Stack Temperature Estimation in System Environment by Utilizing the Design of Experiments Methodology

Reproduced by the permission of ECS – The Electrochemical Society leakages to fuel system will retain the anode in oxidized state. Moreover, some performance loss was measured when the stack was heated to 400 C before fuel supply was started. Therefore, it is recommended that the supply of hydrogen-rich reducing gas is started already below 350 C, or as low temperature as possible, to prevent oxidation of the Ni-cermet. During the system experiments it was noted that sufficient temperatures for pre-reformer light-off were not possible by relying only on the heat recuperated from the fuel systemheat exchanger. Thus electrically or otherwise assisted heating of the pre-reformer (i) to 400 C enables reformer light-off without the short-term hydrogen pulse, thus simplifying the system layout even further and (ii) above 500 C shifts the hydrogen production from the stack to pre-reformer, which increases the amount of hydrogen when the reforming activity of the stack is still low and thus enhances the quality of the reducing gas. Additionally, if the pre-reformer would be mainly responsible of the hydrogen production, the stack temperature can potentially be lower than 300 C when the fuel is introduced to the system. This would significantly decrease the risk of oxidizing the Ni-cermet anode. The results show that a heat-up from room temperature to the operating temperature of SOFC stack is possible without premixed gas and without significant loss of stack performance. This finding allows reducing the premixed gas storage capacity in a SOFC system and thus the physical size of the system as well capital and servicing costs.