Method to inhibit scale formation in cooling circuits using carbon dioxide

Abstract

Scaling is controlled in a cooling water system with CO2 based upon measurements of the cooling water's pH, alkalinity and Ca 2+ concentration.

1 . An assembly for controlling scale formation in a cooling water system, comprising:
 a) an inlet conduit adapted to withdraw a sample of cooling water from a cooling water system;   b) a cooling water sampling unit adapted to measure a Ca 2+  concentration and an alkalinity of the withdrawn sample of cooling water;   c) a pH probe adapted and configured to measure a pH of the cooling water in the cooling water system;   d) a CO 2  injector;   e) a first programmable logic controller written with an algorithm, said first programmable logic controller being adapted and configured to receive a signal from said cooling water sampling unit representing the cooling water Ca 2+  concentration and alkalinity measured by said cooling water sampling unit, said algorithm of said first programmable logic controller being adapted to calculate a pH setpoint based upon both a desired scaling index value stored therein and the measured cooling water Ca 2+  concentration and alkalinity; and   f) a second programmable logic controller written with an algorithm, said second programmable logic controller being adapted to receive a signal from said first programmable logic controller representing said pH setpoint and a signal from said pH probe representing a pH of the cooling water measured by said pH probe, said algorithm of said second programmable logic controller being adapted to determine how much CO 2  should be added to the cooling water based upon the pH setpoint and the pH probe signal representing the cooling water pH, wherein said CO 2  injector is adapted to:
 i) receive a signal from said second programmable logic controller representing the determined amount of CO 2  to be added to the cooling water; and 
 ii) add the determined amount of CO 2  to the cooling water. 
   
     
     
         2 . The assembly of  claim 1 , wherein:
 said cooling water sampling unit is further adapted to measure both a temperature and also either a total dissolved solids or a conductivity of the withdrawn sample of cooling water;   said first programmable logic controller is further adapted and configured to receive a signal from said cooling water sampling unit representing the measured cooling water temperature and either the measured cooling water total dissolved solids or conductivity, as measured by said cooling water sampling unit; and   said algorithm of said first programmable logic controller calculates the pH setpoint based upon:   i) a desired scaling index value stored therein; and   ii) the measured cooling water Ca 2+  concentration, alkalinity, temperature, and either the measured cooling water total dissolved solids or conductivity.   
     
     
         3 . The assembly of  claim 1 , further comprising a mineral acid injector and third and fourth programmable logic controllers, wherein:
 said cooling water sampling unit is further adapted to measure a Ca 2+  concentration and alkalinity of makeup water introduced into the cooling water system;   said third programmable logic controller is adapted to receive a signal from said cooling water sampling unit representing the measured makeup water Ca 2+  concentration and alkalinity;   said third programmable logic controller is written with an algorithm adapted to calculate a second pH setpoint based upon both a desired scaling index value stored therein and the measured makeup water Ca 2+  concentration and alkalinity;   said fourth programmable logic controller being adapted to receive a signal from said third programmable logic controller representing said pH setpoint and a signal from said pH probe representing a pH of the makeup water measured by said pH probe, said fourth programmable logic controller algorithm being adapted to determine how much mineral acid should be added to the makeup water based upon the second pH setpoint and the pH probe signal representing the makeup water pH, wherein said mineral acid injector is adapted to:
 i) receive a signal from said fourth programmable logic controller representing the determined amount of mineral acid to be added to the makeup water; and 
 ii) add the determined amount of mineral acid to the makeup water. 
   
     
     
         4 . The assembly of  claim 1 , further comprising a mineral acid injector and a third programmable logic controller written with an algorithm, wherein:
 said cooling water sampling unit is further adapted to measure an alkalinity of makeup water introduced into the cooling water system;   said third programmable logic controller is adapted to receive a signal from said cooling water sampling unit representing the measured makeup water alkalinity;   the algorithm of the third programmable logic controller is adapted to determine an amount of mineral acid to be added to the makeup water based upon the signal representing the measured makeup water alkalinity; and   said mineral acid injector is adapted to receive a signal from said third programmable logic controller representing the determined amount of mineral acid and add the determined amount of mineral acid to the makeup water.   
     
     
         5 . The assembly of  claim 1 , further comprising a mineral acid injector and a third programmable logic controller written with an algorithm, wherein:
 said third programmable logic controller is adapted to receive a signal from said cooling water sampling unit representing the measured cooling water alkalinity;   the algorithm of the third programmable logic controller is adapted to determine an amount of mineral acid to be added to the makeup water based upon the signal representing the measured cooling water alkalinity; and   said mineral acid injector is adapted to receive a signal from said third programmable logic controller representing the determined amount of mineral acid and add the determined amount of mineral acid to the makeup water.   
     
     
         6 . The assembly of  claim 1 , further comprising a mineral acid injector and third and fourth programmable logic controllers, wherein:
 said cooling water sampling unit is further adapted to measure an alkalinity of makeup water introduced into the cooling water system;   said third programmable logic controller being adapted to receive a signal from said cooling water sampling unit representing said measured cooling water alkalinity and determine a makeup water alkalinity setpoint to be maintained in the makeup water;   said fourth programmable logic controller is adapted to receive a signal from said cooling water sampling unit representing the measured makeup water alkalinity;   said fourth programmable logic controller is written with an algorithm adapted to determine how much mineral acid should be added to the makeup water based upon the makeup water alkalinity setpoint from said third programmable logic controller;   said mineral acid injector is adapted to:
 i) receive a signal from said fourth programmable logic controller representing the determined amount of mineral acid to be added to the makeup water; and 
 ii) add the determined amount of mineral acid to the makeup water. 
   
     
     
         7 . An assembly for controlling scale formation in a cooling water system, comprising:
 a) an inlet conduit adapted to withdraw a sample of cooling water from a cooling water system;   b) a cooling water sampling unit adapted to measure a Ca 2+  concentration and an alkalinity of the withdrawn sample of cooling water;   c) a pH probe adapted and configured to measure a pH of the cooling water in the cooling water system;   d) a CO 2  injector; and   e) a control system written with an algorithm, wherein
 i) said control system is adapted and configured to receive a signal or signals from said cooling water sampling unit representing the cooling water Ca 2+  concentration and alkalinity measured by said cooling water sampling unit and receive a signal from said pH probe representing a pH of the cooling water measured by said pH probe; 
 ii) said algorithm is adapted to calculate a pH setpoint based upon both a desired scaling index value stored therein and the cooling water Ca 2+  concentration and alkalinity measured by said cooling water sampling unit and determine how much CO 2  should be added to the cooling water based upon the pH setpoint and the pH probe signal representing the cooling water pH; and 
 iii) said CO 2  injector is adapted to receive a signal from said control system representing the determined amount of CO 2  to be added to the cooling water add the determined amount of CO 2  to the cooling water. 
   
     
     
         8 . The assembly of  claim 7 , wherein:
 said cooling water sampling unit is further adapted to measure both a temperature and also either a total dissolved solids or a conductivity of the withdrawn sample of cooling water;   said control system is further adapted and configured to receive a signal or signals from said cooling water sampling unit representing the measured cooling water temperature and either the measured cooling water total dissolved solids or conductivity, as measured by said cooling water sampling unit; and   said algorithm calculates the pH setpoint based upon:
 i) a desired scaling index value stored therein; and 
 ii) the measured cooling water Ca 2+  concentration, alkalinity, temperature, and either the measured cooling water total dissolved solids or conductivity. 
   
     
     
         9 . The assembly of  claim 7 , further comprising a mineral acid injector, wherein:
 said cooling water sampling unit is further adapted to measure an alkalinity of makeup water introduced into the cooling water system;   said control system is further adapted to receive a signal from said cooling water sampling unit representing the measured makeup water alkalinity;   the algorithm is further adapted to determine an amount of mineral acid to be added to the makeup water based upon the signal representing the measured makeup water alkalinity; and   said mineral acid injector is adapted to receive a signal from said control system representing the determined amount of mineral acid and add the determined amount of mineral acid to the makeup water.   
     
     
         10 . The assembly of  claim 7 , further comprising a mineral acid injector, wherein:
 said cooling water sampling unit is further adapted to measure a Ca 2+  concentration, alkalinity, and pH of makeup water introduced into the cooling water system;   said control system is further adapted to receive a signal or signals from said cooling water sampling unit representing the measured makeup water Ca 2+  concentration, pH and alkalinity;   the algorithm is further adapted to calculate a second pH setpoint based upon both a desired makeup water scaling index value stored therein and the measured makeup water Ca 2+  concentration and alkalinity;   the algorithm is further adapted to determine an amount of mineral acid to be added to the makeup water based upon the second pH setpoint and the measured makeup pH; and   said mineral acid injector is adapted to receive a signal from said control system representing the determined amount of mineral acid and add the determined amount of mineral acid to the makeup water.