Chemical-looping combustion using combined iron/manganese/silicon oxygen carriers
Journal article, 2015
Combined oxides of iron, manganese and silicon have been used as oxygen carriers for chemical-looping
combustion. Three materials with varying composition of iron, manganese and silicon have been evaluated
in oxygen release experiments and during continuous operation with syngas and natural gas as fuels. The concentration of oxygen released increased as a function of temperature and the highest concentrations of oxygen were measured with the material with the highest fraction of manganese. It was also this material which gave the best conversion of both syngas and natural gas; essentially full conversion of syngas and above 95% conversion of natural gas above 900° C. The other two materials showed
similar performance, albeit with higher syngas conversion for the material with the lowest manganese
fraction and the lowest conversion of natural gas for the same material. The materials lasted for 10–14 h of operation with fuel addition before circulation disruption occurred, which was likely caused by
particle attrition in all three cases. A phase diagram of the iron–manganese–silicon–oxide system was
constructed and the possible relevant phase transitions were identified. This analysis showed that more
phase transitions could be expected for the materials with higher manganese content which could
explain the superior performance during fuel operation of the material with the highest manganese content.
It should however be noted that this material was operated with the highest fuel reactor inventory
per thermal power which could also be a contributing factor to the better performance of this material.
The study shows that it is possible to achieve very high fuel conversion with combined oxides of iron,
manganese and silicon as oxygen carrier. The mechanical stability of the particles was rather poor though
and would need to be improved. On the other hand the findings relating to material stability is not necessary
valid for natural materials containing a number of additional elements. The results are also of interest
as an indication of how natural materials with similar composition, i.e. manganese ores, would
perform as oxygen carriers.
Carbon dioxide capture
Chemical-looping with oxygen uncoupling