Method, apparatus and system for desalinating saltwater

Abstract

An apparatus, method and plant for desalinating saltwater and contaminated saltwater. The apparatus includes a stack and a manifolding assembly. The stack includes a product chamber, a first and second concentrate chamber, an anion exchange membrane forming a boundary between the first concentrate chamber and the product chamber and a cation exchange membrane forming a boundary between the second concentrate chamber and the product chamber. The manifolding assembly includes product and concentrate manifolding fluidly coupled to the product and concentrate chambers respectively, to convey a saltwater being desalinated to and away from the product chamber, and a concentrate to and away from the concentrate chambers. The stack may include a diluent chamber and adjacent anion or cation exchange membranes between the product chamber, diluent chamber and concentrate chamber to respectively convey anions or cations across multiple chambers.

We claim: 
     
         1 . A method of reducing salinity of a product in a stack comprising:
 (a) flowing a product feed through a first product chamber in the stack, the first product chamber having a first anion exchange membrane on one side of and in ionic communication with the first product chamber and a first cation exchange membrane on another side of and in ionic communication with the first product chamber;   (b) flowing a concentrate feed through a first concentrate chamber in the stack in ionic communication with the first anion exchange membrane;   (c) flowing the concentrate feed through a second concentrate chamber in the stack in ionic communication with the first cation exchange membrane;   (d) flowing an electrolyte through a first and second electrolyte chamber in the stack, the first electrolyte chamber bounded on one side by and in ionic communication with a first stack end cation exchange membrane and on another side by and in electrical communication with a first electrode, the second electrolyte chamber bounded on one side by and in ionic communication with a second stack end cation exchange membrane and on another side by and in electrical communication with a second electrode;   (e) flowing a rinse solution through a first and second rinse chamber in the stack, the first rinse chamber bounded on one side by and in ionic communication with a first stack end anion exchange membrane and on another side by and in ionic communication with the first stack end cation exchange membrane, the second rinse chamber bounded on one side by and in ionic communication with a second stack end anion exchange membrane and on another side by and in ionic communication with the second stack end cation exchange membrane; and   (f) applying a voltage across the stack to force anions and cations respectively across the first anion and exchange membrane and the first cation exchange membrane from the product feed to the concentrate feed, thereby producing a product output with a reduced salinity relative to the product feed and a concentrate output with an increased salinity relative to the concentrate feed,   wherein the rinse solution consists of a conductive non-scaling aqueous salt to minimize transfer of scaling cations from the rinse solution to the electrolyte.   
     
     
         2 . The method of  claim 1  further comprising flowing the product feed through a second product chamber in the stack having a second anion exchange membrane on one side of and in ionic communication with the second product chamber and a second cation exchange membrane on another side of and in ionic communication with the second product chamber, the second anion exchange membrane being in ionic communication with the second concentrate chamber or the second cation exchange membrane being in ionic communication with the first concentrate chamber, such that first or second concentrate chamber positioned between the first and second product chambers receives anions from one of the first or second product chambers and cations from another of the first or second product chambers. 
     
     
         3 . The method of  claim 2  further comprising periodically switching the direction of migration of anions and cations from the product feed to the concentrate feed to descale the anion and cation exchange membranes by switching flow direction between:
 (a) a forward flow direction comprising:
 (i) flowing the product feed through the first and second product chambers; and 
 (ii) flowing the concentrate feed through the first and second concentrate chambers
 (b) a reverse flow direction comprising: 
 
 (i) flowing the product feed through the first and second concentrate chambers; and 
 (ii) flowing the concentrate feed through the first and second product chambers, 
 
 and switching the voltage between a forward polarity direction and a reverse polarity direction simultaneously with switching the flow direction between the forward and reverse flow directions respectively. 
 
     
     
         4 . The method of  claim 1 , wherein the aqueous salt is sodium chloride. 
     
     
         5 . The method of  claim 1  further comprising flowing a cleaning solution through the stack during a cleaning cycle. 
     
     
         6 . The method of  claim 5 , wherein the cleaning cycle is initiated at system shut down. 
     
     
         7 . The method of  claim 5  further comprising calculating system resistance and flowing the cleaning solution through the stack at a threshold resistance. 
     
     
         8 . The method of  claim 7 , wherein the system resistance comprises at least one of hydraulic resistance of solutions flowing through the stack and electrochemical resistance of the anion and cation exchange membranes in the stack. 
     
     
         9 . The method of  claim 8 , wherein the hydraulic resistance and the electrochemical resistance are calculated from information obtained by one or more sensors or transducers in the stack or in a manifolding assembly conveying solutions to and away from the stack. 
     
     
         10 . The method of  claim 7 , wherein the cleaning cycle comprises a slug wash comprising flowing a slug of the cleaning solution through the stack at the threshold resistance. 
     
     
         11 . The method of  claim 7 , wherein the cleaning cycle comprises a stack wash comprising flowing the cleaning solution through the stack for a set period of time at the threshold resistance. 
     
     
         12 . The method of  claim 7 , wherein the cleaning cycle comprises a stack chemical clean comprising flowing the cleaning solution through the stack for a set period of time at the threshold resistance, wherein the cleaning solution comprises a chemically enriched water. 
     
     
         13 . The method of  claim 5  further comprising actuating a plurality of valves to control flow of the cleaning solution to and away from the stack during the cleaning cycle.