• Tunnel and Underground Space
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• v.25 no.6
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• pp.568-576
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• 2015

In this study, scenarios based on the leakage of highly compressed air and fire occurrence turned out to be high risks in an operation stage of CAES facility were constructed and estimated. By combining Bernoulli equation with momentum equation, an expression to calculate an impact force of a jet flow of compressed air was derived. An impact force was found to be proportional to the square of diameter of fracture and the pressure of compressed air. Four types of fire scenarios were composed to evaluate an effects that seasonal change and location of fire source have on the spread behavior of smoke. Smoke from the fire ignited in the vicinity of CAES opening descended more quickly below the limit line of breathing than one from the fire occurred 10 m away from CAES opening, which is expected to occur due to a propagation of wave front of smoke. It was shown that a rate of smoke spread of the winter fire is faster than one of the summer fire and smoke from the winter fire spreads farther than one of the summer fire, which are dependent on the direction of air flow into access opening. Evacuation simulation indicated that the required safe evacuation time(RSET) of the summer and winter fires are 262, 670 s each.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.241-259
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• 2013

A packed bed thermal energy storage (TES) consisting of solid storage medium of rock or concrete through which the heat transfer fluid is circulated is considered as an attractive alternative for high temperature sensible heat storage, because of the economical viability and chemical stability of storage medium and the simplicity of operation. This study introduces the technologies of packed bed thermal energy storage, and presents a numerical model to analyze the thermal energy balance and the performance efficiency of the storage system. In this model, one dimensional transient heat transfer problem in the storage tank is solved using finite difference method, and temperature distribution in a storage tank and thermal energy loss from the tank wall can be calculated during the repeated thermal charging and discharging modes. In this study, a high temperature thermal energy storage connected with AA-CAES (advanced adiabatic compressed air energy storage) was modeled and analyzed for the temperature and the energy balance in the storage tank. Rock cavern type TES and above-ground type TES were both simulated and their results were compared in terms of the discharging efficiency and heat loss ratio.

• Tunnel and Underground Space
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• v.24 no.4
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• pp.289-296
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• 2014

A simple analytical approach for stability assessment of underground storage caverns against ground uplift of overburden rock above the rock caverns for high pressurized fluid such as compressed air energy storage (CAES) and compressed natural gas (CNG) was developed. In the developed approach, we assumed that failure plane of the overburden is straight upward to ground surface, and factor of safety can be calculated from a limit equilibrium analysis in terms of this cylindrical shape failure model. The frictional resisting force on the failure plane was estimated by Hoek-Brown strength criterion which replaces with Mohr-Coulomb criterion such that both intact rock strength and rock mass conditions can be considered in the current approach. We carried out a parametric sensitivity analysis of strength parameters under various rock mass conditions and demonstrated that the factor of safety againt ground uplift was more sensitive to Mohr-Coulomb strength criterion rather than Hoek-Brown criterion.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.67-80
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• 2014

Long-term stability and delayed failure of granite were evaluated through the laboratory test based on Wilkins method and Brazilian disc test (BDT) which yields tensile strength, mode I fracture toughness and subcritical crack growth parameters. Then, the long-term strength of granite was estimated by using analytical models and long-term stability of compressed air-energy storage (CAES) pilot cavern pressurized up to 5 ~ 6 MPa was evaluated using numerical code, FRACOD with the determined subcritical crack growth parameters. The results of test and analyses showed that the subcritical crack growth index, n was determined as 29.39 and the inner pressure of 5 ~ 6 MPa had an insignificant effect on the long-term stability of pilot cavern. It was also found that the measurement and analysis of acoustic emission events can describe the accumulation of damage due to subcritical crack growth quantitatively. That is, AE monitoring can provide the current status of rock under loading if we make an identical installation condition in the field with that of the laboratory test.