1. Clean/Screen/Deaerate II PPT 210

2. Pressure Screens Police filter – get rid of any coarse … Extremely long fiber – no –no Remove dirt and debris – holes vs slots Defloc stock – improve formation

3. Headbox Screen

4. Special Characteristics Position before the headbox Very low to no pulsation Polished Metal to metal flanged connections – accepts Trouble-free operation- availability high Optimized design – no air pockets

5. Pressure Screen

6. Slots vs Holes Much More efficient Finer the slot the bigger the screen – capacity Higher slot velocity - plugging potential More opportunity to pressure pulse Lower consistency – higher stringing Tradeoffs

7. Deaeration Gas in the stock Free air vs bound air Factors –Water temperature –Surface tension –Pressure Affects –Adsorption and desorption –Bubble stability –Bubbles coalescing –Water viscosity Henry’s Law – Air solubility increases linearly with pressure

8. Foam

10. Deculator

11. Cause of Foam 1. Surface Active Agents Pulp Mill Organics/SodaPulp Mill Organics/Soda Bleaching ChemicalsBleaching Chemicals Strength AdditivesStrength Additives DyesDyes Deposit Control ChemicalsDeposit Control Chemicals Deinking/Repulping AidsDeinking/Repulping Aids

12. Cause of Foam 2. Solid Particulates FinesFines Rosin/Alum CompoundsRosin/Alum Compounds FillersFillers Retention AidsRetention Aids

13. Other Causes Splashes in cleaner reject discharge Splashes in cleaner reject discharge Faulty deaeration system Faulty deaeration system Other chemical reactions Other chemical reactions Leakage Leakage Biological activity Biological activity

14. Antifoam Classes ClassDefinition Oil Based Contains no water Water-extended Contains <50% water Water-based Contains >50% water Water-based, oil free Contains no oil

15. Air in stock affects performance Pumping efficiency decrease Screening efficiency decrease Reduction in drainage Accumulation of hydrophobic and sticky matter Increase in microbio – leading to slime Pressure and flow variations Instability and noise by cavitation

16. Air in stock affects quality Pinholes and holes Spots, specks, and lumps Decrease in wet web strength Deteriorating formation –Decrease in smoothness –Decrease in tensile

17. Economics Mechanical versus Chemical Deaeration