The Boc Group, Inc.

John T Lavin

Thomas Rathbone

David J Layland

Timothy D Atkinson

David Mark Stuart

Michael W Biddulph

Paul M Latham

Satish C Kler

David T Linnett

A product cryogenic liquid mixture comprising oxygen and nitrogen having a chosen mole fraction of oxygen is produced by expanding, typically through a valve, a pressurized stream of a precursor fluid mixture, which may be liquid air, having a mole fraction of oxygen greater than said chosen mole fraction, and thereby forming a vapor phase depleted of oxygen and a liquid phase enriched in oxygen. The vapor phase is disengaged from the liquid phase in a phase separator. A stream of the vapor phase is condensed in a condenser. The condensate is collected in a storage vessel as the product cryogenic liquid mixture.

Production of cryogenic liquid mixtures

A liquefied gas mixture comprising at least two components of which one is more volatile than the other or others is boiled in an apparatus including stripping passages for vaporising part of a flow of the mixture. The passages are arranged alternately with condensing passages. The stripping passages each have at least one heat exchange surface which is heated to a temperature which causes the liquid to boil and along which the liquefied gas mixture flows in countercurrent mass exchange relationship with a vapour flow evolved from such liquid. The more volatile component is progressively stripped from the liquefied gas mixture such that the vapour flow is enriched in its direction of flow in the more volatile component and the mixture itself is depleted of the more volatile component in its direction of flow. Accordingly, separation of the mixture takes place in addition to its boiling. The apparatus can be employed as a reflux condenser for an argon distillation column connected to a lower pressure column of a double column air separation unit. Condensation in such apparatus can be effected while separating oxygen-rich liquid produced in a higher pressure column. The products of such separation can then be introduced into the lower pressure column to reduce the separation work that would otherwise have to be performed in the lower pressure column.

Method and apparatus for reboiling a liquefied gas mixture

An heat exchange-cum-rectification apparatus comprises a heat exchanger having a first set of passages for separating by dephlegmation a first flow of compressed vaporous air into nitrogen-rich fluid and oxygen-enriched liquid air, and, in heat exchange relationship with said first set of passages, a second set of passages for separating by stripping reboiling an oxygen product from the oxygen-enriched liquid air. A valve is provided for reducing the pressure of the oxygen-enriched liquid air intermediate the said first and second sets of passages.

Separation of gas mixtures

An apparatus comprising a liquid-vapor contact column housing an array of vertically spaced liquid-vapor contact trays and an arrangement of downcomers that conduct liquid from tray-to-tray down the array. In a vapor space between the trays there are liquid-vapor disengagement devices having vapor passages therethrough and defining surfaces for the flow thereacross of any liquid disengaged from vapor ascending the column. Each of the devices is typically provided by a sheet of expanded metal and has an outlet edge in liquid flow communication with the next lower tray via the downcomer.

Liquid vapor contact apparatus

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 separation

Iron ore, coal and oxygen are fed to a reactor to produce iron and a fuel gas. The fuel gas leaves the reactor at a temperature of at least 200.degree. C. and is passed through a hot filtration apparatus. The resulting hot, filtered gas then passes through a heat exchanger. A heat exchange fluid, preferably a stream of nitrogen at above ambient pressure passes through the heat exchanger countercurrently to the hot filtered as stream. The heat exchange fluid is thereby heated. The hot heat exchange fluid stream is then expanded with the performance of external work in an expansion turbine, for example it may be used in the generation of electrical power. The hot, filtered, fuel gas may be sent for power recovery downstream of the heat exchanger or may be separated into its constituent components. If the heat exchange fluid is nitrogen it may be separated from air in the same plant that is used to feed the reactor with oxygen.

Fluid production method and apparatus

The present invention provises a method and apparatus for separating a gas mixture. In accordance therewith, the gas mixture is rectified in a dephlegmator. The dephlegmator has first and second sets of heat exchange passages which are in a heat exchange relationship with the gas mixture being rectified. A stream of a first heat exchange fluid is passed through a first of the set of heat exchange passages so as to condense some of the gas mixture. A stream of a second heat exchange fluid is sub-cooled by passage through a second set of the heat exchange passages.

An air stream is compressed in a compressor, and purified in an apparatus. A major portion of the compressed, purified air stream is then cooled in a main heat exchanger to a temperature suitable for its separation in a double rectification column comprising a higher pressure column and a lower pressure column. The lower pressure column typically operates at a pressure in the range of 2.5 to 4.5 bar. A minor portion of the compressed, purified air stream is employed to generate refrigeration for the air separation by being further compressed in the compressor and expanded in a turbine. Oxygen and nitrogen product streams are withdrawn from the lower pressure column. The nitrogen product stream is passed through the main heat exchanger countercurrently to the major air stream. A part of this nitrogen stream is withdrawn at an intermediate region of the heat exchanger and is expanded in an expansion turbine. The resulting expanded nitrogen passes through the heat exchanger from its cold to its warm end thereby creating additional refrigeration so as to maintain a mean temperature different from end to end of the heat exchanger of at least 10K between the streams being warmed and the streams being cooled. A substantial reduction in the size of the heat exchanger compared with that of a conventional plant thereby becomes possible. The expanded nitrogen stream leaving the warm end of the heat exchanger may also be used to perform a cooling duty at about ambient temperature.

A liquid-gas contact device comprising a liquid-gas contact tray comprising a multiplicity of the elongate apertures in the tray for the passage of gas from below to above the tray, each aperture having a gas deflector associated therewith in being so disposed as to impart to the gas a component of velocity in the general direction of liquid flow, and at least several liquid flow in impedance members arranged so as to control the liquid velocity on the liquid-bearing surface to prevent it from reaching so great a magnitude that the residence time of liquid on the tray is insufficient for adequate gas-liquid contact to take place. Preferably the tray comprises a sheet of expanded metal.

Liquid-gas contact device

A method and apparatus for recovering work from a nitrogen stream, wherein the nitrogen is preheated via heat exchange with hot fluid from a chemical process, which process utilizes the oxygen product of the air separation. Preferably at least a part of the expanded nitrogen is utilized to preheat at least one fluid reactant of the chemical process. The chemical process may be gasification or direct reduction of iron oxide, as well as the conversion of natural gas into synthesis gas.

Air separation in combination with a chemical process

An improved process and apparatus for separating air to form oxygen and nitrogen in at least one cryogenic distillation column is disclosed. Nitrogen vapor taken from the colunm is warmed in countercurrent flow to incoming air in a heat exchanger wherein compressed air is being cooled for separation. A portion of the warm nitrogen is compressed, cooled in the heat exchanger and passed through an expansion turbine. The expanded nitrogen is passed through a reboiler associated with the column and further cooled in the heat exchange means. Part of the resulting liquid nitrogen is used to provide reflux for the column and the remainder is taken as product. Preferably, at least a portion of the compressed air stream is expanded in a turbine, passed through the reboiler associated with the column to provide reboil therefor, liquified by heat exchange and introduced to the distillation column through a throttling valve. Further, an argon product can be recovered by withdrawing an argon-rich stream from a distillation column and passing it to a further column for purification. Vapor from the distillation column, or another in a plurality of distillation columns, is used to provide reflux for the further column with the resulting condensed vapor being returned to the column from which it was withdrawn.

A packing for a liquid-vapor contact column is provided which comprises metallic sheets defining liquid-vapor passages and having at least one wettable surface comprised of a coating of porous metal. The sheets are perforated to permit vapor to pass between them. The porous metal coating is formed by spraying a particulate mixture of metal and a plastics material onto the sheet to form a coating of plastics particles embedded in metal and then heating to volatilize the plastic thereby forming porosity in the metal coating.

Liquid-vapor contact columns

A process for the separation of air to obtain oxygen, nitrogen and argon is disclosed which comprises: subjecting air from which carbon dioxide and water have been removed to fractional distillation in a first column to form oxygen-nitrogen vapor and argon-enriched oxygen; separating argon from the latter in a second column operating at substantially lower pressure than the first; liquefying a portion of the nitrogen vapor in a cycle including heat exchange with incoming air and compression to a pressure above that of the first column, a portion of the liquid nitrogen being taken as product and a second portion being returned to the first column as reflux. Liquid-oxygen and nitrogen vapor from the first column are mixed in a liquid-vapor contact column, impure liquid nitrogen is withdrawn therefrom and used as reflux in the first column. A remixed oxygen-nitrogen stream is withdrawn from the contact column and expanded to create refrigeration for the system. Also, disclosed is apparatus for carrying out the subject process.

An improved process and apparatus for separating air to form oxygen and nitrogen in at least one cryogenic distillation column is disclosed. Nitrogen vapor taken from the column is warmed in countercurrent flow to incoming air in a heat exchanger wherein compressed air is being cooled for separation. A portion of the warm nitrogen is compressed, cooled in the heat exchanger and passed through an expansion turbine. The expanded nitrogen is passed through a reboiler associated with the column and further cooled in the heat exchange means. Part of the resulting liquid nitrogen is used to provide reflux for the column and the remainder is taken as product. Preferably, at least a portion of the compressed air stream is expanded in a turbine, passed through the reboiler associated with the column to provide reboil therefor, liquified by heat exchange and introduced to the distillation column through a throttling valve. Further, an argon product can be recovered by withdrawing an argon-rich stream from a distillation column and passing it to a further column for purification. Vapor from the distillation column, or another in a plurality of distillation columns, is used to provide reflux for the further column with the resulting condensed vapor being returned to the column from which it was withdrawn.

An incoming stream of gas mixture typically comprising methane and up to 12% by volume of carbon dioxide is subjected to rectification in a first column to form a carbon dioxide depleted fraction that is withdrawn as product from the top of the column and a carbon dioxide-enriched fraction which is withdrawn from the bottom of the column is warmed in a heat exchanger and is introduced into a second rectification column operating at a higher pressure than the first column. A stream in which carbon dioxide predominates is withdrawn from the bottom of the higher pressure column while a stream 34 containing a lower proportion of carbon dioxide than said enriched fraction is withdrawn from the top of the higher pressure column is throttled through a valve and is united with the incoming stream of gas mixture upstream of or in the lower pressure column.

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Guildford, United Kingdom

John T Lavin