WO2006057023A1

WO2006057023A1 - Yankee cylinder for the papermaking industry, with peripheral circulation of the head transfer fluid

Info

Publication number: WO2006057023A1
Application number: PCT/IT2005/000684
Authority: WO
Inventors: Marco Celli
Original assignee: A. Celli Paper S.P.A.
Priority date: 2004-11-26
Filing date: 2005-11-23
Publication date: 2006-06-01
Also published as: EP1838922A1; ATE394540T1; EP1838922B1; DE602005006626D1; ITFI20040245A1

Abstract

The Yankee cylinder comprises: a cylindrical wall (3) defining an outer cylindrical surface; along said cylindrical wall and therewithin, a chamber (11) divided into annular compartments (11A) for the circulation of a heat transfer fluid; a shaft coaxial with the cylindrical wall and with said chamber, and a plurality of supply conduits (31) of the heat transfer fluid to the annular compartments and a plurality of discharge conduits (33) of the spent heat transfer fluid from the annular compartments (11A).

Description

YANKEE CYLINDER FOR THE PAPERMAKING INDUSTRY WITH PERIPHERAL CIRCULATION OF THE

HEAT TRANSFER FLUID

DESCRIPTION Technical field

5 The present invention relates to a Yankee cylinder, also called Yankee dryer, to be used in a continuous papermaking machine, for example to produce tissue paper.

The invention also relates to a continuous papermaking machine or system comprising one or more Yankee cylinders. 0 State of the art

To produce paper, for example and in particular tissue paper, a pulp made of paper fibers and water is distributed on a forming wire by means of a head box. This thin layer, characterized by a very low dry content (i.e. of fibers), of around 10%-20% in weight, is transferred from one or other of several forming wires or 5 felts to reduce the water quantity. Having reach a suitable consistency, i.e. a suitable percentage of dry content, the ply is transferred from a felt to the outer surface of a Yankee cylinder, characterized by a smooth and shiny outer surface and^" heated ^"infernally with a heat transfer fluid, typically steam. The Yankee cylinder has a very large diameter and steam is made to circulate therewithin at 0 high pressure. The heat supplied by the steam dries the ply, further reducing the humidity content.

The dried ply is then detached from the Yankee cylinder by means of a creping blade or in another way, and the ply is wound in a reel.

The Yankee cylinder is normally made of cast iron, although examples of embodiments in steel (JP-A-55-48146 and US-A-4, 196,689) also exist.

Currently known Yankee cylinders normally have an outer cylindrical surface closed at the ends by variously shaped end walls. A central shaft or axle passes through the cylinder and is used to supply steam therewithin and to collect the condensate, which forms through the effect of transfer of heat through the cylindrical surface towards the paper ply to be dried.

Examples of Yankee cylinder structures of this type are described in the following US patents: 2,685,139; 2,817,908; 2,879,039; 3,061,944; 3,099,543; 3,116,985; 3,118,743; 3,299,530; 3,299,531 ; 3,675,337; 3,911,595; 4,183,149; 4,320,582; 4,501 ,075; 5,335,427; 5,864,963; 5,900,120; 4,196,689. The high pressure of the steam inside the Yankee cylinder and the high inner volume of said cylinder make these machine parts particularly dangerous. In fact, if the cylinder breaks it explodes with the risk of causing serious damage to both systems and people. US patent 3,060,592 describes a "double shell" Yankee cylinder. In this cylinder steam is confined in an single chamber with an annular section, delimited by an outer shell or wall, forming the outer cylindrical surface of the cylinder, and an inner wall coaxial with the outer part and with the axis of the cylinder. The chamber with annular section is connected, by means of a first series of steam supply conduits, to a first portion of the shaft of the cylinder, through which hot steam is fed. A second series of discharge conduits connects the annular chamber to a second portion of the cylinder shaft, through which the spent steam is discharged together with the condensate. The configuration described in this prior patent allows a reduction in the quantity of steam inside the cylinder, but the outer part of the cylinder is nonetheless subject to the same high stresses typical of Yankee cylinders with a single shell, i.e. completely filled with steam.

Yankee cylinders are difficult to produce due to the need to withstand high internal pressures and to the large dimensions of these machine parts. Walls of considerable thickness are required which, besides reducing the heat exchange speed, also cause a considerable increase in the weight of the cylinder. Objects and summary of the invention

The object of the present invention is to provide a Yankee cylinder of new conception, the structure of which is simpler and safer than the structures of currently known cylinders. In substance, according to the invention a Yankee cylinder is provided for papermaking machines, comprising: a cylindrical wall defining an outer cylindrical surface; along said cylindrical wall and therewithin, a chamber for the circulation of a heat transfer fluid divided into a plurality of annular compartments placed side by side along the longitudinal extension of the cylinder, each of which is connected to at least one supply conduit and to at least one discharge conduit of the heat transfer fluid. Therefore, contrary to conventional cylinders, according to the invention the circulation of heat transfer fluid is confined to a chamber with an annular section around the outer cylindrical wall, while most of the inner volume of the cylinder can be devoid of heat transfer fluid. Moreover, the chamber is divided into a plurality of compartments, in each of which the heat transfer fluid is made to circulate by suitable supply and discharge conduits. In this way optimal heating of the surface of the cylinder is obtained and, if required, it is also possible to modify the supply of heat in the various annular sections of the cylinder. The compartments are defined by elements rigidly connected to the outer cylindrical wall of the Yankee cylinder. This considerably increases the rigidity of the cylinder, an important factor especially in view of the fact that a press, for example a shoe press, often acts against the Yankee cylinder. This press exerts high compressive stress to eliminate water from the paper ply fed around the cylinder. The latter must be constructed with sufficient rigidity that it does not become deformed to any significant extent under this load and in some cases it must even be cambered to compensate flexural strain. Strain on the cylinder leads to phenomena of fatigue failure, extremely dangerous for the safety of systems and people. The construction according to the invention, with circulation compartments of the heat transfer fluid produced adjacent to the inner cylindrical wall and integral therewith, allows the cylinder to be stiffened considerably without making it heavier, with consequent advantages in terms of weight, fatigue and buckling strength. The high degree of rigidity is obtained with thinner outer walls compared to those of conventional cylinders, with consequent advantages in terms of heat transmission.

The heat transfer fluid can advantageously be fed through the cylinder shaft, although other solutions for supply and discharge of the fluid would also be possible.

When the heat transfer fluid is fed through the cylinder shaft, each compartment into which the chamber is divided is connected by means of at least one conduit to supply heat-carrying fluid to the central shaft and to a conduit to discharge the spent heat transfer fluid from the central shaft. Preferably, however, several conduits to supply the heat transfer fluid and several conduits to discharge the spent heat transfer fluid are provided for each compartment of the heated chamber, to obtain better distribution of the fluid and consequently better heating of the entire active cylindrical surface of the Yankee cylinder. - A -

In an advantageous embodiment of the invention, the conduits to supply and discharge the heat transfer fluid to and from the chamber are connected to respective headers, in fluid communication with supply and discharge paths of the heat transfer fluid associated with the central shaft, and preferably produced therewithin. Advantageously, more than one header to supply the hot heat transfer fluid and more than one header to collect the spent heat transfer fluid can be provided. These headers can be distributed more or less evenly around the axis of the central shaft and parallel thereto.

The heat transfer fluid can be fed to the cylinder passing through a first projecting end of the central shaft, while the flow of spent heat transfer fluid can be collected through the opposite end of the same shaft, although other solutions, in which the inward and outward flows of the heat transfer fluid occur through the same end of the shaft, would also be possible.

The cylindrical wall of the Yankee cylinder is suitably made of a single piece of sheet metal folded and welded at the ends to ensure continuity of the outer cylindrical surface, while the inner chamber, which may be divided into adjacent annular compartments, is produced by welding components which delimit the individual compartments. In this way a particular strong structure is obtained which allows the thickness of the outer wall to be reduced as the elements welded to one another, forming the individual compartments into which the chamber for circulation of the heat transfer fluid is divided, contribute towards the overall strength of the cylinder.

This results in a simple and particularly light construction of the cylinder with considerable saving of material and noteworthy decrease in the volume occupied by the heat transfer fluid, typically steam.

A further advantage of this is the drastic reduction of the risk of explosion. Further advantageous characteristics and embodiments of the cylinder according to the invention are indicated in the accompanying claims and will be described in greater detail hereunder with reference to a non-limiting embodiment of the invention.

Brief description of the drawings

The invention will be better understood by following the description and accompanying drawings which show preferred although non-limiting embodiments of the invention. More specifically: Figure 1 shows a longitudinal section according to l-l in Figure 3 of a cylinder according to the invention;

Figure 2 shows a front view according to H-Il in Figure 1 ;

Figure 3 shows a cross section according to Ill-Ill in Figure 1 ; Figure 4 shows an enlargement of the section of figure 1 ; and

Figure 5 shows a diagram of a continuous papermaking machine using a Yankee cylinder according to the invention. Detailed description of a preferred embodiment of the invention.

With reference to the accompanying figures, the Yankee cylinder is indicated as a whole with 1. It has an outer cylindrical wall or shell 3 composed of a single steel sheet of adequate thickness, for example, typically 40 mm. The ends of the steel sheet forming the wall 3 are abutted and welded in order to form a continuous outer cylindrical surface.

The cylindrical wall 3 is connected at the ends to two end walls 5, substantially equal, a front view of one of which is shown in Figure 2. The two end walls 5 are fastened to flanges 7 keyed onto a central shaft 9 with ends 9A projecting from the cylinder composed of the walls 3, 5.

The end walls 5 have wide openings 5A delimited by portions of wall 5B having an extension inclined with respect to the radial direction and curvilinear shape. The openings 5A form passages to access the inside the cylinder 1.

A heating chamber, indicated as a whole with 11 and divided into a plurality of annular compartments 11 A, shown in greater detail in the enlargement in Figure 4, extends around the inner surface of the cylindrical wall 5. The individual compartments can be in fluid communication with one another, although in the example shown they are separate from one another, in order to control and regulate the flow of heat transfer fluid in each of them individually, if necessary.

The compartments 11A are defined and delimited externally by the continuous cylindrical wall 3 and at the ends by rings welded to the inner surface of the cylindrical wall 3. In particular, two end rings 13 of greater thickness are provided, welded at the level of the edges of the cylindrical wall 3. These rings 13 have threaded blind holes for screws 15 to clamp the end walls 5. Several intermediate rings 17, thinner than the rings 13 and distributed along the axial extension of the cylinder 1 , are positioned between the two end rings 13. These rings 17 divide the chamber into the compartments 11A. Metal sheets 19, folded to form cylindrical surfaces coaxial with the cylindrical wall 3, are welded to adjacent pairs of rings 13, 17 or 17, 17.

Ultimately, therefore, each compartment 11A is delimited by a portion of the outer cylindrical wall 3, by two consecutive rings 17 (or 13, 17) and by the cylindrical wall formed by a respective metal sheet 19. Consecutive metal sheets

19 are welded to one another along the entire circumferential extension at the level of the respective ring 17, and to the ring itself. Perfectly sealed compartments 11A and a particularly rigid cylindrical structure formed by the continuous outer wall 3, by the walls 19 welded to one another and by the rings 13, 17, are thereby obtained.

The thickness of the metal sheets 19 forming the inner cylindrical walls of each compartment 11A can be substantially lower than the thickness of the continuous metal sheet forming the outer cylindrical wall 3. For example, the metal sheets 19 can have a thickness ranging from 10 to 20 mm. The rings 17 can have thicknesses of the same order of magnitude, typically ranging from 15 to 25 mm, while the end rings 13 can have thickness approximately 4 times greater.

Positioned inside the Yankee cylinder are headers 21 to supply the heat

Transfer^' fluid. typically steam, and headers 23 to collect the spent heat transfer fluid, composed at least in part of condensate. As can be seen in particular in Figures 1 and 3, in the example shown there are four supply headers 21 and four collection headers of the heat transfer fluid 23. The headers 21 and 23 are positioned evenly around the axis AA of the shaft 9 of the cylinder and extend parallel to said axis.

The headers 21 are connected by couplings 21A to a conduit 25 produced inside the shaft 9 and connected, by means of a rotating distributor (not shown and known per se) to a steam source. The steam is thus supplied through the conduit 25 and the couplings 21 A to the four headers 21.

The headers 23 are, on the other hand, connected by couplings 3A to a conduit 27, also produced inside the shaft 9, to collect the spent steam and condensate. Just as the conduit 25, the conduit 27 is also in connection with a rotating distributor for the collection of the steam and condensate. In the example shown the conduits 25 and 27 are produced on two opposed ends of the shaft 9, although it would also be possible to produce them on the same end.

Each header 21 is connected by means of a respective conduit 31 to one of the compartments 11A into which the chamber produced inside the cylinder 1 adjacent to the wall 3 is divided. As four headers 21 are provided, each compartment 11A is supplied by four separate radial conduits 31. Likewise, each compartment 11A is connected through a radial conduit 33 to a respective discharge header 23, so that each compartment 11A is connected by three conduits 33 to the steam discharge.

As can be seen in Figure 1, each header 21 consequently supplies a number of conduits 31 equivalent to the number of compartments 11A and, to obtain an even flow of heat transfer fluid, the header 21 has a variable cross section along the axial extension of the cylinder 1 to take account of the variable flow rate of fluid along this extension. In combination or alternatively, the conduits 31 can be produced with cross sections varying from the first to the last. Similar considerations are valid for the conduits 33 to collect the spent heat transfer fluid and the headers 23, also produced with a variable cross section. Moreover, the conduits 31 and 33 are produced in individual sections joined to one another. More specifically, each conduit 31 and 33 is produced in three sections. The first and the third are connected to the respective header 21 or 23 and the second to the respective inner cylindrical wall 19. The central portion of each conduit is mounted and connected to the end sections after these have been mounted.

As can be seen in particular in Figure 4, the distal ends of the conduits 31 terminate substantially flush with the inner surface of the respective metal sheets 19, which are suitably perforated to allow the passage and discharge of the conduits 31. Instead, the radial extension of the conduits 33 for collection of the spent steam and condensate is greater and the ends thereof, indicated with 33A in Figure 4, are adjacent to the inner surface of the outer cylindrical wall 3 of the Yankee cylinder 1. This is the area in which during rotation of the cylinder 1 the steam condensate collects through centrifugal force. Consequently, the arrangement described allows optimal collection of the condensate, avoiding the needless recirculation of high temperature steam.

Advantageously, flow regulating devices, such as adjustable throttle valves, can be positioned along all or some of the conduits 31 and optionally the conduits 33. In this way it is possible to modify the through section of each conduit, and therefore the flow rate of the heat transfer fluid in the individual compartments 11 A of the chamber 11.

The Yankee cylinder described is advantageously assembled in the following way. Firstly the outer cylindrical wall 3 is produced by folding and butt welding the ends of the metal sheet. After this wall has been produced, the rings 13 and 17 are welded. This operation can start from the end ring 13 and continue with consecutive welding of the various inner rings 17 until reaching the opposite end where the second end ring 13 is welded.

Subsequently the metal sheets 19 are welded to one another and on the rings 17 and 13, as shown in Figure 4. Then the conduits 31 and 33 are mounted, each of which can be formed by several sections assembled together inside the cylinder to simplify mounting. The conduits 31 and 33 are then joined to the headers 21 and 23. As mentioned, the conduits 31 and 33 can also be produced in sections, connected to the headers 21 and 23 and to the walls 19, and central sections connected to the end sections. It would also be possible to produce the headers 21 and 23 in several portions connectable to one another with suitable couplings.

Finally, the end walls 5 are clamped and the cylinder thus completed is subjected to the usual machining for surface hardening, such as spray or plasma treatment of the continuous outer surface of the wall 3. The Yankee cylinder 1 thus obtained can be used in a continuous wet papermaking machine. A schematic example of a machine of this type is shown in Figure 5. A head box 50 distributes a thin ply of a watery pulp of cellulose fibers onto a forming wire 51. The wire, which moves according to the arrow f51 , transfers the ply towards a felt 53. Systems to remove water, of various types and know per se, can be arranged along the wire 51. The ply of cellulose fibers and water is then made to advance from the felt 53 according to the arrow f53 towards the surface of the Yankee cylinder 1 , onto which the ply is transferred and along which it is further dried. The dried ply is then detached from the Yankee cylinder 1 by means of a creping blade 55 and the ply V, dried and creped, is wound to form a reel B. The Yankee cylinder can naturally be used in any other type of system for wet papermaking, even in structures differing substantially from the one provided by way of example and represented schematically in Figure 5.

It is understood that the drawing only shows a simplification provided purely as a practical example of the invention, which may vary in forms and arrangements without however departing from the scope of the concept on which the invention is based.

Claims

1. A Yankee cylinder for papermaking machines, comprising: a cylindrical wall defining an outer cylindrical surface; along said cylindrical wall and therewithin, a chamber for the circulation of a heat transfer fluid; a shaft coaxial with the cylindrical wall and with said chamber, and a plurality of conduits to supply the heat transfer fluid to said chamber and to discharge the spent heat transfer fluid from said chamber; characterized in that said chamber is divided into a plurality of annular compartments placed side by side along the longitudinal extension of the cylinder, each of which is connected to at least one supply conduit and to at least one discharge conduit of the heat transfer fluid

2. Yankee cylinder as claimed in claim 1 , characterized in that said compartments are rigidly connected to said outer cylindrical wall and form a rigid structure therewith.

3. Yankee cylinder as claimed in claim 1 or 2, characterized in that the heat transfer fluid is supplied and discharged through the shaft and in that each annular compartment is connected to the shaft by means of at least one supply conduit and one discharge conduit of the heat transfer fluid.

^"4. ^"Yankee cylinder as claimed in claim 1 , 2 or 3, characterized in that said outer cylindrical wall is continuous and said compartments are produced by components welded to the inside of the continuous cylindrical wall, said continuous cylindrical wall being composed of a single metal sheet.

5. Yankee cylinder as claimed in one or more of the previous claims, characterized in that each annular compartment is delimited by a portion of the outer cylindrical wall of the cylinder, by an inner wall coaxial with the outer cylindrical wall and by two annular end elements, each inner cylindrical wall being welded continuously and tightly along the edges thereof to corresponding annular elements, so that the outer cylindrical wall, the inner cylindrical walls and the annular elements form a monolithic structure.

6. Yankee cylinder as claimed in one or more of the previous claims, characterized in that each compartment of said chamber is connected with a plurality of supply conduits of said heat transfer fluid and with a plurality of discharge conduits of the heat transfer fluid.

7. Yankee cylinder as claimed in one or more of the previous claims, characterized in that the supply conduits and the discharge conduits of the heat transfer fluid are connected to respective headers.

8. Yankee cylinder as claimed in claim 7, characterized in that said headers are in fluid connection with supply and discharge paths of the heat transfer fluid associated with said shaft.

9. Yankee cylinder as claimed in claim 7 or 8, characterized in that it comprises a plurality of headers each connected to a plurality of supply conduits of the heat transfer flow in said compartments, and a plurality of headers each connected to a plurality of discharge conduits of the heat transfer fluid from said compartments.

10. Yankee cylinder as claimed in claim 8 or 9, characterized in that said headers are arranged around the shaft of the cylinder and extend parallel thereto.

11. Yankee cylinder as claimed in claim 8, 9 or 10, characterized in that said headers have a variable cross section along the longitudinal extension thereof, to obtain uniform flow rate of heat transfer fluid in the individual compartments.

12. Yankee cylinder as claimed in one or more of the previous claims, characterized in that it comprises flow regulation means, to vary the flow of heat transfer fluid in said annular compartments.

13. Yankee cylinder as claimed in one or more of the previous claims, characterized in that the heat transfer fluid is fed into the cylinder at a first end of said shaft and discharged therefrom at the opposite end.

14. Yankee cylinder as claimed in one or more of the previous claims, characterized in that the conduits through which the heat transfer fluid is fed into the chamber have a smaller radial extension than the conduits through which the heat transfer fluid is discharged from the chamber.

15. Yankee cylinder as claimed in claim 14, characterized in that the conduits through which the heat transfer fluid is discharged have an inlet adjacent to the inner surface of said outer cylindrical wall of the cylinder.

16. Yankee cylinder as claimed in one or more of the previous claims, characterized in that it comprises end walls, to which said outer cylindrical wall and said shaft are connected.

17. Yankee cylinder as claimed in claim 16, characterized in that at least one of said end walls has one or more openings to access the inside of the cylinder.

18. Yankee cylinder as claimed in claim 17, characterized in that said opening or openings are delimited by portions of wall having an extension inclined with respect to a radial direction.

19. Yankee cylinder as claimed in claim 18, characterized in that said portions of wall have a curved extension.

20. Yankee cylinder as claimed in one or more of claims 16 to 19, characterized in that the outer cylindrical wall is integral with two end rings, which frontally close the annular end compartments into which said chamber is divided, and to which said end walls are connected.

21. Yankee cylinder as claimed in one or more of the previous claims, characterized in that said heat transfer fluid is steam or a mixture of steam and water.

22. Yankee cylinder as claimed in one or more of the previous claims, characterized in that it is made of steel.

23. A continuous papermaking machine comprising at least one head box, wires or felts for forming a paper ply, and at least one Yankee cylinder as claimed in one or more of the previous claims.