US3145979A

US3145979A - Rotary drums

Info

Publication number: US3145979A
Application number: US215987A
Authority: US
Inventors: Madsen Frederick Rancke
Original assignee: FLSmidth and Co AS
Current assignee: FLSmidth and Co AS
Priority date: 1962-08-09
Filing date: 1962-08-09
Publication date: 1964-08-25
Anticipated expiration: 1981-08-25

Description

F. R. MADSEN Aug. 25, 1964 ROTARY DRUMS 5 Sheets-Sheet 1 Filed Aug. 9, 1962 FIG. 1

7 2:221; 72* M iMf W F. R. MADSEN Aug. 25, 1964 ROTARY DRUMS 3 Sheets-Sheet 2 Filed Aug. 9, 1962 FIG. 4

FIG. 3

FIG. 6

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ATTORNEY5 INVENTOR F. R. MADSEN Aug. 25, 1964 ROTARY DRUMS 3 Sheets-Sheet 3 Filed Aug. 9, 1962 United States Patent 3,145,979 ROTARY DRUMS Frederik Rmclre Madsen, Copenhagen, Denmark, assignor to F. L. Smidth & C0., New York, N.Y., a corporation of Delaware Filed Aug. 9, 1962, Ser. No. 215,987 6 Claims. (Cl. 263-33) This invention relates to rotary drums and, in particular, to drums provided with conveyer flights and drying chains.

Rotary drums are often used to dry or preheat a slurry of raw mineral material which is to be burned, typical sluiries being those of cement raw materials, lime, and Mesa, which is a spent lime material produced in the paper industry. Rotary drums used for such purposes are generally part of a rotary kiln but may be independent structures. In such a drum, the slurry is heated by hot kiln gases evolved in the kiln as the slurry and the gases travel in opposite directions through the drum. The slurry is moved through the drum by tilting the drum and the drum may also be provided on its inner surface with conveyer flights of helical form which, on rotation of the drum, pick up the slurry and move it axially through the drum.

The heat exchange between the hot gases and the slurry in a simple rotary drum is inefficient, because the gases can only give up their heat to the walls of the drum and to the surface of the slurry. Accordingly, to improve the operation, lengths of chain are often suspended inside such drums to increase the surface area of the slurry subjected to the drying gases. Such chains may be secured at one end to rings on the interior of the drum so that, during rotation of the drum, a number of chains will hang in groups to form curtains across the drum, while other chains on the diametrically opposite side of the ring will rest on the bottom of the drum in the slurry. Each chain lies within the slurry when it rests on the bottom of the drum and, when the drum is rotated, the chain lifts the slurry adhering to it and thus exposes the slurry coating on the chain to the hot gases in the middle of the drum.

In rotary drums having both conveyer flights and chains, the conveyer flights conveying the slurry and the chains exposing the slurry to the hot gases act independently of each other in that the conveyer flights have little eflect on the movement of the chains in the drum and the chains have little eflect on the movement of the slurry by the conveyer flights. The reason is that the conveyor flights in such drums are narrow and of a width generally less than or at most 12%, of the internal diameter of the drum, so that a chain, which rests on a flight at the bottom of the drum soon hangs free and out of contact with the flight as the drum rotates.

Slurry is removed from a chain in such drums when the chain rubs against other chains during the rotation of the drum but slurry can be sticky and, when it is in such a condition, it cannot readily be removed from a chain, to which it adheres. With such slurry, the chains and flights in the drums soon become heavily coated and, in some instances, individual chains may stick together when hanging suspended in the drum. The result is that the coated chains obstruct the free flow of gases through the drum and the efliciency of heat exchange between the hot gases and the slurry is impaired, since the slurry coating on the chains is not constantly renewed. In addition, the slurry in such drums tends to adhere to the conveyor flights and does not move readily through the drum.

The difliculties encountered in the drying and preheating of slurry in rotary drums as heretofore constructed are overcome in a drum embodying the present invention. In the new drum, the width of the conveyor flights, the

3,145,979 Patented Aug. 25, 1964 pitch of the helix formed by each flight, and the length of the chains are so co-ordinated that, on each revolution of the drum, a substantial length of each chain slides and rubs over part of the surface and the edge of at least one flight. As a result, the slurry is scraped from both the chains and the surface of the flights, and an undesirable accumulation of slurry on the chains and flights is prevented.

The dimensions of a rotary drum embodying the invention vary with the size of the rotary kiln, with which it is used or of which it forms a part, and depend to some extent on the composition of the slurry to be treated. However, it is preferable to use flights which make an angle between 40 and with the generatrix of the drum and have a width of between 12% and 45% of the interior diameter of the drum. The length of the chains may then vary between 50% and of the internal diameter of the drum. The chains are so arranged that they extend in a plurality of groups to form curtains lying in radial planes which are axially spaced along the length of the drum and, in addition, a flange may be attached to the edge of each flight to improve the scraping eflect between the chain and flight when a chain slides over the edge of the flight.

A preferred embodiment of the invention is shown in the accompanying drawings, in which FIG. 1 is a cross-sectional view of a rotary drum showing the disposition of the groups of chains;

FIG. 2 is a fragmentary longitudinal sectional view on the line 2-2 of PEG. 1 with chains omitted;

FIGS. 310, incl., are diagrammatic views similar to FIG. 1 showing the positions of a single chain at different stages during a rotation of the drum; and

FIG. 11 is a fragmentary perspective view of a modified conveyor flight.

In the drawings, the rotary drum 1 is shown as forming an integral part of a kiln, in which the slurry moves toward the right in FIG. 2 and the hot gases move in the opposite direction. The drum has a cylindrical steel casing 2 with a refractory lining 3 and includes a section 4 containing the conveyer flight 5 and chains 6 of the invention and a section 7 free of chains. The section 7 extends to a zone 8 containing conventional drying chains 9 connected at both ends to the wall of the drum. The drum is provided with a plurality of rings 10 secured to the interior of the drum to lie in spaced planes normal to the drum axis and the chains 6 are secured at one end to the rings in spaced relation and thus hang free vertically to form a curtain ll, when that part of the ring to which they are attached is at the top of the drum.

The rings 10 are so disposed that the chain curtains 11 are axially spaced along the drum, preferably between 4" and 24", depending on the size of the drum and the properties of the slurry being treated. The flights may project beyond the chains at either end or both ends of the chain section and the distance, through which the flights project, may be as much as the diameter of the drum. The points of attachment of the chains are spaced apart 2 to 8 inches on each ring except that a chain may be omitted, where a flight intersects a chain curtain. Additional chains may be omitted to form gaps in one or more curtains to regulate the flow of gas through the drum.

The flights may extend beyond the last curtain 11 approximately half-way across the zone 7 towards the drying zone 8 and, if desired, may extend entirely through the zone '7. The width of the flights shown in FIGS. 1 and 2 is approximately 20% of the interior diameter of the drum and, as a general rule, the width may vary between 12% and 45% of the internal diameter depending on the drum size and the slurry being treated in the drum. Also, while the drum 1 is shown as being provided with six flights, it is to be understood that the number of flights used is conveniently from 4 to 10 with the number varying according to the drum size and with large drums usually having more flights than small drums.

The length of the chains shown in FIG. 1 is approximately 75% of the interior diameter of the drum. However, the length of the chains may range between 50% and 150% of the internal diameter of the drum with the actual length determined by such factors as the width of the flights and the number of flights used. Thus, in a drum having six flights of a width about 20% of the internal diameter of the drum, the length of the chains may advantageously be about 75% of the diameter.

The movement of a single chain 6 as the drum is rotated may be readily understood by reference to FIGS. 3-10. In explaining the movement of the chain, the flight immediately behind that part of the ring 10, to which the chain is attached, will be referred to as the central flight and the flights on opposite sides of the central flight will be referred to as the rear flight and the front flight, respectively.

In FIG. 3, the chain 6a is shown hanging vertically from its ring 10, which is at the top of the drum, and the chain is obstructing the flow of gases and the chain and its slurry coating are being heated or dried. The group of chains depending from the ring 10 form a curtain 11.

When the drum is rotated approximately an eighth of a revolution in a clockwise direction, as shown in FIG. 4, the chain will assume a position, in which it no longer hangs directly across the path of the gases, and Will come into initial contact with the central flight 5a and the rear flight 5b, although there has been little relative movement between the chain and these flights.

Further rotation will cause the chain to take the position shown in FIG. 5, and, in reaching that position a substantial length of the chain will have slid and scraped across the edges of the central and

rear flights

5a, 5b. The result of the sliding and scraping is that slurry will be removed from the chain and the edges of the flights, on which the chain slides.

Further rotation of the drum through an eighth of a revolution to the position shown in FIG. 6 does not move the chain significantly relative to the central flight 5a but the chain begins to slide back across the edge of the rear flight 5b into the space between the

flights

5a and 5b. In this position, the chain picks up fresh slurry from the bottom of the drum.

Further rotation through an eighth of a revolution to the position shown in FIG. 7 causes the chain to slide back along the edge of the flight 5b until most of the chain lies between the

flights

5a and 5b. The movement of the chain from the position shown in FIG. 6 to that of FIG. 7 causes further scraping of slurry from the chain and the flights.

When the drum rotates so that the chain takes the position shown in FIG. 8, the chain continues to slide into the space between the

flights

5a and 5b and the part of the chain hidden from view will sweep over a substantial area of the flight 5a to remove slurry from it and advance the slurry through the drum. Still further rotation of the drum will cause the chain to take the position shown in FIG. 9, in which the chain will have swept over a further area of the flight 5a.

As the drum continues to rotate, the chain reaches the position shown in FIG. 10, in which it hangs in contact with the edge of the forward flight 5c.

During the rotation of the drum, a chain does not remain in the plane of the curtain, of which it forms a part. Thus, in moving from the position shown in FIG. 3 to that shown in FIG. 4, the chain is pushed forward toward the mouth of the drum by the flight 5a. During the later stages of the revolution of the drum, the chain slides out of the plane of the curtain in the opposite direction. This may be seen in FIG. 2 where the

chains

6a and 6b extend down part of the surface of the flight, with which they are in contact, and are displaced to the right of the plane of the curtain.

In operation of the rotary drum shown in FIGS. 1 and 2, there is at all times a mass of chains slidiing along the surfaces of the

flights

5a and 5b and the weight of the chains insures that the slurry will be freed from the surfaces of the flights. During a complete revolution of the drum, a chain is scraped by the edges of flights both during the downward part of a revolution of the drum and also during the upward part. The sweeping action of the chains along the surface of the flights, however, only takes place when the chains are moving in an upward direction.

A modified form of conveyor flight is shown in FIG. 11 as including a flange 12 secured to the inner edge of the flight 13 to lie normal to the flight. Such a flange improves the scraping action as a chain slides over the edge of the flight.

I claim:

1. A rotary drum having a plurality of axially extending conveyor flights of helical form, mounting means within the drum, and a plurality of chains each secured at one end only to the mounting means between the flights, characterized in that the length of each chain is between 50% and 150% of the internal diameter of the drum, the width of each flight is between 12% and 45% of th internal diameter of the drum, and the interior of the drum inward from the free edges of the flights is open.

2. The drum of claim 1, in which each flight forms an angle between 40 and with the generatrix of the drum.

3. The drum of claim 1, in which the chains are arranged in groups to form a plurality of curtains hanging in respective radial planes spaced axially along the drum.

4. The drum of claim 3, in which the curtains are spaced between 4 and 24 inches.

5. The drum of claim 3, in which the points of attachment to the drum of the chains of each group lie in a plane normal to the axis of the drum and the points are spaced from 2 to 8 inches.

6. A rotary drum for treating a cement raw slurry and having a plurality of helically shaped conveyor flights and a plurality of chains each attached at one end only to the interior of the drum, characterized in that the drum has at least six conveyor flights each of a width between 12% and 45% of the internal diameter of the drum, with each flight making an angle with the generatrix of the drum between 40 and 80, and each chain is of a length between 50% and of the internal diameter of the drum, the chains are arranged in groups to form curtains lying in radial planes with adjacent curtains spaced between 4 and 24 inches, and the points of attachment to the drum of adjacent chains in a group lie spaced between 2 and 8 inches.

References Cited in the file of this patent UNITED STATES PATENTS 2,001,227 Vogel-Jorgensen May 14, 1935 2,230,601 Puerner et al Feb. 4, 1941 FOREIGN PATENTS 473,553 Great Britain Oct. 14, 1937 881,927 Germany July 6, 1953 1,017,007 France Sept. 10, 1952

Claims

1. A ROTARY DRUM HAVING A PLURALITY OF AXIALLY EXTENDING CONVEYOR FLIGHTS OF HELICAL FORM, MOUNTING MEANS WITHIN THE DRUM, AND A PLURALITY OF CHAINS EACH SECURED AT ONE END ONLY TO THE MOUNTING MEANS BETWEEN THE FLIGHTS, CHARACTERIZED IN THAT THE LENGTH OF EACH CHAIN IS BETWEEN 50% AND 150% OF THE INTERNAL DIAMETER OF THE DRUM, THE WIDTH OF EACH FLIGHT IS BETWEEN 12% AND 45% OF THE INTERNAL DIAMETER OF THE DRUM, AND THE INTERIOR OF THE DRUM INWARD FROM THE FREE EDGES OF THE FLIGHTS IS OPEN.