Sulfur transformation and thermogravimetric analysis of model compounds in oxygen carrier aided pyrolysis/gasification process

Sulfur impurity in solid fuel should be paid attention to in the thermal process from the perspective of environment and sulfur recovery, especially the auto-thermal oxygen carrier aided pyrolysis/gasification (OCAP). To uncouple the complex sulfur transformation during OCAP of solid fuel and elucidate the main mechanism, several typical model compounds of various functional groups were used to investigate the kinetic analysis and sulfur transformation through temperature-programmed method. The OCAP process consisted of devolatilization and partial gasification. The activation energy of sulfur models devolatilization was less than that of partial gasification, because the required energy was much more to release lattice oxygen from oxygen carrier. Furthermore, the actual oxygen transport capacity of oxygen carrier (OC) redistributed the sulfurous gases. It was found that H2S was released earlier than SO2. H2S release was ascribed to the devolatilization including the reactions between radicals and hydrogen abstracted from base at low temperature (200-300 degrees C). The different contact modes between sulfur compounds and OC proved that S could be absorbed in the form of iron sulfide and incorporated into char at low temperature but released in the form of SO2 by OC oxidation at the elevated temperature (400-600 degrees C), which was in accordance with the kinetic analysis. The migration of sulfur from disulfide had priority over that from monosulfide, and the sulfur connecting with dialkyl (benzyl) was easier to escape than that with diaryl (phenyl) in OCAP process. The fate of sulfur model compounds was conducive to reveal the complex behaviors of solid fuel with different sulfur species, and this work provides evidence to implement the desulfurization and sulfur recovery strategy.