Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B3/00—Drying solid materials or objects by processes involving the application of heat
  • F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
  • F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
  • F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
  • F26B3/092—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed agitating the fluidised bed, e.g. by vibrating or pulsating
  • F26B3/0923—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed agitating the fluidised bed, e.g. by vibrating or pulsating by mechanical means, e.g. vibrated plate, stirrer
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement
  • F26B17/10—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by fluid currents, e.g. issuing from a nozzle, e.g. pneumatic, flash, vortex or entrainment dryers
  • F26B17/101—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by fluid currents, e.g. issuing from a nozzle, e.g. pneumatic, flash, vortex or entrainment dryers the drying enclosure having the shape of one or a plurality of shafts or ducts, e.g. with substantially straight and vertical axis
  • F26B17/103—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by fluid currents, e.g. issuing from a nozzle, e.g. pneumatic, flash, vortex or entrainment dryers the drying enclosure having the shape of one or a plurality of shafts or ducts, e.g. with substantially straight and vertical axis with specific material feeding arrangements, e.g. combined with disintegrating means

Definitions

• the present invention relates to a method and apparatus for fluid-bed drying, particularly for simultaneous drying and disintegrating a heat sensitive material.
• Fluid bed treatment of various materials has been known for decades and has become a widely used technology in industry and manufacturing, due to the many advances of the technology.
• EP 0 141 403 discloses an apparatus for heat treatment of a material in a fluid-bed.
• the material to be treated in the fluid-bed is led to the fluidised bed through an inlet in the side wall of the apparatus above a rotating fluidised layer.
• the drying air is supplied via an annular distributor surrounding the lower part of the cylindrical wall of the chamber and a circular slit between the conical bottom and the cylindrical wall.
• Some materials are of a very sticky nature and tend to deposit on the interior surface of the drying chamber walls. This is particularly inconvenient for heat sensitive materials because of the risk of discolouring and decomposition.
• German patent no. 3612049 and additionally application no. 3633125 discloses an apparatus for drying of hen droppings.
• the hen droppings are led to the drying chamber via the bottom of the apparatus and introduced to the drying chamber by use of compressed air or a fan which creates an upward stream of air.
• the hen droppings are dried by use of warm air from the chicken run.
• the disclosed apparatus is very ineffective as a drying apparatus, as the temperature is low and the compressed air does not create a fluidised layer .
• the present invention provides a method and apparatus by which heat sensitive material can be dried without the risk of discolouration and decomposition which may appear when drying heat sensitive material.
• the invention provides a method and apparatus in which the material to be dried is almost instantly after entering the drying chamber caught in an upwards stream of fluidization and drying medium thereby avoiding contact with the hot walls of the apparatus.
• one aspect of the invention relates to a method for fluid-bed drying of wet material in a drying chamber comprising an upper part and a lower part, the upper part having an outlet for dry material and the lower part comprising a substantially horizontal bottom part with a least one inlet for wet material and at least one inlet for a stream of fluidization and drying medium, said method comprising the steps of:
• the fluidization and drying medium is normally a gas, preferably atmospheric air which is heated to a temperature between 100-500 °C.
• the horizontal bottom part is constructed to be substantially horizontal and comprises one or more inlets for the fluidization and drying medium placed around one or more inlets for the wet material to be dried in such a away that the fluidization and drying medium constitutes a substantially circular or cylindrical upward stream of fluidization and drying medium, and the wet material to be dried enters substantially into the centre of the circular or cylindrical upward stream thereby being caught in the circular or cylindrical upward stream of fluidization and drying medium.
• the wet material to be dried is in the form of a paste or filter cake.
• the wet material to be dried is in the form of a mixture of liquid and solid particles wherein the mixture contains 10-90 % by weight of solid material.
• the wet material is stirred and/or disintegrated by stirring and/or disintegrating means in the drying chamber.
• stirring or disintegrating means are blades, paddles, knifes or similar devices fastened to a vertical rotating shaft protruding from the centre of the horizontal bottom.
• the residence time for exposing the wet material to be dried to the stream of fluidization and drying medium is adjusted by adjusting the size of orifices.
• the residence time is the average time required for a given material to be exposed to the fluidization and drying medium to obtain a satisfactory dryness.
• the skilled person is able to determine the residence time for a material as a matter of routine.
• the adjustable orifices are placed in the upper part of the drying chamber.
• the orifices are adjustable in an annular wall protruding horizontally into at least a part of the upper drying chamber.
• the wet material to be dried is provided to the substantially horizontal bottom part of the drying chamber vertically upwards, preferably by means of paddles or transporting screws or belts, etc.
• the invention also comprises use of the method for drying wet material, and preferably for drying heat sensitive material.
• the invention relates to an apparatus for fluid-bed drying of wet material with a drying chamber comprising an upper part and a lower part, the upper part having an outlet for dry material and the lower part comprising a substantially horizontal bottom part comprising means for providing an upward stream of fluidization and drying medium in the drying chamber and an inlet for the wet material to be dried.
• the means for providing an upward stream of fluidization and drying medium is a slit in the substantially horizontal bottom part of the drying chamber, preferably the slit is annular-shaped and preferably the annular slit partly or totally surrounds the inlet for the wet material to be dried.
• the slit is annular-shaped and preferably the annular slit partly or totally surrounds the inlet for the wet material to be dried.
• the apparatus for fluid-bed drying according to the invention has a drying chamber with an upper cylindrical part and a lower conical part tapering downwards to the substantially horizontal bottom part. Such a construction establishes the optimal conditions for the material flow in the drying chamber.
• the inlet for the wet material to be dried is placed substantially in the centre of the substantially horizontal bottom part of the drying chamber to provide the best distribution properties of the wet material to be dried in the upward stream of fluidization and drying medium.
• the drying chamber is supplied with means for stirring and/or disintegrating said stirring and/or disintegrating means preferably being a coaxially placed rotating shaft with wings, paddles, knifes or rods.
• said stirring and/or disintegrating means preferably being a coaxially placed rotating shaft with wings, paddles, knifes or rods.
• the wet material to be dried is often cake or paste-like, there is a need for disintegrating the material to obtain a better drying.
• the wet material to be dried is provided upwards to the inlet in the horizontal bottom by means of paddles or transporting screws, belts or pumps.
• the upper part of the drying chamber comprises means for adjusting the upwards stream of fluidization and drying medium, and these means are preferably a substantially horizontal projecting edge in form of an annular-shaped plate fastened to the wall of the upper chamber and with adjustable orifices.
• the invention also comprises use of the apparatus for drying wet material, and preferably for drying heat-sensitive material.
• Figure 1 shows a schematically vertical axial section of the apparatus according to the invention.
• Figure 2 shows the adjustable orifice to determine the residence time for the material in the drying chamber.
• the apparatus comprises a drying chamber 1 with a cylindrical part 2, a top part 3 and a conical part 4.
• the cylindrical part has an orifice 6 and an exhaust aperture 5 for the dried product, carried by the drying medium.
• the drying medium is introduced tangentially through the aperture 7 to the annular distributor 8 and directed into the drying chamber through an annular slit 11, delimited by the conical guide ring 9 and the outer member 10 of the central member 16.
• a rotating driving member 12 with a shaft 13 is placed coaxially in the chamber 1 and in the member 16 and is equipped with paddles 14 in the part enclosed by the member 16 and with wings 15 in the part enclosed by the conical part 4 of the chamber 1.
• the member 16 is provided with a supply member for paste material in the form of a member 17 with a conveyor screw 18.
• the member 16 and its outer part 10 forms a water jacket containing a medium for control of the temperature of the member 16. Circulation of the medium can be provided for by means of an inlet pipe 19 and an outlet pipe, not shown.
• the apparatus operates as follows.
• the material in the form of a cake or paste, which is to be dried and disintegrated, is supplied to the member 16 by means of the screw 18.
• the paste is conveyed upwards and - by act of centrifugal forces - introduced radially outwards into the drying chamber.
• the diameter of the member 16, the number and design of the paddles 14 and the revolution of the shaft 13 are chosen to allow for a vertical transport mass rate of the paste several times that of the supply screw 18.
• the paddles 14 shall supply the paste material to the central drying zone of the chamber in the form of a dispersed cloud of wet material.
• the wet cloud is met by the hot drying medium emanating form the slit 11 and a violent fluidised bed is established in the lower part of the chamber. Immediate initial evaporation from the dispersed wet material takes place. This is supported by the impact from the wings 15, and possible remaining lumps of paste will dry and disintegrate.
• a part of the material in the fluidised bed will leave the bed in the form of small lumps and be carried by the rotating drying medium along the conical walls 4 to the upper parts of the chamber. These lumps will however be dry on the surface and consequently not present any risk of adhering to the chamber walls. Lumps, which have a still wet interior, will move upwards along the conical walls 4 until the flow pattern in the chamber will direct them back into the bed in the bottom.
• the diameter of the central aperture in the orifice 6 has a known effect in terms of the product residence time in the chamber.
• the material in the chamber moves upwards in the form of a rotating fluidized bed, the inner limitation of which is the aperture diameter of the orifice 6.
• the present invention incorporates means for control of the residence time during operation by introducing a segment cut out of the orifice ring 6 and equipped with a slide gate 6a which can be adjusted between an open and a closed position by means of an external activator, see figure 2.
• the activator can be manual or remote operated and in such a way that the gate can be adjusted to any position between open and closed. In the open position the gate edge towards the centre of the chamber is in its maximum distance from the centre line of the chamber. In its closed position the gate edge towards the centre of the chamber is in line with the rim of the circular opening in the orifice 6,
• the mass of the rotating fluidized material will be defined by the position of the controlling edge of the gate. Consequently the residence time of the particle mass in the chamber can be controlled by adjustment of the gate position.
• guide blades may be provided in the distributor 8 to change direction of the medium flow through the slit 11.
• guide blades may be provided in the distributor 8 to change direction of the medium flow through the slit 11.
• the apparatus might also be advantageous for the drying of materials, which can be successfully dried on known apparatuses and at small/medium capacity
• the diameter of the cylindrical part of the apparatus was 1.6 m, and the height from air inlet (9) to the top (3) was 4. m.
• the opening in the orifice 6 was 1 meter . 4161 kg/h wet, pastelike whey concentrate with a total solid content of 85% was fed vertically upwards into the drying chamber and disintegrated by the rotating wings.
• the drying and fluidizing air in an amount of approx . 20,000 kg/h was introduced into the drying chamber through the annular slit (11) at a velocity of 55 m/s and a temperature of 140 °C.
• Partly dried material formed a rotating fluidised bed in the chamber, limited by the orifice 6 and the slit 6a, with 50 % opening.
• Dried powder was separated from drying air in a cyclone (not shown) .
• the experiment was closed by the operator after 4 hours.
• the chamber was free of severe deposits.
• Flowability of a powder was measured by pouring approx. 10 grams of powder in a wide tipped funnel, resting on a table. When the funnel is removed carefully by hand, the powder will be left as a more or less cone-shaped pile.
• Flowability is expressed as the angle of repose, measured by means of a handheld goniometer.
• the normal range for spray dried powders is from 30 degrees or less ("good") to 45 degrees or more ("poor") .
• Residual moisture was measured by weight-loss after 6 hours in oven at 87 °C.
• RRB Rosin- Rammler-Bennett
• Caking properties are estimated by examining the crust formed on a spoonful of powder, subjected to 60% and 80% relative humidity at 20 °C for 24 hours.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Microbiology (AREA)
• Drying Of Solid Materials (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8159000

Family Applications (1)

Country Status (4)

Cited By (1)

Citations (4)

• 2001
  • 2001-01-24 EP EP01946931A patent/EP1250558B1/de not_active Expired - Lifetime
  • 2001-01-24 WO PCT/DK2001/000051 patent/WO2001055657A1/en active IP Right Grant
  • 2001-01-24 DE DE60109576T patent/DE60109576T2/de not_active Expired - Fee Related
  • 2001-01-24 AU AU2001228314A patent/AU2001228314A1/en not_active Abandoned

Patent Citations (4)

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