Method for leaching recovery-boiler ash

Patent metadata

Field	Value
Publication number	US-9719209-B2
Application number	US-201314442165-A
Country	US
Kind code	B2
Filing date	Nov 15, 2013
Priority date	Nov 16, 2012
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

A method to be used in conjunction with a single-stage or multi-stage process for leaching ash originating from the recovery boiler of a pulp mill, particularly when the ash contains a significant amount of carbonate, wherein calcium compounds, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH) 2 ), are employed as additives in one or more leaching stages, a liquid fraction formed in the leaching process is utilized outside the main chemical recovery cycle, such as a substitute for purchased sodium hydroxide in the bleaching line of the pulp mill, and a solids fraction may be mixed with a black-liquor stream of the mill or subjected to further processing to separate calcium compounds for recycle.

First claim

The invention claimed is:

1. A method for treating ash of a recovery boiler of a pulp mill comprising:
performing a single-stage or multi-stage leaching process in which at least one calcium compound is added as an additive to the ash from the recovery boiler in one or more leaching stages, and wherein the at least one calcium compound added is calcium oxide or calcium hydroxide.

2. The method as in claim 1 , wherein both the calcium oxide and the calcium hydroxide are added as the additive to the ash.

3. The method as in claim 1 , further comprising utilizing one or more liquid-fraction streams exiting the single-stage or the multi-stage leaching process outside of a main chemical recovery cycle of the pulp mill.

4. The method as in claim 3 , further comprising utilizing hydroxide ion contained in the one or more liquid-fraction streams.

5. The method as in claim 4 , further comprising utilizing the hydroxide ion in a bleaching line of the pulp mill.

6. The method as in claim 1 , further comprising mixing one or more solids-fraction streams exiting the single-stage or the multi-stage leaching process with black liquor in the pulp mill.

7. The method as in claim 1 , further comprising:
feeding one or more solids-fraction streams exiting the single-stage or the multi-stage leaching process to a dissolving stage,
dissolving in the dissolving stage compounds of the one or more solids-fraction streams in water or an aqueous solution,
after the one or more solids-fraction streams flow through the dissolving stage, separating the streams into solids and a liquid fraction, wherein the separated solids include at least one of calcium carbonate and calcium hydroxide,
feeding the separated solids to a calcium cycle of the pulp mill, and
adding the liquid fraction to black liquor in the pulp mill.

8. A method to treating ash from a recovery boiler comprising:
adding at least one of calcium oxide and calcium hydroxide to the ash;
leaching the ash after or during the addition of the at least one of calcium oxide and calcium hydroxide, and
separating a solid fraction from the leached ash.

9. The method of claim 8 wherein an amount of the at least one calcium oxide and calcium hydroxide added to the ash is greater than an amount of H 2 SO 4 added to the ash.

10. The method of claim 8 further comprising separating a liquid from the leaching of the ash and utilizing the separated liquid outside of a chemical recovery cycle in a pulp mill.

11. The method of claim 10 further comprising utilizing a hydroxide ion contained in the separated liquid.

12. The method of claim 11 further comprising adding the hydroxide ion to a bleaching line in the pulp mill.

13. The method of claim 8 further comprising separating solids from the leached ash and mixing the solids with black liquor in a pulp mill.

14. The method of claim 8 wherein the leaching of the ash is performed in a multi-stage leaching process.

15. The method of claim 8 further comprising:
forming a solids-fraction stream from the leached ash;
dissolving compounds of sodium or potassium from the solids-fraction stream in a water or an aqueous solution;
separating solids and liquids from the solids-fraction stream after the dissolving step;
feeding the separated solids to a calcium cycle of a pulp mill, and
adding the separated liquids to black liquor in the pulp mill.

16. The method of claim 8 further comprising separating a liquid fraction from the leached ash and feeding at least a portion of the liquid fraction to the leaching step.

17. The method of claim 16 further comprising feeding another portion of the liquid fraction to a bleaching process in a pulp mill.

Assignees

• Andritz Oy

Inventors

• Mckeough Paterson

Classifications

• D21C11/0064

  Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor · CPC title

• D21C11/0007 Primary

  Recovery of by-products, i.e. compounds other than those necessary for pulping, for multiple uses or not otherwise provided for (volatile compounds obtained by decomposition of spent liquors in order to regenerate them D21C11/125; compounds obtained by fractionating the liquors in order to regenerate them D21C11/0042) · CPC title

• C22B7/007

  by acid leaching · CPC title

• C22B26/10

  Obtaining alkali metals · CPC title

• D21C11/12

  Combustion of pulp liquors · CPC title