Hydraulic Resistance of Fine Packing in Uranium Hexafluoride Rectification
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HYDRAULIC RESISTANCE OF FINE PACKING IN URANIUM HEXAFLUORIDE RECTIFICATION
V. K. Ezhov
UDC 621.039.543.4
The hydraulic resistance of irregular fine packing is studied as a function of the process parameters for the rectification of metal hexafluorides. It is shown that the dependence of the hydraulic resistance of irregular fine packing on the rectification parameters coincides with the dependence presented in the literature but with different coefficients and exponential factors.
Rectification is one of the effective methods of purifying uranium hexafluoride from volatile impurities. The advantages of this method are high product purity, unlimited nomenclature of impurities, and equipment simplicity. To design packed rectification columns, it is necessary to have, first and foremost, information on the separation power of the packing with the thermodynamic parameters of the process, the maximum vapor velocity determining the capacity of the column, the lag of the liquid, and the hydraulic resistance of the packing. The hydraulic resistance of the packing determines the energy consumption on gas movement through the apparatus and characterizes the state of the packing in the column. Experimental data on the separation power of the packing and the limit velocity of vapor in the column are presented in [1, 2]. The hydraulic resistance of irregular packing in the rectification of organic liquids is calculated according to the equation [3] (Wvap + Wliq )2 a p / l = , (1) 8g (Ff H st H d )3 2 where Δp/l is the resistance of the packing per unit of its length, GPa/m ; ¬ = 4/Re0. vap ; Revap = 4Wγvap/aμvapg; Wvap and Wliq are, respectively, the linear speed of the vapor and liquid in the column, m/sec; g = 9.81 m/sec2; a is the specific surface area of the packing, m2/m3; Ff is the free volume of the packing, m3/m3; ΔHst and ΔHd are, respectively, static and dynamic lags of the liquid in the column; ϕ is an empirical coefficient; γvap is the density of vapor, kg/m3; and μ is the viscosity of the vapor, Pa·sec. 85 Different coefficients of Eq. (1) are proposed in [4, 5]: ¬ = 90/Re0. vap for Revap ≤ 120 for stainless steel packing; 0. 85 0. 2 ¬ = 354/Re vap for Revap ≤ 120 and ¬ = 16/Re vap for Revap ≥ 120 for caprone packing. In [6] the experimental data of [7] are analyzed using the Reed–Fenske equation
p/l m
Wvap + liq a
n
+ liq a 3 vap (Ff
V )3
,
(2)
where m and n are empirical constants; μliq is the viscosity of the liquid, Pa·sec; V is the volume of the apparatus, m3. The value of n was found to be equal to 1.8, which is in agreement with the data of [8]. The following values are recommended for a more detailed study of the rectification of organic liquids: n = 1.8 for 0 < Δp/l ≤ 835 Pa and n = 2 for 835 < Δp/l ≤ 2500 Pa. Information on the hydraulic resistance of packing in the rectification of mixtures of elemental fluorides is limited to studies of mixtures of uranium hydroxide with bromine pentafluoride for 9.5 and 44.5 mm in diameter columns with HeliPack-2019 packing and uranium hexafluor
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