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Replace DEA with MDEA to increase capacity

Replace DEA with MDEA to increase capacity

Replace DEA with MDEA to increase capacity

(OP)
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?

RE: Replace DEA with MDEA to increase capacity

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%20Sweetening

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.

RE: Replace DEA with MDEA to increase capacity

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.

RE: Replace DEA with MDEA to increase capacity

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

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