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Based on: Industry Standards and Best Practices

Languages: English

Sample Transcript

Oxygen was known to be an effective bleaching chemical for many years, but several obstacles prevented commercialization until 1970. The obstacles and their solutions will be discussed in this module. Oxygen delignification processes are located between the pulp mill and the traditional bleach plant. The goal of oxygen delignification is to reduce the lignent content of unbleached pulp before using more expensive bleaching chemicals. Oxygen can reduce the Kappa number more effectively than extending the pulping process. One advantage of oxygen delignification is that the effluent, unlike that from a conventional bleach plant, is compatible with craft pulping chemical recovery processes. Oxygen delignification is an important process contributing to elemental and total chlorine-free bleaching while still economically achieving pulp brightness targets and reducing the environmental impact.

Oxygen Delignification

Training Time: 28 minutes

Oxygen delignification processes are located between the pulp mill and the traditional bleach plant. The goal of oxygen delignification is to reduce the lignin content of unbleached pulp before using more expensive bleaching chemicals. Even though it has been known to be an effective bleaching chemical for many years, several obstacles prevented commercialization until 1970. The obstacles and their solutions will be discussed in this course along with oxygen delignification processes, equipment, and safety.

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Oxygen delignification produces pulp with a higher yield than pulping to the same kappa number

Oxygen is generated by cryogenic air separation where it is separated from nitrogen and the other components in air

In a high consistency reactor, steam is added to pulp at the top of a downflow reactor

Learning Objectives

  • Define the goal of oxygen delignification
  • Describe the advantages and disadvantages of oxygen delignification
  • Describe the basics of oxygen delignification chemistry
  • Define selectivity and identify methods to impact selectivity
  • Identify and describe the variables affecting oxygen delignification
  • State the impact of poor washing
  • Describe the safety hazards and safety guidelines associated with oxygen
  • Identify and describe the processes and equipment used in oxygen delignification
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Oxygen Delignification FAQs

What is the purpose of oxygen delignification?
Oxygen delignification is used to reduce the environmental impact of bleaching pulp by lowering the kappa number before conventional bleaching chemicals are used

Is oxygen a selective chemical?
No, oxygen is not a selective bleaching chemical so it is used early in the process when the lignin content is high

Why is oxidized white liquor used for oxygen delignification?
Oxygen delignification requires an alkaline pH. Oxidized white liquor is used instead of typical alkaline chemicals like sodium hydroxide to maintain the sodium/sulfur balance in the recovery system

What consistency pulp is required for oxygen delignification?
Oxygen delignification can be performed on medium or high consistency pulp, but most processes use medium consistency pulp

What is the benefit of a two stage oxygen delignification process
A two stage oxygen delignification process can improve delignification from 50% -70% by separating the reaction phases and optimizing conditions for each phase

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