Temperature Water-Hydrogen Sulfide Exchange Process

11 DUAL-TEMPERATURE WATER-HYDROGEN SULFIDE EXCHANGE PROCESS 

The D2 S reflux needed for the cold tower is provided by the hot tower. This operates at a 

With a proper flow ratio of hydrogen sulfide to water, this lower separation factor makes possible transfer of deuterium from water to hydrogen sulfide in the hot tower and thus converts the HjS entering the hot tower into the DjS needed for refluxing the cold tower. 

Hydrogen sulfide is conserved by returning depleted Hj S from the top of the cold tower to the bottom of the hot. Heat is conserved by heat exchange between hot and cold liquid and between hot and cold vapor. In principle, no materials other than feed water are consumed in the dual-temperature system energy consumption can be reduced by efficient heat exchange, with a lower bound set by the minimum required by thermodynamics for the separation. 

The detailed maimer in which the dual-temperature system effects separation will be explained in Sec. IIJ. That separation is possible can be made plausible by the simple qu tative considerations of Fig. 13.26. This represents one vessel containing cold water and a second containing hot water throu which water flows in series and through which hydrogen sulfide may be recirculated. 

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In the dual-temperature H2O/H2S process (61,62), exchange of deuterium between H20(l) and H2S(g) is carried out at pressures of ca 2 MPa (20 atm). At elevated temperatures deuterium tends to displace hydrogen in the hydrogen sulfide and thus concentrates in the gas. At lower temperatures the driving force is reversed and the deuterium concentrates in H2S in contact with water on the tiquid phase. 

All of the previously mentioned plants except those employing distillation of water were parasitic to a synthetic anunonia plant. Their deuterium-production rate is limited by the amount of deuterium in ammonia synthesis gas. To produce heavy water at a sufficient rate, a growing industry of heavy-water reactors requires a deuterium-containing feed available in even greater quantity than ammonia synthesis gas. Of the possible candidates, water, natural gas, and petroleum hydrocarbons, water is the only one for which an economic process has been devised, and the dual-temperature hydrogen sulfide-water exchange process is the most economic of the processes that have been developed. 

In many respects, the case history presented by D. W. Jones and J. B. Jones of the DuPont Company is typical, They reported studies conducted on a pair of columns in use at Dana, Indiana, and Savannah River, Georgia, for a heavy-water process using dual temperature exchange of deuterium between water and hydrogen sulfide at elevated pressures. 

In a conceptual, ideal process, water would be continuously converted into hydrogen sulfide and back into water in the arrangement illustrated in Figure 4.6. This is known as a mono-thermal process because deuterium exchange occurs at only one temperature. Between the two conversions, the two species are repeatedly contacted. With an equilibrium ratio around... 

The dual temperature process is based on the atomic exchange of hydrogen and deuterium between hydrogen sulfide gas (H2S) and fresh water with a deuterium concentration of approximately 148 parts per million. 

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