4E Analyses and Tri-objective Optimization of a Gas Turbine-Based Combined Heat and Power System

Abstract

In this paper, a combined heat and power (CHP) system is proposed that comprises a recuperative gas turbine (GT) cycle, a heat recovery steam generator (HRSG), and a recuperative-regenerative organic Rankine cycle (RR-ORC) for the cogeneration of process heat and power. The low-grade heat from the GT exhaust is utilized to operate the HRSG and the RR-ORC. The CHP system is modelled based on energy, exergy, economic and environmental (4E) analyses. The results showed that at the base condition, the GT cycle and RR-ORC provide a net power of 30 MW and 671.40 kW, respectively, while HRSG recovers 40.74 MW of thermal energy from the GT exhaust gas to produce 8.43 tonnes/h of saturated steam for process heat application. The thermal and exergy efficiency of the overall system are 86.81% and 53.38%, respectively, whereas the total product cost rate and the specific CO2 emission are 1569.6 $/h and 234.13 kg/MWh, respectively. Further, a Pareto optimal envelope-based selection algorithm-II (PESA-II) is applied for the tri-objective optimization of the CHP system considering the overall exergy efficiency, total product cost rate, and specific CO2 emission as the objective functions with five decision variables. The intent of this study is to maximize the first objective function and minimize the remaining two. Lastly, the multi-criteria decision analyses is performed by applying the technique for order preference by similarity to ideal solution (TOPSIS) to select the best optimal solution that gives an improvement of 11.12%, 5.73%, and 9.88%, respectively, over the base case condition.