IE52743B1

IE52743B1 - Washing process and apparatus used in the manufacture of mineral fiber mat

Info

Publication number: IE52743B1
Application number: IE756/82A
Authority: IE
Original assignee: Saint Gobain Isover
Priority date: 1981-04-02
Filing date: 1982-03-30
Publication date: 1988-02-03
Also published as: ES8302609A1; FI821117L; YU43513B; ZA822114B; MX156142A; KR830010010A; YU72182A; FR2503134A1; TR21600A; FR2503134B1; KR880002702B1; JPS57177322A; DK158613B; FI821117A0; ATE15025T1; JPH0247250B2; AR227584A1; NZ200123A; ES511043A0; FI71919B

Abstract

1. Process for the manufacture of webs of mineral fibres, in which - fibres are produced and then carried by gas currents to a receiving device (3) where they are collected and separated from the carrier gas, - a finely dispersed liquid binder composition is projected into the gas current carrying the fibres, upstream of the receiving device (3), - the web of fibres (6) is optionally treated, in particular heat treated, to fix the binder, and subjected to transformations leading to its final form, - water is sprayed into the path of the gas which has carried the fibres, downstream of the receiving device, and/or that of the gas emanating from the treatment operations for fixing the binder and/or the transformation of the mat of fibres (6), characterised in that the water is dispersed by the collision of jets directed towards one another so that a sheet of dispersed water forms transversely to the path of the gas.

Description

The invention relates to the washing implemented in the manufacture of mineral fiber mats, and more precisely, to the washing carried out on the path of the effluent gases issuing from this manufacture.

The manufacture of mineral fiber mat, or similar products, comprises a series of operations, and especially: - the formation of fibers, = their advancement toward a receiving element by means of gas currents, 10 - the sizing of the fibers by means of a binder, by projection of the latter, in the form of a finely divided composition, on the path of the fibers between their production and the receiving element, - the formation of the mat on the receiving element, customarily constituted by a perforated support, - the separation of the fibers and the carrier gas currents by passage of these gases across the receiving element, and the evacuation and/or the recycling of the gases recovered downstream of the receiving element, 2o - the treatment of the fiber mat, coated with binder, to adhere this binder, possibly followed by a cooling stage, and the evacuation of the gases issuing from the adhesion treatment of the binder and from the cooling gases, - the transformation of the mat resulting in the fi25 nished form of the product, and the collecting and evacuation @£ the saturated air arising from this transformation. - 2 Regardless of the mode of production of the fibers and the type of binder used, the effluent gases can be neither recycled nor evacuated without minimal treatment because of the polluting elements which they entrain.

Among the polluting elements, those which come from the binder are particularly troublesome. In particular, these are fine droplets whi-ch were not retained in the fiber mat, or gaseous products escaping from the binder compositions. They are also the degradation products which can io be emitted when the binder is placed in contact with the fibers at high temperature.

Of course, fibers not retained by the receiving element, or which are pulled up from the mat during the transformations resulting in the finished product, are added to these polluting elements.

These elements are troublesome for several reasons.

In particular, the binder droplets and vapors rapidly soil the walls of the installations and ducts which convey the effluent gases. In effect., they tend to form adhesive deposits which retain the entrained fibers or fiber fragments. The reconditioning of the installation therefore requires the periodic removal of these deposits. In addition to the stoppages which they cause, the reconditioning operations are quite laborious. The result is an appreciable increase in production costs. - 3 The first treatment carried out on the effluent gases is ordinarily a water atomization for the purpose of cooling and initially removing the maximum amount of polluting elements. Sy means of this atomization, in particular, an effort is made to remove as much binder as possible in order to prevent the fouling of the installation which is known to constitute a significant problem in this type of manufacture.

However, the effective implementation of this water atomization causes some difficulties.

A first difficulty is associated with the extremely large quantity of gas circulating in these installations and, consequently, with the dimensions of the installations themselves in which these operations must be conducted. χη French patent No. 2,247,346 some values of gas volumes are indicated, characteristic of different modes of fiber production. These values are on the order of 0.1 x 106 to 1 x 106 m3/hr. of effluent gas for the operations resulting in the formation of mat. As will be seen, it is difficult to obtain a fine^ homogeneous dispersion on such large volumes while using the traditional techniques in this domain.

A second difficulty, concerning the effluent gases arising from the formation of the fibers, comes from the need to prevent the formation of deposits on the path of the gases as soon as the gases have crossed over the fiber receiving element. In effect, the deposits which are formed directly under this receiving element can modify the passage section of the gases and, consequently, the progression of these gases across the mat being formed.

Such a modification interferes with the homogeneity of the fiber mat.

To prevent the formation of these deposits, it is desirable to effect the washing very close to the receiving element which constitutes a supplemental constraint since the fiber mat formed must not be reached by the water pro10 jected during this washing operation.

A third difficulty comes from the fact that the water used, which becomes saturated with polluting elements, cannot be discarded. Therefore, it is customary to recycle it, after it has been cleansed of a portion of the entrained polluting elements. In order for the cost to be acceptable, the operation (or the operations) aiming to rid the water of its pollutents must be relatively simple. For example, it could involve a summary filtration or a similar operation. At the end of this treatment the recycled water or20 dinarily still contains a substantial quantity of materials in suspension and of stable or unstable dissolved products. Its use in the conventional atomizing apparatus therefore poses problems, in particular, of obstruction or erosioncorrosion.

Conventionally, the atomization of the water is effected under pressure by passing the water through nozzles of small dimensions. For the use considered, this method suffers several disadvantages. First, the quantity of water distributed through each atomizing nozzle and the expanse effectively treated by this atomization are very limited because of the very dimension of the nozzle. Of course, it is possible to increase the number of nozzles accordingly.

Nevertheless, it is difficult to attain a perfect continuity and a good homogeneity of the layer of water droplets throughout the entire space necessary. In practice, even with a greater number of nozzles of this type, it is not possible to effectively treat all of the gas stream and, io consequently, to prevent the formation of deposits on the walls of the chamber or the ducts.

Secondly, because of the nozzle dimensions, frequent blockings are produced, and this -sll the more because the recycled water is more saturated with polluting elements.

Therefore, even a good distribution of the nozzles in the atomizing area could not guarantee a continually homogeneous atomization. These nozzle blockings require, besides, frequent interventions for reconditioning.

In an effort to overcome the difficulties, the con20 ventional nozzles were replaced by apparatus in which the water dispersion is no longer obtained by passage under pressure through small cross section delivery tubes, but by projection on a concave, curved element (a sort of spoon or spatula). The jet, directed on this element, forms a liquid layer which widens and bursts into a multitude of droplets.

This mode of atomizing provides a considerable increase in the output from each jet. However, the formation of - 6 very fine droplets is only possible for relatively low outputs. Furthermore, there is rapid wearing of the element providing the water dispersion. In a few hours it loses its polish in the path of water saturated with abrasive particles. Next, within several days, a phenomenon of erosion-corrosion under these conditions causes the deformation of the dispersion element which then becomes less efficient. The replacement of these elements, in the typical case, must be undertaken after two weeks of continuous operation.

The atomization by collision of jets is known essentially for dispersing combustible liquids in combustion chambers of motors. In these applications the output of liquid is relatively small and the dispersion is realized in a gas at high speed (of on the order of 30 m/s).

It has also been proposed to atomize water by jet collision in the neck of a venturi-type apparatus, this assembly being intended to remove the fine gas like dust from blast furnaces after the latter have sustained a first washing. In such application, the dispersion is effected in a gas, attempted to be maintained at high speed, and at a location where the passage cross section is narrow.

According to this invention there is provided a process for the manufacture of webs of mineral fibres in which: fibres are produced and then carried by gas currents to a receiving device where they are collected and - 7 separated from the carrier gas, - a finely dispersed liquid binder composition is projected into the gas current carrying the fibers, upstream of the receiving device, - the web of fibres is optionally treated, in particular heat treated, to fix the binder, and subjected to transformations leading to its final form, - water is sprayed into the path of the gas which has carried the fibres, downstream of the receiving device, and/or that of the gas emanating from the treatment operations for fixing the binder and/or the transformation of the mat of fibres, wherein the water is dispersed by the collision of jets directed towards one another so that a sheet of dispersed water forms transversely to the path of the gas.

The studies which led to the invention showed that by the collision of two jets it is possible to develop an expanded layer of droplets in comparison to those produced by the conventional means. A dispersion on large surfaces is obtained, without discontinuity in the spatial distribution of the droplets. 2o This represents a real advantage with respect to the prior modes of atomization.

By operating in the manner proposed by the invention, even when the treatment is carried out in very large chambers, it is possible to use only a small number of jet collision devices.

By a suitable choice of parameters for the collision jets and their location, the entire cross section of the chambers, for the installations of the type considered, can be substantially covered. - 8 An advantage of the jet collision technique is that the relatively large size of the nozzles from which water is supplied largely avoids the problems of nozzle blocking and erosion caused by particles in the water.

Ordinarily the form of the layer of droplets developed does not correspond exactly to that of the chamber section, and a portion of the water is projected on the walls. The wall in the impact zone of the droplets is in this way scoured. To obtain this cleaning action of the walls, however, it is not necessary for the impact to be forceful.

Furthermore, experience shows that the washing of the effluent gases by means of homogeneous water dispersion produced by jet collision leads to very clean walls, even beyond the impact zones.

To some degree it is preferable to limit the impact force to prevent the erosion of the walls. This is obtained by adjusting the form and expanse of the layer of droplets by modifying the operating conditions of the jets in the manner described herebelow.

Several conditions determine the form and expanse of the layer of droplets dispersed.

If the two jets are identical at their meeting point, that is to say, if they have the same characteristics of dimension, speed and output, the projection of the droplets is achieved in practically one plane. This plane is orthhonogal to that of the jets and forms a plane of symmetry. Gravity and the gases which pass through the layer of droplets distort this plane. However, for relatively low gas speeds and relatively high jet speeds, such as those implemented according to the invention, this distortion is reduced. For practical purposes, it can be considered that the layer is level.

S3743 In practice, it seems advantageous to have an initially level layer which covers the largest section, the other conditions of the jets being constant. Nevertheless, it is possible to use jets of different intensities (output5 speed). Layers are thus formed having the appearance of a more or less distorted paraboloid. Such an arrangement could appear advantageous when, for example, for a given output of liquid the dispersion is effected in a chamber of which the dimensions are relatively small, and when it is desirable to prevent the liquid layer from hitting the walls. In this case a deformed layer is attempted to be developed, drawn in the longitudinal direction of the chamber.

In all cases the jets, even different ones, have cha15 racteriBtios which remain on the same scale in order that the dispersion is satisfactorily produced.

The general form of the layer was determined experimentally as a function of the angle between the two jets.

This study, made for two identical jets, shows that the layer is developed in-circular form when the convergent jets are aligned, that is, form an angle of 180e between them. If the angle decreases, the layer of droplets tends to take the form of a circular sector of which the angle decreases at the same time that the angle between the jets decreases. In this last case the center of the sector corresponds to the impact point of the jets.

It is preferable that the atomizing apparatus (also called an injector) does not create an obstacle in the path of the gas. In other words, this apparatus is preferably close to a wall of the chamber, or of the duct, in which it is placed. Under these conditions there is a tendency toward seeking to obtain layers in the form of a sector of which the angle is close to 180s in order to cover the space up to the wall from which the atomization is effected. It can even be advantageous to form a layer of which the angle is greater than 180s, which also enables the wall on which the injector is fastened to' be sprayed. Of course, if the io apparatus is situated near a corner, a smaller angle of the layer could be preferable. In this case the angle of the jets is reduced to a smaller value.

Following the description, examples of jet angles and the form of the corresponding layers are given. In general use the angle between the jets is not less than 30s and preferably is comprised between 60 and 130s.

Of course, the layer is also developed with a certain thickness from the point of impact and on both sides of the initial plane. This thickness remains relatively small 2o in relation to the other dimensions. Ordinarily it does not exceed a few tenths of centimeters. It is practically proportionate to the output and is smaller as the angle of incidence of the jets is larger.

Since the general form of the layer is mainly determined by the fact that the jets are identical and by the angle between them, the expanse of the layer is a function of the output and of the speed of the jets.

As has been seen, it is perferable to have sufficiently large layers to prevent discontinuity in the distribution. Therefore, it would appear desirable to create a layer of dimensions such that the entire section is covered. This solution can effectively be adopted. Nevertheless, the use of a single layer is not desirable in all cases.

One reason which can lead to using several layers comes from the fact that, as was.indicated above, the force of the water projection on the walls must preferably be limited. io Xf, to cover the entire surface, a single layer was developed which virtually extended far beyond the limits of the chamber (or the duct), the water would be projected on the walls with superfluous force which could be harmful to the proper operation of the apparatus.

Another reason is associated with the fact that for very large surfaces high yield jets should be used, which would be difficult to implement in industrial installations.

In practice, by the technique of jet collision used 2 as described hereinafter, layers of droplets of 45 m 2o of useful surface or more can easily be formed. For the reasons noted above it is preferable to form layers of which the dimensions are not the largest possible, and to make use of several injectors producing a series of layers being partially covered over.

The quantify of water which each pair of jets must yield depends mainly on the section of the gaseous stream and the wall surfaces to be sprayed. For the implementation - 12 of the atomizing according to the invention the yields currently used are comprised between 10 and 80 m3 per hour.

The bursting of the jets into fine droplets is a function of the collision force and therefore of the speed of the jets.

The speed, itself, is a function of the pressure exerted to create the jets. In industrial installations and for significant yields, it is difficult to exceed pressures of on the order of 10*» Pa. For the dispersion and proporio tionment sought for implementation according to the invention pressure of on the order of 3 to 6 x 105 Pa is satisfactory.

The size of the droplets is a function of the speed of the jets and therefore of the pressure. Experimentally, it has been determined that the higher the pressure, and consequently the greater the force of the jets, the greater the tendency is to form fine droplets. However, this variation is relatively slow. In other words, large variations in pressure only lead to a slight modification in the size of the drops. When pressure of on the order of, or greater than, 2.5 - 3 x 105 is used, a certain percentage of extremely fine droplets appears, that is, of which the dimensions are less than 0.01 mm. In a certain way the presence of these very fine droplets can be favorable to the washing operation, particularly by assuring a very forceful contact of the water and the effluent gases; however, the subsequent removal of these droplets, before the release of the gases, - 13 can require supplementary separation operations.

The quantities of water used in the preferred embodiment of the invention are on the same scale as those used in the prior apparatus. Because of the more regular distribution of the water in the gases these quantities can possibly be reduced.

For the atomization of water on the path of the effluent gases from installations for manufacturing fiber mat, it is ordinarily considered that a volume of water 3 3 3 of on the order of 0.5 to 2 m for 10 m of gas gives satisio factory results. These values are obviously not imperative.

They are a function of numerous factors, and especially of the effluent gases, in particular, their binder content and the nature of the binder, their temperature, but also the quality of the water. Zn effect, for the latter it should be taken into account that it is normally recycled after a more or less forceful purification. The less the recycled water is saturated, the more effective is the treatment and the less the quantity of water necessary.

The quantity of water used can also be related to the section of the chamber or of the canalization in which the dispersion is effected. Advantageously this quantity comprises 3 2 between 2 and 20 m /m /hr. The output per unit of surface obviously depends on the output of effluent gases passing through this surface.

It is preferable to atomize the water at a point - 14 in the path of the effluent gases where the average speed of the latter remains less than 10 m/s, and even less than 5 m/s. This is only a hypothesis but, It appears that when the speed of the gas is slower, and consequently the time of contact with the droplets is longer, better exchanges occur between the gases and the water dispersed.

These preferred conditions of speed are ordinarily present, particularly at the beginning of the path of the , effluent gases, whether this be in the chamber placed diio rectly downstream of the fiber receiving element, or whether this be from the emission of the effluent gases arising from other operations conducted 0£ the fiber mat. Since it is so much more advantageous, it is preferable to effect the atomization of water as soon as possible in order to 15 prevent the deposits which could form upstream of this atomization. The atomization by jet collision is, therefore, preferably realized just downstream of the fiber receiving surface and/or directly at the exit of the chambers for treating and conditioning the fiber mat.

While it seems preferable to proceed to the washing as soon as possible on the path of the effluent gases, it can also be advantageous to repeat this washing at various points on this path. In fact, even if as a result of the qualities of the washing by jet collision the essential pari of the pollutents present in the gases is recovered by droplets of the first layer, a certain quantity of water is carried along by the gases. This water, more abundant when the dispersion is finer, is liable to be deposited on the walls along the path. If the gas is not saturated with moisture, then deposits can be formed, certainly less than in the first part of the path, but which nevertheless can be troublesome. For this reason secondary washings can be joined with the principal washing, advantageously effected as the first by jet collision.

The water projected on the walls runs along the latter , and is recovered below the chamber in which the atomizing is carried out. io The atomized water entrained in the effluent gases is separated from the latter before their release into the atmosphere. Ordinarily a first separation is effected in the atomizing chamber.

The largest drops, or those which are formed from sev15 era! droplets, become separated from the gases without any particular operation and are recovered in the lower part of the apparatus with the water running down on the walls.

For the very fine droplets which are carried along by the gases a traditional method for liquid/gas separation can be used.

The water recovered is advantageously recycled. It is subjected, in advance, to the purification procedures customary in this environment. The minimum purification before recycling consists of decantation to remove at least part of the solids in suspension. - 16 Other physical or chemical methods can complete the purification treatment. In particular, a degassing of the water can be carried out.

Regardless of the purification treatment(s) carried out, it is preferable that the recycled water contain no more than 4% dry matter.

An object of the invention is also to provide an apparatus or equipment for implementing the process described above.

An apparatus for the manufacture of a mat of mineral fibers generally comprises the following elements: a device for the formation of fibres, means for producing one or more gas currents carrying the fibres, means for the projection of a finely dispersed liquid binder composition into the gas current carrying the fibres, a receiving device on which the fibres are collected to form the webs and are separated from the gas current, optional means for the treatment, in particular heat treatment, of the web of fibres and transformation of the web to impart to it its finished form, containers (or ducts) conducting the gas which has carried the fibres downstream of the receiving device and/or the gas issuing from the treatment of transformation of the web of fibres, means for spraying water in these containers (or ducts) into the path of the gas, wherein the means for spraying the water consist of at least one injector forming two converging jets arranged so that a sheet of dispersed water is situated transversely to the path of the gas. - 17 This injector is placed in the chamber (or the duct) con veying the effluent gases so that the layer of water produced extosieis transversely to the path of the gases and preferably in a direction appreciably orthogonal to this path.

The injector contains two blast pipes of which the axes are situated in a same plane. Nozzles for calibrating the jets emitted are attached to the free extremity of these blast pipes.

The blast pipes and the nozzles are preferably of cylinio drleal shape.

To produce identical jets, which, as we have seen, is the preferred case, the blast pipes and the nozzles are o£ identical size and shape, and the distance separating tlio nozzle from the point of convergence is the same for both jets.

The blast pipes of the injector, due to the power of the jets implemented, are subjected to significant force.

To rigorously maintain the geometric conditions initially , - 18 defined, the blast pipes are advantageously mounted stationarily on a rigid plate.

This plate also serves as protection against the erosion which can develop in the immediate vicinity of the injector when the latter, by its structure, guides a large quantity of water directly on the wall on which it is fastened.

The injector is advantageously placed near a wall of the chamber or of the duct The gas flow is thus prevented from being disturbed. Preferably, the injector is fastened 10 on the wall so that only the blast pipes project into the path of the gases. It is even possible for the blast pipes to be placed in a housing, sheltered from the wall, with only the jets passing through the orifices contrived for this purpose.

Depending on circumstances, one or several deflectore can be placed upstream of and close to the injector to rectify the projection of water when the operation of at least one of the jets is momentarily disturbed.

Taking into account the output conditions which were noted above, the injector nozzles according to the invention customarily have an opening greater than 8 mm and more often comprised between 8 mm and 17 mm.

As it has been seen, each injector can produce a large surface layer capable of covering the entire section of the chamber or of the canalization. However, it is generally preferable to use several injectors, each one forming a - 19 layer covering a portion of this section, the adjacent layers partially overlapping.

Under the present conditions for dimensions of the installations it is advantageous to place an injector there2 abouts for each surface cross section of 2.5 m .

To prolong and/or complete the treatment of the invention it is possible to carry out several atomisations placed at intervals along the path of the gases.

For this purpose injectors are placed at various levels io of the chamber (or of the duct).

The installation also contains apparatus for separating the water entrained by the gases. These apparatus are advantageously of the cyclone type. This separation can be facilitated by encouraging the fusion of the drops between themselves.

For the removal of the finest drops traditional coalescence accelerators can be used.

Several separation systems can be used together, one particular combination being constituted by a cyclone fol20 lowed by an ultrafiltration apparatus.

The water separated from the gases is ordinarily conducted to a decanting tank and/or on filters to remove at least a portion of the solids entrained. It is also possible - 20 for a degassing column to be included in the installation.

Other apparatus for the treatment of the water can complete the assembly.

The invention is described by way of example below, making reference to the sheets of drawings in which: - figure 1 is a schematic view of part of an installation for the treatment of gases arising from the formation of fibers, - figure 2 is a schematic perspective view of the wash10 ing zone downstream of the fiber collecting element, - figure 3 is a schematic perspective view of a mode of implementation of gas washing according to the invention, applied to an apparatus for treating fiber mat, such as an oven, 15 - figure 4 is a schematic view similar to that of figure showing another arrangement of the washing means, - figure 5 is a partial transverse section of the apparatus of figure 4 detailing the connections between the chamber for treatment of the mat and the means for washing the gases, 2o - figure 6 represents a particular embodiment of an injector according to the invention.

Figure 1 represents the apparatus in which the operations are conducted resulting in the formation of the fibers, and then of the mat. A series of chambers and ducts, through which the gas aspirated across the receiving surface circulates, is located under this installation.

S2743 - 21 The apparatus for the formation of fibers, for example of the centrifuge type is shown at 1. This apparatus produces a ring of fibers, the attenuation of which is completed by a downwardly directed hot annular gaseous blast or current.

The combination of this blast and the induced air currents from the ambient atmosphere is directed toward a hood with movable walls 2. A fiber receiving surface 3 is located in the lower part of this hood, along the entire width, formed for example by a perforated conveyor belt.

A binder composition is atomized in the path of the fibers between the fiber forming element and the receiving surface. The atomizing means are represented at 4.

Under the receiving surface a first chamber 5 is located, its pressure slightly reduced in relation to the atmosphere of the hood. The gases pass from the hood through the fiber mat 6 and the receiving surface and into the chamber 5.

Collision jet injectors 7 are placed on the walls of the chamber 5 directly below the receiving element.

The characteristics of the injectors 7 are chosen .so that the layer of droplets extends across the entire width of the chamber 5 and totally saturates the gas mass.

The chamber 5 connects with a chamber 9 by a passage 8. The presence of passage 8, having a smaller cross section, provides an acceleration of the gases and favors a redispersion of the water running down from the walls of the chamber 5, thus completing the washing effect.

The gases entering the chamber 9 slow up and the large droplets in suspension are precipitated with the water being evacuated through a conduit 10.

The washed gases are directed through a duct 11 toward a separating apparatus 12 of the cyclone type. In this cyclone the fine droplets entrained are deposited and are recovered at the lower part, while the purified gases which exit at the upper part are aspirated through a blower 13.

It is this blower which assures the maintenance of a reduced pressure in the chamber 5 and the progression of the gases through the portion of the apparatus situated downstream of the fiber receiving element.

Possibly, when very fine droplets are present in the gases, it will be advantageous to complete the separation by passing the gases through an ultrafiltration apparatus, represented at 14. 2o In the diagram described above, the gases used are released into the atmosphere. It is also possible, as described in French patent applications No. 2,247,346, 2,318,121 and 2,368,445, to recycle a part of the gas used. In this case, the recycled gas is taken, for example, at the exit of the blower 13 and returned to the fiber formation chamber.

S2743 - 23 The water recovered at various points of the system is conducted to decanters. The assembly of the system of water conduits and water treatment means is not shown on this figure.

A complete installation usually comprises several fiber forming apparatus, aligned along a fore-hearth introducing the fiberizing material. The conveyor belt 3 forming the receiving element is placed longitudinally under the series of apparatus. To assure the circulation of the gases, it is ordinarily desirable to place several units, such as described above, comprising chamber 5, chamber 9, cyclone 12, ventilator 13, etc., this essentially to take into account the capacity of commercially available elements.

Figure 2 shows in greater detail the form of the in15 stallation represented in figure 1, at the level of the washing.

The representation is limited to the elements associated with a single chamber 5. This chamber 5 forms a part of a series of similar chambers extending along the produq20 Lion line.

The locations of the washing injectors 7 are indicated on the longitudinal walls of the chamber 5. - 24 The four injectors 7 are placed two by two in symmetrical relation, and in the upper portion of the chamber, that is, close to the conveyor belt, not shown.

The base of the chamber is inclined to facilitate the 5 flow of the water.

The chamber 5 and the adjacent chamber 9 are connected all along their length. The connection zone is formed by the passage 8.

The base of the chamber 9 is also sloped. The bottom io part forms a collector 15 which receives the water and funnels it into the duct 10.

The gases crossing the chamber 9 are conducted through the duct 11 and, from there, toward the separating apparatus, not shown.

The diagram of figure 3 shows the apparatus including the chambers for evacuation and washing of the gases coming from an apparatus for treating fiber mat.

This apparatus is, for example, an oven for the hardening of the resins forming the binder. It can also be an assembly for cooling by circulation of air at room temperature. It can also be an apparatus for the aspiration of dust particles formed, for example, from the cutting of the fiber mat. In all these treatments, or similar ones, a gas current saturated with polluting elements is formed. - 25 The treatment is effected in a closed chamber 16, only a part of which is shown. The fiber mat 6 passes through in this chamber.

For reasons of simplification, the treatment means 5 are not shown. In an oven, for example, there are apparatus providing a forced circulation of hot gases across the mat. Such apparatus are described in particular in French patent application No. 2,394,041.

The polluted gases which are formed during the treatlo ment pass from the chamber 16 to a direction changing chamber placed at the upper part of the chamber 16, then into the washing chamber 18. To enable a better representation, the frontal wall of the means conducting the gases is removed The positions of two injectors 7 with converging jets 15 are indicated on the upper cross wall of the washing chamber 18. These injectors are arranged so that the layers of droplets are formed transversely to the trajectory of the gases. Possibly, deflectors such as the one shown in figure 6 prevent any projection of washing water in the direc20 tion of the chamber 17.

Of course, the number, the position and the characterises of the injectors used in such an apparatus are selected by the user as a function of the specific conditions of the washing to be effected.

The base of the washing chamber is formed by an inclined - 26 wall 19 conducting the water deposited toward the collector 20.

At the exit of the washing chamber a narrow cross section 21 contains and accelerates the gases which then expand into the connection conduit 22. This conduit 22 leads to the separator 23 of the cyclone type.

The water separated in the cyclone 23 is evacuated through the collector 24.

In addition, the installation usually comprises a blower io not shown, and, depending on circumstances, complementary filtration means.

On figure 4 certain sides of the apparatus are removed to better show the relative placement of the various elements.

The apparatus of figure 4 and 5 is similar to the preceding one, however, this time the gases exit from the treatment chamber through exit apertures 25 situated on the side walls of the chamber 16.

Sleeves 26 enter into the interior of the direction changing chambers 17, placed on each side of the chamber 16. Each of these chambers 17 connects with a washing chamber 18. The two chambers 18 are joined above the chamber 16. From these chambers the washed gases escape through the common duct 27.

On each washing chamber there are placements 7 of two collision jet injectors. In this apparatus, as in the preceding one, the injectors are arranged so that the layer of droplets extends transversely to the gas current.

The dispersed water is caused to flow on the inclined wall 19, forming the base of the washing chamber, running down on the walls of the chamber 17 and is evacuated through the collector 20. The sleeves 26 separate the running water from the entrance of the gas currents into the chamber io 17.

Other arrangements for the exit of the gases from the treatment chamber can be considered, in particular, it is possible for certain embodiments to evacuate the gases at the base of the chamber. In this case the washing assem15 bly can be arranged in the manner described with regard to figures 1 and 2.

Figure 5 shows, in particular, the downwardly inclined position of the sleeves 26 which is intended to prevent any introduction of water in the chamber 16.

Figure 6 represents a cross section of an injector according to the invention.

This injector comprises two cylindrical blast pipes 28 bearing on their extremities the calibrating nozzles 29. The extremities of the blast pipes 28 is threaded and the nozzles are screwed therein. - 28 The blast pipes 28 are soldered on a plate 30 which forms a wall of the feed chamber 31. The washing water is led to this feed chamber through the conduit 32. The assembly of chamber 31, conduit 32, blast pipes 28 and nozzles 29 is arranged in a rigorously symmetrical manner so that the jets formed are identical.

The plate 30 supporting the blast pipes 28 is fastened onto a second protection plate 33 fastened on the wall 34, for example, by soldering. It is formed by a thick plate, io which directly receives the impact from the part of the layer of water directed toward the chamber wall, and protects the latter from abrasion.

A joint 36 assures the tightness between the plates 30 and 33. The means for fastening these plates together are not shown. They can for example be screwed together.

The plate 30 supports a conical deflector 35 which envelopes one of the injector blast pipes to prevent the propagation of the opposite jet when, accidentally, the enveloped jet is momentarily disturbed. as it has been seen above, this arrangement is particularly useful when the injector is situated in the vicinity of the fiber receiving element and when it is advisable to protect the mat being formed from a possible projection of water.

When the impact of the jets is momentarily interrupted, 53743 the jet which is not enveloped impinges against the deflector 35. Of course, the injector is arranged so that the deflector is situated on the side of the installation requiring protection.

Example 1 The configuration of the atomized layers of water was studied in preliminary tests.

A series of measurements of the opening angle of the layer having the form of a circular sector were thus estab10 lished as a function of the angle between the two identical jets.

These measured values are the following: angle between the jets 30° 60’ 90° 100’ 108’ 120’ opening angle of the layer 40® 80’ 120’ 150’ 180’ 21®° The output values obtained for nozzles of 16 mm and 8.105 Pa reach 50 m3/hr. g For nozzles of 16 mm and a pressure of about 6.10 Pa, under an angle of 120°, the layer of droplets formed is greater than 90 m .

Example 2 The washing according to the invention is used in a washing chamber and in the adjacent chamber, downstream - 30 of the fiber receiving conveyor of an installation for forming fiber mat.

Previously, 13 spoon or spatula-like atomizing elements were placed in the washing chamber and 16 in the adjacent chamber.

These elements are replaced by 2 collision jet injectors on the opposite walls of the washing chamber directly below the conveyor (75 cm below the latter) and two in the adjacent chamber which, by means of ducts, lead the gases toward io a cyclone.

The cross section of the washing chamber under the 2 conveyor is about 7.5 m .

The quantity of gas passing through the washing chamber is about 54.1()3 The injectors placed in the washing chamber have nozzles of 16 mm in diameter; those of the injectors placed in the adjacent chamber are of 11 mm in diameter.

Tbe water pressure is 5.10 Pa.

The jets are directed toward each other following an angle of 120®.

The water used is recycled water which contains on the order of 2.5% by weight of dry matter.

In the washing chamber the output measured is about 3 m /hr. for each injector. It is 18 m /hr. for each injector in the adjacent chamber, therefore, a total of about 108 m3/hr.j that is to say a quantity comparable to that previously used with the conventional atomizers.

No difficulties appeared during the course of a year of continuous operation. Ho interruption of operation was necessary. The injectors never became obstructed. The wear of the nozzles was negligable. For the diameter, it io was less than a tenth of a millimeter.

The walls of the washing chamber, the adjacent chamber, and the ducts were perfectly clean.

Example 3 Following the results obtained and which were reported 15 in Example 2, two entire production lines of fiber mat were equipped with a system for washing by jet collision.

On a line comprising 8 centrifuge fiberizing· elements producing a total of about 140 tons of fiber per day, the reception of the effluent gases under the conveyor belt is assured by four washing chambers.

The total volume of gas passing in these washing cham3 3 bers is of on the order of 288.10 m /hr. t - 32 18 collision jet injectors are placed in the washing chambers and in the adjacent chambers.

The 18 injectors are identical. The angle o£ the jets is 120s. The diameter of the nozzles is 13 mm and the water c 3 pressure 5.10 Pa. Each injector yields about 26 m /hr., a total of 468 m3/hr.

These 18 injectors were introduced into this installation as a replacement for 139 spoon-like atomizing apparatus.

After more than 6 months of continuous operation, an 10 examination of the installation showed the total cleanliness of the entire circuit taken by the gases, particularly the washing chambers, the ducts, the cyclone separators and the blowers. With the previous washing means systematic stoppages were necessary about every six weeks.

Claims

CLAIMS:

1. Process for the manufacture of webs of mineral fibres, in which fibres are produced and then carried by gas currents 5 to a receiving device where they are collected and separated from the carrier gas , - a finely dispersed liquid binder composition is projected into the gas current carrying the fibres, upstream of the receiving device, 10 - the web of fibres is optionally treated, in particular heat treated, to fix the binder, and subjected to transformations leading to its final form, water is sprayed into the path of the gas which has carried the fibres, downstream of the receiving 15 device, and/or that of the gas emanating from the treatment operations for fixing the binder and/or the transformation of the mat of fibres, wherein the water is dispersed by the collision of jets directed towards one another so that a sheet of dispersed 20 water forms transversely to the path of the gas.

2. Process according to claim 1, wherein the collision takes place between the jets of one or more pairs of identical jets to form one or more than one substantially planar sheet of droplets. 25

3. Process according to one of the preceding claims, in which the characteristics of the pair (or pairs) - 34 of jets are chosen so that the sheet (or sheets) of droplets of dispersed water covers the entire crosssection of passage of the gas.

4. Process according to any one of the preceding claims, wherein the water is dispersed on gas flowing at an average velocity below 10 m/s.

5. Process according to any one of the preceding claims, wherein the quantity of dispersed water is from 0.5 to 2 m 2 of water for a volume of gas of 10¾ 3 .

6. Process according to any one of the preceding claims, wherein the rate of supply of water for a pair of converging jets is from 10 to 80 m /h.

7. Process according to any one of the preceding claims, wherein the angle of the converging jets is greater than 30°.

8. Process according to claim 7, wherein the angle of the jets is from 60 to 130°.

9. Process according to any one of the preceding claims, whgrein the dispersed water is raised to a pressure of from 3 to 6 X 10 5 Pa.

10. Process according to any one of the preceding claims, wherein the rate of supply of dispersed water in the container (or duct) per unit surface area of cross-section and 3 2 per hour is from 2 to 20 m /h · m .

11. Process according to any one of the preceding claims, wherein the dispersion of water takes place from the entrance of the effluent gas into the evacuation circuit. - 35

12. Process according to any one of the preceding claims, wherein the dispersed water is subsequently separated from the gas and subjected to one or more operations providing for the removal of at least 5 part of the products with which it is charged in contact with the gas and with the walls of the container (or of the duct) and that it is reused for a fresh washing operation.

13. Process according to claim 12, wherein the 10 water separated from the gas is filtered to remove at least part of the solid products entrained by it, the water which is reused not containing more than 4% of dry matter.

14. Apparatus for the manufacture of a web of 15. Mineral fibres, comprising a device for the formation of fibres, means for producing one or more gas currents carrying the fibres, means for the projection of a finely dispersed liquid 20 binder composition into the gas current carrying the fibres, a receiving device on which the fibres are collected to form the webs and are separated from the gas current, optional means for the treatment, in particular heat 25 treatment, of the web of fibres and transformation of the web to impart to it its finished form, containers (or ducts) conducting the gas which has carried the fibres downstream of the receiving device and/or the - 36 the gas issuing from the treatment of transformation of the web of fibres, means for spraying water in these containers(or ducts) into the path of the gas, 5 wherein the means for spraying the water consist of at least one injector forming two converging jets arranged so that a sheet of dispersed water is situated transversely to the path of the gas.

15. Apparatus according to claim 14, wherein the 10 injector comprises two tubes, the two ends of the tubes carrying nozzles calibrating the jets, and the tubes and nozzles being circular in cross-section.

16. Apparatus according to claim 14 or claim 15, wherein the tubes and the nozzles of one and the same injector 15 have identical forms and dimensions, their axes are converging, and the distances separating the orifice of the nozzle from the point of convergence of the axes are equal.

17. Apparatus according to any one of claims 14 to 16, wherein the tubes are mounted on a plate which is 20 fixed to a wall of the container (or of the duct), only the injector tubes and nozzles projecting along the walls on the inside of the container.

18. Apparatus according to any one of claims 14 to 17, wherein the injector tubes and nozzles are retracted from the 25 surface of the wall so as not to constitute an obstacle in the - 37 53743 path of the gas.

19. Apparatus according to claim 17, wherein a deflector situated upstream of the injector tubes forms an obstacle to accidental projection of water in countercurrent 5 to the gas.

20. Apparatus according to any one of claims 15 to 19, wherein the nozzles of the injector have an orifice diameter greater than 8 mm.

21. Apparatus according to any one of claims 14 to 10 20, wherein, to form a sheet of dispersed water, an injector *2 is used for each portion of surface of about 2.5m .

22. Apparatus according to any one of claims 14 to 21, wherein several injectors are arranged at the same level of the container (or duct) to form several sheets of water 15 which partly overlap.

23. Apparatus according to any one of claims 14 to 22, wherein, for the treatment of gas downstream of the receiving device for the fibres, the injectors are arranged as close to this device as is possible without risking wetting 20 the fibres which form the web.

24. Apparatus according to any one of claims 14 to 23, wherein a zone of reduced cross-section is arranged downstream of the zone of dispersion of water in the path of the gas in order to accelerate the gas.

25. Apparatus according to any one of claims 14 to 24, wherein it comprises a collector arranged in the lower - 38 part of the zone in which dispersion takes place, to collect and evacuate the deposited water.

26. Apparatus according to any one of claims 14 to 25, wherein downstream of the container (or of the duct) 5 in which the water is dispersed, it comprises a separating system for the finest droplets entrained by the gas.

27. Apparatus according to claim 26, wherein the separator consists of a cyclone.

28. A process for the manufacture of mineral fiber 10. mat substantially as herein described with reference to the drawings.

29. Apparatus for the manufacture of mineral fiber mat, constructed and arranged substantially as herein described and shown in the drawings.