SYSTEMS AND METHODS FOR REMOVING HYDROGEN SULFIDE FROM AN AMMONIA STREAM

Abstract

Systems and methods for removing hydrogen sulfide from an ammonia stream in the NH3 purification and liquefaction stage of a conventional two-column sour water stripping system using an adsorbent bed.

Claims

1. A system for removing hydrogen sulfide from an ammonia stream, which comprises: an ammonia vapor stream; a water wash connected to the ammonia vapor stream for removing hydrogen sulfide from the ammonia vapor stream and producing a scrubbed ammonia vapor stream; a caustic wash connected to the scrubbed ammonia vapor stream for removing residual containments in the scrubbed ammonia vapor stream and producing a double scrubbed ammonia vapor stream; at least one of a compressor, a refrigeration unit and an ammonia absorber connected to only the scrubbed ammonia vapor stream or the double scrubbed ammonia vapor stream for producing at least one of an anhydrous liquid ammonia stream and an aqueous ammonia stream; and an adsorbent bed connected to one of the ammonia vapor stream, the scrubbed ammonia vapor stream, the double scrubbed ammonia vapor stream, the anhydrous liquid ammonia stream and the aqueous ammonia stream for removing hydrogen sulfide from the respective stream.

2. The system of claim 1, wherein the adsorbent bed is connected to the scrubbed ammonia vapor stream.

3. The system of claim 2, further comprising another adsorbent bed connected to the double scrubbed ammonia vapor stream for removing hydrogen sulfide.

4. The system of claim 2, further comprising another adsorbent bed connected to one of the anhydrous liquid ammonia stream and the aqueous ammonia stream for removing hydrogen sulfide from the respective stream.

5. The system of claim 1, wherein the adsorbent bed includes an adsorbent selected from the group consisting of zinc oxide, activated carbon, molecular sieves, iron oxides, or a combination of iron oxides, silica, water, and Montmorillonite.

6. A method for removing hydrogen sulfide from an ammonia stream, which comprises: scrubbing an ammonia vapor stream in a water wash to remove hydrogen sulfide and produce a scrubbed ammonia vapor stream; scrubbing the scrubbed ammonia vapor stream in a caustic wash to remove residual containments and produce a double scrubbed ammonia vapor stream; introducing only the scrubbed ammonia vapor stream or the double scrubbed ammonia vapor stream into at least one of a compressor, a refrigeration unit and an ammonia absorber for producing at least one of an anhydrous liquid ammonia stream and an aqueous ammonia stream; and removing hydrogen sulfide from one of the ammonia vapor stream, the scrubbed ammonia vapor stream, the double scrubbed ammonia vapor stream, the anhydrous liquid ammonia stream and the aqueous ammonia stream using an adsorbent bed.

7. The method of claim 6, wherein the hydrogen sulfide is removed from the scrubbed ammonia vapor stream using the adsorbent bed.

8. The method of claim 7, further comprising removing hydrogen sulfide from the double scrubbed ammonia vapor stream using another adsorbent bed.

9. The method of claim 7, further comprising removing hydrogen sulfide from one of the anhydrous liquid ammonia stream and the aqueous ammonia stream using another adsorbent bed.

10. The method of claim 6, wherein the adsorbent bed includes an adsorbent selected from the group consisting of zinc oxide, activated carbon, molecular sieves, iron oxides, or a combination of iron oxides, silica, water, and Montmorillonite.

11. A system for removing hydrogen sulfide from an ammonia stream, which comprises: an ammonia vapor stream; a water wash connected to the ammonia vapor stream for removing hydrogen sulfide from the ammonia vapor stream and producing a scrubbed ammonia vapor stream; a caustic wash connected to the scrubbed ammonia vapor stream for removing residual containments in the scrubbed ammonia vapor stream and producing a double scrubbed ammonia vapor stream; at least one of a compressor, a refrigeration unit and an ammonia absorber connected to only the scrubbed ammonia vapor stream or the double scrubbed ammonia vapor stream for producing at least one of an anhydrous liquid ammonia stream and an aqueous ammonia stream; and a contacting vessel with a liquid scavenger connected to one of the ammonia vapor stream, the scrubbed ammonia vapor stream, the double scrubbed ammonia vapor stream, the anhydrous liquid ammonia stream and the aqueous ammonia stream for removing hydrogen sulfide from the respective stream.

12. The system of claim 11, wherein the contacting vessel is connected to the scrubbed ammonia vapor stream.

13. The system of claim 12, further comprising another contacting vessel with a liquid scavenger connected to the double scrubbed ammonia vapor stream for removing hydrogen sulfide.

14. The system of claim 12, further comprising another contacting vessel with a liquid scavenger connected to one of the anhydrous liquid ammonia stream and the aqueous ammonia stream for removing hydrogen sulfide from the respective stream.

15. The system of claim 11, wherein the contacting vessel includes a liquid scavenger selected from the group consisting of monoethanolamine, triazine, triazine-based chemical mixtures, caustic, polyhydric alcohols, and amine resin solutions.

16. A method for removing hydrogen sulfide from an ammonia stream, which comprises: scrubbing an ammonia vapor stream in a water wash to remove hydrogen sulfide and produce a scrubbed ammonia vapor stream; scrubbing the scrubbed ammonia vapor stream in a caustic wash to remove residual containments and produce a double scrubbed ammonia vapor stream; introducing only the scrubbed ammonia vapor stream or the double scrubbed ammonia vapor stream into at least one of a compressor, a refrigeration unit and an ammonia absorber for producing at least one of an anhydrous liquid ammonia stream and an aqueous ammonia stream; and removing hydrogen sulfide from one of the ammonia vapor stream, the scrubbed ammonia vapor stream, the double scrubbed ammonia vapor stream, the anhydrous liquid ammonia stream and the aqueous ammonia stream using a contacting vessel with a liquid scavenger.

17. The method of claim 16, wherein the hydrogen sulfide is removed from the scrubbed ammonia vapor stream using the contacting vessel.

18. The method of claim 17, further comprising removing hydrogen sulfide from the double scrubbed ammonia vapor stream using another contacting vessel with a liquid scavenger.

19. The method of claim 17, further comprising removing hydrogen sulfide from one of the anhydrous liquid ammonia stream and the aqueous ammonia stream using another contacting vessel with a liquid scavenger.

20. The method of claim 16, wherein the contacting vessel includes a liquid scavenger selected from the group consisting of monoethanolamine, triazine, triazine-based chemical mixtures, caustic, polyhydric alcohols, and amine resin solutions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is described below with references to the accompanying drawings in which like elements are referenced with like numerals and in which:

[0021] FIGS. 1A-1B are schematic diagrams illustrating a conventional two-column sour water stripping system.

[0022] FIG. 2 is a schematic diagram illustrating the NH3 purification and liquefaction stage in FIG. 1B according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The subject matter of the present invention is described with specificity, however, the description itself is not intended to limit the scope of the invention. The subject matter thus, might also be embodied in other ways, to include different steps or combinations of steps similar to the ones described herein, in conjunction with other technologies. Moreover, although the term “step” may be used herein to describe different elements of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless otherwise expressly limited by the description to a particular order. While the following description refers to the oil and gas industry, the systems and methods of the present invention are not limited thereto and may also be applied in other industries, such as the gasification industry, to achieve similar results.

[0024] The present invention provides systems and methods to remove hydrogen sulfide from an ammonia stream using an adsorbent bed. The purpose of the adsorbent bed is to enhance the removal of hydrogen sulfide from the ammonia stream during the NH3 purification and liquefaction processing stage.

[0025] Referring now to FIG. 2, a schematic diagram of the NH3 purification and liquefaction stage in FIG. 1B illustrates the use of an adsorbent bed to remove hydrogen sulfide from the ammonia stream. This stage can consist of various pieces of equipment depending upon the ultimate concentration and quality of NH3 desired. The adsorbent bed 202 may be positioned in one or more of the locations illustrated in FIG. 2. Preferably, however, a single adsorbent bed 202 is positioned at a location that will be the final processing step for processing the scrubbed NH3 vapor stream 160, the anhydrous liquid NH3 stream 170 or the aqueous NH3 stream 180. In other words, the adsorbent bed 202 may be positioned at a location i) before the water wash 142 to process the ammonia vapor stream, ii) after the water wash 142 to process the scrubbed NH3 vapor stream 160; iii) after the compressor 146 or the refrigeration unit 148 to process the anhydrous liquid NH3 stream 170; or iv) after the NH3 absorber 149 to process the aqueous NH3 stream 180. In the event that the NH3 purification and liquefaction stage includes the production of the scrubbed NH3 vapor stream 160, the anhydrous liquid NH3 stream 170 and the aqueous NH3 stream 180, then, optionally, the adsorbent bed 202 may be positioned at a location between the caustic wash 144 and each of the compressor 146, the refrigeration unit 148 and the NH3 absorber 149. In this manner, any conventional two-column sour water stripping system that includes an NH3 purification and liquefaction stage may be easily retrofitted with one or more adsorbent beds. Various combinations of adsorbent beds and their locations in the NH3 purification and liquefaction stage will be apparent to those skilled in the art.

[0026] The adsorbent may include any commercial sulfur adsorbent. The adsorbent may suitably be formed into granules, powders, extrudates, pellets or other shapes to permit the passage of process fluids over (e.g. around and through) the adsorbent. For this purpose, the active component of the adsorbent may consist of high internal surface area materials such as, for example, zinc oxide, activated carbon, molecular sieves, iron oxides, or combination of iron oxides, silica, water, and Montmorillonite. The components of the adsorbent may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica. The relative proportions of active material and matrix vary widely, with the active material content ranging from about 1 up to 100 percent by weight. The adsorbents may or may not be regenerable.

[0027] Alternatively, a liquid scavenger such as, for example, monoethanolamine, triazine, triazine-based chemical mixtures, caustic, polyhydric alcohols, and amine resin solutions, may be used in the same manner and in the same positions as the adsorbent bed described in reference to FIG. 2. In this embodiment, a contacting vessel may be used to replace the adsorbent bed and introduce the liquid scavenger. Optionally, a filter or coalescer may be positioned downstream from each contacting vessel to remove any entrained scavenger liquid from the ammonia stream.

[0028] In the operation of any conventional two-column sour water stripping system with an NH3 purification and liquefaction stage that includes one or more adsorbent beds or contacting vessels with a liquid scavenger, the quality of the anhydrous liquid NH3 recovered may be improved up to Haber quality NH3 (i.e. industry standard for anhydrous liquid NH3). Anhydrous liquid NH3 recovered from a conventional two-column sour water stripping system is frequently sold at a discount to Haber quality NH3 and blended with Haber quality NH3. It is expected that the present invention should enable the production of anhydrous liquid NH3 with significantly less than 5 ppmw hydrogen sulfide that can be sold at the same price as Haber quality NH3-without the additional expense of having to blend the conventionally produced anhydrous liquid NH3 with Haber quality NH3.

[0029] Conventional two-column sour water stripping systems have been around since the 1960's. Anhydrous liquid NH3 produced by such systems is frequently blended with Haber quality NH3. While operators of such systems have recognized the need for producing anhydrous liquid NH3 that meets the standard of Haber quality NH3, they often simply pass on the blending costs to the purchaser of the final product. And the purchasers in the NH3 industry are accustomed to the fluctuations in price that accompany the commodities markets. This explains why the need for producing less costly Haber quality NH3, using one or more adsorbent beds or contacting vessels with a liquid scavenger in the NH3 purification and liquefaction stage of a conventional two-column sour water stripping system, has been unresolved since the 1960's.