Study on the transformation of Zn, Mn and Cr during sewage sludge combustion
Hao Liu, Yajun Wang, Xiaohan Ren, Huanhuan Xu, Juan Chen
Abstract
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 ZnCl 2 (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/Fe 2 O 3 on capturing Cr. The reducing atmosphere caused by high CO 2 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·A1 2 O 3 ·2SiO 2 condensed into solid ash. The generation of CO and H 2 from char-steam/char-CO 2 gasification induced a local reducing atmosphere. It accelerated the transformation of MnO 2 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.