Conventional steam Rankine cycles and open cycle gas turbines play a dominate role in large-scale power production. However there is a large variety of heat sources for which these option do not offer a technically and/or economically viable solution. In these cases the proper selection of the working fluid and of the cycle configuration allow to increase system efficiency, system flexibility and also to reduce the levelised cost of generated energy. Among these solutions the most studied within the GECOS group are the Organic Rankine Cycles (ORC) and the supercritical carbon dioxide cycles (sCO2).
ORC power systems
Organic Rankine Cycles adopt an organic compound (hydrocarbons, halogenated fluids, siloxanes) as working fluid. The possibility to select the main fluid properties allows to obtain large advantages in the design of the components and to always reach high conversion efficiency.
The challenge
The optimisation of an ORC system for a specific application is always a non-trivial task, because of the need to consider simultaneously:
the choice of the best working fluid
the selection and optimization of the best plant layout and components
the effects of fluid properties on expander efficiency
the influence of all these factors on the cost of the plant
Supercritical CO2 power systems
sCO2 cycles can compete with steam Rankine cycles in high temperature applications thanks to the possibility to increase system efficiency and to increase flexibility. The concept is widely studied in literature but this technology is not commercial.
The challenge
The optimisation of these power plant is non-trivial task because of:
The large number (more than 40) of available cycle configurations differing in optimization criteria and strongly affecting the matching with the heat source
The presence of real gas effects at low temperature and high pressure that allow to reduce the compressor consumption but also requires reliable equation of state and a non conventional turbomachinery design
A challenging design of turbine stages and turbine shaft because of the very compact expander dimension and the high specific power
For further information, contact Dr. Marco Astolfi at marco.astolfi@polimi.it or Dr. Marco Binotti at marco.binotti@polimi.it
Related Projects
Recent publications
2019 |
Bernardoni, C; Binotti, M; Giostri, A Techno-economic analysis of closed OTEC cycles for power generation Journal Article Renewable Energy, 132 , pp. 1018–1033, 2019, ISSN: 0960-1481. @article{Bernardoni2019, title = {Techno-economic analysis of closed OTEC cycles for power generation}, author = {C Bernardoni and M Binotti and A Giostri}, url = {https://www.sciencedirect.com/science/article/pii/S0960148118309595}, doi = {10.1016/j.renene.2018.08.007}, issn = {0960-1481}, year = {2019}, date = {2019-03-01}, journal = {Renewable Energy}, volume = {132}, pages = {1018--1033}, publisher = {Pergamon}, abstract = {This study aims at offering a techno-economic evaluation of closed OTEC cycles for on-shore installations. A flexible Matlabtextregistered suite has been developed to identify plant design parameters (temperature difference of cold and warm seawater, pinch-point temperature difference of evaporator and condenser etc.) that guarantee the maximum value of $gamma$ (ratio between electricity output and heat exchangers area). The optimization model is able to handle different working fluids through the addition of specific correlations that consider fluid influence on heat transfer coefficients and turbine performance. Each plant component is technically analyzed and, in particular, plate heat exchangers were considered for evaporator and condenser and sized accurately with Aspen EDRtextregistered, while expander was analyzed with the in-house code Axtur. For warm seawater temperature of 28 °C and cold seawater temperature of 4 °C (8500 kg/s taken from 1000 m depth), ammonia cycle is the best solution characterized by efficiency equal to 2.2% and net power output equal to 2.35 MWe. The obtained LCOE (269 €/MWhe) confirms how OTEC technology is not ready to compete in energy market. Nevertheless, remote zones (i.e. small islands archipelagos), which are often characterized by high electricity price, represent interesting scenarios where OTEC technology could be a promising alternative to conventional power production technologies.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study aims at offering a techno-economic evaluation of closed OTEC cycles for on-shore installations. A flexible Matlabtextregistered suite has been developed to identify plant design parameters (temperature difference of cold and warm seawater, pinch-point temperature difference of evaporator and condenser etc.) that guarantee the maximum value of $gamma$ (ratio between electricity output and heat exchangers area). The optimization model is able to handle different working fluids through the addition of specific correlations that consider fluid influence on heat transfer coefficients and turbine performance. Each plant component is technically analyzed and, in particular, plate heat exchangers were considered for evaporator and condenser and sized accurately with Aspen EDRtextregistered, while expander was analyzed with the in-house code Axtur. For warm seawater temperature of 28 °C and cold seawater temperature of 4 °C (8500 kg/s taken from 1000 m depth), ammonia cycle is the best solution characterized by efficiency equal to 2.2% and net power output equal to 2.35 MWe. The obtained LCOE (269 €/MWhe) confirms how OTEC technology is not ready to compete in energy market. Nevertheless, remote zones (i.e. small islands archipelagos), which are often characterized by high electricity price, represent interesting scenarios where OTEC technology could be a promising alternative to conventional power production technologies. |
2017 |
Bonalumi, D; Bombarda, P; Invernizzi, C Potential performance of environmental friendly application of ORC and Flash technology in geothermal power plants Inproceedings Energy Procedia, pp. 621–628, 2017. @inproceedings{Bonalumi2017621, title = {Potential performance of environmental friendly application of ORC and Flash technology in geothermal power plants}, author = {D Bonalumi and P Bombarda and C Invernizzi}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85029764662&doi=10.1016%2Fj.egypro.2017.09.114&partnerID=40&md5=c518fe637324916ef5dc8107a956cfc8}, doi = {10.1016/j.egypro.2017.09.114}, year = {2017}, date = {2017-01-01}, booktitle = {Energy Procedia}, volume = {129}, pages = {621--628}, abstract = {The successful exploitation of geothermal energy for power production relies on to the availability of nearly zero emission and efficient technologies, able to provide flexible operation. It can be realized with the binary cycle technology. It consists of a closed power cycle coupled to a closed geothermal loop, whereby the closed power cycle is generally accomplished by means of an organic Rankine cycle (in a few cases the Kalina cycle has been adopted). The confinement of the geothermal fluid in a closed loop is an important advantage from the environmental point of view: possible pollutants contained in the geothermal fluid are not released into the ambient and are directly reinjected underground. Although a well-established technology in the frame of geothermal applications, the adoption of the binary cycle technology is at the moment typically confined to the exploitation of medium-low temperature liquid geothermal reservoirs, generally between 100-170°C. The important advantages of the binary cycle technology from the environmental point of view suggest nevertheless that it is worthwhile to investigate whether the application range could be extended to higher temperature reservoirs, and up to which extent. Moreover, the paper investigates the effect of an increasing CO2 content in the geothermal fluid. The paper compares in a convenient high temperature range of the geothermal source the performance of a properly optimized geothermal ORC plant, with the performance of a modified flash plant, whereby the geothermal steam enters a turbine, and the CO2 stream is separated, compressed and finally reinjected. An environmentally friendly working fluid, recently introduced in the market, is considered in the ORC optimization process. The performance comparison will involve the assessment of plant net power. As far as the calculations are concerned, the geothermal fluid is assumed to be a mixture of water and possibly CO2. The auxiliary power consumption is properly accounted for: beyond cooling auxiliaries, a submersible well pump for the ORC plant and a gas compressor for the reinjection of the non-condensable gases in the flash plant are considered. textcopyright 2017 The Author(s).}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } The successful exploitation of geothermal energy for power production relies on to the availability of nearly zero emission and efficient technologies, able to provide flexible operation. It can be realized with the binary cycle technology. It consists of a closed power cycle coupled to a closed geothermal loop, whereby the closed power cycle is generally accomplished by means of an organic Rankine cycle (in a few cases the Kalina cycle has been adopted). The confinement of the geothermal fluid in a closed loop is an important advantage from the environmental point of view: possible pollutants contained in the geothermal fluid are not released into the ambient and are directly reinjected underground. Although a well-established technology in the frame of geothermal applications, the adoption of the binary cycle technology is at the moment typically confined to the exploitation of medium-low temperature liquid geothermal reservoirs, generally between 100-170°C. The important advantages of the binary cycle technology from the environmental point of view suggest nevertheless that it is worthwhile to investigate whether the application range could be extended to higher temperature reservoirs, and up to which extent. Moreover, the paper investigates the effect of an increasing CO2 content in the geothermal fluid. The paper compares in a convenient high temperature range of the geothermal source the performance of a properly optimized geothermal ORC plant, with the performance of a modified flash plant, whereby the geothermal steam enters a turbine, and the CO2 stream is separated, compressed and finally reinjected. An environmentally friendly working fluid, recently introduced in the market, is considered in the ORC optimization process. The performance comparison will involve the assessment of plant net power. As far as the calculations are concerned, the geothermal fluid is assumed to be a mixture of water and possibly CO2. The auxiliary power consumption is properly accounted for: beyond cooling auxiliaries, a submersible well pump for the ORC plant and a gas compressor for the reinjection of the non-condensable gases in the flash plant are considered. textcopyright 2017 The Author(s). |
Elsido, C; Mian, A; Martelli, E A systematic methodology for the techno-economic optimization of Organic Rankine Cycles Inproceedings Energy Procedia, pp. 26–33, 2017. @inproceedings{Elsido201726, title = {A systematic methodology for the techno-economic optimization of Organic Rankine Cycles}, author = {C Elsido and A Mian and E Martelli}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85029757987&doi=10.1016%2Fj.egypro.2017.09.171&partnerID=40&md5=3924dd5914f7bc812a785c2c695e24c8}, doi = {10.1016/j.egypro.2017.09.171}, year = {2017}, date = {2017-01-01}, booktitle = {Energy Procedia}, volume = {129}, pages = {26--33}, abstract = {This work presents a general and systematic methodology for the techno-economic optimization of Rankine cycles. The proposed superstructure for Rankine cycles allows to reproduce a wide range of cycle configurations, such as cycles with/without regenerator, cycles with single or multiple pressure levels, and cycles integrated with multiple heat sources. The model is integrated with a recently developed methodology capable of optimizing also the arrangement and sizing of the heat exchangers of the plant (heat exchanger network synthesis). This allows to perform a full techno-economic optimization of the entire system. The resulting problem is a challenging Mixed Integer Non Linear Problem (MINLP) which is solved with an ad hoc algorithm. The methodology is applied to two case studies for power cycles with single and multiple heat sources. This work can help engineers identify the right thermodynamic cycle to integrate with an industrial process and design techno-economically optimal Rankine cycles for waste heat recovery from single or multiple heat sources, by considering heat integration and cycle design optimization simultaneously. textcopyright 2017 The Author(s).}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } This work presents a general and systematic methodology for the techno-economic optimization of Rankine cycles. The proposed superstructure for Rankine cycles allows to reproduce a wide range of cycle configurations, such as cycles with/without regenerator, cycles with single or multiple pressure levels, and cycles integrated with multiple heat sources. The model is integrated with a recently developed methodology capable of optimizing also the arrangement and sizing of the heat exchangers of the plant (heat exchanger network synthesis). This allows to perform a full techno-economic optimization of the entire system. The resulting problem is a challenging Mixed Integer Non Linear Problem (MINLP) which is solved with an ad hoc algorithm. The methodology is applied to two case studies for power cycles with single and multiple heat sources. This work can help engineers identify the right thermodynamic cycle to integrate with an industrial process and design techno-economically optimal Rankine cycles for waste heat recovery from single or multiple heat sources, by considering heat integration and cycle design optimization simultaneously. textcopyright 2017 The Author(s). |
Astolfi, M; Martelli, E; Pierobon, L Thermodynamic and technoeconomic optimization of Organic Rankine Cycle systems Incollection Macchi, Ennio; Astolfi, Marco (Ed.): Organic Rankine Cycle (ORC) Power Systems, pp. 173–249, Elsevier, 2017. @incollection{Astolfi2016173, title = {Thermodynamic and technoeconomic optimization of Organic Rankine Cycle systems}, author = {M Astolfi and E Martelli and L Pierobon}, editor = {Ennio Macchi and Marco Astolfi}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85017471660&doi=10.1016%2FB978-0-08-100510-1.00007-7&partnerID=40&md5=cec57e36fb72471cd5e83715edbed8da}, doi = {10.1016/B978-0-08-100510-1.00007-7}, year = {2017}, date = {2017-01-01}, booktitle = {Organic Rankine Cycle (ORC) Power Systems}, pages = {173--249}, publisher = {Elsevier}, chapter = {7}, abstract = {The optimization of an organic Rankine cycle is a challenging task that cannot be tackled without the aid of numerical tools for plant simulation and optimization. The large availability of various working fluids, the possibility of adopting several plant layouts, and the need to consider many thermodynamic, technological, and economical aspects lead to a challenging design optimization problem. This chapter describes the most important steps in optimizing the design of organic Rankine cycles. First, general criteria for selecting the best working fluid and the best cycle configuration for a set of the most relevant applications are thoroughly discussed. Moreover, useful guidelines are provided for the definition of the design optimization problem, its objective function, the decision variables, and the constraints. Then, the available simulation and optimization approaches and algorithms are critically reviewed with respect to their suitability for the optimization of power cycles. Finally, three test cases are presented to highlight the importance of optimization in the development of efficient and profitable organic Rankine cycles for geothermal heat sources, biomass-fired boilers, and waste heat recovery. textcopyright 2017 Elsevier Ltd All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {incollection} } The optimization of an organic Rankine cycle is a challenging task that cannot be tackled without the aid of numerical tools for plant simulation and optimization. The large availability of various working fluids, the possibility of adopting several plant layouts, and the need to consider many thermodynamic, technological, and economical aspects lead to a challenging design optimization problem. This chapter describes the most important steps in optimizing the design of organic Rankine cycles. First, general criteria for selecting the best working fluid and the best cycle configuration for a set of the most relevant applications are thoroughly discussed. Moreover, useful guidelines are provided for the definition of the design optimization problem, its objective function, the decision variables, and the constraints. Then, the available simulation and optimization approaches and algorithms are critically reviewed with respect to their suitability for the optimization of power cycles. Finally, three test cases are presented to highlight the importance of optimization in the development of efficient and profitable organic Rankine cycles for geothermal heat sources, biomass-fired boilers, and waste heat recovery. textcopyright 2017 Elsevier Ltd All rights reserved. |
Macchi, E; Astolfi, M Axial flow turbines for Organic Rankine Cycle applications Incollection Macchi, Ennio; Astolfi, Marco (Ed.): Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications, pp. 299–319, Woodhead Publishing, 2017. @incollection{Macchi2016299, title = {Axial flow turbines for Organic Rankine Cycle applications}, author = {E Macchi and M Astolfi}, editor = {Ennio Macchi and Marco Astolfi}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85017421935&doi=10.1016%2FB978-0-08-100510-1.00009-0&partnerID=40&md5=930cf0acc4a01737963b1f2532e5ed98}, doi = {10.1016/B978-0-08-100510-1.00009-0}, year = {2017}, date = {2017-01-01}, booktitle = {Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications}, pages = {299--319}, publisher = {Woodhead Publishing}, chapter = {9}, abstract = {This chapter aims to define a set of general correlations for the estimation of axial-flow turbine efficiency in the Organic Rankine Cycle (ORC) field. A dedicated numerical tool is used for the optimization of several hundreds of turbines and the results are presented in terms of specific parameters (SP, Vr, and Ns) according to similarity rules. The analysis is carried out for single, two, and three stages turbines. For each case a correlation of efficiency at optimal rotational speed is calibrated in function of the equivalent single stage SP and the total isentropic Vr. Three sensitivity analyses are proposed in order to highlight the effects of each single parameter on stage efficiency. Finally, the effect of fluid choice on turbine performance and dimension is discussed with a numerical example.}, keywords = {}, pubstate = {published}, tppubtype = {incollection} } This chapter aims to define a set of general correlations for the estimation of axial-flow turbine efficiency in the Organic Rankine Cycle (ORC) field. A dedicated numerical tool is used for the optimization of several hundreds of turbines and the results are presented in terms of specific parameters (SP, Vr, and Ns) according to similarity rules. The analysis is carried out for single, two, and three stages turbines. For each case a correlation of efficiency at optimal rotational speed is calibrated in function of the equivalent single stage SP and the total isentropic Vr. Three sensitivity analyses are proposed in order to highlight the effects of each single parameter on stage efficiency. Finally, the effect of fluid choice on turbine performance and dimension is discussed with a numerical example. |
Macchi, E; Astolfi, M Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications Book Woodhead Publishing, 2017, ISBN: 978-0-08-100510-1. @book{Macchi20161, title = {Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications}, author = {E Macchi and M Astolfi}, editor = {Ennio Macchi and Marco Astolfi}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85017439359&partnerID=40&md5=f9f816e7d773074ac3d14ce983f6506c}, doi = {10.1016/C2014-0-04239-6}, isbn = {978-0-08-100510-1}, year = {2017}, date = {2017-01-01}, booktitle = {Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications}, pages = {1--679}, publisher = {Woodhead Publishing}, abstract = {Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications provides a systematic and detailed description of organic Rankine cycle technologies and the way they are increasingly of interest for cost-effective sustainable energy generation. Popular applications include cogeneration from biomass and electricity generation from geothermal reservoirs and concentrating solar power installations, as well as waste heat recovery from gas turbines, internal combustion engines and medium- and low-temperature industrial processes. With hundreds of ORC power systems already in operation and the market growing at a fast pace, this is an active and engaging area of scientific research and technical development. The book is structured in three main parts: (i) Introduction to ORC Power Systems, Design and Optimization, (ii) ORC Plant Components, and (iii) Fields of Application. Provides a thorough introduction to ORC power systems Contains detailed chapters on ORC plant components Includes a section focusing on ORC design and optimization Reviews key applications of ORC technologies, including cogeneration from biomass, electricity generation from geothermal reservoirs and concentrating solar power installations, waste heat recovery from gas turbines, internal combustion engines and medium- and low-temperature industrial processes Various chapters are authored by well-known specialists from Academia and ORC manufacturers.}, keywords = {}, pubstate = {published}, tppubtype = {book} } Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications provides a systematic and detailed description of organic Rankine cycle technologies and the way they are increasingly of interest for cost-effective sustainable energy generation. Popular applications include cogeneration from biomass and electricity generation from geothermal reservoirs and concentrating solar power installations, as well as waste heat recovery from gas turbines, internal combustion engines and medium- and low-temperature industrial processes. With hundreds of ORC power systems already in operation and the market growing at a fast pace, this is an active and engaging area of scientific research and technical development. The book is structured in three main parts: (i) Introduction to ORC Power Systems, Design and Optimization, (ii) ORC Plant Components, and (iii) Fields of Application. Provides a thorough introduction to ORC power systems Contains detailed chapters on ORC plant components Includes a section focusing on ORC design and optimization Reviews key applications of ORC technologies, including cogeneration from biomass, electricity generation from geothermal reservoirs and concentrating solar power installations, waste heat recovery from gas turbines, internal combustion engines and medium- and low-temperature industrial processes Various chapters are authored by well-known specialists from Academia and ORC manufacturers. |
Giuffrida, A; Pezzuto, D Assessing the performance of a scroll expander with a selection of fluids suitable for low-temperature applications Inproceedings Energy Procedia, pp. 493–500, 2017. @inproceedings{Giuffrida2017493, title = {Assessing the performance of a scroll expander with a selection of fluids suitable for low-temperature applications}, author = {A Giuffrida and D Pezzuto}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85030656945&doi=10.1016%2Fj.egypro.2017.08.216&partnerID=40&md5=8ec2998dd5ca44a95df4879806a585e7}, doi = {10.1016/j.egypro.2017.08.216}, year = {2017}, date = {2017-01-01}, booktitle = {Energy Procedia}, volume = {126}, pages = {493--500}, abstract = {This paper presents calculations of micro organic Rankine cycles equipped with a scroll expander whose performance is simulated by a model reported in literature. In particular, the original working fluid (R245fa) is replaced with selected hydrofluorocarbons and hydrocarbons for assessing the performance of the power cycle as a function of the specific working fluid. After setting the power output from the expander at 2 kW, the relationship between cycle efficiency and maximum cycle temperature is presented for each fluid. Thus, the possibility of matching the operation of the organic Rankine cycle to heat sources at lower temperature is investigated.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } This paper presents calculations of micro organic Rankine cycles equipped with a scroll expander whose performance is simulated by a model reported in literature. In particular, the original working fluid (R245fa) is replaced with selected hydrofluorocarbons and hydrocarbons for assessing the performance of the power cycle as a function of the specific working fluid. After setting the power output from the expander at 2 kW, the relationship between cycle efficiency and maximum cycle temperature is presented for each fluid. Thus, the possibility of matching the operation of the organic Rankine cycle to heat sources at lower temperature is investigated. |
Iora, P; Di Marcoberardino, G; Invernizzi, C M; Manzolini, G; Belotti, P; Bini, R Dynamic analysis of off-grid systems with ORC plants adopting various solution for the thermal storage Inproceedings Energy Procedia, pp. 216–223, 2017. @inproceedings{Iora2017216, title = {Dynamic analysis of off-grid systems with ORC plants adopting various solution for the thermal storage}, author = {P Iora and G {Di Marcoberardino} and C M Invernizzi and G Manzolini and P Belotti and R Bini}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85029741340&doi=10.1016%2Fj.egypro.2017.09.144&partnerID=40&md5=17f992dc75ae8f06b25455d91f3a9af1}, doi = {10.1016/j.egypro.2017.09.144}, year = {2017}, date = {2017-01-01}, booktitle = {Energy Procedia}, volume = {129}, pages = {216--223}, abstract = {Real time matching of electric power generation is a crucial aspect in off-grid systems as well as in case of use of renewable intermittent sources. In this paper, with reference to 1 MWel Turboden biomass ORC plants operating in off-grid systems, we study the possibility to store thermal energy in the form of sensible heat within a storage composed by a bunch of steel or cast iron pipes with variable thickness and different coating materials. Thermal power is taken in and out of the storage by a flow of thermal oil, heated by a biomass furnace, and eventually supplied and converted into electricity by the ORC plant running in an off-grid area. Starting from steady state conditions at 30% of the nominal power of the furnace, we assume an instantaneous increase to 100% of the electric power demand and we study the transient of the system in correspondence of the furnace power ramp. To this purpose, we developed a dynamic finite difference model, for the system composed by the furnace, the ORC plant, the furnace inlet and outlet piping and the thermal storage. It comes out that with a storage system properly designed as function of the furnace power ramp, it is possible to run the ORC at 100% during the analyzed transient, thus allowing a real time matching of the power demand. textcopyright 2017 The Author(s).}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Real time matching of electric power generation is a crucial aspect in off-grid systems as well as in case of use of renewable intermittent sources. In this paper, with reference to 1 MWel Turboden biomass ORC plants operating in off-grid systems, we study the possibility to store thermal energy in the form of sensible heat within a storage composed by a bunch of steel or cast iron pipes with variable thickness and different coating materials. Thermal power is taken in and out of the storage by a flow of thermal oil, heated by a biomass furnace, and eventually supplied and converted into electricity by the ORC plant running in an off-grid area. Starting from steady state conditions at 30% of the nominal power of the furnace, we assume an instantaneous increase to 100% of the electric power demand and we study the transient of the system in correspondence of the furnace power ramp. To this purpose, we developed a dynamic finite difference model, for the system composed by the furnace, the ORC plant, the furnace inlet and outlet piping and the thermal storage. It comes out that with a storage system properly designed as function of the furnace power ramp, it is possible to run the ORC at 100% during the analyzed transient, thus allowing a real time matching of the power demand. textcopyright 2017 The Author(s). |
Scaccabarozzi, R; Tavano, M; Invernizzi, C M; Martelli, E Thermodynamic Optimization of heat recovery ORCs for heavy duty Internal Combustion Engine: Pure fluids vs. zeotropic mixtures Inproceedings Energy Procedia, pp. 168–175, 2017. @inproceedings{Scaccabarozzi2017168, title = {Thermodynamic Optimization of heat recovery ORCs for heavy duty Internal Combustion Engine: Pure fluids vs. zeotropic mixtures}, author = {R Scaccabarozzi and M Tavano and C M Invernizzi and E Martelli}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85029772039&doi=10.1016%2Fj.egypro.2017.09.099&partnerID=40&md5=5c3f36cb81867eeeedb48a630a3029fa}, doi = {10.1016/j.egypro.2017.09.099}, year = {2017}, date = {2017-01-01}, booktitle = {Energy Procedia}, volume = {129}, pages = {168--175}, abstract = {This article focuses on the optimization of ORCs for heat recovery from heavy duty Internal Combustion Engines (ICEs), with particular attention to the optimal fluid selection. We considered two different ICEs featuring same power (10 MW) but different architectures: a two-stroke engine with exhaust temperature 250°C and a four-stroke engine with 350°C exhaust temperature. The analysis tackles the optimization of the heat integration between heat sources and ORC, the optimization of the cycle variables as well as the selection of the working fluid. In addition to conventional pure substances, such as hydrocarbons, refrigerants, and siloxanes, and recently synthesized refrigerants, (i.e., HFOs, HCFOs, and HFEs), also binary zeotropic mixtures have been considered. The optimization algorithm combines the evolutionary optimization algorithm PGS-COM with a systematic heat integration methodology which maximizes the heat recovered from the available heat sources. The methodology allows optimizing also the mixture composition. In total 36 pure fluids and 36 mixtures have been evaluated. HCFO-1233zde turns out to be the best or second best fluid for most cases. Cyclopentane is the best fluid for the engine with high exhaust temperature. Another promising fluid is NovecTM 649. The optimal cycles are supercritical with T-s diagrams resembling the ideal triangular cycle. The use of the mixtures leads to an increase of the exergy efficiency of around 2.5 percentage points (about 3.5 percentage point increase in net power output). Since the optimal cycle is supercritical, the temperature glide can be exploited only in condensation and, as a result, the advantage of mixtures compared to pure fluids is lower than the values reported in the literature. textcopyright 2017 The Author(s).}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } This article focuses on the optimization of ORCs for heat recovery from heavy duty Internal Combustion Engines (ICEs), with particular attention to the optimal fluid selection. We considered two different ICEs featuring same power (10 MW) but different architectures: a two-stroke engine with exhaust temperature 250°C and a four-stroke engine with 350°C exhaust temperature. The analysis tackles the optimization of the heat integration between heat sources and ORC, the optimization of the cycle variables as well as the selection of the working fluid. In addition to conventional pure substances, such as hydrocarbons, refrigerants, and siloxanes, and recently synthesized refrigerants, (i.e., HFOs, HCFOs, and HFEs), also binary zeotropic mixtures have been considered. The optimization algorithm combines the evolutionary optimization algorithm PGS-COM with a systematic heat integration methodology which maximizes the heat recovered from the available heat sources. The methodology allows optimizing also the mixture composition. In total 36 pure fluids and 36 mixtures have been evaluated. HCFO-1233zde turns out to be the best or second best fluid for most cases. Cyclopentane is the best fluid for the engine with high exhaust temperature. Another promising fluid is NovecTM 649. The optimal cycles are supercritical with T-s diagrams resembling the ideal triangular cycle. The use of the mixtures leads to an increase of the exergy efficiency of around 2.5 percentage points (about 3.5 percentage point increase in net power output). Since the optimal cycle is supercritical, the temperature glide can be exploited only in condensation and, as a result, the advantage of mixtures compared to pure fluids is lower than the values reported in the literature. textcopyright 2017 The Author(s). |
Murgia, S; Valenti, G; Colletta, D; Costanzo, I; Contaldi, G Energy Procedia, pp. 339–346, 2017. @inproceedings{Murgia2017339, title = {Experimental investigation into an ORC-based low-grade energy recovery system equipped with sliding-vane expander using hot oil from an air compressor as thermal source}, author = {S Murgia and G Valenti and D Colletta and I Costanzo and G Contaldi}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85029773407&doi=10.1016%2Fj.egypro.2017.09.204&partnerID=40&md5=4d4d95dc931dfd4e1dbd80cac54798fb}, doi = {10.1016/j.egypro.2017.09.204}, year = {2017}, date = {2017-01-01}, booktitle = {Energy Procedia}, volume = {129}, pages = {339--346}, abstract = {Compressed air production is an energy-intensive sector, thus compressor manufacturers are constantly looking for enhancing the efficiency, by acting on several technological aspects. In an air compressor, about 80-90% of the input electric power used is wasted into the environment through the oil circuit, continuously cooled by ambient air blown via a fan. An interesting way to optimize the overall system efficiency is to exploit this waste heat to produce electrical power. Organic Rankine Cycles (ORCs) are a suitable solution for recovering energy from low-grade heat source. In this paper, an experimental analysis of two low-grade ORC-based recovery systems is presented. The thermal source is the hot lubricant of a mid-size air compressor, while the thermal sink is tap water. The first system is tested in a simple cycle configuration while the second in a recuperative one. An extensive experimental campaign is carried out on a test bench composed by sliding-vane expander, pump and plate heat exchangers. The expander differs in terms of geometry and aspect ratio between the two cycles. R236fa is used as working fluid in both the systems. The expander operating conditions are deeply investigated by using piezoelectric pressure transducers to determine the expansion indicated diagram and the expander mechanical efficiency. Experimental results show that the recuperative cycle has a better performance, in terms of cycle efficiency and expander mechanical efficiency, compared with the simple cycle. For this configuration, two off-design conditions are investigated, acting on the pump rotational speed. Finally, an exergy analysis is conducted, in order to evaluate the irreversible losses produced by each component. textcopyright 2017 The Author(s).}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Compressed air production is an energy-intensive sector, thus compressor manufacturers are constantly looking for enhancing the efficiency, by acting on several technological aspects. In an air compressor, about 80-90% of the input electric power used is wasted into the environment through the oil circuit, continuously cooled by ambient air blown via a fan. An interesting way to optimize the overall system efficiency is to exploit this waste heat to produce electrical power. Organic Rankine Cycles (ORCs) are a suitable solution for recovering energy from low-grade heat source. In this paper, an experimental analysis of two low-grade ORC-based recovery systems is presented. The thermal source is the hot lubricant of a mid-size air compressor, while the thermal sink is tap water. The first system is tested in a simple cycle configuration while the second in a recuperative one. An extensive experimental campaign is carried out on a test bench composed by sliding-vane expander, pump and plate heat exchangers. The expander differs in terms of geometry and aspect ratio between the two cycles. R236fa is used as working fluid in both the systems. The expander operating conditions are deeply investigated by using piezoelectric pressure transducers to determine the expansion indicated diagram and the expander mechanical efficiency. Experimental results show that the recuperative cycle has a better performance, in terms of cycle efficiency and expander mechanical efficiency, compared with the simple cycle. For this configuration, two off-design conditions are investigated, acting on the pump rotational speed. Finally, an exergy analysis is conducted, in order to evaluate the irreversible losses produced by each component. textcopyright 2017 The Author(s). |