I strävan efter att minska textilindustrins omfattande miljöpåverkan utvecklas nya metoder för textilåtervinning. Idag återvinns bomullstyg av Renewcell på deras anläggning i Kristinehamn. Den återvunna produkten, Circulose®, är en dissolvingmassa som kan användas för att spinna nya viskosfibrer som man i sin tur kan använda för att göra nya kläder. Föreliggande arbete är en förstudie om möjligheten att optimera Renewcellls återvinningsprocess. Arbetet inkluderar en optimering av massaprocessen vilket resulterar i en mer effektiv process som minskar förbrukningen av processkemikalier. / To reduce the extensive environmental impact of the textile industry, new methods for textile recycling are being developed. Today, cotton-based fabric is recycled by Renewcell at their facility in Kristinehamn. The recycled product, Circulose®, is a dissolving pulp that can be used to spin new viscose fibers, which in turn can be used to make new clothes. The present work is a feasibility study on the possibility of optimizing Renewcell's recycling process. The work includes an optimization of the pulp process, which results in a more efficient process with a reduced consumption of process chemicals.

Avloppsreningsanläggningar är idag utformade för att rena bort föroreningar i form av organiskt material, suspenderade fasta ämnen och växtnäringsämnen (exempelvis fosfater och nitrater). Myndighet i Sverige har satt upp restriktioner och lagar gällande hur mycket av de olika föroreningarna som det är okej att utgående vatten innehåller. En typ av föroreningar som dock inte blivit undersökt och som inte har lika tydliga restriktioner och utsläppslagar är utsläpp av läkemedelsrester och aktiva läkemedelssubstanser. Den största andelen av läkemedelsrester som återfinns i avloppsvatten är på grund av mänsklig konsumtion. Människan har under evolutionen alltid strävat efter att hitta nya metoder för att leva längre, må bra och undvika smärta. Under de senaste årtiondena har konsumtionen av läkemedel ökat, detta på grund av behandling av åldersrelaterade och kroniska sjukdomar, i kombination med en ändrad och mer generös receptutskrivning från sjukhusen.  Läkemedlen som vi konsumerar kommer inte att brytas ner helt av våra kroppar, och restprodukterna kommer utsöndras vida urinen. Urinen kommer sedan, vi avloppen, komma till ett av de lokala avloppsreningsverken, som idag inte har förmåga att rena bort de aktiva läkemedelssubstanserna från vattnet. Det kommer sedan att påverka omgivande vattendrag, djurliv och på lång sikt även ekosystemen.  Tidigare studier har genomförts med syfte att hitta miljövänliga och hållbara metoder för att rena vattnet från mikroföroreningar och läkemedelsrester. En av teknikerna som undersökts är oxidation och adsorption processer. Ett sätt att genomföra oxidation är genom ozonering, som genom sin höga oxidationspotential och miljövänliga slutprodukter i form av bland annat syre gör den till ett miljövänligt alternativ. Vad gäller adsorption processer så är aktivt kol en av de vanligaste teknikerna som används idag och det har visat på goda resultat. Ett vanligt förekommande problem med aktiva kolfilter är att det måste bytas ut när det blivit mättade vilket både kostar pengar, arbetskostnader och en avstannad vattenprocess.  Denna avhandling behandlar utvärdering och process optimering av vattenrening vid behandling av ozon med avseende att rena vatten från aktiva läkemedelssubstanser. För att göra detta har två pilotanläggningar för vattenrening, placerade på två olika platser i Sverige (plats 1 och plats 2) undersökts och optimerats. Båda systemen är utrustade med ett sandfiltersteg, ozonerigssteg anst ett avslutade poleringssteg i form av aktivkolbädd. De två olika systemen är kopplade så inkommande vatten är utgående vatten från likat avloppsreningsverk. Undersökta variabler är injicerad ozonhalt (uteffekt baserat på ozongeneratorns kapacitet) och i ett av fallen, vattenflödet genom systemet. Syftet med arbetet var att hitta optimala driftförhållande med avseende på reducerad mängd läkemedelssubstanser i vatten och energiförbrukning.  Resultaten visade att den parameter som influerade resultatet mest var mängden ozon som injicerades till systemet. Systemet som var installerat på plats 2 var det mest effektiva baserat på både energiförbrukning per m3 vatten och med avseende på reningsgraden på vattnet. Systemet rena vattnet från läkemedelssubstanser upp till mellan 95–100%, vid ett vattenflöde på 16 m3/h och en uteffekt av ozongeneratorn på 75%.  Systemet på plats 1 hade en halverad ozonkapacitet jämfört med systemet på plats 2 och visade inte på fullt lika effektiv rening. Vattnet som bäst renat till 80%, vid ett vattenflöde på 2,5 m3/h och en uteffekt av ozongeneratorn på 100% (motsvarar 50% på plats 2). / Wastewater treatment plants today are designed to reduce pollutants in the form of organic material, suspended solids, plant nutrients (phosphates and nitrates) and microbes from the water. Governments have set up restrictions and laws around in what amount release of different pollutants is acceptable or not. But one type of pollutant that have not been investigated to the same degree is the micropollutants such as pharmaceuticals or active pharmaceutical ingredients (APIs). The biggest amount of APIs release to water is due to human consumption of medicine. Humans have during the evolution strived to find new ways to live longer, stay healthier and avoid pain. Over the last decade there has been an increased consumption of medicine, due to the need to treated ageing related and chronic diseases, together with a change in the clinical practice leading to a more generous prescription approach.  The APIs that we consume will not be totally decomposed in our body, which means that we sooner or later will exude it in form of example urine. The urine will end up in the local WWTP, which today, does not have the ability to reduce APIs in large amount. Due to this, release of APIs to surrounding watercourse will come to affect the animals and eco-system.  Many studies have been done with a goal to find an environmentally friendly way to reduce micropollutants from the wastewater. One of the techniques that has been investigated is oxidation (e.g., ozonation) and adsorption (e.g., activated carbon) processes. Ozonation is an ideal technique due to the high oxidation potential of ozone, environmentally friendly end-products (e.g. oxygen) and low sludge production. Several reports elucidated that application of ozonation for wastewater can have a reducing effect of APIs, and a more studied technique for removal of micropollutants and APIs is activated carbon (AC). But AC has some common struggle, one example is that it works as a filter and that it due to adsorption can be saturated.  The project contained evaluation and process optimization of water purification by oxidation with ozone with aim to purifying water from APIs. To do this, two pilot plants for water purification, located in two different locations in Sweden (location 1 and location 2) will be evaluated and optimized. Both systems are equipped with a sand filter, ozonation step and a polishing step of activated carbon. The two different systems are connected so that incoming water to the system, is outgoing water from a local wastewater treatment plant. The variables evaluated are injected ozone concentration (output power based on the capacity of the ozone generator) and in one of the cases, the water flow through the system. The purpose of the work was to find optimal operating conditions regarding reduced amount of drug substances in water and energy consumption.  The system installed at location 2 is the most effective system from a perspective of both micropollutants reduced and energy used per m3. The API reduction is between 95-100% for the outgoing water and the ozonation step stands for 95-100% of that reduction, which increases the lifetime of the GAC filter. For optimal process settings a water flow of 16 m3/h and an out effect of 75% from the ozone generator was determined.  At location 1 the APIs reduction achieved was 80% after ozonation and 100% after the GAC filtration, and the process settings were 100% out effect (correspond to 50% at location 2) on the ozone generator and a water flow of 2.5 m3/h.

Process scale-up studies are, generally, non-linear. This basically means that it is not possible to take a chemical process in the laboratory and bring it to a pilot or production plant by simply increasing the quantities of chemicals and the equipment size proportionally. There are many physico-chemical processes involved (such as reaction kinetics, fluid mechanics and thermodynamics), plus over the years a myriad of different equipment (stirrers, baffles, jackets...) have been developed with different geometrical and performance characteristics. Therefore, scale-up studies involve engineering issues, economic considerations, and risks assessment to reduce them to acceptable levels for the successful commercial scale implementation. Mixing and heat transfer assessments are often required when scaling a process, troubleshooting poor performance or transferring from one plant to another. This is because the rates of these physico-chemical processes are a function of the details of the equipment set-up and operating conditions, so they can vary widely from one vessel to another. Due to this series of drawbacks and the large number of parameters involved, there is the increasing interest to make use of scientific approaches in the early stages of process development, both modelling and simulation tools along with experimentation to try to predict the behaviour of chemical processes on a larger scale and, consequently, reduce costs and efforts from the beginning. This project was aimed at implementing a method to characterize production equipment and calculate its heat transfer coefficient experimentally from a thermal test. Both the created database, which contains information of about 70 reactors, and the heat transfer coefficient values are then used in different case studies with the objective of predicting the behaviour of the chemical processes examined at different scales: laboratory, pilot and production. The scale-up parameters calculation is detailed for each project with emphasis on the results and conclusions regarding the mixing and heat transfer performances.

The use of carbon from fossil-based resources result in changes in the earth’s climate due to emissions of greenhouse gases. Biomass is the only renewable source of carbon that may be converted to transportation fuels and chemicals, markets now fully dominated by traditional oil supply. The biorefinery concept for upgrading and refinement of biomass feedstocks to value-added end-products has the potential to mitigate greenhouse gas emissions and replace fossil products. Most biorefineries use biochemical conversion processes and may have by-product streams suitable as feedstocks for thermal conversion and production of syngas. Further synthesis to value-added products from the syngas could increase the product output from the biorefinery. The application of thermal conversion processes integrated into an existing biorefinery concept has been evaluated in this licentiate thesis work. Two by-product streams; hydrolysis (lignin) residue from an ethanol plant and biogas from wastewater treatment, have been investigated as gasification/reforming feedstocks. Also, the pre-treatment method torrefaction has been evaluated for improved gasification fuel characteristics and integration aspects. A new process and system concept (Bio2Fuels) with potential carbon negative benefits has been suggested and evaluated as an alternative route for syngas production by separating biomass into a hydrogen rich gas and a carbon rich char product. The evaluation demonstrated that hydrolysis residue proved a suitable feedstock for gasification with respect to syngas composition. Biogas can be further reformed to syngas by combined biomass gasification and methane reforming, with promising results on CH4 conversion rate and increased H2/CO ratio at temperatures ≥1000°C. The pre-treatment method torrefaction was demonstrated to improve fuel qualities and may thus significantly facilitate entrained flow gasification of biomass residue streams. Also, integration of a torrefaction plant at a biorefinery site could make use of excess heat for drying the raw material before torrefaction. The Bio2Fuels concept was evaluated and found feasible for further studies. The application of thermal conversion processes into an existing biorefinery, making use of by-products and biomass residues as feedstocks, has significant potential for energy integration, increased product output as well as for climate change mitigation.

The replacement of fossil resources through renewable alternatives is one way to mitigate global climate change. Biomass is the only renewable source of carbon available for replacing oil as a refining feedstock. Therefore, it needs to be utilized not just as a fuel but for both biochemical and thermochemical conversion through biorefining. Optimizing and combining various conversion processes using a system perspective to maximize the valorization, biomass usage, and environmental benefits is of importance. This thesis work has evaluated the integration opportunities for various thermochemical conversion processes within a biorefinery system. The aim for all evaluated concepts were syngas production through gasification or reforming. Two potential residue streams from an existing biorefinery were evaluated as gasification feedstocks, thereby combining biochemical and thermochemical conversion. Torrefaction as a biomass pretreatment for gasification end-use was evaluated based on improved feedstock characteristics, process benefits, and integration aspects. A system concept, “Bio2Fuels”, was suggested and evaluated for low-temperature slow pyrolysis as a way to achieve simultaneous biomass refinement and transport driven CO2 negativity. Syngas was identified as a very suitable intermediate product for residue streams from biochemical conversion. Resulting syngas composition and quality showed hydrolysis residue as suitable gasification feedstock, providing some adjustments in the feedstock preparation. Gasification combined with torrefaction pretreatment demonstrated reduced syngas tar content. The co-gasification of biogas and wood in a FBG was successfully demonstrated with increased syngas H2/CO ratio compared to wood gasification, however high temperatures (≥1000°C) were required for efficient CH4 conversion. The demonstrated improved feedstock characteristics for torrefied biomass may facilitate gasification of biomass residue feedstocks in a biorefinery. Also, integration of a torrefaction unit on-site at the biorefinery or off-site with other industries could make use of excess low-value heat for the drying step with improved overall thermal efficiency. The Bio2Fuels concept provides a new application for slow pyrolysis. The experimental evaluation demonstrated significant hydrogen and carbon separation, and no significant volatilization of ash-forming elements (S and Cl excluded)  in low-temperature (<400°C) pyrolysis. The initial reforming test showed high syngas CH4 content, indicating the need for catalytic reforming. The collective results from the present work indicate that the application of thermochemical conversion processes into a biorefinery system, making use of by-products from biochemical conversion and biomass residues as feedstocks, has significant potential for energy integration, increased product output, and climate change mitigation.

Microbial Fuel Cell is a novel technology that can be used for a waste water treatment in order to simultaneously remove carbonaceous matter and nitrogen while producing electrical power. Even if it is not an established technology so far, MFC could be a cost effective option for waste water treatment and the major challenge of this process will be the device scale-up. Exoelectrogenic bacteria are capable of converting the chemical energy of organic matter into electrical energy by transferring the electrons produced in the oxidation to the anode electrode. This project focused on developing a single device for nitrification, denitrification and carbon removal. Two double air-cathode single chamber MFCs are used to test the feasibility of this process that could replace the biological unit in a waste water treatment train. The cells tested in this study were manufactured with the purpose of achieving a high surface area on both the anode electrode (vitreous carbon foam) and the air-cathode electrodes (metallic mesh with diffusion layer and active layer) with different catalysts for the reduction reaction (cobalt and platinum). The bacterial biofilm growth is a fundamental step and the cells Open Circuit Potential was monitored during all the start-up period to determine the microorganism acclimation: a three days lag period was observed in both cells before the potential rise. The second cell was forced to reach higher voltage through an anode polarization and that seems to positively affect the biofilm stability at lower voltages transferring a greater amount of electrons and hence obtaining a higher current and power generation. For this reason after three weeks of inoculation the second cell reached an open circuit potential of 0.76 V which is a promising value for such a system. Electrochemical and biological tests were conduced in order to test the power production of the cell and the substrate removal from the waste water. Polarization curves were used to evaluate power generation (and the maximum production under a specific external load) and the cell voltage trend which is characterized by activation and ohmic losses: 32 mW/ and 41 mW/  are the power density normalized by cathode surface (72 ) reached by respectively first and second cell. The experimental conditions were varied from low to high temperature and from low to high inlet flow rate but the most affecting phenomenon seems to be the biofilm formation since significant voltage drops were noticed after long closed circuit operation. Higher cell voltage characterized the second cell thanks to more active cathode (platinum catalyst used) and more negative bacterial biofilm but a bigger drop in current generation over time affects the system performance and the most reliable reason is the shorter acclimation time compared to the first cell. Cyclic voltammetry tests were carried out on both electrodes to study the potential range of activity and determine an optimal operational voltage despite of mass transport or kinetic limitations. Substrate removal tests at different retention times in power generation conditions (external load 100 Ω) showed a relatively high total nitrogen consumption (maximum 72.2 %) for the first cell while lower values were achieved by the second system meaning that a longer acclimation period is beneficial for nitrifying and denitrifying bacteria to thrive on the cathode biofilm. Effluent pH level are almost similar to the initial values probably because of nitrification and denitrification protons offset.

The degree project was done at Södra Cell Värö with the purpose to investigate how the use of energy for pulp drying in a pulp dryer could be made more effective to decrease the energy consumption or increase the capacity. The pulp dryer is one of the machines that consumes the most energy at SCV. The air that dryes the pulp is heated by low pressure steam, and since the amount low pressure steam was limited, the purpose with the project was to investigate how the low pressure steam best could be used. If the drying capacity could be improved it could enable for an increase in production or a decrease low pressure steam consumption. The task was divided into: 1. Analysis of steam and condensate flows connected to the pulp dryer. Can they be adjusted to improve the drying capacity? 2. Investigation of possible sectors of application for hot air flows from vacuum pumps. 3. Investigation of the condensate system. Can condensate and flash steam be used in a better way to provide more steam to the pulp dryer? For task 1, air and energy balances were made ove the pulp dryer, then temperature, flow and moisture content were measured for all air flows in and out. To investigate how the consumption low pressure steam in the pulp dryer depends on the air flows in to the pulp dryer, tests were made where the rotation speed for the fans and the temperature for the air were varied. The result of measuring the air balance over the pulp dryer was that the same amount air was going in and out, which means that all the air was going in to the dryer preheated. The energy balance over the thermal recycling system showed that 40 % of the energy in outgoing air was being reused. Increasing the rotation speed from 750 rpm to 1000 rpm was favourable when the production was high. Increasing the temperature of the air in to the pulp dryer showed that the consumption low pressure steam decreased. Recommended rotation speeds: December – february: 1000 rpm, all levels of production mars – november: 1000 rpm for high production (over 3 bar low pressure steam to pulp dryer) 750 rpm for low production (below 3 bar low pressure steam to pulp dryer) For task 2, temperature, flow and moisture content were measured for all air flows out from the vacuum pumps. The air flows out from the vacuum pumps had a temperature of 40-50 °C, which was too low to be used for preheating of air to pulp dryer. For task 3, a mapping of the condensate system including all steam and condensate flows connected to the pulp dryer was made. The mapping was made in AutoCAD. Since the experiment with increased temperature of the air in to the pulp dryer showed that an increase in temperature caused the consumption low pressure steam to decrease, calculations of how much more the consumption low pressure steam could be decreased by switching to steam of a higher pressure for preaheating the drying air. By using only steam of higher pressure for air preheating, the amount available low pressure steam to the pulp dryer could be increased with 6 tonnes/h. / Examensarbetet utfördes på Södra Cell Värö med syfte att undersöka hur energianvändningen för massatorkning på torkmaskinen (TM) kunde effektiviseras för att ge lägre energiförbrukning eller högre kapacitet. TM är en av de mest energiförbrukande avdelningarna på bruket. Massan torkas där med luft som värms av processånga vilken utgörs av lågtrycksånga, och eftersom tillgången av lågtrycksånga var begränsad var det önskvärt att undersöka hur den kunde användas på mest effektiva sätt. Om torkkapaciteten kan förbättras kan det möjliggöra en ökning av produktionen alternativt en minskning av förbrukning av lågtrycksånga. Uppgiften delades upp i: 1. Analys av ång- och luftflöden kopplat till TM. Kan de justeras för att ge bättre torkkapacitet? 2. Undersökning av möjliga användningsområden för varma luftflöden från vakuumpumparna. 3. Undersökning av kondensatsystemet. Kan kondensat och flashånga utnyttjas på ett bättre sätt för att tillhandahålla mer ånga till TM? Till uppgift 1 ställdes luft- och energibalanser upp över TM, och sedan gjordes mätningar på temperatur, flöde och fukthalt på in- och utgående luftflöden. För att undersöka hur förbrukningen lågtrycksånga i torkskåpet påverkas av tilluften gjordes försök där varvtal på tilluftfläktar och temperatur på tilluft varierades. Resultatet av luftbalansmätningarna var att inget undertryck rådde över torkskåpet, vilket innebär att all tilluft gick förvärmd in till torkningen. Energibalans över värmeåtervinningssystemet visade att ca 40 % av energin i utgående våtluft återvinns. Försök med varvtal och temperatur på tilluft visade att en ökning av varvtal från 750 rpm till 1000 rpm var gynnsamt vid hög produktion, samt att en temperaturökning på tilluft minskade förbrukningen lågtrycksånga i torkskåpet. Rekommenderade körinställningar: December-februari: 1000 rpm, alla produktionsnivåer Mars-november: 1000 rpm vid hög produktion (över 3 bars tryck på lågtrycksångan till skåpet) 750 rpm vid låg produktion (under 3 bars tryck på lågtrycksångan till skåpet) Till uppgift 2 gjordes mätningar på temperatur, flöde och fukthalt på utgående luftflöden från vakuumpumpar. Luftflödena från vakuumpumpar höll en temperatur på 40-50 °C, vilket var för lågt för att kunna användas till att förvärma torkluft till TM. Till uppgift 3 gjordes en kartering av kondensatsystemet inkluderande alla ång- och kondensatflöden kopplade till massatorkningen. Karteringen utfördes i AutoCAD. Eftersom försöket med temperaturökning på tilluft visade att lågtrycksångförbrukningen i skåpet minskade med ökad temperatur på tilluft, beräknades hur stor en ytterligare besparing lågtrycksånga skulle kunna bli om all tilluft förvärmdes av mellantrycksånga. Genom att använda mellantrycksånga för att förvärma all tilluft till torkskåpet skulle mängden tillgänglig lågtrycksånga till torkskåpet kunna ökas med 6 ton/h.

Användandet av fossila bränslen som energikälla leder till stora utsläpp av växthusgaser och klimatförändringar, vilket börjar bli ett hot som växer sig större för varje år. Genom att använda e-bränslen kan man ersätta fossila bränslen, minska utsläppen av växthusgaser och lyckas uppnå klimatmålen. Examensarbetet specialiserade sig på produktion av e-metanol som är en slutprodukt av e-bränslen. Syftet var att undersöka förutsättningarna för ett ekonomiskt, tekniskt och säkerhetsmässigt hållbart Power-to-X koncept i form av en e-metanolanläggning i Norra Sverige. Detta gjordes genom att ta fram mass- och energibalans för metanolproduktion, dimensionera och genomföra en ekonomisk analys för en e-metanolanläggning. För dimensionering undersöktes metanolbehovet och vad nuvarande konventionella metanolanläggningar producerar. En teknisk kartläggning av e-metanolproduktion och olika elektrolys-tekniker utfördes, för att uppskatta en genomförbar storlek av e-metanolanläggning i Norra Sverige. För examensarbetet utfördes inte en teknisk kartläggning för koldioxidavskiljning, CO2-råvaran valdes att köpas in som en driftskostnad. Ett förenklat flödesschema togs fram med vald PEM-elektrolysteknik och direkt CO2-hydrering baserad på liknande studier inom metanolproduktion. För ekonomiska analysen utvärderades anläggningens totala kapitalinvesteringskostnad och driftskostnad för metanolproduktion och elektrolysör separat. Kostnaden för utrustningen inom metanolproduktionen togs från studier med ett liknande flödesschema. Utrustningen som beaktades var kompressorer, värmeväxlare, reaktor, separator och destillation. Efterfrågan på förnybar metanol i Sverige och resten av världen är stor och förväntas fortsätta att öka, för att användas i flera tusentals vardagsprodukter, inklusive plast, färg, kosmetiska och bränslen. För e-metanolanläggningen krävs det stora mängder el och vatten till elektrolysören och koldioxid för metanolproduktionen. En e-metanolanläggning med 500 kton/år i kapacitet, anses vara fullt genomförbar att realisera i Norra Sverige. Tekniken finns för att kunna skapa den mängd CO2 och H2 som anläggningen kräver. Största svårigheten är att få råvarorna, CO2 och H2, till en rimlig kostnad och kapital för att bygga anläggningen. Vidare är det osäkert ifall det finns tillräckligt med förnybar CO2 från netto CO2-neutrala källor i Norra Sverige. Den totala kapitalkostnaden för denna storlek uppskattades till 1,61 miljarder SEK fördelat på tre konstruktionsår, vilket till största del bestod av kostnaden för elektrolysören med 72 %. Den totala driftskostnaden uppskattades till 1,74 miljarder SEK per år, vilket till största del bestod av kostnaden för elektriciteten med 72 %, där majoriteten gick till elektrolysören. Priset på CO2 har en stor inverkan beroende på val av källa och teknik för koldioxidavskiljning. Dessa kostnader är en uppskattning och kan vara högre för ett verkligt fall, när skatter, plats etc. tas i hänsyn och när elprisets variation är medräknat. E-metanol kan bli konkurrenskraftig med fossil metanol om kostnaden för elektrolysören och elpriset, skulle minska avsevärt och ifall det finns tillräckligt med förnybar CO2 tillgängligt.

The corrugated board is considered as the second most used packaging material and the world’s environmentally acceptable solution for packaging, with wide range of applications. After the manufacturing process, the corrugated board is cut into sheets and stored in a stack until optimum moisture content has been reached in order to avoid undesired properties. However, due to complex and various structures, it is difficult to estimate the appropriate time so to achieve the acceptable moisture level of the corrugated board stack. So a homogenized model of the stack has to be created which will have the same average properties as the real stack. In order to achieve this goal the behavior of a smaller part of the stack, the unit cell, is investigated. In the second step a homogenized model is created with the average transport of mass and heat. At the end, the unit cell is scaled up. In this master thesis, only the first and the second steps were simulated. This was achieved by creating a 3-D mathematical model using finite element method and simulating its properties in COMSOL Multiphysics®. Four mathematical models were used in the description of the 3-D model: the heat transfer, the moisture transfer, the vapour concentration and the gas pressure. Moreover, by applying the gradient in one direction in each case, the behavior of the detailed unit cell was investigated. Finally different simplified geometries were created and investigated so to approach a homogenized model which described better the average properties of the detailed model. By comparing the results of the models, it was concluded that the homogenized models 2 and 3 approached the values of the second detailed model but only inside of the unit cell. However, the deviation was not negligible and further investigation is required in order to find a new homogenized method.

Various distillates are treated with hydrogen gas during hydrotreatment in the presence of catalyst in order to reduce the sulfur and aromatic content of the product. Optimal hydrotreater performance is essential for producing Nynas specialty oils, in order to fulfill the planned production volume and to meet the product specification. Loss of catalyst activity is inevitable during the production. To adjust for the impact of catalyst deactivation, different process variables are manipulated. Different distillates affect the catalyst in different ways due to the variation in distillate composition. Distillates with higher organic nitrogen content and running at a lower temperature tend to deactivate the catalyst more due to the adsorption of nitrogen compounds on the active sites of the catalyst and their slow nature of desorption. In this master thesis, different catalyst deactivation mechanisms with a focus on nitrogen deactivation have been studied. Since nitrogen is not normally measured at Nynas, nitrogen content of different distillates and products and how these values change during operation was not known. Different distillates, blend of distillates and different products were measured to estimate roughly the typical nitrogen value of the distillates and products. The temperature data inside the reactors were analyzed to calculate and plot WABT (weighted average bed temperature) during different product runs and to see whether there is a correlation between the nitrogen content of the feed and operation severity (increase in WABT). Historical process data from hydrotreater unit 2 (mostly from 2013-2014) were analyzed with a view to finding out signs of catalyst deactivation. Similar product runs were also analyzed and compared to see how the catalysts performed at different periods of time. A kinetic model, based on HDS kinetics, has been used for following up two product runs. To do so, sulfur content of the feed and product were measured. Aromatic content of the product was also measured to see whether the product was on specification. .From the calculation and plotting of WABTs, it could be seen that there is an increase in WABT during the product runs operating at lower temperatures and with higher nitrogen content. From the comparison of two P3 product runs at two different time periods, it could be seen that ∆T development over one bed (amount of reaction over the bed) was much lower at one time. This can possibly be a sign of catalyst deactivation since it contributed to lesser amount of reaction over the bed. From the calculations by using the kinetic model, it could be seen that the actual temperatures were higher than the predicted temperatures. The increase in WABTs could also be noticed. These observations can possibly be coupled with nitrogen deactivation of the catalysts.  However, more tests are required to verify whether the temperature differences were significant or not. Other parameters which are also important from product selling point of view such as viscosity, color, flash point, acid number etc. and have not been covered in this degree project need to be taken into consideration before making further conclusions.