6 replies to this topic

Hi,

I am doing a simulation of Integrated Gasification combined cycle (IGCC). At one point, i need to use Selexol solvent to remove H2S and CO2. Below are my questions, hope you could kindly help me.

I am wondering is there a maximum pressure difference (between the top & bottom stage) of a typical absorber?
What is the decomposition point/boiling point of Selexol at 50 bar? ( i am running my simulation at 50 bar & 10C, not too sure if Selexol will be decomposed)
What is the typical amount of Selexol used in industry to remove H2S and CO2? ( i am using about 60kgmole/hr of Selexol in my simulation, not sure if it is feasible for this amount)

Thank you so much!

[Zauberberg]

There is no "typical" amount of Selexol. It depends on:

- Acid gas composition/content
- Type of impurities (e.g. CO2, H2S, , COS, RSH etc.)
- How much deep you need to remove the impurities (= treated gas specification)
- Operating pressure of the absorber

As it is a physical solvent, its use is generally limited on high-pressure lean gas, such as in IGCC plants.

Differential pressure across the Selexol absorber depends on the number of stages (= number of trays or height of packing) required to achieve product gas specification, and design/actual gas and liquid loadings in the column. Selexol towers are known as quite tall towers, but you will rarely see deltaP across the tower exceeding 0.2 - 0.3 bar under normal circumstances.

Both solvent and the feed gas are normally refrigerated, to improve absorption potential of the solvent. In the plant where I used to work, Selexol solvent was chilled down to 4 degC and feed gas chilled to 10 degC. Operating pressure of the Absorber was 33 barg, and operating temperature of the Selexol reboiler/regenerator was 151 degC @ 1.5 barg.

Some more info available at:

http://www.uop.com/o...okeGasifAmm.pdf
http://www.anl.gov/P..._04-73_0142.pdf
http://msdssearch.do...fromPage=GetDoc

Hi

Thank you so much for your reply & advice! Is 60kmole/hr of selexol consider a lot? I am worried that my design may be deem as infeasible due to the amount of selexol involved.

[Zauberberg]

As said before, I have no idea what could be the flow rate of Selexol without knowing (acid) gas composition and absorber pressure. Even with these data available, I could still give only rough estimate since it is difficult to quantify effect of the solvent refrigeration temperature on absorption.

Just as an example, in the before mentioned process plant, we had a 2,000mm diameter Selexol absorber handling flow of 1,185 kgmole/hr of solvent with average Mol Weight of 175 (mixture of Selexol and water). From that point of view, your 60 kgmole/hr is a cup of tea and is in the order of 10-15 m3/hr, I guess. Therefore it is quite feasible.

For more information on the Selexol process, you can refer to the "Gas Purification" book by Kohl & Nielsen.

Thank you for your advice. Your opinion resassured my uncertainty. Thank you!

[sunflower]

What is the general ratio of selexol:feed gas flow rate? Is it feasible to have a selexol flow rate (50% water 50% selexol) that is twice the amount of the feed gas? If not, what recommendation do you suggest? Thanks a lot for your kind help.

[Zauberberg]

Sunflower,

Answer on your questions can never be "general". It varies on many factors, and some of the key factors are listed in my first reply.

Try to obtain the book I referenced in my post and there you can find plenty of information regarding the Selexol process.