Design and optimization of hydrogen production by solid oxide electrolyzer with marine engine waste heat recovery and ORC cycle

Hydrogen is considered as a promising alternative to future energy systems. Water or steam electrolysis at elevated temperature consumes less electricity due to the highly efficient utilization of thermal energy. In this paper, a solid oxide electrolyzer cell (SOEC) is integrated with a marine diesel engine to use both electricity and waste heat for hydrogen production. An Organic Rankine Cycle (ORC) is applied to produce electricity from SOEC production streams. A comprehensive thermodynamic analysis model of SOEC, ORC and marine diesel engine waste heat recovery is conducted. The results indicated that the system could produce hydrogen at a rate of 0.431 kg/s and power output of 32386.45 kW with a power reduction of 60%. An efficiency of 104.41%, 12.12% and 53.56% could be achieved for the electrolyzer cell, ORC and integration system, respectively. The waste heat available efficiency could reach only 44.13% under the design conditions. To study the impact of some key parameters on the system performance, sensitivity analysis of current density, H2O inlet flow rate and total SOEC area were performed. It was found that an optimal current density and H2O flow rate can be obtained. Moreover, higher total cell area benefits the integration system thermodynamically.