Combustion of Coal Using Chemical Looping Oxygen Carriers PDF Download
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Languages : en
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Author: Ronald W. Breault
Publisher: John Wiley & Sons
ISBN: 3527342028
Category : Business & Economics
Languages : en
Pages : 488
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This comprehensive and up-to-date handbook on this highly topical field, covering everything from new process concepts to commercial applications. Describing novel developments as well as established methods, the authors start with the evaluation of different oxygen carriers and subsequently illuminate various technological concepts for the energy conversion process. They then go on to discuss the potential for commercial applications in gaseous, coal, and fuel combustion processes in industry. The result is an invaluable source for every scientist in the field, from inorganic chemists in academia to chemical engineers in industry.
Author: Adánez Rubio, Iñaki
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Languages : es
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Author: Liang-Shih Fan
Publisher: John Wiley & Sons
ISBN: 1118063139
Category : Technology & Engineering
Languages : en
Pages : 353
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This book presents the current carbonaceous fuel conversion technologies based on chemical looping concepts in the context of traditional or conventional technologies. The key features of the chemical looping processes, their ability to generate a sequestration-ready CO2 stream, are thoroughly discussed. Chapter 2 is devoted entirely to the performance of particles in chemical looping technology and covers the subjects of solid particle design, synthesis, properties, and reactive characteristics. The looping processes can be applied for combustion and/or gasification of carbon-based material such as coal, natural gas, petroleum coke, and biomass directly or indirectly for steam, syngas, hydrogen, chemicals, electricity, and liquid fuels production. Details of the energy conversion efficiency and the economics of these looping processes for combustion and gasification applications in contrast to those of the conventional processes are given in Chapters 3, 4, and 5.Finally, Chapter 6 presents additional chemical looping applications that are potentially beneficial, including those for H2 storage and onboard H2 production, CO2 capture in combustion flue gas, power generation using fuel cell, steam-methane reforming, tar sand digestion, and chemicals and liquid fuel production. A CD is appended to this book that contains the chemical looping simulation files and the simulation results based on the ASPEN Plus software for such reactors as gasifier, reducer, oxidizer and combustor, and for such processes as conventional gasification processes, Syngas Chemical Looping Process, Calcium Looping Process, and Carbonation-Calcination Reaction (CCR) Process. Note: CD-ROM/DVD and other supplementary materials are not included as part of eBook file.
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Languages : en
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Chemical Looping Combustion (CLC) could totally negate the necessity of pure oxygen by using oxygen carriers for purification of CO2 stream during combustion. It splits the single fuel combustion reaction into two linked reactions using oxygen carriers. The two linked reactions are the oxidation of oxygen carriers in the air reactor using air, and the reduction of oxygen carriers in the fuel reactor using fuels (i.e. coal). Generally metal/metal oxides are used as oxygen carriers and operated in a cyclic mode. Chemical looping combustion significantly improves the energy conversion efficiency, in terms of the electricity generation, because it improves the reversibility of the fuel combustion process through two linked parallel processes, compared to the conventional combustion process, which is operated far away from its thermo-equilibrium. Under the current carbon-constraint environment, it has been a promising carbon capture technology in terms of fuel combustion for power generation. Its disadvantage is that it is less mature in terms of technological commercialization. In this DOE-funded project, accomplishment is made by developing a series of advanced copper-based oxygen carriers, with properties of the higher oxygen-transfer capability, a favorable thermodynamics to generate high purity of CO2, the higher reactivity, the attrition-resistance, the thermal stability in red-ox cycles and the achievement of the auto-thermal heat balance. This will be achieved into three phases in three consecutive years. The selected oxygen carriers with final-determined formula were tested in a scaled-up 10kW coal-fueled chemical looping combustion facility. This scaled-up evaluation tests (2-day, 8-hour per day) indicated that, there was no tendency of agglomeration of copper-based oxygen carriers. Only trace-amount of coke or carbon deposits on the copper-based oxygen carriers in the fuel reactor. There was also no evidence to show the sulphidization of oxygen carriers in the system by using the high-sulfur-laden asphalt fuels. In all, the scaled-up test in 10 kW CLC facility demonstrated that the preparation method of copper-based oxygen carrier not only help to maintain its good reactivity, also largely minimize its agglomeration tendency.
Author: Sharmen Rajendran
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Category :
Languages : en
Pages : 290
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The vast reserves of Victorian brown coal (VBC), over 400 years at the current rate of consumption, is predominantly used for power generation with over 80% of Victoria's electricity generated from the combustion of this fuel. This results in the emission of vast amounts of greenhouse gases such as CO2. Hence, it is important to investigate carbon dioxide capture and storage technologies for use in power stations employing fossil fuels. Chemical Looping Combustion (CLC) is an emerging CO2 capture technology which is capable of inherently capturing CO2. In CLC, the Oxygen Carrier (OC) provides the oxygen for the combustion of the fuel hence eliminating dilution with N2 from air. Once the oxygen in the OC is depleted, it is regenerated through oxidation in air and is then sent back to react with another batch of fuel. The vast majority of research in the field of CLC has been focussed on gaseous fuels such as natural gas and syngas due to the simplicity of such a process. In recent times, there has been a shift towards the use of solid fuels due to their abundance, widespread availability and lower cost. As such, there are a number of gaps in the field of CLC employing solid fuels; additionally, the only information relating to CLC of VBC is limited to experiments using small scale laboratory equipment. This thesis serves to fill some of the gaps in the field of VBC-fuelled CLC. The first study investigated the effect of inherent coal minerals on the performance of a CLC system; a high ash Canadian lignite was also used as part of this comparative study. The results highlighted that the low ash VBC was more suitable for use as a fuel in CLC as it was highly reactive and its low ash content led to a smaller amount of ash deposition on the OC. The second study involved using synchrotron radiation to perform in-situ X-ray Diffraction studies of a VBC-fuelled CLC process to understand both the changes that the OC undergoes as part of the redox reaction as well as carbon deposition on the OC. The results showed that the reduction of Fe2O3 beyond Fe3O4 was not favourable over long periods of time when using CO2 as the gasification agent as it led to carbon deposition on the OC. The third study is a first-of-its-kind investigation, where the reduction kinetics of an Fe-based OC was determined in the presence of a char derived from VBC. The Shrinking Core Model (SCM) and the Modified Volume Reaction Model (MVRM) were used to model the reduction of the OC. The results showed that both models were capable of predicting the reduction of Fe2O3 in the presence of a solid fuel. The calculations also verified that the rate limiting step in CLC was that of char gasification. The fourth study investigated the effect of the reactor configuration on the performance of the CLC system as such a comparison has never been attempted. A fluidized bed reactor, an atmospheric fixed bed reactor and a pressurized fixed bed reactor operated at 5 bar were used. The amount of the fuel and the OC together with the flow rates of the gases were kept constant so that the results from the different setups could be compared accurately. It was found that using the fluidized bed reactor allowed for the fastest gasification of the fuel due to better contact between the gasification agent and fuel. Although the CO2 yield and carbon conversion in the fluidized bed reactor was lower compared to the other two fixed bed reactors, it is expected that the use of a circulating fluidized bed (CFB) reactor with cyclones, a carbon stripper and a taller expanded freeboard would improve these two parameters. The fifth study involved fabricating and trialling 18 synthetic OCs in which NiO, CuO and Mn2O3 were supported on Fe2O3. This was done as most studies in literature utilize an inert support that is not able to take part in the redox reaction; as such a greater quantity of the OC is needed to provide the necessary oxygen. The results highlight that impregnated OCs were more reactive relative to their physically mixed counterparts. The use of high levels of CuO should be avoided as it led to the defluidization of the bed. Although NiO performed well, it may not be suitable for use due to its toxicity. Taking numerous considerations into account, the use of Mn2O3 was recommended as it led to a synergistic effect with Fe2O3. The sixth and final study of this thesis utilized a 10 kWth alternating fluidized bed reactor to trial the performance of VBC in a large scale reactor. A number of studies on the effects of temperature, fuel type, OC particle size range and long term operation on the performance of the CLC system were done. The NOx emissions were quantified and a carbon balance was also performed. The NOx emissions were found to average around 25 ppm over the course of the reduction reaction. Based on the carbon balance, 6.8% of the introduced carbon was unaccounted for due to the low capture efficiency of the cyclones. The optimum parameters were found to be 900°C for the temperature, 150-350 μm for the OC particle size range and VBC for the fuel. The average carbon conversion and CO2 yield over 35 reduction reactions was found to be 86% and 81% respectively for the conditions optimized for this reactor setup. These studies show that the use of Fe-based OCs is highly promising with VBC. The main recommendation from this thesis is the use of VBC in a CFB reactor as this is expected to significantly improve the carbon conversion and CO2 yield.
Author: Quan Zhang
Publisher:
ISBN:
Category : Coal
Languages : en
Pages : 262
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Traditional chemical looping technologies utilize solid oxygen carriers and has some disadvantages, especially when solid fuels like coal are used. In this work, a novel chemical looping process using gaseous metal oxide as oxygen carrier was proposed. The reaction of activated charcoal with gas-phase MoO3 was studied for the first time. The experiments were conducted isothermally at different temperatures in a fixed-bed reactor. The apparent activation energy of the reaction was calculated and suitable kinetic models were determined. The results and analysis showed that the proposed concept has potential in both coal chemical looping combustion and gasification process. To further investigate the mechanism of carbon oxidation by gas-phase MoO3, the adsorption of a gaseous (MoO3)3 cluster on a graphene ribbon and subsequent generation of COx was studied by density functional theory (DFT) method and compared with experimental results. The (MoO3)n -graphene complexes show interesting magnetic properties and potentials for nanodevices. A comprehensive analysis of plausible reaction mechanisms of CO and CO2 generation was conducted. Multiple routes to CO and CO2 formation were identified. The (MoO3 )3 cluster shows negative catalytic effect for CO formation but does not increase the energy barrier for CO2 formation, indicating CO2 is the primary product. Mechanism of the homogenous MoO 3-CO reaction was studied and showed relatively low energy barriers. The DFT result accounts for key experimental observations of activation energy and product selectivity. The combined theoretical and experimental approach contributes to the understanding of the mechanism of reactions between carbon and metal oxide clusters. To gain a better understanding of the MoO2 oxidation process, the adsorption and dissociation of O2 on MoO2 surface were studied by DFT method. The results show that O2 molecules prefer to be adsorbed on the five-coordinated Mo top sites. Density of states analysis shows strong hybridization of Mo 4d orbitals and O 2p orbitals in the Mo-O bond. Clean MoO2 slab and slabs with O2 adsorption are metallic conductors, while the surface with high O atom coverage is reconstructed and becomes a semiconductor. Surface Mo atoms without adsorbed O or O2 are spin-polarized. The oxygen adsorption shows ability to reduce the spin of surface Mo atoms. The adsorption energy of O2 and O atoms decreases as coverage increases. The transition states of O 2 dissociation were located. The energy barriers for O2 dissociation on five-coordinated and four-coordinated Mo top sites are 0.227 eV and 0.281 eV, respectively.
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Author: Akash G. Basu
Publisher:
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Category : Chemical engineering
Languages : en
Pages : 102
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The rapidly rising population of the world requires us to come up with ways to meet growing energy demands efficiently while taking environmental precautions. Lately, much research has been conducted on various carbon capture utilization and storage (CCUS) methods as a way of providing energy while reducing emissions. An innovative method for carbon capture that has recently garnered attention is chemical looping combustion (CLC), due to its ability to produce a CO2 rich flue gas that can be easily sequestered and stored. The Ohio State University has developed the Coal-Direct Chemical Looping (CDCL) sub-pilot reactor system for coal combustion which uses an iron-based metal oxide as an oxygen carrier and a countercurrent moving bed for the reducer. In this study, sulfur species in the gas and solid phases in the CDCL process are studied in a bench scale moving bed reducer that is scaled down from the sub-pilot reducer to identify the distribution of sulfur species present in the solid and gaseous phases. The effects of operating parameters and the interaction between the oxygen carrier and sulfur species are also explored. It was discovered that increasing the reducer temperature produces more SO2 in the flue gas. It was also observed that the reduced oxygen carrier particles have an increased chance of reacting with H2S to form FeS. However, using CO2 as an enhancing gas can slow the rate of formation for FeS. Using CO2 provides the additional benefit of releasing more SO2 and causes less sulfur to transfer to the oxygen carrier. For the L-valve section, it was determined that using N2 as a carrier gas releases additional SO2 from the particles before transferring to the combustor, and even more SO2 can be released if the size of the L-valve section is increased. Finally, it was observed that increasing the ratio of the oxygen carrier to coal flow rate causes the conversion to increase, COS to form in zone 2 of the reducer, and less SO2 to be carried into the combustor, reducing emissions.
Author: Cheng Lung Chung
Publisher:
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Category : Chemical engineering
Languages : en
Pages :
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This dissertation presents investigations of chemical looping technology as a transformative process for combustion of fossil fuels for power generation with CO2 capture. Specifically, the dissertation seeks to synthesize and characterize a low-cost iron-based oxygen carrier that can be employed in a commercial chemical looping combustion system with realistic material lifetime and adequate resistance to toxicity from pollutants from fossil fuels such as coal. Two secondary metal oxides (Al2O3 and TiO2) as support materials for Fe2O3 and their respective reaction-induced morphological changes are presented. A novel iron-based oxygen carrier was consequently identified to be sustainable over 3000 redox cycles in high temperatures (1000 °C) at the lab scale without chemical and physical degradation. Oxygen carrier of the same design also exhibited high resistance toward attrition from circulation and fluidization in two pilot-scale demonstration units under representative conditions. Tolerance of the active ingredients of the iron-based oxygen carriers against common toxic elements in the fossil fuel feedstock, such as alkaline and sulfur compounds from conversion of coal, through multiple fixed bed experiments under conditions representative of the counter-current moving bed reducer and thermogravimetric experiments up to 9000 ppm of H2S. The likelihood of agglomeration and interaction of alkaline metals (Na, K) with the iron-based oxygen carriers were found to be extremely low under normal operating conditions. Instead, proper distribution of coal was more crucial to avoid agglomeration caused by melting of SiO2. Sulfur deposition on iron-based oxygen carriers, although observed, was reversible through regeneration with air and did not result in degradation in the recyclability of the oxygen carriers. A potential pathway for sulfur emission via the combustor spent air was also identified. The sulfur emission and distribution of the Coal-Direct Chemical Looping (CDCL) 25 kWth sub-pilot unit which utilized the iron-based oxygen carriers was determined with a custom heat-traced gas sampling system. More than 69% of the total amount of atomic sulfur from high sulfur coal was converted to SO2 and H2S in the reducer flue gas stream while less than 5% was released as SO2 in the combustor spent air. The missing atomic sulfur in the balance was attributed to sulfur retained in coal ash as inorganic sulfur compounds. A flue gas clean-up system targeting both H2S and SO2 is therefore recommended to meet the quality of CO2-rich stream for transportation and sequestration in a commercial CDCL system. The projected sulfur emission in the combustor spent air was under the US EPA sulfur emission regulation safe to be released to the atmosphere without a costly acid removal system. The findings demonstrate the robustness of the CDCL system, together with the iron-based oxygen carriers, to handle high sulfur coal without severe performance and economic penalties.
