Composite passivant used for the boiler chemical cleaning of power plant and passivation method

Abstract

The invention discloses a composite passivant used for the boiler chemical cleaning of a power plant and a passivation method. The composite passivant consists essentially of components of the following mass percent: 0.010 percent to 0.025 percent of ethylene diamine tetraacetic acid (EDTA), 0.01 percent to 0.02 percent of trisodium phosphate, 0.2 percent to 0.5 percent of hydrogen peroxide, 0 percent to 0.01 percent of sodium nitrite, 9.2 to 9.6 pH value of chemical pure or analytically pure suitable ammonia adjustment solution, and the balance of water. The invention has the advantages of simple passivation process, safe and non-toxic agent, low washing temperature, short time, energy conservation and environmental protection, and fine passivation effect, does not generate acid corrosionhazard to the unit ignition, and is a novel passivation method. By adopting the passivation method, the copper fouling of the operating unit can be effectively removed.

Description

technical field [0001] The invention belongs to a passivating agent for metal surfaces, in particular to a composite passivating agent and a passivating method for chemical cleaning of boilers in power plants. Background technique [0002] In recent years, most of the large-scale thermal power plants put into operation are subcritical, supercritical and ultra-supercritical units. With the improvement of unit parameters, in order to obtain more pure steam, the cleanliness of the inner wall of the heating surface is also required to be higher and higher. Chemical cleaning is a necessary measure to clean the heated inner surface and prevent accidents caused by corrosion and scaling on the heated surface. It is also one of the effective measures to improve the thermal efficiency of the boiler and improve the water vapor quality of the unit. [0003] The passivation step in the commonly used cleaning process is an important part of the quality of chemical cleaning. The process ...

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Problems solved by technology

[0003] The passivation step in the commonly used cleaning process is an important part of the quality of chemical cleaning. The process generally has high passivation temperature (high energy consumption), long time, and even some passivators themselves are carcinogens, and environmental protection problems are prominent; in addition, for newly built supercritical and ultra-supercritical units, phosphate, polyphosphate The phosphate residue caused by passivation will undoubtedly bring hidden dangers to the safe operation of the unit in the future. The protective film formed by hydrazine passivation is quite different from the ferric oxide-type protective film to be formed in the operation of supercritical and above units, and the passivation The time is 24 to 50 hours, and the temperature needs to reach 90 to 95°C; the temperature for passivation with acetone or acetaldehyde is also high, and the acidic substances generated by the decomposition of residual acetone or acetaldehyde at the high temperature of the next ignition of the unit are not suitable for supercritical The unit is undoubtedly unacceptable. As for the ethylenediaminetetraacetic acid (EDTA) oxygenation passivation process, it is only suitable for EDTA cleaning and the application requirements are relatively high. There have been many cleaning accidents of serious corrosion of the unit. As for The hydrogen peroxide passivation method recommended in "Guidelines for Chemical Cleaning of Boilers in Thermal Power Plants" (DL / T794-2001) requires phosphoric acid and polyphosphate rinsing methods before passivation. The ignition of the unit is likely to cause acid corrosion. Critical units are clearly not the best passivation solution