JPS63190090A - Drying apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a drying device for sheet-like objects such as paper, and particularly in a drying device of the type that presses the sheet-like object against a rotating drum. The present invention relates to a drying device that can effectively control directional moisture content.

(Prior Art) FIG. 2 shows a plurality of rotary drums 2.2 arranged in a staggered manner to carry wet paper 1 sent from, for example, a paper making section (not shown).
−・The paper is shown being handed over to dry. The canvas 3 is a breathable sheet that presses the paper 1 against the rotating drum 2 to make it easier to dry the paper. The campus roll 4 rotates and sends out the campus 3.

The drum 2 is heated by steam introduced into the drum.

FIG. 3 is a diagram showing the inside of the drum. Steam 5 is led into the interior of drum 2 from one end surface of drum 2 through steam pipe 6. Steam 5 is used to heat the surface of drum 2, and a portion of the steam is stored as drain 7 within the drum.

The accumulated drain 7 is discharged from the other end surface of the drum 2 to the outside through a siphon 8 using the differential pressure between the inside of the drum and the outside of the drain along with steam.

Condensation of steam occurs inside the drum, and the high condensation heat transfer coefficient allows for efficient heat transfer from the steam to the drum. Here, in order to always obtain a high condensation heat transfer coefficient, it is necessary to keep the drain film inside the drum thin, and the pressure difference between the inside and outside of the drum is controlled to ensure efficient drum discharge.

Generally, the humidity of paper sent from a papermaking department is not uniform in the width direction of the paper. Further, since the thickness of the drain film inside the drum is not uniform in the paper width direction, the heat transfer coefficient is different in the paper width direction, and the surface temperature of each drum 2, 2-. is also not uniform in the paper width direction. Therefore, the moisture content of the dried paper is not uniform in the width direction of the paper, and this variation in the moisture content of the paper has the disadvantage that it deteriorates the quality when printing on the paper.

In order to eliminate this drawback, a large number of heaters are installed in the width direction of the paper to heat the drum from the outside so that the moisture content in the width direction of the paper can be changed at will. FIG. 4 is a schematic side view and a front view of the same device, showing the state in which a number of heaters 9.9- are installed. The heater 9 may use induction heating or infrared rays, but in either case, the heater 9 applies a heat flux to the drum surface from the outside to locally increase the drum surface temperature. The aim is to improve the moisture content of the paper in that area. In other words, by changing the heat flux given to the drum surface by the large number of heaters 9, 9- arranged in parallel to the axis of the drum 2 in the paper width direction, variations in the moisture content of the paper in the paper width direction can be improved and the paper width can be improved. The aim is to obtain paper with a uniform moisture content in all directions.

Applying a certain heat flux from the outside to a predetermined part of the drum surface using the heater 9 and increasing the drum surface temperature to a greater extent than that heat flux is an effective way to improve the moisture content of paper in that part. It's a method. That is, the smaller the increase in the drum surface temperature with respect to a certain heat flux, the worse the rate of improvement in the moisture content of the paper due to the given heat flux. Therefore, it is desirable to increase the drum surface temperature as much as possible relative to the heat flux given to the drum surface by the heater 9.

Using an equation, we will explain how much the drum surface temperature changes depending on the heat flux applied to the drum surface.

The drum 2 is cylindrical, but since it has a large diameter -i, it is assumed to be a flat plate to simplify the explanation. The heat flux q per unit area on the drum wall can be expressed by the following equation.

q=-(Ti-To)=h(T,-Ti) (1)
δ Here, k Thermal conductivity of the Ni drum wall δ Thickness of the Ni drum wall h Condensation heat transfer coefficient on the inner surface of the Ni drum Ti Ni drum wall inner surface temperature T0 Ni drum wall outer surface temperature T Steam temperature inside the Ni drum On the other hand, the heater 9 is on the drum surface If the heat flux given from the outside is Q, and the heat flux transmitted from the drum surface to the paper is Qo, then
The following thermal equilibrium equation holds true with the heat flux q at the drum wall.

Q 0 = Q + q (2
) The amount of heat transmitted to the paper, Q, can be expressed by the following formula.

Qo = hc (TOTD)
(3) Here, hc is the heat transfer coefficient T between the paper and the drum surface, the temperature of Nizumi. Now, the above (1) To obtain the amount of change ΔT0, the following equation first holds true.

Δq=□(ΔT, -ΔT,) (4) δ Δq=-hΔT i (5) ΔQ
,=ΔQ+Δq(6) ΔQ0=hcΔT, (71Δ indicates the amount of change in each quantity.Here, it is assumed that the drum internal steam temperature T and paper temperature Tp do not change.

(41 (If ΔT; is eliminated from equation 51, the following equation is obtained.

h k/δ (61(71) From equation (8), the following equation holds true.

h k/δ From equation (9), the amount of change in heat flux Δ given by the heater 9 from the outside
The amount of increase ΔT0 in drum surface temperature due to Q can be expressed by the following equation.

ΔT, = □ΔQ QO) h k/δ From the formula 00, it is better to obtain as large a rise in the drum surface temperature as possible with respect to the heat flux given by the heater 9.・ is due to the heat conduction of the drum wall, and is determined by the drum wall's thermal conductivity and the drum wall thickness δ. The thermal conductivity of the drum wall is determined by the metal used, and it is difficult to determine the drum wall thickness δ for reasons of strength.

On the other hand, increasing the thermal resistance □ is achieved by decreasing the condensation heat transfer coefficient on the inner surface of the drum. but,
This is inconsistent with efficient heat transfer from the steam to the drum.

In other words, even if the heater 9 is added to a conventional steam-heated drum, the effective drum surface temperature will be lower than the heat flux that the heater 9 applies to the drum surface from the outside because the condensation heat transfer coefficient is large. I can't get an increase.

As can be understood from the above considerations, it is not effective to add a heater to the steam-heated drum as described above to control the moisture content in the paper width direction.

(Problem to be solved by the invention) In other words, even if the surface of the drum, which has been heated from the inside by steam as in the past, is further heated from the outside by a heater, it will not be effective because the condensation heat transfer coefficient of steam is large. The problem was that it did not work.

The present invention was developed to solve this problem.
The purpose of the present invention is to provide a drying device that lowers the heat transfer coefficient on the inner surface of the drum, maintains the inner surface at room temperature or higher, and increases the amount of increase in drum surface temperature relative to the change in heat flux caused by an external heater. be.

(Means for solving the problem) Therefore, in order to reduce the moisture content of a sheet-like object, the present invention applies a heat flux from the outside to the rotating drum against which the sheet-like object is pressed and heated from the inside. A drying device consisting of a heating device that is arranged inside a rotating drum and effective for reducing the heat transfer coefficient on the inner surface of the drum, and a heater that maintains the member or medium at room temperature or above. This is the structure of the present invention, and is intended as a solution to the above-mentioned problems.

(Function) Hereinafter, the difference in the amount of increase in drum surface temperature due to external heating of the drum surface by a heater when steam is introduced into the drum and when the drum is filled with high-temperature air is expressed as the difference in the amount of increase in drum surface temperature due to external heating of the drum surface by a heater. This will be clarified by performing analytical calculations.

The calculation conditions are as follows.

Drum outer diameter: 1520 Drum inner diameter: 1480 Tsuru drum circumferential speed: 600 m/min Contact angle θ = 180° Steam temperature inside the drum: 125°C Air temperature inside the drum: 125°C Steam condensation heat transfer coefficient h v = 1700 kcal/r
d h ”C Natural convection heat transfer coefficient of air h * = 25k
cal/m h 'C Heat transfer coefficient h between paper and drum surface
c=500kcal/rrfh'c Heater generated heat flux 10900kcal/rd hHere, it is assumed that the heater gives a heat flux over the circumference of A as shown in FIG.

As a result of heat conduction analysis calculation under the above conditions, the drum wall temperatures as shown in FIGS. 6 and 7 were obtained.

FIG. 6 shows the case where steam is introduced into the drum.

In the figure, the broken line indicates the case where the heater 9 does not provide an external heat flux, and the solid line indicates the case where the heater 9 provides an external heat flux. It can be seen from the figure that the drum surface temperature increased by only 1.5°C due to the heater. FIG. 7 shows a case where the drum is filled with air. In the figure, the broken line indicates the case where no external heat flux is provided by the heater, and the solid line indicates the case where external heat flux is provided by the heater.

From the same figure, the drum surface temperature was 11.5℃ due to the heater.
I see that it is rising.

According to this heat conduction analysis, filling the inside of the drum with high-temperature air allows the external heating of the heater to work more effectively and increase the drum surface temperature more effectively than introducing steam into the drum.

Although the results described above are based on strict heat conduction calculations, the effective action of the heater can be approximately confirmed using the 00 formula.

(i) When introducing steam into the drum.

The same values as in the above calculation conditions are used for each variable in the αω formula.

h c= 500kcal/ rrr h”Ch=
hv-1700kcal/m h'Ck =45k
cal/m h'c δ=0.02m The amount of change in heat flux ΔQ due to the heater is considered as follows. The heated area by the heater is the circumference A of the drum surface, but in this approximate calculation, it is assumed that it is uniformly spread over the contact area between the paper and the drum. At this time, the heat flux change ΔQ due to the heater is as follows.

ΔQ = 10900/2-5450kcal/c
d h Therefore, the amount of increase ΔT0 in drum surface temperature due to heater heat flux change ΔQ is ΔT, = X5450 = 3.7
The temperature will be 0.02°C. The amount of increase in drum surface temperature according to the exact solution is 1.5
It is ℃.

(ii) When the drum is filled with air.

Use the following values for each variable in formula 01.

h c-500kcal/ cd h 'Ch = h
, -25kcal/rd h ”ck -45kc
al/m h 'c δ=0.02m ΔQ = 5450kcal/rd h Therefore,
Amount of increase Δ in drum surface temperature due to heater heat flux change ΔQ
T0 is ΔT, = −Ninny−X 5450 = 10.4
The temperature will be 0.02°C. The amount of increase in drum surface temperature according to the exact solution is 11.
The temperature is 5°C.

From the above results, when the drum is filled with air,
It has been found that external heating by a heater leads to a greater increase in drum surface temperature than when steam is introduced into the drum.

Therefore, when using a heater to locally improve the moisture content in the paper width direction, it is necessary to introduce steam into the drum.
It can be seen that using air with poor heat transfer coefficient effectively promotes the temperature rise on the drum surface.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described based on the drawings. Fig. 1(a) (BL indicates different embodiments, and first, the example shown in Fig. 1(a) will be described. As shown in the figure, a heat insulating material 10 is pasted on the inner wall surface of the rotating drum 2. Since the drum surface temperature needs to be kept higher than room temperature, usually 60° C. or higher, in order to lower the moisture content of the paper, the temperature of the heat insulator must also be kept above room temperature.

Therefore, the heater 11 is embedded in the heat insulating material to keep the heat insulating material warm. By doing so, the drum surface temperature can be kept constant and the temperature of the drum surface can be effectively increased with respect to the heat flux provided by the heater 9.

Next, another embodiment will be explained based on FIG. 1(b). On the same side, the drum is filled with a suitable gas, for example, air. Furthermore, since it is necessary to maintain the drum wall temperature above normal temperature, a heater 13 is built inside the drum to keep the internal gas above normal temperature. As a result, the heater 9 can exhibit the same functions and effects as those of the above embodiment.

(Effects of the Invention) As described above in detail, according to the present invention, the inside of the drum is filled with air, which has a low heat transfer coefficient on the inner surface of the drum, and is kept at room temperature or higher by a heater, while the outside Since the drum surface is heated with a heater attached to the outside of the drum, it is possible to increase the temperature of the drum surface effectively with respect to the heat flux given to the drum surface by the drum heater attached to the outside of the drum. By controlling the amount of heat flux from the drum in the width direction of the drum, it is possible to effectively equalize the moisture content distribution in the width direction of the sheet-like object in contact with the drum.

[Brief explanation of the drawing]

1(a) and 1(b) are side sectional views of a drying drum section showing different embodiments of the present invention, FIG. 2 is a schematic side view of a conventional paper drying device, and FIG. 3 is a schematic side view of a conventional rotating drum. 4(a) and 4(b) are front and side views of the rotating drum with the heater attached, FIG. 5 is a side sectional view showing the arrangement of the external heater and the rotating drum, and FIG. 6 is the conventional FIG. 7 is a temperature rise diagram of the rotary drum when the present invention is applied. Explanation of the main parts of the figure 1 - Paper 2 - Rotating drum 9 - Heater 10 - Insulating material 11, 13 - Heater 12 - Medium characteristics such as air
Applicant Mitsubishi Heavy Industries, Ltd. Figure 4 Cb) ((1) Figure 5

Claims (1)

[Claims] In order to reduce the moisture content of a sheet-like object, in a drying device that consists of a rotating drum against which the sheet-like object is pressed and heated from the inside, and a heater that gives heat flux to the rotating drum from the outside, 1. A drying device comprising a rotating drum, comprising a member or medium effective for reducing the heat transfer coefficient on the inner surface of the drum, and a heater for maintaining the member or medium at room temperature or above.