Systems and methods for ammonia purification

Abstract

The present disclosure generally relates to systems and methods for ammonia purification. More particularly, these systems and methods use a unique arrangement of a caustic scrubber, a water scrubber, an ammonia stripper, and a caustic fractionator to recover ammonia that has been lost in some other form during conventional purification.

Description

[Technical Field]

[0001] Related Applications This application claims priority to U.S. Provisional Application No. 63 / 425,583, filed November 15, 2022, which is incorporated herein by reference.

[0002] This disclosure relates generally to systems and methods for ammonia purification, and more particularly, these systems and methods use a unique arrangement of a caustic wash, a water wash, an ammonia stripper, and a caustic fractionator to recover ammonia that is otherwise lost during conventional purification. [Background technology]

[0003] Conventional ammonia refining first attempts to separate ammonia (NH3) and hydrogen sulfide (HS) from a refinery or chemical plant sour water stream, but often encounters difficulties in achieving adequate separation of hydrogen sulfide from ammonia. This typically occurs when using a simple two-column sour water stripping system that produces exclusively hydrogen sulfide in the first column and exclusively ammonia in the second column. Additionally, conventional ammonia refining processes often lose a certain amount of ammonia during refining.

[0004] The detailed description is set forth below with reference to the accompanying drawings, in which like elements are referred to with like reference numerals, and in which: [Brief explanation of the drawings]

[0005] [Figure 1A] FIG. 1 is a schematic diagram illustrating one embodiment of a caustic scrubber system with a caustic wash section for ammonia purification. [Figure 1B]FIG. 2 is a schematic diagram illustrating another embodiment of a caustic scrubber system with a caustic wash section for ammonia purification. [Figure 2] FIG. 1 is a schematic diagram illustrating one embodiment of a compression train system with a water wash for ammonia purification. [Figure 3] FIG. 1 is a schematic diagram illustrating one embodiment of an ammonia stripper system for ammonia purification. [Figure 4] FIG. 1 is a schematic diagram illustrating one embodiment of a caustic fractionator system for ammonia purification. DETAILED DESCRIPTION OF THE INVENTION

[0006] While the subject matter of the present disclosure has been described with particular reference, the description itself is not intended to limit the scope of the disclosure. Accordingly, the subject matter could be embodied in other ways to include different structures, steps, and / or combinations similar to and / or less than those described herein, in conjunction with other current or future technologies. While the term "step" may be used herein to describe different elements of the method employed, it should not be construed as implying a particular order among or between the various steps disclosed herein unless otherwise expressly limited to a particular order by the description. Other features and advantages of the disclosed embodiments will become apparent to those skilled in the art after reviewing the following figures and detailed description. All such additional features and advantages are intended to be included within the scope of the disclosed embodiments. Furthermore, the illustrated figures and dimensions described herein are merely exemplary and are not intended to assert or imply any limitations with regard to the environment, architecture, design, or process in which different embodiments may be implemented. To the extent that temperature and / or pressure are mentioned in the following description, those conditions are merely exemplary and are not intended to limit the disclosure. All flows described herein are carried by physical conduits.

[0007] The systems and methods disclosed herein overcome the drawbacks encountered in conventional ammonia purification processes by using a unique arrangement of a caustic wash, a water wash, an ammonia stripper, and a caustic fractionator to recover ammonia that would otherwise be lost during conventional purification. The disclosed systems and methods remove residual hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants from an ammonia-rich stream to produce a high-quality anhydrous ammonia product stream that can be sold as an ammonia commodity product. The use of a base (sodium hydroxide or potassium hydroxide) to purify another base (ammonium hydroxide) and the recovery of ammonia from spent caustic are also unique.

[0008] In one embodiment, the present disclosure includes a system for ammonia purification comprising: i) a caustic scrubber in fluid communication with a feed gas stream, a caustic solution stream, a first ammonia vapor stream, and a second ammonia vapor stream to produce a scrubbed ammonia stream and a spent caustic stream; ii) a compression train system comprising at least two compression stages to separate the scrubbed ammonia stream into a non-condensable vapor stream and an anhydrous ammonia liquid product stream; iii) an ammonia stripper to separate a sour water liquid stream into a first ammonia vapor stream and a liquid bleed stream; iv) a caustic fractionator in fluid communication with the spent caustic stream to produce a liquid bottoms stream and an overhead vapor stream; v) a condenser in fluid communication with the overhead vapor stream to produce a two-phase stream comprising water and ammonia; and vi) a reflux drum to separate the two-phase stream into a liquid water stream and a second ammonia vapor stream.

[0009] In another embodiment, the present disclosure includes a method for ammonia purification, the method including: i) introducing a feed gas stream, a caustic solution stream, a first ammonia vapor stream, and a second ammonia vapor stream into a caustic scrubber to produce a scrubbed ammonia stream and a spent caustic stream; ii) separating the scrubbed ammonia stream into a sour water liquid stream, a non-condensable vapor stream, and an anhydrous ammonia liquid product stream; iii) separating the sour water liquid stream into a first ammonia vapor stream and a liquid bleed stream; iv) introducing the spent caustic stream into a caustic fractionator to produce a liquid bottoms stream and an overhead vapor stream; v) introducing the overhead vapor stream into a condenser to produce a two-phase stream comprising water and ammonia; and vi) separating the two-phase stream into a liquid water stream and a second ammonia vapor stream. Caustic Scrubber System

[0010] 1A, a schematic diagram illustrates one embodiment of a caustic scrubber system 100A with a caustic wash section for ammonia purification. A feed gas stream 102 containing hydrogen sulfide, carbon dioxide, mercaptans, other contaminants, and ammonia passes through a caustic scrubber 104, where the feed gas stream 102 is contacted with a caustic solution stream 103 of sodium hydroxide and water in a countercurrent arrangement. The caustic solution stream 103 can be an aqueous NaOH solution in the range of about 1 wt. % to greater than 50 wt. %. Alternatively, the caustic solution stream 103 can be an aqueous KOH solution in the range of about 1 wt. % to greater than 50 wt. %. When feed gas stream 102 contacts caustic solution stream 103, hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants are removed from the ammonia-rich vapor to produce a scrubbed ammonia stream 106 that is sent to compression train system 200 illustrated in Figure 2 and a spent caustic stream 108 that is sent to pump 110 to provide the pressure necessary to operate downstream caustic fractionator system 400 illustrated in Figure 4. Thus, caustic solution 103 removes hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants from ammonia-rich feed gas stream 102.

[0011] Referring now to FIG. 1B, another alternative embodiment of a caustic scrubber system 100B with a caustic wash section for ammonia purification is illustrated in a schematic diagram. There may be times when the caustic scrubber 104 needs to operate at a lower temperature than is available given the temperature and flow rate of the feed gas stream 102 and the caustic solution stream 103. When lower temperatures are required, the caustic scrubber system 100B can be effectively used. The capacity of the pump 110 can be increased, thereby diverting a portion of the spent caustic stream 108 through a recycle cooler 112, and returning the cooled spent caustic stream 114 to the caustic scrubber 104. Another portion of the spent caustic stream 108 is sent from the pump 110 to a downstream caustic fractionator system 400, illustrated in FIG. 4, for its operation. If additional pressure is required for proper operation of the caustic scrubber 104, a compressor can be added to the feed gas stream 102.

[0012] Compression Train System Referring now to FIG. 2, a schematic diagram illustrates one embodiment of a compression train system 200 with a water wash for ammonia purification. Compression train system 200 may include up to four compression stages. Each compression stage houses a compressor suction drum, an ammonia compressor, and a condenser cooler. Each condenser cooler effectively functions as a heat exchanger, which may be air-cooled (as shown) or water-cooled. The feed to compression train system 200 includes scrubbed ammonia stream 106 and, optionally, a separate liquid water stream 202. An additional separate liquid water stream 202 may be included after each ammonia compressor and / or each condenser cooler via respective water spray nozzles to enhance removal of impurities in sour water stream 217. A first condenser cooler 203 may optionally be provided to cool scrubbed ammonia stream 106 and the (optional) liquid water stream 202.

[0013] First stage compressor suction drum 204 separates scrubbed ammonia stream 106 and (optional) liquid water stream 202 into a wastewater liquid stream 206 that is purged from compression train system 200 and a caustic vapor stream 207 that is sent to first stage ammonia compressor 208. First stage ammonia compressor 208 increases the pressure of caustic vapor stream 207, which is then sent downstream to second condenser cooler 210. Cooled condensate stream 212, which contains vapor and potentially some liquids (primarily liquid water with some ammonia, hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants), is sent to second stage compressor suction drum 214. Second stage compressor suction drum 214 separates cooled condensate stream 212 into a sour water liquid stream 217 sent to ammonia stripper system 300 illustrated in FIG. 3 and an ammonia vapor stream 216 sent to second stage ammonia compressor 218.

[0014] After removing most of the water from ammonia vapor stream 216, ammonia vapor stream 216 is compressed in second stage ammonia compressor 218 in preparation for ammonia liquefaction. Liquefaction may require multiple compression and cooling stages to achieve the appropriate temperature and pressure required for ammonia liquefaction. Second stage ammonia compressor 218 increases the pressure of ammonia vapor stream 216, which is then sent downstream to third condenser cooler 220. Cooled condensed vapor stream 222 is sent to ammonia separator 224, where it is separated into non-condensed vapor stream 226 and anhydrous ammonia liquid stream 228. Additional pressure and cooling may be required for anhydrous ammonia liquid stream 228 to meet product pressure and temperature requirements. Ammonia Stripper System

[0015] Referring now to Figure 3, a schematic diagram illustrates one embodiment of an ammonia stripper system 300 for ammonia purification. Sour water liquid stream 217 from compression train system 200 is sent to ammonia stripper 302, which separates sour water liquid stream 217 into ammonia vapor stream 304 and a liquid effluent stream 306 comprising stripped water. Ammonia vapor stream 304 may contain trace amounts of hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants contained in sour water liquid stream 217. Ammonia vapor stream 304 may be returned to caustic scrubber 104 of Figure 1A or 1B for ammonia reprocessing and recovery and removal of hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants. If there is little or no mercaptans in sour water liquid stream 217, ammonia vapor stream 304 may instead be returned to compression train system 200 of Figure 2, thereby eliminating reprocessing of ammonia vapor stream 304 in caustic scrubber 104. Liquid effluent stream 306 is sent to cooler 310 and then to pump 312, which provides liquid effluent stream 314 at the required pressure and temperature for downstream processing. Alternatively, liquid effluent stream 306 may be sent to pump 312 and then to cooler 310.

[0016] A separate live steam stream 308 may also be used to strip ammonia from sour water liquid stream 217 and improve the overall recovery of ammonia. For very large systems or alternative energy sources, a reboiler may be used to generate the live steam necessary to strip ammonia from sour water liquid stream 217. The flow rate of live steam stream 308 may be adjusted to meet the requirements of liquid effluent stream 314.

[0017] Caustic Fractionator System Referring now to Figure 4, a schematic diagram illustrates one embodiment of a caustic fractionator system 400 for ammonia purification. The spent caustic stream 108 from the caustic scrubber system 100A or 100B is pumped to a caustic fractionator 402 for ammonia processing and recovery. The spent caustic stream 108 enters the caustic fractionator 402, which produces a liquid bottoms stream 404 containing water, caustic, hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants, and an overhead vapor stream 406 containing ammonia and some water vapor. This liquid bottoms stream 404 is used as feed for a reboiler 408, which produces a reboiler vapor stream 410 containing primarily heating water and ammonia, and a reboiler liquid stream 412 containing primarily heating water, caustic, hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants. Reboiler vapor stream 410 flows countercurrent to the spent caustic stream 108 at the bottom of caustic fractionator 402 and facilitates stripping of ammonia flowing to the top of caustic fractionator 402. Alternatively, reboiler 408, reboiler vapor stream 410, and reboiler liquid stream 412 can be replaced with live steam introduced at the bottom of caustic fractionator 402 to facilitate stripping of ammonia.

[0018] Reboiler liquid stream 412 may be sent to cooler 414 and then to pump 418 to provide reboiler liquid stream 412 at the temperature and pressure required for downstream processing. Alternatively, reboiler liquid stream 412 may be sent to pump 418 and then to cooler 414. Overhead vapor stream 406 passes through condenser 420, which produces a two-phase stream 422 comprising water and ammonia. Two-phase stream 422 is fed to reflux drum 424, which separates two-phase stream 422 into an ammonia vapor stream 426 and a liquid water stream 428. Ammonia vapor stream 426 may be recycled by sending it to caustic scrubber 104 of FIG. 1A or FIG. 1B for ammonia reprocessing and recovery, and removal of hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants. Liquid water stream 428 is pumped to the top of caustic fractionator 402 by pump 430 and may be used as reflux, flowing countercurrent to the vapors in caustic fractionator 402 to wash away a portion of the caustic vapors.

[0019] By directing the spent caustic stream 108 through the caustic fractionator 402, the spent caustic stream 108 can be partially separated into an ammonia vapor stream 426 containing small amounts of hydrogen sulfide and caustic, and a liquid bottoms stream 404 containing most of the caustic, carbon dioxide, mercaptans, other contaminants, and trace amounts of ammonia.

[0020] While the present disclosure has been described in terms of presently preferred embodiments, it will be understood by those skilled in the art that it is not intended to limit the disclosure to those embodiments. Accordingly, it is contemplated that various alternative embodiments and modifications to the disclosed embodiments can be made without departing from the spirit and scope of the disclosure as defined by the appended claims and their equivalents. [Explanation of symbols]

[0021] 100A Caustic Scrubber System 100B Caustic Scrubber System 102 Feed gas flow 103 Caustic Solution Stream 104 Caustic Scrubber 106 Scrubbed ammonia stream 108 Used caustic logistics 110 Pump 112 Recycled Cooler 114 Refrigerated Spent Caustic Distribution 200 Compression Train System 202 Liquid water flow 203 First Condenser Cooler 204 First stage compressor suction drum 206 Wastewater Liquid Stream 207 Caustic Vapor Flow 208 First Stage Ammonia Compressor 210 Secondary Condenser Cooler 212 Cooled condensate flow 214 Second stage compressor suction drum 216 Ammonia vapor flow 217 Sour Water Liquid Flow 218 Second Stage Ammonia Compressor 220 Third Condenser Cooler 222 Cooled condensed vapor flow 224 Ammonia Separator 226 Non-condensing steam flow 228 Anhydrous Ammonia Liquid Stream 300 Ammonia Stripper System 302 Ammonia Stripper 304 Ammonia vapor flow 306 Liquid discharge logistics 308 Live steam flow 310 Cooler 312 Pump 314 Liquid discharge logistics 400 Caustic Fractionator System 402 Caustic Fractionator 404 Liquid bottom flow 406 Overhead Steam Flow 408 Reboiler 410 Reboiler steam flow 412 Reboiler Liquid Stream 414 Cooler 418 Pump 420 Condenser 422 Two-phase flow 424 reflux drum 426 Ammonia Vapor Flow 428 Liquid water flow 430 Pump

Claims

1. 1. A system for purifying ammonia, comprising: a caustic scrubber in fluid communication with the feed gas stream, the caustic solution stream, the first ammonia vapor stream, and the second ammonia vapor stream to produce a scrubbed ammonia stream and a spent caustic stream; a compression train system comprising at least two compression stages for separating the scrubbed ammonia stream into a non-condensable vapor stream and an anhydrous ammonia liquid product stream; an ammonia stripper for separating the sour water liquid stream into said first ammonia vapor stream and a liquid effluent stream; a caustic fractionator in fluid communication with the spent caustic stream for producing a liquid bottoms stream and an overhead vapor stream; a condenser in fluid communication with the overhead vapor stream for producing a two-phase stream comprising water and ammonia; a reflux drum for separating said two-phase stream into a liquid water stream and said second ammonia vapor stream.

2. The compression train system comprises: a first stage compressor suction drum for separating the scrubbed ammonia stream into a wastewater liquid stream and a caustic vapor stream; a first stage ammonia compressor for increasing the pressure of said caustic vapor stream; a first stage heat exchanger downstream of said first stage ammonia compressor for cooling said caustic vapor stream; a second stage compressor suction drum downstream of said first stage heat exchanger for separating said caustic vapor stream into a third ammonia vapor stream and said sour water liquid stream; a second stage ammonia compressor for increasing the pressure of the third ammonia vapor stream; a second stage heat exchanger downstream of said second stage ammonia compressor for cooling said third ammonia vapor stream; 2. The system of claim 1, further comprising an ammonia separator downstream of said second stage heat exchanger for separating said third ammonia vapor stream into said non-condensable vapor stream and said anhydrous ammonia liquid product stream.

3. 10. The system of claim 1, wherein the caustic solution stream comprises about 1 wt% to about 50 wt% aqueous NaOH.

4. 10. The system of claim 1, wherein the caustic solution stream comprises greater than 50 wt% aqueous NaOH.

5. 10. The system of claim 1, wherein the caustic solution stream comprises about 1 wt% to about 50 wt% aqueous KOH.

6. 10. The system of claim 1, wherein the caustic solution stream comprises greater than 50 wt% aqueous KOH.

7. 3. The system of claim 2, further comprising a pre-stage heat exchanger in fluid communication with the scrubbed ammonia stream and upstream of the first stage compressor suction drum.

8. 8. The system of claim 7, further comprising a separate liquid water stream in fluid communication with the scrubbed ammonia stream and upstream of the pre-stage heat exchanger.

9. The system of claim 7 , wherein the pre-stage heat exchanger, the first stage heat exchanger, and the second stage heat exchanger each comprise an air-cooled condenser cooler.

10. 10. The system of claim 1, further comprising a separate live steam stream in fluid communication with the ammonia stripper.

11. 1. A process for ammonia purification comprising: introducing the feed gas stream, the caustic solution stream, the first ammonia vapor stream, and the second ammonia vapor stream into a caustic scrubber to produce a scrubbed ammonia stream and a spent caustic stream; separating the scrubbed ammonia stream into a sour water liquid stream, a non-condensable vapor stream, and an anhydrous ammonia liquid product stream; separating said sour water liquid stream into said first ammonia vapor stream and a liquid effluent stream; introducing the spent caustic stream into a caustic fractionator to produce a liquid bottoms stream and an overhead vapor stream; directing the overhead vapor stream into a condenser to produce a two-phase stream comprising water and ammonia; separating said two-phase stream into a liquid water stream and said second ammonia vapor stream.

12. 12. The method of claim 11, wherein the scrubbed ammonia stream is separated into the non-condensable vapor stream and the anhydrous ammonia liquid product stream by a compression train system comprising at least two compression stages.

13. 12. The method of claim 11, wherein the sour water liquid stream is separated into the first ammonia vapor stream and the liquid effluent stream by an ammonia stripper.

14. 12. The method of claim 11, wherein the two-phase stream is separated into the liquid water stream and the second ammonia vapor stream by a reflux drum.

15. 12. The method of claim 11, wherein the caustic solution stream comprises about 1 wt% to about 50 wt% aqueous NaOH.

16. 12. The method of claim 11, wherein the caustic solution stream comprises greater than 50 wt% aqueous NaOH.

17. 12. The method of claim 11, wherein the caustic solution stream comprises about 1 wt% to about 50 wt% aqueous KOH.

18. 12. The method of claim 11, wherein the caustic solution stream comprises greater than 50 wt% aqueous KOH.

19. 13. The method of claim 12, further comprising introducing another liquid water stream into the compression train system at one of a location upstream of the at least two compression stages and a location downstream of one of the at least two compression stages.

20. 14. The method of claim 13, further comprising introducing a separate live steam stream into the ammonia stripper.

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