Study On Safety Capability And Replacement Scheme Of The Gas Pipeline Network In Kunming During The Artificial Coal Gas Converted To The Natural Gas

The operation of Sino-Myanmar natural gas pipeline made it possible to use natural gas,a cleaner and more efficient energy source,to instead of artificial gas in Kunming city.However,the condition of the artificial gas pipeline network in Kunming city is so complex that it is hard to determine a safe scheme for the natural gas replacement.The wall of the pipeline is obviously corroded,and certain sections of the pipe have serious settlement problems.Besides,the artificial gas is operated under the low or medium pressure,but the pressure is higher with the natural gas.Therefore,it is essential for the pipeline and public safety to judge whether the artificial gas pipeline network is capable for the natural gas replacement and carefully design a safety replacement scheme.The paper first comprehensively collected and analyzes the basic data of artificial gas pipeline network in Kunming city,and effectively identified the main failure modes and typical defects of Kunming artificial gas pipeline network.Based on the theory of fluid mechanics,electrochemistry,structural mechanics and safety evaluation,the corrosion mechanism of the conveying medium is determined by the combination of experimental and theoretical research.Taking the corrosion pipe section and the settlement pipe section as the research object,the safety ability of the artificial gas pipeline network is systematically determined.The calculation model as well as the replacement scheme is established for the artificial-natural mix gas.The achievements provide theoretical and technical support for the formulation and field implementation of replacement schemes.The main contents and achievements of are as follows.(1)The structure and facilities,equipment and operating parameters of the artificial gas pipeline network under the jurisdiction of Panlong district,Wuhua district,Xishan district and Guandu district in Kunming city are investigated.The artificial gas pipeline network in Kunming city is divided into nine areas.The main failure modes of the pipeline network are determined as the electrochemical corrosion induced wall failure as well as the settlement induced pipe suspension and stress overrun.(2)The analysis of compositions in artificial gas and the ion compositions in sewage are carried out.The results showed that the potential causes of pipe corrosion are H2,CO2,H2S and high concentration of Cl-.Experiments on static and dynamic corrosion of artificial gas and natural gas are carried out.Under the condition of artificial gas,the static and dynamic corrosion rates of the pipe are 0.2163 mm/a and 0.2774 mm/a,respectively.Under the condition of natural gas,the static and dynamic corrosion rates of the pipe are 0.0283 mm/a and 0.0552 mm/a,respectively.It is revealed that the electrochemical corrosion under CO2 is the main cause for the corrosion of the pipe under artificial gas condition.(3)Based on the theory of split-phase flow and PIPEPHASE software,the simulation model of artificial gas pipeline network in Kunming city is established.The distribution of pressure,temperature and liquid holdup in the pipeline are analyzed,and the sections with high possibilities to have concentrations are also found.In order to solve the multiphase flow corrosion problem existing in the pipeline,the Arrhenius equation,which describes the relationship between the chemical reaction rate constant and the temperature change,combined with the dynamic reaction experiments under different carbon dioxide partial pressure conditions,are used to establish the Multiphase Flow Corrosion Rate Prediction Model for Gas Pipeline Network.The average relative error between the predicted value of corrosion rate and the experimental value is 8.9%,which is obviously better than OLGA multiphase flow corrosion prediction results.Based on the model,the corrosion rate of artificial gas pipe network is analyzed.It is found that there are 14 kinds of "?" pipe sections with high degree of corrosion,which are mainly distributed in the pipe front with high pressure and high end retention rate.(4)Based on the finite element method,the stress analysis model of the corrosion-settlement free section is established.The equivalent stress values of the pipe at operating pressure of 0.1 MPa-0.6MPa are calculated,and the maximum replacement pressure of natural gas is set as 0.4 MPa(instrument pressure).(5)Based on the Mohr-Coulomb model,the contact mode of the face-face and the large deformation condition of the finite slip,the tangential behavior of the tube-soil which is controlled by the friction coefficient,and the relationship between the self-weight,the soil load and the liquid load,the Nonlinear Contact Finite Element Analysis Model for Settlement Defect Pipe Section is established.The relationship between the diameter,the length of the subsidence,the internal pressure,the retention rate and the equivalent stress and deformation of the pipeline are analyzed.The results revealed that in the actual operation process.when the defect size is 2.4cm × 2.4mm,the length of pipeline settlement should not exceed 60m.(6)The safe operation pressure of 9 areas of the artificial gas pipeline network is determined between 0.1 MPa and 0.4MPa(instrument pressure).(7)Aiming on the application difficulty of the FLUENT software to the large scale network,a one-dimensional displacement model of replacement gas is established with consideration of the mixed gas diffusion mechanism,the mass transfer theory of natural gas and artificial gas,continuous equation,momentum equation and energy equation are considered,and the inlet and outlet boundary conditions of the pipe network.The average relative deviation between the simulated natural gas replacement total time and the measured values is 11.4%,which is usable to the replacement engineering.(8)Based on the established one-dimensional displacement model,the inlet pressure,the natural gas flow rate and the total time required for natural gas replacement are analyzed.The absolute pressure of the pipe inlet is 102kPa,135kPa,170kPa,225kPa and 340kPa.Under the above inlet pressure conditions,the recommended replacement scheme is proposed and the replacement total time is 60.98 h.Based on the recommended scheme,the specific distribution process,the separation point control and safety risk control,including pipe network replacement test for the pipeline network areas of C1-8,C1-9 and C1-10 are established.The achievements provide theoretical and technical support for the safety and efficient replacement of artificial gas pipeline network in Kunming city.The replacement scheme ensures the safe operation of key livelihood projects in Kunming.