気体拡散分離装置の分離パワと最適操作圧

Abstract

Separative power was analysed of a gaseous diffusion separating unit with porous membrane to obtain the optimum operating pressure of a unit.A pore of membrane was assumed to be a circular capillary having uniform radius and length, and the Present-deBethune model was applied to the flow of binary gas mixture through pores in which the non-separative flow caused by the collision of unlike molecules and the viscous Poiseuille flow as a perturbation were added to the separative Knudsen flow.In a close-separation of an isotopic gas mixture at a constant temperature, the flow rate of gas through membrane and the separation factor, therefore the separative power of a separating unit depends only on the product (gas pressure×pore radius). Numerical calculation of the enrichment of 235U in UF6 gas showed that when the separative power was plotted against (inlet gas pressure×pore radius) with a parameter of (outlet gas pressure×pore radius) the curve having a maximum point was obtained. The total number of separating units of cascade necessary for a given separative duty is a minimum when the separative power of a unit has a maximum value, and therefore the inlet gas pressure corresponding to a maximum separative power may be considered as a optimum operating pressure from the standpoint of number of separating units. It was noted that the mean free path of gas molecules may become smaller than pore radius under the optimum inlet gas pressure for the outlet gas pressure exceeding a certain value. The correlation between outlet gas pressure and the corresponding optimum inlet gas pressure was expressed in a curve, which can determine the operating condition of a separating unit.