Purification of produced water from coal seam natural gas wells using ion exchange and reverse osmosis

Abstract

A method and apparatus are provided for treating produced water to lower the total dissolved solids of the water for safe discharge to the environment. The produced water is passed through a weak acid cation resin in H + form to remove cations in the produced water and then preferably through a decarbonator to remove formed CO 2 and to provide a first discharge stream. The cation loaded resin is then regenerated using a dilute acid, preferably diluted with produced water, to regenerate the resin to the H + form. The resultant acid regenerated waste stream is discharged to a reject deep well. The acid regenerated resin is then rinsed, preferably with produced water, to remove residual salts to form a residual salt containing rinse stream. This salt stream is passed into a reverse osmosis unit to form a high salt containing reject stream which is discharged to a waste deep well and a low salt containing product discharge stream which may be safely discharged to the environment.

1 . A method for treating produced water to lower the total dissolved solids (TDS) of the water for safe environmental discharge comprising the steps of: 
 passing the produced water through a cation exchange resin in a H +  form to    remove cations and form a first discharge stream and a solids loaded resin;    discharging the first discharge stream to the environment;    regenerating the solids loaded resin to a H +  form with a dilute acid solution to remove solids from the solids loaded resin into the dilute acid stream forming an acid regenerated waste stream and an acid regenerated resin;    rejecting the acid regenerated waste stream to a deep well or environmentally safe reject site;    rinsing the acid regenerated resin with water to remove residual salts from the acid regenerated resin forming a residual salt containing rinse stream;    passing the residual salt containing rinse stream into a salt separation unit forming a high salt containing reject stream and a low salt containing product discharge water stream;    rejecting the high salt containing reject stream to a deep well or other environmentally safe reject site; and    discharging the low salt containing product water discharge stream to the environment.    
     
     
         2 . The method of  claim 1  wherein the produced water passed through the cation exchange resin forms a reduced dissolved solids produced water stream which stream is passed through a mixer with air to remove CO 2  gases forming the first discharge stream.  
     
     
         3 . The method of  claim 1  wherein the cation resin is a weak acid cation resin.  
     
     
         4 . The method of  claim 1  wherein the dilute acid solution is a H 2 SO 4  solution diluted with produced water.  
     
     
         5 . The method of  claim 1  wherein the salt separation unit is a reverse osmosis unit.  
     
     
         6 . An apparatus for treating produced water to lower the total dissolved solids of the water for safe environmental discharge comprising: 
 a resin held in a tank or other container for contacting produced water to remove cations and form a first discharge stream for discharge to the environment and a solids loaded resin;    means for adding an acid to the solids loaded resin forming an acid regenerated resin and an acid regenerated waste stream, which waste stream is discharged to a deep well or other environmentally safe reject site;    means for adding rinse water to the acid regenerated resin to form a residual salt containing rinse stream; and    a salt separation unit to treat the residual salt containing rinse stream to form a high salt containing reject stream for discharge to a deep well or other environmentally safe reject site and a low salt containing product water discharge stream for discharge to the environment.    
     
     
         7 . The apparatus of  claim 6  further containing a mixing device for mixing the first discharge stream with air to remove dissolved gases in the first discharge stream.  
     
     
         8 . The apparatus of  claim 6  wherein the salt separation unit is a reverse osmosis unit.