The organic Rankine cycle system, which uses different sources of renewable energy, has developed interest due to its favorable support towards greenhouse gas depletion. With this development, what arises as a primary concern to technologists is how to strike a right stability between energy provision and plant cost. Also, the use of multi-objective optimization approach in obtaining this has not been well studied.
Professor Alfredo Gimelli and Colleagues from University of Naples Federico II, Napoli in Italy, discussed the use of a multi-objective optimization process approach to address the organic Rankine cycle ORC while considering the electrical efficiency and overall heat exchangers area in view of cost. They made use of octamethyltrisiloxane MDM as an organic fluid. In their study the authors solved the multi-objective optimization problem of that of an organic Rankine cycle power plant of 1MW with a biomass heat source. The work is now published in peer-reviewed journal, Applied Thermal Engineering.
In the thermodynamic modeling, the cost of the heat exchanger area was a major determinant for that of the organic Rankine cycle system, and it was indirectly linked to the study of the economic potential of the plants.
The decision variables used in the multi-objective optimization approach include thermodynamic design parameters such as the minimum and maximum pressure of the thermodynamic cycle, regenerator efficiency, subcooling at the condenser outlet and superheating at the evaporator outlet.
Results from the multi-objective optimization process, with the use of the MOGA II algorithm when imputed to determine the Pareto optimal front between the two objectives of electric efficiency and plant costs shows a reasonable trade-off. An increase in overall efficiency, characterized high overall heat exchanger area. Likewise, high global electric efficiency resulted in high regenerator efficiency.
The Pareto optimal front solutions provided a range between 12.7 and 20.7KPa for the minimum and maximum pressure of the thermodynamic cycle. Pareto optimal front solutions also had an electric efficiency range between 14.1 and 18.9%, while that of the overall heat exchangers area ranges from 446 to 1097m2.
The proposed methodology in this study provided an avenue for technologists to select the preferred solution for the exact use by making use of decision variables needed for objective functions in order to have a desired balance between cost and electric efficiency.
Gimelli, A., Luongo, A., Muccillo, M. Efficiency and Cost Optimization of a Regenerative Organic Rankine Cycle Power Plant through the Multi-Objective Approach, Applied Thermal Engineering 114 (2017) 601–610.
DII – Department of Industrial Engineering, University of Naples Federico II, Via Claudio 21, 80125 Napoli, Italy.