The Effect of Operating Conditions on the Quality of Saturated Steam in Drum-Type Power Boilers

The effect of the operating conditions on the quality of saturated steam in stationary natural circulation boilers with a superheated steam pressure at the boiler outlet of 3.9 MPa or higher (up to 15.5 MPa) is examined. At present, the need is still urgent in the domestic power industry for thermochemical testing of boilers of various pressures to standardize the quality of boiler water and steam in accordance with the requirements of the applicable regulations for water chemistries. The demand for such testing results from the need to find the cause of salt deposition in the flow path of steam turbines and develop measures to prevent the formation of deposits on turbine blading. The results of these tests have confirmed the correlation among the boiler water salt content, entrainment factor, water level in the boiler drum, and steam quality. In high-pressure drum boilers, the main impurities are iron and copper oxides, i.e., the products of corrosion of power equipment provided that the demineralized water has a high quality with a maximum specific conductivity of 0.5 µS/cm and nо cooling water inleakage occurs in the condenser. Results of the effect of a correcting chemical on the distribution coefficient of iron and copper are presented. The use of ammonia as a correcting chemical decreases the distribution coefficient for iron and copper and, hence, reduces the contamination of steam with corrosion products. The water chemistry has been demonstrated to affect the concentration of corrosion products of iron and copper in the boiler water, i.e., the blowdown efficiency, which is related with changes in the form of these compounds in water. It is pointed out that the contamination of steam with corrosion products is related with droplet entrainment since the saturated steam pressure hardly has any effect on the distribution coefficients for iron and copper. How one and the same impurity enters the steam depends on the water chemistry controlling the form of existence of this compound.