A Design Approach for Compressed Air Energy Storage in Salt Caverns
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This thesis develops a first order design approach for compressed air energy storage. The objectives of this thesis are to inform geomechanical design with specific energy delivery needs and mechanical constraints. Often aspects of CAES design can be divorced from each other, this thesis attempts to provide a design framework that better integrates the disciplines associated with energy storage design. The geomechanical design will be based on CAES in salt caverns, as they are the best medium, and can be dissolution mined to adapted to specific design needs. The first chapter offers the motivation and necessary background on CAES. Introducing the CAES configurations and discussing existing facilities. The second chapter discusses the methodology behind volume calculations and the state-space model used to characterize the loads the cavern experiences. The third chapter provides an overview of salt caverns; describing the mineralogy of rock salt and its behaviour. The operational failure criteria are discussed, which govern the geomechanical feasibility of the cavern. Three possible cavern shapes are established, describing the 2-D approximations and how they are created. The fourth chapter discusses the numerical modelling methodology with which caverns will be assessed for stability. The chapter details the first order assumptions made to simplify modelling. The fifth chapter describes the design algorithm developed, which serves as the basis for first order assessment. In the sixth chapter, the design algorithm is applied in two case studies. The main purpose of this study was to synthesize design components of a facility into a first order algorithm. This design algorithm can be applied to any site and is simplified to accommodate a range of energy storage requirements. The initial stage of design entails an understanding of salt extent and characteristics such as depth and thickness. With a geographic constraint, one may determine the energy needed, as far as delivery requirements. The site’s energy needs will be a design constraint, and appropriate mechanical equipment can be selected which will yield the characteristics of necessary volume, pressure limitations, and discharge times. An energy consumption and production profile can be produced. From here one may assess the cavern’s stability to determine a factor of safety. Upon several iterations to fine tune the shape and operability of the cavern, one may proceed into a cost benefit analysis and more rigorous technical design. To demonstrate the design algorithm, two energy storage applications were developed at the same site location. One application was a small-scale energy storage case, and the other was for a much larger grid scale case. The small-scale case could be achieved with a single cavern of 6000 m3, the cavern would have operating pressures between 5 and 10 MPa. It could provide 30 MWh of energy storage. The cavern was cylindrical, and dimensions made for geomechanically sound design. The other cavern was for 1160 MWh application, the mechanical equipment selected required 270,000 m3 of storage. The operating pressures of the cavern were 4.6 and 7.2 MPa. A cylindrical cavern would not have enough salt thickness, to achieve the necessary volume, an ellipsoid was modelled alternatively. It was determined that the ellipsoid would not provide suitable stability. It is recommended to develop four cylindrical caverns instead.
Cite this version of the work
Arjun Eric Tharumalingam (2019). A Design Approach for Compressed Air Energy Storage in Salt Caverns. UWSpace. http://hdl.handle.net/10012/15183