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Process And Apparatus For The Production Of Gaseous and Liquid Nitrogen

IP.com Disclosure Number: IPCOM000016577D
Publication Date: 2003-Jun-30
Document File: 7 page(s) / 106K

Publishing Venue

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Abstract

The present invention is a process and apparatus for the production of gaseous and liquid nitrogen, comprising a single column nitrogen generator, and at least two expansion turbines, one that expands a portion of the incoming feed air and one that expands the oxygen-enriched waste, both of which are configured to operate with independently adjustable discharge pressures and are warmed separately in the main heat exchanger, thereby utilizing the maximum available expansion ratio.

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Process And Apparatus For The Production Of Gaseous and Liquid Nitrogen

Abstract

The present invention is a process and apparatus for the production of gaseous and liquid nitrogen, comprising a single column nitrogen generator, and at least two expansion turbines, one that expands a portion of the incoming feed air and one that expands the oxygen-enriched waste, both of which are configured to operate with independently adjustable discharge pressures and are warmed separately in the main heat exchanger, thereby utilizing the maximum available expansion ratio.

The ability to produce large amounts of low cost liquid nitrogen is particularly important to the air separation industry. Liquid nitrogen production has been traditionally effected by means of a nitrogen liquefier. The use of such a liquefier adds substantial cost to the plant installation.

Single column nitrogen generators are particularly suited to providing a low cost, gaseous nitrogen product and are well known in the art.� Refrigeration for these nitrogen generators is typically supplied by either expanding feed air (see for example US 5,037,462) or by expanding the oxygen-enriched waste (see for example US 5,396,772).� Such single column nitrogen generators are also capable of supplying a liquid nitrogen product, however as the liquid product increases as a fraction of the total nitrogen product, plant efficiency is reduced and the size of the process equipment increases thus adding capital and operating cost to the installation.

Attempts to use multiple expansion turbines, instead of the traditional single machine, have also been disclosed in the art.� Coakley et. al. (US 5,704,229) discloses a process and apparatus wherein a fraction of the feed air is cooled and passed to an expansion turbine.� This turbine’s exhaust stream is mixed with a oxygen-rich waste stream and further expanded in a second expansion turbine. The remainder of the feed air is further cooled and passed to the distillation column for separation.

A disadvantage of this process of Coakley et. al. is the interaction between the air and waste expansion turbines. The expansion ratio of, and hence work available from, the air expansion turbine is limited since said turbine’s outlet pressure is restricted to the inlet pressure of the waste stream expansion turbine. Lowering the outlet pressure of the air expander to increase it’s expansion ratio results in a corresponding reduction in the expansion ratio of, and hence work available from, the waste stream expansion turbine. The net result is a limitation on the total refrigeration available from the two expansion turbines, and a corresponding limitation on the fraction of liquid nitrogen product that may be produced efficiently.

A further disadvantage of the process disclosed by Coakley et. al. relates to the size of the waste stream expander. Since the waste turbine expands a stream made up of a waste stream and an expanded air stream, the waste expansion tu...