Absorption of ammonia gas by subcoled solution

[JuanBass]

I have to absorb a pure ammonia gas at a pressure of 0,5 bar(a) by a subcooled solution of water and ammonia. In the past I have done it in a vertical column with a single sprayer at the top and the gas entering at the bottom. Now the flows are so large, 75 kg/s liquid (density 915 Kg/m3) and 1,1 Kg/s ammonia gas (density 0,4 Kg/m3), that a single spryer construction seams not the best. I am thinking of using a horizontal column with many sprays.
Has somebody experience with such a design or some better idea how to realise it?

 

[djack77494]

To totally answer your question, more information would be provided. Without that, I'll make what I hope is an "educated guess".

If the gas and liquid compositions remain the same and if the relative amounts of gas and solution are unchanged, then you have not impacted the thermodynamics of your system. Thus, if previously your solution absorbed enough ammonia to attain some concentration (let's just say 25 weight% ammonia) then your current system should be thermodynamically capable of the same.

If you flowrates have changed, however, you may be mass transfer limited OR (even worse) you may have done something to render you system less effective. I could speculate that the effectiveness of your vapor-liquid contacting has deteriorated. You may be able to mitigate such a problem by employing additional spray nozzles or distributors. You could also use trays or packing to improve contact between the phases.

HTH,
Doug

 

[Mutt]

The 75kg/s seems high, how conc is the ammonia in the scrub water? If the liquid was pure water, could reduce to around 12kg/s, dropping column diameter by factor of 2 to 3.

 

[JuanBass]

Doug, Mutt
The solution entering has a concentration of about 17,9% and is sub-cooled. By absorbing the ammonia gas its concentration rises till the saturation at this pressure: 19,5% and 31°C. The sub-cooling of the entering solution is sufficient so that further cooling is not necessary. In fact it is only necessary to have a good contact between the gas and the liquid. I am wondering if it would be possible to use something like a mixer with high turbulence rather than a large packed column.