Systems and methods for enhanced separation of hydrogen sulfide and ammonia in a hydrogen sulfide stripper

Abstract

Systems and methods for enhanced separation of H2S and NH3 in an H2S stripper using carbon dioxide and/or an inert gas.

Claims

1. A method for separating hydrogen sulfide from ammonia, which comprises: introducing a fluid mixture of the hydrogen sulfide and the ammonia into a hydrogen sulfide stripper; introducing a stripping gas into the hydrogen sulfide stripper, wherein the stripping gas comprises only carbon dioxide and an inert gas selected from the group consisting of Helium, Neon, Argon, Krypton, Xenon and Radon; and separating most of the hydrogen sulfide from the ammonia in the fluid mixture using the stripping gas in the hydrogen sulfide stripper, which forms a hydrogen sulfide stripper overheads stream and a hydrogen sulfide stripper bottoms stream.

2. The method of claim 1, wherein the hydrogen sulfide stripper overheads stream comprises the most hydrogen sulfide from the fluid mixture and the hydrogen sulfide stripper bottoms stream comprises the most ammonia from the fluid mixture.

3. The method of claim 1, wherein the stripping gas separates most of the hydrogen sulfide from the ammonia in the fluid mixture by lowering a partial pressure of the hydrogen sulfide in the hydrogen sulfide stripper and providing a stripping action.

4. The method of claim 1, wherein the stripping gas stream comprises equal amounts of the carbon dioxide and the inert gas.

5. The method of claim 1, wherein the stripping gas stream comprises more of the carbon dioxide than the inert gas.

6. The method of claim 1, wherein the stripping gas stream comprises more of the inert gas than the carbon dioxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is described below with references to the accompanying drawings in which like elements are referenced with like numerals and in which:

(2) FIGS. 1A-1B are schematic diagrams illustrating a conventional two-column sour water stripping system.

(3) FIG. 2 is a schematic diagram illustrating the H2S stripping stage in FIG. 1A according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) 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 to achieve similar results.

(5) The present invention provides systems and methods to enhance the separation of H2S and NH3 in an H2S stripper using carbon dioxide and/or an inert gas. The purpose of the carbon dioxide and/or an inert gas, also referred to as a stripping gas, is to enhance the separation of H2S and NH3 during the H2S stripping stage by i) lowering the partial pressure of H2S; and ii) providing a stripping action.

(6) Referring now to FIG. 2, a schematic diagram illustrates the H2S stripping stage in FIG. 1A for a modified system 200 that uses a stripping gas stream 202 to enhance the separation of H2S and NH3 in the H2S stripper 118. This stage can consist of various pieces of equipment depending upon the ultimate concentration and quality of NH3 desired. The stripping gas stream 202 may be introduced anywhere between the top and bottom of the H2S stripper 118. Preferably, however, the stripping gas stream 202 is introduced near the bottom of the H2S stripper 118 because it will contact more of the heated deoiled sour water stream 116. In this manner, any conventional two-column sour water stripping system that includes a H2S stripping stage may be easily retrofitted with the introduction of a stripping gas.

(7) The stripping gas stream 202 may include carbon dioxide and/or any inert gas, which is a gas that does not react with other constituents of the H2S stripper 118 or sour water stripper such as, for example, Hydrogen, Helium, Boron, Neon, Argon, Krypton, Xenon, Radon, diatomic nitrogen, methane, and ethane.

(8) In the operation of a two-column sour water stripping system with an H2S stripping stage that includes a stripping gas stream 202 comprising carbon dioxide, the separation of the H2S and NH3 may be improved by at least five percent. By enhancing the separation of H2S and NH3 in this manner, the consumption of utilities (e.g. reboiler heating media) in the two-column sour water stripping system will be lowered resulting in energy savings or performance may be improved with the same utility consumption.

(9) Conventional two-column sour water stripping systems have been around since the 1960's. While operators of such systems have recognized the need for enhanced separation of H2S and NH3, the characteristics of carbon dioxide are similar to those of an acid gas. This explains why the need for enhanced separation of H2S and NH3 using carbon dioxide in the H2S stripping stage of a two-column sour water stripping system, with another acid gas (H2S), has been unresolved since the 1960's.