Paper pulp, sometimes called pulp, is made of plant fiber. The pulp is the basic raw material of paper. Generally, raw materials for paper pulp include wood, straw, bamboo, reed, sugarcane, jute, rags, waste paper and etc. According to the raw materials, the paper pulp can be divided into straw pulp, wood pulp, and waste paper pulp. Every kind of pulp has individual paper and pulp technology. As for the paper pulping processing, there are chemical pulping, mechanical pulping and chemi-mechanical pulping. Chemical pulping can be commonly classified as pulp cooking processing, pulp washing processing, and pulp bleaching processing.
Paper pulp processing
Paper pulp processing refers to the process that makes the lignocellulosic material into natural color or pulp bleaching. As the first step of paper making, common pulping methods include chemical pulping, mechanical pulping or Chemi-Mechanical pulping. According to the different pulping methods, there are different pulp mills for every process of pulp making, such as pulp digester, disc filter, twin roll press, vacuum drum washer, blow tank and other equipment. Before introducing how to make paper pulp, let’s learn the chemical pulp and mechanical pulp first.
Chemical pulping is a typical pulping method. Under given condition, dissolved lignin from plant fiber and make fiber dispersed into pulp. The pulp cooking process mainly refers to delignin. In the meantime, it will inevitably cause the degradation of partial cellulose and hemicellulose. So, chemical pulp yield is generally lower, only 50%.
Mechanical pulping is that pulps obtained by grinding fibrous woods with mechanical means. By the raw materials or pulping method, there is a variety of pulp, the mechanical wood pulp is one kind of mechanical pulp.
- Chip pulping: it is also known as disk mill pulp, feeding chips between disks of disk mill, and slice into match-shaped batten. These battens rub against each other and are dissociated into a single fiber or fiber bundle.
- Log pulping: the log with certain length first get into the grinder, under certain pressure and temperature, logs were crushed, sheared by grinding stone, occur frictional effect, and logs were dissociated into a single fiber or fiber bundle.
- Chemical pretreatment pulping: the function of chemical pretreatment is softening the fiber, make fiber texture more flabby, and easy to grind.
The basic paper pulp manufacturing: raw material selection→ cook defibre→ concentration→ defibrination→ log storage→ peeling and removing knot→ chip → cooking→ screening and cleaning→ bleaching → bleaching pulp board → soak and defibrination → pulp board.
Log storage: for maintaining the normal production of the factory and improve the quality of raw material. There are two storage ways like water storage and land storage.
Sawmilling: logs should be swan into a certain length, and meet the requirement of the following section. In general, the required length of logs by chipper is about 2-2.5m, the length required by grinder is 0.6-1.2m.
Peeling: due to the bark has low fiber content and high impurities content, which will decrease the efficiency of cooking, increase cooking chemical consumption, increase the dirt count of the paper pulp. So that high-quality paper pulp usually needs peel the bark.
Removing knot: to avoid the knot has a bad influence on pulp quality or grind stone, remove the knot from log before feeding into the grinder.
Chipping: for meeting the needs of chemical wood pulp cooking and chip mechanical pulp production, logs must be chipped. Sliced chips should have same length and thickness. Chip dimensions: 12-20mm long, 3-5mm thick, less than a 20mm width. After chipping, use the rotary screen to choose proper chip, the percent of the pass is required up to more than 85%.
Pulp washing: after cooking, 15% – 50% of fibrous materials will be dissolved into cooking liquor. After completing the pulp cooking in the pulp digester, discharged cooking liquor was simply called waste fluid. The pulp washing is used to fully wash paper pulp, at the same time, extract the cooking liquor with high concentration and high temperature. The organic and inorganic matter will be recycled in the alkali recovery process. There are some components are not be digested in the pulp washing process. Meanwhile, there are many thick battens, chump and coarse fiber bundle in the ground wood pulp. Besides, sand, fly ash, iron wire and other impurities will be mixed into the pulp in the process of production, collection, transportation or storage. These impurities both have a bad effect on the pulp quality and pulp mill machines like vacuum drum washer, disc filter, twin roll press, etc. so that pulp washing is a necessary step for whole paper pulp making.
Bleaching: pulp bleaching is mainly used to remove the colored matters of fiber, and get the paper pulp with whiteness, proper physical and chemical specification. The common pulp machines for pulp bleaching include drum vacuum washer, twin roll press, and other related paper pulp making machines.