Patent ID: 9649598
Date: 2017-05-16
CPC Classifications: B01D,C02F

Claim:
1. A process for purifying water containing soluble species capable of forming two or more sparingly soluble salts or minerals, wherein said process comprises feeding a pressurized water stream containing soluble species capable of forming two or more of the following sparingly soluble salts or minerals: calcium carbonate; calcium sulfate; silica; calcium phosphate; barium sulfate; strontium sulfate and calcium fluoride, into a treatment zone having one or more membranes disposed therein, passing said stream along said membrane(s) to recover a permeate and to withdraw a concentrate therefrom while periodically reversing the direction of the flow of said stream in said treatment zone, wherein the process further comprises determining the induction time τ, which is the time required for a supersaturated water stream to precipitate one or more of said sparingly soluble salts and/or minerals therefrom, and setting the periodic flow reversal to take place at some time less than the induction time τ, whereby said one or more membranes are exposed to supersaturation conditions evolving in said water stream for a period of time which is less then said induction time τ, wherein the induction time τ is either (i) predetermined experimentally; (ii) determined separately for each of the sparingly soluble salts and/or minerals present in the water stream using the following equation: wherein: A and B are constants related to a given sparingly soluble salt or mineral and the membrane used; and S is the ratio between the maximum actual activity product of a given sparingly soluble salt in the solution next to the high pressure side of the membrane and the thermodynamic solubility product, or, for an undissociated mineral, the ratio of the actual maximum mineral concentration to the saturation concentration of that mineral for the given composition; or based on determination of separate induction times for plural ones of said sparingly soluble salts and/or minerals present in the water stream and thereafter setting the periodic flow reversal to take place at some time less than the shortest induction time of said separate induction times; or (iii) determined during treatment zone operation via sensors.