CO2 and H2S Removal from Sour Gas

Removal of CO2 and H2S is one of the processes used in many industrial plants including gas treatment plants, Carbon Capture Plants, refineries, and beverage production plants. It is essential because the Hydrogen Sulfur is corrosive to the equipment and piping, lethal and harmful. CO2 in process gas, when combined with water makes corrosive Carbonic Acid. The CO2 in post-combustion gases, if released to the air increases the concentration of the CO2 and Greenhouse gasses in the atmosphere. Hence there is increasing demand for removal of the CO2 and H2S in industries.

Amine is well known for its reverse reaction with CO2 and can be used for separation purposes from many forms of Co2 and H2O-containing gases. In fact, there are many techniques for the separation of Carbone dioxide however, Amine absorption is an attractive option for its characteristics.

 The removal process, also called Amine scrubbing consists of two main processes: Absorption and stripping cycles.

In Absorption, the contaminated gas, also called sour gas, containing H2S and CO2 reacts with Lean Amin. Carbon or Sulphur molecules react with Ammonia converting lean Amin to Rich Amine.

 In the stripping process, the Rich Amine goes to the stripping column and released the Carbone dioxide/H2S, and goes back to the absorption column to continue the cycle.

This system, sometimes called Amine sweetening unit, consists of 13 main equipment.

1-Inlet Separator:  The sour gas enters the inlet separator ready to be discharged to the Contactor Column.

2-Contactor Column or Absorption column: The Sours Gas enters the Contactor column from the bottom of the vessel rising through the bubble cap on the tray to the topside of the vessel. The liquid Lean Amine enters the topside of the vessel, downward passing through the tray. The vapor and the Sweetened gas are extracted from the top of the contactor and the rich Amin exits the contactor from the bottom of the vessel.

3– Flash Tank: The Contactor column works at elevated pressure. The Rich Amin exiting the contactor goes to the flash tank with lower pressure which caused the gas to flash; like opening a can of cola; the flash tank let the high-pressure Rich Amine depressurize freely while the vapor is separated.

4- Filters: the filters are placed in the Lean/Rich Amin stream to catch the solid particles and contamination. Filtering might also be done on both Lean and Rich side of the column.

10- Lean/Rich heat exchanger: Upstream in the flash tank the temperature of the lean amine increases in the lean/rich heat exchanger before it goes to the Stripper/Regeneration Column. A shell and tube heat exchanger with stainless steel tube is usually selected to exchange heat between Lean and Rich Amine – Rich in the tube and Lean on the shell.

5- Stripper Column: The stripper column is usually tray type and works near atmospheric pressure. the heated-Rich Amine enters from the top, further heated by the rising steam – such that the Acid Gas is stripped from the Amine.

6-7-8 Reflux Condenser – Accumulator and pump. The reflux cycle consists of Reflux Condenser, accumulator, and pump aim to condense the fugitive Amine and water from the Acid Gas and return it back to the Stripper Column.  

9- Reboiler: The Lean Amine gets to the bottom of the stripper column goes to the reboiler and comes back to the column ready to strip the Acid Gases from Rich Amine.

10-Lean/Rich heat exchanger: The Lean Amin exiting from the stripping column goes the Heat Exchanger; on the shell side; to be cooled and ready to be sued in Contactor Column.

11- Surge Tank: The Lean Amine losing its temperature goes to the Surge tank and is kept to be pumped again to the Contactor Column. Water and Amine are periodically added to the Surge Tank to make up for the losses in the process.

12 -13 Circulation Pumps and Trim Cooler: The cooled amine, passing through the Trim Cooler, is pumped back to the contactor. The lean Amin should be 10-degree C hotter than Sour Gas when entering the contactor column so the temperature is adjusted in the Trim Cooler.