Abstract:
With growing population and rising pollution, the demand of energy and utilities has skyrocketed and the world has been compelled to shift towards clean and green alternatives to fossil fuels. The chemical energy of fuel is converted into electrical energy by fuel cells with very low pollutant emissions and thus they are a suitable alternative. High temperature fuel cells exhibit good efficiencies but have high temperature waste gas emissions. The energy from this waste gas can be recovered through various techniques and then employed to productive processes. Therefore, a waste heat recovery multigeneration system is proposed in this work to address the high temperature exhaust emissions of solid oxide fuel cells and the growing demand of power, fresh water, cooling and heating utilities. The proposed system is modelled thermodynamically and mathematically on Aspen Plus and EES software packages and then validated for accuracy. Thermodynamic assessment of the hybrid solid oxide fuel cell, gas turbine integrated system with organic Rankine cycle (ORC) as bottoming loop coupled with liquified natural gas cold energy utilization and humidification dehumidification (HDH) desalination system is conducted. SOFC being the primary mover, a parametric analysis is conducted by varying cell operating temperature and pressure. In addition to the conventional cascade heat recovery mode, a parallel configuration of the system is also designed and analyzed for varying load demand thus providing flexibility in operation. The results revealed that the net power generated, heating load, cooling load and fresh water produced by the system were 2390 kW, 584 kW, 58 kW and 209 kg/hr, respectively. The system achieves net energy, exergy and electrical efficiencies of 85.65%, 63.29% and 64.51% having a total cost of 73 $/h. SOFC subsystem exhibits the highest exergy destruction in both series and parallel designs amounting to about 888 kW. The parallel configuration is flexible in terms of output power, heating load and produced fresh water that have a production range of 2303-2470 kW, 258-784 kW and 189-2493 kg/hr, respectively. In conclusion, this study showed that multi generation systems employing waste heat recovery improve the overall system efficiencies and can be operated to obtain electricity, heating, cooling, fresh water and to utilize LNG cold energy.
