Research On Corrosive Potential And PH Distribution In The Water Cycle Of Supercritical Units

With the rapid development of the national economy, increasing demand for power, now thermal power is still the main form of power.Therefore, the stable run of thermal power plant has an important role to the national economy and security. However, power plant accident occurres frequently, most of them are crack damages. The reason is mainly as a high temperature and pressure of the pressure parts of the superheater, reheater, service of the pipe caused severe corrosion due to its harsh environment, so corrosion and plant protection are particularly important. Potential-pH diagram is an important tool in corrosion research, it can be predicted metal corrosion in theory, and select the method to prevent materials corrosion.By using the concentration comparison method and a graphic algorithm, predominance diagrams and Pourbaix diagrams for Fe-F2O systems were generated in this paper at25℃. The Gibbs free energys of Fe-H2O system substances were calculated at the temperatures below300℃based on the25℃thermodynamic datas. The Gibbs free energy of the substances at10MPa,20MPa,30MPa between400℃and700℃were also calculated by using the software SUPCRT92.With the datas obtained above, the predominance diagrams and Pourbaix diagrams for Fe-H2O systems were generated at60℃,100℃,150℃,200℃,250℃,300℃, and also the Pourbaix diagrams at higher temperatures considering the effect of presure.Then the potential-PH diagrams of the different temperatures and pressures has been simply analied.The paper has explained that Fe3+is not stable in the water cycle power plant,meanwhile proposing FeOH+may promote the flow accelerated corrosion and how to control the PH or potential of supply water to prevent corrosion.