Multi-objective optimization of an indirectly integrated solid oxide fuel cell-gas turbine cogeneration system Leyla Khani, Ali Saberi Mehr, Mortaza Yari * , S.M.S. Mahmoudi Faculty of Mechanical Engineering, University of Tabriz, Tabriz, Iran article info Article history: Received 11 June 2016 Received in revised form 3 September 2016 Accepted 6 September 2016 Available online xxx Keywords: SOFC Exergoeconomic Multi-objective optimization Gas turbine Cogeneration abstract Multi-objective optimization results using genetic algorithm are reported for a cogenera- tion system based on indirect integration of solid oxide fuel cell and gas turbine. In this case, solid oxide fuel cell and gas turbine operate with different working fluids and at different pressures and only heat is transferred between these two systems. A heat re- covery unit is placed to provide hot water from solid oxide fuel cell-gas turbine exiting stream. Multi-objective optimization is applied to determine the optimal design condition in which exergy efficiency is maximum and sum of the unit costs of products is minimum. The result demonstrates that final optimal design has an exergy efficiency of 55.11% and sum of the unit costs of products of 170.5 $/GJ, which is a trade-off between thermody- namic and exergoeconomic single-objective optimization cases. It is also revealed that heat recovery unit, combustion chamber and afterburner have the most contribution to the system's exergy destruction. Furthermore, 44.3% of input exergy is destructed in the sys- tem components. The overall system exergoeconomic factor is 47.31%. Therefore, it is expected that an increase in the components' capital costs may improve the exer- goeconomic performance of the system. Moreover, it is shown that fuel cell current density and gas turbine inlet air flow rate have the highest effect on the trade-off between the defined objective functions. © 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Introduction The tremendous growth in the world's population and global economic energy demand leads to overconsumption of fossil fuel resources. Besides, present energy production, trans- portation and distribution systems are not satisfyingly effi- cient. This waste of energy puts more pressure on fossil fuel extraction. Hence, it is expected that from 2012 to 2040 the increase in the world energy consumption will be around 48%. Moreover, it is predicted that although consumption of non- fossil fuels grows faster than fossil fuels, fossil fuel re- sources will still provide 78% of energy supply in 2040 [1]. In addition, fuels are burnt directly which is an inefficient utili- zation way and has limited efficiency. These issues can also in turn intensify environmental pollution [2], global warming and climate change [3]. On the other hand, fossil fuel sources are limited so the security of global energy supply seems to become a major problem in near future. This suggests a need for urgent actions to find new energy sources and also * Corresponding author. E-mail address: myari@tabrizu.ac.ir (M. Yari). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (2016) 1 e19 http://dx.doi.org/10.1016/j.ijhydene.2016.09.023 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Khani L, et al., Multi-objective optimization of an indirectly integrated solid oxide fuel cell-gas turbine cogeneration system, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.09.023