Effects of Process Parameters on Sulfur Migration and H2S Generation during Supercritical Water Gasification of Sludge

The generation of sulfur-containing pollution products affects the quality of biofuels obtained from the supercritical water gasification (SCWG) of sludge. This study investigates the effects of the gasification temperature, moisture content, and reaction atmosphere on the evolution of sulfur-containing compounds. The results showed that temperature was the key parameter causing the migration of sulfur from sludge to biogas and liquid products. The sludge decomposition reaction was dominated by ionic reactions at 360 degrees C, while the decomposition of organic matter was converted to free radical reactions as the temperature increased from 380 degrees C to 440 degrees C. The mercaptan and thioether contents of the bio-oil decreased to 0.3% at 440 degrees C. Correspondingly, the concentration of H2S increased from 6.7 ppm to 38.0 ppm. The decomposition of organic sulfur with an unstable structure (S-H bond and S-C bond) was the main cause of the increase in the content of H2S. Additionally, the solubility and oxidation properties of supercritical water were extremely strong. Some sulfur-containing organic compounds were converted into SO(4)(2)via hydrolysis and oxidation reactions, forming sulfate crystals with heavy metals in the bio-char, which aided in achieving the synergistic immobilization of sulfur and heavy metals.

Automated summary

This study found that temperature is a key factor affecting the evolution of sulfur-containing compounds during sludge gasification in supercritical water, with the decomposition of organic sulfur playing a dominant role in the conversion process. The unstable structure of organic sulfur was identified as the main cause of an increase in hydrogen sulfide content. Additionally, the strong solubility and oxidation properties of supercritical water facilitated the conversion of sulfur-containing organic compounds into sulfate crystals, aiding in the simultaneous immobilization of sulfur and heavy metals.