Kaarihitsauksen suojakaasun tunnistus ja virtauksen mittaus ultraäänellä

Kaasukaarihitsauksessa suojakaasuna käytetään yleensä argonin ja hiilidioksidin tai argonin ja heliumin seoksia. Suojakaasu vaikuttaa useisiin hitsausominaisuuksiin, jotka puolestaan vaikuttavat hitsauksen laatuun ja tuottavuuteen. Automaattisella suojakaasun tunnistuksella ja virtausmäärän mittauksella voitaisiin tehdä hitsauksesta paitsi käyttäjän kannalta yksinkertaisempaa, myös laadukkaampaa. Työn tavoite on löytää mahdollisimman edullinen ja kuitenkin mahdollisimman tarkasti kaasuseoksia tunnistava menetelmä, jota voitaisiin hyödyntää MIG/MAG-hitsauskoneeseen sisäänrakennettuna. Selvä etu on, jos menetelmällä voidaan mitata myös kaasun virtausmäärä. Äänennopeus kaasumaisessa väliaineessa on aineen atomi- ja molekyylirakenteesta ja lämpötilasta riippuva ominaisuus, joka voidaan mitata melko edullisesti. Äänennopeuden määritys perustuu ääniaallon kulkuajan mittaamiseen tunnetun pituisella matkalla. Kaasun virtausnopeus on laskettavissa myötä- ja vastavirtaan mitattujen kulkuaikojen erotuksen avulla. Rakennettu mittauslaitteisto koostuu kahdesta ultraäänimuuntimesta, joiden halkaisija on 10 mm ja jotka toimivat sekä lähettimenä että vastaanottimena. Muuntimet ovat 140 mm:n etäisyydellä toisistaan virtauskanavassa, jossa suojakaasu virtaa yhdensuuntaisesti äänen kanssa. Virtauskanava on putki, jossa on käytetty elastisia materiaaleja, jotta ääniaaltojen eteneminen kanavan runkoa pitkin minimoituisi. Kehitetty algoritmi etsii kahden lähetetyn 40 kHz:n taajuisen kanttiaaltopulssin aiheuttaman vasteen perusteella ääniaallon saapumisajanhetken. Useiden mittausten, tulosten lajittelun ja suodatuksen jälkeen tuntemattomalle kaasulle lasketaan lämpötilakompensoitu vertailuluku. Tuntematon kaasu tunnistetaan vertailemalla lukua tunnettujen kaasuseosten mitattuihin vertailulukuihin. Laitteisto tunnistaa seokset, joissa heliumin osuus argonissa on enintään 50 %. Hiilidioksidia sisältävät argonin seokset puolestaan tunnistetaan puhtaaseen hiilidioksidiin asti jopa kahden prosenttiyksikön tarkkuudella. Kaasun tilavuusvirtausmittauksen tarkkuus on noin 1,0 l/min.

Arvometallien liuospuhdistus jatkuvatoimisella ioninvaihdolla

Työn tarkoituksena oli tutkia arvometalleja sisältävän liuoksen puhdistamista jat-kuvatoimisella ioninvaihdolla. Teoriaosassa käsitellään ioninvaihdon periaate, sekä jatkuvatoimisen ioninvaihdon laiteratkaisuja ristivirta- ja vastavirtasysteemeissä. Lopuksi esitellään Simuloidun liikkuvapedin (SMB) virtausnopeuksien laske-miseksi käytettävä kolmiomenetelmä. Kokeellisen osan tarkoituksena on demonstroida laboratorioon rakennetun jatku-vatoimisen ioninvaihtimen, Simuloidun liikkuvapedin, käyttö arvometallia sisäl-tävän liuoksen puhdistamiseksi kahdenarvoisista metalli-ioneista. Kokeissa käy-tettiin hopeaa sisältävää NaCl-liuosta, josta pyrittiin puhdistamaan Mg2+, Ca2+, Pb2+ ja Zn2+-ionit ekstraktina. Laitteistolla suoritettiin kolme ajoa, joista kaksi edusti vastavirtasysteemiä ja yksi ristivirtasysteemiä. Ensimmäisessä vastavirta-ajossa sekä ekstrakti että raffinaattin erottuva hopealiuos tulivat puhtaina. Toisessa vastavirta-ajossa pyrittiin parantamaan tuottavuutta nostamalla syötön virtausnopeutta, jolloin raffinaatin puhtaus kärsi Pb2+ ja Mg2+-ionien kulkeutuessa liuosfaasin mukana raffinaattiin. Ristivirta-ajossa vain yksi kolmesta raffinaatista saavutti 100 % puhtauden. Kokeet osoittivat, että Mg2+, Ca2+, Pb2+ ja Zn2+-ionien erottaminen hopeaionista on mahdollista käyttämällämme SMB-laitteistolla. Tuottavuuden parantaminen syötön virtausnopeutta nostamalla kuitenkin heikentää puhtautta. Cross-flow-systeemin erilleenkytkettyjen kolonnien ansioista painehäviö on pienempi, mikä mahdollistaa korkeammat virtausnopeudet, mikäli ei vaadita 100 % puhtautta.

Comparison of Biomass Gasification Technologies for Natural Gas Substitution in Iron Ore Pelletizing Plants

The iron ore pelletizing process consumes high amounts of energy, including nonrenewable sources, such as natural gas. Due to fossil fuels scarcity and increasing concerns regarding sustainability and global warming, at least partial substitution by renewable energy seems inevitable. Gasification projects are being successfully developed in Northern Europe, and large-scale circulating fluidized bed biomass gasifiers have been commissioned in e.g. Finland. As Brazil has abundant biomass resources, biomass gasification is a promising technology in the near future. Biomasses can be converted into product gas through gasification. This work compares different technologies, e.g. air, oxygen and steam gasification, focusing on the use of the product gas in the indurating machine. The use of biosynthetic natural gas is also evaluated. Main parameters utilized to assess the suitability of product gas were adiabatic flame temperature and volumetric flow rate. It was found that low energy content product gas could be utilized in the traveling grate, but it would require burner’s to be changed. On the other hand, bio-SGN could be utilized without any adaptions. Economical assessment showed that all gasification plants are feasible for sizes greater than 60 MW. Bio-SNG production is still more expensive than natural gas in any case.

Chromatographic recovery of chemicals from acidic biomass hydrolysates

Lignocellulosic biomasses (e.g., wood and straws) are a potential renewable source for the production of a wide variety of chemicals that could be used to replace those currently produced by petrochemical industry. This would lead to lower greenhouse gas emissions and waste amounts, and to economical savings. There are many possible pathways available for the manufacturing of chemicals from lignocellulosic biomasses. One option is to hydrolyze the cellulose and hemicelluloses of these biomasses into monosaccharides using concentrated sulfuric acid as catalyst. This process is an efficient method for producing monosaccharides which are valuable platforn chemicals. Also other valuable products are formed in the hydrolysis. Unfortunately, the concentrated acid hydrolysis has been deemed unfeasible mainly due to high chemical consumption resulting from the need to remove sulfuric acid from the obtained hydrolysates prior to the downstream processing of the monosaccharides. Traditionally, this has been done by neutralization with lime. This, however, results in high chemical consumption. In addition, the by-products formed in the hydrolysis are not removed and may, thus, hinder the monosaccharide processing. In order to improve the feasibility of the concentrated acid hydrolysis, the chemical consumption should be decreased by recycling of sulfuric acid without neutralization. Furthermore, the monosaccharides and the other products formed in the hydrolysis should be recovered selectively for efficient downstream processing. The selective recovery of the hydrolysis by-products would have additional economical benefits on the process due to their high value. In this work, the use of chromatographic fractionation for the recycling of sulfuric acid and the selective recovery of the main components from the hydrolysates formed in the concentrated acid hydrolysis was investigated. Chromatographic fractionation based on the electrolyte exclusion with gel type strong acid cation exchange resins in acid (H+) form as a stationary phase was studied. A systematic experimental and model-based study regarding the separation task at hand was conducted. The phenomena affecting the separation were determined and their effects elucidated. Mathematical models that take accurately into account these phenomena were derived and used in the simulation of the fractionation process. The main components of the concentrated acid hydrolysates (sulfuric acid, monosaccharides, and acetic acid) were included into this model. Performance of the fractionation process was investigated experimentally and by simulations. Use of different process options was also studied. Sulfuric acid was found to have a significant co-operative effect on the sorption of the other components. This brings about interesting and beneficial effects in the column operations. It is especially beneficial for the separation of sulfuric acid and the monosaccharides. Two different approaches for the modelling of the sorption equilibria were investigated in this work: a simple empirical approach and a thermodynamically consistent approach (the Adsorbed Solution theory). Accurate modelling of the phenomena observed in this work was found to be possible using the simple empirical models. The use of the Adsorbed Solution theory is complicated by the nature of the theory and the complexity of the studied system. In addition to the sorption models, a dynamic column model that takes into account the volume changes of the gel type resins as changing resin bed porosity was also derived. Using the chromatography, all the main components of the hydrolysates can be recovered selectively, and the sulfuric acid consumption of the hydrolysis process can be lowered considerably. Investigation of the performance of the chromatographic fractionation showed that the highest separation efficiency in this separation task is obtained with a gel type resin with a high crosslinking degree (8 wt. %); especially when the hydrolysates contain high amounts of acetic acid. In addition, the concentrated acid hydrolysis should be done with as low sulfuric acid concentration as possible to obtain good separation performance. The column loading and flow rate also have large effects on the performance. In this work, it was demonstrated that when recycling of the fractions obtained in the chromatographic fractionation are recycled to preceding unit operations these unit operations should included in the performance evaluation of the fractionation. When this was done, the separation performance and the feasibility of the concentrated acid hydrolysis process were found to improve considerably. Use of multi-column chromatographic fractionation processes, the Japan Organo process and the Multi-Column Recycling Chromatography process, was also investigated. In the studied case, neither of these processes could compete with the single-column batch process in the productivity. However, due to internal recycling steps, the Multi-Column Recycling Chromatography was found to be superior to the batch process when the product yield and the eluent consumption were taken into account.

Influence of reactant absorption and dissolution in heterogeneous precipitation processes

In this research work, the aim was to investigate the volumetric mass transfer coefficient [kLa] of oxygen in stirred tank in the presence of solid particle experimentally. The kLa correlations as a function of propeller rotation speed and flow rate of gas feed were studied. The O2 and CO2 absorption in water and in solid-liquid suspensions and heterogeneous precipitation of MgCO3 were thoroughly examined. The absorption experiments of oxygen were conducted in various systems like pure water and in aqueous suspensions of quartz and calcium carbonate particles. Secondly, the precipitation kinetics of magnesium carbonate was also investigated. The experiments were performed to study the reactive crystallization with magnesium hydroxide slurry and carbon dioxide gas by varying the feed rates of carbon dioxide and rotation speeds of mixer. The results of absorption and precipitation are evaluated by titration, total carbon (TC analysis), and ionic chromatrography (IC). For calcium carbonate, the particle concentration was varied from 17.4 g to 2382 g with two size fractions: 5 µm and 45-63 µm sieves. The kLa and P/V values of 17.4 g CaCO3 with particle size of 5µm and 45-63 µm were 0.016 s-1 and 2400 W/m3. At 69.9 g concentration of CaCO3, the achieved kLa is 0.014 s-1 with particle size of 5 µm and 0.017 s-1 with particle size of 45 to 63 µm. Further increase in concentration of calcium carbonate, i.e. 870g and 2382g , does not affect volumetric mass transfer coeffienct of oxygen. It could be concluded from absorption results that maximum value of kLa is 0.016 s-1. Also particle size and concentration does affect the transfer rate to some extend. For precipitation experiments, the constant concentration of Mg(OH)2 was 100 g and the rotation speed varied from 560 to 750 rpm, whereas the used feed rates of CO2 were 1 and 9 L/min. At 560 rpm and feed rate of CO2 is 1 L/min, the maximum value of Mg ion and TC were 0.25 mol/litre and 0.12 mol/litre with the residence time of 40 min. When flow rate of CO2 increased to 9 L/min with same 560 rpm, the achieved value of Mg and TC were 0.3 mol/litre and 0.12 mol/L with shorter residence time of 30 min. It is concluded that feed rate of CO2 is dominant in precipitation experiments and it has a key role in dissociation and reaction of magnesium hydroxide in precipitation of magnesium carbonate.

Kullan talteenotto takaisinuuttoliuoksista

Työssä tutkittiin kirjallisuuden ja laboratoriomittausten avulla vaihtoehtoja kullan pelkistämiseen ja talteenottoon kultauuton takaisinuuttoliuoksista. Tavoitteena oli löytää menetelmä, jolla saadaan puhdasta kiinteää lopputuotetta ilman kullan häviöitä. Käytettyjä pelkistimiä olivat D-(+)-glukoosi, natriumboorihydridi, L-askorbiinihappo, D-(-)-isoaskorbiinihappo ja aktiivihiili. Laboratoriokokeiden perusteella D-(-)-isoaskorbiinihappo sekä aktiivihiili olivat sopivimmat pelkistimet kokeissa käytetylle kultaliuokselle. Isoaskorbiinihapolla suoritettiin panoskokeita lasireaktorissa eri alku-pH:ssa sekä erilaisilla pelkistimen ja kullan moolisuhteilla. Tulosten perusteella havaittiin pH:n ja pelkistimen ylimäärän vaikuttavan merkittävästi lopputuotteen puhtauteen. Myös redox-potentiaalia säätämällä ja happopesulla pelkistyksen jälkeen voidaan vaikuttaa lopputuotteen puhtauteen. Aktiivihiilellä suoritettiin panoskokeita adsorptiotasapainojen (latausisotermi) ja kinetiikan tutkimiseksi. Hiileen on mahdollista saada kultaa 383 mg/g kuivaa hiiltä. Suurempi lataus voitaisiin saavuttaa käyttämällä hiiltä, jolla on pienempi partikkelikoko. Kolonnikokeita tehtiin eri virtausnopeuksilla. Kolonnikokeissa kullan dynaaminen adsorptiokapasiteetti hiileen odotetusti kasvoi virtausnopeuden laskiessa. Pienin käytetty virtausnopeus oli 2,40 BV/h, jolloin kapasiteetti oli 75,4 mg/g kuivaa hiiltä (c (Au feed) = 129 mg/L). Kullasta voidaan poistaa myös kolonnipelkistyksen jälkeen epäpuhtauksia happopesulla. Isoaskorbiinihapolla pelkistyksen kinetiikka on nopea ja sillä saatiin pelkistettyä puhdasta lopputuotetta. Sekä isoaskorbiinihappo, että aktiivihiili ovat potentiaalisia menetelmiä kullan talteenottoon.

Tandem-MAG-welding of high strength steels for shipbuilding applications

Tämän työn tavoitteena oli hitsata tandem MAG –laitteistolla 25 mm paksua Ruukin E500 TMCP terästä. Työssä oli tarkoituksena vähentää railotilavuutta mahdollisimman paljon sekä suorittaa testihitsaukset 0.8 kJ/mm sekä 2.5 kJ/mm lämmöntuonneilla. Teoriaosuudessa käsiteltiin Tandem MAG-hitsaukseen, sen tuottavuuteen ja laatukysymyksiin liittyviä asioita sekä siinä perehdyttiin suurlujuusteräksien käyttöön hitsauksessa sekä laivanrakennuksessa. Kokeellisessa osuudessa perehdyttiin hitsauksessa huomattuihin etuihin, ongelmiin sekä ongelmien ratkaisumahdollisuuksiin. Hitsausliitoksen mekaaniset ominaisuudet tutkittiin rikkomattomin sekä rikkovin menetelmin. Alustavat hitsausohjeet luotiin kummallekin lämmöntuonnille. Testaukset aloitettiin 30 º railokulmalla pienentäen kulmaa mahdollisuuksien mukaan. Testauksissa ei saatu hitsattua onnistuneesti alle 30 º railokulmalla. Hitsaustestien aikana huomattiin magneettisen puhalluksen vaikutus hitsaustapahtumaan. Kaasunvirtausnopeuden tuli olla tietyn suuruinen jotta palkokerrokset onnistuivat ilman huokoisuusongelmaa. Pienemmällä lämmöntuonnilla hitsattaessa kaasunvirtausnopeudet olivat tärkeämpiä hitsatessa ylempiä palkokerroksia. Kääntämällä hitsauspoltinta sivuttaissuunnassa 7-10 astetta auttoi ehkäisemään reunahaavan syntymistä. Rikkovista menetelmistä testitulokset olivat hyväksyttyjä kaikkien muiden paitsi päittäishitsin sivutaivutuskokeen osalta.

Karboksyylihappojen kromatografinen fraktiointi

Suurin osa alifaattisista karboksyylihapoista tuotetaan nykyään synteettisesti, mutta öljyn hinnan nousu ja ekologisempi ajattelutapa on aiheuttanut kiinnostusta tuottaa näitä karboksyyli- ja hydroksihappoja jatkossa fermentoimalla tai sellun valmistuksen sivuvirtana syntyvästä mustalipeästä. Nykyään mustalipeä poltetaan sellaisenaan soodakattiloissa keittokemikaalien regeneroimiseksi, energiaksi ja sähköksi. Jatkossa mustalipeästä voisi erottaa arvokkaat orgaaniset hapot ennen polttamista. Saadusta happoseoksesta tulisi erottaa yksittäiset alifaattiset karboksyylihapot toisistaan jatkojalostusta varten. Tämän kandidaatintyön tavoitteena oli selvittää, millä kromatografisella erotusmenetelmällä fermentointituotteina ja teollisuuden sivuvirtoina syntyvistä karboksyylihapposeoksista saadaan yksittäiset alifaattiset karboksyylihapot erotettua toisistaan. Mittaukset suoritettiin kolonnilla, jossa hartsipedin halkaisija oli 1,5 cm ja korkeus 15 cm. Kolonnin erototusmateriaaleina kokeiltiin vahvoja ja heikkoja kationinvaihtohartseja, vahvaa anioninvaihtohartsia ja polymeerisiä adsorbentteja. Erotettavaksi happoseokseksi valittiin sitruuna-, viini-, glykoli-, maito- ja etikkahapon seos. Tehokkain erotus saatiin Puroliten valmistamalla Macronet 270:lla, joka on mikrohuokoinen polymeerinen adsorbentti. Macronet 270:lla saatiin erotettua erityisesti viini- ja glykolihappo sitruuna-, maito- ja etikkahaposta. Yksittäisiä happoja ei saatu kuitenkaan kunnolla erotettua. Parhaat koeolosuhteet erotustehokkuuden ja retentioaikojen kannalta saatiin vesieluentin virtausnopeudella 2 mL/min, syöttöpulssin tilavuudella 5 mL ja kolonnin lämpötilassa 75 °C.

Recovery and purification of anthocyanins from purple-blue potato

The aim of this work was to study techniques to extract and purify of anthocyanins from purple-blue potato. This topic was determined as a master’s thesis and it was done in collaboration with the Food Chemistry and Food Development Department of University of Turku and Department of Chemical and Process Engineering at Lappeenranta University of Technology. At first, purple-blue potatoes were pretreated in four types of boiled, raw, freeze-dried and dried boiled potato for extraction. They were mixed with aqueous acidified ethanol (ethanol:water:acetic acid 40%:53%:7% v/v) for conventional extraction. Boiled potato was selected as a best pretreated potato. Different ethanol concentration and extraction time were examined and the mixture of 80% in 24 h resulted in maximum anthocyanin content (132.23 mg/L). As conventional extraction method of anthocyanins was non-selective, some of impurities such as free sugars might accelerate anthocyanin degradation. Therefore, to obtain anthocyanins in purified form, adsorption as a promising selective method was used to recovery and isolate anthocyanins. It was carried out with six adsorbents. Among those, Amberlite XAD-7HP, a nonionic acrylic ester adsorbent, was found to have the best performance. In an adsorption column, flow rate of 3 mL/min was selected as the loading flow rate among four tested flow rates. Eluent volume and flow rate were 3 BV of aqueous acidified ethanol (75%, v/v) and 1 mL/min for desorption. The quantification of the total anthocyanin contents was performed by pH-differential method using UV-vis spectrophotometer. The resulting anthocyanin solution after purification was almost free from free sugars which were the major cause for degradation of anthocyanins. The average anthocyanin concentration in the purified and concentrated sample was obtained 1752.89 mg/L.

Development of laboratory exercises for basic nuclear thermal hydraulics measurements

The thesis focuses on light water reactors (pressurized water reactors, boiling water reactors) and measurement techniques for basic thermal hydraulics parameters that are used in a nuclear power plant. The goal of this work is a development of laboratory exercises for basic nuclear thermal hydraulics measurements.

Antitromboottisten lääkeaineiden enantiomeerien kromatografinen fraktiointi

Suuri osa käytössä olevista lääkeaineista on kiraalisia yhdisteitä. Lääkevalmisteet sisältävät yhdisteen enantiomeerien ominaisuuksista riippuen joko yksittäistä enantiomeeria tai näiden seosta. Antitromboottisiin eli veren hyytymistä estäviin lääkeaineisiin kuuluvat varfariini ja rivaroksabaani ovat kiraalisia yhdisteitä, joiden enantiomeerien ominaisuudet poikkeavat antitromboottisen vaikutuksen voimakkuuden suhteen. Varfariinia käytetään kliinisesti enantiomeeriensa raseemisena seoksena, kun taas rivaroksabaani on käytössä lääkevalmisteena puhtaana S-enantiomeerinaan. Lääkeaineen enantiomeerien erottaminen toisistaan on tärkeää esimerkiksi enantiomeerien puhdistamiseksi, lääkevalmisteen oikean koostumuksen varmistamiseksi tai yksittäisten enantiomeerien käyttäytymisen arvioimiseksi elimistössä. Tässä kirjallisuustyössä käsiteltiin nestekromatografian käyttöä antitromboottisiin lääkeaineisiin kuuluvien antikoagulanttien enantiomeerien fraktioinnissa. Kirjallisuudesta saadun tiedon perusteella arvioitiin, millä erotusmateriaaleilla ja millaisissa koeolosuhteissa varfariinin sekä rivaroksabaanin enantiomeerit tulisi erottaa toisistaan. Varfariinin enantiomeerien erotukseen parhaiten sopivaksi erotusmateriaaliksi todettiin kirjallisuuden perusteella kiraalinen vankomysiinipohjainen stationaarifaasi (Chirobiotic V) metanolin, etikkahapon ja veden seoksen toimiessa eluenttina. Eluentin virtausnopeudella 0,3 mL/min ja pienellä injektiotilavuudella varfariinin enantiomeerit saatiin erottumaan täydellisesti ja nopeasti toisistaan. Kirjallisuuden perusteella rivaroksabaanin enantiomeerien erotuksessa erotusmateriaalina toimii parhaiten kiraalinen selluloosapohjainen stationaarifaasi (Chiralcel OD-RH), kun eluenttina käytetään n-heksaanin ja isopropanolin seosta virtausnopeudella 1 mL/min. Varfariinin ja rivaroksabaanin enantiomeerien fraktiointiin parhaiten sopivia menetelmiä voidaan käyttää eri tilanteissa, kuten lääkevalmisteiden laadunvarmistuksessa tai enantiomeerien erotuksessa niiden synteesin jälkeen.

A reaction engineering approach to homogeneously catalyzed glycerol hydrochlorination

The production of biodiesel through transesterification has created a surplus of glycerol on the international market. In few years, glycerol has become an inexpensive and abundant raw material, subject to numerous plausible valorisation strategies. Glycerol hydrochlorination stands out as an economically attractive alternative to the production of biobased epichlorohydrin, an important raw material for the manufacturing of epoxy resins and plasticizers. Glycerol hydrochlorination using gaseous hydrogen chloride (HCl) was studied from a reaction engineering viewpoint. Firstly, a more general and rigorous kinetic model was derived based on a consistent reaction mechanism proposed in the literature. The model was validated with experimental data reported in the literature as well as with new data of our own. Semi-batch experiments were conducted in which the influence of the stirring speed, HCl partial pressure, catalyst concentration and temperature were thoroughly analysed and discussed. Acetic acid was used as a homogeneous catalyst for the experiments. For the first time, it was demonstrated that the liquid-phase volume undergoes a significant increase due to the accumulation of HCl in the liquid phase. Novel and relevant features concerning hydrochlorination kinetics, HCl solubility and mass transfer were investigated. An extended reaction mechanism was proposed and a new kinetic model was derived. The model was tested with the experimental data by means of regression analysis, in which kinetic and mass transfer parameters were successfully estimated. A dimensionless number, called Catalyst Modulus, was proposed as a tool for corroborating the kinetic model. Reactive flash distillation experiments were conducted to check the commonly accepted hypothesis that removal of water should enhance the glycerol hydrochlorination kinetics. The performance of the reactive flash distillation experiments were compared to the semi-batch data previously obtained. An unforeseen effect was observed once the water was let to be stripped out from the liquid phase, exposing a strong correlation between the HCl liquid uptake and the presence of water in the system. Water has revealed to play an important role also in the HCl dissociation: as water was removed, the dissociation of HCl was diminished, which had a retarding effect on the reaction kinetics. In order to obtain a further insight on the influence of water on the hydrochlorination reaction, extra semi-batch experiments were conducted in which initial amounts of water and the desired product were added. This study revealed the possibility to use the desired product as an ideal “solvent” for the glycerol hydrochlorination process. A co-current bubble column was used to investigate the glycerol hydrochlorination process under continuous operation. The influence of liquid flow rate, gas flow rate, temperature and catalyst concentration on the glycerol conversion and product distribution was studied. The fluid dynamics of the system showed a remarkable behaviour, which was carefully investigated and described. Highspeed camera images and residence time distribution experiments were conducted to collect relevant information about the flow conditions inside the tube. A model based on the axial dispersion concept was proposed and confronted with the experimental data. The kinetic and solubility parameters estimated from the semi-batch experiments were successfully used in the description of mass transfer and fluid dynamics of the bubble column reactor. In light of the results brought by the present work, the glycerol hydrochlorination reaction mechanism has been finally clarified. It has been demonstrated that the reactive distillation technology may cause drawbacks to the glycerol hydrochlorination reaction rate under certain conditions. Furthermore, continuous reactor technology showed a high selectivity towards monochlorohydrins, whilst semibatch technology was demonstrated to be more efficient towards the production of dichlorohydrins. Based on the novel and revealing discoveries brought by the present work, many insightful suggestions are made towards the improvement of the production of αγ-dichlorohydrin on an industrial scale.

Variable-speed-drive-based detection methods for problems in fluid handling systems

Fluid handling systems account for a significant share of the global consumption of electrical energy. They also suffer from problems, which reduce their energy efficiency and increase life-cycle costs. Detecting or predicting these problems in time can make fluid handling systems more environmentally and economically sustainable to operate. In this Master’s Thesis, significant problems in fluid systems were studied and possibilities to develop variable-speed-drive-based detection methods for them was discussed. A literature review was conducted to find significant problems occurring in fluid handling systems containing pumps, fans and compressors. To find case examples for evaluating the feasibility of variable-speed-drive-based methods, queries were sent to industrial companies. As a result of this, the possibility to detect heat exchanger fouling with a variable-speed drive was analysed with data from three industrial cases. It was found that a mass flow rate estimate, which can be generated with a variable speed drive, can be used together with temperature measurements to monitor a heat exchanger’s thermal performance. Secondly, it was found that the fouling-related increase in the pressure drop of a heat exchanger can be monitored with a variable speed drive. Lastly, for systems where the flow device is speed controlled with by a pressure measurement, it was concluded that increasing rotational speed can be interpreted as progressing fouling in the heat exchanger.

Failure modes of passive decay heat removing safety systems of modern nuclear power plants

The purpose of this master’s thesis is to gain an understanding of passive safety systems’ role in modern nuclear reactors projects and to research the failure modes of passive decay heat removal safety systems which use phenomenon of natural circulation. Another purpose is to identify the main physical principles and phenomena which are used to establish passive safety tools in nuclear power plants. The work describes passive decay heat removal systems used in AES-2006 project and focuses on the behavior of SPOT PG system. The descriptions of the main large-scale research facilities of the passive safety systems of the AES-2006 power plant are also included. The work contains the calculations of the SPOT PG system, which was modeled with thermal-hydraulic system code TRACE. The dimensions of the calculation model are set according to the dimensions of the real SPOT PG system. In these calculations three parameters are investigated as a function of decay heat power: the pressure of the system, the natural circulation mass flow rate around the closed loop, and the level of liquid in the downcomer. The purpose of the calculations is to test the ability of the SPOT PG system to remove the decay heat from the primary side of the nuclear reactor in case of failure of one, two, or three loops out of four. The calculations show that three loops of the SPOT PG system have adequate capacity to provide the necessary level of safety. In conclusion, the work supports the view that passive systems could be widely spread in modern nuclear projects.