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Your search keyword '"Cai, Runxia"' showing total 34 results
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34 results on '"Cai, Runxia"'

32. Structural and Thermodynamic Assessment of Ba and Ba/Mg Substituted SrFeO3−δfor “Low-Temperature” Chemical Looping Air Separation

Author

Bektas, Hilal, Cai, Runxia, Brody, Leo, and Li, Fanxing

Abstract

The increasing demand for high-purity oxygen has prompted interest in chemical looping air separation (CLAS), a promising approach to reduce cost and energy consumption. The current study presents a structural and thermodynamic analysis of Sr0.75Ba0.25FeO3−δ(SBF628), Sr0.75Ba0.25Fe0.875Mg0.125O3−δ(SBFM6271), and Sr0.25Ba0.75FeO3−δ(SBF268) for CLAS applications. Our results confirm that through partial substitution of A- and B-site cations, we can tailor the thermochemical properties of SrFeO3−δunder practical operating conditions, e.g. 400–700 °C and 0.2–0.01 atm O2. Based on X-ray diffraction (XRD) and Rietveld refinement, 25% Ba can be fully substituted into a SrxBa1–xFeO3−δstructure (SBF628), whereas SBF268 and SBFM6271 form minor secondary phases. An increased Ba:Sr ratio in the A-site favors facile oxygen exchange by reducing partial molar enthalpy and improving redox capacity at low temperatures (400–500 °C) while leading to an increase in Fe–O bond length in the B-site. Our findings support that the Fe–O bond distance can be a useful descriptor in the optimization of redox performance in SrFeO3−δ(SF) based oxygen carrier candidates for CLAS. All the substituted candidates exhibit superior redox performance to unsubstituted SF at temperatures below 600 °C. SBF628 achieves the redox (oxygen storage) capacity of 1.24 wt % under a combined temperature (400–600 °C) and pressure swing (0.2–0.01 atm O2) mode. The introduction of 12.5% Mg in the B-site improves the oxidation kinetics, but it does not have a substantial impact on the oxygen storage capacity. SBFM6271 and SBF628 exhibited excellent recyclability and robustness while a minimal decrease (3%, on a relative basis) in the capacity of SBF268 was observed during 100 redox cycles under pressure swing between 0.2 and 0.01 atm O2at 600 °C.

Published
2024
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34. Effects of the Limestone Particle Size on the Sulfation Reactivity at Low SO 2 Concentrations Using a LC-TGA.

Author

Cai R, Huang Y, Li Y, Wu Y, Zhang H, Zhang M, Yang H, and Lyu J

Abstract

Limestone particle size has a crucial influence on SO 2 capture efficiency, however there are few studies on the sulfation reactivity, which covers a broad range of particle sizes at low SO 2 concentrations. In this paper, a large-capacity thermogravimetric analyzer (LC-TGA) was developed to obtain the sulfur removal reaction rate under a wide range of particle sizes (3 μm-600 μm) and SO 2 concentrations (250 ppm-2000 ppm), and then compared with the results of a traditional fixed bed reactor and a commercial TGA. The experimental results showed that the LC-TGA can well eliminate the external mass transfer and obtain a better measurement performance. Both the final conversion and the reaction rate reduced with the decreasing of SO 2 concentration, but ultrafine limestone particles still showed the good sulfation reactivity even at 250 ppm SO 2 . An empirical sulfation model was established based on the experimental results, which can well predict the sulfation process of different limestone particle sizes at low SO 2 concentrations. The model parameters have a strong negative correlation against the particle size, and the fit of the reaction order of SO 2 was found to be about 0.6. The model form is very simple to incorporate it into available fluidized bed combustion models to predict SO 2 emission.

Published
2019
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