化学プロセス: Amine Gas Treating

A. Introduction

         Amine gas treating refers to a group of processes that use aqueous solutions of various amines to remove hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from gases. It is a common unit process used in refineries, petrochemical plants, natural gas processing plants and other industries. The process is also known as Acid gas removal and Gas sweetening. Processes within oil refineries or natural gas processing plants that remove hydrogen sulfide and/or mercaptans are commonly referred to as sweetening processes because they results in products which no longer have the sour, foul odors of mercaptans and hydrogen sulfide.

      

  There are many different amines used in gas treating:

• Monoethanolamine (MEA)
• Diethanolamine (DEA)
• Methyldiethanolamine (MDEA)
• Diisopropylamine (DIPA)
• Diglycolamine (DGA)

        The most commonly used amines in industrial plants are the alkanolamines MEA, DEA, and MDEA. Amines are also used in many oil refineries to remove sour gases from liquid hydrocarbons such as liquified petroleum gas (LPG).

B.  Description of a Typical Amine Treater

       A typical amine gas treating process (as shown in the flow diagram below) includes an absorber unit and a regenerator unit as well as accessory equipment. In the absorber, the downflowing amine solution absorbs H₂S and CO₂ from the upflowing sour gas to produce a sweetened gas stream (i.e., an H₂S-free gas) as a product and an amine solution rich in the absorbed acid gases. The resultant "rich" amine is then routed into the regenerator (a stripper with a reboiler) to produce regenerated or "lean" amine that is recycled for reuse in the absorber.

        The stripped overhead gas from the regenerator is concentrated H₂S and CO₂. In oil refineries, that stripped gas is mostly H₂S, much of which often comes from a sulfur-removing process called hydrodesulfurization. This H₂S-rich stripped gas stream is then usually routed into a Claus process to convert it into elemental sulfur. In fact, the vast majority of the 64,000,000 metric tons of sulfur produced worldwide in 2005 was byproduct sulfur from refineries and other hydrocarbon processing plants. In some plants, more than one amine absorber unit may share a common regenerator unit.

C.  Process Flow Diagram of A Typical Amine Treating Process Used in Industrial Plants

       Gases containing H₂S or both H₂S and CO₂ are commonly referred to as sour gases or acid gases in the hydrocarbon processing industries. In the steam reforming process of hydrocarbons to produce gaseous hydrogen for subsequent use in the industrial synthesis of ammonia, amine treating is one of the commonly used processes for removing excess carbon dioxide in the final purification of the gaseous hydrogen.

(Instumentation Drawing)