Study On Steady-state Simulations Of Complex Natural Gas Pipeline Network Under The Mixed Transportation Of Multi-source Gas

The operation and management of urban gas pipe network is facing more and more challenges because of the complexity of urban gas pipe network,the formation of multi-source supply pattern and the development trend of intelligent pipe network.The simulation technology of natural gas pipeline network is the core technology in the optimization of complex urban gas supply system.It can accurately calculate the gas pressure and flow rate in the pipeline by computer,and provide an important reference for the operation and management of the pipeline network.Therefore,it has great academic value and engineering significance to develop an efficient and accurate simulation technologystate simulation technology for multi-source gas mixing in complex pipe networks.This technology can study the operation characteristics of multi-source gas mixing in complex urban gas networks and provide certain technical and theoretical support for the operation and management of urban gas network.The traditional mathematical model of natural gas pipe network is mainly established for hydraulic and thermal systems in the pipe network,which is used to reproduce the parameters of gas pressure,flow rate and temperature in the pipe network.However,it has found limited applications in mixed transportation of multi-source gas,due to its incapability in reflecting the influence range of different gas sources and the distribution of different gas components.Therefore,this research combines the traditional mathematical model of natural gas pipeline network with a gas component tracking equation and a gas source proportion equation to construct the mathematical model for mixed transportation natural gas pipeline network of multi-source gas.The correctness of the mathematical model was verified by a case of steady-state mixed transportation of multi-source gas.The results show that the model can accurately describe the distribution of components in the pipe network.The established mathematical model of multi-source gas mixing in complex natural gas network involves a large number of nonlinear equations.By the traditional simultaneous equations method,the hydraulic,thermal and component equations of each component and node in the pipe network are solved simultaneously,which has slow calculation speed,poor stability and even problem of calculation divergence.In order to solve this problem,the methods of linearization,hydrothermal decoupling and iterative solution of algebraic equation are applied to the steady-state simulation of multi-source natural gas pipeline network,and an efficient simulation technique of steady-state mixed transportation of multi-source gas is developed.Firstly,this method linearizes nonlinear hydraulic and thermodynamic equations by matrix Taylor expansion technique to avoid nonlinear iteration between equations.Secondly,based on the decoupling method,the hydraulic,thermodynamic and component equations are solved alternately,and a large-scale algebraic equation system is effectively decomposed into three small-scale algebraic equation systems.Finally,after pre-processing the non-diagona dominance for matrices and irregular algebraic equations,the efficient iterative method is used instead of the traditional Gaussian Elimination method to solve the algebraic equations.The calculation accuracy and calculation speed of the high efficient solution method proposed in this paper are verified by an example of a complex pipe network.The results show that although having the same accuracy with the traditional method,the proposed method turns out to have much higher calculation speed,which is about 8 times of the traditional method.The developed simulation technology is applied to Beijing high pressure gas pipe network,to study the distributions of pressure,gas source structure and gas components of the pipeline network in both summer and winter.The influence of seasonal gas supply scheme adjustment on the fluctuations of gas property is discussed.Also the emergency situation such as the upstream compressor failing to pressurize the gas and breaking of a pipe in the network are simulated.The results show that the adjustment of seasonal gas supply scheme leads to a change of the gas source structure of some gas transmission stations.The pressure,gas methane ratio,hydrogen ratio,Wobbe index and calorific value fluctuate in the pipe network.The pressure fluctuation can reach 20%,Wobbe index fluctuation is as large as 4.9%,while calorific value fluctuation is about 4.61%.These results can provide some theoretical guidance for the safe and stable operation of Beijing gas pipe network.