IE47259B1

IE47259B1 - Improved spray dryer

Info

Publication number: IE47259B1
Application number: IE1745/78A
Authority: IE
Original assignee: Henningsen Foods
Priority date: 1977-08-29
Filing date: 1978-08-29
Publication date: 1984-02-08
Also published as: DE2836712A1; JPS5445678A; SE449397B; CA1133693A; NZ188155A; GB2003042A; ES472901A1; NL191109C; NL7808615A; LU80164A1; NL191109B; AT365048B; FR2401682B1; GB2003042B; JPS62721B2; BE870001A; SE7809034L; ATA623778A; FR2401682A1; IE781745L

Abstract

In a spray drier for drying heat sensitive food products the product being dried is sprayed into the drying chamber by atomisers 12 and mixed therein with hot air supplied by nozzles 32, 34, the nozzles 34 being of smaller cross-section than the nozzles 32. The dried droplets or powder may be removed by an endless conveyor. The air may be exhausted from the drying chamber through filter bags.

Description

The present invention relates to improved method and means for spray drying and, more particularly, to an improved method and means for drying products such as heat sensitive food products under sanitary conditions.

Accordingly, the present invention provides an air distributor for positioning 5 in a hot air dryer between an air supply duct and a drying chamber for distributing air into said drying chamber, comprising a plate member; a plurality of elongated first tubular nozzles mounted in spaced positions in said plate member·, a plurality of relatively smaller diameter second tubular nozzles mounted in said plate member with generally uniform spacing; said first and second nozzles having their axes positioned generally perpendicular to said and plate member;/ means for mounting liquid atomizers at said first nozzles, the air exit ends of said second nozzles being flared for causing the air flowing from said second nozzles to flare.

According to a further aspect, the present invention provides a hot air dryer and comprising an air supply duct; a drying chamber/ an air distributor positioned between the duct and the drying chamber for distributing air into said drying - 2 47259 chamber; said distributor comprising the combination of a plate member; a plurality of elongated first tubular nozzles mounted in spaced positions in said plate member; a plurality of relatively smaller diameter second tubular nozzles mounted in said plate member with generally uniform spacing to surround the first nozzles; said first and second nozzles having their axes positioned and generally perpendicularly to said plate member;/ liquid atomisers mounted at said first nozzles, the air exit ends of said first and second nozzles being flared for causing the air flowing from said nozzles to flare.

In order to promote a fuller understanding of the above, and other aspects of 10 the present invention, an embodiment will now be described by way of example only, with reference to the accompanying drawings in which: Figure 1 is a flow diagram of the operation of the improved spray drying method and means; Figure 2 is a front elevational view of a preferred embodiment of the spray 15 drying means in accordance with the present invention; Figure 3 is a top plan view of the spray dryer of Figure 2; Figure 4 is a vertical sectional view of the air distributor taken along line 4-4 on Figure 2; Figure 5 is a vertical sectional view of Figure 4 taken along line 5-5 on 20 Figure 4; Figure 6 is an enlarged fragmentary perspective view of the air distributor; Figure 7 is a vertical sectional view of an air distributor taken along line 7-7 on Figure 6; Figure 8 is a perspective view illustrating the product removing drag means; and - 3 47259 Figure 9 is a horizontal sectional view taken along line 9-9 on Figure 8.

The improved air dryer and its method of operation will first be described generally with particular reference to Figures 1, 2 and 3. While the spray dryer 1, as described below, is conventionally installed in a suitable plant, it is preferred that the air being used in the drying operation be supplied from and returned to the outdoors. For this purpose, the spray dryer 1 has an elongated air inlet 2 for the drying air supply which extends outside of the dryer building 3. Similarly, an elongated air outlet 4 is connected by suitable exhaust piping to the exit end of the spray dryer 1. The dryer 1 includes a heater 5 to raise the temperature of the air from inlet 2, under suitable thermostatic control to the desired drying temperature. Air is fed to and through the heater 5 by means of an inlet air blower 6 coupled by suitable ducting 7 to the air heater 5. The air inlet 2 includes a filter housing 8 containing a roughing filter and a high efficiency absolute filter of the type commercially used in air flow filtering operations which will remove as much as 99.97% of all contaminants from the incoming air.

The air heater 5 may use heated coils 9 (Figure 3) or it may employ direct or indirect heating furnace 5 employing suitable fuels such as oil or gas.

The heated air is fed downwardly to an air flow duct 13 which communicates through an air distributor 10 to the drying chamber 11 of the dryer 1. A number of atomizing nozzles 12 are mounted on the air distributor 10 which are coupled through an adjustable fluid feed system 14 to a suitable source 23 of the liquid being dried. The construction and operation of the air distribution plate 10 and the related atomizing nozzles 12 will be described in greater detail below.

The drying chamber 11 terminates in a discharge end 15 which completes the removal of the dried or powdered product from the air flow permitting the - 4 4725S separated air to pass upwardly to the air outlet 4. The dried product drops to the floor of the drying chamber 11 and is moved in the direction of air flow by a drag system 16 to the bottom of the discharge chamber 15. A horizontal auger 17 carries the dried product to a removal auger 18 which feeds the dried powder to a vibrating sifter 19.

A final removal of any remaining dried product in the air stream is done at an outlet filter 20. A preferred filter is a pulse-type bag filter. These commercial available filters position a number of filter bags 21 at the air outlet. The air passes through the bags 21 and upwardly through the air outlet 4. Any dried powder which has not already dropped to the drying chamber 11 floor 22 accumulates on the outer surfaces of the bags 21.

This powder is removed from the bags 21 periodically as air is injected from a separate air source into the inside or filtered side of the bags 21 causing the bags 21 to expand. This counter air flow and the bag 21 expansion knocks any accumulated powder from the air bags 21 onto the floor 22 of the discharge end 15 of the drying chamber 11 where it is removed by the above described drag system 16 and the auger 17.

The drag system 16 has a pair of stainless steel sanitary chains 24 mounted on end sprockets 25 at the corners of the drying chamber bottom 22. The chains 24 are driven by a suitable electric drive system 26 to move elongated powder dragging flights 27 along the chamber bottom 22 to carry the dried powder to the exit auger 17. The flights 27 are metal such as aluminium or plastics. Support rods 28 are positioned to engage low friction plastics flight support pads 29 as the flights 27 are returned to the start of their powder moving run.

The air distributor 1U provides an efficient mixing of the atomised products spray with the heated drying air. An air flow is required which provides a maximum and uniform exposure of the atomised product particles to the heated drying air. The desired exposure results in a high efficiency drying action - 5 472SS whereby relatively lower drying temperatures are utilised to protect heat sensitive food products or other products from heat damage.

The air distributor 10 in accordance with the present invention, covers substantially the entire air entry end of the drying chamber 11 and directs a forward flow of air through the drying chamber 11 and generally parallel to the chamber 11 side walls 30, ceiling 31, and floor 22. A number of product atomising nozzles 12 are mounted on the air distributor 10. They are coupled through the supply system 14 to the source of liquid products 23. Each of the atomising nozzles 12 is mounted downstream from the air distributor 10 beyond a relatively large orifice or air nozzle 32. The air nozzles 32 pass air to and past the atomising nozzles 12 at a relatively high velocity which picks up the atomised particles from the atomising nozzles 12 and begins and completes a major portion of the particle drying.

The air distributor 10 also includes a large number of generally uniformly spaced relatively smaller air nozzles 34 which pass a lower velocity of air in air streams surrounding the above described higher velocity air streams from the larger nozzles 32. These lower velocity air streams suppress a back flow or back lash of higher velocity air in zones adjacent to the air distributor 10 and eventually blend further downstream with higher velocity air for drying particles in the final stages of the particle drying action. The overall and combined action of the high and low velocity streams provides for a uniform drying of the atomised product particles with the relatively long drying period permitting minimal air temperatures to be used for the air used in the drying process. For example, in a space starting at a plane parallel to and about one foot downstream from the air distributor 10 to a second parallel plane further downstream, the air flow through and immediately surrounding the spray from atomisers 12 is a relatively high velocity because of the larger nozzle 32 air flow in which the spray is first positioned. Surrounding the high velocity air from the nozzles 32 is the lower velocity air from nozzles 34 - 6 47259 which eventually blends with the high velocity air as both air flows move downstream. The higher velocity air picks up the spray and does the major portion of the drying. The lower velocity air suppresses back lash of the higher velocity air and of the spray and eventually blends in with the higher velocity air and spray for the final stages of drying the atomised particles. This results in the uniform drying of the particles and allows sufficient drying time for the relatively low drying temperatures.

The controlled heated air drying as described above also has been found to provide for a relatively high product density so that the dried product occupies a minimum space. Improvements in density, for example, to provide a specific gravity of about .50 as contrasted with dried products from other spray dryers of from .30 to .45 have been realised. The increased density of the product reduces the package size for the processed product. This higher density is believed to result from the reduced tendency of the atomised particles to agglomerate before drying. This, in turn, results from the improved air flow control and the elimination of a back flow or back lash of the partially dried particles which permits particles to come together and to form into lumps of lower overall density.

The illustrated embodiment of an air distributor plate 10 utilises four spray nozzles 12 where the smaller air nozzles 34 are about 2 (50 mm) in diameter and the large nozzles 32 are about 12 (300 mm) in diameter, i.e. some six times the size of the smaller nozzles. The small nozzles are approximately 6“ (150 mm) in length and the larger nozzles 32 are approximately two feet long, i.e. some four times the length of the smaller nozzles. This array of large and small nozzles not only controls air flow near and beyond the atomising nozzles, but it also provides for a heated air flow parallel to the drying chamber 11, walls 30, roof 31, and floor 22. An air flow is present a foot or two downstream from the larger nozzles 32 which may be as much as ten - 7 47259 times the velocity of the air flow downstream from the smaller air nozzles 34.

At a distance from the air distributor 10, as for example, twelve feet downstream, the air flow through the chamber 11 cross-section becomes relatively uniform throughout the cross-section as a result of a blending process of the drying air.

The above described air control is improved by shaping of the individual air nozzles. As illustrated in Figures 6 and 7, the individual air nozzles 32 and 34 have rounded or flared outlets 37 and 38 which act both to prevent any build-up of dried product at the outlets and which also provide for a desirable flaring of the air flow from the individual air nozzles 32 and 34.

In the above described nozzles 32 and 34, a satisfactory flare is provided by rounded outlets 37 and 38 having a radius of approximately 1/4 (6 mm). The individual nozzles 32 and 34 are mounted in spaced front and rear plates 35 and 36 to which the nozzles 32 and 34 are welded or otherwise fastened.

A typical air distributor, such as the above described distributor 10 having four nozzles 12 and four large air nozzles 32, will have about 300 of the small air nozzles 34 uniformly spaced over the distributor 10. The upstream or air entry portions of the individual nozzles 32 and 34 are conveniently welded or otherwise fastened to outwardly rounded aperture edges 39 on the rear plate 36.

The relative amounts of air flow through the larger and smaller nozzles 32 and 34 may be further adjusted by using added apertured plates 40 on the smaller nozzles 34. The number and size of apertures in the optional plates 40 is set to provide a desired air flow reduction through the nozzles 34. it will be seen that an improved air dryer is provided which is particularly useful for drying powdered products including food products where a minimal - 8 47259 drying temperature is desirable. The improved dryer operation including the improved control of the drying air flow also provides for a finished powder product of increased density to provide a finished product of reduced volume for more efficient handling and packaging. The dryer has a minimal size for the amount of product produced.

Claims

1. , An air distributor for positioning in a hot air dryer between an air supply duct and a drying chamber for distributing air into said drying chamber comprising: a plate member; a plurality of elongated first tubular nozzles member 10 mounted in spaced positions in said plate/; a plurality of relatively smaller second tubular nozzles mounted in said plate member with generally uniform spacing and surrounding said first nozzles, said first and second nozzles having their axes positioned generally perpendicularly to said plate member·, and means for mounting liquid atomisers at said first nozzles, the air exit 15 ends of said second nozzles being flared for causing the air flowing from said second nozzles to flare.

2. The distributor as claimed in Claim 1 which further comprises the air exit ends of said first nozzles being flared for causing the air flowing from said first nozzles to flare. 2U

3. The distributor as claimed in any one of the preceding claims in which the diameter of said first nozzles is approximately six times as great as the diameter of said second nozzles.

4. The distributor as claimed in any one of the preceding claims in which said first nozzles are substantially longer than said second nozzles. - 9 47359 and

5. A hot air dryer comprising an air supply duct; a drying chambei/; an air distributor positioned between the duct and the drying chamber for distributing air into said drying chamber; said distributor comprising the combination of a plate member; a plurality of elongated first tubular nozzles mounted in spaced positions in said plate member; a plurality of relatively smaller diameter second tubular nozzles mounted in said plate member with generally uniform spacing to surround the first nozzles; said first and second nozzles having and their axes positioned generally perpendicularly to said plate member; /liquid atomisers mounted at their first nozzles, the air exit ends of said first and second nozzles being flared for causing the air flowing from said nozzles to flare.

6. The dryer as claimed in Claim 5 which further comprises an enclosure surrounding the duct and drying chamber, air entry means for admitting air to said duct and air outlet means for exhausting air from said drying chamber being positioned outside of said enclosure.

7. The dryer as claimed in Claim 6, in which a filter is disposed between said air entry means and said duct.

8. The dryer as claimed in Claim 6 which further comprises a pulse bag filter in said drying chamber.

9. The dryer as claimed in Claims 5, 7 or 8 which further comprises a powder drag means positioned in said drying chamber for powder removal.

10. The dryer as claimed in any one of Claims 5 through 9 in which the liquid atomisers are positioned downstream from the outlets of said first nozzles on atomiser mounting.

11. The dryer as claimed in any one of Claims 5 through 9 in which the diameter of said first nozzles is approximately six times as great as the diameter of said second nozzles. - 10 47259

12. The dryer as claimed in any one of Claims 5 through 9 in which said first nozzles are substantially longer than said second nozzles.

13. A method of spray drying liquid product comprising the steps of: passing heated drying air from an air supply duct to a drying chamber; distributing the 5 air during the said passage from the duct to the chamber into a plurality of larger flowing streams of heated air surrounded by a plurality of smaller flowing streams of heated air of relatively smaller diameter; spraying the liquid product into said larger flowing streams; and causing said larger and smaller flowing streams to flare slightly and to blend together downstream from said distribution. 10

14. The method as claimed in Claim 13 which further comprises the step of exhausting the blended air from the drying chamber through pulse bag filters.

15. The method as claimed in Claim 13 or 14 which further comprises the step of feeding the air into the duct through a filter.

16. An air distributor member for use in a hot air dryer substantially as 15 herein described with reference to the accompanying drawings.

17. A hot air dryer substantially as herein described with reference to the accompanying drawings.

18. A method of spray drying substantially as herein described with reference to the accompanying drawings.