Effect of operating pressure on H2-HT separative performances of 'cryogenic-wall' thermal diffusion column with continuous feed and draw-offs

By using the two-dimensional rigorous numerical solution of flow and convection-diffusion equations, the H2-HT separative performances of thermal diffusion column with 1,500 mm-height, 15 mm-radius and 77.35 K cold-wall was analyzed with pressure P, temperature difference between hot-wire and cold wall ΔT and feed rate F being parametrically changed. Flow analysis has revealed that the magnitude of the free convection is almost proportional to the pressure, and the secondary circulation is observed near the bottom of the column as the pressure increases. Moreover, laminar solution of free convection could not be obtained at the pressure more than ∼ 0.065MPa. Separative analysis for the 'cryogenic-wall' thermal diffusion column with 77.35 K cold-wall has made it clear in comparison with the separative performances of the 'ordinary cold-wall' column with the same condition except the temperature of the cold wall that: (1) The optimum pressure, being proportional approximately to the cold wall temperature, maximizing separation factor and/or the separative power is fairly smaller. (2) The degree of separation is remarkably larger and the heads separation factor α is nearly equal to the limited value (an inverse of cut θ). The total separation factor αβ exceeds 104 when ΔT=1,200K, F=1cm3 (at 288.15K, 0.1MPa)/min and θ=0.1. (3) Even for the higher feed rate F of 100 cm3 (at 288.15K, 0.1MPa)/min, αβ remains 100. In addition, the optimum pressure increases with ΔT and F. (author)