Thermal Energy Storage in Adsorbent Beds

• Main Author: Ugur, Burcu
• Other Authors: Tezel, Handan F.
• Language: en
• Published: Université d'Ottawa / University of Ottawa 2013
• Subjects: Adsorption; Energy Storage; Long term thermal energy storage
• Online Access: http://hdl.handle.net/10393/24362; http://dx.doi.org/10.20381/ruor-6697

Total produced energy in the world is mostly consumed as thermal energy which is used for space or water heating. Currently, more than 85% of total thermal energy consumption is supplied from fossil fuels. This high consumption rate increases the depletion risk of fossil fuels as well as causing a tremendous release of hazardous gases such as carbon dioxide, carbon monoxide, sulfur oxides, nitrogen oxides and particulate matter that effects both environment and human health. Those drawbacks force humankind to search for new technologies, like renewables, to reduce fossil fuel dependency on thermal energy production. Thermal energy storage in adsorbent beds is one of the resulting technologies. Adsorption is an exothermic process in which a fluid (adsorbate) diffuses into the pores of a porous solid material (adsorbent) and trapped into the crystal lattice. In this system, exothermic adsorption of water vapor from air is carried out by using hybrid adsorbent of activated alumina and zeolite. In previous studies, through literature review, this adsorbent was selected to be the most efficient adsorbent for this process due to its high water adsorption capacity, high heat of adsorption, and stability [Dicaire and Tezel, 2011]. In this study, previous studies started on this project was confirmed and pursued by trying to increase the efficiency of the process and confirm the feasibility and applicability of this system in larger scales. In this thesis, various zeolite and activated alumina hybrid adsorbents with varying zeolite compositions were screened to find the most efficient adsorbent for thermal energy storage process that gives the highest energy density. Then, existing small column was replaced with a new one, which is 16 times bigger in volume, in order to confirm the feasibility of this process at larger scales. Applicability of on-off heat release in adsorption process was also investigated by conducting several on-off experiments at different on-off time periods. Moreover, exothermic adsorption process was modeled by doing mass and energy balances in the column, water accumulation balance in the pellets, and energy balance in the column wall. Validity of this model was confirmed by comparing it with experimental results at different column volumes, and at different volumetric flow rates. Finally, an overall plant design, capital cost and thermal energy price estimations were done for adsorption thermal energy storage plants for different storage capacities and payback periods.