Research On Optimization Technology For Transient Operation Of Natural Gas Trunk Pipelines

As long-distance pipeline transportation of natural gas requires energy supply from compressors and the actual operation condition of pipeline is a function of time,transient optimization technique is more suitable for real condition of gas pipeline transportation than steady one.On the premise of satisfying customer demands,how to appropriately select compressor pattern to achieve optimal operation and minimal energy consumption is key for pipeline operation management.Therefore,it is of great importance to conduct transient operation optimization analysis of natural gas pipeline system.Based on detailed literature review,typical transient operation optimal models combined with their characteristics and limitations are summarized from three aspects(object function,constraints and optimization variables),and the major algorithm,typical cases and application results are analyzed.This study focuses on the optimization of long-distance pipeline transient operation.Optimization model is established according to the characteristics of gas transport process in gas pipelines.Model solving theory and field case study are provided as well.The major content is shown below,and the following conclusions can be drawn from this work:(1)The most energy-saving optimization model for gas pipeline system is developed.Outlet pressure of compressor and compressor number are treated as two critical variables in this model.Both compressor parameters and pipeline properties,such as equation of motion and equation of state in pipeline,and corresponding boundary conditions,are considered as constraints,resulting in a mixed integer non-linear programming.(2)Based on the characteristics of transient operation optimization model,a compressor combined with the pipeline segment connecting its outlet is treated as a calculation element.Partial differential equations are discretized by using implicit central difference method.Because the non-linear nature of this model generates additional difficulties in solving this model,the special order sets(SOS)type2 and type3 are utilized to linearize one-dimensional and high-dimensional non-linear equation of continuity and momentum equation,respectively.(3)The natural gas pipeline transient operation optimization generally involves continuous and discrete variables.To obtain the solutions of optimization model,enumeration method is applied first to determine the number of compressor and the range of their outlet pressure.Then,random search method is used to obtain initial feasible solutions while cutting algorithm is utilized to conduct branch processing and preprocessing on SOS conditions.Useless branches are cut according to optimality condition and the upper and lower bounds of this problem are obtained.In this way,the optimal solutions of the simplified model can be determined through branch cutting algorithm.(4)Field example from the west-east gas pipeline project,namely Zhongwei compressor station to 92#valve chest section,is systematically analyzed using this model.First the basic parameters,such as inlet pressure,flux,compressor characteristics,pipeline properties at each time step,are determined.Through data matching and optimization calculation,the most energy-saving design,including the number of compressor and corresponding time-dependent outlet pressure variation,is obtained.The calculation results from both random search and optimization model are compared.Results prove the effectiveness and reliability of this method.