Plant design and risk assessment of syngas molten carbonate fuel cells

This paper aims at a preliminary assessment of accident risk connected to a fuel cells plant fed with syngas, for electric energy production. The syngas is produced by heavy refinery residues gasification, within a downstream oil plant; subsequently, it is added with pressurized water vapour and cleaned-up, so as to obtain the gaseous mixture to feed the molten carbonate fuel cell unit (MCFC). The proposed approach was developed according to a multi-step procedure, based on the following partially superimposed phases: process development and plant design; primary risk analysis; plant control system design and secondary risk analysis. In particular, dangerous compounds and critical units were identified, together with related critical events. Among these events, the most conservative accident scenario has been analysed, taking into account its causes, consequences and probability of occurrence. Based on the obtained results, a new plant control system has been proposed, according to the multiple layers of protections philosophy. The approach allows operating the plant according to the project intents during normal operations and to shut it down promptly in case of dangerous deviations. The presented methodology can represent a useful tool in fuel cell risk evaluation, so as to identify and analyse possible hazardous deviations, establishing as well effective corrective actions for risk prevention and mitigation.