GREEN LIQUOR CLARIFIERS

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GREEN LIQUOR CLARIFIERS A GLASS BOX APPROACH
E.L. Bibeau
2
PSL SERVICES

• Determine the root cause of process problems
• Evaluate the success of proposed retrofits
• Evaluate new equipment purchases
• Improve equipment efficiency
• Help with environmental emission limits
  compliance
• Reduce operating costs

3
PSL COMPETENCIES

• Extensive experience in industrial process model
  development and application
• Ability to predict equipment behaviour for any
  configuration
• Proven ability to optimise equipment, solve
  complex operating problems, and improve operator
  training
• Leaders in real time process visualisation

4
PRESENTATION
OBJECTIVES

• Clarifier process problems at Weyerhaeuser?
• Review ways to approach
• 1-D, rule of thumb, knowledge base
• Glass box approach
• How to incorporate glass box approach

5
CLARIFIERS

• If dregs flocculate
• liquor will clarify well provided clarifier tank
  is optimised
• Hydraulic short circuiting
• improper bustle design
• poor feedwell design
• unbalanced flow distribution
• leads to low residence time
• floc break-up and poor flocculation

6
PROCESS PROBLEMS AT WEYCO

• Water treatment facilities
• 60 of plants did not meet the desired effluent
  suspended particles
  concentration
• Pulp mills at Weyco
• Average turbidity of effluent?
• Variations of turbidity?

Turbidity
Time
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PROCESS OPTIMIZATION

• Black box approach
• traditional parametric approach
• limited can show serious design flaws in current
  installations and proposed retrofits
• Glass box approach
• look at inside the tank
• look at flow distribution in 3D
• look at real residence time based on design
  details of bustle, feedwell, and tank
  characteristics
• look at density variation effects (gt 2 C)

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Common Feedwell

• Small feedwell
• Complex flow with shear
• Swirl is preserved
• Non uniform flow

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Large Feedwell

• Non uniform flow
• Large section of feedwell not used effectively
• Flow will exit preferentially to one side

Exit downward velocities
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Bustle Pipe Design

• Require uniform velocity distribution
• eliminate short circuits
• use entire tank region for settling
• requires proper design specification of flow
  uniformity

Flow extraction end
Little flow extraction
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CLARIFIER FLOW
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CONCLUSION

• Clarifier Hydraulics Improvements
• Uniform flow drawn from bustle pipe
• Proper feedwell
• Take into account 3D effects
• Glass box approach advantage
• Get firm idea of current problem
• Get firm idea of how well retrofit will work
• Glass box approach disadvantage
• Get involved in the design