Condensed phase thermochemical energy storage based on metal oxide/hydroxide reactions

Thermochemical energy storage (TCES), based on reversible chemical reactions offers insulation-free, high-energy density storage which can help reduce greenhouse gas emissions in industrial heating applications. In almost all instances, TCES systems are designed as (thermodynamically) open systems that exchange mass with their environment, requiring complex, bulky and expensive transfer equipment. Here, we propose and explore a TCES concept based on the hydration/dehydration reactions of CoO/Co(OH)2 that is designed to be closed to mass flows and remains in the condensed phase. When Co(OH)2 is heated in a sealed container in the presence of excess water, the saturation pressure of water controls the reaction equilibrium and drives it toward condensed phase products. At 250-300 oC, heat can be stored through hydrothermal dehydration with density ~500 MJ/m3. The reverse hydration reaction at 70-130 oC provides heat release with energetic efficiency ~60% and exergetic efficiency approaching 50%. We identify the hydration reaction as the key challenge to cycling due to a typical ceiling of ~40% conversion. Using materials characterization techniques, we show that the microstructure of the oxide has a possible role in limiting hydration and explore potential approaches to circumvent the limit. Through composition changes such as doping with MgO and by improving mass transfer through particle size reduction, we find hydration improvements up to ~70%. We discuss future directions in further reducing cycling losses. Complementary to these experiments, we report a finite element simulation of heat transfer coupled with chemical kinetics in a fixed-bed, honeycomb-cell TCES reactor. We choose the more established CaO/Ca(OH)2 chemistry to understand how the cell size affects power output. When choosing few-cm sized cells, power profiles can alternate between that of a thermal battery and a supercapacitor through changes to the convective heat transfer alone. This thesis identifies and explores the materials chemistry behind a novel closed system TCES and advances the potential adoption of TCES by providing quantitative modeling of a reactor based on established chemistry.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Dwivedi, Arpit Kumar

Contributors dc:contributor

• Sinha, Sanjiv
• Miljkovic, Nenad
• Cai, Lili
• Rajagopalan, Kishore

• Energy Storage
• Thermochemical Storage
• Thermal Energy Storage
• Room Temperature Storage
• Insulation Free Storage

Statement dc:rights

• Copyright 2022 Arpit Dwivedi

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/117571

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F117571