Research On Isolator-free Nitrogen Replacement In Large-diameter Long-distance Pipeline

There is a new trend in the field of Nitrogen displacement namely gas displacement for Heavy-caliber pipeline without isolators,which has many advantages:low resistance,effective,reliable,low cost,easy control for flow rate,less influence in complicated topography and pipeline installation,and simpler displacement operation.By and large,that is a new and rapid developing industry process. However, domestic theory circle do not have the relevant theoretical analysis and the specific method of calculation.Base on this situation,applying this technology people have some blindness,and many enterprises give up to apply this displacement process.So it is an urgent task for us to make a deep research about the theory and calculation methods of Nitrigen displacement without isolators.In this paper,the writer shows a new achievement in this field,which can be a guidance for the operation of Nitrogen displacement without isolators, and the research will make a great economic effect on the gas production of oil fields.Applying Fluent software to do numerical simulation in the process of natural gas pipeline's replacement, obtained the mixing gas length changes law with the entrance of velocity at the moment of nitrogen replaced air and natural air replaced nitrogen separately. That is, with the increase of entrance flow rate, the mixing gas length and the average growth rate of it are all grown, so the required amount of liquid nitrogen is grown. The writer makes a model of the replacement of gas pipeline by applying hydrodynamics, heattransfer theory and pipeline transmitting technology.At the same time,the writer does a deep analysis to the influence of pressure,fluent rate,pipeline radius and pipeline length during the gas replacement.Finally with the whole work showing above,the achievement could calculate a precise parameters about replacement.With the support of MATLAB numerical calculating and AI technology,we can develop a calculating sofeware which can amend the parameters and directly indicate the replacement industry process during the start or the maintenance phase of gas pipeline.The results brought in theoretical references to nitrogen replacement production with no isolator.