The Acid Gas Removal Unit (AGRU) is a crucial component in natural gas processing plants, particularly in the removal of acidic gases such as hydrogen sulfide (H2S) and carbon dioxide (CO2) from natural gas streams. These acidic gases can be corrosive and environmentally harmful, so their removal is essential to meet safety standards and product specifications. One common method for acid gas removal is the use of amine-based processes.

Here's a general overview of the amine-based acid gas removal process:

Gas Inlet:

The natural gas containing H2S and CO2 enters the Acid Gas Removal Unit.

Absorption Tower:

The gas stream is directed to an absorption tower, where it comes into contact with a solution of amine, typically monoethanolamine (MEA), diethanolamine (DEA), or a similar chemical.

The amine solution reacts with the acidic gases, forming chemical compounds (ammonium sulfide or carbonate) that can be easily separated from the gas stream.

Chemical Reaction:

The chemical reactions involve the absorption of H2S and CO2 into the amine solution. For example:

H2S + 2MEA → HS-MEA + MEA

CO2 + 2MEA → HCO3-MEA + MEA

Rich Amine Solution:

The amine solution, now containing absorbed H2S and CO2, is referred to as "rich" amine.

Lean Amine Solution:

The treated gas, now depleted of most of its H2S and CO2, exits the top of the absorption tower. This gas is called "lean" gas.

The rich amine solution is then sent to a regeneration unit to remove the absorbed acid gases.

Regeneration Tower:

The rich amine solution is heated in a regeneration tower to release the absorbed H2S and CO2.

The chemical reactions are reversed, separating the acid gases from the amine solution.

The regenerated or "lean" amine solution is then sent back to the absorption tower for reuse.

Recovered Acid Gases:

The separated H2S and CO2, now in a concentrated form, are sent to a separate unit for further processing or disposal.

The recovered acid gases may be converted into elemental sulfur or other by-products, depending on the plant design.

Product Gas Outlet:

The purified natural gas, now meeting the required specifications, is sent out as the final product.

The efficiency of acid gas removal depends on factors such as the type of amine used, process conditions, and the specific requirements of the natural gas being treated. The process is designed to minimize environmental impact and ensure the safety of both the plant and the surrounding community.