Kävelen, siis olen ja tiedän

Kirjallisuusarvostelu

Modelling of calciner in post-combustion carbon capture process

Climate change has given an impetus to research and developed new technologies to reduce significantly carbon dioxide emissions in energy production in the developed countries. The major pollution source, fossil fuels, will be used as an energy source for many decades, which provides the demand for carbon capture and storage technologies. Over recent years many new technologies has been developed and one of the most promising is calcium-looping in post-combustion carbon capture process, which use carbonation-calcination cycle to capture carbon dioxide from the flue gas of a combustion process. First pilot plant for calcium-looping process has been built in Oviedo, Spain. In this study, a three-dimensional model has been created for the calciner, which is one of the two fluidized bed reactors needed for the process. The calciner is a regenerator where the captured carbon dioxide is removed from the calcium material and then collected after the reactor. Thesis concentrates in creating the calciner 3D-model frame with CFB3D-program and testing the model with two different example cases. Used input parameters and calciner geometry are Oviedo pilot plant design parameters. The calculation results give information about the process and show that pilot plant calciner should perform as planned. This Master’s Thesis is done in participation to EU FP7 project CaOling.

Vapaaehtoinen tilintarkastus pienissä yrityksissä - empiirinen tutkimus

Tutkimuksen tavoitteena oli löytää ne tekijät, jotka vaikuttavat vapaaehtoisen tilintarkastuksen valintaan pienissä yrityksissä. Pienen yrityksen rajat määriteltiin noudattaen tilintarkastuslaissa säädettyjä rajoja tilintarkastusvelvollisuudesta. Empiirinen osuus suoritettiin kvalitatiivisena usean tapauksen tutkimuksena haastattelemalla kuutta eri pienyrityksen johtoon tai omistukseen kuuluvaa henkilöä. Aineisto kerättiin puolistrukturoidun ja teemahaastattelun välimaastoon sijoittuvilla haastatteluilla. Tulokset analysoitiin kokoamalla litteroiduista haastatteluista kokonaisuudet teemoittain. Tutkimuksessa haastateltiin myös tilintarkastajaa sekä pankin edustajaa puolistrukturoidulla haastattelulla lisäämään tulosten luotettavuutta. Tutkimuksen tulosten perusteella tilintarkastuksen valintaan vaikuttavia tekijöitä löytyi useita, sekä negatiivisia että positiivisia. Aikaisemmista tutkimuksista tuttujen ulkoisen rahoituksen, verottajan, ulkoistetun taloushallinnon sekä omistusrakenteen lisäksi uudeksi tilintarkastuksen valintaan vaikuttavaksi tekijäksi löydettiin toimiala. Yritysten välisen kaupankäynnin toimialoilla näyttäisi tutkimuksen perusteella olevan vaikutus tilintarkastukseen, mutta tutkimuksessa käytetyn pienen yritysjoukon takia tarvitaan lisätutkimuksia tekijän vaikutuksesta.

Performance and scalability of isolated DC-DC converter topologies in low voltage, high current applications

Fuel cells are a promising alternative for clean and efficient energy production. A fuel cell is probably the most demanding of all distributed generation power sources. It resembles a solar cell in many ways, but sets strict limits to current ripple, common mode voltages and load variations. The typically low output voltage from the fuel cell stack needs to be boosted to a higher voltage level for grid interfacing. Due to the high electrical efficiency of the fuel cell, there is a need for high efficiency power converters, and in the case of low voltage, high current and galvanic isolation, the implementation of such converters is not a trivial task. This thesis presents galvanically isolated DC-DC converter topologies that have favorable characteristics for fuel cell usage and reviews the topologies from the viewpoint of electrical efficiency and cost efficiency. The focus is on evaluating the design issues when considering a single converter module having large current stresses. The dominating loss mechanism in low voltage, high current applications is conduction losses. In the case of MOSFETs, the conduction losses can be efficiently reduced by paralleling, but in the case of diodes, the effectiveness of paralleling depends strongly on the semiconductor material, diode parameters and output configuration. The transformer winding losses can be a major source of losses if the windings are not optimized according to the topology and the operating conditions. Transformer prototyping can be expensive and time consuming, and thus it is preferable to utilize various calculation methods during the design process in order to evaluate the performance of the transformer. This thesis reviews calculation methods for solid wire, litz wire and copper foil winding losses, and in order to evaluate the applicability of the methods, the calculations are compared against measurements and FEM simulations. By selecting a proper calculation method for each winding type, the winding losses can be predicted quite accurately before actually constructing the transformer. The transformer leakage inductance, the amount of which can also be calculated with reasonable accuracy, has a significant impact on the semiconductor switching losses. Therefore, the leakage inductance effects should also be taken into account when considering the overall efficiency of the converter. It is demonstrated in this thesis that although there are some distinctive differences in the loss distributions between the converter topologies, the differences in the overall efficiency can remain within a range of a few percentage points. However, the optimization effort required in order to achieve the high efficiencies is quite different in each topology. In the presence of practical constraints such as manufacturing complexity or cost, the question of topology selection can become crucial.

Applications of Industrial Statistics

This dissertation examines knowledge and industrial knowledge creation processes. It looks at the way knowledge is created in industrial processes based on data, which is transformed into information and finally into knowledge. In the context of this dissertation the main tool for industrial knowledge creation are different statistical methods. This dissertation strives to define industrial statistics. This is done using an expert opinion survey, which was sent to a number of industrial statisticians. The survey was conducted to create a definition for this field of applied statistics and to demonstrate the wide applicability of statistical methods to industrial problems. In this part of the dissertation, traditional methods of industrial statistics are introduced. As industrial statistics are the main tool for knowledge creation, the basics of statistical decision making and statistical modeling are also included. The widely known Data Information Knowledge Wisdom (DIKW) hierarchy serves as a theoretical background for this dissertation. The way that data is transformed into information, information into knowledge and knowledge finally into wisdom is used as a theoretical frame of reference. Some scholars have, however, criticized the DIKW model. Based on these different perceptions of the knowledge creation process, a new knowledge creation process, based on statistical methods is proposed. In the context of this dissertation, the data is a source of knowledge in industrial processes. Because of this, the mathematical categorization of data into continuous and discrete types is explained. Different methods for gathering data from processes are clarified as well. There are two methods for data gathering in this dissertation: survey methods and measurements. The enclosed publications provide an example of the wide applicability of statistical methods in industry. In these publications data is gathered using surveys and measurements. Enclosed publications have been chosen so that in each publication, different statistical methods are employed in analyzing of data. There are some similarities between the analysis methods used in the publications, but mainly different methods are used. Based on this dissertation the use of statistical methods for industrial knowledge creation is strongly recommended. With statistical methods it is possible to handle large datasets and different types of statistical analysis results can easily be transformed into knowledge.

Uusiutuvan energian käytön edistäminen syöttötariffijärjestelmällä

Tässä opinnäytetyössä käsitellään syöttötariffeja, jotka ovat yksi valtion tukikeino uusiutuvalle energialle. Työn tarkoituksena on käsitellä uusiutuvien energialähteiden käytön edistämistä syöttötariffijärjestelmällä. Työssä esitellään lainsäädännön edellytykset kullekin tuotantomuodolle, jotta ne hyväksytään syöttötariffijärjestelmään. Lisäksi käsitellään syöttötariffien piirissä olevien eri tuotantomuotojen kohtaamia ongelmia. Työssä tutkitaan myös syöttötariffien vaikutusta sähkön hintaan tulevaisuudessa. Lopuksi esitellään lyhyesti muualla Euroopassa käytössä olevia tukimuotoja ja niiden määritys perusteita.

Luonto-opastyön taito

Kirjallisuusarvostelu