How Do Amine Units Operate?
“Amine” in refinery and gas processing applications usually refers to a mixture of alkanolamines in water. The solution is basic and will absorb acidic compounds like H2S and CO2 and has been used extensively for H2S and CO2 removal in both liquid and gas process streams. H2S and CO2 absorbed in an amine solution can be removed (stripped) by increasing the temperature of the solution making amine an excellent regenerable acid gas solvent.
Diethanolamine (DEA) and Methyl-diethanolamine are the most commonly used amines for H2S and CO2 absorption. There are also many specialty and proprietary amines formulated to increase absorption capability, hinder degradation, and selectively absorb H2S.
Amine solution that is stripped of acid components is called Lean Amine. Lean Amine enters the top of an absorber column (often called a Contactor or Scrubber), travels down the column either across trays or packing, and contacts gas or liquid traveling up the column. H2S and CO2 in the process solution will be absorbed into the amine solution and exits at the bottom of the column. An amine solution that has absorbed acid compounds is called Rich Amine.
A gas plant will usually have one amine contactor or multiple contactors operated in parallel, while a refinery will have multiple contactors operating at different pressures throughout the complex. Rich Amine throughout the plant is gathered into one stream and usually enters a Rich Amine Flash Drum where light gasses are flashed and vented, and any liquid hydrocarbons are separated from Rich Amine.
Rich Amine is transferred to a low-pressure stripping column (often called a Regenerator or Still) where the solution is heated and H2S and CO2 are stripped out of the amine solution. The overhead vapor enters a partial condenser. Here much of the water in the overhead stream is condensed and returned to the stripping column as reflux. The resulting offgas (called Amine Acid Gas) is normally conveyed to a Sulfur Recovery Unit or Acid Gas Injection Well.
Hot Lean Amine passes from the bottom of the Regenerator to a heat recovery exchanger, called a Lean / Rich Exchanger, which heats the incoming Rich Amine stream and cools the exiting Lean Amine stream. Lean Amine is further cooled in a trim cooler and is either immediately returned to absorption units or transferred to a Lean Amine Storage Tank for later use.