US2433818A - Spray drying starch conversion syrup - Google Patents

Description

Patented Dec. 30, 1947 ,IUNITED STAT srnnr DRYING STABCH CONVERSION snwr Herman H. Schopmeyer, Hammond, Ind., assignor to American Maize-Products corporation ofMaine No Drawing. Application March 20, 1945,

Serial No. 583,859

This invention relates to spray drying starch conversion syrup.

Considerable success has been realized in recent years in drying corn syrup in finely atomized condition, to give a highly desirable form of syrup solids. These solids may be shipped in bags, not only saving on the cost of the containers over the cost of cans or drums ordinarily used for syrup but also reducing freight charges uponthe water content of usual corn syrup. In addition the syrup solids have been found to have advantages in certain'arts over the original syrup fro which the solids are made. 7

In spite of. these advantages, the production of the spray dried syrup solids has beenlimited.

"3 Claims. (01.127 34) The chief reason for the limitation is the costliness of the equipment and the expense of operation per ton of product, 7 r

The equipment that'has been in useincludes a large cylinder which is ordinarily 20 ft. or so in diameter with a conical bottom, theshape being generally that of a large cyclonic collector such ,as is in common use for separating suspended the droplets during the drying operation, carefulcontrol being necessary with corn syrup especially .because of the known fact'that the solids of corn syrup are subject to discoloration and the development of off-flavored material if local over heating is permitted or a given droplet, in the spray is exposed for too long a time to the temperature of drying. I

In this operation as performed heretofore, the syrup to be sprayed is preheated to about as high a temperature as permissible without developing off-color or objectionable flavor and the air delivered to the drying chamber or cyclone is also preheated. In order to reduce the temperature gradient as much as possible and thus prevent a scorching, the temperature to whichthe air is ordinarily preheated in drying the corn syrup in commercial operations has been kept at a temperature of about 320 F. or below and the size of the atomized droplets of syrup'kept very small, the smallness of size minimizing the difference of temperature between the inside and outside of the droplets during heating, so as to avoid scorch- Company, a

ing the exterior-while at the same time causing drying of the interior.

I have now discovered a method of increasing by three to five times the capacity of commercial spray drying units for corn syrup or like starch conversion syrup. This increase of capacity has been attained by discarding and proceeding contrary to the previously accepted practices'which were considered necessary with the heat-'decome posable solids of the. syrup.

Briefly stated, the invention comprises preheating starch conversion syrup, spraying the preheated syrup in the form of coarse droplets, of average diameter about to 40 microns, into a stream of moving air preheated to an abnormally high temperatureof about 400 to 520 F., and separating the, resulting dried particles of the'syrup solids from the air at a moisture content of the solids of at least approximately 1. per cent. In the preferred embodiment, the invention comprises the use of somewhat more restricted conditions which givev particularly desirable results, namely, making thev average dimeter of the droplets to microns, preheating the mass of air to 440 to 490, and separating the resulting driedparticles of syrup solids when the moisture content has been reduced .to approximately 0.5% to 4%.- In one embodiment the invention comprises spraying the preheated syrup at-a density of to B. and preferably at about42 to 44 B. I

It will be noted that .two conditions have been changed which should be expected to make for a greater difference of temperature'between the outside and the inside of the droplets of corn syrup and thus increase the danger of overheating of the exterior of the droplets.

First, the droplets have been mademuch larger than those heretofore used. Since the volume of a sphere varies with the cube of the diameter, the droplets which I use are many times greater in weight than .the smaller droplets referred to. Thus a droplet of 15 microns diameter has a volume and therefore weight that is 6 hr 216 times as great as droplets of diameter 2.5 microns.

In the second place, the temperature of drying has been made much higher than that heretofore considered necessary, this again seeemingly increasing the likelihood of local overheating and scorching of the solids of the exterior portions of the relatively large droplets to a certainty.

I have found, however, that the operation may be conducted smoothly and successfully under the extreme conditions recited. Instead of the two changes in conditions contributing each to the overheating or scorching or the exterior, I have found thatthe largcr droplets are able to withstand higher air temperatures, presumably because the wet core protects them until the temperature of the drying air is greatly reduced.

Thus it is possible to work. with air admitted to the cyclonic chamber at temperatures as high as 490 to 520 F. with the product of. dried material of satisfactory flavor and color, whereas, with the smaller and presumably more uniformly heated droplets, temperatures substantially above 320 F. in the inlet air are to be avoided.

In general, the equipment used in my improved process is conventional except for changes of a simple mechanical nature in the spraying mech. anism. These changes involve increase in the size of openings through which the syrup is forced in the spraying process and suitably also increase in the speed of the centrifugal spinner which is provided with these openings and which atomizes the syrup. The size of the openings and speed of rotation required to give the coarse droplets are easily determined by a few simple experiments with any given syrup being sprayed. Thus, I have used to advantage a conventional type of spray mechanism with fans, the atomizer proper consisting essentially of a basket type centrifuge of diameter 14 inches with vertical slots in the outer wall thereof, the slots being spaced apart laterally by V inch on centers and each slot A; inch wide and V inch long, and the basket being rotated at a speed of 14,500 R. P. M. A fan within the mechanism assists indelivering the,

syrup through the slots and a second fan promotes quick removal of the syrup from the outside of the basket and suspension in a rapidly moving stream of air, all in accordance with mechanism heretofore known except for the stated modification of size of slots and speed of rotation.

The starch conversion syrup to be used may be usual corn syrup such as socalled corn syrup unmixed (C. S. U.) or a like material made by conversion of potato, wheat, rice or like starch.

The temperature of preheating of the syrup before spraying may be and preferably is much higher than that previously used in this art, as, for instance, 220 to 280 F., and preferably 240 to 260 F.

This higher temperature of heating by reducing the viscosityof the syrup makes possible spraying more concentrated syrups and thus reduces the evaporation load on the spray drier.

Thus, I may use corn syrups of water content as 50 5 such quantity that the suspended air which is separated from the dried syrup solids at the bottom of the cyclone issues from the cyclone at a temperature around 160 to 200 F., the syrup solids themselves are dried to a moisture content of /2 to 4% and their temperature is about 110 to 130 F. at the time of the separation.

Plant scale data, on a. typical run using the corn syrup unmixed (C. S. U.) and spray drying it as large droplets predominantly'of size to 40 15 microns, are given below:

n F... 230 Density of C. S. U. feed, 315. ....degrees 43 Intake air temperature of spray dryer Outlet air temperature from spray dryer-- 186 Temperature of discharge of product- F... 119 Color of product .86 Moisture content of product per cent 1.0

Volume of intake air for C. S. U. equivalent to 2,950 lbs. of product per hour cu. ft./min 7,500

C. SLU. feed (temperature. of preheat- In spite of the high temperature of the air usual type and in spite of the large droplets, showing'necessarily an abnormally large difference of temperature between the outside and inside of the droplets, the product was of excellent quality. It was granular and free flowing and entirely satisfactory in color and flavor.

It will be understood that. it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of illustration which does not constitute departures from the spirit and scope of the invention.

What I claim is: 1. The method of spray drying starch conver- 45 sion syrup which comprises preheating the syrup, spraying the preheated syrup, at a temperature low as 19% or slightly less as against 35% which was formerly about the minimum in this operation. In general, I may high as Be. as compared to syrup of density 37 B. that has been found heretofore to work best when the atomization and the temperature of the inlet air were controlled in accordance with. the practice understood to be necessary.

My method of operation is that which is conventional except as specified herein. to be otherwise. The preheated syrup is sprayed into the mass of heated air, the syrup being sprayed in use syrup of density as the form of droplets of averag diameter 15 to 40 microns and preferably 20 to 30 microns. This 65 means that the maior part of the mass of the to B. and preferably 43 to 44 syrup is in the form of droplets of the range of diameters stated and that droplets of smaller diameter constitute at most only a minor part by weight of the total mass of the syrup sprayed.

The syrup is sprayed into the preheated mass of air moving through the drier chamber. As the heat of the air is utilized in evaporating water from the droplets, the temperature of the air falls. The air must be used in quantity ade- Name Date 1,670,101 Dickerson May 15, 1928 2,192,951 Wolfl Mar. 12, 1940 2,324,113 Schopmeyer July 13,1943 2,317,479 Peebles et a1. Apr. 27, 1943 of aboutv 220 to 280 F. and in the form of droplets averaging 15 to 40 microns in diametenintd a moving mass of air preheated to a temperature between 400 and 520 F., and separating the resulting particles of dried syrup solids from the air at a moisture content of the solids of at least approximately 0.5-per cent. 1

2. The method described in claim 1, the syrup I 55 being sprayed at a concentration corresponding to:

a density of 40 to 45 B15. and the preheated air being-used in proportion to dry the syrup solids to a moisture content of 0.5% to 4% as the temperature of the air falls about 250 F. during the drying.

3. The method described in claim 1, the temperature of the preheated air-being 440 to 480 F. HERMAN H. SCHOPMEYER.

rtnrnanncns crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS I Number at the intake to the cyclonic drying chamber of