Views: 0 Author: Site Editor Publish Time: 2022-03-29 Origin: Site
The blow box concept has proven to be a reliable means of increasing the productivity and efficiency of paper and board machines. Its leading idea is to improve the running performance of the paper machine through air treatment technology. The working principle of the blowing box: it is characterized by the wonderful application of the Coanda effect blowing principle, that is: the high-speed airflow along the surface of the object is at the corners The phenomenon that can be adsorbed to the surface. There is no mechanical contact between the blow box and the felt or dryer wire, but the suction of the airflow is very uniform.
2 Classification of hair dryers
Depending on the arrangement of the drying section, the following different types of blow boxes are recommended (see picture)
(1) Press Nip Blow Box
Press nip blow boxes are installed before the separate press nips to support the sheet and prevent damage to felts and rolls.
(2) PressRun Blow Box
The press running blow box is installed between the press section and the dryer section to support the sheet and minimize the free draw section of the most dangerous area during the transfer of the sheet from the press section to the dryer section.
(3) Uno Run Blow box
The dryer wire running blow box is installed between the lower row of drying cylinders in the single dryer running drying section to prevent the upper sheet from leaving the dryer.
(4) Sym RunHS Blow Box
The dryer wire combination blow box has been specially developed for high-speed paper machines with a speed of more than 1000 m/min. For this high-speed paper machine, the sheet
In both parts running up and running down, the running performance of the paper sheet needs to be controlled. This blow box can be used in grooved rolls or vacuum
Negative pressure is created over the entire pocket area above the roll to provide good runnability. In addition, the suction volume of the vacuum roll is also reduced, so it is possible to reduce
total energy consumption.
(5) Uno Run Ventilator
Wire fume boxes are used to ventilate the pocket area of a single wire dryer and improve runnability.
(6) Twin RunBlow Box
The double-drying net blow box is installed in the double-drying group of the high-speed paper machine to support the sheet in order to reduce the flapping of the sheet and to ventilate the pocket area.
(7) Dry mesh bag ventilation box (Uniflow Pocket Ventilator
Dryer mesh bag ventilation boxes are used for double dryers on high-speed paper machines. This fume box can increase the thermal landscape of the pocket area to improve drying efficiency and can help
Helps control moisture distribution across pockets.
(8) Dry mesh bag ventilation box B (Uniflow Pocket Ventilator
Dry mesh bag ventilation box B is suitable for board machines that require high drying capacity. The Valmet blowbox concept is a proven technology that has been used on more than 1,000 paper and board machines around the world. These paper mills benefit from the technology.
3 Advantages and scope of use of the blower
(1) Blower box in press nip
Modern paper machines often add a separate press before the sheet enters the dryer section. When air entrapped by the sheet and felt enters the nip, it causes the sheet to separate from the felt. In the worst case, it may cause damage to the paper, felt or rollers. The negative pressure created by the press nip blow box prevents the sheet from fluttering before the press nip and keeps the sheet in good contact with the press felt. If a Tail Run Blow BOX is installed on the operating side in the area behind the vacuum roll, the threading can be made more reliable. The blow box uses compressed air to keep the paper tail in good contact with the press felt.
(2) Press running blow box
The sheet between the press section and dryer section on a conventional paper machine is unsupported, but in this area the sheet is very weak and is often affected by unstable airflow. The weak sheet is also stretched, which forces the paper machine to operate at low speed to avoid flapping and wrinkling of the sheet. Higher sheet tension, in turn, can lead to reduced quality and even frequent breaks.
To solve this problem, the first step is to bring the dryer wire on the first dryer closer to the center roll, so that the unsupported length of the sheet is as short as possible. Run the blow box with a press to keep the sheet snug under the dryer wire. The blow box generates a very effective negative pressure between the sheet and the dryer wire, but there is no mechanical contact between the blow box and the dryer wire, thus ensuring that the dryer wire is free of any wear.
Using the press-run blow box can reduce sheet elongation, reduce the number of breaks, and greatly improve running performance. Valmet's press run concept is suitable for
Suitable for different kinds of press configurations, such as 3-nip press, independent press, shoe press, etc. Press running blow box on low basis weight paper machine
Good results have been achieved on both the machine and the cardboard machine.
(3) Dry net running blower box
In the single-wire dryer section, the adhesive force between the sheet and the smooth cylinder surface, as well as the surging internal pressure caused by the high-speed movement, will cause the sheet to leave one dryer and travel to the other. Separating the sheet from the dryer wire, causing the sheet to wrinkle or break. Use the dryer fabric running blow box to install it between the upper and lower rows of drying cylinders in the single dryer section to prevent the upper sheet from separating from the dryer fabric. Often used on modern paper machines with grooves
The lower row of dryer cylinders or drilled vacuum rolls to further increase the effect of negative pressure.
(4) Dry net combination blower box
Good runnability is provided due to the fact that the combined dryer fabric blow box generates negative pressure over the entire pocket area above the vacuum roll. In addition, the exhaust volume of the vacuum roller can be reduced, and the total energy consumption can be reduced. The concept utilizes dedicated blowing nozzles on both sides of the pocket area to generate negative pressure between the blowing box and the dryer fabric. This blow box has no contact with the dryer wire and has no mechanical seal, so it does not wear out the dryer wire. The concept is applicable to all types of dryer sections running on a single dryer wire.
(5) Dry net ventilation box
The drying net ventilation box is used in the pocket area between the lower drying cylinders in the drying section of single drying net operation, which can improve the ventilation in this area, increase the drying capacity, and make the pressure in the pocket area more uniform and improve the running performance.
(6) Double-dry net hair dryer
The double dryer wire blow box generates negative pressure to keep the paper in good contact with the dryer wire and at the same time to ventilate the pocket area. The main idea of this fume box is to support the sheet behind the dryer as long as possible. The felt roller is not installed in the center, but is biased towards the wet end, shortening the unsupported free pulling section of the sheet by 30% to 50%. Not only does the dual dryer wire blow box improve runnability because it increases sheet stability, it also improves runnability because of the controlled airflow into the pocket area.
Makes evaporation and removal of moist air more effective. The uniform distribution of air humidity in the dryer bag area can improve the uniform distribution of moisture in the transverse direction of the paper
The double-wire blow box operates most efficiently in the first double-wire dryer group, but is also suitable for the entire double-wire dryer section of a high-speed paper machine.
(7) Dry mesh bag ventilation box
Valmet blow boxes can be installed throughout the drying section. Good pocket ventilation and axial controllability, as well as increased airflow due to roller rotation, are typical features of this fume box. If necessary, the fume box can be fitted with adjustable sections on both sides to control airflow distribution throughout.
(8) Dry mesh bag ventilation box B
Dry mesh bag ventilation box B is specially designed for cardboard machines. It is characterized by large hot air flow, low pressure and very uniform distribution of hot air. A new air distribution system is used. The dry mesh bag ventilation box B is equipped with a local airflow adjustment mechanism on both sides of the paper sheet, which can control the air volume on both sides of the paper sheet.
4 Air supply system for the blower box
In order to achieve reliable operation of the blow box, it is very important to blow a sufficient flow of hot air to the blow box. Depending on the form of the blower, different
For the purpose, the gas supply methods that can be adopted are as follows:
(1) For the air supply of the blow box in the press nip and the blow box in the pressing operation, the indoor air in the papermaking workshop is usually used.
(2) Most of the air supply to the Uno Run blow box comes from the hood, but dry air can also be used.
(3) For the Twin Run blow box, dry air is usually used, and a mixture of dry air and circulating air from the hood can also be used.
(4) For all bag ventilation boxes, use dry hot air from the hood air supply system.