US 3756855 A
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Description (OCR text may contain errors)
Sept. 4, 1973 G. F. DUCHATEAU L 3,755,855
METHOD FOR DRYING CRYSTALLIZED SUGAR Filed May 28. 1971 1 FIG/I.
'I FIG.2. 1 i
/NVE/YTOI2J A T T R/YE) United States Patent Oflice Patented Sept. 4, 1973 3,756,855 METHOD FOR DRYING CRYSTALLIZED SUGAR Georges Francois Duchateau, Tienen, and Paul Joseph Dewulf, Outgaarden, Belgium, assignors to Rafiiuerie tirlemontoise, Brussels, Belgium Filed May 28, 1971, Ser. No. 148,042 Claims priority, applicatisrin Luxemburg, June 3, 1970,
Int. 01. 61st /00 US. Cl. 127-63 5 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a method for drying crystallized sugar within a heated environment.
By the term crystallized sugar must be understood within the scope of the present patent application in particular crystallized sugar in bulk, lump sugar, crystallized sugar in slabs as well as crystallized sugar in loaves.
The aim of the invention is to provide a drying method which may be used:
(a) For the manufacture of crystallized and granulated sugar if it is desired to obtain bright crystals;
(b) For the manufacture of lumps, slabs and loaves of sugar, by molding and compression, in order to provide products having physical characteristics similar to those of products furnished by the Adant method the principal pysical characteristics aimed at are: hardness, resistance to abrasion, porosity, rate of dissolution, density.
(c) For the manufacture of lumps, slabs and loaves of sugar by the Adant method, in order to improve the physical characteristics which are already excellent.
According to present drying methods for sugar, sugar is placed in an environment at as high a temperature as possible and of fairly low humidity. Consequently the water included in the syrup surrounding the crystals evaporates very rapidly which results in the syrup becoming sursaturated with sugar and, consequently, a very fast crystallization takes place; it follows that instead of being deposited on the crystals present the sugar included in the syrup crystallizes in an irregular fashion, in the majority in the shape of very fine grains, which afiect unfavorably the physical characteristics of the finished product, such as hardness, resistance to abrasion, porosity, rate of dissolution and density. When it is a question of sugar in lumps, slabs, loaves, the very fine grains adhere inadequately to the existing crystals, so that the latter are poorly joined together. Moreover, such very fine grains clog the voids between the crystals.
It may be of interest to recall here that when moist sugar is placed in an atmosphere of more or less humid air, two equilibria are simultaneously set up between the three phases present (crystals, syrup and air):
An equilibrium between the crystals and the syrup covering them, the syrup being the more enriched in sugar the higher its temperature and which subsists in the state of saturation, either by dissolveing sugar from the crystals, or by crystallizing part of its sugar.
An equilibrium between the water included in the syrup which covers the crystals and the water contained in the air surrounding the crystals-syrup mixture. This equilibrium is by far the most important, as it is the one which, in the last resort, conditions the first one. This equilibrium is reached when the vapor tension of the syrup is equal to that of the air with which it is in contacting relationship.
It is possible, when studying such equilibrium, to use the concept of relative humidity, which is the actual vapor tension at the temperature considered, expressed as a percentage of the saturating vapor tension of the sugar to be dried at the same temperature; the value at equilibrium is then termed equilibrium relative humidity. When the relative humidity of the air is less than that at equilibrium sugar dries; otherwise it humidifies. This equilibrium relative humidity is mainly conditioned by the putty of the sugar and by the temperature.
In order to meet the disadvantages of the known drying method, in the method according to the invention, the heated environment in which the sugar dries has a relative humidity less than, but close to the equilibrium relative humidity of the sugar to be dried, at the temperature of said environmentBy proceeding in this manner the supersaturation of the syrup surrounding the crystals is maintained in a zone which prevents crystallization in the shape of fine grains, but permits on the contrary to direct it onto existing crystals.
The process according to the invention is particularly suitable for the manufacture of sugar into elements achieved by molding and compressing such as lumps, slabs, loaves. According to this implementation of the method according to the invention, the mixture of crystallized sugar and water is brought to the drying temperature and moulding and compression are carried out in an environment having substantially the same conditions of temperature and relative humidity as those which shall rule during drying. By proceeding in this manner it is not necessary to heat up the moulded and compressed elements to ambient temperature, without losing water by evaporation, which would represent a delicate operation of the process, as regards the control of the ambient relative humidity.
Other details and features of the invention will become apparent from the description hereinafter given by way of non-limiting example, particularly with reference to the accompanying drawing, the three figures of which show three modified forms of plant layouts for working the process according to the invention.
Each of the figures shows a drying enclosure 1 wherein are brought in either the crystallized or granulated sugar in bulk after centrifuging, or elements such as lumps, slabs, loaves obtained by moulding and compression or by the Adant method.
The temperature of the enclosure 1 is selected as high as possible, generally between C. and 85 C., but if it is desired to prevent the sugar taking on colour again, the temperature should for preference be kept below C. Knowing the purity of the sugar to be dried and the drying temperature being set, the equilibrium relative humidity is determined and the relative moisture at which drying inside the enclosure 1 is carried out is then selected, i.e. it will be less than 100% but for preference exceed of the equilibrium relative humidity of the sugar to be dried.
Various means may be applied in order to keep the enclosure 1 at the selected conditions of temperature and relative humidity.
According to FIG. 1, conditioned air, admitted to the enclosure, flows inside a circuit 2 wherein is mounted a selected temperature and relative humidity conditioning set 3; upstream of the conditioning set 3 is branched olf a 3 fresh air inlet 4 in order to make good possible losses of circulating air.
According to FIG. 2, a fan 5, provided inside the enclosure 1, forces the conditioned air admitted at 6, after having fiown through a conditioning set 7 receiving the fresh air to flow in circular manner inside the enclosure, before leaving in 8.
According to FIG. 3, the air leaving the enclosure 1 in 9 is partially discharged to atmosphere in 10 and partially returned to the circuit in 11; the air discharged is replaced by fresh air which passes through a conditioning set 12 and is mixed in 13 with the portion of air not discharged to atmosphere, the mixture being subsequently delivered in 14 to the enclosure 1.
For drying elements such as lumps, slabs, loaves, obtained by moulding and compression, the mixture of sugar and water is moulded and compressed under the same conditions of temperature and relative humidity as those ruling inside the drying enclosure 1. The operations of moulding and compression may be carried out either in a zone provided to that effect of the enclosure 1, or inside a chamber separate from, but connected to the enclosure 1.
This manner of proceeding offers certain advantages compared to known sugar moulding and compression methods, carried out under ordinary drying conditions; indeed, the hot mixture of sugar and moistening water is more fluid than the same mixture when cold, which affords greater ease of moulding; moreover, the hot sugar syrup surrounding the crystals being richer in sugar and therefore of higher density, performs better as a lubricant and enables the crystals to slide more easily one on top of another, which makes the compression easier and ultimately results in a higher density of the finished product.
EXAMPLE The sugar considered is a granulated sugar of 99.95% purity, the equilibrium relative humidity thereof being 82% in a temperature environment equal to 80 C.
The sugar and the water needed for moistening are brought separately to the temperature of 80/ 82 C. and mixed in the ratios of 2 kgs. of water for 100 kgs. of sugar. The mixture, kept at 80 C. is then moulded and compressed in an atmosphere of 80 C. temperature and 72% of relative humidity. The products are subsequently removed from the mould and dried in an atmosphere identical to that of moulding and compressing. The drying time for lumps of sugar having a weight of to 6 grams and an initial moisture of 2% at the start, amounted to 2 hours. The dried products may be packed immediately following their cooling.
Under these conditions lumps, slabs or loaves of sugar are obtained having physical characteristics similar to those of Adant sugar.
Below are listed average values of the results of tests carried out on a lot of samples:
B. Lumps of sugar moulded, compressed and dried according to the method of this invention.
0. Lumps of sugar moulded, compressed and dried according to a conventional method.
The tests were carried out as follows:
Time of dissolution: A lump of sugar is placed on a fine mesh sieve and the whole suspended in distilled water at 20 C. The time of dissolution is determined by monitoring the time needed to bring the weight of the immersed piece of sugar down to zero. In the case of compressed lumps, the piston face is positioned on top.
Test of suction resistance: A lump of sugar is placed inside a rubber appliance connected to a vacuum source. The lump of sugar is immersed in distilled water at 20 C., withdrawn from the water and subsequently dried by suction. This operation is repeated until the lump of sugar collapses. The result of the test is the number of times the lump of sugar resists such operation before collapsing.
Test of resistance to abrasion: This test comprises placing four lumps of sugar in a cylindrical box of 250 cc. which rotates around an axis inclined with reference to the symmetry axis thereof, at the rate of 45 r.p.m. for one hour. The result of the test is the percentage by weight of the lumps after abrasion, with reference to the initial weight of the lumps of sugar subjected to the test.
Density: This is based on the weight and the volume of the tested lumps of sugar.
1. A method for drying crystallized sugar within a heated environment wherein the said environment has a relative humidity less than, but close to the equilibrium relative humidity of the sugar to be dried, at the temperature of said environment.
2. A method as claimed in claim 1, wherein for drying elements of crystallized sugar achieved by molding and compressing crystallized sugar, the mixture of crystallized sugar and water is brought to the drying temperature and molding and compression are carried out in an environment having substantially the same conditions of temperature and relative humidity as those which shall obtain during drying.
3. A method as claimed in claim 1, wherein the drying environment has a relative humidity less than 100% but exceeding 85% of equilibrium relative humidity.
4. A method as claimed in claim 1, wherein the drying temperature is as high as possible in order to increase the rate of crystallization.
5. Method as claimed in claim 4, wherein the drying temperature is between C. and C References Cited UNITED STATES PATENTS 2,249,624 7/ 1941 Bichowsky 3427 3,063,158 11/1962 McFarland 3432 3,257,738 6/1966 Margittai 3427 1,216,554 2/1917 Engel 127-63X 3,175,299 3/1965 BOucher 12763 X OTHER REFERENCES Sugar Industry Abstracts, 27, Abs. 585, p. 139 (1965). Chemical Abstracts, 35: 5739 (1941).
Chemical Abstracts, 48: 11094f (1954).
A. I. Wallis-Tayler, Sugar Machinery, 360-4, William Rider & Son, London, 1924.
MORRIS O. WOLK, Primary Examiner S. MARANTZ, Assistant Examiner US. Cl. X.R.