Pulp Washing Process

Paper pulp washing and pulp washing equipment

On the paper pulp washing process, the brownstock from the blowing goes to the washing stages where the used cooking liquors are separated from the cellulose fibers. Normally a pulp mill has 3-5 washing stages in series. Paper pulp washing stages are also placed after oxygen delignification and between the bleaching stages as well. Pulp washers use counter-current flow between the stages such that the pulp moves in the opposite direction to the flow of washing waters.

As a professional manufacturer of paper pulping machines, Anyang Machinery can produce different types of equipments for the paper pulp washing process, such as vacuum drum washer, single screw press, and twin roll press. Among them, the vacuum drum washer method is well-known to paper mills for a long time. This method of pulp washing is employing a series of vacuum drum washers working in a counter-current flow system. The vacuum drum washer applies conical channel technology which greatly enhances the production capacity per unit area. Along with the increasing market demands, Anyang Machinery constantly satisfies customers by renovation equipment, inaugurating technology. Our pulp washing equipment has exported to Russia, Southeast Asia, and other regions.

Flow chart of paper pulp washing process

flow of paper pulp washing process

Pulping washing process

There are different methods available for pulp washing. Most of them rely on displacing the dissolved solids (inorganic and organic) in a pulp mat by hot water, but some use pressing to squeeze out the chemicals with the liquid. An old, but still commonly used method is to use a drum, covered by a wire mesh, which rotates in a diluted suspension of the fibers. The fibers form a mat on the drum, and showers of hot water are then sprayed onto the fiber mat.

In the process of pulp washing, there are many factors that affect the brown stock washing displacement efficiency, like fiber characteristics, shower characteristics, sheet formation/thickness, and operating factors. Fiber characteristics involve pulping process, species, stock hardness, and freeness, whereas shower characteristics engage the method of showering application, nozzles, temperature, and shower distribution. If the shower does not place in the right position and does not choose the right nozzles, then it may create foam and affect the brown stock washing.

Dilution factor, air in stock, stock temperature, fabric mesh, and fabric unclean are the most significant operating factors. Normally, a higher dilution improves pulp washing performance. But at this time it dilutes the black liquor that affects evaporation. Hence, it is better to keep balanced to get washing benefit achieved. In this system a specific amount of air is continuously pulled throughout the pulp sheet, it may create foaming problems and affects on pulp washing. It could be overcome by installing large seal tanks; it helps air to escape and foam bubbles to break. Sheet formation that depends on loading, Vat consistency and rotational speed also affects the pulp washing.

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