Method and System for Treating Produced Water

Abstract

Embodiments of the present invention provide systems and methods for purifying produced water. The system comprises: a closed loop cation exchange unit, wherein the cation exchange unit comprises a cation resin bed; a closed loop anion exchange unit, wherein the anion exchange unit comprises an anion resin bed; an intermediate degasifer, wherein the cation exchange unit and the anion exchange unit are connected in series through the intermediate degasifier, wherein each of the exchange units further comprises a plurality of treatment zones, wherein the treatment zones comprise at least an adsorption zone, a rinse zone, a regeneration zone and a pulsing zone and a backwash zone; and a rinse tail outlet collector for collecting and removing the rinse fluids from the rinse zone.

We claim: 
     
         1 . A system for purification of produced water, the system comprising:
 a closed loop cation exchange unit, wherein the cation exchange unit comprises a cation resin bed;   a closed loop anion exchange unit, wherein the anion exchange unit comprises an anion resin bed;   an intermediate degasifer, wherein the cation exchange unit and the anion exchange unit are connected in series through the intermediate degasifier,   each of the exchange units further comprises a plurality of treatment zones, and wherein the treatment zones comprise at least an adsorption zone, a rinse zone, a regeneration zone and a pulsing zone and a backwash zone; and   a rinse tail outlet collector for collecting and removing the rinse fluids from the rinse zone,   wherein the rinse tail outlet collector is positioned within the rinse zone and above a caustic regenerant inlet distributor to prevent dilution of the caustic regenerant while the anion resin bed is rinsed,   wherein the rinse tail outlet collector and the caustic regenerant inlet distributor are located in a portion of the closed loop anion exchange unit where the resin moves upwardly,   wherein the rinse zone is positioned between the adsorption zone and the regeneration zone,   wherein a volume of the produced water is flowed through the adsorption zone of the cation exchange unit to remove cations comprising Na+ from the produced water and produce an acidic decationized effluent,   wherein, in the regeneration zone of the cation exchange unit, the cation resin bed is regenerated by contacting it with an acid regenerant,   wherein, in the degasifier, carbon dioxide gas is released from the acidic decationized effluent to produce an acidic degasified effluent,   wherein deionized treated water having a neutral pH is produced by flowing a volume of the acidic degasified effluent through the adsorption zone of the anion exchange unit,   wherein, in the regeneration zone of the anion exchange unit, the anion resin bed is regenerated by contacting it with a caustic regenerant, wherein the regenerated anion resin bed is rinsed in a two-stage process, comprising:
 i) in a first stage, piping a slip stream flow of the acidic degasified effluent through the rinse zone of the anion exchange unit; and 
 ii) in a second stage, passing a stream of the deionized treated water through the rinse zone of the anion exchange unit, and 
   wherein after the anion resin bed is regenerated, acidic degasified effluent and the deionized treated water which were used in the anion resin rinsing zone are collected and discharged through the rinse tail outlet collector as a rinse tail stream.   
     
     
         2 . The system according to  claim 1 , further comprising a feed tank, wherein the acidic degasified effluent is recycled from the rinse tail to the feed tank. 
     
     
         3 . The system according to  claim 1 , wherein the cation resin bed is regenerated by diverting a stream of the acidic degasified effluent for preventing the evolution of carbon dioxide gas within the cation resin bed. 
     
     
         4 . The system according to  claim 1 , wherein the acid regenerant is selected from the group consisting of HCl, H 2 SO 4 , HNO 3 , H 3 PO 4 , and H 2 CO 3 , citric acid, methane sulfonic acid acetic acid. 
     
     
         5 . The system according to  claim 1 , wherein the cation resin bed further comprises a strong acid cation resin bed. 
     
     
         6 . The system according to  claim 1 , wherein the anion resin bed further comprises a weak base anion resin bed. 
     
     
         7 . The system according to  claim 2 , wherein upon the condition that the produced water is pre-treated using reverse osmosis (RO) and a RO concentrate is produced, the RO concentrate in the feed tank, and wherein a sufficiently large volume of the deionized treated water is recycled internally to the feed tank to dilute the RO concentrate. 
     
     
         8 . The system according to  claim 7 , wherein the RO concentrate is diluted for mitigating an excessive evolution of carbon dioxide in the cation exchange unit. 
     
     
         9 . The system according to  claim 1 , wherein at least one of the anion exchange unit and the cation exchange unit operates with continuous counter-current flow. 
     
     
         10 . The system according to  claim 1 , wherein the produced water comprises elevated levels of total dissolved solids, Na+, carbonate and Cl −  ions. 
     
     
         11 . The system according to  claim 1 , wherein calcium salt is added to the deionized treated water to buffer it prior to discharge.