The invention concerns a chamber for the production of an agglomerated product and equipped with one or more inlets for admitting solid matter in e.g. powder form into the chamber; one or more liquid inlets for admitting liquid into the chamber; an atomizer arranged in the chamber for bringing the liquid into an atomized state in the form of fine drops; a gas inlet for admitting a flow of gas into the chamber; a gas discharge channel for discharging the gas from the chamber; and a product discharge for dis¬ charging the agglomerated product from the chamber, the space of said chamber being defined by a flexible wall at least in a zone around the atomizer, means being arranged externally of said wall to deform the wall in operation.

In products such e.g. milk, coffee, baking powder, medi¬ cine, detergents and chemicals, the solid content consti- tutes the component which is of greatest value in terms of use. The residue, which is frequently mostly water, is therefore separated off industrially to a great extent by means of e.g. atomization drying leaving the solid matter as fine powdered articles. In this state the product has a greatly reduced volume entailing that it can be packaged, stored and transported even over great distances in an economically advantageous manner. Furthermore, long natural shelf life is imparted to otherwise perishable products, such as e.g. milk.

However, it is difficult to work with the fine powder, because it has poor flowing properties and is very dust¬ ing. The latter property may be unhealthy and even cause allergy in some cases in the individuals who come into contact with the dusting product.

For the consumer to be able to use the product, it must generally first be dispersed or dissolved again in a liquid, which may e.g. often be water. However, this process is very difficult to carry out when the product is in powder form, because owing to their minimum extent the fine particles per se are liquid-repelling and tend to remain on the surface of a liquid without sinking down into it.

Therefore, with a view to remedying these drawbacks the powder is subjected to an agglomeration process in most cases, which basically comprises wetting the fine par¬ ticles so that their surface becomes sticky, and then bringing them into mutual contact and binding them together to larger particles or agglomerates. The agglo¬ merates are fluid and dustless and can easily be dispersed and dissolved in a liquid.

The agglomeration may e.g. take place in direct connection with atomization drying in a drying chamber, the fine par¬ ticles - fines - being recirculated back to the wet zone around the atomizer where the particles are wetted and agglomerated. However, separate agglomeration chambers may also be used, which receive powder that has been dried beforehand and which is wetted and agglomerated likewise in the wet zone around an atomizer in the agglomeration chamber.

As mentioned, in this agglomeration process the surface of the particles is made sticky, and they will therefore tend to settle as a coating on the chamber wall if they impinge on it. This might entail that often expensive products would be wasted, and that the chamber would frequently have to be subjected to cumbersome and expensive internal cleaning.

For these reasons it is therefore necessary to build chambers of this type so big that the chamber wall is kept constantly spaced from the agglomeration zone. This entails that the chambers are expensive to manufacture and will often take up unduly much space in the production system. Moreover, it is difficult completely to avoid the situation that there are nevertheless particles to some extent which reach the container wall and stick to it.

A solution to these problems might comprise providing a flexible wall at least around the agglomeration zone which is successively deformed locally so that coatings, if any, on the wall are loosened and fall off. The wall would hereby be self-cleaning.

Such a flexible wall is known from DE Auslegeschrift 2 150 708 and US Patent Specification 3 887 166, which, however, do not concern agglomeration chambers, but devices for continuously mixing powdered solids with a liquid or granulating such solids by mixing them with a liquid. In this process a plurality of rollers, arranged in groups, are moved up and down the rear side of a wall, which is thus successively deformed with inward bends extending in a curve along the periphery, and inwardly directed beads extending along generatrices between these inward bends. A possible coating, which might have stuck to the flexible wall, will therefore be bent by the inward bends and pressed together by the beads at right angles to the in¬ ward bends in operation. This simultaneous action effectively loosens the coating from the wall, which thus automatically cleans itself.

In addition to the flexible wall the two above-mentioned known mixing and granulating devices are provided with a rotor having blades which, in both cases, just serve to mix and granulate the powdered solids. The blades in the

rotor described in the US patent specification are adjustable to influence the properties of the resulting mixture, the size of the granulates and the residence time of the substances in the device.

Furthermore, Danish Patent Application 3969/83 discloses an apparatus having a chamber which is likewise equipped with a flexible wall, but which, in this case, is intended for treating dust-laden gases, a liquid being injected for cooling and/or otherwise conditioning or reacting with the gases. The flexible wall is suspended from the top of the chamber at a relatively small distance from the chamber wall. In operation a pulsating gas and/or liquid flow is sent into the ring-shaped space between the chamber wall and the flexible wall, which should hereby be caused to move in a sort of undulating manner.

It is common to the three above-mentioned known construc¬ tions that they are in no case intended for agglomeration of powdered particles, and they can in no case be used for this purpose. The movements performed by the respective flexible walls are of a type which is just capable of making possible coatings peel off in the form of major or minor flakes or lumps which would fall down into the agglomerate and be mixed with these, so that the resulting product would be unuseful or would at any rate not be up to the quality requirements which must be made with respect to products of this type.

The object of the invention is therefore to provide an agglomeration chamber of the type mentioned in the opening paragraph whose flexible wall is controlled in such a pattern of movement that sticky powdered particles imping¬ ing on the wall are agglomerated and repelled in the form of agglomerates of a desired size and quality.

Another object of the invention is to utilize the agglome¬ ration effect on the flexible wall optimally to increase the capacity of the chamber by arranging it in a manner such that the powdered particles present at a given moment in the space of the chamber are quickly and safely ex¬ pelled to contact the wall.

A third object of the invention is to provide the chamber with a more compact structure than known before while maintaining maximum capacity.

These objects are achieved by the novel and unique fea¬ tures of the invention, which are that the means for deforming the flexible wall consists of an elastomeric base which contacts the outer side of the wall and contains a plurality of cavities connected individually or groupwise with their respective sources of fluid having a cyclically varying fluid pressure, and the cycles of at any rate one source of fluid are phase-shifted with respect to the cycles of the other sources of fluid. An undulating movement is hereby imparted to the flexible wall, having standing or travelling waves of predetermined height and width. Sticky powdered particles settling on the wall will therefore be pressed together and be agglomerated when the wall moves down into a trough, and the resulting agglomerates break off and are repelled when the wall subsequently rises in a crest. The chamber can be built with a very small diameter since its wall no longer has to have a great radial distance from the atomization zone, but, on the contrary, may advantageously be arranged close to it.

Thus, in this context the flexible wall serves not only to keep the inner side of the chamber self-cleaning, but additionally it forms a direct and important part of the actual agglomeration process. To promote this effect to

increase the agglomeration capacity of the chamber, the chamber may advantageously be equipped with a rotor having a shaft which is coaxial with the chamber axis and which mounts a plurality of arms extending outwardly towards the wall of the chamber. The rotor circulates the gas in the chamber violently, whereby the particles in the gas will be affected by a correspondingly great centrifugal force which safely and effectively throws the particles against the wall. The concurrently formed flows and turbulences in the gas contribute themselves to promoting the agglomera¬ tion. The particles will moreover be agglomerated to a certain extent when they are directly hit by the arms of the rotor.

The agglomeration degree as well as the size and quality of the agglomerates can be influenced in different ways by a suitable design of the arms. These may e.g. have the shape of blades forming an angle with the direction of rotation. This angle may be adjustable in operation, but also be determined beforehand when the blades are fixedly mounted on the shaft of the rotor.

Chambers of this type generally terminate downwardly in a conical funnel having such a small apex angle that the products unobstructedly slide down along the inner side of the funnel to a discharge or a fluid bed arranged down¬ wardly in the funnel. This pointed funnel accounts for a considerable portion of the overall height of the chamber, and in many cases more than 50%. When the flexible wall is arranged closely around the atomization zone, the chamber may be constructed with a very small diameter. When the pointed conical funnel is replaced by a plane or slightly inclined bottom, the overall height of the chamber may be reduced to the height of the cylindrical part of the chamber, in which the actual process takes place. In this case the flexible wall may be extended to cover the bottom

as well, which can hereby stand being hit by sticky particles, which are agglomerated and repelled in the same manner as on the cylindrical part of the flexible wall. Also the bottom can therefore be arranged close to the agglomeration zone, so that the cylindrical part of the chamber just has to have such a vertical extent as is necessary for the process to be performed. The presence of the flexible wall along the vertical interior side of the chamber as well as its bottom thus entails that the chamber can be built as an extremely compact structure.

When in this manner the chamber downwardly terminates in plane or slightly inclined bottom coated with the flexible wall, the discharge opening of the gas and the product may advantageously be arranged in the side wall in connection with the flexible wall of the bottom, and the waves in it may be travelling waves running toward the discharge open¬ ing. The flexible wall of the bottom will hereby serve as a conveyer conveying the agglomerates out of the chamber.

In an advantageous embodiment the cavaties in the base of the flexible wall in an unloaded state may have the form of substantially rectangular channels which are arranged transversely in at least one row along the flexible wall, and the channels in the row may be divided into groups connected with their respective sources of fluid, so that the channels in one group are separated by a channel from each of the other groups, and the channels in the row alternate and the cycles of the fluid sources are phase- shifted in the same groupwise order. This structure entails that the wave pattern on the flexible wall can be controlled precisely as desired, and that the wall can therefore produce agglomerates having the prescribed size and quality.

As desired, the channels may extend in various ways in the base of the flexible wall. Thus, the channels may extend along helical lines, which makes the connection of the channels with the fluid sources particularly simple. In other cases the channels advantageously extend along a vertical line or with an inclination with respect to such a vertical line.

In a particularly advantageous embodiment the channels may be formed by elastomeric tubes which, in an unloaded state, have a substantially rectangular cross-section and are arranged juxtaposed. These tubes may e.g. be wound along helical lines and be supported by a stationary outer wall in the chamber. Optionally, the tubes may addition- ally be adhered to this outer wall. Further, a negative pressure may prevail between the tubes and the flexible wall to keep the flexible wall constantly and safely en¬ gaged with the tubes.

The flexible wall may consist of an elastomeric membrane having a smooth inner side with a small coefficient of friction, which effectively ensures that the resulting agglomerates can release the wall.

The agglomeration process per se may be promoted by using a fluid having such a low temperature that the temperature on the inner side of the flexible wall is below the dew point in the chamber. This entails that liquid condenses on the flexible wall, which will hereby be wet. This moisture contributes to making the surface of the powdered particles sticky so that they more easily bind together to agglomerates. If rapid drying of the agglomerates on the flexible wall is desired, a fluid having such a high tem¬ perature that the inner side of the wall is kept suitably warm may be used instead. The two methods may expediently be combined, using a cold fluid for the cylindrical part

of the wall and a warm fluid for the part covering the bottom. The agglomeration on the cylindrical part of the wall is promoted hereby, while the resulting agglomerates undergo expedient subsequent drying on the bottom, while the flexible wall on it conveys the agglomerates out the chamber.

The chamber may just serve to agglomerate powdered particles which are separately conveyed into the chamber and are wetted in it by a liquid added to the atomizer without any independent solid matter content. However, the solid matter may also be added in full or in part together with the liquid as is the case with atomization drying chambers proper. The two methods may advantageosly be com- bined in many cases.

The invention will be explained more fully by the follow¬ ing description of embodiments, which just serve as examples, and further advantageous properties and effects will be stated with reference to the drawings, in which

fig. 1 is a schematical lateral sectional view of a first embodiment of an agglomeration chamber according to the invention having a flexible wall and a pointed conical bottom,

fig. 2 is a schematical lateral sectional view of a second embodiment of an agglomeration chamber according to the invention having a flexible wall and a flat bottom,

fig. 3 is a schematical lateral sectional view of a third embodiment of an agglomeration chamber according to the invention having a flexible wall, a flat bottom and a rotor.

fig. 4 is an enlarged section of the rotor shown in fig. 3,

figs. 5a-d are enlarged sectional views through a first embodiment of a flexible wall according to the invention having fluid chambers in four different situations,

fig. 6 shows curves illustrating the pressure development in the channels belonging to figs. 5a-d,

figs. 7a-d are enlarged sectional views through a second embodiment of a flexible wall according to the invention having fluid chambers in four different situations,

fig. 8 shows curves illustrating the pressure development in the channels belonging to figs. 7a-d,

fig. 9 is an enlarged sectional view of a fraction of the lower left corner of the chamber shown in fig. 2 having an agglomerating flexible wall,

fig. 10 is a perspective view of a fraction of a first em¬ bodiment of a base in the form of elastomeric hoses belonging to the flexible wall and wound along helical lines, and

fig. 11 is a perspective view of a fraction of a second embodiment of a base in the form of elastomeric tubes belonging to the flexible wall and arranged vertically side by side.

When the chamber is described below and shown in the draw¬ ing in a vertical position, i.e. with a vertical axis, this just serves as an example. It is practical to arrange the chamber in this manner in many other cases, but in other cases it is more convenient for the production and

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the associated production system if the chamber is arranged with a horizontal or inclined axis.

Fig. 1 shows a first embodiment of an agglomeration chamber according to the invention. The chamber, which is generally designated by the reference numeral 1, comprises an upper cylindrical part 2 which merges into a lower conical part 3. A gate 4 for discharging the finished pro¬ duct is arranged below the conical part 3. Solid matter in the form of powdered particles (not shown) are stored in a supply container 5 and is fed to the chamber via another gate 6 and a solid matter inlet 7. For the powdered par¬ ticles to bind together to larger particles in the agglo¬ meration chamber, the chamber must also receive a liquid, e.g. water for wetting the particles and making their sur¬ face sticky. This liquid is added via a liquid inlet 8 to a centrifugal atomizer 9, which is caused to rotate at a very great speed by means of a motor 10, so that the liquid is atomized to very fine drops which are thrown outwardly against the wall 11 of the chamber, which is coated with a flexible wall whose structure and function will be described below.

The chamber is moreover equipped with a gas inlet 12 for conveying a gas, e.g. hot air, via a gas distributor 13 into the chamber to dry the agglomerated product. The gas and the liquid absorbed by it in the process are again discharged from the chamber via a gas outlet 14.

Fig. 2 shows a second embodiment of an agglomeration chamber according to the invention. This chamber, which is generally designated by the reference numeral 15, substan¬ tially corresponds to the chamber 1 shown in fig. 1, and identified parts are therefore indicated by the same reference numerals. However, the chamber 1 has a bottom in the form of the lower conical part 3, which must

necessarily be very pointed for the finished agglomerates to slide freely down the sides of the cone under the action of gravity. The small apex angle of the cone entails a correspondingly great overall height, and the structure shown in fig. 1 therefore has a much greater overall height than the chamber of fig. 2 which is provided with a plane bottom 16. In this case the flexible wall 11 also covers the bottom 16. A combined gas and product discharge 17 is provided in the cylindrical part 2 of the chamber in connection with the flexible wall 11 of the bottom 16.

Finally, fig. 3 shows a third embodiment of an agglomera¬ tion chamber according to the invention. This chamber, which is generally designated by the reference numeral 18, substantially corresponds to the chamber shown in figs. 1 and 2, and the same reference numerals are therefore used for identical parts in this case too. The chamber 3 is basically identical with the chamber shown in fig. 2, but is additionally provided with rotor 19, which consists of a rotor shaft 20 having a plurality of outwardly protrud¬ ing blades 21 and which is rotated at a speed of up to 3000 rpm by means of a motor 22. The structure and func¬ tion of this rotor will be explained below.

As shown in figs. 1, 2 and 3 and described above, the above-mentioned three embodiments of agglomeration chambers are equipped with centrifugal atomizers for atomizing the liquid. However, this atomization may equal- ly well take place by means of other methods within the scope of the invention, such as e.g. two-matter nozzles, pressure nozzles or ultrasound.

A first embodiment of the flexible wall is depicted in various situations in figs. 5a-d. Inwardly the wall con¬ sist of a membrane 23 which may consists of rubber or

elastomeric plastics and may have a thickness of between e.g. 0.1 and 10 mm. This elastomeric membrane 23 prefer¬ ably has a very smooth surface on the side facing the space of the chamber. The membrane 23 is supported on the outer side by a base which is generally designated by the reference numeral 24. This base is composed of a number of tubes which are positioned juxtaposed and may have a height of e.g. between 10 and 200 mm and a width of e.g. between 0 and 50 mm in an unloaded state. These tubes, too, are made of rubber or elastomeric plastics. These tubes define two groups of channels 25a, 25b which are conencted with their respective sources of compressed fluid (not shown). The pressure of the sources of com¬ pressed fluid cyclically varies in the manner illustrated by the curves in fig. 6, the pressure in the channels 25a being shown in solid line and the pressure in the channels 25b in dashed line. The pressure in the channels may vary between e.g. 0 and 7 bars absolute. The cyclically varying pressure in the channels 25a, 25b entails that they are alternately pumped up and sucked in in a specific pattern which, as shown in figs. 5a-d, is in the nature of stand¬ ing waves running through a full cycle of e.g. between 0 and 5 min, preferably between 1 and 2 min. To prevent the membrane 23 from disengaging the base 24 during this wave movement, a negative pressure may advantageously prevail between these two parts. However, the membrane may also be glued on the tubes of the base 24, which may likewise be glued together.

Fig. 7a-d show a second embodiment of a flexible wall according to the invention. In this case the membrane 23 is supported by a base 26 which, like the structure shown in figs. 5a-d, is composed of elastomeric tubes, but in this case with a front and a rear row of channels 27a, 27b; 28a, 28b, respectively, which are connected groupwise with their respective sources of compressed fluid (not

shown). This pressure varies cyclically in the same manner as in the embodiment shown in figs. 5a-d between e.g. 0 and 7 bars. The variations are illustrated by the curves shown in fig. 8, when the upper curves show the variations in the front channels 27a, 27b, and the lower ones in the rear channels 28a, 28b, and the curves shown in solid line indicate the pressure in the channels 27a, 28a, respec¬ tively, and the curves shown in dashed line indicate the pressure in the channels 27b, 28b, respectively. The combined effect of these pressure variations entails that a regular wavy movement is imparted to the membrane 23, but now a movement with travelling waves.

Fig. 9 is an enlarged cross-sectional view of a detail of the lower left corner in the second embodiment of an agglomeration chamber according to the invention shown in fig. 2. Outwardly the chamber is composed of a cylindrical wall 29 and a plane bottom wall 30. A rib 31 extends in the corner between these walls. The walls 29, 30 and the ^r ib 31 may e.g. be made of stainless steel. Interiorly the chamber is coated with a flexible wall 1 which, in this case, is of the type shown in figs. 7a-d, having two rows of groupwise divided channels 27a, 27b; 28a, 28b, respec¬ tively.

When the agglomeration chamber is in operation, the powdered particles, added from the supply container 5 via the gate 6 and the solid matter inlet 7, are wetted by the finely atomized liquid drops which the atomizer 9 sends into the chamber in a direction toward the flexible wall. The surface of the powdered particles is hereby made sticky, and when the particles impinge on the flexible wall, they will therefore settle on it as a coating, which is generally designated by the reference numeral 32. As will be readily visible, the coating 32 will be compressed when the membrane 23 runs down into a trough. This entails

that the particles in the coating are bound together to agglomerates. When subsequently the membrane 23 rises in crests 34, the coating is stretched and the formed agglo¬ merates are broken apart and are loosened from the smooth surface of the membrane 23.

Thus, the flexible wall is not only self-cleaning, but directly capable of independently forming agglomerates on its wavy surface. The agglomerates formed on the vertical part of the flexible wall fall down on the part of the flexible wall which coats the bottom of the chamber. Since also this part of the flexible wall is agglomerating, the bottom of the chamber may be arranged at a relatively small distance from the atomizer. Thus, also the bottom will be hit by powdered particles which, as shown in fig. 9, are agglomerated in the troughs and are loosened on the crests. Thus, the bottom face positively contributes to increasing the agglomeration capacity of the chamber.

The base of the flexible wall shown in fig. 9 is of the type which is provided with two rows of channels forming travelling waves in the membrane 23 in operation. In the case shown in figs. 2 and 9, these travelling waves run in the direction of the arrow toward the combined gas and product discharge 17 and therefore serve as a conveyer conveying the finished agglomerates out of the chamber via the discharge 17, the waves successively pushing the agglomerates in front of them toward this discharge. Thus, the structure in which the bottom of the chamber is coated by the flexible wall and the bottom is made plane, select¬ ing a flexible wall having waves travelling and transport¬ ing the agglomerates toward the gas and product discharge of the chamber, not only entails that the agglomeration capacity of chamber is increased, but also that the over- all height of the chamber can be reduced considerably with respect to the structure shown in fig. 1, which is pro-

vided with a long, pointed conical funnel for discharging the agglomerates from the chamber.

The capacity of the chamber may be increased additionally by means of the rotor 19 shown in fig. 3. In operation, this rotor circulates the gas in the chamber strongly, entailing that the powdered particles in the gas are thrown against the wall by the centrifugal force and are agglomerated. Further, a secondary agglomeration will occur in the turbulent flows imparted to the gas by the rotor. Additionally, particles hit directly by the blades 21 of the rotor will be agglomerated.

As shown in figs. 3 and 4, the blades are arranged setwise with a mutual distance along the shaft 20 and at a distance to the flexible wall of e.g. between 0.1 and 10 mm. The angle a formed by the blades with a plane at right angles to the shaft 20 is of great importance to the agglomeration process. When, as shown in figs. 3 and 4, all the blades form a positive angle with the direction of rotation, the rotor operates as an axial ventilator which sends a strong central gas flow down through the chamber. This may be advantageous in some cases, while in other cases a less strong downwardly directed central gas flow and on the other hand a stronger eddy formation with great turbulence are desired to promote the agglomeration. Such a state of flow may be obtained when e.g. some of the blades form a positive angle and others a negative angle with the direction of rotation, or when blades in the upper set form a positive angle with the direction of rotation and the blades in the lower set a negative angle with the direction of rotation. Oppositely directed gas flows will be formed in this manner, which, when they meet, create a very strong turbulence and are turned out- wardly in a direction toward the wall of the chamber. A corresponding effect is obtained when the blades alter-

nately form a positive and a negative angle with the direction of rotation. When the blades are constructed with a cross-section which is symmetrical about a tangent plane to the surface of revolution described by the blades during the rotation, the effect of the rotor as an axial ventilator will be eliminated completely, and the rotor will only impart a whirling and turbulent flow to the gas.

The flow sequence in the chamber exerts a considerable influence on the agglomeration process and the quality of the resulting agglomerates. This flow sequence can be con¬ trolled carefully when the rotor is arranged such that its blades can currently be adjusted in operation.

Fig. 10 is a perspective view of a fragment of a first embodiment of a base for a flexible wall according to the invention. The base, which is generally designated by the reference numeral 35, is composed of eleastomeric tubes 36a, 36b; 37a, 37b, which have a rectangular cross-section in an unloaded state. The tubes are arranged juxtaposed in two rows, the tubes in one row being vertically offset half the height of a tube with respect to the tubes in the other row. The configuration and the groupwise division of the channels correspond to those shown in figs. 7a-d, and the base 35 will thus correspondingly generate travelling waves in operation. Each tube is wound along a helical line extending from the lower edge of the base to the upper edge of the base. This structure entails that the number of channels in the base is reduced to very few long channels or tubes which simplify and reduce the number of connections of the fluid sources to the base. The struc¬ ture is particularly useful for the cylindrical part of the chamber.

Fig. 11 is a perspective view of a fraction of second embodiment of a base for a flexible wall according to the

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invention. In this case too the base is composed of elastomeric tubes 39a, 39b; 40a, 40b, which have a rect¬ angular cross-section in an unloaded state. The tubes are arranged juxtaposed in two rows in the same manner as in the base shown in fig. 10, but extend vertically between the upper and lower edges of the base. This base too will generate travelling waves in the elastomeric membrane cm which the agglomerates are formed, but the waves now extend longitudinally along the generatrices of the mem- brane. This may be advantageous when the base is used in an inclined agglomeration chamber, since this structure permit the resulting agglomerates to slide down along the inclined inner side of the membrane unobstructed by trans¬ verse waves.

In a developed state the second embodiment shown in fig. 11 lends itself for positioning on top of the plane bottom in the agglomeration chambers shown in figs. 2 and 3. The tubes are then to be arranged transversely to the gas and product discharge 17 in the longitudinal direction, and the waves are to travel toward it. In addition to partici¬ pating in the agglomeration process, an elastomeric mem¬ brane having a base of the type 38 shown in fig. 11 will therefore also serve as a conveyer which safely and effectively conveys the finished agglomerates out of the chamber.

The cavities, the channels or the tubes may be connected groupwise with the respective fluid sources via their respective manifolds (not shown). The fluid, which may e.g. be air or water, may just serve as a medium for deforming the flexible wall. In this case the connections may advantageously be made at one end of e.g. each tube. Then, the fluid will pulsate substantially merely to an fro in the tube in operation and soon assume the same temperature as the flexible wall. The fluid used will then

have no influence on the temperature development on the flexible wall. This temperature development is determined solely by the production parameters inside the chamber, including in particular the temperatures of the gas, the liquid and the powdered particles.

The matter is different if the temperature of the fluid, as mentioned before, is to contribute to controlling the agglomeration process on the flexible wall. In this case one end of e.g. a tube may connected with a source of positive pressure and the other end with a source of nega¬ tive pressure; the terms possitive pressure and negative pressure are to be understood in relation to an average pressure. The fluid present in the tube will then successively be replaced by new fresh fluid, which can constantly keep the wall at the intended temperature either by absorbing or releasing heat to the wall.

Figs. 5a-d and figs. 7a-d show two preferred embodiments of a base for a flexible wall according to the invention. The base shown in figs. 5a-d is unique in having a simple and inexpensive structure. The generated waves are stand¬ ing, and this entails that the membrane 23 is not deformed completely uniformly across the waves. Thus, the membrane is deformed most in the central area of the waves and to a minor degree in the transition between the waves. Agglome¬ rates having a rather disuniform size are formed hereby, and this may be an advantage in some cases since the finished agglomerates can hereby be packed more densely together. In contrast, the base 26 shown in figs. 7a-d with two rows of tubes deforms the membrane 23 completely uniformly with travelling waves. This provides a product with agglomerates of a more uniform size.

However, the invention is not restricted to the two embodiments shown in figs. 5a-d and figs. 7a-d having one

and two rows of channels or tubes, respectively. According to the wave formation desired on the membrane 23, there may be three as well as more rows of channels or tubes, and the channels in each row may be divided into more than two groups. For a regular wave movement to be obtained, it is important that the channels in a group are separated by a channel from each of the other groups, and that the channels in the row alternate and the cycles of the fluid sources are phase-shifted in the same groupwise order.

In all the embodiments of the base of the flexible wall described above and shown in the drawing the cavities or channels in it have a uniform cross-section. However, embodiments are conceivable within the scope of the invention in which the cavities or the channels in each row and/or row by row have a different cross-section at least partially with a view to generating precisely the wave pattern desired on the flexible wall.