Amine scrubbing tower

When both HjS and mercaptans are to be removed in the light ends treating plant, the amine scrubbing tower precedes the caustic washing step. If the order were reversed, the large quantity of HjS present would "fix" the caustic. Also, the caustic will act to remove any final traces of HjS when it follows the scrubbing tower. 

Figure 7.4 Air Liquide/Medal membrane unit replacement of amine scrubbing towers (used with permission).

To prevent this situation from developing, hydrocarbon skimming taps should be provided in the bottom of natural gas amine H2S scrubbing towers. 

In a C02 removal system that uses wet scrubbing, the existing towers are the major limit to more capacity because they are expensive to replace. In an amine system, absorption increases as amine concentration increases. But a higher amine concentration requires (1) more filtration to clean the solution and (2) the addition of corrosion inhibitors. Another option is to change from monoethanolamine (MEA) to methyl diethanolamine (MDEA).86... 

For difficult cleanup jobs, a vertical tower is used instead of a mix valve and settler. It will provide several theoretical equilibrium stages. The mix valve provides one stage. Figure 14-3 shows a typical arrangement propane scrubbing to remove H2S with amine. Carry-over of amine in the treated propane and high residual H2S are the two usual complaints. 

A process gas containing 0.18% sulfur oxides is being scrubbed countercurrently and differentially with an aqueous solution of completely unloaded hindered amines in a tower packed with structured packing. The height of a transfer xmit, based on an overall gas-side mole fraction driving force, is 41 cm. The amine solution, flowing at twice the minimum rate, has an equilibrium line of... 

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