The Gas Concentration during Gas Purging in Oil Tank (1st Report)

Abstract

For the analysis on the distribution of gas concentration during gas-purging in oil tank of a tanker, it is necessary to determine quantitatively the dispersion coefficient and the interception rate of gas-purging caused by existance of circulated gas flow and dead zones in tank.In this paper, the values of dispersion coefficients are calculated by use of the distribution of flow velocity and the interception rate ξ by stagnated flow is introduced in analytical method for one dimensional model. Besides, two dimensional analyses by finite element method are carried out to investigate the variation of distribution of flow velocity and gas concentration in tank using various conditions of decisive factors governing gas diffusion, i. e. position of inlet and outlet, volume of supplied gas and tank geometry. By the results of analyses, the relations between above-mentioned factors and dispersion coefficient or interception rate ξ are clarified.The actual values of dispersion coefficient and interception rate ξ are obtained from measured values of gas concentration in a 250, 000 DWT oil tanker by means of one dimensional analysis.