Technical Field of the Invention

[0001] The present invention relates to a process for separating air into its components. More specifically, embodiments of the present invention are related to producing oxygen and optionally nitrogen at moderate pressures by the use of a warm expander.

Summary of the Invention

[0002] Certain embodiments of the present invention relate to a method for producing pressurized gaseous oxygen through the cryogenic separation of air at moderate pressures by the use of a warm expander.

[0003] In one embodiment, the method can include the steps of obtaining a main air feed comprising filtered and compressed air; splitting the main air feed into at least a first air fraction, a second air fraction, and a third air fraction; fully cooling the first air fraction in a heat exchanger to a temperature suitable for rectification of the first air fraction to form a cooled air feed; withdrawing the cooled air feed from the heat exchanger and introducing the cooled air feed to a column system under conditions effective for rectification of the cooled air feed into low pressure gaseous nitrogen (LP GAN), liquid oxygen (LOX), liquid nitrogen (LIN), and high pressure gaseous nitrogen (HP GAN), wherein the column system comprises a double column having a higher pressure column and a lower pressure column; warming the LP GAN, LOX, and HP GAN in the heat exchanger; boosting the second air fraction in a warm booster to form a boosted second air fraction; partially cooling the boosted second air fraction in the heat exchanger and then expanding the boosted second air fraction in a turbine to form an expanded second air fraction; introducing the expanded second air fraction to the column system; expanding the third air fraction using a warm expander to create an expanded third air fraction; and cooling the expanded third air fraction in the heat exchanger before introducing the expanded third air fraction to the column system for rectification. In one embodiment, LIN can be warmed in the heat exchanger. In one embodiment, the main air feed is at a pressure of at least 10 bar, preferably at least 20 bar.

[0004] In another embodiment, the expanded second air fraction is at about the same pressure as the higher pressure column. In another embodiment, the turbine is coupled to the warm booster. In another embodiment, the warm expander is not coupled to a booster. In another embodiment, the method can include the step of withdrawing LIN from the column system as product.

[0005] In another embodiment, the step of splitting the main air feed further includes the step of splitting the main air feed into a fourth air fraction, and the method further comprises the steps of expanding the fourth air fraction across a pressure valve; and then introducing the fourth air fraction into the heat exchanger for cooling before introducing the fourth air fraction to the column system.

[0006] In another embodiment, the LOX can be vaporized in the heat exchanger and have a pressure of about 5-15 bar. In another embodiment, substantially all of the main air feed is introduced to the column system for rectification. In another embodiment, substantially none of the main air feed is vented to the atmosphere. In another embodiment, the third air fraction is at substantially the same pressure as the second air fraction and the first air fraction.

Brief Description of the Drawings

[0007] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

[0008] The Figure provides an embodiment of the present invention.

Detailed Description

[0009] While the invention will be described in connection with several embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all the alternatives, modifications and equivalence as may be included within the spirit and scope of the invention defined by the appended claims.

[0010] FIG. 1 represents an embodiment of the present invention. In this embodiment, main air feed 2 can be split into four streams, first air fraction 3, second air fraction 4, third air fraction 6, and fourth air fraction 8. First air fraction 3 is then introduced to the warm side of heat exchanger 10 and is fully cooled therein, and preferably condensed, to form cooled air feed 12, before being expanded through valve 51 and introduced to column system 20 for rectification. Preferably, main air feed 2 has a pressure of at least 10 bar, preferably at least 20 bar.

[0011] Low pressure gaseous nitrogen 22 is withdrawn from column system 20 and is warmed in heat exchanger 10 before exiting, to be eventually used to regenerate compressed air filters (not shown), vented to the atmosphere, or used as product. Liquid oxygen 24 is also withdrawn from column system 20 pressurized in a pump and then vaporized in heat exchanger 10 to form high pressure gaseous oxygen. Liquid oxygen product stream 25 is taken as a slip stream of liquid oxygen 24 and can be stored as product. High pressure gaseous nitrogen 26 and liquid nitrogen 27 are also withdrawn from column system 20. High pressure gaseous nitrogen 26 is warmed in heat exchanger 10 and liquid nitrogen 27 can be stored as product. In another embodiment, liquid argon 29 leaves column system 20 and can be stored as product. In an embodiment not shown, waste gas from column system 20 can be used to provide cooling to heat exchanger 10 and/or used to regenerate air adsorbers.

[0012] In one embodiment, second air fraction 4 is compressed in warm booster 30 and cooled in aftercooler 33 to form boosted second air fraction 32. Boosted second air fraction 32 is then partially cooled (i.e., taken out at an intermediate location of heat exchanger 10) in heat exchanger 10 and expanded across turbine 35 to form expanded second air fraction 36 and then introduced to column system 20 for rectification. Turbine 35 is connected to warm booster 30 by a common shaft, such that turbine 35 provides the power needed to drive warm booster 30.

[0013] In one embodiment, third air fraction 6, which is preferably at ambient air temperatures, is expanded across warm expander 40 to form expanded third air fraction 42. Expanded third air fraction 42 is then introduced to heat exchanger 10, preferably at an intermediate location, fully cooled and combined with expanded second air fraction 36 before introduction to column system 20 for rectification. In the embodiment shown, the warm expander is not coupled to a compressor or a warm compressor.

[0014] In one embodiment, fourth air fraction 8 is withdrawn from main air feed 2 and expanded across pressure valve 50 and cooled in heat exchanger 10 before being combined with expanded second air fraction 36 before introduction to column system 20 for rectification. In one embodiment, fourth air fraction 8 can be combined with expanded third air fraction 42 within heat exchanger 10 to form combined cooled fractions 44 before being combined with expanded second air fraction 36 and introduced to column system 20.

[0015] The advantage of including pressure valve 50 is to allow for partial loading of the plant or to produce reduced quantities of liquid products. This permits the plant to operate with the optimum flow of Joule-Thompson air per the liquid vaporization occurring in heat exchanger 10. Certain embodiments of the invention are suitable for the production of gaseous oxygen in the range of about 5 to 15 bara as it does not require further boosting of the Joule-Thompson air beyond that of the main air compressor (not shown). Typically, for higher pressures of gaseous oxygen product, the Joule-Thompson air stream needs to be further compressed prior to being liquefied in the heat exchanger. Certain embodiments of the present invention allow for moderate quantities of liquid products (e.g., 10% of the total air flow) while consuming less power than a "lost air" process and with less complexity. Additionally, in certain embodiments of the present invention, essentially all of the main air enters the column system for separation (as opposed to a portion being used for refrigeration and then vented), thus permitting maximum product recoveries.

[0016] 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, language referring to order, such as first and second, 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 or devices can be combined into a single step/device.

[0017] The singular forms "a", "an", and "the" include plural referents, unless the context clearly dictates otherwise. [0018] 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.

[0019] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.