Improving the efficiency of A-CAES systems by preconditioning discharge air stream

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Compressed Air Energy Storage: Types, systems and applications

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A-CASE performance, Cavern air quality, Compressed air energy storage

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This chapter explores the effects of variations in cavern air quality on the overall performance of adiabatic compressed air energy storage (A-CAES) systems. Components of A-CAES systems interact in dynamic ways and often have compounding effects. A small change in the state of one of the key process parameters can therefore propagate through and alter the status of the entire system. In case of a discharging A-CAES system, the key process parameters (mass flow rate, temperature, pressure, and humidity) of the inlet air stream will therefore significantly influence the performance of an A-CAES plant. However, these parameters—particularly temperature and relative humidity—are not generally controlled for an A-CAES facility. They are instead allowed to settle to natural values which depend on operational frequency, ambient conditions, and cavern design choices. It would however be possible to control these parameters, at the cost of the infrastructure (heaters, coolers, humidifiers, regulators, etc.). This chapter analyzes the effect of variations in these parameters on the performance of A-CAES systems by thermodynamic simulation of a 100 MW plant with three stages of expansion. For a fair comparison in between generated models, the atmospheric condition, the volume of the hot thermal store, and the efficiency of expanders were fixed for all cases. Simulations were performed for systems with cavern pressures between 4 and 8 MPa, where the ratios between hot water mass flow and air mass flow were between 0.65 and 0.85. The obtained result shows that the maximum reachable power and efficiency in the considered ranges are 117 MW and 80.3%, respectively. Also, the maximum and the minimum accessible energies are 482 and 324 MWh, respectively, with corresponding discharge durations of 4.5 and 3.4 h. The optimum performance of the system was observed when the ratio of hot water to air mass flow was 0.8. Moreover, this work revealed that every 25% increase in humidity percentage can increase the total expander power by about 0.1%. The output of this work can also be used for the management of the thermal systems according to the cavern air property.



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