Method for utilizing waste air to improve the capacity of an existing air separation unit

Abstract

A method for improving the capacity of an existing air separation unit employing a lost air turbine is provided in which the capacity is increased by operating the existing air separation unit as previously operated, with the exception of collecting the lost air from the lost air turbine, and instead of venting said lost air to the atmosphere, the lost air is compressed in a supplemental air compressor and returned to the air separation unit at a location downstream a front-end purification unit and upstream a booster. This setup advantageously allows for increased production without having to adjust the sizing of the front-end purification unit or main air compressor.

Claims

1. A method for improving the capacity of an existing air separation unit comprising a lost air turbine, wherein the existing air separation unit further comprises a main air compressor, a precooling unit, a front-end purification unit, a booster, a main heat exchanger, and a column system, the method comprising the steps of: a. compressing air in the main air compressor; b. cooling the compressed air in the precooling unit; c. removing water and carbon dioxide from the compressed air in the front-end purification unit to form a dry air stream; d. boosting the pressure of the dry air stream in the booster to form a boosted air stream; e. cooling at least a first portion of the boosted air stream in the heat exchanger and expanding the first portion of the boosted air stream in a valve before sending the resulting fluid to the column system under conditions effective for separating air into nitrogen and oxygen; f. withdrawing a first stream from the column system and warming the first stream in the heat exchanger; g. withdrawing the first stream from an intermediate section of the heat exchanger and expanding the first stream in the lost air turbine to produce an expanded first stream, wherein the lost air turbine is configured to drive the booster; h. warming the expanded first stream in the heat exchanger; i. withdrawing the expanded first stream from a warm end of the heat exchanger; j. compressing the expanded first stream in a supplemental air compressor to form a second compressed air; and k. combining the second compressed air with dry air stream downstream the front-end purification unit.

2. The method of claim 1, wherein the booster comprises a first booster and a second booster, wherein the lost air turbine is configured to drive the first booster or the second booster, wherein the method further includes the step of cooling a second portion of the boosted air stream in a second turbine and introducing the second portion of the boosted air stream after expansion into the column system for separation therein.

3. The method of claim 1, wherein the capacity of the air separation unit is increased without making adjustments to the capacity of the front-end purification.

4. The method of claim 1, wherein the first stream has a composition substantially similar to air.

5. A method for improving the capacity of an existing air separation unit comprising a main air compressor, a precooling unit, a front-end purification unit, a booster, a main heat exchanger, a lost air turbine, and a column system, wherein the existing air separation unit provided a portion of its refrigeration by expanding a first stream withdrawn from the column system across the lost air turbine and said first stream was vented to the atmosphere following warming in the heat exchanger, wherein the method for improving the capacity of the existing air separation unit comprises the steps of: operating the existing air separation unit as previously operated, with the exception of introducing the first stream, after warming in the heat exchanger, to a supplemental air compressor to form a second compressed air; and introducing the second compressed air to a point that is located downstream the front-end purification unit and upstream the booster.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a process flow diagram of an existing ASU; and

(3) FIG. 2 is a process flow diagram for improving the capacity of an existing ASU as known in the prior art;

(4) FIG. 3 is a process flow diagram for improving the capacity of an existing ASU in accordance with an embodiment of the present invention.

(5) FIG. 4 is a process flow diagram for improving the capacity of an existing ASU in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) Referring to FIG. 3, the overall setup does not change with respect to the setup shown in FIG. 2, with the exception that supplemental air compressor 15 is configured to use waste air 62, instead of atmospheric air 4. By using waste air 62 instead of atmospheric air, the resulting compressed air stream does not need to be purified of water and carbon dioxide, which means that the compressed air stream coming from supplemental air compressor 15 can bypass front-end purification unit 30, and be introduced to the system at a location downstream front-end purification unit 30.

(7) Referring to FIG. 4, the overall setup is similar to that of FIG. 3, with the exception that stream 72 can be split into a first fraction 73 and a second fraction 75, wherein first fraction 75 is introduced to the cold end of heat exchanger 80 while second fraction 75 is introduced to medium pressure column 90. In one embodiment, first fraction 73 accounts for between 30 and 50% of the volumetric flow of stream 72.

(8) In another embodiment not shown, lost air turbine 60 can be configured to drive second booster 50 and turbine 70 can be configured to drive first booster 40.

(9) Consequently, embodiments of the current invention allow for a user to increase production of an existing air separation unit without having to alter the capacity of the front-end purification unit.

(10) As used herein, a composition substantially similar to air is one that has a nitrogen composition between 68% to 88% and an oxygen composition between 11% to 31%.

(11) Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

(12) 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 or reversed in order.

(13) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(14) 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.

(15) 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.

(16) 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.

(17) 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.

(18) 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.