Evaluation Research And Engineering Application Of Iron Scale Generation On High Temperature Heat Surfaces In Supercritical Boiler

Adopting supercritical (ultra-supercritical) unit is the inevitable trend in China for effective utilization of energy, increase of the power generation efficiency and improvement of the environment. But, with the increase of the steam parameters, the problem of tube-bursting caused by the exfoliation of the iron scales of the high temperature heating surface is becoming serious.Based on a great deal of domestic and foreign laboratory and field test results of iron scales, the reason for generation and exfoliation of the iron scales on high temperature heating surface of the boiler is analyzed in detail, and the affecting mechanism of wall temperature, operating time and material on generation of the iron scales are illustrated by comparing the structural characteristics of steam corrosion of the typical materials used for high temperature heating surface in supercritical unit, such as T23,T91,TP347HFG. The influential factors for iron scales exfoliation are also analyzed from the aspects of internal growth stress, scales cumulative thickness and running condition variations, and the influence of geometric structure of the tube coils on exfoliation of the iron scales is specifically analyzed. The possible reason why the damage caused by iron scales in supercritical (ultra-supercritical) unit is more serious than that in sub-critical unit is discussed from the aspects of operational parameters and structure parameters, etc.An on-line calculation model for thickness of iron scales is established according to the analysis and comparison of different dynamic models for scales growth and lots of the domestic and foreign experimental data. The model shows acceptable error and good reliability after a comparative study between fitted data and measured data, and the model can reflect the growth of iron scales on tube wall of high temperature heating surface. After that, fuzzy comprehensive evaluation (FCE) is introduced for the first time into condition assessment of iron scales of boiler high temperature heating surface. By selecting representative factors such as wall temperature, thickness of the iron scales, etc. and establishing judging collection according to the practical condition of the power plant, the primary fuzzy comprehensive evaluation model is set up. Collecting the assessments of all the indexes, the comprehensive condition of the iron scales can be intuitively estimated. And the assessed results can be used to check the state of the iron scales on heating surface.Depending on the intelligent management system SPERI-1 independently developed by SPERI (Shanghai Power Equipment Research Institute) for wall temperature, secondary development is completed for the sub-system of on-line monitor and evaluation of iron scales based on the on-line calculation model for thickness of iron scales and fuzzy comprehensive evaluation model. The sub-system is applied to an actual power plant to realize real-time monitor and evaluation for the state of oxide-scales, providing effective basis for decision-making of the operator.