JPH0414270B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an obari dryer, a paper machine dryer,
The present invention relates to a multistage hot air dryer in a paper drying device that can be applied to a general hot air dryer.

(Prior Art) A hot air dryer is used for drying paper, mainly coated paper. Figure 1 shows an overview of a conventional hot air dryer. The dryer is main body 12
A, a blower 10A, and a heater 11A. In addition, the flow of hot air enters the heater 11A from the blower 10A, heats it to a constant temperature, and heats it to the line 5A.
The liquid enters the dryer body 12A from the nozzle 13A and is blown onto the wet paper 1A to dry it. Main body 12A
Dry waste gas from line 4 from line 3A
A is circulated by blower 10A. In this case, in order to keep the humidity of the hot air constant, fresh air is introduced through line 7A and a portion is discharged out of the system through line 8A. In the paper drying system, hot air dryers 12A are combined in multiple stages as shown in FIG. 2, and wet paper 1A is output as dry paper 2A.

Now, when the supply/discharge ratio η of the hot air dryer is defined by the following formula, η = (Amount of hot air extracted from the circulation line to the outside of the system) / (Amount of circulating hot air) The conventional hot air dryer has the dryer group shown in Figure 2. All of them are operated without constant supply/discharge rates or control. If the supply/discharge ratio is made small (for example, η≈0), the energy loss will be reduced due to heat radiation only from the duct and the hot air dryer body, but the paper will be difficult to dry.

This is because the driving force for drying is the humidity in the hot air and the vapor pressure on the paper surface. Therefore, if η is increased, the amount of hot air released outside the system will increase, resulting in an increase in energy loss. Therefore, conventional dryers are normally operated with η=0.1 to 0.15.

(Problems to be Solved by the Invention) The present invention has developed a drying system with low energy loss and drying characteristics comparable to conventional ones, which can eliminate the conventional drawbacks and is a paper drying device with high thermal efficiency. The purpose is to provide a multi-stage hot air dryer.

(Means for Solving the Problems) Therefore, the present invention provides a multi-stage hot air dryer in a paper drying device having each drying area of a preheating zone, a constant rate zone, and a lapse rate zone, and a paper temperature detector is installed at each dryer outlet. Based on this, the hot air supply and discharge rate is controlled for each drying area, and the dryer in the preheating zone detects the outlet paper surface temperature and is controlled to reach the set temperature in the constant rate zone, and the dryer in the constant rate zone adjust the opening degree of the exhaust control valve within the supply and discharge ratio range of 0.05 to 0.15, and the dryer in the decreasing rate zone
It has a configuration in which the opening degree of the exhaust control valve is adjusted by detecting the outlet paper surface temperature at 0.05 or less.

(Function) Now, in the above configuration, the dryer that grasps the drying characteristics of the paper and is in charge of preheating the paper has a small η (for example, η=0.05), and the dryer that is in charge of the constant rate region has a large η (for example, η=0.05). 0.1 to 0.15), and in the dryer in charge of the lapse rate region, η is small (for example, η
= 0.05), the paper surface temperature can be detected and the opening degree of the exhaust control valve can be adjusted. As described above, in the present invention,
Since the temperature of the paper surface is detected, it is direct and responsive to drying.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows an embodiment of the hot air dryer of the present invention. FIG. 3 shows an example of hot air drying of coated paper, and the hot air dryers are comprised of numbers 1 to 6. Further, one hot air circulation line is configured for each dryer (for example, 1, 6) or for every two dryers (for example, 2, 3). This circulation line is provided with one blower 10a to 10c and one heater 11a to 11c each.

In addition, there are control valves 12a to 12c in the exhaust gas line of the circulation line, and non-contact thermometers, such as infrared thermometers 13a to 13, are provided at each dryer outlet.
c is applied, and its output is sent to the arithmetic and control units 14a to 1
4c, and sends an output signal instructing the control valves 12a to 12c to open from 0 to 100%, respectively. Others, paper feed reel 20
The base paper 15 for coating is sent out from the coating device 22.
The film is coated with dryers 1 to 6, dried by dryers 1 to 6, and wound up by a take-up reel 21. Note that the dryers 4 and 5 are also provided with similar hot air circulation lines.

Next, the operation of the embodiment constructed as described above will be explained. As shown in FIG. 4, the drying characteristics of paper include preheating, constant rate, and decreasing rate processes. In the dryer 1 corresponding to the preheating zone, based on the paper temperature detected by the thermometer 13a, an opening setting signal (preferably η = 0.01 to 0.05) is sent from the arithmetic and control unit 14a to the control valve 12a to control the supply/discharge rate η. ). In this case, if η is made too small (for example, η=
0.01 or less), the paper temperature is as shown in Figure 4, which means that excessive thermal energy was given to the shaded area. On the other hand, when η is increased (for example, η = 0.15), water evaporates at a very low temperature, but a large amount of thermal energy is released outside the system, increasing heat loss. Therefore, in order to maximize thermal efficiency, it is preferable to reduce η so that the paper temperature is approximately the same as the paper temperature during constant rate drying.

Next, the dryers in charge of the constant rate region, for example dryers 2 and 3 in Fig. 3, desirably
The opening degree of the control valve 12b is set so as to control the opening to about 0.1 to 0.15. Furthermore, in the constant rate region, the higher the paper temperature and the lower the water concentration in the hot air, the greater the driving force for water evaporation.
However, the temperature of the paper and the moisture in the hot air are as shown in the following equation:
The paper temperature TS is determined by determining the moisture concentration in the hot air (=hydrothermal partial pressure Pa).

q=UA(TG-TS) =hD・A・Lr/R(PS/TS−Pa/TG) however q is the amount of heat given to the paper by hot air, U is the heat transfer coefficient between paper and hot air, A is the heat transfer area, TG is hot air temperature; TS is paper temperature, hD is mass transfer coefficient, Lr is the latent heat of vaporization, R is the gas constant.

On the other hand, the moisture concentration in hot air decreases as η increases. Therefore, as for thermal efficiency, the relationship shown in Figure 5 is obtained. η when the thermal efficiency is the best is
Although it varies depending on the operating conditions, η = 0.05 to 0.15 is generally the most effective.

Thermal efficiency = amount of heat removed from paper water/amount of heat heated by the heater Therefore, if the operating conditions are known in advance, the paper temperature at which the thermal efficiency is maximized can be calculated, so this temperature (for example, η = 0.1, U = At 80Kcal/m ² h℃, the paper temperature is approximately 50
℃) by controlling the opening degree of the exhaust valve 12b so that the thermometer 13b in FIG. 3 indicates the temperature. Next, in the dryer 6 which is in charge of the decreasing rate region, moisture evaporation is rate-determined by moisture diffusion in the thickness direction of the paper, so no matter how large the supply/discharge rate η is, evaporation is no longer promoted. Therefore, the moisture concentration of paper is closely related to paper temperature, and as shown in Figure 6, there is a uniform relationship between paper surface temperature and moisture content with little variation in the lapse rate region. By monitoring the temperature of the paper surface on the outlet side with the thermometer 13c, the moisture concentration of the product (paper) will show a substantially constant value.

In this case, the temperature at the exit side of the dryer 6 is the supply/discharge rate η
= 0.05 or less (heat loss to the outside of the hot air system is reduced), and even if η is increased (heat loss increases), the product moisture content will hardly change.

(Effects of the Invention) As explained in detail above, the present invention is configured, and the hot air supply/discharge rate η of each dryer is adjusted according to the preheating zone, constant rate zone, and lapse rate zone, and the outlet paper surface temperature of the dryer in the preheating zone is adjusted. The dryer in the constant rate zone is controlled to reach the set temperature in the constant rate zone, and the dryer in the constant rate zone is controlled at the surface temperature that maximizes thermal efficiency in the range of η = 0.05 to 0.15, and the dryer in the decreasing rate zone is controlled to reach the set temperature in the constant rate zone.
The paper surface temperature is controlled at a preset moisture content of 0.05 or less. Therefore, in the present invention, since the paper surface temperature is detected, the paper surface temperature is directly responsive to drying.
Energy saving can be achieved.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a conventional hot air dryer, Fig. 2 is an explanatory diagram showing a state in which the dryers of Fig. 1 are combined in multiple stages, and Fig. 3 is a system diagram of a hot air dryer showing an embodiment of the present invention. FIG. 4 is a diagram showing drying characteristics of paper, FIG. 5 is a diagram showing thermal efficiency, and FIG. 6 is a diagram showing the relationship between paper moisture and paper surface temperature. Explanation of main parts of the diagram 1-6...Dryer, 10
a to 10c...Blower, 11a to 11c...Heater,
12a-12c...control valve, 13a-13
c... Non-contact thermometer, 14a to 14c... Arithmetic control device, 15... Base paper for coating, 20... Paper feed reel.

Claims (1)

[Claims] 1. In a multi-stage hot air dryer in a paper drying device that has each drying zone: a preheating zone, a constant rate zone, and a lapse rate zone, a paper temperature detector is installed at the outlet of each dryer, and based on this, the hot air supply is adjusted for each drying zone. In addition to controlling the discharge rate, the dryer in the preheating zone detects the outlet paper surface temperature and controls the temperature to the set temperature in the constant rate zone, and the dryer in the constant rate zone controls the supply and discharge rate.
Adjust the opening degree of the exhaust control valve in the range of 0.05 to 0.15,
A multi-stage hot air dryer in a paper drying apparatus, characterized in that the dryer in the lapse rate zone adjusts the opening degree of the exhaust control valve by detecting the outlet paper surface temperature at a supply/discharge ratio of 0.05 or less.