US3385581A

US3385581A - Rotatable tubular structure embodying a large reserve section and heat exchanger andfurnace embodying same

Info

Publication number: US3385581A
Application number: US535910A
Authority: US
Inventors: Cerles Georges
Original assignee: Pechiney SA
Current assignee: Pechiney SA
Priority date: 1965-03-19
Filing date: 1966-03-21
Publication date: 1968-05-28
Anticipated expiration: 1985-05-28
Also published as: NO117697B; GB1146017A; OA01926A; ES324368A1; SE302661B; LU50698A1; AT274640B; DE1291757B; DE1291757C2; FR1436820A; BE678078A; CH517928A; NL6603548A

Description

G. CERLES ROTATABLE TUBULAR STRUCTURE EMBODYING A LARGE RESERVE SECTION AND HEAT EXCHANGER AND FURNACE EMBODYING SAME Filed March 21, 1966 4 Sheets-Sheet l FIG.I

FIG. 2

m m ma 5 m n 0 BY 77m 14, 7%, M /add May 28, 1968 .CERLE 3,385,581

ROTATABLE TUBULAR ST TURE EMBO INGA LARGE RESERVE TION AND HEAT EXCHANGER AND FURNACE EMBODYING SAME Filed March 1966 4 Sheets-Sheet 2 INVENTOR. GEORGES CE/PLES 777Dw dl, 74/141, lhdzzladai.

fry:

May 28, 1968 G. CERLES 3,385,581

ROTATABLE TUBULAR STRUCTURE EMBODYING A LARGE RESERVE SECTION AND HEAT EXCHANGER AND FURNACE EMBODYING SAME Filed March 21, 1966 4 Sheets-Sheet 3 l' 2s 24 2s 22 1 2a 27 2a FIG. 5

INVENTOR. GEO/P656 CEPLES BY 77 0 1M, M5 4 G. CERLES May 28, 1968 ROTATABLE TUBULAR STRUCTURE EMBODYING A LARGE RESERVE SECTION AND HEAT EXCHANGER AND FURNACE EMBODYING SAME Filed March 21, 1966 4 Sheets-Sheet 4 FIG. 6

ms WA mg F VP M 5 C H M G W 7 E F United States Patent "ice ROTATABLE TUBULAR STRUCTURE EMBODYING A LARGE RESERVE SECTION AND HEAT EX- CHANGER AND FURNACE EMBODYING SAME Georges Cerles, Gardarme, France, assignor to Pechiney- Compagnie de Produits Chimiques et Electrometallurgiques, Paris, France Filed Mar. 21, 1966, Ser. No. 535,910 Claims priority, appliczgio rlisFrance, Mar. 19, 1965, 8

12 Claims. c1. 263-33) ABSTRACT OF THE DISCLOSURE %4-A grade and offset one from the other by a rotation of the same angle of 400/11 grads about the common axis with the direction of winding of the helicoids being opposite to the direction of the rotation of the tube in at least the downstream portion and in which each of the threads is formed of a helicoid segment having a pitch fraction equal to the nth part of the center angle A of the desired reserve and which may include two edges prolonging the grads having a pitch fraction equal to A/2 and formed by the section of the elongation of the helicoid through two planes tangential to the internal cylinder at a tangent to the plane limiting the desired bank, one of the planes passing through one end of the guiding helix traced on the tube while the other plane passes through the other end of the helix.

This invention relates to a method for establishing a reserve of large section in a rotating tubular member and it relates particularly to the means for giving effect to same and to the application thereof to a heat exchanger or tubular furnace (kiln).

In a rotating furnace, having a horizontal or slightly inclined axis about which it is rotated, the furnace is usually supplied at one end with non-gaseous material that normally assumes the form of the receptacle in which it is contained, such as a liquid or a pulverulent material, and the product is usually delivered from the other end. The size of the transverse section of the stream of material traveling along the tube, usually referred to as the bank depends generally on the speed of rotation, the cross-section of the tube, and the instrinsic qualities of the material, particularly the angle of internal friction of the material.

When it is desired to increase the section of the bank independently of the aforementioned parameters, for such reasons as the residence of time in the tube or heat exchange between the material in the tube and a gas in the free portion of the tube, one or more rings, generally called barriers, are positioned coaxially in the tube with the internal diameter of the rings being smalled than that of the tube.

This process has the disadvantage that the section of the material exposed to the gases, either in counter-current or in unidirectional flow, becomes greatly reduced.

3,385,581 Patented May 28, 1968 For example, when the angle below which the bank is seen changes from to 133 and then to grads (90=10O grads), the maximum flow passage at the barrier, compared with the section of the tube, changes from /2 to A and then to /2.

The gas velocities increase in the inverse ratio to the flow section whereby such increased velocity and turbulence causes considerable quantities of solid or even liquid material to be entrained and blown away.

It is an object of this invention to provide a method of establishing a reserve of large section in a rotating tube corresponding to an angle A at the center which may reach 200 grads without causing excessive restrictions in the flow section of the vapors or gases, without causing excessive increase in the velocity or turbulence of the vapors or gases passing through the tube in counter-current or unidirectional flow and without causing excessive loss of material.

It is another object of this invention to provide an arrangement of the type described for carrying this method into effect and it is a related object to practice same in a heat exchanger or in a tubular furnace.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, embodiments of the invention are shown in the accompanying drawings, in which:

FIG. 1 is a sectional view along a plane perpendicular to the axis of a tubular cyclic or rotating heat exchanger;

FIG. 2 is a sectional View similar to that of FIG. 1 but showing a modification in the heat exchanger;

FIG. 3 is a sectional view of the heat exchanger of FIG. 1 which includes a ring designed to provide the reserve of the material in accordance with the practice of this invention;

FIG. 4 is a sectional view of an exchanger in which the reserve is obtained by a helicoidal barrier;

FIG. 5 represents a geometric construction intended to assist in the understanding of the operation of the barrier shown in FIG. 4;

FIG. 6 is a sectional view along a plane perpendicular to the axis, showing a liquid reserve of 155 grads, obtained by means of 8 helicoids with a pitch fraction of 205 grads, with downstream and upstream truncation through planes which are tangential to the internal cylinder and pass through the ends of the external helices; and

FIG. 7 is a view of a thread providing a reserve of 155 grads, formed by a helicoid segment with a pitch fraction of 50 grads and extended by two wedges of 77.75 grads.

In accordance with the practice of this invention, at least one barrier formed by an assembly of n threads is interposed in the flow passage of the material, each of said threads being composed, at least in part, of a helicoid coaxial with the rotating tube. The threads have a pitch fraction equal to g A grads and being derived one from the other by a rotation of the same angle of 400/11 grads about a common axis. The winding direction of the helicoids is opposite to the direction of the rotation of the tube, at least in the downstream portion of the barrier.

The arrangement in accordance with the practice of this invention is formed by at least one barrier in the form of a rotating tube having at least one assembly of n threads therein composed, at least in part, of a helicoid coaxial with said tube. The threads are formed with a pitch fraction equal to %+A grads and are offset one from the other by an angle equal to 400/11 grads. The winding direction of the helicoids is opposite to the direction of rotation of the tube, at least in the downstream barrier portion.

The exchanger shown in FIG. 1 comprises a tube 1 having a horizontal or inclined axis and which is mounted for turning movement about its axis 2 in the direction of the arrow 10. Circulating within the tube and in the vicinity of its lower generatrix is the material 5 that is to be treated. The hot gases for heating or the cold gases for cooling the material circulate at 4 in the vicinity of the highest generatrix of the tube. A segment 3 of the tube 1 is situated between two close axial planes and thus passes successively into the zone 4, where it absorbs units of heat or cold, and into the lower zone, where it gives up the heat units or cold to the material 5. In practice, calorific mass of the exchanger is increased by concentric rings 6, 7, etc. disposed within the tube 1 and in the form of an assembly of hoops held together by spokes 8, as shown in FIG. 2.

From the axis 2 of the tube 1, the mass of material occupies an angle 9, known as the center angle. The quantity of heat transmitted to the material with each revolution of the tube 1 will depend on the center angle. The quantity of heat transmitted will be a maximum for a certain value of this angle, depending somewhat on the nature of the material. In the case of alumina (A1 this optimum value is 135 grads, but the quantity of heat transmitted decreases by an amount of only 5% when this value changes up to 155 grads on down to 100 grads. For reasons of rate of flow, it is preferred to make use of a value between 135 and 155 grads.

When the tube 1 is turning about its axis 2, the straight line forming the section through the plane of FIG. 1 of the plane which limits the desired bank 5 has as its envelope a circle 11 on the center 2.

The center angle 9 is usually obtained (as shown in FIG. 3), by a continuous ring 12 coaxial with the furnace, limited by the internal circle 11. For an angle of 155 grads, only an extremely reduced passage is available to the vapors or to the gases, this passage being of the order of of the total section. The speed of the gas, which is inversely proportional to the flow section, is high, resulting in an increased turbulence that causes considerable quantities of the material 5 to be entrained and blown away, whether the material is liquid or solid.

This invention overcomes this disadvantage by a barrier formed of an assembly of helicoids coaxial with the tube 1 and interposed in the flow of the material 5, as shown in FIG. 4. These helicoids are all of the same pitch fraction and derived from one another by rotation of a same angle about the common axis 2. The winding direction of the helicoids is opposite to the direction of rotation of the tube 1.

The helicoids are truncated by the cylinder 11 coaxial with the rotating tube. The plane 1819, which is tangential to this cylinder and cuts the tube 1, forms with this latter, the cylindrical sector 5, the transverse section of which represents the maximum section of the bank.

If the center angle 9 is equal to A grads and if the carrier is formed by 11 threads of helicoidal form, the pitch fraction of each thread F is determined by:

F=$+A grads Such a pitch fraction permits a liquid reserve to be obtained with a center angle A. In the case of a product in powder form, in which the angle of internal friction is substantial, the pitch fraction can be reduced.

Each helicoid can be truncated by two planes at a tangent to the internal cylinder 11, with each passing through one of the extreme points of the helix representing the intersection of the helicoid in question with the wall of the tube 1.

The pitch can be arbitrary; however, it should not be made too small, so as to avoid an exaggerated pressure drop in the gases or vapors which are passing through the zones free from the helicoids, nor should it be too large, in order to permit the retrogression by a sliding action of the material during the rotation.

The operation of the barrier is explained by assuming that the material to be retained to form a reserve is a liquid and that the rotating tube 1 has a horizontal axis. The explanation is also applicable to the case where the material is a powder and/or the tube is slightly inclined relative to the horizontal.

In the heat exchanger of FIG. 4, a reserve A, which in the case illustrated has a center angle of grads, is obtained by n helicoids, in the present case 8 helicoids. The pitch fraction F is thus:

In order to facilitate the understanding of the operation of the helicoidal barrier, the assembly of FIG. 4 is projected onto the wall of the rotating tube 1 by means of straight lines perpendicular to the axis 2 and passing through this latter, as shown in FIG. 5. This projection is developed along one plane, as illustrated by the lower part of FIG. 5.

The different helicoids 21 to 28 are represented by the straight lines 2121'28-28 inclined on the generatrices of the cylinder, the limits of the

bank

18 and 19 being shown by two straight lines 18' and 19' parallel to the generatrices of the tube 1. The tube is assumed to be seetioned along the generatrix 20, which is represented on the development by two straight lines 20' and 20", which is also parallel to the generatrices. On the development, the upstream edge is at the top of the figure.

As the tube is given only a slow rotational movement (arrow 10), the spaces between helicoids, brought into communication with a plane of upstream liquid, are filled to a level corresponding to this plane. On the development of FIG. 5, it is seen that the liquid, leveled in the compartments between helicoids, always finds an obstacle which prevents the bank from falling below 155 grads. Taken as an example, because of the rotation, the

compartment

23, 22, 22, 23 is invaded by the liquid, the instant 23' comes up to 19'. By following the figure in its rotational movement, it is seen that, at this moment, the point 22 is on the line 18'. The result of this is that after the leveling, the thread formed by the helicoid 22, 22' forms an obstacle to the flow.

This reasoning enables it to be understood that each reserve-forming thread can finally be formed by a helicoid fraction of 400/n grads, at the end of which are added two wedges formed by the section prolonging the helicoid through two planes tangential to the internal cylinder. One of these planes passes through one end of the guiding helix traced on the tube, and the other through the other end of this guiding helix. The pitch fraction of each of these wedges is thus: A/2. FIG. 6 represents such a retaining device for providing a reserve. Comparison with FIG. 4 enables appreciation of the importance of the truncations. FIG. 7 represents a retaining thread of 155 grads formed by a helicoid segment 31 with a pitch fraction 32 equal to:

205 grads =50 grads prolonged by two

wedges

33 and 34 with a pitch fraction 35 equal to:

-7775 grads It is thus seen that, by means of such an arrangement,

the obstruction to the flow of the gases or vapors is reduced to a minimum which is equal to the total section of the tube reduced by the section 36 of the bank. This flow section is thus much greater than that which is obtained by a ring coaxial with the tube, reference being made to 4 of FIG. 3.

Finally, it is possible to localize the reserve to a predetermined length of the tube by providing two helicoidal barriers similar to those described above, but with the upstream barrier having a pitch opposite to that of the downstream barrier. Above the upstream barrier and below the downstream barrier, the movement of the materials is due only to the general parameters including inclination of the tube, speed of rotation, and angle of internal friction.

Where the material to be stopped is a powder and not a liquid, the pitch fractions which have been calculated can be more or less reduced, depending on the angle of the bank.

The applications of the arrangement of this invention are numerous. It can be applied to all the heat exchangers between a gas or a vapor, on the one hand, and a liquid or a powder, on the other hand, with heat exchange taking place in either direction. As a particular example, the invention finds excellent application to a calcining furnace for aluminum oxide and to a cooling arrangement for calcined aluminum oxide.

It is obviously possible to combine the helicoidal barrier with other means, such as, for example, the rings 6 and 7 of FIG. 2 in the same exchanger. It is also possible to multiply the number of helicoidal barriers or the number of pairs of barriers with an opposite winding direction.

It will be understood that changes may be made in the details of construction, operation and arrangement without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A method of establishing, in a rotating tubular structure, a reserve of large section corresponding to a center angle A of up to 200 grads without causing any excessive restriction of the free flow passage for vapors and gases comprising providing at least one barrier formed by an assembly of 11 threads interposed in the flow of the material, at least a part of each thread being composed of a helicoid coaxial with the rotating tube, said threaded portions having a pitch fraction equal to +A grads and being offset one from another by a rotation of the same angle of 400/ n grads about the common axis, the direction of winding of the helicoids being opposite to the direction of rotation of the tube in at least the downstream barrierportion, where said n is equal to the number of threads.

2. The method as claimed in claim 1 in which each of the threads is formed of a helicoid coaxial with the rotating tube.

3. The method as claimed in claim 1 in which each of the threads is formed by a helicoid segment having a pitch fraction equal to the nth part of the center angle A of the desired reserve.

4. The method as claimed in claim 3 in which the grads are prolonged by two wedges having a pitch fraction equal to A/2 and formed by the section of the elongation of the helicoid through two planes tangential to the internal cylinder at a tangent to the plane limiting the desired bank, one of the planes passing through one end of the guiding helix traced on the tube, the other plane passing through the other end of the helix.

5. The method as claimed in claim 1 in which the threads are truncated by a cylinder coaxial with the rotating tube and tangential to the plane limiting the desired bank.

6. The method as claimed in claim 1 in which the reserve is localized to a predetermined length of the rotating tube by providing two similar helicoidal barriers in which the upstream barrier is at a pitch opposite to the downstream barrier.

7. A tubular heat exchanger having a reserve of large cross-section corresponding to a center angle A of up to 200 grads comprising an elongate tube, means mounting the tube for rotation about its lengthwise axis, at least one barrier mounted Within the tube in the form of n threads at least a portion of each of which is composed of a helicoid coaxial with the tube, the threads having the same pitch fraction equal to and offset one from another by an angle equal to 400/n grads, the winding direction of the helicoids being opposite to the direction of rotation of the tube in the downstream portion and in which each of the threads is in the form of a helicoid segment having a pitch fraction equal to the nth part of the center angle A defining the reserve, where said n is equal to the number of threads.

8. A tubular heat exchanger as claimed in claim 7 in which each of the threads is in the form of a helicoid coaxial with the rotating tube.

9. A tubular heat exchanger having a reserve of large cross-section comprising an elongate tube, means mounting the tube for rotation about its lengthwise axis, at least one barrier mounted within the tube in the form of n threads at least a portion of each of which is composed of a helicoid coaxial with the tube, the threads having the same pitch fraction equal to a -FA grads and offset one from another by an angle equal to 400/n grads, the winding direction of the helicoids being opposite to the direction of rotation of the tube in the downstream portion and in which each of the threads is in the form of a helicoid segment having a pitch fraction equal to the nth part of a center angle A defining the desired reserve and in which the threads are prolonged by two wedges having a pitch fraction equal to A/2 and formed by the section of the elongation of the helicoid through two planes tangential to the internal cylinder at a tangent to the plane limiting the desired bank, one of the planes passing through one end of the guiding helix traced on the tube while the other plane extends through the other end of the helix, where said 11 is equal to the number of threads.

10. A tubular heat exchanger as claimed in claim 7 in which the threads are truncated by a cylinder coaxial with the rotating tube and tangential to the plane limiting the desired tank.

11. A tubular heat exchanger as claimed in claim 7 in which a reserve is localized to a predetermined length of the rotating tube by providing two similar helicoidal barriers in which the upstream barrier is at a pitch opposite the downstream barrier.

12. A tubular structure as claimed in claim 7 which comprises a rotating kiln.

References Cited UNITED STATES PATENTS 414,556 11/1889 Lindenthal 263-33 727,540 5/ 1903 Harvey 263-33 3,201,100 8/ 1965 Dossossoy 263-33 FREDERICK L. MATTESON, I 11., Primary Examiner.

JOHN J. CAMBY, Examiner.