What is the method used to separate water from bleached wood pulp?
The method used to separate water from bleached wood pulp is commonly known as "dewatering" or "water removal." There are several techniques employed in this process, but one of the most widely used methods is called "mechanical dewatering." Here is an explanation of how mechanical dewatering is usually carried out:
1. Pressing: After the bleaching process, the wood pulp is typically mixed with water to form a slurry. One of the first steps in dewatering is pressing the slurry using mechanical devices such as roller presses or screw presses. These presses apply pressure to the slurry, squeezing out the water. The water is then collected and separated from the pressed wood pulp.
2. Filtration: Another method often used is filtration. In this technique, the slurry is passed through a series of screens or filters. The screens have fine pores that allow water to pass through while trapping the wood pulp solids. Depending on the specific requirements, different types of filters like rotary drum filters, belt filters, or vacuum filters may be employed.
3. Centrifugation: Centrifuges are occasionally used in the dewatering process. In a centrifuge, the slurry is spun rapidly, causing the heavier wood pulp solids to move towards the outer edge of the centrifuge while the water is forced towards the center. The separated water and wood pulp are then collected and further processed.
4. Evaporation: After the initial mechanical dewatering process, some residual water may still remain in the wood pulp. To remove this remaining water, the wood pulp can be subjected to evaporation. This involves heating the pulp under controlled conditions, causing the water to vaporize and leave the pulp as steam. The steam is then condensed and collected as water.
It's important to note that the specific method or combination of methods employed can vary depending on the type of wood pulp, the desired final moisture content, and the equipment available in the pulp and paper industry.