Over the past few decades, combustion of fossil fuels has released greenhouse gases such as CO2 and NOx into the atmosphere. It has been realized that a mean temperature increase of the Earth, also known as global warming, has resulted from the increase of CO2 concentration in the air. Hence, there is a growing tendency to establish novel methods of burning fossil fuels in order to mitigate CO2 concentration. Chemical Looping Combustion (CLC) is a method of burning fuel with inherent separation of CO2 while curbing the formation of NOx, typically by circulating an oxygen carrier between an air (oxidation) reactor and a fuel (reduction) reactor. An oxygen carrier, mainly a metal oxide, circulates between the reactors providing the oxygen for conversion of fuel to CO2 and H2O. Thus, having a pure CO2 stream, CO2 sequestration becomes economically feasible. Fe2O3, due to its availability and properties, could be an apposite oxygen carrier for CLC. Reaction kinetics of reduction of Hematite with methane, in the absence of gaseous oxidant, was studied. Temperature Program Reduction (TPR) experiments were carried out in a fixed bed tubular reactor. Reduction gas was composed of 15% methane and 85% argon. Thermogravimetric Analysis (TGA) was carried out on TPR products using air as the oxidant. Iron oxide samples were analyzed through X-ray diffraction (XRD) analysis and scanning electron microscopy. Two-stage reduction of iron oxide was observed: Fe2O3 reduced to Fe3O4 and then reduced to FeO. The activation energy of each stage was calculated from Kissinger’s method. For the first and second stage of reduction the activation energies were 10.58±0.86 and 25.77±0.83 kJ/mol, respectively. In addition, different kinetic models were assumed and compared to the actual data. A random nucleation mechanism can be assigned to the first stage and a two-dimensional diffusion mechanism can be assigned to the second stage of the reduction.

Global warming and climate changing are serious problems challenging humanity, therefore important steps needed to be taking to neutralize such challenge. From the last century huge amount of carbon dioxide released to atmosphere cause huge damages to our globe. Technologies such as oxycombustion and chemical looping combustion had been discussed to capture and sequestration carbon dioxide at lower cost. Separation air from fuel using chemical looping or separation nitrogen from air using oxygen transport membrane (OTM) then combust pure oxygen with fuel are the main step to capture carbone dioxide in less expensive method. Each technology had its own drawback, therefore, to overcome these drawbacks an integrated system is proposed combined oxycombustion, chemical looping and OTM technologies into one system. This work aimed to model and simulate an integrated system in single reactor using liquid Antimony and Antimony trioxide as an oxygen carrier to pick up oxygen from the OTM and reduce fuel using natural circulation due to density difference between metal and metal oxide. Heat is being released inside the reactor due to exothermic oxidation reaction and temperature is increased. The temperature profile is studied in all reactor zones with respect to oxidation and reduction rate, operation temperature, metal viscosity and radiation effect. The result show that the system had a good potential to transfer heat generated from the oxidation and transfer to other zones, in which heat can be utilized and been used for heating water or generate steam.

Amin Bagheri, for the Master of Science degree in MECHANICAL ENGINEERING AND ENERGY PROCESSES, presented on June 23, 2014, at Southern Illinois University Carbondale TITLE: STUDYING THE MAGNETIC SEPARATION OF OXYGEN CARRIER IN COAL DIRECT CHEMICAL LOOPING MAJOR PROFESSOR: Dr. Tomasz S. Wiltowski Magnetic separation of oxygen carrier from coal after combustion by-products was studied. Samples were prepared using iron metal, hematite and magnetite mixed with quartz in three different concentrations. A variable speed and magnetic field intensity separator unit was designed and constructed to prove the concept of magnetic separation. The unit went through trial and error steps to improve overall functionality and efficiency including belt material selection, electromagnet selection, feeder and collector buckets, drive drum and idler manufacturing. Prepared samples were tested in different velocities and magnetic field intensities.

The focus of this work is to investigate the feasibility of oxygen extraction from CO2 by doped ceria in chemical looping process. In order to increase the oxygen capacity and oxygen release rates, Cerium- based oxygen carriers are doped with ZrO2. Additionally, the zirconia-doped ceria is modified by iron and copper to boost the oxygen release in the fuel reactor. It should be noted that the level of doping allows the solids to maintain the cubic fluorite structure of CeO2. The redox activity of oxygen carriers is studied in order to determine the most promising material due to the oxygen transfer capacity and methane conversion. The chemical looping dry reforming in a quartz fixed-bed reactor is carried out in two steps. In the first step, the oxygen carriers are reduced by methane through the combustion reaction. In the second step, CO2 is used for oxidation of reduced metal oxides. The obtained results at different doping levels were compared to determine the optimal oxygen carrier. The results indicate that doping ceria can boost the reactivity with methane and enhance the methane conversion during combustion reaction. CeO2 modified by Fe presents a progress in both oxygen release and uptake with an increase in oxygen capacity of metal oxide. However, zirconia and copper ceria show different effect on reduction and oxidation. This means that zirconia doped ceria results in an increase in oxygen release during reduction and decrease in oxygen uptake during oxidation with CO2. In contrast, addition of copper to ceria metal oxides shows a negative effect on oxygen release, while it enhances the ability of oxygen uptake. Out of all mixed cerium oxides investigated in this study, cerium oxide containing 10% mole iron is determined as the most promising oxygen carrier for CLDR due to the methane conversion, facilitating oxygen release, increasing the level of reduction and improving the oxidation uptake of the metal oxide in the reaction with CO2.

No description available.

No description available.

This work aimed to evaluate the subsystems of a novel mediated oxycombustion system and determine the expected final conditions of the integrated subsystems. The subsystems included a cerium based oxygen transport membrane, transport membrane coatings to assist in the pickup and release of oxygen, and a molten intermediary oxygen carrier. Various doping levels of yttrium and zirconium were investigated, both as singular dopants and in a co-doped scheme. Regression analysis was performed to quantitatively evaluate how each dopant affected the material properties. Zirconium was not found to have statistically significant effects, although an effect was clearly noted on pure ceria. Functions of the doping level of yttrium were found for relative density, hardness, and the contributing factors of electrical conductivity. Chemical looping combustion experiments were performed to determine viable candidates for oxygen pickup and release coatings. It was discovered that a release coating was not necessary due to the use of a reactive fluid, and iron showed promise as a pickup coating but short of showing statistical significance. The ability of antimony oxide to react with hydrocarbon fuels and be regenerated by oxygen was investigated to determine the reaction rates. It was discovered that a co-doping scheme of yttrium and zirconium at a level of 8.33% (1/12th) each achieved the highest oxygen flux with a value of 3.671x10-7 mol O/s/cm2. All of the subsystems were we analyzed and a complete, theoretical system was described. It is recommended that the shape of the oxygen transport membrane be of a single-closed-end cylinder. This allows the increase of oxygen permeation with a smaller device footprint. It was found that the system would be capable of combusting 6.699 grams of carbon based fuel per minute per square meter of footprint. This equates to a heat rate of 3.6 kilowatts per square meter when utilizing a medium volatile bituminous coal. This value will continue to be improved as further research is conducted into the components of the system.

In this work the performance of cerium-based oxygen carriers is investigated in a simulated chemical looping dry reforming system using methane and carbon dioxide as fuel and oxidizing gas respectively. The samples to be studied are pure cerium oxide and cerium oxide doped with zirconium, yttrium, samarium, and scandium more specifically: CeO2, Ce0.8Y0.2O1.9, Ce0.85Y0.05Zr0.1O1.975, Ce0.95Zr0.05O2, Ce0.9Sm0.05Zr0.05O1.975, and Ce0.9Sc0.05Zr0.05O1.975. Characteristics such as crystallography including lattice parameter and particle size of the samples are evaluated using X-ray diffraction (XRD) and particle size analysis. The oxygen transport capacity will also be measured using a thermogravimetric analyzer (TGA). This method of measurement also allowed for insight on oxygen release temperatures as well as recyclability of the samples. The particle size analysis showed that the synthesis method of precipitation-agglomeration resulted in samples with consistent particle size distribution indicating the method can be scaled up. The X-ray analysis of samples before and after the TGA tests show that all the materials tested had a cubic fluorite crystal structure which was maintained through the oxidation reduction cycles. The lattice parameter was found to increase slightly with a loss in oxygen content in the samples. The addition of trivalent dopants resulted in a decrease in the temperature of initiation of reduction in methane. While reduction of commercial ceria initiated near 800 oC. the addition of trivalent dopants resulted in a lowering of the initialization temperature between of 150 – 200oC. The activation energy of commercial ceria was 248.42 kJ/mol for reduction in methane, indicating that the rate controlling mechanism is chemical reaction rather than diffusion. The addition of trivalent dopants resulted in a significant lowering in the activation energy. The activation energies obtained in this study show that the addition of dopant increased the significance of diffusion through the solid and the controlling mechanisms were both diffusion and chemical reaction. Overall, the addition of trivalent dopants enhanced the extent of oxygen exchange in CLDR process.

No description available.

No description available.