Tubular-type SOFCs

Fliwatashi, K., Murakami, H., Shiono, M., Saito, T., A. Abe, T., and Ueno, A. (2007) Development Status of Tubular type SOFC in TOTO in Proceedings of the Fuel Cell Seminar, Palm Springs, CA. 

Diagram showing how the tubular-type SOFC can be constructed with (almost)... 

A. Kawakami, S. Matsuoka, N. Watanabe, A. Ueno, T. Ishihara, N. Sakai, K. Yamaji, H. Yokokawa, Development of low-temperature micro tubular type SOFC. Proceedings of the 13th Symposium on Solid Oxide Fuel Cells in Japan, 54-57 (2004)... 

La, Ca)(Cr, M)Cr03 Good sinterability at lower temperature Lower conductivity at fuel side Adopted in tubular type SOFC stacks... 

In tubular type SOFC, the interconnects cover a part of the electrode substrate as thin films with thickness of several ten micrometers. Sakai et al. have found that calcium substituted... 

Similar problems are also encountered for cathodes and interconnects which are complex oxides of rare earths and transition metals. For the cathode supported tubular type SOFCs, the cost of lanthanum manganite cathode is very important because it is a large fraction of the total cell capacity. 

There are two types of SOFC planar type and tubular type. An SOFC operates at 800 °C or higher temperatures. Although it can operate with high power density due to its high temperature, the stability of the component materials should be checked for a longtime operation. 

Yoshida S, Kabata T, Nishiura M, Koga S, Tomida K, Miyamoto K, Teramoto Y, Matake N, Tsukuda H, Suemori S, Ando Y, Kobayashi Y (2011) Development of the SOFC-GT combined cycle system with tubular type cell stack. ECS Trans 35( 1) 105-111... 

Fig. 3a. Schematic view of SOFC cell design tubular type.

Although cathode-supported tubular SOFCs in large-scale stacks are the type of SOFC stack most widely commercialized, recent alternative tubular cell designs have been developed with anode-supported designs for smaller-power applications. Cells in these stacks have diameters on the order of several millimeters rather than centimeters,... 

For placing tubular SOFCs in the cathode matrix, a bonding paste was used, prepared by mixing the LSCF powder, the binder (cellulose), the dispersant (polymer of an amine system), and the solvent (diethylene glycol monobutyl ether). The paste was painted on the surface of the cathode matrices, followed by the placement of tubular cells and sintered at 1000 °C for 1 h in air. Two types of bundles were prepared a bundle with five >0.8 mm tubes and a bundle with three <)>2 mm tubes whose volumes are 0.2 and 0.33 cm, respectively. 

Two types (type A and B) of micro SOFC stacks were prepared as shown in Fig, 2 using those micro tubular SOFC bundles. The type A was constructed using four micro bundles with. 8 mm tubes, vertically connected in series after applying sealing layer and interconnects to each bundle. Fuel and air were applied using ceramic manifolds as shown in Fig. 2 (a). The type B consists of three bundles, sealing layers and interconnects, and fuel manifolds. The size of the stack A without fuel manifold is I x I x 0.8 cm ( 0.8 cm ) and the size of the stack B without fuel manifold is 1 x 3 cm with tlie thickness of 3.3 mm ( 1 cm ). 

Fabrication and characterization of tubular SOFC stacks designed for low temperature operation were shown. Two types of stacks were proposed and demonstrated using the micro tubular SOFC bundles the type A was a vertically assembled stack, four-story cube-type stack with the volume of about 0.8 cm The performance of the type A stack was shown to be 3.6 V OCV and 2 W maximum output power under 500 °C operating temperature. Another type of the stack was also fabricated, which consists of three bundles and fuel manifolds, where the air was applied only by natural convection. Open circuit voltages of the type B stack were shown to be 2.85 and 2.73 V at 450 and 500 C operating temperatures, with the maximum power outputs of 0.91 and 1.54 W. Overall, both types of stacks showed reasonably sufficient performance for application use. 

From the structure point of view, there are two types of structures of SOFC tubular and planar. Tubular SOFCs have shown some desirable characteristics over systems with planar SOFCs [4]. Tubular SOFCs can alleviate the sealing problem arose by CTE mismatch of planar SOFC therefore, they are robust for repeated cycling under rapid changes in electrical load and in cell operating temperatures. The large form factor tubular SOFC built by Siemens Westinghouse has successfully conducted long-term operation over 70,000 h. Small-scale tubular SOFCs could... 

Fig. 18.8 Impurities in anodes for four SOFC stacks with different materials and designs. Impurities were determined with SIMS on the 24 h operation and on the longer (about 5,000 h) operations, (a) High-temperature segment-in-series cell by MHI, (b) intermediate flatten tubular cell by Kyocera, (c) high temperature sealless tubular cells by TOTO, and (d) intermediate temperature disk-type planar cells by Mitsubishi Materials corp...

Suzuki T, Funahashi Y, Yamaguchi T, Fujishiro Y, Awano M (2008) Cube-type micro SOFC stacks using sub-millimeter tubular SOFCs. J Power Sources 183(2) 544-550... 

Any of these components can dominate the ohmic resistance, depending on the cell type. For example, in planar electrolyte-supported SOFC the ionic resistance usually dominates in tubular SOFC the electronic bulk resistance usually dominates, and in planar thin-electrolyte SOFC contact resistances often dominate. 

In this code, a 1-dimensional electrochemical element is defined, which represents a finite volume of active unit cell. This 1-D sub-model can be validated with appropriate single-cell data and established 1-D codes. This 1-D element is then used in FLUENT, a commercially available product, to carry out 3-D similations of realistic fuel cell geometries. One configuration studied was a single tubular solid oxide fuel cell (TSOFC) including a support tube on the cathode side of the cell. Six chemical species were tracked in the simulation H2, CO2, CO, O2, H2O, and N2. Fluid dynamics, heat transfer, electrochemistry, and the potential field in electrode and interconnect regions were all simulated. Voltage losses due to chemical kinetics, ohmic conduction, and diffusion were accounted for in the model. Because of a lack of accurate and detailed in situ characterization of the SOFC modeled, a direct validation of the model results was not possible. However, the results are consistent with input-output observations on experimental cells of this type. 

Although the Siemens Westinghouse design of tubular SOFC is by far the best-known and most developed, two other types of tubular SOFCs, shown in Figure 7-9 illustrate ways in which the cells are interconnected. Numerous other designs have been proposed, but are no longer pursued (14). 

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