| 1. |
- Wang, Wujun
(författare)
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Development of an Impinging Receiver for Solar Dish-Brayton Systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A new receiver concept utilizing impinging jet cooling technology has been developed for a small scale solar dish-Brayton system. In a typical impinging receiver design, the jet nozzles are distributed evenly around the cylindrical absorber wall above the solar peak flux region for managing the temperature at an acceptable level. The absorbed solar irradiation is partially lost to the ambient by radiation and natural convection heat transfer, the major part is conducted through the wall and taken away by the impingement jets to drive a gas turbine. Since the thermal power requirement of a 5 kWe Compower® micro gas turbine (MGT) perfectly matches with the power collected by the EuroDish when the design Direct Normal Irradiance (DNI) input is 800 W/m2, the boundary conditions for the impinging receiver design in this work are based on the combination of the Compower®MGT and the EuroDish system.In order to quickly find feasible receiver geometries and impinging jet nozzle arrangements for achieving acceptable temperature level and temperature distributions on the absorber cavity wall, a novel inverse design method (IDM) has been developed based on a combination of a ray-tracing model and a heat transfer analytical model. In this design method, a heat transfer model of the absorber wall is used for analyzing the main heat transfer process between the cavity wall outer surface, the inner surface and the working fluid. A ray-tracing model is utilized for obtaining the solar radiative boundary conditions for the heat transfer model. Furthermore, the minimum stagnation heat transfer coefficient, the jet pitch and the maximum pressure drop governing equations are used for narrowing down the possible nozzle arrangements. Finally, the curves for the required total heat transfer coefficient distribution are obtained and compared with different selected impinging arrangements on the working fluid side, and candidate design configurations are obtained.Furthermore, a numerical conjugate heat transfer model combined with a ray-tracing model was developed validating the inverse design method and for studying the thermal performance of an impinging receiver in detail. With the help of the modified inverse design method and the numerical conjugate heat transfer model, two impinging receivers based on sintered α-SiC (SSiC) and stainless steel 253 MA material have been successfully designed. The detailed analyses show that for the 253 MA impinging receiver, the average air temperature at the outlet and the thermal efficiency can reach 1071.5 K and 82.7% at a DNI level of 800 W/m2 matching the system requirements well. Furthermore, the local temperature differences on the absorber can be reduced to 130 K and 149 K for two different DNI levels, which is a significant reduction and improvement compared with earlier published cavity receiver designs. The inverse design method has also been verified to be an efficient way in reducing the calculation costs during the design procedure.For the validation and demonstration of the receiver designs, a unique experimental facility was designed and constructed. The facility is a novel high flux solar simulator utilizing for the first time Fresnel lenses to concentrate the light of 12 commercial high power Xenon-arc lamps. Finally, a prototype of a 253 MA based impinging was experimentally studied with the help of the 84 kWe Fresnel lens based high flux solar simulator in KTH.
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| 2. |
- Zhang, Xiaoxiang, 1984-
(författare)
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Numerical Study on Combustion Features of Gasified Biomass Gas
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a great interest to develop biomass combustion systems for industrial and utility applications. Improved biomass energy conversion systems are designed to provide better combustion efficiencies and environmental friendly conditions, as well as the fuel flexibility options in various applications. The gas derived from the gasification process of biomass is considered as one of the potential candidates to substitute traditional fuels in a combustion process. However, the gascomposition from the gasification process may have a wide range of variation depending on the methods and fuel sources. The better understanding of the combustion features for the Gasified Biomass Gas(GBG) is essential for the development of combustion devices to be operated efficiently and safely at the user-end.The objective of the current study is therefore aiming to achieve data associated with the combustion features of GBG fuel for improving the efficiency and stability of combustion process. The numerical result is achieved from the kinetic models of premixed combustion with a wide range of operating ranges and variety of gas compositions. The numerical result is compared with experimental data to provide a better understanding of the combustion process for GBG fuel.In this thesis the laminar flame speed and ignition delay time of the GBG fuel are analyzed, using 1-D premixed flame model and constant volume model respectively. The result from different kinetics are evaluated and compared with experimental data. The influences of initial temperature, pressure and equivalence ratio are considered, as well as the variation of gas compositions. While the general agreement is reached between the numerical result and experimental data for laminarflame speed prediction, deviations are discovered at fuel-rich region and increased initial temperature. For the ignition delay time, deviations are found in the low-temperature and low pressure regime. The empirical equations considering the influence of initial temperature,pressure and equivalence ratio are developed for laminar flame speed and ignition delay times. The influence of major compositions such as CO, H2 and hydrocarbons are discussed in details in the thesis. Furthermore, a simplified kinetic model is developed and optimized based on the evaluation of existing kinetics for GBG fuel combustion. The simplified kinetic model is expected to be used for simulating the complexc ombustion process of GBG fuel in future studies.
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| 3. |
- Binti Munajat, Nur Farizan
(författare)
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Combustion of gasified biomass: : Experimental investigation on laminar flame speed, lean blowoff limit and emission levels
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass is among the primary alternative energy sources that supplements the fossil fuels to meet today’s energy demand. Gasification is an efficient and environmental friendly technology for converting the energy content in the biomass into a combustible gas mixture, which can be used in various applications. The composition of this gas mixture varies greatly depending on the gasification agent, gasifier design and its operation parameters and can be classified as low and medium LHV gasified biomass. The wide range of possible gas composition between each of these classes and even within each class itself can be a challenge in the combustion for heat and/or power production. The difficulty is primarily associated with the range in the combustion properties that may affect the stability and the emission levels. Therefore, this thesis is intended to provide data of combustion properties for improving the operation or design of atmospheric combustion devices operated with such gas mixtures.The first part of this thesis presents a series of experimental work on combustion of low LHV gasified biomass (a simulated gas mixture of CO/H2/CH4/CO2/N2) with variation in the content of H2O and tar compound (simulated by C6H6). The laminar flame speed, lean blowoff limit and emission levels of low LHV gasified biomass based on the premixed combustion concept are reported in paper I and III. The results show that the presence of H2O and C6H6 in gasified biomass can give positive effects on these combustion parameters (laminar flame speed, lean blowoff limit and emission levels), but also that there are limits for these effects. Addition of a low percentage of H2O in the gasified biomass resulted in almost constant laminar flame speed and combustion temperature of the gas mixture, while its NOx emission and blowoff temperature were decreased. The opposite condition was found when H2O content was further increased. The blowoff limit was shifted to richer fuel equivalence ratio as H2O increased. A temperature limit was observed where CO emission could be maintained at low concentration. With C6H6 addition, the laminar flame speed first decreased, achieved a minimum value, and then increased with further addition of C6H6. The combustion temperature and NOx emission were increased, CO emission was reduced, and blowoff occurs at slightly higher equivalence ratio and temperature when C6H6 content is increased. The comparison with natural gas (simulated by CH4) is also made as can be found in paper I and II. Lower laminar flame speed, combustion temperature, slightly higher CO emission, lower NOx emission and leaner blowoff limit were obtained for low LHV gas mixture in comparison to natural gas.In the second part of the thesis, the focus is put on the combustion of a wide range of gasified biomass types, ranging from low to medium LHV gas mixture (paper IV). The correlation between laminar flame speed or lean blowoff limit and the composition of various gas mixtures was investigated (paper IV). It was found that H2 and content of diluents have higher influence on the laminar flame speed of the gas mixture compared to its CO and hydrocarbon contents. For lean blowoff limit, the diluents have the greatest impact followed by H2 and CO. The mathematical correlations derived from the study can be used to for models of these two combustion parameters for a wide range of gasified biomass fuel compositions.
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| 4. |
- Cardozo, Evelyn, 1984-
(författare)
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Combustion of agricultural residues : Application for Stirling micro-combined heat and power
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Access to energy services is crucial for the development of countries. Therefore, in developing countries, the access to modern conversion technologies would contribute to reduce the poverty, improve health services and promote the economy especially in rural areas. Around 2.5 billion people in these countries use biomass for cooking. However, major concerns are due to the unsustainable use of biomass and the inefficient conversion technologies employed in rural areas. Therefore, the use of locally available biomass in modern biomass conversion technologies would significantly reduce emissions and improve the energy efficiency. These modern technologies may include residential pellet stoves and boilers which at the moment only are used for heating appliances in industrialized countries. Their combination with a prime mover like a Stirling engine could a very attractive solution to produce combined heat and power (CHP) though still in prototype stage. In this context, this study is mainly focused on the development of an energy system fuelled by locally available biomass to produce heat and electricity based on a Stirling engine. The main objective is to perform experiments to find relevant parameters that characterize the energy system proposed.In the first stage of this work, the suitability of using agricultural residues in a pellet boiler was evaluated in comparison to commercial wood pellets. The agricultural residues used during the tests were: sugar cane bagasse, sunflower husks and Brazil nut shells. The first two residues were pelletized and the last one was reduced to a uniform size. Parameters and energy used during the pelletizing were found. Emission levels and boiler efficiency under steady-state and transient conditions were also presented for the different biomass sorts. In the second stage, the integration of the same pellet burner and the Stirling engine was characterized in terms of losses and efficiency calculations. Finally, the integration of the pelletizing, combustion, and heat and power generation was discussed based on experimental and predicted results.
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| 5. |
- Mayorca, Maria Angelica, 1983-
(författare)
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Numerical Methods for Turbomachinery Aeromechanical Predictions
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In both aviation and power generation, gas turbines are used as key components. An important driver of technological advance in gas turbines is the race towards environmentally friendly machines, decreasing the fuel burn, community noise and NOx emissions. Engine modifications that lead to propulsion efficiency improvements whilst maintaining minimum weight have led to having fewer stages and lower blade counts, reduced distance between blade rows, thinner and lighter components, highly three dimensional blade designs and the introduction of integrally bladed disks (blisks). These changes result in increasing challenges concerning the structural integrity of the engine. In particular for blisks, the absence of friction at the blade to disk connections decreases dramatically the damping sources, resulting in designs that rely mainly on aerodynamic damping. On the other hand, new open rotor concepts result in low blade-to-air mass ratios, increasing the influence of the surrounding flow on the vibration response. This work presents the development and validation of a numerical tool for aeromechanical analysis of turbomachinery (AROMA - Aeroelastic Reduced Order Modeling Analyses), here applied to an industrial transonic compressor blisk. The tool is based on the integration of results from external Computational Fluid Dynamics (CFD) and Finite Element (FE) solvers with mistuning considerations, having as final outputs the stability curve (flutter analysis) and the fatigue risk (forced response analysis). The first part of the study aims at tracking different uncertainties along the numerical aeromechanical prediction chain. The amplitude predictions at two inlet guide vane setups are compared with experimental tip timing data. The analysis considers aerodynamic damping and forcing from 3D unsteady Navier Stokes solvers. Furthermore, in-vacuo mistuning analyses using Reduced Order Modeling (ROM) are performed in order to determine the maximum amplitude magnification expected. Results show that the largest uncertainties are from the unsteady aerodynamics predictions, in which the aerodynamic damping and forcing estimations are most critical. On the other hand, the structural dynamic models seem to capture well the vibration response and mistuning effects. The second part of the study proposes a new method for aerodynamically coupled analysis: the Multimode Least Square (MLS) method. It is based on the generation of distributed aerodynamic matrices that can represent the aeroelastic behavior of different mode-families. The matrices are produced from blade motion unsteady forces at different mode-shapes fitted in terms of least square approximations. In this sense, tuned or mistuned interacting mode families can be represented. In order to reduce the domain size, a static condensation technique is implemented. This type of model permits forced response prediction including the effects of mistuning on both the aerodynamic damping as well as on the structural mode localization. A key feature of the model is that it opens up for considerations of responding mode-shapes different to the in-vacuo ones and allows aeroelastic predictions over a wide frequency range, suitable for new design concepts and parametric studies.
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| 6. |
- Monaco, Lucio
(författare)
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Remote Laboratories in the Training of Turbomachinery Engineering Students
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When practicing their profession, engineers use their analytical and creative thinking to develop solutions for problems that require the application of scientific knowledge and experience in a dependable and sustainable way. Laboratory exercises represent an ideal scenario for engineering students to comprehend through the application in actual situations of fundamental concepts and to analyze, synthetize, and make judgments based on evidence. Furthermore, in case of group work, students collaborate on an assignment taking decisions and sharing responsibilities thus training their social skills.The use and development of information technology have in the past few decades increased at a very high pace and have had considerable effects on various domains of society, including education. Although distance learning has existed for a while, it is the widespread access to the Internet and familiarity of the current young generation with information technology that has led to the recent boom of interest in massive open online education (MOOC) as well as in various forms of blended learning.Laboratories in education are traditionally hands-on activities carried out on-campus by students with the assistance of an instructor. New laboratory environments such as virtual and remote laboratories have in the past decades been introduced in several disciplines to improve access to distant students, cut down costs, and reduce obsolescence of hands-on labs. Yet many are the doubts concerning their effectiveness in tackling the development of engineering skills, as well as their technical capability of being 24/7 worldwide accessible professional remote infrastructures. The present thesis work is concerned with the conceiving, implementation and evaluation of a set of remote laboratories to be used in the training of turbomachinery engineering students. The focus is put on three new remote laboratory exercises:a pump laboratory exercise focusing on the assessment of operation of pumpsa turbine cascade laboratory exercise focusing on the measurement of aerodynamic losses anda turbine cascade laboratory exercise focusing on the measurement of aeroelastic properties in a vibrating blade row.The laboratories are developed using state-of-the-art instrumentation and a design that allows for reusability of common hardware and software resources. Different technologies are explored for the remote operation of the equipment while laboratory exercises are constructed that include interactive learning material, online self-assessments, and tools for analysis of the experimental test data.Extensive field-testing within ongoing courses at the department proves an overall good technical performance of the remote laboratories. Accessibility is significantly improved with the use of new web technologies while integration in existing networks of remote laboratories and use of remote experiment management systems is perceived as necessary for future scaling up of the application.The concept of the remote laboratory exercises is critically evaluated and leads to changes in the structure of the exercises that improve development of certain laboratory skills and student’s perception of the remote experience. The same experimental setup is used to address different learning outcomes and, in turns, different target audiences showing the potential of significantly improving the economical sustainability of the labs, especially in the case these are integrated in courses at other universities.The generality of conclusions is partially validated by the involvement of external students, researchers and professional in energy technology in the testing of the remote laboratory exercises as part of collaborative initiatives that raise also the interest for a possible application of remote experimentation in research activity.Keywords: remote laboratory, distant education, engineering education, turbomachinery training
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| 7. |
- Sanz Luengo, Antonio, 1986-
(författare)
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Experimental Investigation of the Influence of Local Flow Features on the Aerodynamic Damping of an Oscillating Blade Row
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The general trend of efficiency increase, weight and noise reduction has derived in the design of more slender, loaded, and 3D shaped blades. This has a significant impact on the stability of fan, and low pressure turbine blades, which are more prone to aeroelastic phenomena such as flutter. The flutter phenomenon is a self-excited, self-sustained unstable vibration produced by the interaction of flow and structure. These working conditions will induce either blade overload, or High Cycle Fatigue (HCF) produced by Limited Cycle Oscillation (LCO).The main objectives of the present work are on the investigation of the aeroelastic properties of a high-lift low-pressure in the light of the local flow features present in such profiles, in nominal and extreme off-design conditions both in high and low subsonic Mach number, for three dif-ferent rigid body modes. In addition, the validity of the linearity assump-tion of the influence coefficient technique has also been investigated, in order to expand the understanding of the physical limits of this assumption.This work has been designed as experimental investigation in the influence coefficient domain focused on a high-lift low-pressure turbine designed by ITP within the framework of the European FP7 project FU-TURE. These experiments have been carried out in the Aeroelastic test rig (AETR), at KTH Stockholm, which consist of an instrumented annular sector cascade with a single oscillating blade. The results acquired have been supported by numerical results provided by a non-propietary commercial software package (ANSYS CFX).The results suggest that the typical three-dimensional effects associated secondary flow features and tip leakage flows have a significant influence on the aeroelastic performance and the cascade stability. However the major influence appears as a consequence of the separation surface on the pressure side which appears at extreme off-design operating conditions. The contribution to stability of this local feature depend on the oscillation mode showing for the axial and torsion mode a neutral stability contribution, which is directly associated with the geometrical properties of the cascade. However, on the circumferential mode this separation surface has a stabilizing effect much more independent of the blade geometry.The study of the linearity assumption of the influence coefficient domain has revealed, that an apparent linear relation between the integrated unsteady response and the vibrational amplitude, does not necessary imply that the local unsteady response is linear with respect to the oscillation amplitude. The results also suggest that the validity of the linearity as-sumption is more sensitive to high oscillation amplitudes at high Mach conditions.
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| 8. |
- Udomsri, Seksan
(författare)
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Combined Electricity Production and Thermally Driven Cooling from Municipal Solid Waste
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasingly intensive efforts are being made to enhance energy systems via augmented introduction of renewable energy along with improved energy efficiency. Resource constraints and sustained high fossil fuel prices have created a new phenomenon in the world market. Enhanced energy security and renewable energy development are currently high on public agenda worldwide for achieving a high standard of welfare for future generations. Biomass and municipal solid waste (MSW) have widely been accepted as important locally-available renewable energy sources offering low carbon dioxide (CO2) emissions. Concerning solid waste management, it has become a critical issue in Southeast Asia since the most popular form for waste disposal still employs open dumping and landfilling. While the need for a complete sustainable energy solution is apparent, solid waste management is also an essential objective, so it makes sense to explore ways in which the two can be joined. Electricity production in combination with energy recovery from flue gases in thermal treatment plants is an integral part of MSW management for many industrialized nations. In Sweden, MSW is considered as an important fuel resource for partially meeting EU environmental targets within cogeneration. However it is normally difficult to justify traditional cogeneration in tropical locations since there is little need for the heat produced. Similarly, MSW-fired cogeneration usually operates with low capacity during non-heating season in Sweden. Therefore, it is very important to find new alternatives for energy applications from waste, such as the implementation of thermally driven cooling processes via absorption cooling in addition to electricity production. The work presented herein concentrates first on an investigation of electricity generation from MSW power plants and various energy applications from waste in tropical urban areas. The potential for various types of absorption chillers driven by MSW power plants for providing both electricity and cooling is of particular interest. Additionally a demonstration and analysis of decentralized thermally driven cooling in district heating network supplied by low temperature heat from a cogeneration of MSW have been conducted. This study aims at developing the best system configuration as well as finding improved system design and control for a combination of district heating and distributed thermally driven cooling. Results show that MSW incineration has the ability to lessen environmental impacts associated with waste disposal, and it can contribute positively towards expanding biomass-based energy production in Southeast Asia. For electricity production, the proposed hybrid dual-fuel (MSW/natural gas) cycles feature attractive electrical efficiency improvements, leading to greenhouse gas emissions reduction. Cogeneration coupled with thermally driven cooling is a solution that holds promise for uniting enhanced sustainability with economic advantages. The system offers great opportunity for primary energy saving, increasing electrical yield and can significantly reduce CO2 emissions per unit of cooling as compared to compression chiller. The demonstration and simulation have also revealed that there is a potential with some modifications and improvements to employ decentralized thermally driven cooling in district heating networks even in temperate regions like Sweden. Thus, expanding cogeneration towards trigeneration can augment the energy supply for summer months in Europe and for year-round cooling in tropical locations.
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| 9. |
- Araoz Ramos, Joseph Adhemar, 1982-
(författare)
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Thermodynamic analysis of Stirling engine systems : Applications for combined heat and power
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing energy demands and environmental problems require innovative systems for electrical and thermal energy production. In this scenario, the development of small scale energy systems has become an interesting alternative to the conventional large scale centralized plants. Among these alternatives, small scale combined heat and power (CHP) plants based on Stirling Engines (SE) have attracted the interest among research and industry due to the potential advantages that offers. These include low maintenance, low noise during operation, a theoretically high electrical efficiency, and principally the fuel flexibility that the system offers. However, actual engine performances present very low electrical efficiencies and consequently few successful prototypes reached commercial maturity at elevated costs.Considering this situation, this thesis presents a numerical thermodynamic study for micro scale CHP-SE systems. The study is divided in two parts: The first part covers the engine analysis; and the second part studies the thermodynamic performance of the overall CHP-SE system. For the engine analysis a detailed thermodynamic model suitable for the simulation of different engine configurations was developed. The model capability to predict the engine performance was validated with experimental data obtained from two different engines: The GPU-3 Stirling engine studied by Lewis Research Centre; and the Genoa engine studied on the experimental rig built at the Energy Department at the Royal Institute of Technology (KTH). The second part of the research complemented the study with the analysis of the overall CHP-SE system. This included numerical simulations of the different CHP components and the sensitivity analysis for selected design parameters.The complete study permitted to assess the different operational and design configurations for the engine and the CHP components. These improvements could be implemented for test field evaluations and thus foster the development of more efficient SE-CHP systems. In addition, the detailed thermodynamic-design methodology for the SE-CHP systems was established and the numerical tool for the design assessment was developed.
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| 10. |
- Baagherzadeh Hushmandi, Narmin, 1978-
(författare)
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Numerical Analysis of Partial Admission in Axial Turbines
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- HTML clipboard Numerical analysis of partial admission in axial turbines is performed in this work. Geometrical details of an existing two stage turbine facility with low reaction blades is used for this purpose. For validation of the numerical results, experimental measurements of one partial admission configuration at design point was used. The partial admission turbine with single blockage had unsymmetrical shape; therefore the full annulus of the turbine had to be modeled numerically. The numerical grid included the full annulus geometry together with the disc gaps and rotor shrouds. Importance of various parameters in accurate modeling of the unsteady flow field of partial admission turbines was assessed. Two simpler models were selected to study the effect of accurate modeling of radial distribution of flow parameters. In the first numerical model, the computational grid was two dimensional and the radial distribution of flow parameters was neglected. The second case was three-dimensional and full blades’ span height was modeled but the leakage flows at disc cavity and rotor shroud were neglected. Detailed validation of the results from various computational models with the experimental data showed that modeling of the leakage flow at disc cavities and rotor shroud of partial admission turbines has substantial importance in accuracy of numerical computations. Comparison of the results from two computational models with varying inlet extension showed that modeling of the inlet cone has considerable importance in accuracy of results but with increased computational cost. Partial admission turbine with admission degree of ε = 0.524 in one blocked arc and two opposing blocked arcs were tested. Results showed that blocking the inlet annulus in one single arc produce better overall efficiency compared to the two blocked arc model. Effect of varying axial gap distance between the first stage stator and rotor rows was also tested numerically for the partial admission turbine with admission degree of ε = 0.726. Results showed higher efficiency for the reduced axial gap model. Computations showed that the main flow leave the blade path down to the disc cavity and re-enter into the flow channel downstream the blockage, this flow would pass the rotor with very low efficiency. First stage rotor blades are subject to large unsteady forces due to the non-uniform inlet flow. Plotting the unsteady forces of first stage rotor blades for partial admission turbine with single blockage showed that the blades experience large changes in magnitude and direction while traveling along the circumference. Unsteady forces of first stage rotor blades were plotted in frequency domain using Fourier transform. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Results obtained from the numerical computations showed that the discs have nonuniform pressure distribution especially in the first stage of partial admission turbines. The axial force of the first rotor wheel was considerably higher when the axial gap distance was reduced between the first stage stator and rotor rows. The commercial codes used in this work are ANSYS ICEM-CFD 11.0 as mesh generator and FLUENT 6.3 as flow solver.
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| 11. |
- Baina Veizaga, Fabiola, 1985-
(författare)
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Externally fired gas turbine cycle based on biomass gasification gas as fuel
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Energy services are essential for the development of societies, reduce poverty, and improve the living standards of inhabitants. The conventional routes to provide energy services employ fossil fuels. However, this involves environmental and availability concerns. Environmental issues and the need for energy security demand the use of alternative energy sources. Biomass is a renewable energy source that is advantageous because of its dispatchability and local availability worldwide. Local generation at small scales is interesting because it reduces energy losses when transporting electricity and heat. The development of sustainable decentralized small scale heat and power plants (CHP) using biomass is thus important.In this context, this work is mainly focused on the development of an energy conversion technology based on an externally fired gas turbine using biomass gasification gas as fuel. Although this system is not new, its applicability with biomass gasification gas has not been widely studied. This work is divided in three parts. In the first part, the effect of the fuel composition and fuel inlet temperature on the performance of an externally fired gas turbine prototype is analyzed through simulations. Then, the performances of two types of heat exchangers are compared under the operational conditions of the prototype taking into account different thicknesses of deposit materials. The results shows that the composition of the fuels and the corresponding flue gas temperatures affect the electrical power output of the system. However, this is limited by the operating temperature of the heat exchanger. It is also reported that a decrease in the effectiveness of the heat exchanger has a greater influence on the electrical power output than an increase in the pressure drop as a result of deposit materials. High pressure drops in the hot side of the heat exchanger slightly affect the electrical power output. If biomass gasification gas is to be used after the gasifier with reduced cleaning steps, the effect of contaminants such as tar in the combustion performance is important. The last part in this work describes experimental studies of the effect of benzene as tar representative in the combustion performance of a surrogate mixture of biomass gasification gas. Polyaromatic hydrocarbons such as benzene, present in tar in biomass derived gas, affect the combustion emissions depending on their concentration in the fuel gas.
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| 12. |
- Erlich, Catharina
(författare)
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Comparative study of residue pellets from cane sugar and palm-oil industries with commercial wood pellets, applied in downdraft gasification
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- While biomass utilization for energy conversion in the industrialized nations is being largely developed, highly efficient and environmentally friendly, many tropical countries still use biomass at low efficiencies and high emission levels. The main reasons for these gaps are both political and technological: the energy markets are different, the Gross National Product (GDP) differs widely, and the feedstock differs in form and conversion behaviour. By implementing newer technologies adapted for tropical biomass feedstock, there would be a large potential in these countries for increased energy services since access to modern energy still is an essential step for improving the GDP for a country. Two dominant and tropically placed industries available for energy improvements are the cane sugar and palm-oil industries, which both produce an abundant amount of biomass residues. One step towards enhanced utilization of the residues, which would not require large investment costs in the power plant section nor in the processes of these industries, would be to install a pelletizing unit in the industry area to make fuel out of the excess residues for sale to the nearby villages. The pellets could be used both for cooking/heating and for small-scale power generation in a gasification-IC engine plant. The overall objective of this study is to experimentally evaluate the biomass residues in pellet form from the cane sugar and palm oil industries during conversion to useful energy in small-scale systems. The thesis is built upon five publications which include experimental analysis on flaming pyrolysis and rapid heating of pellets (paper I), pyrolysis in oxygen-free atmosphere and slow heating with subsequent steam gasification (paper II), global pelletizing data such as relative energy consumption, temperature levels, particle size and moisture content for successful pelletizing process (paper III), downdraft gasification evaluation including reactor temperature distribution, gas composition, cold-gas efficiency and packed-bed mechanics (paper IV) and a numerical model including the overall system efficiency for residue-to-electric power based in a small-scale gasifier system (paper V).The single-pellet studies revealed that pyrolysis in reducing atmosphere is to prefer compared to flaming pyrolysis in oxidizing environment with regards to the char quality. The studies also showed favourable thermochemical and mechanical behaviour for smaller size pellets (Ø6- Ø8mm) compared to larger size ones (Ø12 mm). Therefore, a downdraft gasifier of closed constricted type was designed for real gasification tests of the residue pellets of sizes Ø6- Ø8mm. These tests showed that all the studied pellet sorts could be used in one and the same gasifier, resulting in different reactor temperature distributions and gas compositions with lower heating values in the range of 4.1-5.4 MJ/m3n dry gas. The reactor bed dynamics showed to be dependent both on the fuel reactivity and the size, with less pressure drop for larger size pellets with lower reactivity. The pelletizing process itself revealed that the selected residues all needed higher moisture content and smaller particle size than recommended for wood for successful pelletizing. The relative electric energy consumption was lower when producing larger size pellets Ø8 mm than smaller ones (Ø6 mm) of same material. For untreated wet empty-fruit bunch (EFB) a stand-alone power plant with integrated EFB pre-treatment and gasification could generate 380 kWh of net electricity per ton of EFB at a “well-to-wheel” efficiency of 15%.
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| 13. |
- Fan, Liangdong, 1985-
(författare)
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Development and characterization of functional composite materials for advanced energy conversion technologies
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The solid oxide fuel cell (SOFC) is a potential high efficient electrochemical device for vehicles, auxiliary power units and large-scale stationary power plants combined heat and power application. The main challenges of this technology for market acceptance are associated with cost and lifetime due to the high temperature (700-1000 oC) operation and complex cell structure, i.e. the conventional membrane electrode assemblies. Therefore, it has become a top R&D goal to develop SOFCs for lower temperatures, preferably below 600 oC. To address those above problems, within the framework of this thesis, two kinds of innovative approaches are adopted. One is developing functional composite materials with desirable electrical properties at the reduced temperature, which results of the research on ceria-based composite based low temperature ceramic fuel cell (LTCFC). The other one is discovering novel energy conversion technology - Single-component/ electrolyte-free fuel cell (EFFC), in which the electrolyte layer of conventional SOFC is physically removed while this device still exhibits the fuel cell function. Thus, the focus of this thesis is then put on the characterization of materials physical and electrochemical properties for those advanced energy conversion applications. The major scientific content and contribution to this challenging field are divided into four aspects except the Introduction, Experiments and Conclusions parts. They are:Continuous developments and optimizations of advanced electrolyte materials, ceria-carbonate composite, for LTCFC. An electrolysis study has been carried out on ceria-carbonate composite based LTCFC with cheap Ni-based electrodes. Both oxygen ion and proton conductance in electrolysis mode are observed. High current outputs have been achieved at the given electrolysis voltage below 600 oC. This study also provides alternative manner for high efficient hydrogen production. Compatible and high active electrode development for ceria-carbonate composite electrolyte based LTCFC. A symmetrical fuel cell configuration is intentionally employed. The electro-catalytic activities of novel symmetrical transition metal oxide composite electrode toward hydrogen oxidation reaction and oxygen reduction reaction have been experimentally investigated. In addition, the origin of high activity of transition metal oxide composite electrode is studied, which is believed to relate to the hydration effect of the composite oxide.A novel all-nanocomposite fuel cell (ANFC) concept proposal and feasibility demonstration. The ANFC is successfully constructed by Ni/Fe-SDC anode, SDC-carbonate electrolyte and lithiated NiO/ZnO cathode at an extremely low in-situ sintering temperature, 600 oC. The ANFC manifests excellent fuel cell performance (over 550 mWcm-2 at 600 oC) and a good short-term operation as well as thermo-cycling stability. All results demonstrated its feasibility and potential for energy conversion.Fundamental study results on breakthrough research Single-Component/Electrolyte-Free Fuel Cell (EFFC) based on above nanocomposite materials (ion and semi-conductive composite) research activities. This is also the key innovation point of this thesis. Compared with classic three-layer fuel cells, EFFC with an electrolyte layer shows a much simpler but more efficient way for energy conversion. The physical-electrical properties of composite, the effects of cell configuration and parameters on cell performance, materials composition and cell fabrication process optimization, micro electrochemical reaction process and possible working principle were systematically investigated and discussed. Besides, the EFFC, joining solar cell and fuel cell working principle, is suggested to provide a research platform for integrating multi-energy-related device and technology application, such as fuel cell, electrolysis, solar cell and micro-reactor etc.This thesis provides a new methodology for materials and system innovation for the fuel cell community, which is expected to accelerate the wide implementation of this high efficient and green fuel cell technology and open new horizons for other related research fields.
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| 14. |
- Fridh, Jens
(författare)
-
Experimental Investigation of Performance, Flow Interactions and Rotor Forcing in Axial Partial Admission Turbines
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis comprises a collection of four papers with preceding summary and supplementary appendices. The core investigation solely is of experimental nature although reference and comparisons with numerical models will be addressed. The first admission stage in an industrial steam turbine is referred to as the control stage if partial admission is applied. In order to achieve high part load efficiency and a high control stage output it is routinely applied in industrial steam turbines used in combined heat and power plants which frequently operate at part load. The inlet flow is individually throttled into separate annular arcs leading to the first stator row. Furthermore, partial admission is sometimes used in small-scale turbine stages to avoid short vanes/blades in order to reduce the impact from the tip leakage and endwall losses. There are three main aspects regarding partial admission turbines that need to be addressed. Firstly, there are specific aerodynamic losses: pumping-, emptying- and filling losses attributed to the partial admission stage. Secondly, if it is a multistage turbine, the downstream stages experience non-periodic flow around the periphery and circumferential pressure gradients and flow angle variations that produce additional mixing losses. Thirdly, the aeromechanical condition is different compared to full admission turbines and the forcing on downstream components is also circumferentially non-periodic with transient load changes. Although general explanations for partial admission losses exist in open literature, details and loss mechanisms have not been addressed in the same extent as for other sources of losses in full admission turbines. Generally applicable loss correlations are still lacking. High cycle fatigue due to unforeseen excitation frequencies or due to under estimated force magnitudes, or a combination of both causes control stage breakdowns. The main objectives of this thesis are to experimentally explore and determine performance and losses for a wide range of partial admission configurations. And, to perform a forced response analysis from experimental data for the axial test turbine presented herein in order to establish the forced response environment and identify particularities important for the design of control stages. Performance measurements concerning the efficiency trends and principal circumferential and axial pressure distortions demonstrate the applicability of the partial admission setup employed in the test turbine. Findings reveal that the reaction degree around the circumference varies considerably and large flow angle deviations downstream of the first rotor are present, not only in conjunction to the sector ends but stretching far into the admission sector. Furthermore, it is found that the flow capacity coefficient increases with reduced admission degree and the filling process locally generates large rotor incidence variation associated with high loss. Moreover, the off design conditions and efficiency deficit of downstream stages are evaluated and shown to be important when considering the overall turbine efficiency. By going from one to two arcs at 52.4% admission nearly a 10% reduction in the second stage partial admission loss, at design operating point was deduced from measurements. Ensemble averaged results from rotating unsteady pressure measurements indicate roughly a doubling of the normalized relative dynamic pressure at rotor emptying compared to an undisturbed part of the admission jet for 76.2% admission. Forced response analysis reveals that a large number of low engine order force impulses are added or highly amplified due to partial admission because of the blockage, pumping, loading and unloading processes. For the test turbine investigated herein it is entirely a combination of number of rotor blades and low engine order excitations that cause forced response vibrations. One possible design approach in order to change the force spectrum is to alter the relationship between admitted and non-admitted arc lengths.
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| 15. |
- Fruth, Florian, 1981-
(författare)
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Reduction of Aerodynamic Forcing inTransonic Turbomachinery : Numerical Studies on Forcing Reduction Techniques
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to more and more aggressive designs in turbomachinery, assuring the structural integrity of its components has become challenging. Also influenced by this trend is blade design, where lighter and slimmer blades, in combination with higher loading, lead to an increased risk of failure, e.g. in the form of blade vibration. Methods have been proposed to reduce vibration amplitudes for subsonic engines, but cannot directly be applied to transonic regimes due to the additional physical phenomena involved. Therefore the present work investigates numerically the influence of two methods for reducing blade vibration amplitudes in transonic turbomachines, namely varying the blade count ratio and clocking. As it is known that clocking affects the efficiency, the concurrent effects on vibration amplitudes and efficiency are analyzed and discussed in detail.For the computational investigations, the proprietary Fortran-based non-linear, viscous 3D-CFD solver VolSol is applied on two transonic compressor cases and one transonic turbine case. In order to reduce calculation time and to generate the different blade count ratios a scaling technique is applied.The first and main part of this work focuses on the influence of the reduction techniques on aerodynamic forcing. Both the change in blade count ratio and clocking position are found to have significant potential for reducing aerodynamic force amplitudes. Manipulation of the phasing of excitation sources is found herein to be a major contributor to the amplitude variation. The lowest stimulus results are achieved for de-phased excitation sources and results in multiple blade force peaks per blade passing. In the case of blade count ratio variation it was found that blockage for high blade count ratios and the change in potential field size have significant impacts on the blade forcing. For the clocking investigation, three additional operating points and blade count ratios are analyzed and prove to have an impact on the force reduction achievable by clocking.The second part of the work evaluates the influence of clocking on the efficiency of a transonic compressor. It is found that the efficiency can be increased, but the magnitude of the change and the optimal wake impingement location depend on the operating point. Moreover it is shown that optimal efficiency and aerodynamic forcing settings are not directly related. In order to approximate the range of changes of both parameters, an ellipse approximation is suggested.
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| 16. |
- Jayasuriya, Jeevan, 1967-
(författare)
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Experimental Investigations of High Pressure Catalytic Combustion for Gas Turbine Applications
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work is devoted to generate knowledge and high quality experimental data of catalytic combustion at operational gas turbine conditions.The initial task of the thesis work was to design and construct a high pressure combustion test facility, where the catalytic combustion experiments can be performed at real gas turbine conditions. With this in mind, a highly advanced combustion test facility has been designed, constructed and tested. This test facility is capable of simulating combustion conditions relevant to a wide range of operating gas turbine conditions and different kinds of fuel gases. The shape of the combustor (test section) is similar to a “can” type gas turbine combustor, but with significant differences in its type of operation. The test combustor is expected to operate at near adiabatic combustion conditions and there will be no additions of cooling, dilution or secondary supply of air into the combustion process. The geometry of the combustor consists of three main zones such as air/fuel mixing zone, catalytic reaction zone and downstream gas phase reaction zone with no difference of the mass flow at inlet and exit. The maximum capacity of the test facility is 100 kW (fuel power) and the maximum air flow rate is 100g/s.The significant features of the test facility are counted as its operational pressure range (1 – 35 atm), air inlet temperatures (100 – 650 °C), fuel flexibility (LHV 4 - 40 MJ/m3) and air humidity (0 – 30% kg/kg of air). Given these features, combustion could be performed at any desired pressure up to 35 bars while controlling other parameters independently. Fuel flexibility of the applications was also taken into consideration in the design phase and proper measures have been taken in order to utilize two types of targeted fuels, methane and gasified biomass.Experimental results presented in this thesis are the operational performances of highly active precious metal catalysts (also called as ignition catalysts) and combinations of precious metal, perovskites and hexaaluminate catalysts (also called as fully catalytic configuration). Experiments were performed on different catalytic combustor configurations of various types of catalysts with methane and simulated gasified biomass over the full range of pressure. The types of catalysts considered on the combustor configurations are palladium on alumina (Pd/AL2O3), palladium lanthanum hexaaluminate (PdLaAl11O19), platinum on alumina (Pt/AL2O3),and palladium:platinum bi-metal on alumina (Pd:Pt/AL2O3). The influence of pressure, inlet temperature, flow velocity and air fuel ratio on the ignition, combustion stability and emission generation on the catalytic system were investigated and presented.Combustion catalysts were developed and provided mainly by the project partner, the Division of Chemical Technology, KTH. Division of Chemical Reaction Technology, KTH and Istituto di Ricerche sulla Combustione (CNR) Italy were also collaborated with some of the experimental investigations by providing specific types of catalysts developed by them for the specific conditions of gas turbine requirements.
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| 17. |
- Manrique Carrera, Arturo, 1974-
(författare)
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Catalytic Combustion in Gas Turbines : Experimental Study on Gasified Biomass Utilization
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Environmental and geopolitical concerns encourage societies towards the utilization of renewable energy sources (RES). Photovoltaic and wind power can produce electricity directly, although their intermittent characteristic negatively affects the security and safety of the energy supply chain; moreover, in order to be viable it is necessary to establish energy storage systems and to find mechanisms to adapt the power distribution grid to larger production variability. In contrast, biomass (a carbon neutral fuel if adequately managed) can be stored, is relatively widely available, and after simple treatments can be gasified and ready to be used for power production. Correspondingly, gas turbines are a well-established technology that first became relevant in industrial applications and power production since 1940’s. The use of biomass in gas turbines is an important step forward towards more sustainable power production; however, this combination presents some technical challenges that have yet to be overcome.Gasified biomass is generally a gas with low or medium heating value that is usually composed of a mixture of gases such as CO, H2, CH4, CO2, and N2 as well as other c60*6nents in small fractions. Its firing in standard gas turbine combustors might be unstable at certain load conditions. Moreover, gasified biomass contains undesirable compounds; in particular the nitrogen-containing compounds that may produce elevated NOx emissions once the biomass is burned.Catalytic combustion is an alternative for using gasified biomass in a gas turbine, and it is investigated in this study. Using catalytic combustion is possible to burn such a mixture of gases under very lean conditions, extending the normal flammability limits, reducing the maximum temperature of the reaction zone, and thus reducing the thermal NOx formation. It also reduces the vibration levels, and it is possible to avoid fuel-NOx formation using alternative catalytic techniques, such as Selective Catalytic Oxidation (SCO).In the present study the feasibility of using catalytic combustion in a gas turbine combustor is evaluated. The tests performed indicate the necessity of using hybrid combustion chamber concepts to achieve turbine inlet temperatures levels of modern gas turbines. The different catalytic burning characteristic of H2, CO and CH4 was evaluated and different techniques were applied to equalize their burning behaviour such as the diffusion barrier, and partially coated catalyst. Fuel-NOx is another subject treated in this work, where a Selective Catalytic Oxidation (SCO) technique is applied reaching up to 42% of fuel NOx reduction. Finally, the use of Catalytic Partial Oxidation (CPO) of methane was experimentally investigated.In this study, two one-of-a-kind test facilities were used directly, namely the high-pressure test facility and the pilot scale test facility. This gives a unique characteristic to the study performed. Finally, the catalytic combustion approach allows the utilization of gasified biomass with some restrictions depending on whether it is a Catalytic Lean, Catalytic Rich or Catalytic Partial Oxidation (CPO) approach.
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| 18. |
- Saha, Ranjan, 1984-
(författare)
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Aerodynamic Investigation of Leading Edge Contouring and External Cooling on a Transonic Turbine Vane
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficiency improvement in turbomachines is an important aspect in reducing the use of fossil-based fuel and thereby reducing carbon dioxide emissions in order to achieve a sustainable future. Gas turbines are mainly fossil-based turbomachines powering aviation and land-based power plants. In line with the present situation and the vision for the future, gas turbine engines will retain their central importance in coming decades. Though the world has made significant advancements in gas turbine technology development over past few decades, there are yet many design features remaining unexplored or worth further improvement. These features might have a great potential to increase efficiency. The high pressure turbine (HPT) stage is one of the most important elements of the engine where the increased efficiency has a significant influence on the overall efficiency as downstream losses are substantially affected by the prehistory. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Hence, this study has been incorporated into a research project that investigates leading edge contouring near endwall by fillet and external cooling on a nozzle guide vane with a common goal to contribute to the development of the HPT stage. In the search for HPT stage efficiency gains, leading edge contouring near the endwall is one of the methods found in the published literature that showed a potential to increase the efficiency by decreasing the amount of secondary losses. However, more attention is necessary regarding the realistic use of the leading edge fillet. On the other hand, external cooling has a significant influence on the HPT stage efficiency and more attention is needed regarding the aerodynamic implication of the external cooling. Therefore, the aerodynamic influence of a leading edge fillet and external cooling, here film cooling at profile and endwall as well as TE cooling, on losses and flow field have been investigated in the present work. The keystone of this research project has been an experimental investigation of a modern nozzle guide vane using a transonic annular sector cascade. Detailed investigations of the annular sector cascade have been presented using a geometric replica of a three dimensional gas turbine nozzle guide vane. Results from this investigation have led to a number of new important findings and also confirmed some conclusions established in previous investigations to enhance the understanding of complex turbine flows and associated losses. The experimental investigations of the leading edge contouring by fillet indicate a unique outcome which is that the leading edge fillet has no significant effect on the flow and secondary losses of the investigated nozzle guide vane. The reason why the leading edge fillet does not affect the losses is due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. The investigation of the external cooling indicates that a coolant discharge leads to an increase of profile losses compared to the uncooled case. Discharges on the profile suction side and through the trailing edge slot are most prone to the increase in profile losses. Results also reveal that individual film cooling rows have a weak mutual effect. A superposition principle of these influences is followed in the midspan region. An important finding is that the discharge through the trailing edge leads to an increase in the exit flow angle in line with an increase of losses and a mixture mass flow. Results also indicate that secondary losses can be reduced by the influence of the coolant discharge. In general, the exit flow angle increases considerably in the secondary flow zone compared to the midspan zone in all cases. Regarding the cooling influence, the distinct change in exit flow angle in the area of secondary flows is not noticeable at any cooling configuration compared to the uncooled case. This interesting zone requires an additional, accurate study. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the suction surfaces and does not reach the pressure side of the hub surface, leaving it less protected from the hot gas. This indicates a strong interaction of the secondary flow and cooling showing that the influence of the secondary flow cannot be easily influenced. The overall outcome enhances the understanding of complex turbine flows, loss behaviour of cooled blade, secondary flow and interaction of cooling and secondary flow and provides recommendations to the turbine designers regarding the leading edge contouring and external cooling. Additionally, this study has provided to a number of new significant results and a vast amount of data, especially on profile and secondary losses and exit flow angles, which are believed to be helpful for the gas turbine community and for the validation of analytical and numerical calculations.
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| 19. |
- Salomón Popa, Marianne, 1976-
(författare)
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On the optimal use of industrial-generated biomass residues for polygeneration
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing energy demand as well as climate change concerns call for an analysis and optimization of energy services. Efficient use of energy resources, mitigation of environmental effects and supply an increasing demand are just some of the issues that are relevant nowadays in the energy system. In this regard, worldwide efforts are being made to increase the use of renewable energy and to promote energy efficiency measures in order to reduce the emission of greenhouse gases.Thus, sustainable solutions that take a holistic approach on covering the demands of the society are needed. The work presented herein addresses the use of industrial derived biomass residues for energy purposes in different contexts. The analysis was focused on: a) different alternatives to use solid palm oil residues in the Colombian mills for energy purposes including services b) the possibilities of implementing biomass-based heat and power plants in the Swedish energy system and their integration with already established biomass processing industries for polygeneration purposes.The assessment of the palm oil residues consisted on a technical analysis of the possible alternatives for electricity, heat, and biofuels production. For that, a thermodynamic approach was used to evaluate different alternatives. The assessment of biomass power plant integrated with the Swedish industry considered the thermodynamic, economic and environmental factors associated with certain energy conversion technologies. In this case a multiobjective optimization methodology was used to perform the thermoeconomic analysis. This allowed the evaluation of two contrasting scenarios were polygeneration at industrial level could be suggested: a less economically developed country where environmental policies are limited and industrial energy efficiency has not been implemented and a high income country with energy and environmental policies well established and energy efficiency measures being encouraged.Results show that the palm oil industry in Colombia has the capacity of being self-sufficient to cover of all their energy needs using the solid residues available. In the case of the thermoeconomic assessment of biomass-based integrated polygeneration plants in Sweden the results indicate that it is feasible to produce power while supplying the process steam required by nearby industries and district heating.
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| 20. |
- Wei, Bo, 1986-
(författare)
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A novel solar-driven system for two-step conversion of CO2 with ceria-based catalysts
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global warming is an unequivocal fact proved by the persistent rise of the average temperature of the earth. IPCC reported that scientists were more than 90 % certain that most of the global warming was caused by increasing concentrations of greenhouse gases (GHG) produced by human activities. One alternative to combat the GHG is to explore technologies for utilizing CO2 already generated by current energy systems and develop methods to convert CO2 into useful combustible gases.Two-step conversion of CO2 with catalysts is one of the most promising methods. Ceria (CeO2) is chosen as the main catalyst for this conversion in the thesis. It releases O2 when it is reduced in a heating process, and then absorbs O2 from CO2 to produce CO when it is re-oxidized in a cooling process.To make the conversion economic, solar power is employed to drive the conversion system. In this thesis, a flexible system with fluidized bed reactors (FBRs) is introduced.The thermogravimetric analysis (TGA) was carried out to examine the performance of ceria during its reduction and oxidation. Subsequently, the exergy analysis was used to evaluate the system’s capability on exporting work. The theoretical fuel to chemical efficiency varied from 4.85 % to 43.2 % for CO2 conversions.To investigate the operation mechanism of the system, a mathematical model was built up for the dynamic simulation of the system. Variables such as temperatures and efficiencies were calculated and recorded for different cases. The optimum working condition was found out to be at 1300 ⁰C for the commercial type of ceria.Finally, an experimental system was set up. The hydrodynamics and heat transfer in the fluidized bed reactor were studied. A CFD model was built up and validated with the experimental trials around 120 ⁰C. The model was then used as a reliable tool for the optimization of the reactor.The entire work in the thesis follows the procedure of developing an engineering system. It forms a solid basis for further improvements of the system to recycle CO2.
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| 21. |
- Ferria, Hakim
(författare)
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Contribution to Numerical and Experimental Studies of Flutter in Space Turbines. Aerodynamic Analysis of Subsonic or Supersonic Flows in Response to a Prescribed Vibratory Mode of the Structure.
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern turbomachines are designed towards thinner, lighter and highly loaded blades. This gives rise to increased sensitivity to flow induced vibrations such as flutter, which leads to structure failure in a short period of time if not sufficiently damped. Although numerical tools are more and more reliable, flutter prediction still depends on a large degree on simplified models. In addition, the critical nature of flutter, resulting in poor well-documented real cases in the open literature, and the lack of experimental database typical of engine flows make its apprehension even more challenging. In that context, the present thesis is dedicated to study flutter in recent turbines through aerodynamic analysis of subsonic or supersonic flows in response to a prescribed vibratory mode of the structure. The objective is to highlight some mechanisms potentially responsible for flutter in order to be in better position when designing blades. The strategy consists in leading both experimental and numerical investigations. The experimental part is based on a worldwide unique annular turbine sector cascade employed for measuring the aeroelastic response by means of the aerodynamic influence coefficient technique. The cascade comprises seven low pressure gas turbine blades one of which can oscillate in a controlled way as a rigid body. Aeroelastic responses are measured at various mechanical and aerodynamic parameters: pure and combined modeshapes, reduced frequency, Mach number, incidence angle. In addition to turbulence level measurements, the database aims at assessing the influence of these parameters on the aerodynamic damping, at validating the linear combination principle and at providing input for numerical tools.The numerical part is based on unsteady computations linearized in the frequency domain and performed in the traveling wave mode. The focus is put on two industrial space turbines:2D computations are performed on an integrally bladed disk, also called blisk; its very low viscous material damping results in complex motions with combined modes and extremely high reduced frequency. The blisk operates at low subsonic conditions without strong non-linearities. Although the blades have been predicted aeroelastically stable, an original methodology based on elementary decompositions of the blade motion is presented to identify the destabilizing movements. The results suggest that the so-called classical flutter is surprisingly prone to occur. Moreover, the aerodynamic damping has been found extremely sensitive to the interblade phase angle and cut-on/cut-off conditions.3D computations are then performed on a supersonic turbine, which features shock waves and boundary layer separation. In contrast, the blade motion is of elementary nature, i.e. purely axial. The blades have been predicted aeroelastically unstable for backward traveling waves and stable for forward traveling waves. The low reduced frequencies allow quasi-steady analysis, which still account for flutter mechanisms: the shock wave motion establishes the boundary between stable and unstable configurations.
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| 22. |
- Mayorca, María Angélica, 1983-
(författare)
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Development and Validation of a Numerical Tool for the Aeromechanical Design of Turbomachinery
- 2010
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In aeromechanical design one of the major rules is to operate under High Cyclic Fatigue (HCF) margins and away from flutter. The level of dynamic excitations and risk of HCF can be estimated by performing forced response analyses from blade row interaction forces or Low Engine Order (LEO) excitation mechanisms. On the other hand, flutter stability prediction can be assessed by calculation of aerodynamic damping forces due to blade motion. In order to include these analyses as regular practices in an industrial aeromechanical design process, interaction between the fields of fluid and structural dynamics must be established in a rather simple yet accurate manner. Effects such as aerodynamic and structural mistuning should also be taken into account where parametric and probabilistic studies take an important role. The present work presents the development and validation of a numerical tool for aeromechanical design. The tool aims to integrate in a standard and simple manner regular aeromechanical analysis such as forced response analysis and aerodynamic damping analysis of bladed disks. Mistuning influence on forced response and aerodynamic damping is assessed by implementing existing model order reduction techniques in order to decrease the computational effort and assess results in an industrially applicable time frame. The synthesis program solves the interaction of structure and fluid from existing Finite Element Modeling (FEM) and Computational Fluid Dynamics (CFD) solvers inputs by including a mapping program which establishes the fluid and structure mesh compatibility. Blade row interaction harmonic forces and/or blade motion aerodynamic damping forces are inputs from unsteady fluid dynamic solvers whereas the geometry, mass and stiffness matrices of a blade alone or bladed disk sector are inputs from finite element solvers. Structural and aerodynamic damping is also considered. Structural mistuning is assessed by importing different sectors and any combinations of the full disk model can be achieved by using Reduced Order Model (ROM) techniques. Aerodynamic mistuning data can also be imported and its effects on the forced response and stability assessed. The tool is developed in such a way to allow iterative analysis in a simple manner, being possible to realize aerodynamically and structurally coupled analyses of industrial bladed disks. A new method for performing aerodynamic coupled forced response and stability analyses considering the interaction of different mode families has also been implemented. The method is based on the determination of the aerodynamic matrices by means of least square approximations and is here referred as the Multimode Least Square (MLS) method. The present work includes the program description and its applicability is assessed on a high pressure ratio transonic compressor blade and on a simple blisk.
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| 23. |
- Mölleryd, Bengt A, 1947-
(författare)
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An anatomy of technological innovation in infrastructure and defence systems in Sweden after the Cold War
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dual interaction of science and technology with defence, security and infrastructures for service provision as energy is a major theme in modern times. The era after the Second World War and in the course of the Cold War was accompanied and spurred by an amazing number of great technological advances and changes. The study investigates and discusses dimensions of the interaction between technology changes and innovation and defence, security and infrastructure systems in a small country as Sweden after the Cold War. The main result of the study is a proposal for an anatomy of technology innovation which can be seen as a predecessor to a system (or enterprise) architecture for technology innovation in defence, security and infrastructure systems. The approach is developed from previous international research and theories of innovation systems. Infrastructure and defence systems are investigated on three levels, technologies, system integration and services provided. Establishing an anatomy is supported by case studies which apply a stake holder perspective on development and innovation in systems. Prominent elements of the proposed anatomy for technology innovation are framework conditions or context, economic organizational factors such as people, knowledge, business models and finance, and last but not least culture for development and innovation, and the customer and user in the processes. Contexts and environmental conditions in recent times are characterised by more complicated threats and disturbances which potentially imply larger disruptions. The study explores how contexts and emerging conditions translate into plausible scenarios and their effect on the anatomy and the various stages of the innovation processes. The vital role in the anatomical framework played by culture for innovation is illuminated in the case studies. Other basic elements of the anatomy are the people, inventors and developers as the knowledge underpinning. Risk taking and sharing and the rights and responsibilities of the stake holders play substantial roles in the anatomy as some main economic organizational factors and elements of innovation.
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| 24. |
- Noor, Hina
(författare)
-
Preliminary Design Investigations for the Selection of Optimum Reaction Degree for 1st Stage of a High Pressure Gas Turbine
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One-dimensional (1D) turbine design calculation phase requires a handful of input data and choice of design parameters to provide the blade flow path geometry along with the flow kinematics and thermodynamics properties at the blade mid-span. The choice of important aerodynamics design parameters namely reaction degree, nozzle guide vane NGV exit flow angle or flow coefficient and stage loading defines the mid-span flow velocity triangles. Despite being a very initial turbine design phase the implication of 1D calculation are such that the design choices made based on the design parameters at this design phase cannot be altered as the design proceeds towards detailed three-dimensional (3D) flow field analysis. Thus an optimum choice of the design parameters is essential for maximum turbine performance. There exist certain design recommendations for the selection of reaction degree, stage loading and flow coefficient for uncooled turbines. The rationale and underlying flow physics is straight forward for an uncooled case but a highly cooled case can benefit from a lower relative flow velocity. The aerodynamic design parameters have their own implications on the design of a cooled turbine, where the choice of reaction degree and flow coefficient has a strong impact on the stage design for a given stage loading. For a design of a cooled turbine, selection of a lower flow coefficient and lower reaction degree seems opportune from the heat transfer and the performance point of view. The flow coefficient has traditionally, in some cases, been set to a higher value on basis of the Smith charts which were originally devised for uncooled turbines. The reaction degree sets the relative rotor inlet temperature (hence cooling requirements) and should be carefully chosen for a high performance. However, presently there do not exist recommendations for the selection of optimum reaction degree for cooled turbine for given stage loading and NGV exit flow angle.This thesis work aims to contribute in developing the recommendations for the choice of optimum reaction degree for a cooled turbine. The goal is to determine the range of optimum values for reaction degree for given stage loading and NGV exit flow angles. A parametric study has been formulated to perform this goal. 1D meanline design tool (LUAXT) is used to implement different loss models. These models are validated using experimental results. The validation showed that Craig & Cox is the most accurate when tested against the test data obtained from two different stage geometries. A discussion on flow physics as represented in different loss models is presented to develop further understanding of loss physics. Craig & Cox loss model is further considered for the parametric design investigations using LUAXT 1D design tool to develop design recommendations for optimum reaction degree values.The performed design investigations indicated that a choice of low reaction value along with a low stage loading and a low flow coefficient reduces the overall stage coolant consumption and results in overall increased stage performance. Since for a HPT 1st stage, the interest lies in a high stage loading, a range of reaction degree has been recommended to be between 0.20 to 0.37 to provide the optimum stage design when chosen for stage loading in between 1.40 to 1.80 and the stator exit flow angle in range of 74o to 78o. A two-dimensional (2D) blade profiling and blade to blade flow field analysis is carried out for one of the recommended cases to verify the velocity triangles as obtained from meanline design. Small differences in the flow velocities were found mainly due to the difference in fluid properties and differences in throat calculations which can be resolved with 1D-2D design iterations. The profiling and the blade to blade flow field analysis for one of the recommended design justified it to have a reasonable cascade. The recommendations on optimum reaction degree for cooled turbine as obtained from the performed calculations can be used for future 1D design investigations of a high pressure cooled turbines.Keywords: 1D design, aerodynamic design parameters, flow kinematic, thermodynamics, rotor inlet temperature, cooled turbine, reaction degree, flow coefficient, stage loading
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| 25. |
- Olwa, Joseph
(författare)
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Investigation of thermal biomass gasification for sustainable small scale rural electricity generation in Uganda
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the increasing need for renewable energy technologies in the world, biomass fuel transformation technology is growing towards meeting that need, among others. Challenges remain certain and new innovations are being tested in bid to overcome them with the application of biomass as energy source. This report presents some studies carried out into understanding the potential and challenges associated with utilization of biomass fuel, especially for technologies that are appropriate for rural applications. Utilization of biomass gasification technologies is in the focus of this study. The great potential biomass fuel provide to Uganda for possible energy production in small scale application is presented. This study was carried out to understand the possibility of using biomass as fuel in electricity power generation in Uganda. It takes into consideration the use of biomass gasification technology in energy production. Challenges related to the application of biomass fuels are discussed, mostly with tar and alkali metal compounds in the gas stream. Suggested methods to combat some of the challenges with biomass fuels are pointed out in this study. Application of externally fired gas turbine (EFGT) system is a particular approach discussed and its technical performance analyzed. The analysis revealed that efficiency of the EFGT system is greatly dependent on the heat exchanger effectiveness and on turbine inlet temperature. Optimum performance can be realized with air compression ratio of 3.4. It is also noted that fouling and deposition in the heat exchanger can affect its performance. A related study carried out was on the retention of alkali metals in an updraft gasifier. The gasifier was chosen for possible integration with the EFGT system. Finding was that about 99% of the alkali metals are retained in the gasifier. It is anticipated that this would reduce on the deposition in the heat exchanger, reducing on maintenance time. A need is identified to determine the level of deposition mentioned. A simple thermodynamic modeling of the alkali metals condensation reaction on a high temperature heat exchanger surface was conducted. The results showed that with appropriate quantity of S in the raw fuel, alkali metals bounding with Cl are greatly reduced. Cl is passed out as gaseous HCl, leaving deposition of none corrosive sulphates. Recommendation is made to study this phenomenon in an experimental setting. Biomass gasification technology integration with an internal combustion (IC) engine is also studied. Here requirements for the producer gas quality have been discussed. Some tests carried out with wood pellets and wood cylinders compared the yield of tar from the two physically different fuels. Wood pellets were found to yield more tar than wood cylinders. Economic analysis of biomass gasifier integrated with an IC engine running a generator of 100 kWe was carried out. Comparison with a diesel electricity generator of similar capacity was made for a scenario in Uganda over a project life of 20 years. Different Plant Capacity Factors (PCF) and fuel costs including subsidies were considered. The analysis showed that over long period of time biomass power plant was more beneficial than the diesel power plant at PCF over 40%. This is more pronounced with unsubsidized diesel fuel.
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| 26. |
- Saha, Ranjan, 1984-
(författare)
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Aerodynamic Investigations of a High Pressure Turbine Vane with Leading Edge Contouring at Endwall in a Transonic Annular Sector Cascade
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficiency improvement is an important aspect to reduce the use of fossil-based fuel in order to achieve a sustainable future. Gas turbines are mainly fossil-fuel based turbomachines, and, therefore, efficiency improvement is still the subject of many on-going research activities in the gas turbine community. This study is incorporated into a research project that investigates design possibilities of efficiency improvement at the high pressure turbine (HPT) stage. In the search for HPT-stage efficiency gains, leading edge (LE) contouring near the endwall is one of the methods found in the published literature that has shown a potential to increase the efficiency by decreasing the amount of secondary losses. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Particularly, the influence of the LE fillet on losses and flow structure is investigated concentrating on the secondary flow. The core investigation is of an experimental nature. Detailed investigations of the flow field in an annular sector cascade (ASC) are presented with and without the LE fillet, using a geometric replica of a modern gas turbine nozzle guide vane (NGV) with a contoured tip endwall. Furthermore, a separate investigation is performed on a hub-cooled NGV, which focuses on endwalls, specifically the interaction between the hub film cooling and the mainstream (MS). The experimental investigations indicate that the LE fillet has no significant effect on the flow and energy losses of the investigated NGV. The reason why the LE fillet does not affect the losses might be due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. Oil flow visualisation for the baseline case displays a clear saddle point, with a separation line where the horseshoe (HS) vortex separates into the suction side (SS) and the pressure side (PS), whereas for the filleted case, the saddle point is not noticeable. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the SS surfaces and does not reach the PS of the hub surface, leaving it less protected from the hot gas.
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| 27. |
- Siddique, Waseem
(författare)
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Design of Internal Cooling Passages: Investigation of Thermal Performance of Serpentine Passages
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas turbines are used to convert thermal energy into mechanical energy. The thermal efficiency of the gas turbine is directly related to the turbine inlet temperature. The combustion and turbine technology has improved to such an extent that the operating temperature in the turbine inlet is higher than the melting temperature of the turbine material. Different techniques are used to cope with this problem. One of the most commonly used methods is internal cooling of the turbine blades. Conventionally air from the compressor is used for this purpose but due to higher heat capacity, steam can be used as coolant. This opens up the possibility to increase the gas temperature. In the case of a combined cycle power plant, its availability provides a good opportunity to be used as a coolant. The trailing edge of the gas turbine blades is an important region as it affects the aerodynamics of the flow. The aerodynamics demands a sharp and thin trailing edge to reduce profile losses. The conventional method is the release of a lot of cooling air though a slot along the airfoil trailing edge. However in the case of internal only cooling designs, the coolant is not allowed to leave the channel except from the root section to avoid mixing of the gas in the main flow path with the coolant and loss of cooling medium. The challenge is to design an inner cooling channel, with the cooling medium entering and leaving the blade at the root section, which reduces the metal temperatures to the required values without an increase of the profile losses and at acceptable cooling flow rate and pressure drop. This thesis presents Computational Fluid Dynamic (CFD) based numerical work concentrated firstly on the flow and heat transfer in two-pass rectangular channels with and without turbulator ribs. The aspect ratio of the inlet pass was reduced to accommodate more channels in the blade profile in chord-wise direction. Additionally, the divider-to-tip wall distance was varied for these channels. Their effect on heat transfer and pressure drop was studied for smooth as well as ribbed channels. It was followed by a numerical heat transfer study in the trapezoidal channel. Different RANS based turbulence models were used to compare the numerical results with the experimental results. Further, new designs to enhance heat transfer in the channel’s side walls (named as trailing edge wall) were studied. These include the provision of ribs at the trailing edge wall only, inline arrangement of ribs at the bottom as well as at the trailing edge wall and a staggered arrangement of these ribs. The final study was a conjugate heat transfer problem with an aim to propose the best internal cooling channel design to reduce the metal temperature of the trailing edge surface for the given thermal and flow conditions. A number of different options were studied and changes were made to get the best possible channel design. The results show that for a two-pass rectangular channel (both smooth and ribbed), the reduction in inlet channel aspect ratio reduces the pressure drop. For a smooth channel the reduction in the width of the inlet pass does not affect the heat transfer enhancement at the inlet pass and outlet pass regions. In case of ribbed channels, heat transfer decreases at the tip and bend bottom with decrease in the width of the inlet pass. Among different turbulence models used to validate numerical results against experimental results for case of trapezoidal channel, the low-Re k-epsilon model is found to be the most appropriate. Using the turbulence model that yields results that are closest to the experimental data, the staggered arrangement of ribs at the trailing edge wall is found to have maximum thermal performance. The results from the conjugate heat transfer problem suggest using steam as coolant if it is available as it requires less mass flow rate to get similar wall temperature values as compared to air at similar thermal and flow conditions. It is also found that staggered arrangement of ribs is the best option compared to others to enhance heat transfer in trailing edge of the gas turbine blade with the pressure drop in the cooling duct in the acceptable range.
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