US3532151A - Thin film continuous evaporating apparatus - Google Patents

Description

Unite States aient lnventors Masahiko Hachiya;

Kosai Hiratsuka; Hiromasa Fukumori, Kudamatsu-shi, Japan Appl. No. 711,107

Filed March 6, 1968 Patented Oct. 6, 1970 Assignee Hitachi, Ltd.

Tokyo, Japan,

a corporation ol'Japan, April 5, 1967 Japan Priority THIN FILM CONTINUOUS EVAPORATING APPARATUS 14 Claims, 10 Drawing Figs.

U.S. Cl 159/111,

159/1Z;259/6,104 Int. Cl BOld 1/22 Field ofSearch 159/9-12,

6(W),6(WH),2(F.),49; 202/236: 18/9, 11:259/6, 1114.131115/(lnquired) Primary Examiner- Norman Yudkoff Assistant Examiner-J. Sofer Atlorney-Craig, Antonelli, Stewart & Hlill ABSTRACT: A thin film continuous evaporating apparatus having at least one substantially frustoconically multi-stepped roll disposed in a casing for rotation therein, said apparatus being operative in such a way that a liquid to be treated supplied into the casing and attached to the stepped tapered sur faces of said roll forming a thin film thereon is transferred from one step to another successively by the action of the rotating r011 while having the surface thereof renewed on every revolution of said roll as a result of being stirred and mixed with the liquid accumulated at each step.

HEAT TRANSFER ffc K E r Mfg/UM CASING H 1 END PLATE/0 9 HOW 7 I 9 J L/0u/0 PRfVfNT/NG Siam/mag gfg'ggjfi JACKET/2 w L I I /2 H047 3 5 TRANS/15R ,TPANS/LP/ Mw/u/w MED/UM 1 BAR/NG{ --zfa za v f H in 4- Q PORT /3 {I SUPPLY PoPr 5 f A 1 -2 l1 ROLLS A Patented Oct. 6, 1970 Sheet 3 of 5 ATTORNEYS THIN FILM CONTINUOUS EVAPORATING APPARATUS The present invention relates to a thin film continuous evaporating apparatus using a roll or rolls.

An apparatus to be used for the continuous treatment of a viscous substance is required to be capable of mixing the substance uniformly, renewing the surface of the substance frequently and preventing back flow of the substance and transferring the substance successively therein. For instance, in the continuous polymerization reaction ofa high molecular compound which is carried out by releasing the volatile substances present in the reaction system therefrom, the reaction can be accomplished in a short period of time by making the thickness of the film of the compound thin and constantly renewing the surface of said compound. Of the conventional apparatus used for the treatment of a highly viscous liquid, however, only a few are capable of processing such a liquid quantitatively continuously by forcibly spreading said liquid into the form of a thin film, exposing said thin film ofliquid to the predetermined pressure condition used and renewing the surface of said thin film-forming liquid periodically.

The object of the present invention, therefore, is to provide a thin film continuous evaporating apparatus which comprises a casing and at least one multi-stepped roll, and which is operative in such a way that a liquid to be treated, supplied into the casing, is attached to the surface of said roll to be exposed to the atmosphere in the form of a thin film of a predetermined thickness and is transferred from one step to another successively by the action of the rotating roll while forming a thin film on each surface, said thin film of the liquid on each step being stirred and mixed with the liquid accumulated at said step on every revolution of said roll. Namely, the present invention is intended to promote a removal of volatile substance and thereby to increase the amount of the liquid which can be processed in a unit time, by increasing the surface area of the liquid and simultaneously by increasing the frequency of the surface renewal of said liquid.

Other objects and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate embodiments of this invention and in which:

FIG. I is a transverse cross-sectional plan view of an embodiment of the substantially frusto-conically multistcpped roll type thin film continuous evaporating apparatus according to this invention, which comprises two taper rolls;

FIG. 2 is a cross-sectional view taken on line II-II of FIG. 1;

FIG. 3 is a detail enlargement ofa portion indicated by A in FIG. 2;

FIG. 4 is a transverse cross-sectional plan view of another embodiment ofthis invention which comprises one roll;

FIG. 5 is a cross-sectional view taken on line V-V of FIG. 4;

FIG. 6 is a transverse cross-sectional plan view of still another embodiment of this invention which comprises two rollsconsisting ofa multistepped roll having concave roll surfaces and a multi-stepped roll having convex roll surfaces;

FIG. 7 is a transverse cross-sectional plan view of still another embodiment of this invention, which comprises two rolls consisting ofa multi-stepped roll having concave roll sur faces and a multi stepped roll also having concave roll surfaces;

FIG. 8 is a diagram graphically illustrating the relationship between the axial distance of the roll and the peripheral speed of the roll surfaces, in the apparatus shown in FIG. I, in which numerals I and 2 scaling the abscissa indicate the position of the end surface of each step respectively;

FIG. 9 is a diagram graphically illustrating the relationship between the axial distance and the peripheral speed of the roll surfaces, in the apparatus shown in Fl(i. 6, in which numerals I and 2 scaling the abscissa indicate the same as in FIG. 8; and

FIG. I0 is a diagram graphically illustrating the relationship between the axial distance and the peripheral speed of the roll surfaces, in the apparatus shown in FIG. 7, in which numerals I and 2 scaling the abscissa indicate the same as in FIG. 8.

One embodiment of the present invention, which comprises twosubstantially frusto-conically multistepped rolls, will be described with reference to FIGS. 1, 2 and 8. Referring first to FIG. 1, a pair of main working substantially frusto-conieally multi-stepped rolls'l and 2 are axially disposed in a casing 7 in such a manner that the roll surfaces of the respective rolls converge in opposite direction to each other and define a slight space therebetween. At'one end of the rolls 1 and 2 is provided a supply port 13 for a liquid to be treated, while at the other end thereof is provided scraper :means 14. The rolls 1 and 2 are provided at those end portions thereof which are closed to the liquid supply port 13 with back-flow preventing roll segments 3 and 4 respectively, and these segments are sharper than the other working roll segments of the respective multi-stepped rolls. These back-flow preventing roll segments 3 and 4 also define therebetween a slight space which is smaller in width than the space defined between the working roll segments of the respective rolls. At the other ends of the frusto-conically multi-stepped rolls 1 and 2 are provided liquid discharging roll segments 5 and 6 respectively and the surfaces of those portions of said roller segments which are adjacent to the discharge port and scraper means 14 are parallel to each other. Each of the discharging roll segments 5 and 6 is provided on that portion of the surface thereof located rearwardly of the scraper means with a reverse screw by which the liquid is prevented from flowing rearwardly of the scraper means.

The peripheral wall of the casing 7 is surrounded by a heating jacket 8, while end plates 10 of the casing 7 are covered by respective heating jackets 12, so that the interior of the casing is maintained at a desired temperature. The end plates 10 are fixed to flanges 9, formed at the opposite ends of the casing 7, by means of bolts. Reference numeral 11 designates bearings in which the axes of the respective rolls are journaled.

Now, a liquid discharge device of the apparatus will be described with reference to FIG. 2. The discharge port and scraper means 14, which as described previously, is disposed adjacent the liquid discharging roll segments 5 and 6 for scraping the liquid from said rolls, is fixedly mounted on a supporting member 15.'The supporting member 15 is fixed to fittings 16 by such means as bolts, which fittings are in turn secured to the casing 7. Disposed below the scraper means 14 is a vertically extending screw conveyor 19 which is housed in a barrel 18 with a slight space therebetween. The barrel 18 has a liquid receiving cone l7 tightly screw threaded to the top end thereof surrounding the top end of the screw conveyor 19. This liquid receiving cone 17 serves to accumulate a viscous liquid therein so that said liquid may be drawn by the screw conveyor smoothly continuously. The barrel 18 is secured in position with its flange 21 fixed to a barrel supporting member 20 by means of bolts, said barrel supporting member being fixed to the casing 7. The screw conveyor 19 is maintained at a predetermined temperature by a heating jacket 22 surrounding the barrel 18, so as to prevent deterioration of the liquid being conveyed thereby. At the lower end of the barrel 18 is provided a discharge nozzle 23. That portion of the screw conveyor 19 extending downwardly of the discharge nozzle 23 is formed with a screw the direction of which is opposite to that of the screw above said discharge nozzle to cause a reverse flow of the liquid. The lower end of the screw conveyor 19 is journaled in a bearing 24 in which it is connected to a driving shaft. The interior of the casing 7 is maintained at a predetermined pressure by a vacuum pump not shown which is in communication with a gas bleeding port 25 provided at the top of j the casing. The heating jacket 8 and the casing 7 therefore are fixedly held in position by supporting arms 26.

In operation, when a liquid to be processed is supplied through the liquid supply port 13 into the casing 7, while rotating the rolls 1 and 2 in the directions of the arrows respectively and maintaining the interior of the casing at a desired temperature by a heating medium circulating through the heating jackets 8 and I2, the liquid is attached to the surfaces of said rolls to form a thin film thereon. When the thin film-forming liquid on each working surface of the roll is brought to a portion where the distance between the surfaces of the counterrotating taper rolls 1 and 2 is minimum, the liquid is scraped from said surface of the roll and subjected to an action which urges said liquid in a direction in which the diameter of the roll decreases in a vertical cross section through the axis of said roll. In this case, if the rates of rotation of the taper rolls 1 and 2 are the same, the liquid is not subjected to any feeding action by the mutual action of said taper rolls, but if the rates of rotation of said rolls 1 and 2 are differentiated by rotating the roll 1 at a rate lower than that of the roll 2, the liquid at the portion where the distance between the surfaces of the taper rolls 1 and 2 is minimum or the minimum spacing portion of said taper rolls 1 and 2, is urged to move towards the discharge rolls 5 and 6. This will be explained in further detail with reference to FIG. 8, The liquid is supplied through the liquid supply port 13 which is located above the minimum spacing portion of the first steps of the respective rolls 1 and 2 adjacent to the back flow preventing roll segments 3 and 4. Since the diameter of each frusto-cone on the roll 1 becomes increasingly larger and that of each frusto-cone on the roll 2 becomes increasingly smaller in going from left to right as seen in FIG. 1, the peripheral speed of each step of the roll 1 becomes increasingly higher and that of each step of the roll 2 becomes increasingly lower in going from left to right as seen in FIG. 1. Therefore, when the peripheral speeds of the taper rolls 1 and 2 are selected such that the latter is always higher than the former, an average peripheral speed at the minimum spacing portion of the rolls 1 and 2 becomes lower towards the right as viewed in FIG. I as indicated by the dotted line in FIG. 8. In other words, the velocity at which the liquid is carried into the engaging portion of the rolls 1 and 2 becomes lower towards the right and accordingly the gradient of the pressure developed by the viscosity of the liquid declines towards the right, with the consequence that the liquid is urged towards the discharge roll segments 5 and 6. In this case, back-flow of the liquid from the working roll segments of the rolls 1 and 2 is completely prevented by the back-flow preventing roll segments 3 and 4 which, as described previously, are tapered sharper than said working roll segments and which are arranged with an extremely small space between the roll surfaces and an extremely short distance between the end surfaces thereof.

The liquid thus moved by the cooperating surfaces of the respective rolls 1 and 2 is led into a gap between the end surface of roll 1 and the confronting end surface of roll 2. In this case, the gap between the confronting end surfaces of the respective steps of the rolls acts as a weir. The action of the gap as a weir becomes stronger when said gap is reduced by sliding either one of the rolls in an axial direction but is mitigated when said gap is increased, providing for smooth flow of the liquid. When the gap is reduced, the liquid is accumulated above the nip of the rolls 1 and 2 at each step. The liquid thus accumulated is renewed on each revolution of said rolls and the thin film of the liquid on each step is also renewed on each revolution of said rolls at the engaging portion of the cooperating steps as a result of being stirred and mixed with the liquid accumulated on said steps. Thus, the counter-rotating rolls I and 2 serves as a sort of multi-step continuous tank, with the confronting end surfaces of said steps acting as weirs through which the liquid is forwarded by the aforementioned action of the surfaces of the rolls. The processing speed of the liquid to be treated can be varied by changing the rates of rotation ofthe taper rolls I and 2. Namely, the quantity of the liquid which can be processed per unit time, can be increased by increasing the average peripheral speed of the rolls 1 and 2 and reduced by lowering said average peripheral speed. The liquid on the surfaces of the rolls 1 and 2 is exposed to the predetermined pressure condition in the form of a uniform thin film during the latter half part ofa complete revolution of said respective rolls and trans ferred from one step to another while having the volatile substances removed therefrom. Upon completion of the process, the liquid remaining on the rolls is scraped by the scraper means 14 which is slightly spaced from the discharge roll segmenls 5 and 6. and drawn by the screw conveyor 19 shown in FIG. 2. The volatile substances removed from the liquid in the casing 7 are discharged to the outside through the bleeding port 25.

Now, another embodiment of the present invention which comprises a single muIti-step taper roll will be described with reference to FIGS. 4 and 5. According to this embodiment, a substantially frusto-conically multi-stepped roll 27 is axially slidably disposed in the casing 7 for rotation therein. A scraper 28 is provided for each step of the taper roll in one side of the casing below said step with a slight space therebetween. In the figures, like numerals indicate the same parts in the embodi-.

ment shown in FIGS. 1 and 2. When a liquid is supplied into the casing 7 through the liquid supply port 13 while rotating the roll 27, the liquid is attached to the surfaces of the respective steps of said roll forming a thin film thereon and scraped by the associated scrapers 28. These stationary scrapers 28 of this embodiment shown in FIGS. 4 and 5 function in the same manner as the roll 1 of the embodiment shown in FIGS. 1 and 2 would function when the peripheral speed of the roll 1 is reduced to zero. More specifically, the relationship between the roller 27 and the scrapers 28 can be compared to the rela tionship between the roll 1 and the roll 2 shown in FIG. 8 as suming that the peripheral speed of the roll 1 is reduced to zero and the curve showing the rate of rotation of the roll 1 agrees with the axis of abscissa while the rate of rotation of the roll 2 remains as it is. The liquid on this taper roll is transferred from one step to another towards the other end of the casing where a discharge port 29 is provided, by the mutual action of the individual steps of the roll and the associated scrapers 28 in the same manner as in the apparatus comprising two taper rolls. By changing the space between each step of the roll 27 and the associated scraper upon sliding said roll axially, the thickness of the thin film of the liquid on the surfaces of the individual steps can be adjusted. On the other hand, the advancing speed of the liquid can be varied by changing the rate of rotation or the average peripheral speed of the roll 27. Thus, it will be understood that the apparatus comprising a single taper roll enables an effect to be obtained which is substantially the same as that obtainable with the apparatus comprising two taper rolls.

Still another embodiment of the present invention which comprises two multi-step rolls, of which one has concave roll surfaces and another has convex roll surfaces, will be described with reference to FIGS. 6 and 9. As shown in FIG. 6, a multi-step roll 30 having concave tapered roll surfaces and a multi-step roll 31 having convex tapered roll surfaces are axially slidably disposed in the casing 7 for rotation therein, in such a manner as to form a slight space therebetween. In the figure. like numerals indicate the same parts as in FIG. 1. When a liquid is supplied into the casing through the liquid supply port 13 while rotating the multi-step rolls 30 and 31 in the directions ofthe arrows. the liquid forms a thin film on the surfaces of the respective rolls 30 and 31. and scraped at the minimum spacing portion of the cooperating steps of said rolls. By selecting the rates of rotation of the rolls 30 and 31 such that the latter is always higher than the former, the average peripheral speed at the minimum spacing portion of the rolls 30 and 31 decreases in the converging direction of the tapered steps, drawing a convexed curve as indicated by the dotted line in FIG. 9. Therefore, the reaction liquid on the surfaces of the rolls 30 and 31 is urged towards the discharge port 14. In this case. the force urging the liquid axially ofthe rolls towards the discharge port 14 is greater in the front half portion and small in the rear half portion of each step ofthe roll, so that the liquid can be accumulated at the rear half portion of each step.

Still another embodiment of the present invention which comprises two multi-step rolls each having concave tapered roll surfaces, will be described with reference to FIGS. 7 and 10. According to this embodiment, two muIti-step rolls 34 and 35 each having concave roll surfaces are axially slidably disposed in the casing 7 in such a manner as to form a slight space therebetween. In this figure. like reference numerals indicate the same parts as in FIG. 1. When a liquid is supplied into the casing through the liquid supply port 13 while rotating the respective rolls 34 and 35 in the directions of the arrows,

the liquid forms a thin film on said respective rolls and scraped at the engaging portion of said rolls. By selecting the rates of rotation of the rolls 34 and 35 such that the latter is always higher than the former, the average peripheral speed at the engaging portion of the rolls 34 and 35 decreases in the converging direction of the roll surfaces of the respective rolls, drawing a concave curve as indicated by the dotted line in FIG. 10. Therefore, the reaction liquid on the surfaces of the rolls 34 and 35 is urged to move towards the discharge port 14. In this case, the thickness of the thin film of the liquid on each step of the rolls 34 and 35 is largest at the central portion thereof, so that the quantity of the liquid accumulated at each step can be increased.

As will be understood from the foregoing description, it is possible according to the present invention, not only to increase the surface area of a reaction liquid to be processed but also to renew the surface of the liquid more frequently than has been possible heretofore, so that the removal of volatile substance can be accomplished in a short period of time and the quantity of the reaction liquid which can be processed for a unit time can be increased.

We claim:

1. A thin film continuous evaporating apparatus comprising a casing, at least one substantially frusto-conically multistepped roll axially and slidably disposed for rotation in said casing, a liquid supply ort and a liquid discharge pon provided in said casing, drive means for rotating said roll in said casing, means associated with the surfaces of said multi stepped roll for scraping the liquid being treated and attached to said surfaces from said surfaces by sliding said roll axially to change the distance between said surfaces and said scraper means and means for transferring the scraped liquid to the succeeding step successively on every revolution of said roll.

2. The evaporating apparatus of claim 1, wherein the casing is provided with a heating jacket.

3. A thin film continuous evaporating apparatus comprising a casing, at least one substantially frusto-conical multi-step roll axially and slidably disposed for rotation in said casing, a liquid supply port at one end and a liquid discharge port at the other end provided in said casing, drive means for rotating said roll in said casing, means for scraping a liquid to be treated attached as a film to the surfaces of each step of said roll from said surfaces and means for transferring the scraped liquid to the succeeding step successively on every revolution of said roll.

4. A thin film continuous evaporating apparatus as set forth in claim 3, which comprises a pair of multi-stepped rolls arranged side-by-side in such a manner that the roll surfaces of the respective rolls converge in opposite directions to each other and each of said rolls has a plurality of steps, each of said steps comprising a frusto-eonical surface, all frusto-cones on each roll being similarly directed but those of one roll being oppositely directed to those of the other roll.

5. A thin film continuous evaporating apparatus as set forth in claim 4 wherein, the surface of one of said rolls is concave and each step of the surface of the other roll is convex.

6. A thin film continuous evaporating apparatus as set forth in claim 4, wherein each step of each roll is concave.

7. The apparatus of claim 4, wherein the casing is provided with a gas bleeding port.

8. The evaporating apparatus of claim 4, wherein the roll is provided with back-flow preventing segments, working roll segments and liquid discharging segments.

9. The evaporating apparatus of claim 8, wherein the angle of the step surfaces of the back-flow preventing segments with respect to the axis of the roll is greater than that of the working roll segments.

10. The evaporating apparatus of claim 9, wherein the liquid discharging segments of said pair of rolls are provided with surfaces which are parallel to each other and adjacent to the scra er means.

ll. e evaporating apparatus of claim 10, wherein each of the liquid discharging segments of said pair of rolls is provided with a reversing screw thread at its end. portion to prevent the liquid from flowing rearwardly of said scraper means.

12. The evaporating apparatus of claim 11, wherein a vertically extending screw conveyor means housed in a barrel is disposed below the scrapper means, said barrel being provided with a liquid receiving means adjacent to said scraper means.

13. The evaporating apparatus of claim 12, wherein the screw conveyor means is provided with a discharge nozzle, the direction of the screw threads below said nozzle being opposite to that above said nozzle to cause a reverse flow of the liquid being treated.

14. The apparatus of claim 13, wherein the screw conveyor means is provided with a heating jacket.

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