Concentration of Corrosive Impurities Due to Early Condensation - Effect of pH and Their Concentration in Steam

摘要

The concentration ratio of corrosive impurities due to early condensation was measured using our experimental early condensation device presented at IWC-'97. In this paper we report the behavior of NaCl and NH_4Cl as an impurity in steam. In the case of NaCl the concentration ratio increased with lowering the concentrations in steam. With NH_4Cl we confirmed also its concentration in early condensate. The dependecy of concentration ratio on NH_4Cl concentration was similar to that of NaCl. Even though the impurities concentration in steam was several order of magnitude higher than that in power plant steam, we could estimate the concentration ratio roughly, extrapolating the relation curve. This suggests that the ratio could go up to several orders of magnitude. On the contrary, in the case of NFL as an impurity, the concentration peak was not observed. This is understandable because of its high volatility. When pH of sample water containing NaCl was adjusted to about 10 with ammonia, we could not observed the concentration peak due to early condensation. This was quite different from the behaivior of neutral steam containing NaCl, in which case the peak was clearly observed. In the ammoniacal water three intermediats of impurities such as NaOH, NaCl and NH_4Cl could exist in steam. As NaOH of them has largest affinity for H_2O, this was preferentially dissolved in early condensates. This might be the reason for that the ammoniacal water behaved similarly to NaOH water in the early condensate process.