The paper industry is a capital-intensive industry. The paper machine is the largest investment among them. Its electric and steam consumption (including beating and seasoning) exceeds the pulping section, which is also the largest, and also determines the production efficiency and the quality of the final product. Therefore, people are constantly conducting paper machine technology research. Development.
1. Speed ​​and Width of Paper Machines Historically, paper machine speeds have increased by 2.5% annually. If this happens, by 2000, the speed of the tissue paper machine will reach 2,450 m/min, the speed of newsprint machines will reach 1800 m/min, and the speed of advanced paper machines will reach 1,525 m/min. For the linerboard machine, the maximum speed of 42 lbs (204.8g/m2) is now 760m/min. If you copy the lower volume, the speed can reach 1000m/min, or even 1100m/min.
Although it is predicted that the speed of the paper machine will further increase, from the economic point of view, its widening has reached the limit. This is because the deflection of the roller is proportional to the length of the roller. With the increase of the width of the roller, the diameter of the web roller, the roller, and the felt roller must be greatly increased to make the equipment investment excessive.
According to Mr. Skaugen's forecast from Beloit, the newsprint machine width is 10.8m in the next century, and the paper width is 9.78m. In addition, the widths of the high-quality paper, mid-range low-quantity coated paper and board machine are all about 10m. Similarly, there are reports that, when the speed of a printing paper machine is fixed, when the width is within 10m of its limit, the ratio of equipment investment to annual production capacity (t) decreases as the width increases.
2. The headbox The headbox was initially open, followed by a closed pressurized rectifying headbox. Since then, it has evolved into a hydraulic fluid that generates countless tiny turbulences in the headbox to prevent fiber flocculation. (Hydraulic) (or turbulent) headbox. In recent years, in order to adapt to the use of waste paper, a multi-layer headbox has also been developed, that is, delaminating in the headbox according to the type of fiber, ejecting the Internet, and manufacturing a multi-layered paper. For example, using secondary fibers as the core layer and primary fibers as the top layer optimizes the degree of folding and smoothness of the paper, reduces the generation of paper dust, improves the appearance of the paper, and influences the impurities on the runnability of the paper web. drop to lowest.
The multi-layer headbox also optimizes the quality of all papers that use primary fibers. For example, for the production of tissue paper, papers with excellent softness can be produced. Multi-layer headboxes can also be used for board papers, including in board liners that use a portion of waste paper. People want to use it for printing paper.
The control of paper distribution (quantitative, moisture distribution of banners) is arguably the most important control. Over the years, this has been achieved by adjusting the lip opening of the headbox. But this not only changes the flow, but also has the problem of changing the fiber orientation.
Recently, a concentration-adjusting headbox has been developed that adjusts the slurry concentration in the direction of the banner to control the distribution and is gradually becoming practical. It is common to instruct the main pipe to send the slurry (higher concentration) to the header. Many thin pipes separated from the header are sent to the head box. There is also a thin header for the thin slurry and White water is transported, and many of the upper fine tubes are respectively connected to the fine tubes on the thick slurry header, that is, the concentration of the thick slurry is adjusted by adding a low concentration of slurry and white water. Compared with the previous adjustment method, the quantitative change of the direction of the banner is reduced, the control range is also increased, and the time is shortened after adapting to the change of the process conditions. However, this type of equipment is complicated and the investment is large, and it is limited to papers with very strict quality requirements.
3. The network department - the network type will occupy the dominant position There are now thousands of single-line paper machines in the world. Many experts predict that they will rapidly become historical products in a few decades. The hybrids currently used (hydridfomers, also known as pre-grind paper machines), will soon fall behind in the days of Single Longnet, which will dominate the 21st century.
Ordinary single-long wire and hybrid paper machines have a free slurry surface. Therefore, there is a problem of instability. The higher the speed is, the more obvious the vehicle speed is. When the vehicle speed reaches 1200-1300 m/min, the quantitative fluctuation is quite large and affects the quality of the product. . There is no free pulp surface in the screen machine, so there is no problem with the speed limit. In addition, its dewatering capacity is large, the equipment is compact, the length of the net part is reduced by almost half, and there is an advantage of less land occupation, and the power consumption of the net part is reduced by about 10%. Grid-laid paper machines are now standard equipment for newsprint and tissue paper and are expected to be commonly used in other paper types in the future. Due to the use of a paper-folding machine, the speed of newsprint, low-quantitative coated paper, and super-pressure paper machines may increase to 1500m/min or more, and the network department has no effect on further increasing the vehicle speed. In the long period of time after the development of the grid paper machine, it was limited to copying newsprint and thin pages. The use of paper for copying advanced printing paper and linerboard was only recently possible, but it has developed rapidly. This seems to indicate that the above prediction is Correctly, but some people still think that there are still some need for the existence of certain long paper machines and hybrid long paper machines. For example, a double-layer papermaking machine for copying papermaking boards and a single-wire papermaking machine are used. A variety of combinations of paper machines, including sandwich models.
4. Press Section - Shoe Press 4.1 Development of the Shoe Press The shoe press technique is a great hope for the press section. In 1980, a company in the United States first used the shoe press technology, which was initially split, and since then, it has been widely used only on boxboard base papers. Since the late 1980s, it has also begun to be used in paperboard sheets with a high bulkiness. In 1994, it was also used in newsprint, followed by advanced printing paper. Split type is prone to oil spills and dirt. Since then it has developed a closed type and is now moving towards a closed type.
4.2 advantages of the boot press The advantages of boot presses, the first is the ability to dewater. In previous roll presses, the nip was narrow (20-50 mm), the peak pressure acting on the paper was too high, and the web was crushed, so the low pressurization load had to be controlled.
The wide nip width of the shoe press (210-310mm) avoids high peak pressures. At the same time, it can increase the load and enhance dewatering. As a result, the moisture at the press exit of the paper is reduced by approximately 5% over the roller press, saving 20% ​​of the dry steam.
The second advantage of the shoe press is that it increases the strength of the paper. Every 1% decrease in paper moisture increases the tensile strength of the wet web by 7%. Therefore, the shoe press can improve the runnability of the paper machine and improve the efficiency of the paper machine. In addition, for the linerboard base paper, the density of the paper can be increased without damaging the paper web, and various strength characteristics such as ring pressure strength and burst strength are improved.
Shoe-shaped presses can also produce papers that are more bulky than roll presses. If a shoe press is used, paper with the same stiffness as a roller press can be produced with a reduced basis for the use of inexpensive fiber raw materials, as well as increased vehicle speed and steam savings.
Compared with roller presses, shoe presses consume less electricity. It has been reported that, in actual production, the power consumption of the press section is reduced by 13%, the equipment is compact, and it is possible to reduce the area, which is also an advantage.
5. Drying section 5.1 Single-layer dryers With the increase in the desire to increase the speed, the open threading section of the dryer section has become increasingly unsuited. In order to solve this problem, various studies have been conducted. One method is to use a single-layered felt. The first step is to use this technique in the front section of the paper where the moisture is high and the strength is poor. However, as a result, half of the two-layer dryer loses its function. With the development of high speed, there has been a problem with the drying department becoming longer and longer. In the 1990s, especially for high-speed paper machines, single-cylinder machines were used. A vacuum-steering roller was used between the two dryers. This roller was made as large-diameter as possible to increase the paper dryer. The angle of the bag increases the drying efficiency. The entire process of running the paper is affixed with a blanket, reducing the end of the break.
The greater advantage of this drying method is to improve the quality of the paper. If the dryer section has an open guide, the web will shrink in the direction of the banner. The closer it is to the sides, the greater the shrinkage. Therefore, in order to publish a uniform paper in the direction of a banner, it is necessary to reduce the amount of pulp discharged from both ends of the headbox, which leads to an increase in yarn breakage and poor fiber orientation. If the carton is firmly affixed to the blanket, the above phenomenon will not occur, and the reduction of pleats will increase the dimensional stability.
5.2 The Challenge of Shortening the Length of the Drying Section--Research on the Hot Air Hood In order to shorten the drying section, various researches are most likely to be made on the use of high-speed, high-humidity air drying methods for high-speed tissue machines. Yankee hood.
This is a high-temperature air with a temperature of 300°C. It is blown onto the paper at a high speed of 60-100m/sec. The hot air passes through the paper and passes through a large-diameter vacuum suction roller. Its drying capacity is usually a drying cylinder (evaporation per unit area is 20-40kg). /m2/h).
According to the results of the experimental equipment, the high temperature had no effect on the quality of the paper as long as the paper was not left at a high temperature for a long time.
In addition, from the following two points, it can be seen that the energy efficiency is equal to or higher than the ordinary dryer drying.
(1) The hot air hood is a closed-loop system, and the amount of air required is much less than that of dryer drying, because it is discharged at a higher humidity and is more conducive to heat recovery.
(2) The power consumption of the power plant is almost unchanged because a lot of dryer group motors and ventilation are not needed.
Due to the use of this hot air hood drying, a paper machine for making 45 g/m2 news paper at a speed of 2000 m/min was shortened from 79 m to 50 m, which was shortened by about 40%. Now that the paper machine is transformed into this way, the drying capacity can be improved. The first half is a single-layer dryer, and the latter is a double-drum existing paper machine. If only the latter half is converted to this type, the drying capacity is increased by 25%. If only the first half is modified, the drying capacity is improved. 25%.
Taking a newsprint machine as an example, the maximum speed of 66 years was 914m/min, and the length of the paper machine was 110m. In the following 30 years, the maximum speed had doubled. Due to the increased efficiency of the dryer section, the overall length of the paper machine has hardly changed. It is estimated that by 2000, the speed of newsprint machines will reach 2010m/min. At that time, the length of the paper machine was estimated to be only half of the current 54m due to the introduction of hot air hoods.
The change in the drying section will not be too great. In the future high-speed paper machines, the most important part of the drying section is its running performance. The transfer from the traditional press section of the paper machine to the dryer section is usually an open-end feed. The sheet between the dryer and the dryer is often an open-end feed, and the sheet is vacant between the dryers. The cylinder contact portion is supported by the cylinder blanket. This can easily cause a break in the paper machine when it is running fast. The new paper machine uses a full length of cylinder blanket to convey the paper sheet in the dryer section. The paper sheet is supported by the cylinder blanket throughout the drying section. The tension of the paper web is no longer required to maintain the stability of the paper sheet. The operation performance of the paper machine is improved, the chance of paper machine breakage is greatly reduced, and the quality of the paper is also improved. At present, there are several paper machines abroad and this technology is adopted.
As the speed of vehicles continues to increase, the number of drying cylinders will inevitably increase. This will increase investment and operating costs, and will increase the size of the paper machine. In order to solve this problem, Beloit has developed a new technology, namely, Dry paper sheets by blowing hot air. In the hood, the hot air blows at a high speed in the running direction of the paper sheet. The hood is located on a large-diameter vacuum roll. After the sheet is dried, it enters the dryer to dry. It is expected that the combination of drying technology using hot air and dryer drying will become the mainstream of the new generation of paper machine drying technology.
6. The development and application of calendered soft roller calender is a major development of the papermaking technology in the 1980s. Kuster Corporation of West Germany took the lead in the development and achieved the desire of the paper industry to use internal soft calendering to achieve high-speed decorative effects.
Soft roller calendering allows the sheet to retain high levels of smoothness, gloss, brightness, and other properties while retaining high bulk, stiffness, opacity, and strength. In the world, hundreds of soft calenders have been put into operation. Most of them are used in calendering and have good effects. They are widely used in newsprint, printing paper, dictionaries, kraft paper, and filter papers. , carbonless paper, advanced paper, etc. There are several paper machinery companies currently producing soft roll calenders such as Kleinewefers, Valmt, NB, Allibe, H & Escher, Wyss and others.
7, rewind
The Latest Technology and Development Direction of Paper Machine in China
December 24 08:07:23, 2023
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