Direct capture of CO2 from ambient air is a developing technology, which is capable of removing CO2 directly from the atmosphere. Moreover, this technology is independent from sources of CO2 emissions. Hence, it can be set up at locations where pure stream of CO2 is needed such as in enhanced oil recovery. In this research, the performance of pelletized and natural limestone for CO2 capture from air in a fixed bed is studied. To compare the performance of sorbents for air capture, the effects of particle type (natural limestone and pelletized limestone), particle size (250-425 µm and 425-600 µm), gas flowrate (0.5 L/min and 1 L/min), and relative humidity, on the breakthrough time, breakthrough shape, and the global reaction rate are examined. Moreover, carbonation decay of sorbents over series of capture and regeneration cycles is studied. If the inlet stream (air) is humidified at 50% relative humidity, but the lime sorbents are not pre-hydrated, an axially non-uniform carbonated bed results. This phenomenon is due to the partial carbonation of sorbents at the first layers of the bed. While there is a competition between CO2 and water to react with CaO, partial carbonation reaction on the surface of the sorbents not only prevents further hydration, but also decreases the reaction rate at the surface. However, in comparison with a dry system where relative humidity was negligible and sorbents were not pre-hydrated, the observed carbonation conversion was higher. The best results were seen from experiments with pre-hydrated sorbents and humidified inlet stream. The smaller sorbent particles had a better performance (sharper breakthrough curve and longer breakthrough time) due to their greater surface area. A gas-solid reaction model was fitted to the breakthrough curves. Since at the beginning of carbonation there is no resistance of the product layer, it can be assumed that the process is reaction controlled. While after formation of the product layer (CaCO3), it becomes diffusion controlled. Results from fitted data also confirmed these conclusions. Moreover, each of sorbent went through 9 cycles and after each cycle the carbonation conversion of the sorbents was measured by TGA and the surface area by BET.

Direct capture of CO2 from ambient air is a developing technology, which is capable of removing CO2 directly from the atmosphere. Moreover, this technology is independent from sources of CO2 emissions. Hence, it can be set up at locations where pure stream of CO2 is needed such as in enhanced oil recovery. In this research, the performance of pelletized and natural limestone for CO2 capture from air in a fixed bed is studied. To compare the performance of sorbents for air capture, the effects of particle type (natural limestone and pelletized limestone), particle size (250-425 µm and 425-600 µm), gas flowrate (0.5 L/min and 1 L/min), and relative humidity, on the breakthrough time, breakthrough shape, and the global reaction rate are examined. Moreover, carbonation decay of sorbents over series of capture and regeneration cycles is studied. If the inlet stream (air) is humidified at 50% relative humidity, but the lime sorbents are not pre-hydrated, an axially non-uniform carbonated bed results. This phenomenon is due to the partial carbonation of sorbents at the first layers of the bed. While there is a competition between CO2 and water to react with CaO, partial carbonation reaction on the surface of the sorbents not only prevents further hydration, but also decreases the reaction rate at the surface. However, in comparison with a dry system where relative humidity was negligible and sorbents were not pre-hydrated, the observed carbonation conversion was higher. The best results were seen from experiments with pre-hydrated sorbents and humidified inlet stream. The smaller sorbent particles had a better performance (sharper breakthrough curve and longer breakthrough time) due to their greater surface area. A gas-solid reaction model was fitted to the breakthrough curves. Since at the beginning of carbonation there is no resistance of the product layer, it can be assumed that the process is reaction controlled. While after formation of the product layer (CaCO3), it becomes diffusion controlled. Results from fitted data also confirmed these conclusions. Moreover, each of sorbent went through 9 cycles and after each cycle the carbonation conversion of the sorbents was measured by TGA and the surface area by BET.

Many reports, scientific papers, patents, and scientific news investigate the feasibility and affordability of direct carbon dioxide capture from the atmospheric air (DAC). Since carbon dioxide (CO2) is extremely diluted in the atmosphere, large volumes of air have to be handled to capture comparable amounts of CO2. Therefore, both the energy consumption and the plant size are expected to be 'prohibitive'. On the other hand, some analyses have shown that DAC is feasible and can become affordable with essential research and development. DAC has been regarded as an optional bridging or a transitional technology for mitigating CO2 emissions in the medium-term. Priorities include investing in renewable and low-carbon technologies, efficiency and integration of energy systems, and realisation of additional environmental benefits. A heavy reliance on negative emission technologies (NETs), and consequently DAC, may be extremely risky as NETs interact with a number of societal challenges, i.e. food, land, water and energy security. Although, "... capturing carbon from thin air may turn out to be our last line of defence, if climate change is as bad as the climate scientists say, and if humanity fails to take the cheaper and more sensible option that may still be available today" MacKay (2009). Certainly, more research is necessary to bring down both cost and energy requirements for DAC. This work firstly predicts the adsorption equilibrium behaviour of a novel temperature swing adsorption process, which captures carbon dioxide directly from the air, concentrates, and purifies it at levels compatible to geological storage. The process consists of an adsorption air contactor, a compression and purification train, which is a series of packed beds reduced in size and connected in-line for the compression and purification purposes, and a final storage bed. The in-line beds undergo subsequent adsorption and desorption states. The final desorbed stream is stored in a storage bed. This cyclic process is repeated for a number of times imposed by the required purity and pressure in the final bed. The process is been thermodynamically verified and optimised. Since, the overall performance of this process does not only depend on the design of the process cycle and operating conditions but also on the chosen adsorbent material, further optimisation of the adsorptive and physical properties of the solid adsorbent is investigated. Thus, the optimal parameters of the potentially used porous materials is identified. Continuing the research on different adsorbent materials, an experimental investigation on the equilibrium properties of two competitive adsorbents is also performed. Besides the thermodynamic analysis, a dynamic model is presented for the investigation of the mass and heat transfer and its influence on the adsorption rate and consequently on the overall process performance. Since the initial stream is very dilute, it is expected that the adsorption rate will be low compared to other temperature swing processes and the capture rate will be affected by the heat transfer. Finally, the design and development of an experimental laboratory-scale apparatus is presented and analysed. Future design improvements are also discussed.

The overall objective of this thesis is to evaluate the fundamentals of current low concentration CO2 separation technologies and to provide an alternate method using adsorption technology with existing as well as new adsorbents. Two different applications for the adsorption of CO2 are explored; Direct Air Capture (DAC) and excimer gas purification. The investigation of aerogels as possible adsorbent for these applications was also explored. The first application, DAC of CO2 using adsorbents, addresses climate change by reducing the amount of atmospheric CO2 levels that are directly correlated to global warming. Because of DAC being carbon negative, this field has gained significant attention in the literature. DAC as a CO2 reduction strategy was approached in two ways: 1. Chapter 2 investigates capturing and concentrating CO2 from 0.04% in the air to 95% to be able to sequester it into the ground. This research began by doing an adsorbent selection using pure gas gravimetric measurements on seven different commercially available type X zeolites that were determined to have potential for this separation. Breakthrough experiments were then carried out with the most promising zeolite by perturbing the bed with compressed ambient air. In the process studied, a basic four step temperature vacuum swing adsorption (TVSA) cycle was investigated comprising the following steps: pressurization, adsorption, blowdown, and desorption. Four different regeneration temperatures were tested along with four different gas space velocities. With this cycle configuration, CO2 was concentrated to 95% from 0.04% with total capture fractions as high as 81%. This study highlighted methods to reduce the energy consumption per ton of CO2 captured in the system as well as the potential of using low Si/Al ratio faujasite structured zeolites in DAC of CO2 for greenhouse gas reduction. 2. Chapter 3 expands on the research of Chapter 2 by capturing CO2 from 0.04% in the air and concentrating it to high purity CO2 levels where the cost for operating the process will be reimbursed through the value of the produced CO2. The goal of this research was to increase the CO2 to as high as possible because the purer the CO2, the more valuable it is. This research started by conducting an in-depth investigation into the pure gas adsorption of CO2, N2, O2, and Ar on the most promising zeolite from Chapter 2. The data was then fitted to the TD-Toth model which allowed for the evaluation of the TVSA cycle and showed the potential of reducing the pressure and/or elevating the temperature during the blowdown step in order to produce high purity CO2. To confirm this, the TVSA cycle was run on a fixed bed breakthrough experiment where high purity CO2 was produced between a concentration of 99.5% and 99.96% by lowering the blowdown pressure. By controlling the blowdown temperature, the concentration of the product was increased from 99.8% to 99.95%, however with a significant loss of CO2. This effect of N2, O2, and Ar desorbing during the blowdown step with CO2 desorbing during the evacuation step is shown graphically by measuring the concentration and flow rate of the exiting gas species. The results from this study show the potential for producing a valuable product of high purity CO2 from atmospheric concentrations. The second application in this thesis that is explored in Chapter 4 is the purification of trace impurities of CO2, CF4, COF2, and O2 from F2, Kr, and Ne for applications in excimer lasers. Due to the incompatibility of many adsorbents to F2 and HF, aluminas and polymeric adsorbents were selected as potentially compatible materials. To increase the compatibility of these adsorbents, the use of a cryo-cooler was determined to be feasible to precool the feed stream before separation, which increases the adsorption capacity and compatibility of the material to F2 and HF. To determine the adsorption potential in the low concentration of these adsorbents, the concentration pulse chromatographic technique was chosen to determine the Henry’s Law constants of CO2, CF4, and O2. This data was then plotted on the van’t Hoff plot and extrapolated to colder temperatures to determine the benefit of using a cryo-cooler. From this study, it was determined that HayeSep Q was the best polymeric adsorbent with significant adsorption of CO2 at temperatures below -50˚C while being the best performing CF4 adsorbent. AA-300 was the best performing alumina in this study while having significant adsorption of CF4 at temperatures below -135˚C. However, from a compatibility standpoint, both of these materials need to be tested to determine their robustness in the presence of F2 and HF at room and reduced temperatures. Chapters 5 & 6 in this thesis explore the fundamentals of adsorption on aerogels as a prelude to using aerogels as possible adsorbents for DAC of CO2. This investigation into aerogels looks at silica aerogels and carbon aerogels, which are both industrially produced and explores their adsorption with relation to like materials such as silica gel and activated carbons. Both of these Chapters utilize experimentally determined adsorption isotherms of CO2, N2, O2, and Ar as well as characterization to determine adsorption trends in the materials. Some major conclusions for silica aerogels were that common surface modifications to make the material more resilient against water adsorption impacts the adsorption of CO2 significantly with roughly 4 fold difference in adsorption capacity. For carbon aerogels some major conclusions were that the adsorption was increasingly dominated by the heterogeneous nature of the surface at lower pressures and increasingly dominated by the pore size at the higher pressures. Both chapters discuss the adsorption of air along with ideas such as the influence of gas thermal conductivity in the pores with respects to adsorption. L'objectif général de cette thèse est d'évaluer les principes fondamentaux des technologies actuelles de séparation du CO2 à faible concentration et de fournir une méthode alternative utilisant la technologie d’adsorption avec des adsorbants actuels ainsi que d'en découvrir de nouveaux. Deux applications différentes pour l'adsorption du CO2 ont été explorées; la capture directe dans l’air ambient (CAD) et la purification des gaz excimères, ainsi que la recherche d'aérogels comme adsorbant possible pour ces applications. La première application, le CAD du CO2 utilisant des adsorbants, pourrait répondre aux changements climatiques puisque les niveaux de CO2 atmosphérique sont directement corrélés au réchauffement climatique. Dernièrement, le CAD a fait l'objet d'une attention particulière en tant que stratégie de réduction du CO2, par conséquent, deux voies différentes ont été explorées dans cette thèse: 1. Le chapitre 2 étudie la capture et la concentration du CO2 de 0,04% dans l'air à 95% afin de pouvoir l’enfermer dans la terre. Pour ce faire, une sélection d'adsorbant a été effectué en utilisant des mesures gravimétriques à gaz pur sur sept zéolithes de type X disponibles dans le commerce qui ont été déterminés comme ayant un potentiel pour cette séparation. Des expériences révolutionnaires ont ensuite été réalisées avec la zéolite la plus prometteuse en perturbant le lit avec de l'air ambiant comprimé. Dans le processus étudié, un cycle basique à quatre étapes d’adsorption modulée en température et pression (AMTP) a été étudié, comprenant les étapes suivantes: pressurisation, adsorption, purge et désorption. Quatre températures de régénération différentes ont été testées ainsi que quatre vitesses spatiales de gaz différents. Avec cette configuration de cycle, le CO2 était concentré à 95% de 0,04% avec des fractions de capture totales aussi élevées que 81%. Cette étude a mis en évidence des méthodes pour réduire la consommation d'énergie par tonne de CO2 captée dans le système ainsi que le potentiel d'utilisation de zéolithes structurées à base de faujasite à faible rapport Si/Al dans le CAD du CO2 pour la réduction des gaz à effet de serre. 2. Le chapitre 3 approfondit les recherches du chapitre 2 en capturant le CO2 de 0,04% dans l'air et en le concentrant à des niveaux de très haute pureté où le processus sera remboursé par la valeur du CO2 produit. L'objectif de cette partie était d'augmenter la pureté du CO2 le plus possible car plus le CO2 est pur, plus il est précieux. Une enquête approfondie sur l'adsorption de gaz pur de CO2, N2, O2 et Ar sur la zéolite la plus prometteuse du chapitre 2. Les données ont ensuite été ajustées au modèle TD-Toth qui a permis d'évaluer le cycle AMTP et a montré le potentiel de réduire la pression et/ou d'élever la température pendant l'étape de purge afin de produire du CO2 de haute pureté. Pour confirmer cela, le cycle AMTP a été fait par le biais d’une expérience dans un lit fixe où du CO2 de haute pureté a été produit entre une concentration de 99,5% et 99,96% en abaissant la pression de purge. En contrôlant la température de purge, la concentration du produit est passée de 99,8% à 99,95%, mais avec une perte importante de CO2. Cet effet de la désorption de N2, O2 et Ar pendant l'étape de purge avec la désorption du CO2 pendant l'étape d'évacuation est illustré graphiquement en mesurant la concentration et le débit des espèces de gaz sortant. Les résultats de cette étude montrent le potentiel de production d'un produit précieux de CO2 de haute pureté à partir des concentrations atmosphériques. La deuxième application de cette thèse qui est explorée au Chapitre 4 est la purification des traces d'impuretés de CO2, CF4, COF2 et O2 de F2, Kr et Ne pour des applications dans les lasers à excimère. En raison de l'incompatibilité de nombreux adsorbants avec le F2 et le HF, les alumines et les adsorbants polymères ont été sélectionnés comme matériaux potentiellement compatibles. Pour augmenter la compatibilité de ces adsorbants, l'utilisation d'un cryoréfrigérant a été jugée possible pour pré-refroidir le flux d'alimentation avant la séparation, ce qui augmente la capacité d'adsorption et la compatibilité du matériau en F2 et HF. Pour déterminer le potentiel d'adsorption dans la faible concentration de ces adsorbants, la technique de chromatographie pulsée de concentration a été choisie pour déterminer les constantes de la loi de Henry de CO2, CF4 et O2. Ces données ont ensuite été tracées sur le graphique van’t Hoff et extrapolées à des températures plus froides pour déterminer les avantages de l’utilisation d’un cryoréfrigérant. À partir de cette étude, il a été déterminé que HayeSep Q était le meilleur adsorbant polymère avec une adsorption significative de CO2 à des températures inférieures à -50 ° C tout en étant l'adsorbant CF4 le plus performant. L'AA-300 était l'alumine la plus performante de cette étude tout en ayant une adsorption significative de CF4 à des températures inférieures à -135 °C. Cependant, du point de vue de la compatibilité, ces deux matériaux doivent être testés pour déterminer leur robustesse en présence de F2 et de HF à température ambiante et réduite. Les chapitres 5 et 6 explorent les principes fondamentaux de l'adsorption sur les aérogels en prélude à l'utilisation d'aérogels comme adsorbants possibles pour le CAD du CO2. Cette enquête sur les aérogels examine les aérogels de silice et les aérogels de carbone, qui sont tous les deux fabriqués industriellement et explore leur adsorption par rapport à des matériaux similaires tels que le gel de silice et les charbons actifs. Ces deux chapitres utilisent des isothermes d'adsorption déterminés expérimentalement de CO2, N2, O2 et Ar ainsi que la caractérisation pour déterminer les tendances d'adsorption dans les matériaux. Certaines conclusions majeures pour les aérogels de silice étaient que les modifications de surface courantes pour rendre le matériau plus résistant à l'adsorption d'eau ont un impact significatif sur l'adsorption de CO2 avec une différence d'environ 4 fois dans la capacité d'adsorption. Pour les aérogels de carbone, certaines conclusions majeures étaient que l'adsorption était de plus en plus dominée par la nature hétérogène de la surface à des pressions plus faibles et de plus en plus dominée par la taille des pores aux pressions plus élevées. Les deux chapitres discutent de l'adsorption d'air ainsi que des idées telles que l'influence de la conductivité thermique du gaz dans les pores en ce qui concerne l'adsorption.

According to the Intergovernmental Panel on Climate Change, Carbon Dioxide Removal (CDR) technologies play a significant role in deep mitigation pathways to limit global temperature rise to 1.5°C. As a result, interest in them is becoming increasingly prevalent, the most widely discussed being Direct Air Capture (DAC), or active removal of carbon dioxide from atmospheric air. While DAC processes have indeed been successfully tested, one of the most prominent being that developed by Canadian company Carbon Engineering, their widespread deployment faces significant headwinds due to prohibitively high energy consumption and its associated costs. Before DAC can be considered to exist in a state of technological readiness, reductions to the installations' energy demand must be realized. This thesis analyzes the thermodynamic behavior of Carbon Engineering's proposed 1 Mt-CO2/year natural gas fuelled DAC plant, which they describe as “a low-risk starting point rather than a fully optimized least-cost design” [Keith et al., Joule 2, 1573], with the aim to illustrate key areas to which energy efficiency improvement measures must target. With an understanding built of the mechanisms by which energy is utilized and irreversibly lost within their plant, suggestions are put forth for directions to pursue for process improvements, with further analysis included on potential alternative plant configurations which would reduce overall heat and power consumption. A thermodynamic work loss analysis is performed on their plant design at a system level, which finds 92.2% of incoming exergy being lost to thermodynamic irreversibilities. A component-level analysis is then performed to detail the mechanisms by which these losses occur in the most energy-intensive plant segments, namely, the calciner and preheat cyclones, air separation unit, water knockout system, CO2 compression system, and power island. The dissipation of chemical exergy in the air contactor component, i.e., the release of stored chemical exergy as low-grade heat to the environment due to the exothermic reaction of CO2 and aqueous KOH, was determined as the largest unavoidable source of work loss. The most avoidable losses were found to be associated with use of natural gas as a feedstock for heat and power, namely, through its introduction of additional CO2 and water to be processed within the plant, and due to gas turbine power production's inherent Carnot efficiency limits. Additional analysis and discussion follows regarding possible loss reduction measures and modifications, the key concept presented being the use of renewable energy to provide plant power, combined with a calciner using electric resistance heating to meet its reduced thermal demand. Use of a readily-available high-temperature heat source for calciner heat is also considered, with thorough description included of its thermodynamic advantages. Finally, the all-electric plant concept is analyzed at a system level, and its advantages compared to the original natural gas fuelled case. / Graduate

abstract: As the global community raises concerns regarding the ever-increasing urgency of climate change, efforts to explore innovative strategies in the fight against this anthropogenic threat is growing. Along with other greenhouse gas mitigation technologies, Direct Air Capture (DAC) or the technology of removing carbon dioxide directly from the air has received considerable attention. As an emerging technology, the cost of DAC has been the prime focus not only in scientific society but also between entrepreneurs and policymakers. While skeptics are concerned about the high cost and impact of DAC implementation at scales comparable to the magnitude of climate change, industrial practitioners have demonstrated a pragmatic path to cost reduction. Based on the latest advancements in the field, this dissertation investigates the economic feasibility of DAC and its role in future energy systems. With a focus on the economics of carbon capture, this work compares DAC with other carbon capture technologies from a systemic perspective. Moreover, DAC’s major expenses are investigated to highlight critical improvements necessary for commercialization. In this dissertation, DAC is treated as a backstop mitigation technology that can address carbon dioxide emissions regardless of the source of emission. DAC determines the price of carbon dioxide removal when other mitigation technologies fall short in meeting their goals. The results indicate that DAC, even at its current price, is a reliable backup and is competitive with more mature technologies such as post-combustion capture. To reduce the cost, the most crucial component of a DAC design, i.e., the sorbent material, must be the centerpiece of innovation. In conclusion, DAC demonstrates the potential for not only negative emissions (carbon dioxide removal with the purpose of addressing past emissions), but also for addressing today’s emissions. The results emphasize that by choosing an effective scale-up strategy, DAC can become sufficiently cheap to play a crucial role in decarbonizing the energy system in the near future. Compared to other large-scale decarbonization strategies, DAC can achieve this goal with the least impact on our existing energy infrastructure. / Dissertation/Thesis / Doctoral Dissertation Sustainable Engineering 2020

To meet ambitious climate goals, of keeping global warming below 2°C, past emissions need to be removed from the atmosphere with the help of negative emissions technologies (NETs). The transition of energy systems, however, needs to follow the requirements of sustainable development to benefit all three pillars of sustainability, those are the environment, society, and economy. A NET that has gained increased attention from policymakers and businesses in recent years is direct air capture (DAC). The technology is currently on a small scale and faces challenges for scale-up such as energy and water intensity, the unclear requirements of resources and uncertain environmental, social, and economic impacts. The aim of this study was, therefore, to address DAC's impact on the three pillars of sustainability to answer the research question: How does direct air capture influence or connect to the three pillars of sustainable development? Because of the lack of research on DAC in connection with sustainability a qualitative interview approach was chosen where five interviews were conducted with researchers working with DAC. The findings derived from the interviews were separated into the different pillars of sustainability. The finding for the sustainability aspect included the definition of sustainability, various justice aspects and contributions to the SDGs. For the environmental aspect, DAC's carbon footprint and impact on mitigation were highlighted. The economic aspect of DAC showed the need for a clear business model and a supportive carbon mechanism. Lastly, for the social aspect low level of knowledge and the importance of social acceptance were recognized. Concluding, these different aspects influence the pillars of sustainability and need to be considered before further scale-up of DAC.

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Det är välkänt att klimatförändringar på grund av global uppvärmning är en av de största kriserna som hotar jorden. Det är en enorm utmaning för mänskligheten att minska koldioxidutsläppen, den främsta orsaken till global uppvärmning. Enkelt genomförbara åtgärder är inte tillräckliga och teknik för att ta bort koldioxid från atmosfären anses nödvändig för att temperaturökningen inte ska överstiga de 1,5 °C som anges i Parisavtalet. Direkt infångning av koldioxid från luft (vanligen kallad direkt luftinfångning, (Eng. Direct air capture - DAC)) är en ny teknik som kan ta bort koldioxid direkt från atmosfären. För närvarande är denna metod dyr; upp till 1000 USD per ton avlägsnad koldioxid. Denna höga kostnad beror främst på den relativt låga koldioxidkoncentrationen i luften, vilket leder till att en stor anläggning behövs för att fånga upp gasen och därmed stora investeringar. Tekniken är mycket energiintensiv, antingen elektrisk eller termisk, och för att göra en direkt infångning effektivare, måste anläggningen drivas med energi som inte har några eller mycket låga koldioxidutsläpp. Energin på Island är billig och dess produktion innebär ett mycket lågt koldioxidavtryck. Syftet med arbetet i denna avhandling är att utforska om metoden för direkt infångning av koldioxid från luft kommer att vara en mer genomförbar metod än koldioxidinfångning från punktkällor (eng. point source - PS) på Island på grund av god tillgång till billig och ren energi. Lärandekurvan för direkt luftfångning studerades tillsammans med scenarier för metodens tekniska utveckling. Tre olika fall med punktkällor på Island studerades för jämförelse. Två olika direkta luftinfångningstekniker analyserades också, en som drivs av en stor mängd elektricitet och en som drivs mestadels av termisk energi. Det resulterade i att i bästa fall, där inlärningshastigheten är hög och tekniska förbättringar är signifikanta, så skulle produktionskostnaden för direkt luftinfångning (levelized cost of energy, LCOC) vara lägre än motsvarande för infångning från en punktkälla. Energikostnaden påverkar LCOC för DAC idag men med teknisk utveckling förväntas energibehovet minska och därför kommer energikostnadens påverkan att bli lägre. Det är dock fortfarande viktigt, med tanke på bidraget till att minska globala uppvärmningen, att energin som driver DAC-anläggningen har ett lågt koldioxidavtryck, vilket kan garanteras på Island. Tvärtom, om inlärningshastigheten för DAC-tekniken är låg och inga tekniska förbättringar sker i lösningsmedel eller sorbenter, är och kommer DAC-tekniken att bli dyrare än infångning från punktkällor om båda anläggningarna finns på Island. En hög inlärningshastighet och teknikutveckling är beroende av trycket att nå målen i Parisavtalet. Det är därför mycket viktigt för DAC att efterfrågan på koldioxidinfångning ökar. Dessutom har DAC mer potential att påverka klimatförändringarna eftersom DAC kan vara en kolnegativ teknik om den kombineras med permanent lagring av koldioxid. PS-avskiljningen kan endast vara en kolneutral teknik och detta om den kombineras med permanent lagring av koldioxid. / It is well known that climate change due to global warming is one of the greatest crises facing the Earth. It is a huge challenge for mankind to reduce CO2 emissions, the major cause of global warming. Mitigation measures are not enough. Technologies to remove the CO2 from the atmosphere are considered necessary, so the temperature rise does not exceed 1.5°C as stated in the Paris Agreement. Direct air capture (DAC) is a new technology that can remove carbon dioxide directly from the atmosphere. Currently, this method is expensive, up to 1000 USD per ton CO2 removed. This high cost is mostly due to the relatively low concentration of CO2 in the ambient air, leading to a large unit to capture the gas and therefore high capital investment. The technology is very energy-intensive, either electrical or thermal, and to make direct air capture more efficient the plant needs to be powered with energy that has no or very low CO2 emissions. The energy in Iceland is low cost and its production has a very low carbon footprint. This thesis aims to find out if the direct air capture method will be more feasible than a point source CO2 capture in Iceland due to good access to low-cost and clean energy. The learning curve for direct air capture was studied along with scenarios for its technological development. Two different direct air capture technologies were analyzed, one that is powered by a large amount of electricity and one powered mostly by thermal energy. Three different point source cases in Iceland were studied for comparison. For the best-case scenario, where the learning rate is high and technological improvements are significant, the levelized cost of direct air capture is lower than levelized cost of point source capture. The cost of energy affects the levelized cost of direct air capture today but with technical development, the energy needed is expected to go down, and therefore the effect of energy cost will be lower.  However, it is still important, concerning contribution to reducing global warming, that the energy powering the direct air capture plant has a low carbon footprint, which can be assured in Iceland. On the contrary, if the learning rate of the direct air capture technology is low and no technical improvements occur in solvents or sorbents the direct air capture technology is and will be more expensive than point source capture considering both located in Iceland. The high learning rate and development in technology are dependent on the pressure to reach the goals of the Paris Agreement. It is therefore vital for direct air capture that the demand for carbon removal measures is enhanced due to pressure to reach the Paris Agreement goals. Furthermore, direct air capture has more potential to affect climate change than point source capture as direct air capture can be a carbon-negative technology if coupled with the permanent storage of CO2. The point source capture can only be a carbon-neutral technology if coupled with the permanent storage of CO2.

In light of escalating concerns over climate change and the imperative to mitigate greenhouse gas emissions, particularly carbon emissions, the pursuit of negative emissions technologies (NETs) has gained significant attention. Direct air capture (DAC) stands out as a promising avenue, offering the potential to actively remove carbon dioxide from the atmosphere. This degree project provides a thorough examination of two leading DAC projects, Mammoth and Stratos, which exemplify innovative approaches to achieving negative emissions at scale. By employing low-temperature DAC (LT DAC) and high-temperature DAC (HT DAC) respectively, Mammoth and Stratos confront the challenge of carbon capture with distinct technological strategies. This degree project employs a Techno-Economic Analysis (TEA) to estimate the Levelized Cost of CO2 Capture through DAC (LCOD), revealing Mammoth'sLCOD at $260/tCO2and Stratos at $608/tCO2, excluding costs for carbon transport and storage.The TEA is followed up with a Sensitivity Analysis to assess how the LCOD is affected by variations in input parameters, such as capital costs and electricity demand/costs among several parameters. Furthermore, this degree project identifies that uncertainties remain regarding the carbon storage solution, including its efficiency, long-term environmental implications, and associated costs. Given the Stratos projects’ dependence on Enhanced Oil Recovery (EOR) as the method of storing the captured carbon, the concern regarding efficiency and environmental implications is particularly relevant, as this method could potentially optimize oil production by 5-20%. As the discourse on DAC continues to evolve, this degree project advocates for the integration of Life Cycle Analysis (LCA) to comprehensively evaluate environmental impactsof both projects. This would guide the path towards sustainable carbon capture solutions, aiding in informed decision-making and guiding future DAC endeavors.