Method and apparatus for obtaining strong white liquor and lime mud with low residual alkali level

Patent metadata

Field	Value
Publication number	US-10011947-B2
Application number	US-201214412822-A
Country	US
Kind code	B2
Filing date	Jul 9, 2012
Priority date	Jul 9, 2012
Publication date	Jul 3, 2018
Grant date	Jul 3, 2018

Abstract

The method and apparatus are for obtaining strong white liquor and lime mud with low residual alkali content from causticized liquor. The first filter (F WL ) receives causticized liquor from causticizing vessels (CT 1 -CT 2 -CT 3 ) and is designed as pressurized two stage disc filter with 2 separate vat parts. In the first vat part non-diluted white liquor is obtained as a filtrate from the causticized liquor. The first lime mud cake accumulated on the filter discs in the first vat part is scraped off and diluted before being fed to the second vat part. In the second vat part weak liquor is obtained as a filtrate from the re-slurried first lime mud cake. The second lime mud cake accumulated on the filter discs in the second vat part is washed before being scraped off and diluted before being fed to subsequent lime mud handling.

First claim

We claim:

1. A method of extracting strong white liquor and lime mud with low residual alkali content from causticized liquor emanating from causticizing vessels in the recovery process of a pulp mill, comprising the following steps in sequence:
adding burnt lime to green liquor to start a causticizing reaction to produce a causticized liquor;
feeding the causticized liquor to a first part of a vat of a pressurized disc filter wherein the first part of the vat has a first set of filter discs and a separate first filtrate reception system, thereafter
extracting strong white liquor from the causticized liquor in the first filtrate reception system by passing the liquid part of the causticized liquor through filter media of the first set of filter discs, while collecting the residual lime particles of the causticized liquor as a first lime cake on the face of the filter media of the first set of filter discs and using no wash water on the formed first lime cake on the filter media, thereafter
scraping off at least a part of the first lime cake from the face of the filter media on the first set of filter discs, wherein the dry matter content of the scraped off first lime cake is higher than 50 wt-% and collecting the scraped off first lime cake in a first lime cake collection system while diluting the scraped off first lime cake with a suitable low alkali liquid to a dry matter content of the diluted first lime cake slurry less than 25 wt-%;
feeding at least a part of the diluted first lime cake slurry to a second part of the vat of the pressurized disc filter wherein the second part has a second set of filter discs and a separate second filtrate reception system, thereafter
extracting weak white liquor from the diluted first lime cake slurry in the second filtrate reception system by passing the liquid part of the diluted first lime cake slurry through filter media of the second set of filter discs, while collecting the residual lime particles of the diluted first lime cake slurry as a second lime cake on the face of the filter media of the second set of filter discs and using wash water on the formed second lime cake on the filter media in order to displace residual alkali in said second lime cake, thereafter
scraping off at least a part of the second lime cake from the face of the filter media on the second set of filter discs, wherein the dry matter content of the scraped off second lime cake is higher than 50 wt-% and collecting the scraped off second lime cake in a second lime cake collection system while diluting the scraped off second lime cake with a low alkali liquid to a dry matter content of the diluted second lime cake less than 25 wt-% and passing the diluted second lime cake slurry to at least one lime mud thickening stage before feeding the thickened lime mud to a lime kiln.

2. A method according to claim 1 , wherein the method further comprises pressurizing the pressurized disc filter with at least 0.7 bar above atmospheric pressure in both the first and second vat part.

3. A method according to claim 2 , wherein the method further comprises pressurizing the pressurized disc filter with at least 1.0 bar above atmospheric pressure in both the first and second vat part.

4. A method according to claim 3 , wherein the method further comprises providing the pressurized disc filter with a number of filter discs in the first set of filter discs greater than the number of filter discs in the second set of filter discs.

5. A method according to claim 3 , wherein the method further comprises establishing a level of the causticized liquor in the first vat part that is higher than the level of diluted first lime cake slurry in the second vat part, thus obtaining a height difference (ΔH) between liquid surfaces in first and second vat part.

6. A method according to claim 3 , wherein the method further comprises using the extracted weak white liquor from the diluted first lime cake slurry as at least part of the suitable low alkali liquid used as dilution liquid diluting the scraped off first lime cake.

7. A method according to claim 3 , wherein the method further comprises feeding a part of the diluted first lime cake slurry to a subsequent lime mud thickening stage before feeding the thickened lime mud to a lime kiln.

Assignees

• Ingelman Magnus
• Hogebrandt Eva
• Jansson Roger
• Valmet Oy

Inventors

• Ingelman Magnus
• Hogebrandt Eva
• Jansson Roger

Classifications

• Y02P40/40

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

• D21C11/00

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

• Y02P40/44

  Cross-Sectional Technologies · mapped topic

• B01D33/21 Primary

  with hollow filtering discs transversely mounted on a hollow rotary shaft · CPC title

• D21C11/04 Primary

  of alkali lye · CPC title