Thermodynamic analysis of different modes of a multigeneration SOFC-CCHP system with freshwater production and LNG cold energy utilization

A multigeneration system is proposed to address the high temperature exhaust emissions of solid oxide fuel cells and the increasing demand for power, fresh water, cooling, and heating utilities. Thermodynamic assessment of the hybrid solid oxide fuel cell system integrating gas turbine, organic Rankine cycle (ORC) and humidification dehumidification (HDH) desalination system with liquified natural gas cold energy utilization is conducted. SOFC being the primary mover, the influence of key parameters such as cell operating temperature and pressure on overall system output performance is studied. In addition to the conventional cascade heat recovery mode, a parallel configuration of the system is also designed and analyzed for varying load demand. This design provides flexibility in operation. Under design conditions the net power generated, heating load, cooling load and fresh water produced by the system are 2390 kW, 584 kW, 58 kW and 209 kg/hr, respectively. The results show that the system net energy, exergy and electrical efficiencies are 85.65%, 63.29% and 64.51%. The major exergy destruction sources are the air preheater, afterburner and water preheater contributing to 28.3%, 16.5% and 15.8% of the total destruction. The exergy destruction of the SOFC subsystem is highest in both series and parallel designs amounting to about 888 kW. In parallel mode, the exergy destruction rate of ORC decreases from 15% to 10% while that of heating and desalination subsystem increase by 2% each. The parallel configuration is flexible in terms of output power, heating load and produced fresh water that have a range of 2303-2470 kW, 258-784 kW and 189-2493 kg/hr, respectively.