Sulphation and carbonation properties of hydrated sorbents from a fluidized bed CO2 looping cycle reactor

Sulphation and carbonation have been performed on hydrated spent residues from a 75 kWth dual fluidized bed combustion (FBC) pilot plant operating as a CO2 looping cycle unit. The sulphation and carbonation tests were done in an atmospheric pressure thermogravimetric analyzer (TGA), with the sulphation performed using synthetic flue gas (0.45% SO2, 3% O2, 15% CO2 and N2 balance). Additional tests were carried out in a tube furnace (TF) with a higher SO2 concentration (1%) and conversions were determined by quantitative X-ray diffraction (QXRD) analyses. The morphology of the sulphated samples from the TF was examined by scanning electron microscopy (SEM). Sulphation tests were performed at 850 °C for 150 min and carbonation tests at 750 °C, 10 cycles for 15 min (7.5 min calcination + 7.5 min carbonation). Sulphation conversions obtained for the hydrated samples depended on sample type: in the TGA, they were ∼75–85% (higher values were obtained for samples from the carbonator); and in the TF, values around 90% and 70% for sample from carbonator and calciner, respectively, were achieved, in comparison to the 40% conversion seen with the original sample. The SEM analyses showed significant residual porosity that can increase total conversion with longer sulphation time. The carbonation tests showed a smaller influence of the sample type and typical conversions after 10 cycles were 50% – about 10% higher than that for the original sample. The influence of hydration duration, in the range of 15–60 min, is not apparent, indicating that samples are ready for use for either SO2 retention, or further CO2 capture after at most 15 min using saturated steam. The present results show that, upon hydration, spent residues from FBC CO2 capture cycles are good sorbents for both SO2 retention and additional CO2 capture.