Air separation method and apparatus

Abstract

An air separation method and apparatus in which a supercritical oxygen product is produced by heating a pumped liquid oxygen stream having a supercritical pressure, through indirect heat exchange with a boosted pressure air stream. The indirect heat exchange is conducted within a heat exchanger and a liquid nitrogen stream is vaporized in the heat exchanger to depress the pressure that would otherwise be required of the boosted pressure air stream to heat the pumped liquid oxygen stream. The pumped liquid oxygen stream constitutes 90 percent of the oxygen-rich liquid removed from an air separation unit in which the air is rectified, the liquid nitrogen constitutes at least 90 percent of the liquid nitrogen that is not used as reflux and a flow-rate ratio between the liquid nitrogen stream and the oxygen-rich liquid is between about 0.3 and 0.90.

Description

RELATED APPLICATION[0001]This application claims the benefit of U.S. patent application Ser. No. 12 / 855,313, filed on Aug. 12, 2010, which is incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates to a method and apparatus for separating air in which oxygen-rich liquid is pumped to produce a pumped liquid oxygen stream having a supercritical pressure that is in turn warmed to a supercritical temperature through indirect heat exchange with a boosted pressure air stream to produce an oxygen product as a supercritical fluid. More particularly, the present invention relates to such a method and apparatus in which a liquid nitrogen stream is simultaneously vaporized while the pressurized liquid stream is heated, so as to depress the pressure that would otherwise be required of the boosted pressure air stream to heat the pumped liquid oxygen stream alone.BACKGROUND OF THE INVENTION[0003]There exists an emerging market for very high pressure supercritica...

AI Technical Summary

Benefits of technology

[0013]It is to be noted that the heating and cooling curves represent the aggregate heat transfer from the boosted pressure air stream and any other streams to be cooled to the warming oxygen and warming / vaporizing nitrogen stream and any other streams to be warmed. The composite curves combine multiple cooling streams (“hot” streams) into a single curve and multiple warming streams (“cold” streams) into a single stream. At a given temperature within the heat exchanger, the composite curve is defined such that the sum of the energy change of each hot or cold stream defines the duty for the hot or cold composite curve, respectively. Composite curves are used to simplify and idealize the analysis of heat exchangers with more than two streams transferring heat simultaneously.

Problems solved by technology

The use of such heat exchanger banking saves fabrication costs in that it is only the higher pressure heat exchanger that must be fabricated to withstand the high oxygen pressure and the even higher pressures of the boosted air stream that are necessary to heat the oxygen.

The problem with this is that the cost in fabricating such a heat exchanger to withstand the pressure of the boosted air stream can become prohibitively expensive, as well as the cost of the associated pipework and valves which must also be rated to the same very high pressure.

In addition, there can be increased energy costs in that an inline barrel compressor might be required, depending on the pressure, that has an efficiency that is less than an integrally geared compressor that could be employed at a lower pressure.

Finally, during the startup of such a system the consequences of a failed pressure test at very high pressures can be quite severe.

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