Analysis Of Airflow Pulsation In Large Reciprocating Compressor

As a power equipment for gas pressurization and transportation,large reciprocating compressor is one of the most important equipment in petroleum,machinery,chemical industry,metallurgy and other industries.Due to the intermittent and cyclical suction and exhaust of large reciprocating compressors,airflow pulsation can not be avoided in the pipeline.Airflow pulsation will not only affect the performance of the compressor,but also the air column resonance could cause severe vibration of the pipeline,leading to a great threat to production safety.Therefore,it is of great practical significance to study the airflow pulsation in the pipeline of a large reciprocating compressor.In this paper,the airflow pulsation is studied from three aspects: theoretical analysis,suppression of airflow pulsation and test.The main contents are as follows.1.Based on the plane wave theory and the network transfer matrix method,a network calculation model for the airflow pulsation analysis of large reciprocating compressor pipes is established,and the Matlab program code is developed.The natural frequencies and fluctuating pressures of the gas column in the pipeline system are calculated respectively by using the developed calculation and analysis algorithm.And the calculation results in the references are compared.The comparison results show that the calculated results are in good agreement with the calculated values of the references,and the correctness of the mathematical model and the analysis program is verified.2.Aiming at two practical engineering cases,a network computing model of pipeline system is established.And the calculation and analysis algorithm is used to analyze the airflow pulsation and provide support for pipeline design.In case 1,the air pulsation in the exhaust pipe system of a large reciprocating compressor is analyzed.The first ten order natural frequencies of the gas column and the fluctuating pressure amplitude of each node are calculated.The results show that the frequency of the first ten gas columns in the pipeline system is between 1~25 Hz,which can avoid the excitation frequency of the compressor 33.13 Hz.The result shows that the system does not produce low order air column resonance.In addition,the maximum value of pressure unevenness ? at the compressor exhaust end is 5.87%,less than the API618 standard allowable value 7%,and the maximum value of pressure unevenness at the buffer tank outlet ? is 0.25%,less than the allowable value 0.65%,indicating that the pipeline system design is reasonable,and will not cause a strong vibration.In Case 2,the airflow pulsation in the intake and exhaust piping systems of a large reciprocating compressor was analyzed separately.The results show that gas column resonance occurs in the intake and exhaust pipeline.For the intake pipeline,it is advisable to do some modification.Firstly to add an orifice plate at the outlet flange of the intake tank.Then decreasing the pipe length between the intake tank and the compressor.Lastly increasing the inlet pipe length.For the exhaust duct,it is also advisable to make some improvement.Firstly to add an orifice plate at the inlet flange of the exhaust buffer tank.Secondly increasing the length of the exhaust buffer tank.Then reducing the length of the pipe between the compressor and the exhaust buffer tank and increasing the length of the pipe after the exhaust buffer tank lastlyAfter modification,the percentage of pressure drop in the inlet and exhaust pipes due to the orifice plate is 0.44% and 0.11% respectively,which is less than the allowable pressure drop of the API618 standard 1.02%.Moreover,the excitation frequency of the compressor 33.33 Hz is not at the resonance zone of the inlet and exhaust pipeline.So there will be no air column resonance generated in the pipeline.In addition,both the compressor inlet ? 6% and the compressor exhaust ? 3.98% are less than the allowable value 7%.The inlet ? of the inlet buffer tank is 0.55%,less than the allowable value 0.8%.The outlet ? of the exhaust buffer tank is 0.57%,less than the allowable value 0.634%.The amplitude of fluctuating pressure at each point is within the standard allowable range,which shows that the scheme is feasible.3.In order to verify the theoretical analysis results,two sets of air flow pulsation test program which are actual unit test and small acoustic test are designed.In actual unit test,the time domain chart of pressure fluctuation signal is measured by pressure sensors at case 2 pipeline system.Then through the fast Fourier transform the time domain graph is transformed into a frequency domain graph,getting the pressure unevenness and each order frequency peak size.In small acoustic tests,gas column natural frequency testing and fluctuating pressure testing are conducted.In the test of natural frequency of gas column,the signal generator is used instead of compressor as the excitation source of frequency,and the natural frequency of gas column is measured by sweep frequency method.In the test of pulsating pressure,the pressure fluctuation in the buffer tank is tested by the pressure sensor,and then the pressure unevenness is obtained.