The Use of Gaseous Metal Oxide as an Oxygen Carrier in Coal Chemical Looping Combustion PDF Download
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Author: Quan Zhang
Publisher:
ISBN:
Category : Coal
Languages : en
Pages : 262
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Book Description
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.
Author: Quan Zhang
Publisher:
ISBN:
Category : Coal
Languages : en
Pages : 262
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Book Description
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.
Author: Akash G. Basu
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 102
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Book Description
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: Chern Yean Sim
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
It is well known that carbon dioxide (CO2) is a greenhouse gas that contributes to global warming. Nowadays, a third of the worldwide anthropogenic CO2 emissions arise from fossil fuel fired power production. Meanwhile, fossil fuels continue to be the main source of energy for the foreseeable future. The increasing threat posed by enhanced global warming, as well as the requirement for sustainable energy supplies around the world, have led to the development of several novel technologies to produce clean energy from fuels. Among these new technologies is chemical looping combustion (CLC) that uses a solid metal oxide (oxygen carrier) to react with fuels. This technology has the potential advantage that it produces a pure stream of CO2 that can then be sequestrated. In a CLC process, the oxygen carrier is reduced by fuels in one reactor while being oxidised by air in a separate reactor. As the oxygen carrier circulates through the system, it is subjected to morphological and compositional changes such as sintering, attrition and reactions between various metal oxides and fuels. These changes tend to cause the reactivity of the oxygen carrier to decrease over time. The main objective of this PhD study was to investigate and characterise the morphological and compositional changes of the oxygen carrier particles after they have undergone multiple reduction oxidation cycles in a CLC system. A single fluidised bed system was used in this study. Fuel was fed into a bed of oxygen carrier consisting of mechanically mixed iron oxide or wet impregnated copper oxide supported on alumina. The bed was fluidised by a stream of CO2 and/or steam. Pyrolysis gases from the fuel gasification process reduced the oxygen carrier while forming char in the bed. Thus char was oxidised and the oxygen carrier was regenerated when the fluidising gas was switched to air. Five different types of fuels were initially used in the tests. They were lignite coal, lignite char, activated carbon, US bituminous coal and Taldinski bituminous coal. The rates of gasification of the bituminous coal and activated carbon were much slower than those of the lignite coal and lignite char, resulting in an unfavourably large accumulation of char during the reduction stage. Subsequent experiments were conducted with UK bituminous coal to determine the effect of ash on the oxygen carrier particles over a long operational period. The series of analytical tests included; stereo microscopy, porosimetry analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy with an energy dispersive system (SEM/EDS) and Page ii X-ray photoelectron spectroscopy (XPS). Tests were performed on both the fresh and reacted oxygen carriers. Analytical results showed that when the pyrolysis gases react with the oxygen carrier, mineral matter left behind from the gasification process will deposit on the surface of the particles and diffuse into the core of the particles. This is due to the fact that mineral matter has a higher melting point compared to iron oxide and copper oxide. Iron oxide and copper oxide diffusing to the surface of the particles will replace those that are lost via attrition. As a result, the composition of the surface of these particles remains relatively unchanged. As more mineral matter diffuses into the core of the oxygen carrier particles, they can segregate metal oxide molecules located at the surfaces from those located at the core of the particles. When this occurs, there is a possibility that the segregated material formed will reduce the ability of oxygen to diffuse to the surface of the oxygen carrier particles. Hence this will reduce the conversion of the pyrolysis gases. This will thus lead to the reduction in the conversion of the pyrolysis gas and possibly in the deactivation of the oxygen carrier. It was found that the support structure played a key role in maintaining the structural integrity of the metal oxide particles during repeated reduction and oxidation cycles. Experimental results showed that the rate of attrition initially increases with time indicating that the oxygen carrier structure weakens as it interacts with the mineral matter in ash. Results from this research study have shown that the semi-batch chemical looping combustion of solid fuels is feasible provided reactive fuels that produce a large quantity of pyrolysis gases are used. Less reactive fuels will lead to the accumulation of a large inventory of char in the bed. The slow rate of gasification of char will then result in a lower carbon capture efficiency. In order to operate a semi-batch chemical looping combustion system with solid fuel, temperatures of above 1000°C are most likely required. However, this would exclude metal oxides with low melting points to act as potential oxygen carriers and may cause other problems such as ash fusion. A possible solution is to gasify the solid fuels in a separate reactor and channel the resulting pyrolysis gases into the chemical looping combustion system.
Author: Ronald W. Breault
Publisher: John Wiley & Sons
ISBN: 3527342028
Category : Business & Economics
Languages : en
Pages : 488
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Book Description
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: Liang-Shih Fan
Publisher: John Wiley & Sons
ISBN: 1118063139
Category : Technology & Engineering
Languages : en
Pages : 353
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Book Description
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.
Author: Cheng Lung Chung
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages :
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Book Description
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.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Chemical looping combustion (CLC) is a combustion technology that utilizes oxygen from oxygen carriers (OC), such as metal oxides, instead of air to combust fuels. The use of natural minerals as oxygen carriers has advantages, such as lower cost and availability. Eight materials, based on copper or iron oxides, were selected for screening tests of CLC processes using coal and methane as fuels. Thermogravimetric experiments and bench-scale fixed-bed reactor tests were conducted to investigate the oxygen transfer capacity, reaction kinetics, and stability during cyclic reduction/oxidation reaction. Most natural minerals showed lower combustion capacity than pure CuO/Fe2O3 due to low-concentrations of active oxide species in minerals. In coal CLC, chryscolla (Cu-based), magnetite, and limonite (Fe-based) demonstrated better reaction performances than other materials. The addition of steam improved the coal CLC performance when using natural ores because of the steam gasification of coal and the subsequent reaction of gaseous fuels with active oxide species in the natural ores. In methane CLC, chryscolla, hematite, and limonite demonstrated excellent reactivity and stability in 50-cycle thermogravimetric analysis tests. Fe2O3-based ores possess greater oxygen utilization but require an activation period before achieving full performance in methane CLC. Particle agglomeration issues associated with the application of natural ores in CLC processes were also studied by scanning electron microscopy (SEM).
Author: Paul Fennell
Publisher: Elsevier
ISBN: 0857097601
Category : Technology & Engineering
Languages : en
Pages : 467
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Book Description
Calcium and Chemical Looping Technology for Power Generation and Carbon Dioxide (CO2) Capture reviews the fundamental principles, systems, oxygen carriers, and carbon dioxide carriers relevant to chemical looping and combustion. Chapters review the market development, economics, and deployment of these systems, also providing detailed information on the variety of materials and processes that will help to shape the future of CO2 capture ready power plants. - Reviews the fundamental principles, systems, oxygen carriers, and carbon dioxide carriers relevant to calcium and chemical looping - Provides a lucid explanation of advanced concepts and developments in calcium and chemical looping, high pressure systems, and alternative CO2 carriers - Presents information on the market development, economics, and deployment of these systems
Author: L Zheng
Publisher: Elsevier
ISBN: 0857090984
Category : Technology & Engineering
Languages : en
Pages : 397
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Book Description
Oxy-fuel combustion is currently considered to be one of the major technologies for carbon dioxide (CO2) capture in power plants. The advantages of using oxygen (O2) instead of air for combustion include a CO2-enriched flue gas that is ready for sequestration following purification and low NOx emissions. This simple and elegant technology has attracted considerable attention since the late 1990s, rapidly developing from pilot-scale testing to industrial demonstration. Challenges remain, as O2 supply and CO2 capture create significant energy penalties that must be reduced through overall system optimisation and the development of new processes.Oxy-fuel combustion for power generation and carbon dioxide (CO2) capture comprehensively reviews the fundamental principles and development of oxy-fuel combustion in fossil-fuel fired utility boilers. Following a foreword by Professor János M. Beér, the book opens with an overview of oxy-fuel combustion technology and its role in a carbon-constrained environment. Part one introduces oxy-fuel combustion further, with a chapter comparing the economics of oxy-fuel vs. post-/pre-combustion CO2 capture, followed by chapters on plant operation, industrial scale demonstrations, and circulating fluidized bed combustion. Part two critically reviews oxy-fuel combustion fundamentals, such as ignition and flame stability, burner design, emissions and heat transfer characteristics, concluding with chapters on O2 production and CO2 compression and purification technologies. Finally, part three explores advanced concepts and developments, such as near-zero flue gas recycle and high-pressure systems, as well as chemical looping combustion and utilisation of gaseous fuel.With its distinguished editor and internationally renowned contributors, Oxy-fuel combustion for power generation and carbon dioxide (CO2) capture provides a rich resource for power plant designers, operators, and engineers, as well as academics and researchers in the field. - Comprehensively reviews the fundamental principles and development of oxy-fuel combustion in fossil-fuel fired utility boilers - Provides an overview of oxy-fuel combustion technology and its role in a carbon-constrained environment - Introduces oxy-fuel combustion comparing the economics of oxy-fuel vs. post-/pre-combustion CO2 capture
Author: Liang-Shih Fan
Publisher: Cambridge University Press
ISBN: 1107194393
Category : Technology & Engineering
Languages : en
Pages : 497
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Book Description
The first comprehensive guide to chemical looping partial oxidation processes, covering key principles, techniques, and applications.
