Study On The Kinetic Characteristics Of Oil And Gas Explosion In Pipeline And Its Mitigation Mechanisms

As the economy continues to grow,fossil fuels(representing primary energy sources)are being consumed at an accelerating rate as the main source of energy for comsumption,and the pollution caused by their combustion is becoming more and more serious.To alleviate this pressure,more clean energy sources such as hydrogen,ethanol,LPG and ethanol gasoline are being widely used.Among them,ethanol is a biofuel that can be processed by working corn,wheat,sugar cane and other crops.It can promote combustion and reduce HC,CO and NOx emissions when mixed with gasoline because ethanol contains oxygen,therefore ethanol gasoline is one of the alternative energy sources widely used in automobiles.Studies on ethanol gasoline have mainly focused on its combustion and exhaust emission characteristics,less research has been done on its explosion characteristics under different initial conditions.However,in the process of production,transportation and use of ethanol gasoline,etc.,once a leak occurs into the restricted space to form gasoline steam,an explosion will occur when being ignited,resulting in heavy property losses and casualties.Therefore,it is of great scientific importance and practical value to carry out experimental research on oil and gas explosion to better understand the mechanism of the accident.Firstly,the characteristics of ethanol gasoline such as flame propagation and explosion overpressure under different initial concentrations,initial blended ratios,initial temperature were carried out through small-scale experimental studies and CFD numerical simulation.The two states of oxygen-rich and oxygen-poor ethanol gasoline with an initial ratio of 10%were determined experimentally,and it was found that the severity of the ethanol gasoline explosion with an initial blended ratio of 10%was the highest at 1.0 mL.In addition,the initial blended ratio has an important effect on the explosion characteristics of ethanol gasoline.At the initial volume of 1.0 mL,with the increase of the initial blended ratio,the flame propagation speed and maximum explosion overpressure of the ethanol-gasoline increased linearly at the same time,while the time of maximum overpressure appeared decreased on the contray.At the initial volume of 1.8 mL,the flame propagation speed and maximum explosion overpressure decreased and then increased,and the explosion overpressure was maximum near E10(Ethanol content of 10%).The relationship between explosion overpressure and explosion sound pressure was qualitatively determined.With the initial blended ratio increases,the trend of maximum sound pressure and explosion overpressure is almost the same,so that the change of explosion overpressure can be predicted to some extent by the non-contact measurement of sound pressure.Secondly,the ultimate goal of the study of explosion characteristics is to be able to control the occurrence of explosions or mitigate the hazard of explosion by understanding the mechanism of their occurrence.The explosion mitigation by different suppressant such as heptafluoropropane(representing gas explosion suppressant)and water mist(representing water-based explosion suppressant)were investigated using a small-scale explosion test platform,and the explosion suppression effect of the two suppressants was compared and analyzed.The ethanol-gasoline explosion can be mitigated by heptafluoropropane.When the concentration of heptafluoropropane increased from 1%to 10%,the maximum explosion overpressure reduction of 1.0 mL E10 explosion changed from more than 30%to more than 60%.In addition,the explosion is completely mitigated when the concentration of heptafluoropropane continuously increases.It was observed that the flame color changed from blue and yellow to purple with the effect of heptafluoropropane.In the process of ethanol-gasoline explosion mitigation by heptafluoropropane,it was observed that the flame color changed from blue or yellow to purple in response to heptafluoropropane.A GC-MS analysis of reaction product of the E10 explosion indicated that the products of explosion mitigation contained plenty of nitrogen-containing substances,which indicateds thet the purple color may have been caused by the spectrum of CN radicals during the mitigating reaction.When the concentration of water mist is 160 g/m3,the maximum explosion overpressure of ethanol gasoline decreased by 52.3%;with the concentration of water mist continuously increases,the explosion was effectively suppressed.The application of water mist in the mitigation process will cause the flame color from blue to dark yellow.Finally,from the perspective of combining practical applications,the results of small-scale explosion suppression experiments were verified through a large-scale explosion chamber.Due to the limitations of the small-scale chamber,the water mist applied in the mitigation process is ultra-fine water mist which has very small momentum,and the actual fire extinguishing nozzle can not be installed.In order to deepen the understanding of the use of actual fire extingushing nozzle for oil and gas explosion mitigation process,a large-scale explosion chamber was used to carry out a series of explosion and its mitigation tests,to determine effects of the different fine water mist application position,chamber constraints,water mist additives and fog on the explosion mitigation process.The location of the fine water mist application has a significant infuuence on explosion suppression.When water mist is applied 1.5m away from the ignition electrode,the explosion is enhanced because the slow flame propagation speed cannot meet the requirements of droplet break-up.However,the deflagration is suppressed when water mist is applied 6 m away from the ignition electrode under strong constraint.This is because the flame propagation speed exceeds the critical velocity required for the break-up of droplets,the Weber number greater than 12,droplet undergoes a secondary fragmentation process.The mitigation effect of explosion by water mist is affected by the constraint conditions of chamber.here was little effect on the explosion when fine water mist was applied at the back end under weak confinement conditions,because of the pressure relief that occurred quickly after the explosion occurred;while the application of fine water mist at the back end presented well explosion suppression effect under strong confinement conditions.Using water mist with additives,to a certain,may improve its effects on explosion suppression.Similar to previous small-scale experimental results,water mist containing K2CO3 additive further reduces the intensity of the explosion in the large-scale explosion test compared to with only water mist.The particle size of water mist has an important influence on explosion suppression,i.e.,a small D32 of the mist spray implies good explosion mitigation.Moreover,the impact is much greater than that using additives.Therefore,it is preferred to design a water mist system with a small droplet size among the conditions for ensuring the water mist transport distance and spray intensity in practical applications.