Method and arrangement for generating steam at a digester plant of a chemical pulp mill

Patent metadata

Field	Value
Publication number	US-10329713-B2
Application number	US-201515123949-A
Country	US
Kind code	B2
Filing date	Mar 4, 2015
Priority date	Mar 5, 2014
Publication date	Jun 25, 2019
Grant date	Jun 25, 2019

Abstract

The present invention relates to a method of producing steam at a digester plant of a chemical pulp mill. Black liquor is discharged from the digester at a first temperature and pressure. The black liquor is treated in a flash tank for generating flashed black liquor and flash steam at a second temperature and a second pressure, which are lower than the first temperature and pressure. The flashed black liquor is taken for further treatment to the evaporation plant. The flash steam is led to an indirect heat exchange contact with clean liquid in the reboiler for boiling the liquid and for generating steam. The steam is led from the reboiler into a fan or compressor for increasing the steam pressure to a third pressure, which is higher than the second pressure and for adjusting the pressure of the steam in the flash tank. Steam at a third pressure is used for pretreating comminuted cellulosic fiber material, such as chips, prior to cooking.

First claim

The invention claimed is:

1. A method for producing steam at a digester plant of a chemical pulp mill, the method comprises:
a) a suspension formed of pretreated comminuted cellulosic fiber material and liquid is fed into a digester for producing chemical pulp;
b) the pretreated comminuted cellulosic fiber material is treated in the digester with a treatment chemical for producing the chemical pulp and black liquor;
c) the black liquor is discharged from the digester at a first temperature and a first pressure;
d) the black liquor is treated in a flash tank which produces flashed black liquor and flash steam at a second temperature and a second pressure, which are lower than the first temperature and the first pressure;
e) the flashed black liquor is fed to an evaporation plant;
f) the flash steam is fed to a reboiler in which the flash steam is in indirect heat exchange contact with a clean liquid in the reboiler which boils the clean liquid and generates;
g) the steam formed in step f) is fed from the reboiler into a fan or compressor which increases a pressure of the steam to a third pressure, which is higher than the second pressure and regulates the second pressure of the steam in the flash tank in step d); and
h) the steam at the third pressure is applied to heat the comminuted cellulosic fiber material before the pretreated comminuted cellulosic fiber material is fed to the digester.

2. The method according to claim 1 , wherein in step g) the third pressure of the steam being discharged from the fan or compressor and the second pressure of the steam in the flash tank are adjusted according to a requirement for steam in the pretreatment of the comminuted cellulosic fiber material.

3. The method according to claim 1 , wherein the digester produces high kappa pulp.

4. The method according to claim 1 , wherein the temperature of the black liquor discharged from the digester is below 145° C.

5. An arrangement for producing steam at a digester plant of a chemical pulp mill, said arrangement comprising:
a vessel configured to steam a cellulosic fiber material;
a feed system in which a suspension of cellulosic fiber material and liquid is formed and the suspension is pressurized;
a continuous digester configured to digest the suspension, which digester is connected to a black liquor conduit configured to discharge the black liquor stream from the digester;
a flash tank connected to said black liquor conduit, and in which the pressure of the black liquor is decreased for producing flashed black liquor and flash steam, whereby the flash tank is provided with a conduit for discharging the flashed black liquor and feeding the flashed black liquor to an evaporation plant of the chemical pulp mill;
a flash steam conduit for feeding the flash steam from the flash tank to a reboiler, in which clean steam is generated due to an indirect heat exchange relationship with the flash steam and a clean liquid; and
a steam conduit for feeding the clean steam generated in the reboiler into the steaming vessel, whereby the steam conduit includes a fan or a compressor which increases a pressure of the clean steam generated in the reboiler.

6. The arrangement according to claim 5 , wherein the fan or compressor is connected to a pressure indicator controller which receives a pressure signal from a pressure sensor located in the flash tank.

7. The arrangement according to claim 5 , wherein at least one vessel for treating the suspension is arranged between the feed system and the digester.

8. A method to produce steam comprising:
feeding a suspension of pretreated comminuted cellulosic fiber material and liquid into a digester vessel in a chemical pulp mill;
adding a treatment chemical to the pretreated comminuted cellulosic fiber material in the digester vessel;
converting the pretreated comminuted cellulosic fiber material to pulp in the digester vessel, wherein the conversion produces black liquor;
discharging the black liquor form the digester vessel;
flashing the discharged black liquor in a flash tank and discharging from the flash tank flash steam and flashed black liquor;
feeding the flashed black liquor to an evaporation plant in the chemical pulp mill;
feeding the flash steam to a heat exchanger and transferring heat energy from the flash steam to vaporize a clean liquid to produce clean steam;
increasing the pressure of the clean steam to a pressure greater than a pressure of the flash steam when discharged from the flash tank, wherein the increase of the pressure of the clean steam is performed using a fan or centrifugal compressor and the amount of the increase in the pressure is based on a requirement for steam to pretreatment the comminuted cellulosic fiber material; and
after increasing the pressure of the clean steam, pretreating comminuted cellulosic fiber material with the clean steam to produce the pretreated comminuted cellulosic fiber material fed to the digester vessel.

9. The method of claim 8 wherein the heat exchanger is included with a reboiler and the reboiler transfers heat to contribute to the vaporization of the clean liquid.

10. The method of claim 9 wherein the reboiler is a falling film tube reboiler.

11. The method of claim 8 wherein the steps of the method are performed continuously.

12. The method of claim 8 further comprising applying suction from a fan to a clean steam discharge port of the heat exchanger to draw the clean steam from the heat exchanger.

13. The method of claim 8 wherein the digester vessel is a continuous digester vessel.

14. The method of claim 8 further comprising regulating the pressure of the flashed steam in the flash tank.

15. The method of claim 8 further comprising controlling the fan or centrifugal compressor based on information indicating a pressure of the flashed steam in the flash tank, wherein the information indicating the pressure is provided by a pressure indicator controller which receives a signal from a pressure sensor located in the flash tank.

Assignees

• Andritz Oy

Inventors

• Engstrom Johan
• KETONEN Paivi
• Koistinen Peter

Classifications

• D21C7/14

  Means for circulating the lye · CPC title

• D21C7/10

  Heating devices · CPC title

• D21C1/02

  with water or steam · CPC title

• D21C11/0042 Primary

  Fractionating or concentration of spent liquors by special methods (concentration by evaporation D21C11/10) · CPC title

• D21C11/10

  Concentrating spent liquor by evaporation (evaporators B01D) · CPC title