Method and apparatus for producing oxygen

An air separation apparatus for producing a gaseous oxygen product at a delivery pressure:

• low temperature rectification means configured to operate in accordance with a Claude cycle, said low temperature rectification means including filtering, compression and purification means for filtering, compressing and for purifying said air, main heat exchange means configured for cooling the air, rectification means employing higher and lower pressure columns connected to one another in a heat transfer relationship to separate the air and thereby to produce liquid oxygen as a column bottom of the lower pressure column, and a Claude expansion means for expanding at least a major portion of the air into said higher pressure column and with the performance of work;
• means for forming a supplemental refrigerant stream having substantially said delivery pressure;
• a pump connected to said lower pressure column for pumping a stream of said liquid oxygen from said lower pressure column to substantially said delivery pressure;
• a mixing column connected to said pump and said supplemental refrigerant stream means at top and bottom regions thereof, respectively, for vaporizing said liquid oxygen contained within said stream of said liquid oxygen through direct heat exchange with said supplemental refrigerant stream, thereby collecting a liquid in said bottom region of said mixing column;
• the mixing column connected to said main heat exchange means so that a product stream from the top region of said mixing column flows through said heat exchange means and fully warms to form said gaseous oxygen product;
• and
• a pressure reduction valve in communication with said bottom region of said mixing column and said lower pressure column so that a liquid stream composed of said liquid from said bottom region of said mixing column undergoes a pressure reductions and flows into an intermediate location of said lower pressure column to add refrigeration to said lower pressure column.