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[0001]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[0002]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 ...

AI Technical Summary

Benefits of technology

The patent describes a process for refining fuel gas by using an amine compound to remove acid gas and carbonyl sulfide, followed by a water wash to remove residual amine and caustic. The process can also include a second water wash to remove residual amine. The technical effect of this process is the production of a refined fuel gas that is free of amines and caustic, which can improve the quality of the fuel gas for use in various applications.

Problems solved by technology

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.

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.

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.

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