US2391033A - Drying hygroscopic plastics - Google Patents

Description

Dec. 18, 1945. R. T. NoRTHcUTT Erm. 2,391,033

DRYING HYG'ROSCOPIC PLASTICS Filed March 2 8, 1942 R www w w R N a a EN.N lum VTT. mlm mi@ mw Y B Patented Dec. 18, 1945 DRYING HYGROSCOPIC PLASTICS Robert T. Northcutt, Westfield, and Robert T. N orthcutt, Jr., Fanwood, N. J., assgnors to Food Concentrates, Inc., New York, N. Y., a corporation of Delaware Application March 28, 1942, Serial No. 436,638

14 Claims.

This invention relates to the drying of hygroscopic plastics and more particularly to an iniproved procedure for drying molasses and other similar substances.

The drying of substances composed principally of sugars but also containing organic and' other salts, such as molasses, is very diicul-t because the vapor pressure of the water at temperatures below the boiling point of the substance is too low to permit drying within a reasonable time and, at temperatures above the boiling point, charring and discoloration are likely to take place. The mineral salts in the molasses act as catalyzers in the reduction and charring of the sugars and such reactions will take place even at temperatures considerably below the boiling point, for example, at temperatures of 120 F., if such temperatures are maintained for a suicient time. It has therefore been impractical heretofore to prepare dried molasses or other similar substances by the drum drying process. The drying of molasses by the spray drying process has been used in the past, but such drying requires expensive equipment and involves bad economy and heat exchange, large losses of material due to wall deposits and the production of considerable insoluble material. With such a process it has been diicult or impossible to reduce the moisture content to below 3 to 312% residual moisture. Also, with spray drying, even under the best conditions, a deepening of the color of the syrup takes place and when the product is brought back to its original consistency by addition of water, the product will be of darker color than the original product.

It is an object of this invention to provide an improved proces-s for drying molasses or other hygroscopic plastics whereby these and other objectionable features are avoided. A further object is to provide a method in which the water may be substantially completely removed from. such substances containing invert sugars and mineral salts without deterioration of the product. It is also an object to provide a. new molasses product. Another object is to provide an improved apparatus for use in drying such liquids. Other objects will become apparent.

We have found that by subjecting the molasses on a drying drum to carefully controlled temperatures, above the boiling point of the molasses and below the caramelizing point of the sugars contained in it, for a carefully limited time, the water may be reduced to a residual moisture content of less than 2%. As the amount of water decreases, the boiling point of the molasses Will increase and the temperature to which the molasses is heated must be gradually increased so that it is always maintained in excess of its rising boiling point. This can be accomplished by drying the molasses on the outer surface of the drum internally heated, by steam or by other means, sufficiently so that at the rate of rotation of the drum the molasses will be heated to a maximum temperature of at least 306 F. and not over about 335 F. It is preferred to operate at a maximum temperature on the drum of between 310 and 320 F., although one can operate at higher temperatures, for example, 330 F. if the time is sufciently short. Molasses caramelizes very quickly at 340 F. so the maximum temperatures should be kept below this value, The required temperature may be obtained, for example, by using steam under gauge pressures of about to 110 pounds per square inch (about 338 to 345 F.) and over and rotating at such a rate that the molasses will be on the drum for 6 or 7 seconds. With the apparatus used, this may be accomplished on a drum revolving once in 8 or 9 seconds.

After the molasses has been on the drum a sufcient length of time, it may be scraped off by means of the usual doctor blade and may be flowed in a still plastic condition into molds. When the material comes 01T the doctor blade, it is quite sticky and does not ow readily away from the blade. Also, great numbers of bubbles of hot gas are formed and retained within the material which is very frothy as it leaves the doctor blade. This retention of hot gases within the mass results in a rapid deterioration of the product. We have found that by subjecting the material as it comes off the doctor blade to surface agitation in order to quickly liberate the gases from the bubbles in the material, the liquid may be caused to ow quickly away from the drum and may be collected in molds without deterioration. This agitation may be done by hand, for example, by means of trowels or other devices by which the material may be rapidly and thoroughly agitated to liberate the gases. It is preferred, however, to use a mechanical means for effecting this agitation. For this purpose, a plate, over which the dried liquid is to flow, may be positioned just beneath the doctor blade and a series of blades may be made to reciprocate over this surface and close to, but spaced from it, the distance apart of the blades and the length of the reciprocation being such that the paths of the blades overlap each other. By reciprocating the blades in this manner, the bubbles in the foamy mass scraped from the drum by the doctor blade may be broken to liberate the contained gases and the resultant liquid product may be caused to flow smoothly and in a thin lm down the plate and into molds.

An apparatus suitable for carrying out the process is illustrated in the drawing in which Figure 1 is an end elevation of the apparatus with certain portions illustrated in section, and Figure 2 is a similar side elevation.

In the apparatus illustrated, the hollow drums I, I, about 2 feet in diameter and six feet long, are supported and rotated in the usual manner for double drum drier rollers; for example, they may be rotated by a chain 2 contacting sprockets 3, 3 and rotated by the motor 4, preferably through a variable speed transmission. Steam is supplied to the interior of the drums in the usual manner; for example, through the perforated pipes 5, 5 which also serve as the axles supporting the drums in suitable bearings (not shown), but under somewhat higher pressures than is customary, for instance, under pressure of 100 pounds per square inch or over. The material to be dried is fed through a pipe 6, having a series of nozzles 6a, into the trough formed by the surfaces of the two drums and the two oppositely positioned end plates 1. 'Ihe drums may be adj stably positioned to leave the required space betvuti'ld'runmrovide continuous layers of molasses on the drums as they rotate in the direction indicated by the arrows. This distance may vary from .001 inch apart to any distance at which the material will not drop through, but is preferably adjusted by bringing the drums close enough together so that the visible bubbles on the surfaces of the drums are maintained at a minimum. A distance of about .005 to .006 inch a@ has been found satisfac ory or this purpose.

Doctor blades 8, 8 are provided for removing the material after it has been on the drum a Sullicient length of time. Adjacent and extending close to each doctor blade is provided a flow plate 9, over which the hot dried material will iiow to molds or trays I0 or other suitable receiving devices. In order to liberate the entrained gases and prevent deterioration of the product by the gases occluded in the foamy mass scraped off by the doctor blades, the material should be agitated rapidly on the flow plate 9. This may be done manually by means of trowels but is preferably done by means of a device similar in construction and operation to a series of windshield wipers, as illustrated in the drawing.

In the device illustrated, a plurality of blades II, I I are carried on each of the reciprocating rods I2, I2 and are spaced thereon at distances less than the distance through which the rods I 2, I2 reciprocate so that their paths will overlap. For example, in the apparatus illustrated, the blades are spaced about 2 inches apart and the rods I2, I2 are reciprocated about 4 inches by bell cranks I3, I3 or by other suitable means. The blades II, II are shown as of quarter round material, with the curved surfaces toward the plates 9, 9, each blade extending in vertical planes and parallel to the surface of the plate 9 and having its rounded surface spaced about 1/2 to inch from the plate 9. In the apparatus illustrated, the upper edge of the plate 9 is placed about 1/ inch below the scraper 8 and about 1A inch from the surface of the drum I and the upper ends of the wiper blades II extend beyond the plate 9 and cover the space between the scraper 8 and plate 9. The wiper blades I I overlap the scraper blade 8 about M2 inch, that is, the wiper blades are placed so that the top edges are about an inch higher than the upper edge of the plate 9. Of course, it may be desirable to use other shaped blades or to position them differently, for example, in planes inclined to the vertical and/or in planes inclined toward or away from the plate 9. Also, the slope of the plate 9 may be changed, but should be such that the material removed will iiow from it at about the rate of delivery by the scraper blade or faster, so that it will not pile up.

Also, if desired, other means may be provided for removing the entrapped gases. For example, a blast of air or other gas, such as is used in a sand blaster, may be applied to the material as it leaves the doctor blade 8.

As an illustration of the procedure, a molasses containing solids and 20% moisture, having a boiling point of about 235 F., was fed through the pipe 6 into the space between the drums I, I, rotating at a speed of about 8 to 9 seconds a revolution. As the rollers rotated, the film of liquid was heated, by means of steam within the drums under gauge pressures of about 100 to 110 pounds per square inch, to gradually increasing temperatures, ranging from an initial temperature of about 240 F. to a final temperature of about 310 F., and was scraped 01T by a doctor blade as a frothy mass, when the desired temperature had been reached. Most of the moisture, for example about was removed in the rst second of the heating and the remaining 5 or 6 seconds were required to reduce the remaining content of water. With the procedure as described, the moisture content was reduced to about 3A of 1%.

The dried molasses is very hygroscopic and the atmosphere around it should be carefully controlled during the cooling and subsequent steps. For example, the dried molasses will rapidly take up moisture at ordinary room temperature in an atmosphere having a 33% relative humidity. Therefore, it should be placed in a safe atmosphere, i. e., one having a relative humidity of less than about 33%, before cooling to below about 130 F. For example, in an atmosphere having 27% relative humidity, the material may be cooled down to 80 F. and may be crushed to granules and, if desired, ground to a line powder in a grinding mill, The very hygroscopic powder containing less than 2% moisture may be stored in a safe atmosphere and packed in hermetically sealed containers, in which condition it will keep indefinitely and will stand temperatures up to F. or higher, without packing or losing its powdered form.

Water m-ay be added to the dried material and if the proper percentage is added, a material like the original molasses will result. Or, the powder may be used in a dry state, for example, in the preparation of dry mixes. These, of course, should be stored in a dry atmosphere in order to avoid absorption of Water.

It is obvious that many variations may be made in the above procedure, which is described as illustrative. For example, steam under higher pressure, for instance 250 pounds pressure, may be used in the drums by speeding up their rate of rotation so as to avoid raising the temperature of the film excessively. The maximum temperature to which the material should be heated on the drum will vary with the content of invert sugar in the material being heated. With a higher percentage of invert sugar, it may be desirable to increase the maximum temperature, and with less invert sugar, it may be reduced. In any event, the maximum temperature should be above the boiling point of the molasses reduced to the desired moisture content and should be below the charring temperature for the time of exposure used.

The concentration of the material fed to the drums may be varied, the higher the concentration the greater the output of the drum under given conditions. In practice molasses of commerce is used and is found as a rule to contain about 75 to 80% solids, such a density being necessary to protect the product from fermentation. Of course, if desired, the molasses may be concentrated to a greater degree or it may be preheated before it is fed onto the drying drums, thus permitting more rapid rotation of the drums and greater capacity thereon.

The agitation of the surface of the foamy material leaving the doctor blades is a very important factor in the preferred operation of the process. This should be continued until a sufficient amount of the entrained gases are removed and the temperature has dropped suciently to avoid deterioration of the product. During this agitation the temperature of the dried material drops fairly rapidly, for example through '70 to 100 F. In the illustrative run described above, the temperature of the mass had dropped to about 240 F. by the time it flowed downward half the width of the plate 9. By the time it reached the lower edge of the plate 9 it had cooled to about 200 F. Unless a safe atmosphere is maintained around the apparatus, the mass should not be permitted to cool below about 120 to 130 F. before removing it to a safe atmosphere, i. e., one containing unsufcient moisture to be absorbed by the hygroscopic material.

The invention may be used in the drying of cane or beet sugar molasses or in the drying of other hygroscopic plastics that are likely to char at the temperature of drying and is particularly useful in the drying of materials that foam during drying. Solutions of corn or malt sugar or other solutions composed chiefly of invert sugars are examples of such solutions.

By quickly drying as described herein color changes in the product are avoided and the moisture may be reduced to from a fraction of one percent to under two percent, which permits the product to be powdered and remain a mobile powder at temperatures under 100 F. At temperatures above 100 F. there is likely to occur a softening of the powder and the formation of a hard caked mass. Some types of molasses or other sugar solutions are more sensitive to heat and moisture than others. Blackstrap molasses, for example, containing less invert sugar than higher grades, will remain a mobile powder at higher temperatures and larger moisture content. Blackstrap will be satisfactory with 1%% moisture. Purer molasses, such as second or third molasses, will require drying to less than one percent. It is preferred to dry to about of 1% in order to maintain a safety margin.

The terms used in describing the invention have been used in their descriptive sense and not as terms of limitation and it is, of course, intended to include equivalents of the terms used and of the method and apparatus described within the scope of the appended claims.

We claim:

1. A method of drying a hygroscopic plastic molasses comprising flowing it onto a heated drying surface and forming a thin lm of said molasses thereon, heating said lm of molasses at atmospheric pressure to produce a hot frothy film containing occluded gases, scraping the film from the surface and breaking bubbles of the froth to release occluded gases.

2. A method of drying a hygroscopic molasses solution containing sugars and mineral salts comprising flowing the solution onto the outer cylindrical surface of an internally heated cylindrical rotating drying drum to form a thin lm of molasses thereon, heating said film of the solution thereon at atmospheric pressure to produce a frothy film, scraping the film from the surface of the drum and agitating the froth to break bubbles therein and release occluded gases, and then cooling the molasses product thereby produced.

3. A `method of drying molasses comprising flowing the molasses onto the outer cylindrical hot surface of an internally heated rotating cylindrical drying drum to form a thin film of molasses thereon, heating said lm of the molasses at atmospheric pressure to produce a frothy lm, scraping the film from the surface of the drum and agitating the froth to break bubbles therein and release occluded gases, whereby to dry said molasses.

4. A method of drying molasses comprising flowing the molasses onto the outer hot cylindrical surface of an internally heated cylindrical rotating drying drum to form a thin film of molasses thereon, heating said film of the molasses thereon at atmospheric pressure to a maximum temperature of 305v to 335 F. whereby to drive off water from said lm of molasses to dry the same and scraping the dried molasses from the drum.

5. A method of drying molasses comprising flowing the molasses onto the outer hot cylindrical surface of an internally heated rotating cylindrical drying drum to form a thin film of molasses thereon, heati-ng said lrn of the molasses thereon to a maximum temperature of 305 to 335 F. to drive off water from said film, scraping the dried molasses onto a iiat surface from the drum thereby producing a mass of molasses froth on said flat surface and agitating the molasses scraped from the drum onto said flat surface to release bubbles in said froth, then removing the dried molasses from said surface while maintaining the temperature thereof above atmospheric.

6. A method of drying molasses comprising flowing the molasses onto the outer cylindrical hot surface of an internally heated rotating cylindrical drying drum, heating a lm of the molasses thereon to a maximum temperature of 310 to 320 F. to drive off water and produce a frothy lm, scraping the film from the surface of the drum and agitating the froth after it is scraped from said surface to break bubbles therein and release occluded gas as the molasses cools through 70 to 100 F.

7. A method of drying molasses comprising flowing the molasses onto the outer hot cylindrical surface of an internally heated rotating cylindrical drying drum, heating a film of the molasses thereon to a maximum temperature of 310 to 320 F. to drive off moisture and to produce a frothy film, scraping the film from the surface of the drum, agitating the froth as it is scraped from said surface to break bubbles therein and release occluded gas as the molasses cools through 70 to 100 F., and cooling the molasses until it solidies.

8. A method of drying molasses comprising flowing the molasses onto the outer hot cylindrical surface of an internally heated rotating cylindrical drying drum, heating a lm of the molasses thereon to a maximum temperature of 310 to 320 F. to drive 01T moisture and to produce a frothy film, scraping the film from the surface, agitating the froth as it is scraped from the surface of the drum to break bubbles therein and release occluded gas as the molasses cools through 70 to 100 F., then cooling the molasses product to a temperature below about 130 F. in an atmosphere containing less than about 33% relative humidity.

9. A method of drying molasses comprising flowing the molasses onto a rotating drying drum, heating a film of the molasses thereon to a maximum temperature of 305 to 335 F., scraping the dried molasses from the drum and agitating the molasses scraped from the drum by reciprocating blades over the surface of the mass of molasses scraped from the drum whereby to break bubbles and free occluded gases which exist in said mass as a result of said heating and scraping.

10. In an apparatus for drying hygroscopic plastics, a drying drum, a scraper positioned to scrape the film of dried plastic from the drum, a surface over which said dried plastic ows and a reciprocating member positioned above and spaced from said surface to contact the surface of the material scraped from the drum.

11. In an apparatus for drying hygroscopic plastics, a drying drum, a scraper positioned to scrape the film of dried plastic from the drum, a surface over which said dried plastic flows and a plurality of reciprocating members, said reciprocating members being spaced apart a distance less tha-n their path of reciprocation and positioned above and spaced from said surface to contact with the surface of the material scraped from the drum.

12. In an apparatus for drying hygroscopic plastics such as molasses, a rotatable drum having a heated smooth surface upon which a film of said plastic may be heated and dried, a scraper mounted adjacent said surface and adapted to scrape the dried heated film of plastic from said surface and agitating members mounted adjacent said scraper operative to contact and agitate the plastic scraped from said surface, to break up the surface film of bubbles existing in the heated plastic scraped from said drum to release gas occluded in said bubbles.

13. In an apparatus for drying hygroscopic plastic material, such as molasses, a drying drum having a smooth cylindrical surface upon which a thin film of said material may be heated and dried, a scraper mounted to contact said surface to scrape a film of material off of said surface after it has been heated a-nd dried, a member mounted adjacent said scraper operative to cause agitation of said material as it is removed from said drum and a surface adjacent said scraper providing means for removing said material after agitation.

14. A method of drying hygroscopic plastic material, such as molasses and the like, which comprises introducing said material on to a heated moving surface and causing same to spread into a thin lm on said surface, controlling the temperature of said surface above the boiling point of said material, retaining the lm on said surface at atmospheric pressure for a time suicient to dry the same without charring said material, and then scraping the dried film from said surface while simultaneously mechanically agitating the material as scraped to cause any froth produced to be broken up, whereby the dried material scraped from said surface may be flowed substantially free from froth into a collecting vessel.

R. T. NORI'HCUTT.

R. T. NORTHCUTT, JR.

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