Bleaching Equipment
After wood chips are pulped, either by chemical or mechanical means, the resulting pulp has a brownish color. In order to create a white or lighter colored final product, the pulp much be bleached. This course describes the equipment used in the pulp bleaching process including pumps, mixers, reaction or retention towers, and washers.
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Learning Objectives
• Identify and describe key equipment used in bleaching operations
• Describe the purpose and application of each piece of equipment
• Identify and describe typical bleach stage layouts
• Identify key considerations in selection of pump types
• Describe advantages and disadvantages of different tower types
• Identify and describe safety hazards associated with equipment used in bleaching
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, French, Polish |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What are the major pieces of equipment need in a bleach plant and what is their purpose?
A pump is needed to move the pulp. A mixer blends chemicals and steam with the pulp. A bleaching tower provides time for the bleaching reactions to occur. Finally, a washer is used to remove the chemicals and dissolved lignin from the pulp.
What type of mixers are used to mix bleaching chemicals with pulp?
Some common mixer types are static, peg, dynamic, and high shear.
What are the common bleaching tower designs?
Upflow, downflow, upflow-downflow, and displacement towers.
What type of washers can be used in a bleach plant?
Bleach plants can use vacuum drum washers, wash presses, compaction baffle filters, and drum displacement (DD) washers.
What type of pump can be used for pumping pulp in the bleach plant?
A centrifugal pump can be used for low consistency pulp and a modified centrifugal or a positive displacement pump can be used for medium consistency pulp.
Sample Video Transcript
A bleach plant is made up of many stages. Each stage is made up of four components: a pump to move the pulp, a mixer to blend the bleaching chemicals and sometimes steam into the pulp, a reaction or retention tower, which the pulp moves through slowly allowing time for the bleaching reactions to occur, and a washer to remove the bleaching chemicals and dissolved lignan from the pulp. Some stages operate at low consistency, 0 to 6% pulp, and some operate at medium consistency, 6% to 18% pulp. Some bleach towers are up flow towers, some are down flow, and some are both. The equipment and process conditions of each stage can vary considerably depending on the bleaching chemical and the goals of the stage.
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