8 replies to this topic

[HenryB]

Hello guys,

I am process engineer working in an Ethylene plant, I would like to know if anyone has a "procedure" to startup a cryogenic ethylene tank.

The tank is in maintenance and they want to know how to start it up? any help

Thanks

[rizaldi]

You need to look up the P&ID and see interconnecting system to it.

Then you need to purge your tank. Set which valve should be in open and close position, (also which are by passed)..can only determine by knowing your system through the P&ID.

Then set your boil off gas system ready before pouring the ethylen into the tank.

That's the far i can imagine without looking up at your system. Please CMIIW.

regards,

-rzd-

[HenryB]

Newbie,

What fluid do we use to purge the tanks N2? If so we have to vent to the flare right? and then we start filling up with ethylene?

Thanks

[fallah]

At first, you should refer to the relevant plant operating manual.

[Evgeny]

first you fill/purge with N2 to get rid of O2. then fill/purge with ethylene, and recieve liquid ethylene. This is general procedure

[PKS]

first you fill/purge with N2 to get rid of O2. then fill/purge with ethylene, and recieve liquid ethylene. This is general procedure

Let me add to the discussion...

1. After a shut-down and maintenance, first step is get rid of O2 (rightly said by Evgeny)as well as attain the required dew point of -50 deg C (approx.)with bone-dry N2.
2. After attaining the required Dew Point.. the tank is ready to take Liquid Ethylene. So, purge the tank with ethylene (as said by Evgeny).. and finally take the Ethylene Level in the tank...
3. Despatch the product.

The main concern is the time, that the tank takes to attain the dew point and get rid of O2 (depending on the volume of the tank). So, it is very important to plan, about the start of the operation.


PKS

[SSWBoy]

On the tank I worked on there was a small startup Ethylene line, no more than 2" for startup of tank. Having purged through the tank with N2 you want to slowly start introducing liquid ethylene to the tank, this should be done at a controlled rate as you do not want liquid ethylene flashing to -100 and damaging the base of the tank, in fact the startup line may have a RO installed in light of this. From memory the rate of cooling you want to be below is something like -5C per hour. As you begin the cooldown you can then start up the BOG compressor on discharge to flare mode. Continue cool down of tank until you reach -100ish. Done.

[Evgeny]

Hi PKS,

Just for my curiosity (and since my english isnt perfect)

what is bone-dry N2? and how you achieve dew point -50 with it?

thanks
Evgeny

[HenryB]

After attaining the required dewpoint.. the tank is not ready. Before you have to purge the N2 with ethylene gas until you reach 98-100% vol. Then you start the cooldown process using a 2" line, this is the most complicated step because the cooling rate is ~ 5C/hr and there are a lot of pressure variations. This step need to be done very carefully.