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 H-2-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 DELTA-T 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 approximately 0.065 MPa. 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 alpha-is nearly equal to the limited value (an inverse of cut theta). The total separation factor alpha-beta exceeds 10(4) when DELTA-T = 1,200 K, F = 1 cm3 (at 288.15 K, 0.1 MPa)/min and theta = 0.1. (3) Even for the higher feed rate F of 100 cm3 (at 288.15 K, 0.1 MPa)/min, alpha-beta remains 100. In addition, the optimum pressure increases with DELTA-T and F.