Sulphur, nitrogen and mercury emissions from coal combustion with CO2 capture in chemical looping with oxygen uncoupling (CLOU)

• The fate of S, N and Hg during the CLOU process is analyzed.
• A lignite was burnt in a 1.5 kW unit during more than 35 h with a CuFe oxygen carrier.
• The reaction of sulphur with the oxygen carrier has been deeply analyzed.
• Most of the N present in coal was found as N2 at the outlet of the fuel reactor.
• Hg0 is the main specie in the CO2 stream but Hg emissions are under EU legislation.

Chemical looping with oxygen uncoupling (CLOU) is a chemical looping combustion (CLC) process for the combustion of solid fuels with the use of a solid oxygen carrier that releases gaseous oxygen inside the fuel reactor. The aim of this work was to study the fate of pollutant elements present in fuel, i.e. S, N and Hg, during CLOU combustion. Experiments using lignite as fuel were carried out in a 1.5 kWth unit operating continuously for more than 35 h of coal combustion. Novel particles containing 50 wt.% CuO, 10 wt.% Fe2O3 and 40 wt.% MgAl2O4 prepared by spray drying were used as the oxygen carriers in the CLOU process. Most of the sulphur introduced with the fuel exited as SO2 at the fuel reactor outlet, although a small amount of SO2 was measured at the air reactor outlet. Most of the nitrogen present in coal was found as N2 at the outlet of the fuel reactor, although 20 wt.% of N in the coal was converted to NO. Mercury speciation was also analyzed. The major mercury species in the fuel reactor was Hg0 (g), and the Hg0 (g)/Hgtotal (g) ratio in the air reactor was 0.5.