Removal of trapped hydrocarbons from ethylene dryer bed

[amar122amar]

Recently Ethylene dryer bed got fully choked, taken out of service and isolated. While N2 purging to remove hydrocarbons entrapped there is no flow of N2 through the bed. What are the alternate methods to make the bed hydrocarbon free?

 

[StoneCold]

You might want to pull vacuum on both the inlet and the outlet of the columns to try to suck the hydrocarbon out as much as possible. This will only work if your columns are vacuum rated, but since you are handling ethylene and it has a high vapor pressure I assume that your vessels are rated for that. You could try to steam it out. Realize that the molecular sieves (I assume that is how you are drying the ethylene) are going to get very hot. You should calculate the heat of adsorption and feed the steam at an appropriate rate until you have saturated the sieves. If those two operations fail you might be down to something much more serious. You might post a P&ID or vessel drawings to give people and idea of how big your system is.

Regards
StoneCold

 

[mallikarjun07]

but what about the trapped hydrocarbons inside the bed ! how to remove them ? we can't take the risk of opening the bed without removing the trapped HC.

 

[EmmanuelTop]

Seems almost impossible to enter in a situation like yours. The only thing that crosses my mind is that you might have had the Sieve bed cemented prior to shutdown. In such case you would either encounter high DP or restricted flow (particularly for the regeneration gas). Can you check for that in the DCS trends?

A solution that might work if purging is impossible, is to have the bed water-flooded. This leaves a lot of mess behind but could be the only way to go.


Dejan IVANOVIC
Senior Process Engineer