Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
  • B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
  • B05B7/14—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas designed for spraying particulate materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
  • B01F23/30—Mixing gases with solids

Definitions

• the present invention relates to a method and to apparatus for generating an aerosol from a fluidized bed in an enclosure.
• the aerosol When generating an aerosol of this kind, the aerosol is normally used as a medium for transporting material in a fluid state to a point at which the material shall be treated in different ways, e.g. packaged or mixed with other materials .
• the solid particles to be fluidized are placed in the form of a bed on a fluid-permeable grate in a vertical column (FIG. 1) and pressurised fluid is caused to flow through the material from beneath and therewith set the solid particles in motion.
• the fluid looses energy as it passes through the channels and passageways formed between the particles.
• the pressure drop in a stationary bed of solid particles can be calculated with Ergun's equation. If the rate at which the fluid moves is constantly increased, there is finally reached a point at which the particles no longer remain stationary and fluidized under the effect of the fluid.
• the drop in pressure sometimes decreases to an insignificant extent from point B to point F.
• the particles progressively move more violently and in random directions from point F and onwards.
• the linear velocity of the fluid between the particles is much higher than the velocity of the fluid in the space above the bed.
• Even with violent fluidization only the smallest particles (particles with the highest fluidizing capacity) are entrained by the fluid and carried away.
• the porosity t: of the bed will also increase and the bed therewith expand and its density decrease.
• the extent to which the particles are entrained does ⁇ not become noticeable until point P has been transgressed, whereafter entrainment is considerable and finally complete.
• the porosity obtains the value 1 at the point Q, wherewith the bed ceases to exist and obtains a state with simultaneous flow in two phases.
• the pressure drop is almost constant from point F to point P.
• the particles at the bottom of the column require more energy to achieve the fluidized state than particles located on the upper side of the solid bed. This is the reason why it has not hitherto been possible to fluidize a bed partially or to only a limited extent. In conventional fluidizing processes, the bed can thus either be fluidized completely or not at all.
• the fluid When producing aerosols with the aid of a conventional fluidizing method according to the aforegoing, the fluid will move at a speed which is equal to or greater than the speed at which permanent entrainment of the particles is achieved.
• the particles introduced into the fluidizing column with the aid of suitable means will therefore be fluidized immediately and carried away.
• the fluid is a gas
• there is formed an aerosol which consists of gas and solid particles, the mass flow of the solid particles being determined by the mass flow input of the solid particles in the column.
• the aerosol flow exiting from the column can only be controlled by the supply of solid particle material, since this material is fluidized immediately upon entry into the column.
• An object of the present invention is to provide a method and an apparatus of the kind described in the introduction which will enable a fluidizable bed to be fluidized partially or to a limited extent with lower energy consumption and more accurate control of an aerosol flow from the bed enclosure.
• FIG. 1 is a schematic illustration of a known aerosol generator
• FIG. 2 is a diagram illustrating fluid pressure drop on the one hand and the bed porosity and volume as a function of the fluid flow rate during fluidizing of a bed of solid particles with the aid of an aerosol generator according to FIG. 1 on the '-ether hand
• FIGS. 3A-C are respective sectional views of a laboratory arrangement according to the invention during different stages of partially fluidizing a bed of solid particles, with parts of the arrangement being partially broken away
• FIG. 4 is a diagram that shows the mass flow of solid particles from an arrangement according to FIG. 3 as a function of the time at varying inlet flows;
• FIG. 1 is a schematic illustration of a known aerosol generator
• FIG. 2 is a diagram illustrating fluid pressure drop on the one hand and the bed porosity and volume as a function of the fluid flow rate during fluidizing of a bed of solid particles with the aid of an aerosol generator according to FIG. 1 on the '-ether hand
• FIG. 5 is a part sectional view of an arrangement corresponding to Fig. 3, where the vehicle fluid inlet to the enclosure opens out at out at a level beneath the upper side of the bed of solid particles; and
• FIG. 6 illustrates schematically an inventive aerosol generator which includes a system for controlling or regulating the exiting aerosol flow.
• FIG. 3A Shown in FIG. 3A is an enclosure in the form of an E-flask 10 which is closed with a stopper 12 through which there extends an inlet conduit 16 that includes a pair of inlet pipes which are connected commonly to a source of pressurised fluid, in this case air, via lines external of the flask 10, and an outlet conduit 18 in the form of an angled pipe through which aerosol is discharged from the enclosure.
• the flask 10 is filled partially with a solid particle material, which forms a bed B on the bottom of the flask.
• the pressurised fluid hereinafter referred to alternately as the vehicle fluid as a result of its particle transporting ability, is introduced into the enclosure through the ends of the inlet pipes at a level LA above the bed B, although in certain instances, e.g. for fluidizing a bed of agglomerated material, the fluid may alternatively be introduced at a level beneath the level LT of the upper surface of the bed, as illtietrated in FIG. 5.
• the fluid causes no motion in the particles in the bed B.
• the energy supplied is less than the lowest energy required to fluidize particles in the illustrated system, the vehicle fluid will pass through the enclosure without affecting the bed of solid particles.
• the whole of the bed of solid particles can be fluidized instantaneously, wherewith the system in this respect is equivalent to the aforedescribed known system.
• the bed will be fluidized only partially at each other energy level between these two points .
• the concentration of the solid phase is constant in the vehicle fluid during the process, as is also the mass flow of solid particles in the outfeed qo .
• the energy of the vehicle *luid is no longer used to bring particles to a fluidized state, when the last particle in the bed of solid particles has been fluidized.
• the mass flow rate increases momentarily and then ceases as a result of the reduction in the concentration of solid particles in the primary aerosol.
• Total energy limited fluidization energy + transport energy.
• the aforedescribed system can be considered as being analogous with a liquid-vapour system in a closed vessel.
• the partial pressure of the vapour above the liquid phase in a closed system is a function solely of temperature. Should the concentration (partial pressure) of the gas phase decrease in some way, the molecules will leave the liquid phase from its upper surface and keep the partial pressure constant if the temperature is constant.
• Aerosol generators can be formed for different purposes, by varying the distribution of the totaV energy of a vehicle fluid, e.g. by varying the flow rate in different ways, including the choice of outflow nozzles of different sizes and shapes and different nozzle distances from the bed.
• the aforedescribed laboratory arrangement was tested by charging an aerosol generator according to FIG. 3 with 0.24 kg of A1 2 0 3 in powder form.
• the vessel 10 was emptied in 100 min., corresponding to a particle mass flow qs of slightly more than 3.33 ' 10 "5 kg/s (2 g/min.).
• the concave surface' (c.f. FIG. 3B) of the bed B was formed at the beginning of the process and causes minimum resistance to fluid flow.
• the mass velocity increased significantly (c.f. FIG. 4) during this period, which never exceeded 5 min. (typically about 2.5 min.).
• the described aerosol generator based on restricted fluidization exhibited calibration times within two seconds (the time required to achieve 99% of the nominal mass flow after changing the flow rate of the vehicle fluid). This enables the aerosol generator to be regulated very easily, by restoring regulation via sensing with the aid of flow rate sensing or weighing.
• FIG. 6 is a schematic illustration of an inventive aerosol generator provided with a regulating system which is constructed to control the exiting aerosol flow qo in a relatively simple fashion. Similar to that described with reference to FIG. 2 above, a bed B of solid particle material is provided in the enclosure 10. This material is to be fluidized with the aid of a vehicle fluid to form an aerosol A which is transported by the fluid to a consumer point (not shown) such as a mixing or packaging station. Many other applications are possible, however.
• a flow regulated device in accordance with the invention can be used to meter a predetermined quantity of airborne particles into a ventilation system with a high degree of accuracy, to enable the particle concentration to be later measured at different measuring points in the system and therewith obtain information relating to the flow through the system and therewith evaluate the efficiency and effectiveness of the system.
• the vehicle fluid e.g. air
• the vehicle fluid is fed into the enclosure 10 by means of a compressor 14 having a variable, adjustable displacement.
• the flow of vehicle fluid may, however, be adjusted via other means (not shown), such as a pressure limiting valve.
• the vehicle fluid is introduced into the enclosure 10 in the earlier described manner at the flow rate qi, via a plurality of inlet openings in the enclosure 10 and comes into contact with the bed B, where the downwardly acting vehicle fluid flow is reflected at the surface of the solid bed B and fluidizes particles at this surface, these particles being entrained by the reflected flow and form the fluidized part of a partially fluidized bed, or form an aerosol A above the bed.
• the aerosol A is discharged through the outlet line 18 for transportation to said consumer point.
• the outlet line 18 incorporates a sensor 20 which senses the outflow qo.
• the sensor 20 used to achieve desired adjustment of the outflow may be any type of flow sensor
• the sensor 20 of the illustrated embodiment is an optical reflection sensor which continuously delivers a signal a in accordance with the percentage of light that is reflected from particles in the aerosol flow.
• the signal a is a measurement of the quantity of particles that pass a section of the line 18 at each point in time.
• the signal a is then compared with a preset control value or reference value r in a comparator 22, to form a difference value therebetween.
• the difference value is then delivered to an appropriate converter or amplifier 24, such as a PID regulator, from which a signal is- sent for adjusting displacement of the compressor 14.
• the flow of fluidizing fluid may alternatively be obtained by a fan mounted inside the enclosure.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
• Glanulating (AREA)
• Agricultural Chemicals And Associated Chemicals (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=20404010

Family Applications (1)

Country Status (4)

Family Cites Families (2)

• 1996
  • 1996-09-24 SE SE9603488A patent/SE507132C2/sv not_active IP Right Cessation
• 1997
  • 1997-09-19 WO PCT/SE1997/001581 patent/WO1998013134A1/en not_active Application Discontinuation
  • 1997-09-19 EP EP97943258A patent/EP0942779A1/en not_active Withdrawn
  • 1997-09-19 AU AU44774/97A patent/AU4477497A/en not_active Abandoned

Non-Patent Citations (1)

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