Numerical Study on the Leakage and Diffusion Characteristics of Low-Solubility and Low-Volatile Dangerous Chemicals from Ship in Inland Rivers

Considering the accidents of ships for dangerous chemicals transportation in inland rivers,a numerical method for the simulation of the leakage and diffusion processes of dangerous chemicals in inland rivers is proposed in this paper.Geographic information,such as rivers and buildings in the model,is obtained through Google Earth and structures of rivers and buildings are described by Auto CAD.In addition,the Fluent is adopted to simulate the leakage and diffusion processes of the dangerous chemicals where the standard k-εmodel is used to calculate the turbulent flow.Considering the interaction between chemicals and water,the VOF method is used to describe the leakage,drift and diffusion process of dangerous chemicals groups on the water surface.Taking a section of the Yangtze River as an example,the leakage and diffusion processes from a ship carrying 3,000 tons of low-solubility and low-volatile dangerous chemicals are studied,and the characteristics of leakage and diffusion are analyzed in detail.During the simulation,the area of the maximum group of leaked dangerous chemicals reaches up to about 1800 m2,and the number reaches up to 45.Furthermore,the influence of density,viscosity,water velocity and leakage velocity on the leakage and diffusion processes is investigated in this paper.

Numerical study on effects of the cofferdam area in liquefied natural gas storage tank on the leakage and diffusion characteristics of natural gas

The leakage and diffusion characteristics of natural gas were investigated in the condition of the leakage of liquefied natural gas(LNG) in the storage tank.Fluent was adopted to simulate the process in a series of three-dimension unsteady state calculations.The effects of different heights of the cofferdam(1.0 m, 2.0 m and 3.0 m),wind directions,ambient temperature,leakage location,leakage volume on the diffusion process of natural gas were investigated.The diffusion characteristics of the natural gas clouds over cofferdam were found.Under windless condition,when the gas clouds met,the gas clouds rose due to the collision,which made them easier to cross the cofferdam and spread out.The higher the ambient temperature was,the higher the gas concentration around the cofferdam was,and the smaller the gas concentration difference was.When the leakage occurred,the higher coffe rdam was more beneficial to delay the outward diffusion of gas clouds.However,when the leaka ge stopped,the higher cofferdam went against the dissipation of gas clouds.Under windy condition,the time to form stable leakage flow field was faster than that of windless,and the lower cofferdam further reduced this time.Therefore,considering the effect of barrier and dissipation,it was suggested that the rational height of cofferdam should be designed in the range of 1.0 m to 2.0 m.In case of emergency,the leakage of gas should be deduced reasonably by combining the measurement of gas concentration with the rolling of gas clouds.When windless,the leakage area should be entered between the overflows of gas clouds.

Bibliometric Analysis of Research Trends and Hot Spots of Leakage and Diffusion of Hazardous Gases

Dangerous gases widely exist in modern production and people’s daily life.Once they are used or maintained improperly,they are very easy to leak,leading to major accidents seriously endangering people’s health and asset safety,such as fire,explosion,burns,poisoning,asphyxia,etc.In this paper,the data collected from CNKI was taken as the research object,and the relevant research in the field of leakage and diffusion of hazardous gases was analyzed through visual analysis by using the VOSviewer software,so as to provide reference for subsequent scholars.

CFD Investigation of Diffusion Law and Harmful Boundary of Buried Natural Gas Pipeline in the Mountainous Environment

The leakage gas from a buried natural gas pipelines has the great potential to cause economic losses and environmental pollution owing to the complexity of the mountainous environment.In this study,computational fluid dynamics(CFD)method was applied to investigate the diffusion law and hazard range of buried natural gas pipeline leakage in mountainous environment.Based on cloud chart,concentration at the monitoring site and hazard range of lower explosion limit(LEL)and upper explosion limit(UEL),the influences of leakage hole direction and shape,soil property,burial depth,obstacle type on the diffusion law and hazard range are analyzed.Results show that the leakage gas is not radially diffused until it reaches the ground,and the velocity of gas diffusion to the ground and the hazard range decrease as the angle between the leaking direction and the buoyancy direction increases.Triangular and square leak holes have a faster diffusion rate and a wider hazard range than circular.The diffusion rate of leakage gas in soil rises as soil granularity and porosity increase.The time of leakage gas diffusion to the ground increases significantly with the increase of burial depth,and the hazard range reduces as burial depth increases.Boulder-type obstacles will alter the diffusion path of the leakage gas and accelerate the expansion of the hazard distance,while trench-type obstacles will cause the natural gas to accumulate in the trench and form a high concentration region slowing the expansion of the surface gas concentration.

Safety design analysis of a vent mast on a LNG powered ship during a low-temperature combustible gas leakage accident

Liquefied natural gas(LNG)is a kind of clean energy,and many LNG-powered vessels have been de-signed and built around the world.However,LNG introduces the potential risk of leakage and explosion accidents;thus,it is necessary to conduct safety assessments on the layout of typical facilities during the initial design stage.In this paper,an on-deck LNG fuel area model is established by employing the computational fluid dynamics(CFD)method according to an LNG-powered Aframax oil tanker.The distri-bution of potential dangerous areas on the concentration field and temperature field is presented under leakage and diffusion accident conditions with vent masts of different heights.The results show the fol-lowing:the gas concentration rises rapidly at the initial stage of leakage and tends to stabilize after a certain period;the leakage and diffusion trend of light gas is basically the same as that of heavy gas,and the lowest heavy gas and light gas temperature on the deck between the storage tank and the upper building is-7.9 C and 4.7°C,respectively,when the venting mast leakage point is at the height of 6 m;and the higher the mast leakage point is,the more safe the ship design.For safety considerations,the height of the venting mast designed in this paper should not be lower than the height of the LNG storage tank,which is 10 m.