Structural concrete for thermal energy storage in power generation facilities: Modular demonstration and reinforcement creep testing

Abstract This dissertation presents an examination of thermal performance of concrete used for thermal energy storage (TES) applications. Novel TES modules are developed to evaluate the thermal charge and discharge of concrete as solid media of thermal energy storage system. The (TES) systems are essence for providing continuous energy in solar power systems and for reducing daily ramping of energy production in power plants that use fossil fuels. The performance of a lab-scale concrete thermal energy storage (TES) module with a 2-kWh thermal capacity is evaluated at temperatures up to 400℃ over a 6-month period. The TES module uses concrete with enhanced thermal and mechanical properties as the solid storage media and a thermosiphon heat exchanger. The charging and discharging cycles are examined to assess the thermal performance of the concrete and thermosiphon. No significant degeneration of the solid storage media or separation at interfaces between thermosiphon, concrete and steel jacket are observed after 2250 hours of charge and discharge cycles. Large scale thermal energy storge module is tested with a finned thermosiphon consists of a vertically oriented sealed pipe partially filled with HTF. The thermosiphon consists of two main regions: the evaporator which contains the liquid HTF and the condenser where the evaporated HTF condenses. The TES module uses enhanced concrete as the solid storage media. The charging and discharging cycles are examined to assess the thermal performance of the concrete and thermosiphon. The pipe systems rely on turbulent flow of HTF within the pipes to transfer the thermal energy into the concrete elements. The different in temperature between inlet and outlet is demonstrate that the energy transferred to fins of thermosiphon in both phases (charging and discharge). The study examines the performance of these high strength reinforcements with respect to conventional strength reinforcement at elevated temperatures typical of fire events and thermal energy storage application, with a focus on the development of a high temperature constitutive creep model. The high strength rebars are ideal for thermal energy storge systems (TES) to mitigate the thermal stresses and compensate the outer steel jacket. This work presents an experimental examination of the creep strain rate of ASTM A615 Grade 420 (60), 520 (75), and 690 (100) at various stress levels and temperature demands. The creep results are used in a numerical study to examine the performance of a reinforced concrete component subject to elevated thermal demands. Data from experimental study indicates that the creep rate for all rebar grades under a given temperature, increases with increasing stress level, likewise, creep rate for all rebar grades under given stress level, increase with increasing temperature. Experimental work presents to examine the mechanical properties of 7-wire starnds7-wire ASTM-A416-12a at steady state transient creep tests were conducted in the temperature range 250-450℃ and various percent of ultimate stress. Evaluate the performance of cable reinforcement under high temperature is expand the knowledge of reinforcing materials that may use in thermal storage energy system. Numerical prediction of temperature distribution in cross section exposed to actual temperature curve to verify the time that cable needs to reach up the target temperature. Data from this test are utilized to determine the response of 7-wire strand to high temperature creep as a function of time till rupture by taking account the stress rate effect. The outcomes of this dissertation indicate that the reinforced concrete is ideal solid media material for the thermal energy storage systems based on the stable thermal performance concrete and reinforcements under high level temperature.