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  Logo EFPG     VIII - Ozonation of high kappa pulps
New possibilities (slides 1-8)


Dinah Nyangiro (EFPG)
 
     
 
1 - State of the art
  Environmental protection legislation: levels of
bleaching process waters containing suspended
solids, dissolved organic matter and AOX
  Process economy: water, wood and reagent
consumption, effluent treatment
  Oxygen delignification industrial practice: increase
selectivity, yield, reduced AOX and reagent costs
  Ozone is a powerful oxidant with no AOX production:
possible alternative to oxygen delignification
  Use of ozone to substitute chlorine dioxide has proved
very promising: reduction of chlorine dioxide load
   
2 - Objective
DEVISE NEW METHODS OF OZONE
APPLICATION TO INCREASE OZONATION
SELECTIVITY
 
     
 
3 - Oxygen delignification
  Oxygen delignification upstream before bleach plant
is a common industrial practice
  OO- delignification stage significantly reduces the
boiler load, as wood consumption for constant
bleached pulp production is reduced
  AOX level (directly proportional to KN of pulp going
into the bleach plant) reduces as the kappa number
into bleach plant is lower
   
4 - Conventional kraft pulping yield
Screened yield on wood for kraft pulping process, as a
function of kappa number. For kappa numbers less than
30 KN, yield loss or shrinkage was 0.27% per unit kappa
drop (yield - kappa line gradient).
Data from: Homer 96/PPT
 
     
 
5 - Pulping with conventional bleaching
Screened yield on wood as a function of kappa number for
pulping with conventional bleaching.
Data from: Homer 1996/PPT
   
6 - Pulping with oxygen delignification
Screened yield on wood as a function of kappa number
for pulping with oxygen delignification.
High KN of 40 to 50 instead of the conventional 30 KN,
followed by an oxygen delignification: up to 2% pulp yield
increase.
Data from: Homer 1996/PPT
 
     
 
7 - Ozonation conditions
     HC ozonation, 20C at pH 2, kraft softwood
(Norwegian spruce)
  2% (on OD pulp) ozone charge at 70 g/m3
concentration
  kraft pulp at 52 kappa number
   
8 - Ozone delignification
Comparison of ozone treated pulp yields (for 60 and 27 KN
pulps) with kraft pulping process yield.
Variation of overall yield with kappa number.
 
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