Effects of CO and CO2 on the Removal of Elemental Mercury over Carbonaceous Surfaces.

Abstract

Coal gasification is a popular method for the optimization of coal utilization and the reduction of environmental pollutant emissions. However, the reductive atmosphere of its products is disadvantageous for removing elemental mercury (Hg0). Activated cokes (AC) was employed in this work for mercury capture in a reducing atmosphere. The high-temperature heating decreases the mercury-removal capability of carbon sorbents because the carbonaceous surface is becoming oxygen-depleted and micropore-decreased after the heating treatment. The mechanism of mercury adsorption in pure nitrogen follows the Mars–Maessen mechanism over the carbon sorbents. To identify the effects of carbon monoxide (CO) and carbon dioxide (CO2) on Hg0 removal, the Hg0-adsorption and thermal desorption experiments were carried in a fixed-bed reaction system. CO inhibits both the chemisorption and physisorption of Hg0. CO2 competes for the active sites, lactone groups and hydroxyl groups, and occupies the micropores, which is beneficial to adsorb Hg0 physically. When CO and CO2 coexisted, the removal efficiencies show steadier than those in monocomponent gas (only CO or CO2). CO2 can resist the negative effect of CO on Hg0 removal, to some extent, because CO2 can inhibit the oxidation and disproportionation of CO. This experimental study provides practical guidance for the development of mercury-removal technology with carbon materials in the coal gasification plant.