Back to results
US 5,309,721 AGranted
Air separation
AssigneeThe BOC Group, Inc.
InventorThomas Rathbone
Life of this patent
Estimating the term…
Abstract
An improvement to a gaseous oxygen cycle in which refrigeration is provided by two expansion turbines each fed with nitrogen. In addition, some nitrogen is recompressed, returned though the main heat exchanger, condensed and used to form a liquid nitrogen product.
Claims12
A method of separating air comprising the steps of:
- a) reducing by heat exchange the temperature of a compressed air feed stream to a level suitable for its separation by rectification;
- b) separating the air stream by rectification in a double rectification column comprising a higher pressure column and a lower pressure column, wherein the pressure at the top of the lower pressure column is at least 2 bar;
- c) withdrawing a stream of gaseous oxygen product from the lower pressure column and warming it by heat exchange countercurrently to the feed air stream;
- d) withdrawing a product stream of nitrogen from the lower pressure column and warming it by heat exchange countercurrently to the feed air stream;
- e) withdrawing at different temperatures from one another first and second side streams of nitrogen from the product nitrogen stream being heat exchanged countercurrently to the feed air, expanding the first and second side streams in, respectively, first and second expansion turbines, and warming the resultant expanded side streams by heat exchange countercurrently to the feed air stream;
- f) compressing at least part of the warmed product stream of nitrogen;
- and
- g) cooling the compressed product stream of nitrogen by heat exchange countercurrently to the oxygen product stream and then condensing the cooled product stream of nitrogen to form a liquid nitrogen product.
5 more elements
An apparatus for separating air comprising:
- a) a main heat exchanger for reducing by heat exchange the temperature of a compressed air feed stream to a level suitable for its separation by rectification;
- b) a double rectification column for separating the air stream comprising a higher pressure column and a lower pressure column;
- c) passages through the main heat exchanger communicating with an outlet from the lower pressure rectification column for a gaseous oxygen product to enable a stream of the oxygen product to flow through the main heat exchanger countercurrently to the feed air stream;
- d) passages through the main heat exchanger communicating with an outlet from the lower pressure rectification column for gaseous nitrogen to enable a product stream of the gaseous nitrogen to flow through the main heat exchanger countercurrently to the feed air stream and thereby be warmed;
- e) first and second expansion turbines for withdrawing at different temperature from one another respectively first and second side streams from the product stream of gaseous nitrogen at different regions of the main heat exchanger;
- for expanding the side streams, and for returning the side streams to further passages through the main heat exchanger for flow therethrough countercurrently to the feed air stream;
- f) a compressor for compressing at least part of the warmed product nitrogen stream;
- g) yet further passages through the main heat exchanger for the flow of the compressed product nitrogen stream countercurrently to the product oxygen stream so as to cool the compressed product nitrogen stream;
- and
- h) a condenser for condensing the cooled product nitrogen stream thereby to form liquid nitrogen product.
7 more elements
Dependencies are inferred from the claim text.