by Mars G. Fontana
RECENT
article in the popular press
A described hydrazine as a chemical that “does everything.” It is used for medicines, sleeping pills, vulcanizing rubber, crepe rubber, solders, fabrics, pest control, storing food, restricting growth of grass on lawns and elsewhere, and a host of other uses. This column concerns one sentence from the newspaper article. One hydrazine compound boilers from pitting.
stops
Hydrazine is used as a corrosion inhibitor and oxygen scavenger. It is effective in treating boiler feed waters. The over-all reaction with oxygen is NzH4
+
0 2
=
N P +2H20
It is a well-known fact that oxygenfree water is practically noncorrosive to steel as compared with water containing oxygen. Hydrazine costs less than sodium sulfite on basis of actual use
One advantage of hydrazine for feed water treatment is that no additional solids are added to the steam generating system. Although hydrazine is more expensive per pound on the basis of use it is less costly than sodium sulfite. I n one application, 10 pounds of sodium sulfite was replaced by 0.375 pound of hydrazine solution (54.4% KzH4) a t an annual saving of $200 for material. Another plant saved $425 per year where sodium sulfite treatment was costing $1.95 per day and hydrazine solution now costs $0.78 per day. Ferric iron oxide in boilers is reduced to magnetic iron oxide thus increasing heat transfer. Boiler cleaning time is reduced substantially. Theoretically one pound of 1 0 0 ~ o hydrazine removes one pound of oxygen. During initiation of treatment hydrazine should be added not in excess of five times the equivalent oxygen content of the deaerated feed water. Some reports suggest that ammonia is October 1955
formed; this is theoretically possible if 6 to 10 times the proper concentration is used. It has not occurred with proper control. Residual is maintained a t 0.1 p.p.m. hydrazine in the water. Meters are available to indicate automatically the residual present. The small dosage and the liquid form offer advantages from the storage and handling standpoints. The solution is shipped in 18-8 stainless steel returnable drums. Hydrazine i s used successfully both here and abroad in high pressure plants
Hydrazine is used in a power plant in Germany with a superheater outlet steam temperature of 1130’ F. Operation for more than 10,000 hours showed no failure in the steam generators. Superheater material, removed and examined after 6400 hours of service, showed no discernible damage outside or inside. Other high pressure boiler plants in Europe and the United States are using hydrazine successfully for removing oxygen. These plants run with boiler pressures in the range of 900 to 1850 pounds per square inch gage. Fiss (1) reports that the Duke Power Co., Charlotte, N.C., first used deaeration equipment and then sodium sulfite treatment to control boiler corrosion. However, certain undesirable properties of sodium sulfite, such as its decomposition to sulfide and its tendency to seep around hand hole gaskets, valve stems, and pump glands, resulted in corrosion and scale formation and the resultant maintenance was considered excessive, particularly in the case of the 900-pound per square inch gage boilers. Hydrazine was first tried in 1951 in a 380,000 pounds per hour, 450-pound per square inch gage boiler and satisfactory residuals were obtained. Hy-
drazine has been used in one or more boilers since that time. Hydrazine treatment has been satisfactory in two 620,000 pounds per hour, 1350-pounds per square inch gage boilers since 1952. Removal of tube sections from other high pressure (1350 pounds per square inch gage) boilers showed evidence of corrosion. All such units are now treated with hydrazine including two operating a t 1850 pounds per square inch gage. Material is purchased as 85y0 hydrazine hydrate and the feed solution contains 0.295 pound of 85% hydrazine hydrate per gallon. KO appreciable deterioration of this solution was observed after several weeks in a covered tank made of Type 304 stainless steel. Hydrazine i s used successfully in low pressure plants
The Doe Run petroleum chemical plant of Olin Mathieson Chemical Corp. switched from sodium sulfite to hydrazine and after approximately 9 months reported practically no corrosion in the boilers. This is an example of using hydrazine successfully in a low pressure industrial plant. Hydrazine solutions below 40% have no flash point, but high concentrations should be protected from flame. These solutions should be handled like other strong alkalies. Fumes are toxic and contact with the skin should be avoided. Related applications of hydrazine hydrate as a corrosion inhibitor in water are (a) closed circulating cooling water systems for industrial gas engines, Diesel engines, and air and gas compressors; ( 5 ) the water layer a t the base of oil storage tanks to prevent corrosion of the bottoms and lower sides; (c) water circulating through secondary coils absorbing heat from atomic reactors; (d) protecting standby boilers from rusting by filling them completely with water containing 50 p .p.m. hydrazine.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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a
Corrosion ~
Materials of construction are discussed
Preferred materials for handling hydrazine solutions are glass-lined steel, borosilicate glass, and Types 302, 303, 304, 321, and 347 stainless steels. Molybdenum bearing alloys such as Type 316 and Hastelloy C are not recommended because molybdenum could cause catalytic decomposition of the hydrazine. Copper and copper alloys should be avoided and galvanized steel is not satisfactory. Teflon, polythene, and Type 304 gaskets are used. Asbestos impregnated with carbon is not recommended for gaskets or packing. Centrifugal pumps with Teflon packing or carbon and Teflon mechanical seals are recommended. Acknowledgment
Information furnished by E. R. Woodward, Olin Mathieson Chemical Gorp., Baltimore, Md., is hereby gratefully acknowledged. Referenc e s (1) Fiss, E. C., “Experience with Use of Hydrazine as an Oxygen Scavenger in High Pressure Boilers,” presented a t 16th Meeting, Annual Power Conference. Chicano. March 1954. (2) Montville, R . V, Jenkins, G. R., and Woodward, E. R.. POWER, 99,
(March 1966). Correspondence concerning this column will be forwarded if addressed t o the author, c/o Editor, INDUSTRIAL AND ENQINEERINQCHEMISTRY, 1155-16th St., N.W., Washington 6, D. C.
cost, but often makes substantial savr o d u c t i o n procedures. Smooth surfaces, with i o n of detail; uniform density, l i g h t w e i g h t . f e w Shellcast advantages that b r i n g savings i n ine-finishing, a n d assembly. ESCO Shellcast is o w alloy steels, stainless steels a n d h i g h alloys.
..
I
ELECTRIC STEEL FO U N D R Y CO.
2161 N. W. 25th AVENUE,
PORTLAND, OREGON
(
)
Send me a free copy of “Cut Production Costs With ESCO Shellcast”.
(
)
Have an application engineer call for an appointment.
Name Company Address State
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 4’2, No. 10
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