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The preparation of CaO/CuO composites with high performance is essential for combined Ca–Cu looping process, where the exothermic reduction of CuO with methane is used in situ to calcine CaCO3.
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Page 1. 19 Overview of Oxy-Combustion Technologies with Pure Oxygen and Chemical Looping Combustion Ben Anthony and Ali Hoteit 19.1 Introduction As the existing fleet of power plants continues to age, operators of coal ...
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Significant research has been carried out to investigate the carbonation of CaO as a potential method for CO2 capture and sequestration. Up to date, the majority of this work has been related with CO2 removal from combustion flue gases... more
Significant research has been carried out to investigate the carbonation of CaO as a potential method for CO2 capture and sequestration. Up to date, the majority of this work has been related with CO2 removal from combustion flue gases with little attention focused on the carbonation reaction kinetics under gasification syngas conditions. The intrinsic rate constants of the CaO-CCh reaction was studied via a grain model for two naturally occurring calcium oxide based sorbents using a thermogravimetric analyzer. An apparent kinetic model was used to cover both the chemical reaction and diffusion rate control regimes to enable the development of a single phase, plug flow, moving bed carbonator reactor model. Over temperatures ranging from 580-700°C, it was observed that the presence of CO and H2 during carbonation caused a significant increase in the initial rate of carbonation which has been attributed to the CaO surface sites catalyzing the water-gas shift reaction increasing the lo...
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A probabilistic modelling approach was developed and applied to investigate the energy and environmental performance of an innovative sanitation system, the "Nano-membrane Toilet" (NMT). The system treats human excreta via an... more
A probabilistic modelling approach was developed and applied to investigate the energy and environmental performance of an innovative sanitation system, the "Nano-membrane Toilet" (NMT). The system treats human excreta via an advanced energy and water recovery island with the aim of addressing current and future sanitation demands. Due to the complex design and inherent characteristics of the system's input material, there are a number of stochastic variables which may significantly affect the system's performance. The non-intrusive probabilistic approach adopted in this study combines a finite number of deterministic thermodynamic process simulations with an artificial neural network (ANN) approximation model and Monte Carlo simulations (MCS) to assess the effect of system uncertainties on the predicted performance of the NMT system. The joint probability distributions of the process performance indicators suggest a Stirling Engine (SE) power output in the range o...
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The importance of calcium-based sorbents, especially natural limestones, for COâ removal necessitates an investigation into the sotbent decay mechanism. This study starts from pore size distributions for samples from tests under various... more
The importance of calcium-based sorbents, especially natural limestones, for COâ removal necessitates an investigation into the sotbent decay mechanism. This study starts from pore size distributions for samples from tests under various calcination/carbonation cycling conditions. A sintering model is formulated to describe the cyclic behavior of sorbents during cyclic calcination and carbonation. It explains the similar reversibility shown by sorbents under different test conditions. A balance between shorter cumulative sintering time and higher calcination rates appears to be responsible for the similar degrees of sintering and sorbent reversibility.
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In this study, pretreatment of CaO-based sorbent in a CO2 atmosphere at high temperature is investigated for its effect on CO2 capture. Three limestones from three widely different geographical locations are used for the tests: Kelly Rock... more
In this study, pretreatment of CaO-based sorbent in a CO2 atmosphere at high temperature is investigated for its effect on CO2 capture. Three limestones from three widely different geographical locations are used for the tests: Kelly Rock (Canada), La Blanca (Spain), and Katowice (Poland). The particle sizes used are typically as employed in fluidized bed conversion systems. Pretreatment was done
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CaO-based looping cycles are promising processes for CO Capture from both syngas and flue gas. The technology is based on cyclical carbonation of CaO and regeneration of CaCO in a dual fluidized-bed reactor to produce a pure CO stream... more
CaO-based looping cycles are promising processes for CO Capture from both syngas and flue gas. The technology is based on cyclical carbonation of CaO and regeneration of CaCO in a dual fluidized-bed reactor to produce a pure CO stream suitable for sequestration. Use of spent sorbent from CO looping cycles for SO capture is investigated. Three limestones were investigated: Kelly
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Effects of impurities in CO2 streams on geological storage of CO2 have been investigated. A number of key issues have been addressed, and several significant findings have been made. Highlighted among the findings are: (1) non-condensable... more
Effects of impurities in CO2 streams on geological storage of CO2 have been investigated. A number of key issues have been addressed, and several significant findings have been made. Highlighted among the findings are: (1) non-condensable impurites such as N2, O2 and Ar greatly reduce CO2 storage capacity of geological formations, and there is a maximum reduction of the storage capacity at a certain pressure under a given temperature. By contrast, impurities which are more condensable than CO2, such as SO2, can increase the storage capacity, and there is a maximum increase at a certain pressure under a given temperature; (2) change of density caused by non-condensable gas impurities results in lower injectivity of impure CO2 into geological formations. However, above a threshold pressure range the injectivity could reach the level of pure CO2 due to lowered viscosity; (3) non-condensable impurities increase the buoyancy of the CO2 plume. This would negatively affect the efficiency of solubility trapping and residual trapping of CO2. (4) the effect of SO2 on reduction of rock porosity and hence CO2 injectivity would be much smaller than previously thought. A simple formula has been developed to enable quick determination of the effect.
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ABSTRACT This study explores the effect of calcium bromide (CaBr2) doping of lime-based sorbents in the presence of steam during calcination/carbonation cycles. Two sorbents were tested: natural limestone (Cadomin, Canada) and a synthetic... more
ABSTRACT This study explores the effect of calcium bromide (CaBr2) doping of lime-based sorbents in the presence of steam during calcination/carbonation cycles. Two sorbents were tested: natural limestone (Cadomin, Canada) and a synthetic sorbent (pellets) prepared from Cadomin limestone with addition of calcium aluminate cement. The mixture of calcined limestone and cement was pelletized in a mechanical granulator that uses spray water as the part of the pelletization process. Both the original limestone and the prepared pellets were impregnated with a dilute CaBr2 solution to achieve a Ca/Br mole ratio of 500:1. The CO2 carrying activities of the sorbents were tested during calcination/carbonation cycles in a thermogravimetric analysis (TGA) apparatus. Realistic calcination conditions during the reaction cycles were employed: 900 °C with a CO2 sweep gas. Multicycle tests were carried out with steam 15% and without steam present in the carbonation gas stream (20% CO2, 15% steam or 0% steam, N2 balance in both cases). The results showed that doping with CaBr2 has a beneficial effect on sorbent CO2 capture activity, and in particular, the conversion rate during the diffusion-controlled stage of carbonation was found to exhibit a strong synergic enhancement in the presence of steam. The effects of doping and steam were more pronounced in the case of synthetic pellets, resulting in an uptake of 23.8 g of CO2/100 g of sorbent after 31 cycles, which represents a conversion of 35.6%. This CO2 capture uptake is very high compared with that of pellets with no CaBr2 addition and no steam present during the reaction cycles, where only 15.0 g of CO2/100 g of sorbent (22.5% conversion) was seen after 10 cycles. These results suggest that the preparation of synthetic sorbents for calcium looping using solutions containing small amount of bromides would be beneficial in practical applications, and steam will either be produced by firing almost any fuel or be found in flue gas suitable for processing by calcium looping.
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ABSTRACT Sorbent utilization of CaO-based sorbents for in situ SO2 capture in fluidized bed combustion (FBC) is far from quantitative, and in consequence FBC residues contain a significant amount of unreacted CaO. Treatment of bed... more
ABSTRACT Sorbent utilization of CaO-based sorbents for in situ SO2 capture in fluidized bed combustion (FBC) is far from quantitative, and in consequence FBC residues contain a significant amount of unreacted CaO. Treatment of bed materials by hydration with liquid water or steam can reactivate the spent sorbent for further SO2 capture, although, to date, the costs of such processes have deterred its practical use. By contrast, fly ash is already very reactive, but given its short residence time in the combustor, direct reuse of fly ash appears to be an ineffective strategy. This is significant as fly ash often accounts for the majority of solid waste streams discharged from FBC systems. This paper describes a new technique for reactivation of FBC spent sorbent and preparation of pellets suitable for SO2 capture, which can also incorporate the fly ash into the pellets so that it has an adequate residence time in the primary combustion loop of a CFB to realize improved sulfur capture. Reactivation and pelletization of the spent sorbent were achieved simultaneously in a mechanical pelletizer with the addition of spray water. Four types of pellets were prepared with various proportions of bed ash and fly ash. Quick lime (CaO) powders were also tested as a useful additive for the pelletization process. The effectiveness of the reactivation technique was tested by the nitrogen physisorption, which confirmed that a more suitable pore surface area and pore volume distribution for sulfation were developed. The SO2 capture potential of the pellets was also examined in a thermogravimetric analyzer. The reactivated pelletized sorbents showed an improved sulfation rate in comparison to both the original sorbent and the spent sorbent, particularly during the diffusion-controlled reaction stage.
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Calcium looping (CaL) is a post-combustion CO2 capture technology that is suitable for retrofitting existing power plants. The CaL process uses limestone as a cheap and readily available CO2 sorbent. While the technology has been widely... more
Calcium looping (CaL) is a post-combustion CO2 capture technology that is suitable for retrofitting existing power plants. The CaL process uses limestone as a cheap and readily available CO2 sorbent. While the technology has been widely studied, there are a few available options that could be applied to make it more economically viable. One of these is to increase the oxygen concentration in the calciner to reduce or eliminate the amount of recycled gas (CO2, H2O and impurities); therefore, decreasing or removing the energy necessary to heat the recycled gas stream. Moreover, there is a resulting increase in the energy input due to the change in the combustion intensity; this energy is used to enable the endothermic calcination reaction to occur in the absence of recycled flue gases. This paper presents the operation and first results of a CaL pilot plant with 100% oxygen combustion of natural gas in the calciner. The gas coming into the carbonator was a simulated flue gas from a co...
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CaO-based looping cycles for CO2 capture at high temperatures are based on cyclical carbonation of CaO and regeneration of CaCO3. The main limitation of natural sorbents is the loss of carrying capacity with increasing numbers of reaction... more
CaO-based looping cycles for CO2 capture at high temperatures are based on cyclical carbonation of CaO and regeneration of CaCO3. The main limitation of natural sorbents is the loss of carrying capacity with increasing numbers of reaction cycles, resulting in spent sorbent ballast. Use of spent sorbent from CO2 looping cycles for SO2 capture is a possible solution investigated in this study. Three limestones were investigated: Kelly Rock (Canada), La Blanca (Spain) and Katowice (Poland). Carbonation/calcination cycles were performed in a tube furnace with original limestones and samples thermally pretreated for different times (i.e., sintered). The spent sorbent samples were sulphated in a thermogravimetric analyzer. Changes in the resulting pore structure were then investigated using mercury porosimetry. Final conversions of both spent and pretreated sorbents after longer sulphation times were comparable or higher than those observed for the original sorbents. Maximum sulphation levels strongly depend on sorbent porosity and pore surface area. The shrinkage of sorbent particles during calcination/cycling resulted in a loss of sorbent porosity (≤48%), which corresponds to maximum sulphation levels ˜55% for spent Kelly Rock and Katowice. However, this is ˜10% higher than for the original samples. By contrast, La Blanca limestone had more pronounced particle shrinkage during pretreatment and cycling, leading to lower porosity, <35%, resulting in sulphation conversion of spent samples <30%, significantly lower than for the original sample (45%). These results showed that spent sorbent samples from CO2 looping cycles can be used as sorbents for SO2 retention if significant porosity loss does not occur during CO2 reaction cycles. For spent Kelly Rock and Katowice samples final conversions are determined by the total pore volume available for the bulky CaSO4 product.
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Research Interests: Carbon Dioxide, Scanning Electron Microscopy, Multidisciplinary, Environmental science and technology, Adsorption, and 12 moreSolid waste, X ray diffraction, Particle Size, Waste Treatment, Surface Properties, Oxides, Calcium Compounds, Adsorbent, Water Vapor, Fluidized Bed Combustion, Sulfur Dioxide, and Flue Gas Desulfurization
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Fluidized bed combustion (FBC) has the considerable advantage of being capable of burning high-sulphur fuels while achieving in situ sulphur capture by means of limestone addition. Unfortunately the efficiency of this process is limited,... more
Fluidized bed combustion (FBC) has the considerable advantage of being capable of burning high-sulphur fuels while achieving in situ sulphur capture by means of limestone addition. Unfortunately the efficiency of this process is limited, and limestone utilization in the range of 30–45% is not uncommon. In consequence, improving limestone utilization has long been an aim of FBC research. The principal
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Research Interests: Mechanical Engineering, Chemical Engineering, Scanning Electron Microscopy, Comparative Study, Quantitative analysis, and 11 morePorosity, Fuel, Atmospheric Pressure, Fluidized Bed, Thermogravimetry, X ray diffraction, Quantitative Analysis, Fluidized Bed Reactor, Carbonation, Pilot Plant, and Fluidized Bed Combustion
ABSTRACT The hydration of partially-sulphated fluidized bed combustor (FBC) ash with water was carried out at laboratory scale. The bottom ash fractions and the as-received fly ash were hydrated for different lengths of time, at different... more
ABSTRACT The hydration of partially-sulphated fluidized bed combustor (FBC) ash with water was carried out at laboratory scale. The bottom ash fractions and the as-received fly ash were hydrated for different lengths of time, at different temperatures between 5°C and 80°C. The free lime and calcium hydroxide content in the samples were analyzed before and after the hydration process. Scanning electron microscopy (SEM) with an energy dispersive X-ray system (EDX) was employed to investigate the physical characteristics of the samples. X-ray diffractograms (XRD) were used to obtain information on the phase composition. The current results show that, during the hydration treatment, the unreacted CaO in the partially-sulphated material can be almost quantitatively converted to Ca(OH)2 but that the free lime content is not constant. It is also clear that effectiveness of the hydration depends on hydration time and temperature. In addition, the behaviour of different particle size fractions is different and there is evidence that the hydration of CaO is not the only reaction occurring in this system.On a procédé à l&#39;échelle de laboratoire à l&#39;hydratation de la cendre partiellement sulfatée avec de l&#39;eau d&#39;un appareil de combustion en lit fluidisé (FBC). Ces fractions et les cendres volantes ainsi obtenues ont été hydratées pour différents temps d&#39;hydratation différents et différentes températures comprises entre 5 °C et 80 °C. La teneur en chaux et en hydroxyde de calcium libres dans les échantillons a été analysée avant et après le procédé d&#39;hydratation. On a eu recours à la microscopie électronique à balayage (SEM) avec un système à rayons X à dispersion d&#39;énergie (EDX) afin d&#39;étudier les caractéristiques des échantillons. Des diffractogrammes X (XRD) ont été utilisés pour obtenir de l&#39;information sur la composition des phases. Les résultats actuels montrent que, durant le traitement d&#39;hydratation, le CaO non réagi dans le matériau partiellement sulfaté peut être presque converti quantitativement en Ca(OH)2, mais que la teneur en chaux libre n&#39;est pas constante. Il apparaît également clairement que l&#39;efficacité de l&#39;hydratation dépend de la durée et de la température de l&#39;hydratation. En outre, le comportement des différentes fractions de taille des particules est différent et il est clair que l&#39;hydratation du CaO n&#39;est pas la seule réaction à se produire dans ce système.
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ABSTRACT