Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1981-12-11
1984-04-10
Sever, Frank
Gas separation
Means within gas stream for conducting concentrate to collector
62 17, 62 20, 423359, C01C 110
Patent
active
044418957
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the separation of mixtures, which in different phase states circulate in countercurrent and at least partly in a closed circuit. A mass transfer takes place between the two mixtures and the separating effect is caused by a partial change of the phase state of at least one of the components to be separated.
Dual-temperature processes are known in which the mass flow rate of both circulating substances, apart from any superimposed flows in the closed circuit remains almost constant. Such processes may well be suitable for separation if the mass transfer is accompanied by chemical reactions and if the temperature dependence of the equilibrium constants of these reactions causes adequate separating effects. However, in general only a limited separating effect can be produced by means of absorption or adsorption exchange without chemical reactions and without any phase transition with respect to the temperature change.
In addition, dual-temperature or dual-pressure processes are known in which the circuit of at least one phase of the circulating mixture is not closed. For example a gaseous component is absorbed in a liquid and then this gaseous component is driven out of the liquid by means of a different gas, by means of its own vapour or by reducing the pressure. However, these processes are relatively unsuitable for the separation of valuable substances, whose losses must be limited to the maximum. It is also impossible to drive out the absorbed gaseous component from the liquid by means of its own vapour at supercritical pressure.
In the separating process according to the invention the separating problem is solved in that the mixtures to be separated in two different phase states circulate in countercurrent at least partly in a closed circuit in which part of the mass transfer devices operate at a higher temperature or a higher pressure and another part of these devices operate at a lower temperature or a lower pressure, the separating effects being caused through at least one third of one of the components of the mixture also changing the phase state with respect to the particular temperature or pressure change. There is also a reversal of the flow direction of that part of the mass flow, which changes the phase state. Therefore this part of the mass flow will recirculate in a part of the said circuit between the two temperature or pressure change points, so that a vital prerequisite for a good separating effect is obtained.
If one of the mixtures circulating in said circuit in liquid and the other gaseous, known mass transfer devices can be used, e.g. columns with plates or packings. However, one mixture can also be in the solid phase state. According to the invention the process is then performed in such a way that the relative circulation of said mixture with respect to the second, fluid mixture takes place either by means of fluidized beds of existing contact devices or by means of suitable periodic reversals of the flow paths of said fluid mixture through immobile layers of said mixture in the solid phase state.
The process described in general terms hereinbefore is particularly suitable for improving ammonia production. Ammonia is produced from a synthesis gas consisting of hydrogen, nitrogen and small amounts of methane and inert gases, the latter being mainly argon. Both methane and inert gases are enriched in the synthesis circuit of an ammonia plant and must be removed from it. Part of these gases is dissolved in the ammonia product flow and is conventionally removed together with the latter. In addition, normally part of the synthesis gas is drained off from the synthesis circuit in order to reduce the methane and argon proportions therein. This leads to losses of this valuable synthesis gas and the already synthesized ammonia.
Processes are already known for the separation of methane and argon from the synthesis circuit by means of low-temperature rectification. The main disadvantage of these processes is that the rectification process must take place bel
REFERENCES:
patent: 4060591 (1977-11-01), Garber et al.
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