GREEN LIQUOR CLARIFIERSGREEN LIQUOR CLARIFIERSA GLASS BOX APPROACHA GLASS BOX APPROACH

E.L. Bibeau

PSL SERVICESPSL SERVICES

Determine the root cause of process problemsDetermine the root cause of process problems

Evaluate the success of proposed retrofitsEvaluate the success of proposed retrofits

Evaluate new equipment purchasesEvaluate new equipment purchases

Improve equipment efficiencyImprove equipment efficiency

Help with environmental emission limits Help with environmental emission limits compliancecompliance

Reduce operating costsReduce operating costs

PSL COMPETENCIESPSL COMPETENCIES

Extensive experience in industrial process Extensive experience in industrial process model development and application model development and application

Ability to predict equipment behaviour for Ability to predict equipment behaviour for any configurationany configuration

Proven ability to optimise equipment, solve Proven ability to optimise equipment, solve complex operating problems, and improve complex operating problems, and improve operator trainingoperator training

Leaders in real time process visualisationLeaders in real time process visualisation

PRESENTATIONPRESENTATION

Clarifier process problems at Clarifier process problems at Weyerhaeuser?Weyerhaeuser?

Review ways to approach Review ways to approach

- 1-D, rule of thumb, knowledge base

- Glass box approach

How to incorporate glass box approachHow to incorporate glass box approach

OBJECTIVES

CLARIFIERSCLARIFIERS If dregs flocculate If dregs flocculate

- liquor will clarify well provided clarifier tank is optimised

Hydraulic short circuitingHydraulic short circuiting

- improper bustle design

- poor feedwell design

- unbalanced flow distribution

- leads to low residence time

- floc break-up and poor flocculation

Feed well

Rotor blade

Bustle Pipe

Feeder pipe 60’ tank dia

50% Level

PROCESS PROBLEMS AT WEYCOPROCESS PROBLEMS AT WEYCO

Water treatment facilitiesWater treatment facilities

- 60% of plants did not meet the desired 60% of plants did not meet the desired effluent suspended particles effluent suspended particles concentrationconcentration

Pulp mills at WeycoPulp mills at Weyco

- Average turbidity of effluent?Average turbidity of effluent?

- Variations of turbidity?Variations of turbidity?

Time

Tur

bidi

ty

PROCESS OPTIMIZATIONPROCESS OPTIMIZATION Black box approachBlack box approach

- traditional parametric approach

- limited: can show serious design flaws in current installations and proposed retrofits

Glass box approachGlass 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 (> 2 C)

Common FeedwellCommon Feedwell

Small feedwellSmall feedwell

Complex flow with shearComplex flow with shear

Swirl is preservedSwirl is preserved

Non uniform flowNon uniform flow

Non uniform flowNon uniform flow

Large section of Large section of feedwell not used feedwell not used effectivelyeffectively

Flow will exit Flow will exit preferentially to preferentially to one sideone side

Large Feedwell Large Feedwell

Exit downward velocitiesExit downward velocities

Bustle Pipe DesignBustle Pipe Design Require uniform velocity distributionRequire 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

CLARIFIER FLOWCLARIFIER FLOW

CONCLUSIONCONCLUSION Clarifier Hydraulics ImprovementsClarifier Hydraulics Improvements

- Uniform flow drawn from bustle pipe

- Proper feedwell

- Take into account 3D effects

Glass box approach: advantageGlass box approach: advantage

- Get firm idea of current problem

- Get firm idea of how well retrofit will work

Glass box approach: disadvantageGlass box approach: disadvantage

- Get involved in the design