The Boc Group, Inc.

Thomas Rathbone

John T Lavin

Brian Anthony Keenan

David Mark Stuart

Michael Ernest Garrett

Air is separated in a double rectification column comprising a higher pressure column and a lower pressure column, the latter operating at pressures of less than 2 bar absolute. An oxygen product is withdrawn from the column by a pump. A first vaporous nitrogen stream is taken from the top of the higher pressure column, is compressed in a compressor and is used in a gas turbine. Feed to the lower pressure column is derived from a stream of the bottom oxygen-enriched liquid fraction obtained in the higher pressure column. To this end, this stream is subjected to further separation (typically in further rectification column) to form a vaporous nitrogen fraction (a flow of which is condensed and is used as reflux in the lower pressure column) and an oxygen-containing feed to the lower pressure column which flows via an outlet and a condenser to the column. At least 60% of the nitrogen product flowing to the gas turbine is taken from the higher pressure column.

Air separation

Air is separated in a main rectification column comprising a higher pressure column, a lower pressure column and a condenser-reboiler replacing the higher pressure column in heat exchange relationship with the lower pressure column. A first liquid oxygen fraction concentrated in krypton and xenon is formed at the bottom of the lower pressure column and is withdrawn through outlet. Argon-oxygen separation takes place in the column and a vaporous argon-oxygen stream depleted of krypton and xenon is taken from the outlet as it is subjected to further rectification in a column, a second liquid oxygen fraction containing argon impurity being obtained. A stream of the second liquid oxygen fraction is withdrawn from the column through the outlet and is purified in the column so as to obtain a purified oxygen product.

Separation of air

A heat exchange apparatus, typically for use in association with a double rectification column for the separation of air, has a downflow reboiler with boiling passages. In addition, there is a condenser in a position at a higher elevation than the reboiler. The condenser is fed with liquefied gas to be reboiled from the sump of a lower pressure column forming part of the double rectification column. A first conduit feeds the liquefied gas under gravity to the reboiler. The feeding of the condenser is effected by a vapor lift pump comprising a second conduit and an expansion valve disposed therein. Some of the liquefied gas is vaporized by passage through the expansion valve, and this vapor provides the vapor lifting pumping effect. The vapor is recondensed in the condenser.

Heat exchange method and apparatus

An elevated pressure nitrogen stream from an air separation plant is used to provide cooling for one or more sulphur condensers in an oxygen-enhanced Claus process for recovering sulphur.

Treatment of gas

An air separation method and apparatus in which a flow of air is subjected to a first rectification so as to separate therefrom an oxygen fraction and a nitrogen fraction. An argon-containing stream comprising argon, oxygen, and, as an impurity, nitrogen is withdrawn from the first rectification and is subjected to a second rectification so as to separate an impure argon fraction containing nitrogen. Nitrogen impurity is stripped from a stream of the argon fraction in a stripping column. A stream of sub-cooled liquid cools a condenser associated with an upper region of the stripping column by indirect heat exchange with condensing argon-nitrogen vapor mixture, and passes out of said indirect heat exchange still in sub-cooled state.

Air seperation

Air is compressed in an arrangement of compressors. A first flow of the thus compressed air flows through a main heat exchanger from its warm end to its cold end and is liquefied by passage through a valve. Two second stream of compressed air are taken. One is expanded in one expansion turbine and the other in another expansion turbine. The streams leaving the valve and the one expansion turbine are separated in a double rectification column. Liquid oxygen product is extracted from outlet thereof. Part is taken as liquid product and the rest is vaporized by passage through the heat exchanger from its cold end to its warm end and taken as gaseous oxygen product. The ratio of liquid oxygen product to total oxygen product is capable of being varied. Accordingly a chosen but variable proportion of the two second air streams flows to the double rectification column and a chosen but variable proportion of the two second air streams is returned to the arrangement of compressors to an intermediate compressor.

Method and apparatus for air separation

Cooled and purified air is introduced into a higher pressure rectification column and separated into oxygen-enriched liquid and nitrogen vapour. A stream of the oxygen-enriched liquid is flashed through a pressure reducing valve to form a mixture of liquid further enriched in oxygen and vapour depleted of oxygen. The liquid is reboiled by reboiler. A stream of the further enriched liquid is reboiled in condenser and is introduced into a lower pressure rectification column for separation into oxygen and nitrogen products. Reflux for the columns and is formed by condensing in condenser nitrogen vapour separated in the higher pressure rectification column. A reboiler provides an upward flow of vapour through the column. The condenser and reboiler take the form of a single heat exchanger. The reboiler is located in a phase separator, the reboiler is located in a rectification column containing liquid-vapour contact devices above the level at which fluid issuing from the valve is introduced. Oxygen-depleted vapour is condensed in the condenser by heat exchange with the further enriched liquid and at least some of the resulting condensate introduced into the lower pressure rectification column.

Compressed, purified, vaporous air and liquid air streams are introduced into a higher pressure rectification column. A stream of oxygen-enriched liquid flows from an outlet of the higher pressure rectification column via a reboiler and an expansion valve into a vessel. The oxygen-enriched liquid is partially vaporised in a boiler located in the vessel. The residual liquid flows from the vessel and a condenser to a lower pressure rectification column in which oxygen and nitrogen products are separated. A stream of vapour flows from the boiler through an outlet from the vessel to a pipeline which leads the air back for compression with incoming air. A greater yield of oxygen, and, if separated, argon is made possible by this recycle.

A stream of compressed air is purified in a unit by removal of carbon dioxide and water vapour. The air is cooled by passage through a heat exchanger to a temperature suitable for its rectification. The air is separated in a higher pressure rectifier into oxygen-enriched liquid and nitrogen vapour. A stream of the oxygen-enriched liquid is reduced in pressure and introduced into a phase separator provided with a reboiler with the result that further separation takes place and a liquid further enriched in oxygen and an intermediate vapour are formed. A stream of the further-enriched liquid is separated into oxygen and nitrogen in a lower pressure rectifier. A stream of the intermediate vapour is condensed in a condenser and is introduced into the lower pressure rectifier. A part of the liquid nitrogen reflux for the higher and lower pressure rectifiers is formed by condensing nitrogen vapour separated in the higher pressure rectifier by indirect heat exchange with liquid from an intermediate mass transfer region the rectifier. Another part of the liquid nitrogen reflux is formed by vaporising impure oxygen product of the lower pressure rectifier in a condenser-reboiler by indirect heat exchange with nitrogen vapour taken from the lower pressure rectifier.

A first flow of air is compressed in a first air compressor associated with a gas turbine and is purified in an adsorptive purification unit which separates water vapour and carbon dioxide from the air. The purified first flow of air is further compressed to a pressure at least 5 bar higher than that at which it is purified in a second air compressor whose outlet pressure is independent of fluctuations in the power output of the gas turbine, is cooled in a main heat exchanger, is passed through an expansion valve, and is introduced into a higher pressure rectification column. A second flow of air is compressed in a third air compressor which is independent of the gas turbine. The compressed second flow of air is purified in an adsorptive purification unit by the separation of water vapour and carbon dioxide therefrom. The purified second flow of air is cooled in the main heat exchanger and is introduced into the higher pressure rectification column. The air flows are rectified in the higher pressure rectification column and an associated lower pressure rectification column operating at pressures above 2 bar. A nitrogen product is withdrawn from the top of the lower pressure rectification column and a liquid oxygen product from the bottom thereof. The liquid oxygen is revised in pressure to at least 25 bar by a pump and is warmed to ambient temperature in the main heat exchanger.

Cooled and purified air is introduced into a higher pressure rectification column and separated into oxygen-enriched liquid and nitrogen vapor. A stream of the oxygen-enriched liquid is flashed through a pressure reducing valve to form a mixture of liquid further enriched in oxygen and vapor depleted of oxygen. The liquid is reboiled by reboiler. A stream of the further enriched liquid is reboiled in condenser and is introduced into a lower pressure rectification column for separation into oxygen and nitrogen products. Reflux for the columns and is formed by condensing in condenser nitrogen vapor separated in the higher pressure rectification column. A reboiler provides an upward flow of vapor through the column. The condenser and reboiler take the form of a single heat exchanger. The reboiler is located in a phase separator, the reboiler is located in a rectification column containing liquid-vapor contact devices above the level at which fluid issuing from the valve is introduced. Oxygen-depleted vapor is condensed in the condenser by heat exchange with the further enriched liquid and at least some of the resulting condensate introduced into the lower pressure rectification column.

Air is compressed in a compressor, cooled in a main heat exchanger, partially condensed in a reboiler-condenser, introduced into a higher pressure rectifier, and separated therein into nitrogen and oxygen-enriched liquid. Resulting nitrogen is condensed in further reboiler-condensers. One part of the condensate is used as reflux in the higher pressure rectifier and another part as reflux in a lower pressure rectifier. A stream of oxygen-enriched liquid is withdrawn from the high pressure rectifier and sent to an intermediate pressure rectifier which is reboiled by one of the further reboiler-condensers and in which further nitrogen is separated. A stream of liquid further enriched in oxygen is withdrawn from the bottom of the intermediate pressure rectifier and is separated in the lower pressure rectifier and impure and pure oxygen products are withdrawn respectively therefrom. In addition an argon-enriched oxygen stream is withdrawn from the lower pressure rectifier through an outlet and separated in an argon rectifier. Further impure oxygen product is withdrawn from the bottom of the argon rectifier.

Cooled and purified air is introduced into a higher pressure rectifier in at least partly vaporous state and is separated therein into oxygen-enriched liquid air and nitrogen. One part of the nitrogen so separated is condensed in a reboiler-condenser and another part in a reboiler-condenser. Some of the condensate is used as reflux in the high pressure rectifier, and the rest of the condensate as reflux in a lower pressure rectifier. Oxygen-enriched liquid air is taken from the bottom of the higher pressure rectifier and is separated into oxygen and nitrogen in the lower pressure rectifier. A liquid argon-enriched oxygen stream is withdrawn from the lower pressure rectifier through an outlet and is separated into argon and oxygen fractions in a further rectifier. The further rectifier is reboiled by the reboiler-condenser.

Air is introduced through an inlet into a higher pressure rectification column. A stream of oxygen-enriched liquid is withdrawn through an outlet from the higher pressure rectification column. A part of this stream is introduced into a low pressure rectification column through an inlet. The stream is separated in the column low pressure rectification into oxygen and nitrogen. In addition, an argon-enriched vapor stream is withdrawn from the low pressure rectification column through an outlet, and is at least partially condensed in a reboiler-condenser which reboils oxygen separated in an argon column. One part of the resulting at least partially condensed argon-enriched oxygen stream is reduced in pressure by passage through a valve and is introduced through an inlet into an intermediate mass exchange region of the argon column in which it is separated into argon and oxygen. Another part of the at least partially condensed argon-enriched oxygen stream is returned by a pump to the low pressure rectification column.

A stream of air is compressed in compressor and has water vapor and carbon dioxide removed therefrom in purification unit. A part of the resulting purified air is cooled by passage through heat exchanger and is employed to heat an intermediate reboiler in a lower pressure rectification column. The air flow from the reboiler passes into a higher pressure rectification column which supplies a stream of oxygen-enriched liquid air for separation in the lower pressure rectification column. Liquid nitrogen reflux for the higher pressure column is provided by taking nitrogen vapor from this column through an outlet and condensing it in another intermediate reboiler located above the reboiler in the lower pressure rectification column. The condensed nitrogen is returned to the top of the column. Another air stream is employed to reboil a further reboiler at the bottom of the lower pressure rectification column with the resulting condensed air stream being introduced into the higher pressure rectification column through an inlet. An impure oxygen product is withdrawn from the bottom of the lower pressure rectification column through outlet in liquid state and is vaporized in the heat exchanger. The arrangement of reboilers facilitates operation of the apparatus with a relatively low pressure ratio between the operating pressure of the higher pressure rectification column and that of the lower pressure rectification column.

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Farnham, United Kingdom

Thomas Rathbone