Mercury removal over waste-derived sorbent in oxy-fuel combustion flue gas and its regeneration performance

Oxy-fuel combustion is a promising carbon capture technology. However, elemental mercury (Hg⁰) present in oxy-fuel combustion flue gas poses significant safety risks due to its potential to cause embrittlement of aluminum-based CO₂ compression equipment and heat exchangers. The challenge of Hg⁰ removal from oxy-fuel flue gas primarily stems from the lack of cost-effective, efficient sorbents with excellent resistance to SO₂ and H₂O. Previously, waste-derived sorbents were synthesized through the co-pyrolysis of waste tire and biomass under SO₂ atmosphere, which exhibited high performance for Hg⁰ removal from traditional coal-fired flue gas. The behavior of Hg⁰ removal over waste-derived sorbents from oxy-fuel combustion flue gas is further explored. The involved Hg⁰ removal mechanisms and regeneration performance of waste-derived sorbents are also revealed. The results indicate that the sorbents perform better in Hg⁰ removal under oxy-fuel conditions compared to air combustion. This is mainly because the presence of CO₂ promotes the generation of C=O and O—C=O functional groups on the sorbent surface. SO₂ promotes Hg⁰ removal by reacting with surface sulfides to form functional groups (such as sulfur-containing functional groups). NO promotes Hg⁰ removal by being oxidized into NO₂ on the sorbent surface, which further reacts with Hg⁰ to form Hg(NO₃)₂. HCl contributes to the formation of C—Cl functional groups on the sorbent surface, increasing the active sites for Hg⁰ removal. However, H₂O slightly inhibits the Hg⁰ removal process due to competitive adsorption. After three regeneration cycles, the Hg⁰ removal performance of sorbent surpasses its initial state whereas a decline occurs after the fourth cycle. This indicates that there are some limitations in the regeneration of sorbents, but it still exhibits satisfactory Hg⁰ removal performance under suitable conditions.