Investigation of a Dilute Flow Particle Reactor for Coupling Thermochemical Energy Storage to Supercritical Carbon Dioxide Brayton Cycles
Open Access
- Author:
- Siefering, Bryan
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 16, 2024
- Committee Members:
- Alexander Rattner, Major Field Member
Nicholas Meisel, Outside Unit & Field Member
Stephen Lynch, Major Field Member
Brian Fronk, Chair & Dissertation Advisor
Robert Kunz, Professor in Charge/Director of Graduate Studies - Keywords:
- particle heat exchanger
thermochemical energy storage
sCO2 Brayton Cycle
particle to sCO2 - Abstract:
- Particle based energy storage technologies show promise to link the temporal mismatch between energy demand and energy availability in renewable resources such as solar thermal. The objective of this thesis is determining the feasibility of recovering energy from dilute streams of particles that store sensible and chemical energy, referred to as thermochemical energy storage (TCES). TCES materials such as non-stoichiometric perovskite oxides can be used for multi-day energy storage needs because of their increased energy storage density and duration compared to inert systems that do not utilize chemical energy storage. The TCES materials are charged and discharged in a two-step cyclic process. During periods of high renewable energy availability, particles are heated, reduced and stored in a high energy density state. During discharging, the particles are re-oxidized and the chemical and sensible energy of the particles is recovered and transferred into a working fluid to drive a heat engine such as a recompression supercritical carbon dioxide (sCO2) Brayton cycle. The device that performs this task is referred to as an Energy Recovery Reactor (ERR), and the development of this component based on theoretical and physical considerations is the specific focus of this thesis. Within the ERR, reduced TCES particles re-oxidize in a counterflow air stream at temperatures >900°C and near atmospheric pressure, using the O2 in the air as a reactant. Reduced order numerical models developed in this study analyze the heat transfer and re-oxidation performance of the particle stream based on moving equilibrium reaction conditions at varying temperatures and partial pressures of O2. Within the model, a particle numbering up approach is used to evaluate the individual heat transfer of a single particle with its surrounding using well established heat transfer correlations. Within the ERR, the particles flow in a dilute flow regime where the solid volume fraction is ~1%, enabling high view factors and effective particle-to-heat exchanger wall radiation. From these models, two prototype ERR devices were designed, fabricated, and tested at various conditions with inert and reactive particles and pressurized air and sCO2 as the working fluids. The tradeoff between the heat transfer performance and the hydrodynamics of a dilute flow particle stream with counterflow air must be balanced which leads to a design with surface area enhancements. The first prototype, a shell and tube design described in Phase 1 of this work, was tested using ¬pressurized air as the heat transfer fluid and inert particles but did not effectively transfer heat from the particle domain into the working fluid due to a thermal bottleneck caused by high thermal resistances in the heat exchanger core containing the working fluid. A second prototype, with a counterflow tube-in-tube design increased the heat transfer effectiveness from the dilute particle flow to the working fluid through by 272% by balancing the thermal resistance between the particles and the working fluid in the design of the heat exchanger. Experimental results are compared with the reduced order model and show predictive capabilities with MAPE of under 20%. The model also predicts the behavior of the ERR prototypes when tested with reactive particles at design conditions, showing that for equal heat duties, reactive particles streams require flow rates 35.8% less than inert particle streams, highlighting the increased energy storage density of reactive particle media used in TCES system compared to inert particle media used in more conventional TES systems. The tools and methods described in this thesis can be used to guide the design of future dilute particle-to-sCO2 heat exchangers to increase the technology readiness level of particle based thermochemical energy storage.