Sulfur migration and conversion during co-combustion of sewage sludge and coal slime

Abstract

Co-combustion is an effective way to achieve high-value utilization of sewage sludge (SS) and coal slime (CS). In this study, thermogravimetric-mass spectrometry and X-ray photoelectron spectroscopy were combined to investigate the morphology and changing law of sulfur in the gas-solid phase. H₂S, COS, and SO₂ were detected in SS and CS mono-combustion, and the SO₂ release from CS was 8.8 times that of SS. During SS combustion, the oxidation of aliphatic-sulfur and thiophene led to a staged increase in sulfone content. Sulfate was generated after 500 °C and decomposed after 700 °C to form SO₂. During CS combustion, aliphatic-sulfur was converted to H₂S, thiophene was sequentially oxidized to sulfoxide and sulfone, and a part of sulfone and sulfate decomposed to SO₂ at high temperature. During co-combustion, the release of H₂S was inhibited after the CS ratio reached 50 %, and the release of COS was promoted at different ratios. Co-combustion significantly promoted the sulfur fixation of the inorganic components, which led to the inhibition of SO₂ release, and the deviation between the experimental and theoretical values was as high as 91.3 % at a CS ratio of 50 %, as well as the content of sulfate in the solid phase was significantly increased.