Gas Sweetening
Many produced gas streams are sour, that is, they contain hydrogen sulfide (H²S). The H²S must be removed due to its toxicity and its impact on the environment. Gas may also contain carbon dioxide (CO²), which must be removed to raise the heating value of the product sales gas. Both H²S and CO² are also corrosive, especially in the presence of water, and must be removed to protect downstream equipment.
Amine-based systems are the most commonly used process for removal of H²S & CO². The technology of using alkanolamines for removal of hydrogen sulfide and carbon dioxide from natural gases has been used for decades. Selecting the right amine for the process is very critical for design of the plant.
Design
The selection of amine depends upon H²S & CO² concentration in inlet gas stream. Diethanolamine (DEA) and Methydiethanolamine (MDEA) are commonly used in gas plants because they selectively remove H²S while removing only part of the CO².
The sour gas is brought into contact with lean amine in an absorber column. The absorber column is provided with structured packing or trays. The amine adsorbs the H²S and some of the CO², resulting in sweet gas.
The rich amine circulates from the absorber to the regenerator in which the adsorbed acid gases are removed from the amine using heat. The lean amine is cooled and circulated back to the absorber.
Acid gas from the regenerator is primarily H²S and CO² and it is toxic. Therefore, it is either incinerated or it is further processed in a Sulfur Recovery Unit to recover the sulfur as a product.
