Experiment And Simulation On Prevention And Removal Of Natural Gas Hydrate Blockage Via Hydrogen Blending And Purging

The natural gas hydrate blockage will seriously affect the normal operation of transmission pipelines,so oil&gas companies have made a lot of investment to prevent and unblock hydrates.Blending hydrogen（H₂）into pipelines can be used to remove the threat of hydrate because of its extremely severe hydrate formation conditions.Compared with the traditional injecting alcohol,blending H₂ into pipelines is expected to not only reduce the preventing and unblocking cost,but also realize low-cost large-scale H₂ transmission.However,there are few reports about preventing and unblocking natural gas hydrate by blending H₂.In order to study its performance,in this work,a model used to predict the hydrate phase equilibrium conditions of hydrogen-natural gas blends（HNGB）in pure water was established firstly,then the model was verified by conducting experiments and the inhibition effect of blending H₂ on the formation of natural gas hydrate was also studied.Finally,unblocking natural gas hydrate by hydrogen purging was well investigated by experiments.Firstly,taking CH₄,C₂H₆,C₃H₈ and H₂ as representative components of HNGB,and the Patel Teja+Chen Guo（PT-CG）model was established to predict the phase equilibrium conditions of HNGB with different H₂ content.In the temperature and pressure range of273.85 K-291.45 K,1.23 MPa-20.73 MPa and H₂ content 4.55%-88.93%in the literatue data,the average absolute deviation of pressure（AADP）of PT-CG model of predicting the hydrate formation pressure in this work was 8.11%,while the phase equilibrium prediction software,i.e.,Multiflash and PVTsim,were 16.32%and 30.94%respectively,and it showed that the overall accuracy of PT-CG model is high.Then through experimental verification,it showed that PT-CG model established in this work is adaptive for binary,ternary and quaternary HNGB systems.The hydrate formation conditions of M1（20%CH₄+80%H₂）,M2（80%CH₄+20%H₂）,M3（73%CH₄+7%C₂H₆+20%H₂）and M4（43%CH₄+5%C₂H₆+2%C₃H₈+50%H₂）systems in pure water were determined by the isochoric pressure-search method.The AADP of M1-M4 systems predicted by PT-CG model was 7.12%,1.63%,3.52%and 4.96%,respectively.When the H₂ content was 80%,the model deviation increased.The hydrate dissociation enthalpies of M1-M4 systems were calculated by the Clausius Clapeyron equation,and their values were 90.16,68.02,74.43 and 76.92k J·mol^-1,respectively.Finally,the performance of removing s I（CH₄）and s II（90%CH₄+10%C₂H₆）hydrate blockage by H₂ purging was studied in a self-designed tubular reactor,and results showed that the performance of removing hydrate blockage by H₂ purging was better under the conditions of high purging flowrates and low purging pressure.The greater the purging flowrate,the stronger the heat transfer capacity of H₂ gas flow and the gas separation capacity of removing hydrate plug.After purging s I hydrate plug for 0.83 h at 275.15 K,3.4 MPa and 1.0 SLM（Standard liter per minute）,the hydrate blockage dissociation ratio reached the highest 64.5%,which was 23.3%higher than that of 0.4 SLM.Under the same purging pressure,s II hydrate plug is more stable than the s I.After purging s II hydrate plug for 0.83 h at 275.15 K,1.0 SLM and 3.4 MPa,the hydrate blockage dissociation ratio was 42.0%,which was 34.9%lower than s I hydrate plug.The research of this work provides a new method and basic data for the hydrate prevention and removal technology.