Research on Vapor Mercury Adsorption by Ca-Based Sorbents

Mercury in power plant emission is present mainly in the vapor form and is not captured effectively by existing particulate removal systems. The characteristics of mercury sorption by Ca-based sorbents were experimentally measured. Experiments were carried out in a bench-scale fixed-bed mercury sorption facility with mercury permeation tube embedded in an isothermal water bath and simulated flue gas compositions. It has been shown that the performance of Ca-based sorbents including lime, hydrated lime and a mixture of fly ash and hydrated lime was better with the presence of SO₂ than the baseline conditions. The presence of SO₂ in the simulated flue gas enhanced the Hg⁰ capture from about 15% to 20%, and the adsorption capacity more than 50% at 30 min of exposure of sorbents to flue gas. It is also shown higher capture at higher temperature. It is supposed that heterogeneous reactions of Ca-based sorbents and SO₂ can increase Hg⁰ uptake, the sites for Hg⁰ capture are influenced positively by the presence of SO₂. The behavior is correlated with the chemisorption mechanism. The results show both mercury and SO₂ may be captured in fixed-bed applications using Ca-based sorbents common for SO₂ capture, hinting that mercury emissions may be controlled in a cost-effective manner wherever SO₂ control also is desired.