1. GREEN LIQUOR CLARIFIERS A GLASS BOX APPROACH E.L. Bibeau

2. PSL SERVICES lDetermine the root cause of process problems lEvaluate the success of proposed retrofits lEvaluate new equipment purchases lImprove equipment efficiency lHelp with environmental emission limits compliance lReduce operating costs

3. PSL COMPETENCIES lExtensive experience in industrial process model development and application lAbility to predict equipment behaviour for any configuration lProven ability to optimise equipment, solve complex operating problems, and improve operator training lLeaders in real time process visualisation

4. PRESENTATION lClarifier process problems at Weyerhaeuser? lReview ways to approach - 1-D, rule of thumb, knowledge base - Glass box approach lHow to incorporate glass box approach OBJECTIVES

5. CLARIFIERS lIf dregs flocculate - liquor will clarify well provided clarifier tank is optimised lHydraulic 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 lWater treatment facilities - 60% of plants did not meet the desired effluent suspended particles concentration lPulp mills at Weyco - Average turbidity of effluent? - Variations of turbidity? Time Turbidity

7. PROCESS OPTIMIZATION lBlack box approach - traditional parametric approach - limited: can show serious design flaws in current installations and proposed retrofits lGlass 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)

8. Common Feedwell lSmall feedwell lComplex flow with shear lSwirl is preserved lNon uniform flow

9. lLarge section of feedwell not used effectively lFlow will exit preferentially to one side Large Feedwell Exit downward velocities

10. Bustle Pipe Design lRequire 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

11. CLARIFIER FLOW

12. CONCLUSION lClarifier Hydraulics Improvements - Uniform flow drawn from bustle pipe - Proper feedwell - Take into account 3D effects lGlass box approach: advantage - Get firm idea of current problem - Get firm idea of how well retrofit will work lGlass box approach: disadvantage - Get involved in the design