System layout anode

Figure 3.24. System layout for SOFC plant based on natural gas fuel (NG), with gas cleaning except for CO2 and with the possibility of combined power and heat output. "Anode" and "cathode" are obsolete names for the negative and positive electrodes. (From Fontell et al. (2004). Conceptual study of a 250 kW planar SOFC system for CHP application. /. Power Sources 131,49-56. Used by permission from Elsevier.)...

Figure 4.31 shows a simplified system layout for a liquid-fed DMFC system. In order to benefit from the high energy density of methanol, it is necessary to operate the DMFC system from a supply of pirre methanol. However, since water is required in the electrochemical reaction, and to suppress the formation of mixed potentials at the cathode, the anode should be fed with aqueous methanol. Therefore, a mixing imit for water and methanol needs to be present in the system. 

Figure 1-14 shows a simplified layout for an SOFC-based APU. The air for reformer operation and cathode requirements is compressed in a single compressor and then split between the unit operations. The external water supply shown in figure 1-14 will most likely not be needed the anode recycle stream provides water. Unreacted anode tail gas is recuperated in a tail gas burner. Additional energy is available in a SOFC system from enthalpy recovery from tail gas effluent streams that are typically 400-600°C. Current thinking is that reformers for transportation fuel based SOFC APUs will be of the exothermic type (i.e. partial oxidation or autothermal reforming), as no viable steam reformers are available for such fuels. 

Trials. In several cases it has proved to be useful to carry out a trial, that is a small part of a structure to which CP is applied in order to test various aspects of the proposed system(s) [59]. Usually a trial area is between 10 and 100 m. Various anode layouts or different anode systems can be tested. Monitoring probes and other control systems can be tested as well. Seasonal variations can be estabhshed. 

By analyzing the different layouts discussed above and using a payback time of 3 years, the allowable cost of the SOFC APU systems was calculated as function of electrical efficiency. It was found that a system employing an autothermal reformer (ATR) with an average efficiency would have an allowable price of 2,660 with the fuel price in Table 20.10. Operation without desulfurization is feasible even with conventional NiA SZ anodes because the penalty incurred in the form of extra stack area needed is relatively modest with ULSD. Other studies have arrived at similar results [48-52]. 

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