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[AyrtonB]

Hello everyone,

 

I'd be grateful for any advice on the design of my CO2 absorption unit within an Ammonia plant, thank you in advance for all replies.

 

Question

 

I have opted for a tray column as the high liquid hold-up is recommended for a highly reactive system, I had also seen a Shell CO2 absorption column using the same solvent use trays. My question is whether this is the method that anyone here in industry uses? if you use packing instead why is that?

 

Other considerations such as that my column diameter is 3.7m would also push me towards using a tray column as there will be lower manufacturing costs.

 

Context:

 

I am using activated MDEA (aMDEA) at a concentration of 30 wt% MDEA, 3 wt% Piperazine (PZ) with the remaining solution being water, it enters the column at 32 degC. The gas stream from which CO2 is being removed enters at 35 degC and contains:

H2O = Neglibile 

CH4 = 0.69%

CO = 0.2%

CO2 = 17.87%

H2 = 61.42%

N2 = 19.5%

Ar = 0.23%

Total Flowrate = 224,910 kg/hr

 

Much of the literature I have read suggest that both Aspen Plus and HYSYS model the reactions between CO2, MDEA and PZ poorly, as I don't have access to software such as ProMax or ProTreat I have opted to base my design off of experimental data. Using a paper which gave partial pressures and CO2 loading across a range of temperatures I have formed a model in Matlab which accounts for the high heat of reaction.

 

For a removal of 99% at a column pressure of 25.7 bar my model had a result of 18 trays required and the gas stream leaves at 60 degC. The plot is shown at the bottom of this submission. The CO2 loading is at 0.5 (mol CO2/mol amine) and the lean solvent enters at 508 L/s. Further calculations gave the column diameter to be 3.7m with a height of 12.4m.

 

Please also comment if any of these values seem wildly off.

Edited by AyrtonB, 28 January 2018 - 08:58 AM.