Exploring the concept of compressed air energy storage (CAES) in lined rock caverns at shallow depth: A modeling study of air tightness and energy balance

Abstract

This paper presents a numerical modeling study of coupled thermodynamic, multiphase fluid flow and heat transport associated with underground compressed air energy storage (CAES) in lined rock caverns. Specifically, we explored the concept of using concrete lined caverns at a relatively shallow depth for which constructing and operational costs may be reduced if air tightness and stability can be assured. Our analysis showed that the key parameter to assure long-term air tightness in such a system was the permeability of both the concrete lining and the surrounding rock. The analysis also indicated that a concrete lining with a permeability of less than 1×10 -18 m 2 would result in an acceptable air leakage rate of less than 1%, with the operational pressure range between 5 and 8 MPa at a depth of 100 m. It was further noted that capillary retention properties and the initial liquid saturation of the lining were very important. Indeed, air leakage could be effectively prevented when the air-entry pressure of the concrete lining is higher than the operational air pressure and when the lining is kept moist at a relatively high liquid saturation. Our subsequent energy-balance analysis demonstrated that the energy loss for a daily compression and decompression cycle is governed by the air-pressure loss, as well as heat loss by conduction to the concrete liner and surrounding rock. For a sufficiently tight system, i.e., for a concrete permeability off less than 1×10 -18 m 2 , heat loss by heat conduction tends to become proportionally more important. However, the energy loss by heat conduction can be minimized by keeping the air-injection temperature of compressed air closer to the ambient temperature of the underground storage cavern. In such a case, almost all the heat loss during compression is gained back during subsequent decompression. Finally, our numerical simulation study showed that CAES in shallow rock caverns is feasible from a leakage and energy efficiency viewpoint. Our numerical approach and energy analysis will next be applied in designing and evaluating the performance of a planned full-scale pilot test of the proposed underground CAES concept.

Characterizing Excavation Damaged Zone and Stability of Pressurized Lined Rock Caverns for Underground Compressed Air Energy Storage

“…As indicated in Table 3, the permeability of the concrete lining was 7.0 × 10 -20 m 2 , while the permeability of the host rock and EDZ was estimated 1.5 × 10 -19 and 2.5 × 10 -17 m 2 , respectively. Kim et al (2012) showed that a concrete permeability as low as 1.0 × 10 -20 m 2 was sufficient to keep air leakage insignificant, regardless of the permeability of the EDZ and surrounding rock mass. We therefore focus our investigation on the tangential stress evolution in the concrete lining, which could potentially lead to fracturing and thus more significant leakage.…”

“…Model geometry and grid were similar to that used in Kim et al (2012) and Rutqvist et al, (2012), except for EDZ thickness and properties, which have since been updated based on investigation at the pilot test cavern ( Figure 9). It is a 2D model domain, corresponding to a 1 m thick vertical cross-section through the storage cavern, with a radius of 2.5 m, and with thicknesses for the concrete lining and EDZ of 0.5 and 0.6 m, respectively.…”

“…For this modeling effort, we used TOUGH-FLAC coupled analysis (Rutqvist, 2011), following a modeling approach and setup recently used by Kim et al (2012) and Rutqvist et al (2012) on an equivalent CAES system. The principles of TOUGH-FLAC coupled analysis are shown in Figure 8.…”

“…Recently, Kim et al (2012), showed that CAES in shallow lined rock caverns is feasible from a leakage and energy-efficiency viewpoint, provided that mechanical stability can be achieved.…”

A Novel Hybrid-Fuel Storage System of Compressed Air Energy for China

“…Salgi et al [19] analyzed the energy-balance effects of adding CAES to an energy-system. Kim et al [20] conducted a numerical modeling study of coupled thermodynamic, multiphase fluid flow and heat transport associated with CAES. The estimated GHG emission rate of a CAES plant combined with wind power is one-fourth that of cycle plants combined with natural gas (NG) and approximately one-tenth of that of pulverized coal plants [21].…”