Simulation study of a molten-salt Carnot battery energy storage system for retrofitting a thermal power plant

doi:10.19799/j.cnki.2095-4239.2023.0547

Abstract

Abstract:

Coupling a thermal power plant and its thermal energy storage through a molten-salt Carnot battery energy storage system is an effective retrofit method. The energy storage system uses the abandoned electric or the power to heat molten salt directly or indirectly through the heat-pump cycle, converting electrical energy into high-temperature thermal energy storage. The high-temperature molten salt and the boiler are subsequently used together as a heat source to drive the steam engine to generate electricity, which achieves the purpose of reducing or replacing the boiler. In this report, the pattern of component parameters influencing the efficiency of a molten-salt Carnot battery energy storage system used in retrofitting a thermal power plant is explored. A thermodynamic model of the molten-salt Carnot battery energy storage system is constructed using the Aspen Plus platform; the model consists of a heat-pump cycle, a molten-salt evaporator, and a typical 600 MW subcritical power block. Influence of the cycling medium, regenerative/nonregenerative properties, and component key parameters on the performance of heat pump and overall system are analyzed. The system efficiencies for the system using electric heating and heat-pump heating are compared under variable operating conditions. The results show that the regenerative storage system has a higher coefficient of heat-pump production and higher round-trip efficiency than that for the nonregenerative system. The regenerative storage system requires the lowest return heater heat by using argon as the heat-pump circulating medium and can achieve the highest round-trip efficiency by using helium as the heat-pump circulating medium. When the cold-source temperature is 67 ℃, isentropic efficiency is 0.9, and mechanical efficiency is 1.0, the round-trip efficiency under the rated working condition can reach 61.46%. In addition, the round-trip efficiency at rated operating conditions of the storage system with the heat pump is 45.16% higher than electric heating. These findings can help in the further design and analysis of molten-salt Carnot battery energy storage systems for retrofitting thermal power plants.

Key words: Carnot battery, coal power plant renovation, system efficiency, molten salt thermal storage, numerical simulation

CLC Number:

TQ 028

Rui HAN, Zhirong LIAO, Boxu YU, Chao XU, Xing JU. Simulation study of a molten-salt Carnot battery energy storage system for retrofitting a thermal power plant[J]. Energy Storage Science and Technology, 2023, 12(12): 3605-3615.

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References 23

1	刘振亚, 张启平, 董存, 等. 通过特高压直流实现大型能源基地风、光、火电力大规模高效率安全外送研究[J]. 中国电机工程学报, 2014, 34(16): 2513-2522.
	LIU Z Y, ZHANG Q P, DONG C, et al. Efficient and security transmission of wind, photovoltaic and thermal power of large-scale energy resource bases through UHVDC projects[J]. Proceedings of the CSEE, 2014, 34(16): 2513-2522.
2	刘畅, 卓建坤, 赵东明, 等. 利用储能系统实现可再生能源微电网灵活安全运行的研究综述[J]. 中国电机工程学报, 2020, 40(1): 1-18, 369.
	LIU C, ZHUO J K, ZHAO D M, et al. A review on the utilization of energy storage system for the flexible and safe operation of renewable energy microgrids[J]. Proceedings of the CSEE, 2020, 40(1): 1-18, 369.
3	马汀山, 王妍, 吕凯, 等. "双碳"目标下火电机组耦合储能的灵活性改造技术研究进展[J]. 中国电机工程学报, 2022, 42(S1): 136-148.
	MA T S, WANG Y, LYU K, et al. Research progress on flexibility transformation technology of coupled energy storage for thermal power units under the "dual-carbon" goal[J]. Proceedings of the CSEE, 2022, 42(S1): 136-148.
4	张显荣, 徐玉杰, 杨立军, 等. 多类型火电-储热耦合系统性能分析与比较[J]. 储能科学与技术, 2021, 10(5): 1565-1578.
	ZHANG X R, XU Y J, YANG L J, et al. Performance analysis and comparison of multi-type thermal power-heat storage coupling systems[J]. Energy Storage Science and Technology, 2021, 10(5): 1565-1578.
5	GEYER M, GIULIANO S. Conversion of existing coal plants into thermal storage plants[M]//Encyclopedia of Energy Storage. Amsterdam: Elsevier, 2022: 122-132.
6	BAUER D. Carnot-Batteries[C]//10th German-Japanese Environment and Energy Dialogue Forum, 2019.
7	DUMONT O, FRATE G F, PILLAI A, et al. Carnot battery technology: A state-of-the-art review[J]. Journal of Energy Storage, 2020, 32: 101756.
8	MCTIGUE J D P. 'Carnot Batteries' for Electricity Storage[R]. National Renewable Energy Lab. (NREL), Golden, CO (United States), 2019.
9	圣力, 薛新杰, 孛衍君, 等. 基于相变储能介质热泵储电系统的模拟与分析[J]. 储能科学与技术, 2022, 11(11): 3649-3657.
	SHENG L, XUE X J, BO Y J, et al. Simulation and analysis of pumped thermal electricity storage system based on phase change energy storage medium[J]. Energy Storage Science and Technology, 2022, 11(11): 3649-3657.
10	BLANQUICETH J, CARDEMIL J M, HENRÍQUEZ M, et al. Thermodynamic evaluation of a pumped thermal electricity storage system integrated with large-scale thermal power plants[J]. Renewable and Sustainable Energy Reviews, 2023, 175: 113134.
11	ZAMENGO M, YOSHIDA K, MORIKAWA J. Numerical evaluation of a Carnot battery system comprising a chemical heat storage/pump and a Brayton cycle[J]. Journal of Energy Storage, 2021, 41: 102955.
12	YONG Q Q, TIAN Y P, QIAN X, et al. Retrofitting coal-fired power plants for grid energy storage by coupling with thermal energy storage[J]. Applied Thermal Engineering, 2022, 215: 119048.
13	LIU X, JIN K L, XUE X, et al. Performance and economic analysis of steam extraction for energy storage to molten salt with coupled ejector and thermal power units[J]. Journal of Energy Storage, 2023, 72: 108488.
14	VINNEMEIER P, WIRSUM M, MALPIECE D, et al. Integration of heat pumps into thermal plants for creation of large-scale electricity storage capacities[J]. Applied Energy, 2016, 184: 506-522.
15	MAHDI Z, DERSCH J, SCHMITZ P, et al. Technical assessment of Brayton cycle heat pumps for the integration in hybrid PV-CSP power plants[C]//AIP Conference Proceedings", "SOLARPACES 2020: 26th International Conference on Concentrating Solar Power and Chemical Energy Systems. Freiburg, Germany. AIP Publishing, 2022: 2445.
16	WANG B G, MA H, REN S J, et al. Effects of integration mode of the molten salt heat storage system and its hot storage temperature on the flexibility of a subcritical coal-fired power plant[J]. Journal of Energy Storage, 2023, 58: 106410.
17	赫广迅, 宋业琛. 基于火电站转型储能电站的超高温热泵及熔盐储换热系统工程应用设计[J]. 汽轮机技术, 2023, 65(2): 93-96, 146.
	HE G X, SONG Y C. Engineering application design of ultra-high temperature heat pump and molten salt heat storage and exchange system based on the rmal power station transformation to energy storage power station[J]. Turbine Technology, 2023, 65(2): 93-96, 146.
18	王辉, 李峻, 祝培旺, 等. 应用于火电机组深度调峰的百兆瓦级熔盐储能技术[J]. 储能科学与技术, 2021, 10(5): 1760-1767.
	WANG H, LI J, ZHU P W, et al. Hundred-megawatt molten salt heat storage system for deep peak shaving of thermal power plant[J]. Energy Storage Science and Technology, 2021, 10(5): 1760-1767.
19	古雯雯. 基于Aspen Plus的太阳能与火电机组集成与性能分析[D]. 北京: 华北电力大学, 2009.
	GU W W. Integration and performance analysis of solar energy and thermal power units based on aspen plus[D].Beijing: North China Electric Power University, 2009.
20	蔡小刚. 100 MW熔融盐塔式太阳能光热电站设计优化研究[D]. 北京: 华北电力大学, 2019.
	CAI X G. Study on design optimization of 100 MW molten salt tower solar photothermal power station[D].Beijing: North China Electric Power University, 2019.
21	GEYERR M, TRIEB F, GIULIANO S. Repurposing of existing coal-fired power plants into Thermal Storage Plants for renewable power in Chile[J]. Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH (GIZ): Bonn, Germany, 2020.
22	SALOMONE-GONZÁLEZ D, GONZÁLEZ-AYALA J, MEDINA A, et al. Pumped heat energy storage with liquid media: Thermodynamic assessment by a Brayton-like model[J]. Energy Conversion and Management, 2020, 226: 113540.
23	杨鹤, 杜小泽. 布雷顿循环热泵储能的性能分析与多目标优化[J]. 中国电机工程学报, 2022, 42(1): 196-211.
	YANG H, DU X Z. Performance analysis and multi-objective optimization of brayton cycle pumped thermal energy storage[J]. Proceedings of the CSEE, 2022, 42(1): 196-211.

工况	指标	实际值	模拟值	误差/%
100% 额定工况	电功率/kW	600085	600322	0.04
	热耗率/(kJ/kWh)	7989	7991.34	0.02
	热效率/%	40.96	40.95	-0.02
75% 额定工况	电功率/kW	450112	450524	0.09
	热耗率/(kJ/kWh)	8271	8273.88	0.03
	热效率/%	39.56	39.55	-0.03
30% 额定工况	电功率/kW	180058	180244	0.09
	热耗率/(kJ/kWh)	9005	9007.34	0.03
	热效率/%	36.34	36.33	-0.03

设备名称	熔盐侧		汽水侧
过热器	入口熔盐温度/℃	560	入口蒸汽温度/℃	350.9
	入口熔盐流量/(kg/s)	2278	入口蒸汽流量/(kg/s)	502.8
	出口熔盐温度/℃	405	出口蒸汽温度/℃	537
	出口熔盐流量/(kg/s)	2278	出口蒸汽流量/(kg/s)	502.9
再热器	入口熔盐温度/℃	560	入口蒸汽温度/℃	318
	入口熔盐流量/(kg/s)	1121.8	入口蒸汽流量/(kg/s)	424.8
	出口熔盐温度/℃	396	出口蒸汽温度/℃	537
	出口熔盐流量/(kg/s)	1121.8	出口蒸汽流量/(kg/s)	424.8
蒸发器	入口熔盐温度/℃	402	入口蒸汽温度/℃	349
	入口熔盐流量/(kg/s)	3399.8	入口蒸汽流量/(kg/s)	502.8
	出口熔盐温度/℃	350	出口蒸汽温度/℃	351
	出口熔盐流量/(kg/s)	3399.8	出口蒸汽流量/(kg/s)	502.8
预热器	入口熔盐温度/℃	350	入口蒸汽温度/℃	272
	入口熔盐流量/(kg/s)	3399.8	入口蒸汽流量/(kg/s)	502.8
	出口熔盐温度/℃	290	出口蒸汽温度/℃	349
	出口熔盐流量/(kg/s)	3399.8	出口蒸汽流量/(kg/s)	502.8

状态点	文献[22]	模拟
热源入口温度/℃	270.85	270.85
热源出口温度/℃	584.35	580.07
冷源入口温度/℃	26.85	26.85
冷源出口温度/℃	8.55	10.06
压缩机入口温度/℃	21.05	20.98
压缩机出口温度/℃	589.05	589
膨胀机入口温度/℃	287.65	295
膨胀机出口温度/℃	-31.25	-31.25
COP	1.2	1.19

变量	其他变量取值
变量	热源入/出口温度/℃	等熵效率	机械效率	冷源入口温度/℃	压缩机入/出口温度/℃	工质流量/(kg/s)
循环工质	290/560	0.9	1.0	27	—/589	—
热源入口温度	—/560	0.9	1.0	27	261.5/589	6800
等熵效率	290/560	—	1.0	27	261.5/589	6800
机械效率	290/560	0.9	—	27	261.5/589	6800
冷源入口温度	290/560	0.9	1.0	—	261.5/589	6800
压缩机入口温度	290/560	0.9	1.0	27	—/589	6800
工质流量	290/560	0.9	1.0	27	261.5/589	—

工质类型	比热容比	工质流量/(kg/s)	压缩机入口温度/℃	回热器热负荷/MW	COP	RTE
氩气	1.66	6800	261.5	883.02	1.299	56.73%
氮气	1.40	4250	350	1508.07	1.306	57.03%
二氧化碳	1.30	5822.5	432	2552.38	1.296	56.60%