US 2188371 A
Description (OCR text may contain errors)
Jan. 30, 1940. MERRIAM 2,188,371
METHOD OF IHPREGNATING PRODUCTS WITH LIQUID AGENTS Filed Sept. 15, 1938 Patented Jan. 30, 1940 PATENT OFFICE METHOD OF IDIPREGNATING PRODUCTS WITH LIQUID AGENTS Charles J. Merriam, Winnetka, Ill., assignor to The Guardite Corporation, a corporation of Illinois Application September 15, 1938, Serial No. 230,111
This invention relates to an improved method of impregnating products with a liquid agent.
In Patent 2,080,179, Russell Wiles and I have disclosed a method of freeing bulk products from non-condensible gas in order to permit the introduction of fumigant or other agent, and particularly of moisture. In that patent the material is subjected without the addition of heat, to a vacuum sufliciently high to boil water from the material at its normal temperature, and the evacuation continued long enough to wash from the material all residual air. Thereafter the product is free to receive any fluid impregnating agent.
In moistening material, however, there is a limit to the amount of moisture which may be added in the form of steam, inasmuch as the condensation of the steam necessarily raises the temperature of the bulk product and with organic materials a few percent of moisture added in this fashion generally or frequently brings the temperature to undesirable heights. For instance wheat increases from 'to F. for each percent moisture condensed from steam.
The repetition of steaming cycles does no good, because the amount of moisture removed by evaporation in cooling the material is equal to the amount added in procuring the equivalent increase in temperature.
In accordance with the present invention means are provided by which an indefinite amount of moisture may be added to bulk products within any given temperature range. This is accomplished by the use of steam at high temperatures and pressures at which it has less heat content than is necessary to expand it to a low temperature and pressure. It is particular- 1y preferred to employ steam above the critical temperature (about 374 C. 706 F.) and above or near the critical pressure (about 3226 lbs. per sq. in. Abs).
At this temperature the steam has a calorific content in the neighborhood of 925 B. t. u.s per pound, whereas the same amount of steam at 150 F. and the equivalent pressure (about 3.7 lbs.) has a heat content of about 1125 B. t. u.s. This means that the deficiency has to be supplied by condensation of moisture inthe steam, or its equivalent, where steam at the-higher uum sufilciently high to evacuate water theretemperature and pressure is expanded to the from, and the evacuation is continued long enough to lower the temperature of the tobacco say, 8-15 F. (from, say, to 65 F.), the vacuum for this purpose reaching around 29.7 inches of mercury (on the basis of a thirty-inch 6 barometer) and then steam at 706 F. and 3226 lbs. pressure is introduced until the temperature in the tobacco has reached F. the moisture picked up will be substantially more than would be added by the use of ordinary steam. Moreover, by evaporating some of the condensed moisture, to markedly reduce the temperature, and then repeating the steaming operation with the supercritical steam a further gain may be accomplished. The cycle may of course be 15 repeated as often as desired, there being a gain each time of 10 to 20% on the total water added by the step. Normally the temperature will be lowered 15-60 F. on each evacuation step.
With tobacco it is generally preferable not 20 to exceed F., and for the many types of tobacco lower limits are observed. Many organic products should not exceed 212 F. and of course, many are heat susceptible at temperatures far lower.
It is preferred that the steam be introduced as close as possible to the material to be treated, in order that the material rather than the evacuating equipment or the nozzles obtain the benefit of the refrigeration.
The process is applicable primarily to organlc products in bulk, but it may be used in any case where the ordinary impregnation methods fan. It is particularly valuable with tobacco in bales or hogsheads, but may be employed to advantage with grain such as wheat, or other organic materials.
While the invention is primarily useful in connection with water, due to the high latent heat thereof, it may be used with other gaseswhere such use becomes necessary or desirable.
The amount of vaporized liquid, such as steam, is generally small compared to the amount of material being treated. The amount is of course not such as to raise the pressure to anything approaching the pressure of the gas used. For most purposes the final pressure will be below atmospheric, or at least close to it because of the nature of the products generally employed. Pressures of several atmospheres however, do not 50 greatly affect the refrigerating effect.
In any event, the final pressure is always one sufficiently low to have'permitted expansionenough to obtain a substantial refrigerating effect from the gas.
A diagrammatic pressure time graph is shown in the drawing. The point marked A illustrates the break in the curve when water begins to boil from the tobacco upon lowering of the pressure to a point equal to the vapor pressure of the water in the tobacco. The point B represents the point at which supercritical steam is introduced; the line 3-0 represents the rise in pressure during the steaming operation; the line C-D represents the evacuation curve followin the steaming, the slope of this curve having been somewhat steepened in order to get the diagram on one page; the line D-E represents a subsequent steaming operation with supercritical steam; the line E--F is a subsequent evacuation curve, likewise steepened; and the line F-G represents a third steaming operation with supercritical steam. The time intervals will. of course, de'pendupon the supply of steam and the capacity of the evacuating equipment. 4
The foregoing detailed description has bee given for ciearness of understanding only, and no unnecessary limitations should be understood therefrom.
1. The method of liquid impregnating a product which comprises substantially freeing it from noncondensible gas and then introducing thereto a substantially saturated gas at a temperature' and pressure at least approaching the critical, and markedly above the temperature and pressure of the product, whereby the temperature ofthe product is raised by condensation of gas thereon.
2. The method of moistening an organic product in bulk which comprises freeing the product substantially from noncondensible gas and producing a subatmospheric pressure thereon, and introducing substantially saturated steam at a temperature and pressure at least approaching the critical to raise the temperature and pressure upon the material.
3. The. method as set forth in claim 2 in which the final temperature of the product is less than 212 F.
4. The method as set forth in claim 2 in which the product is tobacco and the final temperature is below 190 F.
5. The method as set forthin claim 2 in which the product is tobacco.
6. The method which comprises subjecting a bulk product without substantial addition of heat, to a vacuum sufliciently high to cause contained moisture in the product to boil, continuing the evacuation to wash substantially all non ccndensible gas from the product, and then introducing steam at substantially its critical temperature and pressure thereto to increase the pressure to a higher, but subatmospheric pressure.
7. The method as set forth in claim 6 in which the product is again subjected to a vacuum sufficient to cause boiling of contained moisture, the evacuation is continued until the temperature of the product has been markedly reduced, and the steaming step is then repeated whereby the moisture content of the product is progressively increased in each cycle.
CHARLES J. BEER-1AM.