Numerical Simulation Study On Hydro-thermal Characteristics And Mechanical Properties Of Pipeline For The Transportation Of Natuaral Gas-hydrogen Mixtures

Hydrogen is a kind of clean energy,which is of great significance to promote the transformation of energy structure and reduce carbon emissions.At present,the development of infrastructure transmission facilities for hydrogen energy is still insufficient.How to achieve the large-scale and efficient hydrogen transportation is an important issue in the whole industrial chain “production-storage-transport-use” of hydrogen energy.Blending a certain proportion of hydrogen into natural gas and using existing natural gas pipelines or pipe networks for transportation is an effective way to achieve large-scale and high-efficient transportation of hydrogen.However,due to the large difference between the properties of hydrogen and natural gas,blending hydrogen into natural gas will affect the hydro-thermal characteristics of natural gas transportation and the mechanical properties of pipeline steel.Therefore,it is of great significance to carry out research on the influences of hydrogen on the hydro-thermal characteristics of pipelines and pipe networks and the mechanical properties of pipeline steel during the transportation of hydrogen-blended natural gas mixtures.In this paper,firstly,the mathematical model of pipelines and pipe networks for the transportation of hydrogen-natural gas mixtures is established.By using the numerical simulation method,the influence of hydrogen blending ratio on the hydro-thermal characteristics of high-pressure gas pipeline and centrifugal compressor,medium pressure gas pipeline and pipe network is simulated and analyzed.The results indicate that under the same working condition,hydrogen blending will increase the volume flowrate of gas pipelines and pipe networks,while the energy flowrate will decrease.At the same rotational speed of the centrifugal compressor,as the hydrogen blending ratio increases,the pressure ratio and shaft power of the centrifugal compressor show a downward trend,and the joint operation point of the centrifugal compressor and the gas pipeline gradually moves to the direction of high flowrate and low pressure.The temperature drop along the pipeline will slow down with the blending of hydrogen.Secondly,the basic theory of molecular dynamics simulation is introduced,and the influence of hydrogen atoms on the tensile mechanical properties of ?-Fe system without and with point defects is studied by molecular dynamics simulation method.It is found that during the stretching process,the lattice structure in the ?-Fe system is basically unchanged at the elastic deformation stage,while the body-centered cubic structure in the ?-Fe system is changed to the face-centered cubic structure in the ?-Fe system at the yield stage.After hydrogen atoms are added into the ?-Fe system,the tensile strength and Young's modulus of the system are reduced,and the more the number of hydrogen atoms incorporated,the greater the reduction of the tensile strength and Young's modulus of the system.Finally,molecular dynamics simulation methods are used to study the influence of hydrogen atoms on the tensile mechanical properties of X80 and X70 pipeline steels without and with point defects,in which both the X80 and X70 pipeline steels are simplified as Fe-C alloys.The simulation results show that the varying law of tensile strength and Young's modulus during the stretching process is similar to that of the?-Fe system.Through comparison with the experimental results in literature,it is found that the molecular dynamics method is capable of accurately simulating the tensile mechanics of X80 and X70 pipeline steels which are infiltrated into hydrogen atoms from a qualitative point of view.The simulation results and varying law are qualitatively consistent with those obtained in the macro experiments.