WO2007129276A2

WO2007129276A2 - Axial flow cyclone separator with variable swirl means

Info

Publication number: WO2007129276A2
Application number: PCT/IB2007/051700
Authority: WO
Inventors: Paolo Andreussi; Paolo Ciandri; Alberto Ansiati
Original assignee: Tea Sistemi S.P.A.
Priority date: 2006-05-10
Filing date: 2007-05-07
Publication date: 2007-11-15
Also published as: WO2007129276A3; ITFI20060114A1

Abstract

An axial flow cyclone for the abatement of liquid or solid particulate from a gas stream, comprising a separator tube (1, 4) to which the stream of gas is delivered and swirler means (8) for imparting a centrifugal acceleration to the gas stream sufficient to drive the particulate against the walls of the separator tube. The swirler means (8) are arranged substantially at the inlet of the tube and are formed by a central supporting element (9) extending coaxially to the tube (1, 4) and a plurality of angularly equally spaced, axial fins (10) extending from the supporting element. The fins comprise at least two portions, one (10a) of which lies substantially on a meridian plane with respect to the axis of the tube, while the other (10b) slopes away from the same axis, the sloping portion of each fin being hinged to the respective substantially meridian portion and means (12, 13, 14, 15) being provided for the adjustment of its angle of inclination as a function of the gas flow rate.

Description

TITLE

AXIAL FLOW CYCLONE WITH A VARIABLE INTERNAL ARRANGEMENT FOR ABATING LIQUID OR SOLID PARTICULATE FROM A GAS STREAM

DESCRIPTION Field of the Invention

The present invention relates generally to the field of plant and apparatuses for cleansing gas streams of solid and/or liquid particulate entrained thereby, and refers in particular to an axial flow cyclone for the abatement of this particulate. Background Art

Axial flow cyclones are normally used in the processing industry to separate liquid and solid particulate from a gas stream. In such systems, the centrifugal acceleration of the fluid is induced by swirler means consisting of a system of fins of suitable shape and size. The swirler is contained inside a vertical separator tube placed over a container where a preliminary, gravity-driven separation of the entrained liquids or solids takes place. The gas and particulate enter the vertical tube from below and flow upwards, passing through the swirler, which imparts a strong centrifugal force on the fluid. The particulate is driven against the walls of the tube and is continuously removed through a number of openings formed in the walls of the tube and communicating with a ring-shaped chamber where the separated particulate is conveyed towards an outlet. The gas, after being cleansed of particulate in the ring-shaped chamber, is then fed back into the main stream leaving the separator. Axial flow cyclones are sized with the aid of semi- empirical design equations, e.g.

V, 4K=k where p_G is the density of the gas and K is an empirical constant, that enables the maximum velocity of the gas, v_G, to be calculated, and consequently also the maximum allowable gas flow rate that can be treated. At the maximum gas flow rate the separation efficiency amounts to 100% for particles with a diameter below up to a given size. The reduction in the gas flow rate and the related reduction in the velocity v_G, results in a reduction in the centrifugal effect of the swirler system on the particles. Such a reduction in the centrifugal effect leads to an unavoidable loss of separation efficiency for the same separator length and the same particle size distribution of the particulate entering the separator. The variation in separation efficiency with varying gas flow rate is clearly evident in the diagrams shown in figures 1 and 2, where the separation efficiency is given as a function of the length of the separator for different classes of particle diameter and for two different gas flow rates, i.e. 8000 Sm³/h and 4000 Sm³/h, respectively. In particular, as shown in figure 1, for instance, an axial flow cyclone with a total length of 1500 mm and designed for a flow rate of 8000 Sm³/h has a particle size cut-off of 5 μm and a separation efficiency of 100% for particles with diameters below 10 μm, while the same cyclone has a lower separation efficiency (approximately 97%) for particles lower than 10 μm in diameter, if the gas flow rate drops to around 4000 Sm³/h.

To keep the separation efficiency high and maintain it near maximum values even in the event of a reduction in the gas flow rate, the axial flow cyclones currently available on the market consist of a large number of small diameter separators. In other words, manufacturers have produced modular separators of standard shape and size for assembly in separator batteries, in which single units or subsets of units can be enabled or disabled by an on-off system depending on the gas flow rate to be processed.

To avoid the use of a large number of separator units and the associated high costs, the present applicant has proposed the use of a large diameter axial flow cyclone with a special shaping of the system of fins forming the swirler that enables a high separation efficiency to be maintained even in the event of relatively low flow rates of the gas being treated; see Italian patent application n. FI2003A000197 in the name of the same applicant. However, the problem of the decline in separation efficiency due to a drop in the gas flow rate vis-a-vis the design flow rate is felt in large diameter axial flow cyclones too and the only solution found to date was to renounce to the use of this type of separator, despite the fact that it is economically more convenient, in favor of the batteries of separators proposed to date.

The object of the present invention is to provide an axial flow cyclone for the abatement of liquid and solid particulate from a gas stream that allows for the field of motion of the flow to be modified in order to maintain the same separation efficiency over a wide range of gas flow rates .

Another object of the present invention is to provide an axial flow cyclone of the above mentioned type wherein the angle of inclination of the fins on the swirler can be varied with respect to the direction of the flow . Summary of the Invention

These objects are achieved with the axial flow cyclone according to the invention, wherein the swirler comprises a plurality of shaped fins, placed axially and angularly equally spaced around a supporting element extending coaxially inside the separator tube. The fin comprises two portions, one of which is substantially on a meridian plane with respect to the axis of the tube and the other slopes away with respect to the same axis. The sloping portion of the fin is hinged to the substantially meridian portion and means are provided for adjusting the angle of the sloping portion as a function of the gas flow rate . Brief description of the drawings Further characteristics and advantages of the axial flow cyclone according to the present invention will be apparent from the following description of an embodiment, provided herein as a non-limiting example with reference to the attached drawings, wherein: - figures 1 and 2 are diagrams showing the separation efficiency as a function of the length of a conventional separator for different particle diameter classes and for two different gas flow rates being treated; - figure 3 is a partial axial section through an axial flow cyclone according to the invention;

- figure 4 is a schematic view from below of the set of fins in the cyclone of figure 3;

- figure 5 is another view from below of the set of fins in figure 4, but showing only one fin; figure 6 is a schematic side view of the set of fins, showing only one fin as in figure 5; - figure 7, details a, b and c, is a schematic side view as in figure 6, but rotated axially through 90°, showing the different angles of inclination that can be adopted for the movable part of the fin; - figures 8 and 9 are schematic side views, rotated through 180° with respect to one another, of a possible fin operating mechanism. Detailed description of the Invention

Figures 3 and 4 show an axial flow cyclone whose overall configuration is substantially the same as the one shown in the patent application n. FI2003A000197 in the name of the same applicant. The axial flow cyclone shown in figures 3 and 4 comprises a tube 1 on a vertical axis, having flanged ends, one of which indicated by the numeral 2 in figure 3, is designed to be connected to a container underneath (not shown) , where a preliminary separation of the entrained material, e.g. of a liquid, takes place due to the effect of gravity. An inner tube 4 of narrower diameter is fixed coaxially inside the tube 1, thereby forming with the outer tube 1 a ring-shaped chamber 5. The inner tube 4 is formed with a plurality of axial slits 6 along its length and a radial sleeve 7 is provided at the bottom of the tube 1, forming the outlet from the ring- shaped chamber 5. A swirler 8 is installed axially at the bottom of the inner tube 4, in the vicinity of the flanged end 2, and comprises a central supporting element 9 consisting of two coaxial cylindrical portions of different diameter, called the head and stem of the supporting element and indicated by the numerals 9a and 9b, and connected by a conical intermediate portion 9c. Six shaped axial fins, indicated by the numeral 10, are attached to the supporting element 9, angularly equally spaced on the surface of the supporting element 9. With reference also to figures 5 and 6, each fin 10, shaped as explained in the above-mentioned Italian patent application, is formed by at least two portions, one of which, indicated as 10a, lies substantially on a meridian plane with respect to the axis of the tube 4 and, more particularly, it extends tangentially from the stem 9b of the supporting element 9, one side of the fin being fixed to a generatrix of the stem 9b by welding or other known means. The other portion, indicated as 10b, slopes away from said axis and is movable with respect to the fixed portion 10a, being hinged to the latter by means of a pin 11, whose axis orthogonally intersects said generatrix. It should be noted that the term "substantially meridian portion" is used to indicate the portion of the fin lying on a plane passing through the axis of the tube 4, or parallel thereto, and at a distance no greater than the radius of the stem 9b of the supporting element 9. The pin 11 is connected to drive means, described later on, which control its rotation and the consequent angular displacement of the movable part 10b of the fin 10, as illustrated in figure 7, from its normal position in which it slopes at a 45° angle away from the fixed portion 10a, into sloping positions at angles greater or lower than 45°.

Figures 8 and 9 show a possible configuration of the means for operating the rotation of the pin 11 integrally attached to the movable part 10b of the fin 10. According to this configuration, a pinion 12 keyed onto the pin 11 engages on a rack portion 13 of a stem 14 of a piston 15 sliding inside the stem 9b of the supporting element 9. The sliding of the piston 15 is controlled hydraulically or pneumatically by means of an actuator fluid fed through a duct 16 to the chamber 17 and is opposed by elastic means 18 acting on the rack portion 13 at the opposite side of the piston 15. The stem 14 is arranged inside the stem 9b of the supporting element 9 and has a number of rack portions 13 corresponding to the number of fins. In the example, since the set of fins consists of six fins, the stem 14 is formed with a portion having a hexagonal cross-section on which six rack portions 13 are formed, a pinion 12 of a corresponding pin 11 engaging with each of these rack portions 13.

Varying the angle of inclination of the fins, and particularly increasing their angle of inclination with respect to the direction of flow, induces an increase in the tangential component of the flow velocity, thus increasing the centrifugal effect on the particles, this resulting in an increase of the separation efficiency. In an axial flow cyclone with sloping fins according to the above-mentioned Italian patent application, the optimal inclination of the fins - in terms of both separation efficiency and pressure drop - is 45°: for the same incoming gas flow rate, the pressure drop increases with increasing angles of inclination of the fins. According to the present improvement the angle of inclination can be adjusted as a function of the flow rate at the separator inlet: if the flow rate decreases with respect to the design flow rate, the drive device increases the inclination of the fins; vice versa, if the flow rate increases, the inclination is reduced. This adjustment may be done manually or automatically.

Variations of and/or modifications to the axial flow cyclone according to the present invention may be made without departing from the scope of the present invention as set forth in the following claims.

Claims

1. An axial flow cyclone for the abatement of liquid or solid particulate from a gas stream, comprising a separator tubular conduit (1, 4) to which said gas stream is delivered and swirler means (8) for imparting a centrifugal acceleration to said gas stream sufficient to drive said particulate against the walls of said separator tubular conduit, said swirler means being arranged substantially at the inlet of said tubular conduit and comprising a central supporting element (9) extending coaxially to said tubular conduit and a plurality of angularly equally spaced axial fins (10) extending from said supporting element, each of said fins being formed by at least two portions, one of which (10a) lies substantially on a meridian plane with respect to the axis of the tubular conduit and the other (10b) sloping away from the same axis, characterized in that the sloping portion (10b) of each fin (10) is hinged to the respective substantially meridian portion (10a), means (12, 13, 14, 15) being provided for adjusting the angle of inclination of the sloping portion (10b) as a function of the flow rate of said gas stream.

2. An axial flow cyclone according to claim 1, wherein actuating means (15) are provided inside the portion (9b) of said supporting element (9) to which said substantially meridian portion (10a) of each fin (10) is attached, to control the angular displacement of the sloping portion (10b) of said fins with respect to the substantially meridian portion (10a) thereof in order to adjust their angle of inclination as a function of the flow rate of said gas stream.

3. An axial flow cyclone according to claims 1 or 2, wherein said sloping portion (10b) of each fin (10) is hinged to its respective substantially meridian portion

(10a) by means of a pin (11) carrying a pinion (12) engaging on a rack portion (13) of the stem (14) of a piston (15) sliding inside said supporting element (9).

4. An axial flow cyclone according to claim 3, wherein said piston stem (14) has a number of rack portions (13) equal to the number of fins (10), whereby all the fins can be operated at the same time.

5. An axial flow cyclone according to any one of the previous claims, wherein said piston (15) slides in a chamber (17) of said supporting element (9) under the effect of an actuating fluid acting in opposition to elastic means (18).

6. An axial flow cyclone according to any one of the previous claims, wherein said separator tubular conduit (1) comprises a pair of coaxial tubular members (1, 4) forming a ring-shaped chamber (5) therebetween and communicating with each other through openings formed on the inner tubular member (4) in which said swirler means (8) are arranged.

7. An axial flow cyclone according to any one of the previous claims, wherein said supporting element (9), from which said shaped fins (10) extend, comprises an axially elongated body with two portions (9a, 9b) of different width, the substantially meridian portion (10a) of said fins (10) being attached to the narrower portion

(9b) of said supporting element (9), while the sloping portion (10b) of the fins extends along a part of the wider portion (9a) of said supporting element (9) .