Tubular stacked fuel cells

SOFC are produced with either tubular or planar stack configurations investments for planar design are a rough estimate, as no prototypes exist. Specific investments for PAFC are in the range 4000- 4500/kW (IEA, 2007). For further fuel-cell R D needs see IEA (2005). 

Ciano C., Cali M., Melhus O., Verda V., 2006. A model for the configuration design of a tubular Solid Oxide Fuel Cell Stack. ASME Paper IMECE2006-16141, Chicago, IL, November 5-10, 2006. 

Saito T., Abe T., Fujinaga K., Miyao M., Kuroishi M., Hiwatashi K., Ueno A. (2005) Development of tubular SOFC at TOTO. In Proceedings - Electrochemical Society, v PV 2005-07, Solid Oxide Fuel Cells IX Cells, Stacks, and Systems, Proceedings of the International Symposium, ECS, Electrochemical Society Inc., pp. 1039-1040. 

The interconnect normally links the anode of one cell to the cathode of the next. It must, of course, be an electronic conductor and also a gas barrier preventing the direct meeting of fuel and oxidant gases. Fig. 4.27 illustrates how the interconnection is achieved in the case of the so-called planar fuel cell stack. In the later discussion of the ceramics-based cells a tubular configuration is described, but the principles are the same. 

Fig. 4.32 (a) The arrangement of the electrodes in a tubular SOFC [13]. (b) Schematic of a stack of series/parallel fuel cells. The diagram should be viewed in conjunction with (a). 

The most common configuration is the block type fuel cell stack. Other configurations are tubular and planar (flat) stacks. 

Goal of a joint Dutch/Danish project is the installation and operation of a 100 kW SOFC power plant to be connected to the electricity grid in The Netherlands. Based on the Westinghouse tubular design, the stack consists of 1152 fuel cell tubes which have a lengdi of 1.5 m and a diameter of 2.2 cm. Testing of this SOFC unit was successfully done over 300 hours. It was put into operation at the end of 1997. The efficiency is expected to approach 47 % at 100 kW(e). If in addition the waste heat of 150 kW could be utilized in a gas turbine, the overall efficiency could be raised to 70 % [15]. 

Figure 9.14 (a) An expanded view of a stack of planar design solid-oxide fuel cells (SOFCs) (b) tubular design of an SOFC (c) a stack of tubular SOFCs... 

A 100-kW power plant was built by S-W in Westervoort (Netherlands) from tubular cells. The fuel cell stacks used in this plant contained four bundles of said type, combined in series to form a row, 12 rows then being placed in parallel. Between the rows, units for conversion of natural gas were installed. The plant also included units for desulfurization and pre-reforming of the natural gas. 

Lawlor V, et al. (2009) Review of the micro-tubular solid oxide fuel cell part I. Stack design issues and research activities. J Power Sources 193 387-399.doi 10.1016/j.jpowsour.2009.02.085... 

The above results were for SOFC buttrui cells, and more work is needed to demonstrate direct-methane utilization in stacks. One step towards this goal is simulation of stack operation. Such results indicate that in a tubular stack with a barrier layer over the first 30 % of the fuel-flow field, the anode-gas composition is maintained in the thermodynamically non-coking regime. Furthermore, the direct-methane feed case yielded overall stack performance nearly as good as the anode recycle case [33]. 

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