US2590849A - Method for drying fibrous sheet material - Google Patents

Description

April 1, 1952 J. DUNGLER METHOD FOR DRYING FIBROUS SHEET MATERIAL Filed Dec. 21, 1948 2 SHEETS-SHEET 1 i M a 1 ,m W M. 7/ Q Q QM 35% /\N A ril 1, 1952 J. DU NGLER METHOD FOR DRYING FIBROUS SHEET MATERIAL Filed Dec. '21, 1948 2 SHEETSSHEET 2 LI I IL l l l nMH .llll'l R q u Patented Apr. 1, 1952 METHOD FOR DRYING FIBROUS SHEET MATERIAL J ulicn Dungler, Basel, Switzerland Application December 21, 1948, Serial No. 66,519 In France December 31, 1947 1 Claim. 1

The present invention relates to a method of and an apparatus for drying fabrics, paper and similar fibrous sheet material.

The method ordinarily used for drying fabrics, which have undergone, for example, a dyeing or finishing or similar treatment, consists in blowing hot air upon the fabric or fiber material while it travels in a continuous motion past a blowing device. The temperature of the heated air vary according to the nature of the drier apparatus and are mostly kept below 100 C. The moisture-laden air is continuously removed by a ventilating system and is replaced by a corresponding quantity of freshair. These apparatus generally operate on the principle of counter fiow, whereby the intake of fresh air occurs at the discharge end of the apparatus in such manner that the material to be treated prior to leaving the machine, comes into contact with hot and dry air. Such a process is rather uneconomical, even if the drying is effected in a heat-insulated chamber, in view of the fact that the moisture-laden but still hot air must be constantly removed, thus resulting in appreciable losses of heat. Another inconvenience of this process resides in the overdrying of the treated material which, in the case of a fabric, renders it hard and brittle, on the one hand, and results in a loss of time and heat on account of the unnecessary expulsion of moisture on the other hand.

The present invention concerns a drying processwhich avoids these and other disadvantages and has as one of its objects to provide means ensuringa predetermined moisture content in the treated material.

A further object of the invention is to provide means affording the steps of effectively vaporizing and drying the fabric or other material within the inner fiber layers thereof as well as on its surface, whereby the time for eliminating or driving out excessiy e moisture may be appreciably cut.

Another objector the present invention is to provide means permitting treatment of elongated material, such as a roll of fabric, in a very economical and uniform manner from start to finish to thereby obtain a predetermined degree of dryness.

A further object of this invention is to provide means for exposing the material to be dried to a gaseous atmosphere of elevated temperature; moisture, temperature and time of exposure bein related and controlledso as to result in a predetermined or desired degree of dryness of the material.

A still further object of the invention is to provide means capable ofmaintaining humidity and pressure of the atmosphere within-'afheating or treatment chamber at predetermined levels.

Yet a further object of the'inven'tion' is to provide means facilitatingpassage of fabric .tobe treated in a continuous path through atreatment chamber, whose inlet and outlet aree'ffectively prevented from losing any appreciable amount of heat from within said chamber while the fabric or material is conveyed to and from said chamber.

It is also an object of the present invention to provide means utilizingand/or reutilizing ina very efiicaciousmanner at least part'of the moisture driven out of the materialunder treatment.

More specifically, it is an object ofthis invention to provide means rendering the possibility of withdrawing or extracting moisture fromthe material under treatment by exposing said material to superheated steam, vapor or similar fluid.

A further object of the invention-is toiprovide means contributing to the conversion of moisture driven out of the material into superheated steam or vapor which is adapted to extract further moisture from said material.

The above and other'objects of the invention will become more apparent from the following description of preferred embodiments, reference being had to the accompanying drawings in which:

Fig. 1 shows, schematically, a longitudinalsection of an apparatus according to the invention.

Fig. 2 is an end elevation of the apparatus of Fig. 1; and

Fig. 3 isa sectional view similar to-tthat of Fig. 1, showing a modified form of an apparatus according to the invention.

Referring now more particularly "to Figs. 1 and 2, there is shown a heat-insulated chamber I provided with two rectangular slots "2 and '3 "in the opposite walls 2a, 2b thereof, these slots forming the delivery and discharge end, respectivelyj for fibrous sheet material or similar article 5 such as a piece of fabric, which'is'tobetreated and which is supplied in bulk and in continuous fashion by means of feed rollers 5 to and'removed from said chamber by means of engageable V rollers 6.

Within the chamber l there are "providedtwo flexible and porous conveyor means I and 38 passing over rollers 9 and [0, respectively; these conveyor means may consist of endless wideime'sh wire bands, spaced-apart and-guided perforated belts of nylon, sisal, hemp and the like or endless and contiguous chains, and are designed to guide the fabric 4 during its passage through said chamber I while the surface of the fabric remains accessible to the drying fluid.

The continuous and uniform drive of these conveyor means I, is indicated in dotted lines in Fig. 1 for claritys sake.

Two blower units II and I2 are disposed in the upper and lower half, respectively, of chamber I. These units are provided, at their sides facing the fabric 4, with respective sets of discharge tubes or nozzles I3 and I4 of any suitable construction such as described in my copending U. S. application Serial No. 762,776, filed July 2 2, 1947, now Patent No. 2,495,163. Furthermore, the blower units II and I2 are equipped with blowers I5 and I6, respectively, whose respective intake pipes I? and I8 open into the interior of chamber I.

A pair of preferably electric-operated heating elements,schematically indicated at 20 and 2|, are mounted in the blower units II and I2, respectively, for heating the drying fluid which the blowers I5 and I6 discharge through upper and lower nozzles I3 and I4.

Two pairs of slidable plates 22 and 23 are arranged above and below the feed or entrance slot 2 and, the exit or discharge slot 3, respectively, in such fashion as to be capable of at least partially blocking or covering these slots in an adjustable manner. Plates 22 and 23 may be fixed in their positions by means of wing nuts 24 engaging threaded bolts 25 which are mounted on the end walls 2a, 2b of chamber I and pass through elongated guide holes 25 provided in said plates 22 and 23.

The operation of the above-described apparatus is as follows:

At the beginningof the drying or treatment operation, the chamber I is filled with air which is drawn into the pipes I! and It by the blowers I5 and I6, respectively, and is forced out through the nozzles I3, l4 after having been heated by the heating elements 20, 2|. The air leaving the discharge nozzles I3, I4 impinges upon the surface of the fabric or other article & passing intermediate said sets of nozzles.

According to an important feature of the invention, the heating elements 23 and 2i raise the gaseous fluid leaving the nozzles I3, I4 to a temperature higher than the boiling point of the liquid which permeates and is contained in fabric 4.

In the case where the liquid to be expelled is water, the temperature of the discharged gaseous fluid is preferably raised to a value between 110 and 130 C., or even higher, if the article under treatment is capable of withstanding such higher temperature.

Assuming the most common case of the liquid to be expelled being water, the air initially present in the chamber I is thus raised to approximately 120 C'. The contact of this hot air with the fabric 4 causes the evaporation of the water contained within the fabric fibers. Since theair temperature is above 100 C., the water already evaporated will be unable to condense, so that the chamber I will become more and more filled with continuously produced water vapor by the action of the drying fluid which is discharged through the tubes or nozzles I3, I4 upon the fabric i. Asa -result, the pressure mountsinside the chamber, thereby giving rise to aflo'w of'the gaseous fluid which tends to escape through slots 2, 3 so as to equalize the pressure prevailing inside the chamber with that of the atmosphere.

According to another feature of the invention,

the intake pipes IT, IS of the blowers I5, I5 feed the nozzles I3, I4, which discharge into the interior of the chamber I, by drawing upon the gaseous fluid existing within the chamber. Since vapor is continuously produced inside the chamber and, for the major part, is recirculated by the blowers I5, I6 upon the continuously moving fabric 4 after being reheated by the heating elements 20, 2I while only a small fraction escapes through the slots 2, 3 to effect the aforesaid equalization, the air present in the chamber I is progressively replaced by superheated steam.

Since the only connection between the interior of the chamber I and the atmosphere is by way of the slots 2, 3, and since the continuous vaporization produces a pressure greater than atmospheric pressure within the chamber, the equalizing fluid flows are directed from the interior toward the exterior of the chamber, thereby opposing the entry of fresh air of atmospheric pressure.

Thus, after a certain starting period, the fluid inside the chamber will consist substantially exclusively of superheated steam having a suitable temperature ranging, preferably, between and C. and maintained at this level by the heating'elements 20 and 2I.

The pressure differential desired to be maintained between the interior of the chamber I and the atmosphere may be controlled by means of the plates 22, 23 which may be adjusted as to the clearance of the slots 2 and 3, i. e. the

cross section of the discharge channels con-.

stituted thereby.

It may be mentioned that it is desirable to reduce the volume of the chamber I to a minimum, in order to decrease the surface of radiation and also the quantity of air which is to be heated.

The method according to the invention offers substantial advantages in comparison with known drying precesses. With respect to drying. by hot air, the method according to the invention affords an appreciable saving of heat by eliminating the large heat losses which are due to the necessary discharge of saturated and hot air into the atmosphere. Furthermore, the process according to the invention permits of a more rapid and uniform drying operation than heretofore known processes operating with temperatures below 100 C. It is to be stressed that the moisture to be expelled is present not merely on the surface of the fabric but also bound in the very interior or center (core) of the flbers.

While, in conventional drying processes, the surface moisture is evaporated directly by the blowing hot air, the liquid or water present in the core of the fibers (bound moisture) must first rise to the surface by capillary action before being able to evaporate, which requires a relatively long time. According to the present invention and in contradistinction to the prior art the use of superheated steam with temperatures above 100 C. and having sufiicient high velocity when impinging on the material results in the partial condensation of said superheated steam, whereby latent heat thereof is liberated which causes increase of the temperature of the mate:

rial to the boiling point of the liquid or water and thus direct vaporization in and elimination of the waterfrom the very heart of the fibers occurs by expansion, so that said liquid escapes in the form of vapor or steam instead of rising to the surface in liquid state by capillarity as is the case in said conventional drying precesses.

According to a feature of the invention, the apparatus described is preferably operated at a speed such that the article to be dried emerges from the heating chamber as soon as a sufficiently high degree of dryness is reached.

It is pointed out that, in a process according to the invention, it is impossible ever to arrive at a complete dryness even if the article should remain in the chamber for a time longer than necessary for the expulsion of the excessive moisture resulting from the treatment or impregnating liquid. One of the reasons therefor is that drying may take place in an atmosphere represented by the vapor of the permeating or impregnating liquid. Accordingly, there will never occur so much loss of moisture that the article dried will become brittle and unmanageable i yet the resulting degree of dryness is at least equal to, if not greater than that generally attainable by drying in the open air. In this connection it may be mentioned that the normal moisture content inherent in wool is about 18%, while that of most other fabrics ranges from 3% to about 16%; these percentages are readily obtainable by the method according to the invention.

Should, therefore, the article be accidentally left in the apparatus for a period longer than normal, no hardening or other harmful effects will result such as would occur if the drying took place in an atmosphere of dry and warm air; this is one of the important advantages of the invention.

Referring, now, to the apparatus shown in Fig. 3, there is provided a chamber 3| which is divided by a partition 32 into two compartments A and B through which passes a web 33 of fabric or any other endless fibrous material or article to be treated. This web enters the chamber 3! through the entrance slot 35;, passes subsequently through slot 35 of partition 32 and leaves the apparatus by way of the exit slot 35.

Each of the compartments A, B comprises an upper and a lower blower unit 3? and .38, re-

spectively, which are provided at their opposed surfaces with discharge tubes or nozzles 39 and Gil, respectively. Heating elements GI, 42 are disposed within the units 3?, 38. The discharge nozzles 39, iii are supplied with circulating fluid by the blowers d3, 44.

The fluid, such as steam, is injected'into the units 31 and 38 by means of perforated pipes 45 and 56, respectively, which are connected to a common inlet duct M.

The web 33 to be treated, which is transported toward the inlet slot 3!; by way of suitable guide roller means 4-3, passes over rollers 39 and 5d disposed, respectively, adiacent the inlet and the outlet of chamber 3i.

Exhaust pipes 5! and 52, which communicate with a common outlet duct 53 leading toa regenerator or heat exchanger (not shown), extend into the compartments A and B, respectively.

The vapors escaping through the inlet and outlet slots 34, 36, owing to the superatmospheric pressure prevailing in the compartments A and B, are directed to collector pipes 56, 5'5 which likewise communicate with the duct 53. Each collector is, for this purpose, arranged to dorm a tight seal substantially preventing the escape of fluid into the atmosphere while allowing for the movement of the web 33. As shown on the left-hand side of Fig. 3, the lower end of the collector pipe 55 is provided with two lips 56, 5'! bearing in a fluid-tight manner upon the roller 49 and an auxiliary roller 58, respectively. A slightly different construction is shown on the right-hand side of Fig. 3 where the lips 56a and 51a, provided on the lower end of collector pipe 55, bear upon the roller 50 and upon the underside of the web 33, respectively.

The heat exchanger connected to the duct 53 may take the form of a condenser serving as a source of hot water, obtained from the condensation of the vapors from chamber 31 and adapted to feed, for example, a boiler, and also as a source of heat which is liberated in the condensation process. The vapor collected by duct 53 may, of course, also be utilized for any other purpose; thus it may, for example, serve to energize a lowpressure turbine or similar machine before being conducted to a heat exchanger or condenser.

To promote the circulation and the recovery of the vapors, ventilatin means 53a similar to the blowers d3, d4 may also be disposed in the outlet duct 53 and/or in the collectors 5d, 55.

The c aeration of the apparatus shown in Fig. 3 isas follows:

In accordance with a further feature of the invention, the air initially present in the compartments A, B is removed from the chamber 3i before the drying process proper gets under way, in order to insure that the article to be dried be treated in substantially air-free atmosphere from the very beginning; in this manner the drying of the entire web or other article tai-zes place under essentially uniform conditions. To this end, the compartments A and B are first heated by means of the heating elements all and t2. 'As soon as the desiredtemperature is reached seturated steam (or atomized hot water admitted through the perforated pipes 53 by way of the common inlet duct il provided, for this purpose, with a valve 59, shown. The saturated vapor thus admitted (or produced by vaporization of the introduced water as the result of the high temperature obtaining the chamber 3 i) is now circulated ide t partments A B by means of the blows I in such manner to drive the air out of the chamber This notion is assisted by rise in pressure, pr iuced by the introduction of the vapor and may be further accelerated by the provision of additional ventilating means as previously mentioned.

After the air in the chamber Si is srificientiy rarefied or removed, the web 33 to M dried is introduced into the compartment A in order to be dried the manner described in connection with Figs. 1 and 2, Since the evaporation of the moisture contained in the web 33 produces additional steam, the 'ection of vapor by way of the pipes Q5 and 4t be stopped or at least throttled to such an extent that the added vapor, together h the vapor produced inside the chamber, just i .eintain the desired operatin conditions, that is so say, to maintain a slight gauge pressure is]. preventing the re-entrance of any air.

As above described, the heat required to maintain the temperature in the compartments A, Bis produced by heating elements ii, It is, however, also possible to obtain the necessary heat dur the operation of the apparatus by admitting, through the duct ii, steam of such temperature, pressure and degree of saturation that, upon a sudden expansion of that steam in entering the compartments A and B, a transformation into superheated steam of suitable temperature takes place. In such case, it will be possible to entirely dispense with the heating elements 43 and 44, or at least to reduce their capacity. Assuming, by way of example, that saturated steam under a pressure of kg./cm. is admitted into the chamber, one obtains, upon a sudden expansion, superheated steam of a calculated temperature of 150 C. in the compartments A and B. This superheated steam, when discharged with high velocity through the nozzles 39, 40 by means of the blowers 43, 44 so as to repeatedly impinge upon the web 33, effects through partial condensation upon contact with the web material (liberated latent heat) the vaporization of a large portion of the permeating liquid in the web material.

The use of superheated vapor, in the manner just stated, should be controlled in dependence upon the temperature of the vapor, on the one hand, and its speed of circulation over and across the article to be dried, on the other hand.

Each article has a critical temperature above which the article may suifer damage, yet this temperature may be exceeded for a certain critical timewithout harmful elfects to the article. It is, therefore, necessary to produce. the desired effect (1. e., to obtain the desired degree of dryness) within a period not greater than this critical time; the temperature may then be safely raised above the critical limit referred to.

To this end, it is necessary to circulate the drying fluid or vapor, at a speed such that the operation will be completed within a time less than the critical time. Let us assume, for example, that the critical temperature of an article is 150 C. and that, at this temperature, the critical time is five (5) minutes. It will then be necessary to complete the operation in less than five minutes if the operating temperature is of the order of 150 0., better results being obtainable with shorter operating periods so that a two-minute treatment is to be preferred over a threeminute treatment.

The desired shortness of the treatment may, in all instances, be obtained by suitably conditioning, for example, by increasing the velocity of the circulating treatment vapor (superheated steam). This velocity, in turn, may be held to reasonable values by arranging the layout of the apparatus so that the treatment vapor may impinge readily upon the surface of the article, whereby the projected vapor molecules do not meet any obstacles, thus avoiding the formation of a static layer or stratum of fluid adjacent the article to be treated. It will also be evident that the nozzles are to be designed for maximum efllciency, by providing them with a sufiiciently large cross section and reducing the number of elbows and other obstacles to a minimum.

A construction of such nozzles is more explicitly described in my copending application Serial No. 756,876, filed June 25, 1947.

In view of fresh vapor supply by means of pipes 45 and 45 and due to continuous evaporation which takes place in chambers A and B the quantity of vapor existing in these chambers is constantly increased and must be removed in order to maintain a constant superatmospheric pressure within the apparatus. This withdrawal of vapor is effectuated by means of collectors 5i and 52. Besides, this, vapor escapes in'a spontaneous manner under the influence of the prevailing overpressure (superatmospheric pressure) through the slots at the inlet and outlet 34 and 36 and is captured and conducted into exhaust pipes 54 and 55.

It is further possible, in the plant shown in Fig. 3, to introduce the vapor through the conduit 41 and let said vapor pass first through the heating elements 6!, 42 before conducting the same through perforated pipes 45, 46, the vapor thus serving, indirectly, as a heating means before serving as a drying means.

It will be understood that the vapors collected in the outlet duct 53 need not be utilized in any external device but may be returned to the system, to be reinjected (after reheating and/or recompression, if necessary) by way of the inlet duct 41. While, in the preceding description, the permeating liquid has been assumed to be water, the invention is equally applicable to the expulsion of other liquids from articles of various descriptions.

Thus, the invention will be seen to provide a method of drying an article permeated by a liquid which comprises exposing said article to a gaseous fluid having a temperature higher than the boiling point of said liquid, preferably the vapor oi the liquid itself, and substantially excluding air from contact with the article during such exposure.

According to another of its aspects, the invention will be seen to provide a drying apparatus comprising a chamber I, 35 provided with one or more openings 2, 3, t l, 36 for the insertion and/or withdrawal of the article, and heating means 20, 2|, 4|, 32, 45, 46 inside said chamber adapted to raise the temperature therein above the boiling point of said liquid, whereby part of said liquid will change into vapor, thereby raising the pressure inside said chamber, said opening or openings having a size such as to enable said pressure substantially to prevent the entrance of fresh air into said chamber.

It will thus be seen that there has been provided according to the invention a method of treating or drying fibrous sheet material which contains an impregnating liquid and which is adapted to be moved through a substantially airfree heating enclosure; comprising the steps of impinging on spaced surface areas of said material jets of superheated steam conditioned with respect to its velocity to partly condense said superheated steam and to liberate enough latent heat therefrom on.said material to thereby raise the temperature of the material to the boiling point of said liquid and to transform bound moisture within the material to vapor, which is forced by expansion within said material to the surface thereof, creating suction between said spaced surface areas to thereby draw off said vapor from said surface of said material, and reheating said vapor to arrive at the condition of said superheated steam.

It will further be understood that the invention is capable of numerous adaptations and modifications, particularly in regard to the constructive details shown; for example, the adjusting means 22, 23 may be modified, or supplemented by additional adjusting means, so as to not enable only the width but also the length of the slots 3, 4 to be varied. Other changes will undoubtedly occur to those skilled in the art and are intended to be included in the scope of the invention as defined in the objects and in the appended claim.

Having thus described the invention what is claimed as new and desired to secure by Letters Patent, is:

The method of treating fibrous sheet material which contains an impregnating liquid and which is adapted to be moved through a substantially air-free heating enclosure; comprising the steps of impinging on spaced surface areas of said material jets of superheated steam conditioned :ith respect to its velocity to partly condense said superheated steam and to liberate enough latent heat therefrom on said material to thereby raise the temperature of the material to the boiling point of said liquid and to transform bound moisture within the material to vapor, which is forced by expansion within said material to the surface thereof, creating suction between 10 said spaced surface areas to thereby draw oii said vapor from said surface of said material, and reheating said vapor to arrive at the condition of said superheated steam.

JULIEN DUN'GLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,228,225 Lynah May 29. 1917 2,008,230 Spooner July 16, 1935 2,119,261 Andrews May 31, 1938 2,189,915 Mellor et a1 Feb. 13, 1940 2,225,505 OiTen Dec. 17, 1940

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