Preparation of Wood Raw Material
Stock preparation of wood raw material
Different pulping methods have different requirements for wood raw materials. Some require slicing, such as chemical pulp, chemical mechanical pulp, etc.; some use logs directly, such as stone-ground wood pulp; the preparation process of wood that needs to be sliced mainly includes the following steps:
- Debarker;
- Sawing;
- Removing knots and splitting;
- Chipping;
1.Debarker
（1）Why need debarker?
It is because the bark of wood usually has a low content of fiber and a high content of ash and impurities. Removing it before pulping could reduce the consumption of chemicals in successive procedures and improve the quality of the pulp. Besides, shaving off the bark will make wood become dry easily and prevent bacterial contamination.
（2）Peeling method
- Man-made barking
- The fresh peeling method is to wash the tree roots with water and place them in the open air for 2-3 days to allow the water in the roots to evaporate, and then use a knife to pry up and peel off the bark from the fracture. This method will damage the root material and destroy the texture if you are not careful.
- The soaking method is suitable for dry root materials that have been placed for a long time. The method is to immerse the root material in water for several days until it can be peeled off. Both methods are time-consuming and labor-intensive. The more popular method is to use a high-pressure cleaner to remove the bark.
- Another method is to use a high-pressure cleaner to remove the bark. The working principle is: the bark and the tree trunk have different tissue structures and different hardness. The high-pressure cleaner is used to generate a strong impact force of high-pressure water to quickly separate the bark, but this strong impact force of high-pressure water cannot damage the tree trunk, achieving a good debarking effect.
- Mechanical barking(most commonly adopted)
Main equipment:
a. Circular peeler
b.Rotary peeler
- Hydraulic barking
- Chemical barking
2.Sawing
Sawing timber means sawing large diameter logs or cutting overlong logs as required.
Main equipment:
- Single-blade circular saw
- Multi-blade circular saw
- Band saw
3.Knotting and splitting
Why do we need to remove knots?
Generally, the knots of logs are relatively hard and contain a lot of resin and dust. The presence of knots not only easily damages the surface of the grinding stone, damages the blade of the film machine, reduces the production capacity of the wood grinder, and increases power consumption, but also causes increased dust to affect the quality of pulp and cause problems such as difficulty in the penetration of cooking liquid.
Knot removal generally uses a knot remover. Splitting and sawing are similar. In order to adapt to the loading of chippers and wood grinders, large-diameter logs are split. The equipment used is a wood splitter. After the raw materials are peeled, sawn, removed, and split, the last step is chipping.
4.Chipping
Generally speaking, the production of chemical wood pulp and chemical mechanical wood pulp requires the raw materials to be made into wood chips for subsequent production.
The general specifications of wood chips are: 15-25mm long, 3-5mm thick, and the width should not exceed 20mm.
The qualified rate of log wood chips is generally required to be greater than 90%, while the qualified rate of board wood chips is generally required to be greater than 75%.
The chipping equipment commonly used in production mainly includes disc chippers, drum chippers, etc.
The qualified rate of wood chips sent to pulping is required to be greater than 90%, while the qualified rate of wood chips from chippers is generally around 75%-85%. Therefore, it is necessary to separate oversized or undersized chips through screening, and re-crush or re-chip oversized wood chips to meet the requirements of pulping.
The production machinery generally includes: disc chippers and drum chippers
Wood chip screening and quality control
The pass rate from the chipper is generally around 75-85%, so the wood chips need to be screened to separate the oversized or undersized wood chips, and the oversized wood chips need to be crushed or chipped again to meet the pulping requirements.
Screening machine
The commonly used machines for screening chips are circular screen, flat screen and disk screen.
The qualified wood chips need to be stored.
Transportation and storage of wood chips
Transportation of wood chips
1.Belt transport: Among the three modes of transport, belt transport is currently more commonly used due to its simple structure, low power consumption, large production capacity, long conveying distance, and low noise.
2.Bucket conveying: Although with rather simple equipment, low maintenance cost, small occupation of the area and high altitude for conveying, it is unsuitable for long-distance conveying.
3.Pneumatic conveying: Its equipment is simple and maintenance costs are low, but its power consumption is large. The wood chips are easily broken during transportation, thereby reducing the qualified rate of wood chips, so it is rarely used at present.
Storage of wood chips
Common storage equipment: wood chip warehouse
According to its location, it can be divided into:
- Pot-top chip bin
- Ground chip bin
Preparation of Wood Raw Material
Stock preparation of non-wood raw materials
Among papermaking raw materials, non-wood raw materials account for a large proportion. There are many types of non-wood raw materials, and each has its own characteristics, so their preparation processes also vary greatly.
The stock preparation procedures for two kinds of non-wood raw materials.
The stock preparation for straw raw materials
1.Dry method: It is more commonly used in our country. It mainly consists of feeding, cutting, screening and dust removal. The process is mature, low investment, low energy consumption and easy to operate. Its disadvantages are poor dust removal effect and large flying dust pollution. .
2.Wet method: The most advanced method of preparing grass raw materials at present. Compared with the dry method of material preparation, this method completely solves the problems of flying dust and poor working conditions. At the same time, it has good impurity and dust removal effect and can make the silicon content obvious. The pulp strength is significantly improved, but its disadvantages are large equipment investment, high maintenance costs, large power consumption, high production costs, and sewage discharge problems.
3.Combining dry and wet method of material preparation: Combining some processes of dry material preparation and full wet material preparation to make it have the characteristics of both. It is the preparation of grass alkali pulping, especially rice straw and wheat straw, and is a direction for the development of material preparation.
The stock preparation of bamboo raw materials
1.Chipping process
It is a kind of dry method, and it is similar to the raw material in the stock preparation of wood, mainly including slicing and screening.
2.Shredding and depithing
An American company invented it and has already been used in many factories now. The key equipment of this method lies in the bamboo ripper, and its mechanism is similar to that of the hammer mill used in the mine.
The transportation and storage of non-wood materials
Transportation of slides:
1.Belt conveying
2.Pneumatic conveying
The storage of slides: Stock bin
1.Straw bin: Since straw is light and soft, it is easy to have “bridge phenomenon”, so the commonly used straw bins are reciprocating loose mechanical bins and live bottom bins.
2.Bagasse bin
For more infos , pls ref video below:
