RU2705504C2 - HOUSEHOLD PURPOSE PAPER DRYING DEVICE WITH WEIGHT FROM 10 TO 40 g/m2, AS WELL AS NEWSPRINT WEIGHT 51 g/m2, ON A PAPER MAKING MACHINE AT A SPEED OF 2,000 m/min AND HIGHER BY A CONTACTLESS METHOD USING INFRARED ENERGY - Google Patents

Abstract

FIELD: pulp industry.

SUBSTANCE: invention relates to pulp and paper industry and concerns a drying device for drying household paper, as well as newsprint drying, on paper machines by means of energy of infrared rays of certain length by a contactless method at speed of 2,000 m/min and higher. On the proposed drying device by means of infrared rays it is possible to transfer to the dried paper a greater amount of heat per unit of time and to achieve rates of evaporation of moisture and evaporation vapors many times exceeding rates of evaporation at traditional contact drying, which will allow to carry out drying of any types of paper with weight from 10 to 500 g/m², as well as all types of cellulose fibers with weight of up to 700 g/m².

EFFECT: disclosed is a device for drying household purpose paper with weight from 10 to 40 g/m², as well as newsprint weight 51 g/m², on a paper making machine at speed of 2,000 m/min and higher by a contactless method using energy of infrared rays.

1 cl, 1 tbl, 3 dwg

Description

The invention relates to the field of the pulp and paper industry and can be used for drying all types of industrial paper weighing 1 m ² up to 400 g, all types of cardboard weighing up to 500 g / m ² , as well as drying all types of cellulose fibers cast on press weighing up to 700 g / m ² .

The invention has no analogues of high-speed drying of porous materials in both domestic and foreign industries.

Currently, more and more attention is paid to the production of products from thin types of paper weighing from 10 to 40 g / m ² . In this regard, issues of increasing the productivity of paper machines and increasing the speed of drying paper are extremely relevant to meet the growing demand for such products.

The main brake on increasing productivity on a paper machine is the drying section. Therefore, as a rule, at present, paper is manufactured on high-speed machines with a minimum weight of 1 m ² : tissue paper - 16-22 g / m ² , fruit paper - 16-20 g / m ² , paper for towels - 18-22 g / m ² , toilet - 15-20 g / m ² , etc.

At the same time, products in marketable form from these types of paper are made of two, three, four or more layers of paper, since with an increase in mass on a paper machine by 10 g / m ^2, the drying speed decreases by 15-20% or more.

On self-shooting machines of domestic enterprises, thin types of paper are produced with a weight of 1 m ² from 16 to 45 grams at a speed of up to 1000 m / min.

The achieved speeds in the production of toilet paper weighing 17-35 g / m ² with a speed drying hood are from 500 to 915 m / min. When replacing the high-speed drying hood with a modernized hood with a coolant for heating the drying air, which allowed maintaining the temperature of the drying air to 450 ° C, the working speed of the drying part exceeded 1000 m / min. The increase in speed over 1300 m / min was made possible thanks to the advent of double-mesh paper machines.

Abroad, at the end of the 20th century, the working speed of paper machines was reached 2000 m / min. Moreover, the mass of the elementary layer of paper on the net of the machine was 16-19 g / m ² .

The speed of drying paper in a contact way with a cap of high-speed drying of paper largely depends not only on the temperature of the contact surface of the drying cylinder, but also on the parameters of the drying air, as well as on the rate of removal of the vapor-air mixture from under the hood.

The steam-air mixture under the hood of high-speed drying, above the drying cylinder, is saturated steam, when removed by blowing with hot air it scatters in all directions, which represents a high fire hazard from paper dust generated by blowing. In addition, with this method of removing the vapor-air mixture, a large percentage of "knocking out" the vapor-air mixture from under the hood is formed due to the unregulated difference between the supply of hot air and the removal of the mixture from under the hood.

What is the effect of speed drying?

From molecular physics it is known that with saturated vapor every second - how much it evaporated from 1 m ^{2 of} the evaporation surface, the same number of vapor molecules returns back from saturated vapor to the evaporation surface, i.e. into the liquid.

When drying, the steam to be removed must be replaced continuously by new, and the water must be turned into steam all the time. Only then will there be a continuous process of drying the paper web.

The most important point of high-speed drying is the timely and continuous removal of moisture vapor every fraction of a second, because an evaporated molecule can be above the surface for an average of 10 ^-7 seconds and if it is not removed, it will return back [1, p. 395].

Calculations show that with 1 m ^{2 of the} open surface when water is heated at t = 200 ° C in 1 second, 449.7⋅10 ²³ molecules can be evaporated, which corresponds to a water mass of 1349 g / s (see calculation, p. 12).

What we have in practice when drying paper:

- the evaporative capacity of water with 1 m ^{2 of} heating surface on the drying cylinder by the contact method when producing toilet paper using high-pressure steam reaches 100 kg / h = 27.8 g / s [2, p. 641].

- the amount of water evaporated in 1 hour from 1 m ^{2 of the} surface of 28 drying cylinders in the manufacture of newsprint is 163.332 kg / hour = 45.4 g / s [3, p. 143].

This suggests that the mechanism of drying paper on the machine by the contact method has been studied very poorly. “Until now, even the question of the ratio of the amount of moisture evaporated in individual sections of the paper web path remains unclear” [3, p. 88].

In the manufacture of paper of increased weight 1 m ^{2, the} process of drying it by the contact method on rotating drying cylinders with heating them from the inside with water vapor is one of the most complex processes in the pulp and paper industry and is still poorly understood.

As you know, decontamination of the paper web in the drying part of the paper machine is 10-12 times more expensive than in the press, metal consumption of the drying part is more than 70% of the entire adjustable part of the machine, heat loss to the environment is more than 50% of all losses in the drying part machines, the drying part consumes 25-30% of all electricity consumed to drive the machine. (3. p. 76)

And this is not surprising. Paper is a complex multicomponent structural material, characterized by a diverse composition of cellulose fibers of various origins, as well as filling, sizing and dyeing substances with varying degrees of dispersion. In addition, paper contains more than 60% of pores of various sizes and shapes. The pore size ranges from 0.005 μm to 0.5 μm. In shape, they represent cells of open and closed vessels containing moisture, which is firmly held in many capillaries of the paper sheet (about 1.5% moisture) and which can only be removed by converting this moisture into steam. (8. s 285-288)

The difficulty of drying the paper also lies in the fact that moisture converted into steam must be removed from the thickness of the paper web through a labyrinth of tiny pores, passing through which the steam molecules, when cooled, are again converted into moisture, which requires heat again to turn it into steam. This conversion cycle can be repeated several times until the molecules of evaporated moisture come out of the paper into the free space, followed by removal by exhaust ventilation and blowing with hot air.

Contact Dryer

The drying part of the contact-drying paper machine consists of two rows of drying cylinders, which are arranged in separate groups. Each group includes a certain number of paper drying cylinders heated from the inside with water vapor. In each group, the contact surface of the cylinders covers the drying cloth, closely fitting to the surface of the cylinders.

After the press part, the wet paper web, passing between the hot surface of the cylinder and the cloth, is tightly pressed by the cloth to the surface of the cylinder on an arc of girth of about 50-60%. The temperature of the contact surface when drying paper on high-speed machines is up to 170 ° and above. On the contact surface, moisture in the paper web instantly boils, the exit to the free space of evaporation vapors is closed. About 2/3 of the vapor vapor penetrates deep into the paper web, condensing along the path through the paper, some breaks into the cloth and remains in the cloth.

From molecular physics it is known that the boiling point is equal to the condensation temperature. Thus, saturated steam is formed on the arc of felting over the contact surface of the drying cylinder. After a moment, a dynamic equilibrium sets in: this means how many molecules have evaporated, the same amount in such a time returns to the liquid. With further heating, the pressure of saturated steam increases, exceeds the pressure of the drying cloth to the surface of the cylinder, the cloth with paper rises above the cylinder, and the contact of the cloth with the cylinder is broken. A drying crisis sets in - energy is wasted, drying efficiency drops. The first drying cycle ends. There are as many such cycles of the drying process in contact drying of paper on a multi-cylinder drying part of a paper machine as there are drying cylinders. The used technique of blowing off vapor vapor in the spaces between the cylinders with hot air with a high temperature does not significantly increase the drying speed of the paper.

According to the law of molecular physics, it is known that with increasing temperature of evaporation, the rate of evaporation of a liquid increases significantly. But this does not mean that the drying speed of the paper web grows in proportion to the rate of evaporation.

The calculation (see the appendix) shows that from 1 m ^{2 of the} free surface when heating water at t = 200 ° C, 1349 g of water per second can be evaporated. (L. 12)

At the same time, the rate of moisture removal from 1 m ^{2 of the} heating surface of the drying cylinder when drying toilet paper weighing 15-20 g / m ² at a speed of a paper machine up to 2000 m / min at a drying temperature of 170-190 ° C is 30-40 g / sec (on a self-filming machine).

As you know, with an increase in the mass of 1 m ^{2 of} paper by 10 grams, the drying speed of paper decreases by 10-15% or more [2, p. 466].

When drying newsprint with a mass of 51 g / m ² at a speed of 600-700 m / min, I take moisture from 1 m ^{2 of the} heating surface of the cylinder during contact drying is 50-70 g / s. Therefore, 50 drying cylinders are required to dry the paper web. (13. p. 15)

The reasons for the low moisture removal from 1 m ^{2 of the} heating surface of the cylinder when drying newsprint is that:

1) the mass of 1 m ^{2 of} paper is higher than the mass of toilet paper,

2) when drying newsprint, drying press cloths are used, in which there is significant resistance to moisture vapor, which is removed mainly in the spaces between the cylinders. Drying of toilet paper weighing up to 30 g / m ^{2 is} carried out, as a rule, without drying cloth: it adheres freely to the heating surface of the drying cylinder due to the higher moisture content of the sheet, in which more pores are formed than in newsprint, and the evaporated moisture in the form of steam passes freely through the paper and is removed during the drying process. With this drying process, I will take moisture from 1 m ² higher, but the performance of the paper machine decreases.

The low moisture removal from the heating surface of the drying cylinders during contact drying of the paper is due not only to these reasons.

From physics it is known that the amount of evaporated water is proportional to the amount of energy supplied.

On modern high-speed high-performance machines, this principle is widely used.

To achieve the highest drying speed, they began to raise the temperature of the heating surface of the drying cylinders to 200 ° C and above. The vapor pressure in the cylinders reaches 12 atm or more.

And what is it?

With increasing temperature of the heating surfaces of the drying cylinders, the amount of evaporated moisture increases, but the number of cylinders in the drying part also increases, and the removal of moisture from 1 m ^{2 of the} heating surface remains almost at the same level.

What is the essence of the problem?

The above calculations (see the appendix) show that at a water temperature of 200 ° C from 1 m ^{2 of the} open evaporation surface, 449.7⋅10 ²³ moisture molecules evaporate in 1 second, which, in terms of the mass of water, is 1349 g / s (see payment). (L. 12) The velocity of vapor molecules during evaporation of moisture from an open evaporation surface at t = 200 ° C is v = 774 m / s.

At the same time, under real conditions, the speed of molecules at the same evaporation parameters is v _p = 1.59 m / s (see table of evaporation rate No. 1).

Table 1 shows the calculation data of the rate of vaporization of vapor molecules from a free surface and their passage through a paper sheet during the evaporation of moisture at a heating temperature from 100 to 260 ° C (see Appendix):

As already noted above, with increasing temperature of heating the paper during drying, the concentration of evaporated moisture molecules proportionally increases in the pores of the paper sheet. Therefore, the exit of steam into the free space through numerous paper pores is difficult due to the random movement of its molecules in the paper sheet, and accordingly, the vapor pressure also increases rapidly. In addition, steam, breaking through and in contact with non-evaporated moisture, becomes saturated. A significant part of the vapor molecules due to irregular motion gets stuck in the paper and, cooling, turns into moisture.

With further heating, the rate of formation of evaporated moisture molecules outstrips the rate of their release into free space. With increasing pressure, the vapor density increases (see table 1), its viscosity increases, and the coefficient of kinematic viscosity decreases significantly, due to which the rate of moisture molecules evaporating through the thickness of the paper sheet decreases sharply. Accordingly, the paper drying speed is significantly reduced.

Based on the foregoing, it should be noted and recognized that when contact drying paper on drying cylinders heated from the inside with steam, there is no alternative to increase the rate of removal of moisture vapor through the thickness of the paper sheet, and therefore increase the speed of drying paper.

Therefore, modern paper machines have so many drying cylinders.

At the same time, it is already widely known that drying of porous materials is more economical to produce using infrared rays.

Radiant energy is the energy of electromagnetic waves with different wavelengths. When radiant energy acts on a porous body, a significant part of it penetrates deep into the body. These rays are absorbed by bodies, and when absorbed, the radiant energy again turns into heat, as a result of which the body heats up faster than by contact drying, which is confirmed experimentally: “... already at an infrared temperature of 100 ° C, waves of this length penetrate to the greatest depth of the dried material, heat spreads evenly and penetrates deep into it ”[4].

Domestic researchers say: “... using infrared rays with a wavelength of 8-10 microns, it is possible to transfer more heat to the dried porous material and achieve a moisture evaporation rate many times higher than its evaporation rate by contact or convective drying” [5, p. 797]. However, this method of drying paper on a paper machine is still not widely used.

The aim of the invention is the creation of a compact, small-sized, high-performance drying device for the manufacture of conditioned paper on a paper machine using infrared rays with a wavelength of 8-10 μm in a non-contact way with a significant reduction in the metal consumption of the drying part, saving energy, clothes, drying part and other auxiliary equipment.

The essence of the drying device is the use of infrared radiation energy, as the most effective for drying porous materials in one cyclic drying period.

The drying device consists of two main parts, on which both surfaces of the paper web are heated simultaneously with the heat generated by radiation (Fig. 1). (L. 20)

The first part consists of a stationary non-rotating cast-iron cylinder with a smooth inner cylindrical surface heated by an open gas flame or combustion products of combustible gases to a temperature of approximately 650 ° C in order to regenerate the thermal energy of gases into the energy of infrared rays of a certain wavelength depending on the mass of 1 m ² dried paper. On the outside of the device, the surface has the appearance of a faceted glass, consisting of 6-8 flat faces.

The second part of the device consists of separate flat hollow cast iron, steel or ceramic panels with dimensions corresponding to the dimensions of the flat faces of the first part of the device. The panels are installed above the surface of the flat faces of the first part of the device in a continuous arc at a certain distance from the surface of the planes of the cylinder. The panels are heated to the required temperature from the inside by the products of combustion of combustible gases.

In the free space between the surfaces of the cylinder and the panels, mesh-guiding rollers are placed along which a paper web is rolled, sandwiched between two metal grids, which, in turn, are rolled along the rollers using a traction mesh-guiding drum.

A distinctive feature of the drying device is that the process of rapid drying of the paper occurs with infrared rays with a wavelength of 8-10 microns, with which you can transfer the greatest amount of heat per unit time to the dried paper and achieve a moisture evaporation rate many times higher than its evaporation rate contact drying.

Fig. 1 - The drying cylinder is heated from the inside by an open gas flame moving in a spiral spiral inside the cylinder. The hollow panels are heated by the combustion products of gases moving inside the panels (Fig. 2).

The most important feature of the device is that the vapor generated from the dried paper is instantly removed by means of vacuum-suction rollers (Fig. 1). To accelerate the escape of steam from the paper itself, hot air is fed into the vacuum zone of the suction rollers: fast-flying atoms of hot air, crashing into the paper pores and capturing the vapor molecules, transfer them from the chaotic movement to the directed one, using the vacuum-suction rollers, the steam is released into the outer space. In addition, to accelerate the removal of molecules of evaporated moisture from the smallest pores of the paper web, a method of elastic transverse forced vibrations on traveling nets (5, 6) with drying paper using vibration rollers (11) installed under the supporting nets in the spaces between the suction rollers (9) was used , 10). Vibrators are equipped with rigid ribs up to 3 mm high for the entire length of the rollers. The number of edges is determined by the weight of the paper.

From research works it is known [1, p. 250-251], that when the moving section of the perforated mesh oscillates, the layer of air space at the border with the mesh vibrates with it under the influence of hydrodynamic forces, deviating back and forth. This is possible when the vibrators rotate in contact with the traveling grid, when during the collision of the ribs with the grid, the latter instantly “flies up” to a certain height, and a pressure difference arises at the boundaries of the upper and lower grids with air (Fig. 3).

When the rollers are rotated by a small angle, the grid instantly falls from the ribs onto the smooth surface of the rollers, and a shock is formed. With such a collision, the pressure difference again appears above and below the grids, only with the opposite sign.

This difference (p ₁ -p) and (p ₂ -p) pressures increases by a constant value in time, since the gas, oscillating in both directions, inevitably creates a boundary layer; and the faster the gas flows back and forth outside the boundary layer, the pressure in the boundary layer reaches a constant value - up to 0.1 mm water column, which helps repel molecules and gas atoms from the surface of the paper and push molecules of evaporated moisture from the thickness of the porous surface to the outer space , from where exhaust ventilation they are emitted from under the hood into the atmosphere [1, p. 250-251].

One of the most important features of high-speed drying of paper on the proposed drying device is the use of a high-speed method of heating the radiating surface of the drying cylinder (1), with an open gas flame, which is used in the pyrometallurgical industry for “processing pyrite ores mixed with silica sand without coke additives in shaft furnaces” [6, p. 358].

The fact is that when any metal object is heated by an open flame, the flame of the burning torch "licks" only that part of the surface with which it is in contact. With this interaction of the flame with the material, the heat transfer process affects only part of the total surface of the material.

Many researchers have tried to eliminate the shortcomings of existing processes. And only in the 70s of the last century, domestic researchers found that the heating process during smelting of pyrite ores in an atomized state with the addition of high dispersion quartz sand (with particle sizes up to 0.1 mm) in non-ferrous metallurgy is one of the main ways of technological progress .

Success in this process is associated with the creation of the aerodynamic structure of the stream in the sprayed state of fire jets of gas or other type of fuel, the corresponding shape of the working space with the addition of quartz sand with a developed surface of particles.

Research led to the creation of a cyclone unit, the prototype of which was cyclone furnaces designed to intensify the process of burning fuel.

Cyclone smelting is as follows. Air is blown into the cylindrical chamber through a nozzle located tangentially to it at a speed of up to 100 m / s. Picking up particles of gas or liquid fuel, the air stream forms a rotating fiery vortex. This vortex is more voracious than any nozzle, since it forms a flame structure unsurpassed in efficiency. In such a vortex, ten times more fuel burns and, accordingly, the heat generation per unit of the furnace space is quadrupled [7, p. 37].

A similar method of heating the radiating surface of the drying cylinder is used in the proposed invention for drying a paper web on a high-speed paper machine.

The process of heating the radiating surface of the drying cylinder (Fig. 2) with an open gas flame proceeds as follows. Gaseous fuel and heated natural air enters the mixing chamber (B) of the reactive installation [24, 25] at an overpressure, after which the propelled mixture is ignited by incendiary candles (C) and forced to the jet nozzle (E), where the burning mixture is made of centricliner (29) quartz sand is dosed with a particle size of not more than 0.1 mm. The amount of dosed quartz sand is determined practically depending on the required heating temperature and fuel consumption, as well as the size and shape of the working space of the combustion chamber.

Next, the mixture of the burning flame through the jet nozzle (E) located tangentially to the heated surface of the drying cylinder is blown into the cylinder at a speed of up to 100 m / s. Hitting the stationary heated surface of the cylinder, the fiery-air stream forms a rotating fiery vortex. Picked up red-hot particles of quartz dust together with an actively burning flame are brought into rotation along the entire length of the surface of the drying cylinder and, under the action of centrifugal forces, begin to describe spirals, pressing against the heated surface of the cylinder, actively giving off their heat to it.

Thus, the role of quartz dust, according to the researchers, consists not only in the fact that it more actively gives off heat to the cylinder wall, but also contributes to the most active burning, in which a burning flame torch is crushed into many separate burning small balls of flame, which transmit a larger amount heat than one large torch, and intensifies the process of mass transfer in a unit of the heated space.

The exhaust gas is fed to the centricliner (29) where quartz dust is separated from the air and again fed to the nozzle (E) of the reactive installation (24, 25)

To increase the heat transfer coefficient from combustible gases, the gas leaving the cylinder is used to heat the air entering the reactive installation.

Thus, when the surface of the drying cylinder is heated to a temperature of 650-700 ° C with an open gas flame mixed with high dispersion quartz sand, this surface emits infrared rays with a wavelength of 8-10 μm, with which it is possible to transfer more heat to the drying paper unit of time, many times higher than the rate of moisture evaporation during contact drying.

The above calculations show that the proposed drying device with a heated surface area of about 14-15 m ² can replace 50-60 drying cylinders used on modern high-speed paper machines for producing newsprint.

APPENDIX

Calculation of the productivity of a drying device for drying household paper weighing 10-40 g / m ² and newsprint weighing 51 g / m ² at a speed of a paper machine 2000 m / min

This calculation of the productivity of the drying device is carried out according to the indicators of newsprint with a mass of 51 m ² because the specialized literature contains the most complete data on newsprint, on the basis of which one can verify the validity of the calculations of the drying performance at a speed of a paper machine 2000 m / min [8, p. . 285].

The initial data for the calculation

The main characteristics of newsprint:

- weight 1 m ² - 51 g,

- thickness - 85 microns,

- volume 1 m ² - 85 cm ³ ,

- pore volume 1 m ² - 49.64 cm ³ ,

- average pore radius of 3.9 μm,

- humidity of the paper web received in the drying of 50%,

- humidity of the paper on the coast 5%.

The main characteristics of the paper machine:

- the width of the paper web 2.5 m,

- working speed 2000 m / min,

- coefficient of net working time (without idling) 0.95.

The calculation of the performance of a paper machine is made according to the formula:

Q = k⋅0.06⋅v⋅b⋅m⋅t kg / h, where

Q - hourly paper production, kg / hour,

v - operating speed of the machine, m / min,

b is the width of the paper web, m,

m is the mass of 1 m ^{2 of} paper, g / m ² ,

t - 1 hour

k is the coefficient of net operating time of the machine,

0.06 is a conversion factor. [2, p. 598]

1. Q = 0.95⋅0.06⋅2000⋅2.5⋅51 = 14535 kg / h (at 5% humidity)

2. Second output: 14535: 3600 = 4.0375 kg / s (at 5% humidity)

3. Second generation by a.s. fiber: 4.0375-0.95 = 3.835 kg / s.

4. The amount of fiber (with a moisture content of 50%) entered the dryer: Q ₁ = 7.670 kg / s.

5. The amount of moisture evaporated in the drying part:

Q ₁ -Q ₂ = 7.670-4.037 = 3.633 kg / s.

6. The amount of moisture that needs to be evaporated in the dryer is denoted by “mass of moisture” - m = 3.633 kg and transferred to the volume of steam.

It is known that at a temperature of 200 ° C the volume of steam from 1 kg of water is 0.1272 m ³ [9, p. 111, table].

Then the volume of steam will be: 3.633⋅0.1273 = 0.462 m ³ - this figure will be required for further calculations.

It is known that the number of water molecules escaping from 1 m ^{2 of the} open evaporation surface in 1 second at an evaporation temperature of 200 ° C can be calculated by the formula:

[1, с. 394], где

[1, p. 394] where

N is the number of volatiles evaporated from an open surface of moisture from 1 m ² per second at an evaporation temperature of 200 ° C (m / s),

F is the evaporation area (m ² ),

t is the volatilization time (1 s),

0.4 - thermal coefficient of evaporation,

P _atm is the saturated vapor pressure on the saturation line at a temperature of 200 ° C (P _atm = 15.5 atm) [8, p. 111, table],

N _A is the specific number of molecules (6.02⋅10 ²³ ) [1, p. 394],

R is the gas constant (8.31⋅10 ³ W⋅s / kmol⋅grad. [1, p. 362],

T _abs. = 273 ° K + 200 ° C = 473 °.

For the convenience of calculations, we perform the following transformations:

P = 15.55 atm⋅760 mm Hg ⋅133 kg / m⋅s = 1571895 kg / m⋅s [1, p. 471],

R = 8.31-10 ³ : 18 (molecular weight of water) = 4.616-10 ² m ² / s

N _A = 6,02⋅10 ^23: 18 (molecular weight of water) = 0,334⋅10 ²³ kg.

Then:

The number of evaporated moisture molecules will be transferred to the mass of water that has evaporated from 1 m ² in 1 second according to the formula: [1, p. 340]

где

Where

M is the molecular weight of water.

Then

Next, we transfer the mass of water to the volume of steam:

1 kg of evaporated water occupies a volume of 0.1272 m ³ ,

1.349 kg of evaporated water occupies a volume x.

Then x = 1.349⋅0.1272 = 0.1716 m ³ (pair) [9, p. 111].

7. For further calculation, we transfer the mass of water (m = 3.633 kg) to the number of evaporated molecules according to the formula:

где

Where

m is the mass of water, g

N _A - specific number of molecules (6.02,010 ²³ )

M is the molecular weight of water (18 g) [10, p. 49].

(примерный результат).

(approximate result).

8. Thus, if there were no resistance during the evaporation and volatilization of moisture molecules (except for the force of gravity and air space resistance), then for the evaporation of moisture at a temperature of 200 ° C, the total evaporation area would be required:

9. Determine the actual free evaporation area in 1 m ^{2 of} paper sheet.

From molecular physics it is known that evaporation of moisture occurs from the surface. Evaporation occurs at any temperature, even below zero. The most intense evaporation occurs at high temperature.

But the concepts of “evaporation” and “volatilization” of molecules of evaporated moisture are not equivalent. When boiling water in a closed vessel, no volatilization of moisture molecules will occur. To escape, a free surface is required through which the evaporated moisture molecules must leave the liquid.

A porous material, like paper, is a filter through which pores gases pass into the open. The amount of “filtered” gases will depend on the area of free pores at the exit of the vapor molecules from the paper “filter”.

Therefore, the drying speed of the paper web will depend on the growth rate of the concentration of molecules of evaporating moisture, on the speed of their movement through numerous pores in the thickness of the paper sheet, on the presence of the area of free volatilization and the speed of volatilization through this surface.

9.1 To do this, first determine the free pore thickness in 1 m ² newsprint:

- pore volume in 1 m ^{2 of} paper Vп = 49.64 cm ³ (see sheet),

- area 1 m ² in cm ² F = 10 ⁴ cm ² ,

Then the pore thickness will be

9.2 Calculation of the area of free pores in the outer layer of 1 m ^{2 a} sheet of newsprint

Initial data:

- paper thickness 85 μm,

- the volume of free pores in 1 m ^{2 of} paper Vп = 49.64 cm ³ = 49.64⋅10 ^-6 m ³ ,

- pore radius r = 3.9 μm.

Conventionally, we divide the thickness of the paper by the radius of the pore to determine the number of layers: 85: 3.9 = 22 (layers).

Determine the amount of free pores in each conditional layer in 1 m ^{2 of} paper:

Vp = 49.64: 22 = 2.256 (cm ³ ).

Suppose, for convenience of calculation, that each pore is a small ball with a radius of 3.9 μm. Then the volume of one pore will be:

V'n = 4/3 πr ³ (cm ³ )

V'n = 4 / 3⋅3,14⋅ (3,9⋅10 ^-4 ) ³ = 4 / 3⋅3,14⋅59,32⋅10 ^-12 = 248,35⋅10 ^-12 (cm ³ )

Determine the number of pores in one outer layer per 1 m ^{2 of} paper:

2.256 cm ³ : 248.35 × 10 ^-12 cm ³ = 9.1 × ^{10 9} (pore).

Define the area of one pore:

S'n = πr ² = 3.14⋅ (3.9⋅10 ^-4 ) ² = 3.14⋅15.2⋅10 ^-8 = 47.76⋅10 ^-8 (cm ² )

The area of free pores in the outer layer of 1 m ^{2 of} paper will be:

ΣS cm ² = 47.76⋅10 ^-8 ⋅9.1⋅10 ⁹ = 4346 cm ² (0.4346 m ² ).

10. The calculation of the geometric coefficient "G" filtering ability of the grid

When drying the paper web on the proposed drying device, two metal nets are used as carriers of the drained paper web located between them, which also have another function: filtering the vapor evaporating from the paper web.

On the proposed drying device, the drying speed of the paper sheet depends not only on the porosity, thickness and free open area of the outer surface of the paper sheet, but also on the filtering ability of the mesh.

The quantitative value of the filtering ability of each grid should be found experimentally, since each grid number has its own and only its characteristics.

We offer calculation of the filtering ability of mesh No. 26 with the following characteristics:

- based - the number of threads per 1 cm ² = 26 (n ₀ ),

thread diameter = 0.23 mm (d ₀ );

- for weft - the number of threads per 1 cm ² = 16 (n _y ),

- thread diameter = 0.25 mm (d _y ).

гдеWe calculate by the formula:

Where

G is the geometric characteristic of the filtering ability of the grid,

F _W - the living area of the grid (mm ² ). [11, p. 22]

The living cross-sectional area of the grid is calculated by the formula [11, p. 19]:

Then, the geometric characteristic of the filtering ability (filtering coefficient) of mesh No. 26:

11. Calculation of the rate of volatilization of moisture molecules evaporated from the free surface of evaporation at a temperature of 200 ° C

It is known that vapor molecules freely evaporate above the surface during liquid evaporation. With chaotic thermal motion, they move randomly, colliding with each other. Each collision gives them impulses of power.

The combination of these impulses manifests itself as pressure.

The current pressure can be expressed as the equation of the kinematic theory of gases:

P = 1 / 3ρ⋅V ² , where

P is the vapor pressure on the saturation line at a temperature of 200 ° C (15.55 atm),

ρ is the vapor density at a temperature of 200 ° C (7.86 kg / m ³ ),

V is the average value of the quadratic velocity of the molecules (m / s).

[1, p. 184]

From here:

Pressure P = 15.55 atm translate in kg / m⋅s ² :

1 mmHg = 1.33⋅10 ² kg / m⋅s ² (1, p. 471)

1 atm = 760 mmHg = 760⋅1.33⋅10 ² = 101080 (kg / m⋅s ² )

15.55⋅101080 = 1571794 (kg / m⋅s ² )

Then:

Thus, the rate of escape of moisture molecules from the free surface is 775 m / s.

12. The calculation of the kinematic coefficient of viscosity

From molecular physics it is known that with the thermal motion of gas molecules or atoms, resistance always arises, as a result of which moving molecules or atoms lose their speed of movement.

Such resistance during liquid evaporation is the kinematic viscosity coefficient, which depends on the viscosity and density of the vapor at a given evaporation temperature, which is equal to:

где

Where

μ is the viscosity of the vapor in the saturation line at a temperature of 200 ° C (0.0161 kg⋅s / m ² )

ρ - vapor density at a temperature of 200 ° C (7.86 kg / m ³ )

[4 p. 126, p. 822].

Then

We already know from the calculations the rate of volatilization of molecules of evaporated moisture V = 775 m / s, then the rate of volatilization, taking into account other resistances, will be:

V ₀ = V⋅ν = 775⋅0.002 = 1.55 (m / s).

From here it is clearly seen how much the viscosity coefficient decreases the rate of volatilization of the molecules during drying of the paper web.

For evaporation of moisture from 1 m ^{2 of} an open surface at an evaporation temperature of 200 ° C in 1 second, according to the calculations, N = 449.7⋅10 ²³ molecules, which in terms of the vapor volume V _p = 0.1716 cm ³ / s (see calculation , l.).

With the evaporation of moisture from a porous body, the equation is true:

F⋅b = U⋅V, where

F is the evaporation area for 1 s (m ² / s),

b is the thickness of the porous material (m),

U is the pore volume in 1 m ² area (m ³ ),

V is the volume of vapor evaporated in 1 s (m ³ / s)

[4, p. 255].

When drying a paper web on the proposed device to calculate the volume of steam vaporized in 1 s taking into account the speed of movement of steam molecules through the paper pores, pore diameter and their curvature, resistances in the paper web, filtering resistance through the mesh, total pore area and their thickness in the volume of 1 m ^{3 of the} paper web, the resistance forces when steam moves through the pores, the above equation can be represented as follows:

где

Where

F is the area of the dried paper (1 m ² ),

b - paper thickness (m),

V is the rate of vaporization of vapor molecules from the open evaporation surface at a temperature of 200 ° C (according to calculations of 775 m / s),

ν is the kinematic coefficient of vapor viscosity at a temperature of 200 ° C (0.002 m ² / s),

μ is the viscosity of the vapor at a temperature of 200 ° C 0.0161 kg⋅s / m ² [4, p. 821],

ρ is the vapor density at a temperature of 200 ° C of 7.86 kg / m ³ [4, p. 822],

- площадь пор в 1 м² бумажного полотна (0,435 м² - см. расчет, л.),

- pore area in 1 m ^{2 of} paper web (0.435 m ² - see calculation, l.),

G - coefficient of the filtering ability of the grid (0.296 - see calculation, l),

b ¹ - pore thickness in a volume of 1 m ^{2 of} paper (49.64⋅10 ^-6 m),

V ^I - the volume of vapor during the volatilization of molecules with 1 m ² open surface for 1 s in terms of steam (0.1716 m ³ / s - see calculation, l. 13),

R is the resistance force when steam moves inside the paper web (N or kg⋅s / m ² ).

13. Calculation of the resistance force R during the movement of moisture molecules evaporated from the outer surface of the paper sheet.

When moisture is evaporated from a paper web on a drying device, vapor molecules escape from the outer surface, where the molecules experience resistance when they move through numerous capillary pores and channels of variable cross section and of different curvatures.

Regardless of the pressure regime and pore shape, molecules of evaporating moisture during movement experience local resistance forces, friction forces, pressure difference and vapor density, the weight of the molecules in the pores and overcome the force of free attraction.

With this movement, the resistance force R can be expressed in general terms by Newton's law:

R = r⋅S⋅H⋅p⋅g [12, p. 45],

Where:

R is the resistance of the medium (N),

r is the coefficient of local resistance (0.4 m⋅s) [4, p. 158],

S is the pore area in the outer layer of paper (0.435 m ² ),

N - pore height in the outer layer of paper (determined by dividing the value of the paper thickness by the number of conditional layers

N = 85⋅10 ^-6 : 22 = 3.86⋅10 ^-6 m,

ρ is the vapor density at an evaporation temperature of 200 ° C (7.86 kg / m ³ ),

g - acceleration of gravity (9.81 m / s ² ).

Hence the value of the resistance force will be:

R = 0.4⋅0.435⋅3.86⋅10 ^-6 ⋅7.86⋅9.81 = 51.8⋅10 ^-6 (N)

From the general equation given on l. 17, we determine the volume of steam passing through the thickness of the paper web with an area of 1 m ² for 1 second, with evaporation of moisture on the proposed drying device:

Thus, on the proposed drying device, it is estimated that it is possible to evaporate moisture from 1 m ^{2 of} paper paper and remove it in the form of steam 0.033 m ³ in 1 second.

We translate the volume of steam into a mass of water:

1 kg of water = 0.1272 m ³ steam (8, p. 111, table), then 0.033 m ³ steam corresponds to 0.26 kg of water.

14. Determine the total required heated surface evaporation.

From the conditions it is known: it is necessary to evaporate and remove from the 1 m ² paper web in 1 second 3.633 kg of moisture. To do this, we need a heated area on a drying device:

F = 3.633: 0.26 = 14 (m ² ). or 0.462: 0.033 = 14 m ² / s

where: 0.462 m ³ / s (calculation. l. 12)

OUTPUT

On the proposed dryer for drying a paper web weighing 51 g / m ² with a humidity of 50%, installed on a paper machine operating at a speed of 2000 m / min, it is possible to evaporate 3,633 kg of moisture and dry the paper to a standard humidity (5%) of 14 m ² heated surfaces of the drying device in 1 second.

Fig. one

Drying device for radiation drying of paper on PM using a non-contact method:

1 - a drying cylinder, the radiating surface of which is heated from the inside of the cylinder by an open gas flame to transfer energy to the drained paper web;

2 - conical cylinder for maintaining a turbulent fire vortex of a gas flame along the conical surface of the drying cylinder;

3 - exhaust pipe to remove exhaust gases from the inside of the drying cylinder;

4 - steel heat-resistant panels, heated by the products of combustion of combustible gases moving inside the panels;

5, 6 — drying metal grids carrying a drained paper web in the radiation drying zone;

7, 8 - metal mesh, carrying a wet paper web after the press part of the paper machine to the drying device;

9, 10 - mesh-leading vacuum-suction rollers to remove the vapor-air mixture from the drained paper web;

11 - vibrating rotating rollers equipped with longitudinal rigid ribs along the length of the rollers, contributing to the accelerated removal of vaporized moisture from the dried paper;

12 - supply of hot air to the vacuum zone of the suction rollers;

13 - net-driven rollers bearing drying nets on the drying device;

14 - drive traction cylinder, which drives the drying nets (5, 6) with a drained paper web;

15 - clamping shaft of the traction cylinder;

16 - conditioner paper;

17 - a carrying cylinder;

18 - tambour shaft for winding paper;

19, 20 - air showers;

21 - vacuum-resorption rollers;

22 - a cap of a drying device;

23 - exhaust steam-air mixture from under the hood.

Fig. 2

The scheme of radiation drying paper on PM non-contact method

1 - drying cylinder, heated by an open gas flame;

2 - a truncated conical cylinder for a concentrated and uniform distribution of a gas flame moving in a spiral along the heated inner surface of the drying cylinder;

3 - exhaust pipe for exhaust gas from the drying cylinder;

4 - steel heat-resistant panels, heated by the combustion products of combustible gases moving inside the emitters;

5, 6 — drying metal grids supporting a paper web along grid-guiding rotating rollers along the radiating surfaces of the drying cylinder and panels;

24, 25 - air-jet installations in which for the combustion of combustible fuel uses atmospheric oxygen from the environment from the compressor station:

And - air supply under pressure to the jet installation,

K - the supply of combustible gases,

B - mixing chamber,

C is the spark plug

F - nozzle,

E - jet nozzle,

P is the lattice.

26, 27 - gas heat exchangers;

28 - ejector for supplying exhaust gas to the centricliner,

29 - centricliner for separating sand dust from the air mass,

30 - sand feeder,

31 - filter for cleaning exhaust gases,

32 - exhaust pipe.

Literature

1. Paul R.V. Mechanics, acoustics and the theory of heat. - M .; Science, 1971.

2. Ivanov S.N. Paper technology. - M .; Goslesbum, 1960.

3. Shukhman F.G. Paper machines. - M .; Goslesbumizdat, 1957.

4. Infrared radiation. // Science and life, 1985. - No. 7. - from. 97.

5. Planovsky A.N., Ramm V.M., Kagan S.Z. Processes and devices of chemical technology. - M .; Chemistry, 1968.

6. Polytechnical dictionary. - M .; 1976. - p. 358.

7. In a fiery whirlwind. // Science and life, 1972. - No. 10, - p. 37.

8. Flate D.M. Paper properties. - M .; Timber industry, 1976.

9. Sinyavsky Yu.V. Collection of tasks on the course Heat Engineering. - SPb .; GIORD, 2010.

10. Nemchenko K.E. Physics in diagrams and tables. - M .; 2012.

11. Shukhman F.G. Grids of paper machines. - M .; Timber industry, 1988.

12. Trofimova T.I. Physics course. The classic textbook. - M .; 2010. - p. 45.

13. Modern machines for the production of newsprint IBT.I. 1958 Moscow.

Claims (1)

A compact drying device for drying sanitary-hygienic types of paper 50% humidity on a paper machine, containing a heat-resistant cast iron cylinder and steel panels, the heating of the emitting surfaces of which is carried out by an open gas flame or by the combustion products of gases moving inside the emitters, characterized in that in order to reduce energy consumption , metal consumption of the drying part, operating costs and increase the speed of drying paper, structuring and drying of the paper web, placed between the lump of metal nets rolled on rotating rollers with the pulling force of the drive drum is carried out in a non-contact way using the energy emitted by infrared rays with a wavelength of 8-10 microns, with which it is possible to transfer large amounts of heat to the dried paper and achieve a moisture evaporation rate of many times the evaporation rate with other drying methods; An exceptional feature of increasing the speed of drying paper on a drying device is that the rate of evaporation of the molecules is equal to or may be greater than the rate of evaporation of moisture by adjusting the depth of vacuum on the suction net guiding rollers during drying of the paper and increasing the rate of advancement of steam molecules from the depth of the paper web by feeding overpressure hot air into the vacuum zone to transfer molecules of evaporated moisture by flying atoms of hot air from chaotic to directed motion as well as due to mechanical vibrations of a moving mesh with a paper web using vibrating rollers to increase the number of vaporized molecules of steam from the surface of the paper web per unit time, the emission of which is carried out by exhaust ventilation from under the hood.

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