Characterization of an Australia hematite oxygen carrier in chemical looping combustion with coal

Abstract

Chemical looping combustion (CLC) is a promising technology to capture CO2 at low cost with solid fuels. This paper presents a continuous operation chemical looping process with a natural Australia hematite. To fulfill this, the prototype of a 1kWth interconnected beds was employed equipping with a stable coal feeding device. In this prototype, a spouted fluidized bed was used as a fuel reactor and a fast fluidized bed as an air reactor. The oxygen from air was transferred to the fuel by the solid hematite that circulated between the interconnected fluidized bed reactors. Experimental results indicated that the Australia hematite showed a stable reactivity and resistant to agglomeration and to attrition ability. At a fuel reactor temperature 950°C, a little CH4 was measured and there were neither hydrocarbons heavier than CH4 nor tars in the exit of the fuel reactor. The carbon conversion efficiency was about 81.2%, and the loss rate of this hematite oxygen carrier due to attrition is about 0.0625%/h. XRD results showed that the active phase Fe2O3 of the hematite oxygen carrier was mostly reduced to Fe3O4 phase by coal gasification products in the fuel reactor, and only small part of oxygen carrier is further reduced to FeO. No tendency of decreased reactivity of the hematite oxygen carrier was observed during 10h of operation. This hematite has a good behavior as an oxygen carrier, suitable for use in CLC with coal. Further, with regards to improve the carbon conversion efficiency, a few of Ni-based particles were mechanically mixed with the hematite particles to improve the coal gasification rate. The effect of Ni-based particles addition on the gas conversion and char conversion were evaluated. Also, the possible catalytic mechanism was discussed.