What are the most commonly used drying techniques?

There are two ways for the drying section of the paper machine to dry the wet paper web. One is the contact drying of the paper web on the surface of the drying cylinder. The other is the convection drying during the operation of the paper web. Many modern new energy-saving drying technologies are developed on the above ideas. Many large-scale high-speed paper machine speed is faster and faster, paper breadth is wider and wider, the ventilation technology of the drying section has also been greatly improved.

General drying technologies are as follows:

1.) through drying

In the penetrating drying device, the hot air box is installed on the guide roller, because the guide roller supports the dry net and the wet paper web, the hot air blown out of the hot air box directly blows to the paper web at the speed of 5400m / min, the temperature is as high as 400 ℃, the high-speed hot air impacts the wet paper web to evaporate the moisture in the paper web, and blows the steam away in time, which is the penetrating drying method of the steam to the paper web. The penetration drying efficiency is higher than contact drying, which can reduce the hot air overflow in the closed area, improve the waste heat recovery efficiency, reduce the steam consumption and reduce the energy consumption.

2.) impact drying

The nozzle sprays high temperature and high speed steam to the surface of the web. The surface of the web is impacted by air, the retention layer disappears, and the drying efficiency is high. The high temperature and high speed airtight hood is used in the drying part, which can meet the requirements of low humidity and high dew point in the hood with less leakage of high temperature and high humidity air and less inflow of external air. Therefore, it has high evaporation efficiency, high drying rate, low energy consumption and investment cost.

3.) microwave drying

Microwave drying is internal drying. When the airtight hood manufacturer points the paper into the wet paper, the paper absorbs the microwave energy, converts the microwave medium into heat, and the heat evenly penetrates into the paper. Without heat transfer, the heating purpose can be achieved in a short time. Therefore, the microwave drying paper is evenly dried without heat loss. Put the wet web in the high-frequency electric field, because the water molecules in the wet web have polarity, water molecules are arranged under the action of the external electric field. When the high-frequency direction of the external electric field changes, the water molecules rotate and sway rapidly, and the adjacent molecules have thermal movement and interaction. The swing of the molecules under the change of the external electric field is affected and blocked, and this irregular movement makes the molecules produce friction Heat, temperature rise, so as to achieve the purpose of drying wet web.

4.) infrared drying

Infrared drying is radiation drying. Irradiating the wet paper with the infrared ray with the wavelength of 5.6-1000, the water molecules in the wet paper absorb the infrared ray, and the water molecules vaporize due to the increase of the internal energy absorbed by the infrared ray, thus realizing the purpose of wet paper drying. Infrared drying can heat the inside and the surface of the web at the same time, so the web is evenly heated without temperature difference, and it can be evenly dried along the Z direction of the web, with mild effect. Because infrared drying can directly transfer heat energy, no intermediate medium is needed, and heat loss is avoided, so the drying effect is very good, the dryness of the web is improved, and the steam consumption of the drying cylinder is reduced.

5.) pulse drying

Pulse drying in Jinan airtight hood is generally installed before drying in the drying cylinder. Before entering the drying cylinder, the moisture content in the wet paper web decreases by about 38%. The pressure roller is heated to 150-480 ℃ by using induction power or infrared ray, the pressure roller is pressed at 275-690kpa, and stays for 100-150ms. The pressure roller transmits the heat on the surface to the paper web and moves the steam generated in the pressure area out of the paper web. The web is heated through the contact of the heating roller side to generate water vapor, which is pushed out of the blanket by the larger steam.

Before the wet paper enters the drying section, the moisture content is about 50-60%. The moisture is evaporated by heating in the drying section to realize the drying of the paper web.