RU2418123C1 - Method to externally dry paper on paper-making cylinder - Google Patents

Abstract

FIELD: textile, paper. ^ SUBSTANCE: method includes supply of dried paper to a drying cylinder, supply of steam into its inner cavity, supply of air into the air header with a radial cap facing the surface of the drying cylinder, supply of air jets via holes in cap that tightly fits along the cylinder generatrix. Air jets outgoing to the moist surface of the cylinder are exposed to the acoustic effect from the gas-jet acoustic radiator. The working gas of the gas-jet acoustic radiator is directly air used in the air header and supplied into the nozzle of the gas-jet radiator and further into a resonator. Frequency of applied acoustic oscillations makes 100-4000 Hz. ^ EFFECT: increased intensity of external drying, higher efficiency of paper-making machine drying part, reduced steam flow for internal drying and reduced air flow for external drying. ^ 2 dwg

Description

The invention relates to the field of paper industry and can be used for drying paper on drying cylinders.

Known methods: external drying of paper on a drying cylinder [1, 2]. In this case, additional external drying of the paper is carried out by jets of air supplied from a collector located along the radius of the drying cylinder. Also known is a method of external drying of paper with heated jets to a temperature of 500 ° C [3] - prototype. However, the disadvantage of these methods is the reduction of the heat transfer coefficient, heat flow and drying optimality due to the laminar boundary layer of evaporating moisture formed along the cylinder of the dried paper. This leads to reduced productivity of the machine, excessive consumption of steam for internal drying and excessive consumption of air for external drying.

An object of the invention is to increase the intensity of external drying, increase the productivity of the drying part of the paper machine, reduce the consumption of steam for internal drying and reduce air consumption for external drying.

The technical problem is achieved as follows. The method of external drying of paper on a paper cylinder, including the supply of dryable paper to the drying cylinder, the supply of steam to the inner cavity of the cylinder, the air supply to the air collector with a radial hood facing the surface of the drying cylinder, the flow of air jets through the openings of the hood surrounding the cylinder forming, is different the fact that the jets of air coming out onto the wet surface of the cylinder are subjected to acoustic impact from a gas-jet acoustic emitter, while the working gas of a gas-jet aka cally emitter is directly air used in the air manifold, the nozzle feed gas jet emitter and into the cavity, and the frequency of acoustic oscillations superimposed is 100-4000 Hz.

This frequency range is due to the following. At a frequency of more than 4000 Hz, the cavity length sharply increases, which leads to a significant increase in overall dimensions. And at a frequency of less than 100 Hz, it is impossible to initially produce a resonator.

Figure 1 shows the formation of a laminar boundary layer of evaporating moisture when exposed to external jets of air. Here 1 is the outer surface of the liner of the drying cylinder; 12 - laminar boundary layer of evaporating moisture; 4 - output nozzles; 11 - jets of air.

The heat flux from the surface of the paper, taking into account the laminar boundary layer upon evaporation of moisture from the surface, is [2]

where α is the heat transfer coefficient from the jet to the surface;

T _a and T _s are the temperatures, respectively, of the supplied jets and the surface of the paper (see figure 1);

where T _ƒ is the temperature of the outer surface of the laminar layer;

C _ρν is the heat capacity of moisture vapor;

A is the open surface of the paper;

m _eν is the film velocity or evaporation rate.

According to [2], the presence of the evaporation factor and the laminar boundary layer (factor E) reduces the heat flux and, consequently, the drying rate by more than 10%.

The use of a gas-jet acoustic emitter in this invention provides for the imposition of acoustic vibrations on the air stream supplied to the surface of the cylinder. The presence of acoustic vibrations near the surface of the dried paper creates the corresponding oscillatory motion in the laminar layer of evaporating moisture. These oscillatory movements lead to local destruction of the integrity of the laminar layer, provide direct contact of the air jets to the surface of the paper, which in accordance with formulas (1) and (2) increases the heat transfer from the surface of the paper to the supplied air jets. Therefore, we can assume that the claimed method meets the criterion of "inventive step".

Comparison of the proposed solution with the prototype shows that it meets the criterion of "novelty."

Thus, the drying process is accelerated, machine productivity is increased and the required steam consumption for internal drying is reduced.

The design and parameters of a gas-jet acoustic emitter are described in [2].

In this case, the advantages of a gas-jet acoustic emitter are the use of direct air as the working generating gas, which is used for external drying of paper.

The proposed method is implemented using the device shown in figure 2. It includes the sleeve of the drying cylinder 1, the drying paper 2, the jet collector 3, the output nozzles 4, the gas-jet acoustic emitter 5.

In turn, the gas-jet acoustic emitter consists of an air supply pipe 6; nozzle 7; resonator 8; reflector 9; the pipeline from the gas-jet acoustic emitter to the air manifold 10.

The device operates as follows. Drying paper 2 is supplied to the surface of the rotating drying cylinder 1. Air for external drying is supplied through a pipe 6 and through a nozzle 7 is supplied to the resonator 8, generating acoustic vibrations with a frequency of 100-4000 Hz. Reflecting from the reflector 9, acoustic vibrations through the pipeline 10 are supplied to the collector 3 and then through the output nozzles 4 with the jets attacking the outer surface of the paper, they act on this outer surface, contributing to the oscillatory movement and destruction of the laminar boundary layer of evaporating moisture. This, in turn, leads to an increase in the heat transfer coefficient and heat flux from the dried paper to the air jets.

In this case, the heating of the air supplied to the external dryer contributes to the intensification of the acoustic effect, since with increasing medium temperature the speed of sound propagation in this layer increases in proportion to the square root of the absolute temperature of the medium.

To enhance the acoustic feedback acoustic preferable to increase the supply air pressure until obtaining at the outlet section of the nozzle of an acoustic sound emitter critical velocity that corresponds to the air environment minimum braking pressure p _m = 1.4-1.6 atm (0,14-0,16 MPa) [4].

Here is an example implementation of the invention.

Air braking pressure p _in = 0.15 MPa and braking temperature T _in = 300 K.

According to [2], the required air flow for external drying will be 140.5-150 t / h.

.Then, with the diameter of one nozzle d _c = 5 mm, its cross-sectional area is

.

We accept the number of nozzles per drying cylinder n _c = 180.

Then the total area of the nozzles corresponds to ω _cΣ = n _c ω _c = 180 19.6 = 3534.3 mm ² .

According to [1], the velocity distribution at the exit of existing nozzles is up to 80 m / s.

Then, when the nozzle diameter d = 5 mm _{with a} flow rate density ρ = 1,2 kg / m ³ per nozzle will be at a temperature T = 300 K _at a pressure p _in = 0,15 MPa (15.3 x 10 ³ g / m ² ).

With the total number of nozzles n _s = 180, we obtain the total flow rate per cylinder G in _Σ = n _s · G _sun = 180 · 0.21 = 36.8 kg / s = 132.5 t / h.

The gas-jet acoustic emitter, based on the calculation, allows to obtain a critical speed in the exit section of the nozzles during braking motion p _in = 0.15 MPa (see figure 2).

The area of the output section of the nozzles of the acoustic emitter is determined by the formula [3]

where k _p - expenditure coefficient, equal to air to _p = 0,0104.

Then

and the diameter of the output section of the nozzles of the acoustic emitter is determined from, respectively

In accordance with the recommendations of [3], the residual parameters of the gas-jet acoustic emitter were determined.

Resonator Diameter

d _p = 1.5 d _a = 1.5 · 7.14 = 10.7 mm.

The cavity length l _{p is} determined for the frequency of acoustic vibrations ν = 950 Hz.

, l_p=25,7 мм

, l _p = 25.7 mm

The distance between the nozzle and the resonator l _{s.r. is} found from the relation

;

.

;

.

The radius of the reflector R _from = 40 mm.

Thus, all parameters of the gas-jet acoustic emitter are calculated.

The invention provides an increase in the intensity of external drying, an increase in the productivity of the drying part of the paper machine with a decrease in steam consumption for internal drying and a decrease in air consumption for external drying.

Information sources

1. Flate D.M. Paper technology. Textbook for high schools. M .: Lesn. industry, 1988 .-- 440 s.

2. Papermaking Science and Technology. Book 9. Papermaking Partz. Drying / Book editor Karlson M., Farpetoy. Helsinki. Finland, 2000. P. 496.

3. Lisienko V. G., Schelokov D. M., Ladygichev M. G. Fuel: Reference edition in 3 books. Book 2 / Under. ed. V.G. Lisienko. M .: Heat engineering, 2004 .-- 832 s.

4. Kitaev B.I., Zobnin B.F., Ratnikov V.F. and others. Thermotechnical calculations of metallurgical furnaces. Textbook / Ed. A.S. Telegin. M .: Metallurgy, 1970 .-- 528 p.

Claims (1)

The method of external drying of paper on a paper cylinder, including supplying drainable paper to the drying cylinder, supplying steam to the inner cavity of the cylinder, supplying air to the air collector with a radial hood facing the surface of the drying cylinder, supplying air jets through the openings of the hood surrounding the forming cylinder, the fact that jets of air coming out onto the wet surface of the cylinder are subjected to acoustic impact from a gas-jet acoustic emitter, while the gas A blast acoustic emitter is directly the air used in the air manifold supplied to the nozzle of a gas-jet emitter and further to the resonator, and the frequency of acoustic superimposed oscillations is 100-4000 Hz.

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