Author: Nur Sena YüzbasiPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Development of Iron and Copper Oxide Based Oxygen Carriers for Chemical Looping Applications - Structural Insight and Performance Assessment
Author: Nur Sena YüzbasiDevelopment of Iron-based Oxygen Carriers in Recyclability, Physical Strength and Toxicity-tolerance for Coal-direct Chemical Looping Combustion Systems
Author: Cheng Lung ChungPublisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages :
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.
Catalytic Modification of Oxygen Carriers for Chemical Looping Applications
Author: Mengqing GuoPublisher:
ISBN:
Category : Metallic oxides
Languages : en
Pages :
Book Description
The kinetics of iron-based oxygen carriers were studied as well to show the increment performance of the chemical looping process with doped iron-based oxygen carriers. With the development of chemical looping scaling up, there are more opportunities and challenges in this process and oxygen carriers. Outcomes from this research on the development of oxygen carriers throw lights on the commercialization of the chemical looping technology in the near future.
Modeling Chemistry of Copper-based Oxygen Carriers in Chemical Looping Combustion Systems
Author: Eli A. GoldsteinPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Development of a model that can be used to predict oxidation rates of copper to cuprous and cupric oxide (Cu2O and CuO, respectively) in the air reactor of a Chemical Looping Combustion (CLC) system is the primary focus of this thesis. The proposed oxidation model, which is based in Wagner Theory and defect chemistry, describes the fundamental processes occurring during copper oxidation. Consequently, it provides better predictive capabilities over a wide range of temperatures and pressures, as well as characteristic particle geometries (spheres, cylinders and plates) than the phenomenological models that are currently being used to predict oxidation rates of copper-based oxygen carriers used in CLC systems. In addition to developing this oxidation model, cuprous and cupric oxide reduction experiments with gaseous fuels like carbon monoxide, hydrogen and methane, and solid fuels like char, wyodak coal, and corn stover, were performed to characterize reaction rates in the fuel reactor of CLC systems. Oxidation rates obtained from the oxidation model, and measured rates from the reduction experiments were used to estimate the size and oxygen carrier loading for a 10 MWth CLC system.
Fe2O3-based Oxygen Carriers for Gaseous and Solid-fueled Chemical Looping Processes
Author: Ankita MajumderPublisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 204
Book Description
Chemical looping is an efficient, economic and sustainable means for electricity and/or chemicals production with inherent CO2 sequestration ability. Oxygen carriers play a crucial role in the successful operation of a chemical looping system as their physical and chemical properties dictate the fuel conversion efficiency of the system. They are expected to undergo multiple redox cycles while maintaining their reactivity and mechanical strength in order to improve the overall process economics for commercial viability. This research investigates the behavior of oxygen carriers under different reactive conditions and evaluates their feasibility for biomass chemical looping systems. The reduction kinetics of OSU’s iron titanium complex metal oxide (ITCMO) oxygen carrier particles are investigated at elevated pressures with H2 and CH4 for application in OSU’s Shale gas-to-Syngas process. Under CH4, there is almost a 5-fold increase in the reduction rate with an increase in pressure from 1 to 10 atm. Solid characterization revealed increased porosity and surface area at elevated pressures. Faster reaction kinetics at higher pressures can translate into increased processing capacity, reduced reactor sizing, and decreased capital costs. The steam to H4 conversion efficiency of Fe2O3 based oxygen carriers using Al2O3, MgAl2O4 and TiO2 as support materials is investigated in a fixed bed for chemical looping H2 generation. All supported-Fe2O3 based oxygen carriers exhibited >70% steam conversion, close to thermodynamic predictions. Due to its ability to not form complexes with the active material, MgAl2O4 -supported Fe2O3 was selected for further investigation. Thermogravimetric studies with steam oxidation exhibited excellent recyclability and no significant drop in reactivity. MgAl2O4 -supported Fe2O3 also exhibited enhanced steam oxidation kinetics at elevated pressures. Tar derived from biomass pyrolysis is a major concern for biomass thermochemical conversion processes. For biomass fueled chemical looping processes, it is important to evaluate effects of tars on the oxygen carriers. Fixed bed experiments demonstrated that OSU’s ITCMO oxygen carriers have reasonable reactivity for cracking most biomass-derived tar components. To further enhance the tar cracking ability of Fe2O3 -based oxygen carriers, they are combined with traditional tar cracking catalysts. Based on thermogravimetric reactivity and fixed bed tar cracking experiments, NiO is selected as an additive for Fe2O3 -based oxygen carriers for biomass chemical looping systems. The outcomes from this research will help in the development of economic and efficient oxygen carriers for the commercialization of the various chemical looping applications.
Fundamental Aspects of Chemical-looping with Oxygen Uncoupling Using Copper Oxide-based Oxygen Carriers
Author: Christopher K. ClaytonPublisher:
ISBN:
Category : Copper oxide
Languages : en
Pages : 152
Book Description
Handbook of Chemical Looping Technology
Author: Ronald W. BreaultPublisher: John Wiley & Sons
ISBN: 3527342028
Category : Business & Economics
Languages : en
Pages : 488
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.
A Systematic Investigation of the Performance of Copper-, Cobalt-, Iron-, Manganese- and Nickel-based Oxygen Carriers for Chemical Looping Combustion Technology Through Simulation Models
Author: Redox Kinetics Study for Chemical-looping Combustion, Water and CO2 Splitting Using Nickel and Cerium-based Oxygen Carrier
Author: Zhenlong ZhaoPublisher:
ISBN:
Category :
Languages : en
Pages : 448
Book Description
Chemical-looping (CL) is a novel and promising technology for several applications including oxy-combustion for carbon capture, hydrogen production and CO2 reuse. In this process, oxygen carriers are utilized to cyclically adsorb and release oxygen producing two separated exhaust streams with desirable products. A rotary reactor design with micro-channel structure was developed in the Reacting Gas Dynamics Lab (RGDL) at MIT, which exhibits superior performance over conversional designs. Preliminary simulation identified OC redox kinetics and material characteristics as keys to the success of CL technology. This thesis examines the fundamentals of the reduction and oxidation (redox) processes with the aim of achieving fast and reliable reaction kinetics for CL applications. Experiments are conducted in a button-cell fixed-bed reactor with an on-line mass spectrometer. The timeresolved kinetics are modeled with consideration of thermodynamics, surface chemistry, transport mechanism, and structural evolution. Our approach, combining well-controlled experiment and detailed kinetics modeling, enables a new methodology for identifying the rate-limiting mechanism, examining the defect electrochemistry, and designing alternative materials for chemical-looping technology. Redox study with nickel thin foils reveals that structural evolution is the determining factor. Nickel oxidation starts via nucleation of oxide grains, which overlap and annihilate the fast diffusion paths. The model shows that the reaction is limited by the decreasing ionic diffusivity. To achieve practical redox repeatability, NiO fine particles supported on YSZ nanopowder is tested, and superior kinetics and cyclic stability are observed. Fast oxygen exchange is achieved from 500 to 1000°C with sufficient utilization of the carrying capacity within 1 min. Improvement is attributed to the enhanced ionic diffusivity with YSZ. The use of ceria nanopowder exhibits an order of magnitude H2 production rate improvement as compared to the state-of-the-art. Ceria reduction is slow with a threshold temperature of 700°C. The model reveals that the charge transfer is the rate-determining step for H2 production. Improving H2 splitting requires: (i) reducing the defect formation enthalpy, and (ii) accelerating charge-transfer. The addition of Zr lowers the threshold temperature to 650°C with 60% improvement in the rates, resulting from 40% decrease in the defect formation enthalpy. Doping ceria with Pr 3+ further lowers the threshold temperature to 600°C while doubling the peak rate. The model reveals that the high concentration of surface defects achieved from either approach promotes adsorbate formation, thus accelerating the splitting steps. Similar conclusions are obtained for CO2 splitting. Using the derived kinetics, H2-syngas co-production with CH4 as fuel is examined. Two important stages are identified: the formation of the complete products on oxidized surface, and syngas on the reduced surface. CH4 reduction is found to be rate-limited by the slow fuel cracking reaction. To accelerate the kinetics, a novel perovskite-nickel composite OC is examined, in which nickel effectively catalyzes reduction, leading to an order of magnitude faster kinetics at 600-700°C. This project has clearly demonstrated that using novel materials, CL technology can provide an efficient solution to oxy-combustion based CO2 capture, and H2/syngas co-production. Specifically, the use of NiO/YSZ achieves fast kinetics, robust stability and sufficient OC utilization from 500 to 1000°C, enabling complete CO2 capture with minimum energy penalty. The ceria-, and perovskite-based OCs exhibit over an order-of-magnitude faster kinetics compared to the state-of-the-art, enabling improved H2 production/CO 2 reduction efficiency isothermally at 600-700°C. In-depth understanding gained on the redox fundamentals will shed light on the design and fabrication of new materials as well as optimization of the CL applications.
Author: Wenting Hu