G. Anaya, K. Armijo, A. Overacker, A. Blumenthal, D. Madden
Sandia National Laboratories,
United States
Keywords: ice thermal storage, packed bed, concentrated solar powe, pumped thermal energy, sCO2
Summary:
Pumped Thermal Energy Storage (PTES) in general terms has been utilized as a complementary system for different energy producing systems as it utilizes a type of pump to move “waste” heat that is dumped into a cold reservoir into a hot reservoir to be re-implemented on the energy production cycle. Concentrated Solar Power (CSP) in simplified terms utilizes concentrated solar energy as a heat source, heat that is deposited into a Heat Transfer Media (HTM) playing the role of the hot reservoir for a Brayton or Carnot cycle. This paper will talk about how a hybrid CSP, and PTES system can be integrated utilizing three main energy storing components, a Brayton Cycle, and utilizing CO2 as the main HTM between the components. This paper will analyze the expected efficiency of the system as well as the work performed for the development of two of the three main energy storing components of the system. An axial packed bed with basalt rocks as the storing media, and an Ice Thermal Storage, intended to take advantage of the latent heat of the water during phase changes between solid and liquid phase. Work here presented for the design of the packed bed component includes the process followed to determine the required volume to achieve desired energy storing and thermocline, along with a study of how the geometry of the packed bed affects the expected pressure losses and the thermocline. The packed bed is set to reach maximum temperatures of 130 °C, set by the limitations for the current configuration of the thermal pump. The present work will also include the analysis done towards the design of the ice thermal storage component, going from calculating physical requirements for storing the desired energy in latent heat form. This work will also present a mathematical model developed to ensure the CO2 going through this component achieves the necessary thermophysical properties to meet the expected performance of the system. As per the design of this system the ice thermal storage component is to be kept at 0 °C as it will be a water-ice mixture. Allowing for CO2 to condense as it passes through with a pressure of 3.67MPa, as well as to allow for boiling of liquid CO2 at a 3.24MPa pressure. An analysis on these phase changes is undergoing to better understand the system behavior at the different operational modes to improve on the system design.