Simulation of gas-solid flow characteristics of the circulating fluidized bed boiler under pure-oxygen combustion conditions

Under the pressure of carbon neutrality,many carbon capture,utilization and storage technologies have witnessed rapid development in the recent years,including oxy-fuel combustion(OFC)technology.However,the conventional OFC technology usually depends on the flue gas recirculation system,which faces significant investment,high energy consumption,and potential low-temperature corrosion problem.Considering these deficiencies,the direct utilization of pure oxygen to achieve particle fluidization and fuel combustion may reduce the overall energy consumption and CO_(2)-capture costs.In this paper,the fundamental structure of a self-designed 130 t·h^(-1) pure-oxygen combustion circulating fluidized bed(CFB)boiler was provided,and the computational particle fluid dynamics method was used to analyze the gas-solid flow characteristics of this new-concept boiler under different working conditions.The results indicate that through the careful selection of design or operational parameters,such as average bed-material size and fluidization velocity,the pure-oxygen combustion CFB system can maintain the ideal fluidization state,namely significant internal and external particle circulation.Besides,the contraction section of the boiler leads to the particle backflow in the lower furnace,resulting in the particle suspension concentration near the wall region being higher than that in the center region.Conversely,the upper furnace still retains the classic core-annulus flow structure.In addition to increasing solid circulation rate by reducing the average bed-material size,altering primary gas ratio and bed inventory can also exert varying degrees of influence on the gas-solid flow characteristics of the pure-oxygen combustion CFB boiler.

Electro-assisted photocatalytic reduction of CO_(2) in ambient air using Ag/TNTAs at the gas-solid interface

The direct conversion of atmospheric CO_(2) into fuel via photocatalysis exhibits significant practical application value in advancing the carbon cycle.In this study,we established an electro-assisted photocatalytic system with dual compartments and interfaces,and coated Ag nanoparticles on the titanium nanotube arrays(TNTAs)by polydopamine modification.In the absence of sacrificial agent and alkali absorption liquid conditions,the stable,efficient and highly selective conversion of CO_(2) to CO at the gas-solid interface in ambient air was realized by photoelectric synergy.Specifically,with the assistance of potential,the CO formation rates reached 194.9μmol h^(−1) m^(−2) and 103.9μmol h^(−1) m^(−2) under ultraviolet and visible light irradiation,respectively;the corresponding CO_(2) conversion rates in ambient air were 30%and 16%,respectively.The excellent catalytic effect is mainly attributed to the formation of P–N heterojunction during the catalytic process and the surface plasmon resonance effect.Additionally,the introduction of solid agar electrolytes effectively inhibits the hydrogen evolution reaction and improves the electron utilization rate.This system promotes the development of photocatalytic technology for practical applications and provides new insights and support for the carbon cycle.

Numerical Simulation and Optimization of the Gas-Solid Coupled Flow Field and Discharging Performance of Straw Crushers

The quality of crushing,power consumption,and discharging performance of a straw crusher are greatly influenced by the characteristics of its internalflowfield.To enhance the straw crusher’sflowfield properties and improve the efficiency with which crushed material is discharged,first,the main structural parameters influencing the airflow in the crusher are discussed.Then,the coupled gas-solidflowfield in the straw crusher is numerically calculated through solution of the Navier-Stokes equations and application of the discrete element method(DEM).Finally,the discharge performance index of the crusher is examined through detailed analysis of the crushed material dynamics.Additionally,a multi-island genetic algorithm is used to optimize the structure and operational factors that have significant effects on the discharge performance.With optimization,the accumulation rate of crushed materials in the bottom region of the straw crusher decreases by 20.08%,and the massflow rate at the discharge outlet increases by 11.63%.

Identifying the enhancement mechanism of Al/MoO_(3) reactive multilayered films on the ignition ability of semiconductor bridge using a one-dimensional gas-solid two-phase flow model

Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge(SCB)during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices.In this study,a one-dimensional(1D)gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO_(3) RMFs.In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process,the heat release of chemical reaction in RMFs was used as an internal heat source in this model.It is found that the exothermal reaction in RMFs improved the ignition performance of SCB.In the process of plasma rapid condensation with heat release,the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle,which accelerated the expansion of hot plasma,and heated the solid charge particle as well as gas phase region with low temperature.In addition,it made up for pressure loss in the gas phase.During the plasma dissipation process,the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle,making the surface temperature of the charge particle,gas pressure,and gas temperature rise continuously.This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices.

One‑Step Gas-Solid‑Phase Diffusion‑Induced Elemental Reaction for Bandgap‑Tunable Cu_(a)Agm_(1)Bim_(2)I_(n)/CuI Thin Film Solar Cells

Lead-free inorganic copper-silver-bismuth-halide materials have attracted more and more attention due to their environmental friendliness,high element abundance,and low cost.Here,we developed a strategy of one-step gas-solid-phase diffusioninduced reaction to fabricate a series of bandgap-tunable Cu_(a)Agm_(1)Bim_(2)I_(n)/CuI bilayer films due to the atomic diffusion effect for the first time.By designing and regulating the sputtered Cu/Ag/Bi metal film thickness,the bandgap of Cu_(a)Agm_(1)Bim_(2)I_(n)/CuI could be reduced from 2.06 to 1.78 eV.Solar cells with the structure of FTO/TiO_(2)/Cu_(a)Agm_(1)Bim_(2)I_(n)/CuI/carbon were constructed,yielding a champion power conversion efficiency of 2.76%,which is the highest reported for this class of materials owing to the bandgap reduction and the peculiar bilayer structure.The current work provides a practical path for developing the next generation of efficient,stable,and environmentally friendly photovoltaic materials.

Gas-solid catalytic reactions over ruthenium-based catalysts

Ruthenium （Ru）‐based catalysts are widely employed in several types of gas‐solid reactions because of their high catalytic activities. This review provides theoretical research on Ru‐based catalysts and an analysis of their basic properties and oxidation behavior. There is particular emphasis on Ru‐catalyzed gas‐solid catalytic reactions, including the catalytic oxidation of VOCs, preferential oxidation of CO, synthesis of ammonia, oxidation of HCl and partial oxidation of CH4. Recent litera‐ture on catalysis is summarized and compared. Finally, we describe current challenges in the field and propose approaches for future development of Ru‐based catalysts.

α-硫辛酸联合MIRE治疗对糖尿病足部自主神经病变患者血Hcy的影响

目的探讨应用α-硫辛酸联合单频红外线能(MIRE)干预对糖尿病自主神经病变(DAN)患者血清同型半胱氨酸(Hcy)的影响。方法将2型糖尿病(DM)患者132例分为DAN组和NDAN组,以28例健康体检者作为健康对照组,应用α-硫辛酸联合MIRE治疗DAN组中高Hcy血症患者,2周后观察血液中Hcy浓度,并通过欧米诺诊断膏贴评估自主神经病变的改善程度。结果 DAN组、NDAN组及健康对照组血Hcy浓度分别为(16.82±4.21)μmol/L、(12.42±3.06)μmol/L和(10.72±3.24)μmol/L,两两比较差异均有统计学意义(P<0.05)。经α-硫辛酸联合MIRE干预后,高Hcy组患者血浆Hcy水平由(19.22±2.45)μmol/L下降至(16.10±2.68)μmol/L(P<0.05),左足欧米诺膏贴完全变色时间由(24.81±7.60)min下降至(19.25±5.42)min(P<0.05),右足由(23.44±7.40)min下降至(17.63±5.11)min(P<0.05)。结论 DAN组患者血清Hcy水平明显高于NDAN组患者,α-硫辛酸联合MIRE干预后可降低患者血清Hcy水平,改善患者足部自主神经功能。

泥炭沼泽退化过程中枯落物的分解速率及碳、氮、磷释放动态特征

为明确湿地退化过程中枯落物分解动态和营养元素变化趋势,本研究采用空间替代时间的方法选取未退化原始沼泽(UP)、轻度退化沼泽(LDP)、重度退化沼泽(HDP)和排水造林地(DA)内的枯落物为研究对象,探讨泥炭沼泽退化过程中枯落物的分解速率及碳、氮、磷释放动态特征。结果表明,不同退化阶段枯落物失重率、分解速率及营养元素相对归还指数均具有显著的差异。0~90 d内各样地枯落物的分解速率和失重率较高,分解120 d后,UP、LDP、HDP和DA样地枯落物的失重率分别为初始质量的15.31%、11.69%、7.16%和20.11%,总体表现为DA样地的分解速率最快。碳相对归还指数(CRRI)依次为17.32%、16.72%、4.22%和20.17%,氮相对归还指数(NRRI)依次为-0.86%、-25.22%、28.03%和5.15%,磷相对归还指数(PRRI)依次为-4.57%、-97.03%、6.19%和-29.56%。总体上各样地碳元素表现为净释放模式;HDP和DA样地枯落物氮元素总体上表现为净释放模式,LDP表现为净积累模式;LDP、HDP和DA样地枯落物磷元素总体上表现为净积累模式,UP表现为净释放模式。

Review of gas-solid two phase flow rate-concentration detection technology

The indirect detection method basic principle of rate and concentration,application range and research results on gassolid two phase flow were discussed.The present development situation and the existing problems of rate and concentration detection technology were analyzed and summarized.Emphatically analyzed the existing problems in the industrial application and research status of electrostatic method in measuring phase concentration.Design criterion of electrostatic phase concentration sensor is given,the superiority and wide industrial application prospect of the sensor used for phase concentration measurement are clarified.

A Case Study Applying Mesoscience to Deep Learning

In this paper,we propose mesoscience-guided deep learning(MGDL),a deep learning modeling approach guided by mesoscience,to study complex systems.When establishing sample dataset based on the same system evolution data,different from the operation of conventional deep learning method,MGDL introduces the treatment of the dominant mechanisms of complex system and interactions between them according to the principle of compromise in competition(CIC)in mesoscience.Mesoscience constraints are then integrated into the loss function to guide the deep learning training.Two methods are proposed for the addition of mesoscience constraints.The physical interpretability of the model-training process is improved by MGDL because guidance and constraints based on physical principles are provided.MGDL was evaluated using a bubbling bed modeling case and compared with traditional techniques.With a much smaller training dataset,the results indicate that mesoscience-constraint-based model training has distinct advantages in terms of convergence stability and prediction accuracy,and it can be widely applied to various neural network configurations.The MGDL approach proposed in this paper is a novel method for utilizing the physical background information during deep learning model training.Further exploration of MGDL will be continued in the future.

Numerical Simulation of Wet Particles Motion in a Vertical Powder Dryer

In this study,the motion of wet particles in the drying unit of a vertical powder dryer is investigated by using a Discrete element method(DEM)coupled with a liquid bridge force.In particular,by varying parameters such as the particle mass flow rates,the superficial gas velocities,and superficial gas temperatures,the influence of the moisture content on the flow behavior is examined.The results show that when the moisture content increases,the mean particle velocity decreases while the bed mean solid“holdup”and the mean residence time(MRT)of particles grow.It is also found that the local solid holdup is relatively higher in the near-wall region and decreases towards the near-fluid region.Two regression models are introduced accordingly for the mean particle velocity and the bed mean solid holdup by means of the RSM-BBD(Response surface methodology-Box-Behnken design)method to obtain the optimal combination of parameters for flooding prevention.Finally,the optimal results are compared with numerical observations.As the relative error is less than 10%,this demonstrates that the proposed methodology can accurately describe the particle flow dynamics in the drying unit.

Dynamics of dissolved organic carbon in the mires in the Sanjiang Plain,Northeast China

Mires in boreal area had proved to be an important dissolved organic carbon （DOC） reserve for the sensitivity to climate change and human interfering. The study was focused on the temporal and spatial dynamics and controlling factors of DOC in a seasonallywaterlogged mire （SLM） and perennially-waterlogged mire （PLM） in the Sanjiang Plain, Northest China. In the two mires, DOC concentrations in both surface water and upper soil strata experienced pronounced seasonal variation. DOC concentrations in the surface waters were the greatest and averagely was 47.82 in SLM and 34.84 mg/L and PLM, whereas that in soil water at 0.3-m depth had little difference （20.25 mg/L in SLM and 26.51 mg/L in PLM）. Results revealed that DOC concentrations declined 5-8 times vertically from the surface down to groundwater. DOC in the groundwater only was in a very small part with the average concentration of 5.18 mg/L. In relation to the surface water, DOC concentrations varied positively with temperature just before 8 August, and only in early spring and later autumn DOC concentrations exhibited identifiable spatial trends along with standing water depths in PLM. It was supposed that the influences from standing water depth took effect only in conditions of low temperature, and temperature should be the most powerful factor controlling DOC dynamics in the mires. Redox potential （Red） showed negative relationship with DOC values while total nitrogen （TN） and the majority of free ions in the soil solution exhibited no relationship. High soil TOC/TN ratio and low redox potentials also led to DOC accumulation in the mires in the Sanjiang Plain.

Discrete Particle Simulation of Gas-Solid Flow in Air-Blowing Seed Metering Device

In this paper,the gas and seed flow characters in the air-blowing seed metering device are investigated by using the coupled computational fluid dynamics and discrete element method(CFD-DEM)in three dimensions(3D).The method of establishing boundary model based on the computer-aided design(CAD)drawing,has been used to build the boundary model of seed metering device.The 3D laser scanning technique and multi-element method are adopted to establish the particle model.Through a combined numerical and experimental effort,using 3D CFD-DEM software,which is based on the in-house codes,the mechanisms governing the gas and solid dynamic behaviors in the seed metering device have been studied.The gas velocity field and the effect of different rotational speeds and air pressures on the seeding performance and particle velocity have been studied,similar agreements between numerical and experimental results are gained.This reveals that the 3D CFD-DEM model established is able to predict the performance of the air-blowing seed metering device.It can be used to design and optimize the air-blowing seed metering device and other similar agriculture devices.

Modularized dry coal beneficiation technique based on gas-solid fluidized bed

A 40-60 t/h modularized dry coal beneficiation process with a novel method to control the bed was designed around a gas-solid fluidized bed separator. Furthermore, the hydrodynamics of medium-solids consisting of wide-size-range magnetite powder （0.3-0.06 ram） and 〈1 mm fine coal were numerically studied. The simulation results show that the fluidization performance of the wide-size-range medium-solid bed is good. The separation performance of the modularized system was then investigated in detail using a mixture of 〈0.3 mm magnetite powder （mass fraction of 0.3-0.06 mm particles is 91.38 %） and 〈1 mm fine coal as solid media. The experimental results show that at separation densities of 1.33 g/cm^3 or 1.61 g/cm^3, 50-6 mm coal can be separated effectively with probable error, E, values of 0.05 g/cm^3 and 0.06 g/cm^3, respectively. This technique is beneficial for saving water resources and for the clean utilization of coal.

Modeling of gas-solid flow in a CFB riser based on computational particle fluid dynamics

A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport（DPT） regime and a fast fluidization（FF） regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.

Flow Behaviors of Gas-Solid Injector by 3D Simulation with Kinetic Theory of Granular Flow

A computational study on the flow behavior of a gas-solid injector by Eulerian approach was carried out. The gas phase was modeled with k-ε turbulent model and the particle phase was modeled with kinetic theory of granular flow. The simulations by Eulerian two-fluid model （TFM） were compared with the corresponding results by discrete element method （DEM） and experiments. It was showed that TFM simulated results were in reasonable agreement with the experimental and DEM simulated results. Based on TFM simulations, gas-solid flow pattern, gas velocity, particle velocity and the static pressure under different driving jet velocity, backpressure and convergent section angle were obtained. The results showed that the time average axial gas velocity sharply decreased and then slightly increased to a constant value in the horizontal conveying pipe. The time average axial particle velocity increased initially and then decreased, but in the outlet region of the convergent section the particle velocity remarkably increased once more to the maximal value. As a whole, the static pressure distribution change trends were found to be independent on driving gas velocity, backpressure and convergent section angle. However, the static pressure increased with increase of convergent section angle and gas jet velocities. The difference of static pressure to backpressure increased with increasing backpressure.

Numerical Simulation on Gas-Solid Two-Phase Turbulent Flow in FCC Riser Reactors(Ⅰ) Turbulent Gas-Solid Flow-Reaction Model

Gas-solid two-phase turbulent flows,mass transfer,heat transfer and catalytic cracking reactions areknown to exert interrelated influences in commercial fluid catalytic cracking(FCC)riser reactors.In the presentpaper,a three-dimensional turbulent gas-solid two-phase flow-reaction model for FCC riser reactors was devel-oped.The model took into account the gas-solid two-phase turbulent flows,inter-phase heat transfer,masstransfer,catalytic cracking reactions and their interrelated influence.The k-V-k_P two-phase turbulence modelwas employed and modified for the two-phase turbulent flow patterns with relatively high particle concentration.Boundary conditions for the flow-reaction model were given.Related numerical algorithm was formed and a nu-merical code was drawn up.Numerical modeling for commercial FCC riser reactors could be carried out with thepresented model.

Gas-solid coupling laws for deep high-gas coal seams

A better understanding of gas-solid coupling laws for deep, gassy coal seams is vital for preventing the compound dynamic disasters such as rock burst and gas outburst. In this paper, a gas-solid coupling theoretical model under the influence of ground stress, gas pressure, and mining depth is established and simulated by using COMSOL Multiphysics software. Research results indicate that under the influence of factors such as high ground stress and gas pressure, the mutual coupling interaction between coal and gas is much more significant, which leads to the emergence of new characteristics of gas compound dynamic disasters. Reducing the ground stress concentration in front of the working face can not only minimize the possibility of rock burst accidents, which are mainly caused by ground stress, but also can weaken the role of ground stress as a barrier to gas, thereby decreasing the number of outburst accidents whose dominant factor is gas. The results have a great theoretical and practical significance in terms of accident prevention, enhanced mine safety, disaster prevention system design, and improved accident emergency plans.

Experimental Study on Gas-Solid Mass Transfer in Circulating Fluidized Beds

This study is devoted to gas-solid mass transfer behavior inheterogeneous two-phase flow. Experiments were carried out in a coldcirculating fluidized bed of 3.0 m in height and 72 mm in diameterwith naphthalene particles. Axial and radial distributions ofsublimated naphthalene concentration in air were measured with an on-line concentration monitoring system HP GC-MS. Mass transfercoefficients were obtained under various operating conditions,showing that heterogeneous flow structure strongly influences theaxial and radial profiles of mass transfer coefficients.

Mechanisms for Particle Clustering in Upward Gas-Solid Flows

Two-dimensional unsteady cocurrent upward gas-solid flows in the vertical channel are simulated and the mechanisms of particles accumulation are analyzed according to the simulation results. The gaseous turbulent flow is simulated using the large eddy simulation (LES) method and the solid phase is treated using the Lagrangian approach, and the motion of the gas and particles are coupled. The formation of clusters and the accumulation of particles near the wall in dense gas-solid flows are demonstrated even if the particle-particle collisions were ignored. It is found that a cluster grows up by capturing the particles in the dilute phase due to its lower vertical velocity. By this way the small size clusters can evolve to large-scale clusters. Due to the interaction of gas and particles, the large-scale vortices appear in the channel and the boundary layer separates from the wall, which results in very high particle concentration in the near wall region and a very large-scale cluster formed near the separation point.