Natural gas from some wells contains significant amounts of hydrogen sulfide (H2S) and carbon dioxide (CO2). This natural gas, because of the rotten smell provided by its sulfur content, is commonly called “sour gas”. Gas that contains CO2 or H2S is referred to as “Acid Gas”. Sour gas is undesirable because the sulfur compounds it contains can be extremely harmful, even lethal, to breathe. Acid gas can also be extremely corrosive to pipes.
CO2 forms carbonic acid when in the presence of water. Pipeline specifications require CO2 and H2S to be below certain levels in order to protect the integrity of the pipe and to prevent corrosion that can lead to leaks or ruptures. Thus, the removal of these contaminants is critical to having safe and reliable energy in your home or office.
The following paragraphs provide an outline of the amine treating process used to sweeten natural gas.
What is an Amine Plant?
An amine plant removes CO2 and H2S (so called “Acid Gases”) from natural gas via chemical reactions in the contactor tower (absorber) by combining these weak acids with a water solution of a weak base, namely, an alkanolamine. This reaction forms a soluble salt (amine carbamate or amine hydrosulfide) in water solution. This reaction is fully reversible with the addition of heat, typically occurring at ~225°F. This process is commonly referred to as gas sweetening.
Amine Sweetening Units and Solutions
Amine sweetening units can treat both CO2 and H2S to meet pipeline specifications and reduce corrosion. A typical amine unit consists of an absorber (contactor) and regenerator (stripper) along with their ancillary equipment. A process gas stream is first passed through the absorber, where H2S and CO2 are removed by the “lean” solvent. The now “rich” solvent is sent to the regenerator where the acid gases are removed and either vented, sent to flare, or a Sulfur Recovery Unit (SRU). Amine units are generally more cost-effective than other treating systems because they regenerate amine for continual use which reduces chemical costs.
Amines that are commonly used in industry today:
- Primary Amines: MEA, DGA®
- Secondary Amines: DEA, DIPA
- Tertiary Amines: MDEA, TEA
- Mixed Amines
- Formulated Amines: aMDEA, UCARSOL™, FLEXSORB™
Formulated amine solvents have been specifically designed to perform a specific task. There is a wide variety of formulated amines that consist of different amine blends and different reaction promoters.
Sweetening Process through Amine Treating
The sour gas enters the bottom of the contactor tower and rises through the internals of the tower. The liquid amine/water solution flows from the top of the contactor and is in direct contact with the sour gas throughout the tower. The sweetened gas exits the tower through the top. The amine, now considered “rich” exits the bottom of the contactor and over to the regeneration section of the amine plant.
Rich amine is heated in a regeneration process with heat supplied from the reboiler. The rich amine enters the top of the still column and flows downward. Steam, which is created by the reboiler, flows upward through the still column and is in direct contact with the rich amine. The sour gases and steam flow through the top of the still column and are then cooled in order to separate the acid gas from water. The condensed water is then separated in the reflux accumulator and sent back through the process. To complete the cycle, the regenerated, “lean” amine will be cooled using an aerial cooler and will then be circulated back to the contactor tower.
Natural gas processing is a complex process that requires a thorough understanding of the chemical composition of lean, rich, and natural gas. Kinder Morgan Treating LP (KMT) has the industry knowledge and offers years of experience backed by highly-qualified engineers, operators, inspectors, and subject matter experts.
Call Kinder Morgan for More Information Today
At Kinder Morgan Treating, we have sixty (60) plant operators and are a leading manufacturer with a 65-acre fabrication facility. We provide an array of services for gas processing facilities and amine treating plants, including plant start-up assistance, operations, and engineering. Contact us at 713-369-8544 or 713-369-8535 to connect with your dedicated project manager.