The continuous tubular digester is one of paper pulp making machines. It is mainly made up of three parts including screw charging machine, digester, discharging machine. The continuous tubular digester generally applies for neutral sulfite pulp processing and virgin or bleached sulfate wood pulp processing. It is suitable for wood pulp making, in addition, crop straw pulp making, wheat straw pulp making, and reed pulp making are also available.
With the development of people’s living standard, the demand for paper is increasing fast. At present, wood pulp is the main source of papermaking. However, the wood resource is limited and very important to the environment, it is necessary to develop paper pulp making with non-wood fiber. Common non-wood fibers for paper pulping include straw, reed, bamboo, sugarcane bagasse, cotton, jute and etc.
After many years’ study, the continuous tubular digester is considered as the perfect equipment for non-wood fiber paper pulp making. What are the advantages of continuous digester compared with traditional pulp digester?
Advantages of the continuous tubular digester
The continuous tubular digester has a small covering area and a concentrated space. All operations can be controlled by PLC and DCS. In addition, the continuous tubular digester has advantages of strong intuitive operation, good adjustable operation process, and a high degree of automation, superior working environment, fixed personnel, stable product quality, high pulp yield, and large-scale production.
Due to the dry and wet preparation and equipment structure characteristics, which decide the uniform and continuous materials, low alkali content, low steam consumption, small environmental protection burden. The economic benefits and social benefits are satisfactory.
Improve the quality of grass
There are many impurities in grass materials, which are artificial and natural to dope in the straw, including stones, broken bricks, and scrap iron and mildew materials. What’s more, the removal rate of the wheat leaves, minced meat is large, generally reaching 30-32%. The dry and wet preparation process ensures the quality of the straw pulping as much as possible. The removal rate of the conventional dry preparation pulping process is generally only 15%, which is less than the removal rate of the dry and wet preparation. In addition to, the increase of dust rate effectively protects the operation of cooking, washing and bleaching equipment, reduces the amount of chemicals, reduces the load of washing and bleaching process and the dustiness of pulp, especially the removal rate of silicon in wheat straw can reach 15% even more, effectively reducing the interference of silicon on the alkali recovery process and improving the evaporation efficiency.
Reduce the alkali consumption of pulp cooking
The separating rate of impurity of the dry-wet method is 15% higher than that of the traditional preparation material, and alkali amount is calculated according to 13%. Compared with the rotary digester, pulp produced by continuous tubular digester reduces 19.5kg alkaline per ton. The purity of the wheat straw also ensures the accurate delivery of alkaline liquor, which can bring direct economic benefits.
Fast pulping and low steam consumption
The purity of the material processed by the dry-wet method is increased by 15%. Except for the amount of steam that is omitted, the material is also treated with a double treatment due to the double action of the grass washing machine on the material washing and milling. The small wheat straw is washed and decontaminated, and the long wheat straw is milled and combed into silk. The total area of each piece of wheat straw after treatment is close to each other, and there is an intentional tip of sputum. The permeate rate of lye to each piece of wheatgrass is close. Under the cooking temperature condition, complete the mixing process quickly. During the high-temperature cooking period, the pulp yield is high, the output is large, and the steam load is uniform. Due to the stable quality of the pulp, the whole process of pulping adheres to the principle of fast cooking, quick washing and fast bleaching. These are incomparable for batch cooking and pulping.
Stable pulp quality
The stability of raw material is the basis of stable pulp quality. In the pulp processing, steam conditions, liquid conditions, ambient temperature conditions, and item conditions absolutely have fluctuation, and the stability of each condition is relative. Pulping equipment should have good versatility, and the pulping quality will have relative stability with minimal fluctuations. The specific guiding principles are as follows:
- When the steam pressure is unstable, the rotation speed of the continuous steaming system is adjusted, and extend the cooking time;
- When using aged wheat straw, adjust the amount of alkali supplied to the system, and adjust the rotation speed, change the cooking time;
- When the steam pressure and raw material is relatively good, adjust the overall speed of the system, increase the feed amount, increase the temperature, shorten the cooking time, and increase the pulp production.
Grasping these indicators and adjusting equipment in time. This is the guarantee of the quality of the pulp and pulp production.
