A simple formula for predicting settling velocity of sediment particles

Based on the general relationship described by Cheng between the drag coefficient and the Reynolds number of a particle, a new relationship between the Reynolds number and a dimensionless particle parameter is proposed. Using a trial-and-error procedure to minimize errors, the coefficients were determined and a formula was developed for predicting the settling velocity of natural sediment particles. This formula has higher prediction accuracy than other published formulas and it is applicable to all Reynolds numbers less than 2× 10^5.

Numerical simulation of flocculation and settling behavior of whole-tailings particles in deep-cone thickener

Rapid dewatering and thickening of whole-tailings with ultrafine particles is one of the most important processes for the whole-tailings paste preparation. Deep-cone thickener, a kind of such process for the flocculation and settling of whole-tailings, is particularly necessary to study. However, there exist many problems in observing the flocculation and settling process of whole-tailings, as well as the particle size distribution(PSD) of whole-tailings floccules in deep-cone thickener. Population balance model(PBM) is applied to predict the PSD in deep-cone thickener, and LUO model and GHADIRI model are employed to study the aggregation and fragmentation mechanism of the whole-tailings particles, respectively. Through three-dimensional numerical simulation on the whole-tailings flocculation and settling in deep-cone thickener using computational fluid dynamics(CFD)-PBM, the distribution of density and turbulent kinetic energy in deep-cone thickener were obtained, at the same time the spatio-temporal changes of whole-tailings floccules particle size distribution are analyzed. Finally, the major flocculation position in deep-cone thickener is found and the flocculation settling rules of whole-tailings are achieved.

Settling behavior of spherical particles in eccentric annulus filled with viscous inelastic fluid

Hole cleaning is a complex process as there are many variables affecting cuttings removal(e.g.drilling fluid type,density,flow rate and rheological properties,cuttings size,drill pipe rotation speed).With the increasing number of drilling small diameter wells(e.g.coiled tubing drilling applications,ultra-deep wells drilled for exploitations of unconventional oil and gas resources),the wall resistance of the micro annulus also emerges as one of the most critical factors affecting the cuttings accumulation in wellbore.The eccentricity of drill pipes commonly observed during the drilling process of ultra-deep well and coiled tubing well makes the wall resistance effect on the cuttings transport even more prominent.Understanding the wall resistance effect on the particle settling behavior in eccentric annuli is,therefore,crucial for hydraulic design of efficient cuttings transport operations in these wells.In this study,a total of 196 sets of particle settling experiments were carried out to investigate the particle settling behavior in eccentric annuli filled with power-law fluids.The test matrix included the eccentricity ranges of 0-0.80,the dimensionless diameter ranges of 0.13-0.75 and the particle Reynolds number ranges of 0.09-32.34.A high-speed camera was used to record the particle settling process and determine the influences of the eccentricity,the dimensionless diameter,the fluid rheological properties,and the solid particle characteristics on the wall factor and the particle settling velocity.The functional relationship among the dimensionless diameter,the particle Reynolds number,and the wall factor was determined by using the method of controlling variables.An eccentric annulus wall factor model with average relative error of 5.16%was established.Moreover,by introducing Archimedes number,an explicit model of particle settling velocity in the eccentric annulus with average relative error of 10.17%was established.A sample calculation of particle settling velocity was provided to show the application of the explicit model.Results of this study can be used as a guideline by field engineers to improve hydraulic design of cuttings transport operations in concentric and eccentric annuli.

Motion behavior of particles in air-solid magnetically stabilized fluidized beds for separation

In order to study the settling mechanism of particles in an air-solid magnetically stabilized fluidized bed(MSFB) for separation,we carried out free settling and quasi-zero settling tests on the tracing particles.The results show that the main resistance forces as the tracing particles settled in an air-solid MSFB were motion resistance force and yield force.The motion resistance and yield forces greatly hindered the free settling of the particles by greatly decreasing the acceleration for settling process of the particles.The acceleration decreased from 3022.62 cm/s 2 to zero in 0.1 s,and in the end,the particles stopped in the air-solid MSFB.The yield force on particles increased with increasing the magnetic field intensity,resulting in decrease of the quasi-zero settling displacement.However,the yield force on particles decreased with increasing the fluidized air velocity,leading to increase of the quasi-zero settling displacement.When the structure and operating parameters of the air-solid MSFB were set up,the yield stress on particles stopped in an air-solid MSFB was a function of diameter and density of particles.The settling displacements of equal diameter particles increased with increasing their densities,and the settling displacements of equal density particles increased with increasing their diameters.

Investigation on Settling Characteristics of Floes in the Changjiang Estuary, China

Settling characteristics of floes, including relative settling velocity, relative flocculation coefficient and flocculation exponent, are obtained by the suspended load equations for different size fractions. Data of the Changjiang Estuary suggest that level of flocculation changes from river section, river mouth (turbidity maximum) to offshore area in sequence of low, very high and high. The settling characteristics of floes reflected by in situ estimation performs a similar feature as that obtained from still water experiment.

Particle flux through the Huanghai Sea cold water mass

Settling particulate matter （SPM） was collected by using sediment traps at four stations in a survey section from Qingdao to Cheju-do, across the Huanghai Sea cold water mass （HSCWM）, in August 2002. The sediment traps were planted in three layers： the upper layer of the thermocline （ULT） above the HSCWM, the lower layer of the thermocline （LLT）, and the bottom layer of water column （BL）. To determine the particle flux, the contents of organic carbon （POC）, organic nitrogen （PON）, total carbon （PC）, and total phosphorous （PP） in SPM were analyzed, and two flux models （Ⅰ and Ⅱ） were improved to calculate the resuspension ratio, with an assumption in Model Ⅰ that the vertical flux of SPM in the LLT equals the net vertical flux of SPM in the whole water column. An X value, i.e., the fraction of the resuspension flux originating from the surficial sediments nearby the sampling station, was deduced from Model Ⅰ to estimate the contribution of lateral currents to the total resuspension flux. The results showed that inorganic particles, fecal pellets, and miscellaneous aggregates were the major types of SPM in the HSCWM, and the contents of POC, PON, PC, and PP all decreased with water depth. A great deal of fecal pellets found in the LLT indicates that the main space producing biogenic SPM is the thermocline, and especially the LLT, where the C/N ratio is lower than that in the ULT. The resuspension ratios, 90%-96% among stations, imply strong impact ofresuspension on particle flux in the BL. These values were not significantly different between the two flux models, suggesting that the hypothesis in Model Ⅰ that the flux in the LLT equaling the net flux to the bottom is acceptable for shallow waters with stratification like the HSCWM. The POC export ratio from the HSCWM ranges from 35% to 68%. It benefits from the short sinking distance in shallow water. The upwelling in the HSCWM enhanced the POC flux through the water mass, and the lateral currents provides up to being greater than 50% ofresuspension flux in the BL according to evaluation of the X value.

Numerical modeling of fluid-particle interaction in granular media

Fluid-particle interaction underpins important behavior of granular media. Particle-scale simulation may help to provide key microscopic information governing the interaction and offer better understanding of granular media as a whole. This paper presents a coupled computational fluid dynamics and discrete element method （CFD-DEM） approach for this purpose. The granular particle system is modeled by DEM, while the fluid flow is simulated by solving the locally averaged Navier-Stokes equation with CFD. The coupling is considered by exchanging such interaction forces as drag force and buoyancy force between the DEM and CFD. The approach is benchmarked by two classic geomechanics problems for which analytical solutions are available, and is further applied to the prediction of sand heap formation in water through hopper flow. It is demonstrated that the key characteristic of granular materials interacting with pore water can be successfully captured by the proposed method.

沥青质颗粒在垂直井筒中的运移特征流速

为防止沥青质沉积堵塞油井,需明确垂直井筒内流体携沥青质颗粒运移特性。通过静态沉降试验探究不规则形状沥青质颗粒沉降末速规律,采用垂直井筒液携固流动试验装置研究不同因素对沥青质运移临界流速的影响程度,建立沥青质颗粒沉降末速和运移临界流速计算公式。结果表明:沥青质表面不均匀性增大了沉降阻力,使沉降等效直径小于颗粒实测粒径;运移临界流速与颗粒粒径成正比、与液相黏度成反比,颗粒体积分数对运移临界流速影响较小;相同条件下流体携沥青质运移临界流速为沉降末速的1.182倍。

延迟焦化装置酸性水除油脱焦粉技术改造

某石化公司1.2Mt/a延迟焦化装置在生产运行过程中存在分馏塔顶酸性水带油、带焦粉问题,在焦炭塔预热,污油、废渣回炼时尤为明显。分析原因为加工原料组成变化、酸性水量增加等导致分馏塔顶酸性水发生乳化、沉降时间不足,影响下游酸性水汽提装置的稳定运行。为解决以上问题,通过实施技术改造,在原分馏塔顶油水分离罐后增上一座酸性水沉降罐,将酸性水停留时间由1.10~2.56h增加至3.50~8.10h;在新增酸性水沉降罐后增加一台自动反冲洗过滤器,脱除酸性水中≥10μm的焦粉颗粒。技术改造实施完成投用后标定结果表明:酸性水中油含量从882mg/L下降至162mg/L,使油水充分分离,除油率达到81.63%;≥10μm的焦粉颗粒含量从463mg/L下降至9mg/L,脱除率达到98.06%,有效降低了酸性水油含量和焦粉颗粒含量,为下游酸性水汽提装置的稳定运行创造了条件。

给料浓度对浓密机内颗粒絮凝及沉降影响研究

基于CFD-PBM耦合数值模拟方法,采用RNG k-ε湍流模型、Euler-Euler多相流模型以及所建立的微细矿物颗粒絮凝动力学数学模型,对直径为600 mm的实验室深锥型浓密机内铁尾矿颗粒絮凝及沉降行为进行了模拟研究,探究了给料浓度对颗粒复杂运动行为的影响。结果表明,在所研究给料浓度范围内,给料井出口位置絮团平均粒度随着给料浓度的增加先增加后减小,约为8%的给料体积浓度条件下铁尾矿颗粒絮凝效果较好;絮团沉降速率随着给料浓度增加而逐渐降低,且给料浓度增加,不同粒度絮团沉降速率差异逐渐减小。本研究为揭示浓度特性对微细矿物颗粒絮凝及沉降行为影响机制提供理论依据,为浓密机给料浓度调控提供技术指导。

基于CFD-DEM方法的饱和砂土场地液化模拟研究

砂土液化是常见的地震灾害,目前应用于研究砂土液化动力特性的室内试验以及模型试验还不能全面反映土体液化全过程。计算流体动力学(computational fluid dynamics,CFD)与离散元法(discrete element method,DEM)耦合模拟方法能够准确地模拟各类水土耦合问题。通过二次开发的CFD-DEM流固耦合模块实现离散元软件PFC3D与计算流体力学软件OpenFOAM之间的力学信息交互,利用颗粒水下自由沉降验证该方法的可行性。利用PFC3D软件模拟室内循环三轴试验标定出具有真实饱和砂土动力特性的数值砂样。根据已有的参数信息以及耦合模拟方法建立了饱和砂土的场地液化模型。模拟结果表明,离散元法能够复现室内砂土液化试验,标定参数可应用于场地液化模拟;单颗粒沉降速度与理论解一致验证了CFD-DEM耦合方法的准确性;峰值加速度0.25g下不同深度处土体均会发生液化,液化时超孔压比无法达到1,超孔压累计值由浅层往深层递增;液化后土体强度自下而上逐渐恢复,再固结的场地土体结构呈现均匀化发展趋势。

Settling behavior of non-spherical particles in power-law fluids:Experimental study and model development

Solid-particle settling occurs in many natural and industrial processes, such as in the transportation of drilling cuttings and fracturing proppant. Knowledge of the drag coefficient and settling velocity of cuttings and proppant is of significance to hydraulics design, wellbore cleanout, and fracture optimization. We conducted 553 tests to investigate the settling characteristics of spherical and non-spherical particles in power-law fluids. Three major particle shapes (spherical, cubic, and cylindrical) and eight different particle sphericities were used to simulate cuttings and proppant, and power-law fluids were applied to simulate drilling and fracturing fluids. Based on the data analysis, a new drag coefficient-particle Reynolds number correlation was developed to determine the drag coefficient in a power-law fluid for spherical and non-spherical particles. The drag coefficient increases as the sphericity decreases for the same particle Reynolds number. For a specific particle shape, the drag coefficient decreases as the particle Reynolds number increases, but the decreasing trend is reduced at high particle Reynolds number conditions. An explicit settling-velocity equation was proposed to calculate the settling velocity of spherical and non-spherical particles in power-law fluids by considering the effect of sphericity. A suitable range for the proposed model is 0.0001 < Re <200, 0.471 <φ< 1, and 0.505 < n < 1. An illustrative example is presented to show how to calculate the drag coefficient and settling velocity in power-law fluids with given particle and fluid properties.

Settling behavior of spherical particles in vertical annulus:Experimental study and model development

Coiled tubing(CT)drilling technology offers significant advantages in terms of cost and efficiency for exploitations of unconventional oil and gas resources.However,the development of CT drilling technol-ogy is restricted by cuttings accumulation in the wellbore due to non-rotation of the drill string and limited circulating capacity.Cuttings cleaning becomes more difficult with the wall resistance of pipe-wellbore annulus on the cutting transport.Accurate description of particle transport process in the pipe-wellbore annulus is,therefore,important for improving the wellbore cleanliness.In this study,high-speed cam-era is used to record and analyze the settling process of particles in the transparent annulus filled with power-law fluids.A total of 540 tests were carried out,involving dimensionless diameters of 0.10-0.95 and particle Reynolds Numbers of 0.01-12.97,revealing the effect of the dimensionless diameter and particle Reynolds number on the annulus wall effect,and the wall factor model with an average relative error of2.75%was established.In addition,a dimensionless parameter,Archimedes number,independent of the settling velocity,was introduced to establish an explicit model of the settling velocity of spherical particles in the vertical annulus,with the average relative error of 7.89%.Finally,a calculation example was provided to show how to use the explicit model of settling velocity in annulus.The results of this study are expected to provide guidance for field engineers to improve the wellbore cleanliness of coiled tubing drilling.

Characteristics of settling of dilute suspension of particles with different density at high Reynolds numbers

Dilute suspension of particles with same density and size develops clusters when settle at high Reynolds number(≥250).It is due to particles entrapment in the wakes produced by upstream particles.In this work,this phenomenon is studied for suspension having particles with different densities by numerical simulations.The particle-fluid interactions are modelled using immersed boundary method and inter-particle collisions are modelled using discrete element method.In simulations,settling Reynolds number is always kept above 250 and the suspension solid volume fraction is nearly 0.1 percent.Two particle density ratios(i.e.density of heavy particles to lighter particles)equal to 4:1 and 2:1 and particles with same density are studied.For each density ratio,the percentage volume fraction of each particle density is nearly varied from 0.8 to 0.2.Settling characteristics such as microstructures of settling particle,average settling velocity and velocity fluctuations of settling particles are studied.Simulations show that for different density particles settling characteristics of suspension is largely dominated by heavy particles.At the end of paper,the underlying physics is explained for the anomalies observed in simulation.

基于绿色勘查的净化式泥浆沉淀箱的净化技术探讨

为减少矿产资源勘查开发对环境造成的扰动和破坏,介绍了绿色勘查钻探泥浆净化技术的发展现状,提出绿色勘查钻探泥浆净化思路,根据泥浆净化自然沉淀法原理研制出一种净化式泥浆沉淀箱,在某矿区进行泥浆净化系统应用试验。结果表明,净化式泥浆沉淀箱的应用在净化、节地、节水、节能、经济性方面取得了良好成果,环保性好,可满足绿色勘查钻探需求。

干气脱硫塔压力降控制方法与实践

介绍了某公司液相柴油加氢装置干气脱硫塔压力降高的解决方法。通过Storks定律理论分析与试验相结合的方法,确定控制干气脱硫塔压力降主要措施:降低含硫干气流量和解决填料层堵塞问题。将含硫干气流量由7600 m^(3)/h降至6500 m^(3)/h,干气脱硫塔压力降下降6.5 kPa,效果不佳。填料层堵塞主要是因上游贫胺液中含有大量高碳固体颗粒,且其在贫胺液中悬浮沉降。根据Storks定律并利用该项曳力特征,固体黑色颗粒沉降速度为0.012 m/s,故通过满塔操作快速外送填料塔内贫胺液,高速流动产生与沉降相反的曳力足以使其悬浮,将大量高碳固体颗粒从填料中清除,干气脱硫塔压力降从53 kPa快速降至1 kPa,解决了填料层因高碳固体颗粒物堵塞而导致压力降高的问题,可操作性较强,效果显著。

卧式沉降离心机参数对固体回收率的影响研究

煤炭领域细粒煤泥处理属于行业煤泥处理的主要难题,卧式沉降离心机在煤炭领域上具有广泛的应用,其适用于各种固液分离,尤其应用于细粒级煤炭回收以及降低煤炭水分。为有效降低部分细煤泥处理费用,增加回收后细煤泥的增值利用,以河北、山西、内蒙古地区3个洗煤厂细煤泥为试验对象并开展离心机参数变量对固体回收率的试验研究,重点探究转鼓转速、转速差、堰高、入料质量分数和粒度组成对回收率的影响规律。试验结果表明:转速增加将提高回收率、降低分级粒径,极限转速后变化不显著;随着速度差的增加则回收率逐步增加,较高的入料质量分数下则回收率变化较小;一定范围内增加堰高有利于回收,需调整堰高至合理区间;随着入料质量分数上升则回收率逐步上升,其质量分数超过40%,回收率上升趋势变化较小;回收率随物料粒度变大而增加,而分级粒径变化很小。

北京市六种针叶树叶面附着颗粒物的理化特征

对北京市6种针叶树叶面颗粒物附着密度、叶表面微形态、颗粒物矿物与元素组成的研究结果表明：同一树种叶面颗粒物附着密度随大气颗粒物浓度增加而增大；同一地点不同树种叶面颗粒物附着密度存在很大差异，圆柏、侧柏颗粒物附着密度最高，其次为雪松、白皮松，油松、云杉最低；受地面扬尘影响，低矮叶片较高处叶片颗粒物附着密度大；受降雨和新生叶片稀释影响，夏季颗粒物附着密度小于冬季．叶表面粗糙程度越大，颗粒物附着密度越高．SiO2、CaCO3、CaMg（CO3）2、NaCl、2CaSO4·H2O、CaSO4·2H2O、Fe2O3 7种主要矿物占叶面颗粒物总质量的10％～30％，其中，SiO2含量最高，其次为CaMg（CO3）2、CaSO4·2H2O和CaCO3．此外，还含有蒙脱石、伊利石、高岭石等粘土矿物及长石．21种测定元素占叶面颗粒物总质量的16％～37％，其中Ca、Al、Fe、Mg、K、Na、S7种元素占测定元素总质量的97％以上。其它痕量污染元素含量很少，并且受采样地点和树种影响较小．

泥沙颗粒团沉速

针对现有的泥沙沉速公式大多适用于单颗粒泥沙沉降的情形,基于前人对单颗粒泥沙沉速规律的研究成果,利用试验测得不同泥沙颗粒团在水中沉降时的沉速数据,引入泥沙颗粒团特征粒径及附加粒径2个因子,对多个广泛运用的单颗粒泥沙沉速公式进行了修正.用修正后的公式计算得到的泥沙颗粒团沉速与用试验测得的泥沙颗粒团沉速较接近,可推广运用到计算泥沙颗粒团在水中的沉降速率.

细粒煤在Falcon分选机中的运动特性及其脱硫研究

简述了Falcon离心重力分选机的特点及工作原理,通过细颗粒在Falcon离心重力场中的受力分析和沉降末速的计算,得出了颗粒沉降时间与离心加速度的关系,结果表明:颗粒的离心加速度越大、固体颗粒与介质的密度差越大、颗粒直径越大,则沉降时间越短.通过对转筒内流膜运动特性分析,研究了处于转筒内不同流膜微层中的颗粒切向速度的变化规律,结果表明:流膜内各微层的切向流速沿径向递增.分析对比了Falcon离心分选和浮选分步释放试验脱硫效果,结果表明了细粒煤在离心重力场中的全硫脱除率要比基于颗粒表面性质分选的浮选过程平均高5%左右.