basic claims of nitrogen generator

basic claims of nitrogen generator

basic claims of nitrogen generator

Abstract

A method and apparatus for generating nitrogen from the separation of air in a single column nitrogen generator. Nitrogen rich vapor is condensed to form reflux through the vaporization of an oxygen-rich liquid stream produced as column bottoms. The vaporized oxygen-rich stream is in part recompressed in a recycle compressor, cooled and reintroduced back into the column to increase nitrogen production. The vaporized oxygen-rich stream is also in part expanded with the performance of work. The work of expansion is applied to the compression. A supplemental refrigerant stream produced by a nitrogen liquefaction unit allows the nitrogen to be taken as a liquid and increases the amount of work of expansion able to be applied to the compression.

Claims I claim: 1. A method of producing nitrogen, said method comprising: cooling compressed, purified feed air to a temperature suitable for its rectification; introducing said compressed, purified feed air into a distillation column to produce a nitrogen rich tower overhead of high purity and oxygen-rich liquid as column bottoms; condensing at least part of a nitrogen-rich stream composed of said nitrogen-rich tower overhead and introducing part of the resulting condensate into said distillation column as reflux; forming a nitrogen product stream from a remaining part of the resulting condensate; compressing a recycle stream, cooling said recycle stream to said temperature and introducing said recycle stream into said distillation column to increase recovery of said nitrogen product; expanding a refrigerant stream with the performance of work to form a primary refrigerant stream and indirectly exchanging heat between said primary refrigerant stream and said compressed and purified air and said recycle stream; applying an amount of said work to said compression of said recycle stream; vaporizing and then reliquefying a supplemental refrigerant stream; said supplemental refrigerant stream being at least partly vaporized by indirectly exchanging heat with said at least part of said nitrogen-rich stream, thereby to help effect said condensation of said part of said nitrogen-rich stream; and prior to said reliquefaction of said supplemental refrigerant stream, indirectly exchanging heat between said supplemental refrigerant stream and said compressed and purified air and said recycle stream to increase said amount of said work able to be applied to said compression, over that obtainable had said supplemental refrigeration not been added, thereby to increase compression and to further increase recovery of said nitrogen product. 2. The method of claim 1, wherein: a stream of said oxygen-rich liquid is withdrawn from said distillation column, valve expanded, and passed in indirect heat exchange with said nitrogen-rich stream to help condense said at least part of said nitrogen-rich stream and thereby to form a vaporized oxygen-rich stream; said recycle stream is formed from part of said vaporized oxygen-rich stream; and said refrigerant stream is formed from a remaining part of said vaporized oxygen-rich liquid stream. 3. The method of claim 2, wherein said supplemental refrigerant stream is completely vaporized by said indirect heat exchange with said nitrogen-rich tower overhead. 4. The method of claim 3, wherein said supplemental refrigerant stream is liquefied by compressing said supplemental refrigerant stream and expanding said supplemental refrigerant stream at two temperature levels. 5. The method of claim 2, wherein: said nitrogen product comprises part of said condensate and is divided into two product streams; one of said product streams is vaporized through indirect heat exchange with said compressed and purified air; the other of said product streams is subcooled through indirect heat exchange with a subsidiary stream composed of part of said supplemental refrigerant stream; and said subsidiary stream is combined with a remaining part of said supplemental refrigerant stream prior to liquefaction. 6. A nitrogen generator comprising: main heat exchange means configured for cooling compressed, purified feed air to a temperature suitable for its rectification; a distillation column connected to said main heat exchange means to rectify said compressed and purified feed air and thereby to produce a nitrogen rich tower overhead of high purity and oxygen-rich liquid as column bottoms; a head condenser connected to said distillation column for condensing at least part of a nitrogen-rich stream composed of said nitrogen rich tower overhead and for reintroducing part of the resultant condensate back into said distillation column as reflux so that a remaining part of the resultant condensate can be removed as a product stream; a compressor for compressing a recycle stream; said main heat exchange means interposed between said compressor and said distillation column so that said recycle stream cools to said temperature and is introduced into said distillation column to increase recovery of said nitrogen product; a turboexpander for expanding a refrigerant stream with performance of work to form a primary refrigerant stream; said turboexpander connected to said main heat exchange means so that said primary refrigerant stream indirectly exchanges heat with said compressed and purified air; means for coupling said turboexpander to said compressor so that an amount of said work is applied to said compression of said recycle stream; and a supplemental refrigerant circuit for circulating a supplemental refrigerant stream vaporized during the circulation, said supplemental refrigerant circuit including, said head condenser, said head condenser configured such that said supplementary refrigerant stream is at least party vaporized through indirect heat exchange with said at least part of the nitrogen-rich stream, said main heat exchange means, said main heat exchange means also configured to indirectly exchange heat between a supplemental refrigerant stream and said compressed and purified air to increase said amount of said work able to be applied to said compression, over that obtainable had said supplemental refrigeration not been added, thereby to increase compression and to further increase recovery of said nitrogen product, and a liquefier interposed between said main heat exchange means and said head condenser to re-liquefy said supplemental refrigerant stream after having been vaporized. 7. The nitrogen generator of claim 6, further comprising: said head condenser also configured to indirectly exchange heat with a stream of said oxygen-rich liquid; an expansion valve interposed between said head condenser and said distillation column for valve expanding said stream of said oxygen-rich liquid, thereby to form a vaporized oxygen rich stream; said compressor and turboexpander connected to said head condenser so that said recirculation stream comprises part of said vaporized oxygen-rich liquid stream and said refrigerant stream comprises a remaining part of said vaporized oxygen rich liquid stream. 8. The nitrogen generator of claim 6, wherein supplemental refrigerant stream liquefier comprises a nitrogen liquefier having two turboexpanders operating at two different temperature levels.

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