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[en] Highlights: • Developed model-based efficiency performance metrics for industrial pneumatic systems. • Quantified system efficiency increases due to the Pneumatic Strain Energy Accumulator. • Experimentally validated model efficiency increases ranging from 32% to over 78% - Abstract: A number of national organizations have recently expressed interest in research to develop materials and devices that achieve greater energy storage capacity, power density and increased energy efficiency on the heels of a report finding that the pneumatic sector of the fluid power industry averages only 15% efficiency. One way of improving efficiency is the use of compressed air storage and recycling devices. The pneumatic Strain Energy Accumulator is a recently developed device that recycles exhaust gas from one pneumatic component, stores it in a highly efficient process, and reuses the stored exhaust gas at a constant pressure to power another pneumatic component. This work analyzes system efficiency increases directly attributable to the implementation of a pneumatic strain energy accumulator by applying an analytical methodology for system level efficiency improvement calculations, experimental validation, and compressed air savings projections. Experimentally determined efficiency increases ranged between 32% and 78%, demonstrating that the pneumatic strain energy accumulator can be a viable part of the solution to the fluid power efficiency challenge.
[en] Highlights: • Thermodynamic analysis is presented for a LAES system combined with packed bed units. • The LAES system round-trip efficiency is in the range 50–62%. • Cold box inlet temperature and discharge pressure have significant influence on system performance. • LAES system has smaller air storage volume and higher ASED compared with A-CAES system. - Abstract: Energy storage is a key technology required to manage intermittent or variable renewable energy, such as wind or solar energy. In this paper a concept of an energy storage based on liquid air energy storage (LAES) with packed bed units is introduced. First, the system thermodynamic performance of a typical cycle is investigated and temperature distribution in cold boxes is discussed. Then, the effects of inlet temperature of cold boxes, charge and discharge pressures on thermal behaviors of LAES system are analyzed, as well as the system round-trip efficiency. Finally, an overall comparison between this LAES system and an adiabatic compressed air energy storage (A-CAES) system is conducted. The system could achieve a round-trip efficiency in the range 50–62% depending on the values of process conditions. The system round-trip efficiency decreases with the increase of cold box inlet temperature, and increases with the rise of charge and discharge pressures. Although the round-trip efficiency of the present LAES system is a bit lower than the A-CAES system, however, the air storage volume decreases and the air storage energy density (ASED) increases remarkably for the same operational conditions. The main conclusions draw from this work is beneficial for future LAES development in particular the combination with the packed bed units and the fit with the requirements for large-scale energy storage.
[en] Large-scale energy storage system (ESS) plays an important role in the planning and operation of smart grid and energy internet. Compressed air energy storage (CAES) is one of promising large-scale energy storage techniques. However, the high cost of the storage of compressed air and the low capacity remain to be solved. This paper proposes a novel non-supplementary fired compressed air energy storage system (NSF-CAES) based on salt cavern air storage to address the issues of air storage and the efficiency of CAES. Operating mechanisms of the proposed NSF-CAES are analysed based on thermodynamics principle. Key factors which has impact on the system storage efficiency are thoroughly explored. The energy storage efficiency of the proposed NSF-CAES system can be improved by reducing the maximum working pressure of the salt cavern and improving inlet air pressure of the turbine. Simulation results show that the electric-to-electric conversion efficiency of the proposed NSF-CAES can reach 63.29% with a maximum salt cavern working pressure of 9.5 MPa and 9 MPa inlet air pressure of the turbine, which is higher than the current commercial CAES plants. (paper)
[en] Highlights: • A numerical model is developed to study man-made low-permeability barrier. • The low-permeability barrier can be built and improve CAESA performance. • The grout CSC and viscosity variance can affect permeability distribution. • Special gravity of grout can significantly affect the shape of the barrier. • The impact of water injection rate on barrier performance is not significant. - Abstract: Compressed air energy storage (CAES) is a grid-scale energy storage technology for intermittent energy, as proven by the decades-long successful operation of two existing compressed air energy storage in cavern (CAESC) power plants. Because of the limited availability of salt domes appropriate for CAESC, the more widely available aquifers (compressed air energy storage in aquifers, CAESA) have recently attracted considerable attention as candidates for CAES. An ideal aquifer for CAESA is highly permeable around the well to facilitate easy injection and withdrawal of air, but the high-permeability region is surrounded by low-permeability zones to minimize the loss of injected air and decrease in energy efficiency. However, such ideal geological structures are not always available in nature. Therefore, the potential of creating man-made low-permeability barrier in high-permeability aquifers is very interesting. In this paper, we investigate the feasibility of man-made low-permeability barriers in high-permeability aquifers using the numerical simulator TOUGH2/Gel to calculate the three-component flow (including a miscible gelling liquid). The simulation results show that an expected low-permeability barrier can be created by injecting grout with certain properties, and the altered aquifer performs well for CAESA. Additional sensitivity studies are also performed to reveal the effects of the various factors on the success of the low-permeability barrier creation, including the critical solidification concentration, the scale factor of the time dependence of the grout viscosity, the relative density of the grout, and the volume of the follow-up water injection. The results indicate that, in a horizontal aquifer, low critical solidification concentrations, and small scale factors are generally preferred and the density of grout should be close to that of the in situ water. For the given volume of the injected grout, there is an optimal follow-up water injection that will create the largest storage space without damaging the barrier. These results may help to extend the candidate sites for CAESA and the prospect of large scale energy storage.
[en] Highlights: • Integration of CAES with trigeneration characteristics enriches a CCHP system’s operation mode. • Integrated design method can solve operation mode uncertainty introduced by renewable energy. • Active storing strategy for CAES exhibits significant superiority in peak sheaving and efficiency increase. • Novel algorithm C-NSGA-II provides accurate and efficient solutions for the multi-objective optimization model. - Abstract: The inherent characteristics of renewable energy, such as highly random fluctuation and anti-peak, are essential issues that impede optimal design of a combined cooling, heating and power (CCHP) system. This study presents a novel hybrid CCHP system integrated with compressed air energy storage (CAES). The operation mode of the new system is enriched by the trigeneration characteristic of CAES when compared with a traditional CCHP system. Additionally, an integrated design method based on a tri-level collaborative optimization strategy is proposed for the new scheme. An active storing strategy is introduced to maximize the utility of the superiority of CAES for peak sheaving and efficiency increase. Thus, a novel algorithm based on a hybrid algorithm of Non-Dominated Sorting Genetic Algorithm-II and Multi-Objective Particle Swarm Optimization is employed to solve the multi-objective optimization model with the aim of minimizing the total cost and emissions. A case study shows the effectiveness of the above methods. The implementation of the study fundamentally improves the overall energy utilization degree and the ability for renewable consumption to thereby provide a guiding principle for CCHP system design.
[en] Highlights: • An estimating exergy storage method of cavern-based CAES is developed. • Two cavern operational scenarios, isochoric and isobaric cavern, are studied. • Air temperature variations in cavern significantly affect the exergy storage. • Uncompensated isobaric cavern has high exergy storage per unit cavern volume. • A case study of Hornsea gas storage indicated the potential of CAES in the UK. - Abstract: Accurate estimation of the energy storage capacity of a cavern with a defined storage volume and type is the very first step in planning and engineering a Compressed Air Energy Storage (CAES) plant. The challenges in obtaining a reliable estimation arise in the complexity associated with the thermodynamics of the internal air compression and expansion processes and the coupled heat transfer with surroundings. This study developed the methodology for estimating the exergy storage capacity with a known cavern volume, as well as the cavern volume required for a defined exergy storage capacity with different operation and heat transfer conditions. The work started by developing the mathematical models of the thermodynamic responses of air in a cavern subject to cavern operation in isochoric uncompensated or isobaric compensated modes, and heat transfer conditions including isothermal, convective heat transfer (CHT) and adiabatic wall conditions. The simulated transient air pressure and temperature were verified with the operational data of the Huntorf CAES plant. The study of the Huntorf CAES cavern confirmed the importance of the heat transfer influence on the energy conversion performance. The increase of mass storage due to the reduced temperature variation leads to an enhanced total exergy storage of the cavern. According to our simulations, within the operating range of the Huntorf plant, 34.77% more exergy after the charging and 37.98% more exergy after throttling can be stored in the cavern with isothermal wall condition than those in the cavern with adiabatic wall condition. Also, the nearly isothermal behaviour and high operating pressure in the compensated isobaric cavern resulted in the high effectiveness of exergy storage per unit cavern volume. The required cavern volume of the assumed isobaric cavern operation can be reduced to only 35% of the current cavern volume at the Huntorf plant. Finally, cavern volumes for an operational gas storage facility were used to demonstrate the methodology in estimating the exergy storage capacity, which provided an initial assessment of the storage capacity in the UK.
[en] Highlights: • A novel isobaric A-CAES system based on volatile fluid has been proposed. • Waste heat has employed to make IA-CAES more efficient and stable. • Proposed IA-CAES is more efficient and capacity than A-CAES. • CO2 is selected as volatile fluid for its environmentally properties and high saturation pressure. • Mixtures contain CO2 are investigated to enhance the working temperature range of IA-CAES. - Abstract: Adiabatic compressed air energy storage (A-CAES) is regarded as a promising and emerging storage technology with excellent power and storage capacity. Currently, efficiencies are approximately 70%, in part due to the issue of exergy losses during the throttling of compressed air. To increase the performance of the system, a novel isobaric adiabatic compressed air energy storage (IA-CAES) is proposed on the base of volatile fluid. The air storage vessel is divided into two parts by a piston, one part for air storage and the other has introduced into suitable volatile fluid. The waste heat is utilized to keep the volatile in a desirable pressure in discharging process, which impairs the effect of ambient temperature on pressure of volatile and makes the IA-CAES system stable. CO2 is selected as the pure volatile fluid own to its environmentally properties and high saturation pressure, while the IA-CAES system based on the CO2 can work in the mid and high latitudes only, due to its low critical temperature (304.13 K). 3 binary mixtures namely CO2/HC-600, CO2/HFC-32 and CO2/HFO-1234ze(E) are investigated to improve the critical temperature of CO2, trends to adapt to a wide range of ambient temperatures for IA-CAES system. The thermodynamic analysis including energy analysis, exergy analysis and the parametric analysis are evaluated by using steady-state mathematical model and thermodynamic laws. The calculations show, when CO2 is selected as the pure volatile fluid and the ambient temperature is higher than 288.15 K (15 °C), the average of total exergy efficiency (TEE) of IA-CAES improves more than 4% compared with that of A-CAES. When the waste heat is considered as free, the round trip efficiency (RTE) improved more than 6% and power capacity increased by more than 49% compared to the conventional A-CAES system. The CO2/HC-600 mixture with the compositions 0.85/0.15 has been proposed as the mixture volatile fluid. Compare with the conventional A-CAES system, the RTE and discharge time improved 6.26% and increased by 56.44%, respectively. Meanwhile, a parametric analysis is also carried out to evaluate the effects of several key parameters on the system performance of the IA-CAES systems.
[en] Electricity storage plays an important role for a successful integration of renewable energies into the electric power system. This French-German report presents the different systems and technologies (capacitors, batteries, heat storage, inertial storage, compressed air storage, power-to gas) of electricity storage, and compares them in terms of storage capacity. It more particularly and briefly comments some characteristics of pump-storage power stations, rechargeable batteries, power-to-gas technology, capacitors and spools, inertial systems. The next part proposes an overview of the situation of storage systems in Germany and in France in terms of development during the last decade, and of installed storage power for the different technologies.