Multi-objective optimization of preheating system of natural gas pressure reduction station with turbo-expander through the application of waste heat recovery system

The preheating system is regarded as an integral part of a natural-gas pressure reduction station (NGPRS) when a turbo-expander is substituted with regulators. In this paper, two configurations are compared for optimal designing preheating system used in NGPRS with the turbo-expander system. The first case uses water for a hot fluid that is warmed in the gas-fired heater (GFH), and the second is a Waste Heat Recovery (WHR) configuration. Multi-objective optimization and multi-criteria decision-making (MCDM) methods are implemented to identify the optimal design of mentioned preheating systems and to acquire the ability for the designer to select the optimal solution readily. The total cost and modified exergy efficiency (MEE) are selected as the objective functions. Moreover, sensitivity analyses of design parameters and their effects on objective functions are carried out for both configurations. Results show that the optimal designs suggested by MCDM methods in the WHR configuration provide a substantial reduction not only in total cost up to 98% but also in exergy destruction up to 78%. In addition, MEE increases by as much as 5 percent compared with the conventional configuration. Based on the aforementioned points, the WHR configuration is advantageous in both economic and exergy principles.