Untitled record

PATENT

FRENCH REPUBLIC

MINISTRY

INDUSTRY AND TRADE

SERVICE Gr. 14. - Cl. 6. N ° 1.069.071 of INDUSTRIAL PROPERTY __

Improvements to sensors for particles contained in

Company known as: AIRMECA residing in France (Seine).

Requested on October 27, 1952, at 1 p.m.^h 50 “, in Paris.

Issued February 10, 1954. - Published July 5, 1954.

(Patent of invention whose delivery was deferred in execution of article 11, § 7, of the law of July 5, 1844 modified by the law of April 7, 1902.)

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The present invention, due to Mr. Gérard Micheau, relates to improvements in the sensors of solid or liquid particles contained in fluids and is more particularly aimed at purifiers of liquids or gases, and in particular dust collectors, of the so-called cyclone type, in which we use centrifugal force to separate the particles from the gas that carries them.

Many apparatuses of this type are known, in which the fluid charged with particles is caused to rotate in one or more tubes traversed by the gas, the particles being, by rotation, projected against the walls of the tube or tubes where they are collected and disposed of by appropriate means. The 'rotation is ensured sometimes by providing on the purifier tube (s) a tangential gas inlet, sometimes by ensuring an axial gas inlet in the tube (s) and by providing on this inlet nn set of guiding anchors which put the fluid in rotation.

It is to the devices of this second type, with axial input, that the improvements according to the invention relate.

These devices can comprise a single particle sensor tube or, preferably, a set of tubes mounted in parallel (multicyclone dust collectors). In general, each purifier tube has at its gas inlet end charged with dust a set of blades suitably shaped to give the incoming gas a helical movement. At the opposite end are arranged the means for collecting the particles collected by centrifugal force against the inner wall of a tube and a device for discharging purified gas.

In addition, it is common to provide, at the outlet end of the purifying tubes, rectifying members, such as vanes of inverse conformation to that of the inlet vanes, which receiving the gas in helical movement return it in substantially axial current. This arrangement has the advantage of recovering the energy of rotation of the gas, of reducing pressure losses and also of improving the efficiency of the purification.

In known devices which include the implementation of such rectifying elements, a constant concern has hitherto been to dispose them exclusively in the gas previously purified, in other words to ensure the evacuation of the particles before the rectification of the current gaseous. This concern could appear to be rational, since it was in principle necessary to prevent the rectification of the current from resuspending the particles separated by the helical movement, consequently annihilating the result obtained by the rotation of the gas to be purified.

In application of this design, a first solution consisted in arranging the rectification of a current in the purifier tubes of a conventional type (for example American patent 1,338,143) in which an purifier tube proper is associated with a coaxial tube of smaller diameter serving to collect the purified gas. Between the two tubes is thus formed an annular zone in which the particles collected along the inner wall of a purifier tube are removed away from the gas stream to be collected and deposited in a hopper or other receptacle.

When purifying tubes are fitted with this type of rectifying element, these are placed inside the coaxial tube for the outlet of purified gas (US Patent 1,746,218 to February 4, 1930). In this way, the straightening cannot affect the annular zone for collecting particles.

Experience has shown, however, that the benefits of the recovery thus achieved do not meet

Price of the booklet: 100 francs, - 2 - [1,069,071] not entirely what we were justified in hoping for. The rectification taking place on the gas passing through a narrower section than that of a purifier tube, therefore at high speed, produces substantial pressure drops. In addition, it can be seen that the particles, when they are in the annular space between the inner tube and the outer tube, no longer subjected to entrainment in gas in the axial direction, take an unfavorable circular movement. to their collection and even risk resuspension in particular, in the case of multi-cyclones, by entrainment in the neighboring tubes if they are unevenly supplied.

According to another solution, the purification is carried out in a single purifier tube, without a coaxial inner tube, and at the two ends of this tube are arranged respectively the rotation blades and the rectifier shafts. In this case, provision is made to provide, before the rectifying anbages, the means for evacuating the dust by slots made in the wall of the purifying tubes (American patent 2,201,301 on May 21, 1940), or both by slot and collection chamber (American patent 2,370,629 of March 6, 1945). These provisions, the last especially, provide an axial component for entrainment of the particles. They ensure the rectification of a purified gas stream in a section equal to that of the inlet, therefore with acceptable pressure drops. However, these advantages are offset by a complication of production, due to the arrangement of the particle-removing devices.

The subject of the present invention is an arrangement of the purifier tubes which has the advantages of both of the previous solutions, without having the disadvantages.

It consists in using a purifier tube of conventional type, that is to say with a coaxial inner tube, and in placing the rectifier blades immediately before the coaxial tube in the purifier tube itself, these rectifiers operating not on the purified gas, but on the gas charged with particles.

Contrary to what one might have thought, the arrangement of the rectifying elements in the stream of gases loaded with dust, as long as they are immediately in front of the coaxial outlet tube of purified gas, does not cause the resuspension particles. Experience shows, in fact, that the combined effect of straightening and aspiration of a coaxial tube gives rise to a stream of purified gas, which, in a way, separates from an external film of gas which remains on the wall of the outer purifier tube. The particles separated by centrifugal force and gathered against this wall remain in this film and the latter, being straightened, has an axial drive which ensures the evacuation into the annular space between the inner tube and the outer tube towards the receptacle deposit. In this annular space, the circular movement is eliminated and penetration into the receptacle is ensured without risk of reintroduction into a neighboring tube (case of multieyclones). The rectification of the gas stream taking place over the entire section of the outer tube is effected on the gas at low speed, therefore with low pressure drops. So that without reduction in purification efficiency, there is an appreciable energy gain.

For the implementation of the improvements according to the invention, it is possible to provide separate straightening anbages which are inserted in the purifier tube in front of the outlet tube. Another embodiment derived from the aforementioned American patents 2,201,301 and 2,370,629, consists in providing both the inlet and straightening anbages on the same tubular core, the whole constituting a single part which is inserted in the purifier tube over almost its entire length. However, unlike the aforementioned patents, no particle evacuation slots are provided in the wall of a purifier tube. A tube and its core provided with two sets of reverse blades are associated with a coaxial tube for the outlet of the purified gas conforming to that of the American patents 1,338,143 and 1,746,218.

According to one of its aspects, the invention also consists of a combination of the two known arrangements: the purifier tube with a core furnished with two kinds of blades and the coaxial tube associated with the purifier tube, this combination being characterized moreover in that the axial tube and the straightening blades are contiguous or very close.

Other particularities will follow from the following description of an embodiment of the invention, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal sectional view of a purification device, the inner core being shown, however, in elevation;

Figure 2 is a section along line IIII of Figure 1;

Figure 3 is a section along line III-III of Figure 1;

Figure 4 shows, on a larger scale, the detail of an entry anbage.

In these drawings, only one cvclonary purification or dedusting tube has been shown.

However, it is obvious that the purification installation can consist of any number of identical tubes. In general, it will be formed of a set of tubes of this kind mounted in parallel on an appropriate single frame, according to the usual formula called multicyelone. The purification device consists of a purifier tube proper 1, which receives at its end 2 (from the left in the figure) the gas to be purified. The other end 3 of the tube 1 is mounted on the wall 4 of the receptacle 5, intended to collect the dust or particles separated from the current, for example a hopper. On the side of the end 3, an inner tube 6 is mounted coaxially with the tube 1, extending over a short length inside of it. The tube 6 is mounted on the wall 7 of the receptacle 5. It can be seen that between the tube 1 and the tube 6 is an annular part 8 opening out into the hopper 5.

In the tube 1 is disposed a core 9 carrying on one side the fins 10 and of the antral the fins 11. The fins 10 are shaped so as to transform the gaseous current penetrating into 2 along the axis of the tube 1 in movement helical. The fins 11, on the other hand, have a reverse curvature, intended to straighten the vortex movement in substantially axial current.

The fins 11 are placed, not in the axial tube 6 as previously provided, but in the purifier tube 1 itself, in front of the tube 6, in the vicinity of the inlet 12 of the tube 6.

According to a feature of the invention, the opening 2 of the tube 1 carries an element 13 forming an inlet flag, substituting for the ordinary free edge of the usual purifying tubes, a surface of regular curvature, eliminating the throttling effect due free edge and resulting swirls. The element 13 can simply be constituted by nn rod or nn round probed on the edge of the end 2 of the tube 1. It increases the efficiency of the anbages by eliminating the entry vortices which then reign over a significant height of the fin.

The blades 10 for rotating have the following features.

On their leading edge 14 (FIG. 4), there is provided a recess 15, forming an edge 16. This device, surprising at first sight, has the effect of improving the operation of the purifier. It causes on the upper surface 17 of the fin 10 a desirable turbulent flow to avoid detachment of the gas stream from the "transition point".

In the previous arrangements, the rotation blades, even carefully profiled, are normally found, due to the low speeds involved, in laminar regime. The laminar boundary layer does not have the possibility of making the fluid adhere to the curved surface - [1.069.071] which is the seat of a divergent flow; this takes off from the wall, generating vortices which disturb the helical movement created and help prevent the separation of particles.

The recess 15 avoids this effect. By causing a turbulent flow on the boundary layer from the leading edge 14, at the speeds considered (Reynolds number of the order of 20,000), it ensures constant contact of the gas stream on mowing the length of the fin. One thus benefits, according to the language of aerodynamicists, from high lift coefficients, here very favorable, of approximately 60 to 70% greater than those which would result from the usual laminar flow. Conversely, the offset 15 makes it possible to reduce the wedging angle A to be given to the fins 10 in order to obtain the same helical gas trajectory, which has the result of reducing the pressure losses and facilitating construction.

According to another particular feature, the blades 10 are in contact with the inner wall of the tube 1 only over part of their length. In other words, the anbages 10 carry at their periphery a recess 19, so that their contact with the tube 1 only occurs over a fraction 20 of their length, the remaining part 21 being spaced apart from the tube 1 by a certain distance , for example from 3 to 10% of the diameter.

The recess provided by the part 21 has the effect of keeping in contact with the inner wall of the tube 1 a gas passage zone animated with a tangential speed, moreover low, since it results only from the drive by viscosity. This film of gas in contact with the tube 1 acts as a damper for the jet of particles driven out by centrifugal force following the rotation of a gas by the anchors 10. The damping thus produced by the gas stream retained in the vicinity of the wall and driven in the axial direction, prevents the particles from bouncing in this area and their re-entrainment in the central part of the tube 1.

By these means, the gas charged with dust entering 2, rotated by the anbages 10, traverses the tube 1 in helical movement. The particles, sounds the effect of the rotation, come to be applied on the inner wall of the tube 1. When the gas arrives on the blades 11, its vortex movement is canceled and transformed into an axial movement with partial recovery of dynamic energy in potential pressure energy. The effect of the blades 11, due to their position, operates on gas which has not yet been freed of the particles.

[1.069.071] —

While one might have feared a resuspension of the particles, by the righting effect due to the blades 11, experience shows, on the contrary, that the particles gathered against the inner wall of the tube 1 are entrained in space annular 8 without tending to mix with the purified gas moving in the central part of the tube 1. This gas, freed from the particles, passes into the tube 6 to be collected. The particles having passed into 8 are discharged into 5 where they are deposited.

With the arrangement described above, it is possible, if necessary, to place the wall 4 of the particle reception hopper in any position along the purifier tube 1. In particular, the wall can be arranged at the front part of the tube 1, at 22, ee which makes it possible to shorten the length of the device.

In the case where the wall of the hopper is placed towards the front of the tube 1, slots can be formed therein, such as 23, for discharging the particles.

It is understood that the foregoing description, mainly aimed at the separation of the particles contained in gases, has no limiting character and that the arrangements described and shown are also applicable to the separation of the particles contained in a liquid and to the realization of 'devices of the genus' bydrocylones', such as those used in washing coals, ores, etc.