EP0567560B1

EP0567560B1 - A process for continuous disintegration and/or drying of materials, such as paste, sludge, press cake, filter cake or the like, particularly fibrous materials and an apparatus for carrying out the process

Info

Publication number: EP0567560B1
Application number: EP92904291A
Authority: EP
Inventors: Sven Thorsen Aaen; Halvor Steen Staal
Original assignee: BONTECH ENG AS; BONTECH ENGINEERING AS
Current assignee: BONTECH ENGINEERING AS
Priority date: 1991-01-21
Filing date: 1992-01-21
Publication date: 1995-08-23
Anticipated expiration: 2012-01-21
Also published as: DK9891A; DE69204277T2; DK9891D0; AU1202292A; EP0567560A1; DE69204277D1; WO1992012796A1; DK0567560T3

Abstract

In a processing chamber (12) having a subjacent blast box (16) a continuous supply of drying gas and of the material to be processed, a short-term intensive disintegration and drying of the material as well as removal of a finished fraction thereof together with the exhaust gas (6) are carried out. By means of a drop of gas pressure across the chamber (12) and a blade means (18) arranged between the chamber and the blast box the drying gas is fed into the chamber with a great rate of speed as a fast rotating turbulent gas flow. An intensive agitation, mixing and further disintegration of the material are provided by a coaxially arranged, rotatable disintegrator (20) having disintegrator means (34) extending above the blade means. The blade means (18) is arranged with its inlet opening (36) in flow connection with the blast box (16) and its outlet leading to an annular area (38) of the processing chamber defined by the chamber wall at the bottom thereof.

Description

The invention relates to a process for continuous disintegration and/or drying of materials, such as paste, sludge, press cake, filter cake, particularly fibrous materials in an apparatus comprising a processing chamber having a chamber wall, the main shape thereof being substantially like a surface of revolution, and having an essentially vertical axis and a subjacent blast box, and said process including a continuous :

feeding of a disintegration and drying gas from the blast box to the processing chamber,
feeding of the material to be processed through an opening in the chamber wall,
disintegration and/or drying of the material fed to the processing chamber, and
discharge of a processed fraction of the material together with the exhaust gas,
whereby the feeding of the disintegration and drying gas to the processing chamber and the discharge thereof together with the processed fraction of the material through an exhaust opening at the top of the processing chamber is carried out by means of a drop of gas pressure maintained across the processing chamber, and
the disintegration and drying of the material is intensified by means of a rotation of said gas inside the processing chamber incurred by means of a blade means arranged in the apparatus between the processing chamber and the blast box, said blade means having its inlet opening in flow connection with the blast box and its outlet leading to the processing chamber,
whereby the material currently fed is disintegrated and dried in the form of a fluidized layer slowly ascending within a rotating layer of fluidization gas close to the chamber wall, with a processed fraction of the material being discharged with the exhaust gas,
whereas incompletely processed fractions of the material descends along the chamber wall and in the interior of the processing chamber for being reprocessed.

Similar processes are known and frequently form part of - as in the present case - a process comprising pre-treatment and feeding of the gas flow in the quantity and composition required to the apparatus, a pre-treatment and feeding of the raw material to the apparatus and a finishing treatment of the processed material and the exhaust gas after the discharge thereof from the apparatus.
DK 149.583B thus discloses an apparatus for fluidization drying and disintegration of a paste-like material, wherein the apparatus comprises a cylindrical drying chamber provided with an upwardly tapering bottom, and
wherein the fluidization and drying medium is fed to the chamber through a circumferential slit between the tapering bottom and the chamber wall from an annular distribution chamber surrounding the lower part of the drying chamber. An agitator coaxially arranged in the drying chamber and having blades being parallel to the tapering bottom ensures that no partially dried particles accumulate on the tapering bottom and that an agitation and disintegration of the largest particles from the paste-like material take place.
US-A-4,623,098 discloses a machine for batchwise granulation, coating, mixing and drying of powdery or granular raw materials, in which a rotatable horizontal disc is arranged at the bottom of a casing coaxially therein, said disc leaving an annular slit at the casing wall, through which the drying gas is injected from a subjacent dispersing chamber. Furthermore, drying gas may be injected from another dispersing chamber through perforations in the rotary disc. An agitator is arranged above the rotary disc and coaxially therewith, above which a locally functioning, fast rotating disintegrator is arranged near the chamber wall. The axial speed of gas flow in the drying chamber is so moderate that the material remains at the bottom of the chamber. Processed material is discharged through an discharge opening opposite the rotary disc, the exhaust gas is discharged out through an exhaust opening at the top of the machine. This machine does thus not relate to any actual or particularly effective fluidization drying process and neither to a continuous process.
By the hitherto processes and apparatus for continuous fluidization drying of the materials mentioned above, the average axial flow rates of up-currents are between 1 to 3 m/s in the processing chamber, as the use of higher flow rates at most materials easily results in an excess of the terminal rate of fluidization, whereby a discharge of the incompletely processed material with the exhaust gas will take place. This phenomenon in connection with the limitation in the gas temperature required by materials to be processed has hitherto set an upper limit for the effect or efficiency of fluidization drying, which has been particularly limiting in case of highly heat-sensitive materials, as in this case a rise in the temperature could not be used to increase the production. Such materials have therefore hitherto often been dried by means of contact-drying on heat rollers or in a fluidized bed, which so far has been more economical. However, usually this also results in incomplete disintegration and consequently, in a protracted and uneven drying, often with an unacceptably high degree of heat damage to the product as the result.
DE-A-32 13 250 discloses a method according to the preamble of claim 1 and an apparatus according to the preamble of claim 4 for continuous drying of powdery or granular material and especially non-heat-sensitive material according to the Spin-Flash-method. The material is fed through the wall of the processing chamber above a rotary disc at the bottom of the chamber and the material is deposited on said disc. The disc is provided at its periphery with upstanding guide blades. No further disintegrating means has been disclosed in connection with this apparatus. The drying gas is fed into the processing chamber through vertical extending slots in the chamber wall opposite the guide blades and tangentially to the wall. Inside of the wall the gas is caught by the rotating guide blades and in a rotary way guided towards the central area of the processing chamber, at the same time being carried upwards through the chamber. From the examples axial average gas flow rates of the order of 1.5 m/s and 2.25 m/s are derivable.
The object of the invention is to provide a process of the type stated in the introduction enabling a faster, more uniform, efficient and at the same time lenient disintegration and drying processing of heat-sensitive materials in particular.
The new and special features of the process according to the invention are characterized in that

a drop of gas pressure across the processing chamber is used providing an axial average gas flow rate of at least 3 m/s through the processing chamber,
the outlet of the blade means is leading into an annular area of the processing chamber defined by the chamber wall at the bottom thereof,
by means of a coaxially placed, fast rotating disintegrator provided with disintegrator means arranged above the blade means and projecting towards the chamber wall, a further intensive agitation and mixing of the gas and disintegration of the material fed into the processing chamber is carried out,
depending on the type and quantity of the material fed, the direction and intensity of the gas current induced as well as the rotational direction and speed of the disintegrator are adjusted,
whereby the disintegration and drying of the material is further intensified and carried out in a few seconds within a thin, heavily rotating, turbulent layer of fluidization gas close to the chamber wall.

As a result the material fed does not settle at the bottom of the processing chamber, but is led up along the chamber wall by means of the fast rotating gas current as a thin fluidized layer in the full height of the chamber, preferably at a slight distance from the chamber wall during rotation, fast disintegration and drying, whereupon a fraction of the processed material is discharged with the exhaust gas at the top of the apparatus, while the incompletely processed portion of the material containing partially dry lumps are led downwards along the chamber wall and in the interior of the chamber, respectively. The portion carried downwards is caught again by the heavy up-current at the bottom of the chamber and thus subjected to a further disintegration, carring upwards and drying. As a result of the heavily turbulent and pulsating gas current, and because of the fast rotating disintegrator, a lenient and considerably faster comminution of the material than hitherto known is obtained, and thereby an improved contact between the evaporatable water and the drying gas throughout the chamber is achieved. As a result thereof, a substantially more uniform disintegration and a faster and more uniform drying of the material is obtained than achieved by the hitherto known systems. This effect is enhanced, since it is possible to use higher temperatures of drying gas without damaging the quality of even heat-sensitive products due to the short processing time. On the contrary, it is even possible to obtain a considerably faster process and at the same time an improved quality, even in case of heat-sensitive products, partly as a result of the faster disintegration of the material which ensures that a higher degree of disintegration of the material takes place prior to the drying, whereby the temperature of the material is not substantially increased, before the material is dried to the desired residual moisture, and partly due to the altogether short processing time, whereby heat damage only occurs to a very limited extent, even at considerably higher drying gas temperatures than normally used. Moreover, by the process according to the invention a substantial improvement of the thermal efficiency is obtained as a result of the intensified contact between the drying air and the evaporable water. By regulating the disintegration rate, it is possible at any time to achieve an adjustment of the process conditions to the material currently being processed.
Yet another considerable advantage of the process according to the invention is that a considerably lower quantity of drying gas is used for the process, because of the improved fluidization rate and thermal efficiency. As a result, the physical dimensions of the apparatus may be reduced and as the connecting heating units for the drying gas, powder separators, filters and scrubbers primarily are dimensioned according to the gas quantity flowing through the apparatus, the total initial expenditure is considerably lower than previously. As the operating costs due to the improved thermal efficiency also are substantially lower, the inventive process is financially advantageous.
The axial extension of the fluidized layer above the disintegrator is preferably larger than that of the disintegrator, whereby the upper part of the chamber may function as an area uneffected by the disintegrator said area being used for grading the material according to the degree of drying and particle size.
According to the invention it is advantageous to feed the disintegration and drying gas in varying quantities and/or at varying temperatures and/or gas compositions at different distances from the chamber wall, whereby a most appropriate variation of the gas current is provided in the various areas of the proccessing chamber. It is thus possible, for instance close to the chamber wall, to provide a gas current, being more intensive and of a higher temperature than that further away from the wall, whereby the heavy, wet particles adjacent to the chamber wall, and particularly in the lower area thereof, are subjected to the most intense disintegration and drying effect, while the lighter, more dry fractions of the material further away from the chamber wall are subjected to a more gentle processing.
A further improved turbulence in the gas current may for instance be obtained by at least sporadically feeding the disintegration and drying gas from successive blade interspaces of the blade means at different distances from the chamber wall.
According to the invention, it is advantageous to use a blade means comprising a coaxially arranged, rotatable bladewheel or comprising several blade elements of which at least one is a coaxially arranged, rotatable blade element, and further, to adjust the rotational direction and speed of the rotatable blade means in accordance with the type and quantity of the material fed, whereby the effect of the blade means may be adjusted to the material to be processed, whereby the most advantageous combination of disintegration and drying is obtained. However, the process according to the invention may also be carried out using a blade means being completely or almost stopped, in which case the drop of gas pressure across the chamber may be adjusted.
In this connection experience has shown that advantageous numbers of revolutions of the rotating blade means during processing for many purposes are the ones providing the outer periphery thereof with tangential rates of speed between 1 m/s and 50 m/s, preferably between 2 m/s and 25 m/s, in particular between 2.5 m/s and 20 m/s, and when emptying the processing chamber, stopping the blade means.
Advantageous numbers of revolutions of the disintegrator during processing are such providing the outer periphery thereof with tangential rates of speed between 5 m/s and 180 m/s, preferably between 10 m/s and 100 m/s, most preferred between 20 m/s and 50 m/s, and when emptying the processsing chamber, stopping or nearly stopping the disintegrator.
Applicable drying gas temperatures may be ranging up to approximately 800°C and at heat-sensitive materials preferably up to approximately 600°C, in particular up to approximately 500°C. In many instances, this temperature is considerably above the temperatures usable by the known processes.
It has proved particularly advantageous to maintain a drop of gas pressure across the processing chamber which is sufficient to discharge the material together with the exhaust air, when the blade means and the disintegrator have been stopped, whereby an excellent turbulent flow is obtained in the processing chamber and at the same time and very easily emptying the apparatus of the material merely by stopping the feeding of material, the blade means and the disintegrator.
In this connection it has been found advantageous when by means of the blade means the axial average gas flow rate in the processing chamber is increased by a factor of at least two.
Furthermore, the invention relates to an apparatus for carrying out the process according to the invention, said apparatus comprising a processing chamber having a chamber wall, the main shape thereof being substantially like a surface of revolution, and having an essentially vertical axis, and a subjacent blast box, and said apparatus comprises continuously acting means

for heating disintegration and drying gas to be fed into the blast box,
for feeding disintegration and drying gas from the blast box into the processing chamber,
for feeding the material to be processed through an opening in the chamber wall,
for rotating of the disintegration and drying gas inside the processing chamber,
for agitation, mixing and disintegrating the material fed into the processing chamber, and
for discharge of the exhaust gas and a processed fraction of the material from the processing chamber,
whereby the means for continuous feeding of the disintegration and drying gas and the means for discharge of the exhaust gas and the processed fraction of the material comprise an exhauster for maintaining a drop of gas pressure across the processing chamber, said exhauster being arranged in flow connection with the processing chamber through a discharge pipe, preferably extending into the processing chamber at the top thereof and the means for rotating the disintegration and drying gas is a blade means arranged in the apparatus between the processing chamber and the blast box and having its inlet opening in flow connection with the blast box and its outlet leading into the processing chamber,

characterized

the exhauster is having an effect sufficient to provide an axial average gas flow rate through the processing chamber of at least 3 m/s,
the outlet of the blade means is leading into an annular area of the processing chamber defined by the chamber wall at the bottom thereof,
and that the means for continuous agitation, mixing and disintegration comprise an intensively functioning, fast rotatable disintegrator coaxially arranged at the bottom of the processing chamber, said disintegrator being provided with disintegrator means arranged above the blade means and projecting towards the chamber wall,
whereby the rotational direction as well as the numbers of revolutions of the disintegrator are adjustable.

An apparatus, easy to construct and inexpensive in production is thus obtained, though rich in possibilities of variation, both in relation to adjustment and regulation of the process conditions to the individual apparatus and in relation to variations in the construction of the apparatus. Furthermore, relative to its capacity the apparatus is of a size small, resulting in a reduction in its price.
A particularly simple construction may consist in the blade means having the shape of a coaxially arranged blade wheel. This can either be non-pivotally or rotatably retained. When using the non-pivotally retained blade wheel the gas current in chamber assume the shape of an essentially stationary current flow with a speed profile retained relative to the processing chamber. The contribution of the blade wheel to the rotation of the gas current in the chamber is thus essentially a function of the shape of the blade wheel in question.
By an embodiment of the present invention having adjustable blades a further possibility of regulating the gas current is obtained, however, still maintaining the character of the current as a stationary current in the chamber.
By means of a rotatable blade wheel a rotation of the speed profile of the gas current is furthermore obtained in addition to an extra rotation of the gas current, resulting from the rotation of the blade wheel, and finally, a possibility for intensifying the gas current provided that the blade wheel is shaped as a blower and the rotational speed is sufficiently high. The blade wheel may then be connected pivotally with the disintegrator and rotated with or without a gear ratio thereto or advantageously rotated by means of a separate driven shaft, preferably a hollow shaft enclosing the disintegrator shaft and driven by means of a motor arranged outside of the blast box. In this case, the rotational speed of the blade wheel is regulated independently of the rotational speed of the disintegrator. As an alternative, the blade wheel may be driven by the gas current carried through the apparatus.
According to the invention, the outlets from the successive blade interspaces in the blade wheel may be arranged at varying distances from the chamber wall by means of coverings and openings variedly arranged at the blades for the provision of a more irregular and consequently, more turbulent gas current in the processing chamber. Moreover, according to the invention the blade wheel may comprise blade interspaces, which together with the pertaining part of the inlet opening to the blade wheel each are divided into at least two flow channels by means of guide plates arranged therein and orientated in the flow direction. The flow channels may have varying channel cross sections and the outlets at different distances from the chamber wall. As a result, the gas flow from the same blade interspace is divided into currents flowing into the chamber at different distances from the chamber wall, and if so desired with varying intensity and direction and differing from those from other blade interspaces, whereby an additional turbulent current is produced in the processing chamber.
In this connection the differently shaped flow channels may advantageously be connected to a separate gas supply, whereby gas flows of varying compositions may be fed into the processing chamber at different places. This is particularly advantageous for feeding gas in larger quantities and/or with a higher drying capacity at the places in the processing chamber, where the most intensive disintegration and drying are required, particularly close to the chamber wall, whereas gas in smaller quantities and/or with a lower drying capacity may be supplied further away from the chamber wall. As an alternative, the different flow channels may also be used for differentiating other forms for gas compositions, such as gas compositions low in oxygen in order to decrease the oxidation of the processed materials or other forms of inactive gas compositions or various types of solvents, which may further the disintegration.
Especially in cases where it is desirable to use the blade wheel as a blower, it is particularly advantageous to provide the wheel with a preferably circumferential division plate extending horizontally and/or tapering downwardly to the inlet opening of the blade wheel on the underside thereof, where the division plate is retained relative to the chamber wall or relative to the blade wheel, whereby improved flow conditions are obtained for the blower.
According to the invention, the blade means may also be divided into at least two preferably annular blade elements acting mutually independent. The same possibilities of variations and leading to the same advantages as for the above blade wheel is also valid for each of the blade elements. However, it is further possible to combine the embodiments and the advantages in such a way that it for instance is possible to concurrently employ a non-pivotally retained blade element for instance at the chamber wall, a blade element connected pivotally with the disintegrator, and a blade element being in fixed connection with a driven shaft, whereby the rotational speed of the latter two blade elements may be regulated independently, and furthermore, differently composed gases may be fed through the different elements, if desired with the possibility of regulating the quantitative ratios therebetween and to adjust the blades in the individual elements.
It is preferable to use a blade means fitted and employed as a blower, as the resulting effect of a high gas flow rate and a subsequent intensive, turbulent flow generally is preferred. In particular, a blower of the centrifugal type or a hybrid between a centrifugal and an axial blower, in which the outlet openings from the blade interspaces are turned upwardly in an annular area defined by the chamber wall at the bottom of the chamber. By means of a blower formed and arranged in this manner and with a high rate of flow and speed of rotation, a distinctly turbulent flow profile is obtained, wherein an intensely pulsating gas current is present at place just above the annular outlet area close to the chamber wall. This is due to the fact that the air flow ejected from the individual outlet opening shows a speed profile with the highest speed at a point a short distance away from the chamber wall and from the posterior blade wall in the blade interspace, whereas the flow rate decreases abruptly towards the nearby walls (the chamber wall and the posterior blade wall, respectively) and evenly towards the other delimitations of the outlet opening. Consequently, the particles present within a certain distance above this area, particularly close to the chamber wall are subjected to pulsations of high frequency. The larger and heavier the particles, the more intensive the pulsations, whereby an intensive disintegration and drying take place in this area.
The structure of the disintegrator may be varied in many ways within the scope of the invention. However, it has preferably an essentially axially symmetrical, particularly conical or circular cylindrical upper part, on which the disintegrator means, such as arms or swingles, are arranged and cover a central part of the blade means. As a result, the fast rotating disintegrator is throwing the material outside the central part of the blade means to the up-current at the chamber wall, in cases of larger and heavier particles into complete engagement with the chamber wall, at which they may be crushed.
The disintegrator may advantageously be mounted on one end of a vertical shaft extending down through the blast box and operated by means of a separate motor arranged outside the blast box, whereby the motor is advantageously arranged outside the drying channel and a processing chamber without impeding shafts is obtained.
As the cross sectional shape of the processing chamber effects the disintegration and the drying as well as the grading of the particles and the extraction of the material, it is advantageous that the processing chamber in its axial extension has a varied cross sectional shape, preferably a cross sectional shape widening upwards from the disintegrator area, most preferred a cross sectional shape widening upwardly from the disintegrator area and then narrowing.
Moreover, it is in this connection advantageous that the axial extension of the processing chamber is substantially larger and preferably more than twice as large as the axial extension of the disintegrator, as a satisfactory grading of particles prior to the extraction of the material may thereby be obtained together with a more efficient, uniform and lenient drying, as especially the processing at the top of the apparatus ensures a levelling of variation in the residual moisture of the material.
The invention is described in detail in the following with reference to the accompanying drawing, in which

Fig. 1 is a diagrammatic view of a disintegration and drying system comprising the first embodiment of an apparatus for carrying out the process according to the invention,
Fig. 2 is a diagrammatic axial sectional view through another embodiment of the apparatus according to the invention,
Fig. 3 is the same view as in Figure 2 with a diagrammatic view of the flow pattern,
Fig. 4 is a partial, sectional view of a third embodiment of the apparatus according to the invention,
Fig. 5 is a partial, sectional view of a fourth embodiment of the apparatus according to the invention with indication of the flow pattern in the apparatus,
Fig. 6 is a partial, sectional view of a fifth embodiment of the apparatus according to the invention,
Fig. 7 is a partial, sectional view of a sixth embodiment of the apparatus according to the invention,
Fig. 8 is a partial, sectional view of a seventh embodiment of the apparatus according to the invention,
Figs. 9a, b, c are views of a first blade wheel according to the invention, in a plan view (Fig. 9a), in a sectional view A-A (Fig. 9b) and in a partly axially sectional view (Fig. 9c), respectively,
Figs. 10a, b, c are views of a second blade wheel according to the invention, in a plan view (Fig. 10a), in a sectional view A-A (Fig. 10b) and in a partly axially sectional view (Fig. 10c), respectively,
Figs. 11a, b, c are views of a third blade wheel according to the invention, in a plan view (Fig. 11a), in a sectional view A-A (Fig. 11b) and in a partly axially sectional view (Fig. 11c), respectively,
Figs. 12a, b, c are views of a fourth blade wheel according to the invention, in a plan view (Fig. 12a), in a sectional view A-A (Fig. 12b) and in a partly axially sectional view (Fig. 12c), respectively,
Figs. 13a, b are diagrammatic views of the flow rate distribution in various cross sections of a radially arranged blade interspace (Fig. 13a), and the flow rate distribution above the successive outlets from such blade interspaces, as viewed in the direction of the arrows A-A of Fig. 13a, and
Figs. 14a, b, c are diagrammatic views of the flow rate distribution in various cross sections of the successive blade interspaces in a blade wheel with outlets at two different distances from the chamber wall (Fig. 14a) (Fig. 14 b), respectively, and (Fig. 14c) the flow rate distribution above successive outlets in said blade wheel, as viewed in the direction of the arrows A-A in Figs. 14a and 14b.

Fig. 1 is a diagrammatic view of a disintegration and drying system of the type for carrying out the process according to the invention. The system comprises a disintegration and drying apparatus (10) according to the invention, a feeding means (2) for feeding the material (1) to be processed into the apparatus (10), a gas distribution means comprising a filter (3), a heat exchanger (4), a gas supply channel (5) leading to the apparatus (10), and a discharge channel (6), a bag filter (7) having a bucket wheel feeder (8) for removing the processed material and an exhaust fan (9) for exhaustion of the filtered exhaust gas.
The disintegration and drying apparatus comprises a processing chamber (12) having a chamber wall (14), the main shape thereof being substantially like a surface of revolution, and having a vertical axis, and a subjacent blast box (16). A coaxially arranged blower (18) is arranged between the processing chamber (12) and the blast box (16), said blower having its central inlet opening (36) in flow connection with the blast box (16) and its outlet leading to the top surface of the blower (18) in an annular area (38) defined by the chamber wall (14). The blower is separately driven from a motor (28) outside the blast box (16) through a hollow shaft (24). A rotatable, coaxially arranged disintegrator 20 is arranged above the blower (18), said disintegrator having an upper part (32) of an essentially circular, cylindrical form, on which disintegrator means (34) in form of swingles are arranged projecting towards the chamber wall (14). The disintegrator is mounted on the upper end of a shaft (26) passing through the hollow blower shaft (24) and separately driven from a motor (30) outside the blast box (16). A circumferential, horizontal division plate (22) is arranged below the blower (18) extending from the chamber wall (14) and into the inlet opening (36) of the blower (18).
During operation of the system the exhaust fan (9), the blower (18), the disintegrator (20) and the feeding means (2) are driven continuously. As a result, the exhaust fan (9) causes a drop of gas pressure across the processing chamber (12) which produces a gas flow through the system from the filter (3) to the exhaust fan (9), This gas flow is intensified by the blower (18) additionally concentrating the gas flow into a thin, annular, rotating layer of an up-current having an intensive turbulence close to the chamber wall (14). In combination with the disintegrator (20) this gas current ensures a fast disintegration of the material (1) which is continuously being fed by means of the feeding means (2) through an opening (40) in the chamber wall (14). The heavily disintegrated material is placed by the gas current as a fluidized, thin layer continuously ascending and rotating, mainly along the chamber wall, whereby the smallest particles are dried quickly. When the heavily disintegrated and partially dry material arrives at the top of the chamber (12), the predominant portion of a processed fraction is removed with the exhaust gas, while a minor portion of said fraction together with the incomplely processed fraction is led slowly downwards along the chamber wall (14) and further into the processing chamber (12), until the material comes into contact with the disintegrator (20) and the intense gas current at the bottom of the chamber (12), where it once again is subjected to a further disintegration and is carried upwards in the chamber (12) and dried, before another fraction is removed from the chamber. Even though the process per se is continuous, a portion of the particles is subjected to several processing cycles in the processing chamber (12), before being removed with the exhaust gas. Nevertheless, the total processing of all particles of the material is completed within a few seconds with a relatively small dispersion in the processing time and the quality of the processed material.
Figures 2 to 8 show a plurality of various embodiments of the disintegration and drying apparatus (10) according to the invention and details thereof, wherein the same reference numerals for the same parts have been used to a great extent. However, for some details deviating reference numerals have been used, if necessary by adding an index for mutual similar parts in order to emphasize differences of particular importance.
An apparatus (10) of a type similar to the one of Fig. 1 is thus shown in Figs. 2 and 3. The blower (18) and the disintegrator (20) are arranged on separately driven shafts (24,26), respectively, which are driven in the same manner as previously by means of motors (not shown) outside the blast box (16). The upper part (32) of the disintegrator (20) has, however, in this embodiment the form of an upwardly corbie-stepped cylinder and is provided with swingles (34) of various lengths corresponding thereto. The lowermost part of the upper part (32) of the disintegrator thereby covers a larger section of the central part of the blower than the embodiment of Fig. 1. The radial extension of the blower (18) has further been made relatively shorter, and the underside of the blower has a profile being outwardly tapering towards the chamber wall (14), resulting in more ideal flow conditions through the blower (18). Correspondingly, the division plate 22 under the blower (18) is downwardly and inwardly inclined from the the chamber wall (14), and thereby following the shape of the blower (18).
Fig. 3 further illustrates by examples the ascending and decending motions of the gas flow in the chamber (12) by means of the arrows (42, 44, and 46, 48 and 50), respectively. This pattern of motion may vary depending upon the structural shape of the chamber and depending upon the ratio of the rotational to axial flow rate of the drying gas in the various cross sections of the chamber. At the transition between the lower cylindrical part and the upwards conically widening part of the processing chamber (12), it is moreover illustrated by the reference numeral (52), although in an exaggerated manner, how a distinctly viscous paste-like material may get lumpy above the disintegrator (20) and how the material is completely disintegrated and fluidized by means of the combined effect from the disintegrator (20) and the intense gas current from the blower (18), before it comes into contact with the blower (18). Under normal operating conditions there is no depositing of materials on either the disintegrator (20), which as a result of its high rotational speed is practically self-cleaning, or on the blower (18), which is self-cleaning due to the intense, up-current of gas.
Figs. 4 to 8 illustrate various embodiments of the disintegrator (20), the blade means (18) and the lower part of the chamber wall (14) in the area around these. In all of the examples the disintegrator is shown as a conical disintegrator (20'). In Fig. 4 the disintegrator (20') is provided with four horizontally orientated, oblique, plate-shaped disintegrator arms (34) successively arranged displaced at an angle of 90° relative to each other. Fig. 5 illustrates the disintegrator (20') without the disintegrator arms. Both in Fig. 4 and Fig. 5 the blade means is divided into two mutually independently acting, coaxial blade elements (18', 18''), that is a rotatable blade element (18') pivotally arranged with the upper part (32') of the disintegrator at the underside thereof and a subjacent likewise rotatable blade means (18''), rotatably mounted on its own hollow shaft (24), surrounding the shaft (26) of the disintegrator (20'). The blade element (18') on the disintegrator (20') is of the same outer diameter as the upper part (32) of the disintegrator (20') and has an annular outlet (38') placed above the blade element (18''). The blade element (18) extends further towards the chamber wall (14) and is of principally the same shape as the blade wheel or the blower (18) of Figs. 2 and 3 with an underside having an outwardly tapering profile abutting a division plate (22) parallel thereto and extending from the chamber wall (14) and defining the inlet opening (36'') to the blade element (18''). Furthermore, the blade element (18'') has an inner annular element (36') situated in the same axial area as the innermost part of the blade element (18') on the disintegrator (20') and forming an inlet opening (36') for the blade element (18'). The element (36') is without flow connection to the rest of the blade element (18''). The outlet from the blade element (18'') is as at the blower (18) of Figs. 2 and 3, situated on the top surface of the blade element (18'') in the annular area (38'') at the periphery thereof between the chamber wall (14) and the outlet (38') from the blade element (18').
Fig. 6 illustrates by example an annular blade wheel (18) attached to the chamber wall (14). The wheel may be stationarily or rotatably attached and if so, it is driven by the disintegration and drying gas fed therethrough from the blast box (16). The disintegrator (20') is in this Fig. shown with its upper part (32') arranged within the blade wheel (18) and projecting thereabove. The disintegrator (20') has four sets of disintegrator arms (34'), the successive sets being arranged displaced at an angle of 90° relative to each other. Each set comprises four horizontal arms (34,34') arranged on top of each other.
In the Example shown in Fig. 7 the blade means is shaped as an annular blade wheel (18') attached pivotable to the disintegrator (20') at the underside of the upper part (32') thereof. The blade wheel (18') is of the same outer diameter as the upper part (32') of the disintegrator and has its outlet (38') in the annular periphery thereof. A circumferential, horizontal division plate (22) extends from the chamber wall (14) just under the underside of the blade wheel (18') defining the inlet opening (36') thereto.
In the Example shown in Fig. 8 the disintegrator (20') and the blade wheel (18') are in principle shaped as in Fig. 7, but have an upwardly tapering profile on the underside of the blade wheel (18'). Instead of having a division plate, the chamber wall (14) is brought in under the blade wheel (18') parallel with and just below the bevelled part of the blade wheel (18'). The disintegrator (20') of Figs. 7 and 8 is provided with four sets of disintegrator arms above each other, each set comprising four arms (34). The arms in Fig. 8 are projecting further out at the top corresponding to the upwards conically widening of the chamber (12).
In the Examples shown in Figs. 1, 2, 3, 5, 6, and 7 the lower part of the processing chamber (12) opposite the blade means (18,18') and the disintegrator (20, 20') is cylindrically shaped. In the Example of Fig. 4 the chamber (12) is shaped upwardly conically widening from the division plate (22). In the Example of Fig. 8 the chamber (12) is shaped upwardly conically widening from the underside of the blade wheel (18') until being at level with the disintegrator (20'), then cylindrically shaped up to a level just above the disintegrator (20'), and thereabove upwards tapering.
Figs. 9 to 12 illustrate Examples of various embodiments of a blade wheel (18) according to the invention to be arranged above a division plate (22), in all embodiments intended for mounting on a hollow shaft and provided with a through hole (42) for a disintegrator shaft. Each set of the Figures 9a, b, and c, 10a, b, and c and 12a, b, and c, respectively illustrates the blade wheel (18) in a plan view, in a sectional view taken along the line A-A and in a side view with the right half intersected, respectively. In all the Examples blades (44) are used attached to a top plate (46) and if necessary also to the wheel hub (48).
Figs. 9a, b, and c illustrate a blade wheel (18), where the outlets from all of the blade interspaces are provided at the periphery of the blade wheel simply by extending the blades (44) radially slightly beyond the top plate (46). Every other blade is moreover shortened, so as not to extend completely into the wheel hub (48), whereby the flow resistance in the blade wheel (18) is decreased. The blade interspaces (50) are furthermore downwardly and radially outwardly open. A closure of these openings and thereby an increased effect of the blower are, however, obtained by placing the blade wheel (18) in a processing chamber (12) having an inner diameter only slightly larger than the diameter of the blade wheel and furthermore, having a division plate (22) extending parallel to the bevelled underside of the blades (44) shown in this Fig., as it also appears in principle in Fig. 2 and Fig. 12.
Figs. 10a, b, and c, illustrate a similarly shaped blade wheel (18), wherein the top plate, however, every other blade interspace extends completely to the outermost end of the blades (44), whereby the outlets from successive blade interspaces (50) alternately are only found at the cylindrical end surface of said blade interspaces, and in the intermediate interspaces, at the corresponding end surfaces and at the outer part of the top surface of said interspaces. The effect hereof is in practice that the successive outlets are found at varying distances from the chamber wall (14), under the proviso that the blade wheel (18) is placed in a processing chamber (12) having a slightly larger diameter than the diameter of the blade wheel and having a subjacent division plate (22).
Figs. 11a, b, and c illustrate another way to determine the placing of the blade outlets. Also by this embodiment the outlets from successive blade interspaces are radially displaced relative to each other, however, by every other blade interspace (50) being closed by means of a transverse plate (54) at a distance from the outer periphery of the blade wheel, and in addition hereto an outlet opening (52) is provided in the top plate (46) radially within the plate (54). The plate (54) may be L-shaped with an upper horizontal web flush with the top plate (46) as shown in Fig. 11b. All of the blades (44) extend somewhat beyond the outer periphery of the top plate (46), whereby the outlets from the intermediate interspaces (50) are in the area extending on the outside of the top plate (46).
Figs. 12a, b, c illustrate a blade wheel (18), wherein the outlets are arranged as in Figs. 11a, b, and c. However, additionally hereto, each blade interspace and the subjacent inlet area are divided into two flow channels (51, 53) by means of fixed guiding plates (56) in each of the blade interspaces and by a circumferential fixed guide plate (58) in the subjacent blast box, arranged in extension thereto. In successive blade interspaces, the outlet from one flow channel (51) is then closed, when the outlet from the other flow channel (53) is open and vice versa, whereby is it possible to connect each of the flow channels (51, 53) with a respective separate gas supply source and thus supply gas of different compositions at different distances from the chamber wall (14).
Fig. 13a illustrates an Example of the distribution of the flow rate in various cross sections of a blade interspace and the outlet on the top surface thereof corresponding to a blade wheel as shown in principle in Fig. 9a, b, c, however, with a division plate (22) attached directly to the underside of the blade wheel and with slightly altered inlet conditions. The distribution of the flow rate is illustrated by means of velocity vectors as shown at the inlet, in the middle of the blade interspace and at the outlet thereof. The velocity vectors shown partly illustrate the increasing flow rate out through the blade interspace until the outlet thereof at the chamber wall (14), and partly the distribution of the axial flow rate in the radial direction at the outlet, said flow rate abruptly increasing from a value close to zero at the chamber wall to a maximum value at a short distance from the chamber wall and then slowly decreasing to a minimum value at the innermost edge of the outlet opening.
Correspondingly, Fig. 13b illustrates the distribution of the axial flow rate in the tangential direction at the outlets for the successive blade interspaces seen in direction of the arrows A-A in Fig. 13a under the proviso that the blade wheel as seen in the direction mentioned rotates to the right relative to the Fig. 13b. It is evident from the Figure that the distribution of the flow rate is uneven, also when seen in this direction, whereby the highest outlet flow rate is found at a short distance from the blades (44) advancing the air and with an abruptly decreasing flow rate towards this blade and with a more evenly decreasing flow rate down to a minimum value at the leading blade (44) in the blade interspace (50) in question. On this basis it is clear that a particle found in the area immediately above the outlet openings and being somewhat slow in motion relative to the gas flow is subjected to a series of pulses, the intensity and frequency of which partly depending on the flow rate and the distribution and frequency of the flow rate, that is the rotational speed of the periphery of the blade wheel and partly depending on the size and weight of the particle, and thus its inertia relative to the gas flow. It should be added that in addition to the flow rate component shown in the axial direction above the outlet openings the gas flow is provided with a flow rate component in the tangential direction resulting from the rotation of the blade wheel, which naturally provide the particles with a rotary motion, but does not, however, influence the principle of the aforementioned reflections about the influences to which the particles are subjected. The particles being close to the outlet openings are thus subjected to more or less intensive pulsations.
As in Figs. 13a, b, and c, Figs. 14a, b, and c illustrate the distribution of the flow rate in a blade wheel (18) and above the outlet openings thereof, wherein the outlets in successive blade interspaces (50) are mutually radially displaced and thus is found at different distances from the chamber wall (14), as it appears from Figs. 14a and 14b. This corresponds to the illustration of Fig. 11b, and c. In the present Fig. velocity vectors are shown illustrating the increasing gas flow rate out through the blade interspaces (50) to the outlet openings and also the distribution of the axial flow rate above the outlet openings in the radial direction as seen in Figs. 14a and 14b and in the tangential direction in Fig. 14c, respectively. The same fundamental conditions and considerations as mentioned in connection with Figs. 13a, and b also apply to the present Figs., however, in the present case the outlet openings are mutually radially displaced in successive blade interspaces. Consequently, a more turbulent flow is produced over a wider outlet area than shown in Figs. 13a, b. Moreover, as mentioned in connection with Figs. 12a, b, c this feature may be used to feed gasses of varying compositions through the outlets being mutually displaced.
The process and apparatus according to the invention has proved particularly advantageous for the disintegration and drying of organic material which is particularly sensitive to heat and especially for the disintegration and drying of materials to be used as fodder or foodstuffs. The following Examples are based on a test run of a pilot plant and illustrate the advantages obtained by means of the process and the apparatus according to the invention.
The invention has been described with reference to a preferred embodiment. Many modifications may, however, be carried out without deviating from the scope of the invention. Preferred embodiments of the apparatus according to the inventions are stated in the subclaims.

Example 1

Disintegration and drying of a press cake of organic material with a moisture content of 50% calculated on the wet weight was carried out. Heated atmospheric air was used for the drying. For the processing, an apparatus according to the invention was used comprising a blower of a diameter of 250 mm and thirty-six evenly dispersed, radially arranged blades and a disintegrator with a conical upper part and sixteen horizontal disintegrator arms in form of swingles displaced in sets at the angle of 90°.
The numbers of revoluations of the blower was 1000 r.p.m, whereby the air at the chamber wall opposite the ventilator was provided with a tangential flow rate of approximately 13 m/s. The average axial air flow rate in the processing chamber was about eight m/s in the Example, rendering peak values of 20 m/s or more at the chamber wall as a result of the special flow rate profile for the air flow out of each individual blade interspace in the blower. The absolute peak value for the air flow rate was thus about 24 m/s, which in the drying area ensured substantial heat tranfer coefficient between the drying air and the product which were intensively agitated, mixed and disintegrated by the disintegrator.
The inlet temperature was 400°C.
The outlet temperature was 120°C and a powder residue moisture of 4 percent calculated on the wet weight was thereby obtained.
The capacity was 33 kg/h.
In order to have an indication of the effect of the blower, the blower was stopped, whereafter the residual moisture increased to 8 percent water calculated on the wet weight, and the capacity decreased to 28.5 kg/h. Concurrently, the outlet temperature increased to 130°C, and the product showed signs of incipient heat damage. The effect of the blower is thus essential for the drying effect and for the capacity as well as for the quality of the product.

Example 2

To illustrate the economic aspects of the drying process according to prior art compared to the drying process according to the invention, tests were carried out on animal meat protein from beef and pork with a collagen content of 32 to 34 percent. At first, the product, which is used as additive to foodstuffs such as hamburgers, meet balls, sausages, and to minced and emulsified meet products, was subjected to a process, which stabilized the proteins and made them insoluble in water. In one of the last stages of the process the product has to be dried down from a moisture content of about 27 percent to a moisture content of approximately 6 percent calculated on the wet weight. The product is very high in gelatine and has hitherto been dried in a fluidized bed using a drying air with an inlet temperature of about 130°C and an average outlet temperature of about 75°C.
Tests run on the apparatus of Fig. 1 showed that it is possible to dry the same product to the same powder quality in the system according to the invention using a drying air with an inlet temperature of 330°C and an outlet temperature of 100°C.
At an ambient air temperature of 15°C the thermal efficiency is
in the fluidized bed process:

and is
in the process according to the invention:

In the two tests the ratio of the differences in temperature between the inlet and the outlet drying air broadly represents the drying capacity, and also the inverse ratio of the required drying air flows formulated as follows:

In this case the air flow is approximately four times lower at the process according the invention. As the average fluidization rate according to the invention is higher relative to the prior art, the physical dimensions of the system according to the invention are further much smaller. Moreover, the connected air heaters and the powder separators, including filters and any air washers primarily dimensioned according to the volume of air passing through the system, are also considerably smaller, whereby the total costs of construction are lower at the new process.
The differences in the thermal efficiency demonstrate distinct deviations in the operating costs in favour of the present invention.
Moreover, the cleaning costs are reduced, as the system can be completely emptied automatically by stopping the feeding of the product, whereby cleaning is made practically superfluous.
Furthermore, before starting on a new product, the disintegration and drying apparatus according to the invention may be sterilized immediately by flowing hot drying air through the apparatus prior to feeding the new product into the system. This feature is particularly vital when dealing with foodstuffs systems.
The very short processing time of the product in the apparatus according to the invention (a few seconds) permits the use of the selected temperatures without heat damaging the product, this in spite of the air temperatures utilized at the prior art both to and fro the fluidized bed being lower, but the processing time hereof is on the other hand several minutes.

Example 3

For demonstration of the differences in thermal disintegration of protein products, tests have been carried out on a fish protein product, wherein the chosen raw material in the preceeding processing were treated identically until the drying process, whereafter a portion thereof (product C1) was dried in a conventional drier of the drum type at a hood temperature of maximum 150°C and a powder temperature of 100°C as measured at atmospheric pressure. A second portion of the pre-treated product (product C2) was dried in a conventional drier of the drum tryp subjected to vacuum at a hood temperature of maximum 130°C and a powder temperature of 75°C.
A third portion of the pre-treated product (product C3) was dried in the apparatus according to the invention at an inlet air temperature of 400°C and an outlet air temperature of 120°C at atmospheric pressure. As a measure of the quality of the product dried the concentration of essential amino acids present in the dried powder has been used, calculated in percentages of the total solid matter in the product. The results found for the products mentioned C1, C2, and C3 are stated in the below table, in which also the capacity of water absorption of the products C2 and C3 is indicated measured as absorbable amount of water in gram per 100 g solid matter. It appears from the table that the content of essential amino acid was 9.7% higher and in total content of amino acid was 7.6% higher in the powder dried by means of the process according to the invention (C3) as compared to the powder dried at a low temperature (C2).
The heat damage to the proteins is considerably slighter when using the process according to the invention in comparison with the latest process equipment presently used.
Compared to the standard quality (C1) predominating the world market, it is evident that an even more substantial improvement is obtained, viz. 30.9% more essential amino acids and in total 21.4% more amino acids are present in the powder dried according to the invention (C3) compared to the standard quality (C1).
Moreover, a considerable increase in the capacity of water absorption (about 60%) is obtained, which strongly indicates that the heat damage to the proteins in C3 is significantly lighter compared to C2.
It is to be expected that this improved capacity of water absorption opens up a possibility of improving capability of living organism and animals to absorb proteins in the digestive systems thereof, when the protein is dried by means of the process according to the invention.
The term "hood temperature" in this connection means the condensation temperature of the heating medium.

Claims

A process for continuous disintegration and/or drying of materials such as paste, sludge, press cake, filter cake, particularly fibrous materials in an apparatus (10) comprising a processing chamber (12) having a chamber wall (14), the main shape thereof being substantially like a surface of revolution, and having an essentially vertical axis and a subjacent blast box (16), and said process including a continuous
- feeding of a disintegration and drying gas from the blast box (16) to the processing chamber (12),

- feeding of the material to be processed through an opening (40) in the chamber wall (14),

- disintegration and/or drying of the material (1) fed to the processing chamber (12), and

- discharge of a processed fraction of the material together with the exhaust gas,

- whereby the feeding of the disintegration and drying gas to the processing chamber (12) and the discharge thereof together with the processed fraction of the material through an exhaust opening at the top of the processing chamber (12) is carried out by means of a drop of gas pressure maintained across the processing chamber (12) and

- the disintegration and drying of the material (1) is intensified by means of a rotation of said gas inside the processing chamber (12) incurred by means of a blade means (18) arranged in the apparatus (10) between the processing chamber (12) and the blast box (16), said blade means (18) having its inlet opening (36) in flow connection with the blast box (16) and its outlet leading to the processing chamber (12),

- whereby the material (1) currently fed is disintegrated and dried in the form of a fluidized layer slowly ascending within a rotating layer of fluidization gas close to the chamber wall (14), with a processed fraction of the material being discharged with the exhaust gas,

- whereas incompletely processed fractions of the material descends along the chamber wall (14) and in the interior of the processing chamber (12) for being reprocessed,
characterised in that
- a drop of gas pressure across the processing chamber (12) is used providing an axial average gas flow rate of at least 3 m/s through the processing chamber (12),

- the outlet of the blade means (18) is leading into an annular area (38) of the processing chamber (12) defined by the chamber wall (14) at the bottom thereof,

- by means of a coaxially placed, fast rotating disintegrator (20) provided with disintegrator means (34) arranged above the blade means (18) and projecting towards the chamber wall (14), a further intensive agitation and mixing of the gas and disintegration of the material (1) fed into the processing chamber (12) is carried out,

- depending on the type and quantity of the material (1) fed, the direction and intensity of the gas current induced as well as the rotational direction and speed of the disintegrator (20) are adjusted,

- whereby the disintegration and drying of the material (1) is further intensified and carried out in a few seconds within a thin, heavily rotating, turbulent layer of fluidization gas close to the chamber wall (14).
Process according to claim 1, characterised in that a blade means (18) is used comprising a coaxially arranged, rotatable blade wheel (18) or comprising several blade elements (18',18'') of which at least one is a coaxially arranged, rotatable blade element (18',18''), and that the rotational direction and speed of the rotatable blade means (18) are adjusted in accordance with the type and quantity of the material fed.
Process according to claim 2, characterised in that numbers of revolutions for the rotatable blade means (18) are used during processing providing the outer periphery hereof with tangential rates of speed between 1 m/s and 50 m/s, preferably between 2 m/s and 25 m/s, most preferred between 2.5 m/s and 20 m/s, and when emptying the processing chamber (12), stopping the blade means (18).
An apparatus (10) for carrying out the process according to one or more of the claims 1-3 and of a type comprising a processing chamber (12) having a chamber wall (14), the main shape thereof being substantially like a surface of revolution, and having an essentially vertical axis and a subjacent blast box (16), and comprising continuously acting means
- for heating (4) disintegration and drying gas to be fed into the blast box (16),

- for feeding disintegration and drying gas from the blast box (16) to the processing chamber (12),

- for feeding the material (1) to be processed through an opening (40) in the chamber wall (14),

- for rotating of the disintegration and drying gas inside the processing chamber (12),

- for agitating, mixing and disintegrating the material (1) fed to the processing chamber (12), and

- for discharge of the exhaust gas and a processed fraction of the material from the processing chamber (12), whereby the means for continuous feeding of the disintegration and drying gas and the means for discharge of the exhaust gas and the processed fraction of the material comprise an exhauster (9) for maintaining a drop of gas pressure across the processing chamber (12), said exhauster (9) being arranged in flow connection with the processing chamber (12) through a discharge pipe (6), preferably protruding into the processing chamber (12) at the top thereof,

- and the means for rotating the disintegration and drying gas is a blade means (18) arranged in the apparatus (10) between the processing chamber (12) and the blast box (16), said means having its inlet opening (36) in flow connection with the blast box (16) and its outlet leading into the processing chamber (12),
characterised in that
- the exhauster (9) is having an effect sufficient to provide an axial average gas flow rate through the processing chamber (12) of at least 3 m/s,

- the outlet of the blade means (18) is leading into an annular area (38) of the processing chamber (12) defined by the chamber wall (14) at the bottom thereof,

- and that the means for continuous agitation, mixing and disintegration comprise an intensively functioning, fast rotatable disintegrator (20) coaxially arranged at the bottom of the processing chamber (12), said disintegrator (20) being provided with disintegrator means (34) arranged above the blade means (18) and projecting towards the chamber wall (14),

- whereby the rotational direction as well as the number of revolutions of the disintegrator (20) are adjustable.
An apparatus according to claim 4, characterised in that the blade means (18), or at least one of the blade elements (18', 18'') respectively is connected pivotable with the disintegrator (20), preferably at the lower part thereof.
An apparatus according to one or more of the claims 4-5, characterised in that the blade means (18), or at least one of the blade elements (18',-18'') respectively is connected pivotable with a separate shaft (24) driven independently of the disintegrator (20), said shaft preferably being a hollow shaft enclosing the disintegrator shaft (26) and being driven by means of a motor (28) arranged outside the blast box (16).
An apparatus according to one or more of the claims 5-6, characterised in that the rotational direction of the rotatable blade wheel (18), or of at least one rotatable blade element (18',18'') respectively is reversible.
An apparatus according to one or more of the claims 5-7, characterised in that the rotational speed of the rotatable blade wheel (18), or of at least one rotatable blade element (18',18'') respectively is adjustable.
An apparatus according to one or more of the claims 5-8, characterised in that at least one of the blade elements (18',18'') is connected to a separate gas supply independent of the gas supply to the rest of the blade means (18).
An apparatus according to one or more of the claims 4-9, characterised by a preferably circumferential division plate (22) extending horizontally and/ or downwardly tapering towards the inlet opening (36,36',36'') of the blade means (18) or at least one blade element (18',18''), respectively, said division plate (22) preferably being arranged at the under- side of the blade means (18) or at the blade element (18',18'') respectively, and being retained relative to the chamber wall (14) or relative to the blade means (18) or the blade element (18',18''), respectively.