High temperature behavior of NiO-based oxygen carriers for Chemical Looping Combustion

AbstractHigh temperature behavior of spray-dried NiO-based oxygen carrier samples for Chemical Looping Combustion (CLC) under oxidizing and reducing conditions was studied using a ceramic fluidized bed furnace. Differently from the common CLC process, high enough temperatures were obtained by burning air and methane mixture directly in the bed of carriers, changing the stoichiometric air to fuel ratio in the range of 0.70 to 1.30 and using external electric heating.None of the five particle samples tested showed any sign of defluidization in oxidizing atmosphere at any of the temperatures tested, i.e. up to 1175–1185 ∘C. However, under reducing conditions or in the oxidizing-reducing sequences, shortly after changing the atmosphere from oxidative to reducing, some of the spray-dried samples agglomerated causing defluidization. To study the structure of the carrier particles and to clarify the agglomeration phenomena, SEM and EDX analysis of the initial and treated samples was carried out. It was shown that agglomerates are formed through small bridges between the particles which consist of pure Ni phase. Three samples which were produced using MgO as an additive were tested. For these no defluidization was observed at any of the temperatures tested, i.e. up to 1175–1185 ∘C, neither in oxidizing, nor in reducing atmosphere. So, addition of proper components to the carrier particles can significantly improve reliability of the CLC process at higher temperatures