Pulp cooking is a necessary process of paper pulp making, batch cooking and continuous cooking are two typical methods of pulp cooking process. there are a series of paper pulper machine in the whole pulp cooking process, such as pulp digester, blow tank, heat exchanger, etc. By the main cooking equipment, the continuous cooking pulp machines can be classified into tower-type and tubular digester. From now on, half of the global pulp capacity is made by the continuous digester. As the main equipment, the continuous digesters include Kamyr digester and Pandia continuous digester. The tower-type continuous cooking digester applies for the large and medium-size pulp mill. It is the most widely used in the world.
About continuous cooking
Currently, continuous digester has three types, including tower type, tubular and messing & Durkee inclined digester.
Advantages
- For large-scale cooking equipment, the construction and operation of continuous digester take less cost.
- High pulp yield and less area occupied.
- Less energy consumption, peak load avoided.
- Less labor required. Compared to the highly automated batch cooking equipment, batch digester and continuous digester are same.
- Uniformity of pulp cooking is better than batch cooking.
Disadvantages
- Flexibility and reliability of batch cooking are good than continuous cooking.
- For wood chips, continuous cooking is more suitable than batch cooking.
- Recovery of turpentine is low.
Tower type continuous digester
The tower type continuous digester is a widely used type of continuous cooking equipment in the world. The capacity of tower type continuous digester takes 45% share of soda pulping process capacity. The Kamyr continuous digester is adaptable for various pulp cooking process and raw materials.
The Kamyr continuous digester is a kind of tower-type container that bears 1.0-1.2 Mpa. The digester consists of the separator, dipping area, heating area, cooking area, diffusion washing area, cooling area, discharge device. For gas-liquid type digester, there is a gas-phase space on its top. According to the corrosion of chemical liquor, the shell of digester can be made of common steel plate or clad steel plate.
Except kraft pulping, Kamyr digester also applies for neutral sulfite cooking, acid sulfitation cooking, and pre-hydrolytic sulfate cooking. It is used to manufacturing bleached pulp, dissolving pulp, unbleached pulp, and semi-chemical pulp.
Raw materials of Kamyr digester include softwood, hardwood, and sawdust and grass fiber. Generally, Kamyr continuous digester includes liquid type, gas-liquid type, double-digester type and digester for straw.
Kamyr Liquid type
- The liquid type continuous digester is the most common type in the chemical industry. The internal pressure of digester should be kept under 300-400kpa.
- This type of digester is usually applied to sulfate wood pulp making. There is the blade on the bottom of digester, use the moving blade to beat the softened chips into pulp.
- Cooked pulp is discharged from the digester by internal pressure (about 1.4Mpa), and the pulp is sent into pulp washing process.
Kamyr Gas-liquid type
The gas-liquid type has the same structure with liquid type digester, the separator is only difference between them. The gas-liquid type digester adopts inverted type separator.
Before entering the digester, wood chip from the high-pressure feeder is separated with liquor.
In general, there is a gas-phase space on the top of digester, where can use direct steaming to heat chips up to cooking temperature. Meanwhile, there is no dipping area in the digester.
In the process of gas-liquid cooking, wood chips are only impregnated in the circulated fluid and inverted type separator.
The gas phase part is usually at 2m below shell of digester. The liquid level of chemical liquor is at 1-2m below material level.
This type of digester can be applied for acidic bisulfite cooking, bisulfite cooking, and neutral sulfite cooking and prehydrolysis Kraft cooking.
Double-digester type
Double-digester type digester is also the gas-liquid type digester. It adds a high-pressure infusion kettle between feeder and digester.
Modified Kamyr continuous cooking (MCC)
The modified Kamyr continuous cooking (MCC) digester can be used to making paper pulp with lower Kappa value. Traditional Kamyr continuous digester makes higher lignin concentration of cooking liquor, which limits the delignification of wood chip. So that the Kappa value of paper pulp is limited to around 30. The MCC modify the disadvantages of traditional pulp process. Features of MCC as below:
- Reduce the initial alkali concentration;
- Increase the sulfidity of pulp;
- Decrease the concentration of dissolved lignin and sodium salt in the cooking process.
Tubular continuous digester
The tubular continuous digester is mainly applied to making hardwood pulp, Neutral sulfite semi-chemical pulp. The tubular continuous digester is suitable for straw fiber pulp cooking, so it is popular among large-scale sugarcane pulping and straw pulping mill.
Tubular continuous digester belongs to rapid thermal cooking equipment. When the raw materials enter into the enclosed digester, the direct steam heat the digester up to higher cooking temperature (about 175-190℃). The digester cycle is relatively short, by the different raw materials, impregnation conditions and quality requirement, pulp cooking time is around 10-50 min.
As we all know, except for the digester continuous cooking, there is digester for batch cooking. CNBM is a certified pulp digester manufacturer with rich experience. We supply custom-designed pulp plant solution for every client, also provide paper pulping machine of paper pulp plant, such as digester, blow tank, disc filter, vacuum drum washer, twin roll press and other equipment as you need.
