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.

What is claimed is: 
     
         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 (H 2 S), carbon dioxide (CO 2 ), 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 (H 2 S), carbon dioxide (CO 2 ), 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 (H 2 S), carbon dioxide (CO 2 ), 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.