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Selected Papers from the 3rd International Seminar on ORC Power Systems

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (15 March 2016) | Viewed by 103678

Special Issue Editor

Dr. Sylvain Quoilin

E-Mail Website
Guest Editor
Thermodynamics Laboratory, University of Liège, Campus of Sart Tilman, Bat. B49, B-4000 Liège, Belgium
Interests: rural electrification and microgrids; Integration of high shares of renewable in power systems; Small scale concentrating solar power systems; Organic Rankine cycles; Combined heat & power (CHP); Industrial waste heat recovery; Testing and modeling HVAC components: compressors, cooling coil, heat pumps; Numerical calculation of heat transfer in buildings, transfer function; Heat exchangers

Special Issue Information

Dear Colleagues,

Organic Rankine Cycle (ORC) power plants are gaining ever-increasing interest as cost-effective sustainable energy systems. By using an appropriate organic working fluid in a Rankine thermodynamic cycle, ORC power plants are able to efficiently convert renewable energy sources into electricity. Their power capacity spans from a few kWe to some MWe for a single unit, but multiple units in parallel can make up a multi megawatt power station. Among the multitude of applications of this technology, several stand out: ORC systems can be used to obtain electricity from geothermal reservoirs, biomass combustion and gasification, solar radiation, waste heat recovery from internal combustion engines and gas turbines, as well as a large variety of industrial processes discarding heat at low and moderate temperatures. The ORC market is growing at an impressive pace, with currently many hundreds of units of various sizes operating reliably for many years all over the world. Research and development in scientific and technical fields related to ORC technology is very active and growing, as the room for improvement is still large.

This Special Issue aims to publish selected papers from the 3rd international seminar on ORC power systems. Topics include, but are not limited to:

  • system design and optimization
  • applications
  • volumetric expanders
  • simulation and design tools
  • advanced control strategies
  • operational experience
  • prototypes
  • components
  • working fluids

For more infromation about ASME ORC 2015 please click on http://www.asme-orc2015.be/.

Dr. Sylvain Quoilin
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

 

Keywords

  • system design and optimization
  • applications
  • volumetric expanders
  • simulation and design tools
  • advanced control strategies
  • operational experience
  • prototypes
  • components
  • working fluids

Published Papers (15 papers)

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Research

4048 KiB  
Article
Comparison of Organic Rankine Cycle Systems under Varying Conditions Using Turbine and Twin-Screw Expanders
by Matthew Read, Ian Smith, Nikola Stosic and Ahmed Kovacevic
Energies 2016, 9(8), 614; https://doi.org/10.3390/en9080614 - 04 Aug 2016
Cited by 13 | Viewed by 5224
Abstract
A multi-variable optimization program has been developed to investigate the performance of Organic Rankine Cycles (ORCs) for low temperature heat recovery applications using both turbine and twin-screw expanders when account is taken of performance variation due to changes in ambient conditions. The cycle [...] Read more.
A multi-variable optimization program has been developed to investigate the performance of Organic Rankine Cycles (ORCs) for low temperature heat recovery applications using both turbine and twin-screw expanders when account is taken of performance variation due to changes in ambient conditions. The cycle simulation contains thermodynamic models of both types of expander. In the case of the twin-screw machine, the methods used to match the operation of the expander to the requirements of the cycle are described. The performance of turbine expanders in a superheated ORC has been modelled using correlations derived from operational data for single stage reaction turbines to predict the turbine efficiency at “off-design” conditions. Several turbine configurations have been considered including variable nozzle area and variable speed. The capability of the cycle model has been demonstrated for the case of heat recovery from a steady source of pressurized hot water at 120 °C. The system parameters are optimised for a typical operating condition, which determines the required size of heat exchangers and the expander characteristics. Performance at off-design conditions can then be optimized within these constraints. This allows a rigorous investigation of the effect of air temperature variation on the system performance, and the seasonal variation in net power output for the turbine and twin-screw ORC systems. A case study is presented for a low temperature heat recovery application with system electrical power output of around 100 kWe at design conditions. The results indicate that similar overall performance can be achieved for ORC systems using either type of expander. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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742 KiB  
Article
Cost Engineering Techniques and Their Applicability for Cost Estimation of Organic Rankine Cycle Systems
by Sanne Lemmens
Energies 2016, 9(7), 485; https://doi.org/10.3390/en9070485 - 23 Jun 2016
Cited by 121 | Viewed by 11102
Abstract
The potential of organic Rankine cycle (ORC) systems is acknowledged by both considerable research and development efforts and an increasing number of applications. Most research aims at improving ORC systems through technical performance optimization of various cycle architectures and working fluids. The assessment [...] Read more.
The potential of organic Rankine cycle (ORC) systems is acknowledged by both considerable research and development efforts and an increasing number of applications. Most research aims at improving ORC systems through technical performance optimization of various cycle architectures and working fluids. The assessment and optimization of technical feasibility is at the core of ORC development. Nonetheless, economic feasibility is often decisive when it comes down to considering practical instalments, and therefore an increasing number of publications include an estimate of the costs of the designed ORC system. Various methods are used to estimate ORC costs but the resulting values are rarely discussed with respect to accuracy and validity. The aim of this paper is to provide insight into the methods used to estimate these costs and open the discussion about the interpretation of these results. A review of cost engineering practices shows there has been a long tradition of industrial cost estimation. Several techniques have been developed, but the expected accuracy range of the best techniques used in research varies between 10% and 30%. The quality of the estimates could be improved by establishing up-to-date correlations for the ORC industry in particular. Secondly, the rapidly growing ORC cost literature is briefly reviewed. A graph summarizing the estimated ORC investment costs displays a pattern of decreasing costs for increasing power output. Knowledge on the actual costs of real ORC modules and projects remains scarce. Finally, the investment costs of a known heat recovery ORC system are discussed and the methodologies and accuracies of several approaches are demonstrated using this case as benchmark. The best results are obtained with factorial estimation techniques such as the module costing technique, but the accuracies may diverge by up to +30%. Development of correlations and multiplication factors for ORC technology in particular is likely to improve the quality of the estimates. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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1052 KiB  
Article
Comparison of a Novel Organic-Fluid Thermofluidic Heat Converter and an Organic Rankine Cycle Heat Engine
by Christoph J.W. Kirmse, Oyeniyi A. Oyewunmi, Andrew J. Haslam and Christos N. Markides
Energies 2016, 9(7), 479; https://doi.org/10.3390/en9070479 - 23 Jun 2016
Cited by 22 | Viewed by 6335
Abstract
The Up-THERM heat converter is an unsteady, two-phase thermofluidic oscillator that employs an organic working fluid, which is currently being considered as a prime-mover in small- to medium-scale combined heat and power (CHP) applications. In this paper, the Up-THERM heat converter is compared [...] Read more.
The Up-THERM heat converter is an unsteady, two-phase thermofluidic oscillator that employs an organic working fluid, which is currently being considered as a prime-mover in small- to medium-scale combined heat and power (CHP) applications. In this paper, the Up-THERM heat converter is compared to a basic (sub-critical, non-regenerative) organic Rankine cycle (ORC) heat engine with respect to their power outputs, thermal efficiencies and exergy efficiencies, as well as their capital and specific costs. The study focuses on a pre-specified Up-THERM design in a selected application, a heat-source temperature range from 210 °C to 500 °C and five different working fluids (three n-alkanes and two refrigerants). A modeling methodology is developed that allows the above thermo-economic performance indicators to be estimated for the two power-generation systems. For the chosen applications, the power output of the ORC engine is generally higher than that of the Up-THERM heat converter. However, the capital costs of the Up-THERM heat converter are lower than those of the ORC engine. Although the specific costs (£/kW) of the ORC engine are lower than those of the Up-THERM converter at low heat-source temperatures, the two systems become progressively comparable at higher temperatures, with the Up-THERM heat converter attaining a considerably lower specific cost at the highest heat-source temperatures considered. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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1714 KiB  
Article
Thermo-Economic and Heat Transfer Optimization of Working-Fluid Mixtures in a Low-Temperature Organic Rankine Cycle System
by Oyeniyi A. Oyewunmi and Christos N. Markides
Energies 2016, 9(6), 448; https://doi.org/10.3390/en9060448 - 09 Jun 2016
Cited by 88 | Viewed by 9208
Abstract
In the present paper, we consider the employment of working-fluid mixtures in organic Rankine cycle (ORC) systems with respect to thermodynamic and heat-transfer performance, component sizing and capital costs. The selected working-fluid mixtures promise reduced exergy losses due to their non-isothermal phase-change behaviour, [...] Read more.
In the present paper, we consider the employment of working-fluid mixtures in organic Rankine cycle (ORC) systems with respect to thermodynamic and heat-transfer performance, component sizing and capital costs. The selected working-fluid mixtures promise reduced exergy losses due to their non-isothermal phase-change behaviour, and thus improved cycle efficiencies and power outputs over their respective pure-fluid components. A multi-objective cost-power optimization of a specific low-temperature ORC system (operating with geothermal water at 98 °C) reveals that the use of working-fluid-mixtures does indeed show a thermodynamic improvement over the pure-fluids. At the same time, heat transfer and cost analyses, however, suggest that it also requires larger evaporators, condensers and expanders; thus, the resulting ORC systems are also associated with higher costs. In particular, 50% n-pentane + 50% n-hexane and 60% R-245fa + 40% R-227ea mixtures lead to the thermodynamically optimal cycles, whereas pure n-pentane and pure R-245fa have lower plant costs, both estimated as having ∼14% lower costs per unit power output compared to the thermodynamically optimal mixtures. These conclusions highlight the importance of using system cost minimization as a design objective for ORC plants. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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3915 KiB  
Article
Performance Evaluation of a Helical Coil Heat Exchanger Working under Supercritical Conditions in a Solar Organic Rankine Cycle Installation
by Marija Lazova, Henk Huisseune, Alihan Kaya, Steven Lecompte, George Kosmadakis and Michel De Paepe
Energies 2016, 9(6), 432; https://doi.org/10.3390/en9060432 - 03 Jun 2016
Cited by 38 | Viewed by 8908
Abstract
Worldwide interest in low grade heat valorization using organic Rankine cycle (ORC) technologies has increased significantly. A new small-scale ORC with a net capacity of 3 kW was efficiently integrated with a concentrated solar power technology for electricity generation. The excess heat source [...] Read more.
Worldwide interest in low grade heat valorization using organic Rankine cycle (ORC) technologies has increased significantly. A new small-scale ORC with a net capacity of 3 kW was efficiently integrated with a concentrated solar power technology for electricity generation. The excess heat source from Photovoltaic (PV) collectors with a maximum temperature of 100 °C was utilized through a supercritical heat exchanger that uses R-404A as working medium. By ensuring supercritical heat transfer leads to a better thermal match in the heat exchanger and improved overall cycle efficiency. A helical coil heat exchanger was designed by using heat transfer correlations from the literature. These heat transfer correlations were derived for different conditions than ORCs and their estimated uncertainty is ~20%. In order to account for the heat transfer correlation uncertainties this component was oversized by 20%. Next, a prototype was built and installed in an integrated concentrated photovoltaic/thermal (CPV/T)/Rankine system. The results from the measurements show that for better estimation of the sizing of the heat exchanger a more accurate correlation is required in order to design an optimal configuration and thus employ cheaper components. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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2498 KiB  
Article
Working Fluid Stability in Large-Scale Organic Rankine Cycle-Units Using Siloxanes—Long-Term Experiences and Fluid Recycling
by Tobias G. Erhart, Jürgen Gölz, Ursula Eicker and Martijn Van den Broek
Energies 2016, 9(6), 422; https://doi.org/10.3390/en9060422 - 31 May 2016
Cited by 24 | Viewed by 5147
Abstract
The results in this work show the influence of long-term operation on the decomposition of working fluids in eight different organic rankine cycle (ORC) power plants (both heat-led and electricity-led) in a range of 900 kW el to 2 MW el . All [...] Read more.
The results in this work show the influence of long-term operation on the decomposition of working fluids in eight different organic rankine cycle (ORC) power plants (both heat-led and electricity-led) in a range of 900 kW el to 2 MW el . All case study plants are using octamethyltrisiloxane (MDM) as a working fluid; the facilities are between six to 12 years old. Detailed analyses, including the fluid distribution throughout the cycle, are conducted on one system. All presented fluid samples are analyzed via head space gas chromatography mass spectrometry (HS-GC-MS). Besides the siloxane composition, the influence of contaminants, such as mineral oil-based lubricants (and their components), is examined. In most cases, the original working fluid degrades to fractions of siloxanes with a lower boiling point (low boilers) and fractions with a higher boiling point (high boilers). As a consequence of the analyses, a new fluid recycling and management system was designed and tested in one case study plant (Case Study #8). Pre-post comparisons of fluid samples prove the effectiveness of the applied methods. The results show that the recovery of used working fluid offers an alternative to the purchase of fresh fluid, since operating costs can be significantly reduced. For large facilities, the prices for new fluid range from € 15 per liter (in 2006) to € 22 per liter (in 2013), which is a large reinvestment, especially in light of filling volumes of 4000 liters to 7000 liters per unit. Using the aforementioned method, a price of € 8 per liter of recovered MDM can be achieved. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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937 KiB  
Article
Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part B: Application on a Case Study
by Angelo La Seta, Andrea Meroni, Jesper Graa Andreasen, Leonardo Pierobon, Giacomo Persico and Fredrik Haglind
Energies 2016, 9(6), 393; https://doi.org/10.3390/en9060393 - 24 May 2016
Cited by 18 | Viewed by 5892
Abstract
Organic Rankine cycle (ORC) power systems have recently emerged as promising solutions for waste heat recovery in low- and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging due to [...] Read more.
Organic Rankine cycle (ORC) power systems have recently emerged as promising solutions for waste heat recovery in low- and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging due to the peculiar physical properties of the working fluid and the gas-dynamic phenomena occurring in the machine. Unlike steam Rankine and Brayton engines, organic Rankine cycle expanders combine small enthalpy drops with large expansion ratios. These features yield turbine designs with few highly-loaded stages in supersonic flow regimes. Part A of this two-part paper has presented the implementation and validation of the simulation tool TURAX, which provides the optimal preliminary design of single-stage axial-flow turbines. The authors have also presented a sensitivity analysis on the decision variables affecting the turbine design. Part B of this two-part paper presents the first application of a design method where the thermodynamic cycle optimization is combined with calculations of the maximum expander performance using the mean-line design tool described in part A. The high computational cost of the turbine optimization is tackled by building a model which gives the optimal preliminary design of an axial-flow turbine as a function of the cycle conditions. This allows for estimating the optimal expander performance for each operating condition of interest. The test case is the preliminary design of an organic Rankine cycle turbogenerator to increase the overall energy efficiency of an offshore platform. For an increase in expander pressure ratio from 10 to 35, the results indicate up to 10% point reduction in expander performance. This corresponds to a relative reduction in net power output of 8.3% compared to the case when the turbine efficiency is assumed to be 80%. This work also demonstrates that this approach can support the plant designer in the selection of the optimal size of the organic Rankine cycle unit when multiple exhaust gas streams are available. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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4570 KiB  
Article
Development and a Validation of a Charge Sensitive Organic Rankine Cycle (ORC) Simulation Tool
by Davide Ziviani, Brandon J. Woodland, Emeline Georges, Eckhard A. Groll, James E. Braun, W. Travis Horton, Martijn Van den Broek and Michel De Paepe
Energies 2016, 9(6), 389; https://doi.org/10.3390/en9060389 - 24 May 2016
Cited by 34 | Viewed by 7157
Abstract
Despite the increasing interest in organic Rankine cycle (ORC) systems and the large number of cycle models proposed in the literature, charge-based ORC models are still almost absent. In this paper, a detailed overall ORC simulation model is presented based on two solution [...] Read more.
Despite the increasing interest in organic Rankine cycle (ORC) systems and the large number of cycle models proposed in the literature, charge-based ORC models are still almost absent. In this paper, a detailed overall ORC simulation model is presented based on two solution strategies: condenser subcooling and total working fluid charge of the system. The latter allows the subcooling level to be predicted rather than specified as an input. The overall cycle model is composed of independent models for pump, expander, line sets, liquid receiver and heat exchangers. Empirical and semi-empirical models are adopted for the pump and expander, respectively. A generalized steady-state moving boundary method is used to model the heat exchangers. The line sets and liquid receiver are used to better estimate the total charge of the system and pressure drops. Finally, the individual components are connected to form a cycle model in an object-oriented fashion. The solution algorithm includes a preconditioner to guess reasonable values for the evaporating and condensing temperatures and a main cycle solver loop which drives to zero a set of residuals to ensure the convergence of the solution. The model has been developed in the Python programming language. A thorough validation is then carried out against experimental data obtained from two test setups having different nominal size, working fluids and individual components: (i) a regenerative ORC with a 5 kW scroll expander and an oil flooding loop; (ii) a regenerative ORC with a 11 kW single-screw expander. The computer code is made available through open-source dissemination. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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783 KiB  
Article
Comparison of Moving Boundary and Finite-Volume Heat Exchanger Models in the Modelica Language
by Adriano Desideri, Bertrand Dechesne, Jorrit Wronski, Martijn Van den Broek, Sergei Gusev, Vincent Lemort and Sylvain Quoilin
Energies 2016, 9(5), 339; https://doi.org/10.3390/en9050339 - 05 May 2016
Cited by 42 | Viewed by 7761
Abstract
When modeling low capacity energy systems, such as a small size (5–150 kWel) organic Rankine cycle unit, the governing dynamics are mainly concentrated in the heat exchangers. As a consequence, the accuracy and simulation speed of the higher level system model [...] Read more.
When modeling low capacity energy systems, such as a small size (5–150 kWel) organic Rankine cycle unit, the governing dynamics are mainly concentrated in the heat exchangers. As a consequence, the accuracy and simulation speed of the higher level system model mainly depend on the heat exchanger model formulation. In particular, the modeling of thermo-flow systems characterized by evaporation or condensation requires heat exchanger models capable of handling phase transitions. To this aim, the finite volume (FV) and the moving boundary (MB) approaches are the most widely used. The two models are developed and included in the open-source ThermoCycle Modelica library. In this contribution, a comparison between the two approaches is presented. An integrity and accuracy test is designed to evaluate the performance of the FV and MB models during transient conditions. In order to analyze how the two modeling approaches perform when integrated at a system level, two organic Rankine cycle (ORC) system models are built using the FV and the MB evaporator model, and their responses are compared against experimental data collected on an 11 kWel ORC power unit. Additionally, the effect of the void fraction value in the MB evaporator model and of the number of control volumes (CVs) in the FV one is investigated. The results allow drawing general guidelines for the development of heat exchanger dynamic models involving two-phase flows. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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739 KiB  
Article
Real-Time Optimization of Organic Rankine Cycle Systems by Extremum-Seeking Control
by Andres Hernandez, Adriano Desideri, Clara Ionescu, Robin De Keyser, Vincent Lemort and Sylvain Quoilin
Energies 2016, 9(5), 334; https://doi.org/10.3390/en9050334 - 04 May 2016
Cited by 25 | Viewed by 4862
Abstract
In this paper, the optimal operation of a stationary sub-critical 11 kW el organic Rankine cycle (ORC) unit for waste heat recovery (WHR) applications is investigated, both in terms of energy production and safety conditions. Simulation results of a validated dynamic model of [...] Read more.
In this paper, the optimal operation of a stationary sub-critical 11 kW el organic Rankine cycle (ORC) unit for waste heat recovery (WHR) applications is investigated, both in terms of energy production and safety conditions. Simulation results of a validated dynamic model of the ORC power unit are used to derive a correlation for the evaporating temperature, which maximizes the power generation for a range of operating conditions. This idea is further extended using a perturbation-based extremum seeking (ES) algorithm to identify online the optimal evaporating temperature. Regarding safety conditions, we propose the use of the extended prediction self-adaptive control (EPSAC) approach to constrained model predictive control (MPC). Since it uses input/output models for prediction, it avoids the need for state estimators, making it a suitable tool for industrial applications. The performance of the proposed control strategy is compared to PID-like schemes. Results show that EPSAC-MPC is a more effective control strategy, as it allows a safer and more efficient operation of the ORC unit, as it can handle constraints in a natural way, operating close to the boundary conditions where power generation is maximized. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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4366 KiB  
Article
Multi-Objective Optimization of Organic Rankine Cycle Power Plants Using Pure and Mixed Working Fluids
by Jesper G. Andreasen, Martin R. Kærn, Leonardo Pierobon, Ulrik Larsen and Fredrik Haglind
Energies 2016, 9(5), 322; https://doi.org/10.3390/en9050322 - 27 Apr 2016
Cited by 28 | Viewed by 5158
Abstract
For zeotropic mixtures, the temperature varies during phase change, which is opposed to the isothermal phase change of pure fluids. The use of such mixtures as working fluids in organic Rankine cycle power plants enables a minimization of the mean temperature difference of [...] Read more.
For zeotropic mixtures, the temperature varies during phase change, which is opposed to the isothermal phase change of pure fluids. The use of such mixtures as working fluids in organic Rankine cycle power plants enables a minimization of the mean temperature difference of the heat exchangers, which is beneficial for cycle performance. On the other hand, larger heat transfer surface areas are typically required for evaporation and condensation when zeotropic mixtures are used as working fluids. In order to assess the feasibility of using zeotropic mixtures, it is, therefore, important to consider the additional costs of the heat exchangers. In this study, we aim at evaluating the economic feasibility of zeotropic mixtures compared to pure fluids. We carry out a multi-objective optimization of the net power output and the component costs for organic Rankine cycle power plants using low-temperature heat at 90 °C to produce electrical power at around 500 kW. The primary outcomes of the study are Pareto fronts, illustrating the power/cost relations for R32, R134a and R32/R134a (0.65/0.35mole). The results indicate that R32/R134a is the best of these fluids, with 3.4 % higher net power than R32 at the same total cost of 1200 k$. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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1712 KiB  
Article
Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part A: Turbine Model
by Andrea Meroni, Angelo La Seta, Jesper Graa Andreasen, Leonardo Pierobon, Giacomo Persico and Fredrik Haglind
Energies 2016, 9(5), 313; https://doi.org/10.3390/en9050313 - 25 Apr 2016
Cited by 20 | Viewed by 5719
Abstract
Axial-flow turbines represent a well-established technology for a wide variety of power generation systems. Compactness, flexibility, reliability and high efficiency have been key factors for the extensive use of axial turbines in conventional power plants and, in the last decades, in organic Rankine [...] Read more.
Axial-flow turbines represent a well-established technology for a wide variety of power generation systems. Compactness, flexibility, reliability and high efficiency have been key factors for the extensive use of axial turbines in conventional power plants and, in the last decades, in organic Rankine cycle power systems. In this two-part paper, an overall cycle model and a model of an axial turbine were combined in order to provide a comprehensive preliminary design of the organic Rankine cycle unit, taking into account both cycle and turbine optimal designs. Part A presents the preliminary turbine design model, the details of the validation and a sensitivity analysis on the main parameters, in order to minimize the number of decision variables in the subsequent turbine design optimization. Part B analyzes the application of the combined turbine and cycle designs on a selected case study, which was performed in order to show the advantages of the adopted methodology. Part A presents a one-dimensional turbine model and the results of the validation using two experimental test cases from literature. The first case is a subsonic turbine operated with air and investigated at the University of Hannover. The second case is a small, supersonic turbine operated with an organic fluid and investigated by Verneau. In the first case, the results of the turbine model are also compared to those obtained using computational fluid dynamics simulations. The results of the validation suggest that the model can predict values of efficiency within ± 1.3%-points, which is in agreement with the reliability of classic turbine loss models such as the Craig and Cox correlations used in the present study. Values similar to computational fluid dynamics simulations at the midspan were obtained in the first case of validation. Discrepancy below 12 % was obtained in the estimation of the flow velocities and turbine geometry. The values are considered to be within a reasonable range for a preliminary design tool. The sensitivity analysis on the turbine model suggests that two of twelve decision variables of the model can be disregarded, thus further reducing the computational requirements of the optimization. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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6971 KiB  
Article
Modeling and Experimental Validation of a Volumetric Expander Suitable for Waste Heat Recovery from an Automotive Internal Combustion Engine Using an Organic Rankine Cycle with Ethanol
by José Galindo, Vicente Dolz, Lucía Royo-Pascual, Regine Haller and Julien Melis
Energies 2016, 9(4), 279; https://doi.org/10.3390/en9040279 - 09 Apr 2016
Cited by 20 | Viewed by 7534
Abstract
Waste heat recovery (WHR) in exhaust gas flow of automotive engines has proved to be a useful path to increase the overall efficiency of internal combustion engines (ICE). Recovery potentials of up to 7% are shown in several works in the literature. However, [...] Read more.
Waste heat recovery (WHR) in exhaust gas flow of automotive engines has proved to be a useful path to increase the overall efficiency of internal combustion engines (ICE). Recovery potentials of up to 7% are shown in several works in the literature. However, most of them are theoretical estimations. Some present results from prototypes fed by steady flows generated in an auxiliary gas tank and not with actual engine exhaust gases. This paper deals with the modeling and experimental validation of an organic Rankine cycle (ORC) with a swash-plate expander integrated in a 2 L turbocharged petrol engine using ethanol as working fluid. A global simulation model of the ORC was developed with a maximum difference of 5%, validated with experimental results. Considering the swash-plate as the main limiting factor, an additional specific submodel was implemented to model the physical phenomena in this element. This model allows simulating the fluid dynamic behavior of the swash-plate expander using a 0D model (Amesim). Differences up to 10.5% between tests and model results were found. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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1991 KiB  
Article
Thermo-Economic Analysis of Zeotropic Mixtures and Pure Working Fluids in Organic Rankine Cycles for Waste Heat Recovery
by Florian Heberle and Dieter Brüggemann
Energies 2016, 9(4), 226; https://doi.org/10.3390/en9040226 - 23 Mar 2016
Cited by 41 | Viewed by 6477
Abstract
We present a thermo-economic analysis of an Organic Rankine Cycle (ORC) for waste heat recovery. A case study for a heat source temperature of 150 °C and a subcritical, saturated cycle is performed. As working fluids R245fa, isobutane, isopentane, and the mixture of [...] Read more.
We present a thermo-economic analysis of an Organic Rankine Cycle (ORC) for waste heat recovery. A case study for a heat source temperature of 150 °C and a subcritical, saturated cycle is performed. As working fluids R245fa, isobutane, isopentane, and the mixture of isobutane and isopentane are considered. The minimal temperature difference in the evaporator and the condenser, as well as the mixture composition are chosen as variables in order to identify the most suitable working fluid in combination with optimal process parameters under thermo-economic criteria. In general, the results show that cost-effective systems have a high minimal temperature difference ΔTPP,C at the pinch-point of the condenser and a low minimal temperature difference ΔTPP,E at the pinch-point of the evaporator. Choosing isobutane as the working fluid leads to the lowest costs per unit exergy with 52.0 €/GJ (ΔTPP,E = 1.2 K; ΔTPP,C = 14 K). Considering the major components of the ORC, specific costs range between 1150 €/kW and 2250 €/kW. For the zeotropic mixture, a mole fraction of 90% isobutane leads to the lowest specific costs per unit exergy. A further analysis of the ORC system using isobutane shows high sensitivity of the costs per unit exergy for the selected cost estimation methods and for the isentropic efficiency of the turbine. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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Article
Thermal Stability of Hexamethyldisiloxane (MM) for High-Temperature Organic Rankine Cycle (ORC)
by Markus Preißinger and Dieter Brüggemann
Energies 2016, 9(3), 183; https://doi.org/10.3390/en9030183 - 10 Mar 2016
Cited by 60 | Viewed by 6221
Abstract
The design of efficient Organic Rankine Cycle (ORC) units for the usage of industrial waste heat at high temperatures requires direct contact evaporators without intermediate thermal oil circuits. Therefore, the thermal stability of high-temperature working fluids gains importance. In this study, the thermal [...] Read more.
The design of efficient Organic Rankine Cycle (ORC) units for the usage of industrial waste heat at high temperatures requires direct contact evaporators without intermediate thermal oil circuits. Therefore, the thermal stability of high-temperature working fluids gains importance. In this study, the thermal degradation of hexamethyldisiloxane (MM) is investigated in an electrically heated tube. Qualitative results concerning remarks on degradation products as well as quantitative results like the annual degradation rate are presented. It is shown that MM is stable up to a temperature of 300 °C with annual degradation rates of less than 3.5%. Furthermore, the break of a silicon–carbon bond can be a main chemical reaction that influences the thermal degradation. Finally, it is discussed how the results may impact the future design of ORC units. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Seminar on ORC Power Systems)
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