Method for reducing contaminants in pulp prior to ozone bleaching

A method for reducing contaminants in pulp prior to the ozone bleaching of the pulp, said method comprising:

• pressing pulp between rollers in a pulp consistency increasing stage to provide increased consistency pulp by removing liquid therefrom and expanding the pulp to create voids therein;
• supplying said increased consistency pulp and a gaseous mixture of ozone and oxygen to an ozone-pulp reaction zone;
• contacting said increased consistency pulp with said gaseous mixture in said ozone-pulp reaction zone to bleach said pulp by removing a substantial portion of the lignin therefrom by reaction with said ozone, while consuming a substantial portion of said ozone by reaction with said pulp, thus producing a bleached pulp and an oxygen-rich exhaust gas which contains greater than 50% oxygen;
• and
• purging a portion of said oxygen-rich exhaust gas in an amount of up to about 20% by volume, directing said purged exhaust gas portion to said pulp consistency increasing stage, and forming a surrounding blanket of said purged exhaust gas portion about said increased consistency pulp so that said purged exhaust gas portion contacts substantially all pulp after pressing to fill said voids in said increased consistency pulp with said purged exhaust gas portion.

A method for reducing contaminants in pulp prior to ozone bleaching of the pulp, said method comprising

• providing a source of an oxygen rich gas which contains at least about 50% oxygen;
• increasing the consistency of the pulp by pressing the pulp between rollers and expanding the pulp to create voids therein;
• forming a surrounding blanket of said oxygen rich gas around said pulp at least while the consistency is being increased so that said oxygen rich gas contacts substantially all the pulp to fill substantially all voids therein with said oxygen rich gas;
• and
• supplying said increased consistency pulp to an ozone-pulp reaction zone for reaction with a gaseous mixture of ozone and oxygen, whereby the amount of contaminants in said increased consistency pulp is reduced by the presence of the oxygen rich gas in the voids of the pulp.