SPOUTED BED ELECTRODES (SBE) FOR DIRECT UTILIZATION OF CARBON IN FUEL CELLS
This Phase I project was focused on an investigation of spouted bed particulate electrodes for the direct utilization of solid carbon in fuel cells. This approach involves the use of a circulating carbon particle/molten carbonate slurry in the cell that provides a few critical functions: it (1) fuels the cell continuously with entrained carbon particles; (2) brings particles to the anode surfaces hydrodynamically; (3) removes ash from the anode surfaces and the cell hydrodynamically; (4) provides a facile means of cell temperature control due to its large thermal capacitance; (5) provides for electrolyte maintenance and control in the electrode separator(s); and (6) can (potentially) improve carbon conversion rates by ''pre-activating'' carbon particle surfaces via formation of intermediate oxygen surface complexes in the bulk molten carbonate. The approach of this scoping project was twofold: (1) adaptation and application of a CFD code, originally developed to simulate particle circulation in spouted bed electrolytic reactors, to carbon particle circulation in DCFC systems; and (2) experimental investigation of the hydrodynamics of carbon slurry circulation in DCFC systems using simulated slurry mixtures. The CFD model results demonstrated that slurry recirculation can be used to hydrodynamically feed carbon particles to anode surfaces. Variations of internal configurations were investigated in order to explore effects on contacting. It was shown that good contacting with inclined surfaces could be achieved even when the particles are of the same density as the molten carbonate. The use of CO{sub 2} product gas from the fuel cell as a ''lift-gas'' to circulate the slurry was also investigated with the model. The results showed that this is an effective method of slurry circulation; it entrains carbon particles more effectively in the draft duct and produces a somewhat slower recirculation rate, and thus higher residence times on anode surfaces, and can be controlled completely via pressure balance. Experimental investigations in a rectangular spouted vessel hydrodynamics apparatus (SVHA) showed that hydrodynamics can be used to control the circulation, residence time, and distribution of carbon within the spouted bed, as well as provide good particle contact with anode surfaces. This was shown to be a function of viscosity, carbon loading, and particle size, as well as relative densities. Higher viscosities and smaller particle sizes favor more efficient particle entrainment in the draft duct, and particle recirculation. Both the computational and experimental results are consistent with each another and exhibit the same general qualitative behavior. Based upon this work, a design of a prototype SBE/DCFC cell was developed and is presented.
- Research Organization:
- Brown University (US)
- Sponsoring Organization:
- (US)
- DOE Contract Number:
- FG26-03NT41802
- OSTI ID:
- 841009
- Resource Relation:
- Other Information: PBD: 1 Dec 2004
- Country of Publication:
- United States
- Language:
- English
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