5 replies to this topic

[aanita]

I want to optimize reboiler heat load in gas sweetening plant using MDEA.
Here are some operating parameters:
Gas flow: 300 Knm3/hr
H2S / CO2 inlet to ABS: 5.2 / 6.1%
CO2 outlet : 1.1%
H2S outlet : 2 ppm
Aine flow : 610 m3/hr @ 44% concentration.
Regenerator Presssure: 1.15 barg
Toptemperature : 104 Deg C.
Bottom Temp. : 130 Deg C.
Reflux Temp: 44Deg C.
Rich / Lean Exchanger currently partially by pass.
Present steam floe: 120 m3/hr @ 3.0 barg LP saturated steam.
Lean amine H2S : 22ppm.
I can reduce top temperature gradually to reduce / optimize reboiler duty.
How should I start ?
Regards.

[Root]

You can't reduce reboiler duty because by reducing reboiler duty, you can't strip out H2S from rich amine and finaly, your absorption will also affact (poor absorption).
Indeed this is waste of time and you will not get any benefit by reducing the reboiler duty, you think some other ways to save the money.
Like reduce amine conc, now you areusing 44% amine conc, reduce it to 16~18%, you will see the effacts on your process and also cost of chemicals.

Toor

[aanita]

I beleive still H2S in lean amine quite low. So if I reduce reboiler heat load and increse H2S in lean amine ~100 ppm, sweet gas spec will be within the limit.
Our design amine is 45% concentration.
I think we are using more steam in reboiler.
But how I should start to reduce steam.
I know there is chart to optimize reboiler heat load in DEA / MDEA system for small
gas flow( upto100mmscfd), and low H2S/CO2 in sour gas. But my case is more bigger than the chart I have.
If anybody have any chart to use quick estimate reboiler heat load, will be thankfull.

Thank you Toor for your time.

Regards.

[pawan]

You can do provided you try all the possibilities.
We should never post negative, discouraging answers as nothing is impossible
especially improvements in process industry.

You can go as below.

1. First take your lean/Rich exchanger in line at full load.
2. Try to reduce reflux quantity at top.
3. Try to avoid subcooling of Reflux as there is a big gap in temperature, even if you have to increase it slightly.
4. Maintain proper amine concentration as per design condition. You can vary if you are able to
reduce the amine circulation rate. This will give you direct energy saving at every place.

At the moment I cant recall more

[aanita]

Dear Pawan
Thank you for your time.
As I know reflux will be always subcool.
Otherwise Overhead vapor will not condese.
All other things are manitaing.
However what is the effects if Rgen Top temperatutre reduced to 95 Deg.C , if still H2S in lean within the Spec.
Regards.

[pawan]

Yes but reflux should not have subcooling of more than 2-3°C that is sufficient.
I dont know about top temperature but it is a function of top products bubble point at operating pressure. If it is running much higher than that then you can reduce it no problem.
Try to reduce the steam in reboiler if it is too high instead of reducing reflux temp or increasing reflux.