Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten... – By vibration or agitation
Patent
1995-08-10
1997-05-13
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Formation of solid particulate material directly from molten...
By vibration or agitation
264 14, 425 6, 425 10, 159 44, 159 481, B29B 910, B01D 118, B01D 120
Patent
active
056289375
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the production of solid particles by a process involving atomisation of a liquid formulation and at least partial change of phase of the liquid droplets while in flight.
It is desirable for a number of industrial and other (eg. pharmaceutical) applications to produce particulate materials with a narrow size distribution range.
Spray dryers for the industrial scale production of solid particulate materials from liquid formulations are well known and typically comprise a tower into which the liquid formulation is sprayed by an atomiser with hot gas being introduced into the tower for contact with the spray. Various forms of atomiser are in common use, such as two-fluid pneumatic nozzles for small drops, single-fluid nozzles and high speed rotary disc atomisers.
However, existing industrial scale spray dryers do not readily lend themselves to applications in which the size of the particles can be accurately controlled, particularly in applications requiring narrow size distributions with an SMD (Sauter Mean Diameter) less than 1 mm, and especially less than 500 microns. Also, existing industrial scale spray dryers tend to produce substantial quantities of fines which are entrained by, and have to be subsequently separated from, the gas used to effect drying. Separation equipment for the purpose of gas clean-up constitutes a significant capital cost in building a spray drier plant. There is consequently a need for apparatus and a process capable of producing closely controlled particle sizes with minimal fines production.
It is known from Berglund and Liu (Environmental Science & Technology, Vol 7, No. 2, February 1973, Pages 146-153) to generate aerosols comprising closely monodisperse particle sizes. Droplets are formed from a single liquid jet by feeding liquid under pressure through a single orifice in a disc and mechanically disturbing the disc at a constant frequency by means of an electrically driven piezoelectrical ceramic so that the jet breaks up into uniform droplets. The droplets so formed are then passed through a further orifice together with a turbulent air jet which serves to disperse the stream of droplets into a conical shape. The resulting aerosol is diluted and transported by an air flow passing through a vertical plastic tube and the air may also serve to dry the droplets when the latter comprise a non-volatile solute in a volatile solvent by evaporating the solvent. The aerosol generator disclosed in the Berglund and Liu reference is intended to produce monodisperse aerosols for use in aerosol research, calibration of aerosol sampling and measurement instruments, testing particulate control devices such as cyclones, filters and scrubbers, and for studying the effects of particulate air pollutants.
The use of a sonic device to induce cyclic disturbances on the surfaces of liquid jets formed by a multiple orifice nozzle for the production of a monodisperse spray is disclosed in an article by L F Bouse in Transactions of the ASAE--1975, Pages 618-622.
GB-A-1454597 discloses a method of prilling a liquid in which a liquid is passed under pressure through a flat perforated plate and is subjected to periodic pressure fluctuations in the direction of flow. The perforations are shown as being oriented at different angles relative to one another for reasons that are not disclosed. The resulting liquid droplets solidify to form grains having average diameters of the order of 1200 microns or greater.
EP-A-86704 discloses a process for the production of perfectly spherical and porous granules by dispensing from a plurality of needles liquid droplets which fall on to a moving bed of powdered material, the droplet size and shape being controlled by producing a laminar air flow concentric with each droplet-forming needle so that the droplets emitted individually from each needle is skimmed by the laminar air flow.
The present invention seeks to provide an improved process for the production of solid particles with a controlled narrow size distribution, particularly industrial s
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Environmental Science & Technology, vol. 7, No. 2, pp. 146-153 Feb. 1973 Berglund and Liu.
Transactions of the ASAE, pp. 618-622 Feb. 1975 L. F. Bouse.
Ind. Eng. Chem. Res. vol. 31, No. 3, pp. 959-967 Feb. 1992 Paul A. Haas.
Antonini Alejandro M.
Fairclough Anthony R. N.
Lipscombe Lynn W.
Munro Robert J.
Oliver Raymond
Imperial Chemical Industries plc
Theisen Mary Lynn
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