SYSTEM AND METHOD FOR THE REMOVAL OF NON-PROCESS ELEMENTS FROM ELECTROSTATIC PRECIPITATOR ASHES IN A KRAFT PULP PROCESS

Abstract

The present application relates to a system and a method for the removal of non-process elements, such as K.sup.+ or Cl.sup.?, from electrostatic precipitator ashes in a kraft pulp process comprising the addition of a strong acid containing sulfur and CO.sub.2 in separate steps in the ash treatment step.

Claims

1. A system for removal of non-process elements from electrostatic precipitator ashes in a kraft pulp process with an ash treatment step, the system comprising: a first tank (1) comprising agitation means (2), which is fluidly connected to a second tank (5) comprising agitation means (2); the second tank (5) comprises a recirculation loop (6), wherein the recirculation loop (6) comprises pipes (6.1), at least one pump (6.2), a CO.sub.2 injection line (6.3) and mixing means (6.4).

2. The system of claim 1, wherein the first tank (1) comprises a recirculation loop (11) that comprises pipes (11.1), at least one pump (11.2), a strong acid containing sulfur injection line (11.3) and mixing means (11.4).

3. The system of claim 1, wherein the mixing means (6.4) and (11.4) are selected from a static mixer or a venturi mixer.

4. The system of claim 1, wherein the first tank (1) comprises a vent to the atmosphere (10).

5. A method for removal of non-process elements from electrostatic precipitator ashes in a kraft pulp process with an ash treatment step, the method comprising the following steps: a). in a first tank (1) with agitation means (2), adding a strong acid containing sulfur to a slurry or saturated ash solution (4) to lower its pH between 8 and 10; b). transferring the slurry or saturated ash solution resulting from the previous step (4) to a second tank (5) with agitation means (2); c). in the second tank (5) with agitation means (2), adding CO.sub.2 to the slurry or saturated ash solution (4) via a recirculation loop (6).

6. The method of claim 5, wherein the non-process elements are K.sup.+ or Cl.sup.?.

7. The method of claim 5, wherein the a) and c) steps are performed at a temperature between 50 and 98? C., a pressure between 50 and 150 KPa, and between 10 and 1000 minutes of residence time.

8. The method of claim 5, wherein the slurry or saturated ash solution (4) is obtained by mixing dry ash (8) with water or black liquor evaporation condensate, or with filtrate coming from a previous selective removal of K.sup.+ and Cl.sup.? from recovery boiler electrofilter ashes and water (9).

9. The method of claim 5, wherein between 1 to 2 kg of filtrate and water are added per kg of dry ash (8) to produce the slurry or saturated ash solution (4).

10. The method of claim 5, wherein the strong acid containing sulfur is added in a concentration up to 500 kg of strong acid containing sulfur/ton of dry ash (8).

11. The method of claim 5, wherein between 0.01 and 0.50 kg of CO.sub.2 is added per kg of dry ash (8).

12. The method of claim 5, wherein the CO.sub.2 added has a purity degree between 99.00 and 100.0%.

13. The method of claim 5, wherein the CO.sub.2 added has a purity degree between 1.0 and 98.9%.

14. The method of claim 5, wherein CO.sub.2 is added as a gas, liquid, or solid phase.

15. The method of claim 5, wherein the initial pH of the slurry or saturated ash solution is above 10 and the pH after applying the method is below 9.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0043] For easier understanding of this application, figures are attached in the annex that represent the preferred forms of implementation which nevertheless are not intended to be limiting of the invention, in which:

[0044] FIG. 1 shows a schematic representation of a first embodiment of the present invention; and

[0045] FIG. 2 shows a schematic representation of a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0046] Now, preferred embodiments of the present application will be described in detail with reference to the annexed drawings. However, they are not intended to limit the scope of this application.

[0047] The present application relates to a system and a method for the removal of non-process elements, such as K.sup.+ or Cl.sup.?, from electrostatic precipitator ashes in a kraft pulp process with an ash treatment step.

[0048] The present system and method are suitable for a kraft process system, which comprises an electrostatic precipitator, recovery boiler and at least one tank with agitation where dry ash is added to water (wherein water can be condensate from the evaporation of Black Liquor), or that comprises a filtrate obtained from a previous selective removal of K.sup.+ and Cl.sup.? from recovery boiler electrofilter ashes, this being the first tank (1) of the presently disclosed system, in order to obtain a slurry or saturated ash solution to be further processed through the method of the present application.

[0049] FIG. 1 shows the system for the removal of non-process elements from electrostatic precipitator ashes in a kraft pulp process with an ash treatment step.

[0050] The system comprises a first tank (1) comprising agitation means (2), which is fluidly connected to a second tank (5) comprising agitation means (2), and wherein the second tank (5) comprises a recirculation loop (6).

[0051] In one embodiment, the recirculation loop (6) comprises pipes (6.1), at least one pump (6.2), a CO.sub.2 injection line (6.3) and mixing means (6.4).

[0052] The recirculation loop (6) has the purpose of adding and mixing CO.sub.2 with the slurry or saturated ash solution (4) of the second tank (5).

[0053] The mixing means (6.4) are selected from, but not limited to, a static mixer, a venturi mixer, or any other mixing means suitable for the purpose.

[0054] In one embodiment, as shown in FIG. 2, the strong acid containing sulfur (3) is added directly to the first tank (1).

[0055] In one embodiment, as shown in FIG. 2, the first tank (1) comprises a recirculation loop (11) for the addition of the strong acid containing sulfur. The recirculation loop (11) comprising pipes (11.1), at least one pump (11.2), a strong acid containing sulfur injection line (11.3) and mixing means (11.4). The mixing means (11.4) are selected from, but not limited to, a static mixer, a venturi mixer, or any other mixing means suitable for the purpose. The strong acid containing sulfur added via a recirculation loop (11) allows the slurry or saturated ash solution to passed through the mixing means to eliminate any short circuit in the addition of the strong acid containing sulfur and will cause the strong acid containing sulfur to only react in the first tank (1) with agitation means (2).

[0056] In one embodiment, the first tank (1) comprises a vent to the atmosphere (10).

[0057] The method for the removal of non-process elements from electrostatic precipitator ashes in a kraft pulp process with an ash treatment step, comprises the following steps: [0058] A first reaction step performed in a first tank (1) with agitation means (2) wherein a strong acid containing sulfur is added to a slurry or saturated ash solution (4) to lower its pH between 8 and 10; [0059] The slurry or saturated ash solution resulting from the previous step (4) is transferred to a second tank (5) with agitation means (2); [0060] A second reaction step performed in the second tank (5) with agitation means (2) wherein CO.sub.2 is added to the slurry or saturated ash solution (4) via a recirculation loop (6).

[0061] The recirculation loop (6) circulates the slurry or saturated ash solution (4) from the second tank (2) to the mixing means (6.4) to mix CO.sub.2 with the slurry or saturated ash solution (4) and circulate the resulting mixture back into the second tank (2).

[0062] In one embodiment, the strong acid containing sulfur is added to a slurry or saturated ash solution (4) via a recirculation loop (11). The recirculation loop (11) circulates the slurry or saturated ash solution (4) from the first tank (1) to the mixing means (11.4) to mix the strong acid containing sulfur with the slurry or saturated ash solution (4) and circulate the resulting mixture back into the first tank (1), as shown in FIG. 2.

[0063] In one embodiment, the first and second reaction steps are performed at a temperature between 50 and 98? C., a pressure between 50 and 150 KPa, and between 10 and 1000 minutes of residence time.

[0064] In one embodiment, the slurry or saturated ash solution (4) is obtained by mixing dry ash (8) with water or with filtrate coming from a previous selective removal of K.sup.+ and Cl from recovery boiler electrofilter ashes and water (9), optionally this water is condensate from the black liquor evaporation plant.

[0065] In one embodiment, between 1 to 2 kg of filtrate and water are added per kg of dry ash in order to produce slurry or saturated ash solution (4).

[0066] In one embodiment, the strong acid containing sulfur is selected from, but not limited to, sulfuric acid and/or spent acid. In one embodiment, the spent acid is obtained from a chlorine dioxide plant. In one embodiment, the strong acid containing sulfur is added in a concentration up to 500 kg of strong acid containing sulfur/ton of dry ash.

[0067] In one embodiment, pure CO.sub.2 is added in the method with a purity degree between 99.00 and 100.0%. In another embodiment, impure CO.sub.2 is added in the method with a purity degree between 1.0 and 98.9%.

[0068] In one embodiment, CO.sub.2 is added in the method as a gas, liquid, or solid phase. In one embodiment, between 0.01 and 0.50 kg of CO.sub.2 is added per kg of dry ash.

[0069] In one embodiment, the initial (i.e., pre-method) pH of the slurry or saturated ash solution is above 10. In another embodiment, the pH of the slurry or saturated ash solution is below 9 after applying the method of the present application.

[0070] The presently disclosed method is preferably performed in the presently disclosed system.

Experimental Trials

[0071] In trials of the presently disclosed method, the initial situation of the pulp mill sulfidity was high and above the quality specifications for pulp production due to the sole use of strong acids, such as spent acid from ClO.sub.2 installation and sulphuric acid.

[0072] After treatment with the presently disclosed method, the levels of sulfidity returned to normal values and the removal efficiencies of K.sup.+ and Cl.sup.? were considered normal.

[0073] This description is of course not in any way restricted to the forms of implementation presented herein and any person with an average knowledge of the area can provide many possibilities for modification thereof without departing from the general idea as defined by the claims. The preferred forms of implementation described above can obviously be combined with each other. The following claims further define the preferred forms of implementation.

[0074] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0075] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0076] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of comprising. Comprising is defined herein as necessarily encompassing the more limited transitional terms consisting essentially of and consisting of; comprising may therefore be replaced by consisting essentially of or consisting of and remain within the expressly defined scope of comprising.

[0077] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0078] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0079] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. Any and all ranges recited herein are inclusive of their endpoints (i.e., x=1 to 4 or x ranges from 1 to 4 includes x=1, x=4, and x=any number in between), irrespective of whether the term inclusively is used.

[0080] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.