Study on the transformation of Zn, Mn and Cr during sewage sludge combustion

Sewage sludge combustion experiments were carried out to investigate the migration and transformation of Zn, Mn, and Cr involved with the effects of combustion temperature, atmosphere, and steam concentration. The results showed that the volatilization of Zn was promoted by a temperature increase. Compared to air combustion, the inhibited volatilization of ZnCl2(g) and the production of ZnO promoted the recovery of Zn in ash during oxy-fuel combustion. Furthermore, the increasing temperature typically improved aluminosilicate capture MnO as well as the capability of CaO/Fe2O3 on capturing Cr. The reducing atmosphere caused by high CO2 concentration in oxy-fuel combustion facilitated the enrichment of Mn and Cr in ash. Steam favored the retention of Zn via transformation to form stable ZnO center dot A12O3 center dot 2SiO2 condensed into solid ash. The generation of CO and H2 from char-steam/char-CO2 gasification induced a local reducing atmosphere. It accelerated the transformation of MnO2 to MnO and facilitated the combination between MnO and aluminosilicate. Fe(III) reduced to Fe(II) strengthened the ability of iron oxide to capture Cr. The presence of steam promoted the decomposition of Ca-based minerals in the sewage sludge into a porous CaO, which enhanced the effect on Cr retention. (c) 2022 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

Automated summary

Sewage sludge combustion experiments were conducted to investigate the migration and transformation of Zn, Mn, and Cr, and the results showed that temperature, atmosphere, and steam concentration had significant effects on the process.