Simulation of FCC riser flow with multiphase heat transfer and cracking reactions

A validated Computational Fluid Dynamics (CFD) code ICRKFLO was developed for simulations of three-dimensional three-phase reacting flows in Fluid Catalytic Cracking (FCC) riser reactors. It calculates the product yields based on local flow properties by solving the fundamental conservation principles of mass, momentum, and energy for the flow properties associated with the gas, liquid, and solid phases. Unique phenomenological models and numerical techniques were developed specifically for the FCC flow simulation. The models include a spray vaporization model, a particle-solid interaction model, and an interfacial heat transfer model. The numerical techniques include a time-integral approach to overcome numerical stiffness problems in chemical kinetics rate calculations and a hybrid hydrodynamic-kinetic treatment to facilitate detailed kinetics calculations of cracking reactions. ICRKFLO has been validated with extensive test data from two pilot and one commercial FCC units. It is proven to be useful for advanced development of FCC riser reactors.Dedicated to the memory of Dr. Shen-Lin Chang for his outstanding contributions.This work was supported by U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy and the Office of Industrial Technologies, under Contract W-31-109-ENG-38. The authors are indebted to the refining industrial participants for the technical discussions and the exchange of information.     

催化裂化原位降硫助剂的制备及其性能研究

采用溶胶-凝胶法制备具有介孔结构的降硫基质材料，选择具有降硫选择性的活性元素对合成的基质材料进行改性处理，考察不同的改性方法对制得的催化裂化原位降硫助剂性能的影响，并对基质材料和降硫助剂的结构进行表征。采用美国进口的ACE-R小型催化裂化评价装置将降硫助剂与催化裂化催化剂匹配进行性能评价，在不改变原催化裂化产品分布和产品性质的同时，降低原料的总硫含量，总硫降低可达40％以上。     

Experimental investigation of the hot cracking mechanism in welds on the microscopic scale

The results of the accurate experimental observations on binary Al-Si alloys are presented, which clearly demonstrate that the solidification cracking is a result of the accumulation of macroscopic tensile displacement in aβmicroscopic intergranular liquid film of segregates at the final stage of the weld metal solidification. The reconstructed mechanism of crack initiation provides a clear phenomenological interrelation between the cracking susceptibility, parameters of the welding process and properties of the base and filler material. The correspondent numerical model takes into account the effects of displacement accumulation as well as the influence of thermo-dynamical and thermo-mechanical properties of the welded material. It is successfully applied for development of technological means for elimination of the solidification cracking during welding of aluminium alloys AA6056, such as a multi-beam welding.     

Numerical investigation of effects of particle shape on dispersion in an isotropic turbulent flow

To investigate the effects of particle shape on the dispersion in an isotropic turbulent flow, herein two direct numerical simulations are performed. The six degrees of freedom motion of spherical and spheroidal particles in a vertical uniform flow and a gas-particle two-way isotropic turbulent flow. The former, which is investigated using a numerical simulation with the Arbitrary Lagrangian-Euler (ALE) method, shows that a spheroidal particle travels with rotating and oscillating motions, which significantly affect the pressure and the friction force on the particle’s surface. The trend of the fluid force acting on the spheroidal particle’s surface also oscillates and differs from that on a spherical particle. The time variation of the fluid force on the spheroidal particle is modeled in the $C_D$ equation, which has a sine curve’s PDF relation with ${\mathit{Re}}_p$ and the particle’s maximum and minimum $C_D$ values. The latter simulation examines the effects of the particle shape on the dispersion with the motion model developed above. The particle’s dispersion behavior, which is analyzed by the statistical variable D and the Radial Distribution Function (RDF), shows that the dispersion motion is markedly affected by particle’s sphericity, especially for particles with a relatively small sphericity. The results suggest that this difference can influence ignitability, flammability, and the concentration of combustible gases released by particles, and requires further study.     

客车空调车室气流组织数值模拟分析

以空调客车车室气流组织为研究对象,建立了三维空气流动与传热的物理模型和数学模型,采用计算流体动力学软件Fluent对气流组织进行数值模拟,应用RNG k-ε两方程紊流模型和SIMPLE算法求解控制方程,得到了考虑车内热负荷和太阳辐射时的车内空气温度和速度分布模拟结果,分析了影响速度场和温度场的因素.研究结果为改善车室熟环境提供了理论依据,对客车空调气流组织的优化设计有指导作用.     

冬季最不利情况下车间气流组织数值模拟

气流组织是控制、安排空调区域内空气流动过程的技术,其优劣直接影响室内的空调效果,而室内气流组织与送风温度的大小有直接关系。本文以子午胎车间02区为例,用CFD软件Airpak模拟它在冬季最不利情况下的室内温度场和速度场,并用比例系数指标对其设计效果进行评价。     

激光熔覆温度场和流场数值模拟研究现状和发展趋势

本文回顾了己报道过的激光重熔和激光熔覆熔池温度场和流场的数值模拟，重点评述了激光重熔和激光熔覆熔池温度场及流场数值模拟的数学物理模型和自由表面处理方法，并对这一领域今后的发展提出了自己的看法。     

Numerical simulation of hydrodynamic behaviors in a gas-solids dense downer reactor

A Eulerian-Eulerian model incorporating the kinetic theory of granular flow was adopted to simulate the gas-solids flow behaviors in a dense downer below a conventional downer, which could be used for the further pyrolysis of coal and/or decomposition of tar on the generated char before the char and tar are completely separated in a triple-bed combined circulating fluidized bed (TBCFB) system. The high solids holdup in the dense downer can enhance the heat transfer to completely pyrolyze coal as well as decompose the heavy tar, avoiding the negative impact of pyrolysis products on char gasification. In order to obtain the optimal structural parameters and operating conditions and evaluate the performance of this dense downer, the influences of downer diameter, cone angle and solids mass flux on the hydrodynamic behaviors were investigated in details. The results demonstrate that the solids holdup in the dense downer can be increased, however, the maximum solids holdup is limited to approximately 0.4 owing to the ultimate carrying capacity. Moreover, it is found that there is a peak solids holdup in the annular region near the wall whereas many particles concentrate at the center in the high-density operation states. Meanwhile, the unique solids radial distribution could be caused by the radial movement of particles. Moreover, the intense collisions and turbulence caused by high velocity could inhibit agglomerates, which should be benefit for the heat transfer. It is expected that these results could offer a guidance for the design of such a dense downer for effective improvement of the efficiency of the pyrolyzer.     

Effect of tempering treatment on hydrogen-induced cracking in high-strength steel

The fracture characteristics of high-strength steel ASTM A-490 under a hydrogen environment were investigated, with special emphasis placed on changes in fracture characteristics due to a tempering treatment at temperatures from 200 to 400 °C. A mechanical test was performed on cathodically charged specimens subjected to a constant load. Experimental analyses show that tempering treatment in the range from 200 to 400 °C does not alter the essential nature of delayed fracture due to crack growth. However, the role of intergranular (IG) cracking becomes prominent in the subcritical crack growth period with an increase in the tempering temperature to 400 °C. This development of IG cracks in the subcritical crack growth period is uniquely dependent on the tempering treatment performed in the tempering range from 250 to 400 °C. Furthermore, an increase in the fraction of the IG facet in the subcritical crack growth area is dependent on the increase in the stress intensity at the crack tip in those specimens tempered at 300 and 400 °C.     

Simulation of microstructure and liquation cracking in 7017 aluminium alloy

Welding in a 7000 series aluminium alloy can lead to the development of a white zone microstructure and liquation cracking in the heat affected zone adjacent to the fusion boundary. A Gleeble 1500 thermomechanical system has been used to study the conditions associated with damage development. A range of simulations has been carried out covering thermal and thermomechanical conditions typically encountered during weld manufacture. Results show that both the white zone microstructure and liquation cracking can be simulated at a sufficient scale to permit full characterisation in laboratory testpieces. Data analysis has defined and mapped the stress and temperature conditions leading to crack initiation. This evaluation demonstrates that the susceptibility for cracking is minimised by increasing the cooling rate following weld manufacture.     

Numerical investigation on the hydrodynamic performance of amphibious wheeled armored vehicles

ABSTRACT

Wheeled armored vehicles (WAVs) are designed for military applications, but they are frequently used in special disaster relief missions during floods caused by severe global climate change. To tackle threats arising from environmental change, developing WAVs with amphibious functions will inevitably become a trend in the future. The purpose of this study is to investigate the hydrodynamic performance of WAVs. An existing WAV model is adopted as a starting point, and computational fluid dynamic (CFD) techniques are used for performing analyses. This study analyzes the relationship between the configuration of a WAV and the sailing resistance. Two computation modes are associated with CFD used for flow simulation around the vehicles: the relative motion and absolute motion computation modes. The results of the simulations obtained through these two modes have been discussed and compared to develop an efficient tool for performing hydrodynamic performance analysis of amphibious wheeled armored vehicles (AWAV).     

Numerical simulation of mechanical controlling parameters for Type IV cracking on the welding joints of martensitic heat-resistant steel

The maximum principal stress, von Mises equivalent stress and equivalent creep strain in the welding joint of martensitic heat-resistant steel (9Cr1MoVNb) are simulated by finite-element method (FEM) under the condition of 600°C and applied stress of 80 MPa. The results show that the maximum principal stress and von Mises equivalent stress are high on the curved points of two sides of the groove face near the fine-grain heat-affected zone (HAZ). The creep strain mainly concentrates in the fine-grain HAZ; the maximum creep strain locates in the bottom of fine-grain HAZ of specimen. The stress triaxiality in the fine-grain HAZ is maximum, and creep cracking occurs because of the intensive constrain of base metal and weld. The simulation result is good in agreement with those of crack initiation site and propagation path by using the stress triaxiality as the mechanical controlling parameter of weld joint of martensite heat-resistant steel. Therefore, it is reasonable that the stress triaxiality is used for analysis initiation and propagation of Type IV cracking in the fine-grain HAZ.     

Evaluation of stress corrosion cracking and hydrogen embrittlement in an API grade steel

Stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of pipeline steels in contact with soil was investigated. Different soils were prepared in order to determine their physical, chemical and bacteriological characteristics. Slow strain rate testing was carried out by using aqueous extracts from soil samples and NS4 standard solution. Stress vs. strain curves of API 5L grade X46 steel were obtained at different electrode potentials (E_corr, 100 mV below E_corr and 300 mV below E_corr) with 9 × 10⁻⁶ s⁻¹ and 9 × 10⁻⁷ s⁻¹ strain rate. In addition, the hydrogen permeation tests were carried out in order to evaluate the susceptibility of hydrogen penetrates into theses steels. The results demonstrated the incidence of cracking and their dependence on the potential imposed. In that case, cracking occurred by stress corrosion cracking (SCC) and the hydrogen embrittlement (HE) had an important contribution to cracking initiation and propagation. Cracking morphology was similar to the SCC reported on field condition where transgranular cracking were detected in a pipeline collapsed by land creeping. It was important to point out that even under cathodic potentials the material showed the incidence of secondary cracking and a significant reduction of ductility.     

纤维增强复合材料界面脱层和基体裂纹的模拟分析

基于Ghosh提出的Voronoi单元有限元方法,构造能同时反映纤维增强复合材料界面脱层和基体裂纹扩展的单元(X-VCFEM单元);应用界面力学理论和断裂力学理论,建立界面脱层、界面裂纹扩展方向和基体裂纹扩展的判断准则;结合网格重划分技术,模拟分析了只含有一个夹杂时界面脱层和基体裂纹扩展的过程,并通过与传统有限元计算结果的比较,验证X-VCFEM单元的可靠性和有效性;同时,模拟分析含任意随机分布夹杂的纤维增强复合材料界面脱层和基体裂纹的产生和扩展过程。结果表明：应用该方法模拟复杂多相复合材料裂纹问题具有计算速度快和精度高的优越性。     

Numerical study on the performances of steam-jet vacuum pump at different operating conditions

A mathematic model based on realizable k-? turbulence model for transonic flow was proposed to investigate the mixing flow behaviours of primary and secondary fluids in steam-jet vacuum pump and the affections to the pumping performances. The simulation was carried out to predict the static pressure distribution among mixing chamber wall by a commercial computational fluid dynamics (CFD) code FLUENT 6.2. Close agreements between the predicted results and experimental data validated the present theoretical model. Using the present approach, the velocity vectors and Mach number profiles in mixing chamber at different back pressures and the secondary fluid pathlines and mass flux profiles at different suction pressures were predicted. It is found that there are swirls separated from secondary fluid near the wall and the velocity of secondary fluid was fallen down obviously when the back pressure was bigger than critical back pressure. The above two factors lead to the entrainment ratio (E_m) reduced rapidly. It is also found that the mass flux increased with the increasing of suction pressures and made the entrainment ratios increased. The prediction results show that the pressure ratio (K) is a dominant position in affecting the pump's performances.     

Numerical investigation of matrix cracking propagation in cross‐ply laminated composites subjected to three‐point bending load using concurrent multiscale model

The purpose of the present study is to analyze fiber‐matrix debonding and induced matrix cracking formation as two major micromechanical damage modes in cross‐ply composite laminates using a two‐dimensional numerical approach. To this aim, the cross‐ply laminates containing 90‐degree layers are modeled, where the fibers are arranged randomly in transverse plies. Damage modes in this numerical model are simulated by the cohesive surface method. The performed analyses reveal that in the laminates with 90‐degree layers located in the outer positions, the primary micro damage mode is micro matrix cracking which is initiated from the fiber‐matrix debonding damage mode and will be followed by matrix cracking. The main benefit of the present study in comparison to other numerical methods is proposing a virtual test method for damage analysis of different cross‐ply laminates in which, the matrix cracking formation will emerge physically in a random and antisymmetric pattern similar to the experimental observations.     

结霜工况下热泵空调器性能的数值模拟

本文对热泵空调器在结霜工况下的运行性能进行了理论模拟,建立了热泵空调器制冷系统稳态分布参数模型和结霜过程的动态分布参数模型.在系统模型建立中把结霜过程视为准稳态过程.计算结果表明在霜刚开始形成时,有助于增大管壁和空气之间的换热系数,当霜层达到一定厚度时热泵的制热能力,性能系数等讯速下降.经与其他已发表的文献比较计算结果合理.     

钴系复合催化材料在费托反应前后的结构变化研究

钴系催化材料在费托合成中的反应已有较多研究文献,但对费托反应前后由于水热环境导致钴系催化材料发生结构变化的研究则很少。应用场发射扫描电子显微镜研究了3种新鲜制备的钴系复合催化材料的织构特征,应用粉末X射线衍射技术研究了费托反应前后3种钴系催化材料的结构变化;并且发现含有氧化铝成分的样品在经历费托反应的水热环境之后均在衍射角(2θ)为21.5和23.8°处出现新物相的衍射峰,即形成某种结晶性水合氧化铝;该新物相可能与被H2O氧化的钴物种发生反应生成无催化活性的Co Al2O4相而导致钴催化剂的衰减失活。     

Numerical modeling on simultaneous removal of mercury and particulate matter within an electrostatic precipitator

A computational fluid dynamics (CFD) model coupled with gas-particle mass transfer, electrohydrodynamic (EHD) effect, electric field, particle motion and particle charging is established to advance the understanding of combined particulate matter precipitation and mercury capture within industrial electrostatic precipitators (ESPs). The comparisons between experimental data and numerical results demonstrate that this model can reasonably predict the mercury removal efficiency by powdered sorbent injection (PSI). The mechanism of simultaneous removal of mercury and particulate matter is then discussed in detail by considering the complex interactions among multi-physics. The influences of particle size, mercury concentration, particle injection rate and the EHD effect are investigated. The simulation results indicate that the mercury removal process is primarily controlled by the sorbent particle residence time, surface area and mass transfer rate. Accordingly, reducing the size of sorbent particles (activated carbon) can promote mercury removal efficiency while decreasing the particle collection efficiency. Increasing the initial mercury concentration and adsorbent mass loading also benefit mercury adsorption by influencing the mass transfer rate and the surface area. The EHD effect plays important roles in mercury removal and particle collection by means of altering the flow patterns and particle migration. The two mechanisms of in-flight and wall-bounded mercury adsorption affected by ionic wind are also evaluated and some interesting phenomena are observed.     

Numerical simulation and experimental investigation on friction stir welding of 6061-T6 aluminum alloy

A modified three-dimensional model was established to simulate the friction stir welding of the 6061-T6 aluminum alloy. A detailed calculating method of the heat generation was proposed by taking account of the contact conditions between the tool and the work-piece. The results show that the heat mainly generated within the region close to the shoulder, the high temperature exists within the upper portion of the weld and decreases along the thickness direction. The strong material flow mainly occurs within the region around the tool and the material ahead of the tool sweeps toward the RS and finally deposits behind the tool. During this procedure the material is extruded to experience different shear orientations, and a defect-prone region exists in the region where material flow is weak. The temperature field and material flow behaviors predicted by the simulation method are in good agreement with the results obtained by the experiments.