Investigation of Fluidized Bed Agglomeration of Cu-Based Oxygen Carriers

Combustion of fossil fuels creates environmental concerns due to the emission of flue gases causing air pollution and contributing to global warming. Chemical Looping Combustion (CLC) is a proposed alternative technology for production of energy that has advantages over conventional combustion of fossil fuels, particularly with regard to emission of CO₂. The CLC process employs two interconnected fluidized bed reactors. Air fed to the first reactor (air reactor) oxidizes metal-based “oxygen carrier” particles, which then circulate (“loop”) to a second reactor (fuel reactor) where oxygen (O₂) is released from the oxygen carrier and combusts the fuel injected in the fuel reactor. The process enables isolation of CO₂ since the fuels are combusted in an O₂-containing environment in the absence of nitrogen. Chemical looping combustion with oxygen uncoupling (CLOU) is a derivative of CLC for combustion of solid fuels through specific metal based oxygen carriers with high capacities to release O₂.

Different metal based carriers have been developed for CLOU, and copper based oxygen carriers have shown promising results for oxygen liberation and particle strength in the fluidized bed reactors compared to other metal based particles. In the air reactor, cuprous oxide (Cu₂O) reacts with O₂ in air to form copper oxide (Cu₂O + ½ O₂ ↔ 2 CuO). The reverse reaction happens in the fuel reactor where O₂ is released and cuprous oxide is regenerated and recycled again to the air reactor. The vigorous fluidized bed environment and high temperatures required for efficient fuel combustion poses risks of agglomeration of the particles, where particles adhere to each other to form large lumps causing collapse of the fluidized bed and subsequently costly shutdown of the system.

Agglomeration testing in a fluidizedbed system has been conducted to find suitable operating windows in terms of temperature and superficial velocity for efficient conversion in the air and fuel reactors. Oxygen capacity and absorption and release rates of a set of copper based particles have been evaluated while monitoring fluidization behavior of the particles for potential detection of agglomeration. A differential pressure measurement across the reactor has been found to be valuable for detecting agglomeration when particles start to defluidize in the bed. Higher superficial velocities, lower bed loadings and lower copper loading on the particles were found to reduce risks of agglomeration. This presentation emphasizes different techniques employed for agglomeration testing and detection. Additionally, optimum operating conditions for the carrier particles in fluidized beds will be presented in terms of temperature and superficial velocity.