Compressed Air Storage Research Articles

Development of artificial neural networks for an energy storage system generated power prediction

As energy utility firms expand their production outputs from renewable energy resources, interest in investment in an energy storage system (ESS) will increase in the coming years. This article determines the optimal number of hidden nodes and the maximum number of epochs to generate the best prediction results for this generated power estimation. Primary energy efficiency, energy ratio, and ambient air temperature were used to predict the generated power of an ESS. Experimental data sets for compressed air energy storage (CAES) were used to train a single hidden layer artificial neural network (ANN) model. The developed ANN models for CAES and compressed air storage with humidification (CASH) show quick convergence to the targeted error function. Based on eight different artificial neural network architectures, a 3−5−1 ANN architecture generated the best results. This architecture mean squared error was 0.00042. Using experimental data for CASH to validate the single hidden layer model, the ANN model performed satisfactorily.

Pulsed Electrodeposition of Nanocatalysts for Energy Storage Applications: Mathematical Modeling and Experimental Studies

With the growing demand for clean energy, the need for affordable, efficient energy storage technologies has never been more urgent. Pumped hydro and compressed air storage technologies have been widely used, but they are heavily dependent on location and are not considered to be universal solutions. Secondary batteries, including Li-ion and lead-acid batteries, have played a major role in storing excess electrical energy, but they suffer from high cost, performance degradation over time, and environmental issues during use and disposal. Metal-air batteries have experienced a renaissance on account of their acceptable energy density, superior cycleability, enhanced stability and cost benefits compared with other commercially available batteries. Despite these desirable properties, metal-air batteries suffer from a number of thermodynamics and kinetics hurdles that must be overcome, if their widespread deployment is desired. One of the major impediments to wide-scale commercialization of metal-air batteries continues to be their inferior capacity and cycle stability. Part of these issues can be ascribed to the shortcomings of the cathode materials and structures in general, and the inferiority of their catalyst layers in particular. It is well established that nano-structuring battery components would improve their short- and long-term performance by enhancing reaction kinetics.Nanocatalysts such as transition metals, platinum and manganese dioxide were electrodeposited on a number of conductive substrates, including carbon paper, carbon cloth and titania nanotubes (TNTs) with high aspect ratios. Catalyst electrodeposition was performed utilizing pulsed current electrodeposition with different waveforms, low duty cycles, and high peak deposition current densities. All catalysts were characterized using microscopy, spectroscopy and electrochemical techniques. The presence of nanocatalysts were confirmed by SEM and XRD and were found to be 2-5 nm for platinum and 10-50 nm for nickel and oxides of manganese.A mathematical model was developed to determine the roles of various deposition process parameters on the size and catalytic activity of the resulting nanocatalysts in different environments. The model is based on progressive nucleation and takes into account some key contributing factors towards growth current and, ultimately, nucleation, including diffusion, ohmic and charge transfer phenomena. A varying diffusion coefficient during electrodeposition was also considered and evaluated. Model predictions were confirmed by experimental measurements with emphasis on platinum and manganese dioxide nanocatalysts for use in PEM fuel cells and metal-air batteries, respectively.

Performance analysis of a compressed air energy storage system integrated into a coal-fired power plant

Compressed air energy storage is considered to be a potential large-scale energy storage technology because of its merits of low cost and long design life. Coupling with coal-fired power plant is an attractive way for its competitiveness improvement. A novel compressed air storage system that integrates into the regenerative subsystem of coal-fired power plant is proposed. The mathematical model is established, and the possible coupling schemes are discussed. Furthermore, analyses of thermodynamics, purchased-equipment costs and key parameters are carried out. The results show that at the ambient temperature of 20 ℃ the round-trip efficiency and exergy efficiency of the proposed system are 78.85% and 83.81%, respectively. The largest exergy destruction process is shown to take place in the throttle valve, and heat exchangers are shown to be the equipment with the largest investment. The parametric analysis shows that the proposed system has good performance in a wide range of storage pressures and ambient temperatures. Such good features make the proposed system a promising scheme for prompting energy storage technology.

Demand-Response Application in Wastewater Treatment Plants Using Compressed Air Storage System: A Modelling Approach

Wastewater treatment plants (WWTPs) are known to be one of the most energy-intensive industrial sectors. In this work, demand response was applied to the biological phase of wastewater treatment to reduce plant electricity cost, considering that the daily peak in flowrate typically coincides with the maximum electricity price. Compressed air storage system, composed of a compressor and an air storage tank, was proposed to allow energy cost reduction. A multi-objective modelling approach was applied by analyzing different scenarios (with and without anaerobic digestion, AD), considering both plant characteristics (in terms of treated flowrate and influent chemical oxygen demand, COD, concentration) and storage system properties (volume, air pressure), together with the current Italian market economic conditions. The results highlight that air tank volume has a strong positive influence on the obtainable economic savings, with a less significant impact held by air pressure, COD concentration and flowrate. In addition, biogas exploitation from AD led to an improvement in economic indices. The developed model is highly flexible and can be applied to different WWTPs and market conditions.

Preliminary Design and Performance Assessment of an Underwater Compressed Air Energy Storage System for Wind Power Balancing

Abstract A key approach to large renewable power management is based on implementing storage technologies, including batteries, power-to-gas, and compressed air energy storage (CAES). This work presents the preliminary design and performance assessment of an innovative type of CAES, based on underwater compressed air energy storage (UW-CAES) volumes and intended for installation in the proximity of deep-water seas or lakes. The UW-CAES works with constant hydrostatic pressure storage and variable volumes. The proposed system is adiabatic, not using any fuel to increase the air temperature before expansion; a sufficient turbine inlet temperature (TIT) is instead obtained through a thermal energy storage (TES) system which recovers the compression heat. The system includes (i) a set of turbomachines (modular multistage compressor, with partial intercooling; expansion turbine); (ii) a TES system with different temperature levels designed to recover a large fraction of the compression heat, allowing the subsequent heating of air prior to the expansion phase; (iii) an underwater modular compressed air storage, conceived as a network of rigid but open tanks lying on the seabed and allowing a variable-volume and constant pressure operation. The compressor operates at variable loads, following an oscillating renewable power input, according to strategies oriented to improve the overall system dispatchability; the expander can be designed to work either at full load, thanks to the stability of the air flowrate and of the TIT guaranteed by the thermal storage, or at variable load. This paper first discusses in detail the sizing and off-design characterization of the overall system; then it simulates a case study where the UW-CAES is coupled to a wind farm for peak shaving and dispatchability enhancement, evaluating the impact of a realistic power input on performances and plant flexibility. Although the assessment shall be considered preliminary, it is shown that round-trip efficiency (RTE) in the range of 75–80% can be obtained depending on the compressor section configuration, making the UW-CAES a promising technology compared to electrochemical and pumped-hydrostorage systems. The technology is also applied to perform peak-shaving of the electricity production from an off-shore wind farm; annual simulations, based on realistic wind data and considering part-load operation, result in global RTE around 75% with a 10–15% reduction in the average unplanned energy injection in the electric grid. The investigated case study provides an example of the potential of this system in providing power output peak shaving when coupled with an intermittent and nonpredictable energy source.

Thermodynamic analysis of a compressed air energy storage system with constant volume storage considering different operating conditions for reservoir walls

Abstract In the search for alternatives to fossil fuels, renewable energy sources such as wind and solar are gaining increasing importance in the global energy grid. Despite its reserves are abundant, this type of energy is intermittent, which causes some unpredictability in meeting energy demand through these resources. To mitigate this problem, energy storage systems can be used combined with renewable sources. Compressed air energy storage (CAES) systems stand out for their high efficiency and affinity with the environment. In the present article a thermodynamic analysis of an operating cycle of a small scale CAES system with constant volume reservoir is conducted, taking into account three different operating conditions for compressed air storage walls. The conducted analysis of the CAES system considered includes an energetic and an exergetic investigation, aiming to determine and assess which are the most relevant points of exergy destruction in the system, as well as the effects of air storage conditions on the thermodynamic performance of the global system. Among the main results it was observed that the combustion chamber presented the highest rates of exergy destruction, and that the throttle valve installed on the exit of the air storage reservoir was responsible for an average of 9% of the total exergy destroyed in the CAES system over a complete work cycle.

Aeroderivative gas turbine back-up capability with compressed air injection

The transition to more renewable energy sources of power generation is associated with grid instability and the need for backup power, due to their intermittency. This provides an opportunity for gas turbine engines, especially the aeroderivative (AD) types that generally have higher ramp rates than heavy-duty engines. Nonetheless, higher ramp rates are still necessary to meet more stringent grid requirements, with increased renewables subscription. The study examines ramp rate improvements and performance enhancement through compressed air injection at the back of the high-pressure compressor (HPC). Two configurations of AD engines are considered in the investigation. In-house gas turbine performance simulation software has been used to simulate the steady-state and transient operations for design and off-design performance. Compressed air injection in the study is facilitated by an assumed compressed air storage or an external compressor. The steady-state analysis for power augmentation shows that for the two-spool engine with fixed speed low-pressure compressor (LPC), a 16% increase in power is obtained with 8% of flow injection. The other engine that is intercooled and consists of a variable speed LPC with power turbine shows a 21% increase in power for the same injection amount. Above 8% injection, the HPC of both engines tends towards an adverse rise in pressure ratio. However, up to 15% of flow injection is allowed before the surge point. It is seen generally that the operating point of the LPC moves away from surge, while the opposite is the case for the HPC. For transient simulations focused on ramp rates, the better improvements are shown for the intercooled engine that runs at variable speed. This is a ramp rate improvement of 100% with air injection, while that of the other engine increases by 85%.

Enhancing electricity supply mix in Oman with energy storage systems: a case study

ABSTRACT Over the past decade, population growth and industry expansion in Oman have led to an increase in electricity demand of more than 240%. The main challenges of utilising renewable energy resources in Oman include high capital costs and their intermittent nature. Enhancing the integration of renewable energy sources from wind and solar into the conventional power network requires the mitigation of vulnerabilities posed to the network owing to the intermittent nature of these sources. One possible solution for such a problem is to utilise large-scale energy storage such as pumped-hydroelectric, compressed air, or Hydrogen storage. This paper aims to review energy storage options for the Main Interconnected System (MIS) in Oman. In addition, it presents a techno-economic case study on utilising pumped hydro energy storage (PHES) facilities to supply peak demand. Abbreviations: CAES: Compressed Air Energy Storage; CAPEX: Capital Expenditure or Construction Cost; CCGT: Combined Cycle Gas Turbine; CCS: Carbon Capture and Storage; CF: Capacity Factor; CO2: Carbon Dioxide; COE: Costs of Energy; CRT: Cost-Reflective Tariff; DPS Dhofar Power System; GHG: Greenhouse Gas; IRR: Internal Rate Of Return; MIS: The Main Interconnected System; OCGT: Open Cycle Gas Turbine; OETC: Oman Electricity Transmission Company; OPEX: Operation Expenditure or Running Cost; OPWP: Oman Power and Water Procurement Company; PHES: Pumped Hydro Energy Storage; PPA: Power Purchase Agreement; RAEC: Rural Areas Electricity Company; SMES: Superconducting Magnetic Energy Storage

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.

Energy and exergy analysis of wind farm integrated with compressed air energy storage using multi-stage phase change material

One of the most common issues associated with wind energy penetration as a viable resource is high instability under diverse amplitudes and frequencies. Compressed air storage systems (CAES) and thermal energy storages (TES) not only are promising alternative solution for renewable resources generally, but they are also used with the aim of peak shaving to provide cleaner and affordable power. Due to high storage density with low temperature gradient between storing and retrieving in comparison with sensible heat storage, phase change material (PCM) is selected considering their thermophysical properties. This work, presents a recovery approach by using PCM during 12 h’ compression periods to retrieve it in 12 h’ expansion as a case study in November for Baladeh (a city in north of Iran). It is worthy to mention that, in order to use PCM in multiple mentioned stages, auxiliary heaters facilitate system to provide constant heat load in each used stage. This concludes system to be more efficient, sustainable and can reduce irreversibilities. Temperature of PCMs and amount of heat stored and released versus time are modeled. A good agreement between PCM model and reported results of related articles was seen. Following to the energy and exergy balances calculation, round-trip efficiency (RTE) and total exergy efficiency of system, reach 70.83%, 80.71%. Exergy analysis showed that near 60% exergy destruction occurred in PCMs with major contribution of second ones in both charge and discharge times. Sensitivity analysis is also investigated assuming the effect of number of wind turbines which shows a reduction in RTE, steeper slope in increasing TES volume for PCM3 and amount of heat stored, by increasing them.

The future of underground spatial planning and the resulting potential risks from the point of view of mining subsidence engineering

The topic of ground movements in Germany has been studied extensively in the past, especially in the field of active mines. The active hard coal mines in Germany were finally shut down in 2018 and lignite mining is expected to take place only until 2038. The so-called long-term liabilities of the mine operators in Germany include, among other things, the long-term guarantee of stability and thus the monitoring of ground motion. So far, the economic use of underground mining in Germany was mainly the supply of raw materials. In the future, the underground storage of compressed air, methane or hydrogen will play an important role in renewable energy supply and climate change. Therefore, the underground storage space will become more important and the spatial planning is essential to ensure availability of safe underground openings for the various options of environmentally friendly energy storage. However, this renewed usage of underground openings may also bring new and sometimes unknown challenges of geomechanical influence. The aftermath of hard coal and lignite mining will be an increasing challenge in mining subsidence engineering. On the other hand, new possibilities due to underground spatial planning may lead to subsidence and/or heaving of the upper surface.

An option for integration of Carnot Battery into a small Nuclear Power Plant

This article proposes a combination of nuclear power plant and grid-scale energy storage, classified as Carnot battery. The electric heater heats molten salts when excess electricity is available in the grid. The steam that is produced in a small modular nuclear reactor is heated with hot molten salts in the external super-heater. For continuous superheating to be ensured, the plant is equipped with molten salt thermal energy storage. The combined plant and reference NPP are modelled and simulated at steady-state conditions. Due to the higher turbine inlet temperature, the efficiency of the combined generation-storage nuclear plant is substantially improved. The proposed concept makes the co-location of NPP and Carnot Battery more attractive than the separate plants. The integrated thermal storage acts as secondary electricity storage. As such, it surpasses compressed air storage and is competitive with the pumped hydro storage, in the absence of their geographical and environmental constraints.

Experimental study of pipe-pile-based micro-scale compressed air energy storage (PPMS-CAES) for a building

Compressed air energy storage (CAES) technology has been re-emerging as one of the promising options to address the challenge coming from the intermittency of renewable energy resources. Unlike the large-scale CAES, which is limited by the geologic location, small-and micro-scale CAES that uses a human-made pressure vessel is adaptable for both grid-connected and standalone distributed units equipped with the energy generation capacity. The research team recently suggested a new concept of pipe-pile-based micro-scale CAES (PPMS-CAES) that uses pipe-pile foundations of a building as compressed air storage vessels. To ascertain the mechanical feasibility of the new concept, we conducted lab-scale pile loading tests with a model test pile in both a loose and dense soil chamber that emulates an actual closed-ended pipe pile. The test pile was subjected to a repeated cycle of compressed air charge (to Pmax=10 MPa) and discharge (to Pmin=0.1 MPa) during the experimental study. The displacement at the top of the test pile, with and without a structural loading, in loose and dense sand, was closely monitored during the repetitive air pressurization-and-depressurization. It was observed that the vertical displacement at the pile head under different conditions was accumulated during the extended cycle of air charge and discharge, but the rate of displacement gradually attenuates during the cycle. And, the presence of structural load and density of soil affected the magnitude of the accumulated vertical displacement. From the analysis, it can be concluded that the concept of PPMS-CAES is not likely to compromise the mechanical integrity of pipe piles while showing a promising capacity for energy storage.

Design and Development of Pneumatic Drug Delivery System

Pneumatic delivery system is a popular system during 19th & 20th century where there was internet to send emails. These systems were used to send files from one department to other department in the office environment. Later these were slowly replaced by fax and email. Now-a-days these are being widely used in hospitals to deliver blood samples or drugs through capsule from one block to other block of the hospital to save time since blood samples and drugs weigh very less. Above being the case, a system was developed where a capsule containing blood samples or drugs of minimum 5kg of weight can be carried using less number of air compressors by creating a smart path. Till now there were systems which were designed for apartments and industries for transportation of products from one location to another location, but the developed system can be implemented in hospitals for drug delivery from one place to other place. The capsules can be built using suction pipes to reduce the cost of the system. Cost of the system can be further greatly reduced by using PVC or acrylic sheets. The system can be made more effective by using smart path which is specially designed to reduce traffic and time delay. The developed system allows the reuse and storage of compressed air in the pipes, so that less number of compressors are being used. The system also allows a unique method of finding the location of the drug in the whole system by Radio-frequency identification (RFID) tags. Finally, the developed system is very useful in hospitals for transporting drug by reducing the traffic and time delay. Further, the system can be developed such a way that it can be used to deliver the couriers in a faster rate to save time and the cost to deliver product can also be greatly reduced.

Integration of renewable energies in the electricity grid from energy storage plants in disused mining structures

Energy Storage Plants (ESP) can be considered an alternative to solve the intermittency problems associated to variable renewable energy (VRE), such as wind and solar photovoltaic. This paper explores the use of closed mines as underground reservoir for Underground Pumped Storage Hydropower (UPSH) and Compressed Air Energy Storage (CAES) plants. Investment cost and stored amount of energy are compared in both technologies. Mining structures in disused coal mines in NW Spain have been selected as a case study to analyse the potential of energy storage in disused mining structures. Pumped Storage Hydropower is the most mature large-scale energy storage technology that dominates both the total installed power capacity and the energy storage capacity. An alternative to UPSH plants could be CAES plants, which are systems to store energy in the form of compressed air, and work in a similar way to conventional gas turbines. Abandoned salt cavern or closed coal underground mines are typically used as underground compressed air storage, giving new uses to the infrastructure of abandoned mines. The results obtained show that 130 MW of electrical power could be installed in UPSH and CAES plants in closed mines with an investment cost of about 225 M€.

Research on Selection Method for the Types and Sites of Underground Repository for Compressed Air Storage

[Introduction] The selection of types and sites of underground repository for compressed air storage is one of the most important issues of large scale compressed air energy storage (CAES) plant planning. [Method] The advantages and disadvantages of 4 types of underground repository for compressed air storage were concluded based on comparison of analyzing literatures published domestic and oversea. The geology characteristics and distribution region of the suitable hard stratum for construction of underground rock cavern were also analyzed. The technology feasibility of rock cavern for compressed air storage was validated by the in-situ experiment results obtained from the first pilot repository for CAES in China. Sites planning method of underground repository for large scale CAES plant was studied taking Guangdong province for example. [Result] Rock caverns built in salt and hard rock stratum are the most feasible types of the underground cavern for CAES plant and hard rock stratum widely exists in most windy and solar energy abundant aera in China. [Conclusion] Wide distribution of the suitiable stratum for underground cavern construction in intermittent energy generation area solves the difficult problem of site selection for large scale CAES plant. Experiment data indicates that good quality of the rock mass is helpful for the solution of key problems such stability and sealing of underground cavern. All in all, it is feasiblity in technology at the present stage in China.

Frequency superimposed robust coordinated control in a hybrid microgrid

The paper presents a frequency superimposed robust coordinated control technique for the precise power bifurcation among the multiple energy storage elements. In the proposed control principle, a dynamically computed low voltage virtual frequency is injected into the dc control network. According to the total power demand, and the energy density of the battery units, the virtual frequency is computed in the master controller units. Further, with respect to the measured virtual frequency and their specified drooping gain, the slave units interact. In consequence of the conditional drooping factors, the slave units can locally decide their spell of execution. Thus, the proposed scheme ensures a precise power management among the multiple energy storage elements without introducing any virtual resistance in the dc network. In an addition, accounting the system stability, the proposed scheme controls the amount of ac grid interference into the dc microgrid. Considering two numbers of battery as master controllers and a compressed air storage as a slave unit, the performance and the stability are evaluated and found to be satisfactory.

Design and flow Simulation of compressed Air Energy Storage system in Aquifer

Compressed air energy storage is the most promising energy storage technology at present, and aquifer compressed air energy storage can achieve large-scale storage of compressed air by breaking the dependence of traditional compressed air energy storage on geological conditions such as large rock caves. Based on Kushnir’s study and some hypotheses, the mathematical model of compressed air energy storage in aquifer is established in this paper. Then, taking 3 MW energy storage scale as an example, the energy storage model of underground aquifer with buried depth of 800m in horizontal stratum is established by using numerical simulation method. The initial gas bag formation after gas injection and the parameters of pressure and gas saturation during the system cycle were analyzed. Experimental results show that the pressure and gas saturation change little after a complete cycle, and the effective gas phase volume of the available energy storage and energy release cycle decreases slowly with the cycle going on. The aquifer is widely distributed and well sealed, so it is feasible to store compressed air energy as a gas storage bank.

Design and Feasibility Analysis of Compressed Air Aquifer Energy Storage System

Compressed air energy storage system is developing rapidly as the most promising energy storage technology, and gas storage device is one of the main components of compressed air energy storage system. Aquifer compressed air energy storage can break the dependence of traditional compressed air energy storage on geological conditions such as large rock caves, and can realize large scale storage of compressed air. In this paper, the development and progress of compressed air energy storage in aquifer are summarized firstly. Then, taking 3.5 Mw energy storage scale as an example, the energy storage model of underground aquifer with buried depth of 800m in horizontal stratum is established by using numerical simulation method. The formation of the initial airbag after gas injection and the cycle times of the pressure system during the system cycle are analyzed. The experimental results show that after a complete cycle, the pressure change in the formation is small; as the cycle continues, the effective gas phase volume in the formation for the energy storage release cycle is slowly reduced.The aquifer has wide distribution and good sealing. It is feasible to store compressed air as a gas storage. The corresponding system design should be carried out according to the actual geological conditions.

Reversible solid oxide systems for energy and chemical applications – Review & perspectives

• Use of reversible solid oxide cell technology (rSOC) for energy storage. • Techno-economics of rSOC systems. • Power-to-X-to power concept suing different chemicals and rSOC technology. • Identification of potential application areas for rSOC technology. This paper presents a mini-review in the field of energy storage using reversible solid oxide cells (rSOCs) for development of energy storage systems for the future. Such energy storage systems fall under the category of power-to-X-to power systems where excess electrical energy produced through renewables is stored in the form of chemicals and the same chemicals are used for conversion back to power. The main competitors of energy storage systems based on rSOC are pumped hydro storage, compressed air storage and batteries and it is envisioned that with better heat integration techniques, the round trip efficiency of rSOC systems can be improved to reach the target value of 80% as specified in the joint EASE-EERA report for European energy storage technology.