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EP0397308A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Method of bleaching cellulose pulp with ozone

Assignee: Andritz Oy
•
Filing: 1990-03-20
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Granted: —
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Expires: 2010-03-20
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Abstract

Abstract The present invention relates to a method of bleaching cellulose pulp with ozone. Ozone bleaching has been extensively studied in laboratory and pilot scale. It has been proved that at low consistencies, i.e. less than 5 %, ozone dissolves well in water and thus good transfer of substance between the ozone and the fibers in the water is achieved. On the other hand, it has been discovered that the ozone, being a gaseous substance, reacts well also directly with a fiber surface which, however, presupposes that the consistency of the suspension is over 25 %. Further, it has been discovered that in the intermediate range between said consistencies ozone cannot satisfactorily contact the fibers. However, both environmental and pumping factors determine the operation to be carried out at that particular intermediate consistency range of 5 to 25 %. A characteristic feature of the method of the present invention, which avoids the disadvantages of prior art methods and permits operation at the consistency range of 5 to 25 %, is that cellulose pulp is pumped with a high-­consistency pump to a fluidizing mixer in which O₂/O₃ gas is introduced and mixed into the pulp so as to generate foam in which the fibers in the pulp and the ozone used as the bleaching agent are brought to contact with each other, and that the pulp is discharged from the mixer to a reaction vessel.

Inventors

  • 👤 Henricson
  • 👤 Juhani Peltonen
  • 👤 Torolf Laxen

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-11-09 03:04
CPC Classifications
D; D21; D21C; D21C9/00; D21C9/10; D21C9/147; D21C9/153

Claims Analysis

Total Claims: 15
Claim 1
Independent Claim 31 words
A method of bleaching cellulose pulp with ozone, characterized in that the pulp is bleached in the form of a foam-like mixture at the consistency range of 5 to 25 %.
Claim 2
Independent Claim 31 words
A method of bleaching cellulose pulp with ozone, characterized in that the pulp is bleached in the form of a foam-like mixture at the consistency range of 5 to 25 %.
Claim 3
Dependent Claim 68 words
A method as claimed in claim 1, characterised in - pumping the pulp with a medium consistency pump to a fluidizing mixer, - feeding O₂/O₃ gas into the pulp therein, - bringing the ozone serving as the bleaching agent in contact with the fibers of the pulp by means of mixing said gas into the pulp, and - discharging the pulp from the mixer into a reaction vessel.
Claim 4
Dependent Claim 48 words
A method as claimed in claim 2, characterized in - performing the bleaching in at least two steps such that - residual gas is removed after the previous step in a reaction vessel, and - additional O₂/O₃ gas is added in the mixer prior to the later step.
Claim 5
Dependent Claim 21 words
A method as claimed in claim 1, characterized in that the foam is a mixture of water, fibers, and O₂/O₃ gas.
Claim 6
Dependent Claim 32 words
A method as claimed in claim 1, characterized in - mixing the O₂/O₃ gas into the pulp by a fluidizing mixer, whereby the foam-like mixture required by the bleaching reactions is produced.
Claim 7
Dependent Claim 23 words
A method as claimed in claim 2, characterized in - separating the residual gas from the pulp after at least one bleaching stage.
Claim 8
Dependent Claim 26 words
A method as claimed in claim 3, characterized in - separating the residual gas by a gas-removing pump used for pumping the pump for further treatment.
Claim 9
Dependent Claim 41 words
A method as claimed in claim 7, characterized in that the head produced by the second pump is low or negligible and the pump is used mainly for gas separation and the actual flow is kept up by a previuos pump.
Claim 10
Dependent Claim 48 words
A method as claimed in claim 3 or 6, characterized in that the residual gas is fed to another stage of the process, e.g. to serve as additional chemical in the bleaching plant or as combustion gas in a soda recovery boiler or a lime sludge reburning kiln.
Claim 11
Dependent Claim 63 words
A method as claimed in claim 7, characterized in - introducing the pulp to another mixer after separating the gas therefrom, - feeding O₂/O₃ gas into the pulp in said mixer, - mixing said gas with the pulp so as to produce a mixture permitting the bleaching reaction between the ozone and the fibers, and - discharging the pulp into a reaction vessel.
Claim 12
Dependent Claim 22 words
A method as claimed in claim 1 or 10, characterized in that the bleaching stages are pressurized, pressureless or performed at underpressure.
Claim 13
Dependent Claim 16 words
A method as claimed in claim 2, characterized in agitiating the pulp in a reaction vessel.
Claim 14
Dependent Claim 37 words
A method as claimed in claim 2, characterized in that the ozone bleaching stage is part of a larger bleaching plant where also the other bleaching stages are performed at a consistency of 5 to 25 %.
Claim 15
Dependent Claim 32 words
A method as claimed in claim 13, characterized in that the other bleaching stages use at least one of the following bleaching agents: chlorine, ozone, peroxid, chlorine dioxide, sodium hydroxide or enzymes.

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