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Capacitive Mixing for Extracting Concentration Gradient Energy

Time: Thu 2022-11-03 10.00

Location: F3, Lindstedtsvägen 26 & 28, Stockholm

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Language: English

Subject area: Chemical Engineering

Doctoral student: Zhi Zou , Kemiteknik

Opponent: Professor Chia-Hung Hou, National Taiwan University

Supervisor: Docent Longcheng Liu, Kemiteknik

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Capacitive mixing (CapMix) is a renewable method of extracting energy from the salinity gradient energy (SGE) between seawater and freshwater. The classical CapMix systems using solid electrodes generate electricity by periodically circulating seawater and freshwater into the CapMix system. The major limitation of classical CapMix is intermittent energy production. Therefore, the development of a new CapMix system to solve this limitation is highly desired. This thesis aims to develope an innovative CapMix system for continuous energy production. All the work is based on four papers and can be divided into the following parts.

In Chapter 1, a brief introduction to the SGE and CapMix is presented. 

In Chapter 2, a comparative study on the four classical CapMix systems, namely, capacitive energy extraction based on double layer expansion (CDLE), capacitive energy extraction based on the Donnan potential (CDP), and CDP with additional charging of constant voltage (CDP-CV) and constant current (CDP-CC)., is discussed. The influences of experimental parameters, e.g., applied voltage, applied current, accumulated charge, and the external load on the system performance, were systematically investigated and presented. A comprehensive comparison between these four classical CapMix systems is also given in this chapter.

Chapter 3 and Chapter 4 describe two novel CapMix systems based on flow electrode (F-CapMix) configuration which were developed to realize continuous energy production. The first one is a two-cell F-CapMix system, in which the flow electrode slurry was circulated between the two cells. The second is a one-cell F-CapMix system with cross chambers, in which there are two chambers between one pair of plates in parallel; the flow electrode slurry was circulated within the two graphite plates of the cell. The feasibility of these two F-CapMix systems was examined. The effect of the experimental parameters, e.g., activated carbon loading, carbon black amount, external resistance, feedwater flow rate, and flow electrode flow rate, on the system performance were systematically investigated and presented. 

In Chapter 5, a thorough study of the theoretical models related to the thermodynamic properties of the electric double layer at equilibrium, e.g., the Gouy-Chapman-Stern (GCS), Modified Poisson-Boltzmann-Stern (MPBS), modified Donnan (mD) and improved modified Donnan (i-mD) models is presented. The rationality and the physical interpretation of the parameters used in these models were detailed investigated and presented.