METHOD FOR RECOVERING GASEOUS NITROGEN FROM THE WASTE NITROGEN STREAM OF AN AIR SEPARATION UNIT

Abstract

The method for the production of nitrogen can include the steps of a) providing a waste nitrogen gas stream at a first pressure called low pressure, wherein the waste nitrogen gas originates from a low pressure column of a cryogenic air separation unit; b)compressing the waste nitrogen gas stream to a second pressure in a waste nitrogen compressor to produce a pressurized nitrogen stream; and c) introducing the pressurized nitrogen stream to a nitrogen generator under conditions effective for producing a purified nitrogen product, wherein the purified nitrogen product has a higher concentration of nitrogen as compared to the pressurized nitrogen stream.

Claims

1. A method for the production of nitrogen, the method comprising the steps of: a) providing a waste nitrogen gas stream at a first pressure called low pressure, wherein the waste nitrogen gas originates from a low pressure column of a cryogenic air separation unit; b) compressing the waste nitrogen gas stream to a second pressure in a waste nitrogen compressor to produce a pressurized nitrogen stream; and c) introducing the pressurized nitrogen stream to a nitrogen generator under conditions effective for producing a purified nitrogen product, wherein the purified nitrogen product has a higher concentration of nitrogen as compared to the pressurized nitrogen stream.

2. The method as claimed in claim 1, wherein the method further comprises an absence of a purification step for the waste nitrogen gas stream.

3. The method as claimed in claim 1, wherein the waste nitrogen gas stream consists essentially of nitrogen and impurities, wherein the impurities comprise an absence of water and carbon dioxide.

4. The method as claimed in claim 1, wherein a portion of the purified nitrogen product is expanded in a turbine to provide cooling for the nitrogen generator.

5. The method as claimed in claim 1, wherein a portion of the purified nitrogen product is recycled back to the waste nitrogen compressor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 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.

[0013] FIG. 1 provides an embodiment of the present invention.

[0014] FIG. 2 provides an additional embodiment of the present invention.

[0015] FIG. 3 provides yet another embodiment of the present invention.

DETAILED DESCRIPTION

[0016] 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.

[0017] In a typical air separation unit, a stream of dry enriched nitrogen (typically above 90%) is coming out of the cold box and is usually used for: (1) the regeneration of the dryers, (2) the precooling section as a cooling medium in the chiller tower, or (3) simply venting to the atmosphere. If there is a need of extra gaseous nitrogen or liquid nitrogen in a facility close to an already existing air separation unit and there is no extra capacity available on this existing asset, one solution is to use the previously mentioned enriched nitrogen stream (Waste nitrogen) as a feed to a cryogenic purification unit to produce a gaseous or liquid nitrogen stream at the required purity.

[0018] A particular advantage of the invention is that there is no need to include an additional water/carbon dioxide purification step for this enriched nitrogen stream, as there is no significant carbon dioxide or water amount to be removed. Moreover, the feed is more enriched in nitrogen than air, which allows for an easier distillation compared with the typical process scheme using air.

[0019] In FIG. 1, air enters an ASU cold box under conditions effective for the rectification of air. In the embodiment shown, the ASU cold box produces gaseous nitrogen, liquid nitrogen, gaseous oxygen, liquid oxygen and liquid argon as products. In addition to these products, the ASU cold box also produces waste nitrogen, which is typically vented or used for other purposes and sent to waste nitrogen users. In the embodiment shown, at least a portion of the waste nitrogen from the ASU cold box can be diverted to a separate nitrogen generator in order to produce a purified gaseous and/or liquid nitrogen product. The nitrogen generator will also produce a small amount of waste nitrogen (e.g., enriched nitrogen stream), which can either be vented or sent to the waste nitrogen users.

[0020] FIG. 2 provides a more detailed flow diagram of the nitrogen generator. In this embodiment, the waste nitrogen from the ASU is at a lower pressure as this waste nitrogen stream typically originates from the top of the low pressure column of the ASU, and therefore, the nitrogen stream is compressed in nitrogen compressor before being cooled in a heat exchanger that is separate from the heat exchanger in the ASU. After cooling, the nitrogen is introduced into a single distillation column. Nitrogen vaporizes and accumulates near the top of the column, while other impurities such as oxygen and argon accumulate in the column bottoms. The liquid is removed from the column bottom, expanded across a valve, and then introduced into the top condenser to provide reflux duty (e.g., condense nitrogen in the top condenser coming from the top of the column). The enriched liquid vaporizes in the top condenser and is then warmed in the subcooler and the heat exchanger. To provide additional refrigeration, a portion of this stream can be expanded and then re-warmed in the heat exchanger. The resulting warmed enriched gas is still predominantly nitrogen and can either be vented to the atmosphere or used as a waste gas.

[0021] Purified gaseous nitrogen is removed from the top of the distillation column and warmed in the heat exchanger to produce the final gaseous product. If liquid nitrogen is desired, liquid nitrogen can be withdrawn from the condensing nitrogen stream from the top condenser (not shown).

[0022] FIG. 3 provides an optional embodiment in which a portion of the enriched nitrogen stream (e.g., waste nitrogen from nitrogen generator) can be recycled to the waste nitrogen compressor in order to further improve the overall recovery of the system. In an additional embodiment, the turbine can be configured to at least partially power the waste nitrogen compressor.

[0023] 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.

[0024] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.