超声波振动筛在三氯蔗糖生产中的应用

超声波振动筛是超声波技术与振动筛分技术的有机结合,它可以由普通筛分进行简单的加超声波系统改造而成,利用超声波振动筛进行三氯蔗糖的筛分,能够减少筛分过程的粉尘污染及产品消耗,能够大幅提高筛分效率,节约成本,能够消除或降低筛分过程的静电吸附问题、避免或减少筛网堵塞问题,能够有效提高筛分精度。     

STOCHASTIC MODELING OF NON-LINEAR SIEVING KINETICS

The feed to a sieve is classified as oversize particles, undersize particles, and near mesh size particles. The sizes of the near mesh size particles vary around that of the sieve opening; the passage of these particles through the sieve effects the separation. A stochastic approach is employed for analyzing and modeling the sieving kinetics of the near mesh size particles, usually constituting the bulk of the material required to be separated. The master equation of the process is formulated based on probabilistic considerations, describing the passage of the particles in the presence of sieve blinding. However, an analytical solution cannot be obtained directly and hence a rational approximation technique, the system size expansion, is utilized to solve the master equation. This results in a system of non-linear, coupled, ordinary differential equations for the various statistical quantities characterizing the number of particles retained on the sieve and the number of blinded apertures. These equations are then solved numerically. From these general equations, specific cases as the first order kinetics law, applicable to the terminal stages of sieving, are easily obtained. In the absence of oversize particles, the process is described by a master equation which is solved directly, yielding an explicit analytical solution. The numerical solutions agree at least qualitatively with the available experimental observations     

Densification of monomodal quartz particle beds by tapping

A study has been undertaken to determine how the mean particle size of monomodal quartz particle beds and the bed preparation method affect initial and final bed apparent density and the kinetics of densification by tapping. The study was conducted on eight quartz particle size fractions obtained from a commercial quartz powder by sieving, each having a different mean particle size and a very narrow (monomodal) particle size distribution. The amplitude of the distribution and the particle shape were practically the same for all fractions. Densification experiments were conducted on the beds obtained with each fraction, using an assembly designed for this purpose. A kinetic model representing the densification process of monomodal powder beds by tapping is proposed, in which good relations are obtained between the parameters of the model and the foregoing variables.     

Grade efficiency for sieve classification processes

Modelling of the screening performance for classification processes is important to obtain a first estimate for a new process in the planning phase. In this work especially the grade efficiency curves of sieve classifications with vibrating screens were examined. A sensitivity study was performed by changing the operating parameters of the sieving machine and the parameters of the charging material (i.e. mass flow, particle size, etc.). The aim was to correlate the input parameters with the grade efficiency curve of the classification process. The main aspect of the presented work is to find an appropriate method to adjust four screening parameters in a way that the measured grade efficiency curve is modelled correctly. Several methods for this adjustment step are reviewed. A sensitivity study using a tumbling screen was performed previously. It is apparent that for that study, different methods and models for the parameter adjustment need to be used. Furthermore it is shown that data reconciliation is necessary, since the mass balance of the particle streams may not be closed correctly. In summary this work is the first step to predict the screening performance of a sieving machine without material‐ and time‐consuming experiments.     

A mathematical model of the batch sieving procedure

A mathematical model is developed to describe the batch sieving procedure, for example for a set of sieves on a test sieving engine. This model allows one to evaluate the size distributions on each sieve surface after a sieving time t from the feed size distribution. The solution of the resulting system of ordinary differential equations is written down, the shape of an introduced sieving function is discussed and the theory is illustrated by an example. It is also shown how to generate the presented model to the case of technical continuous screening.     

An algorithm for deducing an effective sieve residue from the rate of powder passage through a sieve

The effect of non-ideal aperture distribution of a sieving surface on the sieve residue has been the object of many experimental studies. Unfortunately, the sieving kinetics of many sieving techniques do not result in a simple probability relationship between the size distribution function of the powder and the sieve aperture distribution function. If one specifies a certain type of sieving kinetics, then one can apply probability theory to the rate of movement of powder through the sieve and the size aperture distribution function of the sieve. Under such specified sieving conditions it can be shown that it is possible to deduce a size characteristic parameter of the powder being sieved, which in this publication is described as the kinetic residue of the sieve. An algorithm for the automatic computation of the kinetic residue from the rate of powder sieving is described. The possible implementation of this algorithm to automate sieve analysis is explored.     

Study of mechanisms of grain dust explosion as affected by particle size and composition.: Part 2. Characterization of particle size and composition of grain dust

Three types of grain dust (corn, wheat, and grain sorghum) and cornstarch (used as a reference) were each divided into varying size fractions (6 to 11) utilizing air and sieve classifications. The particle size distribution and the composition (content of moisture, ash, protein, and starch and fiber) of each size fraction were determined. Dust particles consisting almost entirely of ash material were found to concentrate in specific air-classified size fractions. The total external surface area, the total volume, and the coefficient of variability were calculated from the experimental particle size distribution for each size fraction by utilizing a piecewise log normal approximation. These values were compared with those calculated from the least-squares fitted log normal approximation of the actual distribution.     

The Influence of Dry-Milled Wood Flour on The Physical Properties of Wood Flour/Polypropylene Composites

In this study, we evaluated the influence of wood flour (particle size: <90 μm) on the physical properties of wood flour/polypropylene (PP) composites. Wood flour was obtained by dry ball-milling of forest-thinning material at a rotary speed of 250 rpm for 1, 2, 4, and 8 h. The milled wood flour was filtered using a 90 μm sieve. The water content of the wood flour was adjusted to 5, 10, or 20 wt%. Composite properties, including mechanical properties, water absorption, and thermal expansion, were evaluated at wood flour loadings of 40 wt%. When wood flour with 5 wt% water content was milled for 2 and 4 h, the resulting wood flour was granular rather than fibrous; flocculation of the fine particles was observed for milling times exceeding 4 h. This morphological change in the wood flour reduced its influence on the physical properties of the composites, although some positive influences were observed on the molding properties of the composite, such as an increase in compound fluidity. Milled wood flour with 10 wt% or 20 wt% water content was fibrous. Scanning electron microscopy observation of milled wood flour with 10 wt% water content revealed partial surface fibrillation at widths of tens to hundreds of nanometers. The addition of wood flour with nanoscale surface fibrils to PP composites positively influenced the properties of the composite, resulting in a decrease in the linear coefficient of thermal expansion in the flow direction.     

Studies on the Effect of Graphene Oxide Deposited on Gold and Nickel Microsieves on Prostate Cancer Cells DU 145

This work shows the effect of graphene oxide deposition on microsieves’ surfaces of gold and nickel foils, on DU 145 tumor cells of the prostate gland. The sieves were made by a laser ablation process. The graphene oxide (GO) deposition process was characterized by the complete covering of the inner edges of the microholes and the flat surface between the holes with GO. Electron microscanning studies have shown that due to the deposition method applied, graphene oxide flakes line the interior of the microholes, reducing the unevenness of the downstream surfaces during the laser ablation process. The presence of graphene oxide was confirmed by Fourier infrared spectroscopy. During the screening (sieving) process, the microsieves were placed in a sieve column. Gold foil is proven to be a very good material for the screening of cancer cells, but even more so after screening as a substrate for re-culture of the DU 145. This allows a potential recovery of the cells and the development of a targeted therapy. The sieved cells were successfully grown on the microsieves used in the experiment. Graphene oxide remaining on the surface of the nickel sieve has been observed to increase the sieving effect. Although graphene oxide improved separation efficiency by 9.7%, the nickel substrate is not suitable for re-culturing of the Du 145 cells and the development of a targeted therapy compared to the gold one.     

Dehulling crambe seed for improved oil extraction and meal quality

Crambe seed had low bulk density (328 kg/m³) due to thick hulls (0.23 mm), which made up 21.2% of the seed weight. The mean seed diameter was 2.7 mm (SD±0.2 mm); the thousand-grain-weight was 6.2 g. Dehulling improves oil extraction efficiency and facilitates the marketing of high-protein meal (>40% protein). The effectiveness of roller milling/aspirating and the effectiveness of impact milling/aspirating on dehulling crambe seed were studied and compared by analyzing the meat and hull fractions for oil and protein contents and calculating material balances. Roller milling was more effective than impact milling. The optimal roller mill gap was 7/64 in. (0.28 cm), and the optimal impact mill speed was 2,400 rpm generating 44.7 m/s tangential speed. The optimal aspiration airflow was 1,970 ft³/min (55.7 m³/min). Roller milling/aspirating was projected to produce 46% protein meal at 12% moisture and 1% residual oil (typical of solvent extraction) or 42% protein meal at 12% moisture and 6% residual oil (typical of screw pressing most other oilseeds). Hand-dissected hulls contained 10.4% moisture, and 1.2% oil and 8.8% protein on a dry basis, whereas the meats contained 8.8% moisture, and 47.6% oil and 31.6% protein on a dry basis. Optimal roller milling/aspirating produced hulls with 8.1% oil and 11.4% protein and meats with 42.6% oil and 30.5% protein on a dry basis.     

高性能炭分子筛膜支撑体的制备研究

采用湿法球磨与粒子烧结相结合的方法,以α-Al2O3为主要原料,干压成型法制备出性能较高的炭分子筛膜支撑体.经过各种表征手段分析,所得支撑体具有均布的孔隙结构和较窄的孔径分布,并探讨了致孔剂种类、干燥制度、烧结温度及球磨时间对炭分子筛膜支撑体性能的影响.结果表明,1 250℃下烧结然后保温2h、球磨时间为4h时,制备的高渗透通量炭分子筛膜支撑体平均孔径为0.4μm、孔隙率为46％.     

Mathematical modeling of thin-layer separation of granular materials on sieve classifiers

A mathematical model of the kinetics of the thin-layer separation of granular materials on multiple-deck sieve classifiers was constructed based on the theory of Markovian processes. To derive the kinetic equations, we calculated the probability of sieving into a mesh depending on the shape and size of sieve holes and separated material granules taking into consideration the effect of the relative velocity of their motion. Using the oversize residues from sieves, we identified the kinetic models, performed numerical calculations, and determined the efficiency of separation.     

Rationale of lead immobilization by ball milling in synthetic soils and remediation of heavy metals contaminated tailings

In this work, the use of mechanical milling for the remediation of heavy metals in synthetic soils and tailings sampled from the mining area of “Barraxiutta”, SW of Sardinia, Italy is investigated. Specifically, Pb(II) contaminated synthetic soils of sandy, bentonitic and kaolinitic type are taken into account following the results obtained in previous works. Suitable sequential extraction procedures have been performed on both untreated and treated synthetic soils. It is found that mechanical loads which occur during collisions among milling media and soils are able to modify the distribution of Pb(II) onto the different solid fractions of contaminated synthetic soils. Specifically, for sandy soils the milling treatment induces a significant increase in Pb(II) content in the Fe–Mn oxides fraction. On the other hand, for bentonitic and kaolinitic soils, Pb(II) content in both carbonate and Fe–Mn oxide fractions is augmented after treatment. Such phenomena may contribute to Pb(II) immobilization efficiency since the heavy metal trans-speciation occurs in favor of fractions characterized by stronger bonds and lower solubility.As for the heavy metals contaminated tailings, their immobilization is obtained using both ball and attrition milling devices under specific ball to powder ratio values. The degree of metals immobilization is evaluated by analyzing the corresponding leachable fraction obtained through the Synthetic Precipitation Leaching Procedure (SPLP) proposed by EPA. X-ray diffraction and granulometric analyses revealed no significant alterations of the intrinsic character of the tailings after milling except for a relatively small increase in particles size.The increase in immobilization efficiency when tailings are mechanically treated may be due to specific phenomena induced during milling such as entrapment of heavy metals into aggregates, solid diffusion of metals into the crystalline reticulum of soil particles, the formation of new fresh surfaces onto which heavy metals may be irreversibly adsorbed as well as metal trans-speciation onto tailings fractions characterized by stronger bonds and lower solubility.     

农药乳化剂筛选方法的改进与应用

农药乳化剂的筛选,实质就是含阴离子乳油和含非离子乳油体积比的筛选。原方法对单品种农药液的筛选最适合,但阴离子乳油和非离子乳油体积比完全是凑整10。改进后的筛选方法,二者的体积比则不凑整10,既可对单品种农药液进行筛选,也可对多品种农药液或未知农药液进行筛选,与前者相比,后者具有操作方法简便、经济、操作温度易控制(30℃)、应用范围宽、筛选速度快(10min/个)等优点,非常适合农药厂家在生产乳油时应用。     

Foam extrusion of high density polyethylene/wood‐flour composites using chemical foaming agents

A one‐way analysis of variance and thermal analysis were performed in this study to examine the influences of the contents, types (exothermic vs. endothermic), and forms (pure vs. masterbatch) of chemical foaming agents (CFAs), as well as the use of coupling agents, on the density reduction (or void fraction) and cell morphology of extrusion‐foamed neat high density polyethylene (HDPE) and HDPE/wood‐flour composites. The CFA types and forms did not affect the void fractions of both the neat HDPE and HDPE/wood‐flour composites. However, a gas containment limit was observed for neat HDPE foams whereas the average cell size achieved in the HDPE/wood‐flour composite foams remained insensitive to the CFA contents, irrespective of the foaming agent types. The experimental results indicated that the use of coupling agent in the formulation was required to achieve HDPE/wood‐flour composite foams with high void fraction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3139–3150, 2003     

Storage. effect on selected characteristics and lipids of defatted soy flours

Three defatted soy flours (fully toasted, white and enzyme active) 92 days after production date were stored at 23 C for periods of 0, 60, 120 and 180 days. At each storage period, lipoxygenase activity, thiobarbituric acid number (TBA), Nitrogen Solubility Index (NSI) and total lipid were determined in 5 replications of each flour. The lipid was separated into 3 fractions by silicic acid column chromatography and the fatty acid composition of each fraction was determined by GLC. Lipids in each fraction were identified by TLC procedures. Toasted flour had the greatest amount of total lipid and lowest TBA of the flours and no lipoxy-genase activity. Enzyme active soy flour had the highest NSI and the greatest lipoxygenase activity. During storage, lipoxygenase activity of enzyme active flour and TBA and total lipid of each flour de-creased. Percentages of lipids in fraction I, II or III were different among the soy flours, and the percentages of lipids in fractions I and II changed during storage. In each lipid fraction during storage, linoleic acid decreased in toasted and white flours but remained constant in enzyme active flour. Linoleic acid in any lipid fraction of enzyme active flour was lowest of the soy flours.     

Preparation and morphology of polypropylene/wood flour composite foams via extrusion

In this study, polypropylene (PP)/wood flour composites foams with an average cell size lower than 100 μ were successfully produced by extrusion. The effects of the coupling agent (maleated PP), wood flour content (20%, 30%, and 40% weight), initial wood moisture, and blowing agent content on the cell structure are reported. It was found that the addition of a coupling agent increases the blowing agent efficiency and helps to reduce the density of the composites. Moreover, wood moisture appears to be an effective secondary blowing agent under specific conditions. POLYM. COMPOS., 26:731–738, 2005. © 2005 Society of Plastics Engineers     

Particle size effects on supercritical CO<Subscript>2</Subscript> extraction of oil-containing seeds

Rosehip seeds were milled, sieved, and extracted with 26.3 g/g substrate/h of supercritical carbon dioxide (CO₂) at 40°C and 300 bar. The extraction kinetics were characterized by an initial solubility-controlled period (8.78 g oil/kg CO₂ at 40°C and 300 bar), followed by a transition period to a final mass transfer-controlled process. The integral yield of oil approached an asymptotic value that was dependent on the particle size of the substrate: 57.1 g oil/kg dry oil-free substrate (large particles), 171.0 g/kg (medium-size particles), or 391.5 g/kg (small particles). Based on gravimetric determinations and microscopic analysis, our size-classification process segregated seed parts having different oil contents. Particles ≥0.85 mm were mainly composed of tough, lignified testa fragments devoid of oil, whereas particles ≤0.425 mm contained mostly brittle, oil-rich germ fragments. The segregation of seed in fractions with different oil contents may be a common occurrence in supercritical extraction experiments, especially for seeds with thick and/or hard testa and small germ, whose fractions can be separated by sieving.     

The use of the ring gap sizer for characterization of particle shape in the sieve range

The ring gap sizer sorts particles by their minimum dimension, i.e. thickness. This new instrument has been used to establish particle shape factors and distributions of powders in the sieve range.The powders investigated were quartz and tablet granules, i.e. powders consisting of non-equidimensional particles. It is shown that the combination of results obtained by the ring gap sizer, dry sieving and microscopy gave log-normal distributions of particle flakiness. This was in good agreement with results obtained by a microscopical reference method.For the quartz powder the variation of particle elongation with changing particle size was also determined, using the ring gap sizer to obtain samples of varying particle size, which were then measured on length and breadth by microscopy.Additionally, the two average values of flakiness and elongation have been used to calculate the Heywood surface and volume shape coefficients.     

Strength and breakage of activated sludge flocs

The breakage of activated sludge flocs under turbulent shear conditions was investigated as a function of floc size. Municipal activated sludge flocs were fractionated by sieving to narrow size fractions. Shear stress distribution functions for the breakage of activated sludge floc samples were obtained. It was found that by increasing the floc size, this distribution was skewed towards smaller shear stress values and became broader. Results of experiments showed that the median shear stress, τ₅₀, required for floc breakage reduced by about 23% from 3.9 Pa for 45-63 μm sieve fraction to 3 Pa for the 150-180 μm sieve fraction. Under steady conditions, the median shear stress for the breakage of fragments that formed due to the breakage of larger flocs was as much as three times larger than that of the original flocs.