Air separation method and apparatus

Abstract

A method and apparatus for separating air in which an oxygen-rich liquid stream is pumped and then heated within a heat exchanger to produce an oxygen product through indirect heat exchange with first and second boosted pressure air streams. The first boosted pressure air stream is cold compressed at an intermediate temperature of the heat exchanger, reintroduced into the heat exchanger at a warmer temperature and then fully cooled and liquefied. The second boosted pressure air stream, after having been partially cooled, is expanded to produce an exhaust stream that is in turn introduced into a lower pressure column producing the oxygen-rich liquid. The second boosted pressure air stream is partially cooled to a temperature no greater than the intermediate temperature at which the cold compression occurs so that both the first and second boosted pressure air streams are able to take part in the heating of the oxygen-rich stream.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method and apparatus for separating air in which an oxygen-rich liquid stream produced by a distillation column arrangement is pressurized by pumping and then vaporized to produce an oxygen product as a vapor. More particularly, the present invention relates to such a method and apparatus in which the oxygen-rich liquid stream is heated through indirect heat exchange with an air stream that is subjected to cold compression at an intermediate temperature and another air stream that is partially cooled and expanded in a turboexpander that exhausts into the lower pressure column of the distillation column arrangement in order to impart refrigeration.BACKGROUND OF THE INVENTION[0002]Air is separated to produce oxygen, nitrogen and argon-rich products through the cryogenic rectification of the air. Such cryogenic rectification is conducted by compressing the air, purifying the air of higher boiling contaminants such as water ...

AI Technical Summary

Benefits of technology

The present invention improves the efficiency of air separation plants by using a second boosted pressure air stream to heat the liquid oxygen stream, which leads to higher oxygen recovery and lower energy consumption compared to prior art methods. The use of cold compression and an expander exhausting into the lower pressure column reduces energy consumption, but also requires additional air being sent to the turboexpander to compensate for the increased refrigeration demand. The second boosted pressure air stream helps to reduce the flow rate and pressure of the first boosted pressure air stream, which in turn reduces the demand for heating. The invention also includes the use of an argon column to separate argon and oxygen and produce an oxygen-containing liquid as a column bottoms and an argon-rich vapor column overhead, which increases the oxygen recovery. The use of a nitrogen-rich liquid stream as reflux in the lower pressure column also helps to increase oxygen recovery.

Problems solved by technology

The drawback in cold compression is that energy is added to the plant by the cold compressor that must be compensated for by an increased refrigeration demand.

However, such an increased refrigeration demand requires additional air being sent to the turboxpander exhausting into the lower pressure column.

This results in less air being introduced into the higher pressure column and a decrease in the oxygen recovery.

This in turn will result in lower flow rates and lower pressures for the first boosted pressure air stream than would otherwise be required.

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