Vuotovesien merkitys jätevesihuollossa

Yleisimmät viemäröintijärjestelmät ovat erillisviemäröinti ja sekaviemäröinti. Erillisviemä-röinnissä jäte- ja hulevedet johdetaan omissa verkostoissa. Sekaviemäröinnissä kaikki viemä-röitävät vedet virtaavat samassa verkostossa. Vuotoveden osuus jätevesiviemäriverkostossa virtaavasta jätevedestä on keskimäärin yli 30 prosenttia. Vuotovesiselvityksen avulla pyritään selvittämään vuotoveden esiintymisalueet ja mahdolliset vuotokohteet. Mallintamalla laadittu selvitys tarjoaa mahdollisuuden tarkastella verkostoa kokonaisuutena ja erilaisissa käyttötilan-teissa. Tämä työ perustuu Joensuun kantakaupungin viemäriverkostosta mallintamalla laadit-tuun vuotovesiselvitykseen. Työssä on tarkoitus selvittää vuotovesistä aiheutuvan lisäener-giantarpeen ja kasvihuonekaasupäästöjen kasvua sekä pohtia verkoston omistussuhteiden, sään ääri-ilmiöiden ja taajuusmuuttajien vaikutuksia vuotovesien hallintaan. Lisäksi selvitetään voidaanko tuloksista tehdä valtakunnallisia yleistyksiä. Joensuun viemäriverkostossa jätevesien pumppaukseen käytetystä energiasta noin 43 prosent-tia kuluu vuotovesien pumppaukseen. Siitä aiheutuu vuosittain 480 MWh:n lisäenergiantarve, joka johtaa 106 tonnin hiilidioksidipäästöihin. Lisäenergiantarpeesta aiheutuva hiilidioksidi-päästö on pieni liikenteen aiheuttamaan päästöön verrattuna. Saneerauksilla voidaan saavuttaa 60 prosentin vähennys vuotovesimäärään. Tavoitteeksi tulisi asettaa keskusta-alueella olevien sekaviemäreiden korvaaminen erillisviemäreillä esimerkiksi lähimmän 10 vuoden aikana ja vuotovesimäärän yleinen vähentäminen koko verkoston alueella. Ilmastonmuutoksen myötä yleistyvät rankkasateet lisäävät vuotovesimäärää etenkin sekaviemäröidyillä alueilla. Tämä korostaa sekaviemäröidyn verkoston korjaustoimenpiteiden tärkeyttä. Taajuusmuuttajien yleistyvä käyttö tasaa haitallisia virtaamapiikkejä. Optimaaliseksi säädetty pyörimisnopeus pienentää merkittävästi pumppujen energiankulutusta. Työstä saadut tulokset ovat valtakun-nallisella tasolla suuntaa antavia. Tarkemmat yleistykset vaativat useista erikokoisista verkos-toista tehtyjen vuotovesiselvitystulosten analysointia.

Numerical Modelling of Combustion and Emission Formation in a Diesel Engine with Different Fuel Injection Characteristics

Päästöjen vähentäminen on ollut viime vuosina tärkeässä osassa polttomoottoreita kehitettäessä.Monet viralliset tahot asettavat uusia tiukempia päästörajoituksia. Päästörajatovat tyypillisesti olleet tiukimmat autoteollisuuden valmistamille pienille nopeakäyntisille diesel-moottoreille, mutta viime aikoina paineita on kohdistunut myös suurempiin keskinopeisiin ja hidaskäyntisiin diesel-moottoreihin. Päästörajat ovat erilaisia riippuen moottorin tyypistä, käytetystä polttoaineesta ja paikasta missä moottoria käytetään johtuen erilaisista paikallisista laeista ja asetuksista. Eniten huomiota diesel-moottorin päästöissä täytyy kohdistaa typen oksideihin, savun muodostukseen sekä partikkeleihin. Laskennallisen virtausmekaniikan (CFD) avulla on hyvät mahdollisuudet tutkia diesel-moottorin sylinterissä tapahtuvia ilmiöitä palamisen aikana. CFD on hyödyllinen työkalu arvioitaessa moottorin suorituskykyä ja päästöjen muodostumista. CFD:llä on mahdollista testata erilaisten parametrien ja geometrioiden vaikutusta ilman kalliita moottorinkoeajoja. CFD:tä voidaan käyttää myös opetustarkoituksessa lisäämään paloprosessin tuntemusta. Tulevaisuudessa palamissimuloinnit CFD:llä tulevat epäilemättä olemaan tärkeä osa moottorin kehityksessä. Tässä diplomityössä on tehty palamissimuloinnit kahteen erilaisilla poittoaineenruiskutuslaitteistoilla varustettuun Wärtsilän keskinopeaan diesel-moottoriin. W46 moottorin ruiskutuslaitteisto on perinteinen mekaanisesti ohjattu pumppusuutin ja W46-CR moottorissa on elektronisesti ohjattu 'common rail' ruiskutuslaitteisto. Näiden moottorien ja käytössä olevien ruiskutusprofiilien lisäksi on simuloinneilla testattu erilaisia uusia ruiskutusprofiileja, jotta erityyppisten profiilien hyvät ja huonot ominaisuudet tulisivat selville. Matalalla kuormalla kiinnostuksen kohteena on nokipäästöjen muodostus ja täydellä kuormalla NOx-päästöjen muodostus ja polttoaineen kulutus. Simulointien tulokset osoittivat, että noen muodostusta matalalla kuormalla voidaan selvästi vähentää monivaiheisella ruiskutuksella, jossa yksi ruiskutusjakso jaetaan kahteen tai useampaan jaksoon. Erityisen tehokas noen vähentämisessä vaikuttaa olevan ns. jälkiruiskutus (post injection). Matalat NOx-päästöt ja hyvä polttoaineen kulutus täydellä kuormalla on mahdollista saavuttaaasteittain nostettavalla ruiskutusnopeudella.

Reduction of Greenhouse Gas Emissions in North-West Russia - Finnish Business Opportunities

Tutkimus suomalaisten yritysten liiketoimintamahdollisuuksista hiilidoksidipäästöjen vähentämisen parissa Luoteis-Venäjällä.

Computational Analysis and Optimization of Real Gas Flow In Small Centrifugal Compressors

Small centrifugal compressors are more and more widely used in many industrialsystems because of their higher efficiency and better off-design performance comparing to piston and scroll compressors as while as higher work coefficient perstage than in axial compressors. Higher efficiency is always the aim of the designer of compressors. In the present work, the influence of four partsof a small centrifugal compressor that compresses heavy molecular weight real gas has been investigated in order to achieve higher efficiency. Two parts concern the impeller: tip clearance and the circumferential position of the splitter blade. The other two parts concern the diffuser: the pinch shape and vane shape. Computational fluid dynamics is applied in this study. The Reynolds averaged Navier-Stokes flow solver Finflo is used. The quasi-steady approach is utilized. Chien's k-e turbulence model is used to model the turbulence. A new practical real gas model is presented in this study. The real gas model is easily generated, accuracy controllable and fairly fast. The numerical results and measurements show good agreement. The influence of tip clearance on the performance of a small compressor is obvious. The pressure ratio and efficiency are decreased as the size of tip clearance is increased, while the total enthalpy rise keeps almost constant. The decrement of the pressure ratio and efficiency is larger at higher mass flow rates and smaller at lower mass flow rates. The flow angles at the inlet and outlet of the impeller are increased as the size of tip clearance is increased. The results of the detailed flow field show that leakingflow is the main reason for the performance drop. The secondary flow region becomes larger as the size of tip clearance is increased and the area of the main flow is compressed. The flow uniformity is then decreased. A detailed study shows that the leaking flow rate is higher near the exit of the impeller than that near the inlet of the impeller. Based on this phenomenon, a new partiallyshrouded impeller is used. The impeller is shrouded near the exit of the impeller. The results show that the flow field near the exit of the impeller is greatly changed by the partially shrouded impeller, and better performance is achievedthan with the unshrouded impeller. The loading distribution on the impeller blade and the flow fields in the impeller is changed by moving the splitter of the impeller in circumferential direction. Moving the splitter slightly to the suction side of the long blade can improve the performance of the compressor. The total enthalpy rise is reduced if only the leading edge of the splitter ismoved to the suction side of the long blade. The performance of the compressor is decreased if the blade is bended from the radius direction at the leading edge of the splitter. The total pressure rise and the enthalpy rise of thecompressor are increased if pinch is used at the diffuser inlet. Among the fivedifferent pinch shape configurations, at design and lower mass flow rates the efficiency of a straight line pinch is the highest, while at higher mass flow rate, the efficiency of a concave pinch is the highest. The sharp corner of the pinch is the main reason for the decrease of efficiency and should be avoided. The variation of the flow angles entering the diffuser in spanwise direction is decreased if pinch is applied. A three-dimensional low solidity twisted vaned diffuser is designed to match the flow angles entering the diffuser. The numerical results show that the pressure recovery in the twisted diffuser is higher than in a conventional low solidity vaned diffuser, which also leads to higher efficiency of the twisted diffuser. Investigation of the detailed flow fields shows that the separation at lower mass flow rate in the twisted diffuser is later than in the conventional low solidity vaned diffuser, which leads to a possible wider flow range of the twisted diffuser.

Numerical and ExperimentalModelling of Gas Flow and Heat Transfer in the Air Gap of An Electric Machine

This work deals with the cooling of high-speed electric machines, such as motors and generators, through an air gap. It consists of numerical and experimental modelling of gas flow and heat transfer in an annular channel. Velocity and temperature profiles are modelled in the air gap of a high-speed testmachine. Local and mean heat transfer coefficients and total friction coefficients are attained for a smooth rotor-stator combination at a large velocity range. The aim is to solve the heat transfer numerically and experimentally. The FINFLO software, developed at Helsinki University of Technology, has been used in the flow solution, and the commercial IGG and Field view programs for the grid generation and post processing. The annular channel is discretized as a sector mesh. Calculation is performed with constant mass flow rate on six rotational speeds. The effect of turbulence is calculated using three turbulence models. The friction coefficient and velocity factor are attained via total friction power. The first part of experimental section consists of finding the proper sensors and calibrating them in a straight pipe. After preliminary tests, a RdF-sensor is glued on the walls of stator and rotor surfaces. Telemetry is needed to be able to measure the heat transfer coefficients at the rotor. The mean heat transfer coefficients are measured in a test machine on four cooling air mass flow rates at a wide Couette Reynolds number range. The calculated values concerning the friction and heat transfer coefficients are compared with measured and semi-empirical data. Heat is transferred from the hotter stator and rotor surfaces to the coolerair flow in the air gap, not from the rotor to the stator via the air gap, althought the stator temperature is lower than the rotor temperature. The calculatedfriction coefficients fits well with the semi-empirical equations and precedingmeasurements. On constant mass flow rate the rotor heat transfer coefficient attains a saturation point at a higher rotational speed, while the heat transfer coefficient of the stator grows uniformly. The magnitudes of the heat transfer coefficients are almost constant with different turbulence models. The calibrationof sensors in a straight pipe is only an advisory step in the selection process. Telemetry is tested in the pipe conditions and compared to the same measurements with a plain sensor. The magnitudes of the measured data and the data from the semi-empirical equation are higher for the heat transfer coefficients than thenumerical data considered on the velocity range. Friction and heat transfer coefficients are presented in a large velocity range in the report. The goals are reached acceptably using numerical and experimental research. The next challenge is to achieve results for grooved stator-rotor combinations. The work contains also results for an air gap with a grooved stator with 36 slots. The velocity field by the numerical method does not match in every respect the estimated flow mode. The absence of secondary Taylor vortices is evident when using time averagednumerical simulation.

Gas-liquid mass transfer in bubbly flow: Estimation of mass transfer, bubble size and reactor performance in various applications

Gas-liquid mass transfer is an important issue in the design and operation of many chemical unit operations. Despite its importance, the evaluation of gas-liquid mass transfer is not straightforward due to the complex nature of the phenomena involved. In this thesis gas-liquid mass transfer was evaluated in three different gas-liquid reactors in a traditional way by measuring the volumetric mass transfer coefficient (kLa). The studied reactors were a bubble column with a T-junction two-phase nozzle for gas dispersion, an industrial scale bubble column reactor for the oxidation of tetrahydroanthrahydroquinone and a concurrent downflow structured bed.The main drawback of this approach is that the obtained correlations give only the average volumetric mass transfer coefficient, which is dependent on average conditions. Moreover, the obtained correlations are valid only for the studied geometry and for the chemical system used in the measurements. In principle, a more fundamental approach is to estimate the interfacial area available for mass transfer from bubble size distributions obtained by solution of population balance equations. This approach has been used in this thesis by developing a population balance model for a bubble column together with phenomenological models for bubble breakage and coalescence. The parameters of the bubble breakage rate and coalescence rate models were estimated by comparing the measured and calculated bubble sizes. The coalescence models always have at least one experimental parameter. This is because the bubble coalescence depends on liquid composition in a way which is difficult to evaluate using known physical properties. The coalescence properties of some model solutions were evaluated by measuring the time that a bubble rests at the free liquid-gas interface before coalescing (the so-calledpersistence time or rest time). The measured persistence times range from 10 msup to 15 s depending on the solution. The coalescence was never found to be instantaneous. The bubble oscillates up and down at the interface at least a coupleof times before coalescence takes place. The measured persistence times were compared to coalescence times obtained by parameter fitting using measured bubble size distributions in a bubble column and a bubble column population balance model. For short persistence times, the persistence and coalescence times are in good agreement. For longer persistence times, however, the persistence times are at least an order of magnitude longer than the corresponding coalescence times from parameter fitting. This discrepancy may be attributed to the uncertainties concerning the estimation of energy dissipation rates, collision rates and mechanisms and contact times of the bubbles.

Emission Trading and Tradable Green Certificates Impacts on the Business Activity of Vattenfall Oy

Ihmisen toiminnan vaikutus ilmakehään johtaa todennäköisesti ilmastonmuutoksiin. Eräs näistä muutoksista on maapallon keskilämpötilan nousu, joka aiheutuu kasvihuonekaasujen lisääntyneestä pitoisuudesta ilmakehässä. Vaikutusten vähentämiseksi on hiilidioksidipäästöjä vähennettävä. Kioton pöytäkirja asettaa allekirjoittaneille maille päästövelvoitteet. Euroopan unionin tulee vähentää kasvihuonekaasupäästöjään 8%:lla. Eräs vähennysmekanismeista on päästökauppa. Päästökauppa on sekä keino suojella ympäristöä että ympäristöpoliittinen instrumentti kasvihuonekaasupäästövähennysten kustannusten keventämiseksi. Päästökauppa ei suoranaisesti vähennä kasvihuonekaasupäästöjä, vaan tasaa niitä maiden ja laitosten välillä. Uusiutuvan energian käytön edistäminen sekä kansainvälisesti että kansallisesti johtaa suoriin kasvihuonekaasupäästöjen vähenemiseen. Euroopan unionin jäsenvaltiot ovat asettaneet kansalliset viitearvot uusituvan sähkön kulutukselle. Saavuttaakseen nämä viitearvot maiden tulee tukea uusiutuvia energialähteitä eri menetelmin kuten vihreillä sertifikaateilla. Päästökauppa ja kaupattavat vihreät sertifikaatit tulevat vaikuttamaan energiantuottajien liiketoimintaan. Työssä on tutkittu päästökaupan ja vihreiden sertifikaattien vaikutuksia Vattenfall Kaukolämpö Oy:n, Vattenfall Sähköntuotanto Oy:n ja Vamy Oy:n liiketoimintaan.

Rinnakkaispolttolaitoksen ympäristöntarkkailusuunnitelma

Diplomityössä päivitetään voimalaitoksen ympäristöntarkkailusuunnitelma vastaamaan uudistuneen ympäristöluvan ja lainsäädännön edellytyksiä. Työssä tutkitaan leijupetikatti-loiden tulipesän lämpötiloja, savukaasun viipymäaikoja tulipesässä, leijukerroskattiloiden päästöjä, päästöjen jatkuvatoimista mittaamista sekä päästöjen seurantaa ja raportointia. Tulipesän lämpötiloja mitattiin kupla- ja kiertoleijukattiloilla. Tuloksien perusteella havait-tiin kiertoleijukattilan tulipesän alaosan lämpötilojen olevan lähes riippumaton pedin lämpötilasta ja höyrykuormasta. Tulipesän yläosassa lämpötilat nousevat höyrykuorman kasvaessa, mutta pedin lämpötilalla ei havaittu vaikutusta tulipesän yläosassakaan. Molemmilla kattiloilla havaittiin voimakas vaakatasoinen lämpötilaprofiili. Kuplaleijukattilalla sekä höyrykuorma että pedin lämpötila vaikuttivat tulipesän lämpötilaan. Savukaasun teoreettiset viipymäajat laskettiin kiertoleijukattilalle. Laskelmien ja mittauksien perusteella havaittiin kattilalla mahdollisuus saavuttaa savukaasun kahden sekunnin viipymäaika 850 ºC lämpötilassa. Kattilan käyttäytymisen aukottomaksi selvittämiseksi kaikilla polttoaineseoksilla ja höyrykuormilla tarvitaan lisää toimenpiteitä kattilalla ja lisää tulipesän lämpötilamittauksia. Leijukerroskattiloiden päästöjen syntymistä ja hallintaa tutkittiin teoreettisesti kirjallisuustutkimuksena. Tutkittuihin päästöihin kuuluivat typen oksidit, rikkidioksidi, hiukkaset, hiilimonoksidi, orgaaninen kokonaishiili, suolahappo, fluorivety, raskasmetallit sekä dioksiinit ja furaanit. Jatkuvatoimisten päästömittausmittauslaitteiden toimintaperiaatteita selvitettiin kirjalli-suustutkimuksena. Samoin selvitettiin jatkuvatoimisten päästömittauslaitteiden virhelähtei-tä. Päästömittauslaitteille laadittiin pitkän ja lyhyen ajan laadunvarmistussuunnitelma. Ha-vaittiin, että nykyiset jatkuvatoimiset päästömittauslaitteet eivät täytä kaikkia uusia laatu-kriteereitä. Päästöjen jatkuvatoimiseen seuraamiseen työssä suunniteltiin uusi valvomonäyttö. Uuden näytön avulla tehostetaan päästöjen valvontaa. Päästöjen raportointiin työssä suunniteltiin vuorokausiraportti. Raporttiin kerätään jatkuva-toimisten päästömittauslaitteiden puolen tunnin keskiarvot. Raportin tarkastaa, allekirjoittaa ja arkistoi vuorossa oleva operaattori.

Odor emission control and reduce in betaine manufacture

This thesis was made in Naantali plant of Finnfeeds Finland Oy. In this thesis the main study was in reducing, controlling, measuring and processing odour effluents in various methods. Also are considered legislation, marketing issues and environmental requirements of reducing of odour effluents. The literature review introduces odours complications, legislations and various methods of odour removal. There is also a review of volatile organic compounds detection and measuring methods. The experimental section consists TD-GC-MS-measurements and expansive measurements with electronic nose. Electronic nose is a new solution for recognition and measuring industrial odours. In this thesis the electronic nose was adapted into reliable recognition and measuring method. Measurements with electronic nose was made in betaine factory and main targets were odour removal process and other odours from factory. As a result of experimental work with TD-GC-MS-measurements becomes odour compound of 2-and 3- methylbutanal and dimethyldisulfide, which odour is sweet and fug. Extensive study with electronic nose found many developmental subjects. Odour balance measurements of factory and after calculation made adjustment of odour removal process, over all odour effluent to environment will reduce 25 %.

Performance and Methodological Aspects in Positron Emission Tomography

Performance standards for Positron emission tomography (PET) were developed to be able to compare systems from different generations and manufacturers. This resulted in the NEMA methodology in North America and the IEC in Europe. In practices, the NEMA NU 2- 2001 is the method of choice today. These standardized methods allow assessment of the physical performance of new commercial dedicated PET/CT tomographs. The point spread in image formation is one of the factors that blur the image. The phenomenon is often called the partial volume effect. Several methods for correcting for partial volume are under research but no real agreement exists on how to solve it. The influence of the effect varies in different clinical settings and it is likely that new methods are needed to solve this problem. Most of the clinical PET work is done in the field of oncology. The whole body PET combined with a CT is the standard investigation today in oncology. Despite the progress in PET imaging technique visualization, especially quantification of small lesions is a challenge. In addition to partial volume, the movement of the object is a significant source of error. The main causes of movement are respiratory and cardiac motions. Most of the new commercial scanners are in addition to cardiac gating, also capable of respiratory gating and this technique has been used in patients with cancer of the thoracic region and patients being studied for the planning of radiation therapy. For routine cardiac applications such as assessment of viability and perfusion only cardiac gating has been used. However, the new targets such as plaque or molecular imaging of new therapies require better control of the cardiac motion also caused by respiratory motion. To overcome these problems in cardiac work, a dual gating approach has been proposed. In this study we investigated the physical performance of a new whole body PET/CT scanner with NEMA standard, compared methods for partial volume correction in PET studies of the brain and developed and tested a new robust method for dual cardiac-respiratory gated PET with phantom, animal and human data. Results from performance measurements showed the feasibility of the new scanner design in 2D and 3D whole body studies. Partial volume was corrected, but there is no best method among those tested as the correction also depends on the radiotracer and its distribution. New methods need to be developed for proper correction. The dual gating algorithm generated is shown to handle dual-gated data, preserving quantification and clearly eliminating the majority of contraction and respiration movement

Methods to test gas tightness of packages

One of the primary goals for food packages is to protect food against harmful environment, especially oxygen and moisture. The gas transmission rate is the total gas transport through the package, both by permeation through the package material and by leakage through pinholes and cracks. The shelf life of a product can be extended, if the food is stored in a gas tight package. Thus there is a need to test gas tightness of packages. There are several tightness testing methods, and they can be broadly divided into destructive and nondestructive methods. One of the most sensitive methods to detect leaks is by using a non destructive tracer gas technique. Carbon dioxide, helium and hydrogen are the most commonly used tracer gases. Hydrogen is the lightest and the smallest of all gases, which allows it to escape rapidly from the leak areas. The low background concentration of H2 in air (0.5 ppm) enables sensitive leak detection. With a hydrogen leak detector it is also possible to locate leaks. That is not possible with many other tightness testing methods. The experimental work has been focused on investigating the factors which affect the measurement results with the H2leak detector. Also reasons for false results were searched to avoid them in upcoming measurements. From the results of these experiments, the appropriate measurement practice was created in order to have correct and repeatable results. The most important thing for good measurement results is to keep the probe of the detector tightly against the leak. Because of its high diffusion rate, the HZ concentration decreases quickly if holding the probe further away from the leak area and thus the measured H2 leaks would be incorrect and small leaks could be undetected. In the experimental part hydrogen, oxygen and water vapour transmissions through laser beam reference holes (diameters 1 100 μm) were also measured and compared. With the H2 leak detector it was possible to detect even a leakage through 1 μm (diameter) within a few seconds. Water vapour did not penetrate even the largest reference hole (100 μm), even at tropical conditions (38 °C, 90 % RH), whereas some O2 transmission occurred through the reference holes larger than 5 μm. Thus water vapour transmission does not have a significant effect on food deterioration, if the diameter of the leak is less than 100 μm, but small leaks (5 100 μm) are more harmful for the food products, which are sensitive to oxidation.

Small scale energy production in Helsinki Metropolitan area in emission trading point of view

Emission trading with greenhouse gases and green certificates are part if the climate policy the main target of which is reduce greenhouse gas emissions. The carbon dioxide and fine particle emissions of energy production in Helsinki Metropolitan area are calculated in this study. The analysis is made mainly by district heating point of view and the changes of the district heating network are assessed. Carbon dioxide emissions would be a bit higher, if the district heating network is expanded, but then the fine particle emissions would be much lower. Carbon dioxide emissions are roughly 10 % higher, if the district heating network is expanded at same rate as it has in past five years in the year 2030. The expansion of district heating network would decrease the fine particle emissions about 40 %. The cost of the expansion is allocated to be reduction cost of the fine particle emissions, which is considerably higher than the traditional reduction methods costs. The possible new nuclear plant would reduce the emissions considerably and the costs of the nuclear plant would be relatively low comparing the other energy production methods.

Separation of Gas Bubbles from Circulation Waters and Pulp Suspensions in Open Channel Flow

The objective of this thesis was to study the removal of gases from paper mill circulation waters experimentally and to provide data for CFD modeling. Flow and bubble size measurements were carried out in a laboratory scale open gas separation channel. Particle Image Velocimetry (PIV) technique was used to measure the gas and liquid flow fields, while bubble size measurements were conducted using digital imaging technique with back light illumination. Samples of paper machine waters as well as a model solution were used for the experiments. The PIV results show that the gas bubbles near the feed position have the tendency to escape from the circulation channel at a faster rate than those bubbles which are further away from the feed position. This was due to an increased rate of bubble coalescence as a result of the relatively larger bubbles near the feed position. Moreover, a close similarity between the measured slip velocities of the paper mill waters and that of literature values was obtained. It was found that due to dilution of paper mill waters, the observed average bubble size was considerably large as compared to the average bubble sizes in real industrial pulp suspension and circulation waters. Among the studied solutions, the model solution has the highest average drag coefficient value due to its relatively high viscosity. The results were compared to a 2D steady sate CFD simulation model. A standard Euler-Euler k-ε turbulence model was used in the simulations. The channel free surface was modeled as a degassing boundary. From the drag models used in the simulations, the Grace drag model gave velocity fields closest to the experimental values. In general, the results obtained from experiments and CFD simulations are in good qualitative agreement.

Akustisen emission anturin signaalin esikäsittelypiirin selvittäminen ja prototyypin toteuttaminen

Tämän työn tavoitteena oli selvittää ja toteuttaa esikäsittelypiirin prototyyppi akustisen emission anturin signaalille. Toteutettu esikäsittelypiiri toimii yksipuoleisella käyttöjännitteellä. Työssä käydään läpi esikäsittelypiirin suunnitteluun liittyvät vaiheet laskelmien ja simulaatioiden muodossa. Lisäksi työssä esitetään mittaustulokset esikäsittelypiirin toiminnasta.

A study of combustion phenomena in circulating fluidized beds by developing and applying experimental and modelling methods for laboratory-scale reactors

The results shown in this thesis are based on selected publications of the 2000s decade. The work was carried out in several national and EC funded public research projects and in close cooperation with industrial partners. The main objective of the thesis was to study and quantify the most important phenomena of circulating fluidized bed combustors by developing and applying proper experimental and modelling methods using laboratory scale equipments. An understanding of the phenomena plays an essential role in the development of combustion and emission performance, and the availability and controls of CFB boilers. Experimental procedures to study fuel combustion behaviour under CFB conditions are presented in the thesis. Steady state and dynamic measurements under well controlled conditions were carried out to produce the data needed for the development of high efficiency, utility scale CFB technology. The importance of combustion control and furnace dynamics is emphasized when CFB boilers are scaled up with a once through steam cycle. Qualitative information on fuel combustion characteristics was obtained directly by comparing flue gas oxygen responses during the impulse change experiments with fuel feed. A one-dimensional, time dependent model was developed to analyse the measurement data Emission formation was studied combined with fuel combustion behaviour. Correlations were developed for NO, N2O, CO and char loading, as a function of temperature and oxygen concentration in the bed area. An online method to characterize char loading under CFB conditions was developed and validated with the pilot scale CFB tests. Finally, a new method to control air and fuel feeds in CFB combustion was introduced. The method is based on models and an analysis of the fluctuation of the flue gas oxygen concentration. The effect of high oxygen concentrations on fuel combustion behaviour was also studied to evaluate the potential of CFB boilers to apply oxygenfiring technology to CCS. In future studies, it will be necessary to go through the whole scale up chain from laboratory phenomena devices through pilot scale test rigs to large scale, commercial boilers in order to validate the applicability and scalability of the, results. This thesis shows the chain between the laboratory scale phenomena test rig (bench scale) and the CFB process test rig (pilot). CFB technology has been scaled up successfully from an industrial scale to a utility scale during the last decade. The work shown in the thesis, for its part, has supported the development by producing new detailed information on combustion under CFB conditions.