This paper presents the results of stress analyses of compressed air energy storage (CAES) caverns in hard rock, performed by the finite element method. Detailed descriptions are given for the stress concentrations developed around the cavern periphery for both a single cavern and an array of three caverns. Results are compiled to illustrate stability and support requirements for different cavern height-to-width ratios, in situ stress ratios, and extraction ratios.
The paper also describes a finite element heat transfer analysis of a water compensated CAES cavern during operation. The cyclic temperature response of the rock, induced by the cold-water/warm-air cycle in the cavern, and the corresponding thermoelastic stress perturbation, are discussed. The paper also presents results of a thermomechanical finite element failure analysis of a compensated CAES cavern system for jointed rock.
Storage of compressed air in underground caverns is being considered for use in energy applications in the U.S.A. Electric power plants that have sufficient redundant generating capacities during hours of off-peak power demand, can make use of this resource to accumulate energy in the form of compressed air. During hours of peak power demand, the compressed air can be used as a resource for additional power generation.
The compressed air energy storage (CAES) system considered in this study was a water compensated system; i.e., a constant pressure system in which the internal pressure of the cavern corresponds to the pressure exerted by a column of water extending from a surface reservoir down to the level of the CAES cavern. During the operational phase, the cavern surface will be exposed to cold-water/warm-air cycles which may give rise to structural stability problems. From the standpoint of both operations and economics, it is important to identify the cavern geometry which will minimize any potential for instability.
To assess pre-operational cavern stability, an elastic stress analysis was performed by use of the finite element method. The analysis considered both a single cavern and three caverns in parallel. 80th systems were modeled in plane strain. The horizontal extent of the single cavern model was 100 m, while those of the multi pl e caverns were 150 m and 200 m, depending on the extraction ratio used. Both models had a vertical extent of 400 m. The finite element mesh for the single and the multiple caverns is shown in Figures 1 and 2 respectively. Eight-noded isoparametric elements were used. Excavation was assumed to take place instantaneously. The room geometry is shown in Figure 3. The room width was kept constant and equal to 10 m.
The material properties used in the analyses are listed in Table 1, and are representative of the properties of granite.
(Table in full paper)
.The single cavern was analyzed for in situ stress ratios (sH/sv) ranging from 0.5 to 3.0, and cavern height-to-width ratios (H/W) varying from 0.5 to 3.0. For generalization, the results were normalized with respect to the in situ (pre-mining) vertical stress to obtain stress concentration factors.