Soft-sensor based operation of a solid oxide fuel cell system with anode exhaust gas recirculation

A solid oxide fuel cell (SOFC) converts chemical energy of a fuel gas directly into electrical energy representing an auspicious technology for efficient electricity generation. A SOFC system with anode exhaust gas recirculation (AEGR) enables net electrical DC-efficiency of up to 65%. For efficient and durable operation, it is of crucial importance to monitor relevant characteristic parameters and keep them within safe and durable operating limits. The oxygen-to-carbon-ratio and the fuel utilization are such characteristic parameters and have to be kept within stack-and reformer-specific limits. Their control is not straightforward due to the enhanced complexity of a SOFC system with AEGR and dependence on fluctuating natural gas (NG) quality. In this paper, a soft-sensor concept is presented to determine the H/ C-ratio of NG as measure of its quality with high accuracy. It is composed of an energy balance by means of enthalpy flow rates and Gaussian process regression models for estimation of unknown amount of inert gas species xN(2), xCO(2) in NG as well as the enthalpy error as a corrector term of the ideal energy balance.