EP0165145A1 - Fan silencer which can be regenerated in situ, for use in ventilation plants fed with dusty air, and process to regenerate this silencer in situ - Google Patents

Abstract

1. A fan silencer which can be regenerated in situ, for use in ventilation plats fed with dusty air comprising an external envelope (1) of a plain material, a retaining wall (10) underneath this external envelope (1), a layer (2) of a sound-absorbing substance with an external surface (9) contained by the said retaining wall (10), and a perforated internal wall (5, 6) supporting the said layer (2) of a sound-absorbing substance, characterised in that the retaining wall (10) has large passage apertures, whereas the external envelope (1) is of plain sheet metal and is radially separated from the retaining wall (10) by an interspace presenting a closed volume (3) which is either connected to a fitting (4) outside the silencer for connection to a cleansing fluid supply line or at least partially filled with a layer (14) of an insulating material lining the internal surface of the said external envelope (1), the latter comprising panels which are rendered pivoting by means of hinges (12) and can be opened so as to expose the said retaining wall (10).

Description

In situ regenerable silencer for ventilator in Ventilation systems supplied with dusty air and in situ regeneration process for this silencer.

The invention relates to sound attenuation silencers which are associated with fans supplied with dusty air; It also relates to a process for regenerating these silencers.

Many ventilation systems are used in mines, in particular coal mines. These installations frequently include electric ventilation fans whose powers sometimes reach hundreds of kWh. In order to limit the sound power radiated into the environment to an acceptable level, it is known to equip these fans with silencers placed on their suction and / or their discharge, intended to reduce the sound power radiated by the suction port. and / or backflow and thereby reduce the harmful effect of noise on the environment.

These silencers are generally cylindrical devices comprising an outer sheet metal wall against LaqueLLe is maintained an annular layer of a material with high sound-absorbing power, resistant to heat, humidity and compaction. The sound absorbing substance used can be Rock wool, Glass wool, open cell foam, clay foam, etc.

In general The internal wall of the silencer in contact with the air flow to be soundproofed consists of a perforated sheet, The internal face of this sheet now in place The layer of soundproofing substance.

Inside the muffler there can be a central anaLogue bulb with a domed head generally cylindrical or frustoconical. This bulb ensures better continuity of air flow and promotes the supply of the fan wheel. This bulb also contains a sound absorbing material held in place by a perforated sheet envelope. It also participates in noise attenuation.

One of the problems posed by the use of currently manufactured silencers is that they lose a significant part of their effectiveness after a more or less long service life in a dusty atmosphere. In fact, the dust transported by the air flow is deposited on the internal face of the devices and forms a film which gradually closes the perforations of the sheet. Consequently, the radiated acoustic power gradually increases to tend towards that which would be radiated by the fan in the absence of a silencer.

In order not to exceed the permissible sound level, it then becomes necessary to dismantle all or part of these silencers in order to replace the dusty elements by elements that have been cleaned and dusted. This operation must be repeated frequently and it will cause the fan to stop for a long time. It also requires transporting the dusty elements to the workshop, their regeneration being carried out either by violent shaking on a vibrating frame, or by soaking in a detergent bath followed by drying.

It has been proposed to remedy the problem of the dusting of the silencers by mounting at the inlet of the suction silencer a filter element in the form of panels fixed to a frame or in the form of an interchangeable filter element, in particular folded. in accordion, resting on a fixed frame. But in very dusty environments like coal mines, these filter elements are clogged in just over an hour.

The main object of the invention is to achieve in situ regenerable silencers, if desired while the fans are running, which can be regenerated easily as often as the need arises to keep the noise nuisance below of a fixed threshold.

According to the invention, in an in situ regenerable silencer, intended to be associated with a fan in a ventilation installation supplied with dusty air, comprising an outer casing made of solid sheet metal, a layer of soundproofing material supported by a perforated internal wall , the outer casing made of solid sheet and the layer of sound-absorbing material are separated from each other and there exists on the outer face of this layer of insulating material a retaining wall with large passage openings separate from the envelope outside.

According to a first aspect of the invention, the outer casing in solid sheet metal comprises removable panels, preferably opening panels mounted using hinges relative to the fixed remainder of said outer envelope.

According to a second aspect of the invention, there is between the outer envelope and the retaining wall a gap revealing an annular volume which is connected to a connection end piece of a supply line for a cleaning fluid.

Preferably, in both cases The perforated internal wall which supports the soundproofing material comprises a cage constituted by perforated tubes and connected to a means of connection to a network of pressurized air.

The cleaning fluid is preferably constituted by water added with a detergent.

According to the method of the invention, the regeneration of the layer of the sound absorbing material of the silencer is done in the following way. With a silencer in accordance with the second aspect of the invention, the annular volume comprised between the outer envelope of the silencer and the layer of sound-absorbing material is injected simultaneously with compressed air and cleaning fluid without stopping the fan. The cleaning fluid mist passes through the layer of sound-absorbing material and carries the dust into the air flow sucked in or blown out by the fan. Then one can either stop the introduction of cleaning fluid alone and then continue the introduction of air so as to dry the layer of sound-absorbing material, or simultaneously stop the introduction of cleaning fluid and compressed air. The wet dust obtained during regeneration is not a nuisance. In fact, they are centrifuged during the passage of the fan rotor (s) and thus diverted into the air duct outside the axial position occupied by the electric motor. They are then deposited in the form of sludge at a more or less long distance. The characteristics of the ventilation and the foaming power of the cleaning fluid.

The cleaning fluid is preferably prepared beforehand in a bottle of adequate capacity and resistance to pressure connected on the one hand to the annular volume situated between the outer casing and the layer of sound-absorbing material and on the other hand to a source of compressed air, a cut-off valve being mounted between the cylinder and the compressed air source. The opening of the valve causes spraying of the cleaning fluid in the form of a mist on the layer of sound-absorbing material. When all of the cleaning fluid has been removed from the bottle, drying can be ensured by continuing the introduction of compressed air.

With a silencer in accordance with the first aspect of the invention, iL is preferable but not necessarily necessary to stop the fan before cleaning the layer of sound-absorbing material. A removable panel is moved and a pressurized water jet is sprayed onto the soundproofing material with the addition of a detergent. This is done panel by panel.

According to a preferred embodiment of the invention, the internal face of the layer of sound-absorbing material is supported by a rot-proof fabric made of artificial fibers (polyamide, polyethylene) or non-combustible (fibers glass) with loose texture presenting more than 50% of empty surface. This fabric has the advantage of not catching dust which facilitates its regeneration. On the other hand, this fabric has a higher acoustic efficiency than a perforated sheet.

This fabric is itself supported by a sufficiently rigid mesh but with very loose mesh, for example in galvanized or plasticized wire. It can also rest on a metal cage. This cage is formed of widely spaced metal bars oriented along the axis of the silencer. It has the advantage of protecting against the appearance of dangerous static electricity charges. This metal cage is preferably constituted by tubes capable of being connected to a source of compressed air by means of a flexible hose and an electropneumatic valve; they are arranged so that, after connection, they play the role of ejectors, the jets of which are directed towards the blades of the fan. In addition to rapid drying of the sound-absorbing material after washing, this assembly allows useful automatic emergency ventilation in the event of accidental interruption of the electric current or not.

The external retaining wall of the layer of sound-absorbing material may consist of a metal cage or a sufficiently rigid mesh with loose mesh or holding in place a fabric with a loose texture.

The layer of sound-absorbing material can be constituted in a known manner by rock wool, glass wool or any other porous material.

Depending on the size of the silencer and the power of the source of compressed air available, it may be advantageous to divide the annular volume between the external sheet of the silencer and the layer of soundproofing material into annular elements by partitions so as to form several boxes. can be connected successively to the compressed air source. These boxes can be longitudinal or transverse.

It is thus possible to regenerate by fractions The layer of sound-absorbing substance, as well as by removing or by successively opening the removable panels of the outer envelope.

When the silencers are provided with a central bulb, constituted by a sound-absorbing material held in place by an envelope, there is provided inside this layer of sound-absorbing material a central volume bounded by an internal wall and connected to a connection end piece. a cleaning fluid inlet pipe. The regeneration of the bulb takes place in the same way as that of the annular layer of sound-absorbing material. The regeneration of the bulb and the annular layer can be carried out simultaneously or independently. The external wall of the bulb is as in the case of the external cylindrical wall of the annular layer of the sound-absorbing material constituted by a griLLage or a metal cage holding in place a fabric with loose texture.

• - La figure 1 est une vue en coupe transversale d'un silencieux conforme au second aspect de L'invention et régénérable in situ,
• - La figure 2 est une représentation schématique de côté du même silencieux,
• - La figure 3 est une vue en coupe trànsversale d'un silencieux conforme au premier aspect de L'invention et régénérable in situ,
• - Les figures 4 et 5 sont des schémas montrant L'empLacement de points de mesure au cours d'essais comparatifs d'atténuation acoustique.

A description will now be given of two exemplary embodiments of the invention with reference to the appended drawings in LesqueLs:

• FIG. 1 is a cross-sectional view of a silencer according to the second aspect of the invention and regenerable in situ,
• - Figure 2 is a schematic side view of the same silencer,
• FIG. 3 is a cross-sectional view of a silencer according to the first aspect of the invention and regenerable in situ,
• - Figures 4 and 5 are diagrams showing the location of measurement points during comparative acoustic attenuation tests.

An in situ regenerable silencer in accordance with the second aspect of the invention comprises an outer casing 1 made of solid sheet which is separated, that is to say without definitive connection, from a layer of sound absorbing material 2 which it contains. In this example, there is an interval in the radial direction which causes an annular volume 3 to appear between the outer casing 1 and the sound-absorbing material 2. This annular volume 3 is closed at its opposite ends in the axial direction and it is connected to a nozzle. 4 allowing its connection to a compressed air and water supply containing a detergent.

The soundproofing material 2 is supported on its internal face by a fabric 5 made of loose texture synthetic fibers which is itself supported by a rigid cage made up of tubes 6; the latter are perforated in their inner part with the silencer and, outside of this, they are connected to a flexible pipe 7 terminating in an electropneumatic valve 8 which is part of a compressed air distribution network.

The soundproofing material 2 is supported on its external face 9 by a fabric of synthetic fibers with a loose texture, preferably identical to the fabric 5 of the internal face, which rests on a semi-rigid metallic mesh with large meshes, made of plasticized wire of preference. This external retaining wall 10, not shown in detail, is spaced from the external envelope 1 by the annular volume 3.

Figure 3 shows in cross section a silencer similar to that of Figures 1, 2 where the same references designate the same parts. This example is that of a first aspect of the invention according to LequeL the outer casing 1 ′ made of solid sheet metal is composed of removable panels. A rigid LongitudinaLe frame 11 carries hinges 12 by means of which panels 13 are pivotally mounted by one of their Longitudinal edges; The opposite LongitudinaL edge allows each panel 13 to be fixed to the frame 11, in the closed position. In this example too, the outer envelope 1 ′ is separated from the layer 2 of soundproofing material; however, the annular volume 3 of FIGS. 1 and 2 is no longer necessary. It is therefore possible to lining the inside of the panels 13 with a layer 14 of insulating material. This FIG. 3 also shows that the rigid frame 11 is used to hold the outer wall 10 of the layer of sound-absorbing material 2 in position using spacers 15.

Similar spacers (not shown) can also be provided in the example of FIGS. 1 and 2 without this eliminating the characteristic of the separation which exists between the outer casing 1 and the layer 2 of soundproofing material showing the annular volume 3 used for in situ regeneration.

In the example of FIG. 3, it is preferable to use in the longitudinal direction separate removable panels facilitating a progressive cleaning of the silencer during its use.

The in situ regeneration consists, with the silencer of FIGS. 1 and 2, of connecting the end piece 4 and of opening the valve 8 for cleaning and drying as explained above. With the silencer of Figure 3, we can either stop the fan, open all the panels 13 and send from outside using a nozzle 16 a jet of pressurized water added with a detergent, which runs in one minute per m ³ of soundproofing material 2 cleaned. The water descends through the mass of the material 2. It is advisable to attach to the lower part thereof an impermeable strip 17; by giving the entire installation a slight longitudinal slope, the washing water is collected, channeled and evacuated without difficulty.

Because the silencer of the invention differs in its construction from conventional silencers, it was useful to check the quality of sound reduction.

Comparative tests have been carried out according to French standard NFS 31-021 with various suction silencers mounted on BERRY 26 KW type 1560 HM2 electric fans which provide a flow rate of around 4.3 m3 / / second on a discharge circuit whose pressure is maintained by adjusting a diaphragm to a value of 200 mm (water column).

In Figure 4 are indicated The different points where the acoustic levels were measured in front of the suction mouth and according to the angulations and distances prescribed by Standard NFS 31-021.

• . sans silencieux (SSS) devant un ventilateur de diamètre D = 0,7 m à une distance de r de 1,35 m,
• avec un silencieux classique (SSt) devant un ventilateur de diamètre D 0,8 m à une distance de r de 1,40 m,
• . avec un silencieux conforme au second aspect de L'invention (SPr) de même Longueur que Le silencieux classique devant un ventilateur de diamètre D = 0,7 à une distance r = 1,35 m.

The measurements were made:

• . without silencer (SSS) in front of a fan with diameter D = 0.7 m at a distance of r from 1.35 m,
• with a conventional silencer (SSt) in front of a fan with a diameter of 0.8 m at a distance of r from 1.40 m,
• . with a silencer conforming to the second aspect of the invention (SPr) of the same length as the conventional silencer in front of a fan of diameter D = 0.7 at a distance r = 1.35 m.

The following results were obtained which are summarized in Table 1.

Lp 1, Lp 2, Lp 3 are The acoustic levels, Lp is The weighted surface sound pressure level, Lw is The sound power level according to standard NFS 31-021.

It can therefore be seen that, for the silencer produced according to the invention, the acoustic attenuation coefficient is 22.1 dBA and for a conventional silencer it is only 18.4.

Figure 5 shows the different points where the acoustic levels were measured in an installation, the fan comprising a mouth silencer 18, an electric fan 19 and a conventional outlet silencer 20. All measurements were taken at 1 m walls. The results are summarized in Table 2.

Variant embodiments can be made to the examples described above without departing from the scope of the invention. For example, it is possible to partition the annular volume 3 by transverse and longitudinal partitions in order to reveal boxes capable of being connected all together or separately to the inlet pipe for the cleaning fluid. In the first aspect of the invention, these boxes can correspond to removable panels of the external envelope 1. The internal wall and the external wall are realizable in many ways; but iL is preferable in many circumstances to provide a loose texture support having more than 50% of empty surface.

Claims (16)

1. In situ regenerable silencer intended to be associated with a fan in a ventilation installation supplied with dusty air, comprising an outer casing (1) made of solid sheet metal, a layer (2) of a sound absorbing material supported by a perforated internal wall (5, 6) characterized in that the external face (9) of this layer (2) of soundproofing material is contained by a retaining wall (10) with large passage openings separated from said external envelope (1). 2. SiLencieux according to claim 1 characterized in that the outer casing (1) in solid sheet comprises removable panels (13), preferably opening panels hinged using hinges (12). 3. SiLencieux according to claim 1 characterized in that there is between the outer envelope (1) and said retaining wall (10) a gap showing a volume (3) which is connected to a connector (4) to a supply line for a cleaning fluid. 4. SiLencieux according to any one of claims 1 to 3 characterized in that the perforated internal wall (5, 6) comprises a cage comprising perforated tubes (6) and connected to a means. (7, 8) for connection to a pressurized air network. 5. Muffler according to claim 1 characterized in that the internal face of the layer (2) of sound-absorbing material is supported by a fabric (5) with loose texture having more than 50% of empty surface resting on a mesh or a metal cage (6). 6. Muffler according to claim 1 characterized in that the outer face of the layer (2) of soundproofing material is constituted by a mesh holding in place a loose texture fabric. 7. SiLencieux containing a bulb according to any one of claims 1 to 6 consisting of a soundproofing material held in place by an envelope, characterized in that this bulb has inside the soundproofing material a central space which is connected to a connection nozzle, to a source of compressed air and to a source of cleaning fluid. 8. SiLencieux according to any one of claims 1 and 3 characterized in that the annular volume (3) between the outer sheet (1) and the layer (2) of soundproofing material is divided by partitions so as to form several boxes. 9. SiLencieux according to claim 2 characterized in that an impermeable strip (17) is fixed to the lower part of the outer face of the layer (2) of soundproofing material and all of this layer (2) has after installation a slight Longitudinal slope. 10. A method of in situ regeneration of a silencer according to claim 3 characterized in that injected into the annular volume (3) between the outer wall (1) and the layer (2) of soundproofing material simultaneously with compressed air and a cleaning fluid while the fan is running. 11. Regeneration method according to claim 10 characterized in that one continues the introduction of compressed air after stopping the introduction of cleaning fluid. 12. A method of in situ regeneration of siLencieux according to claim 2 characterized in that at least one removable panel (13) is placed in the open position and the layer (2) of sound-absorbing material is projected onto the outer face, Using a nozzle (16), a jet of cleaning liquid. 13. Regeneration process according to claim 10 characterized in that the cleaning fluid is prepared In a bottle connected on the one hand to the annular volume (3) located between the outer envelope (1) and the layer (2) of soundproofing material and to a source of compressed air, compressed air is introduced into the a bottle so as to expel the fluid for cleaning the bottle in the form of a mist in said annular volume (3). 14. A regeneration method according to claim 13 characterized in that one continues the introduction of compressed air into said bottle when all of the cleaning fluid has been expelled therefrom. 15. A regeneration method according to any one of claims 11 or 14 characterized in that simultaneously introduced, in addition, compressed air at the perforated internal wall (5, 6) towards the blades of the fan . 16. A regeneration method according to claim 12 characterized in c.e that after the end of the projection of the cleaning liquid, compressed air is introduced at the perforated internal wall (5, 6).

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