1. Recovery of Liquors & Bleaching II PPT 110

2. DE(OP)PD
Bleaching
D stage
E(OP) stage
P stage
D stage

3. Why Bleaching
Lignin Itself
Chromophoric Groups Attached

4. Two Approaches Brightening True Bleaching
Selective Destruction of groups
Temporary Effect
True Bleaching
Delignify
Attempt to preserve strength

5. Brightening GW, TMP, NSSC – high yield/lignin
Destroys/reduces color groups
Temporary eye appeal
Will yellow and degrade

6. Bleaching Sequence Symbols
Reeve, Douglas W., TAPPI Bleach Plant Operations Short Course, 1998.

7. Bleaching Objectives Brightening by lignin removal decolourizing
Cleaning
by shive & dirt bleaching
Reeve, Douglas W., TAPPI Bleach Plant Operations Short Course, 1998.

8. Bleaching Objectives Optical Qualities High Brightness
Brightness stability
Cleanliness
Opacity
Strength
Environmental Quality
Reeve, Douglas W., TAPPI Bleach Plant Operations Short Course, 1998.

9. Bleaching at Evergreen
Was
CEHEH
Now
ODE(o)D

10. Easier to Bleach?
Softwood or Hardwood
Why?

11. BLEACH PLANT Chemicals Vapour to Scrubber Water Steam Unbleached
Pulp
Bleached
Pulp
BLEACH PLANT
Effluent
to Recovery
Effluent
to Discharge
Reeve, Douglas W., TAPPI Bleach Plant Operations Short Course, 1998.

12. Upflow and Downflow towers
Multistage Bleaching
Upflow and Downflow towers

13. Simplified Bleaching Reactions

14. Chlorine Make It or Rail Cars Safety Environmental
2-4% cons. – dissipate exothermic
Time & Temperature
Pulp consumption vs solubilize lignin
Proper Mixing

15. Caustic Extraction 12-15% cons 60-80 deg C
Good washing from previous stage
Retention Time up to 2 hrs
Opens up fiber
Remove chlorinated and/or oxidized lignin

16. Reduces Environmental Issues
Oxygen
Reduces Environmental Issues
Watch for pulp degradation

17. O2 Delignification

18. O2 Delignification Reduces Kappa number Reduced effluent loading
BOD5 – 50%
Color – 70%
COD – 50%
Reduces chemical costs – 30%
Lowers pulp viscosity – but equal strength

19. Extended Cooking Leads to Lower Yield

20. Hypochlorite Mix Chlorine with NaOH or Ca(OH)2 Usage is declining
35-40 deg C for 1-2 hrs
pH control to protect cellulose attack
Watch pulp viscosity decreases
Calcium(cheap) but scale vs sodium

21. Damaged Low Viscosity Pulp Fiber

22. ClO2 Plant

23. Chlorine Dioxide Generate from Sodium chlorate
ClO2 gas is explosive but soluble in water
First used in 1946
Highly selective destruction
Preserves strength
High and stable brightness

24. TCF or ECF?

25. Dioxin
1985 – 2,3,7,8, TCDD was found in fish downstream from a paper mill and subsequently found in mill effluent
1988 – National Council for Air and Stream Improvement (NCASI) reported on a five mill study that showed TCDD (Tetrochloro Dibenzo Dioxin) and TCDF (Tetrochloro Dibenzo Furan) were formed in bleaching operations
March, 1988 – PAPRICAN (Pulp and Paper Research Institute of Canada) reported finding precursors DBF (Dibenzo Furan) and DBD (Dibenzo Dioxin) in defoamers and oil

26. World Chlorine Trends 1990-2001
Elemental Chlorine Free and Total Chlorine Free

27. Bleaching Trends Lower incoming Kappa number
Improved washing – reduce black liquor carryover
Oxygen delignification
Lower Cl2 multiplier
High ClO2 substitution
Eo, Ep, Eop
Short sequence bleaching
Pretreatment with NO2
Ozone bleaching OZEoP
Improved mixing technology
Aerated lagoons

28. Final Bleach Plant Washer

29. Decker for Pulp Thickening

30. High Density (HD) Pulp Storage

31. Bleach water Recycling
Less water treatment (in and out)
Heat conservation
Chemical savings
Test for corrosivity
Test for pH