Analysis of hematite re-oxidation in the chemical looping process

Abstract

h i g h l i g h t sRe-oxidation of Fe 2 O 3 CLC carrier is examined to assess O 2 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. a b s t r a c tVery 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 CH 4 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.Published by Elsevier Ltd.

Chemical Looping Combustion of Hematite Ore with Methane and Steam in a Fluidized Bed Reactor

“…This indicated that the remaining percentage of methane (up to around 40%) being fed to the fluidized bed was depositing on the oxygen carrier. This transient effect of the deposition of carbon is a result of the gradual formation of wüstite and elemental iron as the reaction progresses, where the deeply reduced iron helps to catalyze the formation of carbon depositions on the particle, and oxygen transported out of the grain lattice has a much slower reaction [28,29].…”

“…Iron oxide has been extensively studied with methane, isothermally in thermogravimetric analyzers [16][17][18][19][20][21][22][23][24], in fixed bed reactors [25][26][27][28][29], and in fluidized bed reactors [30][31][32][33][34]. Cabello et al [19] studied the kinetics of methane reduction for an iron-oxide/alumina oxygen carrier in a thermogravimetric analyzer.…”

Simulation of two-step redox recycling of non-stoichiometric ceria with thermochemical dissociation of CO2/H2O in moving bed reactors – Part II: Techno-economic analysis and integration with 100 MW oxyfuel power plant with carbon capture

“…The CL model is then connected to oxy-fuel power plant with 100% carbon capture. Presently oxy-fuel combustion technology has received huge interest among fossil based carbon capture power plant [14,15]. In oxy-fuel power plant, oxygen is supplied in combustion chamber instead of air which increases the efficiency and making carbon capture as the exhaust does not have NOx emissions.…”

Techno-economic and exergetic assessment of an oxy-fuel power plant fueled by syngas produced by chemical looping CO2 and H2O dissociation

“…. The oxy-fuel combustion is currently one of the most promising alternatives among the portfolio of all the low-emission technologies (LETs) [15,16]. In this technology, the fuel (coal or natural gas or bio-methane) is burnt in an oxygen (O2) rich environment (near stoichiometric O2 flows), instead of air, thereby improving combustion efficiency [17] and eliminating NOx emissions and generating only CO2 and H2O as the product of combustion unit.…”