Effect of Production Parameters on the Spray-Dried Calcium Manganite Oxygen Carriers for Chemical-Looping Combustion

The oxygen carrier CaMn0.9Mg0.1O3-delta was successfully tested in different chemical-looping units. High methane conversion and oxygen uncoupling properties have been found for this type of material. Most of the CaMn(0.9)Mg(0.1)O(3-delta)oxygen carrier particles tested so far have been produced' using the spray-drying method. In this work, the focus has been on studying the effects of production parameters on the properties of this important oxygen carrier. The effects of three production parameters, i.e., milling time, calcination temperature, and calcination time, were examined for the spray-dried particles. The time of ball milling for the slurry prepared for spray-drying was varied from 5 to 45 min, the calcination temperature from 1300 to 1350 degrees C, and the calcination time from 4 to 16 h. None of these parameters had any influence on the final crystalline phases of the oxygen carrier, yet some of the properties were clearly changed. The bulk density, crushing strength, and resistance against physical attrition can be enhanced by increasing the calcination temperature, calcination time, or milling time. Further, the BET specific surface area and porosity of the oxygen carrier particles decreased when the slurry was milled or particles were calcined for extended periods. The average methane conversion of the oxygen carrier varied in a wide range, from 99% to 55% at 950 degrees C, depending upon the production parameters used. However, no obvious influence of the examined production parameters was observed for the oxygen uncoupling property of the oxygen carrier, which may be due to the thermodynamic limitation during testing.