Development of (Mn0.77Fe0.23)2O3 particles as an oxygen carrier for coal combustion with CO2 capture via in-situ gasification chemical looping combustion (iG-CLC) aided by oxygen uncoupling (CLOU)

Abstract

Chemical looping combustion (CLC) involves the use of a solid oxygen carrier to transport the oxygen from the air to a fuel. Attention has recently been focused on oxygen carriers based on Mn-Fe mixed oxides because they are cheap materials that are able to release oxygen at high temperature, the so-called oxygen uncoupling step. The aim of this work was to assess the use of (Mn0.77Fe0.23)2O3 material as an oxygen carrier with the ability to transport oxygen both by reduction with gaseous fuels and by oxygen uncoupling, i.e. typical mechanisms in CLC and in Chemical Looping with Oxygen Uncoupling (CLOU), respectively. The particles prepared by mechanical mixing were screened to obtain particles of sufficient reactivity and mechanical strength for use in a fluidized bed reactor. The preparation methodology and calcining temperature were varied. The reactivity of one selected material was evaluated by performing redox cycles both in a TGA and a batch fluidized-bed reactor. Thus, its behaviour was assessed during both decomposition-regeneration of bixbyite phase [(Mn0.77Fe0.23)2O3] in CLOU and the reduction-oxidation of spinel phase [(Mn0.77Fe0.23)3O4] with gaseous fuels, i.e. H2, CO and CH4. Its oxygen uncoupling and re-oxidation capability was highly influenced by the reaction temperature and oxygen concentration. On the other hand, CLC redox cycles with gaseous fuels showed high reactivity with H2 and CO and high oxygen transport capacity by reduction to mangano-wüstite phase [(Mn0.77Fe0.23)O]. Good fluid-dynamic behaviour was observed for the oxygen carrier particles along the redox cycles without agglomeration problems, regardless of the operating conditions used in the batch fluidized-bed reactor. Thus, the selected material was considered a promising candidate for use in both in CLC with syngas and CLC with coal.