US3235972A

US3235972A - Method and apparatus for drying of paper, board or pulp webs, formed from cellulosicfibrous material

Info

Publication number: US3235972A
Application number: US250398A
Authority: US
Inventors: Hood Norman Roy; Luckins John; Sutherland Charles Arthur Orr; Carpenter Michael John
Original assignee: British Paper And Board Indust
Current assignee: Research Association for the Paper and Board Printing and Packaging Industries
Priority date: 1962-01-18
Filing date: 1963-01-09
Publication date: 1966-02-22
Anticipated expiration: 1983-02-22
Also published as: GB1028242A; DE1461050A1; SE304675B

Description

Feb. 22, 1966 HOOD ET AL 3,235,972

METHOD AND APPARATUS FOR DRYING OF PAPER, BOARD OR PULP WEBS, FORMED FROM GELLULOSIC FIBROUS MATERIAL 2 Sheets-Sheet 1 Filed Jan. 9, 1963 Feb. 22, 1966 N. R. HOOD ET AL 3,235,972

. METHOD AND APP TUS R ING OF PAPER, BO 0R PULP WEBS. FOR E FR CE LOSIC FIBROUS MA IAL Filed Jan. 9, 1963 2 Sheets-Sheet 2 United States Patent 3,235,972 METHGD AND APPARATUS FOR DRYING OF PAPER, BOARD 0R PULP WEBS, FORMED FROM CELLULOSI FIBROUS MATERIAL Norman Roy Hood, John Luckins, Charles Arthur Orr Sutherland, and Michael John Carpenter, Kenley, England, assignors to The British Paper and Board Industry Research Association, Surrey, England, a British company Filed Jan. 9, 1963, Ser. No. 250,398 Claims priority, application Great Britain, Jan. 18, 1962, 1,972/62 16 Claims. (Cl. 34-9) This invention relates to the drying of paper, board or pulp webs, formed from cellulosic fibrous material.

Hitherto, the drying of continuous webs of cellulosic fibrous material has usually been effected by passing the web around a number of steam heated drying cylinders, there being endless drying felts which are arranged to press the web against the rotating cylinders during the drying operation.

In accordance with the present invention, there is provided a method of drying paper, board or pulp webs of cellulosic fibrous material, wherein a formed but undried, or not sufficiently dried, continuous Web of the material is passed, whilst being substantially vertically disposed, through a fluidised bed, the fluidised bed consisting of solid particles undergoing fluidisation or pneumatic transport in a primary stream of up-flowing gas in an inner region adjacent the web, and of particles undergoing fluidisation in a secondary stream of tip-flowing gas in an outer region remote from the web, there being heating means for the heating of the particles of the fluidised bed to a temperature such that the water content of the web is reduced during passage of the web through the fluidised bed, the fluidised particles in the inner region being more widely dispersed, or diluted to a greater extent, than the fluidised particles in the outer region.

The gas may be air or superheated steam or any other convenient gas. The phenomenon of fluidisation depends on the upward forces imposed on the particles by the upward stream of gas being substantially equal to the weight of the particles. The bed then expands somewhat allowing the individual particles some freedom of movement. The system of particles thus suspended in flowing gas shows a liquid-like behaviour and the solids are consequently said to be fluidised. In particular the ability of a gas stream, containing suspended solid particles, to transfer heat from one surface to another is much greater than the ability of the same gas stream when free from solid particles. Damp paper, board or pulp immersed in or passed through a heated bed of gas fluidised particles is found to dry much faster than in a gas stream at the same temperature. The rate of drying increases with a rise in bed temperature. The steam released by the drying of the paper, board or pulp is rapidly removed from the surface of the sheet and becomes mixed with the gas stream.

In accordance with a preferred example of the method, the mean concentration of the particles in the inner region is less than one-third of the mean concentration of the particles in the outer region. Preferably, the mean concentration of the fluidised particles in the outer region is between 80% and 99% of the bulk density of the particles measured when the flow of fluidising gas is stopped. The expression mean concentration of the particles is intended, as used herein and in the accompanying claims, to indicate the weight in pounds of the particles to be found at any time within a volume of one cubic foot of the fluidised or pneumatically transported bed. It is to be understood that there may be local varia- "ice tions in concentration within such unit volume due to, for example, bubbling in the outer region or to eddying in the inner region, and that the specified mean concentration is the average taken over a volume of one cubic foot.

The invention further provides apparatus for the drying of continuous webs of paper, board or pulp, formed from cellulosic fibrous material, the apparatus comprising a container having openings at the top and bottom thereof to enable a web of the material to pass in a substantially vertical path through the container and having in the lower part thereof inlet means for gas, such as air, for fluidising a bed of solid particles within the container, the apparatus comprising also means adapted, during a drying operation, to provide at each side of the web path, an inner region adjacent the web in which solid particles of the fluidised or pneumatically transported bed, are more widely dispersed, or are diluted, to a greater extent than fluidised particles in an outer region remote from the web path, said apparatus including also means for I heating the fluidised particles so that, during passage of the web through the container, the fluidised particles can be maintained at a temperature for reducing the water content of the web to the desired level. The heating means may comprise an array of heating tubes which extend through opposite vertical walls of the container and which are adapted to receive steam or other heating fluid, for the heating of the fluidised bed to a temperature of between 200 and 900 F.

The gas inlet means may comprise at each side of the web, at least two independent inlets including a first inlet extending along the lower opening and through which a gas stream can be forced to prevent particles falling through said lower opening and to provide an overall upward movement and an adequate but lower concentration of the particles in the inner region adjacent to the web surface, and a second inlet in the form of a porous or perforated plate to the underside of which gas can be supplied to ensure adequate fluidisation of the bed in the outer region remote from the web, so that said outer region will contain a higher concentration of the particles. In this arrangement, the vertical flow rate of gas per unit cross sectional area is greater in the regions adjacent to the web than in the regions remote from the web. In consequence, there is an overall circulation of the fl-uidised particles on each side of the web, as well as their random motions, which circulation is upwards in the region adjacent to the web until the particles reach the top of the baffles where they move outwards to the region remote from the web and therein move downwards past the heating means, until they return inwards to the region adjacent to the web by passing through a gap be tween the lower end of the bafiies and the porous or perforated floor of the container.

The region adjacent to the web may be constricted at two or more levels by pairs of horizontal projections, one of each pair on the inner wall of each baflle, into a plurality of independent pockets located one above another on each side of the web, by which constrictions the upwardly moving fluidised particles are brought into closer proximity with the web which is being dried.

For a better understanding of the invention and the method by which it may be performed, the same will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 is a diagrammatic longitudinal sectional view of drying apparatus according to one constructional embodiment of the invention, and

FIGURE 2 is an elevational view of the apparatus.

Referring to FIGURE 1, the drying apparatus illustrated comprises an upright tank or container 1 having an enlarged lower section 2, an intermediate section 3 which is of rectangular horizontal cross-section throughout, and an upper or top section 4. The lower section 2 of the container has in the base thereof a central transversely extending opening 5 through which a web of paper material, indicated by a broken line at A, can be led into the container for drying purposes. The upper section 4 also has a central transversely extending opening 6 through which the web or paper material is led out of the container.

The lower section of the container is provided also with two primary

gas inlet elements

7, 8 disposed one at each side of the lower opening 5. These

primary gas inlets

7, 8 communicate with a pressure box (not shown) which is supplied with gas, such as air, under pressure. The primary

gas inlet slots

7, 8 extend the full width of the container.

The lower section of the container also includes at each side of the web A and further therefrom than the

primary gas inlets

7, 8, a porous or perforated floor 9 comprising porous ceramic tiles or metal plates pierced by a large number of small holes. Beneath the porous or perforated floor 9 at each side, there is disposed a secondary pressure box 10 adapted to be supplied with compressed gas, such as air, through an associated inlet 11, these secondary gas pressure boxes 10 being separated from or 'sponding projections 16 of the two baflles are located at the same height, so that each pair of projections makes a constriction in the inner regions adjacent to the web.

independent of the pressure boxes associated with the two

primary gas inlets

7, 8. Valve means (not shown) are provided for controlling the pressure of the air or other gas which flows through the primary and secondary inlets into the container.

Above the floor and at each side of the Web A, there is provided within the enlarged lower section 2 of the container, heating means which, in the present embodiment, takes the form of an array of heating tubes 12, these tubes 12 being located in laterally outer regions 13 at opposite sides of and remote from the web A. The tubes 12 extend through the opposite vertical end walls of the container and the ends of the tubes associated with one wall are effectively connected to a source of steam under pressure, the steam being, for example, at a temperature of about 350 C. The other ends of the tubes are conmeet to steam traps (not shown). It will be understood that the heating means may take the form of electrical heating elements or any other convenient means; also, the heat exchange surfaces of the heating means may be finned or extended in other desired manner.

Baflles 14 are provided within the container at each side of the moving web A so as to divide the fluidised bed into two substantially independent regions, comprise ing the outer regions 13 which are remote from the web, and inner regions 15 which are adjacent to and at opposite sides of the web. The baflles 14 comprise two substantially vertical plates spaced apart from opposite sides of the web A and parallel to the side walls of the container. The plates 14 correspond in width to the interior of the container and are fitted at the opposite edges thereof closely against the vertical end walls of the container.

In the present embodiment, the intermediate section 3 of the container is of reduced width and this merges at its upper end into laterally outwardly and upwardly curved wall parts of the upper section 4. Thus, at each side of the web A, the outer region of the fluidised bed, will be somewhat narrower as shown at 21, in the inter-, mediate section of the container than in the bottom and top sections thereof.

The outer faces of the baffles 14 directed towards the outer regions of the fluid bed are substantially flat, but the inner faces bounding the inner regions 15 adjacent the web are provided with horizontally extending projections 16. In the illustrated embodiment, each bafile 14 carries on its inner face a multiplicity of the horizontally extending projections 16, these each being substantially of right-angled triangular shape in cross section and disposed with the face corresponding to' the hypotenuse of the triangle secured to the adjacent baffle. The corre- The projections may be of rounded or of any other convenient shape in cross-section.

Each bafl'le carries an outwardly and downwardly inclined deflector 17 which extends within the lower section 2 of the container and is adapted to deflect the particles of the fluidised bed laterally outwardly, into the laterally extended parts of the lower section of the container. In FIGURE 1, the normal level of the sand before fluidisation is indicated diagrammatically at 18.

The bafl'les 14 extend upwardly into the upper section 4 of the container where the top edges of the baffles are curved outwardly and downwardly to form exhaust ducts 19 which cooperate with the curved wall parts of the top section 4 of the container, to define passages 20 at each side of the web through which the fluidised particles can pass from the inner regions 15 into the outer regions at the outer sides of the bafiles 14. Each bafile 14 extends at its lower end into the lower section 2 of the container, the lower edges of the two bafiles being spaced a short distance above the floor of the container, to provide a gap 22 through which the fluidised particles can pass from one region to another. The lower end of each baffle is extended downwardly by means of an adjustable shutter or damper 23 to allow the lower gap 22 to be varied to provide control, as required, in the passage of particles between the two regions at the bottom of the container.

Means is provided in the top section of the container for the discharge of the upwardly flowing stream of air or gas employed to fluidise the bed, and for the discharge also of steam which is produced by the drying of the web and which becomes mixed with the gas stream. Thus, for the escape of spent air, or gas, and steam from the container, there are provided the exhaust ducts 19 which extend through the opposite vertical end walls of the container, these ducts and the top section 4 of the contamer being shaped to direct the particles back to the outer regions while permitting escape of the spent air or gas from the container.

As shown in FIGURE 1, the top section 4 of the contamer is of gradually increasing width so that, during operation of the fluidised bed, the upward velocity of the gas stream will tend to be reduced, thereby facilitating the return of the particles passing upwardly from the inner regions 15 and over into the outer regions of the fluidised bed. For this purpose, there is also provided in the inner section 4 of the container, transversely extending deflector plates 24. If desired, electrically operated fan means may be provided at the top of the contamer for directing particles back to the fluidised bed. Moreover, the exhaust ducts may be connected to a centrifugal separator (not shown), adapted to remove any particles still suspended in the gas stream, means being connected in circuit with the centrifugal separator to enable the issuing gas stream either to be exhausted to atmosphere or, alternatively, subjected to heat exchange and particle removing processes, to enable the gas to be recycled through the primary and secondary gas supplies.

Where, as in the present embodiment, it is intended that the web A to be dried shall move vertically upwards through the container, means is provided for removing from the web any particles adhering thereto and carried up through the container by the web. Thus, referring to FIGURE 1, there are provided downwardly directed jets of gas, such as air, arranged to impinge on the web surfaces. These downwardly directed gas jets issue from a pair of horizontal slot-like inlets 25 arranged at the top of the apparatus at opposite sides of the upper web opening 6, these upper gas inlets 25 being similar to the primary gas inlet 7 provided at the lower end of the container.

The adjustable shutter or damper 23 allows the gap at the lower ends of the baflles to be varied between, for

example, half an inch when the shutter or damper is fully opened and about the mean diameter of the particles of the fluidised bed, when fully closed. Alternatively, the particles may be allowed to pass from the outer to the inner regions through one or more pipes or holes formed in the baflles and dimensioned and spaced according to the desired rate of flow of the particles from one region to the other.

In the present embodiment, the container 1 comprises two relatively displaceable or separable parts 26, 27 (FIG- URE 2) adapted to be joined together in the vertical plane of the web A. The left-hand part 26 is located fixedly in a vertical position and secured against upper and

lower abutments

28, 29. The right-hand part 27 of the container is arranged for translational displacement in the direction of arrows X (FIGURE 2) away from and towards the fixed part 26. For this purpose, the casing part 27 is formed with vertically spaced upper and lower bearing supports 30, 31 in each of which there is mounted an associated transversely extending shaft 32 carrying pinions 33. Spaced laterally from the movable part 27 of the container, there is disposed a vertical support or wall 34 to which are secured upper and

lower bracket

35, 36 each provided along its upper edge with a rack 37 engageable by the associated pinion 33. Each of the shafts 32 carries a drive sprocket 38 engaged by a driving chain 39. The arrangement is such as to maintain the movable part 27 of the casing in a vertical position during its movement to and from the associated fixed part 26. Power means is also provided for actuating the movable part 27 of the container. In the present embodiment, the power means comprises a double acting fluid pressure operated piston and cylinder device 40, the piston of which is operatively connected by connecting rod means 41 to the container part 27. The piston and cylinder device 40 is provided with

air admission pipes

42, 43, so that, by introducing air under pressure through the pipe 42, the piston and its rod 41 can be displaced to move the right-hand part 27 of the container into an open position removed from the relatively fixed part 26 and, by introducing air through the pipe 43, the movable part 27 can be displaced into a closed position adjacent the fixed part 26. The operating mechanism and the chain-sprocket drive means, is such as to ensure parallel movement of the casing part 27 relatively to the fixed part 26.

To prepare the apparatus for a drying operation, the piston and cylinder device 40 is operated to separate the two parts of the container, as described with reference to FIGURE 2, to facilitate the location of the web A in the medium plane of the apparatus. Upon closing of the container parts, the web which is guided "by upper and lower guide rolls 42, 43, will extend vertically between the upper and lower openings 5, 6.

The outer regions 13 in the lower section of the container, are charged with particles to the level indicated at 18, and gas, such as air, is supplied to the primary and secondary inlets to fluidise the particles. The valves associated with the two sources of gas are so controlled that in the two outer regions, the mean concentration of the fluidised particles, will be between 80% and 99% of the bulk density of the particles when the flow of fluidising gas is stopped. The fluidised particles passed through the lower gaps 22 into the inner regions where the primary gas supply is such that the particles undergo fluidisation or pneumatic transport, the particles in the inner regions adjacent the web, being more widely dispersed, or diluted to a greater extent, than the fluidised particles in the outer regions. In the present example, the particles consist of rounded grain sand. In the two inner regions the particles have a mean concentration which is less than onethird of the mean concentration of the particles in the two outer regions. Thus, there may be a concentration of about 90 lb./cubic foot in the outer regions and less than about 30 lb./ cubic foot in the inner regions. The arrangement is such that there is produced a circulation in which the particles in the two outer regions move slowly downwardly in counter-direction to the upward flow of the air or gas from the secondary supply, and the particles in the two inner regions 15 are in a borderline condition between fluidisation and a pneumatic transport of the bed. Thus, in the inner regions the particles move upwardly between the bafiles 14 and then outwardly over the tops of the bafiles so as to re-enter the outer regions. The particles then pass downwardly for passage over the heating means and thence through the lower gaps 22 into the inner regions.

The speed of the moving web may be [from zero to 5,000 feet per minute or more depending on the paper, board or pulp web machine on which the drying apparatus is being used. The gas may be supplied to the slot-like

primary inlets

7, 8 at a pressure of up to 15 lbs. per square inch gauge, and supplied to the pressure boxes 10 of the secondary supply at a pressure of up to 10 lbs. per square inch gauge, such that the pressure at any height within the regions 13 containing the heating means is substantially equal to the hydrostatic pressure of the fluidised particles therein. The temperature of the fluidised bed may be between 200 and 900 F. to suite the particular nature and speed of the web which is to be dried.

The particles, which should be free from sharp edges and stable at the temperatures to be used, may be between 1.0 millimetre and 0.1 millimetre in size, preferably .between 0.5 and 0.2 mm. They may, for example, be rounded grain sand. Alternatively, the particles may consist of small glass balls known as ballotini of a size between and 500 microns.

The distance between the 'baflles may be from 1 to 6 inches but this spacing is constricted at the necks between the opposed triangular projections 16, to a distance of Lfrom about A to 2 inches. The projections may be spaced apart vertically by a distance of from 1 to 12 inches.

Should it be necessary during operation of the apparatus, to obtain access to the interior of the apparatus, it is necessary merely to shut off the secondary supply of air or gas to the porous floor 9 of the container so that, in the two lower outer regions 13, the particles will no longer be fluidised and the flow of particles from the outer regions 13 through the lower gaps 22 into the adjacent inner regions 15, will also be arrested. The supply of primary air or gas to the

inner inlets

7, 8 may be continued to drive the relatively thinly dispersed or diluted particles within the inner regions 15, upwardly and over the baflles 14 into the adjacent outer regions. This can be facilitated by increasing the flow of air or gas through the primary gas inlets 7, 8.- The supply of primary air or gas is then shut-off and the two

halves

26, 27 of the container separated by operating the piston and cylinder device 40. The drive mechanism is such that the opening of the container can be carried out smoothly and with the two parts maintained substantially parallel to each other. Also substantial loss of particles is avoided since substantially all of the particles are returned to the outer regions 13 of the lower section 2 of the two container parts, before opening of the container.

A moving continuous web of paper, board or pulp may be dried by a combination of conventional means, for example, steam heated drying cylinders, and one or more fluid bed drying apparatus arranged in series to form the drying section of the machine. While the fluid bed drying apparatus is found to be very effective in evaporating water from the web, it will be necessary in the case of paper and board to make provision for smoothing and flattenig the web by conventional means. It is found that by the additional drying effect of the fluidised bed or 'beds, the drying section of a continuous paper, board or pulp machine can be run at a greater speed without increasing the overall length of the machine.

The following Example will serve further to illustrate the drying method employing the aforedescribed apparatus.

Example A damp continuous web one foot wide of Kraft papermaking pulp obtained from the wet-end of a paper forming device, was led in an upward direction through a fluidised bed drying apparatus at a speed of 240 feet per minute. The particles consisted of rounded grain sand of 40 to 60 mesh size and were heated to 300 C. in the outer regions of the container remote from the web path, the heating means consisting of electric heating elements dissipating 62 kilowatts. The particles were allowed to pass continually from the outer regions 13 into the inned regions 15 disposed between the two bafiles 14, the arrangement being such that there was an overall upward movement of the particles within the inner region in contact with the moving web A. The air supplies were so adjusted that the mean concentration of the particles in contact with the moving web in the inner region, was 6 lbs. per cubic foot, and that in the outer regions where the heating elements were situated, the mean concentration was 90 lbs. per cubic foot.

Upon severing of the web passing through the apparatus, for the purpose of taking samples from the web, the supply of air to the outer regions 13 of the container was stopped, thereby preventing the passage of sand from the outer regions into the inner regions. The air supply to the inner regions was continued so that the inner regions were rapidly emptied of sand. The movable part 27 of the container was then operated by the device 40 to split the two parts of the container in the vertical plane of the web, for the purpose of facilitating the re-threading and proper location of the web between the container parts. The two parts or halves were then brought together again and air supplied to re-fluidise the particles.

It was found that the water to solids ratio of the web entering the apparatus was 1.83 and that of the web leaving the apparatus was 1.58. The continuous web employed was of 132 grams per square metre dry basis weight. It was found also that in passing through the apparatus, water was removed from the paper web at a rate of 97 lbs. per hour.

We claim:

1. A method of drying cellulosic fibrous material comprising: providing a bed of solid particles; fluidizing said particles in the form of a vertically extending inner region and a vertically extending outer region by passing a primary stream of fluidizing gas upwardly through said inner region and by passing a secondary stream of fluidizing gas upwardly through said second region; passing a continuous web of the material to be dried substantially vertically through said inner region; dispersing the particles more widely in said inner region than in said outer region; and heating the fluidized particles whereby the water content of the web is reduced.

2. A method as in claim 1 which includes passing said web upwardly through said inner region; maintaining the velocity of said primary gas stream sufficiently high to move the particles in said inner region upwardly and maintaining the velocity of said secondary gas stream lower than the velocity of said primary gas stream to cause the particles in said outer region to move downwardly, said method including the step of providing vertically spaced constrictions in said inner 'region to form substantially independent pockets in said inner region, so that said web passes vertically through said pockets as it passes upwardly through said inner region.

3. Drying apparatus for the drying of webs of cellulosic fibrous material comprising: a container having an upper opening at the top and a lower opening at the bottom; a mass of solid fluidzable particles in said container; means for fluidizing said particles in the form of a vertically extending outer region and a vertically extending inner region in which the particles are dis.-

persed more widely than in said outer region, said means including baffle means in said container defining said regions, primary .gas inlet means for introducing an upward flow of gas into said inner region and secondary gas inlet means for introducing an upward flow of gas into said outer region; means for guiding a web to be dried along a path substantially vertically through said inner region; and heating means in said container for heating said particles.

4. Drying apparatus for drying webs of cellulosic fibrous material comprising: a container having a web inlet opening in its bottom and a web outlet opening in its top; means including two laterally spaced apart baffles forming within said container a centrally disposed inner region between the bafiles and laterally outer regions with the outer sides of the baflles; means for guiding a web of cellulosic fibrous material substantially vertically through said inner region from the lower inlet opening to the upper outlet opening; a mass of solid fluidizable particles in said container; means for fluidizing the particles in said inner region for movement in an upward direction, said means including primary gas inlet means at the lower part of said inner region; means for fluidizing the particles in said outer regions for movement in a downward direction, said means including secondary gas inlet means at the lower part of said outer regions; and heating means in said container for heating said particles.

5. Apparatus as in claim 3 wherein said container is formed of two relatively movable parts, said apparatus further including means for moving said parts relatively one to another into an open position to permit the web to be located vertically in said inner region, said primary gas inlet means including a gas inlet element associated with each container part.

6. A method as claimed in claim 1, which includes moving the particles upwardly in said inner region adjacent the web, and moving the particles downwardly in said outer region remote from the web.

7. A method as claimed in claim 1 which includes introducing air under pressure from a primary source to form said primary stream of fluidizing gas, and introducing air under pressure from a second source to form said secondary stream of fluidizing gas.

8. A method as claimed in claim 1 which includes introducing superheated steam from a first source to constitute and primary stream of fluidizing gas, and introducing super-heated steam from a second source to constitute said secondary stream of fluidizing gas.

9. A method as claimed in claim 2 which includes maintaining the particles in said inner region at a mean concentration which is less that one-third of the mean concentration of the particles in said outer region.

10. A method as claimed in claim 9, which includes maintaining the concentraion of the particles in said outer region between and 99% of the bulk density of the particles as measured when the flow of fluidising gas is stopped.

11. Apparatus as claimed in claim 4, wherein said primary gas inlet means extends along the lower opening for the web and is independant of each secondary gas inlet means, each primary inlet means being disposed to direct a primary gas stream upwardly to prevent particles falling through said web inlet opening and to provide an overall upward movement of the particles in said inner region adjacent to the web surface, and wherein each secondary gas stream through said porous plate and means for supplying a secondary gas stream through said porous plate for the fluidisation of the particles in said outer regions at a higher concentration than the particles in said inner region.

12. Apparatus as claimed in claim 4, wherein said bafilesare substantially vertically disposed and include gaps at their top and bottom to permit the passage of the fluidised bed particles from the inner region to the adjacent outer regions, during a drying operation.

13. Apparatus as claimed in claim 4, wherein said container has an enlarged lower section, and wherein said heating means comprises an array of heating tubes disposed in said outer regions and extending between opposite side walls of said lower section, there being means for supplying said heating tubes with a heating medium for the heating of the fluidised bed to a temperature of between 200 and 900 F.

14. Apparatus as claimed in claim 12, including shutter means for controlling the flow of particles through the lower gap in each bafile.

15. Apparatus as claimed in claim 12, including projections provided on and extending across the opposed surfaces of said baffies, the projections on each baffle being spaced apart from one another and the corresponding projections on said two bafiles being located opposite one another to sub-divide the space between said bafiles into a plurality of substantially separated pockets.

16. Apparatus as claimed in claim 5, wherein said References Cited by the Examiner UNITED STATES PATENTS 2,785,478 3/1957 Audas et al. 34-9 2,938,276 5/1960 Doleman et al 34-95 3,061,941 11/1962 Gay et al. 34-95 3,061,943 11/1962 Bennett et al 3495 FOREIGN PATENTS 887,216 1/1962 Great Britain.

20 WILLIAM F. ODEA, Acting Primary Examiner.

NORMAN YUDKOFF, Examiner.