SCALE INHIBITION AND REMOVAL IN STEAM GENERATION

1,216,781. Composition for removing and inhibiting boiler scale. NALCO CHEMICAL CO. April 11, 1968 [June 22, 1967], No.17722/68. Heading C7E. A composition for removal and inhibition of boiler scale contains 10-90 wt. % of (A) any aminocarboxylate chelate compound or a nitrilo compound N[-(CH 2 ) x -Q] 3 where x = 1 or 2 and Q is where R and R1 are H, alkali metal, or, NH 4 , at least one R and at least two R1 not being H; and 90-10 wt. % of (B) a water soluble sulphoxy-free polar addition polymer having M. W. at least 1000. The polymer may be a water soluble anionic polar vinyl addition polymer having in its structure at least 5 wt. % of hydrophilic side chain groups selected from carboxylic acid, anhydride, salt, ester, amide, or hydroxyl groups, preferred polymers being maleic anhydride polymers, possibly hydrolyzed to the salt form acrylic acid polymers formed by alkaline hydrolysis of polyacrilonitrile, and maleic anhydride-styrene copolymers (A) maybe an E.D.T.A. compound, but is preferably the trisodium salt of nitrilotrimethylphosphonic acid. Scale in boilers is inhibited and removed by incorporating in water from which steam is generated at 15-2000 p. s. i. a suitable quantity of the composition, in general 0À1 to 1000 p.p. m. for a boiler at pH 9-12. It is desirable to maintain a phosphate dosage of at least 5 p. p. m. in the boiler.