"CONICAL-BASE DRIER"

DESCRIPTION

This invention relates to a conical-base drier, particularly for chemical/pharmaceutical products, of the type having a stirrer within the collection chamber.

Units of this kind are very frequently used in the chemical/pharmaceutical industry in the production of active ingredients or other chemical substances in powder form. Because these powders, that is the dry product, have a high added value, the need to recover the maximum possible quantity of product from the drier and to allow easy and complete removal of the dry product to reduce contamination between two successive charges to a minimum, not only when these are part of the same batch but also when they belong to two production batches relating to two different products, is particularly felt.

Driers for chemical/pharmaceutical products, for example having a flat bottom, are already known in the art. Drying is assisted by a stirrer, driven in rotation about its own axis, in such a way as to maintain the mass of product in a state of constant mixing.

When the mass is sufficiently dry the product is removed from the collection chamber via a discharge opening located in the side wall of the collection

chamber; the mechanical action of the stirrer helps to push dry product towards the exterior.

In these units the stirrer does not scrape the bottom, in order to prevent damaging it, but is separated from it by a few millimetres. Towards the end of the drying process this space gives rise to the creation of a dry cake (heel) between the base and the stirrer which has to be completely removed given the high economic value of that cake, but this requires appropriate equipment and long periods of time.

In order to overcome these problems an alternative technology is that of constructing drying units with a conical base having the discharge opening at the centre of their conical base. The complexity of the system is reduced in this way and discharge times for the finished dry product are considerably shortened.

The length of the drying process is therefore a particularly important factor when evaluating the operating costs of driers.

One of the factors influencing time is the formation of compact agglomerations of moist product in areas which are not subjected to sufficient mixing, the presence of which appreciably increases the time required for complete drying of the mass of product.

In view of the state of the art described, the object of this invention is to prevent such agglomerates forming within the mass of moist product, at the same time ensuring an optimum drier geometry for rapid discharge of the finished product.

In accordance with the invention this object is accomplished through a drier having all the features in claim 1.

Further preferred embodiments are described in the dependent claims.

Other advantages and characteristics of the present invention will become clear from the following detailed description which is given with reference to the appended drawings which are provided purely by way of non-limiting example and in which:

Figure 1 shows a perspective view in partial cross-section of a drier according to a preferred embodiment ,

- Figure 2 shows a section along the plane II-II of a detail of the drier illustrated in Figure 1,

- Figures 3 and 4 show a view in partial cross- section of two particular configurations of the drier in Figure 1,

- Figure 5 shows a perspective view of a component of the drier in Figure 1.

As will be seen in Figure 1, drier 1 comprises a collection chamber 2 provided in a main body 3 which in turn comprises a lid 4, which is generally dished, a side wall 5, which is generally cylindrical, and a conical base 6.

Drier 1 has a principal longitudinal axis X-X which is normally also an axis of symmetry of rotation for main body 3; when the drier is mounted in the working position the X-X axis is located in a vertical direction while conical base 6 is at the bottom with respect to lid 4.

Normally the component forming conical base 6 is constructed in such a way as to connect to side wall 5 through a cylindrical portion 6b which is attached to a conical portion 6a; in this description the plane α is regarded as the plane of transition between the conical part 6a and the cylindrical part 6b of main body 3, regardless of where the connection between side wall 5 and conical base 6 is located.

Drier 1 also comprises a stirrer 7, which in turn comprises a shaft 8 located along the X-X axis, and is provided with one or more blades 9.

Drier 1 also comprises a heating jacket 10, which preferably extends over the entire external surface, a loading aperture 11, through which the moist material which is to be dried can be added, and a discharge

opening 12 through which the dry product can be discharged. Both loading aperture 11 and discharge opening 12 are controlled by corresponding valves .

Discharge opening 12 is substantially located on the summit of the generatrix of the cone of conical base 6 in such a way that the dry product can flow through opening 12 by gravity.

Stirrer 7 can rotate about the X-X axis in both directions, driven by drive means of a known type; this can move along its own longitudinal axis (that is along the X-X axis) between a first upper terminal position and a second lower terminal position which thus define its travel .

The travel of stirrer 7 is such as to permit blades 9 to sweep the entire volume occupied by the product being dried and, in particular, makes it possible for the lower extremities of the blades to move in a vertical direction until they reach at least plane α.

When stirrer 7 is in the lower position it does not touch conical part 6a of the conical base, but leaves a few millimetres play which is substantially constant along the entire length of conical part 6a.

In this lower position shaft 8 extends longitudinally substantially as far as plane α. Going on now to a description of a preferred

embodiment of the stirrer, Figures 1, 3 and 4 show that this may have a plurality of blades, preferably two, located in such a way as to balance the mass of the stirrer when it is rotating so as to stir the contents uniformly and effectively.

In the case where stirrer 7 has two or more blades 9, these will be equally distributed around shaft 8.

The blades are preferably constructed from two arms

15, 16: a lower arm 16 and an upper arm 15 having one end connected preferably close to plane α to lower arm 16 and the other end connected to the lower end of shaft 8 of stirrer 7.

The lower arm is substantially parallel to the generatrix of the cone of conical part 6a, while upper arm 15 may be inclined with respect to lower arm 16 through an angle which is greater by approximately 10°-

20° than that formed between lower arm 16 and plane α.

As may be seen in Figures 3 and 4 , at least a part of the profile facing discharge opening 12 of at least one blade 9 has teeth 17 which alternate with gaps 18; preferably there are four to ten teeth 17 and four to ten gaps 18 on each arm.

Teeth 17 and gaps 18 may be provided on the lower profile of lower arm 16 and/or on the lower profile of upper arm 15.

Teeth 17 and gaps 18 form a profile of a periodic nature with a constant spacing and are preferably- arranged in such a way that teeth 17 and gaps 18 in one blade 9 are offset with respect to the adjacent blade by a distance equal to the spacing divided by the number of blades.

If the number of blades is even, the offset may also be equal to twice the spacing divided by the number of blades. For example, with four blades this means that diametrically opposite blades have the same profile of teeth and gaps .

As may be seen from a comparison of Figures 3 and 4 , when the stirrer has only two blades teeth 17 and gaps 18 correspond respectively to the gaps 18 and teeth 17 in the other blade after stirrer 7 has rotated through half a rotation.

Figure 3 in fact illustrates a portion of drier 1 in which stirrer 7 is shown in its lower position in a particular angular position; teeth 17 and gaps 18 are clearly indicated.

Figure 4 shows the same portion of drier 1 in which stirrer 7, still in the lower position, is shown rotated through 180° with respect to the angular position shown in Figure 3. Teeth 17 and gaps 18 corresponding to the new

stirrer position are illustrated by a solid line, while teeth 17 and gaps 18 corresponding to the position of the stirrer in Figure 3 are shown as a dashed line.

As may be seen, where there were previously gaps 18 there are now teeth 17, and vice versa.

In this way the combined effect of teeth 17 and gaps 18 provided on different blades 9 does not create any stationary configuration in the volume of the product swept by the stirrer but on the contrary the teeth of one blade tend to move the volume which has not been affected by the action of the teeth on the other blade (or other blades) .

Teeth 17 are preferably longer than gaps 18 so as to ensure the abovementioned effect even with less viscous products .

Blades 9 are preferably hollow in such a way that heating means 20 can be located within internal cavity 19, for example in the form of a conduit.

In this way the advantageous effect of transferring heat directly from stirrer 7 to the mass of product requiring drying present in collection chamber 2, thus to a greater extent than has hitherto been achievable with driers of the prior art, is achieved.

The "V" shape of the arms of the blades, as illustrated in Figures 1, 3 and 4, makes it possible to

transfer even more heat to the product being dried.

Advantageously lower arms 15 and upper arms 16 comprise a hollow frame to which a member bearing teeth 17 and gaps 18 is attached (or of which it forms an integral part) .

The cross-section of the frame of upper arm 15 may ^¬ be different from that of the frame of lower arm 16; the former may be circular in order to achieve high resistance to bending, while the latter may advantageously be trapezoidal in order to increase the heat exchange surface between blade 9 and the product being dried.

The frame cross-sections of the upper and lower arms may also be both rectangular or both circular, depending upon whether it is desired to give preference to exchange surface area or resistance to bending.

Lower arms 16 comprise a rectangular frame 22, preferably hollow, from which there extends a profile member 23 on which teeth 17 and gaps 18 are provided. With reference to Figure 2 the cross-section of blade 9 may be considered to have a profile provided by the trapezium identified by segments ABCEFGH, where segments CEF and segments GH are preferably on the same line and the angles between segments AB and segments BC are preferably right angles.

The polygon defined by segments ABCEIH corresponds to the cross-section of lower arm 16 when seen along' the cross-section indicated by II-II in Figure 1, that is when this has a gap 18. Rectangle ABCD is the external profile of frame 22, while the triangle DEFGH is the added cross-section of tooth 17 with respect to rectangle ABCD.

As is clear from Figure 2, side C and side EF lie on the same straight line, while side D is common to both profiled member 23 and rectangular frame 22.

The cross-section of gap 18 is represented by the triangle IFG in Figure 2.

Segment CEF, representing one of the active surfaces of the blade, is inclined with respect to radial direction r by preferably approximately 45° while angle GF is approximately 20° - 30°.

Segment I is inclined with respect to radial direction r by an angle such that it diverges from conical reference profile c in such a way as not to compress the material which is caused to pass through the space when stirrer 7 is caused to rotate in a clockwise direction with respect to Figure 2.

With reference to Figures 3 and 4 , outlet opening 12 comprises an opening or initial portion 24 connected to conical part 6a of conical base 6 close to the summit.

A discharge valve 14 which comprises an upper part having a profile of revolution, for example a spherical cap, and a lower part which attaches the upper part to one or more fins 26, is inserted into initial position 24.

Valve 14 can thus rotate about the axis defined by pins 26, opening and closing discharge opening 12.

The centre of the spherical cap advantageously lies on the axis of rotation of the valve so that in any event a seal is ensured between the upper surface of valve 14 and the initial portion 24 of discharge opening 12 during opening and closing.

Advantageously the axis of rotation of valve 14 intersects the longitudinal axis X-X. As may be seen in Figures 1, 3 and 4, at least one of blades 9 has its lower arm 16 ending in an extension 25 which engages the initial portion 24 of the discharge opening .

This extension 25 extends in a radial direction with respect to the X-X axis, preferably so as to project beyond the X-X axis; advantageously lower arms 16 of the other blades (or other blade) end in vertical alignment with discharge opening 12.

In this way, as stirrer 7 rotates extension 25 can also effectively move moist product lying within the

initial portion 24 of discharge opening 12.

Preferably extension 25 has a lower profile which matches the upper profile of valve 14 in such a way that when stirrer 7 is in its lower position the gap between extension 25 and valve 14 is a few millimetres.

At the end of the drying process a certain quantity of dry powder product which it has not been possible to remove from discharge 14, even through the action of the stirrer, will always be present. Areas such as the upper side of arms 9, the bellows covering shaft 8 of stirrer 7, in fact constitute dead spaces where the action of gravity is not sufficient for complete discharge of the product.

In order to overcome this disadvantage the drier to which this invention relates may also comprise upper means 27a, 27b for the admission of fluid connected to the upper part of main body 3 , for example connected to lid 4, and capable of admitting fluid at least in a direction which is capable of varying over time, rotating about at least two axes Y-Y, Z-Z, which are inclined with respect to each other.

The fluid admitted by these admission means 27a, 27b may be gas, of the type of nitrogen or air or dry air, or liquid, of the type of water or solvent. Upper means 27a, 27b comprise one or more devices

28, of which one embodiment is illustrated in Figure 5, each provided with a principal body 29 comprising a first elongated part 30 extending along a first straight axis Y-Y and a second part 31 connected to the first part 30 which has a free end; second part 31 in this way defines the second axis Z-Z which is at an angle with respect to the first axis Y-Y.

First axis Y-Y may be parallel to the longitudinal axis X-X of collection chamber 2 as illustrated in Figure 1, or, more advantageously, perpendicular to lid 4, that is, with an inclination of approximately 20° -30° with respect to the X-X axis in order to locate the free end of second part 26 more centrally with respect to the wall of main body 3. Figure 5 shows a cone of the possible orientations of first axis Y-Y of device 28 with respect to an axis parallel to the longitudinal axis X-X of collection chamber 2.

Considering first part 30 and second part 31 as defining the sides of the angle between them, the opening of the angle can be considered to be between 45° and 135°, preferably between 60° and 120°, with an optimum value of approximately 90°.

At the free end of second part 31 there is a rotating support 32 which is capable of rotating about

second axis Z-Z.

This rotating support 32 has one or more nozzles 33, which may be angularly equally spaced in such a way as to balance the forces resulting from the emission of fl-uid. Devices 28 comprise drive means to rotate principal body 29 about first axis Y-Y, preferably using at least part of the fluid.

Nozzles 33 may be located on the outer circumference of rotating support 32, around the axis of rotation and with their mouths facing the circumferential direction with respect to second axis Z-Z, as shown in Figure 5.

In this way rotating support 32 is caused to rotate about second axis Z-Z purely and simply through the admission of fluid. An alternative arrangement is achieved when the mouths of nozzles 33 are orientated along the radial direction, towards the outside of rotating support 32; in this alternative arrangement separate drive means may be necessary in order to bring about rotation of rotating support 32 about second axis Z-Z.

Preferably devices 28 comprising these means 27a, 27b for the admission of fluid are fixed in the direction of first axis Y-Y in such a way as to ensure a seal at the point where these eject within collection chamber 2. These devices 28 are arranged in such a way as not

to interfere with the volume of action of stirrer 7 during working operations .

If means 28 for the admission of fluid number two or more, it is possible to eliminate almost all dead spaces within collection chamber 2.

As a consequence, by blowing in the fluid, in this case a gas, it is possible to move all the mass of dry residue present within collection chamber 2.

Adapting these means 28 for the admission of fluid to the admission of liquid, for example solvent or water, drier 1 can be provided with upper means 27a for the admission of gas and/or upper means 27b for the admission of liquid connected to two independent circuits as illustrated diagrammaticalIy in Figure 1. Admission means 28 may also be constructed in such a way that they can be fed alternately with liquid and gas . Because liquids generally have better lubricating properties than gases, friction between rotating support 32 and second part 31 of principal body 29 is generally less when liquid is admitted than when gas is admitted. Means 27b for the admission of liquid therefore do not necessarily need separate drive means to rotate rotating support 32 about second axis Z-Z.

Upper means 27a, 27b for the admission of fluid may be activated during drying operations, but it is more

advantageous to active them during subsequent operations in which the dry powder residue is cleaned from collection chamber 2 in the dry.

In fact, by admitting fluid, or more specifically gas, during the stage of cleaning in the dry, powder is removed from the dead spaces previously described.

Also, after a certain number of drying operating cycles it may be necessary to wash the interior of the drier. In these cases it is simply possible to activate upper admission means 27b, if present, admitting liquid, water or solvent, to carry out a wet washing cycle in collection chamber 2.

The washing cycle may be performed, for example, before introducing a different product into collection chamber 2 (or at the end of each run) and makes it possible to further reduce the risk of contamination between two different products without requiring long and costly operations which may even be carried out manually with long machine downtimes . Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated, which have been given purely by way of example, without thereby departing from the scope of the invention.