PROCESSES AND SYSTEMS FOR REFINING FUEL GAS

Abstract

Processes and systems are provided for refining fuel gas. The processes involve first and second water wash stages, before and after a caustic wash stage, in which fuel gas is contacted with water for removing amine and caustic compounds from the fuel gas. The systems for refining LPG comprise a first water wash vessel and a caustic wash vessel, followed by a second water wash vessel, wherein the water wash vessels are each adapted for contacting the LPG with water to remove amine and caustic compounds therefrom.

Description

TECHNICAL FIELD

The technical field generally relates to processes and systems for refining fuel gas, and more particularly relates to processes and systems for the removal of sulfur compounds from fuel gas using an amine and a caustic to produce a refined fuel gas substantially free of residual amine and residual caustic.

BACKGROUND

Fuel gases are a category of hydrocarbon mixtures in which the hydrocarbons have from one to four carbons per molecule (i.e., C₁-C₄ hydrocarbons). Fuel gases are gaseous under normal conditions and useful as sources of energy and light when burned. In particular, natural gas is one type of fuel gas primarily comprised of methane (C₁ hydrocarbons). Mixtures containing primarily C₃-C₄ hydrocarbons (i.e., propane and butane) are also gaseous under normal conditions, but are sometimes converted to liquefied petroleum gas (LPG) by pressurization to convert them to liquid form, which reduces volume and facilitates storage, delivery and use. LPGs are relatively clean burning fuels useful for heating, cooking, and an alternative vehicle fuel, as well as an aerosol propellant and a refrigerant.

Particularly when derived from petroleum, fuel gases often contain undesirable components including sulfur compounds and carbon dioxide, among others, which adversely affect various refining steps and end use application. More particularly, for example, fuel gases are often treated with an amine compound to remove hydrogen sulfide (H₂S) and carbon dioxide (CO₂), followed by removal of carbonyl sulfide (COS) and possibly additional H₂5 by contact with caustic in a prewash unit. After removal of H₂S, CO₂, and COS, mercaptans (R-SH) are removed from the fuel gas, such as by extraction in the presence of caustic, followed by conversion of the extracted mercaptans to organic disulfides and regenerated caustic that can be recycled and reused.

Amine solubility in fuel gases, as well as amine entrainment in the process streams of fuel gas refinement processes, results in the presence of amines in the effluent of the amine treatment stage as well as in subsequent process stages, which is often referred to as amine carryover. Amine carryover in fuel gas refining processes is one of the major causes of amine losses and serious problems in stages downstream of the amine treatment stage. For example, when amines are mixed with caustic solutions in the presence of hydrocarbons, emulsions are formed that adversely affect the composition of the final fuel gas product, cause higher caustic consumption and corrosion of carbon steel in downstream process units, and require operation at lower hydrocarbon flow rates that decreases production. Additionally, any amines remaining in the effluent of the caustic prewash stage, when fed to the mercaptan extraction stage, reduces the capability of the mercaptan extraction stage to produce refined fuel gas having the required low nitrogen content. Amine carryover is often exacerbated when refining LPG derived from fluid catalytic cracking processes or from the coker units of atmospheric or vacuum distillation processes.

Following amine treatment for removal of H₂S and CO₂, but prior to contact with caustic for removal of COS, fuel gas is sometimes subjected to a water wash to remove soluble amines and reduce formation of unwanted emulsions during the caustic prewash step. However, amine carryover remains an issue even in processes that include a water wash stage prior to caustic prewash, or knockout (KO) drums for removing entrained amines, or both, since such apparatus typically does not include internal features to enhance separation between amine and spent water from the hydrocarbons.

Accordingly, it is desirable to develop processes for refining fuel gas that provide improved removal of unwanted compounds. In addition, it is desirable to provide processes for refining fuel gas wherein substantially all the amine is removed prior to subjecting the fuel gas to treatment for mercaptan removal. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.

BRIEF SUMMARY

Processes and systems are provided for refining fuel gas. An exemplary embodiment of the process comprises: providing a fuel gas comprising an amine compound; contacting the fuel gas with water in a first water wash stage to remove at least a portion of the amine compound therefrom and produce a washed fuel gas; contacting the washed fuel gas with either a caustic to remove acid gas (H₂S, CO₂, or both) or a blend of a caustic and an amine to remove both acid gas and carbonyl sulfide (COS) from the washed fuel gas and produce a caustic treated fuel gas comprising residual amine and residual caustic. The process further comprises contacting the caustic treated fuel gas with water in a second water wash stage to remove residual amines and residual caustic therefrom and produce a rewashed fuel gas substantially free of amines and caustic.

In another exemplary embodiment, a process for refining fuel gas comprising: contacting a fuel gas with an amine compound to remove hydrogen sulfide (H₂S), carbon dioxide (CO₂), or both, therefrom and produce an amine treated fuel gas comprising an amine compound; and contacting the amine treated fuel gas with water to remove at least a portion of the amine compound therefrom and produce a washed fuel gas. The process further comprises, contacting the washed fuel gas with either a caustic to remove acid gas or a blend of a caustic and an amine to remove both acid gas and carbonyl sulfide (COS) from the washed fuel gas and produce a caustic treated fuel gas comprising residual amine and residual caustic; contacting the caustic treated fuel gas with water to remove residual amines and residual caustic therefrom and produce a rewashed fuel gas substantially free of amines and caustic; and removing mercaptans from the rewashed fuel gas.

In still another embodiment, a system for refining LPG comprising: a first water wash vessel capable of receiving and contacting LPG with water to remove an amine compound from the LPG and produce a washed LPG; a vessel capable of receiving and contacting the washed LPG with either a caustic to remove acid gas or a blend of a caustic and an amine to remove both acid gas and carbonyl sulfide (COS) from the washed fuel gas and produce a caustic treated LPG comprising residual amine; and a second water wash vessel capable of receiving and contacting the caustic treated LPG with water to remove residual amine therefrom and produce a rewashed LPG substantially free of amines.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

FIG. 1 is a block diagram showing an exemplary embodiment of a refining system including first and second water wash stages that are vertically oriented; and

FIG. 2 is a block diagram showing another exemplary embodiment of a refining system including first and second water wash stages that are horizontally oriented.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the processes and systems contemplated herein, or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

The processes and systems contemplated and described herein are directed to removal of unwanted compounds, including one or more of H₂S, CO₂, COS, and mercaptans, from fuel gas, as well as removing amine compounds and caustic that are often used to remove the aforesaid unwanted compounds but which interfere with other refining stages. The processes and systems contemplated and described herein are suitable for refining any fuel gas, including natural gas (methane), ethane, mixtures of methane and ethane (i.e., mixtures of C₁-C₂ hydrocarbons), propane, butane, mixtures of propane and butane (i.e., mixtures of C₃-C₄ hydrocarbons), and LPG (liquefied mixtures of C₃-C₄ hydrocarbons). More specifically, the processes and systems described hereinbelow are suitable for refining liquid phase fuel gases such as LPG, as well as fuel gases that are in gaseous form such as the others types of fuel gases listed above. The fuel gas may be derived from any one or more of various sources including, without limitation, fractionation processes and apparatus, straight run petroleum refining processes and apparatus, fluidized catalytic cracking processes and apparatus, and thermal cracking processes and apparatus (e.g. coker units).

Additionally, the refining of fuel gas generally involves various treatments, operations, stages, techniques and methods for achieving various goals, all of which are ultimately aimed at producing pure hydrocarbon products having desired characteristics for particular end uses. Accordingly, it should be understood that the processes and systems contemplated and described herein may exist, and be performed or operated, within the context of larger refining processes and systems, or more complex refining processes and systems, or both.

In an exemplary embodiment, the process for refining fuel gas contemplated and described herein comprises providing a fuel gas comprising an amine compound, and contacting that fuel gas with water in a first water wash stage to remove at least a portion of the amine compound therefrom and produce a washed fuel gas. In the first water wash stage, after contacting the fuel gas and water, the amine compound migrates from the fuel gas (organic phase) and is dissolved into the water (aqueous phase) and aqueous and organic phases are separated, such as by gravity separation where both phases are liquid (as when refining LPG), or liquid-gas phase separation where the aqueous phase is liquid and the organic phase is gaseous (as when refining a gaseous fuel gas). The resulting organic phase is the washed fuel gas that is subjected to further processing, and the resulting aqueous phase can be processed or recycled, or both, as desired.

The washed fuel gas from the first water wash stage is then contacted, in a caustic wash stage, with either a caustic to remove acid gas (i.e., H₂S, CO₂, or both) or a blend of a caustic and an amine to remove both acid gas and carbonyl sulfide (COS) from the washed fuel gas and produce a caustic-treated fuel gas. In either case, suitable caustic includes sodium hydroxide (NaOH) and potassium hydroxide (KOH), with NaOH being the more common choice. Where a blend of caustic and amine is used, the amine is comprised of primary amines, secondary amines, or mixtures thereof. Since undesirable emulsions are formed when amines are mixed with caustic solutions in the presence of hydrocarbons, removal of residual amine compounds in the fuel gas before contacting the fuel gas with caustic to remove COS improves the effectiveness and efficiency of the COS removal during the caustic wash stage. However, the first water wash stage removes a majority of the amine compound which improves performance of the caustic wash stage, but the caustic treated fuel gas still contains residual amine compound, as well as residual caustic from the caustic wash stage. Furthermore, additional amine compound may be added during the caustic wash stage to assist in removal of unwanted compounds, such as H₂S, in the washed fuel gas, which consequently increases the total amine compound content of the caustic treated fuel gas. Any additional amine compound used in the caustic wash stage may be the same or different from the amine compound present in the fuel gas prior to the first water wash stage.

Removal of substantially all residual amine compounds is important for today's refining processes to produce hydrocarbon streams having the required low levels of unwanted compounds to avoid downstream operational and product quality issues where the fuel gas will undergo further refinement stages. Consequently, the caustic treated fuel gas containing residual amine compound is contacted with water in a second water wash stage to remove residual amine therefrom and produce a rewashed fuel gas substantially free of amine compounds. The second water wash phase operates substantially the same as the first water wash stage, except that in the second water wash stage, the caustic also migrates from the fuel gas (organic phase) to the water (aqueous phase) so that when the aqueous and organic phases are formed and separated, the aqueous phase contains amine compound and caustic.

“Substantially free of amine compounds,” means that any amines present in the rewashed fuel gas are below the amount that causes downstream operational and product quality issues. For example, “substantially free of amine compounds” as used herein, means that the rewashed fuel gas comprises no more than about 60 parts per million by weight (ppm) total amine compound. For example, without limitation, the rewashed fuel gas may comprise no more than about 50 ppm total amine compound, or no more than about 30 ppm total amine compound, or even no more than about 10 ppm total amine compound.

Similarly, “substantially free of caustic compounds,” means that any caustic present in the rewashed fuel gas are below the amount that cause downstream operational and product quality issues. More particularly, and independently of the amine content, “substantially free of caustic compounds” as used herein, means that the rewashed fuel gas comprises no more than about 60 ppm total caustic compound. For example, without limitation, the rewashed fuel gas may comprise no more than about 50 ppm total caustic compound, or no more than about 30 ppm total caustic compound, or even no more than about 10 ppm total caustic compound.

In some embodiments, such as when the fuel gas being refined is LPG, during either the first water wash stage or the second water wash stage, or both, the fuel gas (or caustic treated fuel gas, as applicable) and water are also contacted with coalescing material to enhance aqueous-organic phase separation and removal of the amine compound from the fuel gas. More particularly, the coalescing material may be any material known now or in the future to be hydrophilic and facilitate aqueous-organic phase separation. For example, without limitation, the coalescing material may be mesh made of metal such as stainless steel, and may further be coated with a hydrophilic material such as a polymer. The coalescing material may be present in a layer that is from about 15.24 centimeters (cm) (6 inches) to about 60.96 cm (24 inches) thick. Additionally, the coalescing material used in each of the first and second water wash stages may be the same or different from one another, in composition as well as physical form and size.

When the fuel gas being refined is a gaseous fuel gas such as including natural gas (methane), ethane, propane, butane, or mixtures of two or more of these hydrocarbons, the fuel gas (or caustic treated fuel gas, as applicable) and water forms a liquid-gas system for which coalescing material is less advantageous. Accordingly, in embodiments where the fuel gas is a gaseous type of fuel gas, the fuel gas (or the caustic treated fuel gas, if applicable) and water may also be contacted with an internal device positioned within one or both of the first and second water wash stages, for enhancing aqueous-organic phase separation and removal of the amine compound from the gaseous organic phase fuel gas. The internal device is not particularly limited and may be any internal device known now or in the future that facilitates phase separation in liquid-gas systems. Suitable internal devices include, for example, one or more bubble trays, sieve trays, packed beds and other contacting devices.

Furthermore, it is noted that when the fuel gas is a gaseous type of fuel gas that is being refined, contacting the fuel gas with water in the first water wash stage, contacting the resulting washed fuel gas with caustic in a caustic wash stage, then contacting the resulting caustic treated fuel gas with water in the second water wash stage may all be performed in the same vessel, such as a single vertical column A suitable single vessel would, of course, be capable of allowing the gaseous fuel gas to flow from one end to an opposite end of the vessel, while also allowing the fuel gas to sequentially contact the water, caustic and then water again to produce a rewashed fuel gas suitable for further refinement. In some embodiments, the vessel is capable of also contacting the liquid-gas mixture comprising gaseous fuel gas and water with internal devices positioned within the vessel to enhance phase separation during the first water wash stage, caustic wash stage, and second water wash stage occurring therein.

In another exemplary embodiment, regardless of whether the fuel gas is gaseous or LPG, providing a fuel gas comprising an amine compound includes first providing a fuel gas comprising unwanted compounds including hydrogen sulfide (H₂S), carbon dioxide (CO₂), and carbonyl sulfide (COS) and contacting that fuel gas with an amine compound to remove hydrogen sulfide (H₂S), carbon dioxide (CO₂), or both, therefrom. Contacting the fuel gas with an amine compound produces an amine treated fuel gas comprising an amine compound. Contacting the fuel gas with an amine compound may, for example, be performed by absorption with an aqueous solution comprising the amine compound. Where the fuel gas is LPG, the absorption will occur as a liquid-liquid absorption process. In such embodiments where fuel gas containing unwanted compounds is contacted with an amine compound, the resulting amine treated fuel gas, which consequently comprises an amine compound, is contacted with water in the first water wash stage. The amine compound may be any amine compound known now or in the future to be a good solvent for H₂S and CO₂ and at least partially soluble in aqueous solution. Suitable amine compounds include one or more compounds chosen from, for example without limitation, monoethanolamine (MEA), diethanolamine (DEA), diglycolamine (DGA), methyl diethanolamine (MDEA), MDEA-based solvents, and diisopropylamine (DIPA), among others.

In still another exemplary embodiment, the process further comprises removing mercaptans from the rewashed fuel gas. Removal of mercaptans may be accomplished by any technique known now or in the future. For example, mercaptans (RSH) may be removed from the rewashed fuel gas by a two stage process in which the first stage involves contacting the rewashed fuel gas with caustic (MOH, where M is sodium, Na, or potassium, K) in the presence of a catalyst capable of catalyzing the conversion and extraction of the mercaptan in metal salt form (M-SR) into an aqueous caustic solution. Suitable catalysts are commercially available, for example, from UOP LLC of Des Plaines, Ill., USA. In addition to the aqueous caustic solution containing the mercaptan derivatives (M-SR), the first stage also produces a refined fuel gas product. In the second stage, generally referred to as regeneration, the aqueous caustic solution containing the mercaptan derivatives (M-SR) is heated and oxidized to form insoluble disulfides (RSSR) and regenerated caustic (MOH). Moreover, in some embodiments such as where the fuel gas is a gaseous phase material, the above-described three contacting steps (first water wash, caustic wash, and second water wash), as well as removing mercaptans from the rewashed fuel gas, may all be performed in the same vessel as described earlier hereinabove.

Amines entering the mercaptan removal phase of the refining process are generally not removed or otherwise altered and, therefore, often cause fuel gas products having unacceptably high nitrogen content, as well as potential process upsets in stages downstream of the mercaptan removal phase. Thus, employing the second water wash stage to remove additional residual amine compounds prior to subjecting the caustic treated and rewashed fuel gas to mercaptan removal processes improves the effectiveness and efficiency of the mercaptan removal process as well as downstream refining stages.

A system for refining LPG will now be described in detail with reference to FIGS. 1 and 2 which provide schematic diagrams of such systems. In an exemplary embodiment, the system 10, 110 for refining LPG comprises a first water wash vessel 12, 112, a caustic wash vessel 14, 114 and a second water wash vessel 16, 116. More particularly, the first water wash vessel 12, 112 is capable of receiving and contacting LPG 18, 118 with water (provided via lines 46, 48, 146, 148, respectively) to remove an amine compound from the LPG 18, 118 and produce a washed LPG 20, 120.

The caustic wash vessel 14, 114 is in fluid communication with, and located downstream of, the first water wash vessel 12, 112. The caustic wash vessel 14, 114 is capable of receiving and contacting the washed LPG 20, 120 with a caustic to remove acid gas, or a blend of caustic and amine (provided via line 15, 115, respectively) to remove both acid gas and carbonyl sulfide (COS) from the washed LPG and produce a caustic treated LPG 22, 122 comprising residual amine. In either case, the caustic is a strong base selected from sodium hydroxide (NaOH) and potassium hydroxide (KOH). Where a blend of caustic and amine is used, the amine is comprised of primary amines, secondary amines, or mixtures thereof. The second water wash vessel 16, 116 in fluid communication with, and located downstream of, the caustic wash vessel 14, 114. The second water wash vessel 16, 116 is capable of receiving and contacting the caustic treated LPG 22, 122 with water (not shown) to remove residual amine and residual caustic therefrom and produce a rewashed LPG 24, 124 substantially free of amine and caustic compounds. The first water wash vessel 12 and second water wash vessel 16 may each be oriented vertically as shown in FIG. 1, or they 112, 116 may be oriented horizontally as shown in FIG. 2. “Substantially free of amine compounds” has the same meaning as stated hereinabove.

As mentioned above in connection with the first and second water wash stages, coalescing material may also be contacted with the LPG and water to facilitate aqueous-organic phase separation. Accordingly, as shown in each of FIGS. 1 and 2, either or both of the first and second water wash vessels 12, 112, 16, 116 may include coalescing material 26, 126, 28, 128 in the interiors thereof, respectively. Suitable coalescing materials are as described above. The coalescing material 26, 126 in the interior of the first water wash vessel 12, 112 may be the same or different, in composition as well as physical form and size, from the coalescing material 28, 128 in the interior of the second water wash vessel 16, 116. As shown in FIG. 1, when the first and second water wash vessels 12, 16, are oriented vertically, the coalescing material 26, 28 is oriented horizontally. When the first and second water wash vessels 112, 116 are oriented horizontally, as shown in FIG. 2, the coalescing material 126, 128 is oriented vertically.

Regardless of whether they are oriented vertically or horizontally, or whether the include coalescing material, each of the first and second water wash vessels 12, 112, 16, 116 produces spent wash water 42, 142, 44, 144, respectively. The spent wash water 42, 142, 44, 144 may be sent for further processing, or recycled to one or both of the first and second water wash vessels 12, 112, 16, 116, as shown in FIGS. 1 and 2. Furthermore, fresh water may be provided to one or both of the first and second water wash vessels 12, 112, 16, 116 via fresh water inlets 46, 146, 48, 148, respectively, which are in direct or indirect fluid communication with the first and second water wash vessels 12, 112, 16, 116, respectively.

In some embodiments, as shown in FIGS. 1 and 2, the system 10, 110 also comprises an absorber 30, 130 capable of receiving and contacting LPG 32, 132 with an amine compound (not shown) to remove H₂S, CO₂, or both, from the LPG 32, 132 and produce an amine treated LPG 34, 134 comprising residual amine compounds. In such embodiments, the first water wash vessel 12, 112 is in fluid communication with the absorber 30, 130 for receiving and contacting the amine treated LPG 34, 134 with water (not shown). Suitable amine compounds are as described above. In such embodiments, i.e., systems that include an absorber upstream of the first water wash stage, the amine treated LPG 34, 134 serves as the LPG 18, 118 that is provided to the first water wash stage for contacting with water.

In still other embodiments, the system 10, 110 for refining LPG further comprises apparatus capable of removing mercaptans from the rewashed LPG 24, 124. For example, as shown in FIGS. 1 and 2, such apparatus may comprise an extractor 36, 136 capable of receiving and contacting the rewashed LPG 24, 124 with caustic (MOH, where M is sodium, Na, or potassium, K). The extractor 36, 136 generally comprises a catalyst (not shown per se) capable of catalyzing the conversion and extraction of the mercaptans, as described above. The extractor 36, 136 produces an LPG product 38, 138 and an aqueous caustic solution 40, 140 comprising the mercaptan in metal salt form, as also previously described above. The system 10, 110 may further comprise a regeneration vessel (not shown) capable of receiving the aqueous caustic solution 40, 140 from the extractor 36, 136 and heating and oxidizing the aqueous caustic solution 40, 140 to form insoluble disulfides and regenerated caustic (not shown).

Although not shown in the figures, it should be appreciated that the system 10, 110 shown in FIGS. 1 and 2 may be modified for refining fuel gas in gaseous form, such as natural gas (methane), ethane, mixtures of methane and ethane (i.e., mixtures of C₁-C₂ hydrocarbons), propane, butane, mixtures of propane and butane (i.e., mixtures of C₃-C₄ hydrocarbons), and mixtures of C₁-C₄ hydrocarbons. Such modifications to the system 10 shown in FIG. 1 will now be discussed in further detail. More particularly, in an exemplary embodiment of a modified system (not shown per se) for refining fuel gas, the first water wash vessel 12, the caustic wash vessel 14, and the second water wash vessel 16 are instead replaced by a vessel, such as a multi-stage column, capable of receiving fuel gas in a bottom portion thereof and allowing the fuel gas to flow upward through the column Furthermore, the multi-stage column comprises a first water wash zone located proximate the bottom portion of the column, a caustic (or caustic-amine blend) wash zone located in a middle portion of the column, and a second water wash zone located an upper portion of the column Instead of coalescing material (see 26, 126, 28, 128 in FIG. 1), the first and second water wash zones of the multi-stage column may each include internal devices such as bubble trays (not shown per se) to facilitate contact between the gaseous fuel gas and water in each water wash stage and, thereby enhance phase separation. Additionally, a system (not shown) for refining gaseous fuel gas may include an absorber adapted for receiving and contacting gaseous fuel gas with a liquid aqueous solution containing an amine compound. For example, such an absorber may comprise a plurality of trays to increase gas-liquid phase contact between the gaseous fuel gas and the aqueous amine solution.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A process for refining fuel gas comprising:

providing a fuel gas comprising an amine compound;

contacting the fuel gas with water in a first water wash stage to remove at least a portion of the amine compound therefrom and produce a washed fuel gas;

contacting the washed fuel gas with either a caustic to remove acid gas or a blend of a caustic and an amine to remove both acid gas and carbonyl sulfide (COS) from the washed fuel gas and produce a caustic treated fuel gas comprising residual amine and residual caustic; and

contacting the caustic treated fuel gas with water in a second water wash stage to remove residual amines and residual caustic therefrom and produce a rewashed fuel gas substantially free of amine and caustic.

2. The process of claim 1, wherein contacting the fuel gas with water in a first water wash stage further comprises using a coalescing material.

3. The process of claim 1, wherein contacting the caustic treated fuel gas with water in a second water wash stage further comprises using a coalescing material, which may be the same or different from the coalescing material used in the first water wash stage.

4. The process of claim 1, wherein providing the fuel gas comprises contacting a fuel gas with an amine compound to remove hydrogen sulfide (H2S), carbon dioxide (CO2), or both, therefrom and produce an amine treated fuel gas comprising an amine compound, and wherein the amine treated fuel gas is then contacted with water.

5. The process of claim 4, wherein contacting the fuel gas with an amine compound is performed by absorption with an aqueous solution comprising the amine compound.

6. The process of claim 4, wherein providing the fuel gas comprises providing liquefied petroleum gas (LPG).

7. The process of claim 1, wherein contacting the washed fuel gas with caustic is performed using a strong base selected from sodium hydroxide and potassium hydroxide as the caustic.

8. The process of claim 1, wherein a single vessel is used for contacting the fuel gas with water to produce the washed fuel gas, and for contacting the washed fuel gas with a caustic to produce the caustic treated fuel gas comprising residual amine and residual caustic, and for contacting the caustic treated fuel gas with water in a second water wash stage to the rewashed fuel gas substantially free of amine and caustic.

9. The process of claim 8, wherein the fuel gas is chosen from: methane, ethane, propane, isobutene and mixtures thereof.

10. The process of claim 1, further comprising removing mercaptans from the rewashed fuel gas.

11. The process of claim 10, wherein removing mercaptans from the rewashed fuel gas comprises contacting the rewashed fuel gas with an aqueous caustic solution in the presence of a catalyst to produce a refined fuel gas product and an aqueous solution comprising mercaptan derivatives; and heating and oxidizing the aqueous solution comprising mercaptan derivatives to convert the mercaptan derivatives to disulfides and regenerated caustic.

12. A process for refining fuel gas comprising:

contacting a fuel gas with an amine compound to remove hydrogen sulfide (H2S), carbon dioxide (CO2), or both therefrom and produce an amine treated fuel gas comprising an amine compound;

contacting the amine treated fuel gas with water to remove at least a portion of the amine compound therefrom and produce a washed fuel gas;

contacting the washed fuel gas with a either a caustic to remove acid gas or a blend of a caustic and an amine to remove both acid gas and carbonyl sulfide (COS) from the washed fuel gas and produce a caustic treated fuel gas comprising residual amine and residual caustic;

contacting the caustic treated fuel gas with water to remove residual amines and residual caustic therefrom and produce a rewashed fuel gas substantially free of amine and caustic; and

removing mercaptans from the rewashed fuel gas.

13. The process of claim 12, wherein contacting the fuel gas with water in a first water wash stage further comprises contacting the fuel gas and water with a coalescing material.

14. The process of claim 12, wherein contacting the caustic treated fuel gas with water in a second water wash stage further comprises contacting the caustic treated fuel gas with a coalescing material, which may be the same or different from the coalescing material in the first water wash stage.

15. The process of claim 12, wherein contacting a fuel gas with an amine compound to remove hydrogen sulfide (H2S), carbon dioxide (CO2), or both therefrom comprises selecting and using, as the amine, one or more compounds chosen from: monoethanolamine, diethanolamine, diglycolamine, methyl diethanolamine (MDEA), MDEA-based solvents, and diisopropylamine.

16. A system for refining liquefied petroleum gas (LPG) comprising:

a first water wash vessel;

a caustic wash vessel in fluid communication with, and located downstream of, the first water wash vessel; and

a second water wash vessel in fluid communication with, and located downstream of, the caustic wash vessel.

17. The system of claim 16, wherein the first water wash vessel comprises an interior and a coalescing material positioned within the interior.

18. The system of claim 16, wherein the second water wash vessel comprises an interior and a coalescing material positioned within the interior, wherein the coalescing material may be the same or different from the coalescing material of the first water wash vessel.

19. The system of claim 16, further comprising an absorber wherein the first water wash vessel is in fluid communication with, and located downstream of, the absorber.

20. The system of claim 16, further comprising mercaptan removal apparatus.