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

• US 9,574,302 B2
• Filed: 01/29/2015
• Issued: 02/21/2017
• Est. Priority Date: 04/08/2011
• Status: Active Grant

• Current Assignee: RGE Pte., Ltd. (RGE Capital Ltd.)
• Original Assignee: RGE Pte., Ltd. (RGE Capital Ltd.)
• Inventors: van Lee, Richard Constantine, Devanesan, Alagaratnam Joseph
• Primary Examiner(s): CALANDRA, ANTHONY J
• Application Number:
  US14/609,385
• Publication Number:
  US 20150204013A1
• Time in Patent Office: 754 Days
• US Class Current: 1/1
• 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 system for selectively producing pulp of different grades, comprising:

a continuous digester operable to selectively carry out kraft cooking of paper grade pulp or dissolving pulp;

a vertical pressure vessel upstream from said continuous digester and coupled to the continuous digester in a manner to allow contents of the vertical pressure vessel to be conveyed to the continuous digester for kraft cooking, said vertical pressure vessel operable to perform pre-hydrolysis and neutralization in a batch mode when the system is producing dissolving pulp but not utilized in connection with making paper grade pulp;

a source of neutralization fluid selectively connected to an intake of the vertical pressure vessel;

a source of cooking fluids suitable for kraft cooking selectively connected to an intake of the continuous digester;

a feeder and pre-treatment system operable to selectively supply organic fiber-containing material to the vertical pressure vessel when making dissolving pulp and to the continuous digester when making paper grade pulp; and

a storage tank interposed between the vertical pressure vessel and the continuous digester for storing treated chips that have been subject to pre-hydrolysis and neutralization in the vertical pressure vessel, to facilitate a steady flow of the treated chips to the continuous digester when making dissolving pulp.

2. The system of claim 1, wherein said vertical pressure vessel is provided as a retrofit addition to the continuous digester at an existing mill, and wherein the feeder and pre-treatment system diverts a normal flow of the organic fiber-containing material from the continuous digester to said vertical pressure vessel for pre-hydrolysis and neutralization prior to being conveyed to said continuous digester when making dissolving pulp.

3. The system of claim 1, wherein said feeder and pre-treatment system further comprises a chip feeder and conveyance system whereby organic fiber-containing material is selectively provided either to the continuous digester when making paper grade pulp or first to the vertical pressure vessel when making dissolving grade pulp.

4. The system of claim 3, wherein said continuous digester is selectively operated for a time and at a temperature suitable to make dissolving grade pulp when it is cooking fiber-containing material received from said vertical pressure vessel after pre-hydrolysis and neutralization, and for a time and at a temperature suitable to make paper grade pulp at other times.

5. The system of claim 4, further comprising, downstream from said continuous digester, a washing and screening station, a bleaching station, and a pulp drying station.

6. The system of claim 1, wherein said continuous digester is a single-vessel type continuous digester.

7. The system of claim 1, wherein said continuous digester is a multi-vessel type continuous digester.

8. The system of claim 1, wherein said vertical pressure vessel is steam pressurized in connection with a pre-hydrolysis step, and is filled with a combination of white liquor and black liquor in connection with a neutralization step.

9. The system of claim 8, wherein substantially all the white liquor and the black liquor used for neutralization are respectively produced in a mill'"'"'s recausticizing facility and pulp-washing facility.

10. The system of claim 1, further comprising a common recovery boiler utilized both when making paper grade pulp and dissolving grade pulp, wherein the operational capacity of the vertical pressure vessel system corresponds to an operational capacity of the recovery boiler.

11. A system for selectively producing pulp of different grades, comprising:

a continuous digester operable to selectively carry out kraft cooking of paper grade pulp or dissolving pulp;

a vertical pressure vessel system comprising one or more vertical pressure vessels upstream from said continuous digester and coupled to the continuous digester in a manner to allow contents of the one or more vertical pressure vessels to be conveyed to the continuous digester for kraft cooking, said one or more vertical pressure vessels operable to perform pre-hydrolysis and neutralization in a batch mode when the system is producing dissolving pulp but not utilized in connection with making paper grade pulp, and said vertical pressure vessel system having a capacity matched to that of the continuous digester, sufficient to provide pre-processed pulp to the continuous digester without interruption when making dissolving pulp;

a source of neutralization fluid selectively connected to an intake of each of the vertical pressure vessels; and

a feeder and pre-treatment system operable to selectively supply organic fiber-containing material to the one or more vertical pressure vessels when making dissolving pulp and to the continuous digester when making paper grade pulp.