Carbon Capture and Storage (CCS) is a suite of technologies available to directly reduce carbon dioxide (CO2) emissions to the atmosphere from fossil fuelled power plants and large industrial point sources. For a safe deployment of CCS it is important that CO2 injected into deep geological formations does not migrate out of the storage site. Characterising and understanding possible migration mechanisms and pathways along which migration may occur is therefore crucial to ensure secure engineered storage of anthropogenic CO2. In this thesis naturally occurring CO2 accumulations in the subsurface are studied as analogue sites for engineered storage sites with respect to CO2 migration pathways and mechanisms that ensure the retention of CO2 in the subsurface. Geological data of natural CO2 reservoirs world-wide has been compiled from published literature and analysed. Results show that faults are the main pathways for migration of CO2 from subsurface reservoirs to the surface and that the state and density of CO2, pressure of the reservoir, and thickness of the caprock influence the successful retention of CO2. Gaseous, low density CO2, overpressured reservoirs, and thin caprocks are characteristics of insecure storage sites. Two natural CO2 reservoirs have been studied in detail with respect to their fault seal properties. This includes the first study of how fault rock seals behave in CO2 reservoirs. It has been shown that the bounding fault of the Fizzy Field reservoir in the southern North Sea can with hold the amount of CO2 trapped in the reservoir at current time. A initially higher gas column would have led to across fault migration of CO2 as the fault rock seals would not have been able to withhold higher pressures. Depending on the present day stress regime the fault could be close to failure. At the natural CO2 reservoir of St. Johns Dome, Arizona, migration of CO2 to the surface has been occurring for at least the last 500 ka. Fault seal analysis shows that this migration is related to the fault rock composition and the orientation of the bounding fault in the present day stress field. Using the U-Th disequilibrium method the ages of travertine deposits of the St. Johns Dome area have been determined. The results illustrate that along one fault CO2 migration took place for at least 480 ka and that individual travertine mounds have had long lifespans of up to ~350 ka. Age and uranium isotope trends along the fault have been interpreted as signs of a shrinking CO2 reservoir. The amount of CO2 calculated to have migrated out of the St. Johns Dome is up to 113 Gt. Calculated rates span from 5 t/yr to 30,000 t/yr and indicate that at the worst case large amounts of CO2 can migrate rapidly from the subsurface reservoir along faults to the surface. This thesis highlights the importance of faults as fluid pathways for vertical migration of CO2. It has been also shown that they can act as baffles for CO2 migration and that whether a fault acts as pathway or baffle for CO2 can be predicted using fault seal analysis. However, further work is needed in order to minimise the uncertainties of fault seal analysis for CO2 reservoirs.

Carbon dioxide enhanced oil recovery (CO2EOR) is a proven and available technology used to produce incremental oil from depleted fields. Although this technology has been used successfully onshore in North America and Europe, projects have maximised oil recovery and not CO2 storage. While the majority of onshore CO2EOR projects to date have used CO2 from natural sources, CO2EOR is now more and more being considered as a storage option for captured anthropogenic CO2. In the North Sea the lack of low cost CO2, in large volumes, has meant that no EOR projects have utilised CO2 as an injection fluid. However CO2EOR has the highest potential of all EOR techniques to maximise recovery from depleted UK oil fields. With the prospect of Carbon Capture and Storage (CCS) capturing large tonnages of CO2 from point source emission sites, the feasibility of CO2EOR deployment in the North Sea is high. This thesis primarily aims to address a number of discrete issues which assess the effectiveness of CO2EOR to both produce oil and store CO2. Given the fundamental shift in approach proposed in North Sea CO2EOR projects, the carbon balance of such projects is examined. Using a life cycle accounting approach on a theoretical North Sea field, we examine whether offshore CO2EOR can store more CO2 than onshore projects traditionally have, and whether CO2 storage can offset additional emissions produced through offshore operations and incremental oil production. Using two design scenarios which optimise oil production and CO2 storage, we find that that net GHG emissions were negative in both ‘oil optimised’ and ‘CO2 storage optimised’. However when emissions from transporting, refining and combusting the produced crude oil are incorporated into the life cycle calculations the ‘oil optimised scenario’ became a net emitter of GHG and highlights the importance of continuing CO2 import and injection after oil production has been maximised at a field. This is something that has not traditionally occurred. After assessing rates of flaring and venting of produced associated gas at UK oil fields it is found that the flaring or venting of reproduced CH4 and CO2 has a large control on emissions. Much like currently operating UK oil fields the rates of flaring and venting has a control on the carbon intensity of oil produced. Here values for the carbon intensity of oil produced through CO2EOR are presented. Carbon intensity values are found to be similar to levels of current UK oil production and significantly lower than other unconventional sources. As well as assessing the climate benefits of CO2EOR, a new assessment of CO2EOR potential in Residual Oil Zones (ROZ) is also made. ROZ resource, which is thought to add significant potential to both the oil reserves and CO2 storage potential in some US basins, is here identified in the North Sea for the first time. Based on the foundation of North Sea hydrodynamics study, this thesis identifies the Pierce field as a candidate ROZ field where hydrodynamic tilting of the oil water contact has naturally occurred leaving a zone of residual oil. To test the feasibility of CO2EOR in such a zone a methodology is presented and applied. Notably the study highlights that in this case study recoverable reserves from the ROZ may approach 20% of total field recoverable reserves and have the capability to store up to 11Mt of CO2. While highlighting the CO2EOR potential in the ROZ the thesis discusses the importance in expanding the analysis to quantify its importance on a basin scale. Discussion is also made on whether new resource identification is necessary in a mature basin like the North Sea. With CO2EOR being considered as a feasible option for storing captured anthropogenic CO2, it is important to assess the security of storage in CO2EOR. Using real geochemical and production data from a pilot CO2EOR development in Western Canada two approaches are used to assess the partitioning of CO2 between reservoir fluids through time. Using a number of correlations it is found that CO2 dissolution in oil is up to 7 times greater than in reservoir brine when saturations between the two fluids are equal. It is found that after two years of CO2 injection solubility trapping accounts for 26% of injected CO2. The finding that significantly more dissolution occurs in oil rather than brine indicates that CO2 storage in EOR is safer than in brine storage. However a number of factors such as the increase in oil/CO2 mobility due to CO2 injection is also discussed. The overall conclusion from the work is that CO2EOR in the North Sea has the potential to be an effective way of producing oil and storing CO2 in the North Sea. A number of design, operational and accounting factors are however essential to operate an exemplar CO2EOR project where low carbon intensity oil can be produced from a mature basin while storing large tonnages of captured anthropogenic CO2.

Chemical looping combustion (CLC) is a technique for separating pure carbon dioxide from the combustion of fuels. The oxygen to burn the fuel comes from the lattice oxygen contained in solid particles of an inorganic oxide (the 'oxygen carrier'), instead of from oxygen in the air. Thus only CO2 and water leave the combustor, or fuel reactor. Next, the water is condensed, leaving pure CO2. The oxygen carrier is regenerated by oxidising it in air in a second reactor, called the air reactor. Accordingly, a stream of pure carbon dioxide can be produced, uncontaminated with gases such as nitrogen, normally present when the fuel burns in air. This intrinsic separation with CLC enables CO2 to be separated more efficiently than with other techniques, such as post-combustion scrubbing of carbon dioxide from stack gases with amine-based solvents. The design of a CLC system and its performance within an electricity system represents a multi-scale problem, ranging from the behaviour of single particles of oxygen carrier within a reactor to how a CLC-based power plant would perform in an electricity grid. To date, these scales have been studied in isolation, with little regard for the vital interactions and dependences amongst them. This Dissertation addresses this problem by considering CLC holistically for the first time, using a multi-scale approach. A stochastic model was developed, combining the particle-and reactor-scales of CLC. It included an appropriate particle model and can be coupled to a detailed reactor model. The combination represented a significant change from existing approaches, uniquely accounting for all the important factors affecting the assemblage of particles performing in the CLC reactors. It was used to determine the regimes of operation in which CLC is sensitive to factors such as the manner in which the particles are reacting, the residence time distribution of particles in the two reactors, the particle size distribution and the reaction history of particles. To demonstrate that the approach could simulate specific configurations of CLC, as well as a general system, the model was compared with results from experiments in which CLC with methane was conducted in a laboratory-scale circulating fluidised bed. The long-term performance of oxygen carrier materials is important, because, in an industrial process, they would be expected to function satisfactorily for many thousands of hours of operation. Long-term experiments were conducted to evaluate the resistance of different oxygen carrier materials to physical and chemical attrition. The evolution of their chemical kinetics was also determined. The results were used to evaluate the impact of different oxygen carrier materials in a fuel reactor at industrial-scale. Finally, a theoretical approach was developed to simulate how a fleet of CLC-based power plants would perform within the UK's national grid. By understanding how different parameters such as capital cost, operating cost and measures of efficiency, compared with other methods of generation offering carbon reduction, desirable design modifications and needs for improvement for CLC were identified by utilising the theoretical and experimental work conducted at the particle- and reactor-scales.

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.

abstract: The large-scale anthropogenic emission of carbon dioxide into the atmosphere leads to many unintended consequences, from rising sea levels to ocean acidification. While a clean energy infrastructure is growing, mid-term strategies that are compatible with the current infrastructure should be developed. Carbon capture and storage in fossil-fuel power plants is one way to avoid our current gigaton-scale emission of carbon dioxide into the atmosphere. However, for this to be possible, separation techniques are necessary to remove the nitrogen from air before combustion or from the flue gas after combustion. Metal-organic frameworks (MOFs) are a relatively new class of porous material that show great promise for adsorptive separation processes. Here, potential mechanisms of O2/N2 separation and CO2/N2 separation are explored. First, a logical categorization of potential adsorptive separation mechanisms in MOFs is outlined by comparing existing data with previously studied materials. Size-selective adsorptive separation is investigated for both gas systems using molecular simulations. A correlation between size-selective equilibrium adsorptive separation capabilities and pore diameter is established in materials with complex pore distributions. A method of generating mobile extra-framework cations which drastically increase adsorptive selectivity toward nitrogen over oxygen via electrostatic interactions is explored through experiments and simulations. Finally, deposition of redox-active ferrocene molecules into systematically generated defects is shown to be an effective method of increasing selectivity towards oxygen. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2019

The increasing trend of world-wide energy consumption emphasizes the importance of ongoing optimization of new and existing technologies. In this dissertation, two energy–intensive systems are simulated and optimized. Advanced estimation, optimization, and control techniques such as a moving horizon estimator and a model predictive controller are developed to enhance the profitability, product quality, and reliability of the systems. An enabling development is presented for the solution of complex dynamic optimization problems. The strategy involves an initialization approach to large–scale system models that both enhance the computational performance as well as the ability of the solver to converge to an optimal solution. One particular application of this approach is the modeling and optimization of a batch distillation column. For estimation of unknown parameters, an L1-norm method is utilized that is less sensitive to outliers than a squared error objective. The results obtained from the simple model match the experimental data and model prediction for a more rigorous model. A nonlinear statistical analysis and a sensitivity analysis are also implemented to verify the reliability of the estimated parameters. The reduced–order model developed for the batch distillation column is computationally fast and reasonably accurate and is applicable for real time control and online optimization purposes. Similar to estimation, an L1-norm objective function is applied for optimization of the column operation. Application of an L1-norm permits explicit prioritization of the multi–objective problems and adds only linear terms to the problem. Dynamic optimization of the column results in a 14% increase in the methanol product obtained from the column with 99% purity. In a second application of the methodology, the results obtained from optimization of the hybrid system of a cryogenic carbon capture (CCC) and power generation units are presented. Cryogenic carbon capture is a novel technology for CO2 removal from power generation units and has superior features such as low energy consumption, large–scale energy storage, and fast response to fluctuations in electricity demand. Grid–level energy storage of the CCC process enables 100% utilization of renewable power sources while 99% of the CO2 produced from fossil–fueled power plants is captured. In addition, energy demand of the CCC process is effectively managed by deploying the energy storage capability of this process. By exploiting time–of–day pricing, the profit obtained from dynamic optimization of this hybrid energy system offsets a significant fraction of the cost of construction of the cryogenic carbon capture plant.

The prospect of rapid changes to the climate due to global warming is subject of public concern. The need to reduce the emissions of atmospheric green house gases and in particular carbon dioxide is greater than ever. Extensive research is performed to find new solutions and new materials, which tackles this problem in economically benign way. This thesis dealt with two potential adsorbents for post combustion  carbon capture, namely, amine modified silica and calcium carbonates. We modified porous silica with large surface area by propyl-amine groups to enhance the carbon dioxide adsorption capacity and selectivity. Experimental parameters, such as reaction time, temperature, water content, acid and heat treatment of silica substrate were optimized using a fractional factorial design. Adsorption properties and the nature of formed species upon reaction of CO2 and amine-modified silica were studied by sorption and infrared spectroscopy. Physisorbed and chemisorbed amount of adsorbed CO2 were, for the first time, estimated directly in an accurate way. The effects of temperature and moisture on the CO2 adsorption properties were also studied. Crystallization of calcium carbonate as a precursor to calcium oxide, which can be used as carbon dioxide absorbent, was studied in the second part of this thesis. Structure of different amorphous phases of calcium carbonate was studied in detail. Crystallization of calcium carbonate with and without additives was studied. Parameters like stirring rate, temperature, pH and polymer concentration showed to be important in selection of phase and morphology. An aggregation mediated crystallization was postulated to explain the observed morphologies. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Accepted.

<p>The rising carbon dioxide emissions contributing to climate change has lead to the examination of potential ways to mitigate the environmental impact. One such method is through the geological sequestration of carbon (CCS). Although there are several different forms of geological sequestration (i.e. Saline Aquifers, Oil and Gas Reservoirs, Unminable Coal Seams) the current projects are just initiating the large scale-testing phase. The lead entry point into CCS projects is to combine the sequestration with enhanced oil recovery (EOR) due to the improved economic model as a result of the oil recovery and the pre-existing knowledge of the geological structures. The potential scope of CCS-EOR projects throughout the continental United States in terms of a systematic examination of individual reservoir storage potential has not been examined. Instead the majority of the research completed has centered on either estimating the total United States storage potential or the potential of a single specific reservoir.</p><p>The purpose of this paper is to examine the relationship between oil recovery, carbon dioxide storage and cost during CCS-EOR. The characteristics of the oil and gas reservoirs examined in this study from the Nehring Oil and Gas Database were used in the CCS-EOR model developed by Sean McCoy to estimate the lifting and storage costs of the different reservoirs throughout the continental United States. This allows for an examination of both technical and financial viability of CCS-EOR as an intermediate step for future CCS projects in other geological formations. </p><p>One option for mitigating climate change is to store industrial CO2 emissions in geologic reservoirs as part of a process known as carbon capture and storage (CCS). There is general consensus that large-scale deployment of CCS would best be initiated by combining geologic sequestration with enhanced oil recovery (EOR), which can use CO2 to improve production from declining oil fields. Revenues from the produced oil could help offset the current high costs of CCS. </p><p>The cumulative potential of CCS-EOR in the continental U.S. has been evaluated in terms of both CO2 storage capacity and additional oil production. This thesis examines the same potential, but on a reservoir-by-reservoir basis. Reservoir properties from the Nehring Oil and Gas Database are used as inputs to a CCS-EOR model developed by McCoy (YR) to estimate the storage capacity, oil production and CCS-EOR costs for over 10,000 oil reservoirs located throughout the continental United States. </p><p>We find that 86% of the reservoirs could store &#8804;1 y or CO2 emissions from a single 500 MW coal-fired power plant (i.e., 3 Mtons CO2). Less than 1% of the reservoirs, on the other hand, appear capable of storing &#8805;30 y of CO2 emissions from a 500 MW plan. But these larger reservoirs are also estimated to contain 48% of the predicted additional oil that could be produced through CCS-EOR. The McCoy model also predicts that the reservoirs will on average produce 4.5 bbl of oil for each ton of sequestered CO2, a ratio known as the utilization factor. This utilization factor is 1.5 times higher that arrived at by the U.S. Department of Energy, and leads to a cumulative production of oil for all the reservoirs examined of ~183 billion barrels along with a cumulative storage capacity of 41 Mtons CO2. This is equivalent to 26.5 y of current oil consumption by the nation, and 8.5 y of current coal plant emissions.</p> / Thesis

Post-combustion carbon capture, wherein the CO2 produced as a result of coal combustion is trapped at the power plant exhaust, is seen as a bridging technology to reduce CO2 emissions and combat climate change. This capture process will however impose a parasitic load on the power plant and technologies need to be developed to minimize this energy penalty. This research focuses on a technology which uses solid sorbents fashioned into a hollow fiber form that allows water-moderated thermal cycling as a means of trapping CO2 from flue gas. While hollow fiber technology has intrinsic advantages over competing liquid amine and packed bed technologies, the materials used to fabricate hollow fibers and the fabrication process itself need to be optimized in order to result in competitive, robust hollow fiber sorbents. This dissertation focuses on the material selection process for each component of the hollow fiber platform and discusses ways to optimize the fiber and barrier layer formation. Different materials were evaluated to function as the solid sorbent, the matrix polymer and the barrier layer; and eventually their performance was measured against past work in this area.

Perfluorocarbon tracers (PFTs) are commonly proposed tracers for use in carbon capture and sequestration (CCS) leak detection and vadose zone monitoring programs. Tracers are co-injected with supercritical CO₂ and monitored in the vadose zone to identify leakage and calculate leakage rates. These calculations assume PFTs exhibit “ideal” tracer behavior (i.e. do not sorb onto or react with porous media, partition into liquid phases or undergo decay). This assumption has been brought into question by lab and field evaluations showing PFT partitioning into soil contaminants and sorbing onto clay. The objective of this study is to identify substrates in which PFTs behave conservatively and quantify non-conservative behavior. PFT breakthrough curves are compared to those of a second, conservative tracer, sulfur hexafluoride (SF₆). Breakthrough curves are generated in 1D flow-through columns packed with 5 different substrates: silica beads, quartz sand, illite, organic-rich soil, and organic-poor soil. Constant flow rate of carrier gas, N₂, is maintained. A known mass of tracer is injected at the head of the columns and the effluent analyzed at regular intervals for tracers at picogram levels by gas chromatography. PFT is expected to behave conservatively with respect to SF₆ in silica beads or quartz sand and non-conservatively in columns with clay or organics. However, results demonstrate PFT retardation with respect to SF₆ in all media (retardation factor is 1.1 in silica beads and quartz sand, 2.5 in organic-rich soil, >20 in organic-poor soil, and >100 in illite). Retardation is most likely due to sorption onto clays and soil organic matter or condensation to the liquid phase. Sorption onto clays appears to be the most significant factor. Experimental data are consistent with an analytical advection/diffusion model. These results show that PFT retardation in the vadose zone has not been adequately considered for interpretation of PFT data for CCS monitoring. These results are preliminary and do not take into account more realistic vadose zone conditions such as the presence of water, in which PFTs are insoluble. Increased moisture content will likely decrease sorption onto porous media and retardation in the vadose zone may be less than determined in these experiments. / text