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14:00   Poster session & Sponsor Exhibition
Bao Junjiang, Zhao Li
Abstract: Organic Rankine cycles (ORC) have received increasing attention for power generation purposes due to their potential for utilizing heat from low-temperature sources and their favourable characteristics for integration into future distributed energy systems. Due to the relative low efficiency for ORC, many researchers are currently working on the design and development of new thermodynamic cycles and the improvement of existing ones. A novel auto-cascade Rankine cycle (ARC) is proposed to reduce thermodynamics irreversibility and improve energy utilization. Like the Kalina cycle, the working fluid for the ARC is zeotropic mixture, which can improve the system efficiency due to the temperature slip that zeotropic mixtures exhibit during phase change. Unlike the Kalina cycle, two expanders are included in the ARC rather than an expander and a throttling valve in the Kalina cycle, which means more work can be obtained. The main advantages of the ALSRC system is that heat from the exhaust stream of the expanders are reclaimed twice, once using an IHE and another time using a regenerator. Using the exhaust gas as the heat source and water as the heat sink, a program is written by Matlab 2010a to carry out exergy analysis and parameter study on the ARC. Results show that the R245fa mass fraction in the primary circuit exists an optimum value with respect to the minimum total cycle irreversibility. The largest exergy loss occurs in evaporator, followed by the superheater, condenser, regenerator and IHE (Internal heat exchanger). As the R245fa mass fraction increases, the exergy losses of different components vary diversely. With the evaporation pressure rises, the total cycle irreversibility decreases and work output increases. Separator temperature has a greater influence on the system performance than superheating temperature. Compared with ORC (organic Rankine cycle) and Kalina cycle in the literature, the ARC has proven to be thermodynamically better.
Yu-Ting Wu, Wei Wang, Ye-Qiang Zhang, Jing-Fu Wang, Chong-Fang Ma
Abstract: Screw machines include single screw machine and twin screw machine. The screw compressors have been worldwide used in refrigeration, air conditioning and industrial gas compression. Twin screw machine as an expander have been developed for the application in energy conservation and renewable energy. However, the use of single screw machine as an expander is a new concept and no any prototype of single screw expander except our team is reported in the world. Single-screw expander can be used as expansion power machine in small capacity ORC power system with output power from 1 to 500 kW. It has many advantages, such as long working life, balanced loading of the main screw, high volumetric efficiency, low noise, low leakage, low vibration and simple configuration, etc. it is suited to superheated steam, saturated steam or wet steam. A single screw expander prototype with 117m Screw Diameter was developed. Compressed air and steam experiment system were built to test the performance of single screw expander. By adjusting the clearances from screw, gate rotor to shell and improving manufacture precision, the total efficiency increased from 30% of first prototype to above 60% of modified prototype. Other three types of single-screw expander prototypes, which are 155 mm screw diameter, 175 mm screw diameter and 195 mm screw diameter, have also been developed. The performances of these prototypes with rotating speed and pressure have been tested. From the results, maximum output power of each type of prototypes is 5kW, 9.9kW, 22.4kW and 51.8kW, and maximum total efficiency of each is 66%, 58.3%, 70% and 63%. An organic Rankine cycle (ORC) experimental system was also built. The preliminary experimental results were obtained. Experimental results indicate that the maximum efficiency of expander reached 80% and that of ORC reached 6%。
Xingyang Yang, Li Zhao
Abstract: In this paper, a distributed combined cooling heating and power (CCHP) generation system based on organic Rankine cycle (ORC) and parabolic trough solar collectors (PTSC) is introduced. This project is the first distributed CCHP system driven by solar energy partially in China and will be finished by 2014. This CCHP system is mainly consisted of parabolic solar collectors, a natural gas boiler, an organic Rankine cycle, a heating process heat exchanger and a LiBr absorption chiller. In this project, 1000m2 parabolic trough solar collectors are used to collect solar energy. The heat transfer fluid (HTF) in the solar subsystem is heated to 330 ℃ from 245 ℃ through PTSC and natural gas boiler and then is cooled to 245℃ after the heat exchange with the evaporator of the ORC. This system is designed to produce 200kW electricity and the electrical efficiency of the ORC is more than 10%, using an organic turbine whose isentropic effectiveness is more than 70%. The evaporating temperature of the ORC is 290℃ and the super-heat temperature is 10℃. The exhaust gas is used to fulfill the heat load in the winter and the cold load in the summer for a 1500m2 residential building, which is about 75kW and 120kW separately. A LiBr absorption chiller is used to produce cooling energy. In the end, a software developed by our group is introduced and it aims at providing users an optimum design after optimizing of the system both economically and technically. The system, a single system or an integrated system, is totally or partially driven by solar energy.
Dongkil Lee, Ho Ki Lee
Abstract: Because of IMO MEPC(International Maritime Organization Marine Environmental Protection Committee) 62nd Session, emission control and efficiency improvements of ships are became more important issue for current marine business. One of ways to achieve the efficiency improvement in the ships is recovering unused source of energy in the ships. Typically, current marine engines use only 50% of fuel energy for the shaft power and dump 30% to 40% as waste heat. For the low grade waste heat, the Organic Rankine Cycle(ORC) is one of the promising heat recovery power generatin cycles. ORC is a rankine cycle that uses organic fluid (High molecular mass fluid) with a liquid-vapor change occurring at a lower temperature than the water-steam phase change. The present work focuses on the heat transfer loop of Organic Rankine Cycle - Waste Heat Recovery System(ORC-WHRS) for the vessel. The considered ship type and engine type were Suez-Max Tanker and MAN Diesel & Turbo 6S70ME-C8.1-TII. The heat transfer loops were evaluated based on the power output of thermal cycle. Performances of ORC were calculated at the different temperature conditions of thermal loop. Calculated results were compared in terms of cycle and system efficiency. The result shows additional electricity of Maximum 660kWe con be produced by using ORC-WHRS, and the system has 9~13% of cycle eiifciency depends on the heat transfer loop design and pinch condition of heat exchanger. In this work show, ORC-WHRS con produce 60~73% of required electricity of Suez-max COT at the normal operation running condition and this lead to fuel saving effect. And Addition of evaporator and pre-heater were studied to maximize output power of ORC-WHRS. Exhaust gas, scavenge air and jacket cooling water were considered as possible heat sources to be recovered. Dual loop system which has multiple heat transfer loops for each waste heat source shows better performance than the single loop system which has only one heat transfer loop. By changing ORC evaporator and preheater, the output of ORC increased by 6~27%
Tiao Yuan Wu, Pai Hsiang Wang, Chun Da Chen
Abstract: Organic Rankine Cycle (ORC) generation system can convert heat to electricity and has been widely applied to in various heat sources with different temperature ranges. This technology helps to save energy consumption, reduce cost, and make more benefit. Especially, it is one of the few technologies that could efficiently recover low-temperature waste heat. In China Steel Corporation (CSC), some technologies such as co-generation have been employed to recover about 40% of waste heat, but no suitable systems could be used in the low-temperature region. Therefore, CSC developed a 10 kW ORC pilot plant and investigated the optimal operation to get higher efficiencies of power generation and net output power. The operation of ORC system involves some controllable and un-controllable parameters, and there are some constraints in the operation, for instance the maximum power generation capacity, and the maximum temperature of working fluid. Besides, some power consumptions from working fluid pump, hot water pump, cooling pump, and cooling tower fan should be considered to get the maximum efficiency of net output power; these will make the problems much complex. To get the maximum efficiencies of power generation and net output power, CSC employed a set of optimization methodology, including Design of Experiments (DOE), Response Surface Methodology (RSM) and Sequential Quadratic Programming (SQP), in a 10 kW ORC pilot plant. The DOE can help to plan the experimental parameters which will be used to effectively build the response surface. The response surface is a model that can predict the performance accurately and is usually used to parametric analysis or optimization analysis. The SQP is an optimization programming and can be employed to search global optimal values with some specified constraints in the response surface model. In the present study, the controllable parameters and the parametric boundaries are working fluid flow rate (20~40 kg/min), hot water temperature (100~120oC), hot water flow rate (70~150 LPM), and cooling water flow rate (130~310 LPM), respectively. By using this set of optimization methodology under the constraints of parametric boundaries and power generation < 10700 W (maximum power generation capacity), the maximum efficiency of power generation increases from 7.48% to 8.03%, about 0.5% better; the maximum efficiency of net output power increases from 3.88% to 4.48%, about 0.6% better. These improvement can be achieved easily only with changing the operating parameters and without any more cost.
Seyed Masoud Haji Seyedi, Seyed Majid Hashemian, Seyed Mohammad Reza Abolhassani, Fiete Dubberke, Amir Mohammad Haddad Momeni
Abstract: In this paper a new methodology is proposed for appropriate integration and optimization of an ORC as a cogeneration process with the background process to generate shaft-work. Hot source and cold sink of ORC cycle has been used as a hot and cold stream respectively in Pinch Design Method (PDM) for both retrofit and grass-root project. The considered working fluids are R245fa, Solkatherm SES36, 1234ze and HDR-14. First, a pre-design model of the ORC and process flow diagram was built and simulations ran with different working fluids. In second step, components and system cost models were built and simulations carried out to evaluate the cost effectiveness of systems associated with different fluids. It has been illustrated that the choice of cycle configuration for appropriate integration with the background process depends on the heat rejection profile of the background process (i.e., the shape of the below pinch portion of the process grand composite curve). Results also indicate that for the same fluid, the point of high performance and that cost-effectiveness does not match. The operating point for maximum power doesn’t correspond to the total specific income. The benefits of integrating ORC with the background process have been demonstrated through illustrative examples. Keywords: Process integration, Pinch Technology, Organic Rankine Cycle, Economic Optimization.
Xiaoye Dai, Qingsong An, Lin Shi
Abstract: Organic Rankine Cycle(ORC) was a suitable promising technology for the mid-and high-grade(180~350℃) heat energy, especially industrial waste heat. And high-temperature ORC gain more interest presently. In recent study, Alkanes were considered as suitable working fluids for high-temperature ORC by analysis of thermodynamic property. In fact, there were more aspects for the choice of working fluids and thermal stability is the important one. The thermal stability of some alkanes were studied by experiments. So the basic data about the thermal stability could be got in different temperatures. But thermal decomposition was not unacceptable certainly. There were different mechanisms of the harm of thermal decomposition, including noncondensable gas, carbon deposits and others. The effect of thermal decomposition of some alkanes was analysed concretely in the base of data about the thermal stability of them. So the suggested use temperature was given finally.
Adrian Rettig, Ulf Christian Müller
Abstract: Generating electricity in an economically reasonable way by utilising waste heat at lower temperature is one of the major challenges in ecological and efficient use of energy. One supporting key technology is the Organic Rankine Cycle (ORC). Integration of this into complex systems such as geothermal plants, biomass combustion or industrial processes to reuse the waste heat needs a sophisticated analysis of the whole process. To ensure an optimized performance of the combined technologies, accurate models of the coupled thermodynamic behaviour are crucial. The ORC performance including all components is of special interest since it mainly influences the investment decision. Thus, a modular simulation platform for ORC-processes based on Modelica and freely available libraries such as the Modelica Standard Library and ThermoPower has been devised. Two ORC-applications in Switzerland will be investigated using the modeling platform: a large scale application in cement industry (MW-scale) and a small bio gas CHP-application (double digit KW-scale). Currently, the focus is on characterizing the steady state behavior of these plants and the validation of the simulation results by on-site measurements. The tool will mainly be used to confirm the design and operation of the ORC-processes including all components and analyzing any unexpected deviations. In a next step, transient models are implemented that allow e.g. the analysis of control systems as well as start-up and shut-down procedures. It is planned to extend the tool by assessing more upcoming ORC-applications. Thus, libraries for components like different expanders or different working fluids will extend and boost the prediction capabilities of the platform. This offers the opportunity of supporting the evaluation of new ORC-processes and core components to contribute to an ecological and efficient use of energy.
Maria Justo Alonso, Yves Ladam, Trond Andresen
Abstract: This work describes the small-scale setup (ROMA) installed at the SINTEF Energy Research/ NTNU (Norwegian University of Science and Technology) laboratory, designed to generate electricity from low temperature heat (120 ºC). The system operates a CO2 power cycle from a hot gas heat source with similar temperature to those of an aluminium production cell. The ROMA set-up was capable of producing up to 0.5 kW electrical power with a maximum turbine efficiency of 40 %. Laboratory test rig construction and results for prototype operation are presented in this paper.
Stephan Paredes, Patrick Ruch, Chin Lee Ong, Brian Burg, Bruno Michel
Abstract: Waste heat is recovered from high concentration photovoltaic thermal (HCPVT) systems with the aim to enable multi-generation of electricity, cooling, and fresh water. This concept involves 80–90°C waste heat recovery from a low thermal resistance multi PV chip receiver package, 120°C from the optics, and thermal energy storage. The system recovers ~80% of the solar irradiation comprising ~30% as electrical energy and ~50% as heat. HCPVT systems provide a higher exergetic output than concentrated solar power installations due to the good conversion efficiency of triple junction photovoltaic cells (up to 44% in laboratory demonstrations) and their low thermal coefficient. A >25% system-level electrical efficiency can be reached while still having 50% medium grade heat. Conversion of the heat into cooling and desalinated water has been demonstrated using adsorption chillers and multi-effect vacuum membrane distillation systems, respectively [1]. We have estimated the economic value of heat with regard to its consumer and observed that this may differ markedly from its thermodynamic value depending on the system location. Using the generated heat in addition to the electricity boosts the economic value of the overall generated output by more than 20% [2]. Conversion of the heat into additional electrical output, however, is lacking an efficient low grade heat conversion process e.g. an organic Rankine process. Exergetic yields are compared between photovoltaic systems, concentrated solar power (CSP) systems, and HCPVT systems with medium grade heat output. From an exergy point of view, direct heat utilization from HCPVT systems for cooling and desalination is beneficial for key locations. Overall exergetic yields, flexibility, optimal plant size, and cost are neither optimal in photovoltaic nor CSP systems but HCPVT systems can compensate the disadvantages of both pure systems. For a successful power station application HCPVT systems require the conversion of low grade heat to electricity with an efficiency of >10%. With this combination an overall electrical system efficiency of >35% becomes possible – more than with any other solar installation. Combinations of HCPVT systems with Rankine processes using different working fluids are modelled. Since electrical power and cooling are in high demand in areas with high direct normal irradiance a combination of power generation and cooling has also been studied (Kalina and Goswami cycles). Finally, economic and technical modelling is carried out to determine the optimal size for HCPVT plants and match them to available heat conversion devices for high-efficiency multi-generation. REFERENCES [1] C.L. Ong, W. Escher, S. Paredes, A.S.G. Khalil, and B. Michel, “A novel concept of energy reuse from high concentration photovoltaic thermal (HCPVT) system for desalination”, Desalination 295, 70-81 (2012). [2] W. Escher, S. Paredes, S. Zimmermann, C.L. Ong, P. Ruch, B. Michel. Thermal management and overall performance of a high concentration PV. Proc. 8th Intl. Conference on Concentrating Photovoltaic Systems CPV8, 11477 (2012) 239-243.
Markus Preißinger, Theresa Weith, Florian Heberle, Dieter Brüggemann
Abstract: The Organic Rankine Cycle (ORC) is a widespread technology for geothermal applications and biomass fired power plants [1,2]. Due to challenging boundary conditions, like fluctuating heat transfer rates and a broad heat source temperature range, ORC units for waste heat recovery are still rare. Therefore, the adjustment of the ORC unit to the heat source is realized by choosing different working fluids and/or adapting the working pressure of the process. However, by changing the fluid, safety issues, plant specific aspects and thermodynamic conditions can change dramatically, especially when the new working fluid corresponds to a different chemical class [3]. From that point of view, the behavior of chemical classes instead of single working fluids is of great interest. In this study, homologous series of alkanes, alkylbenzenes and siloxanes are investigated for heat source temperatures of 300 °C to 600 °C. Firstly, the heat source temperature is varied and the influence of the working pressure on the exergetic efficiency is regarded for each fluid and temperature step. Secondly, the maximum exergetic efficiency and the corresponding fluid are determined from the gained results for each chemical class and temperature step. From these data a correlation for the maximum exergetic efficiency depending on the heat source temperature can be educed. For the homologous series n-pentane (C5) to n-undecane (C11) a polynomial dependency is found which predicts the maximum exergetic efficiency with a relative deviation of less than 2 % for the whole temperature range. Due to the location of the pinch-point at the beginning of the preheater, net power output depends linearly on the heat source temperature. However, pressure ratio in the turbine shows a polynomial dependency on the number of C-atoms. Additionally, main correlations for further thermodynamic and constructional parameters are deduced from simulation results and expressed by known physico-chemical input parameters (e.g. critical temperature, pressure and volume) or boundary conditions (e.g. heat source temperature). The prediction accuracy is better than 5 % for all investigated parameters. In summary, the above mentioned results are a first step towards a fluid-to-fluid modeling technique and, therefore, modular designed ORC power plants for the benefit of reduced simulation efforts for further scientific and industrial investigations.
Wei Wang, Yu-Ting Wu, Chong-Fang Ma, Jing-Fu Wang, Guo-Dong Xia
Abstract: Nowadays, the contradiction between continued growths in energy demand and gradually exhaustion of fossil energy become increasingly sharp, so energy saving has become the most urgent task. Among various waste energy resources, low temperature waste heat has a large proportion and no effective utilization, so people need develop distributed generation system (DGS) to recovery that energy. How to improve the performance of DGS is the key issue because of many technical bottlenecks. In this paper, different performance indexes of DGS based on Organic Rankine Cycle were analyzed by relevant thermodynamic principles. The thermodynamic model of Organic Rankine Cycle was described firstly, in which the thermodynamic performances of R134a, R245fa, R123, R600, R600a and R290 were compared, then the impact of expanders on ORC system was discussed, and finally potential improvement of ORC system using single screw expanders was evaluated. From the calculation results, it was found that there existed maximum net generation and highest thermal efficiency for certain heat sources and working fluids, and the optimized evaporation temperature in the former case was lower than that in the latter case. It was indicated that there existed different choices for difference types of heat sources. Ignoring the limitation of expanders, R245fa had the better thermal efficiency and the worse net generation than those of dry fluids R600a, for the same temperature difference between evaporation and condensation. However, for the same expansion ratio, both net generation and thermal efficiency of R245fa were worse compared with R600a. It was found that adiabatic efficiency would significantly influence the thermodynamic performance of power systems. For existent ORC experimental systems, as compared with refrigeration system, the corresponding indexes of efficiencies had a visible distance. However, it was also indicated that there is still huge room to improve.
Huixing Zhai, Qingsong An, Lin Shi
Abstract: Rational utilization of waste heat resources has great significance for energy saving and environmental protection. At present, medium and high (150-350℃) temperature waste heat from geothermal water, biomass fuel cannot use efficiently and waste heat from industry progress has generally been discarded. However, the most effective utilization is to generate power. Organic Rankine cycle (ORC) is an effective way to convert low-grade waste heat into power. This work studies the type, capacity and utilization situation of the 150-350℃ temperature waste heat in China, mainly including geothermal water, biomass fuel and waste heat from industry progress. The influence of the heat source characters on the ORC system’s payback time is studied based on the present technical status. Industry waste heat recovery system has the lowest cost while geothermal system needs an electricity price subsidy from the government. Finally, an approach to construct suitable heat sources for ORC systems in thermal dynamic and economic perspective is given, thus providing reference for the following ORC system research.
Bruno Vanslambrouck, Sergei Gusev, Tobias Erhart, Michel De Paepe, Martijn van den Broek
Abstract: The main goal of the EraSME project “Waste heat recovery via an Organic Rankine Cycle”, completed by partners Howest (Belgium), Ghent University (Belgium) and University of Applied Sciences Stuttgart (Germany) between 1 January 2010 and 31 December 2012, was to find an entrance in Flanders for the Organic Rankine Cycle (ORC) technology in applications with sufficient amounts of waste heat at high enough temperatures. The project was preceded by a similar study that focused on renewable energy sources. Several tools were developed to aid in the viability assessment, the selection, and the sizing of ORC installations. With these methods, a fast determination of feasibility is possible. The outcome is based on the size, nature and temperature of the waste heat stream as well as the electricity price. An estimate can be given of the net power output, the investment costs and the economic feasibility. The tool is linked to a database of ORC manufacturer specifications. Another objective of the project was to keep track of the evolution in ORC market supply, both commercial and precommercial. We also looked beyond the product line of the main manufacturers. Some ORCs are developed for specific applications. ORC technology was benchmarked against alternatives for waste heat recovery, such as: steam turbines, heat pumps and absorption cooling. ORC in or as a combined heat and power (CHP) system was also examined. A laboratory test unit of 10kWe nominal power was installed during the project, which is now used in further research on dynamic behavior and control. It is still the only ORC demonstration unit in Flanders and has been very instructive in introducing representatives from industry, researchers and students to the technology. A considerable part of the project execution consisted of case studies in response to industrial requests from several sectors. Detailed and concrete feasibility studies allowed us to define the current application area of waste heat recovery ORC in a better way. A knowledge center for waste heat recovery (www.wasteheat.eu) was initiated to consolidate the know-how and to advise potential users.
Stefano Briola, Seyed Majid Hashemian, Seyed Sajad Mousavi, Amir Mohammad Haddad Momeni, Seyed Masoud Haji Seyedi
Abstract: In this paper, an economic optimization of the “Peterson” thermodynamic cycle with a two-phase fluid expander, employed in lieu of a traditional Joule-Thomson (J-T) valve, is performed. A two-phase fluid expander is able to work with chemical species in the wet vapor phase in order to convert its thermodynamic energy in mechanical energy, by means of simultaneous expansion of the two phases. “Peterson” cycle can produce electrical and cooling power by using low temperature heat source. In this paper, some working fluids types (R245fa, Solkatherm SES36, 1234ze and HDR-14) and some two-phase fluid expanders types (scroll, screw and radial) are considered. First, pre-design model of the “Peterson” cycle and process flow diagram was built and simulations ran with different working fluids and two-phase fluid expanders types. In the second step, components and system cost models were built and simulations carried out to evaluate the cost effectiveness of the systems associated with different working fluids and two-phase fluid expanders' types. The operating point for maximum power doesn’t correspond to that of the minimum specific investment cost. The mismatch aforementioned is due to the thermodynamic properties which significantly influence system performance and components sizes. Finally, seeking for profitable environmental solutions, economic optimization has been performed. Keywords: Peterson Cycle, Economic Optimization, Joule-Thomson (J-T) valve
Hyun Dong Kim, Eun Koo Yoon, Kui Soon Kim, Jang Mok Kim, Sang Youl Yoon, Bum Suk Choi, Sangjo Han, Yang Bum Jeong, Kyung Chun Kim
Abstract: This study demonstrates the realization and performance test of an organic Rankine cycle (ORC) power generation system for waste heat recovery. The ORC system consists of two shell and tube heat exchangers for the evaporator and the condenser, a multi-stage centrifugal pump to feed R-245fa refrigerant into the evaporator, a turbo-expander module expected to deliver a power about 250kW and an electric generator. For the turbo-expander, concept of back-to-back two-stage expansion was adopted to increase expansion ratio up to 9.5 to achieve high thermal efficiency of the ORC system. The design point of the rotational speed of the expander was 15,000 rpm. Principal performance parameters of the whole system and of each component have been investigated on the experimental test bench comprised with two heat transfer loops. Thermal energy was provided into the evaporator through pressurized hot water circulating between 2MW electrical heater and evaporator. The influence of temperature of the heat source on the net power output, thermal efficiency, power consumption, mass flow rate and expander outlet temperature at a given pinch point temperature have been analyzed. From the result of performance test of heat exchanger, it is confirmed that the absolute pressure attained to 20bar at the exit of evaporator and amount of exchanged heat between hot water and refrigerant is about 1,700kWth at the design condition of cycle which is 140°C of hot water temperature and 16.5kg/s of water mass flow rate. Moreover, electric power output of 110kWe from the generator is achieved at the condition of mass flow rate of refrigerant of 5kg/s and isentropic efficiency of turbine expander and thermal efficiency of ORC system is about 70% and 8%, respectively. Acquired performance parameters and efficiencies were compared to those expected from the thermodynamic cycle analysis. Base on these results, numerical simulation of the ORC system was conducted using Matlab Simulink capable to calculate thermodynamic cycles in steady and transient conditions. The simulation results could be used to predict the main working parameters and system performance and choose a suitable operation strategy for the entire system.
Eunkoo Yun, Hyun Dong Kim, Sang Youl Yoon, Kyung Chun Kim
Abstract: Organic Rankine cycle (ORC) system has good potential for heat recovery from low-temperature heat sources. But, in some applications including industrial facilities, marine engines, solar thermal heat, and other sources, the heat fluctuation from heat source is very large. Due to the large heat fluctuation, the efficiency of single-expander system could be severely reduced, and the system might be non-operational. In order to overcome the limitation, this study proposes an ORC system with multi-expander in parallel which can actively respond to the large heat fluctuation. This study aims to evaluate the performance of an organic Rankine cycle (ORC) power system adopting multi-expanders in parallel by simulation and experiment. The ORC system consists of two scroll expanders installed in parallel, a hydraulic diaphragm type pump to feed and pressurize the working fluid, two plate heat exchangers for the evaporator and the condenser. The two scroll expanders were modified from two oil-free air scroll compressors (Kyungwon Co., Ltd., Korea) with same specifications, and were tested in the ORC loop with R245fa. The hot water was used as heat source and the temperature was controlled up to 150 °C by the 150 kW-class electric heater. In order to determine the static performance of the system, efficiencies and shaft powers for both single and dual operation modes were measured under various heat source temperature conditions ranged from 110 °C to 140 °C. The maximum isentropic efficiency of each expander was measured about 70%, and the shaft power was reached to about 3 kW at the turbine inlet temperature of 140 °C. In addition, dynamic performance tests were conducted with oscillating heat flux conditions. The characteristics and overall efficiencies of the dual parallel expander ORC system with regards to various heat source conditions and operation modes will be addressed.
Taehong Sung, Hyun Dong Kim, Sang Youl Yoon, Kyung Chun Kim
Abstract: This study aims to develop a hydro-thermal model and simulation code of solar ORC (Organic Rankin Cycle) system, and to predict capable efficiency of energy conversion from solar to electrical and thermal energy for a regional feasibility study. Solar ORC system is one of solar power systems including photovoltaic power generation. The hydro-thermal performance of solar ORC system should be addressed for operating conditions with environment variables, working fluids and mechanical components including solar collector, expander, generator, pump, condenser, ducting, refrigerant storage tank, etc. Recent researches have focused on the system configuration, design point simulation and the suitability of various working fluids. However, the system performance strongly depends on operating conditions, especially the ambient temperature and amount of the solar radiation. In our literature review, the available energy efficiency with operating scenario under regional specific conditions has not been fully studied. We are developing a model of solar ORC system and an in-house simulation code for various classes of solar ORC system, for various working fluids, and for different mechanical components. In the seminar, the hydro-thermal model of solar ORC system and simulation results under various regional daily and annual environmental conditions will be presented. The simulation result includes available electrical and thermal energy efficiencies.
Jing-Fu Wang, Yongzhi Zhang, Yong Zhang, Jifen Liu, Wei Wang
Abstract: The rapid development of social economy is restricted by the energy shortage and the environment deterioration. The development and utilization of renewable energy has been listed as priority areas for energy development. As one of the alternative energy, geothermal energy gets more and more attention. Usually high temperature geothermal energy is the most suitable energy in power generation, but most geothermal energy is low-medium temperature heat source. The key technology which limits the development of low-medium temperature geothermal power generation system is its low efficiency. In this paper, a new low-medium temperature geothermal power generation system with Organic Rankine cycle (ORC) and single screw expander as power engine was developed, which aims to improve the efficiency of low-medium temperature geothermal power generation. Firstly, based on the principles of thermodynamics, the basic operation principle of this power system was analyzed. Then the method of determining the main parameters of this system was proposed. On the basis of theoretical analysis, two circulation types of this system, that are saturated ORC and vapor-liquid two-phase ORC, respectively, were analyzed. In this system, two kinds of refrigerant R601 and R134a were used as the working fluid. The results show that the vapor-liquid two-phase ORC is better than saturated ORC, and the performance of R601 is better than R134a on the basis of comprehensive comparisons at geothermal fluid temperature between 80℃~120℃. However, R134a is better at geothermal fluid temperature between120℃~150℃. In this temperature ranges, the evaporation temperature should be less than critical temperature of working fluid. A regenerative organic Rankine cycle system for low-medium temperature geothermal power generation was also studied in this paper. The influences of evaporation temperature, condensing temperature and extraction pressure on regenerative organic Rankine cycle system, respectively, were analyzed. The properties of ORC system with and without regenerator were compared. It is found that the thermal efficiency of ORC system with regenerator was higher compared to the one without regenerator.
Yuanwei Lu, Guanglin Liu, Yu-Ting Wu, Chong-Fang Ma
Abstract: Organic Rankin cycle for power generation can make an effective use of geothermal heat. Organic working fluids with low boiling point can take advantage of low-to-medium temperature of geothermal fluid for power generation, which has less pollution to the environment than other forms of power generation. Therefore, people pay more attentions on it. Supercritical organic Rankin cycle system can theoretically form a "triangular" shape of cycle, during which the working fluids can change directly from sub-critical to supercritical state in the evaporator and the temperature of it can change continuously with no phase change. Researches showed that exergy efficiency of supercritical organic rankine system can reach 50%. However, there is few research on the effect of expander inlet temperature and pressure on the net power at different geothermal temperature. The working fluids are also need to be studied in supercritical geothermal power generation system. In this paper, a supercritical organic Rankin cycle with heat recovery process (as shown in Fig.1) using medium-temperature geothermal fluid (150 ℃ - 180 ℃) as heat source was built to study the effect of different parameters on the net power. In order to form a supercritical organic Rankin cycle, the critical temperature of working fluids should be lower than the heat source temperature. For the fluorocarbons working fluids can be decomposed when it contact with oil, steel or iron at the temperature above 122℃. Therefore, in this paper the R290 (propane) was choiced as working fluid. The experimental results showed that at the different geothermal temperature there existed an optimal temperature and at the optimal temperature condition there existed the optimal evaporating pressure.
Mohammad Kordi, Vahid Esfahanian
Abstract: The invention of bond graph was driven by the need for a common language to model complex systems involving different energetic domains. Bond Graph is a graphical representation of a physical and energy system model. It is based on the representation of the flow of the different types of energy that are involved. An important advantage of this modelling process is its simplicity lends itself to be used for wider variation of system parameters. In this paper, an ORC-based unit for modelling and simulating its performance has been modelled in unsteady state. Our model subject find out the state space differential equations of the system which contains different subsystems such as burner, pumps, heat exchangers, turbine, generator, fuel injection system, nozzle and shaft dynamics. We use bond graph method for modelling this system especially because of complexity of components and stages in addition to nonlinearity performance of the subsystem. Whereas this system is base on energy distribution in all elements. First we draw our system bond graph then according to bond graph we find our state equations that has been simulated with use of initial conditions. Finally, the variability of pressure, temperature, rotational speed and pressure history in each stage according to time have been showen. The effects of variations for some significant parameters including the main component's pressures, temperatures and mass flow and main shaft inertia and velocity have been presented. The results are validated against published literatures. REFERENCES [1] D. Karnopp, D. Margolis, R. Rosenberg, Systems Dynamics a Unified Approach, John Wiley and Sons, 2000. [2] P.C. Breeveld, Multibond Graph Elements in Physical Systems Theory, J. Franklin Ins., 1985.
Vahid Esfahanian, Mohammad Kordi, Kamran Mahootchi Saeed
Abstract: A comprehensive thermodynamic simulation and modelling of a biomass system for heating, electricity generation and hot water production are needed to design and evaluate a biomass system. This biomass system consists of a gas turbine cycle, an Organic Rankine Cycle (ORC) and a domestic water heater. Energy, exergy, exergoeconomic analyses and environmental impact assessments and related parametric studies of each thermodynamic unit helps designers to find ways to improve the performance of the system in a cost effective way, and parameters that affect environmental impact and sustainability. The objective of this paper is to evaluate irreversibility of a Biomass-ORC Unit and it's thermodynamic modelling. The effect of changes in main parameters on the exergetic efficiency and exergy destruction in the biomass-ORC unit has been evaluated. The exergy destruction and exergy loss of each component of this ORC unit have been estimated. Moreover, the effects of the load variations and ambient temperature have been calculated in order to obtain a good insight into this analysis. The exergy efficiencies of the Burner, ORC-turbine, pump, evaporator and the condenser have been estimated at different ambient temperatures. Additionally, the exergoeconomic and exergoenvironmental analysis have been performed for each component of the ORC unit in order to calculate the cost of exergy destruction. The biomass-ORC unit include of a burner, heat exchanger, evaporator, ORC-turbine and condenser. The design parameters of the unit chose as: ORC-turbine pressure ratio, ORC-turbine isentropic efficiency, combustion chamber inlet temperature, and turbine inlet temperature. The main program has been developed in MATLAB Software programming. In order to find the optimal system design parameters, a exergoeconomic and exergoenvironmental approach also have been followed. In this article, the effect of some thermodynamic or system parameters in a biomass-ORC unit for one region in Iran, with hot–dry climate conditions have been conducted, as a case study. REFERENCES [1] Tj. Kotas, The Exergy Method of Thermal Plant Analysis, Butterworths: London, 1985. [2] M.S. Peters and K.D. Timmerhaus, Plant design and economics for chemical engineers, 4th Edition, McGraw Hill, 1991.
Joon Ahn, Min J. Sung, Byung-Sik Park
Abstract: A series of numerical simulation has been carried out to study thermo-hydraulic characteristics of a primary surface type heat exchanger, which is designed for the evaporator and condenser of a geothermal ORC. Working fluid is geothermal water at hot side and R-245fa, which is a refrigerant designed for ORC, is at cold side. Effects of aspect ratio and amplitude are considered as design parameters. Nusselt number is presented for the Reynolds number ranging from 50 to 150 and compared to existing correlations. The result shows that higher aspect ratio channel gives better heat transfer performance within the range of investigation.
Ye-Qiang Zhang, Hang Guo, Yu-Ting Wu, Guo-Dong Xia, Chong-Fang Ma
Abstract: In order to meet the demand of power in islands and remote regions without electricity, a new distributed trough solar power system based on single expander and organic Rankin cycle (ORC) is proposed. Contrast with popular trough solar power, this type of trough solar power is characterized by small output power from 1 to 500 kW and low temperature of working fluid. Traditional turbines are mainly designed for larger-scale applications and could not be used in so small power plants. Single screw expander can realize 1-200 kW range of output power and has many advantages, such as balanced loading of the main screw, long working life, high volumetric efficiency, high partial loading, low leakage, low noise, low vibration and simplify configuration, etc. R245fa is used as working fluid. A thermodynamic model was set up to calculate the output power and efficiency of ORC system based on the basis of adiabatic efficiency and mechanical efficiency of the single screw expander tested at previous experiment. The results indicate that the efficiency is improved with the increase of expansion ratio at the condition of 3.4MPa evaporating pressure. The efficiency with two-stage expansion is litter higher than single-stage expansion. The ORC efficiencies with regenerator markedly increase as the increase of superheat temperature and significantly higher than that without regenerator. The efficiency of concentrating collector is 72% at top tested before, and usually is 60%. The efficiency of ORC is 19.5%, then the peak efficiency of the trough solar power system is 14.04% and average efficiency is 11.7%.
Giampaolo Manfrida, Daniele Fiaschi, Francesco Maraschiello, Duccio Tempesti
Abstract: Organic Rankine Power Cycles (ORC) are well proven and reliable technology for energy conversion, particularly for exploiting low-temperature heat source. Nowadays, ORCs are increasing in popularity with several manufacturers of equipment available on the market. A lot of research has been dedicated to this subject, either on the heat source or on the system design and analysis, either on the criteria for selection of optimal working fluid or on the design of the expander (scroll, screw, micro-turbine, etc.) [1-3] In this paper, a micro combined heat and power (CHP) plant operating through an Organic Rankine Cycle (ORC) using geothermal energy at low temperature (80-100°C) and solar energy is presented. The system is designed to produce 50 kWe with a single turbine, while the solar field is composed only by evacuated solar collectors. The CHP plant is designed using meteorological data for a city in the centre of Italy and it is optimized in terms of cycle efficiency by varying the upper cycle pressure. Starting from the results of the energy analysis of the CHP-ORC system, a preliminary step by step design of a radial micro-turbine is carried out. The main innovative features of proposed design are the use of real fluid properties instead of ideal gases, and the estimation of turbine losses [4-7]. Six different fluids suitable for low-temperature energy conversion are investigated: R134a, R236fa, R245fa, R1234yf, n-pentane, cyclohexane. All the calculations are carried out with Engineering Equation Solver (EES®). The results show that the system can reach interesting first law efficiency (17% with cyclohexane and 15% with R245fa). Concerning the design of the turbine, for all the working fluids values of turbine efficiency within 0.78 and 0.85 are obtained, with R134a showing the maximum value (0.85). In addition, all the fluids present the same distribution of turbine losses, with friction and secondary flow losses accounting for approximately 70% of all the losses. REFERENCES [1] Schuster A, Karellas S, Kakaras E, Spliethoff H. Energetic and economic investigation of Organic Rankine Cycle applications. Applied Thermal Engineering 2009;29:1809–1817 [2] Heberle F, Brüggemann D. Exergy based fluid selection for a geothermal Organic Rankine Cycle for combined heat and power generation. Applied Thermal Engineering 2006;30: 1326-1332 [3] Tchanche BF, Lambrinos Gr, Frangoudakis A, Papadakis G. Low-grade heat conversion into power using organic Rankine cycles – A review of various applications. 2011;15:3963-3979 [4] Dixon S.L.,” Fluid Mechanics and Thermodynamics of Turbomachinery”, 1998; Butterworth, New York. [5] Whitfield A., Baines N.C.,”Design of radial turbomachines”, 1990; Longman, New York [6] Whitfield, A., “The Preliminary Design of Radial Inflow Turbines”, ASME J. of Turbomachinery, 1990;112:51-57. [7] Benson S. Rowland. " A Review of Methods For Assessing Loss Coefficients In Radial Gas Turbines". Int. J. mech. Sci. Pergamon Press. 1970;12:905-932. ACKNOWLEDGMENT The results here presented have been obtained within the framework of the project BT GEO H&P, funded by Regione Toscana, using European Social Fund (FSE) resources.
Omar Al-Ani, Patrick Linke, Mirko Stijepovic, Athanasios Papadopoulos
Abstract: Organic Rankine Cycles (ORC) received a lot of attention in recent years as a promising technology to convert low grade heat to power. Numerous researches have shown that ORC offers substantial advantage over conventional Rankine cycle. The ORC may be employed to produce power from variety low grade heat sources. The performances of ORC depend of heat source and employed working fluid. Multiple studies have been conducted on different techniques to increase the efficiency of the ORC. Most of studies are devoted to finding of optimal working fluid with favorable thermodynamic and thermo-physical properties. Utilization of working fluids composed of two or more fluids seems to be promising path for enhancing ORC performances. From the other side a few studies are performed with intention to explore possible configuration modifications of ORC. In this study, we examine a novel configuration of an Organic Rankine Cycle (ORC). The use of a novel configuration allows for higher thermal efficiency by decreasing the pinch point between the heat source and the working fluid. Exergy analysis is performed to examine the various thermodynamic performance measures in such a configuration and compared to a simple ORC configuration. The exergy destruction, thermal efficiency, and second law efficiency are compared for each configuration. Also, each component is examined to locate where significant irreversibilities occur. A case study will be used to illustrate the benefits of using the novel configuration.
Theresa Weith, Dieter Brüggemann, Andreas P. Weiß, Gerd Zinn
Abstract: Waste heat of biogas cogeneration units as well as plenty kinds of industrial waste heat provide high potential for power generation by applying Organic Rankine Cycles (ORCs). In this field of application, where high heat source temperatures can occur, conventional ORCs normally comprise an additional thermal oil loop in order to prevent the ORC working fluid from decomposition as well as to avoid self-ignition of the fluid when getting into contact with hot exhaust gas due to leakage. Moreover, when regarding small-scale plants with a power output of less than 30 kWel, scroll or screw expanders are mostly used as an expansion device. The described state-of-the-art systems suffer from several disadvantages, like high investment costs and complex plant design in case of thermal oil loop together with low efficiencies of common expansion devices. Therefore, the present work deals with the development of a 15 kWel ORC plant for waste heat recovery with a direct evaporator and a micro-expansion turbine. Working fluids that come into consideration are preselected by taking into account property data as well as non-thermodynamic issues as for example economic aspects and the fluid’s hazardous potential to health, water and environment. Aside from this, steady-state process simulations have been performed for heat source temperatures in the range of 573 K to 673 K and the effect of fluid specific turbine efficiency on the overall electric efficiency of the ORC has been investigated for three selected fluids. The results show an increase in ORC efficiency as the fluid-specific turbine efficiencies exceed the primarily assumed turbine efficiency of 60 %. For the example of cyclopentane, a relative improvement in overall electric efficiency of up to around 16 % could be observed. Moreover, the maximum of the overall ORC efficiency is shifted towards lower pressures. Turbine optimal design and efficiency strongly depend on several parameters, e.g. operating pressure ratio, volumetric flow ratio or specific speed, which are mainly determined by the applied ORC fluid. Hence, it affects the choice of the proper working fluid as well as the design point of the ORC plant. Based on the theoretical results, cyclopentane was chosen as promising working fluid for the present ORC plant. Process simulations with cyclopentane predict a maximum electric efficiency of 11.65 % for a heat source temperature of 623 K, an upper pressure of 20 bar and an isentropic efficiency of the turbine of 64.3 %. Currently, a pilot plant is under construction consisting of a plate-and-shell heat exchanger for direct evaporation, an axial impulse turbine, a piston diaphragm pump, an air-cooled condenser as well as a gas burner as heat source. The authors gratefully acknowledge financial support by Bayerische Forschungsstiftung.
Deng Pan, Naiping Gao, Feibo Xie, Tong Zhu, Hai Wang, Haiying Wang, Wei An
Abstract: The performance of a scroll expander modified from compressor was tested in an organic Rankine cycle (ORC) system. The ORC system mainly consisted of evaporator, scroll expander, plunger pump and condenser. The test rig employed R123 as working fluid. A natural gas burner was employed as the heat source whose flue-gas temperature was about 250℃. The performance of the scroll expander was investigated under different pump capacity and different electric loads. The maximum output power of the expander was 2.56kw and the maximum isentropic efficiency was 78.75% under the testing conditions. The evolutions of output power and isentropic efficiency with the pressure ratio and rotation speed were obtained. In the second part, a 2-D model was established to simulate the working process of the scroll expander by the approach of computational fluid dynamics (CFD). The pressure distribution in the scroll expander and its variation with the crank angle were analyzed.
Jang-Won Seo, Sanghyuk Woo, Chanyong Cho, Byung-Sik Park
Abstract: A wavy-corrugated primary surface heat exchanger was tested under two-phase flow conditions by using a water/r245fa as the hot and cold stream respectively. Performance experiments for a wavy-corrugated primary surface heat exchanger (PSHE) of high-performance and high-effectiveness on the technologies of high-density fin folding were performed in this study. The wavy-corrugated PSHE were experimentally investigated for Reynolds number in range of 1 ~ 600 under various flow conditions on the hot side and the cold side. The inlet temperatures of the hot side were conducted in a range of 70˚C ~ 80˚C while that of the cold side were fixed at 12˚C. The average heat transfer rate, heat transfer performance and pressure drop increases with increasing Reynolds number in all experiments. Increasing inlet temperature in the experiment range causes the heat transfer performance to increase while the pressure drop decrease slightly. The experimental correlations to the heat transfer coefficient and pressure drop factor as a function of the Reynolds number have been suggested for the wavy-corrugated PSHE.
Amir Mohammad Haddad Momeni, Mohammad Reza Jaffari Nasr, Seyed Masoud Haji Seyedi, Venus Shaker
Abstract: A.M. Haddad Momeni*, M.R. Jaffari Nasr† S.M. Haji Seyedi‡ and V. Shaker‡ *Moshanij Consulting Engineers Co, No. 20, 107 St, Golsar, Rasht, I. R. Iran e-mail: haddad_momeni@moshanij.com Web page: http://www.moshanij.com ABSTRACT In this paper, pinch technology is applied in a transition gas station to decrease energy cost in Organic Rankine Cycle (ORC). A gas station which used gas engine as a driving part of compressor is considered. There are potentials for heat recovery available from waste heats at inner and after cooler of compressor, also at the flue gas, water and oil cooler of gas engine. In addition, there are available cold utilities as air cooler, cooling tower and hybrid cooling tower. So, optimization of process to select the best cold utilities is performed. The considered working fluids are R245fa, Solkatherm SES36, 1234ze and HDR-14. In this study, as a first step, a pre-design model of ORC and the process flow diagram of gas station streams were built and simulated with different working fluids runs. In the second step, components and system cost models were built and the simulations again carried out to evaluate the cost effectiveness of systems associated with different fluids. The results indicated that for the same fluid, the point with high performance and the cost-effectiveness is not match. The operating point for maximum power is not corresponded to the total specified revenue. The benefits of integrating ORC and the applicability of the proposed methodology have been demonstrated through illustrative examples in one of Iranian gas station as a case study. Keywords: Gas Station, Pinch Technology, Organic Rankine Cycle, Economic Optimization. REFERENCES [1] Nishith B. Desai, Santanu Bandyopadhyay, “Process integration of organic Rankine cycle”, Elsevier. Energy Press, Vol. 34, pp. 1674–1686, (2009). [2] R. Smith, Chemical Process Design and Integration, 2nd Edition, John Wiley & Sons, 2005
Sanne Lemmens, Aviel Verbruggen
Abstract: A large technical potential for ORC deployment exists of smaller scale systems, but most commercial applications are in the MW range, and only a few in the kW power range. Today, most research is spent on technical ORC improvements, and cost aspects are treated as an ex-post add-on. Recognizing high investment costs as the main impediment for wide application, this research considers minimization of life-cycle expenses on ORC projects as the main objective.
Lars Bennov, Jorrit Wronski, Wiebke Brix Markussen, Fredrik Haglind
Abstract: n-Pentane is a suitable working fluid for ORC applications exploiting temperatures around 180 ◦C. This work investigates the heat transfer process in brazed plate heat exchangers (BPHE) for n-Pentane. It provides more accurate information regarding the boiling process, which is not much discussed in literature, yet. According to Roser et al., two-phase heat transfer is significantly influenced by mass velocity and is therefore dominated by convective boiling. Whereas Dario et al. conclude that nucleate boiling dominates due to a strong heat flux a dependency. We present a preliminary experimental analysis carried out with a test rig consisting of a plate-type preheater and evaporator as well as an expansion valve, a condenser and a pump. First tests were made with a maximum temperature and pressure of 145 ◦C and 5 bar, respectively, with a mass flow of approximately 0.05 kg/s. A numerical model is developed to compare experimental results with established heat transfer and pressure drop correlations from literature. Based on experimental and modelling results, the influence of nucleate and convective boiling is identified alongside other important parameters. Correlation from Focke et al. correlates the experimental single-phase heat transfer coefficient, whereas correlation from Khan et al. correlates the two-phase data. New correlations for single- and two-phase heat transfer of n-Pentane in BPHE, suitable for small-scale ORC, are developed from existing correlations. The molecular structural similarity of alkanes suggests that results can also be relevant for other alkanes, which yet is to be proven.
Alessio Tafone, Andrea De Pascale, Jorrit Wronski, Lisa Branchini
Abstract: This work investigates the use of advanced organic Rankine cycle designs to exploit a low temperature and a medium grade energy source represented by a solar application and waste heat from a marine diesel engine, respectively. Regarding the latter, we consider two different operating points: full load and at 60 % load. To improve the ORC efficiency and net power output of the classic one stage cycle, different cycle configurations have been considered, such as double stage (DS) and two pressure levels (2PL) systems. The thermodynamics and processes of the different organic Rankine cycles, as well as the heat source models, are described in details and the many assumptions and constrains are pointed out. A thermodynamic optimization and fluid comparison has been carried out for each configuration by means of the numerical software EES, which allows to compute the thermo-physical properties of the considered fluids throughout the whole cycle. Heat exchange is described with the pinch point approach. The ORC performances of each system are compared in terms of different indices such as cycle efficiency, total energy output and power output. Moreover, in order to partially take into account an economic evaluation of the investigated power plants, we have introduced two more parameters: the volumetric expansion ratio (VER) and the total heat transfer capacity (ΣUAtot). The results show a slight superiority of advanced systems compared to single stage configurations in terms of thermal efficiency and power/energy output for both heat sources. Yet, taking into account the economic parameters like the complexity of the advanced power plants due to the introduction of more than one expander and additional heat exchangers, one stage systems appear to be the better way to utilize both low-grade thermal energy sources.
Wei Liu, Dominik Meinel, Christoph Wieland, Hartmut Spliethoff
Abstract: Working fluids, i.e. different refrigerants, with a variety of thermodynamic properties are of great interest for Organic Rankine Cycles (ORC) operating with different low temperature heat sources. However, most of the currently used working fluids have destructive effects on the environment, e.g. depletion of the ozone layer or global warming. To reduce the enviromental effects, refrigerants have been progressed from Chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs) to Hydrofluorocarbons (HFCs) in the past decades. Hydrofluoroolefins (HFOs), i.e. derivatives of propene, have emerged in recent years as the fourth generation of refrigerants which are considered to be one of the most promising replacements for third generation refrigerants like HFCs as it possesses considerably lower effects on the environment. This work will present a study concerning the thermodynamic performances of eight different HFOs as working fluids in ORC applications. The thermodynamic properties of the HFOs are estimated using the Peng-Robinson equation of state in combination with the group contribution method. Simulations are carried out in Matlab, in which the self-developed calling functions are added for calculation of thermodynamic parameters. In this study the heat source is represented by geothermal brine. The temperature region around 140 \degree C is of especial interest for Germany, since these are common temperatures obtained in the Molasse-basin in Germany. On this account, the inlet temperature of the heat source is varied from 120 to 200 \degree C, while the operating system pressure of the ORC-system is increased from 15 to 30 bar. At a constant system pressure the system efficiency is strongly increasing for low geothermal temperatures and changes only slightly beyond a specific temperature. This temperature indicates the point, where the pinch-point changes from evaporator to preheater. These points are determined for the investigated ORC fluids at corresponding system pressures. Depending on the level of the inlet temperature of the heat source the operating pressure influences the system efficiencies in different ways. Taking R1225yeE as an example, at a lower inlet temperature (<=130 \degree C) the system efficiencies reach maxima at intermediate operating pressures (between 15 and 17.5 bar). On the other hand, at a higher inlet temperature (> 130 \degree C) the system efficiencies increase monotonically with increasing system pressures.
Eiichi Sakaue, Katsuya Yamashita
Abstract: In response to growing interest in the global environment, many low-GWP hydro-fluorocarbon fluids have been developed. Some of their accurate physical properties are disclosed to public from their suppliers or from public organizations, such as National Institute of Standards and Technology (NIST). To evaluate the performance of the ORC system, process simulators are often used. In case a new fluid is used as the ORC’s working fluid, its physical properties need to be input to the simulators. Equation of State (EOS), which models the relationship of pressure P, volume V and temperature T, is commonly used to express the thermodynamic properties of the fluid. Many simulators accommodate an option to select the type of EOS and require us to input the parameters for the selected EOS. Cubic EOSs, such as Peng-Robinson, are most popular type and only critical pressure Pc, critical temperature Tc and the eccentric factor ω are required to be input. However they do not perform well near the critical points and do not show accurate ORC performance even if we obtain accurate thermodynamic data of the working fluid. On the other hand, virial types of EOS, which have large degree of freedom, are so complicated formula that they require large computational resources to conduct their parameters while they have the risk to fall into local minimum. To solve above problems, simplified BWR (Benedict–Webb–Rubin) EOS is proposed here. BWR [1] is a virial type EOS. Taylor expansion is applied here to achieve its simplified formula. Accordingly this enables us to use least-square method for curve-fitting from accurate thermodynamic data. Hence the EOS parameters can be solved analytically with small computational power. The proposed method expresses the PVT relationship well near the critical point with providing plenty of neighborhood data to curve fitting. The deviation from the original data decreases to 1/6 compared to the estimation from Peng-Robinson EOS. This will help to evaluate the ORC system which comprises a new fluid as its working fluid. REFERENCES [1] K.E. Starling, Fluid Properties for Light Petroleum Systems, Gulf Publishing,1973
Marcio Verhulst, Andres Hernandez, Bruno Vanslambrouck, Martijn van den Broek, Michel De Paepe
Abstract: As Organic Rankine Cycle (ORC) systems are designed by means of parametric calculations and simulations [1,2], tests should be performed to check if the real setup can deliver the promised specifications. Therefore the research group has built a test bench for ORC systems which is capable of delivering thermal oil, Therminol 66, at a maximum temperature of 350°C and with heat exchange capacity of 250kW. For the cold side a cooling loop was built with a cooling capacity of 480kW at an average coolant exchange temperature of 80°C and outside air temperature of 20°C. Because almost every ORC setup is customer-specific, the heat source simulator can provide a wide variety of standard load patterns such as steady state with added distortion signals, block wave functions, etc. If required, custom load patterns can easily be uploaded and simulated through the LabVIEW [3] control application which was designed by our own team. As the simulator is built to simulate even very dynamic heat sources, it is capable of making large heat supply jumps within seconds (positive and negative). This way ORCs can be tested in both steady state and dynamic behaviour and control strategies can be designed and tested in a fast, easy manner. Considering the large amount of energy for a laboratory environment, and to ensure a stable and safe operation, a Programmable Logical Controller (PLC, in this setup a Siemens S7 1200 series) takes care of the execution of the IO from the LabVIEW control application and has built-in safety procedures. When designing new control strategies for an ORC application, not only the heat and cold source are controlled by this LabVIEW and PLC configuration, also the ORC system is controlled by the latter, offering direct control over the various ORC components and ensuring optimal measurement data. Another benefit of this system is the continuous safety monitoring of the components and complete system. Whilst designing a controller / control strategy, a variety of errors can occur during tests, not always keeping the ORC within its design limits. Therefore we have implemented an algorithm in the PLC which automatically switches to a standard controller, bringing back the ORC to a steady and safe state if the application is going out of design limits. This is a poster abstract.
Stephanie Frick, Stefan Kranz, Ali Saadat
Abstract: ORC power plants using low temperature heat sources (approx. 100 to 200 °C) are characterized by relatively low conversion efficiencies and high amounts of waste heat. Since low temperature ORC are typically located close to the heat source (e.g. waste heat from industrial processes or low temperature geothermal resources), once-through-cooling typically is not applicable so that wet cooling towers or air-cooled condensers have to be used. The net power output of low temperature ORC power plants is hence significantly depending on the condensation temperature as well as the auxiliary power demand of the cooling equipment. The reason is that both gross power output and auxiliary power demand for the cooling equipment increase with decreasing condensing temperatures. Since geothermal driven ORC power plants - in comparison to other ORC applications - are especially dependent on an improved plant design in order to come up for the technical and financial effort when accessing a deep geothermal reservoir, the optimization of the cooling system is part of geothermal research. Experience from running geothermal power plants as well as the planning of the GFZ geothermal research power plant shows that optimization potential exists for the planning and operation of the cooling system. By means of numerical simulation studies in the software environment DYMOLA/Modelica the influence of changing ambient / cold source conditions on the performance of low temperature ORC power plants with different cooling system set-ups and operation strategies has been studied. Based on the study results, the contribution will present and discuss different aspects of optimizing the design and operation of wet cooling towers and air-cooled condensers. Recommendations how an improved cooling system design could be realized will also be addressed.
Piotr Kolasiński, Zbigniew Gnutek
Abstract: The ORC systems used for waste heat recovery are mainly powered from industrial waste heat sources. The industrial waste heat sources are characterized by a set of specific characteristics resulting mainly from their nature. Sources with the large thermal power and steady output characteristics can be used directly for ORC system powering. But, in the industry, an large group of dynamic waste heat sources exists. Such sources often have large thermal potential but their appearance is periodic. They appearing in all industrial energy conversion processes, but practically are not used. The commonness and large potential of such sources are interesting to consider their for the ORC system powering. In case of standard ORC systems dynamic working conditions are inadvisable. The design of special ORC system that can be adaptive to the heat source characteristic fluctuations would be very difficult and expensive as the special heat exchangers, expander and proper control system have to be worked out. Therefore interesting, in authors opinion, is to carry out the theoretical analysis and to find out the possible methods of dynamic heat source characteristic modulation. Application of modulation method will result in steady heat source characteristic which will be acceptable for the standard ORC system powering. This paper presents a theoretical study on a different methods of the dynamic heat source characteristic modulation. The main objectives of this work were therefore proposals of modulation methods and their comparative analysis. Moreover the proposals of configuration of the ORC power systems powered by dynamic heat sources are presented here together with a set of parameters useful for the system work quality assessment. The analysis presented in this paper indicates that dynamic characteristic modulation can be an option for application of the standard ORC system to the dynamic heat source.
Venus Shaker, Mohammad Reza Jaffari Nasr, Seyed Masoud Haji Seyedi, Amir Mohammad Haddad Momeni
Abstract: This study examines the performance of a gas compressor station combined with an organic Rankine cycle (ORC) to optimize energy efficiency. Two gas stations with different drivers associated with reciprocating compressor and axial type turbine are considered. The waste heat can be recovered and used from the compressor’s exhaust gas and from the compressed gas that have to be cooled in order to push a higher volume of gas through the pipeline. A thermodynamic analysis on the exhaust gas is performed to determine likely adequate recoverable heat exist used in a Rankine power cycle. Individual models are developed for each component through applications of the first and second laws of thermodynamics. The effects of working fluid types and operating parameters such as compressor pressure ratio, evaporator temperature and temperature difference in the evaporator, on the first and second-law efficiencies for the cycle exergy destruction rate is studied. Finally the cycle thermodynamically is optimized to achieve the best efficiency.
Byung-Sik Park, Man-Ki Heo, Dong-Hyun Lee
Abstract: Using Orgarnic Rankine Cycle (ORC) power generators is one of the most efficient way to generate electricity from relatively low-grade heat sources. For a given heat source and heat sink conditions, performances of ORC power generaters are strongly depends on the mass flow rate of the working fluids. In this study, simulations were conducted to optimize the cycle with varying the mass flow rate of the working fluid.
Melissa Ireland, Adriano Desideri, Matthew Orosz, Sylvain Quoilin, J.G. Brisson
Abstract: Organic Rankine cycle (ORC) systems are gaining ground as a means of effectively providing sustainable energy. Coupling small-scale ORCs powered by scroll expander-generators with solar thermal collectors and storage can provide combined heat and power to underserved rural communities. Simulation of such systems is instrumental in optimizing the control strategy. Several authors have simulated solar thermal ORC systems in steady-state [1,2], or focused on either ORC or thermal storage dynamics in isolation [1,2], or simulated system dynamics assuming a fixed electrical load and a solar loop modeled as a single lumped component [3]. In this work, a model for the dynamics of the solar ORC system is developed to evaluate the impact of variable heat sources and sinks, thermal storage, and the variable loads associated with distributed generation. This model can then be used to assess control schemes that adjust operating conditions for diurnal to annual environmental variation. The Modelica programming language is used to capture the important dynamics of the system, mainly in the storage tank, solar collectors, plate heat exchangers, and air-cooled condenser. Detailed steady-state component models are first developed in Engineering Equation Solver and serve as guides for the dynamic models. In particular, a detailed simulation of the fin-tube condenser with hexagonal tube array provides a better understanding of the influence of the moving liquid boundary with various working conditions. Measurements on a pilot system at Eckerd College are currently underway to validate the steady-state models to ensure an appropriate baseline for the prospective dynamic optimization. Ultimately, the goal of this work is to identify “optimal” control schemes for a small-scale solar ORC. Operating conditions will be controlled through the variation of the heat transfer fluid mass flow rate through the solar array, the speed of the ORC expanders, and the speed and number of operating ORC condenser fans. The control strategy will focus on maintaining the pressure ratio across the fixed volume ratio scroll expanders necessary to avoid both over- and under-expansion of the working fluid under variable ambient conditions.
Akshay Hattiangadi, Tiemo Mathijssen, Matthias Lampe, David Pasquale, Joachim Gross, André Bardow, Piero Colonna
Abstract: The selection of a working fluid is key to the design of an Organic Rankine Cycle (ORC) system, given the energy source, sink and the power capacity. Up to now the selection of the working fluid is mainly guided by experience and the use of several system simulations. In the attempt to approach the engineering problem in a more systematic way, a software tool has been developed which simultaneously optimizes the energy conversion process and selects the optimum working fluid for a given heat source. The program is based on a framework that uses a continuous-molecular targeting approach which allows for an integrated working fluid and system design \cite{bardow2010continuous} \cite{lampe2012}. The steady-state process is simulated with an in-house program for thermodynamic analysis and optimization of energy conversion systems\cite{cycletempo}. The system model includes a simple model of a radial turbine. Given constrained operating conditions, the ORC system is optimized simultaneously with the molecular parameters defining the fluid properties according to PC-SAFT equation of state\cite{gross2001perturbed}. The optimizer is provided by a state-of-the-art optimization suite \cite{nexus}. The working fluid is selected by comparing the optimized molecular parameters to the ones of real fluids.\\ The procedure has been preliminarily tested using as an example the specifications of a waste heat recovery ORC turbogenerator for truck engines \cite{Lang2013AssessmentWasteHeat}. The choice of the working fluid is restricted at the moment to siloxanes. The preliminary design of the turbine governs the optimization. The turbine has been modeled by applying the methodology described by Whitfield and Baines \cite{whitfield1990}. Future work will be devoted to the implementation of refined component models and to the extension of the fluid selection to other organic fluid classes.
Syunichi Mishima, Yasuyuki Ikegami
Abstract: Kalina cycle is a power generation system for waste heat source of low temperature. This cycle is mainly used to a single heat source. By the way, there are extremely large potential of waste heat having difference temperature region simultaneously. Therefore, this research examined the ORC system which can use two or more heat source effectively by a single system. Four different systems for two waste heat sources were proposed. Their four ORC system were evaluated for waste water (70℃) and exhaust gas(300℃) as hot heat source. As the result, the power output of system which warming the separator latter part of a cycle directly by an exhaust gas was increased about 40 percent than one of conventional system.
Hyung-Chul Jung, Susan Krumdieck
Abstract: In the present study, design and analysis of an organic Rankine cycle (ORC) system and radial inflow turbine is presented for a 250 kW pilot binary cycle power plant to recapture low-grade waste heat released from a petroleum refining process. A total of 12 pure fluids and mixtures are investigated. The refinery heat source is in a kerosene liquid stream with a flow rate of approximately 6000 ton/day at a temperature range of 105 – 140C. The thermodynamic analysis of the ORC is first performed to determine its operating conditions. They are then used as requirements for the preliminary aerodynamic design of a radial turbine for the system. The aerodynamic analysis is based on both the dimensionless parameters, such as the specific velocity and the specific diameter, and the stage loading and flow coefficients. The numerical turbine model developed is validated against experimental data from published literature. Turbine stage efficiency is estimated by means of the rotor flow loss models. Results show that the kerosene stream flow rate needed and the turbine size significantly vary according to working fluids – the flow rates range from about 3070 to 3730 t/d and the rotor blade tip diameter about 0.20 to 0.43 m. Overall, less flow rates and smaller sizes are required for the mixtures than the pure fluids. The turbine design results obey the geometric, flow, structural and vibration design criteria proposed by researchers. The determined geometric and aerodynamic parameters of the turbine stage are considered beneficial for a detailed analysis of the turbine.
Potentials for increased cost efficiency of Modified Rankine Cycle plants using two-phase expansion for Power generation from Low Temperatures
Henrik Ohman, Per Lundqvist
Abstract: The task of reducing global carbon dioxide emissions leads to a need to reduce the average CO2-emission in power generation. A more energy efficient mix of power generation on national, or regional level, will require the re-use of waste heat and use of primary, low temperature heat for power generation purposes. Modified Rankine Cycles (MRC), such as Organic Rankine Cycles, Trilateral Flash Cycles, Kalina Cycles are types of Low Temperature Power Cycles (LTPC,s) offering a large degree of freedom in finding technical solutions for such power generation. Theoretical understanding of MRC’s advance rapidly though practical achievements in the field show very humble improvements at a first glance. Cost of applying the new knowledge in real applications seems to be an important reason for the discrepancy. As LTPC’s generally are small scale power plants, less than 3MWe, an obvious cost driver is size itself. However, another strong reason for the high cost level is the diversity of process fluids required and consequently the lack of standardization and industrialization. Uses of supercritical power cycle technology tend to cause the same dilemma. New, upcoming regulations prohibiting the use of several process fluids could also lead to remedies increasing plant cost. By using 2-phase turbine inlet conditions in MRC’s the need to use many different process fluids is believed to be reduced, allowing simpler and more cost efficient LTPC’s by simplified matching of heat source temperature characteristics. This article explains the opportunities accordingly. Definitions of different sample applications for LTPC’s have been made in order to simulate the different power generation opportunities using fundamentally different process fluids in the particular applications. The methodology is suitable for optimization in specific cost, Net Power Out or efficiency. The results indicate a potential to design LTPC’s with good efficiency in significantly wider thermal conditions than previously, without changing the fluid. Conclusions are made that cost optimization of LTPC’s is possible through the use of 2-phase turbine inlet fluid conditions, allowing cheaper process fluids and standardization of the power plant architecture. Sensitivity to choice of fluid is reduced to 10% in cost and <5% in FractionOfCarnot and Net Power Out when optimization of 2-phase turbine inlet conditions is allowed. Consequences of the conclusions are that LTPC’s can be made more commercially attractive and thereby contribute in decreasing the average carbon emissions from power generation.
Simulations of compressible flows in the liquid-vapour critical point region using non-classical scaling laws
Tiemo Mathijssen, Alberto Guardone, Piero Colonna
Abstract: As it is well known, thermodynamic models based on analytic equations of state fail to reproduce the singular behaviour at the vapour-liquid critical point. For example, cubic equations of state provide inaccurate value of all properties close to the critical point [1]. Multi-parameter equations of state provide accurate estimations of the primary properties thanks to the inclusion of so-called critical terms in the functional form, but derived quantities are a ffected by the inherently incorrect functional form and departure from physical behaviour becomes apparent, especially if fi rst and second order derivative of primary properties are considered [2]. Balfour and collaborators formulated an equation of state using the method of non-classical scaling that is capable to accurately predict the thermodynamic properties at and in the close proximity of the critical point [3]. In order to simulate compressible flows in the vicinity of the critical point, we implemented the non-classical scaling thermodynamic model in our in-house thermodynamic library [4]. A comparison is reported between the values of relevant primary and derived thermodynamic properties for CO2 obtained with the scaling-laws model, the Span-Wagner [5] equation of state and measurement data close to critical conditions, to assess the predictive capabilities of the non-classical scaling model. In particular, the divergence of the fundamental derivative of gasdynamics Gamma to minus infinity approaching the critical point from the two-phase region is predicted by the non-classical scaling model [2]. The negative value of the fundamental derivative of gasdynamics Gamma heralds possible non-classical gasdynamic behaviour in the two-phase critical region. To investigate these phenomena, our in-house real-gas solver, coupled to the thermodynamic library, is used. In particular, numerical simulations of the formation and propagation of non-classical two-phase rarefaction shock waves are carried out. The computed shock velocity and strength are assessed against the exact theory of Rankine-Hugoniot. Non-classical gasdynamic behaviour at the critical point is predicted to impact the design of fluid devices operating in the close proximity of the critical region, such as expanders for advanced Organic Rankine Cycle power systems [6]. [1] M. M. Abbott, "Cubic equations of state", AIChE J., vol. 19, p. 596, 1973. [2] N. Nannan, A. Guardone, and P. Colonna, "On the fundamental derivative of gas dynamics in the vapor-liquid critical region of single-component typical fluids," Fluid Phase Equilibria, vol. 337, pp. 259-273, 2013. [3] F. W. Balfour, J. V. Sengers, M. R. Moldover, and J. M. H. L. Sengers, "Universality, revisions and corrections to scaling in fluids", Phys. Lett. A, vol. 65, pp. 223-225, 1978. [4] P. Colonna, T. P. van der Stelt, and A. Guardone, "FluidProp (Version 3.0): A program for the estimation of thermophysical properties of fluids." http://www.fluidprop.com/, 2010. A program since 2004. [5] R. Span and W. Wagner, "A new equation of state for carbon dioxide covering the fluid region from the triple-point temperature to 1100 K at pressures up to 800 MPa," J. Phys. Chem. Ref. Data, vol. 25, no. 6, pp. 1509-1596, 1996. [6] E. Casati, A. Galli, and P. Colonna, "Thermal energy storage for solar powered organic Rankine cycle engines", Solar Energy, 2013. Submitted for publication.
Remi Daccord, Vincent Rieu
Abstract: The MICROSOL project, initiated by Schneider Electric, aims at developing a 10kW solar power plant for rural electrification in line with projects led by University of Liege [1], EPFL [2] and the STG NGO [3]. One of the two solutions chosen by Schneider Electric is based on two French companies’ know-how: Exosun and Exoès. Their system is based on parabolic trough concentrators, a pressurized water storage, a R245fa Rankine cycle, a scroll turbine, a dry cooler and a recycling water module. The role of Exoès is to convert the thermal power available from the solar plant in electricity, then converted by Schneider Electric’s power electronics. This paper relates the design of the power plant optimizing components, followed by test results and control optimization. GENERAL OVERVIEW The power plant specifications require 24h electricity production: 10kW during the day and 3kW in the night. The source of energy is water at 180°C - 16bars produced by a 600 m² field of parabolic troughs and stored in a 20m3 water tank. The heat is transferred through plate heat exchangers to a R245fa Rankine cycle to produce vapor at 10 to 30 bars. The expander are two 325cc and 108cc scroll turbines operating a volumetric expansion ratio of less than 3. A cold loop condensates the vapor and evacuate the waste heat through a dry cooler. The power output of the plant is controlled by the power demand on the grid. According to the available hot and cold temperatures, the feed pumps must quickly adjust the inlet pressure to reach the power output required while a super capacitor and a few batteries instantly supply the difference. Thanks to a typical load curve and weather files coupled to dynamic solar modeling, the Rankine cycle has been designed to produce 10kW during the day with high outside temperature and high hot source temperature (50% of operating time). During the night, lower temperatures do not enable the expander to produce more than only a third of its maximal load, matching the required 3kW (25% of operating time).The cycle won’t be able to produce the required power when it is too hot or if the hot source is too cold. A load shedding system is thus foreseen. COMPONENTS OPTIMIZATION We chose components providing the best efficiency. All auxiliaries have been designed to reduce their consumptions. Concerning the cold loop, only brushless motors drive pumps and fans. It enables us to reach a higher efficiency than conventional asynchronous motors over a wide range of speeds. On top of that, the dry cooler is large enough to cool down the system even with an extreme 45°C ambient temperature and it has few pressure losses. So that fans run slowly most of time avoiding cubic progression of the consumption. We swapped one turbine working 24h/24 for two parallel turbines, each having its own reserved power range. In both cases, the same 325cc turbine runs during the day so that the power plant can produce 10kWe. During the night, we chose to stop it and start a smaller 108cc turbine to have better efficiency avoiding to empty the storage quickly. This study concludes that this expander optimization leads to the characteristics below that are far more interesting to reach competitive electricity costs of the power plant. TEST AND CONTROL After a year of modeling and prototyping, lab tests by Exoès began in early 2013. Expander isentropic efficiency and filling factor can be compared to the state of the art. A cycle efficiency of the power plant can be pointed out. In this paper, we described both the difficulties we faced to start and run the Rankine cycle and the different ways to reach better performance of the power plant based on the experiment. This project is pursued by field tests in mid 2013 near Marseilles-France that are conducted by CEA (French atomic energy committee). A second test phase will then take place in Africa in 2015. LITERATURE [1] Design and experimental investigation of a small-scale organic Rankine cycle using a scroll expander, Sébastien DECLAYE, Sylvain QUOILIN, Vincent LEMORT, The 20th International Compressor Engineering Conference, Purdue, 2010 [2] Integration and optimization of thermoeconomic & environomics hybrid solar thermal power plants, thesis, Malik KANE, EPFL, 2002 [3] Solar Turbine Group (STG)’ NGO program in Lesotho, 2004
Martin White, Abdulnaser Sayma
Abstract: Despite increasing interest in ORC over recent years, small scale systems have yet to make their mark due to the lack of an efficient, ORC specific expander and high costs. However, with careful component selection and design, an efficient and economical system could see widespread use within applications such as solar power and waste heat recovery. For small outputs, volume expanders such as screw and scroll machines have typically been preferred over turbo-expanders due to lower rotational speeds and ease of conversion from compression machines. However, for 10kWe output screw devices experience high leakage flows, whilst scroll machines remain untested, and are limited in efficiency. An efficient, well designed radial expander could therefore bridge the current gap between the output of scroll and screw based cycles. This paper describes the development of a steady-state ORC sizing and optimisation tool integrated with real fluid properties. The program, implemented in FORTRAN, advances on current models by combining detailed component models, including off-design performance, with multi-objective optimisation. For a pre-defined set of components the objective function is the maximisation of work output which results in an optimal solution which couples component and system performance. Comparatively, the model can also be used for component sizing through the use of an objective function which couples performance with system complexity. A modular modelling approach allows the interchanging of different objective functions in addition to different component models. An initial case study is explored, and R-245fa or R-123 are found to be the most suitable working fluids for an experimental system. This selection is based on thermodynamic, environmental and design considerations, in addition to the practicalities of the available lab space. These results will be used to size the rig and construct a prototype expander. After model validation, more novel working fluids will be explored.
Stephen Streater, Zhiqiu Pan
Abstract: The ability to quickly and accurately model small scale vapour cycle systems is of increasing importance to virtually all sectors of the Automotive industry, and indeed other industries where the internal combustion engine is widely utilised. This is especially the case for heavy commercial vehicles, as well as small scale power generation applications, where duty cycles include prolonged periods at high engine load conditions. The realtively high capital cost and service life of machinery used in these applications makes them particularly suited to maximising the fuel economy benefits associated with Waste Heat Recovery (WHR). Concepts for automotive WHR are tending to focus on systems that use water-steam, and/or Organic Rankine Cycle (ORC) fluids, to recover heat from the vehicle’s exhaust, EGR cooler, or liquid cooling system. These small-scale Rankine Cycle systems are aimed at recovering at least some of the 60-70% of fuel energy that is normally lost to the surroundings. The recovered energy is used to heat the working fluid to a superheated vapour which is then expanded using either a turbine or a piston machine to extract useful work. This is then returned to the vehicle powertrain as either mechanical or electrical energy. The study shows how Flowmaster has extended its existing vapour cycle modelling capabilities, originally developed for water-steam systems in the Power Generation industry, to produce an ORC capability for automotive Vehicle Thermal Management System (VTMS) engineers. Important new numerical models have been developed in order to represent the key components used in the increasingly important application of automotive WHR simulation. These single component models can be successfully used to build Flowmaster system level networks and thereby allow the complete Rankine cycle to be simulated. The resulting system level model uses a recently developed solver that is based on energy conservation at every network node, thus allowing the behaviour of the entire WHR system to be predicted. In addition to the conventional water-steam cycle, the modelling approach has been successfully applied to two of the more commonly used ORC fluids to provide a better reflection of current small scale WHR concepts. Proper calibration of the component numerical models produces an excellent correlation with measured test data, thus validating their use for the design layout and development of small scale WHR systems. The study concludes that this newly developed approach to modelling automotive WHR can effectively meet the new challenges facing VTMS engineers at this time of increased powertrain electrification and engine downsizing.
Errol Yuksek, Parsa Mirmobin
Abstract: EXTENDED ABSTRACT Surveying global heat sources available for generation of electric power both in industrial applications and from natural sources, it is clear that the vast majority of such sources are at the lower end of the temperature spectrum (180 F to 220 F). Access Energy has developed a high efficiency, low temperature organic Rankine cycle (ORC) system to specifically address the largely untapped heat sources available for power production. Access Energy has leveraged its existing ORC products and technologies to develop this extra low temperature (XLT) ORC system. At the heart of the new design is the integrated power module (IPM) - a hermetically sealed, high speed expander coupled to a permanent magnet (PM) generator supported by magnetic bearings. Power from the IPM is fed to an advanced power converter that converts variable frequency, variable voltage power to constant frequency constant voltage grid quality output power with efficiencies in excess of 94%. These key features combine to create a robust, high efficiency, maintenance free power generator. In order to maintain high system efficiency across the wide source temperature range, the turbine is designed to operate across a large range of pressure ratios (2:1 to 8:1). This significant goal has been realized through advanced real gas CFD analysis of the entire IPM assembly together with results from the successful fielded ThermapowerTM 125MT system. The design of the XLT ORC system is most heavily influenced by the heat source conditions, the cooling source and ambient conditions, heat exchanger design, working fluid selection, and turbo-generator design. Results of the turbine and CFD analysis were fed into a high fidelity ASPEN Plus plant model. The ASPEN model incorporates real fluid, pump, turbine and heat exchanger characteristics. Together with advanced solver algorithms, a highly accurate performance prediction for the entire ORC system has been achieved. LITERATURE [1] Hawkins, L., Zhu, L., Blumber, E., et al., 2012. Heat-to-Electricity with High-Speed Magnetic Bearing/Generator System. In: Geothermal Resources Council, Annual Meeting. Reno, NV, USA, 1-3 October 2012.
Ian Bell, Sylvain Quoilin, Jorrit Wronski, Vincent Lemort
Abstract: Modeling and simulation of thermodynamic cycles requires access to thermodynamic and transport properties of the working fluids. It is especially true in the case of Organic Rankine Cycles (ORC), for which the properties of organic fluids are not as easily available as those of water (e.g. when simulating traditional steam cycles) or air (e.g. when simulating gas turbines). Therefore, libraries of thermodynamic and transport properties based on high accuracy equations of states are needed. This work presents a new open-source and computationally efficient thermodynamic properties library named CoolProp. This library has been successfully tested for the simulation of refrigeration and ORC systems in steady-state as well as in dynamic models. %For all manner of analysis, it is useful to have access to thermodynamic and transport properties for fluids. In truth, it is not possible to conduct research in thermal sciences without access to accurate thermophysical properties. It is for that reason that a library of thermodynamic and transport properties has been developed which covers 86 pure and pseudo-pure fluids, and 21 brines and incompressible liquids. The working fluids available in CoolProp include all the most significant Organic Rankine Cycle working fluids, including R245fa, the siloxanes (MM, MDM, MD2M, MD3M, MD4M, D4, D5, D6), water, and many others. Wrappers have been developed that allow the use of CoolProp with Modelica, MATLAB, Python, C\#, Octave, Microsoft Excel, Labview, and EES. CoolProp is cross-platform and can be used on Linux/Unix, Mac OSX and Microsoft Windows. For Organic Rankine Cycles, the ability to capture the transient behavior of the system is very important, and it is here that the routines developed in CoolProp excel. Dynamic modeling involves numerous calls to the thermodynamic properties with p and h as inputs variables, both during the initialization phase and during the integration phase. Advanced lookup table methods have been developed (based on the Tabular Taylor Series Expansion) that allow for computationally efficient evaluation of the thermophysical properties. {\bf HELMHOLTZ ENERGY BASED EQUATION OF STATE} {\bf Core formulation} All the working fluids that are implemented in CoolProp are based on Helmholtz energy equations of state. The total non-dimensionalized Helmholtz energy can be given as the sum of two components, the residual- and ideal-gas components to the Helmholtz energy. Thus the non-dimensionalized Helmholtz energy can be given by \begin{equation} \alpha = \alpha^0+\alpha^r. \end{equation} The elegance of this formulation is that all other thermodynamic properties can be obtained through analytic derivatives of the terms $\alpha^0$ and $\alpha^r$. For instance, the other fundamental thermodynamic properties can be obtained from \begin{equation} \frac{p}{\rho RT}=1+\delta \left( \frac{\partial \alpha^r}{\partial \delta} \right)_{\tau} \end{equation} \begin{equation} \frac{h}{RT}=\tau\left[\left( \frac{\partial \alpha^0}{\partial \tau} \right)_{\delta} + \left( \frac{\partial \alpha^r}{\partial \tau} \right)_{\delta} \right]+\delta \left( \frac{\partial \alpha^r}{\partial \delta} \right)_{\tau}+1 \end{equation} \begin{equation} \frac{s}{R}=\tau\left[\left( \frac{\partial \alpha^0}{\partial \tau} \right)_{\delta} + \left( \frac{\partial \alpha^r}{\partial \tau} \right)_{\delta} \right]-\alpha^0-\alpha^r \end{equation} where $\delta=\rho/\rho_c$, $\tau=T_c/T$, and $\rho_c$ is the critical density and $T_c$ is the critical temperature. The exact form of the non-dimensional Helmholtz energy terms is fluid dependent, but a canonical example is the propane equation of state \citep{Lemmon-2009}. Analytic derivatives of $\alpha^0$ and $\alpha^r$ with respect to $\tau$ and $\delta$ are presented in the paper of Lemmon \citeyearpar{Lemmon-2009}. Additionally, other thermodynamic parameters (speed of sound, specific heats, etc.) can be obtained analytically. As the equations of state use temperature and density as the fundamental properties, if other inputs are desired, it is necessary to employ numerical solvers to obtain temperature and density given the set of inputs. {\bf Saturation curve} In the two-phase region, as well as along the saturation curves, it is necessary to evaluate the phase equilibrium between the saturated liquid and the saturated vapor. For a pure fluid, it is known that at equilibrium the temperatures, pressures and Gibbs free energy in each phase are the same. A number of numerical methods can be used to carry out the necessary equilibrium calculations, but the algorithm implemented in CoolProp is that of Akasaka \citeyearpar{Akasaka-2008}. When this solver begins at the values from the ancillary equations, this solver generally can yield convergence for temperatures below 0.1 K less than critical temperature. In the near vicinity of the critical point, the behavior of the saturation solvers becomes significantly less robust, even with good guess values for the saturation densities. As a result, it is necessary to employ other methods to extend the saturation curves all the way up to the critical temperature. In CoolProp, the saturation solver of Akasaka is used to get as close to the critical temperature as possible. Beyond that point, a spline curve is used for the saturation curve, where the value and derivative constraints can be obtained directly. This yields a smooth ($C_1$ continuous) transition from the EOS to the critical region spline. {\bf TABULAR TAYLOR SERIES EXPANSION INTERPOLATION} While the evaluation of the thermodynamic properties using CoolProp has been optimized in order to achieve computational speeds better than the state of the art thermophysical property databases \cite{Lemmon2010}, the evaluation of thermodynamic properties using the full equation of state is too slow for use in dynamic simulations. For that reason, the tabular Taylor series expansion method has been extended to all the fluids in the CoolProp database. This method was originally proposed for the evaluation of the thermodynamic properties of water \citep{Miyagawa-2001}, but it works just as well for other fluids. This TTSE method is based on a two-dimensional Taylor expansion around each point in a grid of tabulated data points. Thus, the expansion of temperature in terms of pressure and enthalpy can be expressed as \begin{equation} T = T_{i,j}+\Delta h\left(\frac{\partial T}{\partial h}\right)_{p}+\Delta p\left(\frac{\partial T}{\partial p}\right)_{h}+\frac{\Delta h^2}{2}\left(\frac{\partial^2 T}{\partial h^2}\right)_{p}+\frac{\Delta p^2}{2}\left(\frac{\partial^2T}{\partial p^2}\right)_{h}+\Delta h\Delta p\left(\frac{\partial^2T}{\partial p\partial h}\right) \end{equation} where each of the partial derivatives are the values evaluated at the $i,j$ grid point. Thus if the values of $\Delta h = h-h_i$ and $\Delta p = p-p_j$ are known, it is then possible to evaluate the dependent variable ($T$ in this case). The same form of expansion can be carried out with entropy or density as the dependent variable. Pressure and enthalpy are used as the independent variables as they are one of the most computationally expensive pairs of input values, and are most commonly used as the state variables in dynamic modeling. In principle this tabular method can be used with any pair of independent variables. Furthermore, a similar methodology can be employed for the saturation properties, which can be evaluated based on a tabular one-dimensional Taylor series with pressure as the independent variable. As with the single-phase tables, pressure is used as the independent variable as it is the independent variable that requires the most computational effort in the two-phase region. Speed Comparison For pressure and enthalpy as inputs, the TTSE method is extremely fast. For the same configuration in Modelica (a dynamic modeling programming language), the computational time of CoolProp using the TTSE method is 8.1 times less than that when using the full equation of state. Figure \ref{fig:speeds} compares several different thermophysical property packages in Modelica on the same configuration. Transport properties (viscosity and thermal conductivity) are not calculated. This benchmark example can be found in the CoolProp2Modelica package for Modelica. For the sake of the benchmark, the thermodynamic properties are called 20,000 times along an isobar with various libraries spanning the three regions (sub-cooled, two-phase, superheated). One grid point corresponds to one call to the library. The Modelica library CoolProp2Modelica is derived from the ExternalMedia library developed by Casella \citep{Casella-2008}. A speed comparison on a complete ORC model was also performed. The selected ORC model is the one proposed by Quoilin \citeyearpar{Quoilin-2011}, comprising two discretized heat exchangers (20 cells) and pump/expander models based on efficiency curves, plus a control system with variable set point temperature based on two PI controllers. The simulation length is 1669 seconds, it is solved in 142 seconds with TILMedia, 91 seconds with CoolProp and 13.5 seconds with the CoolProp/TTSE method. These results should be considered to be representative, but they are not one-to-one comparisons due to the vagaries of the integrator in Dymola.
Mirko Morini, Claudio Pavan, Michele Pinelli, Eva Romito, Alessio Suman
Abstract: The scroll fluid machine has gained popularity since the 1970s as a compressor in air conditioning and refrigeration applications. Its main advantages are the small number of moving parts and its reduced noise and vibrations. Recently, this technology has gained renewed interest due to its potential adaptability to be used as an expander in micro ORC systems. The ever increasing request for higher efficiency in machine operation (e.g. eco-design) has led to the need for designers to thoroughly investigate the kinematic and thermodynamic behavior of these machines by means of geometric, thermodynamic and, very recently, CFD methods. The relationship between the scroll spiral profiles, and, therefore, scroll pockets evolution, and the machine overall performances both in terms of energy and mechanics is the first step towards understanding scroll machine working behavior. In [1], a method for the design of spiral profiles for performance enhancing of the whole refrigeration plant is presented. In [2], particular attention is paid to the stress to which the scroll profiles are subjected as a function of the geometry of the pockets in order to minimize the thickness of the spiral by saving the mechanical integrity of the scroll. Scroll machine performance evaluation as a function of spiral geometry can be performed by means of thermodynamic models by taking into consideration volumetric loss due to leakage flows [3,4,5]. The use of CFD methods for the evaluation of scroll machine performance is not widespread in literature. In [6] an analysis oriented to the evaluation of the pressure distribution in the pockets and in the leakages through the flank gap is presented. In this paper, geometric, thermodynamic and CFD methods for the modeling of scroll machines are presented. The comparison between two geometric models for the design of the scroll spiral profiles is presented. The two methods are then compared by evaluating overall performances by means of a simplified thermodynamic model. Finally, a CFD transient Dynamic Mesh (DM) strategy is implemented and a sensitivity analysis in terms of grid, boundary conditions and time step performed.
Jarosław Mikielewicz, Dariusz Mikielewicz, Jan Wajs
Abstract: In the paper an attempt is presented to find the method of optimization of microtube diameter with respect to optimal thermal-hydraulic conditions in the single-phase shell-and-tube heat exchangers. The approach is based on consideration of pumping power at the condition of maximum heat transfer by the heat exchanger tube system. In the optimization method the tube diameter is first specified and then appropriate calculations are executed, showing that from the point of heat transfer the lower the diameter of the tube the better the heat transfer, however at the expense of higher pressure drop.
Dariusz Mikielewicz, Jarosław Mikielewicz
Abstract: In the present study cooperation of the ORC cycle with the heat source available as a single phase or phase changing fluids is considered. The analytical heat balance models have been developed, which enable in a simple way calculation of heating fluid temperature variation as well as the ratio of flow rates of heating and working fluids in ORC cycle. The developed analytical expressions enable also calculation of the outlet temperature of the heating fluid.
Jarosław Mikielewicz, Dariusz Mikielewicz, Jan Wajs, Krzysztof Kosowski, Robert Stepien
Abstract: In the paper presented is a new design of the radial-axial microturbine of 3-4kW capacity for operation with ethanol as working fluid
Hideharu Yanagi, Michael Khong, Gayle Tan
Abstract: Current available ORCs on the market are in MW power range and very few are actually made for the kW scale. For ocean voyage ship application, a moderate scale of ORCs is demanded. Current available ORC machines are generally composed of turbo expander or scroll Expander (1-10kWe), shell & tube evaporator and condenser. They are not suitable for installing on board ships under accelerating load of pitching and rolling under marine condition. Turbo expanders are considered to be inappropriate to use and also evaporators with flooded working fluid are not suitable. Employment of screw expander is key issue in an ORC unit for marine use. Authors are planning to develop a modular ORC unit of 200kW which can be recovered from the marine vessel exhaust of both the main engine and auxiliary engine at about 250°C and released at 180°C, thus its electric output of 200kW can replace the use of an auxiliary generator or about 500,000 litres of diesel annually. For a ship with a 1MW auxiliary generator, this represents a 20% increase in electrical efficiency or a potential fuel savings of 20%. This paper presents a proposal system of 20kW for bench scale testing equipment with two stage screw expander for dual purpose operation under high or low temperature heat source. Fig.1 shows the ORC system applying for a SES 36 as a working fluid with cycle efficiency of 18% in high temperature (pressure) operation under an evaporating temperature of 170°C, an inlet pressure of 1st stage of 25.07bar,an outlet of 2nd stage expander of 1.12bar and a condensing temperature of 35.64°C, respectively. Figure also shows a method for operating an ORC system with a high-pressure expander and a low-pressure expander. Therein, the ORC system comprises a bypass line that extends, in a flow direction of the working fluid, from a branching point before the high-pressure expander to the low-pressure expander. In a high temperature operating mode the bypass line is closed and the input control valve of 1st stage expander is opened. In a low temperature operating mode the bypass line is opened and the input control valve of 1st stage expander is closed, and is operated in 2nd stage expander.
Abdul Nassar, Leonid Moroz, Avinash S. Ravi, Oleg M Guryev
Abstract: The Organic Rankine Cycle (ORC) named for its use of an organic, high molecular mass fluid with a liquid-vapor phase change or boiling point, occurring at a lower temperature than the water-steam phase change. Due to its usage of low temperature heat sources, the applications of organic rankine cycle are enumerable such as geothermal power generation, industrial waste heat, power generation using solar troughs etc…. Though the cycle efficiencies of ORC are lower, they still are a viable choice when the heat source is of low grade. When used in generic cycle they complement the overall cycle’s efficiencies by generating power from waste heat. The turbine / expander being major equipment plays a vital role in increasing the overall cycle efficiency. Due to the low heat source and use of organic fluids make the flow path design is interesting and challenging. The designer is always at the cross road in deciding on whether to choose a radial or axial flow path for the turbine. This project involves preliminary and detailed design of a radial and axial turbine for given specifications and details on the issues related to sizing, performance, limitation and viability of each of these machines for the given application. In the detailed design many geometrical parameters are selected for optimizing and the influence of different geometrical parameters on the performance is discussed in detail. This paper describes the procedure for developing an ORC turbine from conceptual stages to detailed flow-path design and development of 3D blades
Jing Li, Gang Pei, Jie Ji
Abstract: A novel CHP system using semi-permeable membrane is proposed. The fundamentals are illustrated. Mathematical models are built. And some results are presented.
Piotr Kolasiński, Zbigniew Rogala
Abstract: One of the problems encountered while designing the ORC systems is the proper selection of the heat exchangers which depends on many factors. Among these factors are: characteristics of the heat source supplying the system, required parameters, type of working medium and auxiliary mediums of the system. Frequently the shell-tube and plate heat exchangers are mainly used in ORC systems. They can be characterized by low ratio of heat flow to heat transfer surface. It influences the size of the heat exchangers, and furthermore, the amount of the material used and the whole installation expense. Interesting alternative for the currently applied heat exchangers might be Rosenblad’s Spiral Heat Exchangers (SHE). What makes this construction so particular is the relatively high ratio of the heat flow to the heat transfer surface. The new modified calculation method dedicated to the Rosenblad’s SHE is presented in this article. The formulated method was applied to the calculations of the Rosenblad’s SHE, which serves as evaporator in the prototype ORC system. The results of these calculations are presented herein. The results of the analysis show that the Rosenblad’s SHE might be an interesting alternative for the other types of the heat exchangers applied presently to the ORC systems. Their application creates a possibility of the reduction of size of the installation, as well as, its expenses.
Man Wang, Jiangfeng Wang, Pan Zhao, Yiping Dai
Abstract: This paper presents a solar-boosted Ocean Thermal Energy Conversion system based on organic Rankine cycle. Flat-plate solar collectors are installed to collect the solar radiation to elevate the temperature of warm surface seawater. By establishing thermodynamic models of system, parametric optimization is conducted to obtain the optimal system performance using different working fluids. Genetic Algorithm is employed to conduct the optimization of the system. The exergy efficiency of entire system is selected as the objective function under given conditions, and turbine inlet pressure, turbine back pressure and pinch point temperature in evaporator are chose to be the decision variable. Optimization results indicate that three parameters all have significant impact on system performance. Compared with other working fluids, the system using R245fa has the best exergy efficiency, shown as 5.23%, and the net power output can be 79.16 kW.
Olivier Dumont, Sylvain Quoilin, Vincent Lemort, Sebastien Declaye
Abstract: This projects presents the design, the modelization and the experimentation of an Organic Rankine Cycle for a small-scale solar power plant (2,5 kWe) in a way to test and optimize control strategies. The final layout and the justifications of technical choices are presented. Simulations predict a global efficiency of 5% and an ORC efficiency of 8.5% for evaporation and condensation temperatures being equals respectively to 140°C and 35°C.
Byung-Sik Park, Muhammad Usman Aslam, Jae Yong Lee, Dong-Hyun Lee
Abstract: This paper presents a model describing dynamics of two-phase flow heat exchanger in variable temperature heat source, based on moving boundary approach. Organic Rankine Cycle (ORC) systems are popular for recovering energy from low temperature heat sources. At small scale, ORC units are reliable and cost effective. Generally the power systems are designed to be operated with constant temperature heat source. Waste heat recovery applications may involve scenarios where source temperature may vary. If system operates at variable heat source temperature, evaporator pressure and outlet enthalpy of working fluid would vary due to variation in amount of heat supplied, which in effect will change the operating conditions of rest of the system.
Andres Hernandez, Adriano Desideri, Clara Ionescu, Sylvain Quoilin, Vincent Lemort, Robin De Keyser
Abstract: The Organic Rankine Cycle (ORC) technology has become very popular, as it is extremely suitable for waste heat recovery from low-grade heat sources. As the ORC is a strongly coupled nonlinear multiple-input multiple-output (MIMO) process, conventional control strategies (e.g. PID) may not achieve satisfactory results. In this contribution our focus is on the accurate regulation of the superheating, in order to increase the efficiency of the cycle and to avoid the formation of liquid droplets that could damage the expander. To this end, a multivariable Model Predictive Control (MPC) strategy with improved disturbance rejection capabilities is proposed, its performance is compared to the one of PI controllers for the case of variable waste-heat source profiles.
Ilaria Guarracino, Richard Mathie, Aly Taleb, Christos Markides
Abstract: The current trend for ever increasing energy prices acts as an important driver for improved efficiency via novel heat integration and energy generation schemes. An Organic Rankine Cycle (ORC) equipped with a low-loss two-stage reciprocating piston expander has been designed and is tested experimentally. The reciprocating expander is a low-cost, low-maintenance, and readily available prime mover option for these engines, with promising performance characteristics (e.g. efficiency). The tested expander is based on a commercially available unit intended for air-compression applications, which was reconditioned for the purposes of the present tests. A novel rotary valve was developed to guarantee a high efficiency and low leakage rate. The test-bed gives a maximum mechanical output of 3 kWe with R245fa as the working fluid at pressure limited to 10 bar. The optimal working-fluid was chosen from 21 possible refrigerants and alkanes based on theoretical efficiency calculations.
George Kosmadakis, Dimitris Manolakos, Erika Ntavou, George Papadakis
Abstract: A subcritical solar two-stage organic Rankine cycle (ORC) has been designed, according to optimization studies that have been conducted [1], and then manufactured. Some of its components have been properly modified (e.g. scroll compressors in reverse operation) in order to operate efficiently, while all components have been placed in a test-rig, equipped with the appropriate measuring equipment for its detailed experimental testing. An important feature of this ORC engine, with a capacity of around 10 kW and an efficiency of 10%, is the use of two similar scroll expanders, placed in series. The reason for selecting such configuration emanates from the requirement to operate these expansion machines at high efficiency (even over 70%). In other words, to keep the pressure ratio close to their built-in value, approximately equal to 3. The total pressure ratio at maximum heat input (maximum heat input: 100 kWth at around 130 oC) with a condensation temperature of 30 oC is close to 9-10, using the organic fluid R-245fa. At such conditions both expanders operate with high expansion efficiency, while at lower heat input when the evaporation temperature/pressure is lower, the first expander is totally by-passed and only the second one operates. By doing so, for the whole heat input range the scroll expanders operate at high efficiency and close to their maximum value, significantly contributing to a high system performance. The experimental testing of such ORC engine includes the controlled heat input from an electric heater (resembling the operation of a solar field), while focus is given on some operating parameters, such as the organic fluid mass flow rate, the rotational speeds of the expansion machines and the pump and the appropriate timing of by-passing the first expander. Acknowledgement: The present work is conducted within the framework of the project with contract No. 09SYN-32-982, partly funded by the Greek General Secretary of Research and Technology (GSRT). REFERENCES [1] G. Kosmadakis, D. Manolakos, G. Papadakis, “Investigating the double-stage expansion in a solar ORC”, Presented in the 1st Int Seminar on ORC Power Systems (ORC2011), Delft, The Netherlands, 22-23 September 2011.
Berend Jan Kleute, Aksel Benlevi, Bram Harmsen, Remi Blokker
Abstract: Ocean Thermal Energy Conversion (OTEC) is the largest untapped source of solar energy in the world. With its capability to generate electricity day and night, year-round, OTEC is destined to become an attractive and essential part of the future global energy mix, enabling low cost and clean electricity production. Today, multiple OTEC pilot plants are under development worldwide. To demonstrate and improve OTEC technology, Bluerise in cooperation with Delft University of Technology has designed and built a room size demonstration of an advanced OTEC power plant. This OTEC demo uses a non-azeotropic working fluid suitable for low-grade, large capacity thermal resources, like the ocean, enabling an improved efficiency compared to standard ORC-based OTEC systems. Initial tests focused on stabilizing OTEC demo operation. An accurate temperature control for the warm and cold water side was installed in order to resemble actual operational conditions. Through real-time measurements and control of the system pressure, liquid levels and flow rates, stable operation was achieved validating our theoretical models. Current research is focusing on further optimizing the system behavior and performance. This working, demonstrable plant is an important step in proving validity of advanced OTEC technology and establishing a research center for (low-grade) thermal energy conversion technologies. Initial test results will be presented at the conference.
Hyungmook Kang, Sarng Woo Karng, Youhwan Shin, Kwang Ho Kim, Seo Young Kim
Abstract: The Organic Rankine Cycle (ORC) is a promising research field in energy conversion. ORC recovers energy from various heat sources by converting low and medium temperature heat into useful work or electricity. The heat used in ORC can come from many different sources (e.g. biomass, geothermal, solar, waste heat from industry, etc.) making the process potentially usable in many commercial or industrial applications. Recently, the commercial applications of ORC technology have been developed with power range of more than 100 kWe. However, the low capacity ORC technologies are still in the research stage. The lack of suitable expander and the difficulty in selecting an appropriate working fluid are main problems in the low capacity ORC research field. The demand of low capacity ORC systems is expected to increase as the distributed combined heat and power supply networks in urban areas are developed. This study conducted performance evaluation of an automotive scroll compressor as an expander which may replace a turbine expander in low power conditions. The performance of a scroll expander was tested with a refrigerant R134a at the various expander inlet pressure, temperature and mass flow rate. The entropic efficiency of the expander was obtained by the experiments. From the experimental results, the cycle analysis was simulated as an optimization process using the genetic algorithm which is one of most powerful optimization method at the multi-domain variations. In addition, the several candidate working fluids were compared by considering efficiency, flow rate, pressure ratio and flammability. The scroll expander is expected to become an advanced alternative main component for low capacity ORC systems.