US1624739A - Spray drying - Google Patents

Description

P" 1927 A. a. JONES SPRAY DRYING Filed June 13, 19:35

A TTORNE Y3 Patented Apr. 12, 1927.

- UNITED STATES PATENT OFFICE.

ARTHUR 3. JONES, OF PLAINFIELD, NEW JERSEY, ASSIGNOR *TO INDUSTRIAL ABSO- CIATES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK,

SPRAY DRYING.

A p'uoamn filed June 1a, 1920. snarno. 116,980.

My invention relates to spray dr ing, and is applicable to the recovery of so ids from organic and inorganic fluids, sem -fluids, plastics, etc., capa le of dispersion in comminuted condition by centrifugal force or otherwise. The object of my invention is to provide improved apparatus and operation for convection current systems, and by which the available heat unlts of the convection current are more completely exhausted in useful work before the gas leaves the dr ing chamber.

In the accompanying drawing- Fig. 1 is a vertical section, through a more or less diagrammatically illustrated layout of apparatus embodying my invention in one form. 1

Referringto the more or less diagrammatic drawing, I have indicated an outer, closed casing or shell 1, which surrounds but is spaced from a sheet metal cylinder 2 arranged on a vertical axis and constituting the dryin chamber proper. The intervening space hetween the casingand cylinder is horizontally divided by partition 3 into upper and lower compartments 4 and 5 respectively. Heated air or other gas is admitted to the u per compartment 4 through port 6, passes t ence through the drying chamber 2, escapes from the bottom of the latter to compartment 5 and exits therefrom through port 7.

Arranged centrally and adjacent the upper margin of the dryin chamber is a centrifugal spray unit 8 w ich receives from feed 9 the fluid or plastic material to be dried, and dis erses the same in a surrounding nebula. n the subjoined claims I employ the word fluid in a sense broad enough to include any material, whether a liquid or a plastic solid or mud which is susceptible of dispersal in the form of a very fine spray or nebula.

In apparatus of this general type, as heretofore constructed, the upper en of the drying chamber 2 has been open throughout its complete diameter. The incoming hot gases have been distributed consequently over the entire cross sectional area of the cylinder, and their downwardflow through the latter has been substantially uniform at all points.

.This arrangement lacks efficiency, since the nebula is most dense in the immediate neighborhood of the spray unit'S and the hot gas passing through this portion of the nebula absorbs more moisture than the surrounding or peripheral portion of the gas current. Thelatter thus gives up a lessproportion of its useful heat and leaves the drying chamher without absorbing all the moisture which it is capable of carrying at its exit temperature.

I have found that this waste of useful heat is greatly reduced, if the upper end of the drying chamber is to a large extent closed by a head 10, preferably inwardly dished as shown, and having acentral inlet port 11. The precise area of this port may vary-but I prefer that its'area shall be approximately four or five times that (if the spray unit 8, which is centrally located with respect thereto.

s a result of this construction, the hot gas enters the drying chamber parallel to the axis of the spray unit and is concentrated on the dispersed nebula in its densest area. The force of the impinging current of gas'deflects the nebula downward and thus causes the heavier particles thereof to travel a downward and outward path at an an tri ugal spray unit. The length of this downwardly deflected path from the spray unit 8 to'thewall of the dryingchamber is materially greater than the ath to the wall in the plane of rotation of t e unit 8; Consequently, the particles are subjected for a greater length of time to the desiccating action of the gaseous current. a

A second important result of the construction is the establishment of an annular upwardly flowing gaseous current which surrounds a central downwardly flowing current in the drying chamber. This is due not only to the usualtendency'to eddy or whirlpool formation incident to the projection of a jet or stream of gas into a larger relatively quiet body thereof, but also to other influences, First, the portion of the gas which contacts with the nebula in its densest area, very rapidly gives up its heat in the absorption of molsture from the nebula, and is therefore chilled to a greater extent than the surrounding portion of the gas which permeates the outer area of the nebula. This central, chilled and moisture laden portion of the gas current tends to sink, by gravity, more rapidly than the gle to the plane of rotation of the cen- =outer, less chilled, less moisture laden, portion thereof and forms in consequence a central downwardly moving column of as, practically saturated with moisture. he surrounding less saturated gas, at hlgher temperature, tends to rise and to form an upwardly flowing current. Second, the portion of the dr ing chamber Wall which lies above the diap iragm 3, and also the head 10 of the drying chamber, are heated by the incoming hot gas in the compartment 4. The peripheral unsaturated portion of the gas in the drying chamber is heated by the wall of the drying chamber and tends to risetoward the head 10 of the drying chamber, where it is further heated. Third, the jet efl'ect of the gas entering the drying chamber through port '11, exerts a suction effort upon the surrounding gas which lies against the inner face of the head 10 and draws this partially saturated hot gas into the jet entering through port 11 and into the dense area of the nebula.

The chilled and saturated gas thus forms a central downwardly flowing column,

which cones outward at its lower end and escapes below the lower margin of the dr ing chamber to the exit compartment 5. Tlie surrounding less chilled and unsaturated gas is caused to flow upward and to re-enter the densest area of the nebula, where its useful .heat' is given up in the absorption of moisture. A marked increase in eflicienc results by reason of the fact that practically only moisture saturated gas escapes the dryin chamber. Per heat unit for a given volume of incoming hot gas, a greater volume of moisture is extracted from the nebula, before the gas escapes from the drying chamber.

While I have referred to the air currents as saturated and unsaturated, it will be understood that these words are not used in their technically exact sense, but to express their relative moisture laden and temperature conditions. Similarly, while the term nebula is also used, it is intended to indicate merely a finely divided condition of the liquid under treatment. I

While I have mentioned onl the fundamental results flowing from t is construction and operation, various modifications will readily occur to those dealing with the problem. Thus I have shown small ports 12 opening through the drying chamber wall just below the head 10. The hot air entering therethrough mingles with the rising gas and not only increases its temperature, but aids the jet action of the gas entering at port 10 in causing the unsaturated .gas to lfi-fil'ltel the nebula in its densest area The solids fall from the drying zone upon the floor 13 of the casing and are recovered in any suitable fashion. For example, they may be swept by rake 14 into a chute 15 which delivers to a hopper, or bagging apparatus, or to further treating apparatus, as

maiy be desired. ith the understanding that onl a typical layout and operation are descri ed to illustrate the thoughts whichv underlie my invention, I claim 1. The method of spray drying which comprises dispersing a fluid as a nebula, causin a convection current to traverse the zone 0 said nebula, leading the chilled and moisture saturated portion of the convection current from the lower end of the. drying chamber, and causing the unsaturated portion of the convection current to rise and to re-enter the nebula zone to there absorb further moisture.

2-. The method ofspray drying which comprises dispersing a fluid as a nebula, causing a convection current to traverse the zone of said nebula, leading the chilled and moisture saturated portion of the convection current from the lower end of the drying chamber, and causing the upward flow of the unsaturated portion of the convection current by bringing it-into contact with a heated wall of the drying chamber.

3. The method of spray drying which comprises dispersing a fluid as a nebula, causin a convection current to traverse the zone 0 said nebula, leading the chilled and moisture saturated portion of the convection current from the lower end of the drying chamber, and causing the unsaturated portion of the convection current to rise and to re-enter the nebula zone to there absorb further moisture, the convection current being concentrated upon the central area of the nebula zone as said current enters the dryin chamber.

4. The method of spray drying which comprises dispersing a fluid as a nebula, causing a convection current to traverse the zone of said nebula, leading the chilled and moisture saturated portion of the convection current from the lower end of the dry ing chamber, and causing the unsaturated portion of the convection current to rise and to re-enter the nebula zone to there absorb further moisture, and augmenting the rise and return of the unsaturated portion of the convection current to the nebula zone by the jet action of the incoming convection current.

5. The method of spray drying which comprises dispersing a fluid as a nebula, causing a convection current to traverse the zone of said nebula, leading the chilled and moisture saturated portion of the convection current from the lower end of the drying chamber, and causing the unsaturated portion of the convection current to rise and to re-enter the nebula zone to there absorb further moisture, and augmentin the return of the unsaturated portion o the convection current by the entraining action of auxiliary hot air jets converging upon the spray zone.

6. A spray-drying apparatus comprising a tubular drying chamber having a restricted top opening, means for dispersing liquid from a point beneath said opening to form a nebula zone of greatest density directly beneath said opening, means for leading a convection current into the drying chamber through said restricted opening, means for leading ofi moist entrained gas from the lower portion of the chamber, and means for recovering solids deposited out of the liquid.

7. A spray-drying apparatus comprising a tubular drying chamber having a restricted top opening, the top of the drying chamber being inwardly dished to said opening, means for dispersing li uid from a point beneath said opening to orm a nebula zone of greatest density directly beneath said opening, means for leading a convection current into the drying chamber through said restricted opening, means for leading off moist entrained gas from the lower portion of the chamber, and means for recovering solids deposited out of the liquid.

8. A spray-drying apparatus comprising a tubular drying chamber having a restricted top opening, means for dispersing liquid from a point beneath said opening to form a nebula zone of greatest density directly beneath said opening, means for "leading a convection current into the drying chamber through said restricted opening, means for leading off moist entrained gas from the into the drying chamber through said restricted opening, means for leading ofl? moist entrained gas from the lower portion of the chamber, and means for. recovering solids deposited out of the liquid. 10. A spray-drying apparatus comprising a tubular drying chamber having a restricted top opening, ports formed in the wall of the drying chamber adjacentthe dished top, means for dispersing liquid from a point beneath said opening to form a nebula zone of greatest density directly beneath said opening, 'means for leading a convection current into the drying chamber through-said restricted opening, means for leading off moist entrained gas from the lower portion of thechamber, and means for. recovering solids deposited out of the liquid.

In testimony whereof I have signed my name to this specification.

' ARTHUR B. JONES.

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