System and method for the removal of non-process elements from electrostatic precipitator ashes in a kraft pulp process
The present application relates to a system and a method for the removal of non-process elements, such as K + or Cl − , from electrostatic precipitator ashes in a kraft pulp process comprising the addition of a strong acid containing sulfur and CO 2 in separate steps in the ash treatment step.
1 . 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 second agitation means ( 2 ′);
c) in the second tank ( 5 ) with the second agitation means ( 2 ′), adding CO 2 to the slurry or saturated ash solution ( 4 ′) via a recirculation loop ( 6 ),
wherein the CO 2 added has a purity degree between 99.00 and 100.0% or a purity degree between 1.0 and 98.9%.
2 . The method of claim 1 , wherein the non-process elements are K + or Cl − .
3 . The method of claim 1 , wherein the a) and c) steps are performed at a temperature between 5° and 98° C., a pressure between 50 and 150 KPa, and between 10 and 1,000 minutes of residence time.
4 . The method of claim 1 , 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 + and Cl − from recovery boiler electrostatic precipitator ashes and water ( 9 ).
5 . The method of claim 4 , 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 ).
6 . The method of claim 4 , 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 ).
7 . The method of claim 4 , wherein between 0.01 and 0.50 kg of CO 2 is added per kg of dry ash ( 8 ).
8 . The method of claim 1 , wherein CO 2 is added as a gas, liquid, or solid phase.
9 . The method of claim 1 , wherein the initial pH of the slurry or saturated ash solution is above 10 and the pH after applying the method is between 8 and 9.