[home] [Personal Program] [Help]

---

Session: Parallel Session: Cycle efficiency
Session starts: Friday 23 September, 16:00
Presentation starts: 16:00
Room: Senaatszaal

---

Daniela Gewald (Technische Universität München)
Andreas Schuster (Technische Universität München)
Sotirios Karellas (National Technical University of Athens)
Hartmut Spliethoff (Technische Universität München)

Abstract:
Due to their high electrical efficiency (up to 47 %), internal combustion engines (ICE) are widely used as independent power producers. In order to further increase the electrical efficiency, an Organic Rankine cycle (ORC) can be applied for waste heat recovery (WHR) of the ICE. The recoverable engine waste heat is usually available at two different temperature levels: 300 °C to 400 °C (exhaust gas) and 90 °C (engine cooling water). The integration of both heat flows and especially the integration of the cooling water heat is a certain challenge for ORC operating with one specific working fluid which is usually optimized to just one temperature level. Therefore only few examples of the recovery of both heat flows can be found both in literature and as existing power stations. This paper presents a two step optimization approach in order to increase the overall system efficiency of an engine-ORC combined cycle by means of the integration of the heat flows at both temperature levels. In a first step the variable cycle parameters both in the topping and the bottoming cycle (e.g. fluid evaporation pressure and temperature of the cooling water) will be defined and evaluated for different working fluids (R245fa, pentane, MDM among other) within the boundary conditions given by the technical feasibility. Furthermore the application of a recuperator is investigated since recuperation and the integration of low temperature heat are often competing efforts. The effect of higher pressure losses throughout the recuperator has to be taken into account as well. This step is aimed at the definition of a set of working parameters, which leads to an optimal system configuration for each working fluid. The optimization parameter is the net electrical power output of the system. Within the second step important constructive aspects of the engine-ORC are rated for the selected fluids. A fast indication of the expenditure of each power-optimized system can be generated by the evaluation of specific constructive parameters such as heat exchanger surfaces and volume flow rates. Based on these design parameters a power independent comparison can be obtained by calculating the influence of relative deviations of the constructive parameters from the optimal system on the net electrical power output. By means of this two-step approach a fast assessment of an ORC system both under thermodynamic and cost-related considerations is possible. Both aspects are necessary for the next steps towards realization of the system. The same approach for the evaluation of an ORC system is used in another investigation presented at the conference [1].