Modelling of organic Rankine cycle power systems in off-design conditions: An experimentally-validated comparative study

Abstract

Because of environmental issues and the depletion of fossil fuels, the world energy sector is undergoing many changes toward increased sustainability. Among the many fields of research and development, power generation from low-grade heat sources is gaining interest and the organic Rankine cycle (ORC) is seen as one of the most promising technologies for such applications. In this paper, it is proposed to perform an experimentally-validated comparison of different modelling methods for the off-design simulation of ORC-based power systems. To this end, three types of modelling paradigms (namely a constantefficiency method, a polynomial-based method and a semi-empirical method) are compared both in terms of their fitting and extrapolation capabilities. Postprocessed measurements gathered on two experimental ORC facilities are used as reference for the models calibration and evaluation. The study is first applied at a component level (i.e. each component is analysed individually) and then extended to the characterization of the entire organic Rankine cycle power systems. Benefits and limitations of each modelling method are discussed. The results show that semi-empirical models are the most reliable for simulating the * Corresponding author Email addresses: rdickes@ulg.ac.be (Rémi Dickes), olivier.dumont@ulg.ac.be (Olivier Dumont), remi.daccord@exoes.com (Rémi Daccord), squoilin@ulg.ac.be (Sylvain Quoilin), vincent.lemort@ulg.ac.be (Vincent Lemort)

Experimental investigation and optimal performance assessment of four volumetric expanders (scroll, screw, piston and roots) tested in a small-scale organic Rankine cycle system

“…By accounting for the most influent physical phenomena in the expansion process with a limited number of parameters, this model demonstrates a good ability to extrapolate the expander performance out of the calibration dataset [25,31] while maintaining low computational times. One advantage of this approach is its common framework to simulate different types of technologies (scroll, screw, piston, vane, etc.)…”

Effects of the Working Fluid Charge in Organic Rankine Cycle Power Systems: Numerical and Experimental Analyses

“…Such a model receives as inputs the working fluid type, the inlet temperature and mass flow rate of the source and sink fluids, the rotational speeds of the pump and expander, and the condenser exit subcooling or the total working fluid charge in the system. A truly mechanistic model is charge-sensitive, meaning the total refrigerant charge is known, but the condenser exit subcooling is determined by the ORC operation [5]. In fact, if the condenser exit subcooling is fixed within the simulation, an assumption is made regarding the system state, which is not known in a real system.…”

“…However, in the vast majority of stationary applications (e.g., solar thermal power, geothermal, waste heat recovery, and combined heat and power), the heat source and heat sink conditions are subjected to fluctuations and the ORC systems often operate at part-load or off-design conditions. To this end, numerical and experimental studies on off-design ORC performance have been published in the scientific literature, as outlined by Dickes et al [5]. Similar to vapor compression systems, ORC performance is sensitive to working fluid charge and an incorrect charge level affects the system performance, especially under part-load conditions.…”

Design and experimental research on the combined flash-binary geothermal power generation system driven by low-medium temperature geothermal system

“…The ORC have been investigated on its working fluid screening [12,13], performance optimization [14,15] and dynamic simulation [16,17] in the past several decades. Meanwhile, medium-large-scale ORC prototypes and engineering cases have been carried out [18][19][20][21]. However, the expensive design and manufacture costs of expander imposes the largest restriction on commercial application of the small-scale ORC system, investment is much larger than 1500 $ per kW.…”