Synergistic removal behaviour of unconventional pollutants by activated carbon injection in coal-fired flue gas

Reducing emissions of unconventional pollutants (UPs: organic pollutants (OPs), gaseous mercury (GM), and condensable particulate matter (CPM)) from coal-fired flue gas is crucial for continuous improvement of atmospheric environmental quality. In this work, activated carbon injection (ACI) was first employed for UPs synergistic removal in a pilot-scale system. At the dust collector outlet, the UPs concentrations in flue gas followed the order: CPM (20.31 mg/m3) > OPs (1.90 mg/m3) > GM (8.11 μg/m3). For unmodified AC, removal efficiency of OPs and GM was related to SBET and Vt, while that was determined by pore size distribution for CPM. With nitric acid modification (AC1-A), the adsorption efficiencies for OPs, GM, and CPM reached 58.4%, 69.2%, and 53.6%, respectively. Among OPs, VOCs adsorption was weaker than that of SVOCs. The increased heteroatomic groups on AC1-A enhanced the hydrogen bonding formation and electron donor–acceptor interactions with oxygenated VOCs. GM was more readily captured near oxygen-containing groups, the surface chemistry had a greater influence than pore structure. For CPM, the inorganic fraction showed higher removal efficiency (61.2%) than that of organic fraction (49.1%). Although organics exhibited stronger affinity to ACs, their larger molecular weight and volume limited the diffusion rate, decreasing the adsorption efficiency. Functional groups showed weaker influence on organic fraction removal. Although competitive adsorption existed among various pollutants, their low total concentration still ensured good removal performance of UPs. Expanding pore size distribution and increasing heteroatomic groups on AC are effective strategies for UPs removal from coal-fired flue gas.