Kvaerner Pulping Ab

Kvaerner Pulping Technologies Ab

Kvaerner Pulping Technologies Aktiebolag

Kvaerner Pulping Aktiebolag

Anders Bergqvist

Johan Engstrom

Stig Andtbacka

Petter Tibbling

Erik Nilsson

Lars Ove Larsson

Daniel Panglsson

Gunnar Wernqvist

H&aring;kan Dahll&ouml;f

Marcelo Leite

Lennart Hagelquist

Elisabeth Andtbacka

A method and device for bleaching chemical paper pulp or dissolving wood pulp, which has been cooked and delignified without employing chlorine-containing chemicals, comprising a bleaching sequence which comprises optionally a first stage comprising a chelation treatment step; a second stage comprising a first peroxide treatment stage, wherein said first peroxide treatment stage is a delignifying peroxide treatment stage in which the amount of peroxide is less than 12 kilo/bone dry metric tons; a third stage comprising an acidic delignifying treatment stage, following said second stage and including a wash, and a fourth stage comprising a second peroxide treatment stage, following said third stage and including a wash, wherein said second peroxide treatment stage is a bleaching peroxide treatment, in which the amount of peroxide exceeds 3 kilo/bone dry metric tons and exceeds the amount of peroxide employed in said second step.

Peroxide bleach sequence including an acidic bleach stage and including a wash stage

Method of bleaching pulp without using chlorine chemicals in a (QP)Z bleaching sequence

The present invention relates to a digester and a method for continuously cooking kraft pulp in a single-vessel system (1), preferably a single-vessel hydraulic digester, with chips (2) being fed in at a first end (3) of the digester (1), white liquor (4) being added at at least one position at or near the said first end (3), the chips being impregnated in a cocurrent impregnation zone (5), the chips being cooked in a cooking zone (6) downstream of the impregnation zone, hot black liquor (7) being extracted from at least one extraction strainer section (8), and cooked pulp being discharged (9) at the other end of the digester, and hot black liquor (7) being added (11), (12) to the said impregnation zone (5), and the extract (13) from the first strainer section (14), which is arranged downstream of the position of addition (11a) of the said hot black liquor (7), being largely removed from the digester.

Black liquor impregnation in digester

The present invention provides a method for continuously cooking kraft pulp in a digester having the steps of:

Method of continuous pulping in a digester with high black liquor usage

Recycling of knots in a continuous process for cooking chemical pulp

A method of integrating bleaching and recovery in connection with the production of chemical pulp that has been digested and preferably delignified with oxygen gas using processes that retain the viscosity and strength, to kappa number less than 16 without the use of chemicals containing chlorine, and using a bleaching sequence including at least one step with sequestering agent and/or acid, and a peroxide step. According to the invention spent liquor (5) from the bleaching department is pre-evaporated in one or more evaporation units (20F, 20G), and the spent liquor (24) from the bleaching department thus pre-evaporated is combined with spent liquor (22) from the digestery and/or with pre-evaporated spent liquor (23) from the digestery obtained by pre-evaporating spent liquor (22) from the digestery in one or more evaporation units (20D, 20E) other than said evaporation units (20F, 20G) for pre-evaporating spent liquor (5) from the bleaching department, after which the mixture of spent liquors (23, 24) is subjected to final evaporation in one or more evaporation units (20A, 20B, 20C) other than said evaporation units (20F, 20G, 20D, 20E) used for pre-evaporation.

Method of integrating bleaching and recovery in the production of pulp

Growing community of inventors

Karlstad, Sweden

Anders Bergqvist