SELECTIVE REMOVAL OF K+ AND CL- FROM RECOVERY BOILER ELECTROSTATIC PRECIPITATOR ASHES IN A KRAFT PROCESS

Abstract

The present application discloses an alternative method for selective removal of K.sup.+ and Cl.sup. from recovery boiler electrostatic precipitator ashes in a kraft-pulp process through the use of pure or impure CO.sub.2, complemented or not with a mineral acid, for instance Sulfuric Acid/Spent Acid.

Claims

1. Method for a selective removal of K.sup.+ and Cl.sup. from recovery boiler Electrostatic Precipitator Ashes in a kraft process comprising introducing CO.sub.2 pure or impure in the ash treatment step wherein: a pump and a Static Mixer is used to react the CO.sub.2 pure with the ash solution or slurry so as to lower pH and which will partially convert the solution or slurry carbonates into bicarbonates; or a Self-Aspirating Turbine to react the CO.sub.2 impure with the ash solution or slurry so as to lower pH and which will partially convert the solution or slurry carbonates into bicarbonates.

2. The method according to claim 1, wherein is used a mixture of a mineral acid with the CO.sub.2.

3. The method according to claim 2, wherein the mineral acid is selected from sulfuric acid, hydrochloric acid, or Spent Acid.

4. The method according to claim 3, wherein the mixtures of mineral acids are used together with CO.sub.2 in which CO.sub.2 is injected as gas, liquid or solid phase in order to react with the ash solution or slurry, at a temperature between 15-95 C. and a pressure between 0-10 atm(abs).

5. The method according to claim 4, wherein is applied a purge in the reactor, when is used a self-aspirating turbine to react CO.sub.2 impure.

6. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0068] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of invention.

[0069] FIG. 1: Diagram representing the typical curves for the concentration of H.sub.2CO.sub.3, HCO.sub.3.sup. and CO.sub.3.sup.2 according to the pH.

[0070] FIG. 2: Representation of a basic process scheme for selective removal of K.sup.+ and Cl.sup. from recovery boiler Electrostatic Precipitator ash.

[0071] FIG. 3: Selective removal of K.sup.+ and Cl.sup.: Ash dissolving tank/ash Leaching tank: Representation of the utilization of a pump and a Static Mixer to react the CO.sub.2 with the slurry so as to lower pH and which will partially convert the solution or slurry carbonates into bicarbonates. A recirculation loop with a pump and a static mixer is used to dose pure CO.sub.2 in order to convert the ash carbonates into bicarbonates.

[0072] FIG. 4: Selective removal of K.sup.+ and Cl.sup.: Ash dissolving tank/ash Leaching tank: Representation of the utilization of a Self-Aspirating Turbine to react the CO.sub.2 with the slurry so as to lower pH and which will partially convert the solution or slurry carbonates into bicarbonates. The self-aspirating turbine is more suitable to be used with an impure gas since it allows the purge of the inert gases coming with the impure CO.sub.2 from the headspace of the reactor.

[0073] FIG. 5: Selective removal of K.sup.+ and Cl.sup. by Metso Ash Leaching, with the incorporation of a CO.sub.2 stream, wherein the CO.sub.2 could be either pure or impure.

[0074] FIG. 6: Selective removal of K.sup.+ and Cl.sup. by HPD CRP crystallisation process, with the incorporation of a CO.sub.2 stream, wherein the CO.sub.2 could be either pure or impure.

[0075] FIG. 7: Selective removal of K.sup.+ and Cl.sup. by Mitsubishi MPR Freeze Crystallisation process, with the incorporation of a CO.sub.2 stream, wherein the CO.sub.2 could be either pure or impure.

[0076] FIG. 8: Selective removal of K.sup.+ and Cl.sup. by EKA PDR evaporation crystallisation process, with the incorporation of a CO.sub.2 stream, wherein the CO.sub.2 could be either pure or impure.

[0077] FIG. 9: Selective removal of K.sup.+ and Cl.sup. by ANDRITZ ARC evaporation crystallisation process, with the incorporation of a CO.sub.2 stream, wherein the CO.sub.2 could be either pure or impure.

[0078] The technology is of course not in any way restricted to the embodiments described herein and a person of ordinary skill in the area can provide many possibilities to modifications thereof as defined in the claims.

[0079] The preferred embodiments described above are obviously combinable. The following dependent claims define further preferred embodiments of the disclosed technology.

[0080] Lisbon, Jul. 18, 2016