| Centrifugal compressors are common pressurized devices in natural gas pipeline system.As a result of the large-scale construction of pipeline network,it is of great value and engineering significance to propose an accurate computational method to describe and predict the steady and transient characteristics of compressors.Thus,it will make sure the safe and effective running of gas pipelines.Aiming at the performance conversion of centrifugal natural gas compressor running in steady-state,complete similarity,the first and second kind of approximate similar calculation are analyzed,and the key parameter pressure ratio is pointed out.Namely,we can improve the accuracy by reducing the error of pressure ratio.So we put forward a new method based on the idea of Predictor-Corrector.The pressure ratio is predicted by the second kind of approximate similar calculation,and then the first kind of approximate similar calculation is used to correct it.Compared with field data of Sichuan to east natural gas transmission project,the error of outlet pressure is about 0.1MPa,the relative error is about 2%,and the error of outlet temperature is controlled within 2 degrees Celsius,than using the first kind or second kind approximate similar calculation separately.Concerning the simulation of characteristics of centrifugal compressors during the transient operation of natural gas pipeline,the physical process of startup and stop of centrifugal compressors is deeply analyzed in this paper.We found that the dynamic change of flow rate and outlet pressure could cause the boundary conditions of downstream pipelines change severely;if the computation not handled properly,it would lead to numerical diffusion.In order to solve the problem,this paper divides the startup process into 3 parts,so the flow rate and pressure can be in smooth change.The instantaneous simulation of the centrifugal compressor is realized by establishing the mathematical model of centrifugal compressors,combining with the model of natural gas pipelines,and using the FORTRAN language.Compared with the field data of compressors in ZY pipeline,it is found that the results of simulation almost keep consistent with it.Finally,the influences on flow rate and pressure of pipe are thoroughly studied by the accurate method for the steady and transient characteristics of compressors developed in this paper on the model of the second Shaanxi-Beijing natural gas pipeline under three kinds of operating conditions: the startup of compressor,the stop of first compressor station and intermediate compressor station.It provides an important reference on the safe and effective operation management of second Shaanxi-Beijing natural gas pipeline on site. |
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