Insights into Nb doping effects on the catalytic activity and SO2 tolerance of Mn-Cu/BCN catalyst for low-temperature NH3-SCR reaction.

Biochar-based supported denitration catalysts have shown tremendous potential in reducing NOx, while improving low-temperature NH3-SCR catalytic activity and SO2 tolerance still faces great challenges. In this work, Mn7-Cu3/BCN and Mn7-Cu3-Nbx/BCN catalysts were prepared by one-step wet impregnation. The enhanced effect of Nb doping on the catalytic performance and SO2 tolerance over the Mn7-Cu3/BCN catalyst was evaluated in the temperature range of 75-275 °C. The denitrification activity test showed that the introduction of an appropriate amount of Nb increased the catalytic activity and N2 selectivity of the catalyst. The NO conversion of Mn7-Cu3-Nb0.05/BCN with an optimum doping ratio of 0.05 wt% Nb was higher than 94% at 150-275 °C. The characterization results indicated that the introduction of Nb enhanced the interaction between the active components MnOx and CuOx, accelerated the electron transfer between elements, and thus improved the Mn4+/Mnn+ and Oα/(Oα+Oß+Oγ) proportions and redox performance. On the other hand, Nb modification increased the number of weakly acidic sites, which was beneficial for the adsorption and activation of the reducing agent NH3 under low-temperature conditions. Meanwhile, Nb could significantly improve the SO2 poisoning resistance of the Mn7-Cu3/BCN-S catalyst when SO2 was added to the reaction system. The NO conversion of Mn7-Cu3-Nb0.05/BCN remained above 75% after a 13.5 h reaction under 100 ppm SO2 and 5 vol% H2O at 225 °C. By combining experimental characterization results with DFT calculation results, we effectively confirmed that Mn7-Cu3-Nb0.05/BCN had good sulfur resistance, mainly because Nb could effectively inhibit the formation of manganese sulfate and promote the decomposition of ammonium bisulfate.

Comparative research on vapor injection heat pump with a novel flash tank.

Two major problems for the vapor injection heat pump systems with the flash tank are the high discharge temperature and the lack of flash tank design theoretical basis, which would limit its wide application in extreme operating conditions. One possible way to overcome these problems is to effectively control the two-phase injection in the flash tank by optimizing its structure. The use of the proposed novel flash tank in the quasi-two-stage vapor injection cycle represents an economic and controllable solution. This research experimentally analyzes the influences of flash tank structure and volume on the system heating performance under different compressor frequencies and injection pressures at the ambient temperature of -10 °C. The comparative analysis is done finding that the novel flash tank could maximumly improve the system Coefficient of Performance (COPh) by 6.4% in this test, compared with the traditional type A flash tank cycle. In the meanwhile, a bad design of novel flash tank size could represent a loss of COPh improvement between 5.73% and 13.5%. Due to the particular structure, the implementation of the novel flash tank also allows the injection mass flow ratio can keep a linear relationship with the injection pressure. Moreover, the refrigerant liquid can be regularly injected into the compression chamber to control discharge temperature under 100 °C. From all the analysis, guidelines for optimizing the control strategy and the flash tank design are put forward, which can be used to perfect the real thermodynamic model of the flash tank rather than the ideal two-phase separation model.

Experimental Study on Reinforcement of Reef Limestone by Magnetic Anchoring System.

The magnetic anchoring system (MAS) for reef limestone reinforcement is proposed in this paper. The mix proportion of the artificial reef limestone was designed, and the parameters of the MAS were determined through orthogonal tests. The effect of the magnetic field on the anchoring materials was analyzed using XRD and the nitrogen adsorption method. The results indicate that the designed artificial reef limestone can be used in place of in situ rock samples for laboratory tests. In air, the bond samples of the anchoring material and reef limestone experienced cohesion failure of the artificial reef limestone. However, in seawater, it was cohesion failure of the reef limestone and interface adhesion failure. During the pull-out test, the reef limestone specimen reinforced by MAS showed interface failure between the anchoring material and the rock mass. The Fe3O4 powder present in the anchoring material has the ability to migrate towards the anchor, thereby enhancing the density of the anchoring material. This, in turn, helps to eliminate the free water present in the anchor hole, and consequently, improves the bonding effect of the interface. The reinforcement effect of MAS is particularly advantageous for rock reinforcement under complex working conditions.

Combustion Characteristics of Low Calorific Value Biogas and Reaction Path of NOx Based on Sensitivity Analysis.

The combustion mechanism of biogas mixture is unclear, which leads to the lack of basis for the control of operating parameters. Combustion characteristics and reaction path of typical low calorific value biogas with variation of preheating temperature and air equivalence ratio (Φ) are discussed in this paper. Preheating can not only improve the flame propagation speed and flame temperature, but also increase the proportion of NO in the product at the end of combustion flame. To some extent, improving combustion efficiency and NOx control are contradictory operating parameters. The amount of NO increases with the increase in flame distance. The maximum value of NO appears when Φ is 1.1. NO formation rate is improved by preheating the biogas. The paths of N2 → N2O →NO, N2 → NNH →NO, and N2 →NO are all enhanced. When the equivalence ratio changes from 1.0 to 0.8, NO formation rates decrease.

Application of ultrasound to enhance the silt drying process: An experimental study.

Scientific and reasonable treatment of dredged silt can not only protect the ecological environment but also play an essential role in the utilization of silt resources. Due to high water content, low permeability and high organic matter content of the silt, a large amount of bacteria and harmful gases are often produced during the process of silt sedimentation. Thermal drying has been taken as a technically attractive method for harmless treatment of contaminated dredged silt. In this study, ultrasound technology is introduced to shorten the time needed for silt drying. A preliminary laboratory study is carried out to assess the effectiveness of ultrasound on thermal drying. A series of thermal drying tests, with and without ultrasound, were conducted on kaolin soil specimens that were prepared by settling and self-weight consolidation. The test results show that the length of drying time can be shortened by increasing temperature and ultrasound power. The drying time plays a dominant role in the determination of the total energy consumption. This is because reduction of drying time leads to significant decrease in energy consumption for thermal drying, and the energy consumption for additional ultrasound is relatively marginal. For thermal drying at temperatures 60 and 100°C, when combined with 100 W ultrasound, the length of drying time was shortened by 44.19% and 45.16%, and the energy consumption was saved by 30.07% and 38.16%, respectively; when combined with 60 W ultrasound, the length of drying time was shortened by 4.65% and 6.45%, but the energy consumption was increased by 9.79% and 0.48%, respectively. The combination of thermal drying and 100 W ultrasound is found to be optimal in terms of drying rate and energy consumption for silt drying.