Preliminary Investigation on the Performance of Red Mud-Based Perovskite Oxygen Carrier on Municipal Sludge Gasification

Abstract

Solid organic waste via chemical looping gasification (CLG) is a promising technology utilizes lattice oxygen for partial oxidation to produce high-quality syngas, wherein, it is so important to apply the low-cost, high-performance oxygen carriers (OCs). The authors mixed the red mud waste from Bayer aluminum production with different proportions of calcium and manganese oxides to prepare CaMn0.5Fe0.5O3-δ perovskite OCs. The compared redox tests were carried out for the the reaction characteristics in a thermogravimetric analyzer (TGA). Multiple cycle CLG experiments of wet sludge were conducted in a lab-scale fluidized bed to produce the hydrogen-rich gas. The results showed that the OC prepared from sodium-removal red mud had higher oxygen transfer capacity and better cycling stability than that of cement binder addition. After the 5th cycle in CLG, the syngas by CaMn0.5Fe0.5O3-δ-washed still kept a hydrogen volume fraction of over 40%, but more CO2 was produced due to the promoting effect of MnO in the OC on the steam reforming reaction of CO. The XRD curves showed that fresh CaMn0.5Fe0.5O3-δ-washed exhibited strong diffraction peaks of perovskite, and after multiple cycles, the presence of iron calcium silicate structures containing Mn was clear due to the attachment of sludge ash, the impurities on the surface of OCs increased and the specific surface area decreased after multiple cycles. Additionally, some of the reacted OC particles exhibited a hollow structure, which would make it easier fluidized. The preliminary study provides the basis for the improvement of the OC performance on the sludge gasification.

Keywords: Red mud, Perovskite oxygen carrier, Municipal sludge, Chemical looping gasification, Hydrogen-rich gas