Hidrociclóns

Descrición

Hidrociclóns are cono-cylindrical in shape, with a tangential feed inlet into the cylindrical section and an outlet at each axis. The outlet at the cylindrical section is called the vortex finder and extends into the cyclone to reduce short-circuit flow directly from the inlet. At the conical end is the second outlet, the spigot. For size separation, both outlets are generally open to the atmosphere. Hydrocyclones are generally operated vertically with the spigot at the lower end, hence the coarse product is called the underflow and the fine product, leaving the vortex finder, the overflow. Figure 1 schematically shows the principal flow and design features of a typical hidrociclón típico : the two vortices, the tangential feed inlet and the axial outlets. Except for the immediate region of the tangential inlet, the fluid motion within the cyclone has radial symmetry. If one or both of the outlets are open to the atmosphere, a low pressure zone causes a gas core along the vertical axis, inside the inner vortex.

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Figura 1. Principais características do hidrociclón.

O principio de funcionamento é sinxelo: o fluído, que leva as partículas en suspensión, entra no ciclón tanxencialmente, espiral cara abaixo e produce un campo centrífugo en fluxo de vórtice libre. As partículas máis grandes móvense a través do fluído cara ao exterior do ciclón nun movemento en espiral e saen pola espiga cunha fracción do líquido. Debido á área límite da espiga, establécese un vórtice interior, que xira na mesma dirección que o exterior pero que flúe cara arriba, e sae do ciclón polo buscador de vórtices, levando consigo a maior parte do líquido e das partículas máis finas. Se se supera a capacidade da espiga, o núcleo de aire péchase e a descarga da espiga pasa dun pulverizador en forma de paraugas a unha "corda" e unha perda de material groso ata o desbordamento.

The diameter of the cylindrical section is the major variable affecting the size of particle that can be separated, although the outlet diameters can be changed independently to alter the separation achieved. While early workers experimented with cyclones as small as 5 mm diameter, commercial hydrocyclone diameters currently range from 10 mm to 2.5 m, with separating sizes for particles of density 2700 kg m−3 of 1.5–300 μm, decreasing with increased particle density. Operating pressure drop ranges from 10 bar for small diameters to 0.5 bar for large units. To increase capacity, multiple small hidrociclóns desde unha única liña de alimentación. may be manifolded from a single feed line.

Aínda que o principio de funcionamento é sinxelo, moitos aspectos do seu funcionamento aínda son pouco entendidos, e a selección e predición de hidrociclóns para a operación industrial son en gran parte empíricas.

Clasificación

Barry A. Wills, James A. Finch FRSC, FCIM, P.Eng., in Wills' Mineral Processing Technology (Eighth Edition), 2016

9.4.3 Hidrociclóns versus pantallas

Hydrocyclones have come to dominate classification when dealing with fine particle sizes in closed grinding circuits (<200 µm). However, recent developments in screen technology (Chapter 8) have renewed interest in using screens in grinding circuits. Screens separate on the basis of size and are not directly influenced by the density spread in the feed minerals. This can be an advantage. Screens also do not have a bypass fraction, and as Example 9.2 has shown, bypass can be quite large (over 30% in that case). Figure 9.8shows an example of the difference in partition curve for cyclonesand screens. The data is from the El Brocal concentrator in Peru with evaluations before and after the hydrocyclones were replaced with a Derrick Stack Sizer® (see Chapter 8) in the grinding circuit(Dündar et al., 2014). Consistent with expectation, compared to the cyclone the screen had a sharper separation (slope of curve is higher) and little bypass. An increase in grinding circuit capacity was reported due to higher breakage rates after implementing the screen. This was attributed to the elimination of the bypass, reducing the amount of fine material sent back to the grinding millswhich tends to cushion particle–particle impacts.

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Figura 9.8. Curvas de partición para ciclóns e pantallas no circuíto de moenda do concentrador El Brocal.

(Adaptado de Dündar et al. (2014))

Changeover is not one way, however: a recent example is a switch from screen to cyclone, to take advantage of the additional size reduction of the denser payminerals (Sasseville, 2015).

Proceso e deseño metalúrxico

Eoin H. Macdonald, in Handbook of Gold Exploration and Evaluation, 2007

Hidrociclóns

Hydrocyclones are preferred units for sizing or desliming large slurry volumes cheaply and because they occupy very little floor space or headroom. They operate most effectively when fed at an even flow rate and pulp density and are used individually or in clusters to obtain desired total capacities at required splits. Sizing capabilities rely on centrifugal forces generated by high tangential flow velocities through the unit. The primary vortex formed by the incoming slurry acts spirally downwards around the inner cone wall. Solids are flung outwards by centrifugal force so that as the pulp moves downwards its density increases. Vertical components of the velocity act downwards near the cone walls and upwards near the axis. The less dense centrifugally separated slime fraction is forced upwards through the vortex finder to pass out through the opening at the upper end of the cone. An intermediate zone or envelope between the two flows has zero vertical velocity and separates the coarser solids moving downwards from the finer solids moving upwards. The bulk of the flow passes upwards within the smaller inner vortex and higher centrifugal forces throw the larger of the finer particles outward thus providing a more efficient separation in the finer sizings. These particles return to the outer vortex and report once more to the jig feed.

The geometry and operating conditions within the spiral flow pattern of a typical hidrociclón típico  are described in Fig. 8.13. Operational variables are pulp density, feed flow rate, solids characteristics, feed inlet pressure and pressure drop through the cyclone. Cyclone variables are area of feed inlet, vortex finder diameter and length, and spigot discharge diameter. The value of the drag coefficient is also affected by shape; the more a particle varies from sphericity the smaller is its shape factor and the greater its settling resistance. The critical stress zone may extend to some gold particles as large as 200 mm in size and careful monitoring of the classification process is thus essential to reduce excessive recycling and the resulting build up of slimes. Historically, when little attention was given to the recovery of 150 μm m gold grains, carry-over of gold in the slime fractions appears to have been largely responsible for gold losses that were recorded to be as high as 40–60% in many gold placer operations.

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8.13. Xeometría normal e condicións de funcionamento dun hidrociclón.

Figure 8.14 (Warman Selection Chart) is a preliminary selection of cyclones for separating at various D50 sizings from 9–18 microns up to 33–76 microns. This chart, as with other such charts of cyclone performance, is based upon a carefully controlled feed of a specific type. It assumes a solids content of 2,700 kg/m3 in water as a first guide to selection. The larger diameter cyclones are used to produce coarse separations but require high feed volumes for proper function. Fine separations at high feed volumes require clusters of small diameter cyclones operating in parallel. The final designparameters for close sizing must be determined experimentally, and it is important to select a cyclone around the middle of the range so that any minor adjustments that may be required can be made at the start of operations.

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8.14. Gráfico de selección preliminar de Warman.

Afirma que o ciclón CBC (leito circulante) clasifica os materiais de alimentación de ouro aluvial de ata 5 mm de diámetro e obtén unha alimentación constantemente elevada do fluxo inferior. A separación ten lugar a aproximadamente  D 50/150 micras baseada na sílice de densidade 2,65. Afirmase que o subfluxo do ciclón CBC é particularmente susceptible de separación por jig debido á súa curva de distribución de tamaño relativamente suave e á eliminación case completa de partículas finas de residuos. Non obstante, aínda que se afirma que este sistema produce un concentrado primario de alto grao de minerais pesados ​​ecuantes nunha única pasada a partir dunha alimentación de tamaño relativamente longo (por exemplo, areais minerais), non hai tales cifras de rendemento dispoñibles para o material de alimentación aluvial que conteña ouro fino e escamoso. . hidrociclóns desde unha única liña de alimentación. para puntos de corte entre 30 e 100 micras.

Táboa 8.5. Datos técnicos de hidrociclóns AKW

Tipo (KRS) Diámetro (mm) Caída de presión Capacidade Punto de corte (micras)
Purín (m3/h) Sólidos (t/h máx).
2118 100 1–2.5 9.27 5 30-50
2515 125 1–2.5 11–30 6 25-45
4118 200 0,7–2,0 18-60 15 40-60
(RWN) 6118 300 0,5–1,5 40–140 40 50-100

Desenvolvementos nas tecnoloxías de trituración e clasificación do mineral de ferro

A. Jankovic, in Iron Ore, 2015

8.3.3.1 Separadores de hidrociclóns

The hydrocyclone, also referred to as cyclone, is a classifying device that utilizes centrifugal force to accelerate the settling rate of slurryparticles and separate particles according to size, shape, and specific gravity. It is widely used in the minerals industry, with its main use in mineral processing being as a classifier, which has proved extremely efficient at fine separation sizes. It is extensively used in closed-circuit grinding operations but has found many other uses, such as desliming, degritting, and thickening.

A typical hydrocyclone (Figure 8.12a) consists of a conically shaped vessel, open at its apex, or underflow, joined to a cylindrical section, which has a tangential feed inlet. The top of the cylindrical section is closed with a plate through which passes an axially mounted overflow pipe. The pipe is extended into the body of the cyclone by a short, removable section known as the vortex finder, which prevents short-circuiting of feed directly into the overflow. The feed is introduced under pressure through the tangential entry, which imparts a swirling motion to the pulp. This generates a vortex in the cyclone, with a low-pressure zone along the vertical axis, as shown in Figure 8.12b. An air-core develops along the axis, normally connected to the atmosphere through the apex opening, but in part created by dissolved air coming out of solution in the zone of low pressure. The centrifugal force accelerates the settling rate of the particles, thereby separating particles according to size, shape, and specific gravity. Faster settling particles move to the wall of the cyclone, where the velocity is lowest, and migrate to the apex opening (underflow). Due to the action of the drag force, the slower-settling particles move toward the zone of low pressure along the axis and are carried upward through the vortex finder to the overflow.

Imaxe 8.12. Hidrociclón (https://www.aeroprobe.com/applications/examples/australian-mining-industry-uses-aeroprobe-equipment-to-study-hydro-cyclone) e batería de hidrociclón. Folleto informativo sobre hidrociclóns Cavex, https://www.weirminerals.com/products_services/cavex.aspx.

Hydrocyclones are almost universally used in grinding circuits because of their high capacity and relative efficiency. They can also classify over a very wide range of particle sizes (typically 5–500 μm), smaller diameter units being used for finer classification. However, cyclone application in magnetite grinding circuits can cause inefficient operation due to the density difference between magnetite and waste minerals (silica). Magnetite has a specific density of about 5.15, while silica has a specific density of about 2.7. In hidrociclóns desde unha única liña de alimentación., os minerais densos sepáranse cun tamaño de corte máis fino que os minerais máis lixeiros. Polo tanto, a magnetita liberada estase a concentrar no subfluxo do ciclón, coa consecuente molienda excesiva da magnetita. Napier-Munn et al. (2005) observaron que a relación entre o tamaño de corte corrixido ( d 50c) and particle density follows an expression of the following form depending on flow conditions and other factors:


d50c∝ρs−ρl−n

 

onde  ρ s é a densidade dos sólidos,  ρ l is the liquid density, and n  está entre 0,5 e 1,0. Isto significa que o efecto da densidade mineral no rendemento dos ciclóns pode ser bastante significativo. Por exemplo, se o  d 50c da magnetita é de 25 μm, entón o  d 50c of silica particles will be 40–65 μm. Figure 8.13 shows the cyclone classification efficiency curves for magnetite (Fe3O4) and silica (SiO2) obtained from the survey of an industrial ball mill magnetite grinding circuit. The size separation for silica is much coarser, with a d 50c for Fe3O4 of 29 μm, while that for SiO2 is 68 μm. Due to this phenomenon, the magnetite grinding mills in closed circuits with hydrocyclones are less efficient and have lower capacity compared to other base metalore grinding circuits.

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Imaxe 8.13. Eficiencia ciclónica para magnetita Fe3O4 e sílice SiO2: estudo industrial.

 

Tecnoloxía de procesos de alta presión: fundamentos e aplicacións

M.J. Cocero PhD, in Industrial Chemistry Library, 2001

Dispositivos de separación de sólidos

Hidrociclón

Este é un dos tipos máis sinxelos de separadores de sólidos. É un dispositivo de separación de alta eficiencia e pódese usar para eliminar eficazmente sólidos a altas temperaturas e presións. É económico porque non ten partes móbiles e require pouco mantemento.

The separation efficiency for solids is a strong function of the particle-size and temperature. Gross separation efficiencies near 80% are achievable for silica and temperatures above 300°C, while in the same temperature range, gross separation efficiencies for denser zircon particles are greater than 99% [29].

O principal inconveniente do funcionamento dos hidrociclóns é a tendencia dalgunhas sales a adherirse ás paredes do ciclón.

Cross micro-filtration

Os filtros de fluxo cruzado compórtanse dun xeito similar ao que se observa normalmente na filtración de fluxo cruzado en condicións ambientais: o aumento das taxas de cizallamento e a reducida viscosidade do fluído producen un aumento do número de filtrados. A microfiltración cruzada aplicouse á separación de sales precipitadas como sólidos, dando unha eficiencia de separación de partículas que normalmente supera o 99,9%. Goemans  et al. [30] studied sodium nitrate separation from supercritical water. Under the conditions of the study, sodium nitrate was present as the molten salt and was capable of crossing the filter. Separation efficiencies were obtained that varied with temperature, since the solubility decreases as the temperature increases, ranging between 40% and 85%, for 400 °C and 470°C, respectively. These workers explained the separation mechanism as a consequence of a distinct permeability of the filtering medium towards the supercritical solution, as opposed to the molten salt, based on their clearly distinct viscosities. Therefore, it would be possible not only to filter precipitated salts merely as solids but also to filter those low-melting-point salts that are in a molten state.

Os problemas de funcionamento debéronse principalmente á corrosión dos filtros polos sales.

 

Papel: Reciclaxe e Materiais Reciclados

M.R. Doshi, J.M. Dyer, in Reference Module in Materials Science and Materials Engineering, 2016

3.3 Limpeza

Os produtos de limpeza ou  hidrociclóns desde unha única liña de alimentación. remove contaminants from pulp based on the density difference between the contaminant and water. These devices consist of conical or cylindrical-conical pressure vessel into which pulp is fed tangentially at the large diameter end (Figure 6). During passage through the cleaner the pulp develops a vortex flow pattern, similar to that of a cyclone. The flow rotates around the central axis as it passes away from the inlet and toward the apex, or underflow opening, along the inside of the cleaner wall. The rotational flow velocity accelerates as the diameter of the cone decreases. Near the apex end the small diameter opening prevents the discharge of most of the flow which instead rotates in an inner vortex at the core of the cleaner. The flow at the inner core flowsaway from the apex opening until it discharges through the vortex finder, located at the large diameter end in the center of the cleaner. The higher density material, having been concentrated at the wall of the cleaner due to centrifugal force, is discharged at the apex of the cone (Bliss, 1994, 1997).

Figura 6. Partes dun hidrociclón, principais patróns de fluxo e tendencias de separación.

Cleaners are classified as high, medium, or low density depending upon the density and size of the contaminants being removed. A high density cleaner, with diameter ranging from 15 to 50 cm (6–20 in) is used to remove tramp metal, paper clips, and staples and is usually positioned immediately following the pulper. As the cleaner diameter decreases, its efficiency in removing small sized contaminants increases. For practical and economic reasons, the 75-mm (3 in) diameter cyclone is generally the smallest cleaner used in the paper industry.

Reverse cleaners and throughflow cleaners are designed to remove low density contaminants such as wax, polystyrene, and stickies. Reverse cleaners are so named because the accepts stream is collected at the cleaner apex while the rejects exit at the overflow. In the throughflow cleaner, accepts and rejects exit at the same end of the cleaner, with accepts near the cleaner wall separated from the rejects by a central tube near the core of the cleaner, as shown in Figure 7.

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Figura 7. Esquemas dun limpador de caudal.

As centrífugas continuas utilizadas nas décadas de 1920 e 1930 para eliminar a area da pasta de papel foron interrompidas despois do desenvolvemento dos hidrociclóns. O Gyroclean, desenvolvido no Centre Technique du Papier, Grenoble, Francia, consta dun cilindro que xira a 1200–1500 rpm (Bliss, 1997; Julien Saint Amand, 1998, 2002). A combinación de tempo de residencia relativamente longo e forza centrífuga elevada permite aos contaminantes de baixa densidade tempo suficiente para migrar ao núcleo do limpador onde son rexeitados pola descarga do vórtice central.

 

M.T. Thew, in Encyclopedia of Separation Science, 2000

Sinopse

Though the solid–liquid hidrociclón típico  estivo establecido durante a maior parte do século XX, un rendemento satisfactorio de separación líquido-líquido non chegou ata a década de 1980. A industria petroleira offshore necesitaba equipos compactos, robustos e fiables para eliminar o aceite contaminante finamente dividido da auga. Esta necesidade foi satisfeita por un tipo de hidrociclón significativamente diferente, que por suposto non tiña partes móbiles.

Despois de explicar esta necesidade máis completamente e comparala coa separación ciclónica sólido-líquido no procesado de minerais, indícanse as vantaxes que o hidrociclón confería sobre os tipos de equipos instalados anteriormente para cumprir co deber.

Os criterios de avaliación do rendemento da separación enuméranse antes de discutir o rendemento en termos de constitución da alimentación, control do operador e enerxía necesaria, é dicir, o produto da caída de presión e o caudal.

O ambiente para a produción de petróleo establece algunhas limitacións para os materiais e isto inclúe o problema da erosión das partículas. Menciónanse os materiais típicos empregados. Descríbense os datos de custos relativos dos tipos de plantas de separación de petróleo, tanto capitais como recorrentes, aínda que as fontes son escasas. Finalmente, descríbense algúns indicadores para un maior desenvolvemento, xa que a industria petroleira busca equipos instalados no fondo do mar ou mesmo no fondo do pozo.

Mostraxe, control e balance de masas

Barry A. Wills, James A. Finch FRSC, FCIM, P.Eng., in Wills' Mineral Processing Technology (Eighth Edition), 2016

3.7.1 Uso do tamaño das partículas

Moitas unidades, como  hidrociclóns desde unha única liña de alimentación. and gravity separators, produce a degree of size separation and the particle size data can be used for mass balancing (Example 3.15).

Example 3.15 is an example of node imbalance minimization; it provides, for example, the initial value for the generalized least squares minimization. This graphical approach can be used whenever there is “excess” component data; in Example 3.9 it could have been used.

Example 3.15 uses the cyclone as the node. A second node is the sump: this is an example of 2 inputs (fresh feed and ball milldischarge) and one output (cyclone feed). This gives another mass balance (Example 3.16).

In Chapter 9 we return to this grinding circuit example using adjusted data to determine the cyclone partition curve.


Hora de publicación: 07-maio-2019
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