Amine Contactor Off gas cooler

[ivegotgas]

Some debate at our plant regarding cooling of the sweet gas from the contactor.

Original design of the plant was (following sweet gas flow) contactor --> knockout (to recover amine) --> Dehydration (glycol, Refrigeration, and Lean Oil)

We are installing two new contactors, and the operations asked the question why we would not install an off gas cooler upstream of the amine knockout to help recover more amine.

My response was that cooling was not necessary as amine carryover due to evaporation was negligable compared to entrainment losses, and the only way to reduce entrainment was to slow the velocity of the gas ie. make the knock out wider.

they doubt my answer as they have worked in another plant that had upstream (of the knock out) off gas coolers. Hard to argue facts like that, but I am not convinced that the other plant installed off gas coolers for amine recovery my suspicion is that they had other motives. Any thoughts?

 

[CJKruger]

ivegotgas, considering you also get plants without a sweet gas KO drum, I would think all three designs are acceptable.

I would however install a sweet gas cooler and KO drum. Cooling will also condense water, which cleans up the fuel gas.

In addition, the key is that your KO drum has a demister pad, which provide most of the benefit. Without cooling you can just as well add the demister to the top of the absorber.

 

[maddocks]

The need for a sweet gas cooler really depends on your temperature rise in the contactor. If you have a heavily CO2 based system, the outlet gas can be quite hot. Cooling can drop out water, minor amounts of amine (hopefully not much is entrained), and finally and most importantly, can reduce the resulting downstream refrigeration load.

The temperature reduction reduces water content in a big way, and reduces the amount of glycol circulation that may be required.

A sweet gas scrubber is really a serious requirement - all it takes is one foaming incident with amine carryover and it's justified to prevent amine losses and downstream contamination.

 

[ivegotgas]

Thanks for both posts. I guess the sense I get from both is that the major benefit of cooling the gas is water removal and the associated reduction in load that is passed on to the refrig system. This is consistant with my thought on the matter, where the difference in opinion has occured is on the topic of amine recovery.

It is my understanding that temperature plays a very small role in reducing amine entrainment therefore a cooler would not help, at least not a whole lot.

I would disagree CJKruger's comment of "just as well add a demister to the top of the contactor" as a knock out helps separate the entrained liquid by slowing down the vapour (larger diameter than the tower). A demister helps but the key is fluid velocity.

Our design is not for high CO2 loading, also we run split flow to the tower (lean + semi lean, the gas off the contactor is only about 55oC. The refrige/dehy system is nowhere near loaded so the benefit of adding cooling upstream of the knockout is lost on me.

I appreciate both your timely responses. Thanks

 

[dcasto]

a 10 deg C drop in temperature through a gas cooler will lower makeup water by 40% and glycol regeneration energy requirements by 30% on that portion of gas treated.