The Operation Optimization Of The Natural Gas Pipelines For The Specified Time Region

Currently,with the growing of the natural gas network scale and the output,the increasing of energy-consuming equipment and the rising of energy costs,the ratio of energy costs account for professional company’s cash cost has up to 45%.It is urgent to concentrate on the pipeline operation optimization when making the long run program for gas pipelines or making the relatively stable daily running program for gas pipeline transmission capacity,steady-state optimization method usually has been used.However,in the daily operation and management of gas pipeline process,when the gas pressure,temperature,flow changes,the user gas consumption changes,turn off a user buffer,start / stop compressor unit,on / off valves,the accident leak or rupture of pipes,the gas pipeline will run into a non-steady-state condition,at this time,the steady-state running optimization method can’t accurately describe the real flow processes in the natural gas pipeline system,so it is not sufficient to provide adequate and reasonable operation schemes.The method of the operation optimization of the natural gas pipelines in the specified time region should be used to guide gas pipeline operation and management system.To solve the problems,the operation optimization technology of the natural gas pipelines for the specified time region has been studied and natural gas pipe network optimization software Opt NGP has been developed in this paper.Firstly,due to all kinds of physical properties of natural gas have impact on the optimization results,this paper analyzed various types of equations of state,researched and calculated natural gas physical parameters by selected BWRS equation of state,combined with characteristics of natural gas pipeline network running optimization to select the suitable gas pipe flow calculations and compressors,compressor station energy consumption calculation method,and developed the natural gas physical properties calculation module,pipeline calculation module,compressor calculation module and the compressor station calculation module.By analyzing the results of calculating each module examples and comparison,it is proved to be reasonable and can be used for subsequent network optimization calculations.Secondly,mathematical model of operating optimization under steady state in gas transmission trunk line is established which solved by dynamic programming method.Based the effect of the outbound pressure discrete steps on optimization results,this paper carry out a detailed analysis.Considering the speed and accuracy of the calculation,the author recommends the outbound pressure discrete steps which from 0.02 to 0.04 MPa is appropriate to solve the gas pipeline operation optimization problem using the dynamic programming method.The variable step dynamic programming method that based on the impact of the discrete steps was put which greatly improved the computing speed.Steady-state natural gas pipeline operation optimization software module was developed which uses Pipeline Studio TGNET software to verify the reasonableness of the optimization program and uses the optimal control condition to verify the optimality.The result showed that the software can be used to optimize the calculation of the steady-state gas pipeline with a high practical value.Finally,the model of the operation optimization of the natural gas pipelines in the specified time region is established which is based on the "independent time layer" hypothesis proposed by Professor Li Ligang and dynamic programming method based on the "independent time layer" is proposed to convert multiple time dynamic optimization problem into several layers separate single-layer optimization problem of time,which greatly improves the computing speed.Based on the above,the software module of gas pipeline operation optimization in the specified period was developed and it is verified reasonable by using TGNET.TGNET running data shows that the precision of the program based on "independent time layer" dynamic programming method is not high,only to provide suggestions for the operation optimization.