Keywords: combined cycle cogeneration, energy analysis, exergy analysis, speco, thermodynamic analysis, thermoeconomic analysis, steam demand variations, exergy costing, cost balances, cost rates, performance evaluation, cycle configuration, condensing steam turbines
Thermodynamic and thermoeconomic comparison of combined cycle cogeneration systems
In this paper, several configurations of combined cycle cogeneration systems are investigated by energy, exergy and thermoeconomic analyses. In each of these configurations, varying steam demand is considered rather than fixed steam demand. Among the different approaches for thermoeconomic analysis in the literature, the specific exergy costing method is applied. Since the systems have more than one product (process steam and electrical power), systems are divided into several sub-systems and cost balances are applied together with the auxiliary equations. Hence, the cost rate of each product is calculated. Comparison of the configurations, in terms of performance assessment parameters and costs per unit of exergy, are also given in this study. In conclusion, it is found that combined cycle cogeneration systems with extraction condensing steam turbines are thermodynamically and thermoeconomically more advantageous when compared to those with back-pressure steam turbines.