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Anthropogenic greenhouse gas emissions have continuously grown since the Industrial Revolution. Global warming is the result of increasing concentrations of these gases in the atmosphere, which create imbalances between inflow and out-flow radiation that lead to the increase of the mean temperature of the planet. There is scientific consensus on that the prolonged temperature rise of oceans and land has altered the climate and jeopardised the biosphere. Temperature increase above 1.5_C with respect to pre-industrial levels is likely to produce deep changes in natural ecosystems, alter biodiversity, and threaten human health and security. Therefore, current mitigation policies aim at reducing the overall emissions of greenhouse gases to restrain this temperature rise. Decarbonisation of the power sector will play a fundamental role in the abatement of global warming as it is the largest CO2 emitter and electrification of other industries is becoming an essential approach to reduce their greenhouse gas emissions. Deployment of intermittent renewable energy sources, mainly wind and solar, has concentrated most of the efforts to reduce the emissions associated with the power sector. However, a broader portfolio of technologies is necessary to meet the increasing power demand whilst ensuring safe and sustainable power generation. In this context, flexibility is and will be the cornerstone of a reliable and efficient electric market. Thermal power plants integrated with carbon capture and storage (CCS) systems can deliver low-carbon electricity at a large scale and balance the differences between power demand and supply originated by the increasing share of renewable sources. Thus, these power generation systems are expected to be one of the foundations of the power sector. This thesis is a summary of a set of scientific contributions that aimed at optimizing the flexible operation of thermal power plants integrated with absorption based post-combustion CO2 capture plants. These included the analysis of the dominant dynamic of this type of power generation systems, the identification of the main bottlenecks hindering their flexible operation and transient performance, and the development of different methodologies that allowed overcoming these restrictions and ensuring safe yet efficient dynamic operation. Thermal power plants and post-combustion CO2 capture systems exhibit distinct dynamic behaviour because their dominant dynamics occur in different time scales. Flexible operation requires understanding the main factors dictating the dynamic performance of each plant and how their integration affects power generation. A qualitative analysis discussed the components and processes governing the dynamic behaviour of thermal power and capture plants, both individually and integrated, whereas dynamic simulations demonstrated the almost negligible effect of the capture plant in the power generation capacity of natural gas combined cycles. This indicated that carbon capture does not limit the dispatchable nature of this type of thermal power plants and highlighted the suitability of thermal power with CCS to balance power markets with large shares of intermittent renewable energy sources. Thermal and mechanical stresses, however, do limit the ramping capacity of thermal power plants. Thick-walled equipment experiences large temperature gradients during flexible operation that generate high peaks of stress in the material and might ultimately lead to deformations and failure. This thesis presents a methodology to operate thermal power plants based on model predictive control that incorporates the calculation of stress in critical components. This control strategy computes optimal power generation ramps that result in the fastest possible operation with stress levels within allowable limits. Stress monitoring can avoid the instant failure of critical components by reducing the maximum peaks of stress. Nevertheless, regular operation of thermal power plants induces damage in the equipment even with safe levels of stress. Flexible operation increases this deterioration and reduces the lifetime operation of the power plant due to the more frequent and pronounced thermal gradients and their associated stress variations. Scheduling can consider these factors to determine operation profiles for thermal power plants that maximise revenue while reducing the deterioration of the equipment and considering the inherent uncertainty associated with intermittent power generation from renewable energy sources. This approach is proposed in a method that formulates the scheduling of thermal power plants as a scenario-tree stochastic optimisation problem where the damage of the equipment is a constraint. Optimisation-based control strategies also enhance the transient performance of thermal power plants integrated with post-combustion CO2 capture. Model predictive control can consider the di_erent dynamic behaviour of both plants and compute optimal control actions according to their dominant dynamics. A control strategy based on offset-free model predictive control is proposed to reinforce the flexible power dispatch of thermal power plants and to stabilise the the main process variables of integrated systems. Dynamic simulations demonstrated the effectiveness of this control strategy to balance drastic changes on power demand, keep specified capture ratios, and reduce the deviations achieved in the main process performance variables of these power systems.

I et etterforbrenning karbonfangstanlegg blir det brukt en aminløsning for å absorbere CO2. Aminløsningen blir regenerert i desorberkolonnen gjennom varme tilført i omkokeren. En stor driftskostnad ved et karbonfangstanlegg er energitilførselen i omkokeren. Det ble i denne masteroppgaven utviklet en kontrollkonfigurasjon for et karbonfangstanlegg med multiple absorbere, basert på ulineær modellbasert prediktiv regulering (NMPC). Målfunksjonen ble formulert på et vis som styrer anlegget mot minimalt energiforbruk samtidig som settpunkt på fansgtgrad opprettholdes. En modell av et karbonfangstanlegg mottatt fra Cybernetica AS ble utvidet til å inkludere multiple absorberkolonner. Modellen ble delt i to deler, en med absorberkolonnene og en med desorberkolonnen og de andre enhetsoperasjonene. Flere enkle absorbermodeller ble utviklet og kombinert med desorberhalvdelen av modellen i to-NMPC kontrollkonfigurasjoner. Konfigurasjonene ble testet og utviklet til en endelig kontrollstruktur ble ferdigstilt. De utviklede to-NMPC konfigurasjonene ble testet og sammenlignet med en referansekonfigurasjon. Referansekonfigurasjonen bestod av én NMPC som bruker den originale modellen. Den originale modellen ble benyttet som anleggerstatningsmodell i Cybernetica RealSim i alle simuleringer. I motsetning til to-NMPC konfigurasjonene hadde ikke referansekonfigurasjonen modellavvik fra anlegget. To-NMPC konfigurasjonene hadde varierende ytelse, men den endelige konfigurasjonen hadde sammenlignbar ytelse med referansekonfigurasjonen med en 73.6 % reduksjon i gjennomsnittlig beregningstid per sampel. Det ble også utviklet en annen konfigurasjon med en individuell NMPC for hver absorberkolonne som reduserte den gjennomsnittlige beregningstiden med 83.1 %. Resultatene viste at de utviklede kontrollkonfigurasjonene kunne levere akseptabel ytelse med redusert beregningstid. Reduksjonen i beregningstid blir enda viktigere jo flere absorberkolonner som blir lagt til i anlegget. In post-combustion CO2 capture, CO2 is absorbed in an amine solvent. The solvent is regenerated in the desorber column by heat supplied in the reboiler. A large cost when operating a post-combustion CO2 capture plant is the reboiler duty. In this master's thesis, a control configuration based on nonlinear model predictive control (NMPC) was developed for a multi-absorber CO2 capture plant, the objective function was formulated in a way that should control the plant towards minimum reboiler duty. A CO2 capture plant model received from Cybernetica AS was expanded to include multiple absorber columns. The model was split into two parts, one with the absorber columns and one with the desorber column and the other process units. Several simple absorber models were developed and paired with the desorber half of the model in two-NMPC control configurations. The configurations were tested and developed until a final control structure was produced. The developed two-NMPC configurations were tested and compared with a benchmark control configuration. The benchmark control configuration consisted of one NMPC using the original model. The original model was used as the plant replacement model in Cybernetica RealSim in all simulations, so the benchmark controller had no model mismatch with the plant, unlike the two-NMPC configurations. The two-NMPC configurations exhibited varying performance, but the final configuration offered comparable performance to the benchmark controller with a 73.6 % reduction in average computational time per sample. There was also developed another configuration with individual NMPCs for each absorber column, which reduced the average computational time by 83.1 %. The results showed that the developed control configurations could deliver acceptable performance while reducing the computational time. The time reduction becomes increasingly significant the more absorber columns are added to the plant.

Membraner aksepteres i økende grad som metode for naturgassrensing ettersom etterspørselen etter naturgass øker og strengere klima- og utslippsregler innføres. I denne rapporten, har et hybrid membransystem for fjerning av vann og CO2 i naturgass blitt studert. En spiralmodul med en MTR Pebax® co-polymer-basert sammensatt membran ble simulert for dehydrering, og to fibermoduler med polyimid-derivert karbonmembran ble simulert i serie for fjerning av CO2. Målet var å evaluere kost-nytte-effekten som et forstudie for systemet. Videre ble en membranmodell utviklet, sammenlignet med eksperimentelle data og analysert for bruk i simuleringsverktøy for å forutsi prestasjonen til membraner for gasseparasjon. Et utvalg av ulike designkonfigurasjoner ble vurdert med hensyn til antallet og utformingen av kompressorer. Hver designkonfigurasjon ble optimalisert ved bruk av Nelder-Mead-metoden med en penalty-funksjon. Optimaliseringsprogrammet ble utført eksternt ved å opprette en COM automatasjonsserver (ActiveX) som koblet det eksterne programmet til brukergrensesnittet for simuleringsprogrammet. Likningssettet for membranmodellen ble diskretisert ved å bruke en ortogonal kollokasjonsmetode som transformerte likningene til ikke-lineære algebraiske likninger som videre ble løst ved bruk av Newton-Rhapson-metoden. Membranmodellen ble deretter integrert i simuleringsprogrammet med den optimale designkonfigurasjon som en Cape-Open enhetsoperasjon basert på COM-teknologi. Det optimale designet besto av to kompressorer i serie mellom enheten for dehydrering og enheten for CO2-fjerning, med kompresjon av den resirkulerte retentatstrømmen fra CO2-enheten, og en trykkventil for å redusere trykket i den resirkulerte permeatstrømmen fra CO2-enheten. Den spesifikke kostnaden for renset naturgass var 2.192E−3 $/m^3 og kravene til gassens sammensetning og utslipp ble innfridd. I det optimale designet med ChemBrane-modellen var duggpunktet til vann -52.5 grader celsius, den rensede naturgassen besto av 97.5% metan og det var 95% CO2 i strømmen for videre bruk i EOR. Gassens duggpunkt var -11.5 grader celsius. Det optimale systemdesignet med membranmodellen utviklet i dette arbeidet ble ikke optimalisert på grunn av tilkoblingsproblemer med COM-serveren og simuleringsprogrammet. Membranmodellen ble validert av ett av to eksperimenter med et relativt avvik ≤ 3.65%, og kunne derfor brukes til simulering av gasseparasjon i fibermoduler. Sammenlignet med data fra det andre eksperimentet, ble membranmodellen funnet å være ugyldig på grunn av store relative avvik i permeatstrømmene og renheten. Membranmodellen viste derimot tilnærmet like resultater som ChemBrane-modellen, men ble vurdert å vise mer realistisk gasseparasjon i fibermoduler. Studiet viser at membraner for naturgassresning er både teknisk og økonomisk mulig, men dehydreringsenheten må forbedres med hensyn til design, modulkonfigurasjon eller membranytelse. Testing av membranene i anleggsskala er nødvendig for å bestemme levetiden og for videre validering av membranmodellen. COM-teknologien og Cape-Open enhetsoperasjon i simuleringsprogrammet må utforskes for ekstern optimalisering av bruker-definerte modeller. Til slutt, en detaljert evaluering av kostnaden, inkludert en økonomisk analyse og en sensitivitetsanalyse, er nødvendig for å forbedre kostnadsberegningene. Membranes for natural gas treatment are gaining increasing acceptance with the increasing natural gas demand and stricter environmental regulations. In this work a hybrid membrane system for natural gas dehydration and CO2 removal was studied. A Spiral-wound MTR Pebax® co-polymer based composite membrane for dehydration was simulated, and a hollow fiber polyimide derived carbon membrane was simulated in series for removal of CO2. The aim was to evaluate the technical end economical feasibility with respect to pipeline and sales specifications and specific cost of natural gas processing. Furthermore a membrane model was developed, compared to experimental data and analyzed for use in the process simulation to predict the membrane performance. Various design configurations were proposed with respect to the number and arrangement of compressors. Each design configuration was optimized using the Nelder-Mead simplex algorithm with a penalty function. The optimization routine was carried out externally by creating a COM automation server (ActiveX) to connect with the simulation interface. The set of membrane model equations were dicretized using the orthogonal collocation method to form a set of non-linear algebraic equations which was solved applying the Newton-Rhapson method. The membrane model was then integrated in the simulation environment with the optimal design configuration as a Cape-Open unit operation based on the COM technology. The optimal design configuration contained two compressors in series between the dehydration unit and the sweetening unit, with compression of the recycled retentate from the sweetening unit, and a pressure relief valve instead of a turbine for expanding the sweetening unit permeate before entering the dehydration unit as sweep gas. The specific natural gas processing cost for the optimal design was 2.192E−3 $/m^3, and the pipeline and sales specifications were met. For the optimal design with the ChemBrane model the water dew point was -52.5 centigrades, the methane purity was 97.5%, the CO2 purity in the gas for enhanced oil or gas recovery was 95%, and the gas dew point was -11.5 centigrades. The design with the model developed in this work was not optimized due to connection issues between the COM automation server and the simulation case. The model was found suitable for gas transport through hollow fiber membranes by one of two experiments with a relative deviation ≤ 3.65%. The other experiment deemed the model invalid due to large deviations in the permeate flow rate and permeate purity. Compared to the ChemBrane model, which was initially applied in the process design, the model showed similar but more realistic performance. In conclusion, the study shows that it is technically and economically feasible to use membranes for gas treatment, but the dehydration unit must be improved in terms of design, module configuration or membrane performance. Testing of the membranes in plant scale is necessary to determine the membrane lifetime and for further model validation. Investigation of the COM-technology and Cape-Open unit operation in the simulation environment is necessary for external optimization of user-defined models. Lastly, a detailed economical evaluation including an economic analysis and a sensitivity analysis is required to improve the cost estimations.

In this project the Power-to-Methane process will be designed and evaluated that consists of an alkaline electrolyser, multi-tubular methanation reactor and polyimide membrane. The feed gas CO2 is modelled in accordance with specifications given from the amine absorber located at the Biokraft plant in Skogn and the product is required to be of liquefaction quality. By applying the Power-to-Methane process the productivity of the plant can be increased while decreasing the CO2 emissions of the plant. The process has been designed and evaluated in HYSYS V10. An advanced MATLAB (R2019a) code for the multi-tubular methanation reactor was connected by using a CAPE-OPEN unit operation. Such an advanced way of modelling the methanation reactor was required because of a high runaway temperature from the highly exothermic methanation reaction. As a consequence of this high runaway temperature, the catalyst can be deactivated which is strongly unwanted. The design work and results are in accordance with similar work in literature. The Power-to-Methane process is rather novel and has become more interesting in industry over the last years. The process becomes more novel in this project since the thought is to include the liquefaction step to produce bio-LNG from the high quality biomethane that is produced. The results of the model suggest that the Power-to-Methane process is favoured at high operating pressure. However, this results in a higher reaction rate which in turn increases the temperature runaway. To solve this challenge, it is possible to reduce the dilution factor to oppose the reaction rate. This suggests that there must be an optimum point at which the pressure can be maximised while maintaining a stable process. The alkaline electrolyser for the production of hydrogen has a high investment cost and electrical energy demand. Therefore, it is the main contributor to the cost for the Power-to-Methane process. In fact, the electrical energy demand is found to be so high, that the cost for producing methane are almost as high as the production cost of hydrogen making the process not profitable for now. However, the electricity cost and investment cost electrolyser are expected to decrease in the next years before the plant is expected to be build.

Målet med dette prosjektet er å studere implementering av ulineær modellprediktiv regulering (NMPC) for en reaktor for emulsjonpolymerisasjon. En modell utledes ved bruk av fysiske prinsipper, og brukes til å erstatte målte data fra prosessanlegget. Den brukes også som modell for NMPC'en. Størsteparten av denne modellen ble utviklet i et tidligere prosjekt, men noen tilpasninger utføres for å gjøre den anvendelig for NMPC. Ytelsen til kontrollsystemet testes og demonstreres ved simuleringer. De teoretiske aspektene ved polymerer og emulsjonspolymerisasjon er spesifikt utdypet i denne oppgaven. Modellikningene som beskriver denne prosessen er implementert i C-kode, i en av Cyberneticas maler for polymerprosesser. Prosessen som studeres er emulsjonspolymerisasjonen av vinyl klorid (VCM), til det ønskede produktet poly-vinyl klorid (PVC). Modellen valideres og modifiseres mot prosessdata fra Inovyn Norge. Modellen ga akseptable resultater sammenlignet med prosessdata. Det understrekes at modellen kan gjøres anvendelig for andre systemer enn PVC, med litt anstrengelse og forståelse av prosessen. Konseptene bak optimalisering, MPC (Modellprediktiv regulering) og tilstands- og parameterestimering er gitt. I tillegg er noen spesifikke aspekter ved regulering og NMPC implementering av en semi-batch reaktor for emulsjonspolymerisasjon presentert. Noen avvik mellom modellene som ble brukt til å erstatte målte data for prosessanlegget, og i NMPC'en, ble bevisst implementert. Dette skal etterligne det faktum at en modell aldri vil være en eksakt representasjon av virkeligheten. Et KF (Kalman Filter) ble implementert som tilstand- og parameterestimator. Applikasjonen testes så både med og uten estimatoren. Implementeringen av NMPC, i kombinasjon med estimering av tilstand og parametere, ansees som vellykket i dette prosjektet. Resultatene indikerer at kontrollsystemet er i stand til å utnytte kjølekapasiteten ved å føde reaktanter og kontrollere temperaturen på en effektiv måte. Sikker drift og kvalitetskrav er da opprettholdt. The objective of this thesis is to study the implementation of NMPC (Nonlinear Model Predictive Control) on a reactor for an emulsion polymerization process. A model is derived using first principles and serves as a plant replacement model, in addition to an integrated part of the controller. The majority of this model was previously developed, and some customization is done to make it applicable for NMPC. The control system is tuned, and the performance is demonstrated by simulations. The theoretical aspects of polymers and emulsion polymerization are explicitly provided in this thesis. Necessary model equations describing this process is implemented in C code, in one of Cyberneticas templates for polymer processes. The process studied is the emulsion polymerization of vinyl chloride (VCM) to the desired product poly-vinyl chloride (PVC). The model is validated and modified against process data provided by Inovyn Norge. It is concluded that the model gave satisfactory results compared to process data. It is emphasized that the model can be done applicable for other systems than PVC, with some effort and an understanding of the process. The concepts behind optimization, MPC (Model Predictive Control) and state- and parameter estimation is provided. In addition, is some specific aspects of control and NMPC implementation on this process, presented. Some deviations between the model used as plant replacement, and in the controller, is deliberately implemented. This is done to imitate the fact that a model never will be an exact representation of reality. A KF (Kalman Filter) was implemented as the state- and parameter estimator, and was tuned and tested. The implementation of NMPC, in combination with state- and parameter estimation, on the reactor, is considered successful in this project. The results indicate that the control system can exploit the cooling capacity by feeding reactants and controlling the temperature in an efficient matter. This is done by still ensuring safe operation and meeting quality requirements.

Aldrende oljefelt opplever ofte fallende produksjon i enkelte brønner som følge av lavere trykk, økende vannmengder og endrede reservoaregenskaper. Ula-platformen har vært i drift siden 1986 og har flere slike brønner. Metoden som brukes på Ula i dag for å hjelpe på produksjonen er gassløft-teknologien. Denne løsningen bruker komprimert gass, noe som gjør det til en energikrevende løsning. En jetpumpe ble foreslått som en alternativ løsning for å øke produksjon og forlenge levetiden til oljefeltet. Den benytter en væske- eller gasstrøm og Venturi-effekten til å senke mottrykket i en lavtrykksbrønn og dermed øke produksjonen. Denne masteroppgaven tok for seg ulike jetpumpeløsninger og undersøkte ytelse og potensiell produksjonsøkning ved ulik anvendelse av jetpumpene. Tre ulike kilder til drivstrøm ble vurdert, injeksjonsgass, injeksjonsvann og væske fra høytrykksbrønner. Det ble inngått et samarbeid med Caltec Production Solutions for å beregne ytelse. Produksjonskurver for de enkelte brønnene ble brukt for å estimere økt produksjon med jetpumpen. En strøm injeksjonsvann på 6402 bbl/d ga en estimert produksjonsøkning på totalt 627 bbl/d når alle fire lavtrykksbrønner ble ledet til jetpumpen. Injeksjonsvannet er i overskudd når begge vanninjeksjonspumpene er i drift og er dermed en energikilde som ellers ville gå tapt. Et arrangement med jetpumpe drevetmed injeksjonsgass må inkludere "in-line" separasjon av lavtrykksstrømmen slik at kun gass ledes inn i jetpumpen. Den nødvendige mengden injeksjonsgass for å få samme produksjonsøkning på 627 bbl/d ble estimert til 6248Mscf/d. Det siste jetpumpearrangementet bruker energien i væskestrømmen fra høytrykksbrønner, en energikilde som vanligvis går til spille ved at trykket i brønnstrømmen reduseres over choke-ventilen. Den estimerte produksjonsøkningen i det tilfellet hvor en høytrykksbrønn ble bruk til å redusere mottrykket i en lavtrykksbrønn til 7 barg var 620 bbl/d olje. En forenklet sikkerhetsanalyse ble gjort for de ulike løsningene. Den viste at nye sikkerhetsbarrierer, blant annet en trykksikkerhetsventil, var nødvendig dersom injeksjonsgass eller injeksjonsvann var drivkilden. For løsningen med brønnstrøm som drivkilde var ikke nytt utstyr påkrevd.

I denne masteroppgaven er en matematisk modell for Fischer-Tropsch syntesen foreslått. Modellen inkluderer effektene av vann på reaksjonskinetikk, selektiviteter, og deaktivering av katalysator. Modellen er basert på 'consorted vinylene'-mekanismen. Fire katalysatorer med ulike karakteriseringer ble testet; tre av katalysatorene svarer til tre ulike Co/Re/γ-Al2O3 katalysatorer, og den fjerde svarer til en Co/Re/α-Al2O3 katalysator. Disse katalysatorene ble testet ved P = 20 bar, T = 210 C, og H2/CO = 2.1. Videre ble en kommersiell katalysator også testet ved P = 22-22 bar, T = 210 C, og H2/CO = 1.12, 1.72, og 2.1. Det konkluderes at den foreslåtte modellen klarer å beskrive hovedresponsene generelt veldig bra. Spesielt for den kommersielle katalysatoren ble metanselektivitetene i perioder hvor vann tilsettes bedre forklart med en modell for metandannelsen der vann er en aktiv del av dannelsesuttrykket. En andre ordens deaktiveringsmodell som inkluderer effekten av vann ble funnet til å beskrive katalysatorens deaktivering over tid på en tilfredsstillende måte. Modellen beskriver også den forventede effekten av vann, nærmere bestemt at vann øker katalysatorens deaktivering. Ved å studere hvordan ulike katalysator karakteriseringer påvirker de estimerte modellparameterne ble det observert at de fleste parameterne følger lineære trender når de plottes mot kobalt dispersjonene til katalysatorene. Den foreslåtte modellen for kjedevekst beskriver selektiviteten til C(5+) veldig bra, og modellen fanger også opp effekten av vann på riktig måte. Denne kjedevekstmodellen inkluderer ikke partialtrykket av hydrogen.

The objective of this thesis is to study the implementation of an on-line bilevel model predictive control (MPC) application to an emulsion copolymerisation process in a semi-batch reactor. Previous work has been performed on a regular MPC layer as well as an off-line open-loop study of the process. Using MPC in the process industry is becoming more common. This allows for the optimisation of chemical processes. However, the implementation of MPC requires a process model that accurately depicts the behaviour of the process plant. This is often time-consuming and cumbersome work. The nonlinear model used for this thesis was developed during the COOPOL EU-project, and had been implemented on a pilot plant. Some differences on behaviour between the model predictions and the plant behaviour were observed. The thesis gives an introduction to polymers, emulsion polymerisation and the most important kinetic mechanisms in free-radical emulsion polymerisation. This provides the equations in the model of the process, which is implemented in the programming language C. Using a standard template, it can be easily accessed by Cybernetica AS' specialised software for nonlinear real-time optimisation. The concept behind MPC is presented, as well as the concerns of the control of polymerisation processes. This provides a sufficient base for the understanding of the main purpose, implementation of a bilevel MPC control of the process. All process plants contain a control hierarchy, from the long-term economic objectives to the fast PID controllers that ensure safe operation of the plant. This thesis presents a hierarchy of two MPC-controllers, one with a long time horizon that provides the trajectories, and the lower which strives to follow these trajectories. This aim is to discover if there is a benefit of bilevel control compared to one single MPC controller. The main objective is to optimise the polymerisation time of the process, by allowing the temperature of the reactor and the flow rate of monomer and initiator feed to vary. However, the final product quality must remain as before. This thesis explores the possibility of controlling the process using two-level MPC control. The results are promising. This thesis shows that the implementation of two control layers is possible, though it requires extensive tuning by the engineer. Under the original conditions of the pilot plant the polymerisation time can be decreased with around five minutes using the bilevel control structure compared to the off-line calculations in the preliminary project.

Today, offshore power is mainly produced onsite by gas turbines and the process is responsible for the majority of the CO2-emissions from the Norwegian offshore industry. To reduce CO2-emissions offshore, electrification of the Norwegian continental shelf by long power cables from renewable onshore power production has been on the political agenda since the mid nineties, however, due to cost, only a few facilities are currently supplied by onshore power. By replacing the gas turbines with a highly effective hybrid fuel cell system, CMR Prototech has suggested an alternative solution that combined with carbon capture and storage may potentially produce clean and highly efficient offshore power (CHEOP). To replace today's offshore gas turbines, a topside concept capable of delivering 32 MW of electrical power is required. In that context, CMR Prototech has developed a proposed P&ID of a scaled-down CHEOP process that delivers 3.2 MW of electrical power at an electrical efficiency of 60% without carbon capture. In this work, a flow-sheet model of CMR Prototech's suggested CHEOP process with carbon capture was simulated in Aspen HYSYS to investigate its potential to produce clean and highly efficient power offshore. However, to be able to implement the proposed process in HYSYS, the membrane reactor of the CHEOP process was replaced by an already existing process route for syngas production and hydrogen separation as there is no specific unit operations that models the behaviour of membrane reactors in Aspen HYSYS, and to model one is outside the scope of this thesis. Hence, based on the nominal operating conditions of CMR Prototech's proposed CHEOP process and a literature review of hydrogen production technologies, an equilibrium-based flow-sheet model of the CHEOP process with carbon capture was developed in Aspen HYSYS to investigate its potential performance in this work. Furthermore, a sensitivity analysis and a heat integration were also performed to study how the process behave and its potential for further improvements. The simulation results show that at nominal operating conditions, the process has a net electrical power output of 2.89 MW and an electrical plant efficiency of 56.4%, which is excellent considered that the carbon capture process is included. Furthermore, approximately 400 kW of high quality excess heat from the oxyfuel-combustor are available for utilization in the reformer that will increase the hydrogen production and thus also the electrical power output and efficiency of the process if utilized. However, even though the additional heat is utilized, the SOFC is responsible for approximately 40% of the electrical power generation of the process. In CMR Prototech's proposed process the SOFC is only responsible for approximately 22% of the total power generation. This means that due to the energy demand of the reformer, a quite big SOFC will be needed in the more conventional process simulated in this work. This may become a problem with regards to size and weight on offshore facilities.

This report focuses on the production of hydrocarbons in a biomass to liquid (BtL) process with integration of hydrogen production. The hydrogen will be produced from high temperature electrolysis of steam utilizing excess heat in the plant. This represents a novelty which will increase the carbon efficiency of the plant, and lower the production cost. The design and evaluation of the plant have been done by simulations in Aspen Hysys V9. The conventional method of producing hydrocarbons in a BtL plant uses steam to adjust the syngas ratio by converting some of the CO into \ch{CO2} and hydrogen. In this case, the \ch{CO2} emissions from the plant are larger and the carbon efficiency is lower, typically 30-40\%. However, the hydrogen enhanced BtL plant in this report has shown a carbon efficiency of 97\%. This is because \ch{CO2} is not removed from the syngas due to the low concentration obtained when using the produced hydrogen to convert \ch{CO2} into CO and simultaneously adjusting the syngas ratio. The only carbon emission is the purge, which nonetheless is required to remove the inerts to avoid accumulation in the process. By heat integrating the whole process, the energy efficiency is found to be 70.4\%. The high temperature electrolysis for production of hydrogen and oxygen from steam currently have a high electrical energy consumption and investment cost. It is expected that the electricity consumption and equipment cost will be significantly reduced between 2020 and 2050. Currently, the HTE technology is only demonstrated in pilot scale for hydrogen production. From the economic evaluation of the profitability of the project it is estimated that the production cost for one liter of products is 5.32 NOK. This is significantly lower than the 7.04 NOK/L estimated for the conventional steam BtL plants. The plant will also be able to tolerate the higher discounted cash-flow rate of return of 15\% compared to 5\% for the steam BtL plant. Compared to a conventional steam BtL plant, the hydrogen enhanced plant will have higher investment and operating costs, but this will be compensated by the increased production of hydrocarbons.

The research is about a chemical process, which turns natural gas into liquid fuel through chemical reactions, and it is called Gas-to-Liquid (GTL) process. The produced liquid fuel is a replacement for liquid fuel derived from oil. This process can be one of the players in the reduction of our dependency on oil. The aim of the research is to increase the profitability of the process by increasing the efficiency through better process design and operation. There is also a great incentive to reduce the investment cost in order to make such process profitable at higher natural gas prices. Mathematical tools were used in our search to find a better process design. Detailed kinetic studies were performed and new relation for product formation is suggested. In this research, a new process configuration is proposed which is suitable for placement in remote locations such as offshore sites. In addition, the proposed process configuration helps in reducing flaring of natural gas in offshore oil platforms. The society benefits from cleaner and cheaper energy source which can have the potential to replace oil at least partly.

By using concentrated solar energy, it is possible to split water to hydrogen and oxygen, or eventually CO2 to CO and oxygen, by using redox materials at temperatures between 1200 1500 °C. One of the best redox materials studied so far, Co-doped-hercynite, has been synthesised by the incipient wetness impregnation (IWI) technique, characterised by surface area/pore measurements (BET/BJH) and X-ray diffraction (XRD), and tested by thermogravimetric analysis (TGA). Successfully tested and characterised material had theoretical production capacities of H2 or CO per mass Fe similar to the ones of other Co-doped-hercynite produced earlier by more advanced techniques. Activity was confirmed for 12 subsequent isothermal redox cycles at 1400 °C. Results and considerations imply that the total yield per mass Fe is dependent on the concentration of Co. Under certain conditions, oxidation was observed to start at about 500 °C, and reduction to start at as low as at around 1000 °C, which is the lowest reduction temperature recorded for Co-doped-hercynite. During CO2 splitting cycles, weight change fluctuations seemed to occur during oxidation, which could be related to simultaneous reduction activity, and another observation indicated carbonization. Observations were also in accordance with theory regarding increasing formation rate of Co alumina compounds when calcination occurs under inert atmosphere. A kinetic study to determine the reduction reaction model was also performed, where the D3 and D4 model seemed to be the best fits. Results from X-ray diffraction strongly indicated formation of α-alumina for all samples made and calcined at only 1000 °C overnight. Apart from this, the expected phases were identified for all samples at the different calcination temperatures, and the XRD pattern of cycled material was found to be as good as identical to a previously reported cycled Co-doped-hercynite material. BET showed an increasing surface area and pore volume the higher metal loadings, but this have to be confirmed by further studies. Samples prepared by calcination at 300 °C is believed to be at least about 200 m3/g, and at least about 8 m3/g when calcined at 1000 °C in air. In addition to experiments, evaluation, testing and further development of the method used for heat integration of a particularly cost efficient process design, studied in the specialisation project prior to this master thesis, was performed. An efficient heat integration is particularly crucial for the profitability of solar thermal splitting processes. The primary cost driver for the process is likely to be the cost of heliostats, and in this supplementary work, an automated techno-economic procedure to balance heat recovery against the cost of heliostats was accounted for.

Hydrocarbons are used in many products, and are the primary energy source for current civilizations, mainly as combustible fuel. There is a rapidly growing demand for environmentally friendly and renewable energy sources due to the depletion in fossil energy reserves and the need to reduce greenhouse gas emissions. The purpose of this work was to further study, optimize and integrate promising process designs for environmentally friendly production of Fischer Tropsch (FT) products, hydrocarbons with a widespread of carbon numbers. Syngas, a mixture of H2 and CO, is the feed for the FT synthesis, and this syngas is derived by using pressure-swing solar thermal water splitting, also known as the pressure swing hercynite cycle. The processes of syngas production from solar thermal water split and the FT synthesis from this syngas are individually studied recently at NTNU. The primary focus in this thesis was on the process development. Key elements were to explore different design alternatives and optimizing independent variables for the conceptual design and for the heat exchanger network. The conceptual design was developed in Aspen HYSYS®. Different conceptual design choices was explored and investigated. Three different conceptual design configurations were optimized in order to be compared and to decide upon a best case. Three different design configurations of heat exchanger networks (HENs) for the best case conceptual design were proposed. Simulations in Aspen Energy Analyzer® (AEA) were used for developing 60 near optimum HENs for all configurations and to decide upon the best HEN configuration. The best case utilizes external methane together with the oxygen produced from the solar thermal water splitting to produce additional syngas. 8716kg/h heavy FT product with mass fraction 0.945 of a lump with average carbon number 60 is produced, about 3.25 times higher flowrate than when no external methane is utilized. The overall energy efficiency and carbon efficiency of the final best case is 71.07% and 99.95%, respectively. Finally, a project evaluation was performed and the economic lifetime of the plant was set to 20years, operating 334days a year, 8 hours a day, in South Africa. The fixed capital investment for the entire plants is MM US$ 269.12, and with the total annual manufacturing cost of MM US$ 31.1, the average sale price of the total FT product has to be US$ 1.89/kg, in order to break even. This sale price is in between the average sale price for FT wax and the sale price of the most valuable FT wax. Several factors, such as the incentives for environmentally friendly production, have not been accounted for when arriving at this number. The debate about green house gas emissions is creating continuously increasing incentives for environmentally friendly production, which indicates a potentially bright future for the plant proposed in this thesis.

A biomass-to-liquid plant consists of pretreatment, gasification , syngas cleaning and conditioning, Fischer-Tropsch (FT) synthesis, and products upgrading. In the FT reactor the syngas is converted to liquid fuels on a cobolt (or iron) catalyst. There exist different reactor types of FT units, such as slurry bubble column, fixed bed and microchannel reactors. Here, we want to make a model of a fixed bed reactor of the FT synthesis in a new simulation system called VMGSim. A gasification model is already in the system. A kinetic model of the FT kinetics should be implemented in the simulation tool. This kinetic model takes into account a limited number of components, both alkanes and alkenes, and the selectivity to different products depends on composition and temperature. New process configuration of the BtL plant will be evaluated.

The world energy demand is increasing, and so is the demand for fertilizer to sustain an exponential population growth. Currently, with low oil prices, asso- ciated natural gas is flared off or re-injected into oil reservoirs for enhanced oil recovery (EOR). A gas-to-liquid process (GTL) for offshore applications aboard a foating production, storage, and offoading vessel (FPSO) incorpo- rating Fischer-Tropsch Synthesis (FTS) seeks to reform natural gas into more valuable liquid products. As the composition of natural gas feeds varies greatly depending on location and other factors, a surplus of hydrogen production is maintained in order to have a steady production of the desired FTS products. An alternative use for this surplus hydrogen is in ammonia synthesis, which in a relatively simple process design using readily available streams in the GTL process, can produce considerable amounts of ammonia. A complimentary design to an existing GTL process designed for offshore appli- cations which seeks to incorporate ammonia synthesis is proposed. Two possible designs are tentatively suggested and evaluated, each design utilising different streams in the GTL process with a high nitrogen content, in addition to the surplus hydrogen stream in the GTL process. The process design features a synthesis loop, as well as removal of compounds containing oxygen, such as CO2 and water, as these compounds are poisonous to the ammonia synthesis catalyst. The ammonia synthesis reactor is simulated as three separate beds, with a refrigeration loop to cool the stream exiting the reactor to sub-zero tem- peratures in order for ammonia to condense and be separated from the synthesis loop. Uncondensed ammonia and unreacted hydrogen and nitrogen gas is recy- cled and reintroduced to the reactor. Two separate process designs were simulated in Aspen HYSYS V8.6, each with a different source of nitrogen. The basis for the nitrogen sources for the ammo- nia synthesis process are the streams pertaining to the GTL process proposed by Hillestad et.al. Two different kinetic models were also evaluated. Heat integration is performed in Aspen Energy Analyzer V8.6, and a heat exchanger network (HEN) is proposed. The best process design features the N2 -rich stream from the membrane in the air enrichment unit in the GTL process, as this offers a simpler process design compared to utilising the tailgas from the GTL process. The system is optimised using the Temkin-Pyzhev kinetic model for the ammonia synthesis reactor. The power-optimal operating pressure is found to be approximately 235 bar, while the optimal operating temperature is found to be approximately 415 ◦C depending on the reaction bed. After heat integration, the process requires no external heat source, and the system power demand is suffciently low to be met by the gas turbine in the GTL process. The process converts 1889 kgmol/h of unprocessed hydrogen/CO2 stream from the hydrogen selective membrane in the GTL process, and 613 kg- mol/h of nitrogen/oxygen stream from the air enrichment unit to produce 1167 kgmol/h, or 19.9 tons/h, of ammonia. The total investment cost of the proposed design is estimated to 87.6 million US$.

Existing bioethanol production relies heavily on the use of corn and sugarcane as feedstocks. A prerequisite for increased consumption of bioethanol is the transition from the current use of corn and sugarcane to lignocellulosic biomass. This includes the use of wood, straws and agricultural residue such as sugarcane bagasse and corn stover, which do not compete directly with food production. Cellulosic ethanol also offers increased reduction in greenhouse gas emissions over both current bioethanol and petroleum based fuels. A biorefinery utilizing corn stover as feedstock has been designed and implemented in HYSYS. The model is based on the process for biochemical conversion of lignocellulosic biomass to ethanol designed by the U.S. National Renewable Energy Laboratory (NREL). The Marcotullio process for the production of furfural from aqueous xylose is integrated by selectively fractionating the feedstock into hemicellulose and cellulose. The model also includes a steam boiler cycle for co-generation of heat and electricity from residual solid material, and the biorefinery is found to be energy self-sufficient. The performance of the biorefinery is comparable to the NREL and Marcotullio processes. The combined conversion of useful carbohydrates into ethanol and furfural is found to be 81.1%, which corresponds to 47% of the total energy content in the corn stover feedstock. The heating demand is slightly increased compared to the NREL process, and generation of electricity is reduced.

The global energy demand is expected to increase by almost 50% by 2040. Simultaneously, fossil energy reserves are threatened to disappear. Thus it is imperative to development renewable technologies such as Biomass-To-Liquid process. This work investigates the performances of a Biomass-To-Liquid process involving a Fischer-Tropsch synthesis and the performances of a hybrid hydrogen-carbon process including hydrogen supply for a biomass feedstock of 20 000 tonnes per day. The processes have been simulated using the software Aspen Hysys and Aspen Properties. The impact of several parameters such as the water and oxygen content in the gasifier as well as the influence of the recycle rate on the Biomass-To-Liquid-Fischer-Tropsch process has been explored. The syngas production reaches a maximum for an oxygen supply into the gasifier of 42.4 tonnes per hour. It has been found that the addition of steam into the gasifier is not beneficial when having a fixed gasifier temperature and that recycling 90% of the tail gas into the Fischer-Tropsch gives the best performances. An optimal configuration of the BTL process which maximizes the carbon and energy efficiencies has been determined. It gives an energy efficiency of 56.55% and a carbon efficiency of 40.23% with a production of 4 257 barrel per day. Results are improved when using the hybrid hydrogen-carbon process and when the gasifier inlets are pre-heated. The highest performances have been found when the feedstock is pre-heated at 100°C and the oxygen supply at 1600°C. It gives an energy efficiency of 63.09% and a carbon efficiency of 79.4%. Greenhouse emissions have been divided by 12 and the production of hydrocarbons has doubled when using the hybrid process. The simulation for the hybrid process requires an important amount of hydrogen which compensates the economic benefit generated by the production rise. An increase in the pre-heating of the gasifier inlet must enhance this aspect.

The worlds energy demand is increasing, and at the same time the amount of easily accessible oil is reduced. Associated gas for most off-shore applications are flared or injected in the reservoir due to transportation challenges. A gas-to-liquid (GTL) process for offshore applications could be a solution to make valuable products of the associated and remote natural gas resources. GTL is a process that converts carbon based feedstock to more valuable liquid products. One of the main technologies used are the Fischer-Tropsch synthesis. A new process design for a GTL process for off-shore applications are proposed. The syngas is produced with an autothermal reformer (ATR) with enriched air as oxidant. The process design is a once-through, to prevent accumulation of nitrogen. Once-through means that no unconverted syngas is recycled in the process. In order to maximize the conversion and production of higher hydrocarbon the Fischer-Tropsch synthesis are staged. Three multitubular fixed bed stages are used with product separation and hydrogen added between each step. Two Fischer-Tropsch reactors in parallel are used for the two first reactor stages. The hydrogen is produced by steam methane reforming in a heat exchanged reformer, where heat needed for reaction is provided from the hot outlet stream from the ATR. The tail gas in the process is used for power production in a gas turbine. The hot effluent gas from the gas turbine is used for pre-heating of the natural gas. The process design is modelled and optimized with the use of Aspen HYSYS V8.6, with some use of Aspen Custom Modeler and MATLAB programming. The kinetic model used for the Fischer-Trospch reactors are proposed by Todic et al., with a product distribution model proposed by Hillestad. There are several parameters in the process that could be optimized. Optimizing in this master thesis are focused on obtaining the maximum production of C5+, which means hydrocarbons with five carbon atoms or more. The optimal distribution of the natural gas in the process was found to be 90% to the autothermal reformer and 10% to the heat exchanged reformer. With a natural gas feed amount of 120 MMSCF or 6,000 kmole/h the total production in the process are found to be 53.9 tonne/h or approximately 10,000 bbl/day. The carbon efficiency in the process is 57% and the energy efficiency is 45%. The process is self-supported with utilities and produces 36.4 MW of external power and 501 tonne/h of medium pressure steam. The total investments cost for the plant is estimated to 543.7 million$.

Two models for the copolymerization of propylene and ethylene in a fluidized bed reactor (FBR) were developed. A simple model for control; and a more advanced model which served as both a replacement for logged industrial plant data, and as a structurally different simulator to test the robustness of the controller. To ensure the best possible consistency between the two models, a set of parameters in the control model (CM) was estimated by fitting it to the plant replacement model (PRM). Additionally, an unscented Kalman filter (UKF) was set up to further mitigate the discrepancies between the models. A nonlinear model predictive control (NMPC) strategy was applied to transition between two different polypropylene (PP) grades. Hard constraints were imposed on the manipulated variables (MVs), while soft constraints were applied on the controlled variables (CVs). The effect of utilizing inert feed as an MV was studied with the CM as the simulator, i.e., no mismatch between the model of the controller and the process simulator. By employing the inert feed, the control of pressure improved; however, more catalyst was required to keep the production at the desired level. In order to demonstrate the effectiveness and robustness of NMPC, despite structural differences between the model and the plant, grade transitions were simulated with the PRM as the process simulator. The controller performed reasonably well, however, further tuning of both the controller and the UKF would result in more effective grade transitions. Nevertheless, the controller proved to be robust and coped well, notwithstanding the model mismatch.

Sulphur dioxide (SO2) is a well-known air pollutant, and is primarily formed as a by-product when fossil fuels are burned at power plants. Due to stringent emission regulations, well-designed and efficient flue gas desulphurization technologies (FGD) are a necessity. One potential FGD technology is the regenerable Labsorb process. However, the process is little applied and limited information is available in the literature from plants, which have installed the process in full scale, pilot scale tests and laboratory studies. This thesis seeks to find an electrolyte Non-Random Two Liquid (eNRTL) thermodynamic model in ASPEN Plus that is able to represent the experimental vapour-liquid equilibrium (VLE) data of the sodium-phosphate-water-SO2-system. Thereafter, the model will be used to identify energy efficient operating conditions in the Labsorb process. In the work to find a suitable eNRTL-model, binary interaction parameters were fitted to VLE data. Absorption and regeneration of SO2 in the Labsorb process were simulated separately in ASPEN Plus. The Buffer 3/1/0.5, i.e. CNa2HPO4= 3 mol/L, CNaH2PO4= 1 mol/L and CNa2SO4= 0.5 mol/L was used as a solvent in the simulations. In this work, it was developed an eNRTL model with an average deviation of 16.8% from experimental VLE data. The model was found to be valid in the temperature range 40 °C to 70 °C and in the SO2 concentration range 0.5 molSO2/L to 1.6 molSO2/L for buffer 3/1/0.5. Furthermore, it was shown that the method used to improve VLE in ASPEN Plus works. When absorption of SO2 was simulated, it was found that the absorption most likely was too ideal as it showed some deviation from available operating data. When regeneration of SO2 was simulated, it was not possible to conclude which operating conditions were most energy efficient. The main challenge in the study was lack of experimental data.

A gas-to-liquid process converts gaseous carbon feedstock into more valuable products. Recent technological improvements have led to an increased interest in this production method. This master s thesis has evaluated three different gas-to-liquid configurations to determine which design favors production of longer hydrocarbon chains (wax). All of the configurations were simulated with the AspenTech process simulator HYSYS V8.0, where kinetics from Todic et al.(2013) describe the Fischer-Tropsch product distribution. Only one pass through the reactor could be simulated because of the HYSYS implementation limitation, where C1-C15 alkanes and C2-C15 alkenes were included as products. Utilization of tail gas from the hydrogen plant resulted in a synthesis gas with a lower H2/CO ratio. Larger amounts of longer chains were detected and methane production was less favorable when this synthesis gas was processed in the Fischer-Tropsch synthesis. Configuration 2, where both water and products were separated between three smaller reactors, gave the highest carbon and energy efficiency, namely 31 and 13 %.

In the last years there have been much research and development regarding gas-to-liquid plants. The fuel demands are growing bigger, and fuels from oil and coal cannot cover the demands in the future. Converting natural gas to liquid fuels is a good way to fill the gap between supply and demand. The fuels from natural gas are cleaner than from oil and coal, because they contain less sulfur and aromatics. In this thesis a gas to liquid plant using Fischer-Tropsch synthesis was investigated. The main focus was the hydrotreater. In the hydrotreater cracking and isomerization reactions took place. Aspen?s simulation program HYSYS combined with Mathworks program MATLAB were used to solve the equations in the hydrotreater. After the simulation was done, an economic analysis of the whole plant was done using Microsoft Excel. The optimal conditions for the hydrotreater were an inlet temperature and pressure of 335 °C and 25 bars. The H2/wax ratio was 0.14 and the minimum reactor volume 33 m3. Recycling the light ends was found to be more profitable and carbon efficient than purging them. The project seemed to be beneficial and the net present value was about 3.8 billion dollars over a 20 years horizon and 9% discount rate. The internal rate of return became 52%, and the return on investment 53%.

In recent years the chemical industry has undergone considerable changes due to increased environmental regulations and energy costs. This master thesis has evaluated three different design considerations of the methanol synthesis loop using Honeywell's general purpose process simulator UniSim Design (R380 Build 14027) combined with MathWorks programming language MATLAB. The three configurations are Lurgis methanol reactor loop as built on Tjeldbergodden, the use of interstage methanol removal by the means of condensation and Lurgis MegaMethanol configuration. It was shown that the base case simulation of Lurgis reactor loop, using kinetics from Vanden Bussche and Froment (1996), gave reasonable results compared to Tjeldbergodden methanol plant. For the interstage methanol removal configuration it was found that the two reactors should be of equal length, 7.25 m, and that a cooling water temperature of 250 degrees C in the first reactor and 255 degrees C in the second reactor produced the highest amount of methanol. When operating with a recycle ratio of 2, this configuration had the potential of a net present worth of 47 million dollars compared to the base case over a 10 year horizon. The addition of a gas cooled reactor for the MegaMethanol process only increased the methanol production by 0.2 tonne/h, making the project unfeasible.

This report is a result of the work performed during the Master Thesis TKP 4900 at the Department of Chemical Engineering, NTNU in the spring of 2011. The problem assigned was "Modelling and fouling monitoring of a condenser at Snøhvit". The work was done in collaboration with Statoil ASA on a Helixchanger condenser at the LNG plant at Melkøya outside of Hammerfest, Norway. The condenser, 25-HA-112, condenses a mixture of propane and ethane by heat exchanging against sea water. A model describing the condenser 25-HA-112, based on the film method, was built in MATLAB. The model consisted of three sections; a cooling section, a section for integral condensation and a section for differential condensation. The differential model equations describing these were approximated by a collocation routine. The equation set consisted of both algebraic and differential equations and was solved using Newton's method. The thermodynamic model, based on Peng-Robinson equation of state, proved to be a challenge for the analysis. When changing the initial conditions for the condenser model, the thermodynamic model was unstable. This resulted in only small adjustments for each iteration could be made. A second model, constructed in the simulation software Unisim, was used to validate the MATLAB model. The results from the two models seemed to coincide, strengthening the condenser model constructed in MATLAB. A sensitivity analysis was carried out on the model using five parameters; vapour heat transfer coefficient, fouling resistance, vapour mass flow, sea water temperature and initial vapour composition. The results obtained in the sensitivity analysis performed as expected from theory, supporting the MATLAB model. Experimental data obtained for 25-HA-112 at Melkøya were compared to a case model built in MATLAB. The results show that the MATLAB model does not predict a satisfactory result for the cooling and integral section of the condenser. Reasons for this deviation are discussed. The main causes are thought to be the use of a too coarse model, the assumption of a binary component model and a higher heat transfer coefficient in the real condenser due to turbulence.

The use and demand of energy by exploiting fossil fuels is increasing. Carbon Capture and Storage (CCS) may be the solution to achieve decreased emissions, from various emitters of climate gases such as carbon dioxide. By permanent storage, the emissions of carbon dioxide will not reach the atmosphere, avoiding the greenhouse effect. The CO2-rich streams resulting from carbon capture need to be processed before transport and storage. Typical CO2 processing systems consist of compression, free-water removal and dehydration. The focus of this thesis is on the processing of captured CO2 from natural gas. Most often, the captured CO2-rich streams from natural gas are not 100% pure, and may contain several impurities in addition to water. The presence of impurities like methane and nitrogen may have a noticeable effect on the choice of design and process operability of the CO2 processing system. The effect of impurities on the phase behaviour of CO2-rich mixtures has been analysed. Predictions from different thermodynamic models have been evaluated and compared with experimental data from literature. Regression of binary interaction parameters has been done based on the assembled empirical data. Aspen Properties has been used to perform the regressions. The following cases were found relevant for design and process operability; four-stage system with reservoir pump, three-stage system with reservoir pump, effect of high level of impurities, effect of type of impurity, effect of impurity concentration, compression-only system (no pump), maximum free-water removal and handling of impurities. Technical solutions for dehydration of CO2 have been discussed. Basic concepts of absorption and adsorption are given together with relevant block diagrams and other key information.

The exergy losses in the thermal cracking of 1,2-dichloroethane (EDC) have been investigated for the EDC cracker in INEOS' vinyl chloride monomer (VCM) plant at Rafnes in Norway. This process section is the most energy demanding section in the plant, and an overview of the distribution of exergy losses was desired as part of the work for reducing energy consumption. The investigations were based on the results of established mass and energy balances for the process section in Aspen Plus. Calculations were done in a spreadsheet. Exergy balances were computed for a base case simulation. Different tests that were developed to investigate different modification's effect on exergy losses. The total exergy losses in the EDC cracking section were found to be 59.5 MW, or 3362 kJ/kg VCM. The largest exergy losses in the process section were located in the cracker unit. The internal losses in the cracker dominated and accounted for 75 % of all the internal exergy losses in the process section. The rest of the noticeable exergy losses were discovered in the heat exchangers in the top system. Preheating the EDC feed and the combustion air was found to give the largest reductions in the cracker exergy losses. This test shows a reduction in fuel gas needs of 6.6 %. Reduction in excess combustion air on the other hand showed no noticeable reductions. Fouling in H1406 and unnecessarily large amounts of excess air under normal conditions both result in large increases in exergy losses, and should be avoided if possible.