What are the drying techniques commonly used in the papermaking process?

For the paper industry, the most important thing is the drying part, which will directly affect the final effect of the paper. there are two ways to dry the paper, one is contact drying, the other is convection drying. Many new energy-saving drying technologies are also gradually developed from the above ideas.

The general drying techniques are as follows: 
1.) penetrating drying. 
In the penetration drying device, the hot air box is installed on the guide roller, and because the guide roller supports the dry net and the wet paper, the hot air blown out of the hot air box blows directly to the paper at the speed of 5400m/min, the temperature is as high as 400C, the high-speed hot air strikes the wet paper to evaporate the moisture in the paper, and blows the steam away in time, this is the steam penetration drying method to the paper. The efficiency of penetrating drying is higher than that of contact drying, reducing the overflow of hot air in the closed area, improving the efficiency of waste heat recovery, reducing steam consumption and reducing energy consumption. 
2) impact drying. 
The nozzle will spray high-temperature and high-speed steam to the surface of the paper, the surface of the paper will be impacted by the air, the retention layer will disappear, and the drying efficiency is high. The drying part adopts a high-temperature and high-speed closed air cover, which has less high-temperature and high-humidity air leakage and less external air in the hood, which meets the requirements of low humidity and high dew point in the hood, so the evaporation efficiency is high, the drying rate is high, the energy consumption is reduced and the investment cost is saved. 
3) Microwave drying. 
Microwave drying is internal drying, when the paper is tapped into the wet paper, the paper absorbs microwave energy, converts the microwave medium into heat, and the heat permeates evenly into the paper, and the heating can be achieved in a short time without heat transfer. therefore, the microwave drying paper is dried evenly without losing heat energy. When the wet paper is placed in a high-frequency electric field, because the water molecules in the wet paper have polarity, the water molecules are arranged under the action of the external electric field, and when the high-frequency direction of the external electric field changes, the water molecules rotate and sway rapidly, and the adjacent molecules have thermal motion and interaction. The swing of the molecules under the change of the external electric field is affected and hindered, and this irregular motion causes the molecules to produce friction and heat, and the temperature rises. In order to achieve the purpose of drying wet paper.

4) Infrared drying. 
Infrared drying is radiation drying. The wet paper is irradiated by infrared rays with a wavelength of 5.6-1000. The water molecules in the wet paper absorb infrared light, and the water molecules vaporize due to the increase of infrared internal energy, thus achieving the purpose of wet paper drying. Infrared drying, the interior and surface of the paper are heated at the same time, so the paper is heated uniformly without temperature difference, and can be uniformly dried along the Z direction of the paper, and the effect is mild, and because the infrared drying transmits heat energy directly, no intermediate medium is needed, and the heat loss is avoided, so the drying effect is very good, the dryness of the paper is improved, and the steam consumption of the dryer is reduced. 
5) Pulse drying. 
Pulse drying is generally installed before drying in the dryer, the moisture content in the wet paper sheet is reduced by about 38% before entering the dryer, the pressure roller is heated to 150-480 ℃ by induction power supply or infrared, and the pressure roller is pressed at 275-690 KPA, staying at 100-150ms, and the heat from the surface is transferred to the paper sheet by the press roller, and the steam generated in the pressing area is moved out of the paper sheet. The sheet of paper is heated through the side contact of the heating roller to produce water vapor, which is pushed out of the blanket by larger steam. The moisture content of the wet paper is about 50-60% before entering the drying part, and the moisture is evaporated by heating in the drying part to achieve the drying of the paper.

The above are several drying techniques commonly used in the process of paper drying. Through these drying technologies, the quality of the produced paper can be improved, its quality can be guaranteed, and it can be better put into the market.