Research On Simulation Technology Of Natural Gas Vent Pipeline At Well Station

The low temperature generated by the venting process of the high-pressure natural gas pipeline is likely to damage the vent pipe,which is very harmful to the safety of the pipeline itself and the surrounding environment.This paper establishes a model for calculating parameters for natural gas throttling and a mathematical model for the simulation of natural gas venting pipelines to determine an effective model solution methodology that provides technical support for the analysis of the natural gas flow law in the venting pipeline and the accurate evaluation of the process parameters of the venting pipeline.(1)Through investigating the calculation parameters of the process parameters of the national and international venting pipeline as well as the design status and production data of high-pressure relief piping in typical gas field service stations,the difficulties in calculating the throttling parameters of high-temperature-pressure natural gas venting pipelines are analyzed.(2)The thermal properties such as compression factor,density,enthalpy and entropy of natural gas calculated by natural gas equations such as PR,SRK,BWRS are evaluated and optimized.Based on the theory of in-phase gas-liquid two-phase volatility,in combination with the preferred BWRS equation,the natural gas property parameter calculation model and gas-liquid equilibrium mathematical model were computed,natural gas phase parameters calculated at different temperatures and pressures,and the model verified accuracy.(3)In view of the choked flow,the critical and subcritical flow state of natural gas in the process of venting,the parameters such as single-phase flow and gas-liquid two-phase flow temperature and pressure of the natural gas vent line are set and resolved.(4)Considering the expansion temperature drop effect of high pressure venting natural gas and the temperature and pressure characteristics of natural gas in throttling process,a mathematical model of high-temperature and high-pressure natural gas for throttling expansion temperature drop is established.Based on the API data sheet and the published experimental data,the accuracy of 12 sets of compression factor values and 6 sets of enthalpy values calculated by the model was verified.(5)Based on the actual venting pipeline structure and process at the site,a simulation model of the venting piping system of different well stations was established.The accuracy of the simulation model was verified by 24 sets of measured venting temperatures.The average relative deviation between the calculated temperature and the measured temperature was 1.79%,which met the actual engineering requirements.(6)Combining the factual venting process of the pipeline,based on the simulation model of the venting piping system,the temperature,pressure and mach number of the pipeline which are in the design condition and the damming flow condition are calculated.In addition,the lowest temperature along the venting line of each well was also analyzed under different wellhead pressures and temperatures.Finally,not only the process parameters of the existing typical high-pressure vent line are calculated,but also the rationality of the design of the process parameters is evaluated.