US2974725A

US2974725A - Process and apparatus for continuously obtaining dry materials

Info

Publication number: US2974725A
Application number: US726406A
Authority: US
Inventors: Samesreuther Reinhard; Strittmatter Werner; Schneider Rudolf
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1954-05-04
Filing date: 1958-04-04
Publication date: 1961-03-14
Anticipated expiration: 1978-03-14

Description

March 14, 19 1 R. SAMESREUTHER ET AL 2,974,725

PROCESS AND APPARATUS FOR CONTINUOUSLY OBTAINING DRY MATERIALS Filed April 4, 1958 INVENTORS I RE/NHARD SAMESREUTHER, ECKARD SAMESREUTHER, WERNER STR/TTMATTER, RUDOLF SCHNEIDER.

States Reinhard Samesreuther, Eckard Samesreutlier, and Werner Strittmatter, Postfach, Butzbach, Hessen, and Rhdolf Schneider, Krefeld-Uerdingen, Germany, assignors to Farhenfahriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany Filed Apr. 4, 1958, Ser. No. 726,406

Claims priority, application Germany May 4, 1954 3 Claims. (Cl. 159-6) This invention relates to the production of material in the form of finely divided particles free ofliquid from liquid compositions containing the material. The invention may be employed, for example, toproduce finely divided salts, sugar, carbon, chemicals, milk powder or egg'powder, from solutions or suspensions of these materials.

It has been proposed heretofore to employ rotary kilns to recover material in finely divided form from liquid compositions thereof. The use of rotary kilns for this purpose has the disadvantage that heat efficiency is low, since only a small proportion of the total surface can be effectively used for heat transfer, and further, that agglomerates of the material to be recovered tend to form in the rotary kiln. The formation of agglomerates further reduces heat efficiency of such equipment, and commonly requires that disintegrating means, such ashammers, be provided within the kiln in order to insure the production of finely divided dry material. Another disadvantage of rotary kilns is that the material to be recovered cakes up on the moving parts, for example, the cylinder wall, hammers used for disintegrating agglomerates, and stirrers which are commonly provided in order to ensure thorough drying of the material. It has also been proposed to recover material in finely divided form from liquid compositions by spray drying. This manner of operation obviates some of the disadvantages of rotary kilns but has the disadvantage that material produced is commonly of low density.

The present invention provides the method and apparatus which are free of the aforementioned disadvantages, and which is suitable for continuously producing well dried, finely divided, material of relatively high density.

According to the invention, the admixture which can be a suspension of the desired material in a liquid or a solution of the desired material is flowed over a heated surface, and as it flows over the surface it is wiped by the application of pressure to the admixture so as to form the admixture into a thin film on the heating surface. The wiping motion is advantageously transversely of the direction of flow, and also advantageously, the wiping pressure is increased as the liquid composition becomes more concentrated, i.e., the wiping pressure increases in the direction of flow of the liquid composition.

Thus the admixture can be spread out in a series of thin films, disposed along the path of flow and each succeeding film in the direction of fiow can be of lesser thickness than the preceding film. The various films can conveniently be considered evaporating zones. As the admixture passes through these zones, it is concentrated until finally the desired material is left in finely divided form and in dry condition. A wiping motion similar to that used to form the films can be employed to remove th dry desired material from the heated surface. 7

Accordingly, the invention provides a method for obevaporating zones, heat supplied to the surface, evaporates liquid from admixture, thus concentrating the material to be recovered, and as flow of admixture is continued through the zones, the liquid is removed leaving the material desired in dried condition, and as finely divided par-.

ticles.

The apparatus provided by the invention comprises a cylindrical walled vessel including an inner heated surface, feed distributing means for depositing liquid composition in layer form on the said surface, and a plurality of wipers disposed in self-superposed relationship and mounted for movement transversely of the height of the heated surface adjacent thereof. The wipers are adapted to spread liquid composition flowing over the inner surface in thin layers. A feature of the apparatus is that means i.e., spacing means are provided for setting clearances between the inner heated surface and the wipers, and thus for setting the layer thicknesses on the surface. A characteristic of the apparatus is that the spacing means provides greater clearance for each wiper (other than the lowermost wiper) than for the wiper next succeeding it in the direction in which the admixture flows.

The invention will now be described with reference to the accompanying drawing, wherein an embodiment of the invention is set forth. This drawing and the ensuing description are presented in order to' illustrate the invention and not in limitation thereof. In the drawing:

Fig. 1 is a schematic, cut-away view of apparatus according to the invention;

Fig. 2 is a cross-sectional view taken along line 2-4 in Fig. 1.

Fig. 3 is a cross-sectional view taken along line 3-3 in Fig. 1.

Fig. 4 is a cross-sectional view taken along line 4-4 in Fig. 1.

Fig. 5 is a cross-sectional view taken along line 5-5 in Fig. 1.

Fig. 6 is a schematic representation of one manner i which wiping pressure can be varied.

Referring to the drawing, the device there shown comprises a vertically extending cylindrical walled vessel, 1, including an inner surface, 1a, an upper portion 1b, and a lower portion 10, and feed inlets 15 which communicate with the cylindrical vessel upper portion 1b. Disposed at spaced intervals along the outer surface of the vessel are heating jackets 2. The heating jackets can be connected in parallel so that they each receive heating medium, for instance, hot water or steam, at the same temperature, or alternatively, each heating jacket can be charged with a heating medium of different temperature.

A shaft 3, is rotatably mounted coaxially in the vessel 1, and a plurality of wipers 6, disposed in self-superposed relationship are secured to the shaft 3 for rotation theretaining material in the form of finely divided particles with. The shaft 3, is journalled in lower bearing 9, and upper bearing 12 and is sealed by stuffing box 5, positioned below the upper bearing 12. A pulley 4, is connected to the upper end of the shaft 3 for connection to a motor (not shown).

Disposed in the upper portion of the vessel 1, and secured to the shaft 3 for rotation therewith is a feed distributing ring 10. The ring 10 includes a side wall 10a upper edge 10b, and lower edge 10c, and is characterized 'ship is to vary the thickness of the wipers.

3 in that the side wall a curves inwardly from the ring upper and lower edges, 10b and 10c, respectively, forming a trough 10a along the sidewall. The feed inlets are positioned to direct liquid composition fed into the vessel for treatment into'the trough 10d and the rotating feed distributing ring '10 receives the liquid composition in the trough 10a, and distributes the liquid composition in layer form on the inner surface 1a of the vessel within the upper portion 1b thereof. The feed distributing ring 10 includes annular bafile 11 which projects radially outward from the trough 10a adjacent the upper edge 10b of the ring. The annular baffle 11 functions to deflect liquid droplets downwardly into the stream of liquid composition.

Arranged below the distributing ring 10 are a plurality of wipers disposed in superposed relationship and secured to shaft 3 for rotation therewith.

The wipers are freely pivotally mounted on wiper support rings which are disposed at spaced intervals along the shaft 3. The wiper support rings are connected to the shaft for rotation therewith by arms 21 which extend radially outward'from shaft collars 8. The mounting of each wiper 6, is by pivots 7 which project one from the upper edge 6a of the wiper and one from the lower edge 6b of the wiper, and are received for free rotation in openings 7a disposed in the two wiper support rings adjacent the wiper. In the embodiment shown in the drawing, the wipers are vertically disposed. Alternatively, the wipers could be merely inclined.

In the drawing, each of the wipers 6 is a rectangular plate disposed upright, and is unsymmetrical about its pivot axis. Thus, as the shaft 3 rotates, an edge portion of the wipers 6 is thrown radially outward by centrifugal force and presses against the inner surface 111 of the vessel 1. Hence, liquid composition flowing downwardly over the vessel inner surface is spread in thin layers over the surface.

The apparatus of the invention is characterized in that spacing means are provided for setting clearances between the vessel inner surfaces and the wipers so that the liquid composition layer thicknesses can be determined. The spacing means provided are such that the clearance for each of said wipers above the lowermost wiper is greater than the clearance for the next succeeding wiper toward the lower portion of the vessel. One manner of providing clearances of the desired relation- Thus the thickness of the wipers can be increased toward the lower portion of the vessel in order to obtain the desired reduced clearance as the lower portion is approached. This manner of obtaining clearance according to the invention is depicted in Fig. 2, Fig. 3, Fig. 4 and Fig. 5. The thicknesses of the wipers shown in these figures are, respectively, s1, s2, s3, and s4. As is indicated in the drawing the wiper thicknesses increase toward the lower portion of the vessel. The apparatus of the invention can conveniently be constructed so that these wipers provide contact pressures'and film thicknesses as is indicated in the following table.

Contact Pressure, gran is/cm. of wiper edge Wipers Film, mm.

1 In heated portion.

be 'obtainedby proportioning the wipers so that the wipers at different levels extend different distances inwardly from their pivot axes. In this manner, as in the case of variation in thickness, the centrifugal force with which the end portions of the wipers is pressed against the vessel can be varied. Referring to Fig. 6, wipers of radial dimension bl. could be used in place of wipers of thickness s1 shown in Fig. 2, and wipers of radial dimension b2 could be used in place of the wipers of thickness s2, shown in Fig. 3, and likewise wipers of radial dimension b3 and b4 could replace respectively the wipers s3 and s4 shown in Fig. 4 and Fig. 5.

A feature of the apparatus of the invention, as can be seen in Fig. 1, is that a portion of the vessel inner surface 1a adjacent the distributor ring 10 is wiped by Wipers 6, but is not heated. This feature is desirable because it reduces foaming and splashing of the liquid composition while it is being deposited on the inner surface of the vessel by the distributing ring 10.

In the operation of the device shown in the drawing liquid composition introduced through feed inlets '15, flows through annular opening 16 between distributor ring 10 and the vessel 1 and then onto the inner surface of the vessel and then downwardly over this surface. As the liquid composition moves downwardly, the wipers 6 form the liquid into thin layers, the thickness of the layers decreasing toward the bottom of the vessel. Thus, the wipers provide a series of evaporating zones, in each of which the thickness of the film present in the zone is constant. As the liquid composition moves through the various evaporating zones, the material to be recovered therefrom is gradually concentrated, until, in the lower portion 1c of the vessel, the desired material has been freed of liquid. The dried material forms on the inner surface in the lower portion of the vessel and is wiped from the surface by the lowermost of wipers 6. The torque imparted to the dry pulverulent material by the rotation of the wipers is such that the material passes over conical bottom 14 and into discharge 17 without adhering to the vessel surfaces. Vapor evaporated from the liquid composition passes upwardly through the vessel around impingement baffle 19 and out through vapor dischargelS.

It has been found that the turbulence generated in the thin layer on the surface during the transition from the liquid to the solid phase enables the particles which have become solid to he recovered directly in powder form without any formation of lumps. The drying operation can be accelerated by blowing suitable amounts of hot gas or superheated steam into the cylinder from the bottom end.

The advantages of the novel process are that evaporation, drying and pulverisation are combined in a single operation. Due to the small amount of material being treated and the short length of time during which the material remains in the cylinder, substances which are sensitive to temperature are not damaged and thus an improved dry substance is obtained. The apparatus which has been described can be sealed easily and can be operated with vacuum.

The specific surface efficiency of this drier is very high, since the heat transfer conditions are very favourable, particularlyin the upper part, in which concentration by evaporation takes place, and all parts of the heating surface are covered with the product. The finely divided dry product is obtained without any lumps and consequently it is not necessary in most cases for any additional comminution to be carried out.

This application is a continuation-in-part of application Serial No. 505,652, filed May 3, 1955, now abandoned.

The inventionis further illustrated by the following examples without being restricted thereto.

Example 1 Caustic soda solution (50%) is fed on to the heated inner wall of the upright evaporator cylinder, being two meters in height and having a heating surface of 2 m3, and flows down the inner wall in a thin layer. In the interior of the evaporator cylinder is a vacuum of 25 mm. Hg (absolute). Heating is effected by a vapor of about 18 atmospheres and a temperature of about 200 C.

Under the action of the wipers 6, which are disposed in self-superposed relationship and secured by hinges to the shaft 3 rotating in the evaporator cylinder, and which press against the inside wall of the evaporator cylinder at relatively low velocity, the liquid material isdistributed on the inside Wall and converted from the liquid state into the solid state. 3

When 150 kg./h. of caustic soda solution (50%) are fed on the inner side of the surface of the upright cylinder, 75 kg./h. of free pulverulent caustic soda of 99.95% dry substance are obtained.

Example 2 80 kg. of dry aluminum-oxide powder are obtained at atmospheric pressure from 1000 kg./h. of an 8% organic solution containing suspended aluminum-oxide powder of the boiling temperature of 110 C., which is treated in an evaporator cylinder according to the invention, having a diameter of 0.45 m., a height of 4.2 m. and a heating surface of 4.2 m. with steam of 18 atmospheres corresponding to a temperature of about 200 C.

We claim:

1. A device for obtaining material in the form of finely divided particles and free of liquid from a liquid composition formed of an admixture of said material and a liquid, which comprises a vertically extending cylindrical walled vessel including an inner surface, an upper portion and a lower portion, a feed inlet communicating with said upper portion, feed-distributing means disposed in said upper portion for distributing liquid composition introduced into said vessel through said feed inlet in layer form on the inner surface thereof within said upper portion, said feed-distributing means comprising a ring including a side wall, an upper edge and a lower edge, said side wall curving inwardly from the ring upper and lower edges forming a trough along said side wall,

a rotatably mounted shaft coaxially positioned in said vessel, said ring being coaxially mounted on said shaft for rotation therewith, said feed inlet being positioned to direct liquid compositions into said trough, at least three radially extending arms disposed at spaced intervals along said shaft and fixedly secured thereto, a Wiper inclined at an angle to the radius having an upper edge and a lower edge, disposed between each two adjacent radially extending arms, each wiper being freely pivotally mounted on its two adjacent radially extending arms, whereby upon rotation of said shaft the Wipers press against liquid composition flowing downwardly over said inner surface from said upper portion spreading the liquid composition in thin layers over the inner surface, the wipers being proportioned so that the wiping pressure of each wiper is less than the wiping pressure of the next succeeding wiper in the direction of flow, and means for heating the walls of said vessel, whereby liquid can be evaporated from liquid composition flowing down said inner surface, leaving said material free of liquid.

2. A device according to claim 1, the wipers being of different thicknesses whereby variation in wiping pressure is obtained.

3. A device according to claim 1, each wiper being pivotally mounted for movement about an aXis extending from a point on the upper edge thereof to a point on the lower edge thereof, the wipers extending different distances inwardly from their pivot axes whereby variation in wiping pressure is obtained.

References Cited in the file of this patent UNITED STATES PATENTS 1,308,819 Taylor July 8, 1919 2,546,381 Zahm Mar. 27, 1951 2,556,185 Joscelyne June 12, 1951 2,596,086 Muller May 6, 1952 2,807,321 Schneider Sept. 24, 1957 FOREIGN PATENTS 1,074,062 France Oct. 1, 1954