US1985987A

US1985987A - Art of spray drying soap

Info

Publication number: US1985987A
Application number: US625892A
Authority: US
Inventors: Hall Thomas Edward
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1932-07-29
Filing date: 1932-07-29
Publication date: 1935-01-01
Anticipated expiration: 1952-01-01

Description

Patented Jan. 1, 193s lUNITED STATES PATENT OFFICE 7 Claims. (Cl. 87-16) My invention relates to the art of spray drying soap, and particularly to the art of controlling the bulking weight of spray dried soap particles while maintaining a substantially uniform moisture content in the finished particles, and while maintaining a uniform temperature of the gaseous medium introduced into the apparatus for drying and puffing thesoap particles.-

. In the spray drying of soap, particularly as taught by Holliday and Lamont, the soap particles are preferably dried in a concurrent heated gas supply which passes through the apparatus in the general direction of the spray of soap being dried.

Where there is any suggestion as to control of .the density vof the dried products, as far as I am y aware such controls have been byvarying the temperature of the drying gas. Lamont, for example, in his Patent #1,734,260 especially provides for the control of the density of the finished product by varying the temperature of the hot gas introduced into the drying chamber at the top ofthe tower. Thediiliculty with controlling the density of the finishedxproduct by varying the temperature of the drying gas is that while a desired density may be obtained by such variation in the temperature ofthe drying gas, it does not necessarily `iollow that a desired moisture content will result. For example, when a more dense product is desired and the temperature of the drying gas is lowered, the soap particle will not be pued out so much, and will consequently occupy a lesser volume for a given amount of soap. Due, however, to the fact that the amount of soap is compressed into a smaller particle, that is a thicker shell particle, it is more dicult to dry it -toa moisture content suiliciently low as to prevent sticking and packing of the powder as it is taken from the bottom of the. drying tower. This objection may be overcome in a concurrent drying tower by atomizing the iiuid much liner so that the individual particles will be smaller and have a greater amount of surface from which moisture may escape for a given weight of soap. Under such conditions,'a lowered temperature will result in a proper con- 45 trol of the moisture content, but it will be noted that such a method of control requires two variables to be accurately governed-first, the temperature of the incoming gas, and second, the degree of neness at .which the soap is sprayed. 5 Further when the spray becomes too minute, the resulting powder may be too dusty for practicable commercial purposes. The practicable density range on a strictly concurrent tower is between' .1 and .3 specic gravity as compared with water, with the moisture content between 5 and 15%,

and with the particle size such that at least of the product will remain on a s ixty mesh screen.

It is the object of my linvention to provide a method of spray drying in which a xed quantity of drying gas heated to a substantially uniform temperature is employed, and in which the particlessprayed are of a size substantially .35 mm. in diameter, with a weight of substantially ,.03 mg.

It is my object in a spray drying tower to control variations in bulking weight while maintaining a normal satisfactory'moisture content by controlling the elevation in the tower at which the drying gases are` introduced. l

` I propose, by means of controlling the level at which the drying gases are introduced into the drying tower, to vary the density range of the .dried soap product between speciiic gravity las compared with water of .10 to .50, and at the same time to control the moisture content of the finished product between 5 and 12%. It is a further characteristic of my proposed process that both the density and moisture can be varied over quite a wide range without varying the weight of the particles greatly.

Another object of my invention is to economize in thev heat units required to dry the product by returning some of the gas as it is drawn from the tower back again into the tower so.that the heat units therein may be utilized for their drying effect on the sprayed soap after the soap particles have passed through the zone of exposure to the regular incoming supply of heated drying gas.

The above objects and other objects to which reference will be made in the ensuring description, I accomplish by that certain combination and arrangement of parts' and by the various controls of the elevation of the incoming drying gas as hereinafter specified.

Referring to the drawing:-

Figure l is a diagrammatic plan view of a proposed dryingv tower.

Fig. 2 is a diagrammatic sectional view showing the drying apparatus indicated in Fig. 1.

I have shown a spray drying tower 1 of dimensions of approximately twenty feet in diameter, with a height of about sixty feet. The tower has a conical'bottom 2 provided with a gas-sealed discharge valve 3, by which'the product-is discharged from the drying tower into conduit 4, where, by means of a suction fan 5, it is drawn into a separating chamber 6, having a gas-sealed feed valve v7, which. feeds the powder into a hopper 8, -from which it is dispensed in desired quantities to conveyors or to filling machines.

A gas heater 9 isshown, which may be a furnace, fired-preferably by either oil or gas, from which the combustion gases pass directly to the tower. It may further be a heat exchanger supplied with steam or'other means for heating the incoming air or gas. A blower fan 10 blows gas through a conduit 11. At different elevations in the tower there are plenum chambers. The plenum chambers are annular conduits extending around the tower with openings through which the gas is blown into the tower.

In the diagrammatic illustration I have shown the top chamber 12 having discharge openings 13, through which gas is discharged into. the tower, and with a gate valve 14 between the conduit 11 and the plenum chamber so that the supply of gas may'be cut ofi if desired.

I have further shown the plenum chamber 15 having inlet openings 16, and with a valve 17 for cutting off the gas supply to the middle plenum chamber.

The bottom plenum chamber 18 has gas admission ports 19, and a valve 20 controlling the entrance of gas from the conduit 11. The bottomplenum chamber further has a valve 21, which controls the re-introduction of a portion of the heated waste gases drawn from conduit 24, through conduit 23, by means of fan 22. The remaindenof the heated waste gases are drawn from conduit 24 through conduit 35 to separator 26 by means of fan 25.

A valve 27 controls the flow of separated powder from a separator 26 to the conduit 4, from which any separated powder is discharged into the chamber 6, where it is mixed with the product being drawn up through the conduit 4. The

other ingredients, such as silicate of soda, salsoda, or other` builders, and the soap from the crutcher is pumped with a pump 30 through the pipe 31 to the spray nozzles 32. The pump 30 is preferably of a type in which the speed may be controlled either by a variable speed motor, or by other suitable mechanical means. A steam jacket 33 is also indicated for controlling' the temperature at which the soap is pumped to the spray nozzles.

In order to explain how I propose to control the bulking weight while maintaining a desired moisture content, and while pumping a fixed supply of gas at a temperature of substantially from 400 to 500 degrees F., I have indicated zones A, B and C, in the drying tower, zone A being the portion between the plenum chamber 12 and the top of the tower; zone B the portion between the

plenum chambers

15 and 12, and zone C the portion between the

plenum chambers

18 and 15.

Any desired type of atomizer that will give the desired size of particle may be used. The conventional type of pressure nozzle has been found satisfactory. 'Y i The control of the Aspray drying of soap is proceeded with as follows: Hot gas from the heater .the heated gas is introduced into the plenum chamber 12 and passes into zone A, in which it meets the sprayed soap sprayed into zone A from the nozzles `32. The temperature of the soap spray may vary between and 220 F., depending on they viscosity of the soap and the ease with which it zsprays. A desirable temperature for spraying the soap has been found to be about 200 F. As the sprayed soap falls through zone A, which is maintained at high' temperature, it is puffed out due to the rapid heat transfer caused by the high gas temperature and the high moisture content of the soap, and the individual particles rapidly assume the size vand shape which they retain until they are discharged out of the bottom of the tower. The particles, however, will not be completely dried in zone-A, and will contain variable quantities of moisture considerably above that contained in the final product.

As has been stated, some of the exhaust gas from the conduit 24 is blown back into the tower,

. The sprayed, partially dried particles of soap falling from zone A through the rising counter- -current gases moving up through zones C and B,

will be further dried to a moisture content of substantially 8%, and the finished product, as it is fed out through the gas locked valve 3 `will have a temperature of about 180 F. During the passage of the product through the gas conveyor the temperature is further substantially reduced.

After establishing the proper operating conditions for each tower, the size and number of nozzles, etc., that will give a bulk density of about .10 to .20 when the heated gas is introduced into zone A with the desired weight ofparticle, then without changing operating conditions except to introduce the hot gas into zone B instead of into zone A, a product with bulk density of about .20 to .30 will be obtained. Likewise without changing operating conditions except to introduce the heated gas into zone C a product with bulk density of about .30 to .50 will be obtained.

To control the bulk density closely to a desired figure within the range mentioned for each zone, the quantity of. s'oap atomized and the temperature of the heated gas may be varied slightly, but the main control to obtain products having bulk density within the three ranges mentioned is by introducing the heated gas at three different elevations, as stated, and as shown the recirculated drying' gas is taken from above the middle of the tower and reintroduced below the middle of the tower.

It appears from the above description that when the hot gas enters at zone A the sprayedpar- -ticles immediately come in contact with the hottest gas and are thereby heated and dried quickly with consequent puffing and therefore a product of low bulk density is obtained. When the hot gas enters at zone B, the sprayed particles do not come in contact with the hottestgas until,

they have' previously passed through zone A where the gas has lost some of its original heat, and

therefore the particles are heated and dried more gradually and they do not puit so much. thus giv- ,y ing a product of higher lulkdensity thanwhen the hot gas is introduced at zone A. In both these cases the particles are further dried, but without further puiling, by falling through the recirculated exhaust gas which is introduced at zone C. When the hot gas and a portion of the exhaust gas are both introduced at zone C the two gases are preferably mixed before entering the tower, and then the sprayed particles are heated and dried still more gradually than when the hot gas is introduced at higher elevations, and

less pufng occurs, thus giving a product of still,

higher bulk density. In these cases thus de-fy scribed, except when the hot gas is introduced directly into zone A, thetemperature of the gas when it comes in contact with the freshly sprayed soap in zone A has been so reduced that it is not high enough to cause the rapid vaporization necessary to 'pulling particles so as to produce a product of lowest bulk density.

It should be particularly noted that the func tion of the recirculated gas is really twofold-mst the heat economy due to using exhaust or waste gas, and secondly, the effect of lowering the temperature of the gas as it passes through thetower without reducing the total quantity of heat introduced into the tower.

By the use of my novel method of spray drying in a counter current of heated drying gas I have produced soap powders with densities varying between .10 and .50 without varying either the weight of the particles of soap as sprayed, without appreciable variation in the temperature or rate of introduction of the incoming heated gas, arid without essentially varying the moisture content in the finished product.

Having thus described my invention, what I g claim as new and desire to secure by Letters Patent, is:

1. In -the spray drying drying tower, the method of controlling the bulk density -of the dried product which consists in spraying the soap downwardly in the tower, in substantially uniformly sized particles in introducing a counter current of heated drying gas into the tower and controlling the elevation within the tower at which ythe drying gas is introduced, and returning a portion of the e'xhaust gas into the bottom of the tower.

2. A soap spray drying process which consists in forcing soap through a spray ynozzle at a pressure of from 250 to 750 pounds per square inch, causing the sprayed soap to bedischarged into a definite volume of acounter currentof heated drying. gas and controlling. the bulking density of the spray dried product by controlling the elevation at which the heated drying gas is introduced. v Y

3. In the art of spray drying soap, a method of controlling the bulking density of the spray dried product while'maintaining the sprayed particles at a substantially uniform weight and moisture of soap in a spray tower so that the exposure of the particles to the drying gas at the level at which said drying gas is introduced will be such -that a desired bulk density will be obtained. Y

4. In the spray drying of soap in a spray drying tower, themethod of controlling the bulk density of the dried product to any desired point between 0.10 and 0.50, which consists in spraying the soap from above so that it falls downwardly in the tower througha rising counter-current of Vfresh heated drying lgas of substantially uniform volume and temperature so controlled and intro-i duced into the tower at various predetermined distances below the spraying nozzles, so as to puff the particles to the desired bulk density.

5. In the spray drying of soap in a spray drying tower, the method of controlling thebulk density of dried product without changing the moisture content o'f the product, which consists in spraying the soap from above so that it yfalls downwardly in the tower through a risingcounter-current of fresh heated drying gas of substantially uniform volume and temperature so controlled and introduced into the tower at various predetermined distances below the spraying nozzles, so as to puif the particles to the desired the required w fresh heated drying gas of substantially uniform .volume and temperature at various predetermined distances below the spraying nozzles, and recirculating a portion of the exhaust gas .from

to various predetermined levels, while controlling the level of introducing the fresh drying gas so as to puff the particles to the desired bulk density.

'1. In the spray drying of soap in a spray drying tower, the method of controlling the bulk density of the dried product to any desired point between, 0.10 and 0.50, which consists in spraying the soap from above so that it falls downwardly in the tower, introducing a ,rising l counter-current of fresh heated drying gas of substantially uniform volume and temperature at various predetermined distances below the rspraying nomles, and recirculating a portion of the exhaust gas from the tower and re-introducing it into the tower at a level below that of the fresh heating gas, while controlling the level of introducing the fresh drying gas to various. predetermined levels so that the sprayed soap particles are first puffed to the desiredl size and partially dried byv contact with the mixture of fresh heated drying gas and recirculated gas, and theny further dried by contact with the recirculated gas alone to obtain the desired final moisture content and the desired bulk density.

' THOMAS EDWARD