Energy and exergy analysis and multi-criteria optimization of an integrated city gate station with organic Rankine flash cycle and thermoelectric generator

The current study deals with the thermodynamic modeling, and multi-objective optimization of a pressure reduction station integrated with an organic Rankine flash cycle (ORFC) and a thermoelectric generator (TEG) waste heat recovery system (WHRS). Using the real operating data of a city gate station (CGS), a thermodynamic simulation was developed using EES (Engineering Equation Solver). The exergy analysis as a rigorous method was applied to find the exergy destructive components of the integrated system. Computations indicate that the exergy efficiencies of the indirect water bath heater (IWBH), ORFC condenser and TEG modules are 1.41%, 30.45%, and 16.34%, respectively, which are the lowest asset values among all components. Five main decision variables were defined as objective functions by the parametric study of the integrated system. Results of multi-objective optimization offer a set of non-dominant optimization solutions. A criterion for optimum state selection is carried out with the definition of an ideal point on the Pareto diagram, where point B is picked as a favorable system state. The scattered distribution of decision variables at points (offered by the Pareto solution) represents that (m)over dot(NG) and TNG-2 tend to be at the lower bound of their allowable range in all optimum states. Moreover, a comparison between the non-optimal and optimal integrated system reveals that the total exergy destruction rate through the system decreases 337.62 kW, and the thermal efficiency increases 8.57% in the optimal state.