Compressed Air Energy System Research Articles

CAES Compressed Air Energy System: Dynamic Simulation & Optimization

Abstract: A CAES (Compressed Air Energy System) plant can be considered as a storage system. The purpose is to store air under pressure and then use it, when required, to generate energy. The system is composed of a series of compressors and heat exchangers and the architecture of the plant aims to reduce compression work and improve storage efficiency. The storage tank can be different depending on the case and the final use, so a cave, a combustion chamber or an expander. Currently the plants that have been built are in Germany (plant built in 1978 with a rated power of 290 MW) and in the USA (built in 1991 with a rated power of 110 MW). In both configurations, the plants use saline caves as reservoirs. Lately, different types of plant are being studied, but they are still in the design phase.
 The objective of the present work is, through a steady-state and then a dynamic simulation, to analyze the positive aspects of this technology and its criticalities, trying to optimize its layout. In addition, through a comparison with the few data available on existing plants, create a database of great interest for researchers and experts in the field. Finally, evaluate, based on the data obtained, the possible developments of technology in the context of the "low carbon transition" through the possible use of renewable sources, such as solar photovoltaic, wind and so on.

Water spray heat transfer gas compression for compressed air energy system

Compared with other types of energy storage systems, compressed air energy storage (CAES) system has the advantages of low cost, long life, and less impact on environmental. Low cycle efficiency limits its development. Enhancement of the heat transfer between air and environment to achieve isothermal compression is an effective method to improve the round trip efficiency of CAES systems. The spray heat exchange method is proposed to achieve isothermal compression. In order to obtain an accurate heat transfer process model, this paper takes into account that the process of water mist spreading from the nozzle to the whole cylinder will lead to local air and water mist heat transfer in the cylinder, and then divides the area in the cylinder into two parts to analyze and calculate the gas state. To verify the rationality of the diffusion model, a high-speed camera is used to observe the spray diffusion process. Meanwhile, the accuracy of the isothermal CAES system model is verified by literature experimental data, and finally the influence of water spray system parameters is obtained. The research results show that to gain fast heat transfer rate, a spray angle is equal to 60°; when the nozzle diameter is reduced from 0.6 mm to 0.4 mm, the compression efficiency of the system increases from 85.53 % to 89.25 %; The orthogonal design method is used to obtain the maximum total efficiency of the system under the given conditions, when the nozzle diameter is 0.6 mm and the water pressure is 0.2 MPa, and its value reaches 88 %. This research provides theoretical support for the in-cylinder spray isothermal CAES system.

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.

Development of a Prototype Uninterrupted Electrical Power Supply System using Compressed Air Storage from Renewable Energy Resources

Over the last two decades, Pakistan’s energy demand has grown exponentially with very diminutive measures taken by the government to fulfill the needs. The large power plant projects are cumbersome, take years to be completed and require plenty of time to get fully operational. The idea of distributed generation works well in this case. Renewable energy comes well into play when we talk about distributed generation but the dependability of renewable energy resources on back-up such as batteries makes them unappealing. The objective of this paper is to practically implement a backup for the renewable energy resources using a mechanical storage such as CAES (Compressed Air Energy System). The proposed model is a composite technology, which comprises of EES (Electrical Energy Storage) and electrical power supply system. Solar energy driven compressor is used to compress the air in a storage tank, which is used on demand to drive the generator coupled air turbine. The fact that the developed system is solar powered, no other fuel is used with air and it uses mechanical storage instead of conventional storage like batteries, which makes the developed prototype system efficient, economical and durable as compared to the existing CAES. This paper focuses on the thermodynamic investigation, design and finally implementing a prototype CAES for a small load as an un-interrupted power supply system.

Compression ratio energy and exergy analysis of a developed Brayton-based power cycle employing CAES and ORC

Energy consumption growth in the world is one of the primary concerns of researchers in the energy fields. Providing demanded power, especially in peak consumption times besides less emission production, is always been the goal of power plants designers. Utilizing auxiliary devices or cycles such as compressed air energy system or organic Rankine cycle can help them to achieve their goal. However, the performance of these auxiliary instruments should be evaluated having the best design achieving the target. In this research, employing compressed air energy besides utilizing an organic Rankine cycle is proposed for improving the performance of a Brayton power cycle; moreover, optimum operating condition for compression ratio of each cycle is found with energy–exergy analysis. Various working fluids for organic Rankine cycle are explored, and the best conditions are introduced based on energy and exergy parameters, namely the first- and second-law efficiencies, power and exergy destruction. Results show that the optimum compression ratio of Brayton cycle is 7.5 for all considered organic fluids, and optimum pressure ratio of organic Rankine cycle is 5.5 for isopentane and n-pentane. Isopentane has the least exergy destruction, while the maximum first- and second-law efficiencies are achieved by R123.

Hybrid compressed air energy storage, wind and geothermal energy systems in Alberta: Feasibility simulation and economic assessment

Fossil fuels are the major source of electric power production in Alberta, Canada (about 90%). This makes electricity generation sector of Alberta an intensive source of CO2 emissions and a good candidate for greenhouse gas (GHG) emission reduction by replacing fossil fuels with low-carbon renewable energy sources. Wind and geothermal energy are two low-carbon energy sources that can be considered for electricity generation in Alberta. However, the relatively high cost of geothermal energy and intermittent nature of wind energy hinder their widespread use in the province.To address these challenges, in this study we develop a model to simulate the performance of conventional geothermal and Compressed Air Energy System (CAES)-geothermal power plants with or without wind energy in a typical hot dry rock (HDR) reservoir using CMG STARS, and Visual Basic Applications (VBA) platform in Excel.Our findings show that wind/CAES-geothermal scenario with McIntosh technology has the lowest LCOE (7.8–11.8 ¢/kWh) with the emission intensity of 88–126 gCO2/kWh. Furthermore, this scenario could reach the 10% IRR value, which results in total GDP impacts of $1,020 to $1,386 million and creation of 4,489 to 6,842 jobs in Alberta and Canada over a 10-year period.

Optimal bidding and offering strategies of compressed air energy storage: A hybrid robust-stochastic approach

Market players face electricity market price uncertainty as a challenging issue in restructured electricity markets. To overcome this problem, taking optimal bidding and offering strategies is very important. This paper proposes a new mathematical model as a hybrid robust-stochastic method in order to maximize the expected profit of a compressed air energy system. Also, this study considers the uncertainty of market price with a set of scenarios via stochastic method while it models the uncertainty of maximum capacity of cavern via robust optimization approach. Furthermore, the proposed model formulates mixed-integer linear programming and obtains optimal offering and bidding curves of a compressed air energy system, which are robust against the uncertainty associated with market price and cavern uncertainty. Obtained results show that total profit, without considering cavern’s uncertainty, is equal to $9585 while this amount for the most robust case obtained as $8753. This means that being robust against the maximum capacity of caver’s uncertainty reduces total profit by about 8.68%.

A robust optimization method for bidding strategy by considering the compressed air energy storage

Power market tariff is a main problem in electricity yields that is challenged by yield markers. For tackling this challenge, optimization of offering/bidding methods is so crucial. Present work suggested a novel method called synthetic stochastic-robust approach for maximization of anticipated revenue of compressed air energy system (CAES), in which, uncertain parameters such as market tariff and max potential of cavern are taken into account. In this proposed method, modeling of market tariff uncertainty is done by means of a collection of cases through stochastic optimization whereas uncertainty of max potential of cavern is modeled by robust method. As well, this paper suggested a new method for achieving offering and bidding profiles that have robustness versus uncertain parameters including: market price and cavern max capacity. Achieved results confirm, entire benefit in absence of cavern uncertainty. In the other words, having robustness versus uncertainty of cavern max potential decreases entire revenue.

Off‐design performance and operation strategy of expansion process in compressed air energy systems

Compressed air energy storage (CAES) systems usually operate under off-design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. In order to optimize design and operation of CAES systems, it is significant to study off-design performance. The expansion process plays an important role in the whole system. The main objective of this study is to explore the off-design characteristics and optimization strategy of the multistage expansion process of CAES systems with thermal storage. Two kinds of off-design operating modes, which are equal-power-ratio (EPR) operation and optimizing variable stator vane rotation angle (OVRA) operation, are proposed and compared for the first time. Correlation between key parameters such as total output power ratio, exergy efficiency, outlet air/water temperature versus mass flow rate ratio, and inlet pressure are revealed. Furthermore, optimal operation principles are obtained. The primary optimizing operation principle is to optimize the isentropic efficiencies of low-pressure stages to improve the whole efficiency of expansion process. Lastly, the optimized regulating law for variable stator vane is expressed in a polynomial form.

An Analysis of an Advanced Compressed Air Energy System (CAES) Using Turbomachinery for Energy Storage and Recovery and for Continuous On-Site Power Augmentation as an Air Brayton Cycle

Abstract A thermodynamic analysis of an advanced CAES for Distributed Power Generation (DPG) is presented that utilizes turbomachinery for energy recovery, but also gives continuous power generation to augment on-site power. The advanced CAES uses renewable energy such as wind power and solar PV in the power range of 1500 to 2500 kW plus recuperation of waste heat from the existing on-site prime mover to improve the utility of the energy storage system. The proposed system also utilizes battery storage to maintain high energy density storage, preferably without the need for costly electrical rectifying and inversion systems to improve the stabilization of power generation. This proposed system may be thought of as a “cross-over” system that combines CAES technology with electric battery storage technology, particularly if the stored electric power is used directly as D.C. power at an industrial facility. The direct use of stored energy from a battery as heat input to the proposed “cross-over” system also may be considered in some limited applications. The ideal application of the proposed system is for isolated DPG systems perhaps in remote sites utilizing “power islands” of renewable energy augmented with on-site fossil fuel prime mover, power generation systems. The proposed “cross-over” system enables higher reliability, faster response to transient power loads, and the efficient use of renewable energy, as well as heat recovery from conventional prime mover systems that are on site.

Analysis of a developed Brayton cycled CHP system using ORC and CAES based on first and second law of thermodynamics

In recent years, studying on energy production processes has been more popular by the sharp increasing trend of energy consumption and loss. One of the effective ways considered for energy loss avoidance in power generation system is using heat loss of power cycles to provide demanded heat for industrial units. Employing auxiliary cycles and compressed air energy system alongside main power production cycle improves the produced power and performance of combined heat and power systems. In this study, a novel combined heat and power system with Brayton cycle as the main power production unit using wind renewable energy, compressed air energy system, and Rankine and organic Rankine cycles is proposed and simulated for residential approaches. All parts of model are validated via the previous published researches and the performance of proposed system in different operating conditions is investigated in detail energetically and exergetically. Results show the acceptable performance of proposed system in peak times as well as low load hours. The increase of gas turbine expansion ratio brings more first and second law efficiencies, while more irreversibility is created by compressor compression ratio increase. In addition, produced power and irreversibility have linear trend by inlet air mass flow rate beside no change in the first and second law efficiencies. Demanded mass flow rate of fuel, Rankine, organic Rankine cycle, and heating system are directly affected by inlet air mass flow rate and overall thermal efficiency can be increased by simultaneous turbine and compressor pressure ratio increase.

Development of compressed air separators based on three-dimensional modeling

Compressed air separators on the basis of jet modules have been considered. It is proposed to solve the problems of their improvement on the basis of three-dimensional modeling. Three-dimensional models of operating channels of compressed air separators are developed. The work processes in separators are analyzed as for gas dynamics and deposition coefficients. There are obtained distributions of velocity, static pressure, dynamic pressure, kinetic energy of turbulence and deposition coefficients for the flow rates of compressed air separators with 1 jet module for the consumption rate of 50...100 m3/h, with 2 jet modules for the consumption rate of 100...200 m3/h, with 4 jet modules for the consumption rate of 200...400 m3/h, and with 6 jet modules for the consumption rate of 400...800 m3/h. Design solutions of separators for compressed air energy systems are developed based on three-dimensional modeling of separating aerosol technologies; their effectiveness is assessed.