| 1. |
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| 2. |
- Andreasen, Jesper Graa, et al.
(författare)
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Multi-Objective Optimization of Organic Rankine Cycle Power Plants Using Pure and Mixed Working Fluids
- 2016
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 9:322
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Tidskriftsartikel (refereegranskat)abstract
- For zeotropic mixtures, the temperature varies during phase change, which is opposed to the isothermal phase change of pure fluids. The use of such mixtures as working fluids in organic Rankine cycle power plants enables a minimization of the mean temperature difference of the heat exchangers, which is beneficial for cycle performance. On the other hand, larger heat transfer surface areas are typically required for evaporation and condensation when zeotropic mixtures are used as working fluids. In order to assess the feasibility of using zeotropic mixtures, it is, therefore, important to consider the additional costs of the heat exchangers. In this study, we aim at evaluating the economic feasibility of zeotropic mixtures compared to pure fluids. We carry out a multi-objective optimization of the net power output and the component costs for organic Rankine cycle power plants using low-temperature heat at 90 ◦C to produce electrical power at around 500 kW. The primary outcomes of the study are Pareto fronts, illustrating the power/cost relations for R32, R134a and R32/R134a (0.65/0.35mole). The results indicate that R32/R134a is the best of these fluids, with 3.4 % higher net power than R32 at the same total cost of 1200 k$.
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| 3. |
- Andreasen, J. G., et al.
(författare)
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Multi-objective optimization of organic Rankine ycle power plants using pure and mixed working fluids
- 2015
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Ingår i: Proceedings of ASME ORC 2015. ; , s. 11-
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Konferensbidrag (refereegranskat)abstract
- For zeotropic mixtures, the temperature varies during phase change, which is opposed to the isothermalphase change of pure fluids. The use of such mixtures as working fluids in organic Rankine cyclepower plants enables a minimization of the mean temperature difference of the heat exchangers whenthe minimum pinch point temperature difference is kept fixed. A low mean temperature differencemeans low heat transfer irreversibilities, which is beneficial for cycle performance, but it also results inlarger heat transfer surface areas. Moreover, the two-phase heat transfer coefficients for zeotropic mixturesare usually degraded compared to an ideal mixture heat transfer coefficient linearly interpolatedbetween the pure fluid values. This entails a need for larger and more expensive heat exchangers. Previousstudies primarily focus on the thermodynamic benefits of zeotropic mixtures by employing firstand second law analyses. In order to assess the feasibility of using zeotropic mixtures, it is, however,important to consider the additional costs of the heat exchangers. In this study, we aim at evaluatingthe economic feasibility of zeotropic mixtures compared to pure fluids. We carry out a multi-objectiveoptimization of the net power output and the component costs for organic Rankine cycle power plantsusing low-temperature heat at 90 ◦C to produce electrical power at around 500 kW. The primary outcomesof the study are Pareto fronts, illustrating the power/cost relations for R32, R134a and R32/R134a(0.65/0.35mole). The results indicate that R32/134a is the best of these fluids, with 3.4 % higher net powerthan R32 at the same total cost of 1200 k$.
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| 4. |
- Andreasen, J. G, et al.
(författare)
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Selection and optimization of pure and mixed working fluids for low grade heat utilization using organic Rankine cycles
- 2014
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Ingår i: Energy. - 0360-5442. ; 73
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Tidskriftsartikel (refereegranskat)abstract
- We present a generic methodology for organic Rankine cycle optimization, where the working fluid is included as an optimization parameter, in order to maximize the net power output of the cycle. The method is applied on two optimization cases with hot fluid inlet temperatures at 120°C and 90°C. Pure fluids and mixtures are compared to see how mixed working fluids affect performance and important design parameters. The results indicate that mixed working fluids can increase the net power output of the cycle, while reducing the pressure levels. The maximum net power output is obtained by fluids with a critical temperature close to half of the hot fluid inlet temperature. For some mixtures we find the maximum net power when the temperature glide of condensation matches the temperature increase of the cooling water, while for other mixtures there are large differences between these two parameters. Ethane is a fluid that obtains a large net power increase when used in mixtures. Compared to pure ethane, an optimized ethane/propane mixture attains a 12.9% net power increase when the hot fluid inlet temperature is 120_C and a 11.1% net power increase when the hot fluid inlet temperature is 90°C.
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| 5. |
- Fuente, Santiago Suárezde la, et al.
(författare)
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Selection of cooling fluid for an organic Rankine cycle unit recovering heat on a container ship sailing in the Arctic region
- 2017
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Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 141, s. 975-990
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Tidskriftsartikel (refereegranskat)abstract
- As Arctic sea ice coverage declines it is expected that marine traffic could increase in this northern region due to shorter routes. Navigating in the Arctic offers opportunities and challenges for waste heat recovery systems (WHRS). Lower temperatures require larger heating power on board, hence a larger demand for waste heat usage, to cover services and maintaining on board spaces temperatures. However, a lower heat rejection temperature increases the WHRS thermal efficiency. The air temperature for the Arctic route selected is colder than that of the seawater, opening the opportunity of having air as coolant. This paper explores the use of two different coolants, air and seawater, for an organic Rankine cycle (ORC) unit using the available waste heat in the scavenge air system of a container ship navigating in Arctic Circle. Using a two-step single objective optimisation process, detailed models of air and seawater heat exchangers are evaluated as the WHRS condensers. The results suggest that an ORC unit using R1233zd(E) as its working fluid coupled with seawater as its coolant is the preferable option to reduce CO2 emissions. Using the ambient air as the coolant while a less effective option could be cheaper to instal
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| 6. |
- Larsen, Ulrik, 1972, et al.
(författare)
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Design and optimisation of organic Rankine cycles for waste heat recovery in marine applications using the principles of natural selection
- 2013
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Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 55, s. 803-812
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Tidskriftsartikel (refereegranskat)abstract
- Power cycles using alternative working fluids are currently receiving significant attention. Selection of working fluid among many candidates is a key topic and guidelines have been presented. A general problem is that the selection is based on numerous criteria, such as thermodynamic performance, boundary conditions, hazard levels and environmental concerns. A generally applicable methodology, based on the principles of natural selection, is presented and used to determine the optimum working fluid, boiler pressure and Rankine cycle process layout for scenarios related to marine engine heat recovery. Included in the solution domain are 109 fluids in sub and supercritical processes, and the process is adapted to the properties of the individual fluid. The efficiency losses caused by imposing process constraints are investigated to help propose a suitable process layout. Hydrocarbon dry type fluids in recuperated processes produced the highest efficiencies, while wet and isentropic fluids were superior in non-recuperated processes. The results suggested that at design point, the requirements of process simplicity, low operating pressure and low hazard resulted in cumulative reductions in cycle efficiency. Furthermore, the results indicated that non-flammable fluids were able to produce near optimum efficiency in recuperated high pressure processes.
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| 7. |
- Larsen, Ulrik, 1972, et al.
(författare)
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Development of a model for the prediction of the fuel consumption and nitrogen oxides emission trade-off for large ships
- 2015
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Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 80, s. 545-555
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Tidskriftsartikel (refereegranskat)abstract
- The international regulations on fuel efficiency and NOx emissions of commercial ships motivate the investigation of new system layouts, which can comply with the regulations. In combustion engines, measures to reduce the fuel consumption often lead to increased NOx emissions and careful consideration of this trade-off mechanism is required in the design of marine propulsion systems. This study investigates five different configurations of two-stroke diesel-based machinery systems for large ships and their influence on the mentioned trade-off. Numerical models of a low-speed two-stroke diesel engine, turbochargers and an ORC (organic Rankine cycle), are used for the optimisation of the NOx andfuel consumption at design and part-load conditions, using a multi-objective genetic algorithm. Moreover, the effects of engine tuning and exhaust gas recirculation are investigated. The results suggest that increased system complexity can lead to lower fuel consumption and NOx. Fuel consumption reductions of up to 9% with a 6.5% NOx reduction were achieved using a hybrid turbocharger and organic Rankinecycle waste heat recovery system.
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| 8. |
- Larsen, Ulrik, 1972, et al.
(författare)
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Expansion of organic Rankine cycle working fluid in a cylinder of a low-speed two-stroke ship engine
- 2017
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Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 119, s. 1212-1220
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Tidskriftsartikel (refereegranskat)abstract
- Electricity and power produced from waste heat is particularly relevant in shipping because fuel expenses constitute the majority of the cost of operating the ships; however, the cost-benefit aspect limits the widespread implementation of waste heat recovery power units on ships. This paper presents the thermodynamic analysis of a concept that aims at reducing the cost of an organic Rankine cycle unit by using one of the cylinders in a large diesel engine as expansion device. Numerical models were used to optimise the process parameters and thereby determine the power potential for this concept. The evaluation of 104 working fluids points to cyclopropane, R245fa and R1234ze(z) as the most promising. The results suggest that the power produced by the organic Rankine cycle cylinder is at least equivalent to that of the cylinders operating with the diesel process. This enables potential fuel savings and emissions reductions of about 8.3% in the studied scenario.
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| 9. |
- Larsen, Ulrik, 1972, et al.
(författare)
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Multiple regression models for the prediction of the maximum obtainable thermal efficiency of organic Rankine cycles
- 2014
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Ingår i: Energy. - 0360-5442. ; 65
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Tidskriftsartikel (refereegranskat)abstract
- Much attention is focused on increasing the energy efficiency to decrease fuel costs and CO2 emissions throughout industrial sectors. The ORC (organic Rankine cycle) is a relatively simple but efficient process that can be used for this purpose by converting low and medium temperature waste heat to power. In this study we propose four linear regression models to predict the maximum obtainable thermal efficiency for simple and recuperated ORCs. A previously derived methodology is able to determine the maximum thermal efficiency among many combinations of fluids and processes, given the boundary conditions of the process. Hundreds of optimised cases with varied design parameters are used as observations in four multiple regression analyses. We analyse the model assumptions, prediction abilities and extrapolations, and compare the results with recent studies in the literature. The models are in agreement with the literature, and they present an opportunity for accurate prediction of the potential of an ORC to convert heat sources with temperatures from 80 to 360 C, without detailed knowledge or need for simulation of the process
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| 10. |
- Mondejar, M. E., et al.
(författare)
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A review of the use of organic Rankine cycle power systems for maritime applications
- 2018
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Ingår i: Renewable and Sustainable Energy Reviews. - : Elsevier BV. - 1879-0690 .- 1364-0321. ; 91, s. 126-151
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Forskningsöversikt (refereegranskat)abstract
- Diesel engines are by far the most common means of propulsion aboard ships. It is estimated that around half of their fuel energy consumption is dissipated as low-grade heat. The organic Rankine cycle technology is a well-established solution for the energy conversion of thermal power from biomass combustion, geothermal reservoirs, and waste heat from industrial processes. However, its economic feasibility has not yet been demonstrated for marine applications. This paper aims at evaluating the potential of using organic Rankine cycle systems for waste heat recovery aboard ships. The suitable vessels and engine heat sources are identified by estimating the total recoverable energy. Different cycle architectures, working fluids, components, and control strategies are analyzed. The economic feasibility and integration on board are also evaluated. A number of research and development areas are identified in order to tackle the challenges limiting a widespread use of this technology in currently operating vessels and new-buildings. The results indicate that organic Rankine cycle units recovering heat from the exhaust gases of engines using low-sulfur fuels could yield fuel savings between 10% and 15%.
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| 11. |
- Pierobon, L., et al.
(författare)
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Multi-objective optimization of organic Rankine cycles for waste heat recovery: Application in an offshore platform
- 2013
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Ingår i: Energy. - 0360-5442. ; 58, s. 538-549
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims at finding the optimal design of MW-size organic Rankine cycles by employing the multi-objective optimization with the genetic algorithm as the optimizer. We consider three objective functions: thermal efficiency, total volume of the system and net present value. The optimization variables are the working fluid, the turbine inlet pressure and temperature, the condensing temperature, the pinch points and the fluid velocities in the heat exchangers. The optimization process also includes the complete design of the shell and tube heat exchangers utilized in the organic Rankine cycle. The methodology is applied to recover the waste heat from the SGT-500 gas turbine installed on the Draugen off-shore oil and gas platform in the North Sea. Results suggest two optimal working fluids, i.e. acetone and cyclopentane. Thermal efficiency and net present value are higher for cyclopentane than for acetone. Other promising working fluids are cyclohexane, hexane and isohexane. The present methodology can be utilized in waste heat recovery applications where a compromise between performance, compactness and economic revenue is required.
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| 12. |
- Pierobon, L., et al.
(författare)
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Optimization of Organic Rankine Cycles for Off-Shore Applications
- 2013
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Ingår i: Proceedings of ASME Turbo Expo 2013. - 9780791855201 ; 5B, s. 11-
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Konferensbidrag (refereegranskat)abstract
- In off-shore oil and gas platform efficiency, the reliability and fuel flexibility are the major concerns when selecting the gas turbine to support the electrical and mechanical demand on the platform. In order to fulfill these requirements, turbine inlet temperature and pressure ratio are not increased up to the optimal values and one or more redundant gas turbines may be employed. With increasing incentives for reducing the CO2 emissions off-shore, improving the thermal efficiency has become a focus area. Due to the peculiar low turbine outlet temperature and due to space and weight constraints, a steam bottoming cycle is not a convenient solution. On the contrary, organic Rankine cycles (ORCs) present the benefits of high simplicity and compactness. Furthermore, the working fluid can be selected considering the temperature profile at which the heat is supplied; hence the heat transfer process and the thermal efficiency of the cycle can be maximized. This paper is aimed at finding the most optimal ORC tailored for off-shore applications using an optimization procedure based on the genetic algorithm. Numerous working fluids are screened through, considering mainly thermal efficiency, but also other characteristics of the fluids, e.g. stability, environmental and human health impacts, and safety issues. Both supercritical and subcritical ORCs are included in the analysis. The optimization procedure is first applied to a conservative ORC where the maximum pressure is limited to 20 bar. Subsequently the optimal working fluid is identified by removing the restriction on the maximum pressure. Different limits on hazards and global warming potential (GWP) are also set. The study is focused on the SGT-500 gas turbine installed on the Draugen platform in the Norwegian Sea. The simulations suggest that, when a high hazard is accepted, cyclohexane is the best solution. With a turbine inlet pressure limit of 20 bar, the combined gas turbine-ORC system presents an efficiency of 43.7%, corresponding to an improvement of 11.9%-points with respect to the gas turbine efficiency. With no upper pressure boundary, cyclohexane at 55.5 bar is the preferable working fluid with a combined thermal efficiency of 44.3%. The supercritical CO2 cycle with a maximum pressure of 192.9 bar is found to be the best alternative if an extremely low hazard is required.
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| 13. |
- Pierobon, L., et al.
(författare)
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Part-Load Performance of a Wet Indirectly Fired Gas Turbine Integrated with an Organic Rankine Cycle Turbogenerator
- 2014
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 7:12, s. 8294-8316
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Tidskriftsartikel (refereegranskat)abstract
- Over the last years, much attention has been paid to the development of efficient and low-cost power systems for biomass-to-electricity conversion. This paper aims at investigating the design-and part-load performance of an innovative plant based on a wet indirectly fired gas turbine (WIFGT) fueled by woodchips and an organic Rankine cycle (ORC) turbogenerator. An exergy analysis is performed to identify the sources of inefficiencies, the optimal design variables, and the most suitable working fluid for the organic Rankine process. This step enables to parametrize the part-load model of the plant and to estimate its performance at different power outputs. The novel plant has a nominal power of 250 kW and a thermal efficiency of 43%. The major irreversibilities take place in the burner, recuperator, compressor and in the condenser. Toluene is the optimal working fluid for the organic Rankine engine. The part-load investigation indicates that the plant can operate at high efficiencies over a wide range of power outputs (50%-100%), with a peak thermal efficiency of 45% at around 80% load. While the ORC turbogenerator is responsible for the efficiency drop at low capacities, the off-design performance is governed by the efficiency characteristics of the compressor and turbine serving the gas turbine unit.
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| 14. |
- Pierobon, L., et al.
(författare)
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Thermodynamic analysis of an integrated gasification solid oxide fuel cell plant combined with an organic Rankine cycle
- 2013
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Ingår i: Renewable Energy. - 0960-1481 .- 1879-0682. ; 60, s. 226-234
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Tidskriftsartikel (refereegranskat)abstract
- A 100 kWe hybrid plant consisting of gasification system, solid oxide fuel cells and organic Rankine cycle is presented. The nominal power is selected based on cultivation area requirement. For the considered output a land of around 0.5 km2 needs to be utilized. Woodchips are introduced into a fixed bed gasification plant to produce syngas which fuels the combined solid oxide fuel cells e organic Rankine cycle system to produce electricity. More than a hundred fluids are considered as possible alternative for the organic cycle using non-ideal equations of state (or state-of-the-art equations of state). A genetic algorithm is employed to select the optimal working fluid and the maximum pressure for the bottoming cycle. Thermodynamic and physical properties, environmental impacts and hazard specifications are also considered in the screening process. The results suggest that efficiencies in the region of 54e56% can be achieved. The highest thermal efficiency (56.4%) is achieved with propylcyclohexane at 15.9 bar. A comparison with the available and future technologies for biomass to electricity conversion is carried out. It is shown that the proposed system presents twice the thermal efficiency achieved by simple and double stage organic Rankine cycle plants and around the same efficiency of a combined gasification, solid oxide fuel cells and micro gas turbine plant.
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