Acid Gas Knock-out Drum, demister change for higher efficiency

[Hadi Khabbaz]

hello everyone,

I would like to know what is the best demister for a acid gas KO drum already being used in a Gas Refinery in order to improve efficiency.
there already are a demister pad of 4" thickness, stainless steel 316 and a 120x120 cm2 plate in front of inlet line.
approximate analysis of inlet gas (@0.68 kg/cm2 pressure and 47c temp.) would be :

COMPONENT WET (%MOL)
H2O 8
CO2 57
H2S 34
CH4+BTEX 1
TOTAL 100

SOME Info regarding the acid gas KOD:

operational pressure: 1.65-1.7 kg/cm2
operational temp.: 40-50 c
maximum flux of inlet gas: 62500 sm3/hr
total height: 3658 mm
internal diameter: 2895 mm
body thickness: 11 mm
inlet gas line diameter: 42 inch
outlet gas line diameter: 42 inch
outlet liquid line diameter: 3 inch
demister pad thickness: 4 inch
demister material: Stainless Steel 316

any suggestion for improving efficiency by changing demister or the plate !? or any other idead ...
thanks in advance for your replies.

 

[georgeverghese]

It should be possible to make some improvements in total separation eff by changing out the simple impact plate with a custom made slotted feed pipe, albeit at a somewhat higher pressure drop, which you can design/ calculate out to be still within allowances. Nothing high tech about the slotted feed distributor. This would be similar in construction to that used in liquid collection nozzles where local high velocity currents are to be reduced. Turndown on throughput for a wiremesh demister is approx 4:1.
Presume your calcs on sizing are correct - I have not checked.
What is your concern with separation eff - is high liquid entrainment / liquid condensation affecting some dowonstream equipment ? You can opt for higher separation eff with another type of phase separator if you have poor separation eff, but not if the problem is unwanted condensation in some downstream equipment.
Obviously, avoid liquid slug flow in the feed piping line to the separator.