High temperature yankee hood

Abstract: A Yankee hood is disclosed for use in drying wet paper webs. The Yankee will provide a manufacturer to operate at supply temperatures above 1000°F at lower total energy costs and at increased production. All major components, supply fans, flow concentrator, air flow equalization plenum and gas burner are consolidated and are mounted directly on the device to eliminate the need for additional space requirements. The hood assembly includes an internal high impingement air system which is supported on a floating structural support member. The nozzle impingement system which incorporates a plurality of nozzle boxes will cover approximately a 240° wrap of a typical Yankee cylinder which will be decoupled from its main support end plate members to allow for increases in cross-machine expansion. The support structure for the externally located direct drive motor is designed to eliminate hood vibrations and operate above the natural building frequency.

Description: FIELD OF THE INVENTION This invention relates to paper drying systems and specifically to a Yankee hood using high temperature impingement air to effect the drying. BACKGROUND OF THE INVENTION Yankee hood systems are used extensively in the manufacture of tissue by the paper industry. Conventionally, the Yankee hood systems have their air processing arrangements located externally of the hood, usually on a mezzanine floor or platform to take advantage of large spaces that are required to install combustion air heaters, circulating fans, their motors and the interconnecting duct work. Such a conventional arrangement would have an air processing system consisting of supply or circulating fans, exhaust fans, combustion chambers and blowers, a burner system and a fuel train all arranged outwardly of the Yankee hood and interconnected with the hood structure through suitable duct work. Large amounts of capital investment are required to engineer and construct a mezzanine floor, equipment foundations and burner room to enclose air heaters and duct work systems. Similarly, large amounts of capital investment are required also to design and build the necessary external air flow duct work distribution systems. Duct work pressure losses between the apparatus and the hood contributes to additional electrical energy consumed by the circulating fans of the air circulation system and this additional energy constitutes upwards of 15 to 20% of the total electrical energy consumed by these fans. As an example, a medium sized Yankee hood system may consume up to 400 kw/hour. Moreover, conventional Yankee hood systems normally operate using maximum supply air temperatures of 537°C (1000°F) and require very large external supply and recirculation air systems. The present invention addresses the shortcomings of the above mentioned conventional hood arrangements that utilize external air heating systems by providing a Yankee hood arrangement which will allow the manufacturer to operate at supply temperatures above 537°C (1000°F) at lower total energy costs while at increased production. The hood according to the invention incorporates an integral air heating system and therefore combines the hood with circulating fans, air heaters and air flow duct work distribution systems into a single assembly with the air system apparatus located inside the hood. PRIOR ART Canadian Patent 677,083 of December 31, 1963 relates to a method and apparatus for drying a web-like material by supplying a gaseous treatment medium to the web in the form of jets being caused to impinge substantially perpendicularly against the surface of the web. The jets are evenly distributed over the entire surface of the web to be treated and the drying medium is discharged from the web at a number of exhaustion points so that the medium is forced to flow along the web from all directions radially towards the exhaustion points. Canadian Patent 713,765 of July 20, 1965 discloses a compact unit including a distribution system within the confines of one enclosure. Canadian Patent 795,026 of September 24, 1968 discloses a compact dryer where the plenum chamber serves simultaneously as a combustion and mixing chamber. US Patent 4,064,637 of December 27, 1977 discloses a cylinder dryer and moisture profiling system. However, the components in this system will distort under heating, and there is no system to compensate for uneven or excessive expansion. As well, this design will suffer from excessive vibration in the air distribution system itself. US Patent No. 5,410,819 of May 2, 1995 discloses a cylinder dryer where the nozzle boxes are slidably fixed to the end walls of the Yankee hood to allow for expansion when heated. However, this attempt at addressing the problem of expansion requires a large number of parts and causes excessive vibration to the transferred to the walls of the Yankee hood. Thus, it is an expensive and unreliable solution to the problem. US Patent 5,416,979 of May 23, 1995 discloses a paper web dryer and moisture profiling system where a plurality of gas burners are individually located in each of the nozzle box interiors and are arranged side-by-side along the length of the nozzle box interiors to produce the hot combustion gases for drying. Other examples of the prior art are to be found in US Patents 3,163,502 December 29, 1964; 5,112,220 May 12, 1992; 4,743,419 May 10, 1988; 4,168,580 September 25, 1979, this arrangement showing a drying installation for a paper web including a drying hood having flow channels, heat sources and blowers for circulation of drying medium; 4,064,637 December 27, 1977; 3,891,500 June 24, 1975; 4,656,759 April 14, 1987; 4,567,673 February 4, 1986; and 4,462,169 July 31, 1984. While some of the above listed specifications are directed to apparatus for increasing efficiency in web drying processes, they do not disclose the assembly of elements and combination of features found in the present invention. SUMMARY OF THE INVENTION Typically, drying costs for a well operated, conventional hood will be fairly low or rise slowly with production increase until the hood is near its capacity limit. At this point, additional drying can only be obtained by reducing the hood's humidity. This rapidly increases the energy cost per ton of paper produced. The present invention will allow the paper manufacturer to operate at supply temperatures above 537°C (1000°F) and at a lower total energy costs but at increased production. Accordingly, one of the primary advantages of the present invention is that the production capacity limit is much greater and therefore increases production at the same or lower total cost per ton of paper produced. Additionally, the present invention consolidates all its major components such as specially designed high temperature supply fans, new combustion chamber uniform flow concentrator, air flow equalization plenum and gas burner. This equipment is mounted directly on the drying device thereby eliminating the need for additional space requirement which is usually located behind or on the drive side of a tissue machine. Further energy savings can be realized by reducing thermal and static pressure losses associated with a convention hood and air system. The hood operation will be extended above 537°C (1000°F) with increased paper production potentials. According to a broad aspect, the invention relates to a Yankee hood assembly for use with drying cylinders in the process of drying wet paper webs, said hood assembly comprising an internally located, high impingement air system including a plurality of nozzle boxes covering approximately a 240° circumferential wrap of a drying cylinder, floating structural members supporting said high impingement system and said air system being decoupled from main support end plate members to accommodate increases in cross-machine expansion. The assembly includes externally located direct drive motor means, support structure for said motor means being so arranged as to eliminate hood vibrations and operate above natural building frequencies. BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way of examples in the accompanying drawings in which: FIGURE 1 is an end elevation of a Yankee hood according to the invention; FIGURE 2 is a plan view of the hood of Figure 1; FIGURE 3 is a cross-sectional view of the interior of the hood; and FIGURE 4 is an elevation view of the support structure for the fan drive of the hood. DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1, the hood assembly shown generally at 10 comprises two hood halves 12 and 14 which are movable by suitable motor means 16, Figure 2, toward and away from one another. In its operative position shown in Figures 1 and 2, both halves 12 and 14 of the hood provide a circumferential wrap of approximately 240° around a drying cylinder, not shown. The wrap area accommodates a plurality of nozzle boxes 18 which are decoupled, as shown in Figure 3, from the main support end plate members 20 of the hood structure. This allows for increased cross-machine expansion which will result from the higher supply air temperatures of the hood according to the invention. The internally located high impingement air system 22 is supported on floating structural support members 24 as shown in Figures 1 and 2 and in order to eliminate structural deformation of the main Yankee hood end plate structures 20, all of the internal hood services are insulated with high temperature ceramic insulation 26 and a vapour barrier 28 including weep holes is located intermediate the insulation 26 and the end plates support structures 20 in order to inhibit vapour penetration. As shown in Figures 2 and 4, the hood incorporates high temperature supply fans 30 which are driven by externally located supply motors 32 by means of suitably coupled drive shafts 34. The support structure 36 for the drive motors 32 is designed to eliminate hood vibrations and operate above the natural building frequencies. All of the internal Yankee components are fabricated of special high temperature alloys in order to eliminate stress and fatigue cracking which is commonly experienced with conventional Yankee hoods. It will be appreciated that a Yankee hood constructed in accordance with this invention will provide a paper manufacturer with means to operate at supply temperatures above 537°C (1000°F) to result in increased paper production potentials with a noticeable reduction of thermal losses and static pressures. While the invention has been described in connection with a specific embodiment thereof and in specific use, various modifications thereof will occur to those skilled in the art without departing from the scope of the invention as set forth in the appended claims. The terms and expressions which have been employed in this specification are used as terms in description and not of limitations, and there is no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claims.

Claims: A Yankee hood assembly (10) for use with drying cylinders in the process of drying wet paper webs, said hood assembly (10) having: a pair of hood halves (12, 14) movable toward and away from one another; motor means (16) to effect said movement of said hood halves (12, 14), said hood halves (12, 14), together, incorporating an internally located, high impingement air distribution system (22), said system (22) including a plurality of nozzle boxes (18) covering approximately a 240 degree circumferential wrap about a drying cylinder; floating structural support members (24) extending through said hood halves (12, 14) in a transverse, cross-machine direction, said high impingement air system (22) being supported on said floating members (24); and main support end plate members (20) forming part of said hood assembly (10), said high impingement air distribution system (22) being decoupled from said main support end plate members (20) to accommodate increases in cross-machine machine expansion of said air distribution system (22), said hood assembly (10) including associated, direct drive motor means (32) and support means (36) therefor. A Yankee hood assembly (10) according to claim 1, wherein all components of said hood (10) are fabricated from high temperature alloys. A Yankee hood assembly (10) according to claim 1, wherein all internal hood surfaces are insulated with high temperature ceramic insulation.

Inventors: NOWAKOWSKI GEORGE Z, RINGER VOLKER J, NOWAKOWSKI, GEORGE Z., RINGER, VOLKER J.
Applicants: ANDRITZ FIBER DRYING LTD, ANDRITZ FIBER DRYING LTD.
Application year: 1998
Main classification: D21F5
IPC codes: D21F5