[0051]To illustrate the invention, FIG. 1 shows the column portion of a process operating according to an embodiment of the invention and FIGS. 2 and 3 show two alternative corresponding heat exchanger portions, to be used for oxygen pressures above 15 bars abs.
[0052]In FIG. 1, gaseous air 2 and liquid air 4 are fed to high pressure column 100. Oxygen enriched liquid 10 formed at the bottom of the high pressure column 100 is divided in two. One portion 12 is expanded and sent to an intermediate level of the low pressure column 101. Another portion 11 is expanded and sent to top condenser 105 of the argon column where it vaporizes to form stream 13 which is sent to the low pressure column 101. Alternatively all the oxygen enriched liquid 10 can be sent to the condenser 105 and partially condensed. In this case, stream 12 is absent and liquid from condenser 105 is sent to the low pressure column 101. The top of the high pressure column 100 is thermally coupled to the bottom of the low pressure column 101 via a condenser-reboiler 104. Nitrogen enriched liquid 40 from the top of the high pressure column 100 is divided in two, one portion 41 being sent to the top of the low pressure column 101 as reflux. Nitrogen enriched gas is removed from the top of the low pressure column 101.
[0053]A side liquid stream 20 with composition similar to air, containing between 18 and 25% mol. oxygen is extracted from column 100. Alternatively the side liquid stream could be replaced or supplemented by a part of liquid air stream 4 or another liquid air stream. A portion 22 of stream 20 (or stream 4, not illustrated) is partially vaporized in the top condenser 107 of intermediate pressure column 103. Condenser 107 could be a falling film vaporizer. The vapor 123 containing around 10% mol. oxygen) is sent to the low pressure column 101. A portion 24 of the liquid fraction 26 of the partially vaporization is then fed to column 103. Column 103 operates at about 2 bar and its condenser 107 at 1.4 bar. Gravity feed or a pump 110 can be used to transfer this liquid from condenser 107 to a position between 2 and 5 theoretical trays above the bottom of intermediate pressure column 103. Oxygen enriched liquid 60 from the bottom of column 103 containing preferably between 70 and 75 mol % oxygen is expanded and sent to the low pressure column. It is useful to note that a liquid air stream formed from the condensation of air for vaporizing liquid oxygen and liquid nitrogen products in the main heat exchanger can be sent to the top condenser of the intermediate column instead of using a part of the liquid stream 20 extracted from the high pressure column.
[0054]Preferably the average temperature difference for condensers 106, 107 should be between 0.8 and 0.9° C. Column 103 produces additional reflux liquid 23 for the top of the low pressure column 101. Column 102 is a typical side-arm argon column for a double column process. A portion 54 of argon enriched feed gas from the low pressure column 101 is separated in the argon column 102 to form argon product 80 in liquid form as shown or in gaseous form. The bottom liquid 52 from the argon column is sent back to the low pressure column 101. A portion 51 of argon enriched feed gas 50 from the low pressure column 101 is condensed in the bottom reboiler 106, preferably of the falling film type, of column 103 to yield liquid 53 which is then fed to column 102 or 101 to be separated. The argon column 102 is equipped with a top condenser 105 which vaporizes a portion 11 of oxygen enriched liquid 10 produced at the bottom of the high pressure column 100.
[0055]Another portion 45 of stream 40 is pumped by pump 121 to high pressure, vaporized and warmed to yield high pressure nitrogen product. Liquid oxygen 30 produced at the bottom of column 101 is pumped by pump 120 to high pressure, vaporized and warmed to yield high pressure oxygen product.
[0056]The embodiment shown in FIG. 2 can be used to vaporize efficiently the liquid products 31, 42. The liquid products are vaporized in pumps 120,121, the oxygen being pressurized to a pressure between 15 and 80 bars abs. The cold compression technique is utilized and is described as follows:
[0057]Feed air compressed by compressor 201 to an elevated pressure of about between 15 and 25 bar is dried and its CO2 content is removed in the front end purification unit 208. The resulting dried and CO2 free stream 80 is divided into several portions. Portion 83 is cooled in heat exchanger 200 to an intermediate temperature thereof, a portion 91 of portion 83 is expanded in turboexpander 204 into the high pressure column 100. Second portion 84 of portion 83 is cold compressed, at a inlet temperature which is an intermediate temperature of the heat exchanger, in cold booster 202 to higher pressure to yield stream 85. Stream 85 is next cooled in exchanger 200 and liquefied to form liquid air stream 4. Another portion 79 of the cooled stream 83 is further cooled and liquefied to yield a second liquid air stream 6. Streams 4 and 6 are fed at least in part to the high pressure column 100 as feeds. A third portion 82 of feed air is further compressed in warm booster 207, cooled in exchanger 200 to yield cooled compressed stream 88 which is then expanded in turboexpander 203 into the high pressure column 100. The power generated by turboexpanders 203 and 204 can be used to drive boosters 202 and 207. Depending upon the pressure levels and the quantities of oxygen and nitrogen to be vaporized in the heat exchanger 200, it is sometime beneficial to also extract a portion of cooled compressed stream 88 and liquefy it in exchanger 200 in a similar fashion as stream 79. The resulting liquid stream (not shown) is then fed to the column system. By generating those auxiliary liquid streams, less liquid, i.e. lower flow, needs to be compressed by the cold compressor to satisfy the refrigeration balance at the cold end of the exchanger. More efficient system can be achieved by reducing the required cold compression flow.
[0058]The embodiment shown in FIG. 3 can be used to reduce the plant power consumption. A multi stage booster compressor comprising several stages 209, 210 and 211 is added to further compress the fraction 82 feeding compressor 207. Multiple pressurized streams 95 and 96 can be generated by the booster compressor to vaporize efficiently the liquid products to form liquid air streams 97 and 99.
[0059]For lower oxygen pressures, more conventional vaporization processes such may be used. For very low pressures, the oxygen vaporizes in a dedicated vaporizer like a bath type vaporizer.
[0060]A cold booster has an inlet temperature of below −20° C.
[0061]While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
[0062]The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
[0063]“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
[0064]“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary a range is expressed, it is to be understood that another embodiment is from the one.
[0065]Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
[0066]Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such particular value and/or to the other particular value, along with all combinations within said range.
[0067]All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.
