Refinery Expertise: Enhancing Propane/Ethane Streams and Quench Processes

[katchum]

Does anyone know how to get more ethene out of a propane/ethane stream? I know you can use a higher temperature, but can you do something with the steam ratio or pressure too?

Also:

After the reaction, we use a quench with water injection. Why should we do a compression step first before removing the acid components of the stream? And why would we remove the water at the end of all the compression steps and not after the quench?

Anyone an expert in refinery here?

Thanks

 

[PRDan4th]

Well, I am an old retired ChE that used to work on refining process design years ago and may be a bit rusty. I have never worked on an ethane cracker, but low pressure should assist the reaction since more moles are being produced than consummed. High temperature helps endothermic reactions. I believe a catalyst is required to assist the reaction.

As to water removal after compression is because it is liquid not gas (steam). If acid gas is present (H2S) that should be removed before condensation to minimize material problems.

 

[katchum]

But that doesn't answer how to get more ethene than propene. (pressure wise)

As for the temperature I know you have to have a very high temperature, because ethene is favored over propene this way.

About the water: I thought that after the quench the steam would have already condensed, so it is removable? But I think, I think...: when you compress everything, there will be more acid soluble in the water so you don't have to scrub the acid gas and waste precious alkaline solution. You can then let some acid solvate into the water and then remove the acid water.

What I don't understand is: why:

quench - compression - acid removal - compression - water removal

Why don't they just do:

quench - acid removal - compression - water removal