Technical operation of the drying part of paper machines. Working principle of the dryer

The paper machine BDM-10 is designed to produce various types of paper: wallpaper, printing, food packaging. In the production of paper, the paper machine is an independent unit, the main components of which are installed strictly sequentially along the mounting axis.

Specification of paper machine

Technical specifications paper machine BDM-10 is shown in table 2.1. General scheme PM-10 is shown in Figure 2.1

Table 2.1 - Technical characteristics of PM-10

Figure 2.1 - Scheme of the paper machine BDM-10:

1 - head box; 2 - mesh part; 3 - press part; 4 - drying part; 5 - calender; 6 - rolling

Composition of paper machine

The paper machine includes: headbox, wire, press and dryer parts, calender and reel. It also includes a machine pool for the mass, equipment for its cleaning, pumps for supplying water and mass, vacuum pumps, devices for processing rejects, equipment for circulating lubrication, a supply and exhaust ventilation system, regulating and instrumentation, etc. 1. The diagram of a closed-type headbox is shown in Figure 2.2.

Figure 2.2 - Headbox:

1 - collector-flow distributor; 2 - perforated plate; 3- perforated shafts; 4 - box body; 5 - front wall; 6 - gap regulation mechanisms; 7 - defoamer; 8 - air cushion

The headbox is intended for:

Distribute the flow of the slurry at the inlet to the mesh of the machine with the same flow rate and speed across the width of the cast web;

Transfer the slurry to the outlet slot without shedding of fibers and without the appearance of transverse jets;

To release a jet of fibrous suspension onto the mesh of the machine at a certain speed with high-intensity turbulence and its small scale.

The mesh part is intended for forming a paper web with a suspension concentration of 0.1 - 1.3%. The process of filtering the fiber from the suspension and forming the web on the mesh part takes place on a relatively short section of the table and is decisive in obtaining paper quality indicators. The main element of the grid part is one endless grid stretched between the shafts. The mesh part of the PM is shown in Figure 2.3.

Figure 2.3 - Grid part:

1 - head box; 2 - chest shaft; 3 - forming box; 4 - a box of hydroplanks; 5 - wet suction box; 6 - register shaft; 7 - suction box; 8 - suction shaft; 9 - drive shaft; 10 - mesh correction; 11 - mesh drive shaft; 12 - mesh tension; 13 - grid

The press mechanism is determined by the amount of water removed and the uniformity of the moisture content of the paper web. The dewatering capacity depends on the contact zone of the rolls and on the number of these zones. When pressed, the structure of the web also changes, the strength of the paper increases, its thickness, density, air permeability, opacity and other properties change. In the press part, the following should be ensured: 1) maximum dehydration of the paper web to obtain the desired physical and mechanical properties; 2) uniform moisture content of the canvas across the width; 3) unbreakable web guiding with minimal free running areas.

The press part of the paper machine is shown in Figure 2.4.

Figure 2.4 - Press part of the paper machine:

1 - grooved shaft; 2 - suction shaft; 3 - rubberized shaft; 4 - smooth shaft; 5 - drive shaft; 6 - suction shaft; 7 - pressure shaft; 8 - felting shaft; 9 - cloth adjuster; 10 - cloth stretch; 11 - cloth

The drying part is intended for dehydration (drying) of the paper web. The drying section consists of drying cylinders heated by steam. They are placed in a checkerboard pattern in two tiers. A paper web passes through the drying cylinders, alternately contacting the lower and upper cylinders with one or the other surface. The tension of the felts and their straightening are carried out by felting, tensioning and straightening rollers, equipped with the necessary mechanisms. Drying of felts is provided by felt-drying cylinders and felt-blown rollers.

The diagram of the drying section is shown in Figure 2.5.

Figure 2.5 - Drying part:

The calender is designed to achieve the required indicators of smoothness, density and uniformity of the web thickness, while maintaining other quality indicators within the specified limits. The calender consists of: metal shafts; beds in which bearing housings and shaft levers are placed; drive for rotation of the lower shaft; lifting mechanism and devices for additional clamping of the shafts. Drive shaft transmits rotary motion adjacent shafts due to frictional forces.

Below is a diagram of the calender in Figure 2.6.

Figure 2.6 - Calender:

1 - mechanism for pressing and lifting the shafts; 2 - bed; 3 - intermediate shafts; 4 - lower (main) shaft

Figure 2.7 - Roll forward:

1 - winding roll; 2 - bed; 3 - reel cylinder; 4 - tambour roller; 5 - receiving levers; 6 - pneumatic cylinder of the tambour clamp: 7 - spreading roller; 8 - filling cord; 9 - cylinder of the drive for turning the receiving levers; 10 - cylinder drive of the main levers; 11 - main levers; 12 - roll brake; 13 - damper

The reel is designed for uniform and dense winding of the paper web into rolls. The higher the quality and uniform winding density of the rolls, the better the cutting process on the slitting machines. The roll-up scheme is shown in Figure 2.7.

Reel includes: reel cylinder; tambour shafts; receiving levers; working levers holding the tambour shaft for winding the web, and drive mechanisms for turning the receiving and working levers.

Description of paper machine operation

Basic operations: accumulation of paper pulp; mass inlet on the grid; forming a paper web on a grid; pressing; drying; machine finishing and winding paper into a roll 3.

Prepared paper pulp with a concentration of 2.5 - 3.5% is fed into the machine pool with a circulation device. For better concentration, it is additionally crushed with conical and disc mills. Further, the mass with a concentration of 0.1 - 1.3% is fed into the headbox.

The mesh part is used for casting and forming the paper web in order to remove excess moisture from the paper pulp. When the mesh passes through the register rollers and hydroplanks supporting it, the paper pulp is dehydrated to a concentration of 2 - 4%. Further dehydration takes place on suction boxes under vacuum to a concentration of 8 - 1.2%. Also, dehydration occurs on the couch shaft under the action of vacuum in the suction chamber. The dryness of the paper web after the mesh part is 12 - 22%.

Then the paper web enters the press section, where it is dehydrated to a dryness of 30 - 42%. The press consists of two shafts, of which the lower one is suction. Between the press rollers passes an endless felt supported by felt rollers, which transports the paper web. The shaped web is automatically transferred by a vacuum transfer device to the felt of the press section. The press section allows the passage of the paper, where the felt is constantly supported, therefore allowing the paper to be passed into the press section without interruption.

The drying part of the paper machine consists of drying cylinders heated by steam. They are arranged in a checkerboard pattern, in two tiers. When passing through the drying part, the paper web, first in contact with the lower cylinder, and then with the upper one, then the other surface. The tension of the felts and their straightening are carried out by means of cloth guides, cloth tensioners and cloth straightening rollers. Dryness after the drying part is 92 - 95%, and the temperature is 70 - 90 °C. Cooling cylinders are installed at the end of drying. When cooled, the paper absorbs moisture and is moistened by 1 - 2%. The paper web then passes through an eight-roll machine calender for compaction and smoothness. The calender of the machine is equipped with a clamping, lifting and lightening mechanism. Further, during the passage of the calender, the paper is wound on tambour shafts into a roll with a diameter of up to 2500 mm. Refueling is carried out using special mechanisms and devices. In the future, the paper is cut on specialized machines and packaged.

paper machine

a multi-sectional unit of continuous operation, on which paper and some types of cardboard are obtained from a fibrous suspension highly diluted with water ( rice. one ).

Two main types of paper are distinguished: flat-grid (table) paper, which is used to produce the main types of paper, and round-grid (cylinder) paper, which is used to produce a limited assortment of paper and cardboard. These types have various devices for discharging paper pulp onto the paper web and casting the paper web, while the design of the remaining units, as well as technological process paper making are similar (with the exception of the "dry forming" machine).

On fig. Figure 2 shows a diagram of a flat-grid paper machine, which, along with the machine itself, includes auxiliary equipment designed to prepare paper pulp before feeding it to the wire. The types of auxiliary equipment and their design are extremely diverse.

The finished paper pulp with a concentration of about 3-4% is pumped from the pulp preparation department to the machine pool, from where it enters the paper mill. Constant mixing of the stock in the machine pool equalizes the degree of grinding and mass concentration throughout the volume. It is preliminarily diluted with recycled water (from dehydration of the paper pulp on the B. m. grid to a concentration of 0.1-1.5%) and passed through the cleaning equipment (knotters, centric cleaners, centric screens, etc.), where various foreign inclusions are removed and coarse particles of mineral and fibrous origin. From the cleaning equipment, the paper pulp enters the headbox, which ensures the outflow of the pulp at a certain speed and the same thickness of the jet over the entire width of the grid.

B. m. consists of the following main parts: mesh, where a sheet of paper is continuously formed from a diluted suspension and the first part of excess water is removed from it; press room, where the paper web is dehydrated and compacted; dryer, in which the moisture remaining in the paper web is removed; finishing, where the web is subjected to necessary processing to give gloss, density, smoothness and is wound into rolls.

Grid part- endless mesh (woven from threads of various copper alloys or synthetic materials). The mesh drive is carried out from the couch-shaft. On new machines with vacuum transfer devices, the driving shaft of the mesh is also driven. To prevent the paper mass from flowing, restrictive rulers are installed along the edges of the grid. The dehydration of the paper stock and the formation of the web of paper occur due to the free flow and suction action of the register rollers. To obtain a more uniform web of paper in the longitudinal and transverse directions, at a machine speed of not more than 300 m/min, the register part is sometimes subjected to shaking in the transverse direction. Further dehydration takes place above the suction boxes under the action of a vacuum created by special vacuum pumps. When producing high-grade papers, a light leveling roller (eguter) is often installed above them. It also serves to apply watermarks to paper (See Watermark). After that, the paper web still contains a relatively large amount of moisture (88-90%), to remove which the mesh, together with the paper web, passes over the couch shaft (on low-speed couch press machines), which has from one to three suction chambers. Couch-shaft - a perforated hollow cylinder made of bronze alloy or stainless steel (perforation area is about 25% of the shaft surface). Inside the body is a stationary vacuum chamber with graphite seals, which are pneumatically pressed against the inner surface of the cylinder. The vacuum chamber is connected to a continuously operating vacuum pump. The couch-shaft completes the formation and dehydration (to dryness of 18-22%) of the paper web on the B. m grid.

Further dehydration occurs in the press section mechanical extraction under the action of pressure and vacuum by passing the web through several (2-3, less often 4-5) roller presses arranged in series (often the first and second presses are combined into a double press). At the same time, the volumetric mass, strength properties, transparency increase, the porosity and absorbency of the paper decrease. Pressing is carried out between woolen felts, which protect the still weak paper from destruction, absorb the squeezed moisture and at the same time transport the web. Each press has its own cloth. On all new high-speed B. m., the lower rolls of the presses are made perforated (like couch rolls). They are covered with special rubber, which improves dehydration and increases the service life. On some B. m., shafts with special grooved corrugations (grooves) are installed instead of the lower suction shafts. On powerful B. m., the lower shafts of the first and second presses are made suction (similar to the couch shaft). Often, in addition to presses with felts, smoothing (or offset) presses without felts are also installed to compact the paper and make it smooth. Then the paper web with a dryness of up to 45% enters the drying section.

Drying part(largest in length) consists of rotating cylinders heated from the inside by steam and usually arranged in 2 rows in a checkerboard pattern. The web is pressed against the heated surface of the cylinders with the help of felts, which improve heat transfer and prevent warping and wrinkling of the paper surface during drying. The upper and lower rows of drying cylinders have separate felts, and one cloth covers several cylinders at once (a group of drying cylinders). The paper web moves from the upper cylinder to the lower one, then to the neighboring upper one, and so on. The paper is then dried to a residual moisture content of 5-7%. On modern paper machines, a two-shaft gluing press is usually placed in the second half of the drying section for surface sizing of the paper and applying a surface layer. The drying section of some paper machines is equipped with automatic regulators for supplying steam to the cylinders, devices for automatically threading the web of paper onto the drying cylinders, and so on. The steam is collected under a hood located above the entire drying part of the B. m., and then it is removed by exhaust fans to the outside. Heat is used in heaters and heat exchangers.

Finishing part is a calender consisting of 5-10 chilled cast iron shafts arranged one above the other. In order to make it more elastic and soft, the paper is preliminarily cooled and slightly moistened on a refrigerating cylinder (cold water is supplied and removed through the hollow necks of which). When moving between the shafts from top to bottom, the web becomes smoother, compacted and leveled in thickness. Then the paper is wound with an endless tape into rolls on the reel (a forcedly rotated cylinder, against which the roller with the paper wound on it is pressed). To moisten the paper during its additional finishing on supercalenders (to obtain paper with increased smoothness, gloss and bulk density), a humidifier is installed above the reel. Next, the roll is cut on a slitting machine into the required formats. At the same time, the paper is sorted, the breaks that have arisen during its development are glued together. When releasing paper in sheets, the rolls for cutting are fed to the self-cutting machine.

BM also has a large number of various equipment necessary to ensure its continuous operation, and automatic devices that regulate technological parameters. For each type of paper, technically and economically justified paper width and working speed are established. The narrowest paper paper (with a paper web width of 1.6-4. m) are designed for the production of the thinnest capacitor papers, special technical, high-quality photographic and document papers. Wide B. m. (over 6 m) are used to produce newsprint and sack paper. The working speed of B. m. in the production of capacitor paper is 40-150 m/min, newsprint - up to 850 m/min, sanitary papers - about 1000 m/min and more. Productivity B. m., manufacturing capacitor paper with a thickness of 4-12 micron, is 1-4 t/day, newsprint - 330-500 t/day and more. The length of the B. m. for the production of newsprint reaches 115 m, weight about 3500 t, height of individual parts up to 15 m, power of all electric motors (including paper stock preparation equipment) about 30,000 kW. The drive of individual sections of the B. m. is carried out by DC motors. Within 1 hour, such B. m. consumes up to 45 t pair. Automatic devices regulate the processes of casting and drying paper at high speeds. The high level of equipment with automatic devices and the accuracy of adjustment and execution of the BM make it possible to reduce the number of workers directly servicing it to 3-8 people.

Many new designs of paper materials are being developed, differing mainly in the methods of forming the web of paper. In inverform-type paper (England), a sheet of paper is cast and molded between two grids - the lower and the upper ( rice. 3 ). The pulp from the headbox is fed into the gripper between the lower and upper screens, which creates pressure on the fluid flow. Some of the water passes down through the deposited layer of fiber on the bottom wire and the rest is removed through the top wire. From the inner surface of the mesh, water is removed by a scraper equipped with a knife made of plastic material and a tray for draining water. Further dehydration is carried out on conventional and "inverted" suction boxes with a vacuum not exceeding 12 kn/m 2 (0,12 kgf / cm 2). A press is installed behind the suction boxes, and the squeezed water is sucked off through the upper grid with a scraper. When producing multilayer paper, there are several upper grids (according to the number of layers). Water is practically removed only through the upper screens along the scrapers and into the “inverted” suction boxes.

In B. m. of the vertiform type ( rice. four ) the paper web is dehydrated on both sides between two vertically moving grids using scrapers and suction boxes, which ensures that fibers of the same fraction are deposited on both sides of the paper web. In this case, short and thin fibers are deposited first, as a result of which a surface is formed that is most suitable for printing, and large fibers appear in the middle of the sheet, which increases the strength of the paper web.

There is a trend towards the use of circular wire machines for paper casting, where the formation of the paper web is carried out on cylinders covered with a net and located in a bath or without a bath, where the paper pulp is fed. In a rotoformer machine ( rice. 5 ) the headbox and the mesh part are made in one compact unit, and dehydration is carried out using a suction chamber located inside the rotating shaft. The speed of such machines is up to 300 m/min. They can work with low concentrations, which is important when making papers from artificial fibers.

In the production of long-staple papers made from cotton, asbestos and synthetic materials, “dry forming” of the paper web is used, based on the principle of deposition on the grid of fibers dispersed in the air stream. It is possible that such molding will receive wide application for the production of technical and special types of paper.

A further increase in the efficiency of papermaking is associated with a change in the technology of paper production, an improvement in the design of the machine and individual components, and an increase in productivity due to speed and width. A sharp increase in the speed and width of the machine will provide: flow distributors and headboxes of a closed type, allowing you to release the mass on the grid at a speed corresponding to the increased speed of the grid; register rolls of grooved and mesh type, hydroplanks, two- and three-chamber suction couch-rolls that intensify dehydration; new types of presses (reverse suction presses, presses with a wide suction chamber, multi-shaft and hot presses); rubberized suction rolls and rolls fixed in the middle, rolls with grooved corrugation, presses with underlay mesh, vacuum suction cloth washers, rolls, installed on the calender bed, open type with articulated arms, fixed in the middle (lower and upper), floating, not needing bombing to compensate for deflection; peripheral type reels for winding rolls with a diameter of up to 2200-2500 mm with pneumatic clamping of the roll and automatic transfer of it from filling to working supports, etc. In the drying part of the B. m., the use of more than high pressure steam, new schemes of steam distributors with steam circulation, siphon removal of condensate, completely closed hoods over the dryer section, installation of dryer nets instead of dryer felts and so on. In addition to the widespread and relatively cheap drying through the contact of the surface of the drying cylinders of the machine with the paper web, new types are being sought that would significantly reduce the working area of ​​the drying part and increase the uniformity of drying. New types of drying are promising: dielectric (due to high-frequency current passed through the paper web); irradiation with infrared rays; hot air blowing; under vacuum.

Lit.: IvanovS. N., Technology of paper, M.-L., 1960; Eidlin I. Ya., Paper-making and finishing machines, 2nd ed., M., 1962; Jahn K., Arbeit an der Papiermaschine, 4 Aufl., Darmstadt, 1958; Hardman H. and Cole E. I., Papermaking practice, Manch., 1960.

V. A. SMIRNOV

PURPOSE, DEVICE OF THE DRYING PART OF PM AND KDM

DRYING PROCESS OF PAPER AND CARDBOARD. CALCULATION METHOD

NUMBERS OF DRYING CYLINDERS, THEIR LAYOUT IN

DRYING PART

Lecture plan

Characteristics of the drying part, its role in common process paper production. Possible methods of drying paper, their advantages, disadvantages. Mechanism of contact drying of paper on cylinders, factors of contact drying. Method for calculating the number of drying cylinders during the warm-up period, in the first period, in the second period.

Possibilities of eliminating the shrinkage of the paper web and the layout of the drying cylinders along the length of the drying part.

Drying part of machines producing sanitary papers.

After the press section, the dryness of the paper is typically between 28 and 45%. Further dewatering to a final dryness of 92 - 95% takes place in the dryer section of the paper machine. The amount of water evaporated here is determined by the dryness of the paper entering and leaving the drying section. It ranges from 1.3 to 2.5 kg of water per 1 kg of paper, which is about 50 to 100 times less than the amount of water removed on the wet part of the machine.

Of all the parts of the paper machine, the dryer part is the longest. The number of drying cylinders, depending on the speed of the machine, the weight of 1 m 2 and the type of paper, can be from 60 to 80 (diameter 1500 mm). The weight of the drying part, excluding auxiliary equipment, is approximately 60 - 70% of the weight of a high-speed machine, and the cost reaches 50% of the cost of the entire machine. The operating costs associated with the operation of the dryer are also significant: the cost of steam for drying and ventilation is 5 - 15% of the cost of paper; the power consumed by the dryer is approximately half of the total power consumed by the machine (excluding the power consumed by the vacuum pumps). Removal of water on the dry end is much more expensive than on the wet end. In this regard, the expediency of the maximum possible increase in the dryness of the paper entering the drying section is obvious, since this reduces the steam consumption and the required number of drying cylinders.

Currently, the main method of drying paper on a paper machine is the contact method. In order to avoid the formation of wrinkles (warping), the paper should be pressed against the cylinders by the felts during drying.

The cylinders are heated by steam. There are designs of drying cylinders heated by organic heat carriers, gas burners and electric heaters, but they have not yet found wide application.

Contact drying of paper in comparison with other methods has a number of significant advantages, the main of which are high economic indicators and high quality of the dried web, in particular, high bilateral smoothness. On the drying part, the sizing of the paper web ends. For good paper sizing, the paper temperature must be brought to 70 - 80°C before the dryness of the paper reaches 50%.

The disadvantages of multi-cylinder drying include high metal consumption (about two thirds of the mass of the entire machine) and insufficient intensity of the process.

In parallel with contact drying in paper and board machines, convective drying with heated air is used. Despite the fact that convective drying, as a rule, has higher energy costs than contact drying, it is used on all modern paper and board machines.

The advantages of the convective drying method include the simplicity of the design, the wide possibilities of controlling the humidity across the width of the paper web, and also, in some cases, the greater intensity of the process compared to contact drying. The highest drying intensity is achieved when using speed drying hoods with nozzle blowing of the moving web.

Along with contact and convective drying of moving webs, combinations of the first two with drying in energy fields, vacuum drying and drying with thermal mechanical removal of moisture are also known.

AT recent times devices with thermal mechanical removal of moisture have found wide application abroad for drying paper and cardboard. With this drying method, not only the evaporation of moisture occurs due to the supply of heat, but also its mechanical displacement and replacement in the pores of the material with a gaseous agent. Drying with the suction of air or gas has a very significant intensity. A drying intensity of about 140 kg/(m2×h) was achieved, which is about 10 times higher than the average drying intensity in the multi-cylinder dryer section.

During contact drying, when a wet web of paper or cardboard comes into contact with the hot surface of the drying cylinder, contact heat transfer begins. Some heat is also transferred by radiation, since there is no absolutely complete contact between the paper and the surface of the cylinder.

The paper machine is a complex mechanism consisting of several blocks: a wire, press and dryer part, a winder and a slitting machine (PRS).

Bottom mesh table

Upper grid table

Pneumatic headbox

Hydroplan packs

Press with extended pressing area

• Drying cylinders

size press

Quality control system CS5 with automatic regulation

Peripheral rollover

Wire section of paper machine

The papermaking process starts at the wire section, which includes the headbox and the wire table.

There are two types of headboxes:

• open;
• closed.

With the help of these boxes, the total paper pulp is continuously and evenly fed to the paper machine mesh, spreading across its entire width. The outgoing mass, once on the grid table, is formed into a paper web.

Externally, the mesh table looks like a horizontal plane of stretched mesh. To support the lower or reverse mesh branch, mesh-guiding, mesh-straightening and mesh-tensioning rollers are designed.

The main element of the mesh table of the paper machine is the mesh. It is directly involved in the process of turning paper pulp into a paper web.

During the molding process, the mesh is exposed to a strong mechanical and chemical effect. The consequence of this are certain characteristics that it must possess in order to perform its work efficiently and fully:

• high tensile strength, abrasion, bending;
• good drainage capacity;
• high density;
• high resistance to acids.

Good culvert parameters are necessary so that the recycled water washes away a minimum amount of fine fibers, and also so that the marking on the paper is as inconspicuous as possible. Marking in this case is the impression left by the mesh that occurs on the side of the web that was in contact with the mesh during molding.

Press section of paper machine

The paper web prepared at the molding stage from the mesh part enters the press part of the paper machine. In it, further dehydration and compaction of the paper web takes place. As a result of the passage of the web between the press rolls, water is removed from it by mechanical pressing.

The press part of the paper machine consists of the following elements:

• bed. It is on it that all the mechanisms and nodes of the press are installed;
• press rolls (lower and upper). The canvas passes between them to remove water;
• press cloth;
• cloth straightening mechanism;
• cloth tension mechanism;
• sprinkler device;
• cloth washer;
• bucket - bath for collecting water;
• upper shaft scraper;
• a device that performs clamping-lightening of the upper shaft;
• cloth-guiding (bypass) shafts.

The press part has a working linear pressure of 120-130 kg/cm2, the format is 1600 mm. The delivery of the press part of the paper machine is carried out with additional fasteners, tires, a platform, a felt straightener and a pneumatic mode. Characteristics of the press rolls: bottom - rubberized, with forged trunnions; upper - rubberized, coated with "artificial stone".

Dryer part of paper machine

The largest in length is the dryer part of the paper machine. Drying cylinders arranged in a checkerboard pattern in two tiers function in it. These cylinders are heated by steam. When passing through them, the paper web alternately comes into contact with the upper and lower cylinders with both of its surfaces.

Drying cylinders dry the paper web up to 5-7%. This part of the paper machine completes the dewatering process.

On some models of paper machines, automatic regulators are additionally installed that monitor the supply of steam to the cylinders; devices that automatically feed the paper web onto the drying cylinders.

Chapter 10 DRYING THE PAPER

PURPOSE OF THE PAPER DRYING PROCESS AND DEVICE OF THE DRYING PART OF THE PAPER MAKING MACHINE - PART 1

The purpose of the paper drying process is not only to further dehydrate the paper web by evaporating moisture from it, but also to bring the fibers together after pressing under the influence of paper shrinkage occurring during drying with the establishment of bonds between the fibers that determine the main properties of the paper web: mechanical strength, absorbency, air permeability and others. In addition, special properties associated with the completion of sizing, coloring, imparting wet strength, etc. can be imparted to paper by the appropriate technological mode of drying. be achieved immediately after drying or after the final paper finishing process.

If we take as 100% the total amount of water removed on the paper machine, then 96-97.5% of this amount is usually removed on the wire table, and about 1.5% on the dryer part of the machine. This 1.5% on the dry end of a modern high speed newsprint paper machine is expressed as 250-300 tons or more of water per day. Dewatering by drying is 10 to 12 times more expensive than dehydration in presses and 60 to 70 times more expensive than dewatering on a paper machine wire bed.

Although the currently widely used method of removing water from a paper web by contact drying it is expensive and the dryer part of a modern paper machine is much more expensive than its other parts, nevertheless, the existing method of drying paper remains the most effective in comparison with other known methods of drying materials.

The drying part of the paper machine (Fig. 72) usually consists of two rows of steam-heated paper drying cylinders 2, arranged in a checkerboard pattern. The total number of paper drying cylinders depends on the speed of the machine and the type of paper being produced. It is usually 6-7 cylinders for capacitor paper, 50-70 cylinders for newsprint and sack paper, and up to 100 or more cylinders for some boards. The paper web sequentially goes around the side surface of the rotating cylinders and passes through them from the bottom to the top, again to the bottom, etc. e. At the same time, in the area of ​​contact with the cylinders, the web is pressed by a drying cloth 4, which ensures tight contact between the paper and the hot surface of the cylinders. The cloth moistened from the paper is dried on the felt cylinder 3. All paper drying cylinders are divided into groups, each consisting of several cylinders covered by one cloth. In the above diagram, the group consists of five paper drying cylinders and one felt dryer.

Each two adjacent groups of cylinders (lower and upper) are a drying section with an independent drive. The paper drying cylinders in each group on the drive side of the machine are coupled to each other by gear wheels mounted on the trunnions of the cylinders.

and driven by a common drive for each section. Cloth drying cylinders and felt rollers are driven by drying felts.

The presence of drying sections, each having an independent drive, makes it possible, within certain limits, to regulate the speed of the cylinders of each section and, consequently, to regulate the tension of the paper web between sections. Obviously, the greater the shrinkage of the paper, the greater the number of drive sections and the fewer paper drying cylinders in each section. Due to this, a smoother adjustment of the web tension in the dryer part of the paper machine will be ensured, there will be no wrinkles in the paper and no web breaks. So, in the production of capacitor and drawing transparent paper, made from the mass of greasy grinding and having a shrinkage of up to 9-12% or more, each cylinder (sometimes 2 cylinders) is an independent drive section. When producing paper with a shrinkage of 2.5-3.5% and containing a significant amount of wood pulp (newspaper, printing, etc.), the drive section can consist of 8-16 cylinders. For drying the drying felts, one and usually no more than two felt drying cylinders are installed in each group of paper drying cylinders.

For the proper operation of the drying felts, each group of cylinders has mechanisms for automatic dressing and tensioning of the felt.