Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1991-12-27
1993-06-29
Spitzer, Robert
Gas separation
Means within gas stream for conducting concentrate to collector
55 58, 55 62, 55 68, 55 75, B01D 5304
Patent
active
052230040
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the production of oxygen through air separation by adsorption and more particularly utilizing two adsorbers and an oxygen accumulator with a cycle for each adsorber extending over a time period T and shifting from one adsorber to the other time period T/2 including the following steps: cycle to an intermediate pressure level by admitting the oxygen product countercurrently; approximately the high pressure level of the cycle by cocurrent admission of air without bleeding off; cocurrently; wherein the admission of air is interrupted; pressure level of the cycle which is below atmospheric pressure.
A process of this type is known from U.S. Pat. No. 3,738,087.
It is an object of the invention to propose a process having great flexibility of use and in particular a so-called mixed "cycle" (super and sub atmospheric) while allowing improved performances whereby oxygen-enriched air is obtained having an oxygen content above 95%, while reducing the investment cost and the production cost because of a selection of appropriate areas of pressure and because of utilizing a high rate of the rotating machines (compressors and/or pumps).
In order to practice the invention according to a feature thereof, the oxygen for the pressurization in step a) is supplied from the oxygen accumulator and the other adsorber which then is operating in its step d).
According to the invention, in order to practice the process the following steps can be accomplished separately or in any combination: 2.times.10.sup.5 Pa absolute and, preferably, between 1.4 and 1.7.times.10.sup.5 Pa absolute while the low pressure level is selected between 0.3 and 0.7.times.10.sup.5 Pa absolute and preferably between 0.35 and 0.5.times.10.sup.5 Pa absolute and wherein the desorption phase is effected at least in its final stage by pumping; high pressure level of cycle; substantially at the low pressure level of the cycle; towards the adsorber which is being pressurized is carried out substantially to pressure equilibrium; is being depressurized and advantageously countercurrently for the adsorber which is undergoing pressurization; for the adsorber being depressurized and countercurrently for the adsorber undergoing pressurization while in a succeeding stage the transfer is cocurrent for the adsorber undergoing depressurization and cocurrently for the adsorber undergoing pressurization; pumping step which is countercurrent, there is provided an intermediate stage of depressurization which is countercurrent, until atmospheric pressure is reached by opening to air; when the low pressure level of the cycle is in the area of 0.3.times.10.sup.5 Pa absolute; a terminal stage with decreasing pressure; starts with the elution stage in the other adsorber effected with gas drawn off from the production flow; depressurization stage (in one adsorber) towards the adsorber undergoing partial pressurization.
Thanks to the adoption of a so-called "mixed" cycle, in an area where pressures are relatively specific and ranges narrow, one can contemplate the utilization of simpler and less expensive machines than that which is necessary during the "pressure" or "vacuum" cycles.
The energy consumed by the machines used when in the narrow range of pressures where their yield is optimal, is thus minimized.
The comparison of the specific energy for the production of high oxygen content for instance above 85% in the "mixed" cycle, to the other cycles at the maximum use of the machines can be established as follows: energy is expended; Pa, again lower energy is expended; 0.2/0.3.times.10.sup.5 Pa, a similar amount of energy is expended.
The maintenance of a high pressure level above atmospheric pressure in the mixed cycle allows an increase in productivity compared to the "vacuum" type cycle.
The cycle according to the invention is aimed only at the production of oxygen, the other fraction of the separation includes only air fairly enriched in nitrogen. On the other hand, the specific energy required for the separation is much lower.
The
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Eteve Sylvie
Hay Leon
Rottner Thomas
L'Air Liquide, Societe anonyme pour l'Etude et l'Exploitation de
Spitzer Robert
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