Replace DEA with MDEA to increase capacity 1

[NghiaPP]

I'm working in a project to find a way to increase the capacity of an amine absorber.
The amine absorber is installed in a diesel HDS unit to remove H2S from the recycle gas. In the future, sulphur in the feed will increase by 50% and the H2S amount to be removed is expected 50% higher. The absorber is currently running close to design capacity. DEA solution at 25 wt% is used with 0.4 mol/mol rich loading. The increase of 50% amine flow will require revamp the most of equipment in amine system. Other option is replacing DEA solution with MDEA 40-50 wt% solution. Rich amine loading is 0.4 mol H2S/mol amine. The amine flow by this way is reduced to an acceptable level such that the revamp of equipment is minimal.
Is it the right approach to solve the problem? What else should be considered for this change?

 

[Montemayor]

NghiaPP:

I highly recommend you go to Bryan Research & Engineering, Inc.’s website:

http://www.bre.com/

and download, read and review the many articles of detailed information regarding the exact type of modification and amine change-out that you are proposing.

Their know-how and experience in this type of amine sweetening modifications is very valuable and can help you get on the right path in short time. BR&E are considered the experts in this field and they seem to do this in their sleep. Their many articles at:

http://www.bre.com/technicalpapers/technicalPaperList.asp?filterCategory=Amine Sweetening

will deal with the very subject you are bring up. Most of these papers deal with real-life conversions and situations and contain a lot of empirical experience. Titles like “Converting to DEA/MDEA Mix Ups Sweetening Capacity” and “Dome's North Caroline Plant Successful Conversion to MDEA” should especially be of interest to you.

Happy reading and studying.

 

[maddocks]

We have used 50 wt% MDEA to increase system capacity in a number of plants, but there are lot more factors at work here. You will probably have some CO2 slip and this may or may not be favourable for your plant. You will also need to look at contactor flooding, residence times, and contactor op pressure. As well, you should limit your rich loading to 0.50 mol/mol. Discuss with your specialty amine vendors like Dow, INEOS, Huntsman or BASF for more details - they have specialty amines that can perform really well.

 

[roymcnally]

Comparison of various parameters of MEA,DEA and MDEA
are given below in TABLES I-VI :
Camparision of Amines

TABLE I

Solvent MEA DEA MDEA
Concentration% 15 30 35-50
Solvent Circulation GPM 100 100 100
Acid Gas Removal
Capacity MOL/HR 49.8 58.6 87.5
Capacity Increase %
(MEA BASE = 100) 100 118 175

Performance of Media

TABLE II

Solvent Concentration% 35-50
Solvent Circulation GPM 10-1600
Rich MDEA Loading MOL/MOL 0.50
Lean MDEA Loading MOL/MOL 0.01
Reboiler Steam, #/GPM 0.67-0.85
Lean MDEA Temperature 0F 130-160
CO2 Slip, % CO2 Rejected 50

Heat of reaction with H2S and CO2

TABLE III

Heat of reaction BTU/POUND
Amines H2S CO2
MDEA 450 577
DEA 493 650
MEA 650 820

Selectivity and Capacity

TABLE IV

Capacity
Amines Selectivity* Mol H2S/Mol Amine Mol CO2/Mol Amine
MDEA 3.85 0.10 0.12
DEA 2.27 0.09 0.32
MEA 0.89 0.07 0.50

*Selectivity is defined as ratio of (mole percent of H2S removed to mole percent of H2S in feed gas) to (mole percent of CO2 removed to mole percent of CO2 in feed gas)

Recommended ranges of Amines Concentration -
Rich and Lean Amines Loading

TABLE V


Amines Conc. Weight % Rich Loading M/M Lean LoadingM/M
MDEA 35-55 0.45-0.55 0.004-0.01
DEA 25-30 0.35-0.40 0.05-0.07
MEA 15-20 0.30-0.35 0.10-0.15


Corrosion

TABLE VI
Solvent Corrosion Rate MPY
30% Wt MEA 32
50% Wt DEA 25
15% Wt MEA 13
20% Wt DEA 8
50% Wt MDEA 3

Taken from:

http://www.amines.com/mdea_comp.htm