A Numerical Procedure for the Preliminary Design of ORC Power Plants with Positive Displacement Expanders
CHALLENGE - Power plants using a high molecular fluid to perform a Rankine cycle are named ORC (Organic Rankine Cycle) power plants. In the present investigation, an automated procedure is proposed for the efficient design of a solar ORC power plant.
SOLUTION - The methodology was implemented in MATLAB in the modeFRONTIER optimization environment, and applied to a small size solar power plant using scroll expander. Goals of the study are maximization of net power, overall expander efficiency, and the minimization of organic fluid flow rate. A multi-objective genetic algorithm is used to select design parameters of the plant (evaporator pressure, overheating, thermal recovering, mass flow rate, etc.). Optimization was based on local radiating solar energy distribution on the local site in Lecce, Italy during 2007. The sizing procedure was applied to two values of the radiant thermal power (10 and 50kW) obtaining the optimum configuration for each power as well as a compromise solution that allows to operate the plant with both values of solar power using the same working fluid and the same volumetric expander.
BENEFITS - MATLAB and modeFRONTIER were coupled in the design of a solar ORC power plant, with the goal of finding optimum parameters. In the case of 10kW, fluid R123 guarantees higher expander efficiencies with the same flow rate while R245fa is better at 50kW. The expander optimized for 50kW presents a larger displacement and a BVR slightly lower compared to the case with 10kW. At 10kW, the system reaches the overall efficiency of about 30% while only 18% is found in the case of 50kW