Analysis of hematite re-oxidation in the chemical looping process. (1st November 2015)

• Record Type: Journal Article
• Authors: Breault, Ronald W.; Monazam, Esmail R.; Carpenter, Jared T.
• Is Part Of: Applied energy. Volume 157(2015:Nov. 01)
• Page Start: 174
• Page End: 182
• Publication Date: 2015-11-01
• Subjects: Chemical Looping Combustion -- Fixed bed reactor -- Hematite re-oxidation; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2015.08.015
• Languages: English
• ISSNs: 0306-2619

Abstract

Highlights: Re-oxidation of Fe2 O3 CLC carrier is examined to assess O2 and temperature. A two process step model has been developed – grain surface and grain core. Grain surface oxidizes which transports oxygen to the core by vacancy diffusion. The surface model is 1st order with a tendency toward nucleation with 1-D growth. The model for the core corresponds to nucleation with 2-dimentional growth. Abstract: Very little attention has been dedicated to the carrier re-oxidation in chemical looping systems. The work presented in this paper is for the re-oxidation of partially reduced hematite from a cyclic chemical looping fixed bed process. The underlying purpose of this work is to develop engineering rates and mechanisms for the re-oxidation of partially reduced hematite that can be included in CFD models for a chemical looping process. To this end, experiments were run using nominally 1000 g of hematite material in a fixed bed reactor cycling between reduction and re-oxidation. The cyclic processing began with the reduction step then proceeded to the oxidation step repeating this analysis for several cycles ranging from 5 to 10. The re-oxidation process was conducted at temperatures ranging from 745 °C to 825 °C and oxygen concentrations ranging between 9% and 11%. The reduction was carried out at the same temperature as the re-oxidation step at various CH4 concentrations from 5% to 9%. In this paper, cyclic induced variations in performance are presented as well as the kinetic parameters for the first cycle. The re-oxidation of the depleted hematite occurs through a 2 step parallel process in which oxygen reacts to fill the surface of each grain within the particles and then migrates through oxygen vacancy diffusion to the depleted cores of each grain.