| 1. |
- Andreasen, J. G, et al.
(författare)
-
Selection and optimization of pure and mixed working fluids for low grade heat utilization using organic Rankine cycles
- 2014
-
Ingår i: Energy. - 0360-5442. ; 73
-
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.
|
|
| 2. |
- Baldi, Francesco, 1986, et al.
(författare)
-
Analysis of the influence of the engine, propeller and auxiliary generation interaction on the energy efficiency of controllable pitch propeller ships
- 2014
-
Ingår i: International Conference of Maritime Technology.
-
Konferensbidrag (refereegranskat)abstract
- In a context of increasing requirements for energy efficiency, this paper aims at improving theunderstanding on the interaction between engine, propeller, and auxiliary heat and power generation in theparticular case of controllable pitch propeller (CPP) ships. The case study of a CPP propelled chemical tankeris used to analyze the application of the proposed approach. The performance of the ship’s standardarrangement using a shaft generator for the fulfillment of auxiliary power demand is compared to theoperational alternative of using auxiliary engines, and with the possibilities for retrofitting with frequencyconverters and waste heat recovery systems. The influence of control systems parameters and of sea state arealso analyzed and compared. The results show a large possibility for improvements, both via operationaloptimization (up to 8.3% increased energy efficiency) and via different types of retrofitting (with increasedefficiencies of up to 11.4% for frequency converters, and 16.5% for WHR systems). The influence of a broadoperational envelope brings even larger improvements to the efficiency of the energy system at low speeds. Theresults of the paper provide useful information about the influence of different technologies for auxiliary powergeneration on the efficiency of CPP propelled vessels.
|
|
| 3. |
- Larsen, Ulrik, 1972, et al.
(författare)
-
A comparison of advanced heat recovery power cycles in a combined cycle for large ships
- 2014
-
Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 74
-
Tidskriftsartikel (refereegranskat)abstract
- Strong motivation exists within the marine sector to reduce fuel expenses and to comply with ever stricter emission regulations. Heat recovery can address both of these issues. The ORC (organic Rankine cycle), the Kalina cycle and the steam Rankine cycle have received the majority of the focus in the literature. In the present work we compare these cycles in a combined cycle application with a large marine two-stroke diesel engine. We present an evaluation of the efficiency and the environmental impact, safety concerns and practical aspects of each of the cycles. A previously validated numerical engine model is combined with a turbocharger model and bottoming cycle models written in Matlab. Genetic algorithm optimisation results suggest that the Kalina cycle possess no significant advantages compared to the ORC or the steam cycle. While contributing to very high efficiencies, the organic working fluids possess high global warming potentials and hazard levels. It is concluded that the ORC has the greatest potential for increasing the fuel efficiency, and the combined cycle offers very high thermal efficiency. While being less efficient, the steam cycle has the advantages of being well proven, harmless to the environment as well as being less hazardous in comparison.
|
|
| 4. |
- Larsen, Ulrik, 1972, et al.
(författare)
-
Design and optimisation of organic Rankine cycles for waste heat recovery in marine applications using the principles of natural selection
- 2013
-
Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 55, s. 803-812
-
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.
|
|
| 5. |
- Larsen, Ulrik, 1972, et al.
(författare)
-
Development of a multi-level approach to model and optimise the Kalina Split Cycle
- 2012
-
Ingår i: Proceedings of the 53rd SIMS conference on Simulation and Modelling.
-
Konferensbidrag (refereegranskat)abstract
- In the marine sector there is a strong motivation for increasing the propulsion system energy efficiency, mainly because of increasing fuel prices and stricter upcoming emission regulations. The Kalina cycle, based on a mixture of ammonia and water as working fluid, exhibits higher conversion efficiencies than conventional power cycles and could be suitable for this purpose. The Split Cycle technique provides a method to further increase the thermal efficiency, by reducing the thermodynamic losses in the heat recovery system. This is achieved by having two separate streams of different ammonia concentrations entering and leaving a first evaporator stage before being mixed at the inlet of a second evaporator stage. It seems that modelling efforts showing the advantages of the Split Cycle have not been presented in the literature yet. Thus, a thermodynamic model of the Split Cycle is introduced in this work. Modelling and optimisation of the rather complex cycle requires approaching the problem at different system levels. This paper investigates tools and methods suitable for demonstrating the feasibility and advantages of the Split Cycle. The integrated model developed and presented in this paper combines three sub-models all using the NIST REFPROP equations of state: a separator and mixing subsystem model to handle the inherent constraints of the Split Cycle, a component-based model to optimise the heat exchanger operating conditions, and a process model to investigate the complete thermodynamic cycle. Results suggest a 9% net power output increase and 7% higher thermal efficiency compared to the baseline case.
|
|
| 6. |
- Larsen, Ulrik, 1972, et al.
(författare)
-
Multiple regression models for the prediction of the maximum obtainable thermal efficiency of organic Rankine cycles
- 2014
-
Ingår i: Energy. - 0360-5442. ; 65
-
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
|
|
| 7. |
- Larsen, Ulrik, 1972, et al.
(författare)
-
System analysis and optimisation of a Kalina split-cycle for waste heat recovery on large marine diesel engines
- 2014
-
Ingår i: Energy. - 0360-5442. ; 64
-
Tidskriftsartikel (refereegranskat)abstract
- Waste heat recovery systems can produce power from heat without using fuel or emitting CO2, therefore their implementation is becoming increasingly relevant. The Kalina cycle is proposed as an efficient process for this purpose. The main reason for its high efficiency is the non-isothermal phase change characteristics of the ammonia-water working fluid. The present study investigates a unique type of Kalina process called the Split-cycle, applied to the exhaust heat recovery from large marine engines. In the Split-cycle, the working fluid concentration can be changed during the evaporation process in order to improve the match between the heat source and working fluid temperatures. We present a system analysis to identify the governing mechanisms of the process, including a comparison of the efficiency of the Split-cycle and a conventional Kalina cycle and an investigation of the effects of using reheat in both cases. Results of a multi-variable optimisation effort using a genetic algorithm suggest that the Split-cycle process can obtain a thermal efficiency of 23.2% when using reheat compared to 20.8% for a conventional reference Kalina cycle. Reheat can increase the thermal efficiency by 3.4-5.9%. A simplified cost analysissuggests higher purchase costs as result of increased process complexity.
|
|
| 8. |
- Nguyen, Tuong-Van, 1988, et al.
(författare)
-
Thermodynamic evaluation of the Kalina split-cycle concepts for waste heat recovery applications
- 2014
-
Ingår i: Energy. - 0360-5442. ; 71
-
Tidskriftsartikel (refereegranskat)abstract
- The Kalina split-cycle is a thermodynamic process for converting thermal energy into electrical power. It uses an ammonia–water mixture as a working fluid (like a conventional Kalina cycle) and has a varying ammonia concentration during the pre-heating and evaporation steps. This second feature results in an improved match between the heat source and working fluid temperature profiles, decreasing the entropy generation in the heat recovery system. The present work compares the thermodynamic performance of this power cycle with the conventional Kalina process, and investigates the impact of varying boundary conditions by conducting an exergy analysis. The design parameters of each configuration were determined by performing a multi-variable optimisation. The results indicate that the Kalina split-cycle with reheat presents an exergetic efficiency by 2.8% points higher than a reference Kalina cycle with reheat, and by 4.3% points without reheat. The cycle efficiency varies by 14% points for a variation of the exhaust gas temperature of 100 °C, and by 1% point for a cold water temperature variation of 30 °C. This analysis also pinpoints the large irreversibilities in the low-pressure turbine and condenser, and indicates a reduction of the exergy destruction by about 23% in the heat recovery system compared to the baseline cycle.
|
|
| 9. |
- Nielsen, R. F., et al.
(författare)
-
Design and modeling of an advanced marine machinery system including waste heat recovery and removal of sulphur oxides
- 2013
-
Ingår i: Proceedings of ECOS 2013 - The 26th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems. ; 2013
-
Konferensbidrag (refereegranskat)abstract
- In order to reduce the formation of acid rain and its harmful effects, stricter legislations on emissions of sulphur oxides from ships applies as of 2015 in emission control areas and globally in 2020 by the international maritime organization (IMO). Consequently, prices on low sulphur fuels are expected to increase drastically compared to those of heavy fuel oil, giving ship owners a strong incentive to find alternative ways of complying with the legislations. In addition, IMO regulations on carbon dioxide emissions and high fuel prices provide incentives for improving the efficiency of the machinery system. The wet sulphuric acid process has shown to be an effective way of removing sulphur oxides from flue gas of land-based coal fired power plants. Moreover, organic Rankine cycles are suitable for heat to power conversion for low temperature heat sources. This paper is aimed at designing and modelling a highly efficient machinery system which includes the removal of exhaust gas sulphur oxides. Numerical simulations are carried out using an open source software developed at Technical University of Denmark called Dynamic Network Analysis (DNA). The machinery system suggested in this paper consists of a two-stroke diesel engine, the wet sulphuric process for sulphur removal and an advanced waste heat recovery system including a conventional steam Rankine cycle and an organic Rankine cycle. The results are compared with those of a state-of-the-art machinery system featuring a two-stroke diesel engine and a conventional waste heat recovery system. The results suggest that an organic Rankine cycle placed after the conventional waste heat recovery system is able to extract the sulphuric acid from the exhaust gas, while at the same time increase power generation from waste heat by 32.9% and the combined cycle thermal efficiency by 2.6%. The findings indicates that the technology has an energetic and environmental potential in marine applications, while still further research and development need to be done before it can be put into operation on ships.
|
|
| 10. |
- Pierobon, L., et al.
(författare)
-
Multi-objective optimization of organic Rankine cycles for waste heat recovery: Application in an offshore platform
- 2013
-
Ingår i: Energy. - 0360-5442. ; 58, s. 538-549
-
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.
|
|
| 11. |
- Pierobon, L., et al.
(författare)
-
Optimization of Organic Rankine Cycles for Off-Shore Applications
- 2013
-
Ingår i: Proceedings of ASME Turbo Expo 2013. - 9780791855201 ; 5B, s. 11-
-
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.
|
|
| 12. |
- Pierobon, L., et al.
(författare)
-
Part-Load Performance of a Wet Indirectly Fired Gas Turbine Integrated with an Organic Rankine Cycle Turbogenerator
- 2014
-
Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 7:12, s. 8294-8316
-
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.
|
|
| 13. |
- Pierobon, L., et al.
(författare)
-
Thermodynamic analysis of an integrated gasification solid oxide fuel cell plant combined with an organic Rankine cycle
- 2013
-
Ingår i: Renewable Energy. - 0960-1481 .- 1879-0682. ; 60, s. 226-234
-
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.
|
|
| 14. |
- Rasmussen, R. F., et al.
(författare)
-
Design and modeling of an advanced marine machinery system including waste heat recovery and removal of sulphur oxides
- 2014
-
Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 85
-
Tidskriftsartikel (refereegranskat)abstract
- Stricter legislation on sulphur oxide emissions from ships will apply as of 2015 in emission control areas. Consequently, prices on low sulphur fuels are expected to increase drastically, providing a strong incentive to find alternative ways of complying with the legislation and improving the efficiency of machinery systems. The wet sulphuric acid process is an effective way of removing flue gas sulphur oxides from land-based coal-fired power plants. Moreover, organic Rankine cycles (ORC) are suitable for heat to power conversion for low temperature heat sources. This paper describes the design and modeling of a highly efficient machinery system which includes the removal of exhaust gas sulphur oxides. The system consists of a two-stroke diesel engine, the wet sulphuric process for sulphur removal, a conventional steam Rankine cycle and an ORC. Results of numerical modeling efforts suggest that an ORC placed after the conventional waste heat recovery system is able to extract the sulphuric acid from the exhaust gas, while at the same time increase the combined cycle thermal efficiency by 2.6%. The findings indicate that the technology has potential in marine applications regarding both energy and the environment; however, further research and development efforts are needed.
|
|
| 15. |
- Scapping, F., et al.
(författare)
-
Validation of a zero-dimensional model for prediction of NOx and engine performance for electronically controlled marine two-stroke diesel engines
- 2012
-
Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 37, s. 344-352
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to derive a methodology suitable for energy system analysis for predicting the performance and NOx emissions of marine low speed diesel engines. The paper describes a zero-dimensional model, evaluating the engine performance by means of an energy balance and a two zone combustion model using ideal gas law equations over a complete crank cycle. The combustion process is divided into intervals, and the product composition and flame temperature are calculated in each interval. The NOx emissions are predicted using the extended Zeldovich mechanism. The model is validated using experimental data from two MAN B&W engines; one case being data subject to engine parameter changes corresponding to simulating an electronically controlled engine; the second case providing data covering almost all model input and output parameters. The first case of validation suggests that the model can predict specific fuel oil consumption and NOx emissions within the 95% confidence intervals given by the experimental measurements. The second validation confirms the capability of the model to match measured engine output parameters based on measured engine input parameters with a maximum 5% deviation.
|
|
