Requirements of paper drying for Yankee hood

At present, hot air hoods are used in the ventilation and drying system of paper machines at home and abroad. According to the different models of paper machines, hot air hoods can be divided into: 1) closed hood; 2) breathing hood; 3) high speed hot air hood (high temperature and high speed Yankee hood).

Airtight Hood: mostly used in corrugating base paper machine and culture paper machine;

Breathing Hood: generally used in circular screen paper machine, mostly used in low-speed paper machine;

High speed hot air hood (Yankee hood): generally used in high-speed tissue paper machine or special paper machine, culture paper machine, toilet paper machine.

Working principle of Yankee hood: using the principles of contact drying and convection drying, when the hot air blows to the paper, the hot air transfers heat to the paper. If the hot air blows vertically to the paper, the air film on the interface will be damaged or the thickness will be reduced, the coefficient of heat and mass transfer will be increased, and the evaporation will be increased, so as to improve the drying rate and output of the paper and reduce the energy consumption.

The combination of Yankee drying cylinder and high temperature hot air hood is used for paper drying to save energy, improve quality and increase output. The specific functions are as follows:

1) Improve drying rate and yield of operation

The drying area of the high-temperature Yankee hood is the same as the speed of paper making. When using the high-temperature hot air Yankee hood, the paper is sprayed with high-temperature air to increase the temperature of the air out of the hood, the heat transfer will be increased, and the drying rate will be increased.

2) Longer service life of high temperature Yankee hood

High temperature and high speed Yankee hood, its structure design and use of high-strength raw materials can withstand high temperature, longer service life;

3) Prolong the service life of Yankee dryer cylinder

With the use of the Yankee dryer, the resistance of the dryer to the steam pressure decreases gradually, because the surface temperature of the cylinder decreases, the drying rate of the paper web decreases, and the output decreases accordingly. After the use of the high temperature Yankee hood, the hot air sprayed by the hood at a higher drying rate just makes up for the deficiency of the drying rate reduction caused by the reduction of the pressure capacity of the cylinder, In addition, there is surplus. Although the pressure of Yankee dryer is reduced, it does not affect its service life.

4) Reduce the energy consumption during the use of hot air hood

In the process of operation, the use of hot air Yankee hood, hot air jet high temperature air consumption of power, steam consumption reduction, because of the reduction of hot air flow speed, high temperature, hot air density reduction, air easy to flow, power consumption reduction.

5) Improve the softness and loose thickness of Web

In the process of production, using high temperature Yankee hood and high temperature air to spray and recoil the paper web attached to the cylinder block of the drying cylinder will help to improve the softness and loose thickness of the paper web. Especially for the paper for daily use, the paper web ration can be reduced by about 3% under the condition of constant thickness.

6) Flexible and convenient change of Web variety during operation

During the operation of the paper machine, the Yankee drying cylinder and the high temperature Yankee hood are used together to dry the paper sheets, which is convenient for the factory to change the product varieties. When changing the paper varieties, according to the process flow, adjust the steam pressure into the drying cylinder and the temperature of the high temperature air in the hood, so as to meet the drying requirements of the changed paper products. For example, in the production of handkerchief paper, the drying of paper web requires that the steam pressure sent into the cylinder body of the drying cylinder is higher, while the air temperature sprayed from the hood should not be too high, so as to make the paper web more compact; however, the drying requirements of the facial tissue paper are the opposite, the steam pressure sent into the cylinder body of the drying cylinder is slightly lower, while the air temperature sprayed from the hood is higher, so the paper web produced is soft Excellent in degree and loose thickness.

Generally, manufacturers of paper for daily use are equipped with Yankee dryer and high temperature Yankee hood in terms of drying and ventilation, so as to meet the requirements of various types of paper products flexibly.