The equations which represent the head-separation factors of the dual-temperature-exchange columns are derived and the optimum operating conditions for them as well as the design of the columns to bring about the following four possible cascade schemes are discussed.
Cascade Schemes:
Non-Mixing cascade (Cf. Fig. 3)
The stripped output from the second stage enters the top of the enriching column together with the enriched output from the first stage.
Scheme 1: Gas is circulated.
Scheme 2: Liquid is circulated.
Mixing cascade (Cf. Fig. 4)
The stripped output from the second stage enters the top of the stripping column.
Scheme 3 Gas is circulated.
Scheme 4: Liquid is circulated.
Assumptions:
(1) Only the low-deuterium-content region is made the subject of study.
(2) Liquid-phase catalysts may be employed in these cascades, although no catalyst will be necessary in water-H2 S system.
(3) The cross sectional area of each column is proportional to its gas throughput.
(4) The stage variables (γ, N, n, δ, Tl, Th, etc.) are constant throughout each of the entire cascades.
Summaries of the results obtained are as follows:
(1) The head separation factors β are given by the following equations,
Scheme 1:
Scheme 2:
Scheme 3:
Scheme 4:
(2) The total volumes of the enriching and stripping columns, V, are given by:
Scheme 1:
Scheme 2:
Scheme 3:
Scheme 4:
(3) Some numerical calculations are carried out for each of the cascade schemes and the following results are obtained.
a) There is an optimum condition for the minimum total volume of the cascade, and it depends upon the variables of each stage.
b) The liquid circulating cascade is preferable to the gas circulating cascade.
c) If the cost of feed may be left out of consideration, the cascade of Scheme 4 will be the most preferable, as shown in Table 1.
