The scope of the present thesis is the development of a Computational Fluid Dynamics model to describe the multiphase flow inside a structured packing absorber for postcombustion carbon capture. The work focuses mainly on two flow characteristics: the interface tracking and the reactive mass transfer between the gas and the liquid. The interface tracking brings the possibility of studying the liquid maldistribution phenomenon, which strongly affects the mass transfer performance. The development of a user-defined function to account for the reactive mass transfer between phases constitutes the second major concept considered in this thesis. Numerical models found in the literature are divided into three scales due to the current computational capacity: small-, meso- and large-scale. Small-scale has usually dealt with interface tracking in 2D computational domains. Meso-scale has usually been considered to assess the dry pressure drop performance of the packing (considering only the gas phase). Large-scale studies the liquid distribution over the whole column assuming that the structured packing behaves as a porous medium. This thesis focuses on small- and meso-scale. The novelty of this work lies in expanding the capabilities of the aforementioned scales. At small-scale, the interfacial tracking is implemented in a 3D domain, instead of 2D. The user-defined function that describes the reactive mass transfer of CO2 into the aqueous MEA solution is also included to assess the influence of the liquid maldistribution on the mass transfer performance. At the meso-scale, the Volume of Fluid method for interface tracking is included (instead of only the gas phase) to describe flow characteristics such as the liquid hold-up, the interfacial area and the mass transfer. At the theoretical level, this model presents the particularity of including both a mass and a momentum source term in the conservation equations. A comprehensive mathematical development shows the influence of the mass source terms on the momentum equation.

Due to their high surface areas and structural tunability, porous metal-organic materials, MOMs, have attracted wide research interest in areas such as carbon capture, as the judicious choice of molecular building block (MBB) and linker facilitates the design of MOMs with myriad topologies and allows for a systematic variation of the pore environment. Families of MOMs with modular components, i.e. MOM platforms, are eminently suitable for targeting the selective adsorption of guest molecules such as CO2 because their pore size and pore functionality can each be tailored independently. MOMs with saturated metal centers (SMCs) that promote strong yet reversible CO2 binding in conjunction with favorable adsorption kinetics are an attractive alternative to MOMs containing unstaurated metal centers (UMCs) or amines. Whereas MOMs with SMCs and exclusively organic linkers typically have poor CO2 selectivity, it has been shown that a versatile, long known platform with SMCs, pillared square grids with inorganic anion pillars and pcu topology, exhibits high and selective CO2 uptake, a moderate CO2 binding affinity, and good stability under practical conditions. As detailed herein, the tuning of pore size and pore functionality in this platform has modulated the CO2 adsorption properties and revealed variants with unprecedented selectivity towards CO2 under industrially relevant conditions, even in the presence of moisture. With the aim of tuning pore chemistry while preserving pore size, we initially explored the effect of pillar substitution upon the carbon capture properties of a pillared square grid, [Cu(bipy)2(SiF6)] (SIFSIX-1-Cu). Room temperature CO2, CH4, and N2 adsorption isotherms revealed that substitution of the SiF62- (“SIFSIX”) inorganic pillar with TiF62- (“TIFSIX”) or SnF62- (“SNIFSIX”) modulated CO2 uptake, CO2 affinity (heat of adsorption, Qst), and selectivity vs. CH4 and N2. TIFSIX-1-Cu and SNIFSIX-1-Cu were calculated to exhibit the highest CO2/N2 and CO2/CH4 adsorption selectivites of the series, respectively. Modeling studies of TIFSIX-1-Cu and SIFSIX-1-Cu suggested that the enhancements in low pressure CO2 uptake and CO2 selectivity in the former arose from the stronger polarization of CO2 molecules by TIFSIX-1-Cu. The stronger framework-CO2 interaction at the primary binding site in TIFSIX-1-Cu correlates with the greater electronegativity of the pillar fluorine atoms relative to those in SIFSIX-1-Cu, and in turn to the higher polarizability of Ti4+ vs. Si4+. The effect of tuning pore size upon the carbon capture performance of pillared square grid nets was next investigated. Linker substitution afforded three variants, SIFSIX-2-Cu, SIFSIX-2-Cu-i, and SIFSIX-3-Zn, with pore sizes ranging from nanoporous (13.05 Å in SIFSIX-2-Cu) to ultramicroporous (3.84 Å in SIFSIX-3-Zn). Single-gas adsorption isotherms showed that SIFSIX-2-Cu-i, a doubly interpenetrated polymorph of SIFSIX-2-Cu with contracted pores (5.15 Å), exhibited far higher CO2 uptake, Qst towards CO2, and selectivity towards CO2 vs. CH4 and N2 than its non-interpenetrated counterpart. Further contraction of the pores afforded SIFSIX-3-Zn, a MOM with enhanced CO2 binding affinity and selectivity vs. SIFSIX-2-Cu-i. Remarkably, the selectivity of SIFSIX-3-Zn towards CO2 was found to be unprecedented among porous materials. Equilibrium and column breakthrough adsorption tests involving gas mixtures meant to mimic post-combustion carbon capture (CO2/N2), natural gas/biogas purification (CO2/CH4), and syngas purification (CO2/H2) confirmed the high selectivities of SIFSIX-2-Cu-i and SIFSIX-3-Zn. Gas mixture experiments also revealed that SIFSIX-3-Zn exhibited optimal CO2 adsorption kinetics. Most importantly, the CO2 selectivity of SIFSIX-2-Cu-i and SIFSIX-3-Zn was minimally affected in the presence of moisture. Modeling studies of CO2 adsorption in SIFSIX-3-Zn (experimental Qst ~ 45 kJ/mol at all loadings) revealed strong yet reversible electrostatic interactions between CO2 molecules and the SIFSIX pillars lining the confined channels of the material. Porous materials based upon the non-covalent assembly of discrete MBBs can also exhibit high surface areas and systematically tunable pore environments. Molecular porous material (MPM) platforms have begun to emerge despite the greater challenge of designing such materials in comparison to MOMs. Herein we report the tuning of pore functionality in an MPM platform based upon an extensive hydrogen-bonded network of paddlewheel-shaped [Cu(ade)4L2] complexes (ade = adenine; L = axial ligand). The substitution of Cl axial ligands with inorganic TIFSIX moieties has produced [Cu2(ade)4(TiF6)2], MPM-1-TIFSIX, a variant with enhanced CO2 separation performance and stability. Single-gas adsorption isotherms reveal that MPM-1-TIFSIX exhibits the highest CO2 uptake and CO2 Qst yet reported for an MPM as well as high selectivity towards CO2 vs. CH4 and N2. Modeling studies indicated strong electrostatic interactions between CO2 and the TIFSIX ligands lining the pores of MPM-1-TIFSIX. In addition to dramatically surpassing MPM-1-Cl with regard to CO2 separation performance, MPM-1-TIFSIX exhibits thermal stability up to 568 K and retains its performance even after immersion in water for 24 hrs. Comprehensively, the results presented herein affirm that porous materials featuring inorganic anions and SMCs can exhibit high and selective CO2 uptake, sufficient stability, and facile activation conditions without the drawbacks associated with UMCs and amines, i.e. competitive water adsorption and high regeneration energy, respectively.

An examination of the stationary power sector is performed using The Natural Step framework and Sustainability Principles (SP), in order to aid decision makers in developing policy to balance energy needs while reducing carbon dioxide (CO2) emissions in order to address climate change. Carbon capture and storage (CCS) is evaluated for its sustainability aspects, and is found to be a potentially sustainable approach which can be a bridging technology to a more sustainable energy mix, as well as a remediation technology which can remove CO2 from the atmosphere when utilized in combination with biomass fuel. Initial actions for restructuring the stationary power sector should emphasise demand reduction and efficiency efforts, followed by switching to renewable energy sources. If the first two strategies can not provide sufficient CO2 reductions, then investments in CCS technology may be an appropriate choice. CCS with coal-fired power can be a means to decouple CO2 emissions from fossil fuel use, but other SP violations associated with coal use must also be fully addressed before this strategy can be considered a truly sustainable option.

Dans ce travail, nous développons deux grands axes de recherche liés aux carbonates fondus. Le premier est l'optimisation des piles à combustible à base de carbonates fondus, avec deux approches : (i) l'amélioration de la durée de vie de la cathode grâce à des couches ultra-minces d'oxydes métalliques élaborés par la technique de dépôt de couches atomiques; (ii) la modification des électrolytes Li-K et Li-Na par addition de Cs ou de Rb. Le second est consacré à la valorisation du CO2 par sa réduction électrochimique dans les électrolytes à carbonates fondus, où nous analysons la réduction du CO2 par chronopotentiométrie et chronoamperométrie. Finalement, afin de tester les modifications subies par certains des composants analysés dans les deux premières parties, nous avons installé et adapté une configuration de cellule complète couplée à la chromatographie en phase gazeuse. Nous avons obtenu quelques résultats significatifs dans l’ensemble des approches abordées ; en ce qui concerne le point (i), nous avons constaté que TiO2 et CeO2 sont appropriés pour protéger la cathode contre la corrosion sans affecter ses propriétés électrochimiques en réduisant presque de moitié la dissolution du Ni. Les résultats obtenus pour le point (ii) sont également fructueux, car nous avons établi une méthode pour comparer deux électrolytes différents en déterminant les coefficients de diffusion des ions superoxyde et du dioxyde de carbone. Nous avons également comparé les performances de la cathode de NiO dans les électrolytes modifiés avec Cs et Rb. De ces études, nous avons constaté que l'addition de Cs améliore significativement le coefficient de diffusion de CO2 en réduisant la résistance de transfert de charge et la résistance totale à l'électrode, étant l'additif le plus prometteur testé ici. En ce qui concerne la réduction du CO2, nous avons constaté que la réaction implique des espèces adsorbées et instables et se produit en deux étapes à un électron ou une étape à deux électrons ; ainsi, il s’agit très probablement d’un mécanisme de réduction simultanée d’espèces adsorbées et dissoutes. Finalement, nous avons effectué les premiers tests sur cellule complète MCFC dans notre laboratoire, obtenant une performance et une puissance acceptables. Cependant, de petites améliorations sont encore nécessaires pour pouvoir tester les composants modifiés de cellule MCFC. / In this work, we develop two major research routes related to molten carbonates. The first one is the molten carbonate fuel cell optimization, with two approaches: (i) cathode lifetime improvement through ultra-thin layers of metal oxides deposited by atomic layer deposition; (ii) Li-K and Li-Na electrolyte modification by Cs or Rb additions. The second one is dedicated to CO2 valorization through its electrochemical reduction in molten carbonate electrolytes, where we analyze CO2 reduction by means of chronopotentiometry and chronoamperometry. Finally, in order to test some of the component modifications described in the two first parts, we installed and adapted a single-cell setup coupled to gas chromatography. We obtained some significant results in all the approaches; concerning point (i), we found that TiO2 and CeO2 are suitable for cathode corrosion protection without affecting the electrochemical properties of the electrode and reducing almost by half the dissolution of Ni. The results obtained from point (ii) are also fruitful, since we established a method for comparing two different electrolytes and obtained the diffusion coefficients of the superoxides and carbon dioxide. We also compared the performance of the state-of-the-art NiO cathode in Cs and Rb modified electrolytes. From these studies, we found that Cs addition improves significantly the CO2 diffusion coefficient and reduces the charge transfer and total resistance at the electrode, being a promising additive. Regarding CO2 reduction, after all the tests performed, we found that the reaction involves adsorbed and instable species and occurs in two one-electron steps or in two-electron unique step; thus, it follows most probably a mechanism of simultaneous reduction of the adsorbed and dissolved species. Finally, we performed the first MCFC single-cell tests in our laboratory obtaining an acceptable cell performance and output power. However, small improvements are still necessary to be able to test MCFC modified components.

Carbon capture and storage technologies are necessary to start lowering greenhouse gas emissions while continuing to utilize existing thermal power generation infrastructure. Calcium looping is a promising technology based on cyclic calcination/carbonation reactions which utilizes limestone as a sorbent. Steam is present in combustion flue gas and in the calciner used for sorbent regeneration. The effect of steam during calcination on sorbent performance has not been extensively studied in the literature. Here, experiments were conducted using a thermogravimetric analyzer (TGA) and subsequently a dual-fluidized bed pilot plant to determine the effect of steam injection during calcination on sorbent reactivity during carbonation. In a TGA, various levels of steam (0-40% vol.) were injected during sorbent regeneration throughout 15 calcination/carbonation cycles. All concentrations of steam were found to increase sorbent reactivity during carbonation. A level of 15% steam during calcination had the largest impact. Steam changes the morphology of the sorbent during calcination, likely by shifting the pore volume to larger pores, resulting in a structure which has an increased carrying capacity. This effect was then examined at the pilot scale to determine if the phase contacting patterns and solids heat-up rates in a fluidized bed were factors. Three levels of steam (0%, 15%, 65%) were injected during sorbent regeneration throughout 5 hours of steady state operation. Again, all levels of steam were found to increase sorbent reactivity and reduce the required sorbent make-up rate with the best performance seen at 65% steam.

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

The master’s thesis addresses the transmedia education strategies applied in the CO2 degrees challenge, a project by the Global Carbon Capture and Storage Institute (GCCSI), dedicated to educating students about the low-carbon technology carbon capture and storage (CCS). Based on the literature review, the thesis theoretically discusses the public perception of low-carbon technology and carbon capture and storage in connection to transmedia storytelling and education. The thesis is structured upon a qualitative approach and conducts a detailed study of a selected single case. In addition, expert interviews are used to support the in-depth analysis of the case study with the use of the transmedia design analytical and operational model by Gambarato et al. (2020). The analysis provides insights into how this technical process was presented to the educators and students and identifies challenges and opportunities of the transmedia education project in the realm of low-carbon technologies. The results of the study show that the CO2 degrees challenge offered a significant contribution to the knowledge dissemination about the CCS technology among students, helped them to understand current problems, and to discuss real-time solutions. The results also point to the challenge of communicating a scientific and engineering topic with the audience outside of the technological and engineering industry, the complicated structure of the project, and difficulties connected with possible financial interests of the private companies supporting and funding the educational material and the project itself.

Soot in coal combustion simulations is often ignored due to its computational complexity, despite significant effects on flame temperature and radiation. In this research, a 40 kW oxy-coal combustion system is modeled using Large Eddy Simulations (LES) and a semi-empirical monodisperse coal soot model. Simulation results are compared to experimental measurements of temperature, species concentrations, and soot concentration. Cases where soot is modeled are compared with cases where soot is neglected to determine the accuracy benefits of modeling soot. The simulations were able to replicate experimental results within an acceptable level of error. Including soot in the simulations did not consistently increase accuracy for the simulation setup and modeling assumptions used in this research.

Increased carbon dioxide in the atmosphere has raised the attention to Carbon Capture and Storage (CCS). Stockholm Exergi is a company conducting research on CCS and bio-CCS, a form of CCS where biogenic CO2 is captured. This master thesis analyzed the possibilities to implement CCS and bio-CCS at Högdalenverket, one of Stockholm Exergi’s combined heat and power plant with waste incineration. The aim was to investigate advantages and disadvantages with different carbon capture technologies (CC technologies) considering technical, economical, and energy related aspects. Industrial and household waste are incinerated in four boilers at Högdalenverket. Two cases were analyzed, one case with all boilers connected to the CC technology and one case with the boiler with the highest degree of CO2 emission connected. The CC technologies taken into consideration were amine technology, Hot Potassium Carbonates (HPC), Compact Carbon Capture (3C), and Svante. Amine technology and HPC use chemical absorption in static columns. The Amine technology is the most investigated and used one. It uses temperature swing absorption with amines as absorbent. HPC uses pressure swing absorption with potassium carbonate as absorbent. The remaining two are new process intensified technologies. 3C uses rotating packed beds and absorbs CO2 chemically using, most commonly, amines. Svante also uses a rotating technique by chemically adsorbing CO2 with nanomaterial as the solid adsorbent. All CC technologies need steam to regenerate CO2. The steam was assumed to be extracted from the existing steam network at Högdalenverket with a pressure and temperature of 36 bar and 400 degrees. The method used in the study was mainly literature review with peer reviewed articles regarding CCS as base. It was of importance to analyze how the flue gases could affect the CC technologies since the waste has an inhomogeneous composition. The flue gas composition was compiled using external and internal measurements from 2019 and 2020. Furthermore, energy and power calculations were performed to investigate how the heat and electricity delivery would be affected if the different CC technologies were implemented. Moreover, economic calculations regarding the cost for heat and electricity were carried out. Two interviews were also conducted, one with a CCS consultant company and one with internal staff at Högdalenverket. According to the literature review, O2, SO2, and NO2 appeared to be the pollutants causing highest risk of solvent degradation in the flue gases. The high O2 content at Högdalenverket could cause oxidative degradation, especially in amine technology. The SO2 and NO2 content in the flue gases was mainly low and would therefore not significantly affect the technologies. Peeks with high content did however occur and amines, especially within the amine technology, could form toxic and cancerogenic nitrosamines with NO2 which should not be released to the atmosphere. The flue gas composition proved not to be the limiting factor for implementation of CC technology on all incinerators. However, it is costly and complex to handle the variations in flue gas flow which can occur when all boilers are used. The technologies showed high need of heat and electricity which would result in significant reductions in delivery from Högdalenverket. The need of heat and electricity would in turn lead to high operating costs. The Amine technology showed the greatest influence on the heat delivery due to the significant steam requirement to regenerate CO2. HPC showed extreme influence on the delivery of electricity due to the flue gas compression needed in pressure swing processes. Both technologies consist of high columns with significant degree of land use which would be difficult to implement within the limited area at Högdalenverket. As a result of these aspects, HPC and Amine technology are not considered to be suitable technologies to implement at Högdalenverket. However, the master thesis presented measures for energy saving that should be considered before excluding the technologies. One energy saving measure is to find the optimal heat recovery, for example by pinch-analysis. Moreover, composition, concentration, and flowrate of the absorbent can be analyzed. In addition, higher columns are associated with lower need of energy. Finally, modifications of the capture process can be investigated, and one example is to split the flow of the absorbent into two streams into the columns. 3C and Svante are compact technologies that require less land and have potential to fit at more locations at Högdalenverket. The compact design also leads to 50 percent less investments costs compared to the other two technologies. Moreover, these technologies are presented as more resistant against degradation of sorbents, and both requires less energy to regenerate CO2. These technologies are therefore more suitable for implementation at Högdalenverket. A drawback is that they are not yet commercially developed, they are only located at 6-7 at the TRL-scale. TRL stands for Technology Readiness Level and implies how developed the technology is. The scale ranges from one to nine where nine means that the technology is commercially developed. Today, there are no economic incentives for the biogenic part of the CO2 emissions. However, there are investigations ongoing to create a market and economic incentives for the bio-genic part, one of the suggestions is reversed auctions. It is important to investigate methods to reduce the technologies need of heat and electricity, e.g., by finding other ways to extract steam instead of using steam with high exergy. Reducing the need of energy is important in the view of cost reduction, but also to avoid potential transfer of emissions to fossil CO2 generating production. The losses of heat and electricity generation that occur when implementing a CC technology need to be replaced. This replacement could end up being production from fossil fuels if no other options are available. Another aspect that needs to be considered is the suitability of using amines to a greater extent since it could cause serious environmental and health issues.

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