Thermodynamic and exergoeconomic assessments of a new solid oxide fuel cell-gas turbine cogeneration system

• A new indirect integration of solid oxide fuel cell and gas turbine is proposed.
• Thermodynamic and exergoeconomic analyses are performed.
• The system efficiency is maximized at some specified conditions.
• The increase in the gas turbine inlet temperature is not in favor of the system performance.
• Lower compressor ratios lead to a reduced value of the total product unit cost.

A new indirect integration of a solid oxide fuel cell, a gas turbine and a domestic water heater is proposed and analyzed in detail. Using a proper working fluid for each subsystem, interacting thermally with one another, the proposed system generates power and hot water simultaneously. Thermodynamic and thermoeconomic principles are used to determine the products costs and the order of significance of system components from the viewpoint of exergy destruction. Parametric studies are carried out to reveal the influence on the system performance of several decisive parameters. The results show that the exergy efficiency is maximized at a compressor pressure ratio of 9.49 and a current density of 1642 A m−2. The increase in pressure ratio however, is not in favor of system’s economic performance. In addition, the sum of unit costs of the products is minimized at a current density of 1523 A m−2. Moreover, it is shown that an increase in the gas turbine inlet temperature or steam to carbon ratio deteriorates both the thermodynamic and economic performances of the system. Furthermore, the results indicate that a higher fuel utilization factor improves the thermodynamic and economic behavior of the system. Finally, it is revealed that an increase in the gas turbine air flow rate enhances the energy efficiency and worsens the sum of unit costs of the products. The exergy efficiency however, is maximized at a gas turbine air flow rate of 15.94 mol s−1.