Canadian Liquid Air Ltd - Air Liquidecanada Ltee

Canadian Liquid Air/air Liquide Canada Ltee

John R Ayton

Derek Hornsey

Gordon H Homer

Michel Epiney

A method of bleaching a pulp at low consistency employs chlorine dioxide and/or chlorine, to partially bleach the pulp. The aqueous partially bleached pulp flows along a sinuous flow path providing a high ratio of flow path of aqueous pulp to length of effective travel of the aqueous pulp. Ozone is introduced to the aqueous pulp at spaced apart locations in the flow path so that a low partial pressure of ozone is established in the flow path which favors chemical oxidation of the lignin and low chemical attack on cellulose. In this way effective bleaching is achieved with reduced use of chlorine or chlorine dioxide and reduced production of chlorinated compounds.

Method for ozone bleaching of cellulosic pulp at low consistency

A method and installation for bleaching a lignocellulosic pulp with ozone, while recovering an oxygen-rich gas which may be recycled or re-used. Bleaching of the pulp with ozone is preferably carried out under conditions in which ingress of air is prevented. In a multi-step bleaching process, an oxygen-rich vent gas typically containing at least 90%, by weight, of oxygen may be recovered from a second contactor for potential use in different oxygen-consuming operations in a pulp mill.

Method of monitoring and recovering oxygen-rich gas from ozone bleaching

A fluffy pulp previously dried, having a consistency by 90%, is introduced in a baler where it is subjected to a carbon dioxide comprising atmosphere in order to both reduce or eliminate the fire risk in the baler and to decrease the pH of the pulp by chemically reacting with it. Both gaseous and liquid (snow) carbon dioxide can be used. Preferably, carbon dioxide snow is injected at the bottom of the baler to accelerate the pH control of the pulp, just before compressing the pulp in bales, which compression enhances the pH control reaction between the pulp and the carbon dioxide.

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Delta, Canada

John R Ayton