In this article, four kinetic models including intraparticle diffusion, pseudo-first-order, pseudo-second-order, and Elovich kinetic models were applied to explore the internal mechanism of mercury adsorption by activated carbon in wet oxy-fuel conditions. Results indicated that the pseudo-second-order model and Elovich kinetic model could accurately describe the adsorption process, which meant that chemical adsorption played an important role in the adsorption of mercury by activated carbon. 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 effect on mercury removal. Meanwhile, the external mass transfer process is more effective in controlling the mercury adsorption process of activated carbon according to the fitting result of the pseudo-first-order model. According to the obtained kinetic parameters, the intraparticle diffusion rate was improved with the increasing bed height. In addition, the higher temperature inhibited the external mass transfer, which was not conducive to the adsorption of mercury by activated carbon in wet oxy-fuel conditions.

This study evaluated the mercury sorption by activated carbon (AC) under an O2/CO2 atmosphere in a fixed-bed reactor. Effects of the oxygen concentration on the mercury sorption efficiency under both air and oxy-fuel atmospheres were explored. The kinetic studies were also used to predict the mercury sorption process by the pseudo-first-order model and the intraparticle diffusion model in this work. The experimental results indicated that the mercury sorption capacity of AC increased with the increased oxygen concentration under both air and oxy-fuel atmospheres. Oxygen might increase the oxidation of mercury by the Mars–Maessen way. A high CO2 concentration promoted AC to generate more active sites under an oxy-fuel atmosphere. Besides, the results of the kinetic analysis illustrated that the pseudo-first-order model showed better agreement with the experimental data compared to the intraparticle diffusion model. These experimental and theoretical results in this work are helpful in mercury capture under an oxy-fuel atmosphere.

No abstract

Mercury from recycled oxy-fuel gas needs to be removed because it can damage the aluminum devices in the system. In this work, low-cost NH4Br-modified rice husk char (RHCBr) was prepared as the biosorbent for mercury removal in an oxy-fuel atmosphere. RHCBr was characterized by scanning electron microscopy, Brunauer–Emmett–Teller, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS) technologies to study the physical and chemical properties of the prepared sorbents. Effects of O2, HCl, SO2, and HCl/SO2 synthesis on mercury removal in a simulated oxy-fuel atmosphere were investigated in a fixed-bed reactor. XPS technology was applied to explore the mercury adsorption species and deduce the potential mercury heterogeneous oxidation mechanism in an oxy-fuel atmosphere. It was found that enriched CO2 in an oxy-fuel atmosphere could facilitate the mercury removal process. Generally, O2 and HCl could promote the mercury removal efficiency in an oxy-fuel atmosphere, while SO2 could inhibit it. However, a low concentration of SO2 could promote it with the presence of HCl and O2. The mercury adsorption species on RHCBr were mainly HgSO4, HgCl2, and HgBr2 in the presence of acid gas components (HCl and SO2). HCl could actively facilitate the generation of C–Cl groups, which were also active sites for mercury removal, while SO2 could generate active site cover NH4HSO4, causing the deactivation of active sites. When HCl/SO2 synthesis was added, active site cover HSO4 – would be removed by HCl, facilitating the mercury removal process. Meantime, HgCl2 species could be further converted to the strong-bonded species HgSO4 in the presence of O2 and SO2, which was also beneficial for mercury removal.

No abstract