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16:20   Session 7: Small-scale ORC's
Chair: Jürg Schiffmann
16:20
20 mins 		System-search VOLUMETRIC EXPANDER VERSUS TURBINE – WHICH IS THE BETTER CHOICE FOR SMALL ORC PLANTS?
Andreas Weiß
Abstract: Since the steam turbine replaced the steam reciprocating engine by the end of 19th century it has been the only expander type in CRC and ORC power plants at least above 1 MWel. Positive displacement expanders like scroll- or screw-machines has often been applied for smaller units – in particular below 100 kWel. One reason for this is that in cooling or compressed air technology those machines are cheaply available as compressors which can be converted “easily” to expanders. In contrast, up to now small turbines are rather seldom in market. One goal of this paper is to discuss whether there are others than the already mentioned reasons to justify technically or economically the choice of volumetric expanders for small ORC plants? Or may small turbines provide benefits which couldn´t have been used in the past just due to a lack of appropriate machines? However, is the choice between volumetric or turbine expander finally made there is still a big variety of working principles and possible shapes for both expander types which have to be considered in order to get the best final expander design. Therefore, the paper introduces briefly the working principles of positive displacement and turbine expanders and evaluates them concerning their application in small ORC-plants. For the author, the advantages of turbines outweigh their disadvantages. Nevertheless, in the following the decision between e. g. impulse or reaction type, axial or radial, single or multistage turbine has to be made. The paper discusses and explains the “pro and cons” of all these turbine types regarding different applications like e. g. low/high temperature ORC, small or bigger units etc.. In summary the paper recommends turbine expanders even for small ORC-Units and provides a brief overview and comparison of different turbine types to facilitate the decision making concerning the best turbine for a given task.
16:40
20 mins 		System-search STUDY OF A VOLUMETRIC EXPANDER SUITABLE FOR WASTE HEAT RECOVERY FROM AN AUTOMOTIVE IC ENGINE USING AN ORC WITH ETHANOL
José Galindo, Vicente Dolz, Lucía Royo, Régine Haller, Julien Melis
Abstract: Waste Heat Recovery in exhaust gas flow of automotive engines has proved to be a path to increase the overall efficiency of automotive vehicles. Recovery potential of up to 7% are shown in several works in the literature. However, most of them are theoretical estimations. Some of them presents results from prototypes fed by steady flow generated in an auxiliary gas tank and not with actual engine exhaust gases. This paper deals with the simulation model of a volumetric expander, integrated in an ORC mock-up, coupled to a 2 l turbocharged gasoline engine and using ethanol as working fluid. An experimental facility of an ethanol ORC using a swash-plate expander coupled to an Ecoboost 2.0 engine has then been used to correlate it. The target is to understand the physical phenomena which are not predictable by simulation and can only be observed by experimentation and secondly, to carry out some parametric studies showing the potential for optimizing different elements of the expander machine.
17:00
20 mins 		System-search COMBINED THERMODYNAMIC AND TURBINE DESIGN ANALYSIS OF SMALL CAPACITY WASTE HEAT RECOVERY ORC
Antti Uusitalo, Teemu Turunen-Saaresti, Grönman Aki, Honkatukia Juha, Backman Jari
Abstract: Organic Rankine Cycles adopting turbine technology have been commercially successful in large-scale ORC application. In small power output systems (about 10-50 kW) a volumetric expander is usually preferred instead of a turbine. However, the limitations of using volumetric expanders are related to the lower achievable expansion ratios over the expanders when compared to the use of turbines and thus, disabling the use of high molecular weight and high critical temperature fluids characterized by large expansion ratios in the cycle. In this paper the design of small capacity ORC turbines is studied and discussed. The selected application is exhaust gas recovery of a small-scale gas turbine. A turbine design tool was coupled with a thermodynamic analysis in order to evaluate the effect of different working fluids and process parameters, not only by taking into account the thermodynamic aspects of the process design, but also evaluating the availability to design turbines with a relatively high efficiency. The studied fluids can be classified as hydrocarbons, siloxanes, and fluorocarbons and the studied turbine type is a radial inflow turbine, since radial turbines represent relatively simple geometries when compared to multistage configurations and can have a high expansion ratio over a single stage. The results indicate that the main difficulties in the design of small capacity ORC turbines are related to high rotational speeds, small turbine dimensions, and relatively large variations in the blade height between the turbine rotor inlet and outlet. In addition, the use of single stage turbines leads to highly supersonic flow in the turbine stator even when adopting low or moderate flow velocities caused by the low speed of sound of the organic fluids. The results highlight the importance of combining both the thermodynamic process design and the turbine design when evaluating suitable working fluids and operational parameters for the cycle.
17:20
20 mins 		System-search EXPERIMENTAL INVESTIGATION OF A RADIAL MICROTURBINE IN ORGANIC RANKINE CYCLE SYSTEM WITH HFE7100 AS WORKING FLUID
Tomasz Kaczmarczyk, Grzegorz Zywica, Eugeniusz Ihnatowicz
Abstract: The paper presents the results of experimental investigation of the ORC system with prototype microturbine. The prototype of biomass boiler has been used as a heat source. The boiler with a power rating of 25 kWth is powered by biomass (wood pellets) using a screw auger. The biomass boiler heats thermal oil which is directed to the evaporator where the low boiling refrigerant evaporates. The maximum temperature of the thermal oil in the evaporator is about 210 °C – 215 °C. The solvent HFE7100 was used as the working fluid in the ORC system. The prototype of four-stage radial microturbine and biomass boiler has been designed and built at the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences in Gdańsk (Poland). The designed electric capacity of microturbine is 2.7 kWe at maximum speed of 24000 rpm. The isentropic efficiency for this fluid-flow machine is about 70%. The generated electricity is dissipated by an electric heater with a power of 5 kWe and eleven light bulbs 100 W each. Electrical load can be adjusted according to your needs. At the inlet of the microturbine a condensate separator was applied to protect the blades from erosion and to ensure the proper operation of gas bearings. In the initial phase steam microturbine is supplied with a high degree of superheat in the range from 30 K to 40 K - the make warm phase of the microturbine. During normal operation of the microturbine, superheating degree of the low boiling fluid in the range of 5 K to 10 K. The working fluid after expansion in microturbine is directed to the regenerator and then to the condenser. The heat supplied to the condenser dissipated a fan cooler with maximum power of 50 kW. Depending on the flow rate of the glycol in the condenser the absolute pressure in the range of 1.2 bar - 3 bar and a temperature of the working fluid in the range from 20 °C to 65 °C can be obtained. The paper presents the characteristics of the ORC system and radial microturbine for different variants of working medium flow rates (thermal oil, HFE7100, glycol). During testing of the ORC system with prototype of radial microturbine and the biomass boiler (fired with wood pellets) the maximum electrical output power was around 1500 We.
17:40
20 mins 		System-search OPERATIONAL EXPERIENCE ON ORC USE FOR WASTE HEAT VALORISATION IN BIOGAS POWER PLANT
Arthur Leroux, Coline Gazet, Benoit Paillette, Antonin Pauchet
Abstract: Development of small ORC systems based on high speed turbine expander Layouts for integration of the ORC process within biogas plants Operational experience of small ORC systems used in biogas plants
18:00
20 mins 		System-search OPTIMIZED EFFICIENCY MAPS AND NEW CORRELATION FOR PERFORMANCE PREDICTION OF ORC BASED ON RADIAL TURBINE FOR SMALL-SCALE APPLICATIONS
Kiyarash Rahbar, Saad Mahmoud, Raya Al-Dadah
Abstract: The expander is considered as the most critical component of the ORC. Radial inflow turbine exhibits unique advantages of high efficiency, compact structure and light weight compared to the axial turbine when employed in the small-scale applications such as distributed CHP systems. In most of the ORC studies the turbine efficiency is assumed as a constant input for the optimization of cycle without assuring that the specified turbine efficiency can be achieved by the imposed thermodynamic conditions. In addition, atypical properties of the high-density working fluid and the near-critical operating condition of the ORC requires the turbine design procedure and parameters to be customized for the ORC. This study presents the optimization of a radial ORC turbine for maximum efficiency using mean-line modelling and genetic algorithm (GA). In contrast to the previous studies, real gas equation of state and the most advanced and recent loss models are employed in the code to capture the non-ideal behaviour of the working fluid. The optimized turbine efficiency is achieved by the GA for a wide range of operating conditions and for four organic fluids (R123, R245fa, R1233zd and isobutane). Such results are presented through new generalized maps based on the non-dimensional parameters as the flow and loading coefficients, specific speed and specific diameter. Using regression analysis a new correlation for the turbine efficiency is also presented. These new maps and the correlation are preliminary steps toward improving the previous constant turbine efficacy assumption and have great potential to be integrated with the general optimization methods of the ORC.