Dual purity oxygen by mixing streams to make low purity oxygen
Publication Date: 2009-Feb-04
The IP.com Prior Art Database
It is known that two different purities of oxygen can be produced from a double column air separation unit by withdrawing a sidestream of impure oxygen several stages above the bottom of the low pressure (LP) column, in addition to a pure oxygen stream from the bottom of the LP column (for example figure 2).
The liquid to vapour ratio is then reduced below the side-draw and, provided the quantity of high purity oxygen is low enough, the same boil-up will suffice as in a low purity plant. Thus some high purity oxygen can be produced for very little power penalty compared to producing all low purity.
The above system has the disadvantage that if the column is packed, the sidedraw requires an additional liquid collector and distributor, with associated extra construction cost.
Instead, it is proposed that the low purity oxygen is made by mixing a lower purity stream from an existing column section break (feed or product location) with high purity oxygen from the bottom of the low pressure column.
In particular, this could be the return from an argon side arm column, or liquid taken from the low pressure column at the location where the side-arm return enters it. If no argon is produced and so there is no argon side arm column, the low purity oxygen could be formed by mixing crude LOX from the HP column with high purity oxygen from the sump of the low pressure column.
Figure 1 shows a simple ASU producing oxygen at a single purity using an internal compression process.
Figure 2 illustrates how two oxygen purities can be made from the same process by splitting the bottom section of the low pressure column and taking the low purity oxygen from an intermediate location. This has the disadvantage that the column design becomes non-stand...