posted on 2024-03-13, 18:10authored byFengxia An, Lingyan Le, Zhaoping Zhong, Zhenggen Lin, Ying Yu, Weijie Yan, Qilei Ma, Hui Wang
The presence of circulating flue
gas in oxy-fuel combustion leads
to mercury pollution. Acid–chlorine-modified biomass coke was
used to prepare mercury adsorbents. The influence of individual flue
gas components (HCl, NO, SO2, and H2O) and complex
flue gas on the behavior of modified straw coke for mercury removal
under an oxy-fuel combustion atmosphere was studied. The mechanism
of the flue gas reaction with mercury was investigated using temperature-programmed
desorption (TPD) characterization. The density functional theory (DFT)
was employed to study the mechanism of mercury removal by the adsorbent.
The results showed that H2O has a dual effect on mercury
removal: the low concentrations of H2O promote mercury
removal, while moderate to high concentrations of H2O inhibit
it. HCl and NO exhibited promotional effects on mercury removal. SO2 competed with Hg0 for active adsorption sites
or adsorbed on the surface of the adsorbent, consuming active oxygen
species and chlorinated functional groups to inhibit the adsorption
and oxidation of Hg0. Under the atmosphere of complex flue
gas, H2O and SO2 inhibited the generation of
highly oxidizing intermediate products from HCl and NO. Additionally,
the coexistence of H2O and SO2 generated H2SO4, further blocking the surface pore structure
and hindering the diffusion of Hg0 on the adsorbent surface.
The result of the electron localization function (ELF) indicated that
the introduction of O and Cl atoms can form stable covalent compounds
(CO and C–Cl) through bonding with the carbonaceous
surface, serving as favorable chemical adsorption sites. The high
reactivity of Cl induces Hg0 adsorption, and the presence
of O atoms not only acts as a chemical adsorption site but also activates
the reactivity of Cl atoms, promoting the efficiency of mercury removal.
This study provided a theoretical basis for the application of mercury
adsorbents in oxy-fuel combustion fuel gas.