Process for peroxide bleaching of chemical pulp in a pressurized bleaching vessel

A process for chlorine-free bleaching of chemical pulp in association with the production thereof, using no chlorine and no chlorine compounds, comprising the steps of:

• (a) providing a chemical pulp having a pulp suspension with a consistency exceeding 8% of cellulose-containing fiber material;
• (b) treating the chemical pulp with at least one acid for adjusting the pH of the pulp to a value below 7;
• (c) treating the pulp with a chelating agent;
• (d) pumping said pull) into at least one bleaching vessel by means of a medium consistency pump to aid in pressurizing said bleaching vessel;
• adding hydrogen peroxide in a quantity exceeding 5 kg/BDMT or a corresponding quantity of another peroxide to said pulp in suspension;
• (f) adding at least one complexing agent to the pulp suspension together with the peroxide, said complexing agent comprising DTPA which substantially withstands a ph-value up to 11;
• and
• (g) bleaching the pulp in a bleaching stage to a brightness exceeding 75% ISO during the bleaching stage, said bleaching stage being effected in a bleaching vessel at a temperature exceeding 90.degree. C. and at a pressure exceeding 2 bar, an area of metal surface exposed on an interior of the bleaching vessel being less than 4V m.sup.2, where V indicates a volume of the bleaching vessel.

A process for chlorine-free bleaching of chemical pulp in association with the production thereof, using no chlorine and no chlorine compounds, comprising the steps of:

• (a) providing a chemical pulp having a pulp suspension with a consistency exceeding 8% of cellulose-containing fiber material;
• (b) treating the chemical pulp with at least one acid for adjusting the pH of the pulp to a value below 7;
• (c) treating the pulp with a chelating agent;
• (d) pumping said pulp into at least one bleaching vessel be means of a medium consistency pump to aid in pressurizing said bleaching vessel;
• and
• (e) bleaching the pulp in a bleaching stage to a brightness exceeding 75% ISO during the bleaching stage using hydrogen peroxide employed in a quantity exceeding 5 kg/BDMT or a corresponding quantity of another peroxide;
• wherein said bleaching stage is effected in a bleaching vessel at a temperature equal to or exceeding 100.degree. C. and at a pressure exceeding 3 bar, and an area of metal surface exposed on an interior of the bleaching vessel is less than 4V m.sup.2, where V indicates a volume of the bleaching vessel in m.sup.3.

A process for chlorine-free bleaching of chemical pulp in association with the production thereof, using no chlorine and no chlorine compounds, comprising the steps of:

• (a) providing a chemical pulp having a pulp suspension with a consistency exceeding 8% of cellulose-containing fiber material;
• (b) treating the chemical pulp with at least one acid for adjusting the pH of the pulp to a value below 7;
• (c) treating the pulp with a chelating agent;
• (d) pumping said pulp into at least one bleaching vessel by means of a medium consistency pump to aid in pressurizing said bleaching vessel;
• (e) adding hydrogen peroxide to the pulp suspension in a quantity exceeding 5 kg/BDMT or a corresponding quantity of another peroxide;
• (f) adding oxygen to the pulp suspension in a quantity which is less than 5 kg/BDMT of pulp;
• and
• (g) bleaching the pulp in a bleaching stage to a brightness exceeding 75% ISO during the bleaching stage, said bleaching stage being effected in a bleaching vessel at a temperature exceeding 90.degree. C. and at a pressure exceeding 2 bar, an area of metal surface exposed on an interior of the bleaching vessel being less than 4V m.sup.2, where V indicates a volume of the bleaching vessel in m.sup.3.