| 1. |
- Buunen, M, et al.
(författare)
-
COLOR II. A randomized clinical trial comparing laparoscopic and open surgery for rectal cancer.
- 2009
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Ingår i: Danish medical bulletin. - 1603-9629 .- 0907-8916. ; 56:2, s. 89-91
-
Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: Laparoscopic resection of rectal cancer has been proven efficacious but morbidity and oncological outcome need to be investigated in a randomized clinical trial. Trial design: Non-inferiority randomized clinical trial. METHODS: The COLOR II trial is an ongoing international randomized clinical trial. Currently 27 hospitals from Europe, South Korea and Canada are including patients. The primary endpoint is loco-regional recurrence rate three years post-operatively. Secondary endpoints cover quality of life, overall and disease free survival, post-operative morbidity and health economy analysis. RESULTS: By July 2008, 27 hospitals from the Netherlands, Belgium, Germany, Sweden, Spain, Denmark, South Korea and Canada had included 739 patients. The intra-operative conversion rate in the laparoscopic group was 17%. Distribution of age, location of the tumor and radiotherapy were equal in both treatment groups. Most tumors are located in the mid-rectum (41%). CONCLUSION: Laparoscopic surgery in the treatment of rectal cancer is feasible. The results and safety of laparoscopic surgery in the treatment of rectal cancer remain unknown, but are subject of interim analysis within the COLOR II trial. Completion of inclusion is expected by the end of 2009. Trial registration: Clinicaltrials.gov, identifier: NCT00297791 (www.clinicaltrials.gov).
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| 2. |
- 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.
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| 3. |
- 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.
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| 4. |
- 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.
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| 5. |
- Andreasen, J. G., et al.
(författare)
-
Design and optimization of a novel organic Rankine cycle with improved boiling process
- 2015
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Ingår i: Energy. - : Elsevier BV. - 0360-5442. ; 91, s. 48-59
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a novel organic Rankine cycle layout, named the organic split-cycle, designed for utilization of low grade heat. The cycle is developed by implementing a simplified version of the split evaporation concept from the Kalina split-cycle in the organic Rankine cycle in order to improve the boiling process. Optimizations are carried out for eight hydrocarbon mixtures for hot fluid inlet temperatures at 120 °C and 90 °C, using a genetic algorithm to determine the cycle conditions for which the net power output is maximized. The most promising mixture is an isobutane/pentane mixture which, for the 90 °C hot fluid inlet temperature case, achieves a 14.5% higher net power output than an optimized organic Rankine cycle using the same mixture. Two parameter studies suggest that optimum conditions for the organic split-cycle are when the temperature profile allows the minimum pinch point temperature difference to be reached at two locations in the boiler. Compared to the transcritical organic Rankine cycle, the organic split-cycle improves the boiling process without an entailing increase in the boiler pressure, thus enabling an efficient low grade heat to power conversion at low boiler pressures.
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| 6. |
- Andreasen, J. G., et al.
(författare)
-
Design of organic Rankine cycles using a non-conventional optimization approach
- 2015
-
Ingår i: Proceedings of ECOS 2015 : 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems. - 9782955553909
-
Konferensbidrag (refereegranskat)abstract
- The organic Rankine cycle is a suitable technology for utilizing low grade heat for electricity production. Compared to the traditional steam Rankine cycle, the organic Rankine cycle is beneficial, since it enables the choice of a working fluid which performs better than steam at low heat input temperatures and at lowpower outputs. Selecting the process layout of the organic Rankine cycle and the working fluid are two key design decisions which are critical for the thermodynamic and economic performance of the cycle. The prevailing approach used in the design and optimization of organic Rankine cycles is to model the heatexchangers by assuming a fixed minimum temperature difference. The objective of this work is to assess the applicability of this conventional optimization approach and a non-conventional optimization approach. In thenon-conventional optimization approach a total UA-value (the product of the overall heat transfer coefficient and the heat transfer area) is assigned to the cycle, while the distribution of this total UA-value to each of the heat exchangers is optimized. Optimizations are carried out for three different marine engine waste heatsources at temperatures ranging from 90 °C to 285 °C. The results suggest that the conventional optimization approach is not suitable for estimating the performance potential when the temperature profiles in the heat exchangers are closely matched. This is exemplified for the fluid MDM where the temperature profile of preheating aligns with the heat source fluid and for the zeotropic mixture R32/R134a where the temperature profile of condensation aligns with the cooling water. Furthermore, the conventional optimization approach shows weaknesses in evaluating the feasibility of using a recuperator, when the expander outlet temperature is high. In these cases the non-conventional optimization approach is the more suited methodology for designing organic Rankine cycles.
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| 7. |
- 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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| 8. |
- 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.
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| 9. |
- Baldasso, Enrico, et al.
(författare)
-
Prediction of the annual performance of marine organic Rankine cycle power systems
- 2018
-
Ingår i: ECOS 2018 - Proceedings of the 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems.
-
Konferensbidrag (refereegranskat)abstract
- The increasing awareness about the environmental impact of shipping and the increasingly stricter regulations introduced by the International Maritime Organization are driving the development of solutions to reduce the pollutant emissions from ships. While some previous studies focused on the implementation of a specific technology, others considered a wider perspective and investigated the feasibility of the integration of various technologies on board vessels. Among the screened technologies, organic Rankine cycle (ORC) power systems represent a viable solution to utilize the waste heat contained in the main engine exhaust gases to produce additional power for on board use. The installation of ORC power systems on board ships could result in a reduction of the CO 2 emissions by 5 – 10 %. Although a number of methods to derive the optimal design of ORC units in marine applications have been proposed, these methods are complex, computationally expensive and require specialist knowledge to be included as part of a general optimization procedure to define the optimal set of technologies to be implemented on board a vessel. This study presents a novel method to predict the performance of ORC units installed on board vessels, based upon the characteristics of the main engine exhaust gases and the ship sailing profile. The method is not computationally intensive, and is therefore suitable to be used in the context of large optimization problems, such as holistic optimization and evaluation of a ship performance given the operational profile, weather and route. The model predicted the annual energy production of two case studies with an accuracy within 4 %.
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| 10. |
- Baldasso, Enrico, et al.
(författare)
-
Technical and economic feasibility of organic Rankine cycle-based waste heat recovery systems on feeder ships: Impact of nitrogen oxides emission abatement technologies
- 2019
-
Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 183, s. 577-589
-
Tidskriftsartikel (refereegranskat)abstract
- The International Maritime Organization recently revised the regulations concerning nitrogen and sulphur oxides emissions from commercial ships. In this context, it is important to investigate how emission abatement technologies capable of meeting the updated regulation on nitrogen oxides emissions affect the performance of waste heat recovery units to be installed on board new vessels. The objective of this paper is to assess the potential fuel savings of installing an organic Rankine cycle unit on board a hypothetical liquefied natural gas-fuelled feeder ship operating inside emission control areas. The vessel complies with the updated legislation on sulphur oxides emissions by using a dual fuel engine. Compliance with the nitrogen oxides emission regulation is reached by employing either a high or low-pressure selective catalytic reactor, or an exhaust gas recirculation unit. A multi-objective optimization was carried out where the objective functions were the organic Rankine cycle unit annual electricity production, the volume of the heat exchangers, and the net present value of the investment. The results indicate that the prospects for attaining a cost-effective installation of an organic Rankine unit are larger if the vessel is equipped with a low-pressure selective catalytic reactor or an exhaust gas recirculation unit. Moreover, the results suggest that the cost-effectiveness of the organic Rankine cycle units is highly affected by fuel price and the waste heat recovery boiler design constraints.
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| 11. |
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| 12. |
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| 13. |
- Bringman, S, et al.
(författare)
-
Is a dissection balloon beneficial in bilateral, totally extraperitoneal, endoscopic hernioplasty? A randomized, prospective, multicenter study
- 2001
-
Ingår i: Surgical Laparoscopy, Endoscopy and Percutaneous Techniques. - 1051-7200 .- 2331-2254. ; 11:5, s. 322-326
-
Tidskriftsartikel (refereegranskat)abstract
- Laparoscopic hernioplasty has been criticized because of its technical complexity and increased costs. Disposable dissection balloons can be used to gain the initial working space in totally extraperitoneal endoscopic (TEP) hernioplasty, but this increases its cost. Forty-four men with bilateral, primary or recurrent inguinal hernias were randomized to undergo TEP with or without dissection balloon, There were two conversions to transabdominal preperitoneal hernioplasty, or open herniorrhaphy, in the group with balloon and four in the group without balloon. There was no difference in the postoperative morbidity or operation time between the two groups, and there were no major complications in either group. The recurrence rate was 4.3% in the group with the balloon and 7.1% in the group without the balloon. There were no statistically significant differences between the groups, Although our study population is too small to detect small differences between the groups, it seems that the use of a dissection balloon is not beneficial in a bilateral TEP.
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| 14. |
- Bringman, S., et al.
(författare)
-
Is a dissection balloon beneficial in totally extraperitoneal endoscopic hernioplasty (TEP)? A randomized prospective multicenter study
- 2001
-
Ingår i: Surgical Endoscopy. - : Springer Science and Business Media LLC. - 0930-2794 .- 1432-2218. ; 15:3, s. 266-270
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Laparoscopic hernioplasty has been criticized because of its technical complexity and increased costs. Disposable dissection balloons can be used to facilitate the creation of the initial working space in totally extraperitoneal endoscopic hernioplasty (TEP), but their use adds to the cost of the operation. Methods: A total of 322 men with unilateral, primary, or recurrent inguinal hernias were randomized to undergo TEP with or without a dissection balloon. Results: In the group with the balloon, three of 161 patients (2.5%) required conversion to transabdominal preperitoneal hernioplasty (TAPP), or open herniorraphy, whereas 17 of 161 patients (10.6%) were converted to TAPP or open herniorraphy in the group without the balloon (p = 0.002). The mean operation time was 55 min in the group with the balloon and 63 min in the group without the balloon (p = 0.004). There was no difference between them in postoperative morbidity, and there were no major complications in either group. The recurrence rate was 3.1% in the group with the balloon and 3.7 % in the group without the balloon (p = 0.8). Conclusion: The use of a dissection balloon in TEP reduces the conversion rate and may be especially beneficial early in the learning curve.
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| 15. |
- Deijen, Charlotte L., et al.
(författare)
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Ten-year outcomes of a randomised trial of laparoscopic versus open surgery for colon cancer
- 2017
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Ingår i: Surgical Endoscopy. - : SPRINGER. - 0930-2794 .- 1432-2218. ; 31:6, s. 2607-2615
-
Tidskriftsartikel (refereegranskat)abstract
- Laparoscopic surgery for colon cancer is associated with improved recovery and similar cancer outcomes at 3 and 5 years in comparison with open surgery. However, long-term survival rates have rarely been reported. Here, we present survival and recurrence rates of the Dutch patients included in the COlon cancer Laparoscopic or Open Resection (COLOR) trial at 10-year follow-up. Between March 1997 and March 2003, patients with non-metastatic colon cancer were recruited by 29 hospitals in eight countries and randomised to either laparoscopic or open surgery. Main inclusion criterion for the COLOR trial was solitary adenocarcinoma of the left or right colon. The primary outcome was disease-free survival at 3 years, and secondary outcomes included overall survival and recurrence. The 10-year follow-up data of all Dutch patients were collected. Analysis was by intention-to-treat. The trial was registered at ClinicalTrials.gov (NCT00387842). In total, 1248 patients were randomised, of which 329 were Dutch. Fifty-eight Dutch patients were excluded and 15 were lost to follow-up, leaving 256 patients for 10-year analysis. Median follow-up was 112 months. Disease-free survival rates were 45.2 % in the laparoscopic group and 43.2 % in the open group (difference 2.0 %; 95 % confidence interval (CI) -10.3 to 14.3; p = 0.96). Overall survival rates were 48.4 and 46.7 %, respectively (difference 1.7 %; 95 % CI -10.6 to 14.0; p = 0.83). Stage-specific analysis revealed similar survival rates for both groups. Sixty-two patients were diagnosed with recurrent disease, accounting for 29.4 % in the laparoscopic group and 28.2 % in the open group (difference 1.2 %; 95 % CI -11.1 to 13.5; p = 0.73). Seven patients had port- or wound-site recurrences (laparoscopic n = 3 vs. open n = 4). Laparoscopic surgery for non-metastatic colon cancer is associated with similar rates of disease-free survival, overall survival and recurrences as open surgery at 10-year follow-up.
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| 16. |
- Ferruzza, D., et al.
(författare)
-
Impact of steam generator start-up limitations on the performance of a parabolic trough solar power plant
- 2018
-
Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 169, s. 255-263
-
Tidskriftsartikel (refereegranskat)abstract
- Concentrating solar power plants are an attractive option in the renewable energy generation market. The possibility of integrating relatively cheap forms of energy storage makes them a desirable solution when power generation must be readily available at any time of the day. Solar power plants typically start-up and shut down every day, so in order to maximize their profitability, it is necessary to increase their flexibility in transient operation and to initiate power generation as rapidly as possible. Two of the key components are the steam generator and steam turbine and the rates at which they can reach operational speed are limited by thermo-mechanical constraints. This paper presents an analysis of the effects of the thermal stress limitations of the steam generator and steam turbine on the power plant start-up, and quantifies their impact on the economy of the system. A dynamic model of a parabolic trough power plant was developed and integrated with a logic controller to identify start-up limitations, and subsequently the dynamic model was integrated in a techno-economic tool previously developed by the authors. The plant was analysed under two different operating strategies, namely solar-driven and peak-load. The results indicate that for steam generator hot start-ups, a 1.5% increase in peak-load electricity production would be achieved by doubling the maximum allowable heating rate of the evaporator. No useful increase would be achieved by increasing the rates beyond a limit of 7–8 K/min, as the turbine would then be the main limiting component during start-up. Similar conclusions can be drawn for the solar-driven case, for which the solar field and the energy source availability would pose the major constraint when starting up the steam generator system.
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| 17. |
- Ferruzza, D., et al.
(författare)
-
Start-up performance of parabolic trough concentrating solar power plants
- 2017
-
Ingår i: SOLARPACES 2016. - : American Institute of Physics (AIP). - 9780735415225
-
Konferensbidrag (refereegranskat)abstract
- Concentrating solar power plants, even though they can be integrated with thermal energy storage, are still subjected to cyclic start-up and shut-downs. As a consequence, in order to maximize their profitability and performance, the flexibility with respect to transient operations is essential. In this regard, two of the key components identified are the steam generation system and steam turbine. In general it is desirable to have fast ramp-up rates during the start-up of a power plant. However ramp-up rates are limited by, among other things, thermal stresses, which if high enough can compromise the life of the components. Moreover, from an operability perspective it might not be optimal to have designs for the highest heating rates, as there may be other components limiting the power plant start-up. Therefore, it is important to look at the interaction between the steam turbine and steam generator to determine the optimal ramp rates. This paper presents a methodology to account for thermal stresses limitations during the power plant start up, aiming at identifying which components limit the ramp rates. A detailed dynamic model of a parabolic trough power plant was developed and integrated with a control strategy to account for the start-up limitations of both the turbine and steam generator. The models have been introduced in an existing techno-economic tool developed by the authors (DYESOPT). The results indicated that for each application, an optimal heating rates range can be identified. For the specific case presented in the paper, an optimal range of 7-10 K/min of evaporator heating rate can result in a 1.7-2.1% increase in electricity production compared to a slower component (4 K/min).
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| 18. |
- 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
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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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| 19. |
- Larsen, Ulrik, 1972, et al.
(författare)
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Development of a multi-level approach to model and optimise the Kalina Split Cycle
- 2012
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Ingår i: Proceedings of the 53rd SIMS conference on Simulation and Modelling.
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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.
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| 20. |
- 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
-
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
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| 21. |
- Larsen, Ulrik, 1972, et al.
(författare)
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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.
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| 22. |
- 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
-
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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| 23. |
- Nguyen, Tuong-Van, 1988, et al.
(författare)
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Thermodynamic evaluation of the Kalina split-cycle concepts for waste heat recovery applications
- 2014
-
Ingår i: Energy. - 0360-5442. ; 71
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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.
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| 24. |
- 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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| 25. |
- 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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| 26. |
- 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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| 27. |
- 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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| 28. |
- Siegel, R., et al.
(författare)
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Laparoscopic extraperitoneal rectal cancer surgery : the clinical practice guidelines of the European Association for Endoscopic Surgery (EAES)
- 2011
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Ingår i: Surgical Endoscopy. - : Springer Science and Business Media LLC. - 0930-2794 .- 1432-2218. ; 25:8, s. 2423-2440
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The laparoscopic approach is increasingly applied in colorectal surgery. Although laparoscopic surgery in colon cancer has been proved to be safe and feasible with equivalent long-term oncological outcome compared to open surgery, safety and long-term oncological outcome of laparoscopic surgery for rectal cancer remain controversial. Laparoscopic rectal cancer surgery might be efficacious, but indications and limitations are not clearly defined. Therefore, the European Association for Endoscopic Surgery (EAES) has developed this clinical practice guideline. METHODS: An international expert panel was invited to appraise the current literature and to develop evidence-based recommendations. The expert panel constituted for a consensus development conference in May 2010. Thereafter, the recommendations were presented at the annual congress of the EAES in Geneva in June 2010 in a plenary session. A second consensus process (Delphi process) of the recommendations with the explanatory text was necessary due to the changes after the consensus conference. RESULTS: Laparoscopic surgery for extraperitoneal (mid- and low-) rectal cancer is feasible and widely accepted. The laparoscopic approach must offer the same quality of surgical specimen as in open surgery. Short-term outcomes such as bowel function, surgical-site infections, pain and hospital stay are slightly improved with the laparoscopic approach. Laparoscopic resection of rectal cancer is not inferior to the open in terms of disease-free survival, overall survival or local recurrence. Laparoscopic pelvic dissection may impair genitourinary and sexual function after rectal resection, like in open surgery. CONCLUSIONS: Laparoscopic surgery for mid- and low-rectal cancer can be recommended under optimal conditions. Still, most level 1 evidence is for colon cancer surgery rather than rectal cancer. Upcoming results from large randomised trials are awaited to strengthen the evidence for improved short-term results and equal long-term results in comparison with the open approach.
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| 29. |
- Topel, Monika, et al.
(författare)
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Towards prioritizing flexibility in the design and construction of concentrating solar power plants
- 2017
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Ingår i: SOLARPACES 2016. - : American Institute of Physics (AIP). - 9780735415225
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Konferensbidrag (refereegranskat)abstract
- In the operation and maintenance of concentrating solar power plants, high operational flexibility is required in order to withstand the variability from the inherent solar fluctuations. However, during the development phases of a solar thermal plant, this important objective is overlooked as a relevant factor for cost reduction in the long term. This paper will show the value of including flexibility aspects in the design of a concentrating solar power plant by breaking down their potential favorable impact on the levelized cost of electricity (LCOE) calculations. For this, three scenarios to include flexibility as a design objective are analyzed and their potential impact on the LCOE is quantified. The scenarios were modeled and analyzed using a techno-economic model of a direct steam generation solar tower power plant. Sensitivity studies were carried out for each scenario, in which the level of improvement due to each scenario was compared to the base case. Then, the results obtained for each scenario were compared for similar levels of LCOE and flexibility improvements. In general, all scenarios were beneficial on power plant performance. Improvements on the LCOE in the range of 3-4% were obtained with different distributions of costs and annual electricity for each case.
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| 30. |
- Veldkamp, R., et al.
(författare)
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Laparoscopic resection of colon Cancer: consensus of the European Association of Endoscopic Surgery (EAES)
- 2004
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Ingår i: Surgical endoscopy. - : Springer Science and Business Media LLC. - 1432-2218 .- 0930-2794. ; 18:8, s. 1163-85
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The European Association of Endoscopic Surgery (EAES) initiated a consensus development conference on the laparoscopic resection of colon cancer during the annual congress in Lisbon, Portugal, in June 2002. METHODS: A systematic review of the current literature was combined with the opinions, of experts in the field of colon cancer surgery to formulate evidence-based statements and recommendations on the laparoscopic resection of colon cancer. RESULTS: Advanced age, obesity, and previous abdominal operations are not considered absolute contraindications for laparoscopic colon cancer surgery. The most common cause for conversion is the presence of bulky or invasive tumors. Laparoscopic operation takes longer to perform than the open counterpart, but the outcome is similar in terms of specimen size and pathological examination. Immediate postoperative morbidity and mortality are comparable for laparoscopic and open colonic cancer surgery. The laparoscopically operated patients had less postoperative pain, better-preserved pulmonary function, earlier restoration of gastrointestinal function, and an earlier discharge from the hospital. The postoperative stress response is lower after laparoscopic colectomy. The incidence of port site metastases is <1%. Survival after laparoscopic resection of colon cancer appears to be at least equal to survival after open resection. The costs of laparoscopic surgery for colon cancer are higher than those for open surgery. CONCLUSION: Laparoscopic resection of colon cancer is a safe and feasible procedure that improves short-term outcome. Results regarding the long-term survival of patients enrolled in large multicenter trials will determine its role in general surgery.
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