Thermodynamic analysis of a novel compressed carbon dioxide energy storage system with low-temperature thermal storage

Research projects on new electrical energy storage (EES) systems are underway because of the role of EES in balancing the electric grid and smoothing out the instability of renewable energy. In this paper, a novel compressed carbon dioxide energy storage with low-temperature thermal storage was proposed. Liquid CO₂ storage was employed to increase the storage density of the system and avoid its dependence on geological formations. Low-temperature thermal energy storage technology was utilized to recycle the heat of compression and reduce the challenges to system components. The system configuration was introduced in detail. Four evaluation criteria, the round trip efficiency (RTE), exergy efficiency (η_Ex), thermal efficiency (η_TE), and energy density (ρ_E) were defined to show the system performance. Parametric analysis was carried out to examine the effects of some key parameters on system performance and the genetic algorithm was adopted for system optimization. The calculated results show that, for the novel EES under the basic working condition, its RTE is 41.4%, η_TE is 59.7%, η_Ex is 45.4%, and ρ_E is 15 kWh m⁻³. The value of ρ_E increases with the increasing pump outlet pressure for a fixed value of pressure ratio, and the changes of RTE, η_TE, and the total exergy destruction of the system (E_D,total) with pump outlet pressure are complicated for different values of pressure ratio. When both pressure ratio and pump outlet pressure are high, the values of RTE and ρ_E can be maximized whereas the value of E_D,total can be minimized. Besides, no matter how pump outlet pressure and pressure ratio change, the exergy destruction of the system mainly come from compressors and regenerators, which accounts for about 50% of the total exergy destruction.     

An exergy analysis of a traditional compressed air energy storage system

压缩空气储能技术是具有较大发展前景的大规模储能技术之一,具有广阔的发展前景。使用Aspen Plus软件以传统压缩空气储能系统为例进行流程模拟,运用分析方法对模拟结果进行热力性能分析。分析结果表明,燃烧室的损失是系统各设备损失中最大的。同时还对压缩空气储能系统各个组成部件的运行效率与储能系统的损失之间的关系进行了敏感性分析,分析结果表明,对系统效率影响最大的参数为燃烧室效率,最小的参数为膨胀透平绝热效率。     

基于压缩空气储能的新型冷热电联供系统性能研究

为了解决用户负荷需求在时间上的变动和传统冷热电联供（Combine Cooling, Heating & Power, CCHP）系统大部分时间处于非设计工况下运行导致系统的能源利用效率较低的问题,提出了一种耦合压缩空气储能系统（Compressed Air Energy Storage system, CAES）和蓄热装置的新型CCHP系统（CAES based CCHP system,CAES CCHP）,建立系统的热力学模型,在给定的充、放电工作条件下对CAES CCHP系统的热力学性能进行分析,并对影响该系统性能的CAES压气机压缩比、透平进气口压力、流经CAES的烟气质量流量3个关键参数进行敏感性分析。研究结果表明：CAES CCHP系统能实现冷热电灵活调控,且系统的CAES功转换效率为57.41%,一次能源利用率、一次节能率及火用效率分别为76.22%,24.84%和31.97%,比传统的CCHP系统分别提高10.97%,18.15%和7.58%。     

Thermodynamic analysis of a novel energy storage system with carbon dioxide as working fluid

Recently, energy storage system (ESS) with carbon dioxide (CO₂) as working fluid has been proposed as a new method to deal with the application restrictions of Compressed Air Energy Storage (CAES) technology, such as dependence on geological formations and low energy storage density. A novel ESS named as Compressed CO₂ Energy Storage (CCES) based on transcritical CO₂ Brayton cycle is presented in this paper. The working principle of CCES system is introduced and thermodynamic model is established to assess the system performance. Parametric analysis is carried out to study the effect of some key parameters on system performance. Results show that the increase of turbine efficiency is more favorable for system optimization and the effect of minimum pressures on system performance is more significant compared with maximum pressures. A simple comparison of CCES system, liquid CO₂ system and Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) system is conducted. It is shown that the system efficiency of CCES is lower than that of AA-CAES system but 4.05% higher than that of liquid CO₂ system, while the energy density of CCES system is 2.8 times the value of AA-CAES system, which makes CCES a novel ESS with potential application.     

Thermodynamic analysis of novel hybrid liquid air energy storage system combined with ORC

为了进一步提高液态空气储能（LAES）的系统效率,提出了一种利用有机朗肯循环（ORC）回收利用LAES放电过程中余冷和余热的新型LAES系统。采用Aspen HYSYS V8.4流程模拟方法研究了系统中不同设备性能参数对LAES系统热力特性的影响。结果表明：低温泵等熵效率和换热器夹点温度对LAES系统效率的影响较小;透平等熵效率和燃烧室出口温度对LAES系统效率的影响非常显著,LAES系统效率随透平等熵效率和燃烧室出口温度的增加而显著增加;LAES系统效率随低温泵出口压力的升高而增加,但增加幅度会逐渐减小。该研究结果可为LAES系统的工程应用和效率提升提供重要参考和依据。     

Techno-economic analysis of compressed air energy storage power plant

压缩空气储能系统被认为是最具发展前景的大规模电力储能技术之一,具有广阔发展前景。本文建立了压缩空气储能系统的技术经济性计算模型,并针对蓄热式压缩空气储能系统应用于工业用户的情景,在有无补贴的两种计算条件下,进行了技术经济性分析。研究结果表明,在无补贴条件下,系统内部收益率为16.3%,投资回收期为9.2年;计算补贴时,系统内部收益率为23.8%,投资回收期为6.2年。同时本文还对该系统进行了盈亏平衡、敏感性等不确定性分析,找出影响系统经济性的敏感因素;并得出政策扶持对提高压缩空气储能电站的财务收益水平和抗风险能力具有重要的作用。本文的研究可以为压缩空气储能系统的研究和工程应用提供理论参考和工程指导。     

Thermodynamic analysis of the CO2‐based Rankine cycle powered by solar energy

Using carbon dioxide as working fluid receives increasing interest since the Kyoto Protocol. In this paper, thermodynamic analysis was conducted for proposed CO₂‐based Rankine cycle powered by solar energy. It can be used to provide power output, refrigeration and hot water. Carbon dioxide is used as working fluid with supercritical state in solar collector. Theoretical analysis was carried out to investigate performances of the CO₂‐based Rankine cycle. The interest was focused on comparison of the performance with that of solar cell and those when using other fluids as working fluids. In addition, the performance and characteristics of the thermodynamic cycle are studied for different seasons. The obtained results show that using CO₂ as working fluid in the Rankine cycle owns maximal thermal efficiency when the working temperature is lower than 250.0°C. The power generation efficiency is about 8%, which is comparable with that of solar cells. But in addition to power generation, the CO₂‐based solar utilization system can also supply thermal energy. Copyright © 2007 John Wiley & Sons, Ltd.     

Energy,exergy, and sensitivity analyses of underwater compressed air energy storage in an island energy system

An underwater compressed air energy storage (UWCAES) system is integrated into an island energy system. Both energy and exergy analyses are conducted to scrutinize the performance of the UWCAES system. The analyses reveal that a round‐trip efficiency of 58.9% can be achieved. However, these two analyses identify different directions for further improvement. The heat exchangers, expanders, compressors, electric motors, and generators account for the most exergy destruction. A sensitivity analysis is also conducted to investigate the importance of different input parameters on the round‐trip exergy efficiency of the UWCAES system. The results of both local and global analyses show that the round‐trip exergy efficiency is most sensitive to the isentropic efficiency of the expanders and compressors, and the efficiencies of the electric motors and generators. The impacts of the heat exchangers, the self‐discharge rate of the air accumulator, the inner diameter of the pneumatic pipelines, and the insulation thickness of the hot‐oil tank on the round‐trip exergy efficiency are shown to be highly nonlinear.     

Performance investigation of a novel near-isothermal compressed air energy storage system with stable power output

As one of the grid-scale energy storage technologies, compressed air energy storage (CAES) is promising to facilitate the permeability of renewable energies. By integrating CAES into renewable sources, the fluctuation and intermittence of renewable energies could be effectively restrained. Among various CAES system configurations, isothermal CAES (I-CAES) is considered as a most competitive technology with expected high efficiency. However, most of the existing I-CAES systems have trouble in keeping a stable power output. To address this issue, a novel near-isothermal CAES system is proposed in this article to acquire a near stable power output. Imitating the concept of hydraulic accumulator, a two pressure vessels structure is employed to maintain the gas pressure stable during discharging. Besides, the turbine power output can be controlled by adjusting the liquid flow rate of the Pelton turbine under this near constant pressure condition. Based on the system transient model and economic model, the system components transient behavior, parametric analysis, off-design performance analysis and economic evaluation issues are also conducted. Results show that system round trip efficiency (RTE) with 61.42% and energy density (ED) with 0.2015 kWh/m³ can be achieved under design condition. In the discharge process, the gas pressure in vessel varies in a small range, from 68 to 72 bar, which is relatively stable. The power output from Pelton turbine can be maintained around 1 kW. Meanwhile, the initial pressure, the pipe diameter, and the spraying flow rates of circulating pumps have significant effects on system RTE and ED. Furthermore, the Pelton turbine power output level can be adjusted by adding jets number, and the higher storage pressure can make the power output unsteady.     

Technical principle of compressed air energy storage system

压缩空气储能被公认为是一种比较适合大规模系统的储能技术.本文对压缩空气储能的技术原理和发展现状进行了简要讲解,包括工作原理,工作过程,关键技术,发展现状,应用领域等.     

考虑空气压缩因子变化影响的地下储气库热力学过程分析CSCD

为了解空气压缩因子变化对压气储能电站地下储气库热力学过程的影响,研究了考虑压缩因子变化条件下的压缩空气热力学过程的计算方法,利用实测数据论证了4种压缩因子计算方法的合理性,结合工程算例,研究了循环充放气状态下地下储气库压缩空气温度及压力变化规律。研究表明,空气压缩因子变化对压缩空气温度和压力计算值有显著影响;循环充放气条件下空气压缩因子、温度和压力均随充放气次数的增加呈现出增大趋势,并逐渐趋于稳定;压缩空气温度计算值对压缩因子的敏感程度大于压缩空气压力计算值。将压缩空气假定为理想气体对储气库温度的估计将产生较大影响,因此,考虑压缩因子的影响是必要的。     

Design and thermodynamic analysis of compressed air energy storage system

压缩空气储能技术具有提升风能与太阳能等可再生资源电能质量的潜力,通过此项技术实现间歇性与不稳定性可再生电力的有效储存,进而在电网负荷高峰期以优质电力的形式稳定输出.结合热力学分析方法设计了储能功率56.58 MW,释能输出功率154.76 MW的压缩空气储能系统.在释能阶段透平机组配置上,参照GE 9171E燃机布置第二级透平入口参数,并以其812.41 K高温烟气余热提供第一级透平工质所需全部热量,无需为第一级透平配备专门燃烧器.在此思路下设计的压缩空气储能系统,热耗可降低至3783.96 kJ/(kW·h),储能系统的能量转换效率也高达56.11%.     

Research progress in compressed air energy storage system: A review

压缩空气储能系统通过压缩空气存储多余的电能,在需要时,将高压空气释放通过膨胀机做功发电,在电力的生产、运输和消费等领域具有广泛的用途,是目前大规模储能技术的研发热点。综述了压缩空气储能技术的研究与应用现状,包括工作原理、功能和应用情况,分析了压缩空气储能系统的类型和技术特点,并对压缩空气储能系统的关键部件和系统性能进行了分析比较,最后指出了压缩空气储能技术的发展趋势。     

Economic analysis of using above ground gas storage devices for compressed air energy storage system

Above ground gas storage devices for compressed air energy storage（CAES） have three types：air storage tanks,gas cylinders,and gas storage pipelines.A cost model of these gas storage devices is established on the basis of whole life cycle cost（LCC） analysis.The optimum parameters of the three types are determined by calculating the theoretical metallic raw material consumption of these three devices and considering the difficulties in manufacture and the influence of gas storage device number.The LCCs of the three types are comprehensively analyzed and compared.The result reveal that the cost of the gas storage pipeline type is lower than that of the other two types.This study may serve as a reference for designing large-scale CAES systems.     

A review on underwater compressed air energy storage

压缩空气储能技术是目前储能技术的研究热点之一。水下压缩空气储能利用水的静压特性实现压缩空气的等压存储,具有系统效率较高、受地形限制小、储能规模灵活可变的特点,尤其适合于海上风能等可再生能源的规模化存储。本文简要介绍了压缩空气储能技术的工作原理与发展,通过对比分析阐明了水下压缩空气储能所具有的优势,全面分析了水下压缩空气储能技术的研究进展,对采用柔性储能包的水下压缩空气储能技术进行了重点分析,并对水下压缩空气储能系统开发的关键技术进行了总结和展望。     

An integrated system for thermal power generation,electrical energy storage and CO2 capture

This work reports a newly proposed system for electrical energy storage. The new system combines a direct open nitrogen (cryogen) expansion cycle with a natural gas‐fuelled closed Brayton cycle and the CO₂ produced in the system is captured in the form of dry ice. Thermodynamic analyses are carried out on the system under the baseline conditions of 1 kg s^?1 natural gas, a combustor operating pressure of 8 bars and a cryogen topping pressure of 100 bars. The results show that the exergy efficiency of the proposed system is as high as 64% under the baseline conditions, whereas the corresponding electricity storage efficiency is about 54%. A sensitivity analysis has also been carried out on the main operating conditions. The results indicate that the baseline performance can be enhanced by increasing the gas turbine (GT) inlet temperature, decreasing the approach temperature of the heat exchange processes, operating the combustor at an optimal pressure of ～7 bars and operating the cryogen topping pressure at ～90 bars. Further enhancement can be achieved by increasing the isentropic efficiency of the GT and the liquefaction process. The results of this work also suggest that the power capacity installation of peak‐load units and fuel consumption could be reduced by as much as 50% by using the newly proposed system. Further work is suggested for an economic analysis of the system. Copyright © 2010 John Wiley & Sons, Ltd.     

300MW超临界二氧化碳锅炉布置浅析

与朗肯循环相比,超临界二氧化碳布雷顿循环在相同的参数下可以达到更高的效率。为了探索超临界二氧化碳锅炉受热面布置,本文通过将其与350MW等级的蒸汽锅炉参数对比和热容量分析提出了一种锅炉布置方案,对进一步详细设计计算具有借鉴意义。     

A novel thermally driven pump and its test in a supercritical CO2 loop system

In this paper, a novel thermally driven pump is introduced, and its test in a closed supercritical CO₂ loop cycle system is studied. The thermally driven pump is a refrigerant‐circulating pump composed of two expansion tanks, which has less electricity consumption and better reliability compared with conventional mechanical pumps. Experimental results showed that the system efficiency of the present thermally driven pump in the supercritical CO₂ loop can be enhanced compared with that using the mechanical feed pump. In addition, it was found that the system efficiency with the thermally driven pump decreases with the outlet temperature of condenser. The thermal energy utilization efficiency of the loop system with the thermally driven pump can be increased when the condenser has higher efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermodynamic simulation of hydrogen based thermochemical energy storage system

The increasing energy demand needs the attention for energy conservation as well as requires the utilisation of renewable sources. In this perspective, hydrogen provides an eco-friendly and regenerative solution toward this matter of concern. Thermochemical energy storage system working on gas-solid interaction is a useful technology for energy storage during the availability of renewable energy sources. It provides the same during unavailability of energy sources. This work presents a performance analysis of metal hydride based thermal energy storage system (MH-TES), which can transform the waste heat into useful high-grade heat output. This system opens new doors to look at renewable energy through better waste heat recovery systems. Experimentally measured PCIs of chosen metal hydride pairs, i.e. LaNi_4.6Al_0.4/La_0.9Ce_0.1Ni₅ (A-1/A-3; pair 1) and LaNi_4.7Al_0.3/La_0.9Ce_0.1Ni₅ (A-2/A-3; pair 2) are employed to estimate the thermodynamic performance of MH-TES at operating temperatures of 298 K, 373 K, 403 K and 423 K as atmospheric temperature (T_atm), waste heat input temperature (T_m), storage temperature (T_s) and upgraded/enhanced heat output temperature (T_h) respectively. It is observed that the system with alloy pair A-1/A-3 shows higher energy storage density of 121.83 kJ/kg with a higher COP of 0.48 as compared to A-2/A-3 pair. This is due to the favourable thermodynamic properties, and the pressure differential between coupled MH beds, which results in higher transferrable hydrogen. Besides, the effect of operating temperatures on COP is studied, which can help to select an optimum temperature range for a particular application.     

Thermodynamics analysis of a hybrid system based on a combination of hydrogen fueled compressed air energy storage system and water electrolysis hydrogen generator

In front of the opportunity of the rapid development of renewable energy power generation, energy storage is playing a more important role in improving its utilization efficiency. In this paper, a hybrid energy system based on combination of hydrogen fueled compressed air energy storage system and water electrolysis hydrogen generator is proposed. The superfluous renewable energy power is charged by compressing the air and/or producing hydrogen through water electrolysis. A hydrogen combustor is introduced to raise the air temperature in the discharging process. A thermodynamic model of the proposed system is built. Energy and exergy analysis found that under the design condition, the proposed system can achieve a round trip efficiency of 65.11%, an exergy efficiency of 79.23%, and an energy storage density of 5.85 kWh/m³. The exergy loss of water electrolysis hydrogen generator and hydrogen combustor rank in the top two of all components. Sensitivity analysis indicates that the outlet temperature of hydrogen combustor and specific energy consumption of water electrolysis hydrogen generator are the crucial influencing factor of system performance.