Homogenisieren von Schüttgütern in Mischsilos

Homogenization of bulk solids in blending silos . Blending silos are used for blending and homogenization of large quantities of bulk solids. Depending on how the energy is introduced, we distinguish between pneumatic, mechanical, and gravity flow blenders. The different blending principles are described and the suitability of the blending systems for certain types of bulk solids is explained. Fluidized bed blenders are suitable for homogenization of free flowing fine powders. Gravity flow blenders are used for blending of granular bulk solids. Homogenization of cohesive powders is accomplished in mechanical blending silos. It is necessary for selection of a suitable homogenization system to know the fluidization behaviour and the flow properties of the respective bulk solids. These properties can be determined in laboratory tests.     

Verhalten feinkörniger Schüttgüter

Behaviour of Fine-Grained Bulk Solids. The behaviour of fine-grained bulk solids embraces such diverse phenomena as the moistening properties or thermal conductivity. Only two aspects are considered in this article, viz, the mechanics of bulk materials and the flow mechanics of fine-grained bulk solids. The interplay of these two areas is illustrated by a detailed analysis of the various kinds of gas fluidisation.     

Entwicklungslinien der Schüttgutdosiertechnik

Developments in dosage of bulk solids. Dosage of bulk solids is a fast developing field of process- and production automation. Developments are determined directly by the current demands of the production process, with the properties of the bulk solids and the process itself playing an important role. A survey of proven dosage techniques from the viewpoint of the operating principles, properties, applications, and limitations demonstrates the great variety of problem solutions. An important difference between the individual dosage techniques is the nature and accuracy of mass limitation. The most accurate techniques are the gravimetric dosage methods, with discontinuous weighing giving the greatest accuracy. Developments have been greatly influenced by the state of weighing cell techniques, weighing electronics and computer engineering. The development of measured data acquisition and processing of control, and of instrumentation are described, compared, and assessed. A trend towards system responsibility and development on the part of manufacturers is noted. A accurate dosage of bulk solids requires constant flow of the solids and finely adjustable control devices. The principal interferences in bulk solids flow and measures for their avoidance are shown by means of examples. Successful solution of dosage tasks ultimately requires agreement between manufacturers and processors with regard to definition, determination, and control of dosage accuracy during calibration and during long term operation.     

Dichtstromförderung

High density pneumatic conveying . In distinguishing between high density pneumatic conveying and low density conveying it is insufficient to merely use the solids loading to characterize the various flow states. Less ambiguous classification is possible only on the basis of the diagram of state of pneumatic conveying. Most flowable bulk solids can be transported through normal smooth-walled piping in the high density mode with normal conveying equipment. In contrast, fine-grained products in particular tend to adhere to the wall and form blockages. Paying due attention to the differing flow properties of various bulk solids and to the mechanisms of blockage formation and clearance, various new conveying techniques and piping types have been developed in recent years, permitting in some cases the transport of adhering, abrasive, and attrition-sensitive materials. Since conveying pressures up to about 6 bar are usual in the high-density regime, various combinations of pressure vessels are primarily used for feeding the bulk solids into the conveying pipes. The advantages of conventional, and also special high-density conveying systems are discussed with the aid of examples.     

Lagern und Umschlagen von Schüttgütern in der Chemischen Industrie

Storage and trans-shipment of bulk solids in the chemical industry. Theoretical fundamentals of the motion of bulk solids in bunkers were considered in detail at the Annual Meeting of Chemical Engineers held at Karlsruhe in 1975 [1]. The present account will deal exclusively with practical aspects playing a role in the building and operation of storage and trans-shipment facilities for bulk solids. Various problems encountered are illustrated for some typical bin storage units in the chemical industry. Moreover criteria are mentioned which can assist the design engineer in the correct choice of silo type and suitable materials of construction, and the ascertainment of the right size of silo. Filling and emptying devices are also proposed for differing spatial circumstances and various tasks. Important ancillary equipment such as ladders, platforms, and devices for monitoring filling levels are also treated. A consideration of the principal regulations governing the operation of silo systems is followed by some hints on the transport, erection, and assembly of silos.     

The modified outflow funnel — A device to assess the flow characteristics of powders

Flow regulators are added to solid pharmaceutical formulations to improve the flow properties of powder mixtures. During the blending process the glidants adsorb successively at the surface of the host particles and thus lead to a reduction of attractive forces. A large variety of flow additives based on silicon dioxide is commercially available, but not all glidants are just as well suited for each technological problem or each cohesive bulk powder. To assess the improvement of the flowability parameters caused by a glidant a classification system and an adequate measuring device is needed. We would like to present a new measuring device to evaluate the flow enhancing potency of glidants. The modified outflow funnel features a stirrer that acts in the region of bulk arches obstructing the outflow process of a cohesive powder. By destruction of the bulk arches powder outflow is enabled and the time needed for emanation can be measured as a parameter of the flow properties. In addition other measuring parameters like the force needed to destroy the bulk arches are capable to evaluate the flowability of the powder mixture. Binary powder mixtures consisting of corn starch and flow regulator were blended in a Turbula® mixer for a defined period of time. The flow regulators were represented by fumed silica and a selection of various types of SIPERNAT^® precipitated silica provided by Evonik Degussa GmbH, Hanau, Germany. Flowability parameters of the mixtures were characterized with a modified outflow funnel, Hausner Ratio and a shear tester.     

Filtration of Colloidal Suspensions – MRI Investigation and Numerical Simulation

The principle mechanisms of solid‐liquid separation processes are sedimentation and filtration, both including the formation and compression of a liquid‐saturated bulk. The compressive properties of the bulk determine the operating parameters of solid‐liquid separation devices and the achievable separation results. Information about the solids volume fraction of the bulk is essential for a better understanding of the physical mechanisms and precise modeling. A numerical model for the calculation of the local solids volume fraction during formation and compression of filter cakes and sediments was developed. The calculated results are compared with experimental NMR data.     

小本体聚丙烯的改性研究

利用双螺杆共混法对小本体聚丙烯进行了改性研究。探讨了小本体聚丙烯熔融流动性对共混增韧的影响，助增韧剂与主增韧剂的协同增韧作用，滑石粉填充小本体聚丙烯的性能变化规律，以及增流剂对改善复合材料流动性和力学均衡性的作用等。     

Systeme zum Ein- oder Austrag von Schüttgütern in oder aus Druckräumen

Systems for the charging or discharging of bulk solids into or out of pressure chambers. In many branches of chemical and dressing technology there are compelling thermodynamic or economic reasons for carrying out various processes at pressures deviating from ambient values. If the reactants and products of these processes are dusts or granular solids then numerous problems are encountered on transfer between regions of higher or lower pressure. On the one hand, the properties of the feed (such as particle size, flow behaviour) should undergo the slightest possible modification, and on the other hand the transport of the material between the regions of differing pressure should be as continuous as possible. Moreover, the gas transport should be kept low. Pressure swing in the process region is to be avoided. The aim of this study was to survey all systems suitable for introduction or removal of bulk solids into or out of chambers at pressures other than the ambient value. The various pressure locks are assessed qualitatively for given tasks. A new solution is presented for the discharge of filter cake from high-pressure chambers.     

Zur Verfestigung von Schüttgütern – Mikroprozesse und Kinetikmodelle

Storage tanks are important elements of a self-operating closed processing system. The reliability and availability of storage equipment essentially depends on the flow behaviour of particulate solids in storage containers. A wide residence time distribution (i.e. too long a storage time at rest) in silos, bunkers or transportation containers, respectively, can lead to the hazardous problem of so-called “time consolidation” of particulate solids. During this hardening process, solid bridges are forming with resulting solidification and solid properties of bulk material. In principle, there are four main physico-chemical effects in bulk materials storing and handling which can produce solid briding between the particle contacts due to crystallisation, chemical reactions, solidification of high-viscous bonding agents and sintering. Generally, new adhesion force based models are presented to describe the consolidation kinetics of particulate solids. Preliminary solutions of kinetic model equations are discussed and compared with new test results and practical conclusions are drawn concerning the reliable processing, storage and transportation of bulk materials.     

Erleichterungen bei der Planung und Auslegung von Schüttgut-Aufbereitungsanlagen am Beispiel der pneumatischen Förderung

Facilitating the planning and design of plant for working of bulk solids, as illustrated by pneumatic conveying . Taking the case of pneumatic conveying as an example, the article shows how plant construction companies can achieve considerable simplifications and time saving in the planning and building of plant for working of bulk solids by adopting a systematic approach utilizing card indexes of bulk materials and working diagrams. Companies operating such plant are made aware of the thorough preparation invested in new projects and of the approach adopted and problems encountered in the preparation of tenders. A simple general view of the present state of knowledge can possibly provide impulses for new considerations.     

Effect of powder properties on discharge characteristics of cohesive carbonaceous fuel powders from a top discharge blow tank at high pressure

Abstract

Discharge experiments of two cohesive carbonaceous fuel powders (anthracite coal and petroleum coke) were carried out in a top discharge blow tank experimental system with design pressure up to 6.4?MPa. The effects of powder properties (particle size and powder category) on the discharge characteristics (including solid discharge rate, solids loading ratio, and discharge stability) from the top discharge blow tank at high pressure were investigated. Meanwhile, shear tests with a ShearTrac II shear tester were performed to investigate the flowability of these two cohesive powders. The results indicate that there exists a near-linear relationship between major consolidation stress and flow function (FF). As particle size decreases, the values of FF decrease and powder flowability becomes worse. However, as particle size decreases, the particle suspension velocity decreases correspondingly, and the gas permeability becomes worse and gas maintain ability becomes better, which contribute to higher solid discharge rate and better discharge stability, whereas solids loading ratio may have opposite variation tendency. Compared to petroleum coke with similar particle size, anthracite coal has better flowability and can obtain higher solid discharge rate and solids loading ratio, as well as better discharge stability. During the discharge processes of petroleum coke, it was found that as the number of discharge experiment increases, the discharge stability decreases correspondingly. After petroleum coke being discharged continuously for 4–6 times, the discharge process could not start again, adhesion phenomena of petroleum coke to the wall of conveying pipelines could be observed.     

Characterization of wet powder flowability by shear cell measurements and compaction curves

Wet powders can be classified into the pendular, the funicular, and the capillary states. The boundaries between the three states depend on particle and bulk properties. The flow properties in each of these states vary with the level of saturation as both the tensile strength and the interparticle friction are a function of the amount of liquid present in the pores. In the frame of this study, it was demonstrated that wet powders can be classified based on shear cell measurements.Compaction curves are an adequate measure of wet powder flowability and its dependency on particle and bulk properties. They can be used to evaluate the risk of blocking in extrusion processes.The significance of the transition from the funicular into the capillary state is highlighted, in particular for its distinct role in improving the flowability and the extrudability.     

Effects of sudden pressure changes in the surrounding gas phase on flow properties of bulk solids

The variation in the behaviour of bulk solids as a result of sudden pressure changes in the surrounding gas phase is of interest in the application of lock hoppers for transfer of bulk solids into pressure vessels. By using such sluice systems, problems occur due to consolidation of the pressurized bulk solids. This paper presents the results of experimental and theoretical research, which allow to describe the influence of several parameters on pressure compensation and the degree of consolidation. With reference to the forces and mechanisms responsible for consolidation, it is possible to describe the different consolidation behaviour of incompressible (limestone) and compressible (hard coal) bulk solids.     

On-line detection of bed fluidity in gas–solid fluidized beds with liquid injection by passive acoustic and vibrometric methods

Passive acoustic and vibrometric methods were investigated for the detection and monitoring of changes in bed fluidity in a large scale gas–solid fluidized bed after liquid injection. Water was injected into a 9 tonne air-fluidized bed of silica sand using an industrial nozzle and pre-mixer assembly. Acoustic signals were recorded using non-intrusive and externally mounted microphones. Vibration data was recorded using an accelerometer mounted to a rod inserted into the bed. The signals were analyzed offline using Fourier and wavelet analysis techniques. The average frequency of the acoustic and vibration measurements decreased as the bed solids dried while the standard deviation of the coefficients in the 10–20 kHz band characterized from wavelet analysis increased during drying. Samples from the bed were taken and evaluated for flowability by measuring the median avalanche time with a Revolution Powder analyzer. Linear and power law regressions of the wavelet and Fourier analyzed vibration measurements provided a reliable correlation of the flowability of the bed solids and thus could be successfully used as a passive and real-time monitoring method of bed fluidity.     

Comparison of different flowability tests for powders for inhalation

A series of placebo powders for inhalation was characterized regarding bulk density and powder flowability using different techniques. The powders were of the ordered mixture type and were prepared by mixing a pharmaceutical carrier grade of lactose with different fractions of intermediate sized and fine (i.e., micronized) lactose. A modified Hausner Ratio was obtained by measurement of the poured and the compressed bulk densities. Other tests investigated were the angle of repose, the avalanching behaviour using the AeroFlow, and the yield strength using the Uniaxial tester. Furthermore, the relation between ordered mixture composition and flowability was examined.Of the methods investigated, the modified Hausner Ratio discriminates well between the investigated powders and seems to have the widest measuring range. It was also found that the poured and compressed bulk densities provide information about the packing of the particles in the powders. A good correlation was obtained between the modified Hausner Ratio and the angle of repose. The AeroFlow was suitable for powders with a low percentage of fine particles, but could not discriminate between the more cohesive powders. The Uniaxial tester, on the other hand, seems to be better suited for more cohesive powders.Regarding the powder composition, addition of micronized particles has a strong influence on the flowability of ordered mixtures, while intermediate sized particles have little impact on the powder flow.     

Effective drag on spheres immersed in a fluidized bed at minimum fluidization—Influence of bulk solids properties

The aims of this work are to elucidate the effects that bulk solids properties have on the effective drag experienced by large spheres immersed in an emulsion of group-B solids under minimum fluidization conditions and to analyze the ways in which the different suspensions react towards different applied shear rates. To investigate this, magnetic particle tracking was applied to resolve the trajectory of falling-sphere measurements in which the size, density, and sphericity of the bulk solids were varied as well as the size and density of the spherical tracers. The resulting experimental scope included both rising and sinking tracers as well as full segregation and in-bed stagnation of the tracers. The set-up provided highly resolved tracer trajectories, from which the drag experienced by the sphere can be calculated. For sinking tracers, the results showed that an increase in bulk solids size, angularity, and density reduced the terminal velocity of the sphere. This effect correlated well with the bed expansion and Hausner ratio, indicating that a reduced void space among the bulk solids is the main reason for the increase in motion resistance. At lower shear rates, namely, during the de-acceleration towards the stagnant state, beds of larger, more angular, or denser bulk solids yield lower levels of shear stress. The angle of repose of the bulk solids correlated with the rate at which the emulsion thins with increasing shear rate. For rising tracers, shear stress did not show any significant dependency on the properties of the bulk solids.     

Improvement of oil flowability by assembly of comb‐type copolymers with paraffin and asphaltene

Comb‐type (maleic acid alkylamides‐co‐α‐octadecene) copolymers (MACs) assemble with long‐chain n‐paraffins and asphaltenes by the hydrophobic alkyl branches and polar groups, respectively, and improve flowability of crude oils upon cooling. Their effects on the crystallization of paraffins from model oils were studied by rheology, optical microscopy, differential scanning calorimetry, and X‐ray diffraction. Upon cooling, MACs change the size and shape of paraffin crystals and reduce the yield stresses of gels generated by precipitated solids. Deposition of wax was significantly suppressed by MAC as observed using a laboratory‐scale deposition apparatus. MACs are more effective than poly(ethylene‐butene) copolymers in improving the flowability of crude oils containing asphaltenes. The interactions between the carboxyl and amide groups of MAC with the polar aromatic asphaltenes appear to stabilize crudes through the steric effects of the long alkyl groups of MAC polymers, thereby reducing the strength of paraffin/asphaltene gels formed on cooling. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Powder flowability and density ratios: the impact of granules packing

The propensity of powders to flow under given circumstances (flowability) affects a large number of industrial applications. A single, reliable and widely applicable flowability test does not exist, because of the variety of both granular materials and influence of handling on the measurements results. Here we critically examined the results provided by Hausner's method, based on apparent densities ratio, with several granular materials. Major limitations appeared to be the achievement and measurement of a dense packing condition, provided by the tapped density in the Hausner's ratio. After a detailed discussion of standard and modified techniques to measure bulk density, we eventually suggest a new flowability criterion based on a novel technique to determine a high packing density. The proposed criterion is more sensitive to differences in flowability, as quantified by the repose angle. In order to investigate also the domain of cohesive powders, we developed a novel procedure to measure the repose angle of such powders. Eventually, the new criterion was able to account consistently for free-flowing and cohesive powders. It also stimulates the discussion on subtle issues involved in the determination and use of elementary powder's properties.     

团聚粉料的流动性和成型性能

以3种具有不同团聚特征的氧化铝粉料为对象,用粉料剪切仪测定了粉料的流动性。以单向加压成型测定了成型过程中压力与成型体密度变化。用压汞测孔仪及扫描电镜研究了团聚体的外形和气孔结构。通过以上各种观察,讨论了3种粉料的团聚体恃征及团聚特征对粉料流动性和成型性能的关系。