| 1. |
- Al-Gburi, Majid
(författare)
-
Restraint Effects in Early Age Concrete Structures
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the widespread issues in concrete structures is cracks occurring at early age. Cracks that appear in the young concrete may cause early start of corrosion of rebars or early penetration of harmful liquids or gases into the concrete body. These situations could result in reduced service life and in significantly increased maintenance cost of structures. Therefore it is important for construction companies to avoid these cracks.Volumetric deformations in early age concrete are caused by changes in temperature and/or the moisture state. If such movements are restrained, stresses will occur. If the tensile stresses are high enough, there will be a damage failure in tension and visible cracks arise. These stresses are always resulting from a self-balancing of forces, either within the young concrete bodyalone, i.e. without structural joints to other structures, or from the young concrete in combination with adjacent structures through structural joints.The decisive situation within a young concrete body alone is typically high stresses at the surface when the temperature is near the peak temperature within the body. This situation occur rather early for ordinary structures, say within a few days after casting for structures up to about some meters thickness, but for very massive structures like large concrete dams, it might take months and even years to reach the maximum tensile stresses at the surface. Usually this type of cracks is denoted "surface cracks", and in some cases only a temperature calculation may give a good perception to make decisions of the risk of surface cracking.On the other hand, the decisive situation within a young concrete body connected to adjacent structures, might include both risk of surface cracking at some distance away from the structural joint and risk of through cracking starting in the neighborhood of the structural joint. If the young concrete body is small in accordance to the adjacent structure, or, in other words, if thereis an overall high restraint situation in the young concrete, the risk of early surface cracking might be out of question. So, restraint from adjacent structures represents one of the main sources of thermal and shrinkage stresses in a young concrete body.This study is mainly concentrated on establishing the restraint inside the young concrete body counteracted by adjacent structures, and how to estimate the risk of through cracking based on such restraint distributions. The restraint values in the young concrete are calculated with use of the finite element method, FEM. Any spatial structure may be analyzed with respect to the level of restraint. Calculations of risk of cracking are demonstrated with use of existing compensation plane methods, and a novel method denoted equivalent restraint method, ERM, is developed for the use of restraint curves. ERM enables the use of both heating ofthe adjacent structure and/or cooling of the young concrete, which are the most common measures used on site to reduce the risk of early cracking.In a design situation many parameters are to be considered, like type of cement, different concrete mixes, temperature in the fresh concrete, surrounding temperatures, temperature in the adjacent structure, measures on site (heating/cooling/insulation), sequence order of casting.Therefore, in general a lot of estimations concerning risks of cracking are to be performed. The main objective with the present study is to develop methods speeding up and shorten the design process.Furthermore, established restraint curves have been applied to the method of artificial neural networks (ANN) to model restraint in the slab, wall, and roof for the typical structure Tunnel. It has been shown that ANN is capable of modeling the restraint with good accuracy. The usage of the neural network has been demonstrated to give a clear picture of the relative importance of the input parameters. Further, results from the neural network can be represented by a series of basic weight and response functions, which enables that the restraint curves easily can be made available to any engineer without use of complicated software.A new casting technique is proposed to reduce restraint in the newly cast concrete with a new arrangement of the structural joint to the existing old concrete. The proposed technique is valid for the typical structure wall-on-slab using one structural joint. This casting method means that the lower part of the wall is cast together with the slab, and that part is called a kicker. It hasbeen proven by the beam theory and demonstrated by numerical calculations that there is a clear reduction in the restraint from the slab to the wall using kickers.Restraint is affected by casting sequence as well as boundary conditions and joint position between old and new concrete elements. This study discusses the influence of different possible casting sequences for the typical structure wall-on-slab and slab-on-ground. The aim is to identify the sequence with the lowest restraint to reduce the risk of cracking.
|
|
| 2. |
- Atta, Khalid
(författare)
-
Extremum Seeking Control : Stability, Accuracy, and Applications
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In many applications, there is a variable that indicates the overall performance and that must be maximized, such as the output of a hydro power turbine or a mineral processing plant, or that must be minimized, such as CO2 emissions or the consumption of resources. Extremization of this variable (maximization or minimization) through adjusting the influencing manipulated variables is occasionally required without prior knowledge of the optimal values of the manipulated variables or of the optimized variable. Extremum seeking control (ESC), which is an on-line concept for the optimization of dynamic systems, can achieve this task.Many types of ESC have been proposed in the literature, and the majority of these approaches are based on the gradient descent optimization method. The most common type of ESC is the classic ESC, which is based on adding a sinusoidal perturbation to the manipulated variables followed by the use of a band pass filter (BPF) to find an estimate of the gradient of the output with respect to the input. The plant is then extremized by adjusting the manipulated variables to make this estimate approach zero.In this work, an alternative approach called phasor ESC is proposed, which is based on estimating the phasor of the plant output at the perturbation frequency rather than the gradient. Stability analysis of the phasor ESC is presented, including local and semi-global practical asymptotic stability for general non-linear dynamic plants. As an improvement of the existing stability analysis of the classic ESC, a less constrained semi-global practical asymptotic stability condition is also presented. In perturbation-based ESC, the output will continuously oscillate due to the input perturbation. As noted in the literature, the averaged system may not converge to the optimum point, and an average offset from the optimal value will emerge. This offset is negligible in the case of a small perturbation signal but will increase as the perturbation amplitude increases. In this work, a modification for the classic ESC and phasor ESC is proposed that improves the accuracy by reducing this offset. Two applications of ESC are considered: cone crushers and hydro power plants. Cone crushers are used for reducing the size of minerals and are considered to be a key component of many mineral processing plants. On-line optimization of the throughput is proposed based on the concept of ESC. A novel model of cone crushers is presented that can predict the flow and the size distribution of the output as a function of the primary manipulated variables, and simulations of ESC control on this model are presented.For hydro power plants, which are considered to be the most important source of renewable energy, phasor ESC is proposed for constructing and correcting the combinator, which ensures the optimal and efficient operation of the Kaplan turbine. Moreover, phasor ESC is proposed as a tool for maximum power point tracking in micro hydro plants by manipulating the turbine speed, and a test rig is used to conduct an experiment to validate this approach.
|
|
| 3. |
- Axelsson, Ann
(författare)
-
Planing wood with twist
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- About half the total volume of sawlogs end up as sawn timber. The rest is lostdue to drying shrinkage or is turned into byproducts like wood chips, sawdustand shavings. As the raw material is a large expense for a sawmill, it is important to fully utilize the logs. The inherent properties of timber are such that warp, such as bow, cup, spring and twist, is inevitable, and extensive knowledge of whether and to what extent warp will appear is therefore important for managing the production. It is also important to develop strategies to handle warped timber, for example in the planing process.This thesis focuses on how twisted timber is affected by the planing process with regard to twist reduction, cross-sectional shape, planer misses and cutting depth. This was studied in three practical tests on sawn timber with differentapproaches. In one test, sawn pine timber with a large variation of twist withinthe group was planed with standard settings, and five evenly spaced crosssections along the length of the sawn timber were subjected to more detailed studies. In the second test, the main yield from spruce logs was planed. One sample board from each log was planed with the normal pressure settings of the planing mill, while the second sample was planed with a pressure either higher or lower than the normal settings. In this study, seven cross-sections were studied in more detail, three close to the top end, three close to the butt end, and one in the middle of the sawn timber. In the third test, sawn pine timber with a more moderate twist was planed with standard settings in another similar planer.
|
|
| 4. |
- Axelsson, Sarianne Wiklund
(författare)
-
Prerequisites for sustainable life style changes among older persons with obesity and for ICT support
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The experiences from persons in the third age of lifestyle changes due to obesity are rarely described in research. Interventions regarding lifestyle changes and obesity show weak evidence for long-term effects. Information and communication technology (ICT) may add an important potential in interventions, but readiness among older persons and the actual needs for support must be explored. Therefore the overall aim for the thesis was to explore the prerequisites for sustainable lifestyle changes among older persons with obesity; and how this could be supported by ICT.Both qualitative and quantitative approaches were used. In paper I, 10 participants were individually interviewed about their experiences of lifestyle changes and in a multistage focus group study (paper IV), 6 participants expressed the support needed for sustainable lifestyle changes in relation to obesity. Qualitative content analysis was used. In a randomly selected population survey, 154 participants responded to an enquiry about general and health related ICT usage (paper II). They also rated scenarios for expected psychosocial impact on web based e-health services and mobile health applications (paper III).An integration of the results identified four main findings: The first finding, A never-ending process of vigilance and vulnerability, showed constant attempts of weight loss and pre-occupation on not to fail in an un-supportive environment. The second finding; Need for psychosocial support marked that the process of lifestyle changes was influenced by factors as sensibility to moods, social support and others’ attitudes. It was therefore essential for the persons to achieve emotional balance. The third finding, ICT as a possible support for adaptability, presented that older Swedes expected a positive psychosocial impact by ICT, especially in a future perspective. ICT was most valued in the domain of adaptability. The degree of usage of health related ICT, however, was low, although persons with overweight had more experience of this usage. Finally, the fourth finding; Reconstructions from weight to health expresses the needs of reconstructing focus towards health, rather than being pre-occupied with weight loss. Physical activity that was associated to joy and to have a functioning body, a body that would serve them as before, were motives to lose weight.In conclusion, this thesis illustrates that a lifestyle change due to obesity in third age is lined with vigilance not to fail and requires a great deal of endurance and effort. The potential of ICT to support lifestyle changes is likely to be substantiated by the positive expectations on ICT from a psychosocial impact perspective, especially in views of the future. Findings indicate a need for moving focus from weight towards health and to see opportunities, and that psychosocial support and enjoyable physical activity are important prerequisites for sustainable change.
|
|
| 5. |
- Biswas, Amit
(författare)
-
Effect of chemical and physical properties on combustion of biomass particle
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass combustion is an interesting alternative to fossil fuel. Modeling and simulation is used for design optimization of biomass boilers and furnace. It is difficult to develop a sufficiently accurate and computationally efficient model because the combustion system is highly complicated multi-scale, multi-phase and multi-physics problem. The study of biomass combustion in different scales allows engineers to understand the combustion process and tochoose necessary simplification to develop a computationally efficient model.The chemical and physical properties of fuels are altered during different fuel preparation methods (i.e. pretreatment and pelletization), and as a result the fuel conversion is also affected. The aim of this thesis is to understand thermal conversion of those chemically or physically altered fuels. Both experimental and modeling techniques were chosen to addressthe aim. Experiments were performed in thermogravimetric analysers, isothermal macro thermogravimeters (iTG), and a pot furnace to account fuel conversion in micro-, meso- and macro scale. In addition, three different types of mathematical model were developed. They are (i) a simplified particle pyrolysis model, (ii) two detailed numerical models that simulate particle pyrolysis and char oxidation and (iii) finally a computational fluid dynamic (CFD) model of combustion of biomass particles in a bed. The results indicate that both the intrinsic and the apparent conversion of the fuel wasinfluenced by the process conditions of fuel preparation methods. Intrinsic pyrolysis reactivitywas reduced due to mild pretreatment; however, it was increased with further increase in pretreatment severity. In contrary, severity of pelletization tends to reduce the apparent reactivity of pellets combustion. It was also investigated that how each physical and chemical parameter should be modelledfor a untreated biomass (i.e. wood logs) and a densified biomass (i.e. pellets) through parametric studies with a detailed particle simulation. The result shows that a model for wood logs should exclude convective heat transfer by volatiles if the fibers align to longitude direction while it is important part in the models for pellets. Devolatilization of wood logs was expressed as endothermic reactions while the model results showed best agreement withexperimental data of wood pellets when the heat of reaction was assumed to be zero, possibly due to the secondary reactions. Then, it was demonstrated that a constitutive equation, i.e. analytical solution of the shrinking core model, is sufficient to express devolatilization rate of thermally-thick particles at the temperature of 1173 K. While studying apparent oxidation of wood pellet char , it was found that change in intrinsic char oxidation reactivity due to different pyrolysis conditions does not influences the model prediction at high temperature. In addition, at high temperature, the reaction front became thin and reaction rate was hardly affected by temperature.It was also found by the simulation of pellet bed combustion that the apparent density of the particle significantly affected the flame velocity.
|
|
| 6. |
- Björklund, Cecilia
(författare)
-
Temporal patterns of daily occupations and personal projects relevant for older persons’ subjective health : a health promotive perspective
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Engagement in daily occupations has been shown to positively influence subjective health of older persons, but there is little knowledge of how such daily occupations should be temporally structured. This thesis is guided by two concepts to explore the temporal structure of daily occupations. Firstly, the concept temporal patterns of daily occupations are used to focus internal relationships and temporal order of daily occupations during 24-hour sequences. Secondly, the concept personal projects are used to focus sets of intentionally performed occupations structured to reach short- or long-term goals of a year. The overall aim of this thesis was to develop knowledge and understanding of temporal patterns of daily occupations and personal projects relevant for older persons’ health and well-being. This thesis includes four studies, according to a multi method sequential design. Participants in all four studies were recruited from retirement organizations in two municipalities in northern Sweden and all of them are living in their private urban or rural homes. For Study I and II, data of daily occupations and of health and well-being were collected from 151 older adults using open time-diaries completed for one week and two health questionnaires. A time-geographic method was used to analyze data from the time-diaries and descriptive and analytic statistics are applied for further analysis including the additional data from the two health questionnaires. The aim of Study I was to expand the knowledge regarding temporal patterns of daily occupations and to explore and describe older Swedish adults´ daily occupations from such a temporal pattern and time-use perspective. In Study I the temporal pattern of daily occupations of older persons was identified as real time-use and added time-use during 24-hour sequences. The pattern of real time-use showed i)a daily routine of six intervals ii) characteristic profiles illustrating number of participants in categorized occupations and iii) a pattern of merged categories of occupations. The pattern of added time-use for frequencies and durations of the 24-hour sequence showed a hierarchical structure with the highest frequencies and durations shown for care for oneself occupations followed by reflection and recreation, home-keeping, procure and prepare food, and transportation occupations (Study I). The aim of Study II was to identify characteristics of temporal patterns of daily occupations that could be related to high and low health among older adults in northern Sweden. The temporal pattern of daily occupations of older persons, identified as real time-use and added time-use during 24-hour sequences, showed similar patterns for groups of older persons reporting high and low health. Persons of high health reported higher frequencies and longer durations for home-keeping, procure and prepare food, and transportation occupations and lower frequencies and shorter durations for care for oneself and reflection and recreation occupations compared to the low health group (Study II). For Study III and IV, data of personal projects relevant for health and well-being were collected by interviews with 11 older persons selected from the high health subgroup in Study II. Data was analyzed by content analysis. The aim of Study III was to explore personal projects described by older persons in northern Sweden relevant to health and well-being during the forthcoming year. A coherent project system was developed. This system was structured as five core projects representing fourteen personal projects each including two to five sequential occupations, relevant to subjective health during the forthcoming year. The project system was anchored by the core projects: keeping the family together; enjoying one’s life at home; being close to nature; cultivating oneself; and promoting conditions for healthy ageing (Study III). In Study IV variations in occupational value were interpreted from older people´s personal projects relevant for health and well-being the forthcoming year. Variations in occupational value were identified from expressions in the 14 personal projects. Value dimensions of concrete and symbolic value were identified as the most frequently expressed and self-rewarding value as the least frequently expressed. Variations in occupational value within each personal project were shown as profiles of occupational value constructing the core projects. Profiles of occupational value of the core project cultivating one-self were dominated by concrete value while the remaining core projects were dominated by symbolic value (Study IV). Conclusions: This thesis contributes with knowledge of temporal patters of daily occupations described as real and added time-use during 24-hour sequences and the characteristics of such pattern showed for high health. Furthermore, it highlights a structure for a coherent project system relevant for occupational health during a year and the imbedded occupational value. This knowledge of the older persons’ structure and experiences of occupations may be used for promoting occupational health in different contexts. Keywords: elderly, temporal routines, structure of occupations, real time-use, added time-use, time-geographic method, core projects, personal projects, occupational value, health and well-being.
|
|
| 7. |
- Brämming, Mats
(författare)
-
An Operational View on Foaming and Slopping Control in Top-blown BOS Vessels
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Slag formation plays a decisive role in all steelmaking processes. In top-blowing Basic Oxygen Steelmaking (BOS) i.e., in the LD process, an emulsion consisting of liquid slag, dispersed metal droplets, undissolved particles and solid precipitates will, together with process gases, form an expanding foam. Extensive research has defined the parameters that govern the foaming characteristics of BOS slag-metal emulsions. It is a well-known fact that certain process conditions in the Basic Oxygen Furnace (BOF) will lead to excessive foam growth, forcing foam out through the vessel opening (mouth). This process event is commonly known as slopping. Slopping results in loss of valuable metal, equipment damage, lost production time, unsafe work environment and pollution. A literature survey covering the slopping phenomena has been carried out, as well as a deeper investigation into the causes behind slopping on the BOF type LD/LBE at SSAB Europe, Luleå, equipped with an automatic system for slopping registration using image analysis Good slag formation and foam-growth control in order to avoid slopping is primarily accomplished by taking preventive “static” measures. The most common pre-blowing operational conditions favouring foam growth and, hence, slopping were found to be linked to oxygen lance positioning, hot metal Si and Mn contents, scrap quality and large additions of iron oxide bearing materials. Improved slopping control may be achieved by developing oxygen lance control schemes with automatic adjustment of the distance between the lance tip and the metal bath (i.e., the lance gap) according to scrap quality and ore additions. If “static” measures cannot be effectuated, a set of in-blow slopping preventive measures is needed. For such “dynamic” measures to be effective, it is necessary to have a system for slopping prediction. Trials with vessel vibration measurements for indirect foam height estimation in industrial scale BOFs, type LD/LBE, have been carried out. FFT spectrum analysis was applied in order to find the frequency band with best correlation to an estimated foam height. The results show that there is a correlation between vessel vibration and foam height which can be used for dynamic foam level and slopping control, and this during the entire blow. The vessel vibration results have been tested against what is the perhaps most commonly implemented technique for dynamic foam height estimation and slopping control, the audiometric system. Parallel vibration and audio measurements have been carried out on 130-tonne as well as on 300-tonne BOFs. The results show that during stable process conditions there is good agreement between the two methods in regard to foam height estimation and that combining the two methods will provide a powerful slopping prediction and control system. A feasibility study has been carried out with the aim to describe the possibilities and limitations of multivariate data analysis, including batch analysis, for dynamic BOS process control, mainly in regard to slopping prevention. Two principal modelling approaches were tested.A central part of this PhD work is the performed emulsion characterisation and the subsequent investigation into the influence of emulsion mineralogy and morphology on slopping in the LD process. The results are based on the study of emulsion samples from trial heats conducted in a 6-tonne pilot plant LD vessel. The main emulsion slag phase mineral species identified were di-calcium silicate, monoxides (mainly FeO, MnO and MgO), calcium ferrites and late-appearing tri-calcium silicate. The study also show that the iron oxidation state has a large influence on the emulsion mineralogy and morphology, as a higher Fe3+ content facilitates the precipitation of calcium ferrites, raising the emulsion apparent viscosity and, hence, the foam index. The same effect is caused by higher MgO contents (i.e., at saturation), resulting in the precipitation of monoxide phase. However, large volume fractions of emulsion precipitates will not always lead to slopping in the LD process. A second “requirement” for excessive foam growth is a simultaneously high gas generation rate. Vice versa; an LD heat may very well slop at low volume fractions of 2ndphase particles in the emulsion if the gas generation rate is sufficiently high. It is an indisputable fact that excessive foaming is one of the main features of the LD process, due to the practice of top-lance oxygen blowing, creating a highly oxidised slag, and heavy batch additions of basic slag formers, causing an initial formation of large quantities of precipitates. Therefore, preventing slopping is primarily a matter of tight process control, most importantly, control of the oxygen lance gap in order to reach a state of sufficiently high liquid MeO phase to minimise the emulsion apparent viscosity, but low enough to avoid over-oxidising and a high gas generation rate.
|
|
| 8. |
- Burström, Per
(författare)
-
Computational Fluid Dynamics of Processes in Iron Ore Grate-Kiln Plants
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computational Fluid Dynamics (CFD) approaches have been developed to studypollution reduction in the manufacturing phase and heat transfer in the packed beds of iron ore pellets. CFD is a versatile tool that can be applied to study numerous problems in fluid mechanics. In the present thesis it is used, verified and validated to reveal the fluid mechanics of a couple of processes taking place during the drying and sintering of iron ore pellets. This is interesting in itself and can facilitate the optimization of the production as to product quality of the pellets, reduced energy consumption and reduction of emissions such as NOx and CO2. The practical aim with the pollution reduction research project is to numerically study the use of Selective Non-Catalytic Reduction (SNCR) technologies in gratekiln pelletizing plants for NOx reduction which had, to the best knowledge of the author, never been used in this context before despite that it is commonly used in cement and waste incineration plants. The investigation is done in several stages: 1)Reveal if it is possible to use the technique with the two most commonly reagents, ammonia and urea. 2) Derive a chemistry model for cyanuric acid (CA) so that this reagent also can be scrutinized. 3) Compare the reagents urea and CA in the gratekiln pelletizing process.A CFD model was developed and numerical simulations were carried out solving the flow field. A model for spray injection into the grate was then included in the model enabling a study of the overall mixing between the injected reagent droplets and the NOx polluted air. The results show that the SNCR technique with urea and CA may reduce the amount of NOx in the grate-kiln process under certain conditions while ammonia fails under the conditions investigated. The work also lays grounds for continued development of the proposed chemistry model by the adding of reactions to the RAPRENOx-process for CA as reagent, facilitating an extension to ammonia and urea as reagents.The grate-kiln plant consists of a grate, a rotating kiln and an annular cooler. The pellets are loaded onto the grate to shape a bed with a mean height of about 0.2 m. The pellets in LKABs processes consist mainly of magnetite and different additives chosen to fit the demand from the customer. Throughout the grate a temperature gradient is formed in the bed. This gradient should be as even as possible throughout the grate to ensure an even quality of the pellets. Method to study this numerically is the second main task in this thesis. The aim is to find out how temperature distributions in the bed can be modeled and adjusted. Of special interest is how the incoming process gas, leakage, and the detailed composition of the pellet bed influence the heat transfer through the bed. To achieve the goals and create a trustful model for the heat transfer through the packed bed the model must be build up in steps. Heat transfer to a bed of iron ore pellets is therefore examined numerically on several scales and with three methods: a one-dimensional continuous model, a discrete three-dimensional model and traditional computational fluid dynamics.In a first study the convective heat transport in a relatively thin porous layer ofmonosized particles is set-up and computed with the one-dimensional continuous model and the discrete three-dimensional model. The size of the particles is only one order of magnitude smaller than the thickness of the layer. For the three-dimensional model the methodology applied is Voronoi discretization with minimization of dissipation rate of energy. The discrete model captures local effects, including low heat transfer in sections with low speed of the penetrating fluid and large velocity and temperature variations in a cross section of the bed. The discrete and continuousmodel compares well for low velocities for the studied uniform boundary conditions. When increasing the speed or for a thin porous layer however, the continuous model diverge from the discrete approach if a constant dispersion is used in the continuous approach. The influence is larger from an increase in pellet diameter to bed height ratio than from increased velocity. In a second study the discrete model is compared to simulations performed with CFD. If local values are of importance the discrete model should always be used but if mean predictions are sufficient the CFD model isan attractive alternative that is easy to couple to the physics up- and downstream the packed bed. The good agreement between the discrete and continuous model furthermore indicates that the discrete model may be used also for non-Stokian flow in the transitional region between laminar and turbulent flow, as turbulent effects show little influence of the overall heat transfer rates in the continuous model.
|
|
| 9. |
- Carlsson, My
(författare)
-
When and why is pre-treatment of substrates for anaerobic digestion useful?
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Anaerobic digestion (AD) plays a key role in the recovery of renewable energy, in the form of biogas, and nutrients from waste materials. Pre-treatment of AD substrates has the potential to improve process performance in terms of increased methane yield and solids reduction, but pretreatments are not yet widely implemented into full-scale AD systems. The aims of this thesis were to identify conditions that determine when pre-treatment has a positive impact on an AD system and ways to improve the practical utility of pre-treatment impact assessment. Key steps towards meeting these aims were to determine and critically analyse effects of pre-treatments on AD, and current evaluation schemes at three levels: AD substrate level – Direct effects on the substrate’s chemical and physical characteristics and its biodegradability/bioavailability; Local AD system level – Effects of pre-treatment on the AD process and its outputs, required inputs and (local) upstream and downstream processes. System boundaries are “at the gate” of the AD plant and the system analysis may consider energy and/or financial parameters; Expanded AD System level – Includes indirect effects of pre-treatment, with system boundaries including external processes. The system analysis may address environmental and/or economic effects. Different substrate traits represent different types and degrees of limitations to optimal AD performance that can be met by different pre-treatment mechanisms. Most importantly, potential mechanical problems must be handled by dilution and/or homogenisation and unwanted components, as generally found in source-sorted food waste from households (FW), must be separated. These traits may hinder the actual operation of AD and the potential for recovery of nutrients, which is often the motivation for biological waste treatment. When these practical barriers are overcome, pre-treatment focus may be directed towards maximizing the conversion of organic material to biogas, which is potentially limited by the rate and/or extent of hydrolysis. Lignocellulosic structures and aerobically stabilised biological sludge represent significant barriers to hydrolysis, which can be overcome by pre-treatment-induced solubilisation. Other particulates are merely hydrolysis-limited by their size, which can be reduced by specific pre-treatments. Finally, substrates may contain non-biodegradable organic compounds, which need to be chemically transformed in order to be converted to biogas. The substrates considered for AD incorporate these traits in varying degrees and even among substrates of the same category, such as plant material and excess sludge from wastewater treatment (WWT), the potential effect of pretreatments may vary considerably. Overcoming the substrate barriers via pre-treatment may potentially improve the AD system by enhancing operational stability, increasing methane yields and solids reduction under similar operating conditions to those without pre-treatment or by increasing methane productivity by allowing reductions in hydraulic retention time without changing the methane yield. However, the required inputs as well as the associated effects on related sub-processes must also be considered. The ultimate usefulness of a pre-treatment in a specific system is determined by the mass- and energy balance and the associated financial or environmental costs/values of inputs and outputs. The accuracy and applicability of pre-treatment impact assessment is challenged by method limitations and lack of transparency. A common measure of the pre-treatment effects is COD solubilisation, but the interpretation is complicated by the application of different measurementapproaches. In addition, solubilisation of COD as a result of pre-treatment does not necessarily translate into increases in operational methane yields. This is due to potential formation of refractory compounds and the fact that hydrolysis is not necessarily rate limiting for all particulates. Pre-treatments’ effects on biodegradability and degradation rates can be better assessed by BMP tests (biochemical methane potential), provided that the test conditions are appropriate and the tests’ limitations are properly considered. However, extrapolation of BMP results to continuous processes is complicated by the batch mode of the tests. On the other hand, results from continuous trials allow assessments of methane yields in practical systems and the digestate’s physico-chemical properties, but are inevitably tied to the specific process conditions tested. Thus, results from multiple experimental conditions, possibly strengthened by computer simulations, are necessary for generalisations of pre-treatment effects on AD process performance. Pre-treatments have the potential to considerably improve AD systems, but their implementation must to be guided by the actual improvement potential of the specific substrate and valued in theirspecific context with respect to process design and framework conditions.
|
|
| 10. |
- Cenamor, Javier
(författare)
-
Managing Platform-Mediated Ecosystems : Investigating ecosystem interdependencies and strategic choices
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rapid and ubiquitous spread of information technologies (IT) is creating unprecedented effects that challenge traditional fundamentals of the business world. Platform-mediated ecosystems are increasingly attracting the attention of practitioners from diverse industries, from telecommunications to video consoles, as well as academics from different fields ranging from management to economics, and information systems (IS) and innovation management. A platform-mediated ecosystem can be defined broadly as an industrial architecture with an infrastructure in the center that facilitates value co-creation among different agents (platform owners, and providers and users of complementary products) and a set of rules governing their interdependencies. The speed and the magnitude at which platforms diffuse are inspiring numerous analyses from diverse perspectives, mainly focused on drivers of success and ecosystem interdependencies in different contexts. This thesis highlights the importance of detangling the different interdependencies within platform-mediated ecosystems, while building a comprehensive approach based on the ecosystem as a whole. The wide range of platform types and their rapid evolution makes it difficult to establish a consensual categorization of platforms. A common aspect among most of them is that platform-mediated ecosystems usually present network effects that is the value of products depend on the number of peers within the ecosystem. In this sense, the number of adopters, known also as the size of the installed base, in a market has traditionally had a central importance in the literature. The platform-mediated ecosystems, however, are becoming more and more complex due to rising competition. Thus, there is a need for advancing understanding of the fundamentals of platform-mediated ecosystems and the management alternatives inherent in designing such systems which would enable a comprehensive platform approach to be built. Consequently, the main purpose of this thesis is to advance the understanding of the strategic management of platform-mediated ecosystems. Specifically, this thesis aims to unravel the ecosystem interdependencies and to identify strategic choices as a source of competitive advantage. To achieve this aim, different methodologies are applied in this thesis. Specifically, Paper I was based on a structured literature review of relevant papers in platform-mediated ecosystems for the period 2000 through 2014. The empirical analyses conducted in Papers II, III, and IV use different secondary samples from the video console ecosystem. Finally, the results in Paper V were based on a qualitative, multiple case study of global manufacturing firms implementing product-service systems (PSS) through a platform architecture. Overall, the findings within this thesis present the following main theoretical contributions. First, the thesis presents a comprehensive approach toward platform mediated ecosystems covering new ways of value creation and value capture, new governance regimes, and new agents making interdependent choices. Precisely, platform ecosystems offer unprecedented efficiencies and innovation enhancements, and the possibility of establishing rules for new role participation and interaction. Thus, the findings shed light on the fundamentals and future trends in the platform approach. Second, different ecosystem interdependencies may increase the platform adoption and performance. Specifically, the thesis highlights the importance of the positive effects from different agents in the complementary product markets. Accordingly, the findings contribute on unraveling the interdependencies within platform ecosystems. Third, platform performance can be enhanced by exploiting complementarities among strategies and regions. Precisely, the findings show significant complementarities from the joint management of different activities related to the complementary products and the platform, and from the presence in several countries. Consequently, the findings provide strategic choices as a source of competitive advantage. Finally, transformation toward global PSS may be guided by a platform approach, which may be helpful to explain the origins in building a platform ecosystem. In this respect, the findings shed light on how platform-mediated ecosystems are created. In sum, these findings have important implications for researchers in strategic management, economics, and information systems as well as managers from highly innovative industries and traditional sectors under structural transformation. This thesis concludes with the limitations that should be considered when interpreting the findings and some suggestions for future researchers.
|
|
