Energy recovery through natural gas turboexpander and solar collectors: Modelling and thermoeconomic optimization

This paper presents a novel dynamic simulation model for the analysis of a hybrid turboexpander systemcoupled with innovative high-vacuum solar thermal collectors. The model is developed in MatLab and itis able to dynamically calculate the energy, exergy, environmental, and economic performances of theinvestigated system, by taking into account the hourlyfluctuation of thermodynamic and economicparameters (e.g. electricity cost, natural gas temperature, andflow rates, etc.). In addition, a computer-based Design of Experiment (DoE) approach was implemented for achieving the optimal design of theproposed system.A suitable case study is presented in order to show the capabilities of the developed simulation tool.Conventional and non-conventional decompression systems located in the weather zone of Messina(South-Italy) are investigated with the aim of assessing the optimal system configuration. By means ofthe computer-based DoE analysis, the optimal values of several design parameters (such as the numberof solar thermal collectors, the volume of the hot water storage tank, and the size of the water looppump) are calculated. Numerical results show significant primary energy savings (1.36 TWh/year) andavoided carbon dioxide emissions (348 tCO2/year). From the economic point of view, a feasible simplepay-back period of 4.51 years is achieved. The destroyed exergy of the system components are calculated,obtaining the highest value for the turbo-expander, equal to 12.0 TWh/year.