Abstract This paper discusses in detail the new technology to further increase the speed of paper machines. A speed-free press section and a dryer section were proposed. Describes new technologies for preventing page breaks, chattering, fluttering, ensuring sheet stability, and improving paper quality at high vehicle speeds. New Technology to Further Increase the Speed ​​of Paper Machines
The speed of paper machines has been the focus of most papermakers and paper machine manufacturers. Increasing the speed of a vehicle since it was a paper machine has always been a major technical issue. At present, under the circumstance of increasing the width potential of the paper machine, it is of great significance to increase the speed of the paper machine and solve the technical problems encountered in increasing the speed of the paper machine.
At the end of the 19th century, the maximum speed of the Fourdrin Paper Machine was only 152m/min. At the beginning of the 20th century, technologies such as a vacuum roll, a vacuum press, a high-pressure headbox, and a paper threading lead were invented, and the speed of the paper machine reached 400m/min in the 20's. Since then, there have been high-speed, closed, uniform, homogeneous headboxes, new formers and dewatering elements, vacuum threading, high-strength, compound presses, high-efficiency drying-through steam dryers, and dry-side ventilation systems. Controlled high rollers, new papermaking nets, wet blankets, dry blankets and high-performance washing devices, thyristor subdivision drive systems, new detection instrumentation and control systems, etc. enabled the speed of Changnet Paper Machines to reach 900m in the 1970s. Min. Afterwards, hydraulic headboxes, gap formers, high-strength presses, single-cylinder single-cylinder arrangements for drying, soft calendering, new reelers, high-speed rewinders, more complete QCS and DCS control systems, and Closed threading technology, etc., made the paper machine speed reach 1500m/min in 1986, reached 1700m/min in 1995, and now it has reached 2000m/min. At the beginning of the 21st century, the speed of paper machines used to produce newsprint, LWC, SC and other paper grades is expected to reach 2,500 m/min. The goal of the papermakers in the 21st century is to achieve a paper speed of 3000m/min.
It should be noted that Valmet, Voith Sulzer and Beloit have done a great deal of work and achieved good results in increasing the speed of paper machines. 1 Key technologies to further increase the speed of paper machines When the speed of paper machines has reached 1,500 to 1,800 m/min, the speed of vehicles has been further increased to 2,000 to 2,500 m/min. Many key technologies need to be solved. However, there are mainly key technologies in the following areas: Must be resolved first. 1.1 Improve the dryness of the wet paper sheet in the press section Currently, the feed from the forming section to the press section has been fully resolved, and the parts that affect the breakage and running stability of the paper at higher speeds are mainly in the press section and press. The sheet transfer between the part and the dryer section and the initial part of the dryer section. Increasing the sheet dryness at the press section and the press section is to increase the strength of the wet paper sheet and to increase the ability of the wet paper sheet to be pulled at high vehicle speeds. When the compound press is used, the wet paper sheet released from the center roll is improved. The ability to resist centrifugal force, at the same time, can also enhance the stability of wet paper sheet operation. 1.2 Reducing the Stress of the Wet-Paper Sheets During Transfer Increasing the Dryness of the Wet Paper Sheet It is necessary to increase the traction strength of the sheet. However, it is not enough to rely on improving the dryness of the sheet to run at higher speeds.
As shown in FIG. 1 , when a center roll press is used, as the speed of the paper machine increases, the centrifugal force of the wet paper sheet discharged from the center roll is also greater. When the vehicle speed is above 1800m/min, the strength value of the wet paper sheet is already close to the centrifugal force, which means that the paper sheet may be broken at any time, thus limiting the further increase of the paper machine speed. Figure 1 With the increase of the speed of the paper machine, how can the typical tension value of the wet paper in the press section of the press section reduce the wet paper sheet stress? Cancel the open-feed, use closed-feed, and the full-web-support wet paper sheet runs Very necessary, the specific approach is:
. From the forming section to the press section, vacuum suction is used to seal the paper. Full-frame blanket support and support wet paper runs. The felt vacuum box and the vacuum roll were used to adsorb wet paper sheets and vacuum transfer wet paper sheets. From the press section to the dryer section, a vacuum roller is used to suck and seal the paper. The press section uses a single-carpet single-cylinder arrangement and applies a dry blanket vacuum roller to achieve a closed draw in the dryer section. 1.3 Improves the stability of the wet paper sheet and prevents paper breaks, chatter, flutter, and wrinkling of the sheet. 1.4 Application Specialized felts Rewetting phenomenon on wet paper sheets is reduced to a minimum 2. The speed limit of the center roll press has been used for a long period of time. The center roll press technology has been used for a long period of time. Such presses have limited the speed of the paper machine to further increase. The speed limit factors are:
. Open traction paper sheet. Center roll wet paper scraped and peeled. There are many opportunities for breakage caused by the press section. The paper after the last nip is large on both sides. Vacuum roller high load. The design problem of composite three nip presses Therefore, the central roller press technology can only make the paper machine speed reach 1500 ~ 1700m/min, and further increase the speed is limited. 3 The introduction of shoe presses has increased the speed of paper machines. Take Valmet's SymPress Press as an example. This type of press has introduced the SymBelt shoe presses to increase the speed, as shown in Figure 2. Figure 2. SymPress press with shoe presses in the third nip of the SymPress B press. Symbelt shoe presses are configured to improve the dryness of the wet paper sheet after peeling from the center roll. The running performance of the paper sheet is improved. This approach tapped the paper machine's speed potential and increased the vehicle speed by 200m/min, which could reach a speed of 1900m/min. However, there is still a limit to further increasing the speed of the vehicle. 4 No Speed ​​Limiting Press Section Valmet first published a new design for the press section of paper and paper for the production of paper presses in 1994, and called the new press the OptiPress press. The press has perfect support and support wet paper sheet technology equipment. It is a press section consisting of two shoe presses. This is a very important press section design for further increasing the speed of the paper machine. The company used this new press design on a new test paper machine with a speed of 2500 m/min and put it into production at the Jyväs Kyl Technical Center in Finland in early 1996. So far, the design of the OptiPress press section has been further improved through testing, as shown in Figure 3. Figure 3 The results of the press section test of the Willamette Hawesville No. 2 machine show that the OptiPress press has surprising results. Almost a press section with no limit on the speed of the paper machine.
The OptiPress press is used on the press section of the Willamette Hawesville 2 paper machine to produce a uniform copy paper. SymBelt shoe presses have great dewatering capacity, which can greatly improve the sheet dryness. There are no two sides of the page. This new press can significantly exceed the speed limit of the SymPress press, which can meet the requirements of the paper machine to further increase the speed of the vehicle and the need to improve the quality of the paper, allowing the paper machine to operate at high efficiency.
The OptiPress press employs two straight-through shoe presses and four loop loops. The fully-closed threading technique is applied. The sheet transfer is run under vacuum control. In some sections, the blanket vacuum box is used. Due to the closed traction, the cut-feed device at the press section is eliminated, so that the entire width of the wet paper sheet enters the first dryer group of the dryer section. The broke scraped off at the beginning of the drying section falls into the pulper installed below. 5 OptiPress Press for the Production of Wood Pulp Papers When using four blankets, in all cases the OptiPress press produces no two-sided paper. However, there is an anti-moistening effect on the sheets, which is a low-quantity production (< 60 g/m2 paper is very unfavorable, which not only affects the improvement of the dryness of the sheet, but also affects the overall economic benefits of the paper machine and the running performance of the paper machine.
Therefore, in the production of low-quantitative paper, it is necessary to design a new type of lower felt to eliminate dewetting or to minimize dewetting. The newly designed Transbelt blanket has the following three functions:
. Good delivery of paper sheets. The paper sheet is well supported. The three functions of good peeling of the sheet enable the sheet to be completely transferred in the closed traction.
This new type of transfer blanket is completed through a very special felt surface treatment. The surface of the felt has a special pattern of patterns, divided into hydrophobic and hydrophilic areas. These areas coexist with the optimally treated surface, giving the felt surface a special pressure-reactive properties. The felt absorbs almost no water, and It does not wet back, which improves the dryness of the sheet and improves the transfer of the sheet, which is surprisingly easy to peel off from the felt. This new type of blanket has been used in industrial applications in Johnsonbury. As shown in Figure 4, this new type of blanket is applied to the press section 2 press felt. Figure 4 OptiPress Two Press Uses Anti-Wet Blanket Transfer As expected, when using this new type of felt to produce wood pulp-containing paper grades, wet paper sheet dryness increases by 4%, saving steam by 16% or increasing by 16 The drying capacity of %, the running performance is improved, the paper production quota can be reduced greatly, can produce 40-45g/m2 low quantitative newsprint paper. Test paper machine speed has exceeded 2000m/min. For non-filled wood pulp paper, the dryness of the paper is 47% to 50%; for papers with high filler content, the paper dryness can be increased to 55% to 59%.
The new surface-optimized transfer blankets are used in OptiPress presses for the production of newsprint, LWC, SC and fine paper.
With the OptiPress press section of the new transfer blanket, the first shoe press that originally used two shoe presses could be replaced by a grooved press. Only the second press was a shoe press. 6 Drying Technology for High-Speed ​​Paper Machines In order to further increase the speed of the paper machine, a completely closed transfer sheet and a single-carpet single-cylinder arrangement drying technique are used in the dryer section, so that the sheet breakage can be prevented and good sheet running stability can be ensured. This drying technology was realized many years ago. Valmet called this drying technology SymRun drying technology. As shown in Figure 5. The SymRun Drying Technology arranges larger diameter steam drying dryers in a row, and below the smaller diameter vacuum rolls (VacRoll). It ensures the stable operation of the paper sheet, ensures excellent paper quality, and completely satisfies the operating requirements of 1800 to 2500 m/min. Figure 5 SymRun drying section with single-carpet single-cylinder arrangement Although SymRun drying technology can meet the high-speed operation requirements, the length of the drying section is too large, which increases the length of the workshop of the paper-making workshop and increases the investment in civil engineering. In order to apply the operating requirements of a high-speed paper machine, shorten the length of the drying section, and save on civil investment, Valmet proposed a drying technology called OptiDry three years ago. As shown in Figure 6. Figure 6 The combination of OptiDry Drying OptiDry Drying Technology and OptiPress Pressing Technology can very well meet the operating requirements of high speed paper machines. The transfer of the sheet from the press section to the first drying section of the dryer section is achieved by the transfer of a vacuum roller to achieve the closed transfer. The drying section does not have a thread cutting device, and the leading strip uses a jet cutter to cut the strips, and an automatic guidance and drying section guides the string to receive the paper to complete the threading. All these devices take into account the higher speed requirements.
The OptiDry Drying Division achieved a fully closed draw, which was achieved through the use of SymRunHS Dry Blanket Vacuum Boxes and Vacuum Rollers. The main function of the SymRunHS Dry Blanket Vacuum Box is to create a vacuum section on the dry blanket and hold the sheet tightly against the dry blanket section between the dryer cylinder and the vacuum roll for effective support of the sheet. Prevents paper breaks, chatter, flutter, and wrinkles, ensuring the stability of the sheet and the quality of the paper.
The OptiDry drying technology has recently made new developments, mainly with the following new technologies, as shown in Figure 7. Figure 7 OptiDry dryer section with pre-drying device. A pre-drying device was added to the initial part of the drying section. The pre-drying device not only imparts better running stability to the sheet, but also improves the drying efficiency in the initial stage of the drying section.
Hey. The use of large diameter vacuum rolls and impingement drying technology has improved the drying efficiency.
Hey. OptiDry drying technology is automated.
Hey. Provides new opportunities and means for controlling the quality of paper, which can effectively control paper properties such as paper curl, moisture, and paper sheets