Sedimentation Tanks for Treating Rainwater: CFD Simulations and PIV Experiments

The removal of solids is the most important step when treating rainwater. The article evaluates two designs of sedimentation tanks that can be used for the continuous separation of fine particles from water: OS—standard sedimentation tanks, and OW—swirl sedimentation tanks. The tanks were studied by conducting computational fluid dynamics (CFD) modeling and particle image velocimetry (PIV) experiments. The settling process in sedimentation tank was carried out at varying operating flow rates. A tank with a modified structure was used for the tests, where water was supplied by a nozzle placed at an angle. This solution made it possible to obtain a rotational flow that transported the suspended particles towards its wall, where downward axial velocity resulted in the settling of particles. Based on the research, it was observed that the flow patterns showed inward flow at the bottom of the tank and an upward flow and the lifting of the settled particles near the hatch at the bottom. The presented experimental measurements provided detailed insight into flow patterns, and valuable calibration and verification data for further CFD modeling. Traditional PIV techniques are useful in the case of standard design, whereas CFD is invaluable for supporting this work and for investigating the design of novel sedimentation tanks.

An LBM Study of the Sedimentation Behaviors of Double Particles With Non-Identical Sizes

In this work, the size effects on the sedimentation behaviors of two non-identical particles are investigated through the lattice Boltzmann method (LBM). The method is first validated by simulating the settling process of single and double particles, which agrees well with analytical and previous results. Then the hydrodynamic behaviors of double non-identical-size particles settling in an infinite-long narrow channel are investigated, in which the larger particle is initially placed above the smaller one. Different sedimentation behaviors are observed with different diameter ratios in the present work. In the first Draft-Kiss-Tumble (DKT) cycle, it is observed that the time durations of both drafting state and kissing state are shortened by the increase of the diameter ratio γ . Considering a longer sedimentation time, three different settling modes are observed with different diameter ratios, which can be summarized as: (1). Repeated DKT cycle (1.0 ≤ γ ≤ 1.13); (2). Repeated DT-DKT after the first DKT cycle (1.14 ≤ γ ≤ 1.22); (3). Separation after the first DKT cycle (1.23 ≤ γ). It should be noted that Mode 2 is first defined in this work, which helps explain the divergence in the threshold diameter ratios of the recurrence of DKT cycles proposed in the previous literatures. In addition, the periodical length of the repeated cycles experiences instant increase and decrease against the diameter ratio near the transition from Mode 1 to Mode 2, while an instant increase is also observed near the threshold diameter ratio between Mode 2 and Mode 3.

Influence of Process Parameters on Copper Content in Reduced Iron Silicate Slag in a Settling Furnace

During the pyrometallurgical extraction of copper, a significant fraction of this metal is lost with discard slag, which decreases profits and overall copper recovery. These copper losses can be reduced by using a settling furnace, in which suspended droplets containing copper separate from slag under the influence of gravity. An industrial trial was conducted in a settling furnace to increase the knowledge of the effect of temperature and settling time on the copper content of slag, and thus enhance the settling process to increase copper recovery. Slag samples were collected from four sample points: the ingoing and outgoing slag stream, within the furnace during settling, and the granulated slag. The chemical composition of the slag samples was analyzed and compared between batches with different temperatures and settling times. The appearance of copper and its associated phases were analyzed using a scanning electron microscope with an energy-dispersive X-ray spectroscopy detector (SEM-EDS). The results indicated that the outgoing slag copper content increased with an increase in temperature, and it was also concluded to be influenced by the attachment of copper to spinels and gas bubbles. The results indicate that regulating the settling furnace temperature to a lower interval could increase copper recovery.

A new model for settling velocity of non-spherical particles

The settlement of non-spherical particles, such as propagules of plants and natural sediments, are commonly observed in riverine ecosystems. The settling process is influenced by both particle properties (size, density and shape) and fluid properties (density and viscosity). Therefore, the drag law of non-spherical particles is a function of both particle Reynolds number and particle shape. Herein, a total of 828 settling data are collected from the literatures, which cover a wide range of particle Reynolds number (0.008–10000). To characterize the influence of particle shapes, sphericity is adopted as the general shape factor, which varies from 0.421 to 1.0. By comparing the measured drag with the standard drag curve of spheres, we modify the spherical drag law with three shape-dependent functions to develop a new drag law for non-spherical particles. Combined with an iterative procedure, a new model is thus obtained to predict the settling velocity of non-spherical particles of various shapes and materials. Further applications in hydrochorous propagule dispersal and sediment transport are projected based on deeper understanding of the settling process.

TECHNOGENIC IMPACT OF RADIOACTIVE CONTAMINATION OF METAL SMELTING PRODUCTS ON ENVIRONMENT AND POPULATION

The analysis of the distribution of radionuclides in the products of blast furnace and steelmaking melting operation processes is carried out. It was shown that the blast furnace melting process is considerably affected by natural radionuclides whereas steelmaking furnace process - by technogenic ones. The main impact on the environment is exerted by the gas-dust fraction, which contaminates the surrounding soil, vegetation and ground water during the settling process. An additional dose of external irradiation of the population and personnel is created by slag and metal fractions. High radiation doses are possible in case of ingestion of high-intensity sources of 60Co and 137Cs into the melt. Internal irradiation of people occurs due to gas and dust emissions.

señorío arzobispal de Yepes (siglos XIII y XIV)

El presente artículo tiene como finalidad contribuir a un mayor conocimiento acerca del señorío arzobispal de Yepes, así como de los diferentes agentes que intervinieron en su origen y posterior desarrollo. Su estudio para los siglos XIII y XIV resulta de gran interés pues nos permite conocer aspectos relacionados no sólo con el devenir de la villa y sus vasallos, sino también con el proceso de asentamiento previo por parte de las tropas cristianas en la región. No obstante, los enfrentamientos protagonizados por el concejo de Toledo y los prelados de la sede primada ocupan un espacio destacado dada su relevancia y el mayor volumen de datos al respecto. The aim of this article is to contribute to a broader learning of the archiepiscopal manor of Yepes and the different agents that took part in its origin and its subsequent development. Its study in the 13th and 14th centuries is of great interest as it allows us to identify not only the aspects related to the evolution of the town and the vassals but also those related to the settling process accomplished by Christians troops in the region. Nevertheless, the conflicts leaded by the council of Toledo and the prelates of the primacy see occupy an important place in this work due to their relevance and the large amount of data relate to them.

Experimental Study on the Wall Factor for Rod-Shaped Proppant Settling in Vertical Fracture

Hydraulic fracturing is an important technology to improve oil and gas production. In recent years, rod-shaped proppant has received increasing attention for its advantages in avoiding fracture closure and enhancing conductivity. Due to its special shape, the settling process in the fracture is more complicated than that of a spherical proppant. Accurate description of the wall factor of fracture on the settling rod-shaped proppant is pivotal in predicting the transport distance of rod-shaped proppant and improving the effect of fracturing. However, few researches have been reported about the fracture wall factor on the settling rod-shaped proppant. In this study, the transparent fracture model with different width and a high-speed camera were used to record the settling process of the rod-shaped proppant in the fracture. A total of 215 tests were carried out to analyze the effects of fluid properties, the equivalent dimensionless diameter, sphericity, and Reynolds number on the wall factor, involving the ranges of the equivalent dimensionless diameter and the particle Reynolds number are 0.03 to 1.47 and 0.03–1354.14, respectively. The settling processes of rod-shaped proppant under horizontal and vertical states were studied, and two wall factor models for the two states were established, respectively. The results show that the wall factor is a function of both the equivalent dimensionless diameter and Reynolds number. Finally, the prediction models of wall factor with the prediction error of 1.70 and 4.44% are established for these two Reynolds number regions, respectively. The results of this study can further improve the performance of rod-shaped proppant in hydraulic fracturing.

A Case Study on Settling Process in Inclined-Tube Gravity Sedimentation Tank for Drip Irrigation with the Yellow River Water

A sedimentation tank which can remove fine sediment with low cost and high efficiency is of great significance for the wide application of drip irrigation techniques with the Yellow River water. In this study, the settling process of an inclined-tube gravity sedimentation tank which has high removal efficiency for fine particles in practice was thoroughly investigated. The sediment concentration distribution in the tank was measured by an optical back-scattering turbidimeter. The sediment thickness at the tank bottom was also measured. In addition, the size grading of sediment deposited at different positions on the tank bottom and at different heights in the inclined tubes was also measured by a laser particle size analyzer. It was found that the removal efficiency of fine sediment was 64.7–69.7% in the inclined-tube gravity sedimentation tank, which was higher than that of the sedimentation tank without inclined tubes (with a sediment removal rate of 20.7–32%). The sediment was mainly deposited in the flow adjustment area and settlement area with inclined tubes. A suitable height for the inclined tubes was 70–90 cm. In addition, the water inlet, baffle, and overflow weir in the tank negatively affected the fine sediment settling in two experiment cases. The experimental results enhance our understanding of the sedimentation characteristics in the tank, and indicate the direction for the subsequent structural optimization of the tank.

Settling process of cassava starch using natural coagulant from Moringa oleifera Lam seed extract

Cassava starch has many known applications in food, paper, glue and textile industries, including even biodegradable packaging. In small and medium industries, the starch is obtained by washing the peeled and grinded manioc roots, followed by leaving the washwater for settling before drying the concentrated slurry. Since starch particles are very fine and have a low density, their settling time is high, resulting in a batch operation that lasts for 18 to 24 h. Therefore, it becomes suitable to form larger and heavier starch sets by means of applying coagulants, allowing the particles to settle faster. In the work reported here, the natural coagulant M. oleifera seed extract was used to decrease the settling time of the cassava starch. The effect of the initial concentration of the particles and the coagulant content on the final sedimentation time was evaluated on the batch settling tests. The results showed that the use of the coagulant reduced the sedimentation time in a beaker from 14h to 2h, allowing a quick batch operation.

The artificial simulation of oilwater emulsions to study emulsion settling process with the use of coalescing element

The article presents the sequence and results of experimental modeling of artificial oil-water emulsions based on anhydrous oil and water with density and mineralization as close as possible to the real field conditions of the researched deposits. The practical importance of simulation of artificial emulsions was due to the need to work with emulsions of different degrees of water cut, which is possible only by laboratory simulation conditions. We prepared artificial oil-water emulsion using a turbine mixer in a thermostated container. Then we set the emulsion preparation mode: number of revolutions (n1, min –1) and mixing time (t, min). We selected the optimal parameters to create stable artificial oil-water emulsions according to different types of oils.