Simulation of the calcination of a core-in-shell CuO/CaCO 3 particle for Ca–Cu chemical looping

The internal heat balance through heat generation due to CuO reduction and its consumption by CaCO3 decomposition makes calcination a critical step in a novel Ca–Cu chemical looping process (CaL–CLC). Thus, the calcination behaviour of composite Ca/Cu particles needs to be well understood, especially taking into account that mismatching of heat generation and consumption in the particles can lead to local superheating, agglomeration and loss of activity due to enhanced sintering. In this work, a composite particle model was developed to study the calcination behaviour within a spherical core-in-shell type of particle containing grains of CuO and CaCO3. Simulation results showed that ambient temperature, shell porosity, particle size, and CaCO3 grain size significantly affected the CuO and CaCO3 reaction processes, while the impact of initial particle temperature and CuO grain size can be ignored in the range of parameters considered in the study. By comparison of different types of particles, it was concluded that the core-in-shell pattern was more advantageous if such particles are being applied in CaL–CLC cycles due to better matching in reaction kinetics resulting in more stable and uniform particle temperature distribution during the calcination stage

Piezoelectric Wind Energy Harvesting from Self-Excited Vibration of Square Cylinder

Self-excited vibration of a square cylinder has been considered as an effective way in harvesting piezoelectric wind energy. In present work, both of the vortex-induced vibration and unstable galloping phenomenon process are investigated in a reduced velocity (Ur=U/ωn·D) range of 4≤Ur≤20 with load resistance ranging in 100 Ω≤R≤1 MΩ. The vortex-induced vibration covers presynchronization, synchronization, and postsynchronization branches. An aeroelectromechanical model is given to describe the coupling of the dynamic equation of the fluid-structure interaction and the equation of Gauss law. The effects of load resistance are investigated in both the open-circuit and close-circuit system by a linear analysis, which covers the parameters of the transverse displacement, aerodynamic force, output voltage, and harvested power utilized to measure the efficiency of the system. The highest level of the transverse displacement and the maximum value of harvested power of synchronization branch during the vortex-induced vibration and galloping are obtained. The results show that the large-amplitude galloping at high wind speeds can generate energy. Additionally, energy can be harvested by utilization of the lock-in phenomenon of vortex-induced vibration under low wind speed

Compatibility of NiO/CuO in Ca‐Cu chemical looping for high‐purity H2 production with CO2 capture

Ca‐Cu chemical looping is a novel and promising approach in converting methane into pure H2 following the principle of sorption‐enhanced reforming. Its operational efficiency is largely determined by an appropriate coexistence of Cu‐based oxygen carriers and Ni‐based catalysts. In this work, NiO/CuO composites were synthesized and their catalytic activity for H2 production was measured using a fixed‐bed reactor system equipped with an online gas analyzer. It is reported for the first time that the presence of CuO could hinder the activity of Ni‐based catalysts in H2 production, and experimental results show that the negative effect of CuO is strengthened with increasing CuO content and calcination temperature during sample preparation. With the help of a series of specific test and characterization techniques (SEM‐EDS, BET, XRD, TPR and XPS), interaction rules between NiO and CuO was further investigated and understood, and based on that an action mechanism model was proposed. Furthermore, an arrangement of mixed particles that avoiding the intimate contact of CuO/NiO was suggested and tested, and a superior performance was demonstrated while observing no restrictions of CuO on Ni‐based catalysts in sorption‐enhanced steam‐methane reforming under the conditions of Ca‐Cu chemical looping

Energy Harvester Based on the Synchronization Phenomenon of a Circular Cylinder

A concept of generating power from a circular cylinder undergoing vortex-induced vibration (VIV) was investigated. Two lead zirconate titanate (PZT) beams which had high power density were installed on the cylinder. A theoretical model has been presented to describe the electromechanical coupling of the open-circuit voltage output and the vibration amplitudes based on a second-order nonlinear Van der pol equation and Gauss law. A numerical computation was applied to measure the capacity of the power generating system. The lift and drag coefficient and the vortex shedding frequency were obtained to verify how the nondimensional parameter reduced velocity Ur affects the fluid field. Meanwhile, a single-degree of freedom system has been added to describe the VIV, presynchronization, and synchronization together with postsynchronization regimes of oscillating frequencies. And the amplitudes of the vibration have been obtained. Finally, the vibrational amplitudes and the voltage output could go up to a high level in the synchronization region. The maximum value of the voltage output and the corresponding reduced velocity Ur were 8.42 V and 5.6, respectively

Negative Group Velocity in the Absence of Absorption Resonance

Scientific community has well recognized that a Lorentzian medium exhibits anomalous dispersion behavior in its resonance absorption region. To satisfy the Krammers-Kronig relation, such an anomalous region has to be accompanied with significant loss, and thus, experimental observations of negative group velocity in this region generally require a gain-assisted approach. In this letter, we demonstrate that the negative group velocity can also be observed in the absence of absorption resonance. We show that the k-surface of a passive uniaxial Lorentzian medium undergoes a distortion near the plasma frequency. This process yields an anomalous dispersion bandwidth that is far away from the absorption resonance region, and enables the observation of negative group velocity at the plasma frequency band. Introducing anomalous dispersion in a well-controlled manner would greatly benefit the research of ultrafast photonics and find potential applications in optical delay lines, optical data storage and devices for quantum information processing

Matching of kinetics of CaCO3 decomposition and CuO reduction with CH4 in Ca-Cu chemical looping

Ca-Cu chemical looping (CaL-CLC) based on calcium looping is a novel and promising process for CO capture. The concept utilizes the heat released from the exothermic reduction of CuO to support the endothermic regeneration of CaO-based sorbents. Therefore, it is important for the two major reactions to have matching kinetics. This work assesses kinetics of the two reactions in a calciner under the conditions of interest for CaL-CLC. The reaction rates of the decomposition of CaCO and reduction of CuO-based material with CH were measured in a TGA by varying the temperature and gas atmosphere, and two gas-solid reaction models were utilized for the determination of the kinetic parameters. On the basis of these results, a dynamic model was developed to investigate the simultaneous reduction of CuO and decomposition of CaCO in an adiabatic fixed-bed reactor operating at 1atm. The simulation results showed that the reduction of CuO completed extremely fast under all test conditions, and it could lead to hot spots in the calciner. It was found that addition of steam into the reducing gas could enhance the reaction rate of CaCO decomposition and help it match the fast rate of CuO reduction, then reduce the formation of hot spots. Also, steam could be used to control the movement of reaction front. Although CO could be used to control the reaction front as well, the higher CO partial pressure in CH was found to slow down the decomposition of CaCO leading to incomplete reaction

Corrigendum: Selective catalytic and kinetic studies on oxydehydrogenation of ethane with CO2 over lanthanide metal catalysts

This note corrects an issue that has been identified in the article in Comptes Rendus Chimie with the above title. It was published online on 6th June 2020 in Volume 23, Issue 1, 2020, pages 33–46, https://doi.org/10.5802/crchim.4

Unraveling Enhanced Activity, Selectivity, and Coke Resistance of Pt–Ni Bimetallic Clusters in Dry Reforming

By introducing Pt atoms into the surface of reduced hydrotalcite (HT)-derived nickel (Ni/HT) catalysts by redox reaction, we synthesized an enhanced active and stable Ni-based catalyst for methane dry reforming reaction. The bimetallic Pt–Ni catalysts can simultaneously enhance the catalyst activity, increase the H2/CO ratio by suppressing reverse water–gas shift reaction, and enhance the stability by increasing the resistance to the carbon deposition during the reaction. Kinetic study showed that 1.0Pt–12Ni reduces the activation energy for CH4 dissociation and enhances the catalytic activity of the catalyst and lowers the energy barrier for CO2 activation and promotes the formation of surface O* by CO2 adsorptive dissociation. It is beneficial to enhance the resistance to the carbon deposition and prolong its service life in the reaction process. In addition, density-functional theory calculations rationalized the higher coke resistance of Pt–Ni catalysts where CH is more favorable to be oxidized instead of cracking into surface carbon on the Pt–Ni surface, compared with Ni(111) and Pt(111). Even if a small amount of carbon deposited on the Pt–Ni surface, its oxidation process requires a lower activation barrier. Thus, it demonstrates that the bimetallic Pt–Ni catalyst has the best ability to resist carbon deposition compared with monometallic samples.publishedVersio