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[en] Highlights: ► In small-scale CAES there are no robust guidelines in choosing an operational pressure for the vessels. ► Through the stress analysis of the vessel, an optimum pressure at minimum cost can be determined. ► One contribution is in determining the optimum pressure is small-scale CAES. ► Another contribution is in determining the shape size, and number of vessels in small-scale CAES designs. - Abstract: The paper reports guidelines for the efficient design and sizing of Small-Scale Compressed Air Energy Storage (SS-CAES) pressure vessels, including guidelines for pressures that should be used in the SS-CAES system to minimize the cost of the pressure vessel. Under a specified energy storage capacity and specified maximum and minimum operating pressures in CAES, the volume of the vessel(s) can be evaluated. The present study provides guidelines for choosing appropriate shape and size for the vessels that minimize material and manufacturing cost for cylindrical vessels. The two main contributions of the paper are that it provides a methodology to determine: (a) an optimum pressure; (b) the shape, size, and number of vessel to be used in a particular application. Results suggest that pressure vessels with a length to diameter ratio of roughly three are the most economical, and that a system should be designed for a pressure of roughly three times the minimum pressure of the expansion device.
[en] Highlights: • A novel, simple, and modular coupon-level cantilever bending test fixture • Simpler geometry, greater measurement accuracy than the existing ASTM-D747 standard • Eliminates need to model contact for accurate CAE representation • Robust alternative to 3-point flexure as CAE material-model validation load case Several conventional CAE material models account for only uniaxial tensile behavior of the material; however, the said models may be required to predict component-level response in a complex loading scenario. Therefore in developing input files for such models, it becomes critical to evaluate their performance in alternative validation loading scenarios such as 3-point bending (flexure). Simulating 3-point flexure requires optimization of contact parameters, thereby introducing an extraneous factor that adds uncertainty to the validation of the material model in bending scenarios. This paper targets to evaluate the opportunity to substitute the conventional 3-point flexure with a cantilever bending exercise as the method of choice for bending load case validation. The cantilever bending test is expected to alleviate several challenges associated with CAE validation using 3-point flexure. We describe a novel test fixture for carrying out cantilever bending at low velocities; the fixture can be conveniently mounted on commercial Universal Testing Machines (UTM), and is capable of generating precise load–displacement information. Cantilever and flexure simulations in LS-DYNA employing piecewise-linear-plasticity formulation (*MAT024) highlight the relative simplicity of validation in bending using cantilever loading. Further, the equivalence of the bending kinematics during cantilever and 3-point flexure is assessed through investigation of stress–strain information.
[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] We investigate the economic viability of coupling a wind farm with compressed air energy storage (CAES) to participate in the day-ahead electricity market at a time when renewable portfolio standards are not binding and wind competes freely in the marketplace. In our model, the CAES is used to reduce the risk of committing uncertain quantities of wind energy and to shift dispatch of wind generation to high price periods. Other sources of revenue (capacity markets, ancillary services, price arbitrage) are not included in the analysis. We present a model to calculate profit maximizing day-ahead dispatch schedules based on wind forecasts. Annual profits are determined with dispatch schedules and actual wind generation values. We find that annual income for the modeled wind–CAES system would not cover annualized capital costs using market prices from the years 2006 to 2009. We also estimate market prices with a carbon price of $20 and $50 per tonne CO2 and find that revenue would still not cover the capital costs. The implied cost per tonne of avoided CO2 to make a wind–CAES profitable from trading on the day-ahead market is roughly $100, with large variability due to electric power prices. - Highlights: ► We modeled a wind farm participating in the day-ahead electricity market. ► We calculated optimal day-ahead market offers based on wind forecasts. ► Revenue is then calculated using measured wind power. ► We find that revenue is insufficient to cover capital costs at current market prices.
[en] Significant natural gas and electricity price variation and volatility, especially during the past few years, raise questions about understanding the value drivers behind electricity storage. The impact of these drivers for pure storage (such as pumped hydroelectric storage) and compressed air energy storage (CAES) are different and in this paper we explore these differences in operation and net revenue over a variety of timescales. We also consider the arbitrage value that is attainable in practice and explain why simple forecasting techniques based on historical data will generally be less successful for CAES. The breakeven cost of storage and how this can depend on regulatory treatment of storage and market structure is also considered. (author)
[en] JAERI, the University of Tokyo, the Central Research Institute of Electric Power Industry and Shimizu Corporation jointing performed and experimental study on two-phase flow in the hydraulically-compensated Compressed Air Energy Storage (CAES) system with a large-diameter vertical pipe two-phase flow test facility from 1993 to 1995. A hydraulically-compensated CAES system is a proposed, conceptual energy storage system where energy is stored in the form of compressed air in an underground cavern which is sealed by a deep (several hundred meters) water shaft. The shaft water head maintains a constant pressure in the cavern, of several mega Pascals, even during loading or unloading of the cavern with air. The dissolved air in the water, however, may create voids in the shaft when the water rises through the shaft during the loading, being forced by the air flow into the cavern. The voids may reduce the effective head of the shaft, and thus the seal may fail, if significant bubbling should occur in the shaft. This bubbling phenomenon (termed 'Champaign effect') and potential failure of the water seal ('blowout') are simulated in a scaled-height, scaled-diameter facility. Carbon dioxide is used to simulate high solubility of air in the full-height, full-pressure system. This report describes the expected and potential two-phase flow phenomena in a hydraulically-compensated CAES system, the test facility and the test procedure, a method to estimate quantities which are not directly measured by using measured quantities and hydrodynamic basic equations, and desirable additional instrumentation. (author)
[en] Highlights: • A multi-stage AA-CAES system model is established based on thermodynamic theory. • Four Cases about pressure loss and effectiveness of heat exchanger are investigated. • The impact of pressure loss on conversion of heat energy in TES is more sensitive. • The impact of heat exchanger effectiveness in charge process on system is stronger. • Pressure loss in heat exchanger affects the change trends of system efficiency. - Abstract: Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) is a large-scale energy storage system based on gas turbine technology and thermal energy storage (TES). Electrical energy can be converted into internal energy of air and heat energy in TES during the charge process, while reverse energy conversion proceeds during discharge process. The performance of AA-CAES system requires further improvement in order to increase efficiency. In this paper, a multi-stage AA-CAES system model is established, and the influence of effectiveness and pressure loss in heat exchanger on energy conversion and utilization efficiency of AA-CAES system is analyzed theoretically based on the theory of thermodynamics. Four Cases about effectiveness and pressure loss of heat exchanger are investigated and compared with each other. It is found that effectiveness and pressure loss of heat exchanger are directly related to energy conversion and utilization in AA-CAES system. System efficiency changes with the variation of heat exchanger effectiveness and the impact of pressure loss on conversion of heat energy in TES is more sensitive than that of internal energy of air. Pressure loss can cause the complexity of system efficiency change. With appropriate selection of the values of heat exchanger effectiveness for both charge and discharge processes, an AA-CAES system with a higher efficiency could be expected
[en] Highlights: • We adapted a turbocharger to work as a micro-CAES system. • We provide an experimental evaluation of this micro-CAES performance. • Overall experimental efficiency was up to 45%, and turbine efficiency 76%. - Abstract: This work presents an experimental evaluation of a micro-CAES system performance, based on the 1st and 2nd laws of Thermodynamics. To build this micro-CAES system we adapted an automotive turbocharger, and also included a generator, an electrical circuit, and a lubricating system. As part of the experimental procedure, we measured the turbine inlet and outlet thermodynamic properties, also the generator power output and the mass flow rate. We imposed the turbine inlet pressure and the electrical load, obtaining as response the generator power output and the turbine outlet temperature. The proposed solution can operate reliably and safely up to 100,000 RPM without load, and 70,000 RPM with 3.5 kW of electrical power output. Overall efficiency was up to 45%, when operating with air at ambient temperatures without external sources of heat.
[en] Highlights: • Performance of novel oil-free co-rotating scroll expander presented. • Water injection allows reaching quasi-isothermal expansion process. • Comparison between experimental data, semi-empirical and deterministic models. • Flank leakage, water injection and rotor speed effects have been analyzed experimentally. • Design guidelines for co-rotating scroll improvement proposed. - Abstract: Efficient compressed air energy storage requires reversible isothermal compression and expansion devices. The isothermal compression and expansion processes can either be approached by several stages with intercooling or by the more convenient injection of a liquid, often water. While volumetric machines are readily available for dry processes the compression and expansion of a gas with the presence of liquid is still problematic. The concept of a co-rotating scroll has been identified as a promising technology to cope with the presence of liquid. The current paper discusses the first experimental results of an oil-free co-rotating scroll prototype tested in expansion mode on a wide range of rotational speeds, varying water injection flow rates and with different nominal flank clearances. A maximal overall isothermal efficiency of 34% and a maximum output power of 1.74 kW_e_l were measured with this first prototype, providing the proof of the technical feasibility of the oil-free co-rotating scroll expander concept. The experimental data indicate a positive effect of water injection suggesting good heat transfer behaviour between the water and the air in the individual chambers, which is a result of the relatively long residence time compared to other volumetric concepts. The experimental sensitivity analysis yields a strong dependency of the machine performance on both the nominal flank clearance and on the injected water rate. The analysis through a semi-empirical model suggests the inversion of a classical trend, i.e. the increase in total leakage area with rotor speed. This is resulting from the centrifugal loads acting on the flanks and deforming them to produce increased radial and flank clearances. The injection of water is suggested to significantly decrease the leakage. A deterministic reduced order model of the co-rotating scroll expander was developed in order to better understand the governing phenomena within the machine and to provide design guidelines for further prototypes. A novel leakage model takes into account for the structural deformation of the flanks and the scroll involutes as a result from the rotor speed. By means of this comprehensive thermodynamic model, mechanical power, mass flow rate and exhaust temperature were predicted within a range of ±12% and ±4 K respectively compared to experimental data. The calibrated model suggests an achievable isothermal efficiency of 87% for an improved co-rotating scroll concept, thus offering promising perspectives not only for compressed air storage, but also for wet expansion in Absorption Power Cycles, trilateral flash cycle and Organic Rankine Cycles.