Steam-Water-Oxygen Cleaning and Passivation Print version

History of the method's development


Fig. 4. the Moscow Physical-Chemical Institute named after L. Karpov

In the mid-50's in the Moscow Physical-Chemical Institute named after L. Karpov special studies were conducted, paving the way to the conscious regulation of the corrosion resistance of metals with the help of oxidants. By the 60’s this work allowed to recommend the method of oxygen protection to deal with corrosion of boiler equipment, working on water and steam, and to show the ways of the method optimization.

Later on the series of bench tests successfully exercised the ability to protect steel from corrosion by oxygen.

By the mid 70’s numerous domestic and overseas researches show that exposure of oxygen-containing water to the surface of carbon steel leads to accelerated formation of oxide films of magnetite with protective properties to the running of general corrosion.

By the beginning of the 80’s the All-Russian Thermal Engineering Institute (VTI), in co-operation with specialists from Mosenergo, Moscow Thermal Power Plant 25 and Mosenergomontazh enterprise developed and implemented a new method of post-installation cleaning and passivation — Steam-Oxygen Cleaning and Passivation (SOCP).

SOCP method lies in the purging of the boiler heating surfaces by side superheated steam from a nearby working boiler, dosing gaseous oxygen into steam at a concentration of 0.5—1 g/kg. Such a purge removes products of corrosion and installation from steam-water circuit, with the formation of an oxide protective film on heating surfaces which dramatically reduces the start-up time of the boiler, and enhances the protection of metal from corrosion for long periods of work and idle of equipment.

Being implemented practically, the technology has identified a number of advantages compared to the WCC which allowed it to quickly become a widely used technology in Russia in the 80's.

SOCP method can be applied in the initial contamination by the corrosion products with their concentration of no more than 200 g/m2. Average efficiency lies within the range of 70—75%.

One of the drawbacks of SOCP technology was a high consumption of high-potential side steam (150—400 t/h, at pressure of 4.6 MPa and a temperature of 400—440 ºC), meaning that it is impossible to implement that technology on the first power unit of power plant.

Further research in the end of the 80’s resulted in development of technology of Steam-Water-Oxygen Cleaning and Passivation (SWOCP) that lacks this drawback.

The method of SWOCP lies in the fact that dozing oxygen into the boiler feed water and maintaining the required operational parameters allow to remove products of corrosion and installation from steam-boiler circuit, with the formation of an oxide protective film on heating surfaces which dramatically reduces the start-up time of the boiler, and enhances the protection of metal from corrosion for long periods of work and idle of equipment. SWOCP can be carried out during the first firing after installation of the boiler, making maximum use of the existing scheme. In this case economizer and evaporative paths of the boiler are processed by hot feed water and steam-water mixture, into which gaseous oxygen at a concentration of 1—1.5 g/kg are dozed under the special scheme. Steam superheater, intermediate steam superheater and steam pipelines are cleaned by its own steam (produced by the boiler at start-up). SWOCP is held on a firing (starting) fuel with 30—40% load of the boiler, for which a starting scheme is calculated, and combined with the blowing of the main steam pipes and steam testing of the boiler. Cleaning efficiency with SWOCP is 70—75%.

During the 90’s SPE Energetika i Nauka represented by A. Storozhuk in co-operation with VTI staff developed the new intensification techniques of oxidizing cleaning . They are based on the application of a steam-water mixture as a working medium in combination with changes in temperature and the dynamic changes in the flow of this medium.

The method of treatment is based on a transition of steam and water superheated in the evaporating section (superheating section of the boiler) into a state of steam-water mixture. This transition is carried out at a maximum rate of temperature change possible for the equipment. The end of treatment is characterized by the lack of deviations of figures of contamination after cleaned circuit which remains at the specified level.

With the use of double-phase medium cleaning efficiency and temperature fluctuations grow due to the following factors:

  • growth of linear and mass flow speed with the transfer of the medium into the steam-water mixture with the range of humidity of 10—50% (depending on the pressure of the medium) by the means of the formed foam or annular flow regime at which water in the wall zone is accelerated multiple times by the steam, moving in the central part of the pipe;
  • the emergence of different linear coefficients of expansion of the heating surfaces pipes metal and sediments after a sudden change in temperature, which leads to the destruction of particles connection with the metal;
  • abrupt change in the direction of the medium to the opposite (“reverse”), amplifying the effect of the dynamic and thermal impacts.

Intensified SWOCP method can be applied with the initial contamination of pipes by more than 300 g/m2 of iron oxides. Efficiency of intensified SWOCP technology is 85%.