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You are here : Home > Training > EFPG Days > 3- Applying ozone on high kappa pulps (kraft and sulfite) to improve the bleached pulp yield (abstract)
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            3 - Applying ozone on high kappa pulps (kraft and sulfite) 
to improve the bleached pulp yield
           
Christine Chirat, Dominique Lachenal, Dinah Nyangiro,
Marie-Thérèse Viardin, Karine Janel (EFPG)

Site Web de l'EFPGThe concept presented in this paper is the application of ozone on high kappa pulps in place of or in combination with oxygen to improve overall yield.

Ozonation was carried out on softwood kraft pulps with starting kappa numbers varying from 27 to 60 and the pulps were then fully bleached with DEDED. The 60 kappa number pulp treated by ozone showed about 2% better yield than the 27 kappa number pulp, both bleached by DEDED. It also showed 1% better yield than the 60 kappa number pulp treated by ODEDED. The more extensive retention of carbohydrates would be related to the higher content in lignin which prevents them from degradation. In the case of the hardwood kraft pulp the similar trend was observed.
Pulp strength properties were measured: for both the hardwood and softwood pulps the high kappa pulps treated by ozone were much easily refined in a PFI mill and showed equal or even better strength properties than the control pulps.

In a second set of experiments, the high kappa softwood kraft pulp was first treated by O and then by ozone: O(ZD)EpDED was then compared to OODEpDED. Even though less ozone was introduced, it was still possible to measure a benefit in yield.

The last part deals with the use of ozone as a first stage in a sulfite mill. There would be several interests of ozone in this case: the pulp is already acidic after the cooking (no acid addition necessary for the ozone stage), and consequently the effluents of the Z stage could be sent to the recovery boiler. This could solve environmental issues encountered in some mills (reduction of COD). Furthermore ozone is very reactive towards extractives.
Ozone was applied on 30 and 50 kappa number sulfite pulps : Z Ep P sequences were compared to the control sequence Ep P. Applying the Ep P sequence on the 30 kappa number pulp led to a kappa number of about 15 at a bleaching yield of 93,3 to be compared to 95,1 for Z Ep using 0,5% ozone, at the same kappa number.
In the case of the higher kappa pulp (50), about 2 points gain in yield could be observed when using Z Ep P instead of Ep P.

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