5 replies to this topic

[processji]

In our unit we use 43% MDEA solution. There is athought that the solution concentration be increased to 50%.The idea is to reduce steam flow in regenerator reboiler. and also reduce circulation rate in absorber and reduce power consumption.

Will this impact acid gas loading, Material of construction.

Any thoughts that can be shared on this please.

Regards

[Zauberberg]

According to my experience, you can increase MDEA concentration up to 55% weight and expect some gains in absorption intensity. After that point, increasing the concentration doesn't bring any good and the rate of absorption actually starts declining.

As long as acid gas partial pressure is unchanged, the maximum rich solvent loading will remain constant as well. By increasing MDEA % you'll cut the solvent circulation rate and increase the residence time in absorber, which is all good. But you can't push the equilibrium point further than it is, at given temperature and partial pressures of acid gas components.

Interesting thing is that - when MDEA concentration is increased - a smaller volume of liquid is available to absorb the reaction heat for each volume of acid gas, so you should see slightly warmer amine exiting the absorber.

Whatever you do, test the plant by increasing the amine concentration very gently - don't push from 43% to 50% or 55% in a matter of few hours. It will give you wrong conclusions.

[aanita]

MDEA concentration should be limited to 50 wt% ( is it 55% is maximum ?), and try to keep rich amine loading 0.55 mol/mol.
Increasing MDEA streangth will not reduce reboiler steam flow, can reduce pumping load and amine flow till your inlet acid gas flow unchnaged. At higher amine concentration amine temperature to contactor should be more. At more than 45% , amine temperature should be more than 60 Deg C.
With an appropriate use of CRA( corrosion resistant alloy) acid gas loading of 0.85 ,or even higher can easily achieved,without velocity limitations on the rich amine line.

You can read the latest paper: "Corrosion control on amine plants:New compact unit design for higher acid gas loadings" ---- Jean Kittel, Michel R. Bonis and Gauthier Perdu.

Best of luck.

[processji]

Thanks

I do not understand why steam reduction will not happen in regenerator reboiler. We are reducing circulation rate.

regards
K Suresh

[Satyajit]

In our unit we use 43% MDEA solution. There is athought that the solution concentration be increased to 50%.The idea is to reduce steam flow in regenerator reboiler. and also reduce circulation rate in absorber and reduce power consumption.

Will this impact acid gas loading, Material of construction.

Any thoughts that can be shared on this please.

Regards

Suresh,
I guess you are talking of AMDEA CO2 removal process in an ammonia plant.
I would say that although you can increase CO2 loading in lean solution by increasing AMDEA concentration, your steam requirement in reboiler will certainly increase.
Don't forget the role and concentration of activator when you are thinking of increasing AMDEA concentration.
Moreover, chances of corrosion and foaming would increase .

Hope this answers your questions.
Kind regards,
Satyajit

[Zauberberg]

The main reason for reboiler duty not changing significantly (it should go down slightly - depending on the % of solvent circulation rate reduction), is in the fact that:

- 50% of energy input goes for acid gas desorption (constant in your case)
- 25% of energy input goes for reflux evaporation (constant in your case, for a given reflux ratio)
- 25% of energy input goes for solvent heating from Regenerator inlet temperature to Regenerator bottoms temperature (the one that changes in your case)

Now, when you look at reduced circulation rate, the percentage of rate reduction should be multiplied by 0.25 and that will be the reduction of total reboiler duty. Going from 45% to 55% MDEA concentration will raise the maximum solvent loading for a fairly small amount, resulting in fairly low difference in solvent circulation rate. Therefore, the expected change in reboiler duty should be fairly small as well.