Design and multi-criteria optimisation of a trigeneration district energy system based on gas turbine, Kalina, and ejector cycles: Exergoeconomic and exergoenvironmental evaluation

A novel trigeneration district energy system (TDES) is designed and evaluated from energy, exergy, exergoeconomic, and exergoenvironmental points-of-view. By recovering the wasted heat of a regenerative gas turbine cycle, a heat exchanger is utilized for heating applications, a Kalina cycle is run for generating some additional power, and an ejector refrigeration cycle is used for producing some cold. The problem is firstly modeled through developing a precise code in Engineering Equation Solver program and then optimal conditions are sought by coupling the outputs of modeling procedure with Artificial Neural Network, and Non-dominated Sorting Genetic Algorithm II approaches. Three new functions of integrated weighted efficiency, exergoeconomic criterion, and exergoenvironmental criterion are defined as the system's evaluation criteria. From a robust parametric study, it is demonstrated that the system's evaluation criteria have the highest and lowest sensitivity on the variation of pressure ratio of compressor and pinch-point temperature difference of heat exchanger 2, respectively. From the optimisation procedure, the optimum values of the system's primary energy ratio, exergetic efficiency, exergoeconomic criterion, and exergoenvironmental criterion are 76.9%, 30.8%, 58.4 $/GJ, and 42.7 kg/GJ, respectively. At these conditions, the capacity of the TDES is 1025.9 kW, 1642.3 kW, and 304.9 kW with the associated cost of production of 149.6 $/GJ, 7.8 $/GJ, and 60.1 $/GJ for power, heat, and cold, respectively.