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Cryogenic Air Separation Plant Mechanical Layout Option

IP.com Disclosure Number: IPCOM000073580D
Publication Date: 2005-Feb-22
Document File: 3 page(s) / 14K

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Cryogenic Air Separation Plant Mechanical Layout Option

This idea relates to the field of cryogenic air separation and more particularly is an improvement whereby oxygen gas may be produced more economically at an elevated pressure.

Background

One of the most widely used cryogenic air separation cycles employs a double column distillation system having a higher pressure column and a lower pressure column thermally linked by a reboiler condenser. Often the lower pressure column is physically located above the higher pressure column. Also, as is normal for such cycles, there is a main heat exchanger for cooling feed air streams against products. In addition it is well known that oxygen can be withdrawn as liquid from the lower pressure column, have its pressure raised by pumping or hydrostatic head rise and be vaporised against a process stream to produce elevated gaseous oxygen product. The pressurised liquid oxygen can be vaporised within the main heat exchanger, or in a separate side reboiler exchanger.

The cryogenic distillation columns and exchangers are insulated by being located inside one or more insulation filled cold enclosures (often called coldboxes). It is a cost advantage to design the cryogenic process to have the minimum number of equipment items and the minimum number of coldboxes.

It is conventional practice to locate the bottom of the double column close to ground level to minimise the coldbox height and to also locate the cryogenic main exchangers close to ground level in the same coldbox, or, if the cross sectional area of a single coldbox would be too large to conveniently transport, in a separate coldbox .

There is a considerable market, particularly in the glass and metallurgical industries for lower purity (e.g. 85 to 98% O2) and lower pressure (e.g. 1.5 to 4.0bara) oxygen  for oxygen enriched combustion processes. There is an incentive to avoid the use of expensive oxygen compressors or LOX pumps for such processes.

For oxygen pressures up to about 2.0 bara  there is sufficient hydrostatic head available to generate the required pressure into an oxygen vaporiser placed alongside the higher pressure column. There is extensive prior art showing oxygen production  in this manner (e.g. EP 1207362).

Problem

For required oxygen pressures above  about 2.0 bara, there is insufficient hydrostatic pressure and therefore pumps would have to be employed for the conventional cycle.

Solutions

US 20030110796 (Rampp et al) overcomes this disadvantage by locating a side condenser (which vaporises the LOX) underneath the higher pressure column, in order to increase the available static head. Furthermore this patent teaches that that the main exchanger can also be located underneath the HP column between the HP column and the side condenser. By doing this not only does the cross-sectional area of the coldbox become smaller, but the LOX static head into the side condenser increases.

There is no suggestion in the patent that the side c...