Studies on the redox reaction kinetics of selected, naturally occurring oxygen carrier

Abstract

This paper presents the results of a chemicallooping combustion (CLC) study. The CLC technology is believed to be one of the most promising combustion technologies. The production of a concentrated CO 2 stream that is obtained after the water condensation without any loss of energy in its separation is one of the most crucial advantages of this technology. The objective of this work was to study the kinetics of both the reduction and oxidation reactions for naturally occurring oxygen carriers that show promising reactivity in CLC reactions, and might therefore be utilized as oxygen carrier materials. Kryvbas, a Fe-based ore, was selected for this analysis because it possessed sufficient concentrations of the active metal oxides (Fe oxide above 80 % and traces of Mn oxide) and a high melting temperature that was above 1500°C. Experiments were conducted under isothermal conditions within the temperature range of 750-950°C with multiple redox cycles using a thermogravimetric analyzer (TG). For the reduction and oxidation reactions, CH 4 (at different concentrations) and air were used, respectively. The sample showed promising results where a sufficient reactivity was observed with the fuel, and these results were reproducible. Both fresh material and samples that were used in multiple redox cycles were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy combined with X-ray Microanalysis (SEM-EDS) in order to detect any structural or morphological changes as well as to determine the stability of the ore in repetitive CLC cycles. Kinetic parameters, such as the activation energy, the preexponential factor, and the reaction model, were determined for the redox reactions. Models of the redox reactions were selected by using a model fitting method. The F1 model (volumetric) was a suitable model for the modeling of the Kryvbas ore reduction reaction kinetics. The calculated E a was equal to 42.00 kJ mol -1 , while the reaction order was determined to be equal to 1.98. The best fit for the oxidation reaction was obtained for the R3 model (shrinking core model). The oxidation (regeneration) reaction activation energy was equal to 16.70 kJ mol -1 , and the reaction order was determined to be equal to approximately 0.49.

Industrial wastewater treatment wastes used as oxygen carriers in energy generation processes

“…It is also known that Fe-based OCs are relatively resistant to poisoning. Their interaction with impurities is minimal within the temperature range of the CLC process and was shown in some papers [4,21].…”

“…However, this behaviour is observed more clearly for the natural sample. The explanation for this behaviour may be the presence of impurities which help to stabilize the structure of the natural material (Table 1) [8,21]. Based on the data shown, it can be concluded that the optimal temperature range for the CLC fuel combustion process for oxygen carriers made from coke oven wastewater is 800-900°C.…”

Fabrication process parameters significantly affect the perovskite oxygen carriers materials (OCM) performance in chemical looping with oxygen uncoupling (CLOU)

“…The OCM is generally a binary, ternary or quaternary transition metal oxide, which utilizes the transition metal redox activity to uptake and release oxygen [1][2][3]. In the context of fast circulating fluidized bed CLC configuration, the OCM is subject to substantial chemo-mechanical stresses during the redox cycling, through which it must retain a high oxygen capacity, fast redox kinetics and good mechanical properties [4][5][6]. Furthermore, for industrial application the cost of materials must be low, the component elements abundant, and the active materials and their by-products must be environmentally benign and nontoxic.…”

Limitation of thermogravimetry for oxy-combustion analysis of coal chars

“…On the other hand, thermogravimetric analysis is a commonly used technique to investigate the kinetics of fast heterogeneous reactions such as the combustion of solid fuels, the oxidation of oxygen carriers [5,6,[11][12][13][14][15][16][17][18][19]. It is well known that kinetic parameters should be obtained under a chemical reaction-controlling regime [5,6,13,14,[17][18][19], which is important for the study of oxy-combustion kinetics.…”