Research On Fault Diagnosis Methods Of Centrifugal Compressor In CCPP Gas System Based On Thermal Parameters

The iron making process produces a large volume of blast-furnace gas(BFG).The gas-steam combined cycle power plant(CCPP)can take the by-product BFG as its fuel for electricity generation.CCPP becomes a preferred solution for recovery and reuse of the by-product BFG.which plays an important role for pollution reduction,energy saving of iron and steel enterprises.As the intermediate transition of upper iron making process and CCPP,the gas system can provide buffer,pressure and heating value adjustment for by-product BFG.Centrifugal compressor is the core equipment of the gas system,and its running status affects the efficiency and stability of CCPP directly.Therefore,the monitoring and fault diagnosis of centrifugal compressor is very necessary.At present,the researches on the fault diagnosis method of centrifugal compressor mainly focus on the diagnosis of mechanical faults using vibration signals.However,as an energy conversion device,any change in gas flow or process parametersof centrifugal compressor can directly affect the change of its thermal performance,which is often the precursor of a mechanical failure.When a fault occurs in the flow path of centrifugal compressor,its thermal parameters(such as pressure,temperature,flow etc.)contain lots of fault information.Therefore,the monitoring and diagnosis of compressor by the thermal parameters are helpful to diagnose and eliminate the fault in its early stage,which is of great significance to the safe operation of centrifugal compressor.In this dissertation,the centrifugal compressors in CCPP gas system of Baosteel reserve power plant are taken as the research object.On the basis of analyzing the operating principle and fault mechanism,the diagnosis methods of common faults in the flow path of centrifugal compressor with thermal parameters are studied.The main research works can be summarized as follows:1.CCPP gas system consists of centrifugal compressors,coolers,and regulating valves,which make it a complex system with multiple factors,strong nonlinearity and strong coupling.In this dissertation,on the basis of existing theory achievements,the single stage mechanism model of centrifugal compressor is established based on the energy transfer and energy loss mechanism of gas isentropic compression process,and then the multistage compressor model is established based on stage-stacking method.Meanwhile,other major components of the gas system are modeled,and the key parameters in these models are identified using the history data of the gas system under normal condition.Based on the above models of gas system,two typical faults of centrifugal compressors in gas system are simulated through analizing the faults mechanism.These work provides the foundation for following researches of the fault diagnosis methods.2.For the typical faults in gas path of centrifugal compressor,a fault diagnosis method based on thermal parameters and qualitative simulation(QSIM)is proposed.QSIM method can build qualitative models of system with the "deep" knowledge like system structure principle,and the "shallow" knowledge like equipment operating experience.It is particularly suitable for the case that the precise mathematical model cannot be established due to the complexity of system or incomplete knowledge.Through the analysis of the principle of centrifugal compressor and faults mechanism,the qualitative models under normal condition and fault conditions are established,respectively.When a failure occurs,the qualitative model which is best matched with system actual behavior is identified through comparing the trends of variables'observations and the qualitative states sequences deduced from qualitative models.The diagnosis result can be obtained according to the fault information contained in this qualitative model.3.For the problem of spurious reasoning results of QSIM method due to its inherent disadvantage,a QSIM based fault diagnosis method combined with causal relation and fuzzy knowledge is proposed,and applied for the diagnosis of centrifugal compressor insufficient discharge.To make QSIM models contain more quantitative information,casual relationship existed between different system variables is defined as a new kind of qualitative constraint.Meanwhile,external variables of QSIM models are also defined,and the qualitative trends abstracted from external variables are treated as the known condition of QSIM models.The operating experiences during the long-term production are summarized as fuzzy knowledge and also contain in QSIM models.A weighted sliding window matching strategy based on qualitative trends of variables and fuzzy qualitative value constraints is proposed to calculate the diagnosis result.Finally,the reasons of compressor insufficient discharge are summarized,and used to validate the proposed method.4.For the surge problem of centrifugal compressors in CCPP gas system,a fault diagnosis and state evaluation method is proposed for centrifugal compressor proximity to surge.Surge may cause serious damage to the compressor and pipe network,so it is a running condition not allowed during the operation of compressor.In this dissertation,the common causes of compressor surge are summarized,and the dynamic model of centrifugal compressor is established,and the surge condition of the compressor is simulated.When the operating point of compressor moves from the safety zone to the surge zone,QSIM based diagnosis method is used to determine whether the compressor exists the possibility of surge.If there is a possibility,the extent of compressor proximity to surge is calculated using the fuzzy comprehensive evaluation method.The experimental results show that the proposed method can give an accurate diagnosis and evaluation result before the compressor surge occurs.It has important and practical significance for preventing compressor surge.Finally,the future research hot topics of centrifugal compressor fault diagnosis methods are prospected after summarizing the whole work in this thesis.