US2891611A - Spray drying apparatus - Google Patents

Description

June' 23, 1959 c. F. FISCHER 2,391,611

SPRAY DRYING APPARATUS Filed March ll, 1955 J/ 32 INVENTOR. J2 cu/mzs fff/SCHER 3/ 5 50 BY,

x 32 ATTORNEY nited States Patent I;

, SPRAY DRYING APPARATUS Charles F. Fischer, Jersey City, NJ., assignor to Colgate- Palmolive Company, Jersey City, N.J., a corporation of Delaware Application March 11, 1955, Serial No. 493,708

4 Claims. c1. 159-4 This invention relates to apparatus for spray drying solid-containing liquids or slurries and has particular reference to apparatus adapted to prevent collision of freshly atomized wet particles with interior walls of spray drying chambers.

Spray drying apparatus usually consists of a drying chamber through which is passed a current of heated drying air into which is atomized solid-containing liquid or slurry, so that intimate contact between the drying air and the minute solid-containing particles is effected with the result that the particles are dried. Means for separating the resulting dry powder from the moisture laden air is provided either in the drying chamberitself or apart therefrom. p

The atomization of the solid-containing liquid or slurry is normally carried out at the top of the drying chamber by any of several means such as centrifugal spinner bowls or high pressure nozzles. From the atomizer, a stream of wet particles flows downwardly and outwardly, generally forming a conical orparabolic body until restricted by the interior of the drying chamber. The particular size and shape of the cone obtained under any one set of conditions is a complex function of many variables. However, as a result of their outward flow, at least some of the particles normally collide with the inner vertical walls of the drying chamber, and frequently some particles adhere thereto. This problem is especially acute at the upper part of the drying chamber where the materials striking the wall of the chamber are wet and plastic, having been subjected to a minimum of drying action. Under such conditions, deposits of solids accumulate on the interior of the chamber wall, and because of their extended exposure to high temperatures, usually char and/ or decompose. These deposits accumulate until they fall of their own weight and then the cycle is repeated.

Various means have been proposed to overcome this difficulty. Thus the diameter of the drying chamber may be enlarged or an atomizer may be employed which disperses particles within a relatively narrow angle of dispersion. However, enlarging the chamber is expensive and diminishing the angle encompassed by the cone of atomized material reduces the amount of material which a drier can process within a given period of time.

A means has now been discovered to facilitate the use of atomizers having a wide angle of dispersion in a drying chamber of moderate or relatively small diameter without experiencing substantial collision of wet particles with the wall under a wide range of operating conditions. In accordance with the present invention such improved spray drying apparatus comprises a drying chamber, defined in part by a substantially vertical wall, means for dispersing material to be dried in said chamber as a paraboloid of wet particles which, if unimpeded, would collide with said substantially vertical wall of said chember, and vertically movable means disposed within said chamber for directing a flow of gas inwardly and downwardly against the upper surface of said paraboloid to Fig. 1 is an elevation of the upper portion of a spray drying apparatus equipped with two independently vertically movable systems of air jets,

Fig. 2 is a detailed drawing, on an enlarged scale, of a portion of one of the systems of vertically movable air jets of Fig. 1, and

Fig. 3 is a plan view of the elevating drive mechanism of Fig. 2 and is taken along a line 33 of Fig. 2..

Referring now to Fig. 1 of the accompanying drawing, the illustrative spray drier comprises a drying chamber 16 defined by a cylindrical shell or wall 18. A truncated conical, cover 20 encloses the top of the cylindrical shell 18. At the apex of the cover 20 is a duct 22 leading to a supply of heated drying air (not shown). Centrally disposed near the top of the chamber is a whirling disc atomizer 26 which communicates with the exterior of the chamber by means of a conduit 28.

Secondary manifolds 31, carrying air jets 32, are mounted adjacent to the chamber wall 18. These secondary manifolds are supported by conduits 38 mounted on primary manifolds 40 which are supported by elevating struts .42 slidably mounted in stationary guide arms 46 affixed to the chamber Wall 18 or other supporting means (not shown) so as to locate the air jet system adjacent to the chamber wall 18 and just above the upper surface of the coneof wet particles 44. Afiixed to each of the struts 42 is a rack 47 which is enmeshed with a pinion gear 48. Flexible conduits50, aifixed to the main manifolds. 40 by, nipples 51 and unions 52, communicate the mainmanifolds 40 with an air supply system exterior of the chamber (not shown).

Referring now to Fig. 2 for details of a portionof the upper of the two air jet systems, the air jets 32 comprise small, hollow nozzles welded to the three secondary manifolds 31 around suitable openings for flow of gas from the manifold through the nozzles. The nozzles or jets have axes directed radially inwardly and downwardly. The secondary manifolds 31 are supplied with air from the primary or main manifold 40 through conduits38, the main manifold being supported by an elevating strut 42 to which is aflixed a rack 47 engaging a pinion gear 48. The elevating strut 42 passes through a sleeve bearing 56 in the stationary guide arm 46.

The pinion gear 48 is driven by rotation of a worm gear 58 which is mounted on a drive shaft 60 adapted to be rotated by a handwheel 62. Two sleeve bearings, 64 and 66, which retain and position the drive shaft 60, are supported in one case (64) directly by the chamber wall and in the other (66) by a bracket 68 which is in turn afi'ixed to the chamber Wall. Also supported by the bracket 68 is the pinion gear 48.

In operation, flow of drying air into the chamber via the duct 22 is initiated and the handwheels 62 are rotated to position the air jet systems at elevations known or expected to be suitable for use under the proposed conditions of operation. Air, preferably heated so as to exert some drying influence, is supplied to the jets 32, and drying of solid-containing liquid is initiated by pumping slurry to the rotating whirling disc atomizer 26 through the conduit 28. The air from the jets 32 blasts inwardly and downwardly against the periphery of the parabolic body of wet particles 44 to diminish the horizontal diameter thereof and thereby prevent the contact of wet particles with the chamber wall 18 which would otherwise normally occur.

After reaching equilibrium spraying conditions, the handwheels 62 are rotated so as to position the air jet systems at the optimum elevation for preventing substantial buildup of wet particles on the chamber walls. This position is best determined by routine experiments, but may be established to a certain extent by visual observation of the interior of the chamber wall by means of portholes (not shown) in the chamber wall and/or conical cover.

While the preferred embodiment which has been illustrated utilizes concurrent flow of drying air and wet solids, i.e., both travel downwardly through the chamber, it is possible, although not as satisfactory, to employ the instant invention in spray drying apparatus wherein drying air passes upwardly through the chamber countercurrently to the downward flow of atomized particles.

From the foregoing it will be seen that the present invention provides a device which is simple and flexible in operation and which faciltates the production of spray dried products of high quality under widely varying conditions.

While there has been shown what is at present considered to be the preferred embodiment of the invention it will be understood, of course, that many modifications and changes may be made therein without departing from the true spirit of the invention which is to be accorded the full range of equivalents comprehended by the accompanying claims.

Having thus described the invention, what is deemed to be secured by Letters Patent is:

1. Spray drying apparatus adapted for both concurrent and countercurrent flow of drying air and material to be dried comprising a drying chamber defined in part by a substantially vertical wall, a gas conduit for drying air having unimpeded access to the top of said drying chamber, means for dispersing material to be dried in said chamber as a paraboloid of wet particles which, if unimpeded, would collide with said substantially vertical wall of said chamber, bodily vertically movable means for directing a flow of gas inwardly and downwardly against the upper surface of said paraboloid to diminish the diameter thereof and thereby prevent contact of said wet particles with said wall of said drying chamber during drying by either concurrent or countercurrent flow of said drying air and said material to be dried, and means for supporting said bodily vertically movable means within said chamber beneath said dispersing means.

2. Spray drying apparatus adapted for both concurrent and countercurrent flow of drying air and material to be dried comprising a drying chamber defined in part by a substantially vertical wall, a gas conduit for drying air having unimpeded access to the top of said drying chamber, means for dispersing material to be dried in said chamber as a paraboloid of wet particles which, if unimpeded, would collide with said wall of said chamber, bodily vertically movable means for directing a flow of gas inwardly and downwardly against the upper portion of said paraboloid to limit the diameter thereof during drying by either concurrent and countercurrent flow of said drying air and said material to be dried, means for supporting said bodily vertically movable means within said chamber immediately beneath said dispersing means and adjacent to said drying chamber Wall, and a flexible conduit communicating with said bodily vertically movable means and adapted to supply gas under pressure thereto.

3. Spray drying apparatus adapted for both concurrent and countercurrent flow of drying air and material to be dried comprising a drying chamber defined in part by a substantially vertical wall, a gas conduit for drying air having unimpeded access to the top of said drying chamber, means for dispersing material to be dried in said chamber as a paraboloid of wet particles which, if unimpeded, would collide with said wall of said chamber, a vertically movable manifold having a plurality of orifices having axes directed inwardly and downwardly so as to direct a stream of gas against the upper surface of said paraboloid to diminish the diameter thereof and thereby prevent contact of wet particles with said wall of said drying chamber during drying by either concurrent or countercurrent flow of said drying air and said material to be dried, a flexible conduit communicating with said manifold and adapted to supply gas under pressure thereto, and means for supporting said manifold below said dispensing means and adjacent to said drying chamber wall and just above the normal upper surface of said unmodified paraboloid.

4. Spray drying aparatus as set forth in claim 3 wherein there is downward flow of said wet particles and of drying air.

References Cited in the file of this patent UNITED STATES PATENTS 1,028,267 Osborne June 4, 1912 1,374,555 Dick Apr. 12, 1921 1,594,065 MacLachlan July 27, 1926 2,035,673 Schultz Mar. 31, 1936 2,144,098 Baker Jan. 17, 1939 2,396,689 Davis Mar. 19, 1946 2,460,546 Stephanofi Feb. 1, 1949 2,703,139 Rappleyea Mar. 1, 1955

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