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] 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 is lost in some other form during conventional purification.

Background Art

[0003] In conventional ammonia purification, initially, an attempt is made to separate ammonia (NH3) and hydrogen sulfide (H2S) from the sour water stream of an essential oil plant or a chemical plant. However, in many cases, it is difficult to achieve proper separation of hydrogen sulfide from ammonia. This occurs when using a simple two-column sour water stripping system that typically produces only hydrogen sulfide in the first column and only an ammonia stream in the second column. In addition, in conventional ammonia purification processes, a certain amount of ammonia is often lost during purification.

[0004] A detailed description will be given below with reference to the accompanying drawings, and similar elements will be referred to by similar reference numerals.

Brief Description of the Drawings

[0005]

Figure 1A

Figure 1B

Figure 2

Figure 3

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Mode for Carrying Out the Invention

[0006] The subject matter of the present disclosure is described with respect to specific things, but the description itself is not intended to limit the scope of the disclosure. Thus, the subject matter may be embodied in other ways in order to include similar and / or different structures, steps, and / or combinations that are similar to and / or less than those described herein in combination with other current or future technologies. The term "step" may be used herein to describe different elements of the methods employed, but should not be construed as implying a particular order among or between the various steps disclosed herein, unless specifically 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 considering the following figures and detailed description. It is intended that all such additional features and advantages be included within the scope of the disclosed embodiments. Further, the exemplary figures and dimensions described herein are merely illustrative and are not intended to claim or imply any limitation regarding the environments, architectures, designs, or processes 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 scrubber, a water scrubber, an ammonia stripper, and a caustic fractionator to recover ammonia that is lost in some other form during conventional purification. The disclosed systems and methods remove residual hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants from ammonia-rich streams and produce a high-quality anhydrous ammonia product stream that can be sold as an ammonia commodity product. It is also unique to use a base (sodium hydroxide or potassium hydroxide) to purify another base (ammonium hydroxide) and to recover ammonia from spent caustic.

[0008] In one embodiment, the present disclosure includes a system for ammonia purification, the system 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 for separating the scrubbed ammonia stream into a non-condensable vapor stream and an anhydrous ammonia liquid product stream; iii) an ammonia stripper for separating a sour water liquid stream into the first ammonia vapor stream and a liquid discharge 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 for separating 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 comprising: 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 effluent 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] Referring now to FIG. 1A, an embodiment of a caustic scrubber system 100A including a caustic wash section for ammonia purification is illustrated in schematic form. 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 flow arrangement. The caustic solution stream 103 can be an aqueous NaOH solution in the range of from about 1 wt% to greater than 50 wt%. Alternatively, the caustic solution stream 103 can be an aqueous KOH solution in the range of from about 1 wt% to greater than 50 wt%. When the feed gas stream 102 contacts the caustic solution stream 103, hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants are removed from the ammonia-enriched vapor and a scrubbed ammonia stream 106 is sent to a compression train system 200 illustrated in FIG. 2 and a spent caustic stream 108 is sent to a pump 110 to provide the pressure required for operation of a downstream caustic fractionator system 400 illustrated in FIG. 4. Thus, the caustic solution 103 removes hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants from the ammonia-enriched feed gas stream 102.

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

[0012] Compression train system Next, referring to FIG. 2, an embodiment of a compression train system 200 with a water washing section for ammonia purification is illustrated in a schematic diagram. The compression train system 200 can 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 that can be air-cooled (as illustrated) or water-cooled. The feedstock supply to the compression train system 200 includes the scrubbed ammonia stream 106 and, optionally, an independent liquid water stream 202. Additional independent liquid water streams 202 are included via respective water spray nozzles after each ammonia compressor and / or each condenser cooler, which can enhance the removal of impurities in the sour water liquid stream 217. The first condenser cooler 203 can optionally be provided to cool the scrubbed ammonia stream 106 and the (optional) liquid water stream 202.

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

[0014] After most of the water is removed from the ammonia vapor stream 216, the ammonia vapor stream 216 is compressed by the ammonia compressor 218 of the second stage in preparation for liquefaction of the ammonia. Liquefaction may require multiple compression and cooling stages to achieve the appropriate temperature and pressure required for liquefaction of the ammonia. The ammonia compressor 218 of the second stage raises the pressure of the ammonia vapor stream 216, which is then sent downstream to the third condenser cooler 220. The cooled condensate vapor stream 222 is sent to the ammonia separator 224, where it is separated into a non-condensable vapor stream 226 and an anhydrous ammonia liquid stream 228. Additional pressure and cooling may be required for the anhydrous ammonia liquid stream 228 to meet the product pressure and temperature requirements. Ammonia stripper system

[0015] Next, referring to FIG. 3, an embodiment of an ammonia stripper system 300 for ammonia purification is illustrated in a schematic diagram. The sour water liquid stream 217 from the compression train system 200 is sent to the ammonia stripper 302, which separates the sour water liquid stream 217 into an ammonia vapor stream 304 and a liquid effluent stream 306 containing stripped water. The ammonia vapor stream 304 may contain trace amounts of hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants contained in the sour water liquid stream 217. The ammonia vapor stream 304 can be returned to the caustic scrubber 104 of FIG. 1A or FIG. 1B for reprocessing and recovery of ammonia and removal of hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants. If little or no mercaptans are contained in the sour water liquid stream 217, the ammonia vapor stream 304 can instead be returned to the compression train system 200 of FIG. 2, thereby saving the reprocessing of the ammonia vapor stream 304 within the caustic scrubber 104. The liquid effluent stream 306 is sent to the cooler 310 and then to the pump 312, which supplies a liquid effluent stream 314 at the pressure and temperature required for downstream processing. Alternatively, the liquid effluent stream 306 can be sent to the pump 312 and then to the cooler 310.

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

[0017] Caustic fractionator system Next, referring to FIG. 4, an embodiment of a caustic fractionator system 400 for ammonia purification is illustrated in a schematic diagram. The spent caustic stream 108 from the caustic scrubber system 100A or 100B is pumped to a caustic fractionator 402 for the treatment and recovery of ammonia. 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 a feed for a reboiler 408, which produces a reboiler vapor stream 410 mainly containing heated water and ammonia, and a reboiler liquid stream 412 mainly containing heated water, caustic, hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants. The reboiler vapor stream 410 flows countercurrent to the spent caustic stream 108 at the bottom of the caustic fractionator 402, facilitating the stripping of ammonia as it flows to the upper part of the caustic fractionator 402. Alternatively, the reboiler 408, the reboiler vapor stream 410, and the reboiler liquid stream 412 can be replaced with live steam introduced at the bottom of the caustic fractionator 402 to facilitate the stripping of ammonia.

[0018] The reboiler liquid stream 412 is sent to the cooler 414 and then to the pump 418, which can supply the reboiler liquid stream 412 at the temperature and pressure required for downstream processing. Alternatively, the reboiler liquid stream 412 can be sent to the pump 418 and then to the cooler 414. The overhead vapor stream 406 passes through a condenser 420 that produces a two-phase stream 422 containing water and ammonia. The two-phase stream 422 is supplied to a reflux drum 424, which separates the two-phase stream 422 into an ammonia vapor stream 426 and a liquid water stream 428. The ammonia vapor stream 426 can be recycled by sending this ammonia vapor stream 426 to the caustic scrubber 104 of FIG. 1A or FIG. 1B for ammonia reprocessing and recovery, as well as removal of hydrogen sulfide, carbon dioxide, mercaptans, and other contaminants. The liquid water stream 428 is pumped by a pump 430 to the top of the caustic fractionator 402 and can be used as reflux, flowing countercurrent to the vapor in the caustic fractionator 402 and washing away a portion of the caustic vapor.

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

[0020] Although the present disclosure has been described with respect to presently preferred embodiments, it will be understood by those skilled in the art that the disclosure of those embodiments is not intended to be limiting. 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.

Description of Reference Numerals

[0021] 100A Caustic Scrubber System 100B Caustic Scrubber System 102 Feed Gas Stream 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 flow 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. A system for ammonia purification, comprising: 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; 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 a sour water liquid stream into the first ammonia vapor stream and a liquid discharge stream; A caustic fractionator in fluid communication with the spent caustic stream to produce a liquid bottoms stream and an overhead vapor stream; A condenser in fluid communication with the overhead vapor stream to produce a two-phase stream containing water and ammonia; A system comprising a reflux drum for separating the two-phase stream into a liquid water stream and the second ammonia vapor stream.

2. The compression train system comprises: A first-stage compressor suction drum for separating the scrubbed ammonia stream into a waste water liquid stream and a caustic vapor stream; A first-stage ammonia compressor for increasing the pressure of the caustic vapor stream; A first-stage heat exchanger downstream of the first-stage ammonia compressor for cooling the caustic vapor stream; A second-stage compressor suction drum downstream of the first-stage heat exchanger for separating the caustic vapor stream into a third ammonia vapor stream and the 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 the second-stage ammonia compressor for cooling the third ammonia vapor stream; An ammonia separator downstream of the second-stage heat exchanger for separating the third ammonia vapor stream into the non-condensable vapor stream and the anhydrous ammonia liquid product stream. The system according to claim 1.

3. The caustic solution stream according to claim 1 contains an aqueous NaOH solution of about 1 wt% to about 50 wt%.

4. The caustic solution stream according to claim 1 contains an aqueous NaOH solution of more than 50 wt%.

5. The caustic solution stream according to claim 1 contains an aqueous KOH solution of about 1 wt% to about 50 wt%.

6. The caustic solution stream according to claim 1 contains an aqueous KOH solution of more than 50 wt%.

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

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

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

10. The system of claim 1, further comprising an independent live steam stream that is in fluid communication with the ammonia stripper.

11. A method for ammonia purification, comprising: 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; separating the scrubbed ammonia stream into a sour water liquid stream, a non-condensable vapor stream, and an anhydrous ammonia liquid product stream; separating the sour water liquid stream into the first ammonia vapor stream and a liquid discharge stream; introducing the spent caustic stream into a caustic fractionator to produce a liquid bottoms stream and an overhead vapor stream; introducing the overhead vapor stream into a condenser to produce a two-phase stream containing water and ammonia; and separating the two-phase stream into a liquid water stream and the second ammonia vapor stream.

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 having at least two compression stages.

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

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

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

17. The caustic solution stream is the method of claim 11, comprising an aqueous KOH solution of from about 1 wt% to about 50 wt%.

18. The caustic solution stream is the method of claim 11, comprising an aqueous KOH solution of more than 50 wt%.

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

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

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