Evaluation of the Thermo-Osmotic Energy Conversion (TOEC) Process for Harvesting Low-Grade Heat Energy
Creators: Moradi, Kazem
Publisher: name: University of Alberta Library
Year: 2024

<p>The growing global demand for energy, coupled with the need for sustainable and efficient energy solutions, has driven the exploration of new energy sources. Low-grade heat, widely available but challenging to convert into usable forms of energy (such as electricity), is a focal point for addressing this energy dilemma. Thermo-osmotic energy conversion (TOEC) has emerged as a promising technology that harnesses electrical energy from low-grade heat sources. This process relies on a hydrophobic membrane to facilitate the transfer of water vapor molecules from a moderately hot aqueous solution to a colder water stream, creating hydraulic pressure that can be harnessed for electricity generation through a hydro-turbine. <br>
This thesis comprises three comprehensive chapters, each contributing to the understanding and advancement of TOEC technology. The first chapter underscores the significance of harvesting low-grade waste heat for energy conversion, emphasizing the pivotal role of membrane technology in renewable energy solutions. It delves into the challenges and opportunities inherent in the TOEC process, emphasizing the necessity for advancements in utilizing low-grade heat for sustainable energy solutions in the 21st century. <br>
The second chapter delves into the development of a comprehensive model for simulating heat and mass transfer within the TOEC process. The innovative application of the ε-NTU method and a detailed examination of various input variables expand the analytical toolkit available for understanding TOEC systems. The chapter presents a theoretical evaluation of the TOEC process based on mass and heat transfer phenomena, validated with experimental data. Our results indicate that employing membranes with smaller pore sizes, low thickness and high porosity, feed temperature, and flowrates can significantly enhance energy efficiency and power density. Specifically, we demonstrate that the utilization of hydrophobic membranes with nanometer-sized pores, coupled with hydraulic pressures ranging from 6.2 bar to 11.8 bar, enables us to achieve power densities exceeding 5 W/m2, given a 20 °C heat sink and a heat source temperature above 65 °C. Furthermore, we have determined that an applied hydraulic pressure of 9.4 bar yields the maximum energy efficiency value of 0.016%. The model offers insights into optimizing the TOEC process, providing pathways for practical applications. <br>
The third chapter introduces a comprehensive life-cycle assessment of membrane synthesis for the TOEC process, addressing a crucial aspect of TOEC technology: the selection of membrane materials. Polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are commonly used materials. This study presents the first-ever comprehensive life cycle assessment (LCA) of PTFE and PVDF membranes, covering both lab-scale synthesis and large-scale production. The assessment evaluates their environmental impact and cumulative energy demand (CED). In the small-scale assessment, key chemical contributors to the CED and environmental impacts of both membranes were identified. In the large-scale analysis, we aimed to assess PTFE and PVDF membranes for electricity generation. The results demonstrate that the PVDF membrane exhibits higher CED than the PTFE membrane for all energy sources except non-renewable biomass. Furthermore, PVDF membrane tends to exert a greater environmental footprint in most impact categories, apart from global warming and ozone depletion. The results provide crucial insights into the environmental implications of membrane materials, aiding in the selection of materials for TOEC applications and advancing sustainable energy generation. <br>
This thesis not only consolidates the understanding of TOEC technology but also paves the way for continued advancements in the pursuit of efficient and environmentally conscious energy generation, marking a notable step towards a sustainable energy future.</p>