4 replies to this topic

[fifi]

Hello,
Does anyone know why Natural Gas is passed through wash water system to saturate with water at the entrance of acid gas removal unit before being sent to the absorber column for acid gas removal.

Regards

[Padmakar Katre]

Hello,
Does anyone know why Natural Gas is passed through wash water system to saturate with water at the entrance of acid gas removal unit before being sent to the absorber column for acid gas removal.

Regards

To start the mass transfer between Vaopr and Liquid you need to have saturated vapor. That is main reason which I know.

[vicini]

you don't have to add water to start the mass transfer, you don't have water wash, it is not mandatory to even do this. I'd say that 95% of all amine treaters don't water wash.

The reason you add water on the top tray and the amine solution on 3 trays down in some situation is because the inlet gas is under saturated with water, which is not typical. Some times there is a pre contactor where the gas is washed, its not really washed, it a saturation 1 stage operation. If you dry gas with no water, it will become saturated in the absorber. The gas will remove water from your amine solution and if you don't add water, your solution will concentrate the amine. SO, you will have add water anyway.

Now, where to add water. You could just add to the surge tank. But lets do something good a least. The process of absorbing/reacting gas with amine is exothermic. The gas temp rises through the absorber. So we add water to the gas at either the front a pre "wash" or before thas leaves the last top tray in the absorber. This way we get to use the heat of eveaporation to cool the gas.

now we did something useful with the addion of the water.

[ravi.s]

Though rarely a problem in natural gas treating plants, ammonia is an impurity which can be present in the feed gas to an H2S absorber in refinery service. A water wash system on the inlet feed gas consisting of a small trayed (4-5 trays) or packed column is the most effective way of removing NH3 from the feed gas to an absorber & subsequently to avoid ammonium-salts build up in the regenerator overhead circuit & to minimize the reboiler heat duty. As all ammonia present in the feed gas will be absorbed by the amine solvent in the absorber and will be stripped from the solvent in the regenerator. After being stripped from the solvent, a significant portion of the ammonia will return to the top section of the regenerator with the condensed reflux water due to the high solubility of ammonia in water.

A water wash system is also effective in removing aerosols formed by upstream equipment. Water wash systems can also be quite effective in the pre-treatment of FCC gas and coker off-gas that can contain substantial amounts of heat stable salt precursors.

Excellent. Thanks for sharing.


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