Analysis of operation of a micro-cogenerator with two solid oxide fuel cells stacks for maintaining neutral water balance

The stationary power systems with fuel cells offer a great advantage for highly efficient production of electricity and heat. Among the existing fuel cell technologies, the solid oxide fuel cells (SOFC) are considered as a suitable technology for micro- and small-scale power units with output in the range from sub-kW to 50 kW. The hydrocarbonaceous fuel supplied to the system requires pre-treatment in order to convert it into hydrogen-rich gases directed to the anodic compartments of the fuel cell stack. The steam reforming is now considered as a leading technology in stationary applications. For prevention of carbon formation and deposition in the anodic compartments, the sufficient steam to carbon ratio (S/C ratio) has to be maintained in the fuel processor. Depending on the working condition, the SOFC-based system can become water neutral and the necessity to supply make-up water for the steam reforming can be eliminated. In the current study, two stacks connected in series were analysed to define the required parameters at the level of the stacks and at the level of system to allow operation in water neutral conditions. The results of the study are presented and the conditions for achieving water neutrality are discussed. The corresponding current densities should be in range 0.17-0.30 A/cm2 and 0.06-0.18 A/cm2 in the first and second stack, respectively.