Amine Problems in Sour Gas Conditioning - Dirty Amine Ruins Operation

Symptoms of a dirty, corrosive amine system are:

•  Carry-over of amine from the scrubbers
• Dilution of the amine system with water due to reboiler leaks
•  Plugging of instrument taps with particulates in the amine
• •Loss of amine to the sewer because of leaks
•  Rich amine leaking into lean amine in the cross exchanger 

Problems related to improper operation of the regenerator are:

•  Too much H2S in sweet gas
•   Excessive energy use in the regenerator reboiler
•  Flooding in the regenerator tower

For troubleshooting an amine system you should first draw a sample of lean amine into a glass container. If the unit is in trouble, the amine will be dirty.

The seeds of destruction

Take a glass quart sample bottle and fill it with unfiltered lean amine. You can rate your amine quality as follows:

 • Bright and clear. Amine is in excellent shape. A yellow tinge indicates the presence of iron, but this is of no great consequence.

 • Grayish cast. Solution is a pale, dull gray. Objects can be seen through the bottle without difficulty. This is okay; however, do not let the amine solution get dirtier.

 • Translucent black. Objects can barely be seen through the bottle. Upon standing 10 minutes, a small amount of sediment is visible. You are now in trouble. Erosion-corrosion is generating particulates faster than they can be removed.

 • Opaque black. Give the bottle a good shake. You will notice a lot of particulates settling in the bottle. It will cause fouling in refinery vessels.

• Brownish. air is getting into the system. Oxidized amine is corrosive

Submit a sample of unfiltered lean amine to the lab to determine quantitatively the wt% particulates. A good solution should be less than 0.01 wt% (i.e., 100 ppm).l

Dirty Amine Ruins Operation

Running a sulfur recovery operation with dirty amine is analogous to deficit spending. You are borrowing against the future, but the day of reckoning will surely come. The insidious aspect of circulating dirty amine is its erosive nature. Carbon steel is corroded by clean amine. However, the sulfide products of corrosion stick to the metal surfaces and inhibit further attack. Particulates in the circulating amine erode this protective layer. New metal is exposed to corrosion and then more particulates are generated as the corrosion-erosion cycle perpetuates itself. This environment is manifested by several signs.

 •Foaming.

 Dirt reduces the surface tension of liquids. Particulates will cause amine to foam. Foaming in regenerators results in high amine concentrations in the regenerator reflux water. Foaming in the scrubbers causes amine to be carried overhead with the hydrocarbon being scrubbed.

• Plugged instrument taps.

 Flow rates in dirty amine systems tend to be erratic. Orifice taps on flow meters and level taps on float chambers often plug. Level control in the bottom of the scrubbers becomes unreliable and massive carry-overs of amine are frequent.

• Condenser fouling.

Rich amine regenerator feed splashes overhead. Particulates accumulate in the regenerator condensers, heat transfer is impaired to a certain extent, and the reflux temperature rises. 

• Reboiler tube failures.

 Enhanced corrosion rates are most evident in the regenerator reboilers. Dirty amine has caused tube failures after six months of service.

 •Filter plugging.

 The dirtier the amine, the shorter the filter life. The shorter the filter life, the dirtier the amine. For really bad amine, filter pressure drop can increase by 1 psi per hour.

•Regenerator flooding.

Eventually, dirty amine plugs the regenerator trays, and the massive carryover of liquid which follows shuts down the sulfur plant .

 by Rais Shaid

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