Adiabatic Compressed Air Energy Storage System Research Articles

Investigation of synergistic integration and optimization in combining compressed-air energy storage and a gas turbine

It is very important to guarantee performance synergy when combining two sub-systems. This study investigated combinations of compressed air energy storage systems (CAESs) and a gas turbine (GT) while considering various design factors. These factors included the CAES type, CAES capacity, and air injection flow rate, which were not considered in previous studies. The feasibility of various integration scenarios was evaluated, and the best scenario with the highest synergistic effect was obtained through an optimization method. When using a conventional CAES (C-CAES), the combined system was undesirable. When using an adiabatic CAES (A-CAES) or regenerative A-CAES, the combined system outperformed the standalone operation. When the flow ratio of the GT and A-CAES was 1:1.33, the percentage increases in net power and generated energy were 31.5 % and 12.6 %, respectively, and the roundtrip efficiency increased by 3.4 %p. When the flow ratio of GT and regenerative A-CAES was 1:0.88, the percentage increases in net power and generated energy were 31.3 % and 20.6 %, respectively, and the roundtrip efficiency was improved by 2.2 %p. This study provides the best synergistic integration between a CAES and GT for the first time by fully considering various scenarios, including thermal and mass integrations.

Economic assessment for compressed air energy storage business model alternatives

Compressed air energy storage (CAES) is a large-scale energy storage system with long-term capacity for utility applications. This study evaluates different business models' economic feasibility of CAES pre-selected reservoir case studies. It assesses several scenarios for each case study and analyzes two business models: one for the storage of excess renewable energy sources (RES) and another for energy arbitrage. The novelty of this work is performing the economic investment assessment using a Monte Carlo Simulation (MCS) methodology applied to CAES, considering the uncertainties associated with such types of projects and evaluating different business models for the technology.The results suggest a better performance from the CAES RES business model than the CAES arbitrage business model. Furthermore, the diabatic CAES assessed scenarios seem to have more attractive results than their equivalent adiabatic CAES systems in the CAES RES business model. However, adiabatic CAES can be economically feasible in both business models. In addition, it was observed that CAES is viable in specific scenarios and can be profitable for the storage of energy from RES, facilitating the management of their variability, decreasing their dependence on weather, and helping their integration into the grid. However, CAES does not seem a good fit for grid energy arbitrage in the generality of the scenarios evaluated.

Discharging strategy of adiabatic compressed air energy storage system based on variable load and economic analysis

It is promising to match the variable loads of the supply objects in different seasons by adjusting the trigeneration of the adiabatic compressed air energy storage system (A-CAES).. In this paper, the thermodynamic model of the A-CAES system was developed to investigate the characteristics of the A-CAES system for trigeneration combined cooling, heating and electric supply. The cooling, heating, and electric load of a typical residential area in different seasons was analyzed. Then the load of residential area and trigeneration of system was matched to increase the efficiency of energy utilization. Finally, the new energy supply method by the A-CAES system for the residential area was compared with the traditional approach through economic analysis. The simulation results show that households' cooling, and heating load vary greatly in different seasons, but the difference in electric load is insignificant. For A-CAES, the mass flow rate of chilled water in the charging process has little effect on the cooling, heating, and electric output, so the minimum value is suggested to improve the thermal storage temperature of chilled water. The ratio of compression heat distributed for preheating the air in the discharging period can greatly change the cooling, heating, and electric output of the system. From the perspective of meeting the hot and cooling load as much as possible, the optimal heat distribution ratio for summer, spring/autumn, and winter were selected as 36.0%, 94.1%, and 36.0%. However, according to the economic analysis, the optimal heat distribution ratio was selected as 94.1%, 94.1%, and 67.5% to maximize daily profit. The economic analysis also found that the annual energy supply cost of the residential area with the A-CAES system is 24% lower than that of the traditional method. The annual energy supply cost decreases by 254.5 thousand dollars. Given the cost of devices, the static investment payback period of the system was calculated as 15.4 years.

Process improvements and multi-objective optimization of compressed air energy storage (CAES) system

Intermittency and high cost were the main barriers to the large-scale commercialization of renewable energy decades ago. The cost of renewable energy has decreased dramatically in the last decade. The intermittency of renewable energy, however, remains a serious challenge to be overcome. Compressed Air Energy Storage (CAES) is widely considered to be a promising energy storage technology at utility-scale and receives increasing attention from both academic and industrial communities. In this study, two novel CAES systems are proposed and a thorough investigation and comparison of the thermodynamic performance of both conventional and novel CAES systems have been performed. The turbine inlet temperature and the maximum cavern storage pressure are identified as the bottlenecks of CAES plants. The round-trip efficiency and energy density are chosen as the conflicting objectives. Pareto fronts are obtained based on the simulation-based multi-objective optimization framework developed in this study. The energy density of a diabatic CAES plant is within the range between 4.24 and 11.58 kWh/m3, while that value becomes 1.28–7.96 kWh/m3 for a conventional adiabatic CAES system. The novel two-pressure level adiabatic CAES system can improve the round-trip efficiency by at least 3.5% compared with the conventional adiabatic CAES system. The novel indirect heating diabatic CAES system can improve the round-trip efficiency by at least 2%. The Pareto fronts can be a useful tool for the grassroot design or retrofit of a CAES plant. Solutions to improve the CAES system performance have been proposed based on the optimization results of this study.

Performance and economy of trigenerative adiabatic compressed air energy storage system based on multi-parameter analysis

The trigeneration combined the electricity, cooling and heating makes adiabatic compressed air energy storage system (ACAES) popular as an energy storage technology. Based on thermodynamic analysis, this paper studies the influence on the system performance of four variable factors, including compression stages, expansion stages, water (heat storage medium) mass flow rates in charging process and discharging process to provide a guidance for the design of ACAES for different user demand. The results show that changing these four factors can achieve different energy output distributions in a very wide range (power supply ratio is 0.50–0.86, heating output ratio is 0.00–0.39, cooling supply ratio is 0.00–0.41). Simulation results also indicate that fewer compression and expansion stages are suggested for the cases requiring shorter running time. Furthermore, according to this study, less compression stages than expansion is good for electricity generation and more compression stages is good for cooling supply. And for large heating supply demand, less compression is suggest. Besides, the energy efficiencies for different configurations of trigenerative ACAES are also achieved which are changed from 0.62 to 0.87 and the best configurations with highest system efficiency are also presented. Finally, by economic analysis, the most economic condition is achieved.

Performance analysis of a novel adiabatic compressed air energy system with ejectors enhanced charging process

In an adiabatic compressed air energy storage system (A-CAES) with isochoric air storage tank, the throttle valve downstream the compressor results in large irreversible loss. In this paper, a novel A-CAES with ejectors in the charging process (ECA-CAES) is proposed to reduce throttling loss and enhance system performance. A thermodynamics model and an exergy calculation model of an ECA-CAES are established. By simulation, the influences of entrainment ratio, heat transfer temperature difference at cooling/heating exchangers and initial storage pressure on system performance are investigated. The simulation results show that a smaller entrainment ratio, a lower initial storage pressure or a smaller heat transfer temperature difference could more obviously improve the system performance. Compared with A-CAES system, the maximum roundtrip efficiency improvement of the proposed system is up to 2.34%, the maximum charge time, energy consumption of compressors and ratio of exergy destruction improvement in charging process are up to 3.63%, 3.64%, 3.85%, respectively. The exergy analysis depicts that the introduction of ejectors decreases the exergy destruction of the CAES, especially the irreversible loss in throttling valve and compressors. Hence, the proposed system is verified to be an effective way to improve the efficiency of compressed air energy storage system.

Adiabatic Compressed Air Energy Storage: An analysis on the effect of thermal energy storage insulation thermal conductivity on round-trip efficiency

Compressed Air Energy Storage (CAES) has demonstrated promising potential for widescale use in the power distribution network, especially where renewables are concerned.Current plants are inefficient when compared to other technologies such as battery and pumped hydro. Presently, the greatest round-trip efficiency of any commercial CAES plant is 54% (McIntosh Plant), while the highest energy efficiency of any experimental plant is 66-70% (ADELE Project). So far, Adiabatic CAES systems have yielded promising results with round-trip efficiencies generally ranging between 65-75%, with some small-scale system models yielding round-trip efficiencies exceeding 90%. Thus far, minimal research has been devoted to analysing the thermodynamic effects of the thermal energy storage (TES) insulation. This metastudy identifies current industry and research trends pertaining to ACAES with a focus on the TES insulation supported by model simulations. Charged standby time and insulation of the TES on overall system efficiency was determined by performing a thermodynamic analysis of an ACAES system using packed bed heat exchangers (PBHE) for TES. The results provide insight into the effect various insulators, including concrete, glass wool and silica-aerogel, have on exergy loss in the TES and overall system efficiency. TES insulation should be carefully considered and selected according to the expected duration of fully charged standby time of the ACAES system.
 Keywords: Compressed air energy storage; adiabatic compressed air energy storage; thermal energy storage; thermodynamic efficiency; renewable energy storage, packed bed heat exchanger

Performance of metal and non-metal coated phase change materials microcapsules when used in compressed air energy storage system

Using phase change material microcapsules (PCMCs) in direct contact with a compressed air in an adiabatic compressed air energy storage system (ACAES) is an effective approach to capture the heat generated during air compression and to recover it later during decompression. In this work, three different PCMCs were investigated, including those coated with metal. The PCMCs were placed inside air-storage cylinder and compressed to 200 bar. The PCMCs stability against air compression/decompression after 20x cycles was investigated using particle size distribution analyser (PSD), differential scanning calorimeter (DSC) and scanning electron microscope (SEM). The Micronal PCMCs show better thermal storing/releasing performance than other microcapsules showing no significant changes in its thermal behaviour after 20 cycles. In terms particle size distribution, Micronal 5038X and metal-coated Microtek24D MPCMCs retained their sizes after 20 cycles. From the DSC analysis, Micronal capsules show minor reduction in heat storage capacity after 20 cycle and retained good morphology based on SEM photo.

A compressed air energy storage system with variable pressure ratio and its operation control

The compressed air energy storage (CAES) system generally adopts compressors and turbines to operate under a constant pressure ratio. The system working parameters cannot adapt to load change, which causes the system efficiency to be limited. In order to improve CAES system efficiency, a novel variable pressure ratio CAES system is proposed to change the operation pressure ratio by controlling the opening or closing of valves between compressors and the opening or closing of valves between turbines. The thermodynamic analysis model of variable pressure ratio CAES system is established. The period of energy storage, the power consumption of compressor, the output work of turbine and the charging and discharging efficiency of system are calculated and analyzed for the 500 kW advanced adiabatic CAES system. The results show that compared with the corresponding constant pressure ratio CAES system, in the variable pressure ratio CAES system, the power consumption of compressor is reduced by 12%, the output work of turbine is increased by 17.9% and the charging and discharging efficiency of system is increased by 13.1%. Therefore, variable pressure ratio CAES system can not only significantly improve its energy storage efficiency, but also be easy to realize.

Compression performance optimization considering variable charge pressure in an adiabatic compressed air energy storage system

In an adiabatic compressed air energy storage system (A-CAES), the storage pressure persistently increases during the energy storage process causing deteriorate of the charge performance under off-design operating conditions. The compression performance with variable backpressure is essential for the energy storage efficiency and density of A-CAES. A thermodynamic model with energy loss analysis is built up to investigate the performance of a multi-stage centrifugal compressor used in an A-CAES (about 6.0 MW). By energy loss analysis, the blade inlet angle is first focused on to improve the disadvantages of narrow operating conditions and low efficiency at large mass flow rate of the original compressor. Then, the variable rotating speed study is applied on to increase the energy charge efficiency with a wide storage pressure range. Using the thermodynamic model, the available rotating speed is determined to be 0.85–1.05 of design value. Furthermore, the rotating speed is optimized to achieve the best efficiency under variable storage pressures and the corresponding correlation is fitted. Using the optimal rotating speed, the compression efficiency can be kept above 80% while the exergy efficiency is above 82% during the whole energy storage process with a wider storage pressure.

Developing a grid-connected power optimization strategy for the integration of wind power with low-temperature adiabatic compressed air energy storage

Abstract Compressed Air Energy Storage (CAES) is considered as one of the key solutions to handle intermittent and random wind power. However, limited energy conversion efficiency and high capital cost of energy storage have restricted significantly the integration of wind power with CAES. In this study, a grid-connected power optimization strategy based on piecewise averaging of real-time wind power and electricity price data is developed to ensure continuous and stable power outputs to the grid using modified profit-maximizing algorithm. Thermodynamic analysis on the performance of low-temperature adiabatic CAES, energy conversion, and economic evaluation were carried out for a hybrid wind/low-temperature adiabatic CAES system (wind/LA-CAES) with pressure vessels. The proposed optimization strategy reduced the required capacity of CAES and the levelized cost of electricity (LCOE) significantly with greater utilization of wind power and operation profitability. The findings presented in this study is of significant reference value to future development of large-scale wind power integrated with CAES.

New radial turbine dynamic modelling in a low-temperature adiabatic compressed air energy storage system discharging process

It is challenging to gain insight of a Compressed Air Energy Storage (CAES) system dynamic behaviour under various operation conditions due to its complexity with mixed mechanical, thermal, chemical and electrical processes in one. Although a number of studies are reported on CAES steady state and dynamic modelling to reveal its characteristics, few studies have been reported in whole CAES system dynamic modelling involving a radial turbine. This paper explores a new method to analyse the transient performance of the radial turbine while it is integrated with whole low temperature Adiabatic-CAES system. The proposed modelling method approximates the average air flow within single stator/rotor stage. By applying the principle of energy and torque balance on the transmission shaft, the dynamic speed-torque characteristics of the turbine is obtained with a “quasi dynamic iterative searching” process. The model is then integrated to a simulation platform, which is created to synchronise the wide range of time scale dynamic responses including heat transfer, mechanical and electrical energy conversion processes. As every component of the low temperature adiabatic CAES system is built on its fundamental physical and engineering principles, the model is capable of revealing the system transient characteristics. Based on the model, various simulation studies are conducted and the results are compared with the operation data from the literature. It provides a valuable tool for preliminary design of a radial turbine to test its suitability in full and partial load operation conditions, and analyse its transient behaviours.

On numerical model of one-dimensional time-dependent gas flows through bed of encapsulated phase change material

Mathematical model and numerical method are proposed for investigating the one-dimensional time-dependent gas flows through a packed bed of encapsulated Phase Change Material (PCM). The model is based on the assumption of interacting interpenetrating continua and includes equations of state, continuity, momentum conservation and energy for PCM and gas. The advantage of the method is that it does not require predicting the location of phase transition zone and can define it automatically as in a usual shock-capturing method. One of the applications of the developed numerical model is the simulation of novel Adiabatic Compressed Air Energy Storage system (A-CAES) with Thermal Energy Storage subsystem (TES) based on using the encapsulated PCM in packed bed. Preliminary test calculations give hope that the method can be effectively applied in the future for modelling the charge and discharge processes in such TES with PCM.

Conceptual Design of Ocean Compressed Air Energy Storage System

AbstractIn this paper, an ocean compressed air energy storage (OCAES) system is introduced as a utility-scale energy storage option for electricity generated by wind, ocean currents, tides, and waves off the coast of North Carolina. Geographically, a location from 40 to 70 km off the coast of Cape Hatteras is shown to be a good location for an OCAES system. Building upon existing compressed air energy storage (CAES) system designs, a conceptual design of an OCAES system with thermal energy storage (TES) is presented. A simple thermodynamic analysis is presented for an adiabatic CAES system which shows that the overall efficiency is 66%. In addition, finite element simulations are presented, which show the flow induced loads that will be experienced by OCAES air containers on the ocean floor. We discuss the fact that the combination of the buoyancy force and flow-induced lift forces (due to ocean currents) generates a periodic loading on the storage container and seabed, and how this presents engineering challenges related to the development of methods for reliably resisting these loads for decades in a corrosive environment. We also present a system, based on hydrolysis, which can be used for storing energy (in the form of oxygen and hydrogen gas) in containers on the ocean floor.