| 1. |
- Bahrami, Saeed, et al.
(författare)
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Identifying a simplified model for heavy duty gas turbine
- 2014
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Ingår i: Journal of Mechanical Science and Technology. - : Springer Science and Business Media LLC. - 1738-494X .- 1976-3824. ; 28:6, s. 2399-2408
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Tidskriftsartikel (refereegranskat)abstract
- A dynamic model was developed for long-term simulation of a heavy duty gas turbine. The model includes the essential control algorithm of the gas turbine as well as the most common outputs and other important intermediate variables. Control algorithm details, such as wind up protection and load limiter algorithm which have large effect on gas turbine transient behavior, are included. The model parameters are identified by applying genetic algorithm and least squares algorithm on regular operational data from a real plant to better match the model response to the real plant. The simulation results have been validated with real plant data and shown to have valid accuracy for many engineering applications.
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| 2. |
- Bahrami, Saeed, et al.
(författare)
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Improving the Transient Performance of the Gas Turbine by Steam Injection during Frequency Dips
- 2013
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 6:10, s. 5283-5296
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Tidskriftsartikel (refereegranskat)abstract
- Single-shaft gas turbines are sensitive to frequency changes which might affect the grid stability during large frequency drops. This paper presents a new control system that uses steam injection as an auxiliary input to improve the transient performance of the gas turbine during frequency drops. Steam injection is beneficial because it reduces the peak temperature in the combustion chamber and augments the output power by increasing the mass flow through the turbine. The use of this auxiliary input is based on the event-based control approach. It means that during the frequency drop, the controller exploits the steam injection to help the main control loop recover the frequency and when the frequency reaches its predefined value, the system will return to its normal operation. The performance of the proposed control algorithm is investigated under different scenarios and the results show that the application of steam injection improves the performance of the regular control algorithm significantly, especially near full load condition.
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| 3. |
- Dahlquist, Adrian, et al.
(författare)
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The influence from the working medium on the profile loss in compressor and turbine airfoils
- 2014
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Ingår i: Proceedings of the ASME Turbo Expo: Turbine Technical Conference And Exposition, 2014, Vol 2C. ; , s. 02-38
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Konferensbidrag (refereegranskat)abstract
- A number of CCS-technologies are currently being developed for the reduction of CO2 emissions from thermal power stations. One such technology is the oxyfuel process, in which a mixture of CO2 and steam is used as the working medium. The semi-closed oxyfuel combustion combined cycle (SCOC-CC) is an oxyfuel cycle where the working medium mainly consists of CO2 (85-95%). Current practice is to design turbomachinery using 1D and 2D flow tools, which primarily rely on loss models derived from experiments with air. For the oxyfuel case, the losses are hence extrapolated from air to a CO2/steam mixture, which can have adverse effects on the accuracy of the loss model. Therefore, the applicability and accuracy in using profile loss correlations derived with air when changing the working medium to the oxyfuel like environment of pure CO2 was investigated. The reason that 100% CO2 was chosen as the working medium and not a CO2/H2O mixture is that the water content present is relatively low and varies from case-to-case. Hence, a general water content could not be specified that was relevant for all cases. The study was done with typical compressor and turbine airfoils using a steady-state Navier-Stokes' 3D flow solver. This solver type can resolve the boundary layer (y(+) of about unity) rather than relying upon a boundary layer equation, - hence eliminating the latter as a source of error. The hypothesis was that the profile loss depended on the viscosity, and that amendments to the viscosity would affect the profile loss. This trend was observed, e.g. when changing the working medium from air to CO2, the profile loss coefficient (Y-p) for the compressor was reduced with 25% and for the turbine with 6%, respectively. A slight difference in profile loss for an individual cascade was found when changing the working medium from air to CO2. Theoretically, this difference leads to an increased mismatch of the stages downstream even at design point, and thus increases the losses and reduces the stability. However, the difference in profile loss is relatively small at the design point, and thus it is the authors' opinion that the practical effect will be quite small. Therefore, it is considered safe to use loss correlations derived from air for design point calculations even when the working medium is CO2. However, there is a certain risk involved that air- based loss models are not capable of predicting the behavior over the full operating range, as the boundary layers risk to behave in a different manner. Another aspect that was considered is how the wet surface area (physical size) of a turbomachine performing the same work (mho) will change between the two gases. This is important as the total profile loss in a whole compressor or turbine is directly proportional to this change. The conclusion was that the total wet area would increase by some 20% for CO2 compared to air.
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| 4. |
- Deshpande, Srikanth, et al.
(författare)
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Reduction in Secondary Losses in Turbine Cascade Using Contoured Boundary Layer Fence
- 2014
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Ingår i: Proceedings of the ASME 2014 Gas Turbine India Conference. - 9780791849644 ; , s. 2014-8175
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Konferensbidrag (refereegranskat)abstract
- Present work deals with reducing secondary losses in turbine cascade by using boundary layer fences in two ways. Firstly, to reduce the strength of vortex which is incident at the leading edge of airfoil and hence reduce the strength of horse shoe vortex, and secondly, to reduce the pressure gradient between the pressure side and the suction side in the flow passage region between airfoils. In previous works, the boundary layer fence followed the profile of airfoil. In this publication, boundary layer fence does not follow the profile of airfoil i.e stagger and camber of boundary fence is different when compared to airfoil. A profiled boundary layer fence is proposed in the present work which reduces the incident voracity and also reduces pressure gradient from pressure side to suction side. Such boundary layer fence was checked on T106 test cascade which is available as open literature. Numerical work is carried out using commercial software Ansys CFX. Viscous RANS simulations are carried out using k-omega SST turbulence model with yplus value around unity on all walls. Coefficient of secondary kinetic energy (CSKE) and Secondary Kinetic energy helicity (SKEH) are used as target functions. Total pressure loss is also monitored. All the three functions show a reduction in secondary loss. The strength of horse shoe vortex is reduced by the fence protruding in front of leading edge. The converging flow passage created by the fence near the pressure side of airfoil reduces the pressure gradient from pressure side to suction side. The total pressure loss was reduced by 1.5 % and CSKE was improved by 36 % when the boundary layer fence was adopted.
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| 5. |
- Duwig, Christophe, et al.
(författare)
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Efficient operation of a gas turbine on methanol using chemical recuperation
- 2012
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Ingår i: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. ; 1, s. 615-623
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Konferensbidrag (refereegranskat)abstract
- Environmental and political concerns, together with new legislations, are pushing for a fuel shift in the power industry and more generally for many thermal applications. Adding to the coming decrease of oil and natural availability (or price increase), it opens avenues for new fuels. Among those, alcohols are strong candidates. In fact, short alcohols are easily produced and stored and require only moderate modifications of existing combustion systems. For example, operating an existing gas turbine (GT) on methanol requires moderate modifications (mainly in the combustion system). However, methanol can be used more efficiently. Unlike methane or other hydrocarbons that decompose at high temperature (1000K), methanol undergoes an endothermic decomposition at low temperatures (400K to 600K) to give CO and H2. It therefore opens avenue for coupling the GT with a chemical recuperation system. In other words, the methanol will be cracked using the waste heat of the flue gases with a gain in fuel heating value hence the original fuel is thermally upgraded. The present study will investigate the upgraded fuel combustion properties. The laminar flame speed of the upgraded fuel/air mixtures will be presented and compared to methane and methanol under conditions relevant to GT combustion. Several upgraded fuel compositions will be considered depending on the water content in the feed methanol. Further, we consider a recuperated micro GT (Turbec T100) based cycle fueled with methanol. The numerical study focuses on different thermodynamic cycles. Firstly, a reference case is considered assuming a direct fueled GT. Further, cycles including the cracker are studied keeping the power constant. The fuel efficiency gain due to the cracker will be investigated as function of the water content in the feed methanol. Finally, a case including CO2-removal will be presented and it will be shown that the cracker enables an efficient carbon capture and sequestration scheme.
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| 6. |
- Mondejar, Maria, et al.
(författare)
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A new IPSEpro library for the simulation of binary mixtures of real fluids in power cycle analysis
- 2014
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Ingår i: Journal of Postdoctoral Research. - 2328-9791. ; 2:3, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Increasing efforts to produce power from renewable resources and improve the efficiency of current industrial processes have turned the spotlight on organic Rankine cycles (ORC). The use of refrigerant mixtures in these cycles offers a wide range of possibilities for fluid selection and optimization. Moreover, zeotropic mixtures are reported to yield better cycle performances due to their better thermal match with the source and sink streams. In this work a new IPSEpro® library for the simulation of power cycles using binary mixtures was developed. With this library the working fluid can be defined as the mixture of any pair of suitable fluids contained in the Refprop database.
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| 7. |
- Mondejar, Maria, et al.
(författare)
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Aerodynamic considerations in the thermodynamic analysis of organic Rankine cycles
- 2014
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Ingår i: [Host publication title missing]. ; 2, s. 002-016
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Konferensbidrag (refereegranskat)abstract
- Due to the increasing interest of producing power from renewable and non-conventional resources, organic Rankine cycles are finding their place in today’s thermal energy mix. The main influencers on the efficiency of an organic Rankine cycle are the working fluid and the expander. Therefore most of the research done up to date turns around the selection of the best performance working media and the optimization of the expansion unit design. However, few studies consider the interaction of the working fluids in the turbine design, and how this fact can affect the overall thermodynamic cycle analysis. In this work we aim at including the aerodynamic behavior of the working fluids and their effect on the turbine efficiency in the thermodynamic analysis of an organic Rankine cycle. To that end, we proposed a method for the estimation of the characteristics of an axial in-flow turbine in an organic Rankine cycle simulation model. The code developed for the characterization of the turbine behavior under the working fluid properties evaluated the irreversibilities associated to the aerodynamic losses in the turbine. The organic Rankine cycle was analyzed by using IPSEpro process simulator. A set of candidate working fluids composed of selected organofluorines and organochlorines was chosen for the analysis. The thermophysical properties of the fluids were estimated with the equations of state implemented in Refprop. Results on the energy and exergy overall performances of the cycle were analyzed for a case study with standard source and sink temperatures. For each fluid the number of stages and geometry of the turbine were optimized. It was observed that some working fluids that could initially be considered as advantageous from a thermodynamic point of view, had an unfavorable impact on the turbine efficiency, thus increasing the irreversibilities of the cycle. We concluded that if the influence of the working fluid on the turbine performance is underestimated, the real performance of the organic Rankine cycle could show unexpected deviations from the theoretical results.
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| 8. |
- Mondejar, Maria E., et al.
(författare)
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Power generation from low heat sources
- 2014
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Ingår i: Advances in Energy Research and Development. - 9780989559010 ; , s. 49-82
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Bokkapitel (refereegranskat)abstract
- In this chapter a thorough review of the latest research findings on power generation from non-conventional low heat sources is presented. Main discoveries and results of research works ranging from source exploitation technologies to final power production are reported and discussed to offer an overview of their potential. Firstly the concept of low-grade source is presented and the main energy sources in this group (i.e. geothermal energy, solar thermal systems, industrial waste heat and ocean thermal energy) are introduced. Each of them is briefly described and the latest developments and improvements on the technologies for their exploitation are enumerated. Afterwards the state-of-the-art available power cycles for the conversion of low heat into electricity are reported. Only thermal power conversion technologies are presented due to their higher presence in commercial applications and their potential for small scale power generation. Among these technologies, last findings and results on organic Rankine cycles (ORC) and power cycles based on working fluid mixtures (e.g. Kalina cycle) are described. A special emphasis is placed on organic Rankine cycles (ORC) since over the last few years this technology has experienced a significant global growth, boosted by their viable performance and the inherited knowledge from the refrigeration industry. In addition, the suitability of less known technologies such as Stirling cycles and their current development status and perspectives are also commented. After this review it follows an examination of the implementation of these technologies in present power production systems. Discussion will be provided on which are the current barriers that the mentioned technologies are facing for their introduction or during their operation. On the other hand, practical restrictions concerning the availability of suitable technology, environmental requirements or economic viability are stated. Limitations regarding thermodynamic and technological aspects, as well as operational concerns will be considered of special interest. In the final section we deal with the future scenario for the integration of small-scale power generation. Potential solutions for overcoming technology development barriers are presented and directions of current research works on this topic are pointed out.
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| 9. |
- Mondejar, Maria, et al.
(författare)
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Non-conventional working fluids for thermal power generation: A review
- 2014
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Ingår i: Journal of Postdoctoral Research. - 2328-9791. ; 2:9, s. 1-14
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Forskningsöversikt (refereegranskat)abstract
- New technology requirements derived from the exploitation of novel energy resources, and the needs for improvement of the energy efficiency of current power generation systems are pushing the industry towards the search of alternative working fluids. The great challenge for these non-conventional fluids is to provide satisfactory performances and fill the existing lack of media for some innovative energy applications. In this review a number of emerging working fluids for thermal power generation are presented. Also, a special emphasis is devoted to the discussion about new promising fluids, such as nanofluids or ionic liquids, that could be an important breakdown for power generation in the near future.
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| 10. |
- Narayanan, Prakash, et al.
(författare)
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Waste Heat Recovery from Multiple Heat Sources in a HD Truck Diesel Engine Using a Rankine Cycle - A Theoretical Evaluation
- 2012
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Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- Few previous publications investigate the possibility of combining multiple waste heat sources in a combustion engine waste heat recovery system. A waste heat recovery system for a HD truck diesel engine is evaluated for utilizing multiple heat sources found in a conventional HD diesel engine. In this type of engine more than 50% of heat energy goes futile. The majority of the heat energy is lost through engine exhaust and cooling devices such as EGRC (Exhaust gas recirculation cooler), CAC (Charge air cooler) and engine cooling. In this paper, the potential of usable heat recuperation from these devices using thermodynamic analysis was studied, and also an effort is made to recuperate most of the available heat energy that would otherwise be lost. A well-known way of recuperating this heat energy is by employing a Rankine cycle circuit with these devices as heat sources (single loop or dual loop), and thus this study is focused on using a Rankine cycle for the heat recovery system. Furthermore, this paper investigates the possibilities and challenges involved in coupling these different sources in a single Rankine cycle and the selection of suitable working fluid for this Rankine cycle. The study shows that with recuperation from these multiple sources it is possible to recover 5-10% of the otherwise wasted heat energy, which results in ~5% power increase. REFPROP was used for studying fluid properties, and the commercial software IPSEpro is used to build and simulate the Rankine cycle.
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