Tubular Westinghouse

Siemens Westinghouse Power Corporation (SWPC) has three TSOFC systems employing tubular cell technology operating on user sites. All were produced in their Pittsburgh, Pennsylvania facility. The capacities of the systems are 220 kilowatts, 100 kilowatts, and 25 kilowatts. 

Siemens Westinghouse is planning a number of tests on power plants that are prototypes of future products. All systems employ the tubular SOFC concept and most are combined with gas turbines in a hybrid configuration. Capacities of these systems are 250 kilowatts atmospheric, 300 kilowatt class hybrid, and 1 megawatt class hybrid. They are to operate at various sites in the U.S., Canada, and Europe. Some of them are discussed below. 

Sealless Tubular Configuration The most developed solid oxide fuel cell is the Siemens Westinghouse tubular cell. This approach results in eliminating seal problems between adjacent cells. A schematic representation of the cross section of the present Siemens Westinghouse... 

United States Siemens-Westinghouse projects on SOFC include a 250 kWe tubular prototype at the Irvine University campus (California), that will be operated by Southern California Edison Company. It is pressurized to 3.5 bar and thus is expected to give 200 kWe a coupled microturbine gives an additional 50 kWe. The have operated a tubular SOFC at pressures up to 15 atm. 

Fig. 35. Arrangement of a single SOFC with tubular design (Westinghouse). From ref. [99]. 1988 IEEE.

Other manufacturers have proposed different solutions. The cell manufactured by Acumentrics is similar to the Siemens Westinghouse tubular SOFC the differences mainly reside in the fuel flowing inside the cell without inlet pipe and in the tube having open ends. Reforming is internal to the tube. The Acumentrics cell operates in the same temperature range than the previously mentioned SOFCs, but... 

Unlike molten carbonates, solid oxides use a hard ceramic electrolyte instead of a liquid. That means the fuel cell can be cast into a variety of useful shapes, such as tubes. With higher temperatures, sofcs may be able to cogenerate steam at temperatures as high as i,ooo°f. The Siemens Westinghouse Power Corporation has built the first advanced hybrid system, which combines a gas turbine with a tubular sofc. As of 2003, the 220 kW hybrid system has operated in California for more than 2,000 hours with a respectable 53 percent efficiency, comparable to current combined cycle gas turbines. The ultimate goal is an efficiency of 70 percent or more. 

Siemens Westinghouse is a major player, with its all-ceramic large-diameter tubular fuel cells. These are to be deployed with integrated gas turbines (Section 4.2). 

An immediate comparison with the Siemens Westinghouse tubular cell reveals that the Rolls-Royce arrangement is likely to be relatively compact. In Figure 4.4 cells, gas passages and dimensions are apparent. 

FIG. 27-68 Configuration of the tubular SOFC. (Courtesy of Westinghouse Electric Corpora-... 

Tubular Design of Westinghouse. Figure 15 shows the principles of the tubular design developed by Westinghouse. A single cell has the form of a long tube. The tube consists of a porous ceramic... 

Fig. 15 Tubular SOFC stack concept of Westinghouse. Advantages no sealing disadvantages ohmic loses, low power density.

The main advantage of the tubular design is the absence of sealing in the stack. Westinghouse built a 25 kW stack and tested single cells up to 40 000 hours. 

One effective method of cost reduction would be to reduce the operating temperature, and in this respect four types of stack have been developed. These include (i) a tubular design, with the tubes closed at one end (Westinghouse prototypes) or opened at both ends (ii) a planar technology (iii) a segmented series arrangement of individual cells (Rolls-Royce) and (iv) a monolith concept (Argonne National Laboratory). 

Figure 12.18 Example of SOFC geometries, (a) Tubular geometry ofthe Siemens-Westinghouse system (b) Planar structure ofthe Sulzer-Hexis SOFC (for details, see the text).

Fig. 7. Solid oxide fuel cell configurations. A Siemens-Westinghouse tubular cell B Tubular integrated interconnector concept. Similar interconnected systems exist in planar geometry C Planar SOFC designs, differing only in gas flow manifolding.

Figure 6.18 Schematics of (a) tubular and (b) planar SOFCs. The tubular design is that of Siemens Westinghouse.

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