Integrated design of process and working fluids for organic rankine cycles

• Simultane Optimierung von Prozess und Arbeitsmittel für Organic Rankine Cycles

Lampe, Matthias; Bardow, André (Thesis advisor); Gross, Joachim (Thesis advisor)

1. Auflage. - Aachen : Wissenschaftsverlag Mainz GmbH (2015, 2016)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge zur Technischen Thermodynamik 7
Page(s)/Article-Nr.: XVIII , 122 Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2015

Abstract

In this thesis, the challenge of an integrated working fluid and process design is tackled. Methods are introduced allowing for the design of ORC and working fluids. As the problem of selecting a fluid for a process is not only relevant for the design of ORC systems, a generic problem formulation for the integrated fluid and process design is derived. Methods for solving the problem are presented and shortcomings in the existing methods are identified. Based on these findings, a method is presented allowing for the integrated design of fluids and processes. The integrated design exploits the underlying perturbed chain statistical associating fluid theory (PC-SAFT) equation of state in a so-called continuous-molecular targeting (CoMT). The PC-SAFT equation is further supplemented with methods to calculate the ideal gas heat capacity and the molar mass of working fluids. The integrated design method is applied to the design of a geothermal ORC system.The basic method for the integrated working fluid and process design is based on the selection of working fluids from a database of known PC-SAFT pure component parameters. However, the method is extended by computer-aided molecular design (CAMD) allowing for the systematic design of novel molecular structures of working fluids. As illustrative example, the geothermal system is revisited and the design of working fluids is performed for this example. Commonly, models of the process used for the working fluid selection are based on the assumption that the turbine efficiency is a constant parameter. To overcome this assumption, a preliminary design model of the turbine is presented enabling to consider the efficiency and key design parameters of the turbine in the selection of working fluids. The results of a case-study for a small-scale solar ORC system show that the turbine design is a relevant parameter for the selection of working fluids and encourage the use of preliminary design models for the turbine in an early stage of the working fluid design. Moreover, the working fluid selection is not only limited to pure components. Similar to the working fluid design of pure components, the consideration of a mixture adds a new degree of freedom to the design problem and allows for the design of more efficient systems. Thus, the method for the working fluid design is extended towards the optimization of working fluid mixtures. The optimization of the zeotropic mixtures is exploited for a comparison between the performance of pure component working fluids and working fluid mixtures.

Institutions

• Chair and Institute of Technical Thermodynamics [412110]