THE merits of producing deuterium by the distillation of hydrogen are quite well known. However, the best methods of distillation column design are not so well established.
The usual correlations available for predicting column design parameters fail when applied to the hydrogen systems, since the bulk of the data for the correlations is obtained from higher boiling systems such as aqueous solutions and hydrocarbons. For example, the optimum downcomer area was found to be much larger than predicted, and one well known correlation I gives an overall plate efficiency of 130 per cent.
These and other correlations are generally applicable only to systems having physical characteristics similar to those for which the data were obtained. The unconventional properties of liquid hydrogen, which has a density one-fourteenth, and a viscosity one-twentieth that of boiling water, give rise to unusual behaviour in a distillation column. Accordingly, research has been conducted at the National Bureau of Standards Cryogenic Engineering Laboratory in Boulder, Colorado, to determine the design parameters for a hydrogen distillation column.
Since the behaviour of packed columns 2-5 and bubble cap columns e has been previously reported, this research was primarily concerned with the characteristics of perforated or sieve plate columns. Such parameters as plate spacing, plate geometry, maximum allowable vapour velocity, weir height, and downcomer area were investigated, and the results of these investigations were applied to the design of a pilot plant column.
Since deuterium occurs naturally in the form of HD rather than D2, the pilot plant was designed to separate the system H2-HD. However, all the experimental work leading to the design of the pilot plant was carried out with the H~.-D~ system, for D2 is readily available, and HD is not. The use of the H2-D2 system in the experimental work rather than the H2-HD system is easily justified. Since the two pairs have very similar physical properties, they should have similar distillation behaviour. As an index for comparison, the Drickamer and Bradford z correlation predicts that the two systems will have the same overall plate efficiency. The O'ConnelF correlation predicts a plate efficiency for the HD system only slightly higher than that for the D~ system.