WO2012146244A1

WO2012146244A1 - Drying plant comprising a hammering device, and method of operating the drying plant

Info

Publication number: WO2012146244A1
Application number: PCT/DK2011/050137
Authority: WO
Inventors: Henrik Schwartzbach; Palle Efland
Original assignee: Gea Process Engineering A/S
Priority date: 2011-04-28
Filing date: 2011-04-28
Publication date: 2012-11-01

Abstract

The drying plant comprises a component in the form of a vessel including a wall structure delimiting an interior of the vessel, and at least one hammering device. The wall structure comprises a first wall (21) constituting an inner wall of the vessel and a second wall (22) positioned outside the first wall at a predefined distance from the first wall such that a space (24) is defined between the first wall and the second wall, and hammering device (30) is acting on the first wall (21). A predefined pressure is provided in the interior of the vessel, and substantially the same predefined pressure is provided in the space between the first wall and the second wall.

Description

Drying plant comprising a hammering device, and method of operating the drying plant

The present invention relates to a drying plant comprising a component in the form of a vessel including a wall structure delimiting an interior of the vessel, and at least one hammering device. The invention furthermore relates to a method of operating a drying plant.

In drying plants, components containing one or more of gases, liquids and/or powders, such as for instance spray drying chambers, cyc- lones, bag filters, fluid bed chambers, process chambers, containers, tanks, ducts or any similar vessel, are prone to the formation of build-up or deposits of material on the inside surface of their walls. Such deposits are undesirable for a number of reasons. For one, the yield may be adversely affected, and in particular in case of expensive materials, this may have a substantial economical effect. In order to reduce or eliminate the build-up or deposits, hammering on the wall of the component is used. The hammering is e.g. carried out by means of pneumatic hammers well-known in the art. The hammers are normally positioned on the outside of the wall and functions in general in the way that short duration vibrations transferred to the wall release and dislodge surface product deposits on the inner side of the walls. The vibrations are for instance generated by allowing compressed air to propel a ball within the hammer on to an impact plate. The force of the impact is transferred to the wall causing vibration thereof.

Some plants, however, include components designed as pressure vessels, i.e. with a relatively large wall thickness of wall plates formed of e.g. stainless steel. This applies to, i.a., so-called aseptic spray drying plants, which are sterilized by means of steam. In order to ensure that the steam is distributed to all areas of the component, the sterilization process is initiated by applying vacuum, which in turn eliminates any air pockets in the component which could prevent correct sterilization at certain locations within the vessel. The components are typically designed to resist pressures ranging from for instance between 0-4 bar (abs), i.e. from a vacuum of -1 bar to 3 bar overpressure, and the plates forming the wall are thus designed with a thickness corresponding to the nominal pressure of the vessel, typical values of the plate thickness being 4 mm or more, even up to 12 mm. As a consequence, the required plate thickness of the wall of the component renders hammer- ing less effective or even impossible, as the thickness of the wall may reduce the flexibility of the wall to such an extent that vibration is not possible.

With this background it is an object of the invention to provide a drying plant, by which the removal of deposits on the inner side of the component is made possible even in plants designed to resist high pressure.

This and further objects are met by a drying plant of the kind mentioned in the introduction, which is furthermore characterized in that said wall structure comprises a first wall constituting an inner wall of the vessel and a second wall positioned outside the first wall at a predefined distance from the first wall such that a space is defined between the first wall and the second wall, and that the hammering device is connected to the first wall.

By dividing the wall structure into a first wall and a second wall, the first wall forming the inner wall facing the interior of the vessel and thus in contact with the product may be formed with a reduced thickness, and as a consequence a number of advantages are obtained. First, the reduced thickness entails a degree of flexibility of the first wall which renders the hammering effective. Second, the surface treatment of the inside surface of the inner wall, such as polishing, which is necessary in aseptic spray dryer plants, is less expensive in a plate of reduced thickness. Third, a pneumatic hammer as used in conventional plants may be used and test results from conventional plants may be applied directly to the aseptic dryer plant. The second wall is formed to resist the operating pressure in both a sterilization phase and during production.

With respect to the term "hammering device", it is noted that this applies to any device relying on the application of a vibrating movement of the wall structure of the drying plant. Thus, the term covers any mechanical vibrating device. The hammering device may be driven me- chanically, pneumatically, hydraulically and/or electrically. The hammering device may also consist of a pneumatic pulse generated to act between the first wall and the second wall. Any driving gas resulting from a pneumatically driven hammering device present in the space between the first and second walls may be ventilated to the exterior by any suitable means.

The invention is applicable in components within a large variety of drying plants. In a particularly advantageous embodiment, the vessel is a spray drying chamber of a spray drying apparatus. Spray drying shall here be understood to include spray cooling as well.

The wall structure according to the invention provides for an optimal dimensioning of the walls in accordance with the operational conditions, and such that the flexibility of the first wall aimed at is achieved. In most cases, the second wall will have a larger thickness than the first wall, but the opposite is conceivable as well. Reinforcement arrangements, such as circumferential rings, may be provided in order to lend sufficient strength to a relatively thinner second wall. Preferred intervals of the respective thicknesses are given in a preferred embodiment, in which the first wall has a thickness of 0.5 to 3.5 mm, preferably 1 to 3 mm, and more preferably 1.5 to 2.5 mm, and the second wall has a thickness of more than 2 mm, preferably larger than 4 mm.

In order to obtain substantially the same pressure in the vessel itself as in the space between the first and second walls, a mechanically simple solution is provided in an embodiment, in which the drying plant comprises means for allowing fluid communication between the interior of the vessel and the space defined between the first wall and the second wall. In a further development of this embodiment, the means for allowing fluid communication comprise one or more membranes and/or one or more valves, or equivalent means. These solutions are easily operable and based on well-proven elements.

Alternatively, the drying plant may comprise means for regulating the pressure in the space defined between the first wall and second wall separately. This may be a preferred solution, in case it is desired to close-off the interior of the vessel, for instance for sterility reasons. The pressure equalizing may take place by means of any suitable fluid, for instance steam, water, nitrogen etc. If necessary, drainage means may be provided in the space in order to drain off condensed water.

The material of the respective walls may be optimized with re- spect to the desired properties, for instance as regards strength, flexibility, ability to be sterilized etc. The first wall may be made from stainless steel, preferably with a polished or highly cleanable stainless steel surface.

Dependent on factors such as the need for thermal or sound in- sulation, the vessel may be insulated in an embodiment, in which a third wall is provided outside the second wall. Preferably, insulating material is provided between the second wall and the third wall.

In a second aspect of the invention, a method of operating a drying plant is provided. The method comprises the steps of:

providing a component in the form of a vessel,

providing the vessel with a wall structure delimiting an interior of the vessel,

forming a space in the wall structure between a first wall forming an inner wall and a second wall positioned at a predefined distance from the first wall,

connecting at least one hammering device with the first wall, providing a predefined pressure in the interior of the vessel, and providing substantially the same predefined pressure in the space between the first wall and the second wall.

In this manner, the first wall may be designed with properties making it possible to induce a vibrating movement rendering deposits on the inner side of the first wall to fall into the vessel. The product obtained as a result of the method consequently includes the material of the deposits hammered down. Thus, in addition to eliminating or at least reducing other adverse effects due to the presence of the deposits, it is possible to increase the yield by reducing the waste that would otherwise have arisen. Even if the yield assumes values of a few percent only of the total amount of material processed in the drying plant, this may represent substantial economical values. As substantially the same pre- defined pressure, an underpressure or an overpressure, is provided in the space between the first and second wall as in the interior of the vessel, the double-walled structure acts as a single wall element from a structural point of view and makes it possible to form the component as a pressure vessel. The combination of the double-walled structure and the pressurized space makes it possible to resist pressures during operation and sterilization that would otherwise have make a single wall of small thickness to collapse. Within the concept of "substantially the same predefined pressure", only slight variations are foreseen, for in- stance within 0.1 bar.

Although the method is applicable in all drying plants, the vessel is preferably a spray drying chamber of a spray drying apparatus.

The step of providing the same predefined pressure in the space between the first wall and the second wall as in the interior of the vessel may be achieved by providing means allowing fluid communication between the interior of the vessel and said space.

Alternatively, the step of providing the same predefined pressure in the space between the first wall and the second wall as in the interior of the vessel is achieved by regulating the pressure in the space defined between the first wall and second wall separately.

The predefined pressure may lie in the interval 0 to 13 bar (abs). For instance, the predefined pressure may lie in the interval 0 to 0.9 bar (abs) or 1.1 to 10 bar (abs).

The connection between the interior of the vessel and said space may be designed to selectively allow a flow of steam from the interior of the vessel.

The at least one hammering device may be operated according to the specific needs of the particular plant. Preferably, the hammering device is operated intermittently and controlled by a compressed air regulating valve to transfer an impact to the first wall thereby causing vibration thereof.

In the following, the invention will be described in further detail by means of the following description of preferred embodiments and with reference to the drawings, in which Fig. 1 shows a schematic overview of a plant including a spray drying apparatus in one embodiment of the invention;

Fig. 2 shows a schematic sectional view, on a larger scale, of a part indicated by the circle II of Fig. 1 of the spray drying apparatus shown in Fig. 1;

Fig. 3 shows a schematic sectional view, on a still larger scale, of the part of the spray drying apparatus shown in Fig. 2;

Fig. 4 shows a schematic overview of a detail of one embodiment of the drying plant according to the invention; and

Fig. 5 shows a view corresponding to Fig. 4, of a detail of another embodiment of the spray drying apparatus according to the invention.

As shown in Fig. 1, a drying plant according to the invention comprises a number of components, in which the drying process and other processes associated with the drying of materials are carried out. In the embodiment shown, the drying plant comprises a spray drying apparatus generally designated 1. The spray drying apparatus 1 comprises a first component in the form of a vessel 2 constituted by the drying chamber of the spray drying apparatus. The functioning of the spray drying apparatus 1 and of the drying chamber 2 corresponds to that of a traditional drying plant, i.e. in the embodiment shown, a feed to be spray dried is introduced into the drying chamber 2 at the top thereof (indicated by arrow 3) by means of suitable atomizing means (now shown) and is set into a, possibly swirling, downward movement in the drying chamber 2 by drying air introduced via an air disperser 4 mounted above the ceiling of the drying chamber 2 of the spray dryer. In the embodiment shown, the drying chamber 2 has an upper, mainly cylindrical part 2a and a lower, conical part 2b but other configurations are conceivable.

The material dried in the drying chamber 2 is discharged at the bottom of the lower part 2b and conducted to further components of the drying plant. In the embodiment shown, these components include a cyclone 5, a bag filter 6, filters 7 and 12, a condenser 8, heaters 9 and 11, and a fan 10. The use of further or alternative components is conceivable. The drying plant of the embodiment shown may be a steam sterilized Aseptic Spray Drying (ASD) plant. Such plants are normally operated in closed cycle due to the feed solvent, which may for instance be ethanol, or due to a wish for protecting the product from oxidation, or to protect from explosion. However, the invention is also applicable to other drying plants, including drying plants operated in open cycle.

Referring now to the more detailed Fig. 2, a part of the drying chamber 2 is shown, at the intersection between the upper, cylindrical part 2a and the lower, conical part 2b. As shown, the vessel which in the embodiment shown is a component of a spray drying apparatus, viz. the drying chamber 2, includes a wall structure generally designated 20 and delimiting an interior of the vessel, and at least one hammering device 30, both of which are to be described in further detail below.

As shown most clearly in further enlarged Fig. 3, the wall struc- ture 20 comprises a first wall 21 constituting an inner wall of the vessel and a second wall 22 positioned outside the first wall 21 at a predefined distance from the first wall such that a space 24 is defined between the first wall 21 and the second wall 22. The hammering device 30 is connected to the second wall 22 in the embodiment shown and acting on the outer side of the inner wall 21. In a manner known per se in this kind of hammering device, a spring guides a ball impacting the inner wall (not shown in detail). In the embodiment shown, the vessel is insulated in that a third wall 23 is provided outside the second wall 22 and insulating material 25 is provided between the second wall 22 and the third wall 23.

The vessel, i.e. in the embodiment shown the drying chamber 2, is thus formed as a pressure vessel having a double-walled configuration which provides possibilities of designing each of the first and second walls in accordance with particular needs and specifications. Additionally, the third wall of the embodiment shown makes it possible to provide insulation without compromising the design of the first and second walls.

In the embodiment shown, the hammering device 30 is pneumatic, but may be driven in other ways, for instance mechanically, hy- draulically and/or electrically", or be any device relying on the applica- tion of a vibrating movement of the wall structure of the drying plant. Thus, the term in principle covers any mechanical vibrating device. Any driving gas resulting from the pneumatically driven hammering device 30 present in the space 24 between the first and second walls 21, 22 may be ventilated to the exterior by any suitable means (not shown).

Possible intervals of the respective thicknesses are: The first wall has a thickness of 0.5 to 3.5 mm, preferably 1 to 3 mm, and more preferably 1.5 to 2.5 mm, and the second wall has a thickness of more than 2 mm, preferably larger than 4 mm. The flexibility of the first wall aimed at is achieved. In most cases, the second wall will have a larger thickness than the first wall, but the opposite is conceivable as well. Reinforcement arrangements, such as circumferential rings, may be provided in order to lend sufficient strength to a relatively thinner second wall.

The material of the respective walls may be optimized with respect to the desired properties, for instance as regards strength, flexibility, ability to be sterilized etc. The first wall may be made from stainless steel.

The distance between the first wall 21 and the second wall 22, i.e. the transverse dimension of the space 24, lies typically in the range 5 to 100 mm.

In the following the method of operating a drying plant will be described.

The steps of providing a component in the form of a vessel, providing the vessel with a wall structure delimiting an interior of the vessel, forming a space in the wall structure between a first wall forming an inner wall and a second wall positioned at a predefined distance from the first wall, and connecting at least one hammering device with the first wall are carried out substantially as described in the above.

The step of providing a predefined pressure in the interior of the vessel takes place in accordance with specifications, for instance during operation or during sterilization.

The step of providing substantially the same predefined pressure in the space between the first wall and the second wall takes place in an appropriate manner to be described in further detail below.

The at least one hammering device may be operated according to the specific needs of the particular plant. For instance, the hammering device may be operated intermittently and controlled by a compressed air regulating valve to transfer an impact to the first wall thereby causing vibration thereof.

Between intervals of drying material, the drying plant is subjected to a sterilization process, for instance by means of steam. In order to ensure that the steam is distributed to all areas of the component, the sterilization process is initiated by applying vacuum, which in turn eliminates any air pockets in the component which could prevent correct sterilization at certain locations within the vessel. Steam and other cleaning fluids may be introduced through CIP devices mounted in the vessel.

Referring now to the schematic overview of Fig. 4, the step of providing the same predefined pressure in the space 24 between the first wall 21 and the second wall 22 as in the interior of the vessel 2 is achieved by providing means allowing fluid communication between the interior of the vessel and said space. In the embodiment shown in Fig. 4, the means for allowing fluid communication comprise a pump 45 and a valve 46. In the embodiment shown, the pump is connected to a suitable vacuum supply. One or more membranes could also have been provided, additionally or alternatively.

In the schematic overview of Fig. 5, the step of providing the same predefined pressure in the space 24 between the first wall 21 and the second wall 22 as in the interior of the vessel 2 is achieved by regulating the pressure in the space defined between the first wall and second wall separately. In this alternative embodiment, a system for regulating the pressure, is represented by valve 145. The pressure equa- lizing may take place by means of any suitable fluid, for instance steam, water, nitrogen etc. If necessary, drainage means may be provided in the space in order to drain off condensed water.

The invention is applicable to other components containing one or more of gases, liquids and/or powders, that is in addition to the spray drying chamber described in the above, the invention is equally applicable to cyclones, bag filters, fluid bed chambers, process chambers, containers, tanks, ducts or any similar vessel, prone to the formation of build-up or deposits of material on the inside surface of their walls.

The invention should not be regarded as being limited to the embodiments shown and described in the above but various modifications and combinations of features may be carried out without departing from the scope of the following claims. Thus, a feature from any embodiment may be combined with any feature from another embodiment.

Claims

P A T E N T C L A I M S

1. A drying plant comprising a component in the form of a vessel including a wall structure delimiting an interior of the vessel, and at least one hammering device, c h a r a c t e r i z e d in that said wall structure comprises a first wall constituting an inner wall of the vessel and a second wall positioned outside the first wall at a predefined distance from the first wall such that a space is defined between the first wall and the second wall, and that the at least one hammering device is connected to the first wall.

2. A drying plant according to claim 1, wherein the vessel is a spray drying chamber of a spray drying apparatus.

3. A drying plant according to claim 1 or 2, wherein the first wall has a thickness of 0.5 to 3.5 mm, preferably 1 to 3 mm, and more preferably 1.5 to 2.5 mm, and the second wall has a thickness of more than 2 mm, preferably larger than 4 mm.

4. A drying plant according to any one of the preceding claims, wherein the drying plant comprises means for allowing fluid communication between the interior of the vessel and the space defined between the first wall and the second wall.

5. A drying plant according to claim 4, wherein said means for allowing fluid communication comprise one or more membranes and/or one or more valves.

6. A drying plant according to any one of claims 1 to 3, wherein the drying plant comprises means for regulating the pressure in the space defined between the first wall and second wall separately.

7. A drying plant according to any one of the preceding claims, wherein the first wall is made from stainless steel, preferably pharma grade stainless steel.

8. A drying plant according to any one of the preceding claims, wherein a third wall is provided outside the second wall.

9. A drying plant according to claim 8, wherein insulating material is provided between the second wall and the third wall.

10. Method of operating a drying plant, comprising the steps of: providing a component in the form of a vessel, providing the vessel with a wall structure delimiting an interior of the vessel,

11. The method of claim 10, wherein the vessel is a spray drying chamber of a spray drying apparatus.

12. The method of claims 10 or 11, wherein the step of providing the same predefined pressure in the space between the first wall and the second wall as in the interior of the vessel is achieved by providing means allowing fluid communication between the interior of the vessel and said space.

13. The method of claims 10 or 11, wherein the step of providing the same predefined pressure in the space between the first wall and the second wall as in the interior of the vessel is achieved by regulating the pressure in the space defined between the first wall and second wall separately.

14. The method of any one of claims 10 to 13, wherein the predefined pressure is in the interval 0 to 13 bar (abs).

15. The method of claim 14, wherein the predefined pressure lies in the interval 0 to 0.9 bar (abs) or 1.1 to 10 bar (abs).

16. The method of any one of claims 10 to 15, wherein the connection between the interior of the vessel and said space is designed to selectively allow a flow of steam from the interior of the vessel.

17. The method of any one of claims 10 to 16, wherein the at least one hammering device is operated intermittently and controlled by a compressed air regulating valve to transfer an impact to the first wall thereby causing vibration thereof.