Treating pulp with oxygen

Claim 2

A wood pulp process comprising continuously digesting wood chips with chemicals under heat and pressure to form delignification products and delignified wood chips, removing at least a part of said delignification products, forming wood pulp from said delignified wood chips by partially releasing the pressure from said wood chips, transporting a slurry containing said wood pulp and remaining delignification products under pressure to a storage tank, and storing said slurry in said tank, prior to said storage, adjusting the pH of said slurry to a pH in the range of 8 to 14, between said pH adjustment and said storage, adding oxygen to said slurry, between said pH adjustment and said storage, mixing said oxygen with said slurry in a mixing zone in which a plurality of rotating members pass through said slurry in a direction transverse the direction of travel of said slurry, said members having a major axis extending in the direction of rotation, said members providing a swept area through said slurry of 10,000 to 1,000,000 square meters per metric ton of oven dry pulp, said members having leading and trailing edges, said leading edge having a radius of curvature in the range of 0.5 to 15 mm.

Claim 3

The process of claim 1 in which said swept area is 25,000 to 150,000 square meters per metric ton of oven dry pulp.

Claim 4

The process of claim 1 in which said swept area is around 65,400 square meters per metric ton of oven dry pulp.

Claim 5

The process of claims 1, 2 or 3 in which said members have elliptically generated cross sections having a major axis extending in the direction of rotation.

Claim 6

The process of claims 1, 2 or 3 in which said mixing occurs in an annular space in which the interior surface of said space has a radius of at least one half of the radius of the exterior surface of said space.

Claim 7

The process of claims 1, 2 or 3 in which said trailing edge has a radius of curvature in the range of 0.5 to 15 mm.

Claim 8

The process of claims 1, 2 or 3 in which said oxygen is added incrementally to said slurry.

Claim 9

The process of claims 1, 2 or 3 in which the amount of oxygen added to said slurry is from 5 to 50 kilograms per metric ton of oven dry pulp.

Claim 10

The process of claims 1, 2 or 3 in which said pH is adjusted by adding alkali, expressed as sodium hydroxide, in an amount in the range of 0.25 to 8% based on the oven dry weight of said pulp.

Claim 11

The process of claims 1, 2 or 3 further comprising prior to said mixing, heating said slurry to a temperature in the range of around 65° C. to around 121° C. during said mixing.

Claim 12

The process of claims 1, 2 or 3 in which said slurry is subject to a pressure of up to 830 kPa gage during said mixing.

Claim 13

A wood pulp process comprising continuously digesting wood chips with chemicals under heat and pressure to form delignification products and delignified wood chips, removing at least a part of said delignification products, forming wood pulp from said delignified wood chips by partially releasing the pressure from said wood chips, transporting a slurry containing said wood pulp and remaining delignification products under pressure to a diffusion washer, washing said pulp in said diffusion washer, prior to said diffusion washing, adjusting the pH of said slurry to a pH in the range of 8 to 14, between said pH adjustment and said diffusion washing, adding oxygen to said slurry, between said pH adjustment and said diffusion washing, mixing said oxygen with said slurry in a mixing zone in which a plurality of rotating members pass through said slurry in a direction transverse the direction of travel of said slurry, said members having a major axis extending in the direction of rotation, said members providing a swept area through said slurry of 10,000 to 1,000,000 square meters per metric ton of oven dry pulp, said members having leading and trailing edges, said leading edge having a radius of curvature in the range of 0.5 to 15 mm.

Claim 14

A wood pulp process comprising continuously digesting wood chips with chemicals under heat and pressure to form delignification products and delignified wood chips, removing at least a part of said delignification products, forming wood pulp from said delignified wood chips by partially releasing the pressure from said wood chips, transporting a slurry containing said wood pulp and remaining delignification products under pressure to a diffusion washer, washing said pulp in said diffusion washer, prior to said diffusion washing, adjusting the pH of said slurry to a pH in the range of 8 to 14, between said pH adjustment and said diffusion washing, adding oxygen to said slurry, between said pH adjustment and said diffusion washing, mixing said oxygen with said slurry in a mixing zone in which a plurality of rotating members pass through said slurry in a direction transverse the direction of travel of said slurry, said members having a major axis extending in the direction of rotation, said members providing a swept area through said slurry of 10,000 to 1,000,000 square meters per metric ton of oven dry pulp, said members having leading and trailing edges, said leading edge having a radius of curvature in the range of 0.5 to 15 mm.

Claim 15

The process of claim 12 in which said swept area is 25,000 to 150,000 square meters per metric ton of oven dry pulp.

Claim 16

The process of claim 12 in which said swept area is around 65,400 square meters per metric ton of oven dry pulp.

Claim 17

The process of claims 12, 13 or 14 in which said members have elliptically generated cross sections having a major axis extending in the direction of rotation.

Claim 18

The process of claims 12, 13 or 14 in which said mixing occurs in an annular space in which the interior surface of said space has a radius of at least one half of the radius of the exterior surface of said space.

Claim 19

The process of claims 12, 13 or 14 in which said trailing edge has a radius of curvature in the range of 0.5 to 15 mm.

Claim 20

The process of claims 12, 13 or 14 in which said oxygen is added incrementally to said slurry.

Claim 21

The process of claims 12, 13 or 14 in which the amount of oxygen added to said slurry is from 5 to 50 kilograms per metric ton of oven dry pulp.

Claim 22

The process of claims 12, 13 or 14 in which said pH is adjusted by adding alkali, expressed as sodium hydroxide, in an amount in the range of 0.25 to 8% based on the oven dry weight of said pulp.

Claim 23

The process of claims 12, 13 or 14 further comprising prior to said mixing, heating said slurry to a temperature in the range of around 65° C. to around 121° C. during said mixing.

Claim 24

The process of claims 12, 13 or 14 in which said slurry is subject to a pressure of up to 830 kPa gage during said mixing.

Claim 25

A pulping apparatus comprising a continuous digester for continuously digesting wood chips to form delignification products and delignified wood chips, and a washer associated with said digester for removing at least a part of said delignification products, said digester having a pressure relief valve for forming wood pulp from said delignified wood chips by partially releasing the pressure from said wood chips, a pipe for transporting a slurry containing said wood pulp and remaining delignification products under pressure from said digester to a storage tank, and said storage tank, means, prior to said storage tank, for adding a pH adjustment chemical to said slurry, means, between said pH adjustment chemical addition means and said storage tank, for adding oxygen to said slurry, and means, prior to said storage tank, for mixing said oxygen with said slurry, said mixing means having a mixing zone, a plurality of rotors in said mixing zone, said rotors having leading and trailing edges, said leading edge having a radius of curvature in the range of 0.5 to 15 mm. said rotors having a major axis extending in the direction of rotation, said rotors being rotatable through said slurry in a direction transverse to the direction of travel of said slurry, means for rotating said rotors, and said rotors providing a swept area of from 10,000 to 1,000,000 square meters per metric ton of oven dry pulp.

Claim 26

A pulping apparatus comprising a continuous digester for continuously digesting wood chips to form delignification products and delignified wood chips, and a washer associated with said digester for removing at least a part of said delignification products, said digester having a pressure relief valve for forming wood pulp from said delignified wood chips by partially releasing the pressure from said wood chips, a pipe for transporting a slurry containing said wood pulp and remaining delignification products under pressure from said digester to a storage tank, and said storage tank, means, prior to said storage tank, for adding a pH adjustment chemical to said slurry, means, between said pH adjustment chemical addition means and said storage tank, for adding oxygen to said slurry, and means, prior to said storage tank, for mixing said oxygen with said slurry, said mixing means having a mixing zone, a plurality of rotors in said mixing zone, said rotors having leading and trailing edges, said leading edge having a radius of curvature in the range of 0.5 to 15 mm. said rotors having a major axis extending in the direction of rotation, said rotors being rotatable through said slurry in a direction transverse to the direction of travel of said slurry, means for rotating said rotors, and said rotors providing a swept area of from 10,000 to 1,000,000 square meters per metric ton of oven dry pulp.

Claim 27

The apparatus of claim 23 in which said rotors provide a swept area of 25,000 to 150,000 square meters per metric ton of oven dry pulp.

Claim 28

The apparatus of claim 23 in which said rotors provide a swept area of around 65,400 square meters per metric ton of oven dry pulp.

Claim 35

A pulping apparatus comprising a continuous digester for continuously digesting wood chips to form delignification products and delignified wood chips, and a washer associated with said digester for removing at least a part of said delignification products, said digester having a pressure relief valve for forming wood pulp from said delignified wood chips by partially releasing the pressure from said wood chips, a pipe for transporting a slurry containing said wood pulp and remaining delignification products under pressure from said digester to a diffusion washer, and said diffusion washer, means, prior to said diffusion washer, for adding a pH adjustment chemical to said slurry, means, between said pH adjustment chemical addition means and said diffusion washer means, for adding oxygen to said slurry, and means, prior to said diffusion washer, for mixing said oxygen with said slurry, said mixing means having a mixing zone, a plurality of rotors in said mixing zone, said rotors having leading and trailing edges, said leading edge having a radius of curvature in the range of 0.5 to 15 mm, said rotors having a major axis extending in the direction of rotation, said rotors being rotatable through said slurry in a direction transverse to the direction of travel of said slurry, means for rotating said rotors, and said rotors providing a swept area of from 10,000 to 1,000,000 square meters per metric ton of oven dry pulp.

Claim 36

A pulping apparatus comprising a continuous digester for continuously digesting wood chips to form delignification products and delignified wood chips, and a washer associated with said digester for removing at least a part of said delignification products, said digester having a pressure relief valve for forming wood pulp from said delignified wood chips by partially releasing the pressure from said wood chips, a pipe for transporting a slurry containing said wood pulp and remaining delignification products under pressure from said digester to a diffusion washer, and said diffusion washer, means, prior to said diffusion washer, for adding a pH adjustment chemical to said slurry, means, between said pH adjustment chemical addition means and said diffusion washer means, for adding oxygen to said slurry, and means, prior to said diffusion washer, for mixing said oxygen with said slurry, said mixing means having a mixing zone, a plurality of rotors in said mixing zone, said rotors having leading and trailing edges, said leading edge having a radius of curvature in the range of 0.5 to 15 mm, said rotors having a major axis extending in the direction of rotation, said rotors being rotatable through said slurry in a direction transverse to the direction of travel of said slurry, means for rotating said rotors, and said rotors providing a swept area of from 10,000 to 1,000,000 square meters per metric ton of oven dry pulp.

Claim 37

The apparatus of claim 32 in which said rotors provide a swept area of 25,000 to 150,000 square meters per metric ton of oven dry pulp.

Claim 38

The apparatus of claim 32 in which

Claim 39

said rotors provide a swept area of around 65,400 square meters per metric ton of oven dry pulp.

Claim 40

said rotors provide a swept area of around 65,400 square meters per metric ton of oven dry pulp.