The Risk Analysis And Evaluation Of LNG Filling Station

With the development of technology in terms of natural gas on traffic usage,the construction and operation of Liquefied Natural Gas(LNG)stations played an important role on gas consumption are investigated.While the risk analysis and evaluation system is still in a unsound condition due to a rather late start in LNG stations compared that to other developed countries.In response to operation conditions of LNG stations nowadays,the risk analysis and evaluation for gas stations have been efficiently conducted in the paper,the detailed information demonstrated as following.The information of LNG filling station related to technological process and key instruments have been investigated by field visit and paper research.The event tree of LNG tank has been established,which obtaineds 52 minimum cut sets.The event tree of process pipeline has been established,which obtaineds 90 minimum cut sets.The event tree of LNG tank car has been established,which obtaineds 26 minimum cut sets.The event trees have been built up by adopting case and event tree analysis methods combined with accidental cases at home and abroad to identify dangerous source.By this way,the reason and way leading to the top events occurrence in event trees have been resulted by calculating minimum cutset and some measures have been proposed for precaution and improvement.The simulation of tanks leakage within the LNG filling stations have been deployed.The basic knowledge of the LNG tanks leakage and numerical models used for accidental leakage calculation by FLACS have been introduced.The extension and variation of evaporation rate of liquid pool under different working conditions have been explored with the varied of wind rate,hole diameter of leakage,and cofferdam depth.The diffusion of LNG vaporous clouds have been deeply analyzed by some data in aspects of the concentration variation in horizontally,in vertically and in monitoring points respectively and safety distance.The simulation results show that(1)the expansion of the liquid pool in the cofferdam is mainly affected by the size of the leakage aperture,the larger the leakage aperture,the faster the expansion of the liquid pool in the cofferdam,the deeper the thickness;(2)the evaporation rate of the liquid tank mainly depends on the size of the liquid tank area;(3)the greater the wind speed,the smaller the area of vapor cloud diffusion,and the lower the concentration of the gas cloud.The diffusion distance of the vapor cloud downwind increases first and then decreases with the increase of the wind speed.When the wind speed is above 5m/s,the vapor cloud diffusion effect is better.(4)the larger the leakage aperture,1/2 LFL gas cloud diffusion distance,the farther the occurrence of leakage,should confirm the size of the leakage aperture,in the safe distance to prohibit the occurrence of various sources of ignition,and do emergency preventive measures;(5)The higher the height of the cofferdam,the smaller the area covered by the vapor cloud,the smaller the methane volume concentration,the smaller the downward wind diffusion distance of the vapor cloud,In this paper,it is suggested to set the height of the cofferdam within the LNG filling station between 2-3m.The accidental consequences caused by LNG tanks continuing leaking have been analyzed.Numerical models adopted to calculation of fire explosion simulation within the FLACS have been introduced detailedly.The accidental scenes of pool fire occurring within cofferdam and vaporous cloud explosion have been built up.By researching flame height,flame temperature and the values of radiant heat flux in LNG stations under fire condition,In this accident scene,the radius of first degree burn is 50 m,the radius of second degree burn is 28 m,and the radius of death is 18.5 m.Assessing the consequence of pool fire and explosion by investigating the variation of flame and temperature as well as the value of explosive blast within LNG stations under the condition of vaporous cloud explosion have been deployed.The result of personal risk value in gas stations calculated by explosion consequence have been compared with risk acceptance criteria.