Influencing Factors Analysis And Nozzle Optimization Of Inerting Operation Process Of LNG Cargo Tanks

In recent years,liquefied natural gas(LNG)has been widely used due to its huge advantages in storage and transportation.The LNG tank should be dry,inert,gas-driven and pre-cooled before the first loading.The purpose of inert is to reduce the oxygen content in the tank to less than 2%,so as to prevent the explosion caused by the mixing of LNG and air.At present,there are few studies on LNG tank gas inerting,which is blind and wasteful only based on experience.In order to optimize the gas inerting process and improve the efficiency of LNG tank gas inerting,the main work of this paper is as follows:Firstly,a numerical simulation model of inert gas inerting LNG tank was established based on the mass conservation and momentum conservation differential equations with nonlinear finite element software,and the accuracy of the model was verified.Second,combining with the mechanism of gas convection and diffusion,the influence of nozzle shape and area,inlet velocity and other parameters on the inerting process is explored.The standard deviation of velocity and concentration in the flow field is directly related to the standard deviation of velocity and concentration in the inert region.When larger nozzles are selected,the standard deviation of velocity and concentration in the flow field is small,which is conducive to the formation of the bed inerting.When the standard deviation of velocity is less than 0.73m/s on the plane 0.5m away from the nozzle,the push-type inertia can be realized.24%of the nozzle size is the critical condition for the realization of the push-type inertia.The push-type inertia can be realized when the proportion of the nozzle size is more than 24%.Based on the rule of the influence of nozzle diameter on inerting effect,three nozzle shape schemes are proposed,and the square order nozzle scheme is selected as the optimization scheme according to the engineering reality.Compared with the original scheme,the optimized scheme can save about 1.58%-11.21%of the gas consumption,shorten 16.9%of the inerting time,and have better economy.The purpose of this paper is to propose an optimal scheme for the inerting of LNG tank gas and provide a theoretical basis for the inerting of LNG tank gas.Through the establishment of mathematical model,the results of numerical simulation are processed and analyzed,and the optimization strategy of inerting scheme is put forward and the optimization results are compared,which provides reliable theoretical basis for practical inerting operation.