FPSO Topside Deck Flammable Gas Cloud Deflagration Process Experimental And Numerical Simulation Studies

FPSO(Floating Production Storage and Offloading)is a marine floating production and storage vessel.It is widely used in offshore oil and gas exploitation due to its wide range of water depth,strong wind and wave resistance,and large oil storage and oil discharge.The FPSO topside deck flammable gas cloud deflagration accident is one of the main risks of the FPSO,and once it occurs,it will cause huge property,personnel and environmental damage.In order to ensure the safe operation of FPSO,research on the FPSO topside deck flammable gas cloud deflagration process is an urgent problem to be solved.This paper conducts experiments and numerical simulations on the FPSO topside deck flammable gas cloud deflagration process.The main contents include:(1)Through the FPSO topside deck flammable gas cloud deflagration experiment system,the variation of flame shape and pressure with time in the process of flammable gas cloud deflagration was explored.The experimental results show that the flame propagation extends from the ignition to the surrounding,generating an expanding flow field,compressing the unburned gas and the surrounding air,and generating a pressure wave in the same direction as the flame.The basic variation of the pressure wave is to experience a number of pressure fluctuations such as a positive overpressure?a negative overpressure,a secondary positive overpressure?a secondary negative overpressure,and the first overpressure with increasing distance from the ignition point delay in the generation;When the concentration of methane is 10%,the peak value of explosion overpressure is increased by 61.26%and 33.33%,respectively,compared with 9%and 11%.This is because the deflagration accident of the premixed gas is affected by the stoichiometric concentration,and the stoichiometric concentration is 1.1 to 1.5 times the most dangerous concentration;The methane/air deflagration overpressure decreases with the distance of the obstacle from the gas cloud.The peak of the deflagration overpressure is larger,the distance is reduced by 100mm,and the overpressure peak is increased by 39.85%.The restraining effect of obstacles increases the deflagration intensity,but the experimental system can not further explain the strengthening mechanism of obstacles on the consequences of deflagration accidents.To solve this problem,a semi-open pipeline methane/air detonation experimental system is built.(2)Through the methane/air deflagration experiment system in the semi-open pipeline,the effects of different equipment spacing,length and steel frame position on the methane/air detonation flame morphology and overpressure law were investigated.The experimental results show that in the flame propagation direction,when the distance between the two obstacles is 200mm and 300mm and the spacing is 100mm,the overpressure peak increases by 62.67%and 99.29%respectively after crossing the second obstacle,and the flame speed increases respectively.290.99%and 90.15%.As the distance between the obstacles increases,the initial velocity of the flame reaching the second obstacle is greater,the turbulence induced by the obstacle is stronger,the flame speed is increased,and the overpressure peak is increased.When the length of the obstacle is 90mm and 60mm,the overpressure peak of the 30mm obstacle is increased by 51.92%and 23.08%.As the flame crosses the obstacle,as the length of the obstacle increases,the longer the stretched distance,the initial velocity of the turbulent vortex increases after entering the obstacle,resulting in the second flame acceleration and the peak of the deflagration pressure.The barbed wire with a blocking rate of 0.32,0.28 and 0.24 filled with wood bars has a blocking rate of 0.2.The overpressure peaks increased by 28.36%,22.39%and 6.72%,respectively.As the blocking rate increases,it is induced when the obstacle is crossed.The turbulence is stronger and more regular.During the deflagration process,the pressure wave advances the flame forward.The accompanying flow field of the unburned gas near the obstacle has been established before the flame reaches the obstacle.After the flame reaches the obstacle,the turbulence induced by the obstacle causes the flame front to bend and wrinkle,which increases the contact area with the unburned gas,and the flame speed increases,and the overpressure peak increases.The reason for the obstruction of the obstacle to the consequences of the deflagration accident is the obstacle-induced turbulence.(3)The FLACS software was used to simulate the FPSO topside deck flammable gas cloud deflagration experiment.The results show that the flammable gas cloud flame surface expands from the near ground to the periphery in an approximately spherical shape;The temperature field expands from the ignition position to the periphery with the near-ball surface facing up,the temperature of the gas cloud burning is higher,and the temperature of the gas cloud gradually decreases toward the surrounding,forming a temperature gradient.The maximum overpressure value appears on equipment that has a significant impediment to pressure waves.The average deviation between the experimental maximum overpressure and the simulation results is 14.96%,which has good consistency.It verifies the feasibility of the FLACS simulation the FPSO topside deck flammable gas cloud deflagration accident.The FLACS software was used to simulate the methane air deflagration experiment in the pipeline.In the experiment and simulation,the flame propagated laterally after the flame front crossed the obstacle.This is because the flame front velocity appeared opposite to the flame propagation direction after the obstacle.The actual proportion of the FPSO topside deck flammable gas cloud deflagration accident process was simulated.The results show that the large-scale methane/air deflagration intensity is very limited,but in the vicinity of the steel frame structure,the pressure rises sharply,even exceeding 22 kPa,causing moderate damage to the steel frame structure and slight injury to personnel.It is further verified that the FPSO upper deck blocking ratio device and steel frame structure have obvious excitation effects on the detonation intensity.This study is of great significance for the prevention,risk assessment and accident consequence investigation of FPSO fire and explosion accidents.