Investointiprosessin kehittäminen: Toimitila- ja yhdyskuntarakentamisinvestointikohteiden laadinta ja toteuttaminen Porin kaupungissa

Julkinen sektori on muutosten edessä, mikä pakottaa kunnat luopumaan vanhoista toimintatavoista. Kuntien taloudellinen tila on heikko, ja samaan aikaan odotukset sekä tarpeet kuntien toimintaa kohtaan ovat kasvaneet pakottaen kunnat seuraamaan yksityisen sektorin esimerkkiä ja siirtymään organisaatiomaisesta ajattelusta prosessimaiseen ajatteluun. Prosessimainen ajattelu tarkastelee toimintaa tehtävien ja toimintojen kokonaisuutena, jossa asioita tarkastellaan toiminnan näkökulmasta. Tällöin organisaatiosta pyritään poistamaan sisäiset tehtävänjaot, ja koko organisaatio toimii yhteisten päämäärien hyväksi. Organisaatiolla on olemassa yksi tai useampi ydinprosessi, joiden vuoksi se on olemassa. Ydinprosesseja on tukemassa yhtä tärkeät tukiprosessit, joiden tehtävänä on auttaa ydinprosessien toteuttamisessa. Tämän tutkimuksen tarkoituksena on kehittää toimintaa prosessimaisesta näkökulmasta ja osaltaan edesauttaa kohdeorganisaation muutosta organisaatiokeskeisestä ajattelusta prosessimaiseen ajatteluun. Tutkimuksen kohdeorganisaationa toimii Porin kaupungin teknisiä palveluita tarjoava Tekninen palvelukeskus, ja tutkimuksen kohteena ovat toimitila- ja yhdyskuntarakentamisinvestoinnit. Tarkoituksena on kuvata nykyiset toimintatavat ja mallintaa ne prosessikuvauksina, joiden pohjalta toiminnan eri osia tarkastellaan kriittisesti. Tällaisen prosessimaisen kehittämisen tarkoituksena ei ole arvioida yksilöiden suorituksia tai ammattitaitoa, vaan tarkoituksena on arvioida muun muassa toiminnan järkevyyttä ja päällekkäisyyttä. Tutkimus noudattaa laadullisen tapaustutkimuksen menetelmiä, ja tietoa kerätään pääosin vapaamuotoisilla haastatteluilla. Tutkimus tuo ilmi toiminnassa piileviä ongelmia ja niille kehitystoimenpide-ehdotuksia. Prosessi ei itsessään juurikaan muutu, mutta siinä tapahtuu paljon toiminnan järkeistämistä, kuten esimerkiksi olemassa olevien tietoteknisten järjestelmien parempaa hyödyntämistä ja joidenkin toimijoiden roolien selventämistä. Organisaation koko toiminta kannattaa käydä läpi prosessimaisen kehittämisen mukaisesti, sillä jo pelkästään prosessien kuvaamisen avulla voidaan kehittää organisaatiota.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Puhdistamotoimintaa ja viemäröintiä koskeva riskinhallintasuunnitelma

Opinnäytetyön aiheena oli puhdistamotoimintaa ja viemäröintiä koskeva riskinhallintasuunnitelma. Riskinhallintasuunnitelma koskee Porin Veden jätevesitoimintaa ja määräys riskinhallintasuunnitelmasta on tullut Länsi-Suomen ympäristölupavirastolta. Riskinhallintasuunnitelmassa selvitettiin jätevedenpuhdistamoiden ja viemäriverkoston mahdolliset riskit, mahdolliset seuraukset riskin toteutuessa, syyt riskin toteutumiseen, nykyinen ohjaus, riskin vakavuus toteutuessaan, riskin toteutumisen todennäköisyys, riskin havaitsemisen todennäköisyys, kuinka suuri riski todellisuudessa on ja suositeltavat toimenpiteet riskin toteutumisen välttämiseksi. Riskinhallintasuunnitelma toteutettiin Vika- ja vaikutusanalyysilla (Failure Mode and Effects Analyses, FMEA). Opinnäytetyö saavutti sille asetetut tavoitteet ja tämän riskinhallintasuunnitelman avulla Porin Vesi voi kartoittaa riskejä, arvioida riskien vakavuutta ja kohdistaa tehtävät toimenpiteet oikeisiin kohteisiin.The purpose of this thesis was to establish a risk management plan related to wastewater treatment plant and sewerage. The risk management plan concerns the wastewater treatment of Porin Vesi. The order to establish a risk management plan has come from the Environmental Permit Authorities of Western Finland. The risk management plan determined the potential failure modes of waste-water treatment plants and sewerages, the possible effects of failure, the causes of failure, the current process, the severity of the risks, the occur-rence of the risks, the detection of the risks, the seriousness of the risks and recommended actions to avoid the risks. The risk management plan was implemented by Failure Mode and Effects Analyses (FMEA). This thesis reached its goals and Porin Vesi can scan the risks, estimate the seriousness of the risks and aim the operations to the right targets with this risk management plan

Modelling of supersonic top lance and the heat-up stage of the CAS-OB process

Abstract The CAS-OB (composition adjustment by sealed argon bubbling - oxygen blowing) process is used in secondary steelmaking to adjust the composition and temperature of the steel melt. The steel melt can be heated by oxidizing aluminium in process which feeds aluminium particles and oxygen to the melt surface. Oxygen is in fed by a top lance, which is an important part of many metallurgical processes and is typically used to deliver oxygen to steel melt surface by supersonic blowing. Because observing and measuring the metallurgical processes is challenging due to the high temperature, numerical models predicting the processes are especially important. In this thesis, both top lances and the heat-up stage of the CAS-OB process were studied, and numerical models were constructed. CFD (computational fluid dynamics) were used to study top lances. A turbulence model was adjusted for supersonic flows with experimental data from literature. The CAS-OB process model involves chemical reactions and fluid flows. In order to keep the computation times reasonable, a full fluid flow calculation is not included in the model but is calculated in advance. Heat and mass transfer correlations are calculated with CFD, and the results are then used in the process simulation model. Chemical reactions are calculated based on the law of mass action and thermodynamics. The results were validated with industrial measurements. The CAS-OB heat-up stage model can be used in its current state in process development, and in the future for online control of the process. The CFD model for the top lance can be applied to a lance in any other process.Tiivistelmä CAS-OB-prosessia (composition adjustment by sealed argon bubbling - oxygen blowing) käytetään teräksen valmistuksessa sulan teräksen koostumuksen ja lämpötilan säätämiseen. Terässulaa voidaan tarvittaessa lämmittää syöttämällä alumiinikappaleita ja happea sulan pinnalle. Hapen syöttö tapahtuu yliäänilanssilla, jota käytetään monissa metallurgisissa prosesseissa, yleensä toimittamaan happea sulan pinnalle yliäänisellä puhalluksella. Metallurgisten prosessien havainnointi ja mittaaminen ovat haastavia korkeiden lämpötilojen vuoksi, joten numeeriset mallit ovat erityisen tärkeitä prosessien ennustamisessa. Tässä työssä on tutkittu yliäänilansseja ja CAS-OB-prosessin lämmitysvaihetta ja luotu niille numeeriset mallit. Yliäänilanssien tutkimiseen käytettiin numeerista virtauslaskentaa (CFD, computational fluid dynamics). Lanssien mallinnusta varten olemassa olevaa turbulenssimallia muokattiin paremmin yliäänivirtausta kuvaavaksi kirjallisuudesta löytyvän mittaustiedon perusteella. CAS-OB-prosessimallissa huomioidaan virtaus ja kemialliset reaktiot. Koska laskenta-ajat haluttiin pitää käytännöllisinä, virtauslaskentaa ei suoriteta mallissa, vaan se tehdään etukäteen. Aineen- ja lämmönsiirtokertoimet lasketaan CFD-laskennalla, ja tuloksia käytetään prosessimallissa. Kemialliset reaktiot lasketaan perustuen massavaikutuksen lakiin ja termodynamiikkaan. CAS-OB-mallin tulokset on validoitu terästehtaalla tehtyjen kokeiden perusteella. Mallia voidaan käyttää nykyisessä muodossaan prosessin kehityksessä ja tulevaisuudessa myös prosessin ohjauksessa. Yliäänilanssin CFD-mallia voidaan soveltaa myös muihin metallurgisiin prosesseihin

An Improved Model for the Heat-Up Stage of the CAS-OB Process

Details of chemical heating in the CAS-OB process are not known exactly, making a computational model valuable in process development and control. A phenomena-based numerical model of the CAS-OB heating stage is presented. Chemical equilibrium at reaction surfaces is assumed to be limited by mass transfer. Making use of a law of mass action based kinetic approach, reactions, and mass transfer rates are solved simultaneously. Computational fluid dynamics is used to derive heat and mass transfer coefficients, which are then used in our model, consisting of only a few computational nodes. The model includes steel melt, slag, and gas phases, bell, and ladle structures, and three reaction fronts. Radiation, conduction, and convection heat transfer are solved in the system. The model outputs temperatures and chemical composition of the system, and the results are validated with industrial data from two measurement campaigns.Peer reviewe

Law of Mass Action Based Kinetic Approach for the Modelling of Parallel Mass Transfer Limited Reactions: Application to Metallurgical Systems

The objective of this paper was to present a new law of mass action based rate expression for mass transfer limited reversible reactions. A simple reaction model was derived for parallel oxidation of silicon,chromium and carbon under conditions relevant to the argon-oxygen decarburization (AOD) process. Our hypothesis is that when the forward rate coefficients approach infinite values, the composition at the reaction surface approaches a constrained equilibrium. In numerical analysis, however, only finite numbers are allowed and therefore only finite values are accepted for rate coefficients. In order to circumvent this problem, additional residual affinity constraints were introduced. This assures that the affinities of all the reactions at the reaction front reach a pre-defined non-zero residual affinity and the rate coefficients remain finite. The calculated equilibrium composition is essentially the same as that obtained with the equilibrium coefficient method. In the case of effective gas side mass transfer, the component having the highest mole fraction or the highest mass transfer rate on the liquid side consumes most of the oxygen. When the gas side mass transfer rate is decreased, the mass transfer rate of oxygen begins to limit the overall rate and the partial pressure of oxygen at the reaction interface decreases. Then, the role of interfacial equilibrium becomes important as the species start to compete for the oxygen. The proposed method provides a transparent and direct solution of the mass transfer limited reaction rates and is thus suitable for process simulators and CFD software.Peer reviewe

Numerical study of multiphase flows in a ladle for different closure models

Abstract Computational Fluid Dynamics (CFD) modelling is increasingly being used for studying various metallurgical processes. In secondary steelmaking, gas stirring is used in ladles to enhance the mixing of the steel. This work aims at numerical study to investigate the effect of different closure models on of the flow analysis in a two-phase gas-stirred ladle. The study represents a cylindrical geometry, in which liquid Wood’s metal represents the liquid metal phase and nitrogen gas is injected through nozzle located centrically or eccentrically at the bottom of the vessel. Three-dimensional CFD simulations were carried out using the commercial software package ANSYS FLUENT using Euler-Euler multi-phase model. To study the influence of turbulence models on the accuracy of the CFD analysis, three different models Standard k-ε, k-ω and Reynolds Stress Model (RSM) were employed. Furthermore, four different gas flow rates (100, 200, 500 and 800 cm3/s) were used for studying the effect of gas flow rates on the flow velocities. The simulation results were compared with the available experimental data of the liquid velocity profiles, volume fraction of gas and turbulent kinetic energy at different heights in the ladle. The RSM model showed a good accuracy of results when compared to experimental results, but it requires more computational time when compared to other turbulence models. The simulation results using the liquid Wood’s metal/nitrogen system were compared to water/air and liquid steel/argon systems to check the effect of material properties on the flow velocities in the ladle. The results provide useful guidelines for numerical modelling of fluid flows in steelmaking ladles and suggest that the RSM turbulence model is better suited for studying gas injection in metallurgical ladles than k-ε or k-ω models

A mathematical model for reactions during top-blowing in the AOD process:validation and results

Abstract In earlier work, a fundamental mathematical model was proposed for side-blowing operation in the argon oxygen decarburization (AOD) process. In the preceding part “Derivation of the Mode,” a new mathematical model was proposed for reactions during top-blowing in the AOD process. In this model it was assumed that reactions occur simultaneously at the surface of the cavity caused by the gas jet and at the surface of the metal droplets ejected from the metal bath. This paper presents validation and preliminary results with twelve industrial heats. In the studied heats, the last combined-blowing stage was altered so that oxygen was introduced from the top lance only. Four heats were conducted using an oxygen–nitrogen mixture (1:1), while eight heats were conducted with pure oxygen. Simultaneously, nitrogen or argon gas was blown via tuye’res in order to provide mixing that is comparable to regular practice. The measured carbon content varied from 0.4 to 0.5 wt pct before the studied stage to 0.1 to 0.2 wt pct after the studied stage. The results suggest that the model is capable of predicting changes in metal bath composition and temperature with a reasonably high degree of accuracy. The calculations indicate that the top slag may supply oxygen for decarburization during top-blowing. Furthermore, it is postulated that the metal droplets generated by the shear stress of top-blowing create a large mass exchange area, which plays an important role in enabling the high decarburization rates observed during top-blowing in the AOD process. The overall rate of decarburization attributable to top-blowing in the last combined-blowing stage was found to be limited by the mass transfer of dissolved carbon

A mathematical model for reactions during top-blowing in the AOD process:derivation of the model

Abstract In an earlier work, a fundamental mathematical model was proposed for side-blowing operation in the argon–oxygen decarburization (AOD) process. The purpose of this work is to present a new model, which focuses on the reactions during top-blowing in the AOD process. The model considers chemical reaction rate phenomena between the gas jet and the metal bath as well as between the gas jet and metal droplets. The rate expressions were formulated according to a law of mass action-based method, which accounts for the mass-transfer resistances in the liquid metal, gas, and slag phases. The generation rate of the metal droplets was related to the blowing number theory. This paper presents the description of the model, while validation and preliminary results are presented in the second part of this work