The Process
Each of a number of steps consists of two sieve tray columns. One column is maintained at 30 °C and is called the cold tower and the other at 130 °C and is called the hot tower. Deuterium extraction is done based on the difference in separation between 30 °C and 130 °C.
Hydrogen sulfide gas is circulated in a closed loop between the cold tower and the hot tower (although these can be separate towers, they can also be separate sections of one tower, with the cold section at the top). Demineralised and deaerated water is fed to the cold tower where deuterium migration preferentially takes place from the hydrogen sulfide gas to the liquid water. This "enriched" water from the cold tower is fed to the hot tower where deuterium transfer takes place from the liquid water to the hydrogen sulfide gas. An appropriate "cascade" setup accomplishes enrichment. Using one tower instead of a cascade is possible, but in practice it never occurs, as the tower size and process inventory would be much larger.
Normally in this process, water is enriched to 15–20% deuterium. Further enrichment to "reactor-grade" heavy water (> 99% deuterium) is done in a vacuum distillation unit.
Read more about this topic: Girdler Sulfide Process
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