Proposal and assessment of a novel combined heat and power system: Energy, exergy, environmental and economic analysis

This research aims at developing a small-scale novel cogeneration system to satisfy all of the electrical and heating demands of a typical residential complex. The proposed system is integrated of a gas turbine cycle (GTC) and a Kalina cycle (KC). A comprehensive parametric study is presented for evaluating the proposed system from energy, exergy, environmental and economic (4E) points of view. The system's governing equations are solved and validated through developing a high-accuracy computational code in Engineering Equation Solver (EES) software. The effects of some important design parameters (including compressor pressure ratio, base ammonia concentration, generator pressure and condenser pinch point temperature difference) are investigated on four appropriate criteria of energy efficiency (eta(th)), exergy efficiency (eta(ex)), levelized total emissions (LTE) and levelized total costs (LTC). Furthermore, two economic methods, payback period (PP) and net present value (NPV), are also investigated. The results show that, the simulation outputs at base design conditions are as eta(th) = 69.43%, eta(ex) = 37.90%, LTE = 87998 kg/kW, LTC = 8958 $/kW, PP = 3.34 years and NPV = 878679 $. The results of parametric analysis reveal that there is an optimal compressor pressure ratio which leads to maximum eta(th) and eta(ex) and minimum LTE and LTC. The combustion chamber of GTC has the maximum share in system's total exergy destruction (with 55.95% of total exergy destruction). Also, the entire KC has a low contribution of 3.396% in total exergy destruction.