Publishing Venue
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Abstract
There are many process cycles designed to meet the wide variety of different product requirements of cryogenic air separation plants. One of the most economic arrangements for the production of low purity (95%) gaseous oxygen, at reasonable pressures (say, 6 bar), is known as the "mixing column cycle." This requires a separate column to produce the product oxygen. This research note describes how this column can be fitted inside an existing column at an overall reduced cost.
Air Separation Low Purity Oxygen Production
There are many process cycles designed to meet
the wide variety of different product requirements of cryogenic air separation
plants. One of the most economic
arrangements for the production of low purity (95%) gaseous oxygen, at
reasonable pressures (say, 6 bar), is known as the “mixing column cycle.” This requires a separate column to produce
the product oxygen. This research note
describes how this column can be fitted inside an existing column at an overall
reduced cost.
Basic Cycle
In the straightforward form of the cycle shown in
Fig. 1, air is purified by refluxing it with fairly pure oxygen pumped, after
having been purified, from the Low Pressure (LP) column.
Thus, the resultant gaseous oxygen product is
available at about the same pressure as the feed air. The column here is a separate pressure vessel handling about a
third of the flow through the conventional high pressure (HP) column.
Higher Pressure Version
A variant of the cycle as shown in Fig. 2 can
deliver gaseous oxygen at a somewhat higher pressure than the feed air. This is done by installing a booster
compressor in the air supply to the mixing column and running the reflux pump
at a higher (matching) pressure. Other
modifications shown in Fig. 2 improve the system.
Since the mixing column and the HP column operate
at about the same pressure, with the same feed, about the same number of
theoretical stages, and with a favorable flow ratio, it is feasible to put the
mixing column inside the HP column. In
the basic cycle, then, the mixing column will no longer be a pressure vessel,
there will be no requirement for a lower hea...