Evaluation of oxygen carriers for chemical looping combustion of coal and solid fuels

Aurora Rubel, Kunlei Liu, Jim Neathery, Darrell Taulbee

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

4 Scopus citations


Chemical looping combustion (CLC) involves the combustion of a fuel using an oxygen carrier (OC) usually a metal oxide as the source of oxygen for combustion. This results in CO2 and H2O as the major gaseous components products. The H2O can be condensed leaving a concentrated stream of CO2 for sequestration. The OC is then re-oxidized with air in a separate vessel and then recycled to burn more fuel. CLC has been investigated for use for the combustion of methane and natural gas for several years as a means for reducing CO2 emissions in the field of natural gas combined cycle processes. There are several obstacles to the use of CLC for coal and other solid fuels, not the least of which is the identification and development of a suitable OC. This work addresses some of the requirements of the OC. The carrier must have good reactivity which is maintained in the presence of ash and gases such as H2, CO, and CO2 likely to be present in any CLC process for solid fuels. Also the OC must have the durability required for recycle and must be easily separated from spent materials. A thermal analyzer-differential scanning calorimeter-mass spectrometer (TG-DSC-MS) was used to study some novel OCs with potential for use with solid fuels. These OCs included Ni/NiO supported on Ca aluminate, fused iron, and iron oxide catalysts. Comparisons were made with pure metal oxides of Cu, Fe, Ni, and Co. The effect of ash and changing reduction gas compositions were studied. Each OC was subjected to multiple oxidation - reduction cycles. Reaction rates, changes in reaction rates with repeated oxidation - reductions and exothermic heats during oxidation were determined. All OCs were first compared in the following mixed gases for reduction: 20% CO2, 5% H2, 5% CO, balance of argon before the effect of different gas combinations was studied. All oxidations were done using 20% O2 in argon. Oxidation rates were greater than reduction rates in all cases studied. The reaction rates were reproducible through multiple oxidation - reduction cycles except where agglomeration occurred with powders. Iron oxide (Fe 2O3 powder) and iron-based catalysts exhibited relatively rapid and similar maximum reduction rates. The same was true for the nickel catalysts studied. Addition of 50% bituminous coal ash by weight to two Fe catalysts resulted in very different effects but indicated that an OC could be tailored for use in the CLC of solids. A higher reducing gas concentration led to a more rapid rate of reduction. However, the total weight loss remained the same regardless of the H2, CO concentration used. That is, varying the concentration of H2, CO impacted the rate but not the extent or the mechanism of the reaction. This is confirmed by the fact that subsequent oxidation resulted in a similar weight gain and energy release regardless of the concentration of H2, CO used during reduction.

Original languageEnglish
Title of host publication24th Annual International Pittsburgh Coal Conference 2007, PCC 2007
Number of pages15
StatePublished - 2007
Event24th Annual International Pittsburgh Coal Conference 2007, PCC 2007 - Johannesburg, South Africa
Duration: Sep 10 2007Sep 14 2007

Publication series

Name24th Annual International Pittsburgh Coal Conference 2007, PCC 2007


Conference24th Annual International Pittsburgh Coal Conference 2007, PCC 2007
Country/TerritorySouth Africa

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geotechnical Engineering and Engineering Geology


Dive into the research topics of 'Evaluation of oxygen carriers for chemical looping combustion of coal and solid fuels'. Together they form a unique fingerprint.

Cite this