Oxyfuel derived CO₂ compression experiments with NOₓ, SOₓ and mercury removal-experiments involving compression of slip-streams from the Callide Oxyfuel Project (COP)

Oxyfuel combustion is a CO capture technology which is approaching commercial demonstration. Of practical interest is the use of the compression circuit to allow low-cost cleaning options for various flue gas impurities. This work has focussed on three species - NOₓ SOₓ and Hg - and their removal during compression of "real" oxyfuel flue gas sampled as a slip stream from the demonstration Callide Oxyfuel Project. The flue gas slip stream was compressed using a bench-scale piston compressor developed to allow measurements of impurity concentrations after each compression stage using adjustable pressures. Several operating configurations were investigated including variable pressures from 5 to 30bar, interstage temperature changes and flow rate. Slip streams taken before and after SOₓ removal allowed the impact of mixed NOₓ/SOₓ gases to also be investigated. The results from the "real" oxyfuel flue gas experiments for the three species were similar to those performed in the laboratory using synthetic flue gas and reported previously. The capture of SO₂ was found at be greater at low pressures than NOₓ capture, with 90% removal of SO₂ by a pressure of 10bar, with NOₓ capture extending to higher pressures. The effect of residence time during compression had the greatest influence at higher pressures (>10bar) where the kinetic rate of NO oxidation to NO₂ increases less with pressure increase. Capture of NOₓ was increased from 55% to 75% by doubling the residence time in the compressor and could be further extended to 83% by increasing back end pressure from 24bar to 30bar. Lowering the temperature during compression produced the greatest NOₓ and Hg capture. Overall, the results indicate that capture of mercury during compression occurred as a consequence of high pressure, longer residence time and concentration of NO₂.