Method for displacement in batch digesters

Patent metadata

Field	Value
Publication number	US-9631317-B2
Application number	US-201514951520-A
Country	US
Kind code	B2
Filing date	Nov 25, 2015
Priority date	Nov 27, 2014
Publication date	Apr 25, 2017
Grant date	Apr 25, 2017

Abstract

The method is for producing pulp in batch digesters. More particularly, the method is for ending a treatment phase of the digester content. In order to obtain a more uniform pulp quality from the process is the treatment phase ended by displacing a liquor volume (WLP) through the digester vessel with an imposed increasing temperature in the displacement liquor added to digester.

First claim

I claim:

1. A method for ending a heated treatment phase in a displacement batch pulping process in a digester vessel, where the treatment phase has been done at a treatment temperature above 130° C., said digester having at least a bottom, a mid-point and a top liquid exchange position, the method initiated after the heated treatment phase and comprising the following steps;
adding a first displacement liquor to the bottom liquid exchange position while having a first lower temperature in the first displacement liquor at start of the displacement filling of a part of the digester with a first volume of the first displacement liquor, wherein the first lower temperature is more than 20° C. below the treatment temperature of the treatment phase;
continuing to add the same first displacement liquor to the bottom liquid exchange position while having a higher second temperature in the first displacement liquor in a later phase of the displacement filling at least a part of the digester with a total second volume of the first displacement liquor larger than the first volume; and
continuing the displacement with a final displacement liquor; and
the first lower temperature in the first displacement liquor is in a range 70-110° C.

2. The method according to claim 1 wherein the final displacement liquor is supplied and displaced until the content of the digester vessel is completely submerged under the total volume of the final displacement liquor added and wherein the first displacement liquor has been displaced from the digester via the top liquid exchange position.

3. The method according to claim 2 , wherein a circulation of the liquor is initiated after the digester vessel has been filled by the final displacement liquor.

4. The method according to claim 1 , wherein the proportion of the first volume of the first displacement liquor in relation to the total volume of the first displacement liquor is in a range 20-50%.

5. The method according to claim 3 , wherein the total volume of the first displacement liquor is in a range 50-75% of the free digester volume.

6. The method according to claim 1 , wherein the heated treatment phase is a prehydrolysis phase wherein the digester content is hydrolyzed at a temperature above 150° C.

7. A method for ending a heated treatment phase in a displacement batch pulping process in a digester vessel, where the treatment phase has been done at a treatment temperature above 130° C., said digester having at least a bottom, a mid-point and a top liquid exchange position, the method initiated after the heated treatment phase and comprising the following steps;
adding a first displacement liquor to the bottom liquid exchange position while having a first lower temperature in the first displacement liquor at start of the displacement filling of a part of the digester with a first volume of the first displacement liquor, wherein the first lower temperature is more than 20° C. below the treatment temperature of the treatment phase;
continuing to add the same first displacement liquor to the bottom liquid exchange position while having a higher second temperature in the first displacement liquor in a later phase of the displacement filling at least a part of the digester with a total second volume of the first displacement liquor larger than the first volume;
continuing the displacement with a final displacement liquor; and
wherein after adding the first displacement liquor with the higher second temperature and before the content of the digester vessel is completely submerged is the displacement continuing by adding the same first displacement liquor to the bottom liquid exchange position while having a third temperature higher than the second temperature in the displacement liquor in a later phase of the displacement filling a part of the digester with a total third volume of first displacement liquor larger than the total second volume.

8. The method according to claim 7 , wherein the temperature in the first displacement liquor increase is done in incremental steps in at least 3 and up to 10 steps during the displacement.

9. The method according to claim 7 , wherein the temperature increase in the first displacement liquor is done continuously during the displacement.

Assignees

• Valmet Oy

Inventors

• Kuusisto Petteri

Classifications

• D21C3/00 Primary

  Pulping cellulose-containing materials (digesters D21C7/00) · CPC title

• D21C1/00

  Pretreatment of the finely-divided materials before digesting (of waste paper D21C5/02) · CPC title

• D21C7/00

  Digesters · CPC title

• D21C7/12

  Devices for regulating or controlling · CPC title

• D21C3/26 Primary

  Multistage processes · CPC title