Method and system for efficient production of dissolving pulp in a kraft mill producing paper grade pulp with a continuous type digester

• US 8,951,388 B2
• Filed: 04/06/2012
• Issued: 02/10/2015
• Est. Priority Date: 04/08/2011
• Status: Active Grant

• Current Assignee: RGE Pte., Ltd. (RGE Capital Ltd.)
• Original Assignee: PEC-Tech Engineering And Construction Pte., Ltd.
• Inventors: van Lee, Richard Constantine, Devanesan, Alagaratnam Joseph
• Primary Examiner(s): CALANDRA, ANTHONY J
• Application Number:
  US13/441,776
• Publication Number:
  US 20130098569A1
• Time in Patent Office: 1,040 Days
• Field of Search: 162/19
• US Class Current: 162/19
• CPC Class Codes: D21C 3/02 with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
• CPC Class Codes: D21C 3/26 Multistage processes
• CPC Class Codes: D21C 7/00 Digesters
• CPC Class Codes: D21C 7/06 Feeding devices

Abstract

A method and system for pulp manufacturing used in connection with a kraft process includes a vertical pressure vessel operated in batch mode, a single-vessel or multi-vessel continuous digester, and other equipment for further processing brown stock, such as for washing, oxygen delignification, bleaching, and drying. A feeder and conveyance system may include a high pressure feeder or direct pump system, and selectively provides fiber-containing material to the continuous digester when making lower grade pulp product and to the vertical pressure vessel when making higher grade pulp such as dissolving pulp. The vertical pressure vessel is used for pre-hydrolysis and neutralization, after which the resulting pulp is fed to the continuous digester for cooking. White liquor and black liquor from the same mill may be used for the neutralization fluids. The same continuous digester is selectively used for cooking in connection with making pulp products of different grades or quality.

Claims

1. A method for selectively producing pulp of different grades using a continuous digester, comprising:

supplying organic fiber-containing material to a vertical pressure vessel system;

performing pre-hydrolysis and neutralization in a batch mode on the organic fiber-containing material in the vertical pressure vessel system;

providing the contents of the vertical pressure vessel system to a continuous digester after pre-hydrolysis and neutralization; and

performing kraft cooking with the continuous digester to produce a brownstock for dissolving pulp;

wherein either (1) the vertical pressure vessel system comprises a plurality of vessels for performing pre-hydrolysis and neutralization in a batch mode, and/or (2) the vertical pressure vessel system transfers organic fiber-containing material to a storage tank after pre-hydrolysis and neutralization to facilitate a steady flow thereof to the continuous digester.

2. The method of claim 1, further comprising performing kraft cooking of the organic fiber-containing material with the continuous digester to produce a brownstock for paper grade pulp and times when it is not being used to make dissolving pulp.

3. The method of claim 2, further comprising storing the organic fiber-containing material from the vertical pressure vessel system in a storage tank after pre-hydrolysis and neutralization, and prior to providing it to the continuous digester, to facilitate a steady flow thereof to the continuous digester when making dissolving pulp.

4. The method of claim 3, further comprising using a high pressure feed to convey the organic fiber-containing material from the storage tank to the continuous digester when making dissolving pulp, and using the same high pressure feed to convey the organic fiber-containing material to the continuous digester when making paper grade pulp.

5. The method of claim 4, wherein the operation of supplying organic fiber-containing material to the vertical pressure vessel system or the continuous digester is carried out with a conveyance system whereby the organic fiber-containing material is selectively provided either to the vertical pressure vessel system when making dissolving grade pulp or to the continuous digester or the continuous digester when making paper grade pulp.

6. The method of claim 2, further comprising selectively operating the continuous digester for a time and at a temperature suitable to make dissolving grade pulp when the continuous digester is cooking organic fiber-containing material received from the vertical pressure vessel system after pre-hydrolysis and neutralization, and for a time and at a temperature suitable to make paper grade pulp at other times.

7. The method of claim 2, further comprising:

washing and screening the brownstock after completion of cooking in the continuous digester;

bleaching the washed and screened brownstock to produce a bleached pulp; and

drying the bleached pulp to produce either a paper grade pulp or a dissolving pulp.

8. The method of claim 2, wherein said continuous digester is a single-vessel type continuous digester.

9. The method of claim 2, wherein said continuous digester is a dual-vessel type continuous digester.

10. The method of claim 2, further comprising:

pressurizing one or more vessels of the vertical pressure vessel system with steam in connection with a pre-hydrolysis step; and

filling the one or more vessels of the vertical pressure vessel system with a combination of white liquor and black liquor in connection with a neutralization step carried out after pre-hydrolysis;

wherein substantially all of the white liquor and black liquor is locally generated at the same mill through related pulp-manufacturing processes.

11. The method of claim 2, further comprising generating approximately the same amount of solids in a recovery boiler when making paper grade pulp and when making dissolving pulp.

12. A method for selectively producing pulp of different grades using a continuous digester, comprising:

supplying organic fiber-containing material to a vertical pressure vessel system in connection with making dissolving pulp;

performing pre-hydrolysis and neutralization with the vertical pressure vessel system operated in a batch mode;

providing the organic fiber-containing material from the vertical pressure vessel system to a continuous digester after pre-hydrolysis and neutralization;

supplying organic fiber-containing material to the continuous digester or to a pre-treatment unit bypassing the vertical pressure vessel system when making paper grade pulp; and

selectively performing kraft cooking with the continuous digester to produce a brownstock for dissolving pulp or a brownstock for paper grade pulp;

wherein either (1) the vertical pressure vessel system comprises a plurality of vessels for performing pre-hydrolysis and neutralization in a batch mode, and/or (2) the vertical pressure vessel system transfers organic fiber-containing material to a storage tank after pre-hydrolysis and neutralization to facilitate a steady flow thereof to the continuous digester.

13. The method of claim 12, further comprising storing the organic fiber-containing material from the vertical pressure vessel system in a storage tank after pre-hydrolysis and neutralization and prior to providing it to the continuous digester, to facilitate a steady flow thereof to the continuous digester when making dissolving pulp.

14. The method of claim 13, further comprising:

feeding the organic fiber-containing material to the continuous digester using a high pressure feed unit when making paper grade pulp; and

conveying the organic fiber-containing material from the vertical pressure vessel system through the high pressure feed unit to the continuous digester when making dissolving pulp.

15. The method of claim 14, wherein the operations of supplying organic fiber-containing material to the vertical pressure vessel system when making dissolving pulp and the continuous digester when making paper grade pulp are carried out with a conveyance system whereby the organic fiber-containing material is provided to the continuous digester when making paper grade pulp and diverted to the vertical pressure vessel system when making dissolving pulp.

16. The method of claim 12, further comprising selectively operating the continuous digester for a time and at a temperature suitable to make dissolving grade pulp when the continuous digester is cooking organic fiber-containing material received from the vertical pressure vessel system, and for a time and at a temperature suitable to make paper grade pulp at other times.

17. The method of claim 12, further comprising:

screening and washing the brownstock after completion of cooking in the continuous digester;

bleaching the brownstock to produce a bleached pulp; and

drying the bleached pulp to produce either a paper grade pulp or a dissolving pulp.

18. The method of claim 12, wherein said continuous digester is a single-vessel type continuous digester.

19. The method of claim 12, wherein said continuous digester is a dual-vessel type continuous digester.

20. The method of claim 12, further comprising:

pressurizing one or more vessels of the vertical pressure vessel system with steam in connection with a pre-hydrolysis step; and

filling the one or more vessels of the vertical pressure vessel system with a combination of white liquor and black liquor in connection with a neutralization step carried out after pre-hydrolysis.

21. The method of claim 20, further comprising generating substantially all of the white liquor and black liquor locally at the same mill through related pulp-manufacturing processes.

22. A method for retrofitting a pulp mill configured to produce paper grade pulp using a continuous digester with a means to selectively produce dissolving pulp, comprising:

connecting a vertical pressure vessel system upstream from the continuous digester;

providing a means to supply organic fiber-containing material to the vertical pressure vessel system;

selectively supplying organic fiber-containing material to the vertical pressure vessel system when making dissolving pulp and to the continuous digester bypassing the vertical pressure vessel system when making paper grade pulp;

performing pre-hydrolysis and neutralization in a batch mode when organic fiber-containing material is supplied to the vertical pressure vessel system in connection with making dissolving pulp;

conveying the organic fiber-containing material from the vertical pressure vessel system to the continuous digester in connection with making dissolving pulp;

selectively performing kraft cooking with the continuous digester to produce a brownstock for dissolving pulp or a brownstock for paper grade pulp; and

further processing the brownstock to produce either a dissolving pulp or a paper grade pulp;

wherein either (1) the vertical pressure vessel system comprises a plurality of vessels for performing pre-hydrolysis and neutralization in a batch mode, and/or (2) the vertical pressure vessel system transfers organic fiber-containing material to a storage tank after pre-hydrolysis and neutralization to facilitate a steady flow thereof to the continuous digester.

23. The method of claim 22, further comprising:

providing a storage tank between the vertical pressure vessel system and the continuous digester;

transferring organic fiber-containing material from the vertical pressure vessel system to the storage tank after completion of pre-hydrolysis and neutralization for temporary storage to facilitate a steady flow thereof to the continuous digester when making dissolving pulp; and

transferring the organic fiber-containing material from the storage tank to the continuous digester as needed for kraft cooking.

24. The method of claim 22, wherein said continuous digester is a single-vessel continuous digester.

25. The method of claim 22, wherein said continuous digester is a dual-vessel continuous digester.

26. The method of claim 22, wherein organic fiber-containing material is fed to the continuous digester through a high pressure feed when making paper grade pulp, and wherein organic fiber-containing material is fed from the vertical pressure vessel system to the continuous digester via the high pressure feed when making dissolving pulp.

27. The method of claim 22, further comprising selectively operating the continuous digester for a time and at a temperature suitable to make dissolving grade pulp when the continuous digester is cooking organic fiber-containing material received from the vertical pressure vessel system, and for a time and at a temperature suitable to make paper grade pulp at other times.

28. The method of claim 22, wherein said further processing of the brownstock comprises:

screening and washing the brownstock after completion of cooking in the continuous digester;

bleaching the brownstock to produce a bleached pulp; and

drying the bleached pulp to produce either a paper grade pulp or a dissolving pulp.

29. A method for retrofitting a pulp mill originally configured to produce paper grade pulp via a continuous digester, and operating the pulp mill so that it produces dissolving pulp, comprising:

connecting a vertical pressure vessel system upstream from the continuous digester;

providing a mechanism to supply organic fiber-containing material to the vertical pressure vessel system;

supplying organic fiber-containing material to the vertical pressure vessel system;

performing pre-hydrolysis and neutralization in a batch mode using the vertical pressure vessel system;

conveying the organic fiber-containing material from the vertical pressure vessel system to the continuous digester;

performing kraft cooking with the continuous digester to produce a brownstock for dissolving pulp; and

further processing the brownstock to produce a dissolving pulp;

wherein either (1) the vertical pressure vessel system comprises a plurality of vessels for performing pre-hydrolysis and neutralization in a batch mode, and/or (2) the vertical pressure vessel system transfers organic fiber-containing material to a storage tank after pre-hydrolysis and neutralization to facilitate a steady flow thereof to the continuous digester.

30. The method of claim 29, further comprising:

providing a storage tank between the vertical pressure vessel system and the continuous digester;

transferring organic fiber-containing material from the vertical pressure vessel system to the storage tank after completion of pre-hydrolysis and neutralization for temporary storage to facilitate an uninterrupted supply to the continuous digester when making dissolving pulp; and

transferring the organic fiber-containing material from the storage tank to the continuous digester as needed for kraft cooking.