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Oxygen carriers transfer lattice oxygen and oxidize elemental mercury in chemical-looping combustion (CLC). This study aims to design a core–shell CuCo2O4@SiO2oxygen carrier to enhance the removal of mercury during CLC. CuCo2O4@SiO2was prapered by combining a salt-assisted combustion method and an impregnation method. The SiO2:CuCo2O4ratio was optimized to achieve a high mercury removal efficiency. Over 10 cycles, CuCo2O4@SiO2oxygen carriers have a stable oxygen release. At 900 °C, in comparison with CuCo2O4, mercury removal efficiency over CuCo2O4@SiO2through oxidation increased from 63.46 to 82.21%. The mercury removal over CuCo2O4@SiO2through chemical adsorption decreased accordingly. This indicated that CuCo2O4@SiO2oxygen carriers promoted the oxidation efficiency of Hg0and reduced the adsorption of mercury on its surface. The DFT calculations revealed that SiO2loading over CuCo2O4surface provided part of the lattice oxygen to supplement the oxygen vacancies on the CuCo2O4surface, promoting the oxygen release from the oxygen carrier. However, the loading of SiO2inhibited the formation of surrounding oxygen vacancies to a certain extent, and the right amount of SiO2improved the oxygen release rate. Therefore, CuCo2O4@SiO2is a suitable oxygen carrier that can be applied in CLC.

The development of compact reactors has attracted wide interest from chemical engineering society. Inspired by the special shape of “sea urchin”, we propose that bionic packings with this type of shape are superior in breaking bubbles in a bubble column, and therefore, the mass transfer rate of gases in liquids may be greatly enhanced. In this study, different structures and quantities of bionic packings were added to a bubble column to enhance SO2absorption into water. The absorption rates of SO2into water with different bionic packings were compared with these systems with commercial packings of Pall rings and Dixon rings. The mass transfer coefficients and gas–liquid specific interfacial areas of different packings with the same volume of packings’ addition were measured. Based on the comparison of SO2removal efficiency for systems with different packings, the system with the addition of 24 ″3.5 mm + 5 mm″ packings presented the optimum promotion effect. The liquid volumetric mass transfer coefficient (kLa) of adding 24 ″3.5 mm + 5 mm″ packings was 1.5 times of the baseline, indicating that the process was mainly controlled by liquid-phase mass transfer. The increase of the liquid volumetric mass transfer coefficient (kLa) was the combined effect of the increased liquid-phase mass transfer coefficient (kL) and the specific interfacial area (a).

Several preparation methods for current spinel compounds are briefly introduced. The effects of temperature and flue gas components on the removal of Hg0over spinel compounds are reviewed. The reaction processes and mechanisms of Hg0adsorption, oxidation, and desorption on the surface of spinel compounds are analyzed deeply. The current methods for improving Hg0catalytic oxidation performance by spinel-based photocatalytic materials are also introduced. There are two main types of spinel compounds for Hg0removal: conventional spinel and loaded spinel compounds. Loaded spinel compounds are favorable for the adsorption and oxidation of Hg0due to more active sites and a larger surface area than ordinary spinel compounds. Both O2and HCl contribute to Hg0removal with Hg0oxidation efficiency being sensitive to both O2and HCl concentrations. The presence of SO2has a detrimental effect on the removal of Hg0due to the competition for the active adsorption sites on the surface of catalysts and adsorbents. The impact of temperature is bidirectional, and an optimum temperature exists. Based on the analysis of three stages (adsorption, oxidation, and desorption) included in the Hg0catalytic oxidation process, it was discovered that for most catalysts the Hg0oxidation process is the rate-limiting step for the reaction.

Acid gas compression and purification are an effective way for the treatment of NOxin oxy-fuel combustion flue gas due to the reduced volume flow rate of flue gas in oxy-fuel combustion in comparison with air combustion. The design of reactors for NOxremoval is particularly important for future CO2utilization and storage and is also rather challenging due to the impact of pressure on both kinetic as well as mass-transfer parameters. To obtain the sensitivity as well as pressure dependence of different parameters, NOxremoval in water under high pressure in both bubbling and film modes was investigated based on both experimental and modeling methods. Six uncertain parameters, including mass-transfer coefficients of NO and NO2(kNO and kNO2), NO oxidation rate constant k1, liquid surface area S1, liquid film surface area S2, and liquid film volume VL, were identified and optimized to minimize relative errors between measurements and simulations. Three most important parameters affecting the simulated NOxabsorption results are kNO2, k1, and S1, followed by kNO. While S2 and VL only affect NO2, these two parameters have little effect on NO, HNO3, and HNO2. In the gas bubbling reactor system, the liquid phase plays the main absorption role in NOxand the liquid film plays a supplementary absorption role. The effective removal of NOxin the high-pressure system can also be achieved by using only liquid film absorption rather than gas bubbling absorption as gas absorption by the liquid film can generate high concentrations of HNO3, which is beneficial for subsequent utilization.