The present invention relates to a spray dryer comprising a drying chamber defining at least a radial direction and an axial direction, with an opening bordered by a rim, a chamber roof having a closing surface facing the rim, the chamber roof being movable between an open position and a closed position, and a seal provided at the interface between the rim of the drying chamber and the closing surface of the chamber roof to seal said inter- face in said closed position.

A spray dryer of this kind is the well-known and commercially available MOBILE MINOR™ (GEA Niro), which is a spray dryer primarily for R&D purposes. It is thus a relatively small unit for exploring the possibilities of spray drying, for making test work and powder samples and for establishing the process data required for scale-up. Thus, small quantities of solutions, suspensions and emulsions can be dried into powder samples for further evaluation. Feed is supplied by a peristaltic or a mono pump and can be atomized by a rotary atomizer or by a nozzle (e.g. two-fluid or pressure) co- current or counter-current to the air flow. The chamber conditions can either be in under or over pressure. Product can be recovered either directly from the drying chamber, or from accessory units such as a cyclone and/or bag filter.

In the above-identified spray dryer, the rim of the drying chamber is formed as a plane surface substantially perpendicular to the axial direction, and the closing surface of the chamber roof is also designed as a plane surface. The seal ensures the required tightness at the interface between the chamber roof closing surface and the drying chamber rim during operation. To that end, the seal of the above-identified spray dryer is provided as a specially configured sealing lip of silicone positioned in a track of the rim. The sealing lip is exposed to the product processed in the spray dryer and to relatively high temperatures during operation. Although the silicone sealing lip provides for excellent tightness under normal circumstances, it must be ensured that it is safely retained in the track when opening the chamber roof. In those cases, there is a risk of partial or full extraction of the sealing lip from the track, if the sealing lip for instance sticks to the closing surface of the chamber roof. Reinsertion of the sealing lip into the track is cumbersome, with a risk of incorrect positioning of the sealing lip in the track or of damaging the sealing lip thus possibly resulting in that the seal needs to be replaced. As the choice of material of the sealing lip is limited due to the special configuration, the required properties as regards chemical and temperature resistance are not always optimal which in turn reduces the lifetime of the sealing lip, thus rendering the use of a silicone sealing lip a relatively expensive solution.

On this background, it is an object of the present invention to provide a spray dryer in which a reliable sealing is achieved in a cost-effective man- ner.

This and further objects are achieved by a spray dryer of the kind mentioned in the introduction, which is furthermore characterized in that a neck section including a circumferential groove facing the outwards radial direction, away from the opening of the drying chamber, is provided on either the rim of the drying chamber or the closing surface of the chamber roof, and that the seal is accommodated in said circumferential groove to seal against the other of the closing surface of the chamber roof or the rim of the drying chamber in said closed position.

In this manner, a more cost-effective solution has been found, as the provision of a groove in a neck section on either the drying chamber rim or the chamber roof closing surface renders the choice of seal more flexible. As the seal is safely retained in the groove of the neck section by positive engagement, i.e. by the shape of the components involved, the risk that the seal is unintentionally moved out of its correct position is limited or even elimi- nated. This reduces the costs involved in incorrect sealing and replacement of the seal.

In principle, the neck section may be provided on either one of the drying chamber or the chamber roof. In a presently preferred embodiment, however, the neck section including the circumferential groove facing the outwards radial direction, away from the opening of the drying chamber, is provided on the rim of the drying chamber, and the seal is accommodated in said circumferential groove. In this manner, the rim of the drying chamber includes the seat of the seal, which in turn allows the chamber roof to be formed in a more simple, lightweight and inexpensive manner.

In a further preferred embodiment, the seal is an O-ring seal. The 0- ring is a well-proven mechanical gasket or packing in the form of a toric joint, i.e. a circular loop with a circular cross-section. When the O-ring is accommodated in the groove, its compression characteristics between the drying chamber and the chamber roof create a reliable seal at the interface. O-rings are known as inexpensive, easy to make, reliable, and have simple mounting requirements. At the same time the sealing properties relative to the silicone sealing lip of the known spray dryer are maintained or even improved.

Further details are described, and further advantages stated, in the description of particular embodiments of the invention.

In the following the invention will be described in further detail by means of examples of embodiments with reference to the schematic draw- ings, in which

Fig. 1 is a front perspective view of a spray dryer in an embodiment of the invention;

Figs 2 and 3 are perspective views of the drying chamber and the chamber roof, respectively, of the spray dryer of Fig. 1 ;

Fig. 4 is a top view of the spray dryer of Fig. 1 ;

Fig. 5 is a perspective view of the chamber roof of Fig. 3, from another angle;

Figs 6 and 7 are plan views of the spray dryer of Fig. 1 , seen from the side and the back, respectively;

Fig. 8 is a partial front view of the spray dryer of Fig. 1 , on a slightly larger scale;

Fig. 9 is a sectional view corresponding to Fig. 8; Fig. 10 is a partial sectional view of the detail marked X in Fig. 9, on a still larger scale;

Fig. 1 1 is a view corresponding to Fig. 10; however with the seal of the spray dryer removed;

Fig. 12 is a view corresponding to Fig. 5, on a larger scale; and

Fig. 13 is a partial view corresponding to Fig. 3, on a larger scale. Referring initially to Figs 1 to 7 of the drawings, an embodiment of a spray dryer generally designated 1 is shown. The spray dryer 1 comprises a drying chamber 2 and a chamber roof 3.

The chamber roof 3 is movable between an open position and a closed position. To that end, an opening device 4 is provided and includes a number of lifting cylinders 41 mounted on the drying chamber 2 and cooperating with fittings 42 positioned on the chamber roof 3. Locking means 5 are also provided in the form of clamps 51 on the drying chamber 2 cooperating with hooks 52 of the chamber roof 3.

The chamber roof 3 is furthermore provided with handles 6 and a supply pipe 8 for drying gas. Feed is supplied directly to the atomizing means (not shown) for which a port 9 is provided.

The drying chamber 2 has an opening 23 to a substantially cylindrical interior upper part of the drying chamber and has a conical lower part 24. Two sight-glasses 7 are provided for visual inspection of the interior of the drying chamber 2 during operation.

The above-mentioned elements are as such well-known from the commercially available spray dryer MOBILE MINOR™ (GEA Niro). The spray dryer is typically applied for small-scale evaluation of spray drying feasibility and testing of the unit in R&D applications. Typical examples of the dimensions of the elements are the following: The drying chamber has a 0.8 m diameter, a 0.6 m cylindrical height and a 60 degree conical bottom. The 100 kg/h of drying air is heated electrically and has a maximum inlet temperature of 350°C. A chamber height extension piece (not shown) is available to increase the height of the drying chamber. Details of the above-mentioned elements will not be elaborated upon. Neither will additional elements including for instance discharge ports for finalized product and other accessory equipment be described in detail.

The configuration of the elements relevant to the sealing between the drying chamber 2 and the chamber roof 3 will now be described in some de- tail.

The drying chamber 2 defines a radial direction and an axial direction. The opening 23 is bordered by a rim 20, and the chamber roof 3 has a closing surface 30 facing the rim 20 in the closed position. To that end, a seal 10 is provided at the interface between the rim 20 of the drying chamber 2 and the closing surface 30 of the chamber roof 3 to seal the interface in said closed position.

Referring now to the more detailed Figs 8 to 13 of the shown and described embodiment, the rim 20 of the drying chamber 2 comprises a neck section 200 including a circumferential groove 25 facing the outwards radial direction, away from the opening 23 of the drying chamber 2.

The seal 10 is accommodated in the circumferential groove 25. In the embodiment shown, the seal is an O-ring seal 10. O-ring seals are well- known in the art as toric joints, i.e. a circular loop of with a circular cross- section. Other seals are conceivable as well, including circular seals or joints having a non-circular cross-section such as an x-shaped profile or rectangular cross-section.

As will be described in the following, the O-ring seal 10 is easily mounted and safely retained on the neck section 200. The material of the O- ring may be chosen from a wide variety, including for instance polymer, rub- ber, elastomer, compound, nitrile, fluorocarbon, ethylene propylene, perfluoroelastomer, chloroprene, fluorosilicone, Teflon®, and polyurethane.

In the embodiment shown, the O-ring seal 10 is furthermore positioned in such a way on the neck section 200 that it provides points of contact with the closing surface 30 of the chamber roof 3 in both the radial and the axial directions.

To that end, the drying chamber 2 comprises an outer wall 21 and an inner wall 22, and the neck section 200 comprises an integral edge part of the outer wall 21. The neck section 200 comprises a seat portion 214 of the groove 25 formed in the integral edge part of the outer wall 21 and facing the outwards radial direction and the upwards axial direction.

Particular safe retention of the O-ring seal 10 in the groove 25 is ob- tained in that the neck section 200 comprises a splayed edge portion 221 of the inner wall 22 located adjacent to the seat portion 214 of the groove 25 formed in the integral edge part of the outer wall 21 . The splayed edge portion 221 faces the outwards radial direction and the downwards axial direction.

In the specific embodiment shown in the drawings, the seat portion 214 of the groove 25 is adjoined by, starting from the outer wall 21 , a first flat portion 21 1 , an inclined portion 212 and a raised second flat portion 213.

Although the profile of the groove 25 is shown as substantially part- circular, other shapes are conceivable, including oval, elliptic, rectangular, triangular or trapezoidal.

In the embodiment shown, the closing surface 30 of the chamber roof

3 comprises a profiled border section 300 facing the neck section 200 of the rim 20 of the drying chamber 2. For ease of manufacture in those cases in which the chamber roof 3 comprises a side wall 31 and a bottom wall 33, the profiled border section 300 is formed as an integral edge part of the bottom wall 33 adjoining the side wall 31 .

To match the neck section 200 of the rim 20 of the drying chamber 2, the profiled border section 300 of the closing surface 30 of the chamber roof 3 comprises a first sealing portion 313 in the inwards radial direction and a second sealing portion 314 in the downwards axial direction.

In the specific embodiment, the profiled border section 300 has a configuration, in which, starting from the side wall 31 , an edge portion 31 1 and a raised flat portion 312 adjoin the first sealing portion 313, and the second sealing portion 314 adjoins the first sealing portion 313 on the outwards radial side and the remaining part of the bottom wall 33 of the chamber roof 3 on the inwards radial side.

The manufacture of the neck section of the drying chamber rim and the profiled border section of the chamber roof closing surface may in princi- pie be carried out in any suitable manner. Suitable techniques include sheet metal forming such as drawing, pressing, pulling, rolling and/or punching.

When operating a spray dryer the exhaust air containing powder particles is passed through a filter, e.g. SANICIP™ bag filter delivered by GEA. It consists of a cylindrical bag housing with a tangential or direct air inlet, clean air plenum on top, and a conical bottom with fluidized powder discharge. During operation, the product collected on the outside of the filter bags is blown off by a compressed air jet stream from the inside of each bag by means of a specially designed reverse jet air nozzle positioned above the bag. When bags are worn down, they need to be changed. Therefore the bag filter housing may have a removable top cover, which gives easy access to the bags and support-cages. Such top covers can be of the type described in this invention using the same or equal sealing design and means.

Although the invention has been described with reference to a specif- ic embodiment in the above, modifications are conceivable. For instance, with appropriate modification of the configuration, the neck section with the groove accommodating the seal may alternatively be placed on the chamber roof to interact with the rim of the drying chamber which has been modified accordingly.

Furthermore, while the drying chamber and the chamber roof have been described as substantially cylindrical, other shapes might be contemplated. In such cases, the term "radial" should be conceived as a transverse direction.