Heavy Metal Migration Characteristics of Co-Combustion between Sewage Sludge and High Alkaline Coal on Circulating Fluidized Bed

The migration characteristics of heavy metals in co-combustion of sewage sludge and high alkali coal in circulating fluidized bed were studied by experiments and simulations. Temperature plays a crucial role in thermodynamic equilibrium distribution and migration characteristics of heavy metals. At the temperature range of 700 degrees C-1200 degrees C, Hg is completely gaseous and the proportion of Pb, Ni, and Cd in the gas phase is also high. As is mainly elemental in the system, and the proportion of Cr in the solid phase is large. Zn compounds are diverse and mostly solid materials. The volatility of Cu is not strong, and it will become gaseous when the temperature exceeds 1700 degrees C. The proportion of heavy metals in the gas phase decreases as the excess air ratio increases. In an oxygen-rich atmosphere, most of Zn and Ni are converted to oxides; Pb and Cd are converted to crystalline silicate; Cu is converted to partial aluminate; Cr compound is decomposed to form Cr2O3; they are good for the solidification and controlling of heavy metals. The elemental Hg is converted to HgCl2 and the elemental As is converted to AsCl3. Temperature also has a great influence on the volatilization rate of heavy metals. The higher the temperature, the shorter the time they reach the maximum volatility.

Automated summary

The migration characteristics and volatility of heavy metals are influenced by temperature during the co-combustion process. The presence and proportion of different heavy metals in the gas phase and solid phase vary at different temperatures. Higher temperatures lead to higher volatility of heavy metals, with shorter time to reach maximum volatility.