Cold side thermal energy storage system for improved operation of air cooled power plants

Abstract

Air cooled power plants experience significant performance fluctuations as plant cooling capacity reduces due to higher daytime temperature than nighttime temperature. The purpose of this thesis is to simulate the detailed operation of a cold side thermal energy storage system in order to evaluate its potential. An organic Rankine cycle geothermal power station is used as an example application. Detailed sizing and operation considerations are discussed. Several representative case studies compare the performance of candidate configurations. Operation of the selected configuration is then simulated for a full year and a proposed integration of the system with existing plant hardware is laid out. A correlation between weather trends and production is outlined. Finally an economic cost/benefit analysis performed to determine the payback period for implementing the proposed system. The cold side TES system is shown to shift substantial power generation capability from nighttime to daytime when electrical demand is highest, especially during hot summer months. For example, daily energy production is shown to increase by up to 18% under particularly favorable conditions. This redistribution of the power generation curve is accomplished with less than a 5% reduction in overall annual energy production in Mega-Watt hours. The system is shown to be more effective at shifting power generation capacity during warmer months than cooler months. The reduced day to night temperature fluctuation during cooler months results in a reduced thermal storage benefit under similar parasitic loads. The economic benefits of this system are dependent upon the on-peak vs off-peak electricity prices. Economic analysis using 2011 transient price data from the U.S. Midwest Region results in a small increase in annual income. The increased income from the proposed cold side TES system is found to be insufficient to outweigh the required capital investment at current electricity prices.