How to improve the quality of tissue paper through Yankee hood

In order to improve the drying capacity and drying rate of the paper machine, the paper machine needs to be equipped with an efficient hot air hood - high temperature Yankee hood. The hot air Yankee hood is generally made of section steel and pipe fittings as the framework, the outer surface is made of aluminum plate as the shell, and the outer surface of aluminum plate is made of thermal insulation material as the insulation layer to prevent the hood temperature from emitting into the surrounding air.

In the production of tissue machine, it is necessary to equip with good drying equipment to improve the quality of paper web.

The quality of tissue can be improved through the following aspects:

1) adding short fiber, coating and chemical toilet paper in raw pulp has good softness;

2) in the press section of the paper machine, the loose thickness of tissue can be improved with lower pressure load and lower inlet dryness;

3) tissue is less dried on Yankee dryer, more dried on Yankee hood, and the softness and loose thickness of paper is further improved.

What are the reasons for the improvement of tissue?

In the production of high-speed and high-temperature Yankee hood, high-temperature air is sprayed on the surface of the paper for drying, which is the problem of moisture transferring heat and quality in a very complex form. When the wet web is introduced into the pressing area, the drying operation occurs at the moment when the web contacts the cylinder block, and then the web is pasted on the cylinder block surface, and the heat conduction between the two dominates the drying process of the web.

When the moisture in the web becomes steam, it flows from the closed space of the wet web to its surface, migrates in the form of liquid, fills all the voids, and then emits to the external environment.

When the paper web of Yankee hood is dry, the evaporation rate of its moisture is in a constant stage, and its surface is always wet. At this time, only in the place where the fiber is covered / exposed, the air in other places cannot enter into the paper web structure. Under the combined action of capillary force of fiber and surface tension of moisture itself, the moisture in the paper web is led to the surface of cylinder block, and the tiny space on the surface of cylinder block is filled with evaporated moisture. At this time, if only relying on the heat energy released by the steam inside the cylinder block to dry the paper web without the hot air from the hood, the moisture on the open surface of the paper web is still. However, due to the capillary force and moisture stress of the fiber, the pulp fiber is pulled back to the closed space near the surface of the cylinder block, resulting in the close and low accumulation of pulp fiber on the surface of the cylinder block, resulting in a dry web.

In the process of paper drying, if the Yankee drying cylinder is used and the new high temperature Yankee hood is used, the paper will be operated together. The heat energy of the wet paper will be transferred by conduction and convection in the cylinder body and the high temperature Yankee hood respectively, that is to say, the drying rate will be accelerated, the fiber structure of the paper will be improved and the good effect will be achieved. The rapid evaporation of water on the open surface of the paper web made by Yankee hood manufacturers makes the water vapor in the semi closed space move to the open surface. High temperature air jet on the open surface of the paper web can easily occupy the space nearby and keep it open. The moisture in the paper web in the closed space changes into water vapor due to the heating of the cylinder block surface, which is easy to move outward and reach the open surface. At this time, the moisture / water vapor existing in the closed space of the web moves towards two heat sources at the same time during the drying process, so that the web structure has good opening performance.

Increase the temperature of the air in the hood of the hot air drying cylinder, reduce the steam pressure inside the cylinder body of the Yankee drying cylinder. When the temperature of the hot air in the hood increases by 10 ℃, and when the steam pressure of the drying cylinder decreases by 0.5 PA, the loose thickness of the dried paper increases by about 1%. At present, many large-scale high-speed paper machines require a high drying rate and a good open structure of paper web. When the improved high-temperature Yankee hood and Yankee dryer work together, the whole drying process can be completed in less than half a second.