(53d) Effect of Oxygen Carrier On Particulate Emissions From Chemical Looping Combustion

Carbon dioxide emitted from fossil energy conversion accounts for roughly 20% of the greenhouse effect. Chemical looping processes, which include chemical looping combustion (CLC) and chemical looping gasification (CLG), utilize a novel, indirect strategy for fossil fuel conversion and in-situ CO₂ capture. The CLC process uses an oxygen carrier particle to oxidize the carbonaceous fuel into concentrated CO₂. The reduced oxygen carrier from the fuel oxidation step is subsequently combusted with air to generate heat/electricity. Although CLC is a promising approach for CO₂ capture, it can cause undesired particulate emission from the circulation of oxygen carrier particles. Small particulates, especially those with less than 10 micron diameter, are particularly harmful to respiratory systems. Despite of the various ongoing pilot scale demonstrations, little research has been conducted on characterizing particulate emissions from CLC processes, to date.

This study represents an attempt to comprehensively evaluate particulate emissions from an experimental CLC apparatus. With methane as the fuel, two Cu based oxygen carrier particles were tested in a laboratory fluidized bed apparatus. One (CuO-Al₂O₃) is prepared by an impregnation method and the other (CuO-MgAl₂O₄) by a solid state method.  A lab scale fluidized bed coupled with an automated gas panel is constructed to conduct multi-cycle redox reactions. Emitted particulates are collected and fractionated into seven particle size ranges using two sets of MRI cascade impactors as well as the filters. The effects of operating conditions including oxygen carrier composition, redox cycles, degree of reduction, etc. on particulates properties are investigated. Our research indicates that the majority of the small particulates from both the reduction and oxidation steps have aerodynamic diameters ranging between 1 and 6 μm. Notable amount of sub-micro (< 1 μm) sized particulates are also identified. Based on our experimental results, particulate control devices besides high efficiency cyclones are likely to be necessary for CLC even for the combustion of methane.