As the world population keeps increasing, ammonia-based fertilizers like urea are essential to provide food security. However, the current fertilizer industry is based on fossil fuel feedstock (mainly natural gas), making the production process CO2 emission-intensive. More specifically, besides the CO2 emitted during the process, the CO2 captured in urea is also released into the atmosphere after the fertilizer is applied to agricultural soils. Thus, positioning the fertilizer industry among the top four industrial emitters globally. Hence, in order to meet the target of limiting global warming to 1.5 ºC and achieve net-zero emissions by 2050, it is necessary to strengthen the carbon mitigation efforts in the current fertilizer industry. This can be achieved in different ways, such as using renewable biofuels and implementing technologies that can lead to zero/negative CO2 emissions. For that reason, the present study presents pathways to achieve a more environmentally friendly fertilizer production process. An overall analysis is performed if negative emissions can be achieved by replacing different fractions of natural gas (used as both feedstock and fuel) with biogas and biomethane and by capturing and storing the CO2 emitted from the process using chemical solvents as activated MDEA and MEA. The results obtained from the study revealed that negative emissions in fertilizer plant can be achieved by retrofitting an existing ammonia plant with a MEA based CO2 capture system (with a carbon capture rate of 90%) for the SMR burner flue gas, and by introducing 50% of biogas in the feedstock (alongside Natural gas), and 75% of biogas in the SMR burner fuel (alongside Natural gas). This initial approach would result in net negative emissions from urea's production and application and require approximately 0.5 kg of biogas per kg of urea produced in this case. Furthermore, the equivalent energy intensity for the negative emission urea plant would be 0.32% and 3.37% lower compared to the fossil fuel-based case without/with CCS, respectively. Ultimately, it is even possible to produce approximately 6% more urea product by replacing a particular fraction of natural gas with biogas. The reason for this increased production is due to the surplus of carbon dioxide by the introduction of biogas. It can be used along with the ammonia product going to storage in the fossil fuel-based case, where there was not enough CO2 to keep the feedstock molar ratio at the urea plant's inlet.

In today’s pulp and paper industry the Kraft process is the most common method for pulp production. This method uses sodium based chemicals (white liquor) in the cooking process to remove lignin from the wood chips and create pulp. The remains from this process is called black liquor and is being sent to a recycling system for the purpose of recovering the cooking chemicals. Evaporation of black liquor is a big part of this recycling, and the evaporation plant consists of many different tanks that stores black liquor. At Smurfit Kappa Piteå a model has previously been created for the purpose of production planning. In this work the opportunity to add a part that simulates how the liquor stock in the chemical recovery system will change based on the planned production was investigated. This was done by estimating the amount of dry black liquor in the tanks through inflows and outflows. A formula for the produced black liquor was also developed. The results showed that simulating tank levels separately was difficult as data was lacking in some key areas. The final model is therefore a simplified version that estimates the total amount of dry black liquor in the evaporation plant. It simulates the black liquor buffer based on the planed production and how it will change over five days. This could be done with an error smaller than 6%, compared to measurements from sensors in the black liquor tanks. Attempts were also made to create similar models for the rest of the chemical recovery system. It was concluded that information about the inflow of green and white liquor has to be further investigated in order to implement these in the production planning model.

Arbetet studerade skillnaderna mellan en användning av kalciumhydroxid samtnatriumhydroxid som pH-reglerande kemikalie i en kemisk vattenreningsanläggning.Samt dess påverkan på filtreringssteg som sandfilter, aktivkol filtrering samt jonbytarfiltrering. Det behandlade hur reningsgraden påverkas sett till metallreduktion av;krom, nickel, koppar och zink. Hur slammängderna är i förhållande tillvarandramellan de olika pH-reglernade kemikalierna och slutligen hur filtreringsstegenpåverkas beroende på vilken pH-reglerande kemikalie som doserats. Resultatet förarbetet har visat på att reningsgraden minskar vid användning av natriumhydroxidsom pH-reglerande kemikalie vilket besvarar en del av syftet samt frågeställningenmed arbetet. Ytterligare har resultatet påvisat att de efterkommande filtreringsstegensom i en eventuell framtid kan implementeras leder till en reducering avmetallhalterna i vattnet, vanligen gick reduceringen inte att statistiskt säkerställa mentendenser på en reducering påvisades. Även de erhållna slammängdernareducerades vid användning av natriumhydroxid som pH-reglerande kemikalie vilketvar ett förväntat resultat sett till hypotes och litteratur. Ytterligare minskadeturbiditeten för klarfasproverna vid en natriumhydroxiddosering i förhållande till enkalciumhydroxiddosering. Arbetets resultat har således påvisat den goda möjlighetenatt ersätta den manuella doseringen av solid kalciumhydroxid som pH-reglerandekemikalie emot en automatisk dosering av natriumhydroxid erhållen i vätskeform. / This work studied the differences between the use of calcium hydroxide and sodiumhydroxide as a pH-regulating chemical in a chemical water treatment plant. As wellas its impact on filtration steps such as sand filter, activated carbon filtration and ionexchange filtration. It dealt with how the degree of purification is affected in terms ofmetal reduction of; chromium, nickel, copper and zinc. How the sludge amounts arein relation to each other between the different pH-regulated chemicals and finallyhow the filtration steps are affected depending on which pH-regulating chemical hasbeen dosed. The results for the work have shown that the degree of purificationdecreases when using sodium hydroxide as a pH-regulating chemical, whichanswers part of the purpose and the question of the work. Furthermore, the resultshave shown that the subsequent filtration steps that can be implemented in thepossible future lead to a reduction of the metal contents in the water, usually thereduction could not be statistically confirmed but tendencies of a reduction wereshown. The amounts of sludge obtained were also reduced by using sodiumhydroxide as a pH-regulating chemical, which was an expected result in terms ofhypothesis and literature. Furthermore, the turbidity of the clear phase samplesdecreased at a sodium hydroxide dosage relative to a calcium hydroxide dosage.The results of the work have thus demonstrated the good possibility of replacing themanual dosing of solid calcium hydroxide as a pH-regulating chemical with anautomatic dosing of sodium hydroxide obtained in liquid form.

Cellulose nanofibrils (CNF) is a renewable material with unique strength properties. A difficulty in CNF production is that CNF suspensions contain large amounts of water. If CNF suspension volume can be decreased by dewatering facilitated by centrifugation, then transportation costs and storage costs can be reduced. The aim of this thesis is to investigate the impact various parameters have on CNF centrifugation dewatering and identify optimal conditions for maximal water removal. A laboratory study was conducted using four materials; 2.0 w% enzymatically treated CNF (CNF1), 1.9 w% carboxymethylated CNF (CNF2) and two commercial samples (1.9 w% CNFA and 1.8 w% CNFB). The main method was analytical centrifugation up to 2330 g. Parameters tested were initial concentration before centrifugation, temperature, NaCl addition, pH, and applied solid compressive pressure (g-force and surface weight). In addition to centrifugation experiments the four materials were characterized with laser diffraction, UV-vis absorption, Dynamic light scattering, and dry weight measurements. Analysis of the experimental data collected show that increase in initial concentration give a higher final concentration, but less water is removed. Furthermore, temperature changes have no effect on separation of CNF and water. At an applied solid compressive pressure of 3 kPa and initial concentration at 1.5 w% the concentrations 5.5 w%, 1.5 w%, 4.0 w%, and 4.3 w% can be reach for CNF1, CNF2, CNFA, and CNFB respectively. After extrapolation of polynomial functions fitted to experimental data an applied solid compressive pressure of 22 kPa and initial concentration at 1:5 w%, the concentrations 9.1 w%, 1.5 w%, 6.9 w%, and 7.9 w% are predicted for CNF1, CNF2, CNFA, and CNFB respectively. The thickening of CNF suspensions achieved and predicted in this thesis implies possibilities for large amounts of water removal, e.g. the water content in a CNF1 suspension is reduced from 65.7 litres/kg CNF to 10.0 litres/kg CNF at the solid compressive pressure 22 kPa. The concentrations at 22 kPa are determined by extrapolation from experimental data <3 kPa solid compressive pressure. The carboxymethylated CNF2 can not be dewatered unless it is diluted or if salt or pH is adjusted. This is directly correlated to the electrostatic forces in the suspension and the Debye length. Addition of salt or lowered pH also eliminate any concentration gradients in diluted and centrifuged CNF2 suspensions. / Cellulosa nanofibriller (CNF) är ett förnybart material med unika styrkeegenskaper. En svårighet med produktion av CNF är att CNF suspensioner innehåller stora mängder vatten. Om volymerna av CNF suspensioner kan minskas med avvattning genom centrifugering, då kan transport- och lagerkostnader sänkas. Målet med det här examensarbetet är att undersöka vilken inverkan olika parametrar har på CNF-avvattning genom centrifugering och identifiera optimala förhållanden för maximalt avlägsnande av vatten. En laboratoriestudie utfördes på fyra olika material. De fyra materialen är 2 w% enzymatiskt behandlad CNF (CNF1), 1.9 w% karboxymetylerad CNF (CNF2) och två kommersiella prover (1.9 w% CNFA och 1.8 w% CNFB). Den huvudsakliga metoden var analytisk centrifugering upp till maximalt 2330 g. De testade parametrarna var initial koncentration innan centrifugering, temperatur, NaCl tillsats, pH, och applicerat fast kompressionstryck (g-kraft och ytvikt). Förutom centrifugeringsexperimenten så karaktäriserades the fyra mmaterialen med laser diffraktion, UV-vis absorption, dynamisk ljusspridning och vägningar av torrhalt. Analys av den experimentella data som insamlats visar att en ökad initial koncentration ger en högre slutkoncnentration, men mindre vatten kan bortföras. Temperaturförändringar har ingen effekt på separation av CNF och vatten. Vid ett applicerat fast kompressibelt tryck på 3 kPa och en initial koncentration 1.5 w% kan koncentrationerna 5.5 w%, 1.5 w%, 4.0 w%, och 4.3 w% nås för CNF1, CNF2, CNFA, och CNFB. Efter extrapolering av polynoma funktioner passad till experimentell data förutspås att koncentrationerna 9.1 w%, 1.5 w%, 6.9 w%, och 7.9 w% kan nås för CNF1, CNF2, CNFA, and CNFB vid 22 kPa och en initial koncentration på 1.5 w%. Förtjockningen av CNF suspensioner som kan, eller förutspås kunna nås genom centrifugering i det här examensarbetet innebär att det är möjligt att avlägsna stora mängder vatten, till exempel kan vatteninnehållet i CNF1 minskas från 65.7 liter/kg CNF till 10.0 liter/kg CNF vid 22 kPa fast kompressionstryck. Koncentrationerna vid 22 kPa fast kompressionstryck är extrapolerade från exprimentell data <3 kPa fast kompressionstryck. Den karboy- metylerade CNF2 kan inte avvattnas om den inte späds ut eller om salt eller pH justeras. Detta är direkt kopplat till de elektrostatiska krafterna i suspensionen och Debye längden. Tillsats av salt eller sänkt pH eliminerar också de koncentrationsgradienter som kan förekomma i utspädda centrifugerade CNF2 suspensioner.

With the continuing transition to renewable inherently intermittent energy sources like solar- and wind power, electrical energy storage will become progressively more important to manage energy production and demand. A key technology in this area is Li-ion batteries. To operate these batteries efficiently, there is a need for monitoring of the current battery state, including parameters such as state of charge and state of health, to ensure that adequate safety and performance is maintained. Furthermore, such monitoring is a step towards the possibility of the optimization of battery usage such as to maximize battery lifetime and/or return on investment. Unfortunately, possible online measurements during actual operation of a lithium-ion battery are typically limited to current, voltage and possibly temperature, meaning that direct measurement of battery status is not feasible. To overcome this, battery modeling and various regression methods may be used. Several of the most common regression algorithms suggested for estimation of battery state of charge and state of health are based on Kalman filtering. While these methods have shown great promise, there currently exist no thorough analysis of the impact of so-called filter tuning on the effectiveness of these algorithms in Li-ion battery monitoring applications, particularly for state of health estimation. In addition, the effects of only adjusting the cell capacity model parameter for aging effects, a relatively common approach in the literature, on overall state of health estimation accuracy is also in need of investigation. In this work, two different Kalman filtering methods intended for state of charge estimation: the extended Kalman filter and the extended adaptive Kalman filter, as well as three intended for state of health estimation: the dual extended Kalman filer, the enhanced state vector extended Kalman filer, and the single weight dual extended Kalman filer, are compared from accuracy, performance, filter tuning and practical usability standpoints. All algorithms were used with the same simple one resistor-capacitor equivalent circuit battery model. The Li-ion battery data used for battery model development and simulations of filtering algorithm performance was the “Randomized Battery Usage Data Set” obtained from the NASA Prognostics Center of Excellence.  It is found that both state of charge estimators perform similarly in terms of accuracy of state of charge estimation with regards to reference values, easily outperforming the common Coulomb counting approach in terms of precision, robustness and flexibility. The adaptive filter, while computationally more demanding, required less tuning of filter parameters relative to the extended Kalman filter to achieve comparable performance and might therefore be advantageous from a robustness and usability perspective. Amongst the state of health estimators, the enhanced state vector approach was found to be most robust to initialization and was also least taxing computationally. The single weight filter could be made to achieve comparable results with careful, if time consuming, filter tuning. The full dual extended Kalman filter has the advantage of estimating not only the cell capacity but also the internal resistance parameters. This comes at the price of slow performance and time consuming filter tuning, involving 17 parameters. It is however shown that long-term state of health estimation is superior using this approach, likely due to the online adjustment of internal resistance parameters. This allows the dual extended Kalman filter to accurately estimate the SoH over a full test representing more than a full conventional battery lifetime. The viability of only adjusting the capacity in online monitoring approaches therefore appears questionable. Overall the importance of filter tuning is found to be substantial, especially for cases of very uncertain starting battery states and characteristics.

This thesis builds around the idea of a biofuel production process that is comprised of biomass production, biomass gasification, gas cleaning, and fuel production. In this work, we specifically looked into H2S removal as a part of cleaning the producer gas and flocculation of microalgae which is involved in the harvesting of microalgae after biomass production. One of the impurities to remove from the producer gas is hydrogen sulfide which can be removed by using a packed bed of zinc oxide. Despite the regular use, it was only recently shown that during reaction with H2S, nano-size particles of ZnO exhibit void formation and outward growth. In this work, a micro-scale model was introduced to describe the void formation and outward growth. On the macro-scale, the simulations captured pore clogging of pellets due to the outward growth. The pore clogging prevents the full conversion of pellets and consequently leads to shorter breakthrough times of beds. The second problem investigated here deals with the flocculation of microalgae. Microalgae is produced in relatively low concentrations in the incubator liquid medium and during the harvesting, the concentration is increased to an acceptable level. The harvesting process includes a flocculation followed by a filtration or centrifuge unit. During flocculation, microalgae are stimulated to aggregate and form clusters. The experiments showed that the mean size of clusters formed during flocculation increases with time to a maximum and then starts decreasing, resulting in an overshoot in the mean size profile. The size of clusters influence the efficiency of the afterward filtration or centrifuge, thus it is of interest to carefully track the size evolution of clusters, making the studying of overshoot a crucial research topic. In this work, the possible mechanisms behind this overshoot were investigated. / <p>QC 20170330</p>

The combustion of fossil fuels has for a long time been a problem from an environmental and sustainability point of view, especially when it comes to the emissions of atmospheric carbon dioxide. The environmental concern has for instance shifted the attention towards finding new sustainable alternatives for producing chemicals and fuels, as a substitute to today’s dependence on fossil based crude oil. Catalytic Fast Pyrolysis of biomass is an excellent way to produce valuable chemicals and fuels using renewable resources. However, the process has some drawbacks, for example rapid deactivation of catalysts due to coke formation. Little is known about the characteristics of the formation of catalytic coke from pyrolysis processes, which should be a vital concern in future industrial processes. This thesis is dedicated to investigate the chemical coke characteristics found on zeolitic catalysts. Four zeolites of the type ZSM-5 were chosen for this thesis to deduce any chemical differences in the coke: HZSM-5, Fe/ZSM-5, Ni/ZSM-5, and Fe-Ni/ZSM-5. The coke were characterized by TGA, GC/MS, and FTIR. The results show that Fe/ZSM-5 produced the highest amount of coke compared to the other zeolites, where HZSM-5 had the lowest amount of coke formation. The coke consisted mainly of aromatic and cyclic hydrocarbons, dominated by polycyclic aromatic hydrocarbons. The content of ketones and alcohols in the coke found on HZSM-5 was higher compared to the metal-doped zeolites, while the formation of naphthalenes was lower. The FTIR results also show that coke was mainly comprised of aromatic hydrocarbons. However, traces of alkanes and alkenes reveal that the coke may have a greater variety than the GC/MS analysis suggests. The results show interesting features when metals are introduced to the zeolitic structure, at least when it comes to coke formation. The metal-doping of zeolites certainly seems to alter the chemistry of the catalytic reactions, compared to the parent zeolite. The differences in the chemical characteristics found in the coke are certainly interesting, and it could mean that the chemistry of the bio-oil also varies depending on the metals chosen for the ZSM-5. The new properties that metals introduce to the parent catalyst may open up new possibilities in industrial catalytic processes, and allow industries to take more advantage of the great benefits that biomass has to offer. / Förbränning av fossila bränslen har under lång tid utgjort ett problem ur miljö- och hållbarhetssynpunkt, i synnerhet gällande utsläppen av koldioxid. En större miljömedvetenhet har gett upphov till sökandet efter nya råvaror för att framställa bränslen och kemikalier, utan att förlita sig på fossil råolja. Katalytisk pyrolys av biomassa är ett utmärkt sätt att framställa värdefulla kemikalier från förnybara källor. Processen står dock inför en del tekniska utmaningar, bland annat en snabb deaktivering av använda katalysatorer genom koksning. Målet med detta examensarbete är att undersöka den kemiska sammansättningen av koks, som bildats på zeolitkatalysatorerna. Mer specifikt, att försöka undersöka huruvida den kemiska sammansättningen av koks skiljer sig mellan katalysatorn HZSM-5 och metalldopad HZSM-5. Fyra katalysatorer valdes för detta examensarbete, nämligen HZSM-5, Fe/ZSM-5, Ni/ZSM-5 och Fe-Ni/ZSM-5. Kokset har analyserats genom termogravimetrisk analys (TGA), gaskromatograf kopplad med en masspektrometer (GC/MS), samt Fourier-transform-infraröd-spektroskopi (FTIR). Resultaten visar att Fe/ZSM-5 bildade en större mängd koks jämfört med de andra zeoliterna, varpå HZSM-5 hade lägst halt koks. Utöver detta bestod kokset till största del av aromatiska- och cykliska kolväten, speciellt polycykliska aromatiska kolväten. Innehållet av ketoner och alkoholer i kokset var störst för HZSM-5, medan bildandet av naftalenföreningar ökade för de metalldopade zeoliterna. FTIR-analysen gav även upphov till signaler som är signifikanta för både alkaner och alkener. Därför kan det innebära att kokset innehar en större kemisk variation än vad GC/MS-analysen påvisade. Resultaten visar intressanta egenskaper hos metallmodifierade zeoliter, i synnerhet gällande koksbildning. Det verkar som att de metalldopade zeoliterna påverkar de katalytiska reaktionerna som sker i katalysatorn, jämfört med den obehandlade katalysatorn. Skillnaderna i den kemiska sammansättningen hos kokset för de olika katalysatorerna är definitivt intressant och kan indikera att det även kan föreligga skillnader i den kemiska sammansättningen hos bio-olja, beroende på vilken metall ZSM-5 har behandlas med. De nya egenskaperna som metaller bidrar med till ZSM-5 kan öppna upp nya möjligheter i industriella katalytiska processer, vilket även kan medföra att industrier bättre kan ta tillvara på de fantastiska egenskaper biomassa innehar.

Vid produktion av biodiesel produceras även råglycerol (10 vikt%) som biprodukt och utbudet av råglycerol har ökat över de senaste åren till följd av att biodieselproduktionen ökat. Marknadsvärdet för råglycerol är lågt, men det är en utmärkt föregångare till att producera mervärdesprodukter för exempelvis läkemedelsindustrin, kemikalieindustrin eller kosmetika. Genom att reformera glycerol till mervärdesprodukter ökar konkurrenskraftigheten för biodiesel och värdekedjans ekonomiska hållbarhet. Elektrokemisk reformering av glycerol är en lovande metod för att producera dess mervärdesprodukter, eftersom processen är justerbar och miljövänlig. En ytterligare fördel är att vätgas kan samproduceras med mervärdesprodukterna genom denna metod och energikonsumtionen för att producera vätgas genom denna metod är ungefär hälften av vad som krävs vid vattenelektrolys. Denna studie utvärderar hur masstransport påverkar selektiviteten och prestandan för elektrokemisk oxidation av glycerol, genom att utföra elektrokemiska experiment, karaktärisera processens katalysator och analysera produkter som produceras.  Den experimentella uppställningen innefattar en roterande diskelektrod med ett elektrodepositerat lager av Pd, på ett Ni-substrat, i varierande tjocklek. Elektroden undersöks i elektrolyter bestående av varierande koncentration av NaOH (1, 0.5 och 0.25 M) och 0.5 M glycerol vid 25 oC. Systemet konstrueras även som modell i Comsol Multiphysics 6.0 för att simulera experiment. Resultaten visar att masstransport av glycerol begränsar systemet genom att orsaka deaktiveringen av katalysatorn. Vid de lägre NaOH koncentrationerna begränsar även masstransport av OH- reaktionshastigheten genom att miljön omgärdande elektroden blir mindre oxidativ. Slutligen visas att reaktionsmekanismen vid alla tjocklekar av katalysatorn utgörs av två parallella reaktionsvägar. En ökande tjocklek hos katalysatorn ökar selektiviteten mot den ena reaktionsvägen framför den andra, samt ökar antal oxidationssteg som åstadkoms vid reaktionen. / Biodiesel production gives rise to 10 wt% crude glycerol as a byproduct, which is becoming increasingly available on the market owing to the increased biodiesel production over the last few years. Crude glycerol has a low market value, but it is an excellent precursor to producing value added products for the pharmaceutical industry, chemical industry or cosmetics to mention a few. By producing value added products with biodiesel derived glycerol, the ability of biodiesel to compete with fossil fuels is improved and its economical sustainability is promoted. One of the most promising methods to convert glycerol into its value added products is electrochemical reforming, as it poses high tunability and is an environmentally friendly process. Additionally, the process produces hydrogen concurrently and halves the energy consumption compared to producing hydrogen from water electrolysis. This study evaluates the impact of mass transport in the glycerol electrooxidation reaction (GEOR), as a parameter that can be used to finetune product selectivity and optimise the system performance. To do so, the study employs electrochemical experiments, catalyst characterisation and product analysis. The experimental setup consists of a rotating disk electrode (RDE) cell with electrodeposited Pd on Ni substrate at varying thicknesses, operating in 1, 0.5, 0.25 M NaOH and 0.5 M glycerol electrolyte at 25 oC. Additionally, the system is modelled in Comsol Multiphysics 6.0 which is used to perform simulations. It is found that mass transport of glycerol is limiting the system by causing the deactivation of the catalyst. At lower NaOH bulk concentrations for the thicker electrodes, the mass transport of OH- also limits the reaction rate by causing the formation of a locally less oxidative environment. Finally, it is found that all electrodes pose dual reaction mechanisms. Increasing the electrode thickness promotes one reaction mechanism over the other as well as it increases the number of oxidation steps achieved in the reaction.

This degree project studies the integration of carbon capture system into biomass fired combined heat and power (bio-CHP) plants. The key disturbances from bio-CHP plants include flue gas flow rate, carbon dioxide (CO2) concentration and available heat for the reboiler because the use of versatile biomass and the dynamic operation of CHP plants results in large fluctuations in the properties of flue gas and the heat input for CO2 capture. To clearly understand the impacts of these disturbances on the performance of CO2 capture, a dynamic CO2 capture model is developed in Aspen Plus Dynamics by using monoethanolamine (MEA) based chemical absorption. Proportional-Integral (PI) feedback controllers are then implemented to further study and compare the performance of the CO2 capture process under different control strategies, the performance with general control settings and fine-tuned controllers are obtained and compared, including both the control performance and system performance. The control performance includes the maximum deviation and settling time, which could reflect only the performance of the controllers.  The system performance includes Captured CO2, reboiler duty and Energy penalty per unit CO2 captured, which could reflect CO2 capture system performance. An equilibrium stage steady state model is first developed for the key components in the CO2 capture plant in Aspen Plus, consisting of the absorber, the stripper, and lean-rich heat exchanger. By sizing the components and employing the pressure driven mode, the steady state model is enabled to be a dynamic model. The disturbances about flue gas and reboiler heat are taken from a real bio-CHP plant in Sweden. Considering the higher flue gas flowrate, the model has been scaled up to meet the requirement of this bio-CHP plant. The addition of controllers are done for the flexible operation of the CO2 capture system and the controlled variables considered in this study are the percentage of CO2 absorbed in the absorber column, reboiler temperature and rich solvent flow in the stripper column. The results show the effects of fluctuations in the key influencing factors on the control performance and the system performance . The fine-tuned controller implemented system showcases better performance when the quantity of CO2 captured is compared with that of the system in the absence of controllers, where a 1.1% increase in the amount of captured CO2 is observed when the flue gas flow rate is increased by 30%. The system also maintains a 1.8% higher capture rate when controllers are implemented. This showcases better system performance when controllers are implemented in the system. To further analyse the effects of control strategies two different control strategies are compared where controllers with general settings are compared to the controllers which are fine-tuning achieved by implementing tuning parameters which were obtained through Internal Model control (IMC) based on the system requirements. The fine tuning of the controllers results in improved system performance where the amount of captured CO2 increases by 1.4% when the reboiler duty is increased by 30% and a 1.7% decrease in the energy penalty per unit CO2 captured. Additionally, the results show that the settling time and maximum deviation are different for the two controllers where the controller which underwent fine tuning maintained the steady set point whereas the controller with general controller tuning showcases deviation before it attained stability. Therefore, the fine-tuned controller is more efficient to enable the flexible operation of CO2 capture when facing disturbance. It is studied that the tuning parameters implemented in the controllers affect the transient operation of the plant and improved the dynamic performance of the capture system. The tuned controllers offered more stability to the capture system while attaining their respective set points in a shorter time frame. It is also found that there exists a big difference between the system’s performance without controllers and that with finely tuned controllers. The difference in captured CO2 amount is approximately 26 ton/h when flue gas flow rate increases by 30%. The percentage difference is 1.1%, 7.7% and  5.9% for Captured CO2, reboiler duty and Energy penalty per unit CO2 captured respectively. In conclusion the control of the transient operation of the CO2 capture system needs the control system implemented and requires fine tuning parameters to achieve the desirable performance.

Utsläppen av växthusgaser ökar över hela världen och nya tekniker används för att minska utsläppen. 7% av utsläppen kommer från stålsektorn. 25% av världens stålproduktion görs via återvinningstekniken ljusbågsugn. Genom återvinningsprocessen släpps det ut 500kg CO2 per ton producerat flytande stål. En möjlighet att sänka dessa direkta utsläppär att koppla ljusbågsugnsprocessen med biomassa förgasnings och koldioxidavskiljning. Den föreslagna lösningen i denna avhandling är att utnyttja avgaserna från stålsmältningen i förgasningsprocessen och skapa värdefulla produkter. Projektet utvärderar den tekniska genomförbarheten i form av energieffektivitet och kolutnyttjande. Den föreslagna processen simulerades med Aspen Plus. Ett problem med ljusbågsugnens avgaser är fluktuationen i sammansättningen. Tre fall avavgassammansättning undersöktes. Fall 1 var den genomsnittliga avgassammansättningen, medan fall 2 och 3 var extrema med högt CO- respektive CO2-innehåll. Resultatet visade att syntetsgassammansättningen starkt beror på förgasningsmedlet. I samtliga fall ökade energieffektiviteten och de direkta utsläppen minskade, jämfört med nuvarande process. Fall 1 visade generellt högst effektivitet och kolutnyttjande, medan det CO2 rika fallet (fall 3) hade lägst. Ett kontinuerligt flöde av förgasningsmedel krävs för att driva förgasningsprocessen. Eftersom ljusbågsugn är en satsvis process, sker luftförgasning när avgaser inte är tillgängliga. Det önskade resultatet av luftförgasning är att producera syntetsgas som liknar avgasförgasningens syntesgas. Resultaten visade att luftinfiltration i avgaser är gynnsamt för mer liknande syntesgas . / Greenhouse gas emissions are increasing worldwide, and new techniques are being adopted to suppress the emissions. The steel sector is responsible for 7% of the emissions. 25% ofthe world’s steel production is made through the recycling technique EAF. Throughout the recycling process, 500 kg CO2 gets emitted per ton of liquid steel produced. An opportunity to lower these direct emissions is to couple the EAF process to biomass gasification and CO2 utilisation process. The proposed solution in this thesis is to utilise the off-gases in the gasification process and create high-valuable products. The project evaluates the technical feasibility via energy efficiency and carbon utilisation. The proposed process was simulated using Aspen Plus. A problem with the off-gases from EAF gasification is the fluctuation in composition. Three cases of off-gas composition were therefore investigated. Case 1 was the average off-gas composition, while cases 2 and 3 were extreme with high CO and CO2 content, respectively. The result showed that the syngas composition strongly depends on the gasifying agent. In all cases, the energy efficiency increased, and the direct emissions decreased. Case 1 generally showed the highest efficiency and carbon utilisation, while the CO2 heavily case (case 3) had the lowest. A continuous flow of gasifying agents is required to run the gasification process. Since EAF is a batch process, air gasification runs when off-gases are unavailable. The desired outcome of air gasification is to produce syngas similar to off-gas gasification. The results showed that air infiltration in off-gases is favourable for more similar syngas composition.