Mercury removal from coal combustion flue gas by mechanochemically sulfur modified straw coke and its mercury stability

Abstract

This work uses widely sourced rice straw as raw material, sulfur containing substances as modifiers, and mechanochemistry as modification methods to prepare the mechanochemical sulfur modified rice straw char mercury removal adsorbent (S-SC). The influence of modifiers, flue gas components, and the environmental stability of mercury removal products were systematically studied. The mechanochemical sulfur modification (elemental sulfur (ES), Na2S, NaHS) can improve the mercury removal performance of raw rice straw char (R-SC). It enhances mercury adsorption and capture. The ES is the best sulfur specie whose mercury removal rate firstly increases and then decreases as the amount of sulfur added increases. Sulfur modification promotes mercury forms convert to HgS (red) or even HgSO4 with higher thermal stability. The thiophene/elemental sulfur are the main sulfur species for promoting mercury removal. SO2 and NO inhibit mercury removal by ES-SC, while HCl has a promoting effect. As their concentration in the flue gas increases, the proportion of mercury removed by adsorption increases, and the adsorbed mercury transforms into a more thermally stable mercury form. The mercury forms of the spent ES-SC are mainly oxidized and residual form with TCLP leaching rate of zero, which has good environmental leaching stability.