Optimization of spray dried attrition-resistant iron based oxygen carriers for chemical looping reforming

Abstract In chemical looping reforming oxygen carriers suffer from attrition, which must be reduced to increase their lifetime. Therefore, the production of Fe-based carriers by spray drying was optimized in order to obtain mechanically strong particles with a homogeneous microstructure and dimensions fit for industrial fluidized CL-processes. The influence of the concentration of the binder and dispersing agent, the amount of solids and the milling procedure used in spray-drying suspensions on the morphology and microstructure of the resulting particles is studied by Hg-porosimetry, tapped density and optical and electronic microscopy. Increasing the amount of solids and reducing the amount of organic binder decreased the size of the internal cavity in the spray dried particles which led to a higher tapped density and better mechanical properties. The heat treatment during post-processing of these oxygen carriers also has a major influence on the remaining porosity of the oxygen carriers and is used to further optimize their mechanical properties as measured by the crushing strength and the attrition resistance. In this way spray-dried Fe-based oxygen carriers on an alumina carrier material with a crushing strength of 3.2 N and an air jet index of 2.1% are obtained at a sintering temperature of 1225 °C. The sample with the best mechanical properties was tested in a small lab-scale fluidized bed reactor during four cycles and compared with a more porous sample. The improvement of the morphology and the reduction of the porosity of the particles did not show a significant influence on the chemical performance of the oxygen carrier. The crushing strength of the oxygen carrier decreased to 2 N during activation and during reaction a slight hercynite accumulation was observed.