The thermal degradation of piperazine (PZ)-promoted tertiary amine solvents for CO2-capture has been investigated and quantified in this study, which takes place in the high temperature (>100 °C) section of the capture plant. PZ-promoted tertiary amine solvents possess comparable energy performance to concentrated PZ, considered a benchmark solvent for CO2 capture from flue gas without its solid solubility limits that hinder operational performance. PZ-promoted aliphatic tertiary amine solvents with at least one methyl group, such as methyldiethanolamine (MDEA), were found to be the least stable solvents and can be regenerated in the desorber between 120 and 130 °C. PZ-promoted tertiary amine solvents with no methyl groups, such as ethyldiethanolamine (EDEA), were found to have an intermediate stability and can be regenerated in the desorber between 130 and 140 °C. PZ-promoted tertiary morpholines, such as hydroxyethylmorpholine (HEM), were found to be stable above 150 °C. Tertiary amines with at least one hydroxyethyl or hydroxyisopropyl functional group form intermediate byproducts that can accelerate the degradation rate of the promoter by a factor from 1.5 to 2.3. Tertiary amines with 3-carbon and 5-carbon functional groups, such as dimethylaminopropanol or dimethylaminoethoxyethanol, form stable intermediate byproducts that do not readily react with the promoter. A degradation model for PZ-promoted MDEA that can be used for process design calculations using acidified solvent degradation to model the initial degradation rate over a range of CO2 loading and initial amine concentration was developed. Thermal degradation was modeled using second-order kinetics as a function of free amine and protonated amine. The degradation kinetics, along with the observed degradation products, suggest that the dominant pathway is by free PZ attack on a methyl substituent group of protonated MDEA to form diethanolamine (DEA) and 1-methylpiperazine (1-MPZ). The model predicts total amine loss from experimental CO2 degradation rate measurements within 20%. The modeling work was extended to other PZ-promoted tertiary amine solvents with bulkier substituent groups. PZ attack on ethyl or hydroxyethyl groups was 17% and 4% as fast, respectively, as attack on methyl groups. / text

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Increasing concerns about global warming have led to the exploration of options to abate CO2 emissions. Recent studies have identified the energy sector as the largest emitting source worldwide. Therefore, the transition towards low-carbon power systems has incorporated larger volumes of renewable generation. This situation is prompting the necessity of improving current strategies to operate power systems, as more variability is introduced in the decision making process. This thesis contributes in two aspects to manage the generation mix of future power systems. Firstly, it addresses the question of how many scenarios are enough to represent the variability of wind power. Results obtained indicate that a balance should be pursued between quality of solution and computational burden, as more scenarios does not significantly change the operational cost. Secondly, an original method to narrow down the number of scenarios is proposed. The so-called severe scenarios outperform typical reductions in the sense that fewer adjustments are required to the generation scheduling programme. Despite the growing renewable generation capacity, the operation of the electric system is likely to continue its reliance on thermal plants. Hence, the need to curb CO2 emissions in the existing thermal plants has led to the development of technologies such as carbon capture. The technical maturity of this technology is still in its early stages, since its application to thermal plants is under development. This thesis bridges the gap of current knowledge on carbon capture in three aspects. Firstly, it presents an innovative methodology to quantify the value of flexibility provided by carbon capture in the context of the British system. Secondly, the role of retrofitted generators as reserve providers is addressed. Finally, the synergy between carbon capture and wind power is assessed. The evaluation considers CO2 pricing, two strategies to manage CO2 capture rate, variability and different levels of wind integration.

In this dissertation a novel ZLC setup has been developed as part of a DOE-funded grant in collaboration with UOP, to provide rapid screening of novel adsorbent materials for carbon capture (CC). The key features of the new apparatus that was developed are: the use of 5-15 mg of sample and a dual detector system – a thermal conductivity detector (TCD) for single component measurements and a mass spectrometer for studying the influence of water and other impurities. Improvements over previous ZLC apparatuses include: 1. Extension to lower flowrates, i.e. < 3 cc/min, thereby reducing consumption of gases and allowing to run the system under equilibrium control conditions; 2. A new gas dosing system that allows the use of vapours without a chilled bath and bubbler system; 3. A new switching valve system, which prevents leakages; 4. Automated series of experiments, which are implemented using Labview. The new ZLC technique was first applied to provide rapid screening capacity ranking of more than 15 MOF materials from the open literature and three typical zeolites for carbon capture. At the point of interest for flue gas application (38°C, 0.1 bar CO2 partial pressure), Mg/DOBDC was found to outperform significantly all other MOFs and benchmark zeolites at the point of interest in low pressure physisorption of CO2. The ZLC was also used to investigate steaming on Ni/DOBDC as well as see the effect of forming powders into pellets. The new ZLC system also enables one to measure micropore and macropore diffusivity. Experiments were carried out on both powders and pellets of typical MOFs and zeolites. For Co/DOBDC crystals, since the system is close to equilibrium control even at the highest flow rate, a low limit of diffusivity can be estimated. For all the formed samples of Ni/DOBDC and 13X pellets, the results indicate that mass transfer is controlled by macropore diffusion. The ZLC technique can also estimate realistic void fraction and tortuosity values for the pellets. The new ZLC technique was applied to study the stability on the MOF M/DOBDC series. The preliminary water tests showed that all M/DOBDC samples are highly hydrophilic. Therefore in a process design using these MOFs, we conclude that there is a needs to use a guard bed layer to adsorb water or use a gas drying unit before the CO2 capture section of the plant. The ZLC system appears to be extremely useful to accelerate the deactivation of samples due to SOX and NOX impurities. The key advantages are based on the fact that the treatment can be repeated in situ, in a relatively simple way using a very small sample. The results show that in the presence of impurities and water the candidate MOFs undergo significant deactivation. The Ni based material shows the best resistance to degradation. This result indicates further that there would be a need for a drying unit prior to the carbon capture adsorption process.

Carbon Capture and Storage (CCS) has been identified as a feasible technology to reduce CO2 emissions whilst permitting the continued use of fossil fuels. Injected CO2 must remain efficiently isolated from the atmosphere on a timescale of the order of 10000 years and greater. Natural CO2-rich sites can be investigated to understand the behaviour of CO2 in geological formations on such a timescale. This thesis examines the reservoir and seal on one such oilfield. Several hydrocarbon fields in the South Viking Graben of the North Sea naturally contain CO2, which is thought to have charged from depth along the western boundary fault of the graben. The Miller oil field which contains ~ 28 mol% CO2, of isotopic composition δ13C = -8.2‰. The Upper Jurassic Brae Formation reservoir sandstones and the Kimmeridge Clay Formation (KCF) seal have been exposed to the CO2 accumulation since its emplacement. Rock samples from the reservoir sandstone and bottom of the seal mudrock were examined using multiple techniques, including XRD, SEM, fluid inclusion and carbonate stable isotope analyses. The sandstones show no features directly attributable to abundant CO2 charge. SEM analyses reveal significant heterogeneities in diagenesis within the KCF. The silt/sand lithologies of the KCF have undergone a diagenetic history similar to that of the Brae Formation sandstones. In contrast, the KCF shales display a distinctly different diagenesis of dominant dissolution of quartz and feldspar with little evidence of mineral precipitation. In both the Brae Formation and the KCF, pore-filling kaolinite, illite and carbonates are relatively late diagenetic events which can be associated with CO2-induced feldspar dissolution. Mudrock X-ray diffraction mineralogical data reveal abrupt vertical mineralogical variations across the reservoir crest in the Miller Field, while such variations are absent in a low-CO2 control well in the same geological settings. This suggests that reactions induced by abundant CO2 dissolved feldspar and produced kaolinite, carbonates and quartz in the seal, while oil emplacement inhibited the reactions in the oil leg. However, petrographic evidence and comparison between different sections argue against CO2 reactions as the sole cause for such large mineralogical variations, especially for quartz. The vertical mineralogical variations to a certain extend represent original sedimentary heterogeneity. Linear variations of carbonate δ13C with depth were discovered in both shale and silt/sand lithologies of the KCF in a 12m zone immediately above the reservoir. These features are absent in the low-CO2 control well. These trends are interpreted as dissolution of original carbonates by CO2 slowly ascending from the reservoir. New carbonates precipitated from a carbon source with upwards decreasing δ13C due to mixing between three carbon sources with different C isotopes at systematically varying ratios. The isotopes in the reservoir and the bottom of the seal suggests initial CO2 charge at about 70-80 Ma. CO2 infiltration rate is estimated at about 9.8×10-7g·cm-2·y-1. Geochemical modelling was applied to reconstruct the reservoir fluid evolution by calibrating it to mineralogy, fluid chemistry, diagenesis and fluid inclusion data. The modelling suggests that CO2 migrated into the reservoir together with a saline basinal fluid derived from the underlying evaporites at ~ 70 Ma. The CO2 and basinal water charge imposed an important influence on the mineral reactions and fluid chemistry. This study suggests that the KCF has formed an excellent CO2 seal, with no substantial breach since its charge at 70-80 Ma.

A widely-proposed way to retrofit coal-fired power plants with post-combustion CO2 capture (PCC) is to supply all the electricity and heat required to operate the capture equipment from the existing steam cycle (an ‘integrated retrofit’), at the expense of a reduction in site power output. As an alternative, it is possible to add a gas turbine (GT) plant to maintain, or even increase, the net site power output. The GT can be integrated with the capture plant in various ways to supply all or part of the heat and power required for the capture and compression systems. But there is then the issue of how to capture the CO2 emissions from the added GT plant. In this study a novel retrofit configuration is proposed. The exhaust gas of the GT replaces part of the secondary air for the coal boiler and a common capture system is used for both coal- and natural gas-derived CO2. This new ‘GT flue gas windbox retrofit’ is based on the principles of previous hot windbox repowering proposals, with additional modifications to permit operation without extensive coal boiler modifications. To achieve this, the heat recovery steam generator (HRSG) attached to GT is designed to maintain the main steam turbine flow rates and temperatures, to compensate for a necessary reduction in coal feed rates, and this, with the GT output, maintains the net power output of the site A techno-economic analysis of coal plants retrofitted with GT power cycles shows that these ‘power matched’ retrofits can be competitive with integrated retrofits at lower natural gas prices (as is now the case in North America). In particular, the novel GT flue gas windbox retrofit provides a promising alternative for adapting integrated capture retrofits that are initially designed for flexible operation with zero to full (~90%) capture (as at the Boundary Dam 3 unit) for subsequent operation only with full capture. In this case the addition of a GT flue gas windbox retrofit will restore the full power output of the site with full CO2 capture and using the original capture plant. In general, techno-economic analysis shows that the economic performance of GT retrofit options depends on the site power export capacity. If there is no limit on power export then retrofits may advantageously also include an additional steam cycle, to give a combined cycle with the GT, otherwise retrofits with a single pressure HRSG producing process steam only are preferred.

This thesis progresses from a ‘science and technology studies’ (STS) perspective to consider the ways that expert stakeholders perceive and communicate uncertainties and risks attached to carbon dioxide (CO2) capture and storage (CCS) research and development, and how this compares with policy framings and regulatory requirements. The work largely falls within the constructivist tradition in sociology, but also draws on literature from the philosophy of science and policy-­‐oriented literature on risk and uncertainty. CCS describes a greenhouse gas (GHG) mitigation technology system that involves the capture, pressurisation, transportation, geological injection and long-­‐term storage of CO2 as an alternative to atmospheric emissions. Only few and relatively small applications exist at the moment and research efforts are on going in many countries. The case for developing CCS towards large-­‐scale, commercial deployment has largely been presented as follows since the mid-­‐ 1990s: climate change mitigation is the developed world’s historical responsibility and must be addressed urgently; chief amongst GHGs is CO2, which makes up more than three quarters of emissions; the vast majority of CO2 is emitted from the combustion and gasification of hydrocarbons – oil, gas and coal – for energy generation; transitioning away from these high-­‐CO2 primary energy sources will likely take several decades at the least; therefore, CO2 capture systems should be designed for power and industrial emissions in developed countries, as well as emerging economies where energy suppliers will continue to construct relatively cheap and well understood high-­‐CO2 generation plants. The development of large-­‐scale CO2 capture has thus arisen from a concern with engineering a technological system to address a CO2 legacy in the developed world, and a high-­‐CO2 trajectory in developing/emerging countries, rather than on the back of purely scientific curiosity. And the potential for large-­‐scale development has been presented on the back of a variety of scientific and technical evidence, as well as the urgency of the policy objective and related aims. Research activities, often concentrated around technology demonstration projects, are the primary focus of the first part of this thesis. In the second part I consider the extent to which research has shaped policy developments, and how regulations have subsequently informed a more detailed research agenda. I follow a ‘grounded theory’ methodology as developed by Glaser and Strauss (1967) and take additional guidance from Glaser’s (1992) response to Strauss’ later writings as well as Charmaz (2006) and Rennie (2000), and use a mix of qualitative and quantitative analytical methods to assess my data. These include information from 60 semi-­‐structured interviews with geoscientists and policy stakeholders; close readings of scientific publications, newspaper articles, policies and regulatory documents; statistical evidence from a small survey; quantitative analysis of newspaper articles; and social network analysis (SNA) of scientific co-­‐authorship networks. Theory is drawn from STS literature that has been appropriate to address case study materials across each of the 7 substantive chapters. The first section of the thesis considers expert claims, with a focus on geoscience research, and draws on literature from the closely related ‘social shaping of technology’ (SCOT) and ‘sociology of scientific knowledge’ (SSK) programmes, as well as Nancy Cartwright’s philosophy of science. The second half of the thesis draws on the ‘co-­‐production’ framework and Wynne’s (1992) terminology of risk and uncertainty, to assess relations between risk assessment and risk management practices for CCS. I likewise draw on literature from the ‘incrementalist’ tradition in STS to ask whether and how understandings of technology risk, governance and deployment could be improved. Each chapter presents new empirical material analysed with distinct reference to theories covered in the introduction. Chapter 2 provides a general overview of the history, technology, economics and key regulatory issues associated with CCS, which will be useful to assess the theoretically driven arguments in subsequent chapters. Chapter 3 draws on the concept of ‘interpretive flexibility’ (Pinch and Bijker 1984) to assess a range of expert perceptions about uncertainties in science, technology and policy, and I develop a substantive explanation, ‘conditional inevitability’, to account for an epistemic tension between expressions of certitude and the simultaneous acknowledgement of several uncertainties. Chapter 4 continues the enquiry into stakeholder perceptions and draws on Haas’ notion of ‘epistemic communities’ (Haas 1992) to assess geoscientists’ work practices. I complement this framing with a close look at how uncertainty is treated in simulation modelling and how conclusions about storage safety are formulated, by drawing on Nancy Cartwright’s philosophy of science (Cartwright 1999) and Paul Edwards’ account of complex system modelling for climate change (Edwards 2010). The chapter shows how shared understandings of adequate evidence and common analytical tools have been leveraged to present relatively bounded and simple conclusions about storage safety, while geoscientists nevertheless recognise a high degree of uncertainty and contingency in analyses and results. Chapter 5 continues the focus on knowledge production in the geosciences and is supported by SNA data of workflow patterns in the Sleipner demonstration project. The analysis shows how a few actors have had a pivotal role in developing insights related to storage safety particularly on the back of seismic monitoring and other data acquired through industry partnerships. I therefore continue the chapter with a deconstruction of how seismic data has been used to make a case for the safety of CO2 storage, again drawing on Cartwright and others (Glymour 1983) to explain how individual findings are ‘bootstrapped’ when conclusions are formulated. I show how a general case about storage safety has emerged on the back of seismic data from Sleipner as well as a shared understanding among geoscientists of how to account for uncertainties and arrive at probable explanations. Chapter 6 considers to what extent scientific research has given shape to, and in turn been shaped by, CCS policy and regulations in the EU, drawing on Wynne’s (1992) terminology of risk and uncertainty as well as legal scholarship (Heyvaert 2011). I conclude that a ‘rational-­‐instrumental’ interpretation of uncertainty and precaution has furnished a compartmentalised understanding of risk assessment and risk management practices. Chapter 7 continues to look at the ways that risk assessment methodologies influence risk management practices through a case study of the Mongstad CCS demonstration project in Norway. I draw on ‘incrementalist’ literature (Lindblom 1979; Woodhouse and Collingridge 1993) to consider alternative conceptualisations of technology development and risk management when expectations clash with scientific uncertainties and criticism. Chapter 8 draws on insights from across STS (Downs 1972; Collingridge and Reeve 1986; Wynne 1992) to create a novel conceptual model that accounts for recent years’ developments in CCS governance. Here I conclude that setbacks and criticisms should be expected when analyses have largely presented CCS as a technical problem rather than a socially contingent system. Following Stirling (2010) I conclude that scientists and policymakers should instead strive to present complexity in their analyses and to engage with wider publics (Yearley 2006) when technical analysis is inseparable from socially mediated indeterminacies (Wynne 1992), to increase the chance of more successful engagement practices (Wynne 2006). The conclusions at the end of the thesis seek to draw out interpretive and instrumental lessons learned throughout.

Growing concerns about climate change and the inevitable depletion of fossil fuel resources have led to an increased focus on renewable energy technologies and reducing GHG emissions. Limiting the atmospheric level of CO2 is essential to prevent the most damaging effects of climate change. Among renewable energy resources, biomass combustion has the largest potential to contribute to global energy demands, however it is considered to be a carbon neutral solution and so only limits CO2 concentrations rather than reducing them. Through pyrolysis rather than combustion, biomass can lead to carbon negative liquid, gaseous and solid fuels while also offering a route for long term carbon storage in the form of biochar. Biochar is a carbonaceous material which has shown potential for improving soil fertility, reducing GHG emissions and most importantly long term C storage in the environment. However many questions still remain unanswered with regard to biochar, especially the influence that process conditions can have on its performance in soil as well as any potential trade-offs between soil amendment, C sequestration and heat/power generation. This thesis is therefore focused on assessing the influence that process conditions and feedstock selection have on biochar properties related to carbon stabilisation, improving soil fertility (functional properties) as well as the distribution of energy amongst the pyrolysis co-products. To achieve this, a systematic set of biochar samples was produced, using a wide range of pyrolysis parameters (highest treatment temperature (HTT), heating rate, residence time, carrier gas flow rate and feedstock type), and analysed for physicochemical and functional properties. Pyrolysis HTT consistently showed a dominant influence on determining the final yields and properties of biochar, while the effect of other production parameters was varied. In this thesis the candidate first studied the effect that process conditions had on the long term stability of biochar, as an important indicator of its ability to sequester carbon. While increasing the HTT resulted in a decrease in biochar yield, overall the yield of stable-C increased with temperature. This meant that by applying a higher HTT during pyrolysis a higher C sequestration potential for biochar was achieved. Next to be examined was the influence that process conditions had on other functional properties (labile-C yield, biochar pH, extractable nutrients and cation exchange capacity (CEC)) was then examined. The labile-C yield of biochar decreased with increasing HTT due to the release of volatile matter, while the CEC and concentration of extractable nutrients tended to be higher in biochar produced at 450oC rather than greater HTTs. Biochar pH was also highly alkaline at elevated HTT. This indicated that while high HTT favoured C sequestration and biochar pH, lower HTT may be more favourable for other functional properties. Furthermore by assessing the mass and energy distribution amongst the solid, liquid and gaseous fractions, it was possible to determine the energy balance of the process and through this evaluate the trade-off between the C sequestration potential of biochar and the energy output of the liquid and gas fractions. As the severity of pyrolysis was raised, the total energy stored within the liquid and gaseous co-products increased at the expense of the energy content of biochar, therefore increasing the available energy output of the system and reducing the energy lost when using biochar for carbon storage rather than for bioenergy. This also demonstrated that the pyrolysis process could be fine-tuned to increase the amount of stored C while also improving the heat/power generation of the system. The higher energy content of the gas stream at elevated HTT was also seen to contain sufficient energy to sustain the pyrolysis process, which would free up the solid and liquid fractions for higher value applications while reducing the necessity for external fuel sources. Finally, the data set was used to produce statistical models enabling the prediction of biochar stable-C yield as well as the heating value of biochar. The results of this thesis therefore demonstrate that through applying high HTT the potential energy output of the pyrolysis system can be increased while producing a biochar product with high C sequestration potential and positive functional properties for soil amendment. Due to potential trade-offs, the final choice of process conditions and feedstock would then be made based on the specific requirements of a selected site for biochar application. Understanding the influence that production conditions have on the functional properties of biochar as well as the energy balance of the system is critical to developing specifically engineered bespoke biochar, be it for agricultural use, carbon storage, energy generation or combinations of the three.

This thesis has addressed several gaps in the knowledge with regards to the calcium looping cycle for carbon dioxide capture, including identification of engineering challenges associated with the scale-up of the technology to pilot scale and beyond; assessment of changes in sorbent morphology during the pilot scale capture process; and partitioning of elemental impurities in the limestone between the solid and gaseous phase during the carbon dioxide capture process. Hydrodynamic investigations identified the optimum superficial velocities required for the reactor in order to optimise solids entrainment and flux, and to minimise gas bypassing. Estimations made in determining how particle attrition would affect minimum fluidisation velocity confirmed a decrease of approximately 0.09m/s for every 5 % reduction in particle size. Amendments made to the exhaust diameter and position, and the loop seals, improved the pressure balance of the system thus enhancing solids transfer. Reactor and process modifications, including modification of carbonator temperature, and maintenance of temperature above 420°C in standpipes resulted in improved carbon dioxide capture %. Increasing bed inventory had a positive effect of carbon dioxide capture % due to an increased Ca looping ratio. Steam addition also benefitted the carbonation process, due to improved sorbent morphology and therefore carbon dioxide diffusion into the sorbent. Sulfur dioxide was considered to have a detrimental effect on carbon dioxide capture due to pore pluggage, although burner- derived steam had a positive effect in maintaining capture %. Gaseous elemental emissions from the process were low for all elements, but concentrations of elements in the solid sorbent phase were influenced by bed inventory, implying that filtering systems may be required in industry for the large masses of sorbent required. Concentrations of elements in the sorbent were identified to be below levels typical of cement, with the exception of Ni, implying that there is potential for spent sorbent to be used in the cement industry with adequate mitigation measures in place.

This thesis investigates membrane gas separation and its application to post-combustion carbon capture from coal-fired power plants as alternative to the conventional amine absorption technology. The attention is initially focused on membrane module modelling, with the aim of obtaining more detailed predictions of the behaviour of the separation though spiral-wound and hollow-fibre modules. Both one- and bi-dimensional models are implemented, compared and tested for different separations. Module geometry is investigated as well as the effect on the performances due to possible fabrication defects. A key part of the work involves the integration of the customised models into UniSim® Design, the Honeywell process simulator. Thanks to the developed interface, multi-stage process designs are developed, compared with the available literature and linked to a rigorous economic analysis. In particular, a long-term indicator such as the Levelised Cost Of Electricity (LCOE) is evaluated and parametric analyses are conducted with respect to both material and process parameters.