Cryogenic liquefier by integration with power plant

Abstract

A method for producing liquid nitrogen using a residual gas stream derived from a flue gas of a power plant is provided. The residual gas stream is purified in a front-end purification unit to remove freezable components and then the purified stream is compressed. Following compression, the stream can be divided into a first portion and a second portion, wherein the first portion is cooled and sent to a distillation column, wherein oxygen and argon are separated, thereby leaving an essentially pure gaseous nitrogen stream. The gaseous nitrogen stream can then be liquefied using refrigeration provided by expanding the second portion of the purified stream. In a preferred embodiment, the second portion is expanded in two turbines, and the gaseous nitrogen is compressed in a cold nitrogen booster, which is powered by one of the two turbines. In an additional embodiment, after warming, the expanded second portion of the purified stream can be used to regenerate the front-end purification unit.

Claims

1. A method for producing liquid nitrogen, the method comprising the steps of: providing a residual gas stream, wherein the residual gas stream is sourced from a retentate stream of a cold membrane, wherein the residual gas stream comprises nitrogen, argon, oxygen, and carbon dioxide; purifying the residual gas stream in a front-end purification unit to remove carbon dioxide, thereby forming a purified residual gas stream; compressing the purified residual gas stream in a first compressor to form a pressurized residual gas stream; introducing the pressurized residual gas stream to a cold box, wherein a first portion of the pressurized residual gas stream is cooled in a main heat exchanger, expanded within the cold box, and then fed to a distillation column system for separation therein, thereby forming a nitrogen stream and a waste stream; withdrawing the waste stream from the distillation column system and warming said waste stream; and withdrawing the nitrogen stream from the distillation column system and compressing the nitrogen stream in a second compressor before liquefying the nitrogen stream within the cold box to produce a liquid nitrogen stream, wherein at least a portion of the liquid nitrogen stream is stored in a liquid nitrogen tank; wherein a second portion of the pressurized residual gas stream is partially cooled in the main heat exchanger and then expanded in a plurality of cold turbines; wherein the second compressor is a cold compressor operating with an inlet temperature less than −100 C.

2. The method of claim 1, wherein the residual gas stream is derived from a flue gas stream from a power plant.

3. The method of claim 1, wherein the plurality of cold turbines comprises a first turbine and a second turbine, wherein the first and second turbines operate in series and at different temperatures.

4. The method of claim 3, wherein the first turbine has a warmer inlet temperature as compared to the second turbine, wherein the first turbine is configured to drive the first compressor, wherein the second turbine is configured to drive the second compressor.

5. The method of claim 1, wherein the second compressor inlet temperature is less than −130 C.

6. The method of claim 1, wherein the plurality of cold turbines power the first compressor and the second compressor, such that the purified residual gas stream and the nitrogen stream are compressed without the use of any externally-powered compressors.

7. The method of claim 1, wherein the first portion of the pressurized residual gas stream is expanded across a Joule-Thompson valve prior to being fed to the distillation column system.

8. The method of claim 1, wherein the liquid nitrogen stream is subcooled in a subcooler before being stored in the liquid nitrogen tank.

9. The method of claim 1, further comprising the step of warming the second portion of the pressurized residual gas stream, after expansion in the plurality of cold turbines, in the main heat exchanger.

10. The method of claim 1, wherein the liquid nitrogen stream is subcooled in a subcooler, and then a first portion of the subcooled nitrogen is stored in the liquid nitrogen tank and a second portion of the subcooled nitrogen is expanded across a second Joule-Thompson valve and heated in the subcooler and the main heat exchanger.

11. The method of claim 10, further comprising regenerating the front-end purification unit using a stream selected from the group consisting of the expanded second portion of the pressurized residual gas stream, the waste stream, the second portion of the subcooled nitrogen, and combinations thereof.

12. The method of claim 1, wherein the residual gas stream is at a pressure above 13 bara.

13. The method of claim 1, wherein the method comprises an absence of providing external refrigeration such that the liquid nitrogen is produced with only cooling provided by the expansion of streams derived from the residual gas stream.

14. The method of claim 1, expanding a second portion of the liquid nitrogen stream across a second Joule-Thompson valve forming an expanded second portion and warming the expanded second portion in the main heat exchanger.

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 power plant and carbon dioxide cold capture; and

(3) FIG. 2 is a process flow diagram of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) Referring to FIG. 2, pressurized residue stream 10, which contains nitrogen, oxygen, argon, and carbon dioxide and is preferably at a pressure of at least 15 bara, is sent to front-end purification unit 30 to remove components such as carbon dioxide that would freeze at cryogenic temperatures (e.g., below −40° C.). Purified stream 32 is then compressed in first compressor 40 to a pressure of about 20 bara in this example to form pressurized stream 42 before being cooled in main heat exchanger 50.

(5) Pressurized stream 42 is split into first portion 52 and second portion 54. In the embodiment shown, the split occurs within main heat exchanger 50; however, the split can also occur upstream heat exchanger 50. First portion 52 is further cooled and expanded across a Joule-Thompson valve before being introduced into distillation column system 70, which in the embodiment shown comprises a nitrogen column (e.g., a single column with top condenser-reboiler). Those of ordinary skill in the art will readily understand that any system that is suitable for separating nitrogen from oxygen and argon can be used, for example, double or triple columns or column setups conducive for producing argon.

(6) In the embodiment shown, distillation column system 70 is preferably configured to produce waste gas 72 and nitrogen enriched stream 74. Waste gas 72 is sent to main heat exchanger 50 for warming.

(7) In the embodiment shown, nitrogen enriched stream 74 is preferably further compressed in second compressor 90 before the compressed nitrogen stream is liquefied in main heat exchanger 50 and then subcooled in subcooler 100. After subcooling, the liquid nitrogen 102 is preferably split into first portion 102a and second portion 102b, with first portion 102a being introduced into storage tank 110 as product, and second portion 102b being expanded in order to provide refrigeration for subcooler 100 and main heat exchanger 50.

(8) Power for the first and second compressors is provided for by expanding second portion of the pressurized stream 54 in the first and second turbines 60, 80. After expansion, the expanded second portion 82 is warmed in the main heat exchanger 50. In the embodiment shown, the expanded second portion 82, the second portion 102b, and the waste gas 72 are combined within main heat exchanger to form combined waste stream 51; however, this is not required.

(9) In a preferred embodiment, a first portion 55 of combined waste stream 51 is warmed and then used to regenerate front-end purification system 30, with the regenerated gas, which now contains the desorbed carbon dioxide, being sent back, along with second portion of combined waste stream 53, to the flue gas vent stack.

Working Example

(10) A simulation was run using the embodiment shown in FIG. 2. 456 mt/h of pressurized residue stream 10 containing 93.7% nitrogen, 3.3% oxygen, 1.1% argon, and 1.9% CO2 and at 15 bara was compressed to 20 bara in first compressor 40. Approximately 246 mt/h (approximately 54%) of flow was sent to the distillation column system 70, with the remainder being expanded in the plurality of turbines. Approximately 923 mtpd liquid nitrogen was produced, all without using any externally powered compressors.

(11) Consequently, preferred embodiments of the current invention allow a user to utilize the pressurized residue stream of a cold membrane separator to produce large amounts of liquid nitrogen with essentially zero compression energy costs.

(12) 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.

(13) 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.

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

(15) “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.

(16) “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.

(17) 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.

(18) 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.

(19) 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.