Feedwater treatment hydrazine

In the case of boilers operating at low pressure, organic materials such as natural and modified tannins, starches, or alginates are added to aid blowdown. For boilers operating at high pressure, synthetic materials such as polyacrylates and polymethacrylates have been developed. The most commonly used chemicals for boiler feedwater treatment are phosphates and hydrazine. 

Modem power utility boiler feedwater treatments commonly include the addition of organic amines to inhibit the corrosion of iron components of the system by scavenging oxygen and increasing the pH of the feedwater. These chemi-Cctls such as morpholine and hydrazine decompose in service to yield ammonia, which can be corrosive to some copper alloys. However, elevated oxygen levels are generally more deleterious than elevated ammonia levels. 

Hydrazine, H2N—NH2, is the simplest diamine. Free hydrazine never has been detected in nature on earth although many hydrazine derivatives have been found. Anhydrous hydrazine was prepared first by Lobry de Bruyn in 1894, In 1938, Fairmont Chemicals began the first production of hydrazine in the United States the quantity produced was small, and the product was mainly for captive use in boiler feedwater treatment. In World War II, hydrazine became important to Germany as a component of missile fuel. In 1954, Olin Chemicals built the first U.S. commercial N2H4 plant, of about 4 million Ib/year capacity. Hydrazine mainly is consumed as a high energy rocket fuel, an oxygen... 

Boiler Feedwater Treatment. The strong reducing characteristic of hydrazine makes hydrazine an oxygen scavenger for the treatment of boiler water to reduce corrosion, with the addition of 0.1 ppm. 

For once-through boilers, the treatment must be without soHd residues, so all-volatile treatment (AVT) is used. AVT, which is also used in some dmm boiler systems, rehes on the feedwater chemical additives, ammonia and hydrazine, to provide water appropriate to the boiler. Because the additives are volatile, they do not accumulate in the boiler and provide only minimal protection during contaminant ingress. Most plants using AVT have some form of condensate poHsher to remove impurities from the condensate. 

Experience has shown that condensate pH will usually stabilize in the range of 8.5-9.5 if a 0.06-ppm hydrazine residual is maintained at the boiler inlet. This eliminates the need for pH treatment of the condensate-feedwater. 

Recommended limits should be low because all solids in the feedwater will either deposit in the boiler or be earned over with the steam to the turbine. Consequently, water-treatment chemicals must be volatile. All cycles should have condensate-polishing systems to meet the limits show ll in Table 3. A schematic diagram is shown in Fig. 11. Laboratory tests as well as field studies show that high-flow-rate condensate-polishing systems 25 to 50 gal per min per sq ft (1015-2030 liters/minute/square meter) of cross-sectional bed area] perform as filters of suspended material and ionized particles. Ammonia is added to control the pH in die system. Fig. 12 indicates the amount of ammonia required, in terms of ppm or solution conductivity, to give a certain pH in the system. Hydrazine is added to the cycle for oxygen scavenging. 

This application, which appears to have matured, is by far the most effective treatment for boiler feedwater because the treatment does not produce solid residues and avoids sulfide corrosion. Hydrazine also helps to form an adherent layer of magnetite, Fe304,... 

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