The cement industry contributes around 5-7% of man-made CO2 emissions globally because of the Portland Cement (PC) production. Therefore, innovative reactive magnesia cement, with significant sustainable and technical advantages, has been proposed by blending reactive MgO and hydraulic binders in various proportions. MgO is currently produced from the calcination of magnesite (MgCO3), emitting more CO2 than the production of PC, or from seawater/brine which is also extremely energy intensive. Hence this research aims to investigate an innovative method to produce MgO from reject brine, a waste Mg source, through carbon sequestration, by its reaction with CO2, to provide a comparable low carbon manufacturing process due to the recycling of CO2. The produced deposits are then calcined to oxides with potential usage in construction industry. The entire system is a closed loop to achieve both environmental optimisation and good productivity. This research focuses on the chemical manufacturing process, integrated with material science knowledge and advancements, instead of concentrating purely on chemistry evaluations. Six series of studies were conducted, utilising MgCl2, CaCl2, MgCl2-CaCl2, MgCl2-CaCl2-NaCl, and MgCl2-CaCl2-NaCl-KCl to react with CO2 under alkaline conditions. The precipitates include hydrated magnesium carbonates, calcium carbonates and magnesian calcite. Generated carbonates were then calcined in a furnace to obtain MgO, CaO or dolime (CaO•MgO). All six series of carbonation processes were carried out under a controlled pH level, to study the constant pH’s effect on the process and resulting precipitates. Other controllable factors include pH, temperature, initial concentration, stirring speed, and CO2 flux rate. In conclusion, the optimum parameters for the production of the carbonated precipitates are: 0.25MgCl2 + 0.05CaCl2 + 2.35NaCl + 0.05KCl, 700rpm stirring speed, 25oC room temperature, pH=10.5, and 500cm3/min CO2 infusion rate. Reaction time is within a day. These parameters are chosen based on the sequestration level, particle performance morphology and the operational convenience. The optimum calcination parameters are at 800oC heating temperature with a 4h retention time.

O principal objetivo deste trabalho foi obter parâmetros reativos para as reações de absorção de SO2 por calcários em leitos fluidizados e procurar correlacionar, através de dois modelos simples, os resultados obtidos para distribuições granulométricas amplas e estreitas. Foram estudadas cinco faixas estreitas, com diâmetros de 385, 460, 545, 650, 775 &#956m para dois tipos de calcários, um dolomítico (DP) e um calcítico (CI). A partir destas faixas estreitas foram compostas quatro misturas, com 498, 540, 543 e 617 &#956m. Um dos dois modelos foi usado para determinar a fração com que cada faixa estreita deveria estar presente na mistura. Uma das misturas, a Mistura 2 (540 &#956m), tinha distribuição de diâmetros aproximadamente normal e a outra, Mistura 3 (543 &#956m), distribuição plana. O leito, de 160 mm de diâmetro, foi fluidizado com ar à temperatura de 850ºC e utilizou areia como material particulado. O calcário foi introduzido em bateladas de 50 g em um leito de areia de mesmo diâmetro com cerca de 2,0 Kg de massa. Uma vazão de SO2 foi misturada ao ar antes que este entrasse no leito, de forma a resultar em uma concentração próxima à 1000 ppm na saída do reator. A concentração de saída foi monitorada e a sua queda, verificada após a introdução da batelada de calcário, foi utilizada em um modelo matemático para determinar os parâmetros reativos, entre eles a conversão, taxa de conversão e o coeficiente global de taxa de reação. Os modelos de distribuição granulométrica empregados produziram boa correlação entre as misturas e as faixas estreitas durante a sulfatação. Na calcinação, o processo mostrou-se mais lento para a distribuição ampla do calcário DP e não foi afetado para o CI. Em todos os casos estudados o diâmetro do calcário mostrou afetar significativamente e de forma inversa, a eficiência dos calcários na remoção do SO2. O calcário DP mostrou-se sempre mais eficiente do que o calcário CI. / The main objective of this work was to compare the reactivity of limestones with narrow and open particle size distribution in a bubling fluidized bed reactor and verify if the reactivity of the open sized mixtures could be predicted, using two simple models, from the known parameters of the narrow sized particles. Five narrow sizes were used, respectively 385, 460, 545, 650 and 775 &#956m for two different limestones, one calcitic (CI) and one Dolomitic (DP). Using this same material and one of the models, four mixtures were prepared with 498, 540, 543 and 617 &#956m of average diameter. The mixture of 540 &#956m had an aproximately normal distribution of sizes and the mixture of 543 &#956m a falt one. The bed, with 160 mm of diameter, was fluidized with air at a temperature of 850ºC, and 2 Kg of sand with the same size as the limestones, was used as the bed material. A flow of SO2 was mixed with the fluidization air prior to the gas distributor, producing a uniform concentration of about 1000 ppm at the reactor gas exaust. The limestone was then intoduced in a batch of 50 g and the SO2 concentration monitored. The change in the SO2 concentration after the limestone was intoduced in the reactor was used to derive the reactive parameters, namely the conversion, rate of conversion and global coefficient of reaction rate. The particle size distribution models produced a good correlation among the mixtures and the narrow sized particlesduring sulfatation. The calcination process was more slow for the open distribution of limestone DP but not affected for CI. In all cases there was a clear increase in the SO2 absorption as the particle size was reduced. Limestone DP was much more effective in the removal of SO2 than CI.

O principal objetivo deste trabalho foi obter parâmetros reativos para as reações de absorção de SO2 por calcários em leitos fluidizados e procurar correlacionar, através de dois modelos simples, os resultados obtidos para distribuições granulométricas amplas e estreitas. Foram estudadas cinco faixas estreitas, com diâmetros de 385, 460, 545, 650, 775 &#956m para dois tipos de calcários, um dolomítico (DP) e um calcítico (CI). A partir destas faixas estreitas foram compostas quatro misturas, com 498, 540, 543 e 617 &#956m. Um dos dois modelos foi usado para determinar a fração com que cada faixa estreita deveria estar presente na mistura. Uma das misturas, a Mistura 2 (540 &#956m), tinha distribuição de diâmetros aproximadamente normal e a outra, Mistura 3 (543 &#956m), distribuição plana. O leito, de 160 mm de diâmetro, foi fluidizado com ar à temperatura de 850ºC e utilizou areia como material particulado. O calcário foi introduzido em bateladas de 50 g em um leito de areia de mesmo diâmetro com cerca de 2,0 Kg de massa. Uma vazão de SO2 foi misturada ao ar antes que este entrasse no leito, de forma a resultar em uma concentração próxima à 1000 ppm na saída do reator. A concentração de saída foi monitorada e a sua queda, verificada após a introdução da batelada de calcário, foi utilizada em um modelo matemático para determinar os parâmetros reativos, entre eles a conversão, taxa de conversão e o coeficiente global de taxa de reação. Os modelos de distribuição granulométrica empregados produziram boa correlação entre as misturas e as faixas estreitas durante a sulfatação. Na calcinação, o processo mostrou-se mais lento para a distribuição ampla do calcário DP e não foi afetado para o CI. Em todos os casos estudados o diâmetro do calcário mostrou afetar significativamente e de forma inversa, a eficiência dos calcários na remoção do SO2. O calcário DP mostrou-se sempre mais eficiente do que o calcário CI. / The main objective of this work was to compare the reactivity of limestones with narrow and open particle size distribution in a bubling fluidized bed reactor and verify if the reactivity of the open sized mixtures could be predicted, using two simple models, from the known parameters of the narrow sized particles. Five narrow sizes were used, respectively 385, 460, 545, 650 and 775 &#956m for two different limestones, one calcitic (CI) and one Dolomitic (DP). Using this same material and one of the models, four mixtures were prepared with 498, 540, 543 and 617 &#956m of average diameter. The mixture of 540 &#956m had an aproximately normal distribution of sizes and the mixture of 543 &#956m a falt one. The bed, with 160 mm of diameter, was fluidized with air at a temperature of 850ºC, and 2 Kg of sand with the same size as the limestones, was used as the bed material. A flow of SO2 was mixed with the fluidization air prior to the gas distributor, producing a uniform concentration of about 1000 ppm at the reactor gas exaust. The limestone was then intoduced in a batch of 50 g and the SO2 concentration monitored. The change in the SO2 concentration after the limestone was intoduced in the reactor was used to derive the reactive parameters, namely the conversion, rate of conversion and global coefficient of reaction rate. The particle size distribution models produced a good correlation among the mixtures and the narrow sized particlesduring sulfatation. The calcination process was more slow for the open distribution of limestone DP but not affected for CI. In all cases there was a clear increase in the SO2 absorption as the particle size was reduced. Limestone DP was much more effective in the removal of SO2 than CI.

The overall objective of the work described in this Dissertation was to develop and verify a general reaction and diffusion model for non-catalytic reactions between gases and porous solids, particularly those relevant to the clean use of fossil fuels. Here, the internal pore structure of the solid was characterised by observing the kinetics in a regime limited only by intrinsic chemical reaction. It was hypothesised that a simple arbitrary function, f(X), determined from experimental measurements of rate vs. conversion in a kinetically-controlled regime, could be used in place of formal, mathematical pore models, to describe the evolution of pore structure during a reaction influenced by intraparticle mass transfer. The approach was used to study (i) the gasification of chars by CO2, where the only product was gaseous, (ii) the calcination of CaCO3 cycled between calcined and carbonated states, where the products were a gas and a solid, and (iii) the sulphation of virgin and sintered CaO by SO2, the only product being solid. Studies of calcination showed that, at least for limestones subjected to a history of cycling between the calcined and carbonated states, a correctly-determined f(X) could be applied to different sizes of particles at temperatures different to that at which f(X) was determined. Somewhat surprisingly, it was found that the f(X) determined from one, cycled, limestone was successful in predicting the conversion of other cycled limestones of different geological origin. It was concluded that the process of cycling between the calcined and carbonated states at the same process condition had significantly reduced the differences apparent in the pore structures of the different limestones when first calcined from the virgin materials. The experimentally-observed effects of pressure, concentration of CO2 and temperature described in the literature were explained successfully by the mathematical model. Finally, the study of sulphation explained satisfactorily (i) the reason for there being a maximum in the ultimate conversion of CaO to CaSO4 at a specific temperature, and (ii) the processes controlling the overall uptake of SO2 by sintered CaO, such as might be produced from a calcium-looping cycle for capturing CO2 from flue gases. For both the virgin and the cycled calcines, the ultimate conversion to CaSO4 seemed to be limited by the pore volume below 300 nm diameter. Two mechanisms were identified to explain why CaO cannot be fully sulphated to CaSO4. In summary, this work has demonstrated the applicability of the general reaction and diffusion model to gasification, calcination and sulphation reactions, and verified the f(X) approach for describing pore evolution during reaction.

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No / It is known that lime was added to historic Roman cement render mortars. The focus of this work is the influence of the combination of NHL5 and CL90 with Roman cement in mortars for restoration; however, the results indicate a wider potential for render applications in general. It is shown that simply adding lime to Roman cement does not retard its hydration and yields mortars where the binding action of the cement is compromised by the mixing process. If the cement is retarded by means of a pre-hydration process, hybrid mortars can be produced with improved workability and workable life as well as permitting the fine control of strength and moisture transport.

Les travaux menés dans cette Thèse ont consisté à développer un pilote expérimental prouvant la faisabilité de la capture de CO2 par boucle chimique calcium en utilisant des chaudières du type Lit Fluidisé Circulant. Ceux-ci ont été conduits en deux phases: une phase expérimentale à l'échelle du laboratoire avec l'interprétation théorique des résultats et une phase expérimentale à l'échelle du pilote dans le but de valider le procédé. Les résultats expérimentaux à 1'échelle du laboratoire ont permis de montrer que le frittage de CaOest la cause de la décroissance du taux de carbonatation au cours des cycles successifs calcination/carbonatation. La vitesse de frittage étant accélérée par la présence de CO2 pendant la phase de calcination. Les analyses menées sur les échantillons calcinés ont révélé l'apparition d'une structure de micrograin à l'intérieur des grains initiaux de carbonate. Les micrograins de CaO non frittés sont le siège de la réaction de carbonatation.Un procédé de capture de CO2 par boucle chimique calcium a été conçu et réalisé. Il se compose de deux lits fluidisés circulants, un réacteur de carbonatation assurant la capture du CO2 et un réacteur de calcination permettant la régénération de la chaux. Ces deux lits fluidisés circulants sont couplés de façon à permettre un fonctionnement continu du procédé de capture de CO2. Malgré le faible rendement de capture obtenu à l'échelle de ce pilote (entre 18 à 23%), ces résultats apparaissent encourageants pour le développement de cette technologie, compte tenu du fait que beaucoup de facteurs limitant le rendement de capture disparaissent avec le changement d'échelle. / The works led in this Thesis consisted in developing an experimental pilot proving CO2 capture feasibility by calcium chemical looping using Circulating Fluidised Bed as boilers. These were undertaken in two step: At the laboratory scale with theoretical interpretation of the experimental results and at the pilot scale in the aim to validate the process.The experimental results on the scale of the laboratory allowed to show that the sintering of CaO bring about the decreasing of the carbonation rate during calcination/carbonation cycles. The sintering velocity are accelerated by CO2 during the calcinations step. The analysis of the calcined samples showed a micrograins structure inside the initial carbonate grains The not sintered CaO micrograins are the location of the carbonation reaction.A process of CO2 capture by calcium chemical looping was designed and built. It was made by two circulating fluidized beds, a carbonator where the CO2 capture were performed and the calcinator allowing the lime regeneration. These two circulating fluidized beds are coupled allowing a continuous CO2 capture.In spite of the low capture efficiency obtained on the scale of this pilot (from 18 to 23 %), these results seem encouraging for the development of this technology, considering the fact that many limiting factors of the capture efficiency disappear with the change of scale.

Cement production is responsible for around 7% of the global anthropogenic carbon dioxide emissions. More than half of these emissions are due to the unavoidable release of carbon dioxide upon thermal decomposition of the main raw material limestone. Many different options for carbon capture are currently being investigated to lower emissions, and one potential route to facilitate carbon capture could be the implementation of an electrified separate calcination step. However, potential effects on the phase composition of cement clinker need to be investigated, which is the aim of the present study. Phases of special interest are alite, belite, aluminate, ferrite, calcite, and lime.  The phase composition during clinker formation was examined through HT-XRD lab-scale experiments, allowing the phase transformations to be observed in situ. Two different methods of separate calcination were investigated, one method in which the raw meal was calcined separately, and one method where the limestone was calcined separately. The former yielded an alite amount similar to that of the reference experiments, whereas the latter method yielded a lower amount. It could, unfortunately, not be excluded that the difference was due to poor experimental conditions, and additional experiments are needed to investigate the matter further. The study does, however, indicate that a calcined raw meal might be used to produce a clinker of similar phase composition concerning major phases belite, aluminate, ferrite, alite, and free lime. A raw meal containing calcined limestone might, however, need longer residence time at clinkering temperature too obtain similar phase composition. In addition, a raw meal containing calcined limestone was observed to be carbonated to a greater extent upon reheating than a calcined raw meal. Further experiments are needed to fully understand the effects on clinker composition of an electrified separate calcination step, and several improvements to the experimental method are given in the study.