ie6b01835_si_001.pdf (61.13 kB)
Evaluating the Effect of Inert Supports and Alkali Sodium on the Performance of Red Mud Oxygen Carrier in Chemical Looping Combustion
journal contribution
posted on 2016-07-07, 00:00 authored by Jinhua Bao, Liangyong Chen, Fang Liu, Zhen Fan, Heather
S. Nikolic, Kunlei LiuChemical
looping combustion (CLC) is an advanced technology with
inherent CO2 capture in which a solid oxygen carrier circulates
between an air reactor and a fuel reactor. For coal-fueled CLC, the
existence of solid impurities requires the oxygen carrier not only
to have good reactivity but also to be contaminant-resistant, low-cost,
and readily available. Therefore, the development of cost-effective
and well-performing oxygen carriers is very meaningful for the coal-fueled
CLC process. Natural red mud, a byproduct from the aluminum industry,
was found to function well as an oxygen carrier and has also been
found to have in situ coal catalytic gasification behavior. A thorough
study on the long-term cyclic performance of red mud with coal char
in a fluidized reactor was conducted in this work. For the purpose
of comprehensively understanding the functions of inert supports as
well as the sodium content in red mud, the effect of various inert
oxides (Al2O3, SiO2, TiO2, and CaO) and the addition of sodium was evaluated. It has been
proven that inert supports, Al2O3, SiO2, and TiO2, have a positive effect on both the reduction
and oxidation reactivity of iron-based oxygen carriers by developing
a porous structure in the particle. Al2O3 and
SiO2 show the ability to stabilize the reactivity of iron
oxide with a gaseous reductant (CO), even under fluidized conditions.
Both Al2O3 and TiO2 can assist in
maintaining the mechanical strength of the oxygen carrier after many
cycles in a fluidized-bed reactor. The addition of sodium (Na) to
red mud does not exhibit much effect on the reactivity of OC with
CO as the fuel. However, it can significantly enhance the char gasification
rate due to its catalytic function. Additionally, interaction between
the active iron oxide and inert supports or sodium in the form of
red mud at high temperatures leads to the formation of spinel phases.
The growth of spinel phases results in the reduction of the oxygen
carrying capacity. However, it helps fix sodium as a relatively stable
chemical compound (NaAlSiO4 or NaFe0.25Al0.75O2). Both inert supports and sodium in natural
red mud play critical roles in the performance of red mud as an oxygen
carrier from either physical or chemical aspects.