Abstract
Recent years, as the development of thermal power plant, superheater oxide film caused by over temperature and tube explosion and the turbine blade erosion problem more and more serious. The research and development of chemical cleaning technology of superheater oxide film is one of the most effective ways to solve this problem. The chemical cleaning of superheater is rather difficult than that of boiler, for mainly the reason as below. First, the scale of superheater tube, differences in microstructure, scales dense and need to use higher cleaning medium concentration and longer cleaning time. Second, the materials of superheater complex, involves ferritic steel and austenitic stainless steel such as 12Cr1MoV, T22, T91, TP347 and SUS304. For controlling chemical cleaning process, the acid corrosion sample is employed to slow inhibitor on different metal and alloys. Also, the traditional weight-loss method to evaluate the corrosion rate of materials in chemical cleaning process is discussed to monitor the corrosion process.
Highlights
The thermal power generation enterprises have long been plagued by the problem of superheater oxide scale
When the scale in the superheater tube grows to a certain extent, the thermal expansion coefficient between the scale and the superheater metal matrix is different, and when the unit starts and stops or the loaded changes
In the "Guidelines for Chemical Cleaning of Boilers in Thermal Power Plants" (DL/T794, China), the guiding principle of "chemical cleaning" can be carried out for the chemical cleaning of superheaters, "the amount of scale exceeds 400g/m2, or when the explosion occurs due to oxide scale falling off." There are no specific rules for cleaning conditions
Summary
The thermal power generation enterprises have long been plagued by the problem of superheater oxide scale. The scale will fall off due to the change of the main steam temperature, and the falling scale may block the superheater tube and cause local over-temperature burst or turbine blade erosion [13]. Chemical cleaning is usually used to improve the heat transfer efficiency of the equipment, slow down the formation and shedding of the superheater scale, reduce the long-term creep damage of the pipeline and the erosion of the turbine[4-5]. The chemical cleaning technology can effectively remove the oxide scale on the surface of the superheater tube, and avoid the superheater tube burst accident caused by the falling off of the scale during the long service period. In the "Guidelines for Chemical Cleaning of Boilers in Thermal Power Plants" (DL/T794, China), the guiding principle of "chemical cleaning" can be carried out for the chemical cleaning of superheaters, "the amount of scale exceeds 400g/m2, or when the explosion occurs due to oxide scale falling off." There are no specific rules for cleaning conditions
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