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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.

Scrubbing of SO2and NOxfrom oxy-fuel combustion flue gas under a high pressure has been well recognized as an effective technique for flue gas purification. Experiments were performed in a bubbling column under high pressure to explore the absorption products and the SO2selectivity during simultaneous absorption of SO2and NOx. The main absorption product in liquid phase at pH > 1 was identified as hydroxylamine disulfonic acid (HADS), which was then quantified by the Raman spectroscopy. The N2O concentration in gas phase was estimated by the nitrogen mass balance across the system. Results showed that N2O and HADS were produced dominantly by the reaction between HNO2and HSO3–at pH > 1, and this followed the Raschig mechanism. However, the absorption of SO2was promoted while the absorption of NOxwas inhibited, and this followed the lead chamber mechanism. Based on the quantification of the nitrogen and sulfur related products in both gas and liquid phase, about 48%–56% NOxand 14%–17% SO2were consumed by the Raschig mechanism, and 15%–23% SO2was consumed by the lead chamber mechanism in the pH range 1.09–1.72. For simultaneous absorption of NOxand SO2, SO2was completely absorbed in different solutions except in the 18.4 mol/L H2SO4. A high concentration of H2SO4suppressed the absorption of NOxbut cannot achieve selective absorption of SO2without absorbing NO. HNO3concentration did not have appreciable effect on NOxabsorption efficiency in the concentration range 0.1–1 mol/L. When the concentration of HNO3was 15 mol/L, NOxwas no longer absorbed into liquid solution. The mixed acids produced by the simultaneous absorption of NOxand SO2can cause severe corrosion to a 316L stainless steel tube.

Controlling carbon emissions is an effective way to mitigate the greenhouse effect. According to the primary energy consumption of China, chemical looping combustion (CLC) using coal as the fuel has great development prospects. In the solid-fuel CLC process, the interaction of char and oxygen carrier cannot be ignored. The CaSO4oxygen carrier is cheap and oxygen-rich. Thus, the interaction of char and CaSO4was investigated in this paper to reveal the reason for the low reaction rate for the char–CaSO4reaction from the perspective of the binding process. It could offer the guide for improving the binding ability of the CaSO4oxygen carrier. The binding process of the char model composed of five benzene rings and the CaSO4cluster was calculated by the semi-empirical tight-binding quantum chemistry method, and the influence of the temperature and pressure was simulated by the grand canonical Monte Carlo (GCMC) method. The interaction of char and CaSO4is the exothermic reaction, and the dispersion contributes the most energy to attractive interaction. The binding system is the typical weak interaction system. From the property analysis, the H1–H2–O ring causes the system to stay stable, and there are hydrogen bonds that appear in the interaction area between the two fragments. The results of the independent gradient model verify the position of the hydrogen bond interaction, and the atom contributions of char and CaSO4to the interaction are 0.1564–0.5958 and 0.2347–0.4854, respectively. The results of the electron density difference demonstrate that most atoms in the interaction area (z= 5.5–9.5 Å) get electrons to cause the positive electrostatic energy. According to the GCMC simulation, the binding process changes from type 2 binding to type 3 binding with the temperature increasing and the binding energy decreases. Meanwhile, the fitted energy curves change from the polynomial function to the exponentiation. To improve the interaction ability of the two fragments, it would be a choice to increase the electron transfer ability between char and the CaSO4surface.