WO2019004926A1

WO2019004926A1 - Device for continuously separating particles from a liquid

Info

Publication number: WO2019004926A1
Application number: PCT/SE2018/050722
Authority: WO
Inventors: Ingvar HÄLLGREN
Original assignee: Alfa Laval Corporate Ab
Priority date: 2017-06-30
Filing date: 2018-07-02
Publication date: 2019-01-03
Also published as: SE541832C2; SE1700137A1

Abstract

The invention relates to an efficient liquid cyclone for particle separation from a liquid. A traditional hydro cyclone with a conical lower part has among others a problem of efficiently handling varying flow rates, and the type with a collecting chamber underneath has drainage problems at large particle loads and a continuous flow. The invention solves this by means of a liquid cyclone with a cylindrical cyclone tube (1), in a preferred embodiment, in the bottom provided with a disc forming a vortex reflector (4) with surrounding slots (5) down to a collecting chamber (3). The particles separated in the boundary layer against the cyclone tube (1), are sucked down through slots (5) and leave the separation process in a partial flow, through one or more suction openings (16) in the side of a collecting chamber and / or in its bottom. Additional boundary layer suction may be provided in the lower part of the cyclone tube (1) above the vortex reflector (4). The invention is suitable for cleaning a scrubber liquid from soot and similar hard heavy particles.

Description

DEVICE FOR CONTINUOUSLY SEPARATING PARTICLES FROM A LIQUID.

Technical field

The invention relates to a device for continuous separation of particles from a liquid of lower density than the particles.

Prior art

Today there are traditional hydro cyclones, i.e. liquid cyclones, which use the centrifugal force in a rotating flow in order to separate particles from a liquid.

Compared to a gas cyclone, a liquid cyclone is more difficult to dimension and has also a very limited separation ability, in part because a high density difference between liquid and particles is required, and in part because the liquid, through its high viscosity, gives a low falling speed for the particles towards the cyclone wall. However, liquid cyclones have found their niche as thickener of a particle-filled liquid and then often in multiple stages, as well as a pre-separator to protect sensitive process equipment from harmful heavy particles, such as gravel.

Traditional liquid cyclones have a tangential inlet at one end and are basically of two types, those that thicken a flow with large sludge content along a tapered tube with central sludge outlet, while the partially purified liquid exits at the opposite end where the inlet is located, and the conical or straight cyclones, which accumulate separated sludge in a collecting chamber underneath, i.e. in the opposite end relative to the inlet and the outlet for the unpurified and purified liquid, respectively.

The disadvantage of the first type is that the ability to concentrate is low and the length tends to be impractically long, and that in the case of a high choking of the sludge outlet, or at increased flow, the efficiency is reduced due to the fact that an inlet for unpurified liquid and outlet for purified liquid are short-circuited, i.e. the flow goes the shortest way to the outlet.

RECORD COPY TRANSLATION

(Rule 12.4) In the latter type, the purified liquid leaves the cyclone upward through a central outlet pipe and deposits trapped particles in a collecting chamber at the lower opposite end, leading to an optimal efficiency, but with the disadvantage that large amounts of sludge are difficult to handle, i.e. to intermittently drain the collection tank, in a continuous process.

In summary, there is no type of liquid cyclone capable of handling a continuous and variable liquid flow and in a robust manner separate particles with an efficiency that is closer to the latter of the above-mentioned types than the former.

The solution

The present invention partially solves the above related problems of the prior art liquid cyclones by having the features specified in claim 1.

An embodiment of the invention is shown in Figure 1, which is a sectional view and in Figure 2 a top view, and in Figure 3 a 3D view in a slightly different embodiment.

Detailed description of the Invention

The present invention is basically a liquid cyclone without a conical bottom part, provided with a so-called boundary layer diversion (or rather boundary layer suction) of the particles separated against the cyclone wall in the boundary layer, including a smaller partial flow of liquid.

The main flow of particles enters the cyclone through a tangential inlet, in its upper part, whose cross sectional area and the flow that the flow-driving pump

accomplishes, define the tangential flow rate of the downward vortex, which in turn provides the centrifugal force, which causes the particles to move towards the cyclone wall and are there captured in the boundary layer. The centrifugal force on a particle is proportional to the square of the tangential flow rate at the point at which it is located, divided by the radius at this point. The downwardly directed vortex finally turns against a vortex reflector, or against a bottom if a vortex reflector is missing, and proceeds out of the cyclone through an upwardly directed central outlet pipe. The particles separated against the cyclone tube, together with a partial flow, can continuously leave the separation process in different ways by means of boundary layer suction. The most effective way is to place a vortex reflector above a collection chamber at the bottom of the cyclone. Between the vortex reflector and the inner wall of the cyclone tube, there is one or more slots through which the trapped particles are sucked down to the collecting chamber. Depending on the width of the slot, a more or less weak swirl is also obtained in the collecting chamber, which prevents the particles from sticking to the wall, while preventing them from leaving the wall on their way toward the sludge outlet. The sludge outlet in its simplest form can be a suction pipe in the wall of the collection chamber, or in its bottom, preferably tangentially oriented. For example, the collection chamber can be made funnel-shaped toward the suction pipe, or provided with appropriate flow conductors to deliver the particles to the suction pipe. Other manners, or complementary, for boundary layer suction, is to suck in one or more slots in the cyclone tube above the vortex reflector, and / or down in the collecting chamber wall. In some situations, it is also possible to omit a vortex reflector and let the vortex turn against the bottom, which is more brutal and also results in a poorer result.

Departing sludge flow should be less than 10% of the main flow and so high that the boundary layer suction becomes effective in relation to the application area, thickening or protection of processing equipment downstream.

The cyclone efficiency can be increased by installing a vortex accelerator below the inlet, where the flow is led between curved guiding vanes which reduces the flow area and increases the tangential velocity of the swirl, while ensuring a laminar flow. However, this arrangement results in a higher pressure drop. Furthermore, the geometry of the cyclone is chosen so that the time to fall, for the smallest particle to capture, from a worst position close to the outlet pipe to the inner wall of the cyclone is shorter than the liquid's residence time in the downward vortex. An approximate measure of residence time is obtained if the rotating amount of liquid (liters) is divided by the flow (liters / sec). Liquid below the vortex reflector is not considered to rotate in this regard. An embodiment of the invention is made up of a cyclone tube 1, which is coupled at 2 with a particle chamber 3. At the interconnection 2, a vortex reflector 4 can be installed consisting of a disc that is centered to form one or more circumferential slots 5 for passage into the particle collecting chamber 3 of particles trapped in the boundary layer. In the upper portion of the cyclone tube 1, a vortex accelerator 6 can be mounted whose outer radius is the same as the inner radius of the cyclone tube 1. An outlet pipe 7 is in this case extending through the vortex accelerator 6 and further extends past one or more tangential inlet tubes 8 to finally pass out of the cyclone tube through its top at the position 11.

The inlet pipe(s) 8 force(s) the liquid with particles to rotate with the tangential velocity given by its area and the flow that the flow-driving pump delivers. Since the density of the particles is higher than that of the liquid, they accumulate on the inner surface of the cyclone tube 1, due to the centrifugal force, in its path down toward the vortex reflector 4. The liquid continues to swirl down toward the vortex reflector 4, forming a stagnation point 9, which forces it to turn, partly because of the actual stop and partly because the only way out is through the outlet pipe 7. The relatively large distance between the separated particles in the boundary layer along the inside of the cyclone tube 1 and the phenomenon at the stagnation point 9, where liquid suddenly accelerates in the opposite direction, allows the particles in the boundary layer to be very effectively sucked into the particulate chamber 3.

The vortex accelerator 6 consists of, for example, two vanes 10 that revolve at least 180 degrees each, seen from above, or three vanes that revolve at least 120 degrees each, or four vanes, etc. The flow area between all vanes 10, as well as the flow determines the instantaneous velocity the liquid and particles obtain as they have just left the vortex accelerator 6.

In order to increase the efficiency, the cyclone tube can be cooled, for example by means of a refrigerant circulating in a double jacket 12, whereby the particles in the process liquid through thermophoresis are influenced by an additional driving force directed towards the inner wall of the chilled cyclone tube (1), while stabilizing the liquid in the boundary layer because of its slightly increased density, as well as an increased viscosity.

If the outlet pipe 7 is extended towards the vortex reflector 4, the efficiency of the cyclone increases, but only to a certain point, and then at further extension rapidly decrease. Depending on the properties of the liquid, there is an optimum for the efficiency when the distance between the point 14 at the outlet pipe 7 and the vortex reflector 4, is 10-50% of the length of the cyclone.

Claims

A device for separating particles from a liquid flow into a thickened partial flow, using a liquid cyclone with cylindrical or near cylindrical geometry in the form of a cyclone tube (1), with one or more tangential inlet(s) (8), whose area together with a flow-driving appliance defines the velocity the flow obtains when entering the cyclone and a central outlet pipe (7), beginning at a lower end (14) and ending in an upper point (11), wherein the cyclone tube (1) can be arranged with or without a vortex accelerator (6) forming a flow rate increasing constriction, in which the outlet pipe (7) extends through, and that the lower portion of the device is arranged with or without a vortex reflector (4) centrally placed and having one or more openings (5) in the periphery in order to suck downwards particles collected in the boundary layer, into a collecting chamber (3), characterized in that the distance between the lower end (14) of the outlet pipe (7) and the vortex reflector (4) is 10-50% of the distance from a point (13) level with the inlet (8) and the plane of the vortex reflector (4), or the bottom (15) of the collecting chamber (3) if vortex reflector (4) is missing, and that against the cyclone tube (1) separated particles leave the separation process in a partial flow, through one or more openings (16), functioning as boundary-layer suction, along the height of the cyclone tube (1) and / or the collecting chamber (3) or the bottom (15).

The device according to claim 1, where the opening(s) (16) is/are tangentially arranged in relation to the local flow direction.

The device according to claim 1, where the liquid has such a tangential velocity, and the distance between the outlet pipe (7) and the inner wall of the cyclone tube (1) and the cyclone tube (1) has an inner diameter and vertical extension so that the rotating liquid volume above the vortex reflector (4), or the volume above the bottom of the collecting chamber (15) if the vortex reflector is missing, divided by the flow is greater than the falling time of a round particle with a diameter of 0.2 μιη and density of 2.5 g / cm³, from a worst position adjacent to the outlet pipe (7) to the inner wall of the cyclone tube (1).

4. The device according to claim 1 or 2, wherein the rotating liquid volume above the vortex reflector, or the volume above the bottom of the collection chamber (15) if a vortex reflector is missing, divided by the flow is at least

25% greater than the fall time for a round particle with a diameter of 0.2 μιη and density 2.5 g / cm³, from a worst position adjacent to the outlet pipe (7) to the inner wall of the cyclone pipe (1).

5. The device according to any one of the preceding claims, wherein the

distance between the outlet pipe (7) and the inside of the cyclone tube (1) is

20-30% of the inner diameter of the cyclone tube (1).

6. The device according to any one of the preceding claims, wherein the

separation distance from a worst position adjacent to the outlet pipe (7) to the inner wall of the cyclone tube (1) is reduced by means of a sleeve mounted on the outlet pipe (7) along its extension.

7. The device according to any one of the preceding claims, wherein a certain portion of the cyclone tube (1) is cooled in order to reduce the fall time of particles by thermophoresis and thereby also stabilize the boundary layer, e.g. by a refrigerant circulating in a double jacket (12).