Ring gap nozzle for distributing a fluid medium over a plate, comprising an axial channel passing through the plate, a cap which covers the channel, leaving a ring gap between it and the plate, and a connecting member extending coaxially through the channel for holding the cap in place. A wall which defines a rotationally symmetrical flow space extends from the connecting member to the outlet edge of the totally free ring gap. The annular flow space comprises a region of the channel, of a deflection space and of the ring gap. All the walls which bound it are arranged so that, starting at least in the deflection space, the flooded area of cross section of the annular flow space decreases continuously in the direction of the flow of medium towards the outlet edge of the ring gap.

BACKGROUND OF THE INVENTION 
The invention relates to a ring-gap nozzle for distributing a fluid medium 
over a plate, comprising an axial channel passing through the plate the 
said channel being covered by a cap so as to leave a ring gap between the 
cap and the plate, whilst the cap is held by means of a connecting member 
which passes coaxially through the channel and is attached to a clamp 
which is mounted at the start of the channel, in the direction of flow of 
the medium, thus forming an annular flow space, in which the medium 
flowing in the channel region axially is deflected in a deflection space 
and flows out radially through the ring gap. 
Ring-gap nozzles of this kind are advantageously used in the bottom plate 
of a fluidised bed apparatus and serve to distribute the flowing medium 
which is to be used for fluidisation of the bed. The ring-gap nozzles are 
arranged on the surface of the plate at a spacing from one another and are 
intended to distribute and conduct the medium so as to form a cushion of 
medium along the surface to prevent the particles of product which are to 
be treated in the fluidised bed from coming into contact with the heated 
plate. This cushion thus prevents the product from being damaged or from 
burning or baking on to the surface of the bottom plate. 
However, the ring-gap nozzles known hitherto do not always meet these 
requirements. Particularly in cases where the medium contains particles of 
solids, these particles may be deposited in the flow chamber of the nozzle 
as they pass through and thus from agglomerations on the walls which 
obstruct the flow of medium or, eventually, block the nozzle completely. 
The desired flow along the plate and the fluidisation of the bed alter and 
become inadequate in the course of time, and the entire fluidised bed 
apparatus has to be shut down in order to restore the nozzles to normal 
operation. In the case of aggressive or abrasive particles, the profiles 
of the nozzles which conduct the current of medium are also affected, and 
sometimes damaged to such an extent that the apparatus has to be put out 
of action to repair the nozzles. In a number of known cases, it has even 
been necessary to replace the entire bottom plate of the apparatus. 
SUMMARY OF THE INVENTION 
The aim of this invention is to provide a ring-gap nozzle wherein the above 
problems known to occur in previous nozzles are substantially eliminated. 
The service life of the nozzles and hence of the entire apparatus in which 
they are used should be lengthened. Any repairs needed on the nozzle 
should be easier to perform. Blockage of the nozzle and damage by 
agressive and/or abrasive particles should be substantially eliminated. 
According to the invention, this aim is achieved in the ring gap nozzle of 
the type described at the beginning in that, from the connecting member to 
the outlet edge of a totally free ring gap, there extends a rotationally 
symmetrical wall which defines at least a portion of an annular, 
rotationally symmetrical flow space for guiding the medium, and that all 
the walls defining the flow space are so arranged that, starting at least 
in the deflection space of the flow space, the flooded area of the cross 
section of the annular flow space decreases continuously in the direction 
of flow of the medium towards the outlet edge of the ring gap. 
In the ring gap nozzle according to the invention, the current of medium 
branches off in front of the totally free, rotationally symmetrical 
deflection space and flows, with continuous acceleration, through the flow 
space, which is adapted to the desired flow, as a current with no dead 
zones where the particles being carried along could be deposited. This 
configuration of the spaces also largely prevents erosion of the nozzle 
walls in the presence of abrasive or aggressive particles. The nozzle 
operates reliably and has a long service life.

DESCRIPTION OF THE PREFERED EMBODIMENTS 
The ring gap nozzle shown is arranged on the bottom plate 1 of a fluidised 
bed drier, for distributing a medium, e.g. hot air, containing particles 
of a substance such as fine sodium chloride crystals, into a fluidised bed 
2. The fluidised bed apparatus is for example the second stage of a drying 
plant and is supplied with hot waste air containing dust particles 
exhausted from a first stage of the plant. 
The medium flows out of a distributor box 3, under the plate 1, through a 
channel 4 which passes through the plate 1 perpendicularly thereto and 
into the fluidised bed 2. Above the channel 4 and at a spacing from the 
plate 1 there is fixed a cap 5, whilst between the plate 1 and the cap 5 
there is an ring gap 7 through which the fluid medium is distributed 
radially outwards relative to the axis of the channel 4. The current 
axially flowing in the region of the channel 4 is deflected radially 
outwards in a deflection space 9. 
The cap is held in position over the channel 4 solely by means of a 
connecting member 8 which is arranged coaxially with the cap 5 and is 
attached thereto and extends coaxially through the channel 4. 
A rotationally symmetrical wall 10 extends from the connecting member 8 to 
an outlet edge 6 of the totally free ring gap 7. This wall, in turn, 
defines at least a portion of a rotationally symmetrical flow space which 
comprises successively the channel 4, the deflection space 9 and the 
annular gap 7. All the walls defining the flow space, i.e. the walls 
bounding the channel 4, the deflection space 9 and the ring gap 7, are 
arranged so that, starting at least in the deflection space 9, the flooded 
area of cross section of the annular flow space decreases continuously in 
the direction of flow of the medium towards the outlet edge 6 of the ring 
gap 7. Thus, as the distance between the centre line of the flow space and 
the axis thereof increases, the clear internal width of the flow space 
decreases so that the said area of cross section of the flow space becomes 
continuously smaller, thus constantly accelerating the flow of medium. 
The rotationally symmetrical deflection space and the ring gap, which is 
totally free in all directions, thus do not present any obstacles 
whatsoever to the flow of medium. For this reason, a clamp 12, provided 
for the purpose of attaching the other end of the connecting member 8, is 
arranged in front of the deflection space, viewed in the direction of flow 
of the medium through the nozzle: In the exemplary embodiment according to 
FIG. 1, the clamp 12 is mounted below the channel 4 and plate 1, inside 
the distributor box 3 on the bottom plate 1, and comprises a U-shaped 
planar strip 13 welded on to the plate, symmetrically with respect to the 
channel 4. Coaxially with the axis of the channel 4, a boss 14 in which 
the lower end of the connecting member 8 is fixed is provided on the strip 
13. 
In order that the spacing between the walls defining at least the 
deflection space 9 and the ring gap 7 can be varied, the attachment of the 
connecting member 8 to the cap 5 or clamp 12 is effected as follows: as 
shown in the drawings, in FIG. 1 the connecting member 8 comprises, at its 
end which is attached to the cap 5, a thread 15 designed to engage in a 
corresponding thread 16 provided in the cap 5. In this way, the cap is 
screwed to the connecting member and the desired accurate positioning of 
the cap above the plate, and hence the desired gap width of the ring gap 
7, can be adjusted. The selected position of the cap is then secured by 
means of an intermediate ring 17. Similarly, an intermediate ring 18 may 
be used on one side of a screw connection between the connecting member 8 
and the clamp 12. 
It would also be possible to construct the connecting member as a screw 
with threads at both ends, in which case the desired axial distance 
between the boss 14 and the cap 5, which would be screwed to the 
connecting member 8, could be fixed by means of a spacing sleeve. Another 
possible construction is shown in FIG. 2. Here, the connecting member 8 is 
a screw passing through the cap 5, comprising a head 29 for retaining the 
cap and having its other end screwed into the boss 14 of the clamp. The 
distance between the boss and the cap is determined by an intermediate 
ring 17. 
In the exemplary embodiment according to FIG. 2, the entire channel 4 in 
the plate 1 is formed by a sleeve 19 which is fixed in a corresponding 
bore 23 provided in the plate 1 for this purpose. The sleeve 19, which 
forms the channel 4 leads into the distributor box 3 underneath and is 
welded to the plate from below. Two flaps 20 are provided in the channel 
4, as clamping means for the connecting member 8. They extend along the 
axial plane of the nozzle, are arranged symmetrically therewith and 
comprise a boss 14 into which the connecting member 8 is screwed. The 
inner wall 21 of the channel 4 and the flaps 20 are designed in accordance 
with the required flow and contributed to the formation of an accelerated 
flow of medium in the channel 4, deflection space 9 and ring gap 7. The 
number of flaps retaining the boss 14 is not restricted to two. Depending 
on the required flow, a different number of flaps, e.g. three, may be 
justifiable or possibly desirable. 
Another important feature of the example shown in FIG. 2 is that the entire 
apparatus, i.e. the ring gap nozzle, comprising the sleeve 19 which 
constitutes the channel, the clamp with the boss 14, the connecting member 
8 and the cap 5, can be mass-produced and, in the case of damage or 
breakdown, all or part of the apparatus can easily be replaced. The 
mass-produced parts are interchangeable. 
This also applies to the ring nozzle according to FIG. 3, wherein a sleeve 
22 forms only part of a longer channel 4 projecting into the distributor 
box 3, and can be screwed into a corresponding bore 23 provided in the 
plate 1. In this embodiment, a boss 24 which retains the connecting member 
8 is also advantageously formed to suit the desired accelerated flow, as 
shown in FIG. 3. 
In the exemplary embodiment according to FIG. 4, some thought has been 
given to the fact that the particles carried by the medium may have an 
abrasive effect, leading to unavoidable erosive damage particularly to the 
walls which form the deflection space 9 and ring gap 7. The outer wall is 
formed by a sleeve 25 which constitutes part of the channel at its mouth 
and is fixed in a corresponding bore 26 in the plate 1. Because of the 
danger of erosive damage, this sleeve 25 is made from an erosion-proof 
material. If damage, e.g. erosion, does occur, this sleeve 25 can simply 
be replaced. 
For the same reason, the wall 10 of the cap 5 defining the deflection space 
9 and ring gap 7 is also made from an erosion-proof material, at least in 
parts, i.e. the parts where erosive damage could occur. The cap 5 is 
subdivided and comprises a rotationally symmetrical part 27 facing the 
plate 1; this part 27 defines the deflection space 9 and the ring gap 7 at 
least partially and is made from an erosion-proof material. The upper part 
28 of this cap 5 is constructed so as to be capable of being screwed to 
the connecting member 8 and thus fixes the readily replaceable part 27 in 
position. Since the upper part 28 of the cap 5 is not exposed to any 
special thermal or mechanical stresses in most applications, it may be 
made from a non-metallic material, for example, as shown in FIG. 4. 
A ring nozzle which is particularly advantageous from the point of view of 
production techniques is shown in FIG. 5. The wall 10 extending from the 
connecting member 8 to the outlet edge 6 of the ring gap is formed by a 
dish-shaped part 30 the outer wall of which has the form of the wall 10. 
The part 30 is advantageously a sheet metal cast part and comprises a wall 
31 which is provided with a central opening 32 for the connecting member 
8. If desired, two identical parts, one of which is designated 30 and 
other 30.sup.1 in FIG. 5, may be assembled facing each other to form an 
upwardly convex cap 5. In the plate 1, the nozzle is formed with an 
annular part 33 inserted in the plate, whilst a clamp 12 (14) for the 
connecting member 8 is attached to said annular part 33.