Comparison of energy balances of steam explosion and torrefaction technologies

The present study introduce two pretreatment technologies which are torrefaction and steam explosion, and compare energy balance for both technologies to investigate and compare the use of these technologies to improve pelletization. In this research, torrefaction and steam explosion pretreatments were accomplished on the mixed small diameter wood (70%) with moisture content of 40 %, and logging residues (30%) with moisture content of 45 % at temperature 230 ̊C, and treatment duration 10 min. Competing methods were evaluated, and the results showed higher volumetric energy for steam explosion pellet than torrefied pellet.

Isentropic Exergy and Pressure of the Shock Wave Caused by the Explosion of a Pressure Vessel

An accidental burst of a pressure vessel is an uncontrollable and explosion-like batch process. In this study it is called an explosion. The destructive effectof a pressure vessel explosion is relative to the amount of energy released in it. However, in the field of pressure vessel safety, a mutual understanding concerning the definition of explosion energy has not yet been achieved. In this study the definition of isentropic exergy is presented. Isentropic exergy is the greatest possible destructive energy which can be obtained from a pressure vessel explosion when its state changes in an isentropic way from the initial to the final state. Finally, after the change process, the gas has similar pressure and flow velocity as the environment. Isentropic exergy differs from common exergy inthat the process is assumed to be isentropic and the final gas temperature usually differs from the ambient temperature. The explosion process is so fast that there is no time for the significant heat exchange needed for the common exergy.Therefore an explosion is better characterized by isentropic exergy. Isentropicexergy is a characteristic of a pressure vessel and it is simple to calculate. Isentropic exergy can be defined also for any thermodynamic system, such as the shock wave system developing around an exploding pressure vessel. At the beginning of the explosion process the shock wave system has the same isentropic exergyas the pressure vessel. When the system expands to the environment, its isentropic exergy decreases because of the increase of entropy in the shock wave. The shock wave system contains the pressure vessel gas and a growing amount of ambient gas. The destructive effect of the shock wave on the ambient structures decreases when its distance from the starting point increases. This arises firstly from the fact that the shock wave system is distributed to a larger space. Secondly, the increase of entropy in the shock waves reduces the amount of isentropic exergy. Equations concerning the change of isentropic exergy in shock waves are derived. By means of isentropic exergy and the known flow theories, equations illustrating the pressure of the shock wave as a function of distance are derived. Amethod is proposed as an application of the equations. The method is applicablefor all shapes of pressure vessels in general use, such as spheres, cylinders and tubes. The results of this method are compared to measurements made by various researchers and to accident reports on pressure vessel explosions. The test measurements are found to be analogous with the proposed method and the findings in the accident reports are not controversial to it.

Ash Particle Erosion on Steam Boiler Convective Section

In this study, equations for the calculation of erosion wear caused by ash particles on convective heat exchanger tubes of steam boilers are presented. Anew, three-dimensional test arrangement was used in the testing of the erosion wear of convective heat exchanger tubes of steam boilers. When using the sleeve-method, three different tube materials and three tube constructions could be tested. New results were obtained from the analyses. The main mechanisms of erosionwear phenomena and erosion wear as a function of collision conditions and material properties have been studied. Properties of fossil fuels have also been presented. When burning solid fuels, such as pulverized coal and peat in steam boilers, most of the ash is entrained by the flue gas in the furnace. In bubbling andcirculating fluidized bed boilers, particle concentration in the flue gas is high because of bed material entrained in the flue gas. Hard particles, such as sharp edged quartz crystals, cause erosion wear when colliding on convective heat exchanger tubes and on the rear wall of the steam boiler. The most important ways to reduce erosion wear in steam boilers is to keep the velocity of the flue gas moderate and prevent channelling of the ash flow in a certain part of the cross section of the flue gas channel, especially near the back wall. One can do this by constructing the boiler with the following components. Screen plates can beused to make the velocity and ash flow distributions more even at the cross-section of the channel. Shield plates and plate type constructions in superheaters can also be used. Erosion testing was conducted with three types of tube constructions: a one tube row, an inline tube bank with six tube rows, and a staggered tube bank with six tube rows. Three flow velocities and two particle concentrations were used in the tests, which were carried out at room temperature. Three particle materials were used: quartz, coal ash and peat ash particles. Mass loss, diameter loss and wall thickness loss measurements of the test sleeves were taken. Erosion wear as a function of flow conditions, tube material and tube construction was analyzed by single-variable linear regression analysis. In developing the erosion wear calculation equations, multi-variable linear regression analysis was used. In the staggered tube bank, erosion wear had a maximum value in a tube row 2 and a local maximum in row 5. In rows 3, 4 and 6, the erosion rate was low. On the other hand, in the in-line tube bank the minimum erosion rate occurred in tube row 2 and in further rows the erosion had an increasing value, so that in a six row tube bank, the maximum value occurred in row 6.

Explosion-proof requirements for Electrical Machines in Chemical, Oil and Gas Industry in Russia and CIS Countries

One of the main industries which form the basis of Russian Economical structure is oil and gas. This industry is also playing a significant role for CIS countries. Oil and gas industry is developing intensively attracting foreign investments. This situation is providing sustainable development of machinery production for hazardous areas. Operating in oil and gas areas is always related with occurrence of explosion gas atmospheres. Machines for hazardous areas must be furnished with additional protection of different types. Explosion protection is regulated with standards according to which equipment must be manufactured. In Russia and CIS countries explosion-proof equipment must be constructed in compliance with GOST standards. To confirm that equipment is manufactured according to standards’ requirements and is safe and reliable it must undergo the approval procedure. Certification in Russia is governed by Federal Laws and legislation. Each CIS country has its own approval certificates and permissions for operating in hazardous areas.

Modelling of the PWR PACTEL vertical steam generator with the TRACE code

The behavior of the nuclear power plants must be known in all operational situations. Thermal hydraulics computer applications are used to simulate the behavior of the plants. The computer applications must be validated before they can be used reliably. The simulation results are compared against the experimental results. In this thesis a model of the PWR PACTEL steam generator was prepared with the TRAC/RELAP Advanced Computational Engine computer application. The simulation results can be compared against the results of the Advanced Process Simulator analysis software in future. Development of the model of the PWR PACTEL vertical steam generator is introduced in this thesis. Loss of feedwater transient simulation examples were carried out with the model.

Modeling of water/steam circulation in Circulating Fluidized Bed boiler

A distinctive design feature of steam boiler with natural circulation is the presence of the steam drum which plays a role of the separator of vapor from the flow of water-and-steam mixture coming into steam drum from the furnace tubes. Steam drum with unheated downcomer tubes, deducing from it, and riser (screen/furnace tubes) inside the furnace is a closed circulation loop in which movement of water (downcomer tubes) and water-and-steam mixture (riser tubes) is organized. The movement of the working fluid is appears due to occurrence of the natural pressure, determined by the difference in hydrostatic pressure and the mass of water and water-and-steam mixtures in downcomer and riser tubes and called the driving pressure of the natural circulation:

Modeling of water/steam circulation in Circulating Fluidized Bed boiler

A distinctive design feature of steam boiler with natural circulation is the presence of the steam drum which plays a role of the separator of vapor from the flow of water-and-steam mixture coming into steam drum from the furnace tubes. Steam drum with unheated downcomer tubes, deducing from it, and riser (screen/furnace tubes) inside the furnace is a closed circulation loop in which movement of water (downcomer tubes) and water-and-steam mixture (riser tubes) is organized. The movement of the working fluid is appears due to occurrence of the natural pressure, determined by the difference in hydrostatic pressure and the mass of water and water-and-steam mixtures in downcomer and riser tubes and called the driving pressure of the natural circulation: S drive = H steam (ρ down + ρ mix) g where: ρ down - density of water in downcomer tubes; ρ mix - density of water in riser tubes; H steam - height of steam content section; g - acceleration of gravity. In steam boilers with natural circulation the circulation rate is usually between 10 and 30. Thus, consumption of water in the circulation circuit “circulation rate times” more than steam output of the boiler. There are two aspects of the design of natural water circulation loops. One is to ensure a sufficient mass flux of circulating water to avoid burnout of evaporator tubes. The other is to avoid tube wall temperature fluctuation and tube vibration due to oscillation of circulation velocity. The design criteria are therefore reduced, in principle, to those of critical heat flux, critical flow rate for burnout, and flow instability. In practical design, however, the circulation velocity and the void fraction at the evaporator tube outlet are used as the design criteria (Seikan I., et. al., 1999). This study has been made with assumption that the heat flux in the furnace of the boiler even all the time. The target of the study was to define the circulation rate of the boiler, thus average heat flux do not change it. I would like to acknowledge professionals from “Foster Wheeler” company for good and comfortable cooperation.

Integration of Torrefaction with Steam Power Plant

Torrefaction is one of the pretreatment technologies to enhance the fuel characteristics of biomass. The efficient and continuous operation of a torrefaction reactor, in the commercial scale, demands a secure biomass supply, in addition to adequate source of heat. Biorefinery plants or biomass-fuelled steam power plants have the potential to integrate with the torrefaction reactor to exchange heat and mass, using available infrastructure and energy sources. The technical feasibility of this integration is examined in this study. A new model for the torrefaction process is introduced and verified by the available experimental data. The torrefaction model is then integrated in different steam power plants to simulate possible mass and energy exchange between the reactor and the plants. The performance of the integrated plant is investigated for different configurations and the results are compared.

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.

Vaneri- ja kertopuutehtaiden kuivatuskoneiden lämmöntalteenottojen järjestelmäselvitys

Vanerin tai kertopuun valmistusprosessissaviilun kuivaukseen käytetään suurin osa koko valmistusprosessin primäärienergiasta. Viilunkuivauskoneessa viilun sisältämä vesi siirretään tyypillisesti prosessihöyryllä lämmitettyyn viilunkuivaajan kiertoilmaan höyrystämällä ja poistetaanviilunkuivaajasta poistoilman mukana. Viilunkuivaajan poistoilma on lämmintä jaerittäin suuren kosteuspitoisuutensa takia sisältää runsaasti energiaa. Tyypillisellä viilunkuivaajalla poistoilmaan sitoutunut lämpöteho vaihtelee prosessiolosuhteista riippuen välillä 2,7-5,7 MW. Diplomityössä tutkittiin viilunkuivaajan poistoilman sisältämän lämmön talteenottoa laitteistolla, johon kuuluu lämmöntalteenottopesuri, jossa poistoilmalla lämmitetään tuotantolaitoksen tukkipuun hautomon kiertovettä sekä ilma-ilma-lämmönsiirrin, jolla lämmitetään pesurista poistuvan ilman jäännöslämmöllä ulkoilmaa tehdassalin tuloilmakäyttöön. Työn tavoitteena oli kehittää lämmöntalteenottojärjestelmän suunnittelua, mitoitusta ja ajotapoja. Työssä analysoitiin teoreettisesti pesuria ja ilmalämmönsiirrintä, kehitettiin lämmöntalteenottopesurin simulointimenetelmä ja mitattiin toiminnassa olevia talteenottolaitteistoja. Tutkimuksessa todettiin lämmöntalteenottohyötysuhteen vaihtelevan lämmityskaudella välillä 50-70 %. Lämmöntalteenottolaitteiston pesurin veteen saatava teho riippuu ensisijaisesti viilunkuivaajan poistoilman lämpösisällöstä, joka on enimmäkseen kosteusriippuvainen ja ilmanvaihtoilmaan saatava teho ulkolämpö-tilan määräämästä tehontarpeesta. Pesurin vesijärjestelmän vaikutusmekanismit pesurin suorituskykyyn tunnistettiin ja niiden pohjalta annetaan suositukset mitoitukseen ja ajotapaan. Lämmöntalteenottolaitteiston lämpötehon tasapainottamiseen pesurin ja ilma-ilma-lämmönsiirtimen välillä mitoituksen avulla esitellään työkalut.

Öljynjalostamon tyhjöyksikön esilämmitysuunin optimointi

Työn tarkoituksena oli vertailla kahta kaupallista prosessiuunisimulointiohjelmaa sekä selvittää onko toinen ohjelma soveltuva Neste Jacobs Oy:n käyttöön. Tavoitteena oli selvittää ohjelmien ominaisuuksien eroja ja rajoitteita sekä tuloksien yhdenmukaisuutta. Kirjallisuusosassa perehdyttiin prosessiuunien toimintaperiaatteisiin, yleisiin mitoitusperiaatteisiin ja säteilylämmönsiirron perusteisiin. Kirjallisuusosassa käsiteltiin myös prosessiuunien polttimien toimintaa ja NOx-päästöjä vähentäviä polttotekniikoita. Molemmilla laskentaohjelmilla laadittiin kuumaöljy- ja tyhjöuuni, joiden tuloksia vertailtiin tärkeimpien prosessiarvojen perusteella ja toisen ohjelman osalta myös laitevalmistajan ilmoittamiin arvoihin. Tällä ohjelmalla tutkittiin tyhjöuunin höyrynruiskutuksen ja koksaantumisen vaikutuksia prosessiin sekä säteilyosan leveyden muutoksen vaikutusta säteilylämmönsiirtoon. Ohjelmien ominaisuuksien keskeisimmät erot liittyivät kaksifaasivirtauksen laskentaan, prosessiaineen massavirran rajoituksiin, ilman esilämmittimen käyttöön ja laskentamallien paineen kontrollointiin. Tulokset erosivat savukaasun ja tuubien lämpötilojen ja painehäviön laskennassa. Tuloksien ja ominaisuuksien perusteella toisen ohjelman ei todettu olevan täysin soveltuva Neste Jacobs Oy:n käyttöön.

Höyrykattiloiden säilöntä

Tässä työssäon tarkasteltu yleisesti höyrykattiloiden säilöntää. Erilaisten säilöntämenetelmien perustietojen lisäksi työssä on pyritty selvittämään eri kattilatyypeille ominaiset säilöntätavat. Märkäsäilönnän jälkeistä käyttöönottoa on pohdittu selvittämällä laskennallisesti, onko tarpeen vaihtaa kattilaan vahvasti kemikaloidun säilöntäliuoksen tilalle puhtaampaa syöttövettä. Esimerkkinä on käytetty Voikkaan paperitehtaan höyryvoimalaitoksen kattila K13:ta. Työtä tehdessä on käytetty apuna aihetta käsittelevää kirjallisuutta, jota on saatu höyrykattiloita säilöviltä voimalaitoksilta, kemikaalitoimittajilta sekä asiantuntijoiden tekemistä luentomonisteista. Lieriökattiloiden höyrypuoli säilötään lähes poikkeuksetta märkänä, sillä se on vaikea tyhjentää täysin kosteudesta. Läpivirtauskattilalaitoksella käytetään usein sekä kuiva- että märkäsäilöntää. Savukaasupuolen korroosio ehkäistään useinmiten pitämällä kattila niin lämpimänä, että kastepistealituksia ei tapahdu.

Voimalaitoksen ylläpitosuunnitelma

Tässä diplomityössä on tehtyylläpitosuunnitelma Oulun Energian Toppila 1 - voimalaitokselle, jota on tavoitteena käyttää vuoteen 2015. Työssä on tarkasteltu aluksi voimalaitoksen tulevaisuuden käytön näkymiä ja tärkeimpien järjestelmien käyttökuntoa. Kattilalaitoksenkriittisille komponenteille on suoritettu ylläpito- ja epäkäytettävyyskustannusten vertailu sekä pyritty selvittämään komponenteille paras ylläpitomalli. Turbiinille on analysoitu erilaisia revisio- ja tarkastusmahdollisuuksia, ja vertailtu niistä muodostuvia kustannuksia. Tulosten perusteella voidaan sanoa, että tehostetut ylläpitotoimenpiteet ovat jatkossa kriittisille komponenteille taloudellisin ylläpitomalli, koska riittävällä määrällä tarkastuksia jakorjauksia voidaan hallita ongelmallisimpien komponenttien vaurioitumiskäyttäytymistä. Jos voimalaitosta käytetään vuoteen 2015, saattavat uusia investointeja olla eko I, eko II ja tertiääritulistin. Tämän työn perusteella investointeja eikannata tehdä, mutta komponenttien kuntoa sen sijaan on syytä arvioida vuosittain. Turbiinin kriittiset komponentit vaikuttaisivat olevan suhteellisen hyvässä kunnossa. Suurimmat vaurioitumismahdollisuudet liittyvät juoksusiipien väsymisvaurioihin.

Primääri-sekundäärivuodon tunnistaminen aktiivisuusmittauksin Loviisan voimalaitoksella

Diplomityössä tutkittiin Loviisan voimalaitoksen primääri- ja sekundääripiirin aktiivisuusmittausten kykyä tunnistaa pienet primääri-sekundäärivuodot. Tarkasteltavat primääri-sekundäärivuotojen suuruudet valittiin laitoksen hätätilanne- ja häiriönselvitysohjeiden mukaisesti. Vuodon vaikutuksia arvioitiin erilaisilla primäärijäähdytteen ominaisaktiivisuuksilla. Ominaisaktiivisuudet primääripiirissä määritettiin nuklidikohtaisesti erilaisille polttoainevuototapauksille. Työssä huomioitiin myös transienteissa mahdollisesti esiintyvä primääripiirin aktiivisuustasoa nostava spiking-ilmiö. Vuodon tarkempaa tunnistamista varten työssä laskettiin tarkasteltaville mittareille kalibrointikertoimet. Primääri-sekundäärivuoto mallinnettiin APROS-simulointiohjelmalla laitoksen eri käyttötiloissa ja kahdella eri vuotokoolla. Varsinainen aktiivisuuslaskenta suoritettiin SEKUN-ohjelmalla. Työssä tätä aktiivisuus- ja päästölaskentaohjelmaa muokattiin ohjelmoimalla siihen tarkasteltavat aktiivisuusmittaukset sekä primääripiirin puhdistus ja ulospuhallus. Laskelmien tuloksena saatiin arviot kunkin tarkasteltavana olleen aktiivisuusmittauksen soveltuvuudesta primääri-sekundäärivuodon tunnistamiseen erilaisissa polttoainevuototapauksissa ja reaktorin eri tehotasoilla. Häiriönselvitysohje I3:n käyttöönottoa edellyttävät vuotokoot määritettiin aktiivisuusmittausten havaitseman perusteella. Erityisesti kuumavalmiustilassa tapauksissa, joissa reaktorisydämessä oletetaan olevan tiiveytensä menettäneitä polttoainesauvoja, spikingin vaikutus jäähdytteiden aktiivisuuspitoisuuksiin ja mittaustuloksiin oli merkittävä. Niiltä osin, kuin tulokset käsittelevät ohjeissa vuodon tunnistamiseen käytettyjä aktiivisuusrajoja, tulokset osoittivat aktiivisuusrajat oikeiksi. Kuumavalmiudessa aktiivisuusmittausten mittausalueet saattavat joissakin tapauksissa rajoittaa primääri-sekundäärivuodon tunnistamista.