7 replies to this topic

[Sbruso]

Hello everyone!

 

I am having some trouble designing a "quench tower" for a CO2 capture system in Aspen Plus.

 

The goals are:

• reduce the temperature of the flue gas from 131 to 40 C in order to prepare the flow for the absorber;
• removing part of the acid component using NaOH.

 

 

For the Quench I think to use:

• RadFrac column, packing column with Mellapack 250Y and Carbon steel for the vessel.

 

 

What steps do I have to follow on Aspen tech to define the solution (water+NaOH), the diameter and the length of the vessel?

 

 

Many thanks!  

[Pilesar]

Mixing water, NaOH, and CO2 yields many more than three components in the system. Is this a student project? The sparse details you gave are not sufficient for me to understand what you are trying to do. Are you trying to model an existing commercial design or trying to invent some new scheme?

[Sbruso]

 

Mixing water, NaOH, and CO2 yields many more than three components in the system. Is this a student project? The sparse details you gave are not sufficient for me to understand what you are trying to do. Are you trying to model an existing commercial design or trying to invent some new scheme?

 

Hello Pilesar!

 

Many thanks for your reply! 

 

It is the project for my thesis. I have to design, using Aspen Plus, a complete CO2 capture system from the flue gas of an industrial plant, including cooling of the flue gas and compression of the CO2 captured.

 

For now, I am focusing on the flue gas cooling system, composed of a "quench tower". The "quench tower" is normally used to bring the flow gas to the absorber working temperature, around 40 C.

 

Characteristics of the flue gas to be treated are: 

 

Flow: 6112 kg/h (130 C and 1,2 bar)

Composition: CO2 = 838 kg/h, H2O = 540 kg/h, O2 = 711 kg/h and N2 = 4023 kg/h.

 

The scheme that I want to use to model the "quench tower" is:

 

<image>

 

From the literature, I found:

 

In Aspen plus, the "quench tower" is modelled using a packed, RadFrac column and using a rate-based approach.

 

The steps involved in the design are:

 

1. Characterization of the flue gas and the liquid solvent (except for the flowrate) and definition of the target performance (temperature of the flue gas output from the "quench tower")

 

2. Infinite packing height column

 

   - Definition of the minimum number of cooling units to respect the constraint on the maximum value of the diameter;

   - Evaluation of the minimum solvent flow rate by means of sensitivity analysis;

 

3. Effective column

 

   - Simulation of the "quench tower" for different multiples of the minimum solvent flow rate and evaluation of the corresponding column dimensions (packing height and diameter);

   - Identification of the extremes of the L/V ratio where isothermal packing zones are avoided;

 

4. Choice of the effective solvent flow rate and effective packing height by means of an optimization problem.

 

My goal is to design the "quench tower", determining the diameter, height and quantity of water to be used to reduce the temperature of flue gas from 130 C to 40 C.

 

I hope it's clearer now! Many thanks! 

 

p.s. To model the CO2 capture system on Aspen Plus, I am using a guide found in literature: CO2 Capture by Reactive Absorption-Stripping, Modeling, Analysis and Design. C. Madeddu, M. Errico and R. Baratti,  2019. However, the reference does not include the "quench tower" and there isn't much on it in the literature.

 

Any comment on the reference used and on the other, it's appreciated.

[Pilesar]

I did not read the details of your references so will make some general comments. NaOH solution to capture CO2 does not easily release the CO2. Amine solutions are more standard since the capture can be reversed to yield a concentrated CO2 stream as a product. I suggest you not start with designing the quench tower, but start with designing the process after the flue gas is cooled. If you know you want 40 C flue gas, just saturate the flue gas with water and use it as the feed to the downstream unit. Why? Well, you might find a use for the flue gas heat in the process later and the quench tower design will be moot. It may be more useful to exchange heat from the flue gas with another process stream before quenching it. Industrial flue gas is not usually found much above atmospheric pressure. You will likely need some sort of fan or compressor in your system. Do you have a flowsheet yet of your process? Get that settled before the equipment design or you will be wasting effort. After the flowsheet is settled, you need a material balance. Are you going through your project systematically? I cannot tell so am offering these comments which you may already understand.

[breizh]

Hi,

You may find pointers in the link attached :

https://www.ogtrt.co...ine Systems.pdf

Note :

Among the chemical reactions you should get Sodium carbonate and bicarbonate.

You must clarify  your Operating condition (  Pressure absolute or Gauge) 

Good luck 

Breizh 

[Sbruso00]

Hi,

You may find pointers in the link attached :

https://www.ogtrt.co...ine Systems.pdf

Note :

Among the chemical reactions you should get Sodium carbonate and bicarbonate.

You must clarify  your Operating condition (  Pressure absolute or Gauge) 

Good luck 

Breizh 

 

Many thanks!

 

I would like to post images to explain well. How could I do?

[breizh]

Hi,

Click on more reply option and then you will find a window to add documents

 

Breizh

[Sbruso00]

I did not read the details of your references so will make some general comments. NaOH solution to capture CO2 does not easily release the CO2. Amine solutions are more standard since the capture can be reversed to yield a concentrated CO2 stream as a product. I suggest you not start with designing the quench tower, but start with designing the process after the flue gas is cooled. If you know you want 40 C flue gas, just saturate the flue gas with water and use it as the feed to the downstream unit. Why? Well, you might find a use for the flue gas heat in the process later and the quench tower design will be moot. It may be more useful to exchange heat from the flue gas with another process stream before quenching it. Industrial flue gas is not usually found much above atmospheric pressure. You will likely need some sort of fan or compressor in your system. Do you have a flowsheet yet of your process? Get that settled before the equipment design or you will be wasting effort. After the flowsheet is settled, you need a material balance. Are you going through your project systematically? I cannot tell so am offering these comments which you may already understand.

 

Many thanks for your answer!

 

The MEA will be used to capture the CO2 from the flue gas. From the scientific literature, I found that NaOH is used in the quench tower with the water (I don't know the specific purpose).

 

Unfortunately, I also have to design the quench tower.

 

A flow sheet of the total CO2 capture system is presented in Fig. 1, in detail A of the same picture is shown the scheme of the quench tower.

 

 Fig.1.png   593.87KB   2 downloads

 

On the scheme of cooling the water used in the quench tower (detail A) there isn't information in the literature. What is it usually used?

 

I have tried to design the quench tower on aspen plus, using the approach written in the previous post. The results are shown in Fig. 2. The flue gas composition is the one shown in the previus 

 

 Fig. 2.PNG   7.19KB   0 downloads

 

Since I don't have sensibility with this data, are they plausible? In case it is necessary to recover the water used to cool the fumes, what kind of system could be used?