Direct internal reforming DIR

Fig. 2.1. Working principle of the Molten Carbonate Fuel Cell (MCFC) with direct internal reforming (DIR).

In this chapter, three applications of this model are demonstrated. The comparison of different reforming concepts reveals the advantages of direct internal reforming (DIR) in the anode channel of the fuel cell. Moreover, with the help of the proposed model, the benefit of fuel cell cascades can be demonstrated and they can be compared to single cells. Results indicate that a considerable power increase can be expected, but the additional hardware required might offset any benefit in the case of smaller systems. The third application demonstrates that anode gas recycle can be simulated with this model, but it also reveals its limitations, as temperature effects are not considered. 

Fig. 4 Schematic representation of (A) direct internal reforming (DIR) and (B) indirect internal reforming (HR) MCFC concepts.

In direct internal reforming (DIR) the reforming reaction is carried out on the fuel cell anode itself (or as close to it as possible) in this way hydrogen produced by reforming is immediately consumed by the electrochemical cell reaction allowing to shift the equilibrium of the reforming and WGS reactions to the right as product is consumed by the electrochemical reaction [13, 95, 133-135]. The DIR approach is best carried out at low pressures with catalyst inside the anode compartment close to the anode of the ceU. 

Reforming As discussed, since the MCFC produces waste heat and steam at the anode like the SOFC and can use CO as fuel, an excellent opportunity exists for internal reformation of the fuel gas. There are two types of internal reformation practiced, indirect internal reformation (IRR) and direct internal reformation (DIR). In IRR, the fuel gas is mixed with water vapor, heated inside the stack with waste heat, and reformed over a catalyst bed into a hydrogen-CO mixture. The reformed mixture then enters the active fuel cell area. In DIR, the fuel gas is reformed directly in the active area flow fields. Although the DIR approach is more compact and can theoretically be used to remove a significant portion of the waste heat from the stack, IRR allows the use of different catalysts specifically for reformation, prolonging system life [32]. 

In the direct internal reforming MCFC (DIR-MCFC) system, the direct reformation of fuel at the anode can give fuel saving of 20%, resulting in 12 /o improvement in fuel cell electrical efficiency. The schematic representation of the HR and DIR concepts is shown in Fig. 4. 

The conditions used in bioethanol reforming are similar to those existing in the anode compartment of MCFCs. It will therefore be possible to use bioethanol directly in direct internal reforming MCFCs (DIR-MCFCs) (see the review by Frasteri and Freni, 2007). 

Developers of internal reforming fuel cells have generally adopted one of two approaches, and these are usually referred to as direct (DIR) and indirect (HR) internal reforming. They are illustrated schematically in Figure 8.4. In some cases, a combination of both approaches has been taken. A thermodynamic analysis and comparison of the two approaches to internal reforming in the MCFC has been completed by Freni and Maggio... 

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