020, 42(4): 1-11.

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The most prominent advantage of Concentrating Solar Power（CSP）technology over photovoltaic power and wind power generation technologies is its large-scale low-cost all-weather operation，by which it lower the power generation cost and improve the energy quality. In recent years，CaO/Ca（OH）2 chemical heat storage system stands out from numerous chemical heat storage technologies for its high heat-storage density，high reaction efficiency，high security and low cost.The research on CaO/Ca（OH）2 chemical heat storage system is reviewed from three aspects which are process mechanism，reactor equipment and system integration，so as to provide references for further optimization of the energy storage system.Firstly，the basic principles of heat storage/release of the system are introduced.Doping and granulation can effectively solve the sintering and agglomeration of solid reactants，but exert negative effects at the same time，such as side reactionproducts，dramatic decrease of heat storage density and low reacting cycle stability. The fixed bed reactor cannot run continuously，and is not suitable for industrial applications. The following research will focus on optimizing fluidized bed reactors and moving bed reactor

Experimental study on preparation of a molten salt nanocomposite by ultrasonic dispersion and microwave method

ZHANG Xiaopan，LU Yuanwei*，YU Qiang，SONG Weilong，WU Yuting

2020, 42(4): 12-16.

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In order to increase the specific heat capacity of molten salt，a low-melting-point molten salt nanocomposite was obtained through ultrasonic dispersion and microwave method，by doping SiO2 nanoparticles with an average size of 20 nm into the independently developed quaternary mixed nitrates . The mass concentration of SiO2 was 1%. The specific heat capacity of molten salt nanocomposite was measured with a differential scanning calorimeter（DSC）. The experimental results showed that the specific heat capacity of nanocomposite could be enhanced by about 38.8%，which was much higher than that of nanocomposite prepared by traditional drying method which can be increased by only 19.4%. The microstructure characterization of the molten salt nanocomposite was analyzed by a scanning electron microscope（SEM）， which showed that the special nanostructure（resembling chain-like nanostructure）formed on the surface of the solid salt who was dried by microwave. The special nanostructure with large specific surface area and high surface energy can enhance the specific heat capacity. Furthermore，the microwave drying can improve the preparation efficiency of the molten salt nanocomposite.

Study on preparation for quaternary nitrates/MCM41 porous composite heat-storage material and its stability

LI Jin，WANG Feng*，ZHANG Shiguang，WU Yuting

2020, 42(4): 17-22.

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：To obtain a composite heat-storage material with good stability，quaternary nitrates/MCM41 porpous composite heat-storage material was prepared with quaternary nitrates as its phase change material and MCM41 as its matrix material. The chemical and thermal stability of the composite material with different mass ratios of quaternary nitrates to MCM41 was verified by 100 thermal cycling experiments. XRD and FT-IR characterization results indicated that the chemical composition of the composite material was unchanged after the experiments and was of positive chemical stability.Its DSC curves showed that the melting point and latent heat of fusion after the thermal cycling experiments were similar with that before the experiments，which confirmed the good thermal stability of the composite material.The density of the composite material was increased with the growth of quaternary nitrate's mass ratio，and its compressive strength was maximum when the mass ratio of quaternary nitrate to MCM41 was 6∶4.Considered the thermal properties，density and compressive strength of the composite material comprehensively，the optimal mass ratio for quaternary nitrate to MCM41 is 6∶4.

Thermal economy analysis of distributed phase change heat storage stations based on urban functional zoning

ZHONG Shengyuan，ZHAO Jun，LI Hao，WANG Xiaoyuan，ZHOU Ying

2020, 42(4): 23-30.

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The operation mode of“ Setting Electricity by Heat”taken by the Three-North Region in China during heating seasons is one of the important causes for the wind power abandoning. The utilization rate of wind power can be improved by taking heat storage electric boilers.Combining distributed heat storage and phase change heat storage technologies can give full play to their advantages of flexible matching，high heat storage efficiency and fast response.To increase the annual return of distributed phase change heat storage stations，the economy analysis of distributed phase change heat storage stations based on urban functional zoning is made，while considering the heat storage constraint，heating constraint and combined heating constraint.The analyzing results show that the annual returns of heat storage stations are affected by the characteristics of the regional heat load. According to the law of marginal benefits，the annual return of a heat storage station in commercial area will be maximized with 13 200 kW·h capacity and 10 800 kW heating power，and that in a residential area will peak with 11 200 kW·h capacity and 9 000 kW heating power. With the selected capacity and heating power，the station can reach the break-even point with the electricity price of 0.218 Yuan/（kW·h）in the commercial area and 0.221 Yuan/（kW·h）in the residential area respectively

Coordinated control and economic analysis on a PV-hybrid energy storage micro-grid system

WANG Hanwen,LU Sheng,ZHOU Zhaoyu

2020, 42(4): 31-36.

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Insufficient capacity and output of black-start power supply for micro-grid will lead to its frequency and voltage instability.Therefore，a hybrid energy storage system（HESS）within lithium batteries and lead acid batteries is proposed as the coordinated control method of the black-start power supply for photovoltaic and energy storage micro-grid.In order to improve the long-term operation of island micro-grid，the low-frequency component of an HESS dispatching command is taken as the power command of a lead-acid battery.Lead-acid batteries provide capacity and power support for the HESS for their high cost performance，while lithium batteries provide voltage and frequency support for the micro-grid for their long service lives. According to the characteristics of the batteries，the cost model including investment，operation and maintenance cost of an HESS is established.Power systems computer aided design（PSCAD）simulation tests can verify the effectiveness of the method proposed.

Optimal power control strategy of grid-side electrochemical energy storage stations considering battery energy efficiency

FENG Liyong，ZHANG Yun

2020, 42(4): 37-41.

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During the operation of current grid-side electrochemical energy storage stations，the main controlling constraint is the maximum chargeable and dischargeable power of the whole station.To make a more sufficient consideration for energy efficiency of the stations，an optimized power control strategy based on battery energy efficiency curve is proposed. Targeting at the output power and energy efficiency，the operation optimization model of grid-side electrochemical energy storage stations considering the dynamic efficiency of energy storage is established.The model considers the variation of energy storage efficiency changing with different power during the charging and discharging，and incorporates the dynamic efficiency into the energy storage station optimization model in the form of an approximate linear function.The simulation analysis is carried out based on the actual operation data on grid side. Comparing the effect of different charging and discharging control strategies on grid operation control，it is proved that the dynamic efficiency characteristics will impact the comprehensive energy efficiency of the energy storage station to some extent and should be take into considering in operation optimization of grid-side electrochemical energy storage power station.

Design for CSP plants' energy storage system and research on preheating strategy with tanks

HAN Wei，CUI Kaiping，ZHAO Xiaohui，Francisco MANGAS

2020, 42(4): 42-46.

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As an important and accident-prone subsystem in CSP plants，heat storage system plays a key role in continuous and steady operation of plants. Thus，a delicate design for the storage system is essential for the cost control and safety operation of CSP plants. A delicate design for molten salt volume and wall thickness of tanks in the thermal storage system of CSP plants has been presented.The preheating strategy with the maximum wall temperature difference allowed by storage tanks was obtained after testing the real-time wall temperature of the storage tank and numerically simulating the air flow process of flue gas and molten salt in the tank. The strategy can relieve the thermal stress during storage tank preheating and reduce its risk and failure rate. The strategy has achieved positive effect in practical cases.

Research progress in ISCC power generation system

YANG Pu，DUAN Liqiang*，PAN Pan

2020, 42(4): 47-56.

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Integrated solar combined cycle（ISCC）power generation system can effectively utilize the solar power by improving the photoelectric conversion efficiency and reducing fuel consumption of original gas-steam combined cycle system，which has attracted more attentions in recent years.The development of four typical ISCC system integration modes were studied and summarized ，and their economic performances and performance evaluation indicators were explored. According to the intermittent of solar power and the peak-shaving characteristic of China's power generation systems，the features of off-design working conditions of the integrated system were analyzed and verified systematically by domestic and foreign engineering demonstration projects. The research achievements will provide guidance for the design and operation optimization of ISCC systems.

Status and prospect of flexibility regulation technology for coal-fired power plants

WEI Haijiao，LU Yuanwei*，ZHANG Cancan，WU Yuting，LI Weidong，ZHAO Dongming

2020, 42(4): 57-63.

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Exploration of renewable energy is a basic state policy in China. The intermittency of renewable energy leads to its power output fluctuation，which would bring a certain impact on the safety of power grid operation and hinder the grid connection of partial renewable energy. In order to increase the to-grid rate of power generated by renewable energy，it is necessary to advance the flexibility of load outputted from traditional coal-fired power plants. Studying the load regulation range of coal-fired units，it was found that hot water storage technology，electric boiler heat storage technology and high back pressure transformation technology could be applied in flexible regulation of combined heat and power plant. The coupling technology for coal-fired units and solar system could improve the operation flexibility of the coupling system. Taking high-temperature thermal energy storage technology ，storage medium can be heated by excessive steam from condensing units during bottom load periods and release the heat during peak load periods，which realizes the wide-range flexibility regulation of units. Comparing the features of five flexibility regulation technologies，it is considered that hightemperature molten salt heat storage technology is one of the development directions of flexibility regulation for coal-fired power plants.

Progress on the peak load regulation，frequency regulation and energy storage technologies for coal-fired power plants

WANG Jinxing，ZHANG Shaoqiang，ZHANG Hanwen，FANG Xu，SONG Haiwen

2020, 42(4): 64-71.

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Insertion of high-proportion intermittent renewable energy has put forward new requirements for the flexible operation of coal-fired power plants.Energy storage technology，as a frequency regulation and load regulation technology ，is irreplaceable. Firstly，three energy storage technologies currently applied in coal-fired power plants are introduced which are pure heat storage device，heat storage device through thermo-electric conversion and heat storage device through thermo-chemical conversion.Their heat storage performances and the economic benefits should be focused. Secondly，the current situation of electric storage devices is introduced which include pure electric storage device， multi-energy complementary electric storage system and electric storage system coupling multiple energy storage technologies. It is pointed out that performance degradation is an important index for optimization and selection of batteries. Finally，the research status of other energy storage technologies represented by pumped storage，compressed air energy storage and flywheel energy storage is summarized. These energy storage technologies need to be optimized and coupled considering adaptive conditions of other energy storage technologies. It is expected to provide a development direction for the peak load regulation，frequency regulation and energy storage technology of coal power plants.

Design and research on energy storage and thermal power combined frequency modulation systems

WANG Xingxing，SUN Jianqiao，CHEN Ming

2020, 42(4): 72-76.

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Batteries have been widely applied in energy storage and coal-fired power plants combined frequency modulation due to the technical advantages and favorable economic performance of the modulation technology. However，the development of the combined frequency modulation system is impeded for lack of sophisticated design scheme.In order to facilitate the scaled and standardized development and the designing level of energy storage and thermal power combined frequency modulation systems in China，analysis was made on 2×350 MW units of Guodian Zhaoqing Thermal Power Company Limited based on the engineering cases of China Huadian Engineering Company Limited.Key technologies in system capacity selection，site planning，overall layout，access accounting，short circuit current calculation，relay protection configuration，control and communication，and fire-fighting system were summarized during the research on the frequency modulation auxiliary service energy storage of the two units.It provides technical basis，impetus and demonstration for the engineering design and construction of new energy storage and thermal power combined frequency modulation systems.

Development status of solar thermal power generation and prospect of supercritical carbon dioxide technology applied in it

HE Zhiqiao，TONG Jialin

2020, 42(4): 77-83.

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Solar thermal power generation technology is of flexible dispatching mode，and can greatly alleviate the abandon of solar power，and is highly complementary with other renewable energy.Research and scale application of solar thermal power generation technology developed early in America，but started late in China.However，the technology is thriving in China and shows distinguished characteristics from that in America and other countries.After introducing the development of solar thermal power generation technology in America and China in recent years，the characteristics and advantages of applying supercritical carbon dioxide Brayton cycle in solar thermal power generation is analyzed，and its prospect in power generation system is expounded.

Analysis of utilization modes combining concentrating photovoltaic power generation and photovoltaic residual heat driving carbon capture

XING Chenjian，QIAN Yu，ZHOU Ran，WANG Ruilin*

2020, 42(4): 84-88.

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Carbon capture in coal-fired power stations is an important measure to alleviate the global greenhouse effect. The equipment for coal-fired power stations taking post-combustion carbon capture technology is generally placed at the tails of stations.It is conducive to the integration and transformation of existing power stations，but is of high energy consumption rate . Powering the carbon capture equipment soley by the coal-fired power stations will impact their power generation efficiencies. There is abundant residual heat in the conversion process of gallium arsenide（Ga-As）concentrated PV batteries，and the temperature is higher than that required as potassium-based carbon capture heat source，which shows potential in driving potassium-based carbon capture reaction. Therefore，this study proposes a comprehensive utilization method of concentrated photovoltaic power generation and carbon capture with residual heat，and explore the influence of PV operating temperature and irradiation on the performance of concentrated photovoltaic power generation and carbon capture，after establishing a model of energy conversion by Ga-As and one of carbon capture by potassium-based absorbent driven by residual heat. Applying it into a 600 MW subcritical coal-fired power station，compared it with a carbon capture system driven coal-fired power station，the power generation efficiency in the integrated system increased by 6.56 percentage points and its total power generation increased by 50% roughly.Compared it with a concentrated PV system，the efficiency of PV power generation is reduced by 4.49 percentage points，but the additional carbon capture per hour is increased by 380.82 t. The method proposed alleviates the impact of carbon capture energy consumption on the efficiency of coal-fired power stations，which realizes the solar energy dual usage of within power generation and carbon emission reduction，and provides a new idea for the efficient cascade utilization of solar energy.

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