Feedwater treatment oxygen scavenging

In lower pressure boilers a variety of additional treatments may be appropriate, particularly if the steam is used in chemical process or other nonturbine appHcation. Chelants and sludge conditioners are employed to condition scale and enable the use of less pure feedwater. When the dmm pressure is less than 7 MPa (1015 psia), sodium sulfite may be added direcdy to the boiler water as an oxygen scavenger. It has minimal effect on the oxygen concentration in the system before the boiler. 

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. 

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. 

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. 

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