Heavy water is used as coolant and moderator in heavy water nuclear reactor, and serves as a source material at nuclear fusion reactor.
Numerous methods, like distillation, electrolysis, and chemical exchange process, have been developed for separation of $D_2O$ from natural water. Among them distillation of water is now generally used for final enrichment of deuterium and for reconcentration of heavy water that has picked up from the nuclear reactor during use. Because the relative volatility for separation of $D_2O$ by the distillation of natural water is around 1.1 at pressure of 100 mmHg, the representative separation factor is only about 1.05, so that many theoretical plates, high reflux ratios, and long columns of large diameter is required. Since $D_2O$ is extremely expensive and economical separation is desired, the plant hold-up should be as small as possible. Consequently, the optimum water distillation column should have 1) small hold-up 2) small pressure drop, and 3) a large number of theoretical plates per meter.
The special corrugated wire mesh packing was developed for the purposes.
In the present work, experiment was carried out in a pilot scale column (4m height) with vacuum condition (50-200 mmHg) at total reflux. Each time when the equilibrium was reached, samples were taken at the top and bottom of the packing and analyzed by Infrared Spectrophotometer. The system was examined over the various range of pressure and flow rates. Initially uniform concentration of $D_2O$ end up with $D_2O$ concentration profile through the column when steady state has been reached. This implies that the packing has the average NTSM value equal to around 2.7 at head pressure of 100 mmHg.
The temperature and concentration profile of the column were predicted and compared with a computer simulation code which was developed in connection with this study. The experimental results show that the packing has improved efficiency and higher capacity (low pressure drop) compared to conventional tower packing for heavy water production. Unsteady state operational phenomena were also analyzed and compared with the experiments using modified Cohen equation.
