Numerical simulations and comparative analysis of two- and three-dimensional circulating fluidized bed reactors for CO2 capture

Carbon dioxide(CO2),the main gas emitted from fossil burning,is the primary contributor to global warming.Circulating fluidized bed reactor(CFBR)is proved as an energy-efficient method for post-combustion CO2 capture.The numerical simulation by computational fluid dynamics(CFD)is believed as a promising tool to study CO2 adsorption process in CFBR.Although three-dimensional(3D)simulations were proved to have better predicting performance with the experimental results,two-dimensional(2D)simulations have been widely reported for qualitative and quantitative studies on gas-solid behavior in CFBR for its higher computational efficiency recently.However,the discrepancies between 2D and 3D simulations have rarely been evaluated by detailed study.Considering that the differences between the 2D and 3D simulations will vary substantially with the changes of independent operating conditions,it is beneficial to lower computational costs to clarify the effects of dimensionality on the numerical CO2 adsorption runs under various operating conditions.In this work,the comparative analysis for CO2 adsorption in 2D and 3D simulations was conducted to enlighten the effects of dimensionality on the hydrodynamics and reaction behaviors,in which the separation rate,species distribution and hydrodynamic characteristics were comparatively studied for both model frames.With both accuracy and computational costs considered,the viable suggestions were provided in selecting appropriate model frame for the studies on optimization of operating conditions,which directly affect the capture and energy efficiencies of cyclic CO2 capture process in CFBR.

CFD-PBM coupled modeling of the liquid-liquid dispersion characteristics and structure optimization for Kenics static mixer

Kenics static mixers(KSM)are extensively used in industrial mixing-reaction processes by virtue of high mixing efficiency,low power homogenization and easy continuous production.Resolving liquid droplet size and its distribution and thus revealing the dispersion characteristics are of great significance for structural optimization and process intensification in the KSM.In this work,a computational fluid dynamics-population balance model(CFD-PBM)coupled method is employed to systematically investigate the effects of operating conditions and structural parameters of KSM on droplet size and its distribution,to further reveal the liquid-liquid dispersion characteristics.Results indicate that higher Reynolds numbers or higher dispersed phase volume fractions increase energy dissipation,reducing Sauter mean diameter(SMD)of dispersed phase droplets and with a shift in droplet size distribution(DSD)towards smaller size.Smaller aspect ratios,greater blade twist and assembly angles amplify shear rate,leading to smaller droplet size and a narrower DSD in the smaller range.The degree of impact exerted by the aspect ratio is notably greater.Notably,mixing elements with different spin enhance shear and stretching efficiency.Compared to the same spin,SMD becomes 3.7-5.8 times smaller in the smaller size range with a significantly narrower distribution.Taking into account the pressure drop and efficiency in a comprehensive manner,optimized structural parameters for the mixing element encompass an aspect ratio of 1-1.5,a blade twist angle of 180°,an assembly angle of 90°,and interlaced assembly of adjacent elements with different spin.This work provides vital theoretical underpinning and future reference for enhancing KSM performance.

Analysis of the Flow Field and Impact Force in High-Pressure Water Descaling

This study aims to improve the performances of the high-pressure water descaling technology used in steel hot rolling processes.In particular,a 2050 mm hot rolling line is considered,and the problem is investigated by means of a fluid–structure interaction(FSI)method by which the descaling effect produced by rolling coils with different section sizes is examined.Assuming a flat fan-shaped nozzle at the entrance of the R1R2 roughing mill,the outflow field characteristics and the velocity distribution curve on the strike line(at a target distance of 30–120 mm)are determined.It is found that the velocity in the center region of the water jet with different target distances is higher than that in the boundary region.As the target distance increases,the velocity of the water jet in the central region decreases.Through comparison with experimental results,it is shown that the simulation model can accurately predict the impact position of the high-pressure water on the impact plate,thereby providing a computational scheme that can be used to optimize the nozzle space layout and improve the slabs’descent effect for different rolling specifications.

碱回收锅炉的计算机模拟及在燃烧系统设计上的应用

介绍了碱回收锅炉计算机模拟的基本原理、应用实例,以及燃烧空气系统的新设计概念。碱回收锅炉的计算机模拟是通过求解质量、动量和能量的守恒方程预测炉内的流动、传热和燃烧过程,给出炉内温度、化学组分及热流等的详细分布,为分析和解决锅炉运行中的问题、优化锅炉的设计和锅炉改造的方案提供了有效的手段。

CFD simulation of impeller shape effect on quality of mixing in two-phase gas–liquid agitated vessel

Mixing efficiency in two-phase gas–liquid agitated vessel is one of the important challenges in the industrial processes.Computational fluid dynamics technique(CFD)was used to investigate the effect of four different pitched blade impellers,including 15°,30°,45°and 60°,on the mixing quality of gas–liquid agitated vessel.The multiphase flow behavior was modeled by Eulerian–Eulerian multiphase approach,and RNG k-εwas used to model the turbulence.The CFD results showed that a strong global vortex plays the main role on the mixing quality of the gas phase in the vessel.Based on the standard deviation criterion,it was observed that the axial distribution of the gas phase in the 30°impeller is about 55%better than the others.In addition,the results showed that the 30°impeller has a uniform radial distribution over the other impellers and the maximum gas phase holdup in the vessel.Investigation of the power consumption of the impellers showed that the 30°impeller has the highest power consumption among the other pitched blade impellers.Also,examine the effect of same power condition for pitched blade impellers showed that the 30°impeller has the best mixing quality in this condition.

Effects of operating parameters on oxidative coupling of methane over Na-W-Mn/SiO_2 catalyst at elevated pressures

The effects of operating parameters on oxidative coupling of methane （OCM） over Na-W-Mn/SiO2 catalyst have been studied at elevated pressures of 0.2, 0.3 and 0.4 MPa under low gaseous hourly space velocity （GHSV） and low temperature conditions. Experimental results show that when the operating pressure is increased, C2＋ yield slightly decreases, while the maximum ratio of ethylene to ethane remains unchanged. Moreover, it has been found empirically that increase of pressure does not affect the catalyst behavior permanently, the catalyst recovers its original low pressure performance without hysteresis behavior by reducing the pressure. Under the investigated conditions, when oxygen is completely consumed, the increase of GHSV leads to improvement in C2 selectivity, while C3＋ and COx selectivities decrease slightly. The C2＋ selectivity increases by increase of nitrogen diluent in the feed, but the C3＋ hydrocarbons selectivities decrease with increase of nitrogen since it is possible that further dilution at high pressure may reduce the probability of collision between CH3 and C2＋ hydrocarbons. During the stability test at high pressure, the catalyst performance remains unchanged throughout the 20 h running. The fresh and used catalysts were characterized using XRD, SEM and N2 adsorption-desorption methods. It was found that the phase transformation of the support from α-cristobalite to tridymite and quartz does not have obvious effect on catalyst performance at high pressure.

Efficient separation of phenols from coal tar with aqueous solution of amines by liquid-liquid extraction

In this paper,a method of extracting phenols from coal tar by amines aqueous solution was proposed.The effects of various amines on the extraction properties of phenols in coal tar were researched from the views of molecular structure.The parameters such as molar ratio,concentration,extraction time and temperature for the extraction of coal tar by the monoethanolamine and ethylenediamine aqueous solution were examined.The results show that the organic amine with more amino groups,hydroxyl structure and strong electronegativity exhibited better extraction performance.Under the optimal conditions,the extraction yields of phenols in coal tar by the monoethanolamine or ethylenediamine aqueous solution are above 80%,and the recovery yields of amines reach 99%.Furthermore,the probable geometries of complexes formed by the combination of phenols and organic amines were calculated by density function theory.In addition,several thermodynamic models were evaluated through comparing the relative deviation of simulation results by ASPEN PLUS to the experimental ones,which provide feasibility thermodynamic models for the simulation of extraction process.The present work affords a mild,efficient and green approach for the extraction of phenols from coal tar by an aqueous solution of amines in industry application.

A multi-functional Ru Mo bimetallic catalyst for ultra-efficient C3 alcohols production from liquid phase hydrogenolysis of glycerol

Ru and Mo bimetallic catalysts supported on active carbon modified by phosphotungstic acid(PW)were designed and applied in glycerol hydrogenolysis reaction.The physicochemical properties of the catalysts were characterized and the presence of active sites was investigated from the perspective of the glycerol hydrogenolysis performance.The MoOxis highly selective for the C—O bond cleavage of glycerol molecules,which can reasonably regulate the strong C—C bond cleavage activity of Ru nanoparticles.By using sequential deposition of Ru and Mo supported on mesoporous PW-C,the characterization results show that the combination of isolated low-valence MoOxwith metal Ru particles can form“MoOx-Ru-PW”,which provides highly catalytic activity toward C—O bond cleavage,selectively producing more C3 alcohols(mainly 1,2(3)-propanediol).The glycerol conversion of 1%Mo/Ru/PW-C catalyst was 59.6%,the selectivity of C3 alcohol was 96.1%,and the selectivity of propanediol(1,2(3)-propanediol)was 94.9%.It is noteworthy that the selectivity of 1,3-propanediol reached 20.7%when the PW was 21.07%(mass).This study provides experimental evidence for the tandem dehydration and hydrogenation mechanism of the multifunctional Mo/Ru/PW-C catalyst.

Experimental and numerical study on plasma nitriding of AISI P20 mold steel

In this study, plasma nitriding was used to fabricate a hard protective layer on AISI P20 steel, at three process temperatures（450℃, 500℃, and 550℃） and over a range of time periods（2.5, 5, 7.5, and 10 h）, and at a fixed gas N2：H2 ratio of 75vol%：25vol%. The morphology of samples was studied using optical microscopy and scanning electron microscopy, and the formed phase of each sample was determined by X-ray diffraction. The elemental depth profile was measured by energy dispersive X-ray spectroscopy, wavelength dispersive spectroscopy, and glow dispersive spectroscopy. The hardness profile of the samples was identified, and the microhardness profile from the surface to the sample center was recorded. The results show that ε-nitride is the dominant species after carrying out plasma nitriding in all strategies and that the plasma nitriding process improves the hardness up to more than three times. It is found that as the time and temperature of the process increase, the hardness and hardness depth of the diffusion zone considerably increase. Furthermore, artificial neural networks were used to predict the effects of operational parameters on the mechanical properties of plastic mold steel. The plasma temperature, running time of imposition, and target distance to the sample surface were all used as network inputs; Vickers hardness measurements were given as the output of the model. The model accurately reproduced the experimental outcomes under different operational conditions; therefore, it can be used in the effective simulation of the plasma nitriding process in AISI P20 steel.

Synthesis and Characterization of Various Protein <i>α</i>-Lactalbumin Nanotubes Structures by Chemical Hydrolysis Method

New water-based nanofluids including unparalleled milk protein α-lactalbumin hollow nano-bio-tubes using low cost, available and advanced partial chemical hydrolysis strategy in bottom-up nano-assembly have been employed in this work. The aqueous sol-gel chemistry in nanotechnology which we selected for this goal offers new fabrication as interesting smart protein nanotubes. The kinds of nanometer sized tubular structures such as waved, helically coiled, bent, bamboo-shaped, bead-like and branched single-walled protein nanotubes (SWPNTs) with a range of 3 - 8 nm in outer diameters were produced by this method. Complete characterization for natural produced nanotubes including SEM, TEM images, G bond and D bond in Raman spectroscopy, XRD patterns, DLS (Dynamic Light Scattering) and FTIR analysis were evaluated which they are most significant experiments in synthesized protein nanotubes soluble in clear water nanofluids and stabilization of transparent nanofluids was proved within more than one year after preparation. Various necessary ligand ion salts such as Mn2+, Zn2+ and Ca2+ or mixtures as bridge makers and producing biological self-assembly hollow SWPNTs were performed and we focused on new chemical technology under specific acidic hydrolysis method not conventional enzymatic proteolysis and applying surfactants, pH reagent, Tris-HCl buffer, polar solvent which could be produced by β-sheet stacked hydrolysed protein α-lactalbumin mechanism under appropriate conditions to achieving high efficiency new protein nanotubes skeleton. They can be promising materials applied in food science, diet nutrition, nanomedicine, nano-biotechnology and surgery.

铸锭宏观组织和偏析的数值仿真（英文）

自1960s Flemings时代起人们经过半个世纪的努力已对铸锭内铸态组织和宏观偏析形成的物理机理有了定性或半定量的认识,但还是难以对其进行定量预测,主要原因是其与各种多相流现象有关,例如凝固糊状区枝晶间的对流,等轴晶区晶粒沉积等。当然这些多相流现象是与凝固过程热力学和扩散动力学以及宏观铸态组织形成过程相耦合的。近20年多相计算流体动力学的发展及其在凝固领域的应用为解决上述问题提供了有效手段。首先对这方面的进展作一个简要综述,通过具体事例重点展示其在铸锭铸态组织和宏观偏析形成过程动态数值仿真的应用前景,指出目前存在的某些局限性。

Solvent-free partial oxidation of cyclohexane to KA oil over hydrotalcitederived Cu-MgAlO mixed metal oxides

A highly efficient and stable hydrotalcite-derived Cu-MgAlO catalyst was developed for the partial oxidation of cyclohexane with molecular oxygen.The physical–chemical properties of Cu-MgAlO catalysts were studied,and the results indicated that the copper component had been successfully introduced into the hydrotalcite unit layer structure.The catalytic reaction results showed that copper as the active species could activate CAH bond and effectively promote the decomposition of cyclohexyl hydroperoxide(CHHP)to the mixture of cyclohexanol and cyclohexanone(KA oil).8.3%of cyclohexane conversion and 82.9%of selectivity for KA oil were obtained over 9%Cu-MgAlO catalyst at 150℃with 0.6 MPa of oxygen pressure for 2 h.Especially,its catalytic performance was still stable after five runs.

Role of fragmentation in as-cast structure:numerical study and experimental validation

A volume average solidification model is extended to incorporate fragmentation as the source of equiaxed crystals during mixed columnar-equiaxed solidification. This study is to use this model to analyze the role of fragmentation in the formation of as-cast structure. Test simulations are made for the solidification of a model alloy(Sn-10wt.%Pb) with two different geometries. The first one is a 2D rectangular domain(50 × 60 mm^2) as cooled from the top boundary. Solidification starts unidirectionally as columnar structure from the top. The solute(Pb) enriched interdendritic melt is heavier than the bulk melt, and sinks downwards, hence leads to solutal convection. Fragmentation phenomenon occurs near the columnar tip front. The fragments are transported out of the columnar region, and they continue to grow and sink, and finally settle down and pile up at the bottom. The growing columnar structure from the top and pile-up of equiaxed crystals from the bottom finally lead to a mixed columnar-equiaxed structure, in turn leading to a columnar-to-equiaxed transition(CET). The second geometry is a 3D plate, 100 × 60 ×10 mm^3, as cooled laterally from one side. It was cast experimentally and analyzed for the as-cast structure. The equiaxed fragments are produced in the solidification front and transported into the bulk melt, leading to a special pattern of as-cast structure: columnar structure in the cool wall side and equiaxed structure in the upper left corner near the hot wall side, extending downwards to the middle bottom region. Numerically calculated as-cast structures agree with the experiment results.

Analysis and Optimization of Flow-Guided Structure Based on Fluid-Structure Interaction

Gases containing sulfur oxides can cause corrosion and failure of bellows used as furnace blowers in high-temperature environments.In order to mitigate this issue,the behavior of an effective blast furnace blower has been examined in detail.Firstly,the Sereda corrosion model has been introduced to simulate the corrosion rate of the related bellows taking into account the effects of temperature and SO_(2) gas;such results have been compared with effective measurements;then,the average gas velocity in the pipeline and the von Mises stress distribution of the inner draft tube have been analyzed using a Fluid-Structure Interaction model.Finally,the semi-closed internal corrosion environment caused by a 5 mm radial gap between the inner draft tube and the bellows has been considered.The gas flow rate in the residential space has been found to be low(0.5 ms–this value leads to a stable semi-closed internal corrosion environment for exhaust gas exchange);water phase in the exhaust gas is prone to accelerate the corrosion rate.On this basis,a bellows with an optimized inner draft tube has proposed,which includes corrosion-resistant honeycomb buffer rings.

A Fine-Mesh Numerical Model with Detailed Boundary Layer Parameterization

A fine-mesh numerical model with thirteen-layer, three-dimensional primitive equation is designed, which has a relatively high vertical resolution in the boundary layer and detailed boundary parameterization. A strong cold frontal process is simulated by the model. Comparison of the simulated results of this process with different models shows that the result of this model is prior to that of others, and that it is necessary to increase the vertical resolution and to take account of the physical processes in the boundary layer.

Cobalt-nitrogen co-doped porous carbon sphere as highly efficient catalyst for liquid-phase cyclohexane oxidation with molecular oxygen and the active sites investigation

The selective oxidation of cyclohexane to cyclohexanone and cyclohexanol(KA oil)is a challenging issue in the chemical industry.At present the industrial conversion of cyclohexane to cyclohexanone and cyclohexanol is normally controlled at less than 5%selectivity.Thus,the development of highly active and stable catalysts for the aerobic oxidation of cyclohexane is necessary to overcome this low-efficiency process.Therefore,we have developed a cobalt-nitrogen co-doped porous sphere catalyst,Co-NC-x(x is the Zn/Co molar ratio,where x=0,0.5,1,2,and 4)by pyrolyzing resorcinol-formaldehyde resin microspheres.It achieved 88.28%cyclohexanone and cyclohexanol selectivity and a cyclohexane conversion of 8.88%under Co-NC-2.The results showed that the introduction of zinc effectively alleviated the aggregation of Co nanoparticles and optimized the structural properties of the material.In addition,Co0 and pyridinic-N are proposed to be the possible active species,and their proportion efficiently increased in the presence of Zn^(2+)species.In this study,we developed a novel strategy to design highly active catalysts for cyclohexane oxidation.

Preparation of biomass-derived carbon loaded with MnO_(2) as lithium-ion battery anode for improving its reversible capacity and cycling performance

Biomass-derived carbon materials for lithiumion batteries emerge as one of the most promising anodes from sustainable perspective.However,improving the reversible capacity and cycling performance remains a long-standing challenge.By combining the benefits of K2CO_(3) activation and KMnO_(4) hydrothermal treatment,this work proposes a two-step activation method to load MnO_(2) charge transfer onto biomass-derived carbon(KAC@MnO_(2)).Comprehensive analysis reveals that KAC@MnO_(2) has a micro-mesoporous coexistence structure and uniform surface distribution of MnO_(2),thus providing an improved electrochemical performance.Specifically,KAC@MnO_(2) exhibits an initial chargedischarge capacity of 847.3/1813.2 mAh·g^(-1) at 0.2 A·g^(-1),which is significantly higher than that of direct pyrolysis carbon and K2CO_(3) activated carbon,respectively.Furthermore,the KAC@MnO_(2) maintains a reversible capacity of 652.6 mAh·g^(-1) after 100 cycles.Even at a high current density of 1.0 A·g^(-1),KAC@MnO_(2) still exhibits excellent long-term cycling stability and maintains a stable reversible capacity of 306.7 mAh·g^(-1) after 500 cycles.Compared with reported biochar anode materials,the KAC@MnO_(2) prepared in this work shows superior reversible capacity and cycling performance.Additionally,the Li+insertion and de-insertion mechanisms are verified by ex situ X-ray diffraction analysis during the chargedischarge process,helping us better understand the energy storage mechanism of KAC@MnO_(2).

基于热溶质对流及晶粒运动的柱状晶-非球状等轴晶混合三相模型

基于Eulerian-Eulerian方法,阐述了简化枝晶状等轴晶、柱状晶以及金属液三相完全混合的凝固模型.模型考虑了等轴晶的移动及柱状晶对等轴晶的捕获,跟踪了柱状晶尖端的位置并考虑了等轴晶和柱状晶的相互竞争生长,因此该模型具备了预测柱状晶向等轴晶转变(CET)的能力;为了在不过量增加计算量的前提下提高模型的精度,模型对等轴晶采取了简单的枝晶化处理,即采用简化方法描述等轴晶包络线内固相分数.分别模拟了3.25和25 t钢锭的凝固过程,成功预测了大型钢锭凝固过程所形成的底部锥形负偏析、"类-A型"偏析以及CET等现象.分析认为长细形状铸锭中出现的顶部负偏析区,是由于凝固后期所形成的局部小钢锭及等轴晶在其内部的沉积聚集而成.

Bi2WO6 quantum dot-intercalated ultrathin montmo- rillonite nanostructure and its enhanced photocatalytic performance

The kinetic competition between electron-hole recombination and water oxidation is a key limitation for the development of efficient solar water splitting materials. In this study, we present a solution for solving this challenge by constructing a quantum dot-intercalated nanostructure. For the first time, we show the interlayer charge of the intercalated nanostructure can significantly inhibit the electron-hole recombination in photocatalysis. For Bi2WO6 quantum dots （QDs） intercalated in a montmorillonite （MMT） nanostructure as an example, the average lifetime of the photogenerated charge carriers was increased from 3.06 μs to 18.8 Ds by constructing the intercalated nanostructure. The increased lifetime markedly improved the photocatalytic performance of Bi2WO6 both in solar water oxidation and environmental purification. This work not oMy provides a method to produce QD-intercalated ultrathin nanostructures but also a general route to design efficient semiconductor-based photoconversion materials for solar fuel generation and environmental purification.

Distributions of Electromagnetic Fields and Forced Flow and Their Relevance to the Grain Refinement in Al–Si Alloy Under the Application of Pulsed Magneto-Oscillation

Distributions of electromagnetic fields and induced forced flow inside a metal melt are crucial to understand the grain refinement of the metal driven by pulsed magneto-oscillation(PMO).In the present study,PMO-induced electromagnetic fields and forced flow in Ga-20 wt%In-12 wt%Sn liquid metal have been systematically investigated by performing numerical simulations and corresponding experimental measurements.The numerical simulations have been confirmed by magnetic and melt flow measurements.According to the simulated distribution of electromagnetic fields under the application of PMO,the strongest magnetic field,electric eddy current and Lorentz force with inward radial direction inside the melt are concentrated adjacent the sidewall of cylindrical melt at the cross section of middle height of coil.As a result,a global forced flow throughout the whole cylindrical column filled with Ga-20 wt%In-12 wt%Snmelt is initiated with a flow structure of two pair of symmetric vortexring.The PMO-induced electromagnetic fields and forced flow in Al-7 wt%Si melt have been numerically simulated.The contribution of electromagnetic fields and forced flow to the grain refinement of Al-7 wt%Sialloy under the application of PMO is discussed.It indicates that the forced flow may play a key role in the grain size reduction.