A syngas fed SOFC cogeneration system using a downdraft gasifier is modeled and optimized from the
viewpoints of thermodynamics and thermoeconomics. A multi-objective optimization method based on
genetic algorithm in the form of two different scenarios is carried out. In scenario I (exergoeconomic) the
total exergy gained (TEGCHP ) and total product unit cost (cp) of the system are considered as two
objective functions, while in scenario II (exergoenviroment) and normalized CO2 emission (ε) are presumed
as the two objectives. In both scenarios, optimization process is performed with the aim of
maximizing the total exergy gained and minimizing the second objective function (in scenario I and in
scenario II). The optimization results demonstrates that minimization of the total product unit cost of
system as the only criterion leads to the higher values of normalized CO2 emission and lower values of
the system exergy efficiency. In addition, it is revealed that, at the optimal conditions, despite the lower
amounts of stack inlet temperature and current density for scenario II, the net electrical power obtained
by scenario I is quite higher.