The Qualitative Reasoning Analysis Of Boiler’s "Four Tubes Leakage" Based On QSIM

In recent years, with the continuous development of high parameter largecapacity units in China, the thermal system of power plant become morecomplicated. Traditional quantitative methods have been unable to detect anddiagnose the complex system timely and accurately. Since the qualitative reasoningmethod was put forward in the1980s, it shows the advantage gradually inprocessing incomplete information system and also the system that quantitativemodel is difficult to establish. Qualitative reasoning processes the input, buildingmodel, behavioral analysis and output of the simulation with the non-digital method,striving to overcome the weekness of quantitative simulation.Superheater, reheater, economizer and water wall refers to the "four tubes"generally, each year the "four tubes leakage" causes accounted for about20%-40%among the unplanned boiler stop accidents, which greatly decreasing the operationefficiency of the boiler. As a result of the same physical heat transfer model in "fourtubes", this paper selects superheater as example, establishing the pressure flowmodel and the temperature model of superheater. Using the QSIM method tosimulate the superheater model, produce all possible successor states of the relevantparameters. Filtering all the successor states according to the relevant constraints,the outlet pressure, flow, steam temperature and the change of metal walltemperature are finally got when the leakge happens.This paper includes four parts. The first part introduce the basic situation of"four tubes leakage" and the development of qualitative simulation and alsoemphatically introduces the basic concept, constraint and the simulation process ofQSIM. The second part sets up the pressure flow mathematical model of thesuperheater, and then gets the qualitative model. Simulate the qualitative model toget the tendency of the change in pressure and flow rate when the superheater leaks.The third part sets up the mathematic model of the temperature of the superheater soto get the qualitative model. The steam temperature and metal wall temperature’schange trend were derived through the qualitative reasoning, constraints filteringand global filtering both in the situation from the normal operation to leakage of10%and that from20%to10%. To summarize the causal relationship between the parameters and reduce the qualitative fault simulation computation of the model, thesuperheater quantitative equations are applied in processing the model of qualitativemodel of the superheate. The outlet pressure, flow, dynamic changes of the steamtemperature and metal wall temperature curve are obtained when the superheaterleakage happens through a simulator of600MW supercritical units which isdeveloped independly by the north China electric power university in he last part.Qualitative reasoning validity is demonstrated through the experiment above.