How to Make Wood Pulp. Part 2

The first step of making paper is making paper pulp. Generally, there are mechanical, chemical and chemi-mechanical ways to process wood to paper pulp.

The basic flow of making wood paper pulp

Log storage - sawmilling - remove the bark and knot - chipping - digesting - washing- screening, refining - unbleached pulp board (or bleaching - bleached paper board) - soaking and pulping

• Sawmilling: the log should be sawed into certain length to match the requirement of the following process. The length of the log should be between 2-2.5m for the wood chipper, 0.6-1.2m for the wood grinder.
• Remove the bark: The bark contains less fibre, but more impurities, which can reduce the digest efficiency, increase the consumption of the digest agent, increase the dust in the paper pulp, reduce the strength of the paper pulp. Therefore, it is necessary to remove the bark if you want to make high quality paper.
• Removie the knot: To avoid the harmful effect to wood grinding machine and paper pulp caused by knot, the wood should be knot-free before entering the wood grinder.
• Wood chipping: To adapt the need of chemical pulping and mechanical pulping process, the log should be processed into wood chips. The wood chip should be uniform and even. Generally, the wood chip specification should be: length 15-20mm, thickness 3-5mm, the width does not have certain limit, though it cannot over 20mm. The wood chips should be screened by rotary strainer, the percent of pass should be greater than 85%.
• Washing: After digesting, 15-50% of the fibre raw material will be dissolved in the cooking liquor. After digesting, the exhaust cooking liquor is waste liquor. The purpose of washing is clean the pulp and refine high concentration and temperature liquor, then the organic matter and inorganic matter can be recycled in the alkali recovery process. After the washing process, there will still be matters that are not digested and other impurities may harm the normal production. Therefore, the screen and refining process is necessary.
• Bleaching: the purpose of bleaching is removing the colored matter in the fibre, to get paper pulp of certain whiteness and physical and chemical properties.

How to bleach wood paper pulp

The main source of the paper pulp is lingin and extraction. There are two ways of bleaching:

1. Dissolved lignin bleaching: With bleaching agent, dissolving lignin by oxidation is bleaching process. For example, chlorine bleaching, chlorine dioxide drifting, peroxide chlorine bleaching. This method is often used when the whiteness requirement of the paper pulp is very high. Chemical pulp is commonly bleached in this way.
2. Retain lignin bleaching: It retains the lignin only to discolor the hair color group. The bleaching loss is minimal and retains the properties of the slurry. For example, two sulfite bleaching and sodium borohydride bleaching. This method is often used in bleaching high yield pulp.

Two ways to pulping wood pulp 

Pulping: The process of grinding fibrous raw material into pulp by mechanical method. There are two main categories:

• (wood chip) Abrasive disk pulping: The wood chips were put into the grinding disc of the grinder, then they are broken into matches, and the small sticks of these matches are separated by friction to form a single fiber or fiber bundle.
• (short-cut wood) Grinding stone pulping: A certain length of log into the mill, under certain pressure and temperature through the grindstone's extrusion, shear, breaking and friction, the log dissolves into a single fiber or fiber bundle.

Paper pulper machine needed in the pulping process

To make wood pulp, you may need these equipment: wood chip hopper, desander, blender, Johnson screen, pressure knotter, fine sieve, digester, heat exchanger, blow tank, vacuum drum washer, reaction tower, bleaching tower, conditioner, vertical pipe, heater, commingler, pulp storage silo, condensate system, exhaust gas collection condensation system, recovery system, pulp board machine, pulp board cutting machine, packing machine, supporting tank, pump valve etc.

CNBM offer all kinds of paper pulp related equipment, please leave us messages for details and quotation. Get in touch now!