The Research Of High-pressure Natural Gas Pipeline Ventilation Noise Suppression Technology

The natural gas station will produce very strong noise during natural gas venting.The gas flow rate from the spout is very high.Expelled gas mixes rapidly with ambient air.Noise is mainly generated in the mainstream area.As the noise has been greatly exceeded the national noise standards.Aiming at this problem,The characteristics of flow field and sound field are simulated by ANSYS FLUENT software in this paper.According to the theory of noise reduction,a vent tube with reduced venting noise was designed to provide reference for noise suppression in the field.The specific research results are as follows:(1)After the vent tube gas is ejected,it is violently mixed with the surrounding gas,resulting in the exchange of momentum,mass and energy.According to the two-dimensional flow field simulation results obtained:The initial length of the vent tube jet is 7 times the diameter of the vent.In this region the same velocity and exit velocity,is the main area of noise.In the transitional section speed decay rapidly,gradually reduced to zero in the main section.(2)Using LES for two-dimensional unsteady simulation of flow field.Capturing the whole process of the gas spout from the nozzle to the full shot.Observing the process of swirling propagation based on the vorticity diagrams at different times.The result is the coherent structure produce the noise.(3)Based on the transient simulation results and the FW-H equation,simulate the Radiated sound field.Set multiple monitoring points in space for getting sound pressure spectrum of different monitoring points.The radiation noise of the vent pipe decreases in the axial direction as the distance increases,while the sound pressure level in the radial direction has a pronounced directivity.At the same radial distance,the maximum sound pressure level decreases with increasing axial distance.When the axial distance is 2.5m,5m,7.5m and 10m respectively,the maximum SPL reaches the maximum at 5m,5m,10m and 12.5m respectively.Combining the human ear senses with the A,B,and C weighting methods to evaluate the noise,the maximum noise levels obtained were 103 dB(A),112.5 dB(B),and 117 dB(C),respectively.(4)Changing the gas vent tube outlet Mach number are simulated.According to the simulation results:As the exit Mach number decreases,the sound pressure level at the same monitoring point decreases and the frequency at which the maximum sound pressure level is reached also decreases.In the actual conditions should be reasonable control of outlet flow rate and pressure in order to achieve the purpose of noise reduction.(5)According to the study of the characteristics of radiation noise,the design of ventilated riser is selected based on the principle of anechoic attenuation of expansion chamber.In order to achieve better noise attenuation,calculate the optimal expansion chamber length and diameter.In order to achieve a wider range of noise cancellation frequencies,two expansion chambers are designed.Insertion tubes of length 1/2 and length 1/4 are inserted on both sides of the chamber.Simulate the venting riser.It can be concluded that the designed vent riser can improve and reduce sound pressure level of vent noise.The sound pressure level reduction amplitude of each monitoring point on the ground is between 0-40dB,the maximum sound pressure level is controlled below 90dB,and the average value is controlled at about 60dB.Achieve a good silencer effect.