3 replies to this topic

Hi,

i am working as phd student on a project regarding co2 capturing from flue gas of coal fired power plants. As most of you might know, a power plant is not always working at 100% load. Therefore, the flue gas steam will also vary between 50 and 100%.

I simulated my co2 capture unit using AspenPlus and found out that for a lower flue gas volume steam (which is basically the input to my absorber column) my rich loading (mol CO2/ mol MEA) at the end of the absorber is increasing an therefore the specific reboiler duty to regenerate is decreasing.

Now I need a more detailed explanation of this effect! At the moment I am always arguing with the increased residence time of the solvent and gas in the absorber. Is this behaviour realistic for the real operation of a capture plant.


Thanks for your help --- Hope somebody will understand my english writing (-;

- No improvements to the process design (basic amine plant configuration)
- Solvent: 30 wt-MEA
- Flue gas composition is kept constant ( about 13 vol-% Co2, p=atm)
- The capture rate is kept constant at 90%.
- The lean loading of the regenerated solvent was also kept constant.
- A structured packing is used (MellapakPlus)
- A packing height of 20m is assumed (I know that is quite a lot – but I optimized it to reduce the energy consumption of the capture process)
- The column diameter is desiged for 100% Flue gas and 90% CO2 Removal.
- FThe flue gas temp. is cooled down to 40°C
- Rate-Based modeling for the absorber
- Stripper pressure is also kept constant
- I realy hope that I did not forget any important information (I didnt want to confuse with to much information )

[Art Montemayor]

Sebastian:

An MEA CO2 removal process is one of the oldest and simplest gas treating processes around. It is even older than I!

You state, “out that for a lower flue gas volume steam (which is basically the input to my absorber column) my rich loading (mol CO2/ mol MEA) at the end of the absorber is increasing an therefore the specific reboiler duty to regenerate is decreasing”. You have failed to tell us if you are adjusting your MEA solution flow rate to correlate to the flue gas turndown ratio in the MEA absorber. I have to assume that your simulation is prepared properly (which is not reflected in the results) and that you are proportionately decreasing your MEA solution flow rate in accordance with your lower flue gas flow rate. If you are, then your rich MEA solution CO2 loadings should be constant. If you are maintaining a constant MEA solution flow rate in accordance with the higher, design flue gas rate then your rich MEA solution CO2 loadings should be reduced.

The fact that your rich MEA solution CO2 loadings are increased shows that your simulation is set up wrong. That is simply not possible under a reduced flue gas flow rate. Think about it: you are putting in LESS CO2, so how can you be removing MORE? Also, be aware that if your rich MEA solution CO2 loadings are increased, then the specific reboiler duty to regenerate is INCREASING – not decreasing.

One more important note: I realize that you are a graduate student, but you should have made an exhaustive research into the use of the MEA CO2 removal process. If you did, you would have found that even a 20% weight solution of MEA is prone to degrade and cause you serious and continuing corrosion problems – even with additives. One of the serious and difficult tradeoffs that proponents of CO2 sequestration refuse to confront is that the use of concentrated solutions of MEA will cause difficult and often serious corrosion problems. They refuse to confront this situation because they know that to use the recommended more dilute solutions (10 to 15% wt.) means that the economics of CO2 removal will be even worse than they already are with 20 or 30%. I would never recommend using an MEA solution higher than 20% - and even that concentration will involve some corrosion. I have used and designed MEA systems since 1960 when I started my engineering career. I have probably forgotten more information about the process than most engineers today know about it.

I hope this information helps you outl

[NGL Licensor]

Hi,

Can you send the whole input/output streams for the amine absorber. This including the feed gas stream composition and conditions

What is the pressure of the feed flue gas to absorber.

A.King

Hi,
sorry for the late reply. See attached the whole input/output streams for the amine absorber. If something is missing just let me know ...

Thanks for your help !


Sebastian

Hi,

Can you send the whole input/output streams for the amine absorber. This including the feed gas stream composition and conditions

What is the pressure of the feed flue gas to absorber.

A.King

Attached Files

•  Absorber.xls   26.5KB   77 downloads