Exergo-economic analysis and optimization of a combined solar collector with steam and Organic Rankine Cycle using particle swarm optimization (PSO) algorithm
Mehran Bahari, Abolfazl Ahmadi, Reza Dashti
Abstract
With the diminution of fossil fuel sources and the substantial importance of CO2 and other greenhouse gasses emission, the usage of enhanced thermal power plants coupled with renewable energies, such as solar, becomes more vital and promising. This paper proposes a novel configuration of the power generation system, featuring a solar collector to supply the heat for a two-stage steam turbine with inter heating and an Organic Rankine cycle as bottoming cycle of the steam turbine. The proposed system has been simulated and optimized using the particle swarm optimization algorithm. A heat storage system with NaNO3 and KNO3 in 3:2 ratios is used to store the extra heat in daylight to extend the operation at nighttime. For achieving the best working conditions for the proposed hybrid system, we employed a multi-objective optimization to maximizing the exergy efficiency while minimizing the levelized cost of electricity production. The simulation was performed using the Engineering Equation Solver (EES), and MATLAB software which is used for receiving the simulation results from EES and optimizing the key design parameters of the system using the PSO algorithm to select the best design variables. The optimization showed that at the optimum point, the exergy efficiency of the system and the levelized cost of electricity production reach to be 63.89% and 0.1529 USD/kWh, respectively. Results also showed that in the proposed system, the solar collector is the most important source of exergy destruction, in which more than 59% of the total destructed exergy happens in it. Sensitivity analysis also revealed that decreasing the turbine's inlet temperature will increase the production cost of electricity due to lower efficiency. Also, any changes (deviation from design point) in the back pressure of the low-pressure turbine will decrease the efficiency; while the production cost of electricity increases if this back pressure increases and vice versa.