Tuulivoimalan lapojen huolto ja tarkastukset

Uusiutuva energia elää voimakasta kasvukautta ja hallituksen tekemien tukipäätösten vuoksi tuulivoimaa tullaan rakentamaan huomattavasti lisää tulevien vuosien aikana. Tuuligeneraattorin siipien huolto- ja tarkastustoiminta on uusi ja kehittyvä toimiala. Tämä diplomityö onkin tehty oppaaksi helpottamaan tuulivoimaa omistavien, rakentavien, tai tuulivoimapuiston perustamista harkitsevien tahojen huoltosuunnitelmien tekemistä varten. Diplomityössä käydään läpi yleisimmät tuulivoimaloiden lapojen vikaantu-miset, sekä työskentelytavat ja käytettävät laitteistot voimaloiden lapojen huoltoja ja tarkastuksia tehtäessä.

Helmimyllyn toimintaparametrien vaikutus jauhautuvuuteen

Työn teoriaosassa tutkittiin materiaalin hienontamista jauhatuksen näkökulmasta. Jauhatuksessa keskityttiin ultrahienojauhatukseen ja siinä käytettäviin myllyihin, jois-ta lähimmin tarkasteltiin helmimyllyä ja sen toimintaparametrien vaikutusta jauhau-tuvuuteen. Lisäksi teoriaosassa tutkittiin jauhatuksen energiankulutusta, joka on yksi jauhatuksen suurimmista ominaisuuksista. Työn kokeellisessa osassa tutkittiin kalkkikiven jauhautuvuutta ja jauhatuksen omi-naisenergiankulutusta käyttäen kolmea erilaista sekoitinelintä. Kokeissa myllynä käy-tettiin helmimyllyä ja jauhinkappaleina 2 mm:n lasihelmiä. Jauhautuvuutta tutkittiin analysoimalla tuotteiden partikkelikokojakaumat Beckman Coulter LS 13 320 partik-kelikokoanalysaattoria. Energiankulutukset määritettiin lietteen lämpötilan muutok-sen perusteella ensimmäisen viidentoista minuutin aikana. Työn tavoitteena oli selvittää, onko uusi lapamainen sekoitinelin tehokas jauhatta-vuuden kannalta mutta samalla myös energiatehokas. Tämän työn perusteella uusi lapamainen sekoitinelin on tehokas jauhautuvuuden kannalta suuremmilla pyörimis-nopeuksilla. Ominaisenergiankulutus on puolestaan samaa luokkaa suuremmilla pyö-rimisnopeuksilla verrattaessa eri sekoitinelimiä.

Working fluid selection and design of small-scale waste heat recovery systems based on organic Rankine cycles

Demand for the use of energy systems, entailing high efficiency as well as availability to harness renewable energy sources, is a key issue in order to tackling the threat of global warming and saving natural resources. Organic Rankine cycle (ORC) technology has been identified as one of the most promising technologies in recovering low-grade heat sources and in harnessing renewable energy sources that cannot be efficiently utilized by means of more conventional power systems. The ORC is based on the working principle of Rankine process, but an organic working fluid is adopted in the cycle instead of steam. This thesis presents numerical and experimental results of the study on the design of small-scale ORCs. Two main applications were selected for the thesis: waste heat re- covery from small-scale diesel engines concentrating on the utilization of the exhaust gas heat and waste heat recovery in large industrial-scale engine power plants considering the utilization of both the high and low temperature heat sources. The main objective of this work was to identify suitable working fluid candidates and to study the process and turbine design methods that can be applied when power plants based on the use of non-conventional working fluids are considered. The computational work included the use of thermodynamic analysis methods and turbine design methods that were based on the use of highly accurate fluid properties. In addition, the design and loss mechanisms in supersonic ORC turbines were studied by means of computational fluid dynamics. The results indicated that the design of ORC is highly influenced by the selection of the working fluid and cycle operational conditions. The results for the turbine designs in- dicated that the working fluid selection should not be based only on the thermodynamic analysis, but requires also considerations on the turbine design. The turbines tend to be fast rotating, entailing small blade heights at the turbine rotor inlet and highly supersonic flow in the turbine flow passages, especially when power systems with low power outputs are designed. The results indicated that the ORC is a potential solution in utilizing waste heat streams both at high and low temperatures and both in micro and larger scale appli- cations.

Prosessiteollisuuden sekoittimen elinkaariarviointi

Työn tavoitteena oli tehdä elinkaariarviointi (LCA) prosessiteollisuuden sekoittimelle Helmix HF-80 ja analysoida LCA-tulokset, vaikutus ilmaston lämpenemisen potentiaalin (GWP) suhteen, sekä tutkia GWP-vaikutuksen pienentämisen mahdollisuuksia. Tutkittavan sekoittimen mahdolliset käyttökohteet ovat sellu- ja paperiteollisuus, raskaiden jätenesteiden käsittely, sekä muut teollisuusalueet, joissa käytetään tämän tyyppisiä laitteita. Työssä on muun muassa käsitelty sekoitusprosessit, sekoituslaitteiden tyypit, niiden rakenteiden ominaisuudet, käyttötarkoitus, toimintaperiaatteet, sekä sellu- ja paperi-teollisuudessa käytettävien sekoittimien yleiskatsaus. Työssä on myös kuvattu elinkaariarviointi (LCA) -menetelmä ja sen käyttötarkoitus. Tärkeimmistä tuloksista voi mainita sen, että sekoittimen (ilman säiliötä, sähkömoottoria ja vaihteistoa) kokoelinkaaren ilmastonlämpenemisen potentiaali (GWP) on noin 750 000 kg CO2-Equiv. Sekoittimen tuotanto- ja kierrätysaikana syntyy vain 1200 kg CO2-Equiv. ja suurin osa 748 000 kg CO2-Equiv. johtuu sähköenergian kulutuksesta käytön aikana. Käyttöajan vaikutusta voisi pienentää arvoksi 0 kg CO2-Equiv. käyttämällä pelkästään uusiutuvaa energiaa. Jos tuotantoaikana käytetty energia myös korvataan uusiutuvalla energialla, niin GWP-arvo koko elinkaaren aikana laskee arvoon 1006 kg CO2eqv., mikä on vain 0,13 % saaduista tuloksista. Suurin osa tästä arvosta liittyy sekoittimen materiaalin, tässä tapauksessa ruostumattoman teräksen tuotantoon.

Droplet Deposition in the Last Stage of Steam Turbine

During the expansion of steam in turbine, the steam crosses the saturation line and hence subsequent turbine stages run under wet condition. The stages under wet condition run with low efficiency as compared to stages running with supersaturated steam and the life of the last stage cascade is reduced due to erosion. After the steam crosses the saturation line it does not condense immediately but instead it becomes supersaturated which is a meta-stable state and reversion of equilibrium results in the formation of large number of small droplets in the range of 0.05 - 1 μm. Although these droplets are small enough to follow the stream lines of vapor however some of the fog droplets are deposited on the blade surface. After deposition they coagulate into films and rivulets which are then drawn towards the trailing edge of the blade due to viscous drag of the steam. These large droplets in the range of radius 100 μm are accelerated by steam until they impact on the next blade row causing erosion. The two phenomenon responsible for deposition are inertial impaction and turbulent-diffusion. This work shall discuss the deposition mechanism in steam turbine in detail and numerically model and validate with practical data.

Computational modelling of non-equilibrium condensing steam flows in low-pressure steam turbines

The steam turbines play a significant role in global power generation. Especially, research on low pressure (LP) steam turbine stages is of special importance for steam turbine man- ufactures, vendors, power plant owners and the scientific community due to their lower efficiency than the high pressure steam turbine stages. Because of condensation, the last stages of LP turbine experience irreversible thermodynamic losses, aerodynamic losses and erosion in turbine blades. Additionally, an LP steam turbine requires maintenance due to moisture generation, and therefore, it is also affecting on the turbine reliability. Therefore, the design of energy efficient LP steam turbines requires a comprehensive analysis of condensation phenomena and corresponding losses occurring in the steam tur- bine either by experiments or with numerical simulations. The aim of the present work is to apply computational fluid dynamics (CFD) to enhance the existing knowledge and understanding of condensing steam flows and loss mechanisms that occur due to the irre- versible heat and mass transfer during the condensation process in an LP steam turbine. Throughout this work, two commercial CFD codes were used to model non-equilibrium condensing steam flows. The Eulerian-Eulerian approach was utilised in which the mix- ture of vapour and liquid phases was solved by Reynolds-averaged Navier-Stokes equa- tions. The nucleation process was modelled with the classical nucleation theory, and two different droplet growth models were used to predict the droplet growth rate. The flow turbulence was solved by employing the standard k-ε and the shear stress transport k-ω turbulence models. Further, both models were modified and implemented in the CFD codes. The thermodynamic properties of vapour and liquid phases were evaluated with real gas models. In this thesis, various topics, namely the influence of real gas properties, turbulence mod- elling, unsteadiness and the blade trailing edge shape on wet-steam flows, are studied with different convergent-divergent nozzles, turbine stator cascade and 3D turbine stator-rotor stage. The simulated results of this study were evaluated and discussed together with the available experimental data in the literature. The grid independence study revealed that an adequate grid size is required to capture correct trends of condensation phenomena in LP turbine flows. The study shows that accurate real gas properties are important for the precise modelling of non-equilibrium condensing steam flows. The turbulence modelling revealed that the flow expansion and subsequently the rate of formation of liquid droplet nuclei and its growth process were affected by the turbulence modelling. The losses were rather sensitive to turbulence modelling as well. Based on the presented results, it could be observed that the correct computational prediction of wet-steam flows in the LP turbine requires the turbulence to be modelled accurately. The trailing edge shape of the LP turbine blades influenced the liquid droplet formulation, distribution and sizes, and loss generation. The study shows that the semicircular trailing edge shape predicted the smallest droplet sizes. The square trailing edge shape estimated greater losses. The analysis of steady and unsteady calculations of wet-steam flow exhibited that in unsteady simulations, the interaction of wakes in the rotor blade row affected the flow field. The flow unsteadiness influenced the nucleation and droplet growth processes due to the fluctuation in the Wilson point.