Dynamic Simulation Of Gas Pipeline Ventilation And Software Development Of Predicting Venting Time

In order to minimize the impact of venting operation on the gas supply from the pipeline to users,reduce the severity of the accident and the comprehensive loss caused by the accident,it is necessary to determine the reasonable duration of the venting process of the pipeline section of the gas transmission pipeline section before the implementation of venting operation,which can be used as an important basis for formulating the emergency plan of the pipeline system accident.Since venting operation corresponds to unsteady gas flow process,dynamic simulation of venting process based on venting scheme is usually needed to accurately determine the duration of venting.This thesis firstly analyzed the flow characteristics of natural gas in the venting process of gas transmission pipeline by integrating the knowledge of gas dynamics in the venting process and the simulation results of OLGA,and determined the variation rule of flow state parameters such as gas temperature,pressure,flow rate and other parameters in the venting process,as well as the characteristics of the outer boundary of the venting system,which provides a theoretical basis for the unsteady simulation of natural gas pipeline venting process.Secondly,establishes unsteady hydro thermal simulation models based on the venting scenarios of three main gas transmission pipeline sections,including venting at one end of a single pipe section,venting at a single point of a double pipe section and venting at both ends of a single pipe section.The model is composed of basic equations of gas pipeline flow,gas state equation,gas physical property equation,initial conditions and appropriate boundary conditions;The implicit central difference method is used to discretize the basic equations of pipe flow,and the fsolve function is called to solve the equations corresponding to each time step,so as to realize the dynamic simulation of the whole venting process.Considering the actual engineering experience of venting,the judgment condition for the end of the venting process is that the average pressure of the vented pipe section is lower than0.01MPa;The simulation results of the model and OLGA software are compared,the trend of flow parameters corresponding to the two methods is very close,and the relative deviation of the two methods in venting time and cumulative venting volume can be guaranteed to be within 10%.The established venting time calculation model of gas transmission pipeline section can provide reference for the operation of gas transmission pipeline venting system.Finally,based on the dynamic simulation data model of venting operation in the pipe section between valve chambers,the software interface is written in C language and the Qt development platform is used to develop the dynamic simulation and venting time prediction software of natural gas venting process of gas transmission pipeline,which is used to realize the input of component parameters,initial conditions and valve opening scheme and the presentation of calculation results;The influence of the parameters of the vent line,the initial conditions of the vent,the opening scheme of the valve and the parameters of the vent pipe section on venting time is analyzed by single variable method,and conclued the two scenarios of single point venting and the relationship between venting time at one end and at both ends of a single pipe section.The control mode of vent valve’s opening is studied.Considering the vent noise,riser outlet flow and vent time,a more favorable valve opening control logic for vent operation is proposed to shorten the vent time as much as possible and ensure safe and stable venting when the noise meets the specified requirements.