Apparatus and air separation plant

Abstract

The present invention relates to an apparatus and air separation plant in which a pumped liquid oxygen stream is heated within a heat exchanger through indirect heat exchange with compressed air to produce an oxygen product. The liquid oxygen stream is pressurized in a range above about 55 bar(a) and no greater than about 150 bar(a) and is a supercritical fluid after having been heated within the heat exchanger. The air is compressed to an air pressure that is a function of the oxygen pressure that will result in a minimum power being expended in the compression of the air. The heat exchanger can be a brazed fin heat exchanger fabricated from aluminum in which the fins located in heat exchange passages have an undulating configuration to increase the flow path length and induce flow separation and thereby increase the heat transfer coefficient within the heat exchanger.

We claim: 
     
         1 . An apparatus for producing an oxygen product from a liquid oxygen stream having a purity of no less than about 90 percent by volume comprising:
 a pump to pump the liquid oxygen stream and thereby produce a pumped liquid oxygen stream;   a compressor to compress air and thereby to produce a compressed air stream;   a heat exchanger connected to the pump and the compressor such that the pumped liquid oxygen stream is heated within the heat exchanger through indirect heat exchange with at least the compressed air stream to produce the oxygen product;   the pump set to pump the liquid oxygen stream so that the pumped liquid oxygen stream is pressurized to an oxygen pressure in a range above about 55 bar(a) and no greater than about 150 bar(a) upon entering the heat exchanger;   the compressor set to compress the air so that the air is compressed to an air pressure upon entering the heat exchanger equal to about a value given by an equation in which the air pressure=0.00003×(oxygen pressure) 3 −(0.01141×(oxygen pressure))+2.263×(oxygen pressure)+2.5175; and   the heat exchanger configured such that the pumped liquid oxygen stream is heated within the heat exchanger to a temperature at which the oxygen product will be a supercritical fluid.   
     
     
         2 . An air separation plant for producing an oxygen product comprising:
 a compressor to compress the air;   a pre-purification unit connected to the compressor to purify the air and thereby to produce a compressed and purified air stream;   a booster compressor connected to the pre-purification unit;   means for cooling part of the compressed and purified air stream and for cooling a compressed air stream formed from a further part of the compressed and purified air stream compressed in the booster compressor;   an air separation unit connected to the cooling means so as to receive the part of the compressed and purified air stream and the compressed air stream after having been cooled and configured to rectify the air and thereby produce a liquid oxygen stream having an oxygen purity of no less than about 90 percent by volume;   a pump connected to the air separation unit to pump the liquid oxygen stream, thereby to produce a pumped liquid oxygen stream;   the cooling means comprising a heat exchanger positioned between the pump and the booster compressor and also configured such that the pumped liquid oxygen stream is heated within the heat exchanger through indirect heat exchange with at least the compressed air stream to produce the oxygen product as a supercritical fluid and the compressed air stream as a liquid;   the pump set to pump the liquid oxygen stream so that the pumped liquid oxygen stream will be pressurized to an oxygen pressure in a range above about 55 bar(a) and no greater than about 150 bar(a) upon entering the heat exchanger; and   the booster compressor set to compress the compressed air stream so that the compressed air stream will have an air pressure upon entering the heat exchanger equal to a value within a range of no less than ten percent below and no greater than 20 percent above a quantity equal to 0.00003×(oxygen pressure) 3 −(0.01141×(oxygen pressure))+2.263×(oxygen pressure)+2.5175.   
     
     
         3 . The air separation plant of  claim 2  wherein:
 the heat exchange means comprises a first heat exchanger and a second heat exchanger; 
 the heat exchanger is the second heat exchanger; and 
 the first heat exchanger is positioned between the pre-purification unit and the air separation unit and configured to cool the part of the compressed and purified air stream. 
 
     
     
         4 . The apparatus of  claim 1  wherein:
 the heat exchanger is a plate-fin heat exchanger comprising parting sheets separated by and connected to fins to form at least air passages for the air and oxygen passages for the pumped liquid oxygen stream; and 
 the fins in at least the air passages having an undulating configuration. 
 
     
     
         5 . The apparatus of  claim 4 , wherein the undulating configuration has regular spaced points of maximum amplitude along a length dimension of each of said fins forming peaks and troughs of arcuate configuration, the peaks and the troughs being connected by straight segments of each of the fins. 
     
     
         6 . The apparatus of  claim 4 , wherein the pump is configured to pump the liquid oxygen stream to an oxygen pressure of at least about 80 bar(a) and the air passages and the oxygen passages have an identical configuration. 
     
     
         7 . The apparatus of  claim 5 , wherein the undulating configuration has a wavelength in a wavelength range no less than about 0.125 inches and no greater than about 1.5 inches. 
     
     
         8 . The apparatus of  claim 7 , wherein:
 the fins have a maximum amplitude greater than a pitch dimension as measured between adjacent fins; and   the fins having a ratio of transverse thickness equal to a pitch dimension which is greater than about 0.4.   
     
     
         9 . The apparatus of  claim 8 , wherein the heat exchanger is of brazed aluminum construction. 
     
     
         10 . The air separation plant of  claim 3 , wherein:
 the second heat exchanger is a plate-fin heat exchanger comprising parting sheets separated by and connected to fins to form at least air passages for the air and oxygen passages for the pumped liquid oxygen stream; and   the fins in at least the air passages having an undulating configuration.   
     
     
         11 . The air separation plant of  claim 10 , wherein the undulating configuration has regular spaced points of maximum amplitude along a length dimension of each of said fins forming peaks and troughs of arcuate configuration, the peaks and the troughs being connected by straight segments of each of the fins. 
     
     
         12 . The air separation plant of  claim 10 , wherein the pump is set to pump the liquid oxygen stream to an oxygen pressure of at least about 80 bar(a) and the air passages and the oxygen passages have an identical configuration. 
     
     
         13 . The air separation plant of  claim 11 , wherein the wavelengths of the fins is in a wavelength range no less than about 0.125 inches and no greater than about 1.5 inches. 
     
     
         14 . The air separation plant of  claim 13 , wherein:
 the fins have a maximum amplitude greater than a pitch dimension as measured between adjacent fins; and   the fins having a ratio transverse thickness to the pitch dimension which is greater than about 0.4.   
     
     
         15 . The air separation plant of  claim 14 , wherein the second heat exchanger is of brazed aluminum construction.