| The blockage of gas pipelines occurs from time to time in the natural gas transmission and distribution systems.Once blockages,especially complete blockages appear,the normal operation of the entire system will be seriously affected,accurate and rapid determination of the blockage location is the key to deblocking.At present,there are relatively few studies on the blockage location of gas pipelines at home and abroad,accurate blockage location of the actual pipeline is still difficult to solve cost-effectively.However,the SCADA system has been widely used in oil and gas pipeline systems,the real-time monitoring of operating parameters like pressure and flow rate is one of its main functions,and it is essential to attempt to use these parameters to determine the blockage location of gas pipelines.Therefore,the transient flow characteristics of the gas pipeline when a blockage occurs were experimentally and numerically investigated,the relationship between blockage location and the duration from transient to new steady state caused by blockage was established,and a blockage location method of gas pipeline and its applicability was discussed,which has important theoretical and practical significance for the safe and steady operation of gas pipeline.The main research contents and results of this thesis are shown as follows:(1)An experimental and numerical simulation method for gas pipeline blockage was proposed.An experimental simulation system for flow characteristics of gas pipeline blockage was independently designed and constructed.The functional characteristics of the commonly used TGNET and SPS softwares for numerical simulation of gas pipelines were compared and analyzed,and the reliability of a gas pipeline physical model built by SPS software was verified using a real example.A visual basic program based on the AGA8-92DC model was written for predicting the compression factor of natural gas,and the effects of gas composition,compression factor,operating temperature,gas transmission volume,starting and terminal pressure,pipeline diameter and length on the steady flow parameters of gas pipeline were analyzed.(2)The processes of filling a storage tank and pipeline with gas and the steady state and blocking transient flow under different operating conditions,i.e.differential pressure(DP)at the near starting point and flow rate(Q)change over time(t),were experimentally simulated and monitored.The influence of blockage location on the differential pressure at the near starting point and flow rate was comparatively analyzed.The duration of gas pipeline flow from transient state caused by blockage to the final steady state was defined as Transition Time from Transient to Steady State(TTts),and then the DP?t and Q?t curves between the duration were fitted to calculate the TTts values corresponding to different blockage locations and the tendency of the distance from the blockage location to the near starting point L changing with TTts was also discussed.It is found that the DP at the near starting point and Q decrease with time as a power function during different TTtss which increase with increasing the distance from the blockage location to the near starting point L.The existing differential pressure and flow rate transmitters can reliably monitor transient signals of the DP and Q in the gas pipeline.(3)Taking the Y-J gas pipeline between stations as the research object,the physical model of its steady flow and transient flow caused by blockage was established by SPS software,the corresponding steady and transient flow characteristics before and after the blockage of the gas pipeline were simulated.The effects of complete blockage at different locations on the near end point and along-line pressure and flow rate in the pipeline were comparatively analyzed,and the influence of partial blockage of 90%,80%and 70%at the location 2.63 km long from starting point of gas pipeline on the near end pressure and flow rate was investigated.The results indicate that the differential pressure and flow rate change more significantly and the transient reaction time is shorter when the blockage location is closer to both ends of the pipeline.(4)The experimental and numerical simulation results of the flow process before and after the blockage of gas pipeline were compared and the compression process in the upstream pipeline and expansion process in the downstream during the complete blockage were analyzed.The TTts based on the differential pressure at the near end point and flow rate of the Y-J gas pipeline was determined,the charts and relation formulae between the corresponding blockage location L and TTts were established,meanwhile the detailed blockage location method and its applicability was illustrated.The results show that the key to blockage location is the real-time monitoring of transient parameters under different operating conditions and the determination of TTts.The variation trends of the curve of blockage location L and TTts are consistent from the experimental and numerical simulation results;The blockage location can be determined based on the real-time monitoring TTts values and the relation charts of the blockage location L and TTts values through numerical simulation.This method is suitable for blockage location of different gas pipelines with a precondition that differential pressure and flow rate variations near end of the pipelines caused by blockage must be within the accuracy of the monitoring instruments. |
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