白钨选矿尾水悬浮物人工湿地基质沉降模拟研究

人工湿地在运用过程中表现出对悬浮物良好的去除作用,但其去除机理和规律的研究却不够透彻。为了探究白钨选矿尾水悬浮物的去除效果及固体颗粒在人工湿地基质中的沉降规律,选择花岗岩或石英,构建水平潜流人工湿地系统,考察水力坡度对悬浮物去除效果的影响,分析沉积颗粒粒径。结果表明:人工湿地对悬浮物有良好的去除效果;6～12 mm的花岗岩作填料,水力坡度为0.25%时,去除效率在60%以上,出水中悬浮物的含量在40 mg/L左右;预处理的絮凝过程将无法沉降的2μm以下的颗粒物从63%降至20%以下,颗粒中值粒径由1.64μm扩大至3.97μm;沉积物粒径分布在3.5～23.6μm间,沉降距离可依据Stokes定律推算。     

氧煤燃烧熔分炉炉料沉降与传热行为数值模拟

 回转窑预还原-氧煤燃烧熔分炼铁工艺直接使用宽粒级的粉矿入炉,炉料颗粒经回转窑内煤气逆流换热和预还原后,通过沉降管到达氧煤燃烧熔分炉。为避免沉降区域内炉料颗粒冲刷炉壁、壁面堆积及气固传热不均现象,实现颗粒沉降与传热过程的耦合控制,最大限度降低炉料与熔池温度差,保证熔池熔炼稳定,达到良好的冶炼效果,利用计算流体力学-离散单元法(CFD-DEM)研究氧煤燃烧熔分炉熔池上部区域煤气流速和炉料粒径对炉料颗粒在逆流煤气作用下的沉降轨迹与传热行为的影响。数值模拟结果表明,随着煤气流速增大,炉料颗粒的沉降速度减小,煤气对小粒径炉料颗粒的作用尤为明显。煤气流速为1 m/s时,每种粒径的炉料颗粒沉降效果良好;煤气流速为2 m/s时,粒径为1.0、1.5、2.0 mm的炉料颗粒沉降效果相对较好;煤气流速为3 m/s时,粒径为1.5、2.0 mm的炉料颗粒能够顺利沉降。针对炉料颗粒传热行为,煤气流速越大,炉料粒径越小,则炉料颗粒的传热效果越好。综合炉料传热与沉降行为,粒径为1.0 mm左右的炉料颗粒在煤气流速为1和2 m/s作用下,炉料颗粒的沉降速度和传热情况均良好。     

喷吹颗粒镁铁水脱硫影响因素的数值模拟

在CFD软件平台上进行了青钢新区喷吹颗粒镁铁水脱硫影响因素的数值模拟,研究了载气流量、喷枪插入深度、喷嘴直径、喷嘴夹角对脱硫过程铁水罐内流场以及混匀死区的影响。结果表明,在原有工艺参数下,随载气流量适当减小、喷枪插入深度最大、喷嘴直径稍微增大和喷嘴夹角适当增大,均可改善铁水罐内速度场和湍动能的分布,减小混匀死区,增加停留时间。推荐的工艺参数为载气流量90 Nm~3/h、喷枪插入深度200 mm、喷嘴直径8 mm、喷嘴夹角60°~90°。     

文丘里供料器在粉体闪速煅烧装置中的应用研究

根据粉体闪速煅烧装置对气力输送供粉系统的要求,选择旋转叶片式供料器与文丘里供料器联合供料。测量了气源、接收室及输送管道压力等工艺参数,分析研究文丘里供料器的几何结构参数对接收室压力及供粉稳定性的影响规律。结果表明：在相同流量条件下,喷嘴尺寸的降低使得喷嘴处流速增加,有利于提高接收室的负压;节流比取0.5时,输粉管道截面处输粉速度均匀,可以减小管道阻力并提升接收室的负压;喷嘴出口到接收室的距离取20 mm时,接收室与负压区匹配度高,输粉稳定;输送介质流量应高于35 m³/h,可有效避免粉料沉降的现象。     

薄板坯连铸单流中间包流场的数学模拟

采用数值计算的方法模拟单流中间包内钢液流动行为。计算模拟了无控流装置,应用挡渣墙坝,以及导流隔墙时中间包内钢液流动分布、温度场。结果表明：中间包无控流装置易在中间包中下部形成贯穿流,不利于新旧钢液混合以及夹杂物去除;导流隔墙可使钢液充分上扬,夹杂物易为覆盖渣俘获,有利于夹杂物去除;加装控流装置后,湍动能在到达控流装置前加强,有利于小粒径夹杂聚合上浮;而湍动能在经过控流装置后减弱,有利于钢液平稳流入结晶器;导流隔墙与堰坝组合均可使中间包内钢液充分混合,温度均匀,进出口温差减小。     

1 850 mm×230 mm板坯连铸结晶器流场与温度场数值模拟

为研究连铸工艺参数对结晶器内部钢液的作用规律,对涟钢1 850 mm×230 mm板坯连铸结晶器流场和温度场进行了系统的数值模拟,研究了不同吹氩量(0～7 L/min)、不同水口浸入深度(110～150 mm)和不同拉速(0.9～1.2 m/min)对结晶器内钢液行为的综合影响。结果表明,随着吹氩量增加,自由液面的钢液流速和温度总体呈现降低的趋势;随着水口浸入深度增加,自由液面的钢液流速先降低后增加;随着拉速增加,自由液面的钢液流速增加;水口浸入深度和拉速对温度场的影响较小。当吹氩量为5 L/min、水口浸入深度为130 mm、拉速为0.9 m/min时,结晶器自由液面具有较小的钢液流速和湍动能,同时液面具有较好的温度均匀性。通过数值模拟研究,为合理选择结晶器相关工艺参数提供了理论依据。     

刚柔组合桨搅拌强化锰矿浸出数值模拟

通过CFD软件对以SO₂气体为还原剂的锰矿浸出过程进行数值模拟,对比刚性单桨、刚性双桨及刚柔组合桨对于气-固-液三相混合强化作用。通过对固相及气相浓度云图分析,比较三种不同结构配置的搅拌反应器对固体颗粒悬浮和气体分散的作用大小,并对搅拌反应器内宏观、介观及其微观混合性能通过轴向和纵向的速度、湍动能及湍动能耗散率进行对比分析。结果表明：刚柔组合桨流场内并未出现颗粒团聚、气体分散不均等现象,并在流场上部对于颗粒悬浮及气体分散作用明显要强于单轴单桨及单轴双桨;刚柔组合桨的宏观、介观及其微观混合性能的表现均优于单轴单桨及单轴双桨。     

选矿废水中悬浮物对磨矿和浮选影响的研究

为了考查选矿废水中悬浮物对磨矿和浮选作业的影响,将添加了悬浮物的清水作为实验用水,进行磨矿和浮选实验。实验结果表明,选矿废水中的悬浮物对磨矿和浮选作业产生影响,循环水中的悬浮物必须经处理后才能回用。     

T形中间包新型控流装置的模拟及试验

针对连铸生产过程中钢包长水口与中间包湍流控制器对中存在偏差的实际情况,基于八流T形连铸中间包,采用三维数值模拟方法研究了对中偏差对流场的影响;同时为减弱对中偏差的影响,设计了新型控流装置,并通过数值模拟和工业试验对其冶金效果进行了验证。研究结果表明,长水口与稳流器对中偏差为50 mm时,中间包流场明显恶化,冲击区液面流速和湍流强度大幅增加,大大增加了卷渣风险,且死区体积增加了4个百分点;而新型控制装置使冲击区最大湍动能降低50%,冲击区液面更加平稳,死区体积基本不变,B类、C类夹杂物的合格率提高约6%。     

吉恩镍业选矿厂工业废水循环利用生产实践

通过对选矿废水循环利用及现场生产问题的研究,通过混凝沉淀的方法去除了工业废水中的悬浮物、重金属离子和部分COD,实现了工业废水的零排放,阐述了选矿废水循环利用是降低选矿成本,提高矿山经济效益和社会效益的有效途径。     

Three-Dimensional Simulation on the Water Flow Field and Suspended Solids Concentration in the Rectangular Sedimentation Tank

A 3D computational fluid dynamics model for describing the water flow and suspended solids (SS) concentration distribution in a rectangular sedimentation tank is presented. The interfacial momentum transfer, buoyant forces, and the effect of sediment-induced density currents are considered. A convection-diffusion equation, which is extended to incorporate the sedimentation of activated sludge in the field of gravity, governed the mass transfer in the clarifier. The double-exponential law is used to describe the dependence of the settling velocity on the concentration. The results show that during the dynamic settling process of the sludge, the mud surface rose slowly, and a period of time later, the mud surface kept stability and reached dynamic equilibrium in the tank. The distribution of velocity along the z axis in the rectangular tank is not uniform, and the surface return flow is found. The turbulent kinetic energy is larger and dropped drastically in the inlet zone, while in the settling zone the turbulent kinetic energy is relatively small. Density current is formed, and the clear water zone, flocculation zone, lamella zone, and compression zone are found. Furthermore, under certain operational conditions, the influence of inlet baffle length on SS settling in the rectangular sedimentation tank is discussed. The prediction by the present model for liquid flow and SS concentration is confirmed by the experimental measurement in a rectangular sedimentation tank in Sweden reported by Larsen in 1977.     

Modeling of Class I Settling Tanks

Sedimentation is one of the earliest and most important unit operations in water and wastewater treatment. Conventional approaches for studying sedimentation of Class I settling tanks did not present enough information on suspended particle size distribution in the effluent. This information is very important for further treatment units such as filtration. In this research, a relatively simple and practical mathematical model is introduced to study sedimentation of non-uniform particle size in Class I settling tanks. The model is capable of providing such information as removal efficiency, size distributions in sludge and in effluent suspension, and thickness of bottom sludge. If desired removal efficiency is provided, the length of the tank can also be determined. Through numerical experiments, a sensitivity analysis was performed to examine the effects of tank dimensions, overflow rate, and detention time on the removal efficiency. Comparison with other models and a set of experimental data indicates a good agreement.     

Pollutant Transport and Mixing Zone Simulation of Sediment Density Currents

Prediction of water column concentrations of suspended sediment is often necessary for environmental impact assessment of point source industrial discharges. For example, in “flow lane” or “open water” disposal, suction dredges discharge large volumes of suspended sediment into shallow water disposal locations. A sediment density current mixing model is presented here as part of the D-CORMIX expert system for hydrodynamic simulation of mixing zone behavior. This density current model extends the CORMIX decision support system to simulate continuous negatively buoyant discharges with or without suspended sediment loads on a sloping bottom with loss of suspended particles by sedimentation. Sedimentation is modeled using Stokes settling for five particle size classes. Density current width and depth, trajectory, total solids, tracer concentration, dilution, and particle size concentration are predicted. In addition, location and widths of sediment deposits, accretion rates, including particle size fractions within the spoils deposit, are predicted. The model results are in good overall agreement with available field and laboratory data.     

Inclined Plate Settlers to Treat Storm-Water Solids

Many pollutants in storm-water runoff associate with the particulate fraction, as well as cause receiving water degradation themselves. Therefore, removing a substantial amount of the solids (such as all particles above a critical particle size) can reduce the concentrations of many pollutants. Enhanced sedimentation methods have been encouraged to reduce the footprint of treatment devices and meet the 80% suspended solids reduction goal established in many locations. Inclined plates/tube settlers, where overlapping plates result in large settling areas and small device footprints, treated multiple contaminants when operated in laminar flow conditions (Pitt et al. 1999). This project extends that work by investigating the potential of inclined plate settlers to treat runoff when Reynolds numbers ranged from 7.5 to 50,000. These settlers achieved high removals for particles with a density of sand over the range of Reynolds’ numbers. The influent-to-effluent median particle-size reduction in field testing was 80–11?μm.     

Assessment of Hydrodynamic Separators for Storm-Water Treatment

Hydrodynamic separators are proprietary underground devices designed to remove floatable debris (e.g., leaves, trash, oil) and to remove suspended solids from storm-water runoff by sedimentation. They are designed for storm-water treatment in urban areas to meet tight space constraints. Limited data on the suspended solids removal performance of installed devices are available, and existing data are questionable because of the problems associated with assessment by monitoring. The objectives of our research are to: (1) investigate the feasibility and practicality of field testing to assess the performance of hydrodynamic separators as underground storm-water treatment devices; (2) evaluate the effects of sediment size and storm-water discharge on the performance of six devices from different manufacturers; and (3) develop a universal approach for predicting the performance of a device for any given application. In the field tests, a controlled and reproducible synthetic storm event containing sediment of a well defined size distribution and concentration was fed to a precleaned device. The captured sediment was then removed, dried, sieved, and weighed. To assess the performance of the devices, suspended sediment removal efficiency was related to a Péclet number, which accounts for two major processes that control performance: (1) settling of particles; and (2) turbulent diffusion or mixing of particles. After analyzing the data, all devices showed similar behavior, therefore, a three-parameter performance function was proposed for all devices. Performance functions were developed from the result of the field tests and parallel testing of two other full-scale devices in the laboratory. The performance functions can be used to determine the efficiency of the tested devices and to improve the selection and sizing of hydrodynamic separators and the assessment of their overall performance after installation.     

Air Injection in Water with Different Nozzles

Air injection systems have a wide range of environmental engineering applications. In this study, we conducted experiments on air injection in a relatively large water tank to investigate the effect of nozzle type, including single/multiple orifice nozzles and a porous airstone, on the characteristics of the bubbles and the induced flow structure. Measurements of bubble characteristics and flow field surrounding the bubble core were obtained using a double-tip optical probe and particle image velocimetry, respectively. The results revealed that bubble velocity did not change significantly with different nozzles, but bubble size decreased significantly while interfacial area, liquid entrainment rate, and kinetic energy of the mean and turbulent flow increased significantly by using the porous airstone instead of nozzles with large orifices. The results for a nozzle with multiple orifices of small diameter are comparable to those for the airstone, which suggests the suitability of its use for systems susceptible to clogging of the pores. Correlations using adequate length and velocity scales are also proposed to describe both bubble and liquid flow characteristics. Finally, applications of the results for different artificial aeration/mixing systems are presented.     

Vortex Plate for Enhancing Particle Settling

The feasibility of enhancing suspended solids settling by using the newly proposed vortex plates in clarifiers, instead of conventional smooth lamellae, was studied using computational fluid dynamics (CFD) modeling and laboratory experiments in which suspended particles were mimicked by crushed walnut shells and glass beads. The vortex plate was formed by attaching perpendicular ribs to the plate, forming slots of 25×25?mm (depth×width) and placing the plate parallel to the longitudinal clarifier axis at an angle of 60° from the horizontal. Rib walls were placed either in vertical planes, perpendicular to the clarifier longitudinal axis, or were slightly sloping in the main flow direction (20° about the vertical). Three hydraulic concepts were explored with respect to enhancing suspended particle settling: (1) the use of flow energy to generate steady vortices inside the slots and thereby entrain particles into the slots, where they would be sheltered from the fast horizontal flow and could settle without much hindrance; (2) enhancing the particle settling by increasing the contact surface area and thereby reducing the length of travel of settling particles; the same principle is used in conventional lamellar settlers but the surface area of a vortex plate is three times that of a smooth lamella; and (3) increasing the particle collision frequency within the swirling flow inside slots to prompt particle flocculation. The CFD modeling and experimental observations confirmed the formation of strong vortices in the parallel slots of the vortex plate. Such vortices entrained the passing by particles and retained some of them in slots, which provided a quiescent settling zone. Both the simulation and measured results indicated that the vortex plate contributed to a slightly improved removal of suspended particles. A CFD particle tracking model was applied to clarifiers with two vortex plates or two smooth plates and indicated that the vortex plate removed about 8% more particles than the smooth plate. In laboratory tests with plate arrays, the vortex plate array also contributed to better particle removals, especially for slower settling particles and larger inflow rates (by up to 26%).     

Using the Kinetics of Biological Flocculation and the Limiting Flux Theory for the Preliminary Design of Activated Sludge Systems. I: Model Development

Current activated sludge models consider that the removal of biodegradable organics by suspended growth includes rapid enmeshment of the organic particles in the microbial floc, hydrolysis of the complex organic molecules into readily biodegradable organic substances, and oxidation of dissolved organic substances. All of the models assume hydrolysis is the rate-limiting step, but none consider the role that the kinetics of biological flocculation and the sludge settling characteristics may play in defining the activated sludge operating parameters. Several researchers have studied the kinetic of biological flocculation, and have analyzed its role on the removal of particulate COD in suspended growth reactors. It has been demonstrated that a large proportion of the organic matter present in sewage can be removed by biological flocculation using short hydraulic retention times and subsequent settling. This paper demonstrates that the one-dimensional limiting flux theory may be useful for coupling the sludge settling properties with the aeration tank behavior, and is a reasonable first approximation that can be used for activated sludge system design and operation.     

An Improved Model for the Flow in an Electromagnetically Stirred Melt during Solidification

A mathematical model for simulating the electromagnetic field and the evolution of the temperature and velocity fields during solidification of a molten metal subjected to a time-varying magnetic field is described. The model is based on the dual suspended particle and fixed particle region representation of the mushy zone. The key feature of the model is that it accounts for turbulent interactions with the solidified crystallites in the suspended particle region. An expression is presented for describing the turbulent damping force in terms of the turbulent kinetic energy, solid fraction, and final grain size. Calculations were performed for solidification of an electromagnetically stirred melt in a bottom chill mold. It was found that the damping force plays an important role in attenuating the intensity of both the flow and turbulent fields at the beginning of solidification, and strongly depends on the final grain size. It was also found that turbulence drops significantly near the solidification front, and the flow becomes laminarized for solid fraction around 0.3.