Three-dimensional modeling of biomass fuel flow in a circulating fluidized bed furnace

The reduction of greenhouse gas emissions in the European Union promotes the combustion of biomass rather than fossil fuels in energy production. Circulating fluidized bed (CFB) combustion offers a simple, flexible and efficient way to utilize untreated biomass in a large scale. CFB furnaces are modeled in order to understand their operation better and to help in the design of new furnaces. Therefore, physically accurate models are needed to describe the heavily coupled multiphase flow, reactions and heat transfer inside the furnace. This thesis presents a new model for the fuel flow inside the CFB furnace, which acknowledges the physical properties of the fuel and the multiphase flow phenomena inside the furnace. This model is applied with special interest in the firing of untreated biomass. An experimental method is utilized to characterize gas-fuel drag force relations. This characteristic drag force approach is developed into a gas-fuel drag force model suitable for irregular, non-spherical biomass particles and applied together with the new fuel flow model in the modeling of a large-scale CFB furnace. The model results are physically valid and achieve very good correspondence with the measurement results from large-scale CFB furnace firing biomass. With the methods and models presented in this work, the fuel flow field inside a circulating fluidized bed furnace can be modeled with better accuracy and more efficiently than in previous studies with a three-dimensional holistic model frame.

The Impact of the 2007-2009 Financial Crisis on the Relationship between Central Bank Rates and the Corresponding Interbank Interest Rates in 2002-2014

The role of central banks throughout the global financial system has become even more important during and after the events of the financial crisis. In order to stabilize the market conditions and provide solid ground for future development, the central banks use discount rate as their primary monetary policy tool in many developed and emerging economies. The purpose of this thesis is to examine how the relationship between central bank rates and corresponding interbank rates has developed before, during and after the crisis period of 2007-2009 in five developed countries and five emerging market countries. The results indicate that during the before-crisis period the interest rate markets reacted diversely but the joint recovery attempts of global economies seem to have stabilized the reactions during and especially after the crisis. The crisis also seems to have highlighted the characteristics of each country’s survival strategy as the role of other policy instruments arose.

Computational models for and from biology : simple gene assembly and reaction systems

The advancement of science and technology makes it clear that no single perspective is any longer sufficient to describe the true nature of any phenomenon. That is why the interdisciplinary research is gaining more attention overtime. An excellent example of this type of research is natural computing which stands on the borderline between biology and computer science. The contribution of research done in natural computing is twofold: on one hand, it sheds light into how nature works and how it processes information and, on the other hand, it provides some guidelines on how to design bio-inspired technologies. The first direction in this thesis focuses on a nature-inspired process called gene assembly in ciliates. The second one studies reaction systems, as a modeling framework with its rationale built upon the biochemical interactions happening within a cell. The process of gene assembly in ciliates has attracted a lot of attention as a research topic in the past 15 years. Two main modelling frameworks have been initially proposed in the end of 1990s to capture ciliates’ gene assembly process, namely the intermolecular model and the intramolecular model. They were followed by other model proposals such as templatebased assembly and DNA rearrangement pathways recombination models. In this thesis we are interested in a variation of the intramolecular model called simple gene assembly model, which focuses on the simplest possible folds in the assembly process. We propose a new framework called directed overlap-inclusion (DOI) graphs to overcome the limitations that previously introduced models faced in capturing all the combinatorial details of the simple gene assembly process. We investigate a number of combinatorial properties of these graphs, including a necessary property in terms of forbidden induced subgraphs. We also introduce DOI graph-based rewriting rules that capture all the operations of the simple gene assembly model and prove that they are equivalent to the string-based formalization of the model. Reaction systems (RS) is another nature-inspired modeling framework that is studied in this thesis. Reaction systems’ rationale is based upon two main regulation mechanisms, facilitation and inhibition, which control the interactions between biochemical reactions. Reaction systems is a complementary modeling framework to traditional quantitative frameworks, focusing on explicit cause-effect relationships between reactions. The explicit formulation of facilitation and inhibition mechanisms behind reactions, as well as the focus on interactions between reactions (rather than dynamics of concentrations) makes their applicability potentially wide and useful beyond biological case studies. In this thesis, we construct a reaction system model corresponding to the heat shock response mechanism based on a novel concept of dominance graph that captures the competition on resources in the ODE model. We also introduce for RS various concepts inspired by biology, e.g., mass conservation, steady state, periodicity, etc., to do model checking of the reaction systems based models. We prove that the complexity of the decision problems related to these properties varies from P to NP- and coNP-complete to PSPACE-complete. We further focus on the mass conservation relation in an RS and introduce the conservation dependency graph to capture the relation between the species and also propose an algorithm to list the conserved sets of a given reaction system.

The feasibility of torrefaction for the co-firing of wood in pulverised-fuel boilers

Torrefaction is the partial pyrolysis of wood characterised by thermal degradation of predominantly hemicellulose under inert atmosphere. Torrefaction can be likened to coffee roasting but with wood in place of beans. This relatively new process concept makes wood more like coal. Torrefaction has attracted interest because it potentially enables higher rates of co-firing in existing pulverised-coal power plants and hence greater net CO2 emission reductions. Academic and entrepreneurial interest in torrefaction has sky rocketed in the last decade. Research output has focused on the many aspects of torrefaction – from detailed chemical changes in feedstock to globally-optimised production and supply scenarios with which to sustain EU emission-cutting directives. However, despite its seemingly simple concept, torrefaction has retained a somewhat mysterious standing. Why hasn’t torrefied pellet production become fully commercialised? The question is one of feasibility. This thesis addresses this question. Herein, the feasibility of torrefaction in co-firing applications is approached from three directions. Firstly, the natural limitations imposed by the structure of wood are assessed. Secondly, the environmental impact of production and use of torrefied fuel is evaluated and thirdly, economic feasibility is assessed based on the state of the art of pellet making. The conclusions reached in these domains are as follows. Modification of wood’s chemical structure is limited by its naturally existing constituents. Consequently, key properties of wood with regards to its potential as a co-firing fuel have a finite range. The most ideal benefits gained from wood torrefaction cannot all be realised simultaneously in a single process or product. Although torrefaction at elevated pressure may enhance some properties of torrefied wood, high-energy torrefaction yields are achieved at the expense of other key properties such as heating value, grindability, equilibrium moisture content and the ability to pelletise torrefied wood. Moreover, pelletisation of even moderately torrefied fuels is challenging and achieving a standard level of pellet durability, as required by international standards, is not trivial. Despite a reduced moisture content, brief exposure of torrefied pellets to water from rainfall or emersion results in a high level of moisture retention. Based on the above findings, torrefied pellets are an optimised product. Assessment of energy and CO2-equivalent emission balance indicates that there is no environmental barrier to production and use of torrefied pellets in co-firing. A long product transport distance, however, is necessary in order for emission benefits to exceed those of conventional pellets. Substantial CO2 emission reductions appear possible with this fuel if laboratory milling results carry over to industrial scales for direct co-firing. From demonstrated state-of-the-art pellet properties, however, the economic feasibility of torrefied pellet production falls short of conventional pellets primarily due to the larger capital investment required for production. If the capital investment for torrefied pellet production can be reduced significantly or if the pellet-making issues can be resolved, the two production processes could be economically comparable. In this scenario, however, transatlantic shipping distances and a dry fuel are likely necessary for production to be viable. Based on demonstrated pellet properties to date, environmental aspects and production economics, it is concluded that torrefied pellets do not warrant investment at this time. However, from the presented results, the course of future research in this field is clear.

Korkokattosäännöksen vaikutukset pikalainamarkkinoihin

Lyhytaikaisista, pienehköistä ja vakuudettomista pikalainoista on muodostunut nopeasti osa suomalaisia kuluttajaluottomarkkinoita. Samalla pikalainatoimintaa koskevaa lainsäädäntöä on uudistettu useaan kertaan. Tämän kandidaatintutkielman tavoitteena on ollut selvittää, miten korkokattosäännös on vaikuttanut pikalainayhtiöiden tarjoamiin tuotteisiin ja alalla toimivan yritysjoukon kokoon. Tutkimus on toteutettu laadullisin menetelmin. Aineistona on käytetty Etelä-Suomen aluehallintoviraston ylläpitämän luotonantajarekisterin tietoja, Tilastokeskuksen tilastotietoja, keskeisiä oikeustapauksia sekä erikseen tutkielmaa varten kerättyjä pikalainayhtiöiden tuotetietoja. Tutkimuksessa havaittiin korkokattosäännöksen voimaantulon vähentäneen pikalainayritysten määrää huomattavasti. Yleisin tuote toimialalla on niin sanottu limiittiluotto joustavalla lainamäärällä ja takaisinmaksulla, minkä lisäksi yhtiöt tarjoavat lyhyitä ja pitkiä kertaluottoja. Korkokattosäännöksen tultua voimaan keskimääräinen luottosumma on kasvanut ja takaisinmaksuaika pidentynyt merkittävästi. Samalla luotoista maksettavien kulujen suhde lainamäärään on pienentynyt ja lainoja on myönnetty niin euro- kuin kappalemääräisesti selvästi aiempaa vähemmän. Tulosten perusteella voidaan sanoa, että lakimuutoksella on ollut selkeitä vaikutuksia pikalaina-alaan. Luotonannon kiristyttyä laskeneet luottokustannukset hyödyttävät kuitenkin vain osaa luotonhakijoista. Muuttuneiden tuotteiden myötä pikalainatoiminta on siirtynyt lähemmäs muuta kuluttajaluottotoimintaa.

Suomalaisen PK-yrityksen etabloitumisen kompleksisuus Venäjälle

Tässä diplomityössä perehdytään suomalaisten pk - yritysten kansainvälistymisen kompleksisuuteen Venäjälle. Tutkimuksen pääkohderyhmänä ovat Etelä-Karjalaiset kone – ja metallialan pienet ja keskisuuret yritykset. Tutkimuksessa selvitettiin myös Pietarin alueen suurten metalliyritysten etabloitumishalukkuutta Suomeen. Työn tavoitteena on tuottaa informaatiota kansainvälisen liiketoiminnan päätöksenteon tueksi. Työn tarkoituksena on myös selvittää lukijalle kansainvälistymiseen liittyvän kompleksisuuden ja yrityksen resurssien välistä yhteyttä. Työn yhtenä tuotoksena luotiin yksinkertainen malli, joka omalta osaltaan selittää haastavalle liiketoiminta-alueelle etabloitumista tavoittelevan yrityksen kokemaa kompleksisuutta ja sen yhteyttä yrityksen resursseihin.