Design and parametric optimization of an organic rankine cycle powered by solar energy

This study presents the simulation and performance analysis of a regenerative and superheated Organic Rankine Cycle (ORC). To this scope, anew simulation model has been developed. The model is based on zero-dimensional energy and mass balances for all the components of the system. Shell and tube heat expanders with single shell and double tube pass have been chosen. Pump and expander have been considered only form a thermodynamic point of view, with constant compressor and expansion efficiency. The simulations havebeen carried out in order to find different optimization criteria to use as preliminary design tools,especially for the organic fluid choice and the heat exchanger design. Firstly, the ORC performances have been evaluated for different organic medium, varying the temperature of the heat source. The global efficiency of the plant, the net electric power generation and the volumetric expansion ratio has been considered as evaluation parameters. The simulation results show that two hydrocarbons demonstrate good performance for low, medium and high heat source, namely Isobutene, n-Butene; R245fa can add to them for the exploitation of heat source up to 170°C. Additional simulations have been carried out to discover an optimization criterion for the heat exchanger design. The plant performances have been first evaluated varying one by one the following parameters: tube length, tube number and shell diameter. Then a global optimization was also performed using the Golden Search technique. The total cost of the plant has been considered as objective functions. With respect to the objective function, higher the boiling heat transfer area higher the electric power generation and the economical benefit. The optimal configuration, compared to the initial one, shows an increase of incomes and mechanical power equal to 60.1 and 48.2% respectively, against a decrease of global efficiency equal to 10.9%