A method of replacing sodium losses in a pulp mill, a method of producing bleached cellulosic pulp, and a system

Patent metadata

Field	Value
Publication number	US-2022106737-A1
Application number	US-202017430737-A
Country	US
Kind code	A1
Filing date	Feb 13, 2020
Priority date	Feb 13, 2019
Publication date	Apr 7, 2022
Grant date	—

Abstract

According to an example aspect of the present invention, there is provided a method of replacing with sodium make-up chemicals sodium losses caused by outflows in a pulp mill which employs a kraft process for producing cellulosic pulp, wherein the pulp mill includes a unit for conversion of sulphurous compounds, which is fed with sulphurous substances of the kraft process to convert said sulphurous substances into oxidized sulphurous compounds, said method comprising using sodium sulphate possibly together with other sodium salts as the main make-up chemical, to achieve an essentially sodium hydroxide free feed of sodium make-up chemicals, and at least a part of the sulphur contained in the sodium sulphate make-up chemical being used for producing oxidized sulphurous compounds in said unit for conversion of sulphurous compounds.

First claim

1 . A method of replacing with sodium make-up chemicals sodium losses caused by outflows in a pulp mill which employs a kraft process for producing cellulosic pulp, wherein the pulp mill includes a unit for conversion of sulphurous compounds, which is fed with sulphurous substances of the kraft process to convert said sulphurous substances into oxidized sulphurous compounds, said method comprising using sodium sulphate optionally together with other sodium salts as the main make-up chemical, to achieve an essentially sodium hydroxide free feed of sodium make-up chemicals, and at least a part of the sulphur contained in the sodium sulphate make-up chemical being used for producing oxidized sulphurous coumpounds in said unit for conversion of sulphurous compounds.

2 . The method according to claim 1 , wherein the plant for conversion of sulphurous compounds comprises a sulphuric acid plant which is fed with sulphourous substances selected from the group of non-condensable gases of the kraft process.

3 . The method according to claim 1 , wherein the oxidized sulphurous compounds are selected from the group of alkali metal bisulphites sulphuric acid SO 2 , and combinations thereof.

4 . The method according to claim 1 , wherein the sodium sulphate, and any other sodium salts used as make-up chemical, make up for at least 80 mole-% of the sodium losses of the pulp mill.

5 . The method according to claim 1 , wherein at least a majority of the sodium compounds used as make-up chemicals comprise sodium sulphate or sodium carbonate or mixtures thereof.

6 . The method according to claim 1 , wherein at least a part of the sodium salts used as make-up chemicals are provided in the form of by-products and residues of a pulp mill.

7 . The method according to claim 6 , wherein the make-up chemicals are provided in the form of by-products and residues of another pulp mill.

8 . The method according to claim 1 , wherein the sodium losses of the pulp mill are replaced by make-up chemicals which contain less than 5 mole-% sodium hydroxide.

9 . The method according claim 1 , wherein the sodium sulphate and optionally other sodium salts used as main make-up chemical for replacing sodium losses, are being fed into the chemical recirculation of the pulp mill for regenerating white liquor.

10 . The method according to claim 1 , wherein;
pulp is produced in a cooking stage using a cooking liquor comprising white liquor which is regenerated in a chemical recirculation of the pulp mill.

11 . The method according to claim 10 , wherein:
at least a part of the regenerated white liquor is oxidized, and the oxidized white liquor thus obtained is used as an alkaline agent in an alkaline stream of the pulp mill to at least partially replace fresh feed of alkaline agent.

12 . The method according to claim 10 , wherein the oxidized white liquor is used as such as an alkaline medium of an alkaline stream in the pulp mill, or it is used for adjusting the pH of a stream in the pulp mill, including effluents thereof.

13 . The method according to claim 10 , wherein the oxidized white liquor is used as such as an alkaline medium of an alkaline stream of bleaching, or it is used for adjusting the pH of an effluent of bleaching.

14 . The method according to claim 10 , wherein the pulp obtained from the pulping stage is subjected to totally chlorine free bleaching using ozone, peroxide, oxygen or a combination thereof, and including at least one alkaline oxidizing step.

15 . The method according to claim 10 , wherein the pulp obtained from the cooking stage is subjected to chlorine dioxide bleaching stage which comprises at least a first chlorine dioxide step carried out at acidic pH, a second chlorine dioxide step carried out at acidic pH, and an intermediate oxidizing step carried out between the first and the second chlorine dioxide steps.

16 . The method according to claim 10 , wherein:
sodium sulphate is used as main make-up chemical for replacing sodium losses, said sodium sulphate at least partially being fed into the chemical recirculation of the pulp mill for regenerating white liquor.

17 . The method according to claim 10 , wherein an effluent of the alkaline oxidizing step is recovered and at least partially recirculated in the chemical recirculation of the pulp mill.

18 . The method according to claim 10 , wherein non-condensable gases containing sulphurous, odorous gases are collected and concentrated before being fed to the sulphuric acid plant.

19 . The method according to claim 10 , wherein sulphuric acid produced in the sulphuric acid plant is used for adjusting the pH of the first and the second chlorine dioxide bleaching steps.

20 . The method according to claim 10 , wherein the sulphuric acid produced in the sulphuric acid plant is used for acidulation of crude tall oil soap, separated from black liquor.

21 . The method according to claim 10 , wherein pulp is produced in the cooking stage of the kraft process in a cooking liquor comprising white liquor having a sulphidity of about 20 to 50%.

22 . A method of producing bleached cellulosic pulp in a pulp mill employing a kraft process -wherein:
pulp is produced from a lignocellulosic raw material in a cooking stage using a cooking liquor comprising white liquor which is regenerated in a chemical recirculation of the pulp mill; and the pulp obtained from the cooking stage is subjected to a bleaching stage, which comprises at least one alkaline oxidizing step in order to produce bleached cellulosic pulp; said pulp mill further including a sulphuric acid plant which is being fed with sulphurous substances—collected from—the kraft process for producing sulphuric acid or alkali metal sesquisulphate or a combination thereof, at least a part of the regenerated white liquor is oxidized, oxidized white liquor thus obtained is used as a medium in an alkaline oxidizing step of the bleaching, and sodium sulphate is used as main make-up chemical for replacing sodium losses, said sodium sulphate at least partially being fed into the chemical recirculation of the pulp mill for regenerating white liquor, and at least a part of the sulphur contained in the make-up chemical feed being used for producing sulphuric acid or alkali metal bisulphites or a combination thereof in the sulphuric acid plant.

23 . The method according to claim 22 , wherein bleaching is carried out as totally chlorine free bleaching using ozone, peroxide, oxygen or a combination thereof.

24 . The method according to claim 22 , wherein the oxidizing step, is carried out in an alkaline medium at a pH of 10 to 14 in the presence of an oxidizing agent selected from the group of oxygen gas, peroxide, and combinations thereof.

25 . The method according to claim 22 , wherein at least 50 mole % of the alkaline agent of the alkaline medium of the oxidizing step of the chlorine dioxide bleaching is comprised of oxidized white liquor.

26 . The method according to claim 22 , wherein at least a part, in particular at least 50% by weight, of the effluent of the alkaline oxidization step is recirculated to the chemical recirculation of the pulp mill for regenerating white liquor.

27 . The method according to claim 22 , wherein:
the pulp obtained from the cooking stage is subjected to a chlorine dioxide bleaching stage, which comprises at least a first chlorine dioxide step carr

Assignees

• Metsae Fibre Oy
• Andritz Oy

Inventors

• Poukka Ari
• Tervola Veli-Pekka

Classifications

• D21C11/00 Primary

  Regeneration of pulp liquors {or effluent waste waters} · CPC title

• D21C11/0078 Primary

  Treatment of green or white liquors with other means or other compounds than gases, e.g. in order to separate solid compounds such as sodium chloride and carbonate from these liquors; Further treatment of these compounds (fractionating of spent liquors D21C11/0042) · CPC title

• D21C11/0035 Primary

  Introduction of compounds, e.g. sodium sulfate, into the cycle in order to compensate for the losses of pulping agents · CPC title

• Y02P40/40

  Production or processing of lime, e.g. limestone regeneration of lime in pulp and sugar mills · CPC title

• D21C9/142

  with ClO2/Cl2 in a multistage process involving ClO2/Cl2 exclusively · CPC title