Comprehensive techno-economic and environmental sensitivity analysis and multi-objective optimization of a novel heat and power system for natural gas city gate stations

In the present study, a novel combined heat and power system is proposed to use in natural gas city gate stations. The proposed cogeneration system is used for power generation and satisfying heating requirements of the natural gas preheating in city gate stations. The system is composed of a regenerative gas turbine cycle, a heat exchanger and a Kalina cycle integrated with a city gate station heater. A comprehensive sensitivity analysis and single- and multi-objective optimizations are applied to investigate the system performance. The analysis is based on energetic, exergetic, environmental and economic standpoints which includes all important effective parameters (compressor presser ratio r_Com, gas turbine inlet temperature T_GT, ammonia base concentration X_NH3 , condenser pinch point temperature difference ΔT_PP,Con, ambient temperature T_amb and inlet NG pressure P_NG,in). Also, in addition to the energetic and exergetic efficiencies, a new performance criterion is defined as the system's annual costs to incomes ratio (this new function covers economic and environmental criteria simultaneously). The outputs of sensitivity analysis reveal that, r_Com affects significantly on all of the three performance criteria; also, T_amb and P_NG,in has the most impact on energetic efficiency. The exergetic analysis at the base system conditions shows that the combustion chamber has the maximum contribution in total exergy destruction with a share of 54.96%. This share is reduced by 3.65% in multi-objective optimization mode. Also, comparing the outputs of the base system and the multi-objective optimization mode for the proposed cogeneration system represents 30.72%, 3.48% and 10.55% improvement in energetic efficiency, exergetic efficiency and system's annual costs to incomes ratio, respectively.