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14:00   Parallel Session: Working fluids
Chair: Nawin Ryan Nannan
20 mins
Gary Zyhowski, Andrew Brown
Abstract: Organic Rankine Cycle system designs that operate with non-flammable hydrofluorocarbon working fluids such as HFC-134a (1,1,1,2-Tetrafluoroethane) and HFC-245fa (1,1,1,3,3-Pentafluoropropane) have been operating in the field for a number of years. Their growing use in geothermal, engine and industrial heat recovery organic Rankine cycle applications is noteable. These systems have demonstrated environmental benefits that validate their current and future use. Even so, there is great interest among system OEMs, equipment end-users, regulatory agencies, and the public to embrace new low global warming working fluid technologies. Honeywell has developed a number of candidate fluids that can serve as replacements for HFC-134a and HFC-245fa in refrigeration, air-conditioning, foam expansion, aerosols, and organic Rankine cycle applications. The two fluids that can serve as replacements for HFC-134a are hydrofluoroolefins HFO-1234yf (2,3,3,3- Tetralfuoroprop-1-ene) and HFO-1234ze (trans-1,3,3,3-Tetrafluoropropene). These two fluids are being commercialized for a number of applications. A third fluid, that is a potential replacement for HFC-245fa, is a candidate to replace HFC-245fa in organic Rankine cycle applications. The environmental and thermophysical properties of the fluids are reviewed. The theoretical thermodynamic efficiency, turbine size, speed, and mach numbers of the new fluids are compared to HFC-134a and HFC-245fa. Conditions for the organic Rankine cycle are those reflecting geothermal organic Rankine cycle applications. In the case of HFC-134a and potential replacements, both sub-critical and supercritical cycles are considered.
20 mins
Anna Lis Laursen, Pierre Huck
Abstract: A Department of Energy funded study of high-potential working fluids for Organic Rankine Cycles (ORC) for use in Enhanced Geothermal Systems (EGS) has been conducted. The worked completed to date, in coordination with AltaRock Energy, Inc., characterized the performance of high-potential working fluids for EGS resource temperatures. From an available list of more than 17,000 pure components, 35 working fluids were identified as high-potential. In addition to the numerous fluids that were screened from commonly available sources, additional fluids were screened from vendors that are less common or even not on the market yet. An additional 3 working fluids were included for comparison to the current state-of-the-art. The performance of the working fluids was evaluated in a subcritical ORC, supercritical ORC, and trilateral flash cycle and compared to the performance in baseline subcritical ORCs. The primary advantage of the supercritical cycle over the subcritical cycle is a better match between resource cooling curve and working fluid heating curve. The lack of constant temperature evaporation allows the heat source to be cooled to a lower temperature despite a similar pinch point as in a comparable subcritical cycle leading to greater utilization of the geothermal resource. The topics that will be presented include a cycle performance comparison and its impact on traditional working fluid (R134a, 245fa, n-butane and n-pentane) resulting in a 30-50% increase in net power output. This material is based upon work supported by the Department of Energy’s Geothermal Technologies Program under Award Number DE-EE0002769. Disclaimer “This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty express or imply, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe on privately owned rights. Reference herein to any specific commercial product, process or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
20 mins
Andreas Grill, Richard Aumann, Andreas Schuster, Jens-Patrick Springer
Abstract: ORC Application for CHP can be considered as state of the art for large biomass boilers. The organic Fluid is therefore evaporated by means of a heat carrier. In a heating condenser the remaining heat from the ORC-system is transferred to a heating system. In smaller block heat and power systems a use of an ORC is also possible. In this study different fluids are compared for different heat carrier and return flow temperatures of an ORC system. In order to evaluate the system in a practical way, a two-step approach for the benchmarking of the suitability of different fluids is done. In a first step, the thermodynamic potential is compared. For each combination of temperatures, isentropic efficiencies for the expansion machine as well as the feed pump are set to a fixed value. Afterwards specific boundary conditions in terms of return flow temperature in the heating condenser and heat carrier temperature in the evaporator inlet are set and optimal operation pressures and temperatures are calculated for each fluid. As optimized parameter the net power output of the system is used. The result gives an overview over which fluid is thermodynamically best for selected applications. In a second step, constructive aspects coming along with different fluids are rated. For a fast assessment of the constructive effort and therefore the cost of the system, specific parameters as heat exchanger surface and volume flow rate are compared. A power-independent comparison is obtained by calculating relative deviations of the constructive parameters from the optimal system of the first step optimization. Furthermore the improvements of the systems by means of the use of a recuperator are investigated. Although theoretically improvements in efficiency and net power output can be achieved, real effects as pressure drop across the component needs to be considered in detailed planning as it decreases the technical power of the expansion machine. Moreover the cost of an extra component coming along with increasing efforts for piping and casing does not necessarily lead to cheaper power related specific costs. By means of this two-step approach a fast evaluation of an ORC system is possible. Not only thermodynamic aspects, but also cost-related aspects can be rated and taken into account for next steps towards the realization of such a system. The same approach for the rating of an ORC system is done in another investigation presented at the conference [1]. REFERENCES [1] D. Gewald, et al, Two Step Optimization approach for increase of engine-ORC efficiency, ORC 2011 TU Delft, NL
20 mins
Matthias Schopf, Guillermo Botti
Abstract: ORC technology power plants using heat transfer fluids (HTF) as organic heating media are widely recognized as highly reliable and safe. Key factors responsible for the huge growth of this industry include: waste heat availability, feed-in incentives and bankable technology. The success of the ORC sector is related to a quick return on investment which is directly linked to a continuous and trouble free plant operation thus maximizing incomes while keeping operational costs minimized. In such context heat transfer fluids play an essential role representing a component that is in contact with both the heat source and the ORC module. Control of the HTF in-service quality can help to monitor operation conditions of the whole plant and facilitate corrective actions ahead of problems. All heat transfer fluids are subject to degradation, which means modification of its original molecular composition can occur. Over time, thermal stress of the fluid may result to the extent it will not be able to safely and efficiently convey the heat from the source to the user. Excessive fluid degradation can lead to higher maintenance works and reduced fluid life, thus increasing the investment return time. Reasons for this excessive degradation may include choosing a fluid with less than adequate thermal stability, operational problems or procedures in the plant, or defects in heater or system design. An accurate HTF system design and regular monitoring of fluid conditions will help to prevent unexpected system troubles and unsafe operating conditions thus enabling operators to provide timely solutions and begin corrective actions. The requirements of an ORC plant require specific properties of the HTF used in this technology. Therminol® heat transfer fluids have been used from the start of ORC power production until today. The proven track record of these fluids contributes to reliable and smooth plant operations. * Copyright 2011 Solutia Inc. ® Registered trademark of Solutia Inc. Notice: Although the information and recommendations set forth herein (hereafter “information”) are presented in good faith and believed to be correct as of the date hereof, neither Solutia Inc. nor any of its affiliates, including Solutia Europe BVBA, makes any representations or warranties as to the completeness or accuracy thereof and assumes no obligation to update any of the information. Information is supplied upon the condition that the persons receiving same will make their own determinations as to its suitability for their purposes prior to use. In no event will Solutia Inc. or any of its affiliates, including Solutia Europe BVBA, be held responsible for damages of any nature whatsoever resulting from the use of or reliance upon information or the product to which information refers. Nothing contained herein is to be construed as a recommendation to use any product, process, equipment or formulation in conflict with any patent, and neither Solutia Inc. nor any of its affiliates, including Solutia Europe BVBA, makes any representation or warranty, express or implied that the use thereof will not infringe any patent. NO REPRESENTATIONS OR WARRANTIES, EITHER EXPRESS OR IMPLIED, OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR OF ANY OTHER NATURE ARE MADE HEREUNDER WITH RESPECT TO INFORMATION OR THE PRODUCT TO WHICH INFORMATION REFERS
20 mins
Frithjof Dubberke, Jadran Vrabec
Abstract: Heat recovery systems, such as organic Rankine cycles (ORC), play an important role for the efficient use of fossil as well as of renewable fuels. Performance improvements of ORC processes are based on the technical development of the hardware and on the selection of appropriate working fluids. The selection of suitable working fluids is made on the basis of their thermo-physical properties and safety requirements, considering the characteristics of the heat source. Thus, efficiency increases for technically well advanced ORC plants require reliable and accurate thermo-physical property data on working fluids. One group of ORC working fluids are the siloxanes, which belong to the wider class of organosilicone compounds. In particular, hexamethyldisiloxane (HMDS) appears to be an eligible candidate for becoming a widely used working fluid for high-temperature processes. However, the current lack of accurate thermo-physical data for siloxanes may lead to sub-optimally designed cycles and processes. Therefore, the measurement of such data is necessary. Thermal properties in the homogeneous fluid region, together with the speed of sound and the vapor pressure are used to generate accurate equations of state (EOS) that describe the entire range of fluid states. “Properly designed multiparameter equations of state are able to represent thermodynamic properties of a certain substance within the accuracy of the most accurate experimental data” [2]. This work aims at closing the gap with respect to the speed of sound of HMDS. The measurement mechanism of the apparatus is based on the puls-echo technique and operates up to 150 MPa in the temperature range between 250 and 600 K [1]. While emitting a high frequency modulated burst signal by a piezoelectric quartz crystal, which is positioned between two reflectors in the fluid, the speed of sound is determined by the traveled distance divided by time the signal propagates through the fluid. For designing and constructing an ORC plant, knowledge on the speed of sound is particularly relevant for the expansion in the turbo-machine. E.g., single stage radial flow turbines rely on supersonic expansion in an upstream Laval nozzle to transform the enthalpy of the superheated working fluid vapor into kinetic energy before interacting with the turbine-wheel. The mass flow rate in Laval nozzles is directly related to the speed of sound. Even small inaccuracies in the underlying data can decrease the performance of the turbo-machine significantly.