Oxygen product production method

Abstract

The present invention relates to a method of producing an oxygen product by heating a pumped liquid oxygen stream within a heat exchanger through indirect heat exchange with compressed air. The 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) and heated within the heat exchanger to form a supercritical fluid. The air is compressed to an air pressure upon entering the heat exchanger 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.

1 . A method of producing an oxygen product comprising:
 pumping a liquid oxygen stream having a purity of no less than about 90 percent by volume to produce a pumped liquid oxygen stream;   heating the pumped liquid oxygen stream within a heat exchanger through indirect heat exchange with at least a compressed air stream to produce the oxygen product; and   the pumped liquid oxygen stream being pressurized by the pumping 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 pumped liquid oxygen stream being heated within the heat exchanger to a temperature at which the oxygen product will be a supercritical fluid and the air being compressed to an air pressure upon entering the heat exchanger at an air pressure equal to about a value given by an equation in which the air pressure=0.0003×(oxygen pressure) 3 −(0.01141×(oxygen pressure) 2 )+2.263×(oxygen pressure) 2 +2.5175.   
     
     
         2 . A method of producing an oxygen product comprising:
 pumping a liquid oxygen stream produced within an air separation plant at a purity of no less than about 90 percent by volume, thereby to produce a pumped liquid oxygen stream;   heating the pumped liquid oxygen stream within a heat exchanger of the air separation plant through indirect heat exchange with at least a compressed air stream to produce the oxygen product; and   the pumped liquid oxygen stream being 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 pumped liquid oxygen stream being heated within the heat exchanger to a temperature at which the oxygen product will be a supercritical fluid and the air being compressed to an air pressure upon entering the heat exchanger at an air pressure equal to a value within a range of about ten percent below and about 20 percent a quantity equal to 0.0003×(oxygen pressure) 3 −(0.01141×(oxygen pressure) 2 )+(2.263×(oxygen pressure) 2 +2.5175.   
     
     
         3 . The method of  claim 2  in which the oxygen pressure is maintained at the oxygen pressure during turn-down operation conditions of the air separation plant. 
     
     
         4 . The method of  claim 1  or  claim 2  wherein:
 the pumped liquid oxygen stream and the air are passed countercurrently through passages within 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;   the fins in at least the air passages having an undulating configuration; and   the air being passed through the air passages at a velocity sufficient to induce flow separations due to the undulating configuration of the fins.   
     
     
         5 . The method 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 method of  claim 4 , wherein the oxygen pressure and is at least about 80 bar(a) and the air passages and the oxygen passages have an identical configuration. 
     
     
         7 . The method of  claim 5 , 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. 
     
     
         8 . The method 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 transverse thickness equal to the pitch dimension which is greater than about 0.4 multiplied by a factor that is equal to the air pressure divided by an allowable tensile stress equal to about the yield stress for a material forming the heat exchanger multiplied by a safety factor of not greater than about 0.5 and no less than about 0.15.   
     
     
         9 . The method of  claim 8 , wherein the heat exchanger is of brazed aluminum construction.