Production of ultra pure salt

Abstract

This invention relates to methods and installations for producing ultra pure sodium chloride salt crystals primarily for use in saturating depleted brine resulting from the electrolytic decomposition of saturated brine in chlor alkali membrane cells for the production of chlorine, caustic soda and hydrogen. More particularly, this invention relates to the production of ultra pure sodium chloride salt crystals by processing primary treated brine by first acidifying the primary treated brine, then stripping the carbonic acid produced by acidification as carbon dioxide, and then returning the brine to a pH of about 6 or higher which is sufficient for processing it in evaporation equipment where the ultra pure salt crystals are produced.

1 : An installation for processing primary treated brine to produce ultra pure salt containing below 500 parts per billion (ppb) of calcium and other multivalent metal ions, which comprises: 
 an acidification reactor for converting metal carbonates in the primary treated brine to carbon dioxide,    a stripper for removal of carbon dioxide generated during acidification,    a neutralization system returning the brine pH to a value above about 6 thereby avoiding metals corrosion,    and a concentrator for evaporating the neutralized stripped brine to produce the ultra pure salt.    
   
   
       2 : The installation of  claim 1  having means for removing entrained acidic brine droplets from the stripper vent gas.  
   
   
       3 : The installation of  claim 2  wherein a water scrubber is employed to remove the entrained brine droplets from the stripper vent gas.  
   
   
       4 : The installation of  claim 1  wherein the acidification reactor is a pipeline acidification reactor.  
   
   
       5 : The installation of  claim 1  wherein the concentrator is a mechanical vapor recompression evaporator.  
   
   
       6 : The installation of  claim 1  having means for removing carbon dioxide.  
   
   
       7 : The installation of  claim 6  wherein a stripper is employed to remove the carbon dioxide.  
   
   
       8 : The installation of  claim 1  wherein the equipment employed in the plant installation is free of fouling by precipitated multivalent metal compounds.  
   
   
       9 : The installation of  claim 1  wherein the ultra pure salt is fed to a membrane chlor alkali electrolytic cell plant to re-saturate depleted recycle brine.  
   
   
       10 : The installation of  claim 9  wherein the ultra pure salt is fed to a nearby membrane chlor alkali electrolytic cell plant thereby simplifying transport of the salt thereby avoiding contamination of the ultra pure salt.  
   
   
       11 : The installation of  claim 9  wherein the membrane chlor alkali electrolytic cell plant has a secondary brine treatment installation including a re-saturated brine filtration system and an ion exchange purification system.  
   
   
       12 : The installation of  claim 9  wherein the ultra pure salt fed to the membrane chlor alkali electrolytic cell plant permits the elimination of said plant's secondary brine treating system.  
   
   
       13 : The installation of  claim 9  wherein the ultra pure salt fed to the membrane chlor alkali electrolytic cell plant permits the elimination of said plant's neutralization and acid adjustment systems.