Interference Effect of Experimental Parameters on the Mercury Removal Mechanism of Biomass Char under an Oxy-Fuel Atmosphere.

Abstract

In this paper, the effect of temperature, adsorption bed height, and initial mercury concentration under oxy-fuel combustion on mercury adsorption by 1% NH4Cl-modified biomass char was studied. Modification enriched the pore structure of biomass char and increased the number of surface functional groups. Higher temperature would lead to the destruction of van der Waals and reduce the adsorption efficiency, while the change of adsorption bed height had no obvious effect. Adsorption thermodynamics shows that the mercury removal process is a spontaneous exothermic process. The increase of initial mercury concentration would increase the driving force of mercury diffusion to the surface and improve the adsorption capacity. Meanwhile, three kinetic models including the intraparticle diffusion model, pseudo-first-order model, and pseudo-second-order model were applied to explore the internal mechanism of mercury adsorption by biomass char. The results showed that the pseudo-first-order model and pseudo-second-order model could accurately describe the adsorption process, which meant that the progress of external mass transfer played an important role in the adsorption of mercury while chemical adsorption should not be ignored. The intraparticle diffusion model indicated that internal diffusion was not the only step to control the entire adsorption process and did not have an inhibition on mercury removal. Higher initial mercury concentration would promote the external mass transfer progress and chemical adsorption progress. In addition, higher temperature inhibited the external mass transfer, which was not conducive to the adsorption of mercury.