US1141705A - Drying system. - Google Patents

Description

WILLIAM M. GBOSVENOR, OF NEW YORK, N. Y.

DRYING SYSTEM.

Specification of Letters Patent.

Patented June 1, 1915.

Applicatlonnled August 17,1908. again No. 443,524.

'1 of New York, have invented certain new and useful Improvements in DryingSysterns; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and 'use the same.

My invention relates to improvements in,

drying systems, and particularly to systems in which the process is carried out for the evaporation of liquids the vapor densities of which are greater than the density of the medium into which they are to be evaporated. These operations have hitherto been carried out in either of three ways. First, air from the, general atmosphere has been forced or drawn by blowers or fans over the product to be dried, usually being first heated but sometimes first cooled to remove the moisture and then heated, and has thenbeen discharged to the atmosphere again. Second, a quantity of air has been circulated repeatedly by fan or by the effect of heat alone over the material to be dried and over condensing pipes or coils. Third, a

combination of the two has been attempted,

having the full advantage of neither.

In the practice of my invention I preferably do without the aid of fans, as being the most rational and the safest where vapors of combustible nature are to be handled. But instead of relying upon differences of temperature alone to promote the active circulation, I arrange in each case to combine with this cause the much more effective action of the difference between the vapor density of the substance being evaporated and the density of the atmosphere into which it is evaporating.

I have found that the maximum range of temperature allowable in most cases does not produce a difference of density between two air columns sufliciently great to give the desired velocity of circulation, unless the columns are made higher than is practicable in most drying apparatus, and the efliciency decreased by the loss of heat through radiation. For instance, with the colder column at deg. F., and a, maximum temperature of 160 deg. in the hotter column, a difference of 100 deg. R, we can produce a difference in density between the two columns of only about one-sixth of the total weight of the denser column. This is not enough to produce the rapidity of circulation required for many purposes and is entirely inadequate to overcome the greater effect produced by vapor densit when one attempts to evaporate such liquids as benzin, alcohol, and particularly carbon tetrachlorid, the vapors of which are much heavier than air. I have discovered the causes of these ,difliculties and devised a means not only to overcome them but to make these same causes work to the advantage of the drying process. In fact they are made the means to greatly increase the rapidity of circulation, equableness of drying and capacity of the apparatus.

In the accompanying drawing Figure 1 represents a cross section of one form of apparatus appropriate for the practice of my invention and particularly adapted to the drying of a loose material in bulk from which a liquid is to be removed, the vapor of which is heavier than air. Example, the drying of oil meal after extracting with carbon tetrachlorid. Fig. 2 represents a like section of a modified form of apparatus, which can be used for drying material on trays.

Similar letters of reference indicate similar parts throughout the several views of the different forms. Arrows indicate air currents and relative densities.

Referring to the drawing and particularly to F 1 thereof, (1 indicates the location of a heating chamber which in this case is shown as a tube, provided with a steam jacket a. The gases or vapors passing through this tube become heated and their density diminished by consequent expansion, tending therefore to rise therein. Upon passing over the edge of the conveying trough these hot ases come in contact with the material in tie trough z in which it is agitated and moved along by the conveyor 9' located within the evaporating chamber 1). Bfy addition of the heavyivapors the densit o the gaseous mixture is greatly increase It is also somewhat increased by the fall of temperature accompanying evaporation. The enriched vapors therefore flow downward over the lower edge of the trough or holding means for the material to be dried into the condensing chamber 0, surrounded by a water jacket h. In this chamber the vapors are cooled, tend to fall, pass through the connection between the two legs of the V-shaped pipe which serves to form both the heating and cooling chambers a ,and 0 respectively, and reenter the heating chamber to repeat the cycle of their movement. The outer wall 0! of the evaporating chamber may be made of any suitable material, one which is nonconducting to heat being preferred. The holding means for the material is thus situated at a point in the path of the gases where the gases will pass from the material and be materially aided in their movement by the vapor density due to theircoming in contact with the material, that is the change in vapor density of the gases due to their coming in contact with the material acts to aid the circulation of the drying medium. The condensed moisture may be discharged through drip-cock n.

In Fig. 2 is shown an apparatus bounded by rectilinear walls 0 in which the two passages are provided with a common inner wall f which in this case must be made of the best insulating material available under the circumstances. After being heated in the chamber a by passing over the steam or hot water pipes g, the gases ascend into the evaporating chamber 6' and come in contact with the upper surface of the material s read upon the perforated support on.

ontact with this material removes heat from the gases, increasing their density by coolin them. It also adds the heavier va pors urther increasing their density and causing them to sink downward through the material into the condensing chamber 0. If the effect of vapor density is less important than that of temperature the condenser will be located in the upper position indicated by the cooling pipes k. If, however, the vapors are like those of carbon tetrachlorid or even benzole, much heavier than air, the condensing or cooling surface will be located in the lower portion of the condensing chamher as indicated by the pipes h. In one wall d may be located an opening 0 for insertion and removal of material to be dried.

In some systems and under some conditions it may be advisable to use both sets of cooling pipes in and it simultaneously.

The radical nature of the improvement, therefore, becomes even more apparent when the evaporation of a liquid like carbon tetrachlorid is considered. The vapor density of CO1, is about ten times that of air, so that a few per cent. more of CCl present in the heated column of gases would counterbalance the effect of heat, which for a ran e of 100 degrees is only about one-sixth o the weight of the column. A few per cent. of CCl, vapor would therefore stop circulation alto ether if it were endeavored to make the rying medium rise; When the CCl, is

to be evaporated at a moderately high temperature so that its partial pressure in the mixture approximates that of the atmosphere, and the mixture at the higher temperature consists of air and CCL, in a proportion approaching and perhaps exceeding one to one, we have a mixture weighing at least five times as much as air and can obtain an actuating pressure approaching .04.- pound per square foot, producing very rapid circulation indeed. In such cases it is even advisable to locate the condensing. surface low down in the cooling leg, as shown in Fig. 2 at h, since the gain by difference in vapor density far exceeds the loss by partly sacrificing iiference of temperature between the columns.

The best conditions and locations of the condensers are, in each case, to be ascertained only by calculation based upon the partial pressures at the required temperatures of the liquids to be evaporated and the resulting effect on the densities of the two columns of mixed gas and vapor at their respective temperatures.

In both modifications the drying medium or gases are given a prolonged upward and downward movement, that is the upward and downward paths are comparatively long in order that the circulation may be more effectively aided by the variations in vapor density.

What I claim is:

1. In a drying system, a suitable chamber forming a closed cyclic path for the drying medium and arranged so that in one portion of the path the drying medium will pass upwardly and in another portion will pass downwardly, means arranged to heat the drying medium as it passes upwardly and means arranged to cool the drying medium as it passes downwardly, said chamber having means for holding the material to be dried in the upper part of said path where the gases will pass downwardly to the cooling means immediately on leaving the material to be dried, whereby an increase in vapor density of the gases, due to the drying medium coming in contact with the material, acts to aid the circulation of the drying medium.

2. In a drying system, a suitable chamber forming a cyclic path for the drying medium and arranged so that in one ortion of the path the drying medium wil pass upwardly and in another portion will pass downwardl means arranged to heat the drying me ium as it passes upwardly and means arran ed to cool the drying medium as it passes ownwardly, said chamber having means for holding the material to be dried at a part of said path where the gases will pass downwardly to the cooling means on leaving the material to be dried, whereby an increase in vapor density of the gases,

due to the drying medium coming in contact with the material, acts to aid the circulation of the drying medium.

3. In a drying system, an evaporating chamber for drying out liquids, two conduits extending downwardly from said chamber and united at their lower extremities to form a continuous passage to and from the evaporating chamber, one conduit being provided with means for imparting heat to a medium therein and the other conduit being provided with cooling means.

4. In a drying system, an evaporating chamber for drying out liquids, two conduits extending downwardly from said chamber and united at their lower extremities to form a continuous passage to and from the evaporating chamber, one conduit being provided with means for imparting heat to a medium therein and the other conduit being provided with cooling means, said cooling means being located in the lower portion of said conduit.

5. In a drying system, a suitable-chamber forming a closed cyclic path for the drying medium and so arranged that the drying medium will pass upwardly in one portion thereof and downwardly in another portion thereof, means arranged to heat the drying medium as it passes upwardly, and means arranged to cool the drying medium as it passes downwardly, said chamber having means for holding the material to be dried, said last-mentioned means being arranged in the upper part of said path so that the medium will pass upwardly thereto and the mixed gases or vapors will pass downwardly therefrom, said cooling means being arranged partly in the upper part of said path so that the drying medium will come in contact therewith immediately after leaving the material to be dried, and partly in the lower portion of said path.

6. In a drying system, a chamber constructed-to form a suitable path for the drying medium, so that the same will pass upwardly and downwardly, means arranged to heat thedrying medium as it passes upwardly and means arranged to cool the drying medium as it passes downwardly, said chamber having means for holding the material to be dried in said path, said holding means being situated at a point where the drying medium will pass downwardly from the material to the cooling means after it has come in contact with the material and after it has been heated by the heating means and before it has been cooled bythe cooling means, whereby an increase in vapor density of the gases, due to coming in contact with the material, acts to aid the circulation of the drying medium.

7. In a drying system, a chamber constructed to form a suitable path for the drying medium so that the same will be given a prolonged upward and downward movement, said chamber having means for holding the material to be dried in said path,

said holding means being situated at a point.

where the drying medium will pass downwardly from the material after it has come in contact with the material, whereby an increase in vapor density'of the gases, due to coming in contact with the material, acts to aid the circulation of the dr ing medium.

In testimony whereof I a x my signature, in presence of two witnesses.

L. HLBAnLow, WILLIAM H. DAVIS.

Correction hi Letters Patent No. '1 .141 ,705

It is hereby certified that in Letters Patent No. 1,141,705, granted June 1, 1915,

g upon the application of William M. Grosvenor, of New York, N. Y., for an i improvement in Drying Systems, an error appears in the printed specification requiring correction as follows: Page 2, line 48. for the referenee-letter 0! read e; and that the said Letters Patent should he read with this correction therein that the same may conform to the record of the ease in the Patent ()fiice.

Signed and sealed this 29th day of June, A. D., 1915.

[same] J. T. NEWTON,

Actvhzg Commispioner of Patents.

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