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Energy Conversion/Systems

Auto Generative Capacitive Mixing for Power Conversion of Sea and River Water by the Use of Membranes

[+] Author and Article Information
O. Burheim

Wetsus, Agora 1,
P. O. Box 1113, The Netherlands;
Department of Chemistry,
Norwegian University of Science and
Technology (NTNU),
N-7491 Trondheim, Norway
e-mail: burheim@ntnu.no

B. B. Sales

Subdepartment of Environmental Technology,
Wageningen University,
Bornse Weilanden 9,
6708 WG Wgeningen, The Netherlands;
Wetsus, Agora 1,
P. O. Box 1113, The Netherlands
e-mail: Bruno.bastos@wetsus.nl

O. Schaetzle

Wetsus, Agora 1,
P. O. Box 1113, The Netherlands
e-mail: olivier.schaetzle@wetsus.nl

F. Liu

Subdepartment of Environmental Technology,
Wageningen University,
Bornse Weilanden 9,
6708 WG Wgeningen, The Netherlands;
Wetsus, Agora 1,
P. O. Box 1113, The Netherlands
e-mail: Fei.Liu@wetsus.nl

H. V. M. Hamelers

Wetsus, Agora 1,
P. O. Box 1113, The Netherlands
e-mail: bert.hamelers@wetsus.nl

Both PRO and RED received renewed research attention both in the late 70 s and the late 00 s after a strong depletion of oil in the market [11].

Studies with algae and NaCl solutions performed with respect to RO and forward osmosis (FO) demonstrated that several fouling mechanisms are almost reversible by regularly flushing sea equivalent solutions through the fresh water compartment.

Recall how we defined the maximum exergy potential in Eq. (1). Despite that the potential free energy is not dissipated we cannot utilize it, hence the exergy output is lowered.

These concentrations corresponds to 0.017 M and 0.51 M, respectively.

This is the case when applying CNaCl of 10 mM instead of 17 mM.

The law states that the maximum power is drawn when the external and internal cell resistors of Fig. 2 are the same.

1Authors share equivalent contributions to this manuscript.

Contributed by the Advanced Energy Systems Division of ASME for publication in the Journal of Energy Resources Technology. Manuscript received November 24, 2011; final manuscript received August 17, 2012; published online December 12, 2012. Assoc. Editor: Gunnar Tamm.

J. Energy Resour. Technol 135(1), 011601 (Dec 12, 2012) (7 pages) Paper No: JERT-11-1153; doi: 10.1115/1.4007717 History: Received November 24, 2011; Revised August 17, 2012

The chemical potential (free energy) of mixing two aqueous solutions can be extracted via an auto generative capacitive mixing (AGCM) cell using anionic and cationic exchange membranes together with porous carbon electrodes. Alternately, feeding sea and river water through the unit allows for the system to spontaneously deliver charge and discharge the capacitive electrodes so that dc electric work is supplied. Having a stack of eight cells coupled in parallel demonstrated the viability of this technology. An average power density of 0.055 W m−2 was obtained during the peak of the different cycles, though reasonable optimization suggests an expectation of 0.26 W m−2 at 6.2 A m−2. It was found that 83 ± 8% of the theoretical driving potential was obtained during the operating process. By studying the polarization curves during charging and discharging cycles, it was found that optimizing the feed fluid flow is currently among the most beneficial paths to make AGCM a viable salinity difference power source. Another parallel route for increasing the efficiency is lowering the internal ohmic resistances of the cell by design modifications.

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References

Figures

Grahic Jump Location
Fig. 1

The AGCM cell, consisting (f.t.) of a CPEC, a CEM (green line in online version), a water flow compartment, an AEM (red line in online version), and one more CPEC. The two electrodes are connected to an external load (R).

Grahic Jump Location
Fig. 2

Circuit analogy for charging/discharging the RC-membrane circuit. Replacing the solutions of the flow compartment converts the chemical potential energy into electric energy by the electrochemical transport processes of the Donnan potentials along the membrane-flow compartment interfaces. Simultaneously, the electrode capacitor double layers are charged/discharged and the flow of electric current in the circuit is dissipated in the resistors.

Grahic Jump Location
Fig. 3

A stack of eight cells coupled in parallel. The sketch depicts the stack cut open. The solution feed and exit are indicated by arrows (blue sections in the online color version). AEM and CEM are indicated by (in the online version green and red) lines, respectively. The black and white patterns illustrate the capacitor materials. On the left side of the stack the coupling to the load, R, is illustrated.

Grahic Jump Location
Fig. 4

Cell potentials and currents of experiments with 11 and 0.5 Ω loads, respectively, (upper) and the peak power densities and potential of the cell as a function of the current density for a constant flow rate (75 mL min−1) and for all the different loads applied

Grahic Jump Location
Fig. 5

Cell potentials of the cell as a function of time for different flow rates (25, 50, 75 mL min−1). The available work is continuously dissipated over a 500 mΩ resistor.

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