WO1994007608A1

WO1994007608A1 - Improved rotary disk atomizer

Info

Publication number: WO1994007608A1
Application number: PCT/CA1993/000404
Authority: WO
Inventors: Claude Bazergui; David Berry
Original assignee: Barr & Murphy (Canada) Ltd.
Priority date: 1992-09-30
Filing date: 1993-09-30
Publication date: 1994-04-14

Abstract

The disk air purge draws air from inside a sealed atomizer housing (14) to cool the inside against heat entering from outside the housing (14). The disk air purge is located below a product feed plate (18) for heating the feed plate (18) and the disk, when used with congealable product. The housing (14) is a split housing whose lower portion (42) may be changed with the atomizer disk (10) for different disk diameters while allowing the bottom surface of the lower portion (42) to match the disk (10). Air passing through the housing to the disk air purge keeps the lower part (42) of the housing from reaching a burning temperature of the product, so that when atomized product contacts the housing before drying, it dries on instead of burning on the housing.

Description

IMPROVED ROTARY DISK ATOMIZER Field of the Invention

The present invention relates to a rotary disk atomizer having an improved disk air purge system. The invention also relates to a rotary disk atomizer having a split housing for facilitating a change in disk diameter. Background of the Invention

Rotary disk atomizers are used in industrial drying processes in which liquid solutions are dried or congealed into powders. In the case of dryers, the liquid is poured into the atomizer disk which is rotated at high speed. The liquid is sprayed through nozzles in the atomizer disk inside a drying chamber where hot air is circulated to mix with and dry the mist of liquid. The dried product is then blown out of the chamber and removed. In the case of a congealer, the liquid is similarly atomized at a temperature above the congealing point and then in the chamber the liquid is allowed to cool and congeal. The congealed product is also blown out of the chamber and removed. The mounting of the atomizer disk in the chamber is done by means of a housing in which the atomizer disk shaft is rotatably mounted by means of bearings. The housing serves largely to place the atomizer disk at a sufficient distance from the top of the chamber, such that the sprayed liquid does not contact the chamber's upper wall. A minimal space between the disk and the housing is provided so that no dried or congealed product flows back into the annular feed opening in the disk. It is known to pressurize this minimal space with a purge gas in order to prevent more effectively product flow back, which also can cause friction between the housing and the disk. For example, a disk steam purge is described in US patent 4,082,221 to Brummelhuis.

The physical parameters which affect atomization are disk speed, disk design and liquid flow rate. Disk speed is by far the easiest and most efficient parameter to control. However, when an electric drive motor is used and no speed reduction means are available, as in the case of a direct drive motor system, the disk speed is best kept at a maximum speed of the motor for the greatest horsepower output of the motor.

Atomizer performance can also be adversely affected when liquid to be congealed congeals prematurely in the atomizer disk or feed system in the housing. Summary of the Invention

It is therefore the object of the invention to provide an improved rotary disk atomizer which is able to resolve the above mentioned drawbacks.

According to the invention there is provided a rotary disk atomizer for spray drying a liquid comprising a sealed housing having an inside and a gas supply inlet, a high speed electric motor mounted in the inside of the housing, the motor having an output shaft, a surrounding fluid cooling jacket, and bearings cooled and lubricated by an oil and air system, a rotary atomizer disk mounted on the shaft outside the housing in close proximity to a bottom surface of the housing, the disk having an annular opening into which the liquid is injected, and an annular disk air purge distribution plate for injecting the purge gas from the inside circumferentially equally into the disk, whereby instruments in the inside are cooled by the gas against heat entering the housing from a surrounding drying chamber.

The invention also provides a rotary disk atomizer for spray congealing or drying a liquid comprising a housing, a drive shaft, bearing means for rotatably holding the shaft in the housing, a rotary atomizer disk mounted on the shaft outside the housing in close proximity to a bottom surface of the housing, the disk having an annular opening into which the liquid is injected, an annular feed distribution plate for receiving the liquid and evenly distributing the liquid into the annular opening, a feed conduit for conducting the liquid through the housing to the feed distribution plate, a feed conduit heating jacket surrounding a substantial length of the feed conduit for preheating the feed conduit using a heated gas, and an annular disk air purge plate located below an underside of the feed distribution plate, the disk air purge plate receiving the heated gas exiting the jacket and injecting the gas into the disk, whereby the feed distribution plate and disk are heated by the heated purge gas.

The invention further provides a rotary disk atomizer for spray congealing or drying a liquid comprising a housing having an upper portion and a lower portion, a drive shaft, bearing means for rotatably holding the shaft in the housing, a rotary atomizer disk mounted on the shaft outside the housing in close proximity to a bottom surface of the lower portion, the disk having an annular opening into which the liquid is injected, and means for releasably interconnecting the lower portion to the upper portion, the bottom surface being circular and having substantially a same diameter as a diameter of the disk, whereby both the disk and the lower portion may be exchanged such that the diameter is different for imparting different atomization velocities at a same rotational speed of the shaft. Brief Description of the Drawings

The invention will be better understood by way of the following non limiting detailed description of a preferred embodiment with reference to the appended drawings in which: Fig. 1 is a partially sectional side view of the preferred embodiment arranged to operate as a dryer, in which the left hand side illustrates a larger disk and lower portion than the right hand side;

Fig. 2 is a detailed view of the lower part of Fig. 1; Fig. 3 is a partially sectional side view of the preferred embodiment arranged to operate as a congealer; and Fig. 4 is a detailed view of the lower part of Fig. 3. Detailed Description of the Preferred Embodiment As shown in Fig. 1, the rotary disk atomizer comprises an atomizer disk (10) mounted on a drive shaft (12) which is the shaft of electric motor (16). The motor (16) is mounted inside housing (14) which is mounted to upper wall (38) of a dryer or congealer. The motor (16) is water cooled by cooling jacket (17) which is supplied with cooling water. The shaft (12) is rotatably mounted in housing (14) by a plurality of bearings (15), which are cooled and lubricated by an oil and air system (not shown). A liquid feed plate (18) is attached to the bottom of the motor (16) to supply feed into the annular opening (11) of disk (10). As disk (10) is rotated at high speeds, feed is injected into the disk and is sprayed (atomized) into the drying or congealing chamber.

Below the feed plate (18), a disk air purge plate (20) is provided which is used to evenly distribute a purge gas (air) into the annular opening (11) so that a positive pressure is created in the narrow gap between disk (10) and the bottom surface (46) of the housing (14). When disk (10) is rotated a high speeds (5,000 to 25,000 r.p.m.), air is forced or pumped out by the acceleration and a negative pressure at the centre of the disk (10) is created. This negative pressure would draw air in through the shaft and even through the narrow gap, were it not for the positive pressure supplied by the purge gas. Without this positive pressure, atomized liquid could be sucked into this gap and could reduce performance or require maintenance. Holes (48) are also provided for supplying additional purge gas to the gap. The holes (48) may be about 4 to 12 in number. The purge gas enters the housing (14) through inlet (26). In the case of a dryer as shown in Figs. 1 and 2, the purge gas is fed into the housing inside and is circulated into plate (20). As shown in Figs. 1 and 2, hot air inlet tube (22) is capped by cap (35). Since the outside of the housing (14) is very hot, this circulation prevents the heat entering the housing from building up. Heat generated by motor (16) is removed by water cooling jacket (17). In this configuration, instruments and materials inside the housing (14) are spared from being exposed to the high temperatures of the drying chamber, since the purge gas circulation maintains a temperature which is closer to ambient.

The circulation of the cool purge gas against the lower part of housing (14) also prevents it from reaching a temperature at which undried, atomized feed would burn onto this lower part. Instead, product which is blown onto the housing (14) while still undried will stick and dry onto the housing. Once dry, the product will either be blown off housing (14) or stay on housing (14) as a solid. In the case of a congealer, as shown in Figs. 3 and 4, the cap (35) is removed from tube (22), and hoses (24) and (34) are used to direct hot air from inlet (26) through feed tube heating jacket (28) to tube (22). In addition, blocking ring (44) is placed between the feed plate (18) and the annular opening of plate (20) so that purge gas must enter through tube (22). The heated purge gas serves many functions. First it heats the feed tube (36) so that the congealable liquid does not congeal in the feed tube (36). It then heats the feed plate (18) since gas circulating in the plate (20) contacts the underside of plate (18). And finally, the purge gas will heat the atomizer disk (10) and keep a positive pressure in the gap between disk (10) and the bottom surface (46). In the figures, disk (10) is shown schematically as having a different radius on each side. The disk (10) is to be of one diameter, and can be changed along with a lower portion (42) of the housing (14) such that the bottom surface (46) remains approximately the same size as the disk (10). This permits a change of disk diameters without sacrificing the design feature that the disk (10) matches the bottom surface (46) and without replacing the entire housing (14). The different diameter disk (10) allows for different disk peripheral speeds at the same rotational speed of the shaft (12). This is particularly advantageous in the preferred embodiment in which the motor (16) is a direct drive motor which has a maximum power output at its maximum rotational speed. The disk speed is a parameter which affects atomization and thus the quality (fineness) of the dried or congealed product.

As shown, means (40) for releasably interconnecting the lower portion (42) to an upper portion (41) of housing (14) are provided, which comprise an annular tongue and groove fitting and a plurality of locking screws (not shown). On the left hand side of the figures, the larger disk (10) is shown and the portions (41) and (42) have a continuous conical shape, but on the right hand side, a smaller disk (10) is shown, and a tapering in the lower portion (42) is shown. Means (40) can also comprise a means for fastening lower portion (42) to the feed plate (18) along with the shown tongue and groove connection or any other suitable fitting between the portions (41) and (42).

Although the invention has been described above with reference to the preferred embodiment, it is to be understood that many variants are possible according to the scope of the invention as defined in the appended claims.

Claims

C L A I M S

1. A rotary disk atomizer for spray drying a liquid comprising: a sealed housing having an inside and a gas supply inlet; a high speed electric motor mounted in said inside, said motor having an output shaft, a surrounding water cooling jacket, and bearings cooled and lubricated by an oil and air system; a rotary atomizer disk mounted on said shaft outside said housing in close proximity to a bottom surface of said housing, said disk having an annular opening into which said liquid is injected; and an annular disk air purge distribution plate for injecting said gas from said inside circumferentially equally into said disk, whereby instruments in said inside are cooled by said gas against heat entering said housing from a surrounding drying chamber.

2. A rotary disk atomizer for spray congealing or drying a liquid comprising: a housing; a drive shaft; bearing means for rotatably holding said shaft in said housing; a rotary atomizer disk mounted on said shaft outside said housing in close proximity to a bottom surface of said housing, said disk having an annular opening into which said liquid is injected; an annular feed distribution plate for receiving said liquid and evenly distributing said liquid into said annular opening; a feed conduit for conducting said liquid through said housing to said feed distribution plate; a feed conduit heating jacket surrounding a substantial length of said feed conduit for heating said feed conduit using a heated gas; and an annular disk air purge plate located below an underside of said feed distribution plate, said disk air purge plate receiving said heated gas exiting said jacket and injecting said gas into said disk, whereby said feed distribution plate and said disk are heated by said heated gas.

3. A rotary disk atomizer for spray congealing or drying a liquid comprising: a housing having an upper portion and a lower portion; a drive shaft; bearing means for rotatably holding said shaft in said housing; a rotary atomizer disk mounted on said shaft outside said housing in close proximity to a bottom surface of said lower portion, said disk having an annular opening into which said liquid is injected; and means for releasably interconnecting said lower portion to said upper portion, said bottom surface being circular and having substantially a same diameter as a diameter of said disk, whereby both said disk and said lower portion may be exchanged such that said diameter is different for imparting different atomization velocities at a same rotational speed of said shaft.

4. Rotary disk atomizer as claimed in claim 3, further comprising: an annular disk air purge distribution plate for injecting disk purge gas circumferentially equally into said disk, whereby atomized liquid is prevented from entering said space.

5. Rotary disk atomizer as claimed in claim 4, further comprising an annular feed distribution plate for receiving said liquid and evenly distributing said liquid into said annular opening, and said disk air purge plate forming part of said lower portion.

6. Rotary disk atomizer as claimed in claim 4, wherein said housing is sealed and is provided with a purge gas inlet, and said disk purge gas is fed through said housing to said air purge distribution plate, whereby instruments in said housing are cooled by said gas against heat entering said housing from a surrounding drying chamber.

7. Rotary disk atomizer as claimed in claim 6, further comprising a high speed electric motor mounted in said inside, said motor including said drive shaft, a surrounding water cooling jacket, and bearings cooled and lubricated by an oil and air system.

8. Rotary disk atomizer as claimed in claim 4, further comprising: an annular feed distribution plate for receiving said liquid and evenly distributing said liquid into said annular opening; a feed conduit for conducting said liquid through said housing to said feed distribution plate; a feed conduit heating jacket surrounding a substantial length of said feed conduit for heating said feed conduit using heated disk purge gas, wherein said air purge distribution plate is located below said feed distribution plate and receives said heated disk purge gas exiting said jacket, whereby said feed distribution plate and said disk are heated by said heated disk purge gas.

9. Rotary disk atomizer as claimed in claim 8, further comprising a removable blocking ring placeable between said feed plate and said disk air purge plate, wherein: said housing is sealed and is provided with a purge gas inlet; said feed distribution plate includes a disk purge gas conduit for conducting purge gas from said jacket to said disk air purge plate inside said blocking ring; and said disk air purge plate forms part of said lower portion, whereby when said atomizer operates as a congealer, the blocking ring is put in place and preheated disk purge gas is fed through said jacket through said disk purge gas conduit, and when the atomizer operates as a dryer, the blocking ring is removed and said disk purge gas is supplied to said inlet, passes through said housing to said disk air purge plate for cooling of instruments in said housing against heat entering said housing from a surrounding drying chamber.

10. Rotary disk atomizer as claimed in claim 9, wherein said disk purge gas conduit comprises a fixed tube connected to said feed plate and a first hose connectable between said fixed tube and one end of said jacket, another end of said jacket being connectable by a second hose to said purge gas inlet, whereby when said first and said second hoses are connected, preheated purge gas can be conducted through said inlet to said jacket to said disk air purge plate, and when said first and said second hoses are disconnected, ambient disk purge gas can be conducted through said inlet to said housing to said disk air purge plate.

11. Rotary disk atomizer as claimed in claim 3, wherein said housing is sealed and is provided with a purge gas inlet, and said purge gas is fed through said housing to said rotary atomizer disk, a lower part of said housing proximate said disk being uninsulated and exposed to said purge gas as said purge gas passes through to said disk in order to maintain said lower part of said housing at a temperature lower than an ambient temperature of a surrounding drying chamber, whereby when said liquid is atomized by said disk and is blown before drying onto said lower part, said liquid dries on said lower part without being burned as a result of the exposure to said ambient temperature.

12. Rotary disk atomizer as claimed in claim 9, wherein said housing is sealed and is provided with a purge gas inlet, and said purge gas is fed through said housing to said disk air purge plate, a lower part of said housing proximate said disk being uninsulated and exposed to said purge gas as said purge gas passes through to said disk air purge plate in order to maintain said lower part of said housing at a temperature lower than an ambient temperature of a surrounding drying chamber, whereby when said liquid is atomized by said disk and is blown before drying onto said lower part, said liquid dries on said lower part without being burned as a result of the exposure to said ambient temperature.

13. Rotary disk atomizer as claimed in claim 4, wherein said disk air purge distribution plate is integral with said bottom surface and includes a plurality of hole means for injecting said purge gas into a space between said bottom surface and said disk, said hole means being located between a periphery of said disk and said annular opening and being spaced at regular intervals to provide for an even flow of said purge gas into said space.