Maintenance of sulfur concentration in Kraft pulp processes
Methods and apparatus for maintaining sulfur concentration in the chemical recovery cycle of a Kraft pulping process. A portion of the recovery boiler ash is dissolved, treated to remove solids, and combined with an acid to provide a solution. The recovery boiler ash may be dissolved directly in the acid. The acid may be effluent from a chlorine dioxide generator. The resulting solution is maintained in a fully dissolved state and subjected to an acid separation step to provide a sodium sulfate enriched phase, which may be used to maintain sulfur concentration in the Kraft pulping process, and a sulfuric acid phase. Chlorine ions can be separated with the sulfuric acid phase. The sulfuric acid phase can be recycled to the chlorine dioxide generator.
1. A method for maintaining sulfur concentration in a Kraft pulping process, the method comprising the steps of:
collecting recovery boiler ash from a recovery boiler of a Kraft pulp mill;
dissolving a portion of the recovery boiler ash in acid;
treating the dissolved recovery boiler ash-acid solution to remove solids;
subjecting the treated solution to an acid separation step to provide a sodium sulfate enriched phase and an acid phase; and
using at least a portion of the sodium sulfate enriched phase to maintain sulfur concentration in the Kraft pulping process.
2. A method according to claim 1 , wherein the step of collecting recovery boiler ash comprises using an electrostatic precipitator to produce an electrostatic precipitator catch purge.
3. A method according to claim 2 , wherein the step of subjecting the solution to an acid separation step comprises separating chloride ions from the solution into the acid phase.
4. A method according to claim 2 , wherein the acid comprises effluent from a chlorine dioxide generator.
5. A method according to claim 2 , wherein the acid comprises sodium sesquisulfate.
6. A method according to claim 2 , wherein the acid separation system comprises a fixed-resin bed acid retardation unit.
7. A method according to claim 6 , wherein the acid separation system comprises a fixed-resin bed retardation unit comprising a particulate quaternary ammonium resin.
8. A method according to claim 2 , wherein the concentration of sodium sulphate in the solution is maintained below about 40 g per 100 g of water.
9. A method according to claim 2 , further comprising the step of providing the acid phase to the chlorine dioxide generator.
10. A method for maintaining sulfur concentration in a Kraft pulping process, the method comprising the steps of:
collecting recovery boiler ash from a recovery boiler of a Kraft pulp mill;
dissolving a portion of the recovery boiler ash;
treating the dissolved recovery boiler ash to remove solids;
combining the treated dissolved recovery boiler ash with acid to provide a solution;
maintaining the solution in a fully dissolved state;
subjecting the solution to an acid separation step to provide a sodium sulfate enriched phase and an acid phase; and
using at least a portion of the sodium sulfate enriched phase to maintain sulfur concentration in the Kraft pulping process.
11. A method according to claim 10 , wherein the step of dissolving a portion of the recovery boiler ash comprises dissolving the portion of the recovery boiler ash in water.