Research On The Safety Of Natural Gas Spherical Tank And It’s Water Cooling System

Both natural gas spherical tank and LPG (liquefied petroleum gas) sphericaltankbelong to the pressure vessel under pressure-bearing condition, and media in themare flammable and explosive.Once an accident occurs in the course of using natural gasspherical tank or LPG spherical tank, disastrous consequences will take place, thus it’spretty significant to make good safetyprotection for them.Atpresent, foreign anddomestic researches mostly start from thermal response laws of LPG spherical tanks infire environment to prove the necessity of water cooling system for them,but researchesfor their mechanics response laws in fire environment are very little. Nevertheless, thereare evenno correlationalstudies about natural gas spherical tank, so there is not a clearproof about the necessity of water cooling system for natural gas spherical tank. What’smore, relevant standards and norms haven’t make clear whether natural gas sphericaltank should set up water-cooling protection system or not. Therefore, in actualconstruction, designers either set up water-cooling protection system for natural gasspherical tankin accordance with the relevant provisions of LPG spherical tank, or notset up.This paper will use ANSYS Workbench to set up a3-D geometry entity model forone10000m3natural gas spherical tank, and performa thermal-stress coupling analysisof the tank by indirect method. Firstly, make a thermal analysis of natural gas sphericaltank under the condition of fire to get the temperature distribution; then regard thethermal analysis result as body load and apply it to the structure analysis in order tocalculate the stress intensity distribution of the tank; after that, through the processingfunction of stress linearization, divide the calculated stress intoprimarylocal membranestress, primarymembrane&bending stress, and primary&secondary stress.Furthermore, on the basis of the third strength theory, evaluate all kinds of stressintensities on the principle of stress intensity evaluation, to check whether the intensitiesmeet the safety requirements or not, thereby verifying the necessity of water coolingsystem for natural gas spherical tank in case of fire.Meanwhile, make a simple analysisoftheactual working data about natural gas spherical tank, toaccount for the function ofcooling water system for natural gas spherical tank under the condition of hightemperature.Through the analysis, the conclusion can be drawn: in the fire environment, the higher the temperature is, the bigger the stress intensity of thenatural gas spherical tankis, while the lower the yield strength is, and when the stress intensity exceeds theallowable stress, the tank will break; therefore, it is necessary to do a timelywater-cooling protection for the tank, in order to put out the fire and lower thetemperature, and avoid the tank breaking because of insufficientmaterial strength beforethe gas pressure in the tank has not yet reached the burst pressure. In the situation ofhigh temperature, the rise or reduction of temperature will not take obvious effects onthe gas pressure in the tank, and the gas pressure won’t exceed the blasting stress of thetank, thus under the circumstance, it’s not necessary to do water cooling for natural gasspherical tank.