Digester Types
The purpose of kraft pulping is to separate fibers from each other so that they can be used to produce paper and other cellulose fiber based products. This type of chemical pulping is accomplished by cooking wood chips in a chemical solution in large pressure vessels called digesters. Pulping can be performed in digesters running in batch or continuous mode. This module describes the advantages and disadvantages of different types of digesters, including: batch systems, continuous cooking systems with one and two vessels, continuous digesters which are hydraulically filled and those which utilize a vapor phase. Pandia and M&D digesters are also described.
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Course Details
Learning Objectives
• Describe the purpose of kraft pulping
• List typical configurations of continuous digester systems
• Describe the major steps involved in batch cooking
• Describe the advantages of continuous digesters
• Identify the advantages of vapor phase continuous digester systems
• Describe the advantages of two-vessel continuous digester systems
• Identify the unique feature that the M&D and Pandia digesters share
• Identify the primary use of M&D digesters
Specs
Frequently Asked Questions
What is the advantage of recirculation in a batch digester?
What is a vapor phase digester?
What is cold blow?
What is an impregnation vessel?
How are M&D and Pandia digesters used?
Sample Video Transcript
In some batch digesters, the chips and a liquor are heated by steam which is injected directly into the closed digester. Additional steam is injected as needed into the digester during cooking to maintain the temperature. In other batch digesters, liquor is withdrawn through screens within the vessel, heated externally in heat exchangers and then returned to the digesters during the heating and cooking phases. This technique has the advantages of not diluting the liquor with condensate, recovering the condensate from the heat exchangers for reuse and some improvement in the uniformity of cooking conditions due to the circulation of the liquor.
