Patent Publication Number: US-9884325-B2

Title: Hydrocyclone with fine material depletion in the cyclone underflow

Description:
BACKGROUND 
     The present invention relates to a hydrocyclone with an inflow region providing tangential inflow for a feed slurry and a separation region following the inflow region with an underflow discharge pipe to carry off heavy materials and an overflow nozzle projecting into the interior of the hydrocyclone. 
     Generally, a hydrocyclone comprises a cylindrical segment with a tangential inflow (inlet nozzle) and a subsequent conical segment with the underflow nozzle or apex nozzle. The vortex finder or overflow nozzle projects axially from above in the form of an immersion tube into the interior of the cyclone. 
     The designations “upward(s)” and “downward(s)” in the present description refer to the overflow (specifically lighter and/or finer-grained fraction) and the underflow (specifically heavier and/or coarser fraction). However, the actual positioning of the hydrocyclone largely does not depend on this, so horizontally installed hydrocyclones are also frequently used. 
     Hydrocyclones are separation units which are used to separate mixtures of solids on the basis of different sinking speeds. In this process, the fractions are not separated fully from one another, and the large differences in the sinking speed are substantiated with greatly varying probabilities of reaching the respective coarse or fine particle outlet. 
     As a rule, the suspension is fed to the head piece of the cyclone, forced from there into a downward orbit and accelerated into the resulting downward spiral due to the conical taper of the bottom cyclone section. This acceleration and the resulting centrifugal forces create a strong force field that drives all particles that are specifically heavier than the surrounding fluid outwards, while all of the lighter particles are conveyed inwards. The layers close to the core in the overflow stream flowing upwards are detached along the entire downward spiral. The thickened stream discharged at the bottom is called the underflow, and the upwardly discharged stream is designated as the overflow or top flow. 
     Naturally, the overflow stream contains significantly less solids than the outer streams flowing downwards. In addition, particles with a very low sinking speed have a much higher probability of entering the overflow stream than is the case for the coarse-grained fractions, with the result that the overflow is enriched with fines (relatively in relation to the solids mass). However, the reverse is true in terms of the volume (in mg/l)—in relation to the volume flow discharged, the fines are depleted in the overflow in fine fractions if these fractions have a higher specific weight than the fluid. 
     Thus, the fines concentration in the underflow increases (often unintentionally) in relation to the fluid volume removed. 
     In order to prevent this, a wash water cyclone was developed with the aim of creating a barrier water layer (auxiliary sedimentation layer) by means of a lamella and which will make it more difficult for the fines to sediment in the area discharged downwards because of the reduced sedimentation speed. This special hydrocyclone is described in WO 2013/117342. 
     However, unstable conditions often arise in this hydrocyclone, particularly in the area of the flow reversal in the conical outlet area, which result in strong movement by the vortex in the core area and can thus cause the fractions originally separated to be mixed together again. In addition, individual streams may be discharged wrongly, which can also increase the amount of grains discharged wrongly, if the upward flowing core stream (with fines) and the downward flowing, washed underflow are close to one another. 
     Additionally, it has been shown that there is an increased amount of wrongly discharged core stream in the underflow, especially if the feed slurry has a high temperature. The problem is aggravated by the addition of wash water, which can also lead to significant dilution in the underflow. 
     SUMMARY 
     The invention is thus based on the task of improving a hydrocyclone operating with a layer of barrier fluid in such a way that it can be operated more easily under stable conditions, which will further reduce wrong discharge of fines or fine grains in the underflow. The fine material is thus to be depleted in the underflow with regard to the volume-related concentration in the inflow. 
     According to the present disclosure, this object is accomplished by the separation region comprising a conical section and a subsequent cylindrical section above the underflow discharge pipe. 
     This increases the distance between the flow reversal and the underflow outlet. The purpose of the cylindrical section is to move the sedimented coarse material concentrated by means of a rotary movement in a defined movement towards the discharge without giving the (transient) core flow the opportunity to run through into the underflow nozzle or the underflow discharge pipe. The cylindrical extension thus offers a kind of “solids cushion”, which creates a calmed outlet zone through the conventionally arranged discharge nozzle. 
     In addition, this enables the use of a larger underflow nozzle than in conventional hydrocyclones with comparable outlet conditions in the underflow and overflow. Due to the possibility of using a larger underflow nozzle or a larger underflow discharge pipe, the operating reliability is enhanced because the risk of the underflow nozzle becoming blocked is reduced substantially. 
     Good separation results are achieved if the diameter of the cylindrical section is smaller than the height of the cylindrical section. It is favourable if the diameter of the cylindrical section measures at least 25 mm, preferably at least 30 mm. 
     The transition from the conical section to the cylindrical section should preferably be located a maximum of 100 mm after the barrier fluid feed, i.e. underneath the end of the lamella. 
     The lamella should preferably have a substantially cylindrical or conical shape. In the feed area or the cylindrical segment, it may extend in this case from the inflow region of the barrier fluid stream to the transition to the conical separation region or be secured in the conical region. As a result, sufficient time remains for a stable circular stream to form, both in the barrier fluid layer and in the feed slurry. 
     It is beneficial if the lamella tapers to a point at its lower end or is made as thin as possible so that the barrier fluid stream and the feed slurry can be combined so as to be as vortex-free as possible. The two streams should also continue to flow separately from one another as far as possible underneath the lamella. 
     In a favorable embodiment, the mouth orifice of the overflow nozzle extends into the region in which the barrier liquid flow and the feed slurry are carried along together. 
     The lamella may also have compensating orifices which form a connection between the feed slurry and the barrier fluid flow, thus resulting in pressure compensation between barrier fluid and suspension before the two layers meet up. Ideally, the barrier fluid is always subject to a somewhat higher pressure than the suspension in this case. 
     The hydrocyclone according to the invention is described below on the basis of three drawings. In these drawings: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a diagrammatic longitudinal section through an exemplary embodiment of the hydrocyclone according to the invention; 
         FIG. 2  shows a cross-section in the region of the inflow through the hydrocyclone according to the invention; 
         FIG. 3  shows a diagrammatic longitudinal section through another exemplary embodiment of the hydrocyclone according to the invention; 
     
    
    
     DETAILED DESCRIPTION 
     The same reference numbers in the drawing refer to the same components or material flows in each case. 
     The hydrocyclone  1  according to the disclosed embodiment of the invention is illustrated in  FIG. 1 . It is composed of an inflow region  2  and a subsequent separation region  3 . The feed region  2  is cylindrical here. The separation region  3  includes an upper, conical section  15 , which directly adjoins the feed region  2 , and a lower, cylindrical section  18  adjoining the conical section  15 . The diameter x of the cylindrical section  18  measures 30 mm here, and its height y (length of the section  18  viewed in axial direction) is 40 mm here. An underflow discharge pipe  8  for removing coarse material or coarse grains adjoins the cylindrical section  18  after the cross-section narrows. This discharge pipe  8  can act as a support for another nozzle or as the discharge nozzle itself. 
     A feed slurry  6  is supplied to the hydrocyclone  1  via the tangential inflow  4 . The feed slurry  6  may be, for example, a gypsum suspension. The specifically lighter or finer-grained fraction can be discharged as overflow  12  through the overflow nozzle  9 , which projects axially in the form of an immersion tube into the interior of the hydrocyclone  1 , into the conical section  15 . 
     In addition to the tangential inflow  4 , the hydrocyclone  1  also has another inflow  5  (illustrated in  FIG. 2 ) for the barrier fluid stream  7 , which is also supplied tangentially to the inflow region  2  here. The barrier fluid  7  may, for example, be water, alcohol or oil. The barrier fluid stream  7  and the feed slurry  6  are fed to the hydrocyclone  1  separately and kept separate from one another in the hydrocyclone  1  by the lamella  10 . The lamella  10  is, for example, a cylindrical, thin-walled component made of metal. The pure barrier fluid stream  7  meets up with the actual suspension flow (feed slurry  6 ) at the lower end  13  of the lamella  10 . This occurs as soon as the streams of the barrier fluid  7  and the feed slurry  6  have a stable form. 
     The distance z from the bottom end of the lamella  10  to the transition from the conical section  15  to the cylindrical section  18  is less than 100 mm here. 
     After the two volumetric flows  6 ,  7  have been merged, a settling movement of heavy fractions (coarse materials) commences through the barrier layer  7 . This results in depletion of the fines in the underflow  11 . In the conical section  15  of the separation region  3 , the stream is routed in the same way as in conventional hydrocyclones. 
     The lamella  10  has compensating orifices  17  here, which represent a connection between the feed slurry  6  and the barrier fluid flow  7 , resulting in pressure compensation between the barrier fluid  7  and the suspension  6 . These compensating holes are also conceivable in the region of the inflow  5 . 
     The flow arrows indicate that the barrier fluid stream  7  and the feed slurry  6  are intermixed with one another as little as possible. The barrier fluid stream  7  thus forms a barrier fluid layer  7  towards the wall of the conical section  15 . 
     In the cylindrical section  18 , the coarse material that has sedimented has enough space to move specifically towards the underflow discharge pipe  8  by means of a rotating movement. In addition, this cylindrical extension  18  prevents the core flow from running through into the actual underflow  11 . 
     The mouth orifice  14  of the overflow nozzle  9  ends at a slightly lower elevation than the lower the end  13  of the lamella  10 . 
     Depending on the respective volume fractions in the barrier fluid flow  7  and in the feed slurry  6 , the heavy fraction (coarse materials) will be discharged with more accuracy or less. 
       FIG. 2  shows a cross-section through a hydrocyclone  1  according to the invention in the region of the inflow. This clearly shows the tangential inflow  4  for the feed slurry  6  and the tangential inflow  5  for the barrier fluid layer  7 . These two inflows  4 ,  5  flow into the inflow region  2  here substantially in parallel. 
       FIG. 3  shows another exemplary embodiment of the hydrocyclone  1  according to the invention. The diameter D 1  of the inlet region is 75 mm here, and the inner diameter D 2  of the overflow nozzle measures 25 mm. This hydrocyclone has a conical lamella  10 , which extends into the conical section  15  of the separation region  3 . The other feed  5  for supplying the barrier fluid  7  is located between the conical lamella  10  and the conical section  15  of the separation region  3 . The cylindrical section  18  adjoining the conical section  15  has a height y of 150 mm here and a diameter x of 37 mm. The underflow discharge pipe  8  with an initial diameter d 2  of 25 mm and a final diameter of 10 mm is arranged underneath the cylindrical section  18 . The sudden change in the diameter in the underflow nozzle occurs here because a nozzle  19  for discharging the underflow Ills pushed into the underflow discharge pipe  8 . Of course, the underflow nozzle can also have a uniform diameter of, for example, 10 mm. The dimensions mentioned here refer to a hydrocyclone that achieved very good results in the test plant; of course, it is also possible to achieve very good results with other dimensions as well.