16:30
Session 5C: Geothermal
Chair: Dr. Lucien Bronicki
16:30
20 mins
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Working fluid parametric analysis for regenerative supercritical Organic Rankine Cycles for medium geothermal reservoir temperatures
Francesca Moloney, Eydhah Almatrafi, D. Yogi Goswami
Abstract: The conversion efficiencies of low heat sources, such as geothermal energy, are very low. Supercritical organic Rankine cycles (SORC) have been shown to operate at higher efficiencies than organic Rankine cycles (ORC). The studies on the numerical modeling of SORCs, have focused on turbine inlet temperatures between 80 and 130˚C. Research has been performed on supercritical carbon dioxide cycles for temperature applications up to 800˚C. However, carbon dioxide achieves low efficiencies at low temperatures, and only a few studies have explored other working fluids between 180 and 350˚C. The pressures explored have also been limited in these analyses. A steady state model of an SORC was created in MATLAB and validated to analyze working fluid performance for turbine inlet temperatures between 170 and 240˚C. A parametric analysis was performed on varying turbine inlet pressure and temperature to optimize performance. Working fluids with critical temperatures between 100 and 200˚C were analyzed. Fluid properties were obtained using NIST REFPROP. Fluids were selected based on their thermal stability, global warming potential, and ozone depleting potential. Various working fluids were tested, including pentane (R601), isopentane (R601a), butane (R600), isobutane (R600a), cis-butene, and butene. Pinch points in the evaporator and the condenser were omitted from the analysis to focus on the parametric analysis of between the pressure and temperature at the turbine inlet of the cycle. A maximum of 50MPa was considered for the turbine inlet. An exergy analysis was performed focusing on the effectiveness of the cycle. This study is beneficial for not only geothermal energy but for other power applications that can provide working fluid temperatures between 180 to 230˚C. Near the critical temperature, lower pressures produced higher efficiencies and higher net work. Cis-butene performed the best in efficiency, effectiveness, and net work output over the whole temperature range analyzed.
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16:50
20 mins
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Field performance evaluation of an operating turbine in design and off-design conditions
Dario Rizzi, Luca Zanellato, Marco Astolfi, Ennio Macchi
Abstract: In these days the ORC market is in expansion and as a matter of fact a rising interest about it can be observed in the scientific community. In terms of system performance, turbine is the most important and critical component of ORC systems (Macchi, 2013).
An interesting innovation in this panorama is the ORC radial outflow turbine developed by Exergy, which has several unique characteristics qualifying this unconventional configuration as advantageous for many ORC applications, as it ideally matches the process conditions typical for these kinds of uses.
In fact, it has been shown that this machine is competitive with both axial and radial inflow turbines, solutions usually adopted in ORC applications (Macchi, 2013 – Spadacini et al., 2013).
Despite the rising interest in this configuration (Spadacini et al., 2011 - Pini et al., 2013 - Persico et al., 2013), nowadays only few experimental data about it have been presented (Frassinetti et al., 2013), compared to those available for different arrangements.
This paper, after a brief description of the radial outflow turbine and of its main features, discloses the field performances evaluation of an operating geothermal turbine in design and off-design conditions: it describes the test procedure, the measurements and calculation methods used to obtain the overall turbine efficiency.
REFERENCES
[1] Macchi E., 2013, “The Choice Of Working Fluid: The Most Important Step For A Successful Organic Rankine Cycle (And An Efficient Turbine)”, in Proc. of 2nd Int. Sem. on ORC Power Systems, Oct., Rotterdam.
[2] Spadacini C., Rizzi D., Saccilotto C., Salgarollo S., Centemeri L., 2013, "The Radial Outflow Turbine Technology: Impact On The Cycle Thermodynamics And Machinery Fluid- And Rotordynamic Features", in Proc. of 2nd Int. Sem. on ORC Power Systems, Oct., Rotterdam.
[3] Spadacini C., Centemeri L., Xodo L.G., Astolfi M., Romano M.C. and Macchi E., 2011, "A New Configuration for Organic Rankine Cycle Power Systems", in Proc. of 1st Int. Sem. on ORC Power Systems, Sept., Delft.
[4] Pini M., Persico G., Casati E. and Dossena V., 2013, “Preliminary Design of a Centrifugal Turbine for ORC Applications”, ASME J. Eng. Gas Turb. Power, Apr., Vol. 115.
[5] Persico G., Pini M., Dossena V. and Gaetani P., 2013, “Aerodynamic Design and Analysis of Centrifugal Turbine Cascade”, in ASME Turbo Expo 2013, Paper No. GT2013-95770.
[6] Frassinetti M., Rizzi D., Serafino A., Centemeri L. and Spadacini, C., 2013, "Operational Results of the World’s First Orc Radial Outflow Turbine, and its Future Development", in Proc. of 2nd Int. Sem. on ORC Power Systems, Oct., Rotterdam.
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17:10
20 mins
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Cycle and turbine re-optimization on geothermal resources significantly deviating from the expected conditions
Nicolò Lazzarin, Marco Frassinetti, Luca Zanellato
Abstract: The economic success of a geothermal exploration program lies in finding the right compromise between exploration costs, risk evaluation analysis and execution timespan. It could frequently happen that the preliminary well test results differ from the real long term operating conditions and in addition they usually vary across the years. The purpose of this study is to analyze the effect of changing resources on performances, in several scenarios with different optimal cycle and turbine design. This study will point out that the re-engineering of the first stage of the radial outflow turbine, the so called "nose cone", may recover a big part of the inefficiencies and lead back to a nearly optimal power conversion, with heavily reduced effects on timeframe and costs, compared to other solutions, like the re-design of the whole turbine.
Key words: ORC; Geothermal; Nosecone; Radial Outflow Turbine; CFD; Thermodynamic optimization;
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17:30
20 mins
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Potential performance of environmental friendly application of ORC and Flash technology in geothermal power plants
Davide Bonalumi, Paola Bombarda, Costante Invernizzi
Abstract: The successful exploitation of geothermal energy for power production is linked to the availability of nearly zero emission and efficient technologies, able to provide flexible operation. The binary cycle technology consists of a closed power cycle coupled to a closed geothermal loop, whereby the closed power cycle is generally accomplished by means of an organic Rankine cycle (in a few cases the Kalina cycle has been proposed). The confinement of the geothermal fluid in a closed loop is an important advantage from the environmental point of view: possible pollutants contained in the geothermal fluid are not released into the ambient and are directly reinjected underground.
Although a well-established technology in the frame of geothermal applications, the adoption of the binary cycle technology is at the moment typically confined to the exploitation of medium-low temperature liquid geothermal reservoirs, generally between 100-170 °C. The important advantages of the binary cycle technology from the environmental point of view suggest nevertheless that it is worthwhile to investigate whether the application range could be extended to higher temperature reservoirs, and up to which extent. The paper compares in a convenient high temperature range of the geothermal source the performance of an advanced properly optimized geothermal ORC plant, with the performance of a reference plant, adopting the conventional flash technology, whereby the geothermal fluid is directly sent to a steam turbine.
Several working fluids will be considered in the ORC optimization process. The performance comparison will entail a parametric analysis and the assessment of net power, first and second law efficiencies. As far as the calculations are concerned, the geothermal fluid is assumed to be a mixture of water, NaCl and possibly CO2; several cases with different contents of NaCl and CO2 will be considered. The auxiliary power consumption will be finally evaluated: beyond cooling auxiliaries, when needed, a submersible well pump for the ORC plant and a gas compressor for the reinjection of the non-condensable gases in the flash plant will be considered
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