On the effects of thermodynamic assumptions and thermoeconomic approaches for optimization and cost allocation in a gas turbine cogeneration system

Abstract

Thermoeconomics connects thermodynamics and economics, providing tools to solve problems in energy systems, both from the point of view of cost allocation, diagnosis and project optimization. A study of a gas turbine would take into account many characteristics: combustion process, change in the composition of the working fluid, irreversibility effects and so on. Considerable simplifications are often required, resulting in several thermodynamic models, which modify the results obtained in thermoeconomic optimization and in different thermoeconomic approaches for cost allocation. In the face of context, a study to verify the influence of thermodynamic models on the results obtained in thermoeconomic optimization and in the allocation of costs, it becomes promising and appreciable as it allows to analyze the difference in results, the reasonableness of simplifications and if it is worth using such a complex model. Thereby, this article compares four thermodynamic models in a cogeneration system: a standard air model, a standard cold air model, a CGAM model and a complete combustion model. The cogeneration system is optimized from the thermoeconomic point of view for each thermodynamic model. After the optimization process, five thermoeconomic approaches are used to allocate costs to the final products. The effects of these thermodynamic assumptions and the thermoeconomic approach on thermoeconomic optimization and cost allocation are presented and discussed. Of the computational effort to optimize the design problem, the complete combustion model is more efficient than the others models, since this model reaches an objective function value 5% lower than the CGAM problem. The analysis of the thermodynamic model variation for the same thermoeconomic method presents that the maximum variation of the unit cost values for useful heat and power is 4.3% and 5%, respectively. Similarly, the variation of the thermoeconomic model to the same thermodynamic model presents that the maximum variation of unit cost values for useful heat and power is 20% and 10%, respectively.