Design of organic Rankine cycles using a non-conventional optimization approach

J. G. Andreasen, Ulrik Larsen, F. Haglind

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Abstract

The organic Rankine cycle is a suitable technology for utilizing low grade heat for electricity production. Compared to the traditional steam Rankine cycle, the organic Rankine cycle is beneficial, since it enables the choice of a working fluid which performs better than steam at low heat input temperatures and at lowpower outputs. Selecting the process layout of the organic Rankine cycle and the working fluid are two key design decisions which are critical for the thermodynamic and economic performance of the cycle. The prevailing approach used in the design and optimization of organic Rankine cycles is to model the heatexchangers by assuming a fixed minimum temperature difference. The objective of this work is to assess the applicability of this conventional optimization approach and a non-conventional optimization approach. In thenon-conventional optimization approach a total UA-value (the product of the overall heat transfer coefficient and the heat transfer area) is assigned to the cycle, while the distribution of this total UA-value to each of the heat exchangers is optimized. Optimizations are carried out for three different marine engine waste heatsources at temperatures ranging from 90 °C to 285 °C. The results suggest that the conventional optimization approach is not suitable for estimating the performance potential when the temperature profiles in the heat exchangers are closely matched. This is exemplified for the fluid MDM where the temperature profile of preheating aligns with the heat source fluid and for the zeotropic mixture R32/R134a where the temperature profile of condensation aligns with the cooling water. Furthermore, the conventional optimization approach shows weaknesses in evaluating the feasibility of using a recuperator, when the expander outlet temperature is high. In these cases the non-conventional optimization approach is the more suited methodology for designing organic Rankine cycles.
Original languageEnglish
Title of host publicationProceedings of ECOS 2015 : 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems
Number of pages12
Publication date2015
Publication statusPublished - 2015
Event28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems - Palais Beaumont, Pau, France
Duration: 30 Jun 20153 Jul 2015
http://ecos2015.sciencesconf.org/

Conference

Conference28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems
LocationPalais Beaumont
CountryFrance
CityPau
Period30/06/201503/07/2015
Internet address

Keywords

  • Waste Heat Recovery
  • Zeotropic Mixture
  • Working Fluid
  • Organic Rankine Cycle
  • Marine Diesel Engine

Cite this

Andreasen, J. G., Larsen, U., & Haglind, F. (2015). Design of organic Rankine cycles using a non-conventional optimization approach. In Proceedings of ECOS 2015: 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems