① Corrosion Inhibitor
The corrosion inhibitor with chromate as the main component is commonly used in cooling water system, and chromate ion is a kind of anode (process) inhibitor, and when it is combined with suitable cathode inhibitor, it can obtain a satisfying and economical anticorrosion effect. Chromate-Zinc-polyphosphate: The use of polyphosphate is because it is a clean metal surface of the role of corrosion resistance, polyphosphate can be partially turned to positive phosphates, they can also produce large colloidal cation with calcium, inhibit the cathode process. Chromate-Zinc-phosphonic acid Salt: This method is similar to the previous one with sodium phosphonic acid instead of polyphosphate, and the amino-methyl phosphate can also be used for occasions where the ph value is higher than that prescribed by polyphosphate. Amino-methyl phosphonic acid salts can prevent scaling, even if the ph value of 9 can also control the precipitation of calcium salts. Chromate-Zinc-hydrolyzed polyacrylamide: The dispersion of polyacrylamide, which is hydrolyzed by cationic copolymer, can prevent or inhibit the generation of fouling.
② Electrochemical Protection
Cathodic protection and anode protection are adopted. Cathodic protection is the use of the external DC power supply, so that the metal surface to the cathode to achieve protection, this method of large electricity consumption, high cost. Anode protection is the protection of the heat exchanger connected with the external power of the anode, so that the metal surface to create a passivation film, thereby being protected.